diff --git "a/A9AyT4oBgHgl3EQf3_rL/content/tmp_files/load_file.txt" "b/A9AyT4oBgHgl3EQf3_rL/content/tmp_files/load_file.txt" new file mode 100644--- /dev/null +++ "b/A9AyT4oBgHgl3EQf3_rL/content/tmp_files/load_file.txt" @@ -0,0 +1,1913 @@ +filepath=/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf,len=1912 +page_content='A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS GABRIEL B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, GEOFFREY BECK, LAURENT CHEVILLARD, ISABELLE GALLAGHER, AND RICARDO GRANDE Abstract.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Turbulent cascades characterize the transfer of energy injected by a random force at large scales towards the small scales.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In hydrodynamic turbulence, when the Reynolds number is large, the velocity field of the fluid becomes irregular and the rate of energy dissipation re- mains bounded from below even if the fluid viscosity tends to zero.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A mathematical description of the turbulent cascade is a very active research topic since the pioneering work of Kolmogorov in hydrodynamic turbulence and that of Zakharov in wave turbulence.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In both cases, these turbu- lent cascade mechanisms imply power-law behaviors of several statistical quantities such as power spectral densities.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For a long time, these cascades were believed to be associated with nonlinear interactions, but recent works have shown that they can also take place in a dynamics governed by a linear equation with a differential operator of degree 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In this spirit, we construct a linear equa- tion that mimics the phenomenology of energy cascades when the external force is a statistically homogeneous and stationary stochastic process.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In the Fourier variable, this equation can be seen as a linear transport equation, which corresponds to an operator of degree 0 in physical space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Our results give a complete characterization of the solution: it is smooth at any finite time, and, up to smaller order corrections, it converges to a fractional Gaussian field at infinite time.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Introduction 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Background and motivation.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This work is mainly motivated by some important aspects of the phenomenology of three-dimensional homogenous and isotropic fluid turbulence [34, 42, 20], of which several aspects have been also observed and formalized for waves in various situations when they are weakly interacting [43, 35].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As has been repeatedly observed in geophysical and laboratory flows, and in numerical simulations of the incompressible Navier-Stokes equations, a fluid that is stirred by a statistically stationary random force f(t, x), assumed to be smooth in space, will eventually reach a statistically stationary state in which the velocity variance is finite.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' To dissipate all the energy that is constantly injected into the system in such an efficient way, the velocity field of that fluid will develop a complex multiscale structure ending up with high values of velocity gradients such that viscosity can easily transform mechanical energy into heat.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In other words, the fluid has transferred the energy pumped at large scales by the forcing towards small scales, at which viscous diffusion efficiently acts.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This picture is known as the cascading process of energy.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The purpose of this article is to model and reproduce this phenomenon of transfer of energy as a cascading process through the scales.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We propose a partial differential equation, which is of course much simpler than the nonlinear Navier-Stokes equations, stochastically forced by an additive random force f(t, x) that we take to be smooth in space and correlated over a typical large lengthscale (known in the turbulence literature as the integral lengthscale), whose solution develops roughness as time goes on.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' More precisely, our goal is to generate rough fractional Gaussian H¨older continuous random fields of parameter H (see for instance the textbook [16]) from smooth forcing through a dynamical evolution, which can be seen as a simple stochastic representation of the phenomenology mainly developed by Kolmogorov [24].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 1 arXiv:2301.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='00780v1 [math-ph] 2 Jan 2023 2 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE As mentioned earlier, a striking feature of three-dimensional turbulent motion is its ability to efficiently dissipate the energy that is injected at large scales in a statistically stationary and homo- geneous manner.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' To be more precise, let us consider a solution of the incompressible Navier-Stokes equation, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' a divergence-free velocity field u(t, x) ∈ R3 with periodic boundary conditions.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This dynamics is stirred by a divergence-free vector forcing term f(t, x), that we take delta-correlated in time and smooth in space, say Gaussian, of zero-average and of covariance E [f(t, x) ⊗ f(s, y)] = δt−sCf(x − y), where ⊗ stands for the matrix product, and the matrix Cf(x) is made of a linear combination of the matrix x ⊗ x and the identity, with multiplicative coefficients depending only on |x|, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' a typical covariance matrix of a statistically homogeneous and isotropic vector field [6, 36].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We furthermore require that these scalar functions of |x| are smooth and compactly supported over a range of the size order of the aforementioned large length scale, so as to mimic the energy injection at the so- called integral length scale.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As time goes on, it has been repeatedly observed that the velocity field u reaches a statistically stationary state, which is furthermore statistically homogeneous, of finite variance, and with the additional striking property that it becomes independent of the viscosity ν as ν goes to zero, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) lim ν→0 lim t→∞ E � |u(t, x)|2� < +∞ for all x.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The former asymptotic behavior of the velocity variance illustrates clearly how a turbulent fluid can dissipate energy with high efficiency.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For instance, in the same setup but considering the heat equation instead of the Navier-Stokes equations, a statistically stationary regime would also be reached at t → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, the variance of the solution is then inversely proportional to the viscosity ν, see [14].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Instead, turbulent motion dissipates energy in a way that the velocity variance is eventually independent of viscosity, which is a far more efficient way of dissipating energy.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In order to ensure the independence of said variance on viscosity, (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1), the fluid develops a rough behavior of H¨older-type at small scales, in such a way that the variance of the velocity increments asymptotically behaves as follows: (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) lim ν→0 lim t→∞ E � |u(t, x + ℓ) − u(t, x)|2� ∝ |ℓ|→0 |ℓ|2H for all x, where the power-law exponent is determined by Kolmogorov’s prediction H ≈ 1/3 [20].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Much more could be said on a more precise characterization of the distribution of the increments than only its variance, (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2), such as its higher order moments that quantify its non Gaussian, skewed and intermittent nature [20].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In this article, we will focus on a second-order modeling of these fluctuations, (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) and (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2);' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' we leave finer descriptions for future research.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A first precise formalization of the cascade phenomenon could be built by imposing a particular dynamical relation between the coefficients of a decomposition of the velocity field, such as a continuous wavelet transform or a discrete (dyadic) decomposition on a tree [18].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This has been explored in the literature [5, 4, 13] leading to precise statements on H¨older regularity and its relationship with scaling behaviors of the coefficients.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Although great progress has been made in the understanding of such models and their formalization, which usually exploits a typical quadratic interaction between neighboring coefficients, these approaches often avoid the important question of the relation of these coefficients in space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This is necessary in order to design a model that leads to statistically homogeneous velocity fields, as observed in nature and in numerical simulations.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Nonetheless, these models can be seen as a sophistication of the so-called shell models1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In this spirit, we believe an important step was made in [32], where the authors investigate a simple linear 1See for instance [10, 9] which consist in exploring quadratic interactions between shells, that share some behaviors with velocity Fourier modes and wavelet coefficients, along a single branch of a tree decomposition, lacking thus a discussion of the spatial relationships between coefficients.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS 3 relation between shells, which is shown to be able to transfer energy from large to small scales.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Let us also mention [30] where some ideas to build a PDE from these shell models are proposed.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' From a somewhat different side of fluid mechanics, more focused on the implications of global rotation [40, 39] or stratification of the density field [29, 41] on a flow, it has been evidenced a phenomenon of focusing of waves onto attractors, whose precise shape are determined by the boundaries.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Based on a linearization of the fluid equations, this phenomenon has been interpreted as a cascading process through scales.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' These ideas have been then formalized and rigorously studied from a mathematical viewpoint in a series of recent articles [17, 19], which underline the importance of operators of degree 0 as a deterministic mechanism able to transfer energy through scales.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Main results.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The rough and disordered nature of a turbulent velocity field u(t, x) has been repeatedly observed in laboratory and numerical flows, and in geophysical situations [42, 20].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' From this signal, considering for instance a component of the velocity vector field as a function of space, depending on the experimental possibilities and the large-scale geometry of the flows, one can construct the energy spectrum |k| �→ E|�u(t, k)|2 where �u stands for the spatial Fourier transform.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' According to the standard phenomenology of fluid turbulence,' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' which has been multiply confirmed by observations in very different situations,' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' the energy-spectrum resembles a curve [42,' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 20] that can be schematically decomposed as follows: (injection range) for small |k| of the order of the characteristic wavelength of energy injec- tion,' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' the energy-spectrum is mainly determined by the forcing and the associated large-scale geometry of the flow,' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (inertial range) for intermediate |k|,' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' the energy-spectrum develops a power-law behavior whose exponent is found universal,' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' independent of viscosity and of the nature of the flow, and can be interpreted as the generation of small scales by the internal motion of the fluid following a transfer of energy from small wave-numbers to large wave-numbers, (dissipative range) for large |k|, the energy-spectrum is governed by dissipation processes which damp efficiently all the energy coming from the large scales, making the spatial velocity profile a smooth function.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The intermediate range of scales, called the inertial range in the turbulence literature [42, 20], is where this mechanism of transport of energy takes place.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The universally observed power-law exponent of the energy-spectrum can be written as −(2H + d), i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' E|�u(t, k)|2 ∼ |k|−(2H+d), where we have introduced for the sake of generality the space dimension d, and the parameter H that will be eventually interpreted as a Hurst, or H¨older, exponent, in a statistically averaged sense.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In real situations, for d = 3, it is indeed observed that H ≈ 1/3, as predicted by dimensional arguments mainly attributed to Kolmogorov [24, 27].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The main goal of this paper is to propose a family of partial differential equations, such that, when stirred by a statistically stationary and spatially homogenous, smooth in space forcing term, its solution u(t, x) reaches at long times a statistically stationary state which displays the typical spectral behavior detailed above.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We will achieve this with the following transport equation in Fourier space: (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) � � � � � � � � � ∂t�u(t, k) + divk � ck |k| �u(t, k) � + cH + 1 2 |k| �u(t, k) = �f(t, k) t > 0, k ∈ Rd, |k| > κ > 0, �u(t, k) = 0 t > 0, k ∈ Rd, |k| ≤ κ, �u(0, k) = 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Here H ∈ R and κ > 0 are fixed, and the source f satisfies E[f(t, x)f(s, y)] = δt−s Cf(x − y), 4 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE where Cf is smooth and satisfies some additional assumptions detailed below.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Our main result is the following: Theorem 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Let H ∈ (0, 1) and let the forcing f be (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) f(t, x) = � Rdy ϕ(x − y) dW(t, y), where dW is a space-time Gaussian real white noise and ϕ ∈ S(Rd x) is a radial function such that �ϕ(k) = 0 for all |k| < κ.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (i) The transport equation in wavenumber space (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) with source (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) can be rigorously formu- lated in physical space as an a.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='s.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' well-posed PDE.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Moreover, at any t > 0, the solution u(t, x) has finite variance and a.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='s.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' smooth paths with respect to x.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (ii) As t → ∞, u(t, x) converges to a zero-mean Gaussian field u∞(x) which has a.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='s.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' α-H¨older continuous paths for any 0 < α < H.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (iii) The correlations are given by E[u∞(x1)u∞(x2)] = C(d, H) KH(x1 − x2) − (KH ∗ JH)(x1 − x2), where KH := F−1 � χ|k|>κ|k|−(2H+d)� , while C(d, H) is an explicit constant and the function JH ∈ S(Rd x) depends explicitly on ϕ in (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A more detailed version of this result is presented in Theorem 4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4 page 23.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The parameter κ can be chosen as the smallest non-vanishing wavenumber in the support of the Fourier transform of the forcing.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Following the analogy with the Navier-Stokes equations presented in the introduction, κ may be interpreted as a quantity linked to the inverse of the integral lengthscale2, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e the typical lengthscale of the correlations of the forcing.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The fact that our force acts at large but finite scales means that κ is small but non-zero.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The kernel KH is a function when H ∈ (0, 1) and κ > 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, when κ = 0 we have the following operator: KH −→ κ→0 (−∆)− H+ d 2 2 .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Note that the limiting Gaussian field u∞ shares some statistical properties, such as roughness, with statistical homogeneous fractional gaussian fields [16, 28] defined by (−∆)− H+ d 2 2 dW, that are classically encountered in the turbulence literature [25, 12, 15].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Indeed, for H ∈ (0, 1) both have a.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='s.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' α-H¨older continuous paths for any 0 < α < H and one can show that (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5) u∞ = (in law) C(d, H)F−1 � χ|k|>κ � ∗ (−∆)− H+ d 2 2 dW − ureg.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Here, ureg is a smooth zero-mean Gaussian field with correlations E[ureg(x1)ureg(x2)] = (KH ∗ JH)(x1 − x2), 2If Lf is the integral lengthscale, then there exists two real positive numbers a < b such that the support of �f is contained in the annulus of inner radius a Lf and outer radius b Lf .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Thus one may set κ = a Lf .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS 5 which is a smooth function with respect to (x1 − x2) even if H ≤ 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The case H ∈ [−d/2, 0] will be discussed in Section 4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' When H ∈ [−d/2, 0], as t → ∞, u(t) still converges to a zero-mean Gaussian field u∞, but this field is not necessarily H¨older continuous with respect to x anymore.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In this case, one may view u∞ as a distribution living in the dual of an appropriate test function space T , see Theorem 4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5 for more details.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The correlation structure of the limiting Gaussian measure is given by: (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6) E[ lim t→∞⟨u(t), g1⟩⟨u(t), g2⟩] = � Rd k χ|k|>κ |k|−(2H+d) � C(d, H) − � JH(k) � �g1(k) �g2(k) dk for any test functions g1, g2 ∈ T , where ⟨·, ·⟩ stands for the duality product in T .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In Theorem 4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5, we show that, for any test functions in T ∩S(Rx d), (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6) yields a rate of convergence proportional to (ct)−(2H+d+2n) for n as large as desired.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The expression (1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6) corresponds to the energy-spectrum picture described above.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Indeed, |k|−(2H+d) corresponds precisely to the inertial range previously described, while � JH(k) captures the contribution from the forcing, which is a correction in the injection range.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In fact, if the source is spectrally supported in small wavenumbers, then � JH(k) vanishes in the inertial range.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Finally, let us highlight the difference between the properties of the solution at finite and infinite time.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' At finite time, the solution is smooth with respect to x, whereas at infinite time the solution is only H¨older continuous (or even rougher if H ≤ 0, as explained in Remark 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This loss of regularity at infinite time is what is expected in linear turbulence.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Turbulence is usually associated to a nonlinear equation.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For example, in the case of wave turbulence, nonlinearities create wave interactions which allow the transfer of energy to higher and higher wavenumbers.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Such transfers of energy typically result in a loss of regularity.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, nonlinearities might not be the only way in which such loss of regularity can occur.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Indeed, Y.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Colin de Verdi`ere and L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Saint-Raymond have shown that, in the context of internal waves, a loss of regularity can also take place in the case of a linear equation with an operator of degree 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Linear equations with operators of degree 0 are also common whenever one introduces a dispersive perturbation in a hyperbolic system.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In such cases, these operators of degree 0 are used to model wave propagation under strong dispersive effects and they are responsible for memory effects.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For example, in the context of wave-energies, the second author and D.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Lannes show that the waves generated by a moving floating object are governed in the linear regime by a non-local transport equation of degree 0, see [8].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In the context of electrical circuits, there are cases in which 1D models of electromagnetic waves propagating along a coaxial cable are governed by operators of degree 0, see for instance [7, Chapter 5].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' One issue of our model is that it only features a single H¨older exponent.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The velocity field of a concrete turbulent fluid consists of many H¨older exponents, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' the H¨older-regularity of the velocity field u(t, x) around a point x ∈ Rd depends on the point itself.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This is known as the multifractal formalism [14, 16].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The term multifractal refers to the fact that the sets of points with same regularity are often fractal.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Moreover, our model does not capture finer descriptions (beyond the variance) of the distribution of the increments of the velocity field.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Such descriptions should quantify its non-Gaussian and intermittent nature [15], and therefore our linear model does not suffice.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' It is known that one can construct a multifractal and intermittent field with the theory of Gaussian multiplicative chaos [38], however our actual goal is to obtain a multifractal and intermittent field dynamically, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' as the solution to a non-linear equation forced by a white-noise in time that admits a rigorous mathematical treatment.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We can also consider a forcing which is not a white-noise in time whose temporal correlation function is given by an oscillating function 6 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE in order to make a comparison with [17, 21, 1] and [11].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Finally, we could investigate other linear models of cascade such as in the case of a compact operator plus a potential of degree 0 as in [31].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' These issues will be tackled in future papers.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Outline.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The article is organized as follows.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In Section 2, we present a simple transport equation that converges to a complex white noise (up to lower order terms).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A small tweak to this model allows us to construct a model that gives rise to a real white noise.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In Section 3, we explain how to generalize the latter model to higher dimensions and give a heuristic proof of the main results in this paper.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In Section 4, we provide a mathematically rigorous study of our model: we introduce the right functional setting, we develop a global well-posedness theory and give a complete description of the asymptotic behavior of the solution, as well as its properties.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This constitutes the proof of Theorem 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Finally, in Section 5 we propose a numerical method and conduct numerical simulations in dimensions 1, 2 and 3 to validate our model.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Acknowledgements.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We thank Oliver B¨uhler for his interesting suggestion about replacing the pure transport term ∂k in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) by sign(k)∂k as a way of fixing the physically undesirable behavior of the solution.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' All five authors were funded by the Simons Collaboration Grant on Wave Turbulence, Simons Award ID: 651475 and 651675.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Notation.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For an integrable function f : Rd → C, we denote by �f its Fourier transform, namely ∀k ∈ Rd k, �f(k) := Ff(k) := � Rdx e−2πix·k f(x) dx.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Whenever defined, the inverse Fourier transform is ∀x ∈ Rd x, f(x) = F−1 �f(x) = � Rd k e2πix·k �f(k) dk.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' It is well know that the Fourier transform is an isometry from L2(Rd x) to L2(Rd k), from S(Rd x) to S(Rd k), where S(Rd x) denote the space of Schwartz functions (i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' smooth functions whose derivatives are rapidly decreasing), and from S′(Rd x) to S′(Rd k) where S′(Rd x) denote the space of tempered distribution (i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' the dual space of S(Rd x)).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We will denote by ⟨·, ·⟩ the duality product between S′ and S.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We will also need some spaces that quantify the regularity of functions more precisely.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For a fixed integer n, Sobolev spaces are defined by Hn(Rd) := {u ∈ L2(Rd) | ∂j xiu ∈ L2(Rd) with 1 ≤ i ≤ d and 0 ≤ j ≤ n}, and their dual spaces are denoted by H−n(Rd).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We will denote by ⟨·, ·⟩H−n,Hn the duality product between Hn and H−n.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For α ∈ (0, 1) the H¨older space C0,α(Rd) is defined by C0,α(Rd) := {u continuous and bounded | ∃C > 0, ∀x, ℓ ∈ Rd, |ℓ| ≤ 1, |δℓu(x)| ≤ C|ℓ|α}, where δℓ denotes the increment defined by δℓu(x) := u(x + ℓ) − u(x) for x, ℓ ∈ Rd.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We will denote by χA the characteristic function3 of the set A.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Let (Ω, σ(Ω), P) be a probability space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A Gaussian field u : Rd → L2(Ω) is a field such that for all n ≥ 1 and for all (x1, x2, · · · , xn) ∈ (Rd)n, the random vector (u(x1), u(x2), · · · , u(xn)) is a Gaussian random vector.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' When d = 1, a 1D Gaussian field is usually called a Gaussian process.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A Gaussian random measure µ acting on S(Rd) is a random tempered distribution 3This means that χA(k) = 1 if k ∈ A and χA(k) = 0 if k /∈ A.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS 7 such that for every g ∈ S(Rd), the random variable ⟨µ, g⟩ is a centered Gaussian.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A white noise dW(x) is a Gaussian random measure acting on L2(Rd) that satisfies the following for any functions f, g ∈ L2(Rd) E ��� Rd f(x)dW(x) � �� Rd g(x)dW(x) �� = � Rd f(x)g(x)dx.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Since we always integrate a deterministic function against dW(x), the choice between Itˆo and Stratonovich integrals is unimportant.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Sometimes we will change variables when integrating against a white noise measure: � t 0 f(t − s)dW(s) = � t 0 f(s)d� W(s).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In such cases, we will use the d� W to denote the new white noise measure after this change of variables.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' One-dimensional transport in wavenumber space 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Building one-dimensional white noise: real vs complex.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In order to mimic the trans- port of energy from large scales to small scales, the authors in [3, 2] proposed a simple transport equation in Fourier space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' To present these ideas, we first consider a one-dimensional model for a velocity field u(t, x), whose spatial Fourier transform aims to solve the linear evolution (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) � ∂t�u(t, k) + c ∂k�u(t, k) = �f(t, k), (t, k) ∈ (0, ∞) × R, �u(t, k)|t=0 = 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Here c > 0 is fixed and can be viewed as a transport rate in wavenumber space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' On the right-hand side of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1), we have included an additive term �f which is the Fourier transform of a spatial forcing term.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The support of �f is localized at small wavenumbers, which is consistent with the assumption that the forcing term in physical space acts at large scales.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As we can see, the dynamical evolution proposed in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) is a genuine transport equation, and only the presence of a forcing makes it inhomogeneous.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Adopting such a setup immediately imposes the complex nature of the velocity field in physical space, as it can be seen when formally taking the inverse Fourier transform of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1), and obtaining the following evolution in physical space: (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) � ∂tu(t, x) − 2πicx u(t, x) = f(t, x), (t, x) ∈ (0, ∞) × R, u(t, x)|t=0 = 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Note that the operator in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) corresponds to multiplication by the space variable 2πicx.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In [3], it is shown that when the forcing f is a white noise in time and statistically homogeneous in space, then the solution to (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2), u : (0, ∞)t × Rx −→ C, converges4 to a complex white noise in space as t → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In other words, the evolution that has been proposed, expressed in Fourier space as a transport equation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) and in physical space as an equation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) involving an operator of degree 0 (multiplication by −2πicx), is able to transfer energy through scales.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Moreover, the solution is statistically homogeneous at any time and it develops the regularity of a white noise as time goes on (technically it’s a sudden drop in regularity at t = ∞).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' To complete the program suggested by the phenomenology of turbulence, the additional linear action of a fractional operator allows, in a similar setup, to generate a solution with asymptotic H¨older-type regularity of parameter H ∈ (0, 1) instead of the one of the white noise, as explained in [3].' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' If some energy is introduced by the forcing at a negative wavelength k < 0, the transport equation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) will move it to smaller negative wavenumbers, going through k = 0, and then to 4Up to lower order terms, see Theorem 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4 for a full asymptotic expansion.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 8 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE infinitely large positive wavenumbers k → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In order to avoid this pathological behavior, one could replace ∂k by ∂|k| = sign(k)∂k which leads to a transport in the direction of |k| instead of k.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Note however that sign(k)∂k is not properly defined at k = 0, and so one needs to be careful in order to propose a well-posed mathematical problem.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' With this in mind, the heart of this article will be the theoretical and numerical study of the following formal evolution: (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) � � � � � ∂t�u(t, k) + c ∂|k|�u(t, k) = �f(t, k), (t, k) ∈ (0, ∞) × R, �u(t, k)|t=0 = 0, �u(t, k)||k|=0 = 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Note that it is necessary to introduce a transmission condition between negative and positive k.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3), we have decided to add the boundary condition �u(t, k)||k|=0 = 0 to decouple negative from positive wavenumbers, so that no energy crosses k = 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In particular, this means that the integral over space of u is zero for all times.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This new dynamics proposed in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) can be written in physical space after formally applying the inverse Fourier transform: (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) � � � � � � � ∂tu + 2πc xH(u) = f, (t, x) ∈ (0, ∞) × R, u|t=0 = 0, � Rx u dx = 0, where H denotes the Hilbert transform defined in the usual way: (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5) Hf(x) := 1 πp.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='v.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' � Ry f(y) x − y dy = − 1 π lim κ→0+ � ∞ κ f(x + y) − f(x − y) y dy.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Notice that we have used the fact the integral of u(t, x) over space vanishes to get the expression of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Notice also that, despite the fact that the spectral evolutions (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) and (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) (whose equivalent expressions in physical space are provided respectively in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) and (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4)), look very similar, the solution to the new dynamics (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) is now real-valued.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Equivalently, the dynamics in Fourier space (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) conserves the Hermitian symmetry of an appropriate initial condition, here assumed to be zero.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Moreover, the solution u : (0, ∞)t × Rx → R of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) can be shown to asymptotically converge to a real white noise in space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As we will explain in the sequel, the additional linear action of a fractional operator will allow the generation, from smooth forcing, of a real fractional Gaussian field.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Finally, it is tempting to generalize (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) to higher dimensions by replacing ∂|k| by k |k| · ∇k.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As we will develop in Section 4, this eventually generates a statistically homogeneous and isotropic solution that will converge to a real d-dimensional Gaussian random measure which is rougher than a white noise (in space) whenever d > 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As we will explain in the sequel, the additional linear action of a fractional operator will us to generate a real d-dimensional Gaussian random measure with the desired H¨older regularity.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Interestingly, it is not obvious to generalize (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) to space dimension d ≥ 1 which would generate a similar statistically homogeneous and isotropic solution in physical space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We provide at the end of the section some additional discussions on this matter.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, for the time being we focus on developing a good understanding in the one-dimensional setting.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In the case of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4), we have the following result: Theorem 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Let the forcing f in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) be (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6) f(t, x) = � Ry ϕ(x − y) dW(t, y), where dW is a space-time Gaussian real white noise, and ϕ ∈ S(R) is a non-negative, non- identically null, even function with null average.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Then: A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS 9 (i) Equation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) admits a global (in time) solution u(t, x), which is a Gaussian process with a.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='s.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' smooth paths in x, and with α-H¨older continuous paths in t for any 0 < α < 1/2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (ii) As t → ∞, the solution u(t) converges in S′(R) to a random Gaussian measure u∞ acting on S(R) with zero-mean, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' for any g ∈ S(R), E[⟨u∞, g⟩] = 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (iii) We have the following asymptotic behavior: E[⟨u∞, g1⟩⟨u∞, g2⟩] = lim t→∞ E[⟨u(t), g1⟩⟨u(t), g2⟩] = C � Rx g1(x) g2(x) dx − � Rx×Ry I(x − y) g1(x) g2(y) dx dy.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='7) for any g1, g2 ∈ S(R).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Here C > 0 is a constant and I is an explicit continuous, even function that depends on ϕ in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A more detailed version of this result is presented in Theorem 4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5, see also Section 4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Note that the first term on the right-hand side of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='7) corresponds to a delta function, while the second term given by I is a smooth lower order term.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The forcing introduced in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6) is indeed a Gaussian white noise in time and statis- tically homogeneous in space, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='8) E[f(s, x)f(t, y)] = Cf(x − y) δs−t , where the spatial correlation function Cf = ϕ∗ϕ is a convolution.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Given that ϕ ∈ S(R), Cf ∈ S(R).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The constant C in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='7) is precisely C = Cf(0) 2c = 1 2c � Rx |ϕ(x)|2 dx > 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The solution to the stochastic PDE (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) is an explicit Gaussian Itˆo process.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A precise formula will be given in Section 4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Even if this solution is continuous in time and space, one can lose regularity at t = +∞, which is why one needs to consider u∞ on the left-hand side of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='7) as a distribution.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The proof of this theorem is posponed to the next section where a more general case, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' multidimesional white noise, will be tackled.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Before we develop the techniques needed to prove Theorem 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1, it is important to understand the asymptotic behavior of solutions to (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) in the complex setting, which is less technical and informative.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In this setting, we have the following result: Theorem 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Let the forcing f in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) be (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='9) f(t, x) = � Ry ϕ(x − y) dW(t, y), where dW is a space-time Gaussian complex white noise, and ϕ ∈ S(R) is a complex, non-identically null, even function.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Then: (i) Equation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) admits a global (in time) solution u(t, x), which is a Gaussian process with a.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='s.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' continuous paths in time and space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (ii) As t → ∞, the solution u(t) converges (in S′(Rd)) to a random Gaussian measure u∞ acting on S(Rd).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 10 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE (iii) We have the following asymptotic behavior (in the sense of distributions).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For any g1, g2 ∈ S(R), E[⟨u∞, g1⟩⟨u∞, g2⟩] = lim t→∞ E[⟨u(t), g1⟩⟨u(t), g2⟩] = 1 2c Cf(0) � Rz g1(z)g2(z)dz + 1 2πic p.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='v.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' � Rz Cf(z) z �� Ry g1(z + y)g2(y)dy � dz .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='10) The function Cf = ϕ ∗ ϕ is the spatial correlation function given by (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='11) E[f(s, x)f(t, y)] = δs−t Cf(x − y), and p.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='v.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Cf(z) z is the principal value of the distribution Cf(z)/z.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' That is, for any test function g ∈ S(R), (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='12) � p.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='v.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='Cf(z) z , g � := p.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='v.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' � R Cf(z)g(z) z dz = � ∞ 0 Cf(z) g(z) − g(−z) z dz.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As we mentioned in Remark 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2, the forcing in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='9) is a complex Gaussian white noise in time and statistically homogeneous in space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Moreover, the solution admits an explicit formula: (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='13) u(t, x) = � t 0 � Ry e2πicx(t−s) ϕ(x − y) dW(s, y).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The same comments as in Remark 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3 apply in this case.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The asymptotic expansion (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='10) remains valid when testing against functions with a finite number of derivatives.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Indeed, u∞ in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='10) can also be interpreted as a Gaussian random measure in H−n(R) for any integer n ≥ 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' More precisely, we will show that for any test functions g1, g2 ∈ Hn(R) one gets E[⟨u(t), g1⟩H−n,Hn⟨u(t), g2⟩H−n,Hn] ∼ t→∞ Cf(0) 2c � R g1(z)g2(z) dz + 1 2πic p.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='v.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' � Rz Cf(z) z �� Ry g1(z + y)g2(y)dy � dz + d(n) ∥g1∥Hn ∥g2∥Hn � 1 ct �n−1 .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='14) where d(n) depends only on n.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This characterizes the rate of convergence.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' One interpretation of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='7) (resp.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='10)) is that the correlation function (resp.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' the real part of it) asymptotically behaves like a white noise.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, this theorem gives a lower-order correction, in the sense that the regularity of the correction is higher than that of the white noise.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='7), such a regular correction is given by a Schwartz function, whereas in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='10), the regular correction is a purely imaginary principal value which has no singularity at zero: by (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='12), the principal value is “controlled” by C′ f(0) near zero.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' It is important to note that in both cases the regular correction is fast-decaying.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='7.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Note that we recover the result in proposition 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1 in [3], i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='15) lim t→∞ E[u(t, x)u(t, y)] = 1 2c Cf(0)δx−y A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS 11 as long as one only tests against even functions with respect to the variable x − y, as is easily seen from the right-hand side of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='12).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' One way to recover a result similar to that in [3] that holds for all test functions is to define the function v(t, x) = e−πictxu(t, x).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This function now satisfies E[v(t, x)v(t, y)] = t sinc (ct(x − y)) Cf(x − y) where sinc(x) := sin(πx) πx denotes the normalized sinc function.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' It immediately follows that (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='16) lim t→∞ E[v(t, x)v(t, y)] = Cf(0) c δx−y.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, it is unclear whether this transformation of u is an interesting object from the physical viewpoint.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Assuming one can take the Fourier transform, (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='16) can be rewritten in wavenumber space as (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='17) lim t→∞ E[�v(t, k)�v(t, k′)] = lim t→∞ E � �u (t, k + πct) �u (t, k′ + πct) � = δk−k′ Cf(0).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The transformation given by v is therefore equivalent to computing the correlation between the k+πct and k′ + πct Fourier modes as t → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Proof of Theorem 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' First of all, note that equation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) admits the explicit solu- tion (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='13) thanks to the Duhamel formula.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Step 1: The solution u is a well defined Gaussian field whose limit at t → ∞ is a Gaussian random measure.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Clearly, u(t, x) is a well defined Itˆo process with zero average and variance (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='18) E[|u(t, x)|2] = � t 0 � Ry |ϕ(x − y)|2 dyds = t ∥ϕ∥2 L2 .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For any test function g (we will soon see that actually g ∈ H1(R) suffices), one gets ⟨u(t), g⟩ = � t 0 � Ry �� Rx e2πicx(t−s) ϕ(x − y) g(x) dx � dW(s, y).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Since Brownian motion has independent, stationary increments we can rewrite the above equation as ⟨u(t), g⟩ = � t 0 � Ry �� Rx e−2πicxs ϕ(x − y) g(x) dx � d� W(s, y) where d� W(s, y) is another Gaussian white noise.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As t → ∞, we find that (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='19) lim t→∞⟨u(t), g⟩ = � ∞ 0 G(s, y) d� W(s, y) where G(s, y) = � Rx e−2πicxs ϕ(x − y) g(x) dx.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This limit is justified only if G ∈ L2(R+ s × Ry), which we set out to prove next.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Firstly, the Young convolution inequality immediately yields ∥G∥L2([0,1]s×Ry) ≤ ∥ϕ∥L1 ∥g∥L2 .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Next, to handle the case |s| ≥ 1, we assume that g ∈ H1(R) and we integrate by parts: 2πics G(s, y) = − � Rx e−2πicxs ∂x � ϕ(x − y) g(x) � dx.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 12 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE By the Young convolution inequality, ∥2πicsG(s, y)∥L2y ≤ ��g′�� L2 ∥ϕ∥L1 + ∥g∥L2 ��ϕ′�� L1 .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Thus one easily finds that: ∥G(s, y)∥L2(R+ s ×Ry) ≲ 1 c ∥g∥H1 ∥ϕ∥W 1,1 , which justifies (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='19).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Step 2: Exchanging expectation and limit as t → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' One could directly use the right-hand side of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='19) in order to compute the correlations of the limiting Gaussian measure.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, this doesn’t allow us to quantify the speed of convergence as t → ∞, so we take a slightly different approach.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We would like to show that E[ lim t→∞ ⟨u(t), g1⟩⟨u(t), g2⟩] = lim t→∞ E[⟨u(t), g1⟩⟨u(t), g2⟩], which happens to be of independent interest.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We justify this exchange of expectation and limit using the Dominated Convergence theorem.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' It suffices to show that there exists a random variable X with finite expectation such that |⟨u(t), g1⟩⟨u(t), g2⟩| ≤ X ∀t ∈ [0, ∞).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In fact one can choose X := sup t≥0 |⟨u(t), g1⟩|2 + sup t≥0 |⟨u(t), g2⟩|2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In order to show that EX < ∞, we use the Monotone Convergence theorem and Doob’s submartin- gale inequality (see for instance Theorem 3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='8 in [22]): E[ sup t≥0 |⟨u(t), g⟩|2] = lim N→∞ E[ sup 0≤t≤N |⟨u(t), g⟩|2] ≤ lim N→∞ 4 E[|⟨u(N), g⟩|2] = 4 ∥G(s, y)∥2 L2(R+ s ×Ry) , which is finite by Step 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Step 3: Calculation of the correlations as t → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We start by computing the correlations for a finite time t > 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' E[u(t, x1)u(t, x2)] = � t 0 e2πic(x1−x2)sCf(x1 − x2) ds = e2πict(x1−x2) − 1 2πic(x1 − x2) Cf(x1 − x2).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This is a well-defined function for each finite t, but we must treat it as a distribution if we want to take the limit t → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' To do so, we test it against some g1, g2 ∈ S(R): E[⟨u(t), g1⟩⟨u(t), g2⟩] = � Rx1×Rx2 E[u(t, x1)u(t, x2)]g1(x1)g2(x2) dx1dx2 = � Rz e2πictz − 1 2πicz ψ(z) dz (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='20) with ψ(z) = Cf(z) � Ry g1(z + y)g2(y)dy, z = x1 − x2 and y = x2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Our goal is to study the last integral as t → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We start with a simple identity that gives us a way to integrate the function (e2πictz −1)/(2πicz).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Note that this function is not absolutely integrable in R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, its integral does converge A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS 13 conditionally, i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' the final result might depend on how we integrate it.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' More precisely, we recall that for all t > 0 (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='21) � R eitz − 1 iz dz := lim R→∞ � R −R eitz − 1 iz dz = π.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As a result of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='21), we have that lim R→∞ � R −R e−2πictz − 1 2πicz ψ(z)dz − ψ(0) 2c = lim R→∞ � R −R e−2πictz − 1 2πicz [ψ(z) − ψ(0)] dz.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In view of ψ(0) = Cf(0) � Ry g1(y)g2(y)dy, it suffices to prove the following in order to obtain (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='10): lim t→∞ lim R→∞ � R −R e−2πictz − 1 2πicz [ψ(z) − ψ(0)] dzdy = 1 2πc � ∞ 0 ψ(z) − ψ(−z) iz dz = 1 2πic p.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='v.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' � Rz ψ(z) z dz.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='22) To prove (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='22), we rewrite the left-hand side as follows: (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='23) lim R→∞ � R −R e−2πictz − 1 2πc ψ(z) − ψ(0) iz dz = 1 2πic � lim R→∞ � R −R e−2πictz ψ(z) − ψ(0) z dz − lim R→∞ � R −R ψ(z) − ψ(0) z dz � Note that the last term gives the desired limit after using the fact that � R −R ψ(z) − ψ(0) z dz = � R 0 ψ(z) − ψ(−z) z dz and taking R → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The final step is to show that the first term on the right-hand side of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='23) tends to zero as t → ∞.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Note that F(z) := ψ(z) − ψ(0) z is not integrable in Rz.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However the following lemma shows that its derivatives have better prop- erties.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Its proof is postponed to the end of the proof of Theorem 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Recall that ψ was defined in terms of g1, g2 right after (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='20).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Lemma 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='8.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Let n ≥ 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' If g1 ∈ Hn+1(R) and g2 ∈ L2(R) then F ∈ W n,1(Rz) and lim |z|→∞(∂m z F)(z) = 0, for any 0 ≤ m ≤ n, (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='24) ∥∂m z F∥L1(Rz) ≲ ∥g1∥Hm+1 ∥g2∥L2 for any 1 ≤ m ≤ n.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='25) We integrate by parts the first term on the right-hand side of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='23) � R −R e−ictz ψ(z) − ψ(0) z dz = − � R −R 1 ict ∂ze−ictz F(z)dz = − 1 ict e−ictz F(z) ��� R z=−R + 1 ict � R −R e−ictz∂zF(z) dz.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 14 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE Using Lemma 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='8, we are able to take the limit R → ∞: lim R→∞ � R −R e−ictz ψ(z) − ψ(0) z dz = 1 ict � Rz e−ictz∂zF(z) dz.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Next, we continue to integrate by parts using (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='24) (which gets rid of the boundary terms) lim R→∞ � R −R e−ictz ψ(z) − ψ(0) z dz = � 1 ict �n � Rz e−ictz∂n z F(z) dz, thus we have ���� lim R→∞ � R −R e−ictz ψ(z) − ψ(0) z dz ���� ≤ � 1 ct �n ∥∂n z F∥L1(R2) .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We use (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='25) to finish the proof of Theorem 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Now, we need to prove the technical Lemma 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='8.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Proof of Lemma 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='8.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' First we can easily show that ∂n z F(z) = � 1 0 sn∂n+1 z ψ(zs)ds (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='26) = � z 0 sn zn+1 ∂n+1 z ψ(s)ds.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='27) Then we show that for all 0 ≤ m ≤ n + 1 and all p ∈ [1, ∞] (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='28) ∥∂m z ψ∥Lp(R) ≲ ||Cf||W m,p(Rz) ∥g1∥Hm ∥g2∥L2 .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Indeed, the Leibniz rule yields ∂m z ψ(z) = m � j=0 � m j � ∂j zCf(z) � Ry ∂m−j z g1(y + z)g2(y)dy.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' By Cauchy-Schwarz inequality, |∂m z ψ(z)| ≤ � � m � j=0 � m j � |∂j zCf(z)| � � ∥g1∥Hm ∥g2∥L2 thus one gets (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='28).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Then we show that for all 0 ≤ m ≤ n, lim |z|→∞ ∂m z F(z) = 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Indeed, by the Cauchy-Schwarz inequality, (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='27) and (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='28), |∂m z F(z)| ≤ ��∂m+1 z ψ �� L2(Rz) �� |z| 0 s2m |z|2(m+1) ds � 1 2 = ��∂m+1 z ψ �� L2(Rz) |z| 1 2 −→ |z|→∞ 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Finally, for all 1 ≤ m ≤ n, (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='26) implies ∥∂m z F(z)∥L1(R2) ≤ � 1 0 sm ��∂m+1 z ψ(zs) �� L1(R2) ds ≤ ��∂m+1 z ψ �� L1(R2) �� 1 0 sm−1ds � and thus we conclude with (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='28).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' □ A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS 15 Natural generalizations of the dynamics in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1)-(2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) to higher dimensions could be obtained in two ways.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Firstly, the product c ∂k�u in the transport equation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) could be generalized to a scalar product of a given unit vector e ∈ Rd with the gradient ∇k�u(t, k).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Unfortunately, this puts too much weight on the constant vector e and results in an obvious statistical anisotropy in physical space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For applications to turbulence, we must require that statistical laws are not only invariant by translation, but also under rotation (i.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='e.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' statistical isotropy), as commonly observed in laboratory and numerical experiments, and as expected from a physical point of view.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Another option would be to replace the multiplication by ix in the physical space formulation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) by the multiplication by i|x|, where |x| is the modulus of x ∈ Rd.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Once again, this would introduce anisotropy in the system, and more importantly, it would break statistical homogeneity even in dimension d = 1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' One may check these claims directly using the exact solution (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) to compute the covariance function at a given time t and any two positions x, y (see [3] for details).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Indeed, this covariance function eventually depends on the difference |x| − |y|, and not on x − y as would be desirable.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Beyond these issues, none of these propositions would ensure that a given real-valued initial condition u(0, x) ∈ R gives rise to a real-valued solution u(t, x) ∈ R at all future times.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In other words, in order to construct a real-valued solution in physical space, one needs to propose a dynamical picture able to preserve the Hermitian symmetry of the Fourier transform �u(t, k), as does the dynamics in (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Higher dimensional real fractional gaussian fields: heuristic In the previous section we gave a rigorous proof of the construction of a dynamical complex white noise.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This proof was carried out in physical space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' For the dynamical real white noise of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3), on the other hand, it is more convenient to think of its wavenumber formulation.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, even in the case of a dynamical complex white noise, the solution u(t, x) is not in Lp(Rx) for any 1 ≤ p < ∞ (see (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='18)), hence its Fourier transform is not defined pointwise.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In conclusion, it is difficult to make sense of equation (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) in wavenumber space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' However, we will not concern ourselves with such difficulties in this section, and we will work as if the solution to (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) were well-defined pointwise: we refer to Section 4 for a rigorous analysis.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As we will later see, working in wavenumber space is very convenient to formally show that (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) builds a dynamical real white noise, as well as to extend this construction to d-dimensional fractional Gaussian fields.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A transport equation in wavenumber space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We propose the following initial value problem as a generalization of (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) � � � � � � � � � ∂t�u(t, k) + divk � ck |k| �u(t, k) � + cH + 1 2 |k| �u(t, k) = �f(t, k) t > 0, k ∈ Rd, |k| > κ > 0, �u(t, k) = 0 t > 0, k ∈ Rd, |k| ≤ κ, �u(0, k) = 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' where H is a real constant (which will be eventually connected with the H��older exponent of the solution), and divk stands for the usual divergence operator in wavenumber space.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As one can easily verify with a few vector calculus identities, (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2) divk � ck |k| �u(k) � + c H + 1 2 |k| �u(k) = c ∂|k| �u(k) + c H + d − 1 2 |k| �u(k) with ∂|k| := k |k| · ∇k.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' When d = 1 and H = −1/2, one recovers (2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) from the above.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The initial value problem (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) can be regarded as a conservation law in wavenumber space with a source term �f(t, k), a damping term (H + 1/2) �u(t, k)/|k| and Dirichlet boundary conditions at the sphere |k| = κ.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Equation (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) has been thoroughly studied when �f(t, k) is regular enough (see [26], [33]), but in our case �f(t, k) is too rough for such classical results to be applicable.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In particular, we will 16 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE assume that the forcing term �f satisfies (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) E[ �f(t, k1) �f(s, k2)] = � Cf(k1) δt−s δk1−k2, where � Cf(k) is radial and null in the ball |k| < κ.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Condition (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) formally follows from considering the Fourier transform of a white noise in time satisfying (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='4) E[f(t, x)f(s, y)] = δt−s Cf(x − y).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remark 3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As part of equation (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) one has the following technical condition (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5) �u(t, k) = 0 t > 0, k ∈ Rd, |k| ≤ κ, for κ > 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Indeed, if |k| = 0, then divk � k |k| · � and H+ 1 2 |k| are not well-defined.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This condition (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5) implies in particular that F−1�u has null spatial average, whenever defined.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' It might be possible to make sense of the problem (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) for κ = 0 by adequately changing condition (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5), imposing �f(t, k = 0) = 0 and an appropriate behaviour near k = 0, but this is outside the scope of this paper.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' 3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Asymptotic behavior: power-law.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In this section, we show that the two-point correlation of the solution to (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) displays a power-law behavior.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In our first result (Theorem 3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2), we obtain this asymptotic behavior as t → ∞ under fairly mild assumptions on the forcing �f.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Under stronger assumptions on �f, we derive a second result (Proposition 3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='5) showing this power law behavior in finite time.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Among other things, such power laws are important because their exponent determines the H¨older regularity of the solution in physical space (should it be possible to take the inverse Fourier transform).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The main idea of the heuristic proof of our desired results is to perform a change of variables to rewrite (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) as a 1D transport equation with respect to |k| and parametrized by the “angular variable” k |k|.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Such an equation admits an explicit solution that we will exploit.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We will further discuss such consequences in Section 4.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Theorem 3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='2 (Heuristic version).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Let the forcing �f satisfy (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='3) in such a way that � Cf(k) = ψ(|k|) is radial, non-negative, non identically null, with s2H+d ψ(s) ∈ L1(R+ s ).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Furthermore, we assume that ψ is null when |k| < κ.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Then, (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) admits a solution that satisfies the following asymptotic behavior lim t→∞ E[�u(t, k)�u(t, k′)] = |k|−(2H+d) (C(d, H) − Ψd,H(|k|)) δk−k′ where (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6) Ψd,H(|k|) := 1 c � ∞ |k| s2H+d ψ(s) ds.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' is a positive non-increasing absolutely continuous function and (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='7) C(d, H) := Ψd,H(0) > 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As we have already pointed out in Remark 2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6, the function Ψd,H can be seen as lower-order correction in comparison with the Dirac distribution.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Moreover, if we assume that ψ is fast- decaying, then Ψd,H will also be fast-decaying.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Heuristic proof.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' In order to find a formal solution to (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1), we let �v(t, k) := |k|H+d− 1 2 �u(t, k), �g(t, k) := |k|H+d− 1 2 �f(t, k).' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' A LINEAR STOCHASTIC MODEL OF TURBULENT CASCADES AND FRACTIONAL FIELDS 17 Next we rewrite (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='1) in terms of �v, namely (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='8) � � � � � ∂t�v(t, k) + c ∂|k|�v(t, k) = �g(t, k) t > 0, |k| > κ, �v(t, k) = 0 t > 0, |k| ≤ κ, �v(0, k) = 0, where we use the fact that ∂|k| = k |k| · ∇k.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Equation (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='8) can be regarded as a 1D transport equation with respect to |k| and parametrized by the “angular variable” k/|k|.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Thus it is easy to give an explicit solution: (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='9) �v(t, k) = � t � t− |k|−κ c � + �g � s, (|k| − ct + cs) k |k| � ds.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Next we compute the correlations of �v(t) using those of �f.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We have E[�v(t, k1)�v(t, k2)] = � t � t− |k1|−κ c � + � t � t− |k2|−κ c � + δcs1−cs2δ |k1|−ct+s1 |k1| k1− |k2|−t+cs2 |k2| k2 � Cg �|k1| − ct + cs1 |k1| k1 � ds1ds2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' We assume that we can write δcs1−cs2δ |k1|−ct+cs1 |k1| k1− |k2|−ct+cs2 |k2| k2 = δcs1−cs2δ |k1|−ct+cs1 |k1| k1− |k2|−ct+cs1 |k2| k2 even if this not mathematically rigorous.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Moreover, by the change of variables from cartesian to polar coordinates δ |k1|−ct+cs |k1| k1− |k2|−ct+cs |k2| k2 = �|k1| − ct + cs |k1| �−(d−1) δk1−k2.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This is possible since the Jacobian � |k1|−ct+cs |k1| �−(d−1) has no singularities in the region of integration thanks to κ > 0.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' As a result, one obtains E[�v(t, k)�v(t, k′)] = � � � t � t− |k|−κ c � + �|k| − ct + cs |k| �−(d−1) � Cg �|k| − ct + cs |k| k � ds � � δk−k′.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' This immediately implies E[�u(t, k)�u(t, k′)] = |k|−(2H+d) � � � t � t− |k|−κ c � + (|k| − ct + cs)2H+d � Cf �|k| − ct + cs |k| k � ds � � δk−k′.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' The change of variables s �→ |k1| − ct + cs yields E[�u(t, k)�u(t, k′)] = |k|−(2H+d) � χ|k|>ct+κ � |k| |k|−ct s2H+d � Cf � s |k| k � ds c � δk−k′ + |k|−(2H+d) � χ|k|≤ct+κ � |k| κ s2H+d � Cf � s |k| k � ds c � δk−k′ where χA denotes the characteristic function of the set A.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Remember that ψ(|k|) := � Cf(k) since Cf is radial.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' Using (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='6), we may rewrite E[�u(t, k)�u(t, k′)] = |k|−(2H+d) � χ|k|>ct+κ [Ψd,H(|k| − ct) − Ψd,H(|k|)] + χ|k|≤ct+κ [Ψd,H(κ) − Ψd,H(|k|)] � δk−k2 .' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' (3.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content='10) 18 G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' B.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' APOLIN´ARIO, G.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' BECK, L.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' CHEVILLARD, I.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GALLAGHER, AND R.' metadata={'source': '/home/zjlab/wf/langchain-ChatGLM/knowledge_base/A9AyT4oBgHgl3EQf3_rL/content/2301.00780v1.pdf'} +page_content=' GRANDE ' 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