The backward Îto method for the Lagrangian simulation of transport processes with large space variations of the diffusivity

International audienceRandom walk models are a powerful tool for the investigation of transport processes in turbulent flows. However, standard random walk methods are applicable only when the flow velocities and diffusivity are sufficiently smooth functions. In practice there are some regions where the rapid but continuous change in diffusivity may be represented by a discontinuity. The random walk model based on backward Îto calculus can be used for these problems. This model was proposed by LaBolle et al. (2000). The latter is best suited to the problems under consideration. It is then applied for two test cases with discontinuous diffusivity, highlighting the advantages of this method

Two-particle models for the estimation of the mean and standard deviation of concentrations in coastal waters

In this paper we study the mean and standard deviation of concentrations using random walk models. Two-particle models that takes into account the space correlation of the turbulence are introduced and some properties of the distribution of the particle concentration are studied. In order to reduce the CPU time of the calculation a new estimator based on reverse time diffusion is applied. This estimator has been introduced recently by Milstein, Schoenmakers, and Spokoiny (2004). Some numerical aspects of the implementation are discussed for relative simple test problems and finally a realistic application to predict the spreading of the pollutant in the Dutch coastal zone is described

Use of groundwater lifetime expectancy for the performance assessment of a deep geologic waste repository: 1. Theory, illustrations, and implications

Long-term solutions for the disposal of toxic wastes usually involve isolation of the wastes in a deep subsurface geologic environment. In the case of spent nuclear fuel, if radionuclide leakage occurs from the engineered barrier, the geological medium represents the ultimate barrier that is relied upon to ensure safety. Consequently, an evaluation of radionuclide travel times from a repository to the biosphere is critically important in a performance assessment analysis. In this study, we develop a travel time framework based on the concept of groundwater lifetime expectancy as a safety indicator. Lifetime expectancy characterizes the time that radionuclides will spend in the subsurface after their release from the repository and prior to discharging into the biosphere. The probability density function of lifetime expectancy is computed throughout the host rock by solving the backward-in-time solute transport adjoint equation subject to a properly posed set of boundary conditions. It can then be used to define optimal repository locations. The risk associated with selected sites can be evaluated by simulating an appropriate contaminant release history. The utility of the method is illustrated by means of analytical and numerical examples, which focus on the effect of fracture networks on the uncertainty of evaluated lifetime expectancy.Comment: 11 pages, 8 figures; Water Resources Research, Vol. 44, 200

Клиническое наблюдение применения тоцилизумаба у пациента с системным вариантом ювенильного идиопатического артрита

The article presents a case of using genetically engineered biopharmaceutical tocilizumab in a child with systemic juvenile idiopathic arthritis. On the initial stage, the treatment was characterized by resistance to high doses of glucocorticoids and cytostatic drugs. Successful termination of visceral and articular manifestations of systemic juvenile idiopathic arthritis and normalization of laboratory indicators of disease activity in the setting of use of interleukin 6 receptor blocker were described. We observed stable improvement of the child’s condition during a year-long follow-up in the setting of the selected anti-inflammatory therapy pattern. В статье рассмотрен пример применения генно-инженерного биологического препарата тоцилизумаба у ребенка с системным вариантом ювенильного идиопатического артрита. Лечение на первоначальном этапе характеризовалось резистентностью к высоким дозам глюкокортикоидов и цитостатиков. Описано успешное купирование висцеральных и суставных проявлений системного варианта ювенильного идиопатического артрита, нормализация лабораторных показателей активности болезни при применении препарата блокатора рецепторов интерлейкина 6. Отмечено стабильное улучшение состояния ребенка при наблюдении в течение года на фоне выбранной схемы противовоспалительной терапии.

Comprehensive psychological correction and prevention of neuroses in cheldren

Available from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Reverse-time diffusion in environmental models

Electrical Engineering, Mathematics and Computer Scienc

Modern aspects of diagnosis of bone metabolism in children with juvenile idiopathic arthritis

The review deals with the diagnosis of changes in bone metabolism in children with juvenile idiopathic arthritis (JIA) in terms of disclosure of the pathogenetic mechanisms of immunopathological disorders in the body. It is shown that timely and adequate characterization of the state of mineralization of bone tissue in patients with JIA — as an indicator of systemic catabolic process, remains an ongoing problem, entailing the need for large-scale introduction of new diagnostic techniques. Through the presentation of the traditional methods of diagnosis of bone metabolism, their capabilities, strengths and weaknesses, analyze the advantages of assessing the level of bone formation, taking into account a variety of biochemical markers. The data on the development of modern diagnostic approaches to the assessment of osteopenia complications in children with JIA, based on the characterization of molecular-genetic targets of the process of osteogenesis. Conclusion: for the adequate therapy and its timely correction in children with JIA in the early stages of the disease it is necessary to carry out a comprehensive study on the identification of metabolic disorders of bone, holding it in the dynamics, and actively introducing the practice of modern and affordable methods of diagnosis of osteopenic disorders

Two-particle models for the estimation of the mean and standard deviation of concentrations in coastal waters

In this paper we study the mean and standard deviation of concentrations using random walk models. Two-particle models that takes into account the space correlation of the turbulence are introduced and some properties of the distribution of the particle concentration are studied. In order to reduce the CPU time of the calculation a new estimator based on reverse time diffusion is applied. This estimator has been introduced recently by Milstein, Schoenmakers, and Spokoiny (2004). Some numerical aspects of the implementation are discussed for relative simple test problems and finally a realistic application to predict the spreading of the pollutant in the Dutch coastal zone is described

Random walk in case of iso- and diapycnal diffusion

Large scale diffusion processes in the ocean occur mostly along isopycnal surfaces, i.e. surfaces of equal density. However, there is also diapycnal diffusion, which is associated with a diffusion flux orthogonal to isopycnal surfaces. The diapycnal and isopycnal diffusion fluxes are commonly parameterized a la Fourier-Fick, a formulation involving a diffusion tensor that is not isotropic. In this case Eulerian discretizations of the isopycnal diffusion term yield discrete operators that are not monotonic. So, the Eulerian approach may not always be the best option. Another way is to use the Lagrangian approach, that follows the particle through space at every time step. The movement of particle is modeled with the help of stochastic differential equation, which is consistent with the advection-diffusion equation. By simulating the positions of many particles the diffusion processes can be described. These random walk models allow to avoid a lot of problems, connected with the Eulerian approach, and this makes them very attractive in a number of applications. In this paper the random walk model for the simulation of diffusion processes with space-varying, general positive definite diffusivity, particularly for iso and dia-pycnal diffusion, is established and analyzed. The Lagrangian approach is applied for linear idealized test problems, for which the exact solution is known. The random walk model is also tested for a sinking-diffusion model and it is shown that the Lagrangian approach can also be used for the solution of the adjoint problem. i.e. computing the residence time. The results obtained show that this random walk model may be a good alternative to commonly-used Eulerian models