# Seminar khoa học của GS. Valeriy Arkhincheev và TS. Lê Đại Nam

Vào 14h00, ngày 21/6/2024 Viện IAST tổ chức buổi trao đổi học thuật tại Lầu 6 Thư viện với nội dung chi tiết như sau:

**GS. Valeriy Arkhincheev trình bày về "Stochastic processes in complex media and fractional calculus. Application for a living systems"**

Tóm tắt:

The report is devoted to the stochastic processes in the complex systems with fractal structure. According to the many investigations in this field the strict and rigorous approach to this problem must be based on the fractional calculus. The brief review and history of fractals was given. The deduction of the diffusion equations of fractional order was proceeded on the basis of the microscopic model of the comb structure. The author was among the first researchers to propose the exact deduction of the fractional order diffusion equations (1991 y.) and obtain the analytic solution of this fractional order equation.

The developed approach was applied to the problem of mass transfer in living plants with finite lengths of bitches in the framework of the mathematical comb model was studied. In our paper (Scientific Reports, 2019) it was established that mass transfer processes in living plants depend on the geometric fractal structure of plants, namely, that the mass transfer is accelerated from steam to bitches. Now this study was continued and the more real model with finite lengths of bitches was studied. From mathematical point of view the solution of fractional order equation with reflecting boundary conditions was obtained. The transition from anomalous character of mass transfer to usual diffusion due to finite length of ribs was proceeded. The anomalous character of mass transfer lead to dependencies of effective diffusion coefficients, describing mass transfer, on the length of bitches. It was shown the control and self regulation of the transfer processes of water, fertilizers in plants and as a result the growth of bitches and leaves in plants was governed by the lengths of bitches. The discussion of obtained results was given.

**TS. Lê Đại Nam trình bày về "Nonlinear effects in manybody van der waals interactions."**

Tóm tắt:

Van der Waals interactions are ubiquitous and they play an important role for the stability of materials. In main-stream computational schemes, current understanding of this type of coupling is based on linear response theory, while optical nonlinearities are rarely considered [1-4]. Many materials, however, exhibit strong optical nonlinear response, which prompts further evaluation of dispersive forces beyond linear response. Here we present a ** discrete coupled nonlinear dipole** approach that takes into account linear and nonlinear properties of all dipolar nanoparticles in a given system [5]. This method is based on a Hamiltonian for nonlinear dipoles, which we apply in different systems uncovering a complex interplay of distance, anisotropy, polarizabilities, and hyperpolarizabilities in the vdW energy. This investigation broadens our basic understanding of dispersive interactions, especially in the context of nonlinear materials, and serves as a stepping stone for future design of mainstream computational schemes for more accurate simulations

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