Manipulation of large systems of active particles is a serious challenge across diverse domains, including crowd management, control of robotic swarms, and coordinated material transport. The development of advanced control strategies for complex scenarios is hindered, however, by the lack of scalability and robustness of the existing methods, in particular, due to the need of an individual control for each agent. One possible solution involves controlling a system through a leader or a group of leaders, which other agents tend to follow. Using such an approach we develop an effective control strategy for a leader, combining reinforcement learning (RL) with artificial forces acting on the system. To describe the guidance of active particles by a leader we introduce the generalized Vicsek model. This novel method is then applied to the problem of the effective evacuation by a robot-rescuer (leader) of large groups of people from hazardous places. We demonstrate, that while a straightforward application of RL yields suboptimal results, even for advanced architectures, our approach provides a robust and efficient evacuation strategy. The source code supporting this study is publicly available at: https://github.com/cinemere/evacuation.

We explore dynamic structural superlubricity for the case of a relatively large contact area, where the friction force is proportional to the area (exceeding $\sim 100\,nm^2$) experimentally, numerically, and theoretically. We use a setup comprised of two molecular smooth incommensurate surfaces -- graphene-covered tip and substrate. The experiments and MD simulations demonstrate independence of the friction force on the normal load, for a wide range of normal loads and relative surface velocities. We propose an atomistic mechanism of this phenomenon, associated with synchronic out-of-plane surface fluctuations of thermal origin, and confirm it by numerical experiments. Based on this mechanism, we develop a theory for this type of superlubricity and show that friction force increases linearly with increasing temperature and relative velocity, for velocities, larger than a threshold velocity. The MD results are in a fair agreement with predictions of the theory.

Molecular dynamics simulation of the benzylpenicillin adsorption and transport in nanoporous silicon has been carried out. For mu s-scale simulations, the coarse-grained model was developed in which the benzylpenicillin molecule was represented as a material point and its motion in an aqueous solution was described by the Langevin dynamics. The interactions of molecules with each other and with the silicon surface were described by potential functions obtained from all-atom simulations. Nanopores had a cylindrical shape, their diameter ranged from 10 to 50 nm. It was found that near the surface of cylindrical nanopores benzylpenicillin forms an adsorbed layer of molecules with a local density exceeding the average value by almost an order of magnitude. The density of molecules in the adsorbed layer and their diffusion mobility increase with increasing nanopore diameter. The duration of the complete molecule release increases nonlinearly with an increase in the length of the nanopore and the initial density of molecules in its space.

The article presents a numerical study of the formation of the amplitude response in a free surface from simultaneous scattering of Rayleigh waves and vertically incident longitudinal waves by an embedded contrast velocity inclusion. It has been established that the significant presence of body waves in a microseismic field does not fundamentally change the result of the microseismic sounding method, which is based on the notion of the overwhelming contribution of the fundamental mode of a Rayleigh wave to the formation of the Earth’s microseismic field. Cases are considered when a microseismic signal at the same frequency is modeled only by the fundamental mode of the Rayleigh wave, only by a vertically incident longitudinal wave, and by both types of waves simultaneously. Variants of inhomogeneities with different dimensions and velocity properties are considered. The analysis was performed in a (λ, r)-space, in analogy with reconstruction of the structure of the geological setting in the microseismic sounding method, where λ is the wavelength of the fundamental Rayleigh mode and r is the coordinate on the Earth’s surface.

The paper is devoted to the analysis of the results of a two-dimensional numerical solution of the direct scattering problem of the fundamental Rayleigh mode on two velocity inhomogeneities located one under another. This model made it possible to analyze some cases of using the method of microseismicsounding (MMS) in conditions of complex structured media. Using the numerical model built from first principles in direct modeling, we obtained estimates of the vertical resolution of the microseismic sounding method. The cases of a number of specific geometrical dimensions and a number of elastic parameters of inclusions with values close to those encountered in natural conditions are considered. Simple practical methods have been developed and formulated, with the help of which one can estimate the vertical resolution of objects when interpreting microseismic sounding sections obtainedexperimentally. Estimation of the vertical resolution of the MMS on synthetic data is that, if the distance between the centers of two small inhomogeneities, one above the other, compared to the depth, is 36‑41 % (or more) of the fundamental mode of the Rayleigh wave, equal to λR = Hcenter/ 0.4, where Hcenter is the midpoint depth between the centers of inhomogeneities, then the images of these inhomogeneities will be resolved in the field of random Rayleigh waves. That is, to ensure the resolution of the MMS, the vertical distance between the centers of small discontinuities should be Hcenter or more. The techniques developed were used to assess the resolution of horizontally-lying layers in the sections obtained during the study of the junction zone of the Taman Peninsula and the Crimea in the course of geological interpretation of microseismic research results.

Работа посвящена анализу результатов двумерного численного решения прямой задачи рассеяния фундаментальной моды Рэлея на двух скоростных неоднородностях, расположенных друг под другом. Данная модель позволила проанализировать некоторые случаи использования метода микросейсмического зондирования (ММЗ) в условиях сложно построенных сред. С использованием численной модели, построенной из первых принципов в прямом моделировании получены оценки вертикальной разрешающей способности метода микросейсмического зондирования. Рассмотрены случаи ряда конкретных геометрических размеров и ряда упругих параметров включений, со значениями, близкими к встречающимся в природных условиях. Выработаны и сформулированы простые практические приемы, с помощью которых можно оценивать вертикальное разрешение объектов при интерпретации разрезов микросейсмического зондирования по экспериментально полученным разрезам. Оценка вертикальной разрешающей способности ММЗ на синтетических данных состоит в том, что, если расстояние между центрами двух малых по сравнению с глубиной залегания неоднородностей, расположенных друг над другом, составляет 36 41 (или более) от длины фундаментальной моды волны Рэлея, равной R Нcenter/ 0,4, где Нcenter глубина середины между центрами неоднородностей, то изображения этих неоднородностей будут разрешены в поле случайных волн Рэлея. То есть, для разрешимости по ММЗ расстояние по вертикали между центрами малых неоднородностей должно составлять Нcenter или более. Выработанные приемы использованы для оценки разрешения горизонтально залегающих слоев в разрезах, полученных в ходе изучения зоны сочленения Таманского полуострова и Крыма при геологической интерпретации результатов микросейсмических исследований. The paper is devoted to the analysis of the results of a twodimensional numerical solution of the direct scattering problem of the fundamental Rayleigh mode on two velocity inhomogeneities located one under another. This model made it possible to analyze some cases of using the method of microseismicsounding (MMS) in conditions of complex structured media.Using the numerical model built from first principles in direct modeling, we obtained estimates of the vertical resolution of the microseismic sounding method. The cases of a number of specific geometrical dimensions and a number of elastic parameters of inclusions with values close to those encountered in natural conditions are considered.Simple practical methods have been developed and formulated, with the help of which one can estimate the vertical resolution of objects when interpreting microseismic sounding sections obtainedexperimentally.Estimation of the vertical resolution of the MMS on synthetic data is that, if the distance between the centers of two small inhomogeneities, one above the other, compared to the depth, is 36 41 (or more) of the fundamental mode of the Rayleigh wave, equal to R Hcenter/ 0.4, where Hcenter is the midpoint depth between the centers of inhomogeneities, then the images of these inhomogeneities will be resolved in the field of random Rayleigh waves. That is, to ensure the resolution of the MMS, the vertical distance between the centers of small discontinuities should be Hcenter or more. The techniques developed were used to assess the resolution of horizontallylying layers in the sections obtained during the study of the junction zone of the Taman Peninsula and the Crimea in the course of geological interpretation of microseismic research results.

Nanostructured metal (oxy)hydroxides acting as an aggregator of coagulation proteins and capable of changing the ion balance and purifying the medium are a promising base for the development of the materials with hemostatic action. In the present study in order to examine the capability of AlOOH and Fe(OH)2 nanosheets to accumulate a bioactive compound, forming a hierarchical nano-agent, the serotonin free energy change during its interaction with these nanosheets was estimated numerically. Using the steered molecular dynamics, it was found that the adsorption of serotonin by AlOOH occurs with the hydrogen bonds formation both by an amino group with surface oxygen atoms and by phenolic ring oxygen with a nanosheet OH-groups, depending on pH. The interaction of both zwitterionic and cationic serotonin with Fe(OH)2 nanosheet is characterized by a weak adsorption.

Study of the statistical parameters of the Earth's random microseismic field makes it possible to obtain estimates of the properties and structure of the Earth's crust and upper mantle. Different approaches are used to observe and process the microseismic records, which are divided into several groups of passive seismology methods. Among them are the well-known methods of surface-wave tomography, the spectral H/V ratio of the components in the surface wave, and microseismic sounding, currently under development, which uses the spectral ratio V/V (0) of the vertical components between pairs of spatially separated stations. In the course of previous experiments, it became clear that these ratios are stable statistical parameters of the random field that do not depend on the properties of microseism sources. This paper proposes to expand the mentioned approach and study the possibilities for using the ratio of the horizontal components H (1)/H (2) of the microseismic field. Numerical simulation was used to study the influence of an embedded velocity inhomogeneity on the spectral ratio of the horizontal components of the random field of fundamental Rayleigh modes, based on the concept that the Earth's microseismic field is represented by these waves in a significant part of the frequency spectrum.

The implications of the Poisson ratio of a heterogeneity for the microseismic image of the latter reconstructed by the microseismic sounding method are studied in the numerical experiments. In particular, the cases are considered with anomalous effective Poisson ratios, which may probably occur if the microseismic waves propagate through fractured zones where the crack opening is commensurate with or larger than the characteristic amplitude of the vibrations. Based on the numerical simulations, the nonlinear distortions in the microseismic sounding method, which arise due to the perturbation of the microseismic (probing) signal by introducing the heterogeneities, are estimated.

On base of new passive seismic technique the deep structure of Astrakhan gas field was investigated. There was found a subvertical stock-type structure associated with the productive area sinking down to depths of at least 30-35 km. This structure was assumed to be a possible fluid conducting channel.

Basing on numerical simulation we suggested criteria of classification for big and small inclusions in comparison to surface Rayleigh wave length. The inclusions with size of 1.5-2 and more of wavelengths could be regarded as large ones since positions of their boundaries could be found precisely in the intensity pattern if the inclusions are exposed with Rayleigh waves from all sides. At such an exposure depth and lateral position of “focal points” of small heterogeneities (when size of heterogeneity is less than Fresnel zone) could also be defined precisely independently from the relation between the size and wave length, however the shape of the heterogeneity takes a form of a generalized cloud with size of about Fresnel zone. Two small heterogeneities begin to break up in the intensity pattern if distance between them constitutes 20% of sounding wave length or more.

Submitted for the MAR07 Meeting of The American Physical Society Modeling of the SWNT-DNA complexes in the water solution ALEXEY A. TSUKANOV, EUGENE A. GRACHEV, Moscow State University, SLAVA V. ROTKIN, Physics Department and Center for Advanced Materials and Nanotechnology, Lehigh University — It is known that the single-wall nanotubes (SWNTs) may form a hybrid with a single-stranded DNA having a regular helical structure of the DNA wrap around the SWNT cylinder. Such DNA wrapping creates a periodic potential at the NT surface, which results in developing a specific modulation of the NT bands. Numerical self-consistent modeling of these effects requires knowledge of the polarization of the environment. We have shown that the result is very sensitive to what extent the exterior water (and ions in the solution) are polarized to screen the potential of the DNA. Both the NT screening and the response of the environment are important to include self-consistently to obtain quantitative results. We present the Monte-Carlo simulation of the interaction of a NT, a DNA and a solvent and provide heuristic physics interpretation of the results. We show that the NT screening is different from what one expects for a metal or insulator material due to non-local Coulomb correlations. An effective dielectric screening of the water exterior is extracted from the simulations. Alexey A. Tsukanov Moscow State University Date submitted: 20 Nov 2006 Electronic form version 1.4