Mechanical systems subjected to generalized nonholonomic constraints

We study mechanical systems subject to constraint functions that can be dependent at some points and independent at the rest. Such systems are modelled by means of generalized codistributions. We discuss how the constraint force can transmit an impulse to the motion at the points of dependence and derive an explicit formula to obtain the ``post-impact'' momentum in terms of the ``pre-impact'' momentum.Comment: 24 pages, no figure

Heat Transfer Model of Hyporthermic Intracarotid Infusion of Cold Saline for Stroke Therapy

A 3-dimensional hemispheric computational brain model is developed to simulate infusion of cold saline in the carotid arteries in terms of brain cooling for stroke therapy. The model is based on the Pennes bioheat equation, with four tissue layers: white matter, gray matter, skull, and scalp. The stroke lesion is simulated by reducing blood flow to a selected volume of the brain by a factor of one-third, and brain metabolism by 50%. A stroke penumbra was also generated surrounding the core lesion (blood volume reduction 25%, metabolism reduction 20%). The finite difference method was employed to solve the system of partial differential equations. This model demonstrated a reduction in brain temperature, at the stroke lesion, to 32°C in less than 10 minutes

A general framework for nonholonomic mechanics: Nonholonomic Systems on Lie affgebroids

This paper presents a geometric description of Lagrangian and Hamiltonian systems on Lie affgebroids subject to affine nonholonomic constraints. We define the notion of nonholonomically constrained system, and characterize regularity conditions that guarantee that the dynamics of the system can be obtained as a suitable projection of the unconstrained dynamics. It is shown that one can define an almost aff-Poisson bracket on the constraint AV-bundle, which plays a prominent role in the description of nonholonomic dynamics. Moreover, these developments give a general description of nonholonomic systems and the unified treatment permits to study nonholonomic systems after or before reduction in the same framework. Also, it is not necessary to distinguish between linear or affine constraints and the methods are valid for explicitly time-dependent systems.Comment: 50 page

Meniscus motion in a prewetted capillary

A conventional description of the effect of meniscus friction is based on the concept of the dynamic contact angle θ, which depends on the meniscus velocity V according to the Tanner law, θ∝ V1/3. However, recent high-resolution experiments on spontaneous uptake of wetting fluids by capillaries have questioned the universality of the Tanner law. We analyze a mechanism underlying the phenomenological concept of meniscus friction, which finds experimental confirmation. As a case study system, we consider a forced flow of meniscus in a cylindrical capillary. It is assumed that the capillary is prewetted and the coating uniform film could coexist with the static meniscus. Numerical analysis is restricted to van der Waals fluids for which the disjoining pressure Π as a function of film thickness h has the form Π ∝ h-3. For these fluids, the equilibrium apparent contact angle is zero. Within the lubrication approximation of the film flow, we show that the nonzeroth dynamic contact angle first appears when the fluid velocity exceeds a certain characteristic value. For smaller velocities, there is no appreciable distortion of the meniscus shape, compared to the equilibrium static configuration. The deformations of the film profile are concentrated at the transition zone between the macroscopic meniscus and the submicron precursor. While the concept of dynamic contact angle seems to be inappropriate for slow flows, the concept of contact line friction serves as a practical alternative to it. We show that when the velocity is slow and there is no visible contact angle, the friction is Newtonian, i.e., the relation between the pressure drop Δ P and the meniscus velocity is linear. As the velocity increases, the linear relation transforms into a nonlinear asymptotic law Δ P ∝ (V In V)2/3. © 2003 American Institute of Physics

The Possibility of Reconciling Quantum Mechanics with Classical Probability Theory

We describe a scheme for constructing quantum mechanics in which a quantum system is considered as a collection of open classical subsystems. This allows using the formal classical logic and classical probability theory in quantum mechanics. Our approach nevertheless allows completely reproducing the standard mathematical formalism of quantum mechanics and identifying its applicability limits. We especially attend to the quantum state reduction problem.Comment: Latex, 14 pages, 1 figur

Sequential Acquisition and Processing of Perfusion and Diffusion MRI Data for a Porcine Stroke Model

An automated data processing pipeline, designed for handling a large throughput of sequentially acquired MRI brain data, is described. The system takes as input multiple diffusion weighted (DWI) and perfusion weighted imaging (PWI) volumes acquired at different temporal points, automatically segments and registers them, and ultimately outputs a database used to track various perfusion and diffusion parameters through time at individual brain voxels. This pipeline has been utilized to successfully process two pig brains from an induced stroke experiment

Microgravity induced changes in horiztonal vestibulo-ocular reflexes of SLS-1 & SLS-2 astronauts

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 45-46).by Matthew A. Neimark.M.Eng

Analysis of Transient Processes in a Radiophysical Flow System

Transient processes in a third-order radiophysical flow system are studied and a map of the transient process duration versus initial conditions is constructed and analyzed. The results are compared to the arrangement of submanifolds of the stable and unstable cycles in the Poincare section of the system studied.Comment: 3 pages, 2 figure

Миграционная политика России: новые точки отсчета

The author traces the evolution of the conceptual foundations of Russia’s migration policy and the features of its implementation at various stages of social, economic and political development of the country. The analysis focuses on the geopolitical specifics of Russia’s migration policy: after the collapse of the USSR, tens of millions of the country’s citizens ended up abroad. Return to the sources of the conceptualization of the Russian migration policy, capture of the underrated factors has a significant practical importance to mainstream and optimize it nowadays. Contradictory tendencies in the development of migration processes, unrealized opportunities, mistakes and miscalculations made in the first post-Soviet years are revealed; all the positive things that have been brought into the migration sphere over three decades are noted. The author identifies several stages that have their peculiarities that characterize the dynamics of changes and the evolution of the conceptual approaches of the state to this very complex and multi-layered problem. And at each stage there is a difficult search for answers to unresolved old and new questions that life poses to Russia with its contradictions, illogisms, and paradoxes. The author concludes that the coronavirus pandemic, which caused global social and economic upheavals in the world, will become a force majeure test for Russia’s migration policy.В статье прослеживается эволюция концептуальных основ миграционной политики России и особенности ее реализации на различных этапах социальноэкономического и политического развития страны. В центре анализа — геополитическая специфика миграционной политики России: после распада СССР десятки миллионов граждан страны оказались за рубежом. Обращение к истокам формирования концептуальной базы миграционной политики России, учет недооцененных в тот период факторов имеет важное практическое значение для ее актуализации и оптимизации в наши дни. Выявляются противоречивые тенденции в развитии миграционных процессов, нереализованные возможности, ошибки и просчеты, допущенные в первые постсоветские годы; отмечается все то позитивное, что было привнесено в миграционную сферу на протяжении трех десятилетий. Автор выделяет несколько этапов, имеющих свои особенности, которые характеризуют динамику изменений и эволюцию концептуальных подходов государства к этой очень сложной и многослойной проблеме. И на каждом этапе — трудные поиски ответов на нерешенные старые и новые вопросы, которые ставит перед Россией жизнь с ее противоречиями, алогизмами, парадоксами. Автор заключает, что коронавирусная пандемия, вызвавшая глобальные социально-экономические потрясения в мире, станет форс-мажорным испытанием для миграционной политики России