939 research outputs found
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
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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 32Β°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
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
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 ΞΈ, which depends on the meniscus velocity V according to the Tanner law, ΞΈβ 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 Ξ as a function of film thickness h has the form Ξ β 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 Ξ P and the meniscus velocity is linear. As the velocity increases, the linear relation transforms into a nonlinear asymptotic law Ξ P β (V In V)2/3. Β© 2003 American Institute of Physics
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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
ΠΠΈΠ³ΡΠ°ΡΠΈΠΎΠ½Π½Π°Ρ ΠΏΠΎΠ»ΠΈΡΠΈΠΊΠ° Π ΠΎΡΡΠΈΠΈ: Π½ΠΎΠ²ΡΠ΅ ΡΠΎΡΠΊΠΈ ΠΎΡΡΡΠ΅ΡΠ°
The author traces the evolution of the conceptual foundations of Russiaβs 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 Russiaβs migration policy: after the collapse of the USSR, tens of millions of the countryβs 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 Russiaβs migration policy.Π ΡΡΠ°ΡΡΠ΅ ΠΏΡΠΎΡΠ»Π΅ΠΆΠΈΠ²Π°Π΅ΡΡΡ ΡΠ²ΠΎΠ»ΡΡΠΈΡ ΠΊΠΎΠ½ΡΠ΅ΠΏΡΡΠ°Π»ΡΠ½ΡΡ
ΠΎΡΠ½ΠΎΠ² ΠΌΠΈΠ³ΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΠΏΠΎΠ»ΠΈΡΠΈΠΊΠΈ Π ΠΎΡΡΠΈΠΈ ΠΈ ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎΡΡΠΈ Π΅Π΅ ΡΠ΅Π°Π»ΠΈΠ·Π°ΡΠΈΠΈ Π½Π° ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΡΡΠ°ΠΏΠ°Ρ
ΡΠΎΡΠΈΠ°Π»ΡΠ½ΠΎΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΈ ΠΏΠΎΠ»ΠΈΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΡΡΠ°Π½Ρ. Π ΡΠ΅Π½ΡΡΠ΅ Π°Π½Π°Π»ΠΈΠ·Π° β Π³Π΅ΠΎΠΏΠΎΠ»ΠΈΡΠΈΡΠ΅ΡΠΊΠ°Ρ ΡΠΏΠ΅ΡΠΈΡΠΈΠΊΠ° ΠΌΠΈΠ³ΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΠΏΠΎΠ»ΠΈΡΠΈΠΊΠΈ Π ΠΎΡΡΠΈΠΈ: ΠΏΠΎΡΠ»Π΅ ΡΠ°ΡΠΏΠ°Π΄Π° Π‘Π‘Π‘Π Π΄Π΅ΡΡΡΠΊΠΈ ΠΌΠΈΠ»Π»ΠΈΠΎΠ½ΠΎΠ² Π³ΡΠ°ΠΆΠ΄Π°Π½ ΡΡΡΠ°Π½Ρ ΠΎΠΊΠ°Π·Π°Π»ΠΈΡΡ Π·Π° ΡΡΠ±Π΅ΠΆΠΎΠΌ. ΠΠ±ΡΠ°ΡΠ΅Π½ΠΈΠ΅ ΠΊ ΠΈΡΡΠΎΠΊΠ°ΠΌ ΡΠΎΡΠΌΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΠΊΠΎΠ½ΡΠ΅ΠΏΡΡΠ°Π»ΡΠ½ΠΎΠΉ Π±Π°Π·Ρ ΠΌΠΈΠ³ΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΠΏΠΎΠ»ΠΈΡΠΈΠΊΠΈ Π ΠΎΡΡΠΈΠΈ, ΡΡΠ΅Ρ Π½Π΅Π΄ΠΎΠΎΡΠ΅Π½Π΅Π½Π½ΡΡ
Π² ΡΠΎΡ ΠΏΠ΅ΡΠΈΠΎΠ΄ ΡΠ°ΠΊΡΠΎΡΠΎΠ² ΠΈΠΌΠ΅Π΅Ρ Π²Π°ΠΆΠ½ΠΎΠ΅ ΠΏΡΠ°ΠΊΡΠΈΡΠ΅ΡΠΊΠΎΠ΅ Π·Π½Π°ΡΠ΅Π½ΠΈΠ΅ Π΄Π»Ρ Π΅Π΅ Π°ΠΊΡΡΠ°Π»ΠΈΠ·Π°ΡΠΈΠΈ ΠΈ ΠΎΠΏΡΠΈΠΌΠΈΠ·Π°ΡΠΈΠΈ Π² Π½Π°ΡΠΈ Π΄Π½ΠΈ. ΠΡΡΠ²Π»ΡΡΡΡΡ ΠΏΡΠΎΡΠΈΠ²ΠΎΡΠ΅ΡΠΈΠ²ΡΠ΅ ΡΠ΅Π½Π΄Π΅Π½ΡΠΈΠΈ Π² ΡΠ°Π·Π²ΠΈΡΠΈΠΈ ΠΌΠΈΠ³ΡΠ°ΡΠΈΠΎΠ½Π½ΡΡ
ΠΏΡΠΎΡΠ΅ΡΡΠΎΠ², Π½Π΅ΡΠ΅Π°Π»ΠΈΠ·ΠΎΠ²Π°Π½Π½ΡΠ΅ Π²ΠΎΠ·ΠΌΠΎΠΆΠ½ΠΎΡΡΠΈ, ΠΎΡΠΈΠ±ΠΊΠΈ ΠΈ ΠΏΡΠΎΡΡΠ΅ΡΡ, Π΄ΠΎΠΏΡΡΠ΅Π½Π½ΡΠ΅ Π² ΠΏΠ΅ΡΠ²ΡΠ΅ ΠΏΠΎΡΡΡΠΎΠ²Π΅ΡΡΠΊΠΈΠ΅ Π³ΠΎΠ΄Ρ; ΠΎΡΠΌΠ΅ΡΠ°Π΅ΡΡΡ Π²ΡΠ΅ ΡΠΎ ΠΏΠΎΠ·ΠΈΡΠΈΠ²Π½ΠΎΠ΅, ΡΡΠΎ Π±ΡΠ»ΠΎ ΠΏΡΠΈΠ²Π½Π΅ΡΠ΅Π½ΠΎ Π² ΠΌΠΈΠ³ΡΠ°ΡΠΈΠΎΠ½Π½ΡΡ ΡΡΠ΅ΡΡ Π½Π° ΠΏΡΠΎΡΡΠΆΠ΅Π½ΠΈΠΈ ΡΡΠ΅Ρ
Π΄Π΅ΡΡΡΠΈΠ»Π΅ΡΠΈΠΉ. ΠΠ²ΡΠΎΡ Π²ΡΠ΄Π΅Π»ΡΠ΅Ρ Π½Π΅ΡΠΊΠΎΠ»ΡΠΊΠΎ ΡΡΠ°ΠΏΠΎΠ², ΠΈΠΌΠ΅ΡΡΠΈΡ
ΡΠ²ΠΎΠΈ ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎΡΡΠΈ, ΠΊΠΎΡΠΎΡΡΠ΅ Ρ
Π°ΡΠ°ΠΊΡΠ΅ΡΠΈΠ·ΡΡΡ Π΄ΠΈΠ½Π°ΠΌΠΈΠΊΡ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠΉ ΠΈ ΡΠ²ΠΎΠ»ΡΡΠΈΡ ΠΊΠΎΠ½ΡΠ΅ΠΏΡΡΠ°Π»ΡΠ½ΡΡ
ΠΏΠΎΠ΄Ρ
ΠΎΠ΄ΠΎΠ² Π³ΠΎΡΡΠ΄Π°ΡΡΡΠ²Π° ΠΊ ΡΡΠΎΠΉ ΠΎΡΠ΅Π½Ρ ΡΠ»ΠΎΠΆΠ½ΠΎΠΉ ΠΈ ΠΌΠ½ΠΎΠ³ΠΎΡΠ»ΠΎΠΉΠ½ΠΎΠΉ ΠΏΡΠΎΠ±Π»Π΅ΠΌΠ΅. Π Π½Π° ΠΊΠ°ΠΆΠ΄ΠΎΠΌ ΡΡΠ°ΠΏΠ΅ β ΡΡΡΠ΄Π½ΡΠ΅ ΠΏΠΎΠΈΡΠΊΠΈ ΠΎΡΠ²Π΅ΡΠΎΠ² Π½Π° Π½Π΅ΡΠ΅ΡΠ΅Π½Π½ΡΠ΅ ΡΡΠ°ΡΡΠ΅ ΠΈ Π½ΠΎΠ²ΡΠ΅ Π²ΠΎΠΏΡΠΎΡΡ, ΠΊΠΎΡΠΎΡΡΠ΅ ΡΡΠ°Π²ΠΈΡ ΠΏΠ΅ΡΠ΅Π΄ Π ΠΎΡΡΠΈΠ΅ΠΉ ΠΆΠΈΠ·Π½Ρ Ρ Π΅Π΅ ΠΏΡΠΎΡΠΈΠ²ΠΎΡΠ΅ΡΠΈΡΠΌΠΈ, Π°Π»ΠΎΠ³ΠΈΠ·ΠΌΠ°ΠΌΠΈ, ΠΏΠ°ΡΠ°Π΄ΠΎΠΊΡΠ°ΠΌΠΈ. ΠΠ²ΡΠΎΡ Π·Π°ΠΊΠ»ΡΡΠ°Π΅Ρ, ΡΡΠΎ ΠΊΠΎΡΠΎΠ½Π°Π²ΠΈΡΡΡΠ½Π°Ρ ΠΏΠ°Π½Π΄Π΅ΠΌΠΈΡ, Π²ΡΠ·Π²Π°Π²ΡΠ°Ρ Π³Π»ΠΎΠ±Π°Π»ΡΠ½ΡΠ΅ ΡΠΎΡΠΈΠ°Π»ΡΠ½ΠΎ-ΡΠΊΠΎΠ½ΠΎΠΌΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΠΏΠΎΡΡΡΡΠ΅Π½ΠΈΡ Π² ΠΌΠΈΡΠ΅, ΡΡΠ°Π½Π΅Ρ ΡΠΎΡΡ-ΠΌΠ°ΠΆΠΎΡΠ½ΡΠΌ ΠΈΡΠΏΡΡΠ°Π½ΠΈΠ΅ΠΌ Π΄Π»Ρ ΠΌΠΈΠ³ΡΠ°ΡΠΈΠΎΠ½Π½ΠΎΠΉ ΠΏΠΎΠ»ΠΈΡΠΈΠΊΠΈ Π ΠΎΡΡΠΈΠΈ
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