842,904 research outputs found
Jet Methods in Time-Dependent Lagrangian Biomechanics
In this paper we propose the time-dependent generalization of an `ordinary'
autonomous human biomechanics, in which total mechanical + biochemical energy
is not conserved. We introduce a general framework for time-dependent
biomechanics in terms of jet manifolds associated to the extended
musculo-skeletal configuration manifold, called the configuration bundle. We
start with an ordinary configuration manifold of human body motion, given as a
set of its all active degrees of freedom (DOF) for a particular movement. This
is a Riemannian manifold with a material metric tensor given by the total
mass-inertia matrix of the human body segments. This is the base manifold for
standard autonomous biomechanics. To make its time-dependent generalization, we
need to extend it with a real time axis. By this extension, using techniques
from fibre bundles, we defined the biomechanical configuration bundle. On the
biomechanical bundle we define vector-fields, differential forms and affine
connections, as well as the associated jet manifolds. Using the formalism of
jet manifolds of velocities and accelerations, we develop the time-dependent
Lagrangian biomechanics. Its underlying geometric evolution is given by the
Ricci flow equation.
Keywords: Human time-dependent biomechanics, configuration bundle, jet
spaces, Ricci flowComment: 13 pages, 3 figure
Coulombic effects on magnetoconductivity oscillations induced by microwave excitation in multisubband two-dimensional electron systems
We develop a theory of magneto-oscillations in photoconductivity of
multisubband two-dimensional electron systems which takes into account strong
Coulomb interaction between electrons. In the presence of a magnetic field
oriented perpendicular, internal electric fields of fluctuational origin cause
fast drift velocities of electron orbit centers which affect probabilities of
inter-subband scattering and the photoconductivity. For the electron system
formed on the liquid helium surface, internal forces are shown to suppress the
amplitude of magneto-oscillations, and change positions of magnetoconductivity
minima which evolve in zero-resistance states for high radiation power.Comment: 9 pages, 6 figure
Impurity in the Tomonaga-Luttinger model: a Functional Integral Approach
In this tutorial notes we review a functional bosonization approach in the
Keldysh technique to one-dimensional Luttinger liquid in the presence of an
impurity.Comment: 15 pages, 1 figure, Proceedings of LXXXI Les Houches School on
"Nanoscopic quantum transport", Les Houches, France, June 28-July 30, 200
Probability Distributions and Hilbert Spaces: Quantum and Classical Systems
We use the fact that some linear Hamiltonian systems can be considered as
``finite level'' quantum systems, and the description of quantum mechanics in
terms of probabilities, to associate probability distributions with this
particular class of linear Hamiltonian systems.Comment: LATEX,13pages,accepted by Physica Scripta (1999
Light absorption coefficient of an ordered array of spherical quantum dot chains
We considered intersubband electron transitions in an array of
one-dimensional chains of spherical quantum dots in the
GaAs/AlGaAs semiconductor system. The absorption coefficient
caused by these transitions was calculated depending on frequency and
polarization of incident light and on Fermi level position, and temperature. We
established the existence of two maxima of the absorption coefficient at the
edges of the absorption band. It is shown that the absorption coefficient
reaches its maximal value at the center of the region between the -,
-like subbands and slightly varies with temperature. The change of the
direction of the linearly polarized light wave incident on the chains from
perpendicular to parallel leads to a sharp narrowing of the absorption band. It
is obtained that the absorption bandwidth increases with the reduction of the
quantum dot radius. We also analyzed the dependence of the absorption
coefficient of GaAs/AlGaAs superlattice on concentration of
aluminium in the matrix.Comment: 9 pages, 7 figure
Fast magnetization reversal of nanoclusters in resonator
An effective method for ultrafast magnetization reversal of nanoclusters is
suggested. The method is based on coupling a nanocluster to a resonant electric
circuit. This coupling causes the appearance of a magnetic feedback field
acting on the cluster, which drastically shortens the magnetization reversal
time. The influence of the resonator properties, nanocluster parameters, and
external fields on the magnetization dynamics and reversal time is analyzed.
The magnetization reversal time can be made many orders shorter than the
natural relaxation time. The reversal is studied for both the cases of a single
nanocluster as well as for the system of many nanoclusters interacting through
dipole forces.Comment: latex file, 21 pages, 7 figure
- …