541 research outputs found
Fluctuations of g-factors in metal nanoparticles: Effects of electron-electron interaction and spin-orbit scattering
We investigate the combined effect of spin-orbit scattering and
electron-electron interactions on the probability distribution of -factors
of metal nanoparticles. Using random matrix theory, we find that even a
relatively small interaction strength %(ratio of exchange constant and mean
level %spacing \spacing ) significantly increases -factor
fluctuations for not-too-strong spin-orbit scattering (ratio of spin-orbit rate
and single-electron level spacing 1/\tau_{\rm so} \spacing \lesssim 1), and
leads to the possibility to observe -factors larger than two.Comment: RevTex, 2 figures inserte
Singularities of the renormalization group flow for random elastic manifolds
We consider the singularities of the zero temperature renormalization group
flow for random elastic manifolds. When starting from small scales, this flow
goes through two particular points and , where the average value
of the random squared potential turnes negative ($l^{*}$) and where
the fourth derivative of the potential correlator becomes infinite at the
origin ($l_{c}$). The latter point sets the scale where simple perturbation
theory breaks down as a consequence of the competition between many metastable
states. We show that under physically well defined circumstances $l_{c} to negative values does not
take place.Comment: RevTeX, 3 page
Marginal Pinning of Quenched Random Polymers
An elastic string embedded in 3D space and subject to a short-range
correlated random potential exhibits marginal pinning at high temperatures,
with the pinning length becoming exponentially sensitive to
temperature. Using a functional renormalization group (FRG) approach we find
, with the
depinning temperature. A slow decay of disorder correlations as it appears in
the problem of flux line pinning in superconductors modifies this result, .Comment: 4 pages, RevTeX, 1 figure inserte
Thermally activated Hall creep of flux lines from a columnar defect
We analyse the thermally activated depinning of an elastic string (line
tension ) governed by Hall dynamics from a columnar defect modelled
as a cylindrical potential well of depth for the case of a small
external force An effective 1D field Hamiltonian is derived in order to
describe the 2D string motion. At high temperatures the decay rate is
proportional to with a constant of order of the
critical force and U(F) \sim{\left ({\epsilon V_{0}})}^{{1}/{2}}{V_{0}/{F}}
the activation energy. The results are applied to vortices pinned by columnar
defects in superclean superconductors.Comment: 12 pages, RevTeX, 2 figures inserte
Free-energy distribution functions for the randomly forced directed polymer
We study the -dimensional random directed polymer problem, i.e., an
elastic string subject to a Gaussian random potential and
confined within a plane. We mainly concentrate on the short-scale and
finite-temperature behavior of this problem described by a short- but
finite-ranged disorder correlator and introduce two types of
approximations amenable to exact solutions. Expanding the disorder potential
at short distances, we study the
random force (or Larkin) problem with as well as the shifted
random force problem including the random offset ; as such, these
models remain well defined at all scales. Alternatively, we analyze the
harmonic approximation to the correlator in a consistent manner.
Using direct averaging as well as the replica technique, we derive the
distribution functions and of free energies
of a polymer of length for both fixed () and free boundary
conditions on the displacement field and determine the mean
displacement correlators on the distance . The inconsistencies encountered
in the analysis of the harmonic approximation to the correlator are traced back
to its non-spectral correlator; we discuss how to implement this approximation
in a proper way and present a general criterion for physically admissible
disorder correlators .Comment: 16 pages, 5 figure
Quantum depinning of a pancake-vortex from a columnar defect
We consider the problem of the depinning of a weakly driven ()
pancake vortex from a columnar defect in a Josephson-coupled superconductor,
where denotes the force acting on the vortex ( is the critical
force).
The dynamics of the vortex is supposed to be of the Hall type. The Euclidean
action is calculated in the entire temperature range; the result
is universal and does not depend on the detailed form of the pinning potential.
We show that the transition from quantum to classical behavior is second-order
like with the temperature of the transition scaling like
Special attention is paid to the regime of applicability of our results, in
particular, the influence of the large vortex mass appearing in the superclean
limit is discussed.Comment: 11 pages, RevTeX, 4 figures inserte
Velocity-force characteristics of a driven interface in a disordered medium
Using a dynamic functional renormalization group treatment of driven elastic
interfaces in a disordered medium, we investigate several aspects of the
creep-type motion induced by external forces below the depinning threshold
: i) We show that in the experimentally important regime of forces
slightly below the velocity obeys an Arrhenius-type law
with an effective energy barrier
vanishing linearly when f approaches the threshold . ii) Thermal
fluctuations soften the pinning landscape at high temperatures. Determining the
corresponding velocity-force characteristics at low driving forces for internal
dimensions d=1,2 (strings and interfaces) we find a particular non-Arrhenius
type creep involving the reduced threshold
force alone. For d=3 we obtain a similar v-f characteristic which is,
however, non-universal and depends explicitly on the microscopic cutoff.Comment: 9 pages, RevTeX, 3 postscript figure
THE APPLICATION OF THE VIRTUAL REALITY FOR TRAINING OPERATORS OF MOBILE OBJECTS
In this paper the formulation of the problem and the results of pilot study in the field of application of the virtual reality for training operators of mobile objects are proposed. The main goal of the research is to assess the “sensitivity” of the operator’s skills and algorithms of their development to the acceleration that are inevitable in mobile controlled objects. This approach allows creating individual trajectories of operator training, in which the combination of training in a physical system and virtual reality is rationally justifiedОбозначены задачи и представлены результаты экспериментальных исследований в области применения систем виртуальной реальности для обучения операторов подвижных объектов управления. Основной целью проведенных исследований была оценка «чувствительности» профессиональных навыков оператора и алгоритмов их развития при перегрузках, которые неизбежны в подвижных объектах. Сделан вывод в том, что такой подход позволяет создавать индивидуальные траектории обучения оператора, в которых рационально обосновано сочетание обучения в физической системе и виртуальной реальности
The competency-based approach in education: issues and options
The paper discusses the systems problems of competency-based approach in education and solutions of them. The main problem of the division of competency into the independent components is systems complexity. Simulation modeling allows to overcome the systems complexity of the object of study by identifying cause-and-effect relationships in the simulation experimentВ работе обсуждаются системные проблемы компетентностного подхода в образовании и пути их решения. Главной проблемой разделения профессиональных качеств на независимые компетенции является их системная сложность. Применение имитационного моделирования позволяет преодолевать системную сложность объекта исследования путем выявления причинно-следственных связей в ходе имитационного эксперимент
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