212 research outputs found
Impact of clinical severity of stroke on the severity and recovery of visuospatial neglect (vol 13, 0198755, 2018)
Історичне краєзнавство як складова національної освіти: теоретичний аспект
Аналізується процес утвердження історичного краєзнавства в системі національної освіти. Розглядаються теоретичні питання про предмет, об’єкт і завдання історичного краєзнавства. Акцентується увага на виховній і консолідуючій функції історичного краєзнавства в процесі відродження української нації.Анализируется процесс становления исторического краеведения в системе национального образования. Рассматриваются теоретические вопросы о предмете, объекте и задачах исторического краеведения. Внимание акцентируется на воспитательной и консолидирующей функциях исторического краеведения в процессе возрождения украинской нации.The processes of the formation of the local history studies in the system of the national education had been analyzed. The theoretical aspects of the objects and tasks of the local history studies had been shown. The educational and consolidation functions of the local history studies in the Ukrainian national resurrection process had been pointed
Theorem on the Distribution of Short-Time Particle Displacements with Physical Applications
The distribution of the initial short-time displacements of particles is
considered for a class of classical systems under rather general conditions on
the dynamics and with Gaussian initial velocity distributions, while the
positions could have an arbitrary distribution. This class of systems contains
canonical equilibrium of a Hamiltonian system as a special case. We prove that
for this class of systems the nth order cumulants of the initial short-time
displacements behave as the 2n-th power of time for all n>2, rather than
exhibiting an nth power scaling. This has direct applications to the initial
short-time behavior of the Van Hove self-correlation function, to its
non-equilibrium generalizations the Green's functions for mass transport, and
to the non-Gaussian parameters used in supercooled liquids and glasses.Comment: A less ambiguous mathematical notation for cumulants was adopted and
several passages were reformulated and clarified. 40 pages, 1 figure.
Accepted by J. Stat. Phy
Dynamical Properties and Plasmon Dispersion of a Weakly Degenerate Correlated One-Component Plasma
Classical Molecular Dynamics (MD) simulations for a one-component plasma
(OCP) are presented. Quantum effects are included in the form of the Kelbg
potential. Results for the dynamical structure factor are compared with the
Vlasov and RPA (random phase approximation) theories. The influence of the
coupling parameter , degeneracy parameter and the form
of the pair interaction on the optical plasmon dispersion is investigated. An
improved analytical approximation for the dispersion of Langmuir waves is
presented.Comment: 23 pages, includes 7 ps/eps-figures and 2 table
First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256
Abell 2256 is one of the best known examples of a galaxy cluster hosting
large-scale diffuse radio emission that is unrelated to individual galaxies. It
contains both a giant radio halo and a relic, as well as a number of head-tail
sources and smaller diffuse steep-spectrum radio sources. The origin of radio
halos and relics is still being debated, but over the last years it has become
clear that the presence of these radio sources is closely related to galaxy
cluster merger events. Here we present the results from the first LOFAR Low
band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our
knowledge, the image presented in this paper at 63 MHz is the deepest ever
obtained at frequencies below 100 MHz in general. Both the radio halo and the
giant relic are detected in the image at 63 MHz, and the diffuse radio emission
remains visible at frequencies as low as 20 MHz. The observations confirm the
presence of a previously claimed ultra-steep spectrum source to the west of the
cluster center with a spectral index of -2.3 \pm 0.4 between 63 and 153 MHz.
The steep spectrum suggests that this source is an old part of a head-tail
radio source in the cluster. For the radio relic we find an integrated spectral
index of -0.81 \pm 0.03, after removing the flux contribution from the other
sources. This is relatively flat which could indicate that the efficiency of
particle acceleration at the shock substantially changed in the last \sim 0.1
Gyr due to an increase of the shock Mach number. In an alternative scenario,
particles are re-accelerated by some mechanism in the downstream region of the
shock, resulting in the relatively flat integrated radio spectrum. In the radio
halo region we find indications of low-frequency spectral steepening which may
suggest that relativistic particles are accelerated in a rather inhomogeneous
turbulent region.Comment: 13 pages, 13 figures, accepted for publication in A\&A on April 12,
201
Harmonic Solid Theory of Photoluminescence in the High Field Two-Dimensional Wigner Crystal
Motivated by recent experiments on radiative recombination of two-dimensional
electrons in acceptor doped GaAs-AlGaAs heterojunctions as well as the success
of a harmonic solid model in describing tunneling between two-dimensional
electron systems, we calculate within the harmonic approximation and the time
dependent perturbation theory the line shape of the photoluminescence spectrum
corresponding to the recombination of an electron with a hole bound to an
acceptor atom. The recombination process is modeled as a sudden perturbation of
the Hamiltonian for the in-plane degrees of freedom of the electron. We include
in the perturbation, in addition to changes in the equilibrium positions of
electrons, changes in the curvatures of the harmonically approximated
potential. The computed spectra have line shapes similar to that seen in a
recent experiment. The spectral width, however, is roughly a factor of 3
smaller than that seen in experiment if one assumes a perfect Wigner crystal
for the initial state state of the system, whereas a simple random disorder
model yields a width a factor of 3 too large. We speculate on the possible
mechanisms that may lead to better quantitative agreement with experiment.Comment: 22 pages, RevTex, 8 figures. Submitted to the Physical Review
Crystal structures and freezing of dipolar fluids
We investigate the crystal structure of classical systems of spherical
particles with an embedded point dipole at T=0. The ferroelectric ground state
energy is calculated using generalizations of the Ewald summation technique.
Due to the reduced symmetry compared to the nonpolar case the crystals are
never strictly cubic. For the Stockmayer (i.e., Lennard-Jones plus dipolar)
interaction three phases are found upon increasing the dipole moment:
hexagonal, body-centered orthorhombic, and body-centered tetragonal. An even
richer phase diagram arises for dipolar soft spheres with a purely repulsive
inverse power law potential . A crossover between qualitatively
different sequences of phases occurs near the exponent . The results are
applicable to electro- and magnetorheological fluids. In addition to the exact
ground state analysis we study freezing of the Stockmayer fluid by
density-functional theory.Comment: submitted to Phys. Rev.
Density fluctuations and single-particle dynamics in liquid lithium
The single-particle and collective dynamical properties of liquid lithium
have been evaluated at several thermodynamic states near the triple point. This
is performed within the framework of mode-coupling theory, using a
self-consistent scheme which, starting from the known static structure of the
liquid, allows the theoretical calculation of several dynamical properties.
Special attention is devoted to several aspects of the single-particle
dynamics, which are discussed as a function of the thermodynamic state. The
results are compared with those of Molecular Dynamics simulations and other
theoretical approaches.Comment: 31 pages (in preprint format), 14 figures. Submitted to Phys. Rev.
Spin injection and spin accumulation in all-metal mesoscopic spin valves
We study the electrical injection and detection of spin accumulation in
lateral ferromagnetic metal-nonmagnetic metal-ferromagnetic metal (F/N/F) spin
valve devices with transparent interfaces. Different ferromagnetic metals,
permalloy (Py), cobalt (Co) and nickel (Ni), are used as electrical spin
injectors and detectors. For the nonmagnetic metal both aluminium (Al) and
copper (Cu) are used. Our multi-terminal geometry allows us to experimentally
separate the spin valve effect from other magneto resistance signals such as
the anomalous magneto resistance (AMR) and Hall effects. We find that the AMR
contribution of the ferromagnetic contacts can dominate the amplitude of the
spin valve effect, making it impossible to observe the spin valve effect in a
'conventional' measurement geometry. In a 'non local' spin valve measurement we
are able to completely isolate the spin valve signal and observe clear spin
accumulation signals at T=4.2 K as well as at room temperature (RT). For
aluminum we obtain spin relaxation lengths (lambda_{sf}) of 1.2 mu m and 600 nm
at T=4.2 K and RT respectively, whereas for copper we obtain 1.0 mu m and 350
nm. The spin relaxation times tau_{sf} in Al and Cu are compared with theory
and results obtained from giant magneto resistance (GMR), conduction electron
spin resonance (CESR), anti-weak localization and superconducting tunneling
experiments. The spin valve signals generated by the Py electrodes (alpha_F
lambda_F=0.5 [1.2] nm at RT [T=4.2 K]) are larger than the Co electrodes
(alpha_F lambda_F=0.3 [0.7] nm at RT [T=4.2 K]), whereas for Ni (alpha_F
lambda_F<0.3 nm at RT and T=4.2 K) no spin signal is observed. These values are
compared to the results obtained from GMR experiments.Comment: 16 pages, 12 figures, submitted to PR
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Target-directed motor imagery of the lower limb enhances event-related desynchronization
Event-related desynchronization/synchronization (ERD/S) is an electroencephalogram (EEG) feature widely used as control signals for Brain-Computer Interfaces (BCIs). Never- theless, the underlying neural mechanisms and functions of ERD/S are largely unknown, thus investigating them is crucial to improve the reliability of ERD/S-based BCIs. This study aimed to identify Motor Imagery (MI) conditions that enhance ERD/S. We investigated fol- lowing three questions: 1) whether target-directed MI affects ERD/S, 2) whether MI with sound imagery affects ERD/S, and 3) whether ERD/S has a body part dependency of MI. Nine participants took part in the experiments of four MI conditions; they were asked to imagine right foot dorsiflexion (F), right foot dorsiflexion and the sound of a bass drum when the sole touched the floor (FS), right leg extension (L), and right leg extension directed toward a soccer ball (LT). Statistical comparison revealed that there were significant differ- ences between conditions L and LT in beta-band ERD and conditions F and L in beta-band ERS. These results suggest that mental rehearsal of target-directed lower limb movement without real sensory stimuli can enhance beta-band ERD; furthermore, MI of foot dorsiflex- ion induces significantly larger beta-band ERS than that of leg extension. These findings could be exploited for the training of BCIs such as powered prosthetics for disabled person and neurorehabilitation system for stroke patients
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