2,013 research outputs found
Neutron diffraction, magnetization and ESR studies of pseudocubic Nd(0.75)Ba(0.25)MnO3 and its unusual critical behavior above Tc
Results of structural neutron diffraction study, magnetization and ESR
measure-ments are presented for insulating Nd0.75Ba0.25MnO3, Tc = 129 K. The
crystal structure is refined in the range 4.2-300 K. The compound is found to
exhibit the Jahn-Teller (JT) transition at 250 K. The field cooled (FC)
magnetization data are in a reasonable agreement with the predictions for a 3D
isotropic ferromagnet above Tc. However, these measurements reveal a difference
between the FC and zero FC data in the paramagnetic region. ESR results are
also in a correspondence with behavior of a cubic ferromagnet above T* = 143 K.
It is shown that an anisotropic exchange coupling of the Mn and Nd magnetic
moments can give a substantial contribution in ESR linewidth masking its
critical enhan-cement. The different temperature treatments of the sample
reveal a temperature hysteresis of the ESR spectra below T* indicating an
anomalous response in the paramagnetic region. The study of phase transition in
this manganite suggests change in its character from the second to first order
at T*. The conventional free energy including the magnetization and magnetic
field is not found to describe the first order transition. This suggests that
the charge, orbital and JT phonon degrees of freedom, in addition to
magnetization, may be the critical variables, the unusual character of the
transition being determined by their coupling. Unconventional critical behavior
is attributed to orbital liquid metallic phase that coexists with the initial
orbital ordered phase below T*.Comment: 18 pages, 5 figures, submitted to Phys. Rev.
Low-temperature kinetics of exciton-exciton annihilation of weakly localized one-dimensional Frenkel excitons
We present results of numerical simulations of the kinetics of
exciton-exciton annihilation of weakly localized one-dimensional Frenkel
excitons at low temperatures. We find that the kinetics is represented by two
well-distinguished components: a fast short-time decay and a very slow
long-time tail. The former arises from excitons that initially reside in states
belonging to the same localization segment of the chain, while the slow
component is caused by excitons created on different localization segments. We
show that the usual bi-molecular theory fails in the description of the
behavior found. We also present a qualitative analytical explanation of the
non-exponential behavior observed in both the short- and the long-time decay
components.Comment: Published in J. Chem. Phys. 114, 1 April (2001
СТРАТЕГІЯ ІНФОРМАТИЗАЦІЇ МЕДИЧНОГО УНІВЕРСИТЕТУ
The work deals with the model of informatization of medical university on the example of Zaporizhyan State MedicalUniversity, built on the principles of systems analysis of pedagogical system of the medical personnel training.В работе рассматривается модель информатизации медицинс о о ниверситета на примере Запорожс о о ос -дарственно о медицинс о о ниверситета, построенная на принципах системно о анализа педа о ичес ой систе-мы под отов и медицинс их адров.В роботі розглядається модель інформатизації медичного університету на прикладі Запорізького державного медичного університету, яка побудована на принципах системного аналізу педагогічної системи підготовки медичних кадрів
The influence of Gaussian pinning on the melting scenario of a two-dimensional soft-disk system: First-Order versus Continuous Transition
Two-dimensional systems are realized experimentally as thin layers on a
substrate. The substrate can have some imperfections (defects of the
crystalline structure, chemical impurities, etc.), which demonstrate stronger
interaction with the particles of the two-dimensional layer than the rest of
the system. Such randomly distributed centers of strong interactions are called
"pinning centers". The presence of random pinning can substantially change the
behavior of the system. It not only shifts the melting point of the system, but
can also change the melting scenario itself. In the present paper the influence
of Gaussian pinning on the melting scenario of a two-dimensional system of soft
disks is studied by means of molecular dynamics simulation. We randomly
introduce into the system of soft disks a set of "pinning centers" which
attract the particles via the Gauss potential. We observe that increasing the
depth of a Gaussian well leads to a change in the melting scenario of the
system. The results demonstrate that simple kind of quenched disorder can
significantly affect the melting scenario of two-dimensional systems, offering
the possibility of its introduction in complex experiments and studying its
influence on the self-assembly and phase diagram of two-dimensional systems in
rotating external fields
Depolarization volume and correlation length in the homogenization of anisotropic dielectric composites
In conventional approaches to the homogenization of random particulate
composites, both the distribution and size of the component phase particles are
often inadequately taken into account. Commonly, the spatial distributions are
characterized by volume fraction alone, while the electromagnetic response of
each component particle is represented as a vanishingly small depolarization
volume. The strong-permittivity-fluctuation theory (SPFT) provides an
alternative approach to homogenization wherein a comprehensive description of
distributional statistics of the component phases is accommodated. The
bilocally-approximated SPFT is presented here for the anisotropic homogenized
composite which arises from component phases comprising ellipsoidal particles.
The distribution of the component phases is characterized by a two-point
correlation function and its associated correlation length. Each component
phase particle is represented as an ellipsoidal depolarization region of
nonzero volume. The effects of depolarization volume and correlation length are
investigated through considering representative numerical examples. It is
demonstrated that both the spatial extent of the component phase particles and
their spatial distributions are important factors in estimating coherent
scattering losses of the macroscopic field.Comment: Typographical error in eqn. 16 in WRM version is corrected in arxiv
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