1,424 research outputs found
Nonlinear acoustic waves in channels with variable cross sections
The point symmetry group is studied for the generalized Webster-type equation
describing non-linear acoustic waves in lossy channels with variable cross
sections. It is shown that, for certain types of cross section profiles, the
admitted symmetry group is extended and the invariant solutions corresponding
to these profiles are obtained. Approximate analytic solutions to the
generalized Webster equation are derived for channels with smoothly varying
cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to
Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic
corrections introduced mainly in the Introduction and References. Several
typos were also correcte
Symmetry, incommensurate magnetism and ferroelectricity: the case of the rare-earth manganites RMnO3
The complete irreducible co-representations of the paramagnetic space group
provide a simple and direct path to explore the symmetry restrictions of
magnetically driven ferroelectricity. The method consists of a straightforward
generalization of the method commonly used in the case of displacive modulated
systems and allows us to determine, in a simple manner, the full magnetic
symmetry of a given phase originated from a given magnetic order parameter. The
potential ferroic and magneto-electric properties of that phase can then be
established and the exact Landau free energy expansions can be derived from
general symmetry considerations. In this work, this method is applied to the
case of the orthorhombic rare-earth manganites RMnO3. This example will allow
us to stress some specific points, such as the differences between commensurate
or incommensurate magnetic phases regarding the ferroic and magnetoelectric
properties, the possible stabilization of ferroelectricity by a single
irreducible order parameter or the possible onset of a polarization oriented
parallel to the magnetic modulation. The specific example of TbMnO3 will be
considered in more detail, in order to characterize the role played by the
magneto-electric effect in the mechanism for the polarization rotation induced
by an external magnetic field.Comment: Conference: Aperiodic`0
Local redistribution of blood under the effect of fixation stress against a background of hypokinesia
Fixation stress was used as a model of emotional disturbance. The effect of previous restrictions on mobility on the local redistribution of blood resulting from fixation stress was examined. Disturbances in carbohydrate which result from prolonged hypokinesia was studied. Radioactivity was used to determine the local redistribution of blood. Modified factor analysis was used to study the results of the experiment
Elementary excitations in the hybrid Bose-Fermi system induced by circularly polarized light in a two-dimensional gas of charge carriers with different masses
We developed a theory describing elementary excitations in the Bose-Fermi
system induced by circularly polarized light in a two-dimensional (2D) gas of
charge carriers with different masses. In such a hybrid system, the Fermi
subsystem is a degenerate Fermi gas, whereas the Bose subsystem is a condensate
of the light-induced composite bosons consisting of two fermions (electrons or
holes) with different effective masses. The interaction of the single-particle
excitations and the collective excitations (plasmons) in the Fermi subsystem
with the Bogoliubov collective modes (bogolons) in the Bose subsystem is
analyzed. The renormalization and damping (lifetime) of the excitations are
calculated, and the possibility of their experimental observation is discussed.
The developed theory can be applied to describe 2D condensed-matter structures
containing charge carriers with different effective masses, including
transition metal dichalcogenide monolayers and semiconductor quantum wells.Comment: Published versio
Optically induced resonant tunneling of electrons in nanostructures
We developed the theory of elastic electron tunneling through a potential
barrier driven by a strong high-frequency electromagnetic field. It is
demonstrated that the driven barrier can be considered as a stationary
two-barrier potential which contains the quasi-stationary electron states
confined between these two barriers. When the energy of an incident electron
coincides with the energy of the quasi-stationary state, the driven barrier
becomes fully transparent for the electron (the resonant tunneling). The
developed theory is applied to describe electron transport through a quantum
point contact irradiated by an electromagnetic wave.Comment: Published versio
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