337 research outputs found
Transverse instability and its long-term development for solitary waves of the (2+1)-Boussinesq equation
The stability properties of line solitary wave solutions of the
(2+1)-dimensional Boussinesq equation with respect to transverse perturbations
and their consequences are considered. A geometric condition arising from a
multi-symplectic formulation of this equation gives an explicit relation
between the parameters for transverse instability when the transverse
wavenumber is small. The Evans function is then computed explicitly, giving the
eigenvalues for transverse instability for all transverse wavenumbers. To
determine the nonlinear and long time implications of transverse instability,
numerical simulations are performed using pseudospectral discretization. The
numerics confirm the analytic results, and in all cases studied, transverse
instability leads to collapse.Comment: 16 pages, 8 figures; submitted to Phys. Rev.
Heavy Carriers and Non-Drude Optical Conductivity in MnSi
Optical properties of the weakly helimagnetic metal MnSi have been determined
in the photon energy range from 2 meV to 4.5 eV using the combination of
grazing incidence reflectance at 80 degrees (2 meV to 0.8 eV) and ellipsometry
(0.8 to 4.5 eV). As the sample is cooled below 100 K the effective mass becomes
strongly frequency dependent at low frequencies, while the scattering rate
developes a linear frequency dependence. The complex optical conductivity can
be described by the phenomenological relation \sigma(\omega,T) \propto
(\Gamma(T)+i\omega)^{-1/2} used for cuprates and ruthenates.Comment: 5 pages, ReVTeX 4, 5 figures in eps forma
Non-Fermi liquid behavior and scaling of low frequency suppression in optical conductivity spectra of CaRuO
Optical conductivity spectra of paramagnetic CaRuO are
investigated at various temperatures. At T=10 K, it shows a non-Fermi liquid
behavior of , similar to the case
of a ferromagnet SrRuO. As the temperature () is increased, on the other
hand, in the low frequency region is progressively
suppressed, deviating from the 1/{\omega}^{\frac 12%}-dependence.
Interestingly, the suppression of is found to scale with
at all temperatures. The origin of the scaling
behavior coupled with the non-Fermi liquid behavior is discussed.Comment: 4 pages, 3 figure
Angular momenta creation in relativistic electron-positron plasma
Creation of angular momentum in a relativistic electron-positron plasma is
explored. It is shown that a chain of angular momentum carrying vortices is a
robust asymptotic state sustained by the generalized nonlinear Schrodinger
equation characteristic to the system. The results may suggest a possible
electromagnetic origin of angular momenta when it is applied to the MeV epoch
of the early Universe.Comment: 20 pages, 6 figure
gravity constrained by PPN parameters and stochastic background of gravitational waves
We analyze seven different viable -gravities towards the Solar System
tests and stochastic gravitational waves background. The aim is to achieve
experimental bounds for the theory at local and cosmological scales in order to
select models capable of addressing the accelerating cosmological expansion
without cosmological constant but evading the weak field constraints. Beside
large scale structure and galactic dynamics, these bounds can be considered
complimentary in order to select self-consistent theories of gravity working at
the infrared limit. It is demonstrated that seven viable -gravities under
consideration not only satisfy the local tests, but additionally, pass the
above PPN-and stochastic gravitational waves bounds for large classes of
parameters.Comment: 23 pages, 8 figure
Soft phonons and structural phase transition in superconducting Ba0.59K0.41BiO3
We have observed a softening of phonons and a structural phase transition in
a superconducting Ba0.59K0.41BiO3 (Tc = 31 K) single crystal using elastic and
inelastic neutron scattering measurements. The soft phonon occurs for the [111]
transverse acoustic mode at the zone boundary. The phonon energies in this
vicinity are found to continuously decrease with decreasing temperature from
above room temperature to 200 K, where a structural phase transition from cubic
to tetragonal symmetry occurs. The overall results are consistent with previous
data that reported phonon softening and a (0.5, 0.5, 0.5) type superstructure
in several Ba1-xKxBiO3 systems. However, we also find weak (0.5, 0.5, 0) type
superstructure peaks that reveal an additional component to the modulation. No
significant change related to the superconductivity was observed for the soft
phonon energies or linewidths.Comment: 15 page
Interacting Agegraphic Dark Energy
A new dark energy model, named "agegraphic dark energy", has been proposed
recently, based on the so-called K\'{a}rolyh\'{a}zy uncertainty relation, which
arises from quantum mechanics together with general relativity. In this note,
we extend the original agegraphic dark energy model by including the
interaction between agegraphic dark energy and pressureless (dark) matter. In
the interacting agegraphic dark energy model, there are many interesting
features different from the original agegraphic dark energy model and
holographic dark energy model. The similarity and difference between agegraphic
dark energy and holographic dark energy are also discussed.Comment: 10 pages, 5 figures, revtex4; v2: references added; v3: accepted by
Eur. Phys. J. C; v4: published versio
Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRuRhO
The solid-solution SrRuRhO () is a
variable-electron-configuration system forming in the nearly-cubic-perovskite
basis, ranging from the ferromagnetic 4 to the enhanced paramagnetic
4. Polycrystalline single-phase samples were obtained over the whole
composition range by a high-pressure-heating technique, followed by
measurements of magnetic susceptibility, magnetization, specific heat,
thermopower, and electrical resistivity. The ferromagnetic order in long range
is gradually suppressed by the Rh substitution and vanishes at .
The electronic term of specific-heat shows unusual behavior near the critical
Rh concentration; the feature does not match even qualitatively with what was
reported for the related perovskites (Sr,Ca)RuO. Furthermore, another
anomaly in the specific heat was observed at .Comment: Accepted for publication in PR
Simulation of dimensionality effects in thermal transport
The discovery of nanostructures and the development of growth and fabrication
techniques of one- and two-dimensional materials provide the possibility to
probe experimentally heat transport in low-dimensional systems. Nevertheless
measuring the thermal conductivity of these systems is extremely challenging
and subject to large uncertainties, thus hindering the chance for a direct
comparison between experiments and statistical physics models. Atomistic
simulations of realistic nanostructures provide the ideal bridge between
abstract models and experiments. After briefly introducing the state of the art
of heat transport measurement in nanostructures, and numerical techniques to
simulate realistic systems at atomistic level, we review the contribution of
lattice dynamics and molecular dynamics simulation to understanding nanoscale
thermal transport in systems with reduced dimensionality. We focus on the
effect of dimensionality in determining the phononic properties of carbon and
semiconducting nanostructures, specifically considering the cases of carbon
nanotubes, graphene and of silicon nanowires and ultra-thin membranes,
underlying analogies and differences with abstract lattice models.Comment: 30 pages, 21 figures. Review paper, to appear in the Springer Lecture
Notes in Physics volume "Thermal transport in low dimensions: from
statistical physics to nanoscale heat transfer" (S. Lepri ed.
Fermi Surface Variation of Ce 4f-electrons in Hybridization Controlled Heavy-Fermion Systems
Ce 3d-4f resonant angle-resolved photoemission measurements on
CeCoGeSi and CeCoSi have been performed to understand the
Fermi surface topology as a function of hybridization strength between Ce 4-
and conduction electrons in heavy-fermion systems. We directly observe that the
hole-like Ce 4-Fermi surfaces of CeCoSi is smaller than that of
CeCoGeSi, indicating the evolution of the Ce 4-Fermi surface
with the increase of the hybridization strength. In comparision with LDA
calculation, the Fermi surface variation cannot be understood even though the
overall electronic structure are roughly explained, indicating the importance
of strong correlation effects. We also discuss the relation between the Ce
4-Fermi surface variation and the Kondo peaks.Comment: 7 pages, 3 figures, submitte
- …