4,857 research outputs found
Electron-Acoustic Phonon Energy Loss Rate in Multi-Component Electron Systems with Symmetric and Asymmetric Coupling Constants
We consider electron-phonon (\textit{e-ph}) energy loss rate in 3D and 2D
multi-component electron systems in semiconductors. We allow general asymmetry
in the \textit{e-ph} coupling constants (matrix elements), i.e., we allow that
the coupling depends on the electron sub-system index. We derive a
multi-component \textit{e-ph}power loss formula, which takes into account the
asymmetric coupling and links the total \textit{e-ph} energy loss rate to the
density response matrix of the total electron system. We write the density
response matrix within mean field approximation, which leads to coexistence of\
symmetric energy loss rate and asymmetric energy loss rate
with total energy loss rate at temperature
. The symmetric component F_{S}(T) F_{S}(T)\propto T^{n_{S}}n_{S}F_{A}(T). Screening strongly
reduces the symmetric coupling, but the asymmetric coupling is unscreened,
provided that the inter-sub-system Coulomb interactions are strong. The lack of
screening enhances and the total energy loss rate .
Especially, in the strong screening limit we find . A
canonical example of strongly asymmetric \textit{e-ph} matrix elements is the
deformation potential coupling in many-valley semiconductors.Comment: v2: Typos corrected. Some notations changed. Section III.C is
embedded in Section III.B. Paper accepted to PR
Why national health research systems matter
Some of the most outstanding problems in Computer Science (e.g. access to heterogeneous information sources, use of different e-commerce standards, ontology translation, etc.) are often approached through the identification of ontology mappings. A manual mapping generation slows down, or even makes unfeasible, the solution of particular cases of the aforementioned problems via ontology mappings. Some algorithms and formal models for partial tasks of automatic generation of mappings have been proposed. However, an integrated system to solve this problem is still missing. In this paper, we present AMON, a platform for automatic ontology mapping generation. First of all, we show the general structure. Then, we describe the current version of the system, including the ontology in which it is based, the similarity measures that it uses, the access to external sources, etc
Local conductivity and the role of vacancies around twin walls of (001)-BiFeO3 thin films
BiFeO3 thin films epitaxially grown on SrRuO3-buffered (001)-oriented SrTiO3
substrates show orthogonal bundles of twin domains, each of which contains
parallel and periodic 71o domain walls. A smaller amount of 109o domain walls
are also present at the boundaries between two adjacent bundles. All as-grown
twin walls display enhanced conductivity with respect to the domains during
local probe measurements, due to the selective lowering of the Schottky barrier
between the film and the AFM tip (see S. Farokhipoor and B. Noheda, Phys. Rev.
Lett. 107, 127601 (2011)). In this paper we further discuss these results and
show why other conduction mechanisms are discarded. In addition we show the
crucial role that oxygen vacancies play in determining the amount of conduction
at the walls. This prompts us to propose that the oxygen vacancies migrating to
the walls locally lower the Schottky barrier. This mechanism would then be less
efficient in non-ferroelastic domain walls where one expects no strain
gradients around the walls and thus (assuming that walls are not charged) no
driving force for accumulation of defects
Dynamic correlation functions and Boltzmann Langevin approach for driven one dimensional lattice gas
We study the dynamics of the totally asymmetric exclusion process with open
boundaries by phenomenological theories complemented by extensive Monte-Carlo
simulations. Upon combining domain wall theory with a kinetic approach known as
Boltzmann-Langevin theory we are able to give a complete qualitative picture of
the dynamics in the low and high density regime and at the corresponding phase
boundary. At the coexistence line between high and low density phases we
observe a time scale separation between local density fluctuations and
collective domain wall motion, which are well accounted for by the
Boltzmann-Langevin and domain wall theory, respectively. We present Monte-Carlo
data for the correlation functions and power spectra in the full parameter
range of the model.Comment: 10 pages, 9 figure
Josephson junction between anisotropic superconductors
The sin-Gordon equation for Josephson junctions with arbitrary misaligned
anisotropic banks is derived. As an application, the problem of Josephson
vortices at twin planes of a YBCO-like material is considered. It is shown that
for an arbitrary orientation of these vortices relative to the crystal axes of
the banks, the junctions should experience a mechanical torque which is
evaluated. This torque and its angular dependence may, in principle, be
measured in small fields, since the flux penetration into twinned crystals
begins with nucleation of Josephson vortices at twin planes.Comment: 6 page
Nature of 45 degree vortex lattice reorientation in tetragonal superconductors
The transformation of the vortex lattice in a tetragonal superconductor which
consists of its 45 degree reorientation relative to the crystal axes is studied
using the nonlocal London model. It is shown that the reorientation occurs as
two successive second order (continuous) phase transitions. The transition
magnetic fields are calculated for a range of parameters relevant for
borocarbide superconductors in which the reorientation has been observed
Dynamic stabilization of non-spherical bodies against unlimited collapse
We solve equations, describing in a simplified way the newtonian dynamics of
a selfgravitating nonrotating spheroidal body after loss of stability. We find
that contraction to a singularity happens only in a pure spherical collapse,
and deviations from the spherical symmetry stop the contraction by the
stabilising action of nonlinear nonspherical oscillations. A real collapse
happens after damping of the oscillations due to energy losses, shock wave
formation or viscosity. Detailed analysis of the nonlinear oscillations is
performed using a Poincar\'{e} map construction. Regions of regular and chaotic
oscillations are localized on this map.Comment: MNRAS, accepted, 7 pages, 9 figure
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