19,387 research outputs found
Influence of the Ground-State Topology on the Domain-Wall Energy in the Edwards-Anderson +/- J Spin Glass Model
We study the phase stability of the Edwards-Anderson spin-glass model by
analyzing the domain-wall energy. For the bimodal distribution of bonds, a
topological analysis of the ground state allows us to separate the system into
two regions: the backbone and its environment. We find that the distributions
of domain-wall energies are very different in these two regions for the three
dimensional (3D) case. Although the backbone turns out to have a very high
phase stability, the combined effect of these excitations and correlations
produces the low global stability displayed by the system as a whole. On the
other hand, in two dimensions (2D) we find that the surface of the excitations
avoids the backbone. Our results confirm that a narrow connection exists
between the phase stability of the system and the internal structure of the
ground-state. In addition, for both 3D and 2D we are able to obtain the fractal
dimension of the domain wall by direct means.Comment: 4 pages, 3 figures. Accepted for publication in Rapid Communications
of Phys. Rev.
Reactor antineutrino spectra and their application to antineutrino-induced reactions. II
The antineutrino and electron spectra associated with various nuclear fuels are calculated. While there are substantial differences between the spectra of different uranium and plutonium isotopes, the dependence on the energy and flux of the fission-inducing neutrons is very weak. The resulting spectra can be used for the calculation of the antineutrino and electron spectra of an arbitrary nuclear reactor at various stages of its refueling cycle. The sources of uncertainties in the spectrum are identified and analyzed in detail. The exposure time dependence of the spectrum is also discussed. The averaged cross sections of the inverse neutron β decay, weak charged and neutral-current-induced deuteron disintegration, and the antineutrino-electron scattering are then evaluated using the resulting ν̅_e spectra.
[RADIOACTIVITY, FISSION 235U, 238U, (^239)Pu, (^240)Pu, (^241)Pu, antineutrino and electron spectra calculated. σ for ν̅ induced reactions analyzed.
Magnon valley Hall effect in CrI3-based vdW heterostructures
Magnonic excitations in the two-dimensional (2D) van der Waals (vdW)
ferromagnet CrI3 are studied. We find that bulk magnons exhibit a non-trivial
topological band structure without the need for Dzyaloshinskii-Moriya (DM)
interaction. This is shown in vdW heterostructures, consisting of single-layer
CrI3 on top of different 2D materials as MoTe2, HfS2 and WSe2. We find
numerically that the proposed substrates modify substantially the out-of-plane
magnetic anisotropy on each sublattice of the CrI3 subsystem. The induced
staggered anisotropy, combined with a proper band inversion, leads to the
opening of a topological gap of the magnon spectrum. Since the gap is opened
non-symmetrically at the K+ and K- points of the Brillouin zone, an imbalance
in the magnon population between these two valleys can be created under a
driving force. This phenomenon is in close analogy to the so-called valley Hall
effect (VHE), and thus termed as magnon valley Hall effect (MVHE). In linear
response to a temperature gradient we quantify this effect by the evaluation of
the temperature-dependence of the magnon thermal Hall effect. These findings
open a different avenue by adding the valley degrees of freedom besides the
spin, in the study of magnons
Predominance of Methicillin Resistant Staphylococcus Aureus -ST88 and New ST1797 causing Wound Infection and Abscesses.
Although there has been a worldwide emergence and spread of methicillin-resistant Staphylococcus aureus (MRSA), little is known about the molecular epidemiology of MRSA in Tanzania. In this study, we characterized MRSA strains isolated from clinical specimens at the Bugando Medical Centre, Tanzania, between January and December 2008. Of 160 S. aureus isolates from 600 clinical specimens, 24 (15%) were found to be MRSA. Besides molecular screening for the Panton Valentine leukocidin (PVL) genes by PCR, MRSA strains were further characterized by Multi-Locus Sequence Typing (MLST) and spa typing. Despite considerable genetic diversity, the spa types t690 (29.1%) and t7231 (41.6%), as well as the sequence types (ST) 88 (54.2%) and 1797 (29.1%), were dominant among clinical isolates. The PVL genes were detected in 4 isolates; of these, 3 were found in ST 88 and one in ST1820. Resistance to erythromycin, clindamicin, gentamicin, tetracycline and co-trimoxazole was found in 45.8%, 62.5%, 41.6%, 45.8% and 50% of the strains, respectively. We present the first thorough typing of MRSA at a Tanzanian hospital. Despite considerable genetic diversity, ST88 was dominant among clinical isolates at the Bugando Medical Centre. Active and standardized surveillance of nosocomial MRSA infection should be conducted in the future to analyse the infection and transmission rates and implement effective control measures
Cavity-assisted spontaneous emission as a single-photon source: Pulse shape and efficiency of one-photon Fock state preparation
Within the framework of exact quantum electrodynamics in dispersing and
absorbing media, we have studied the quantum state of the radiation emitted
from an initially in the upper state prepared two-level atom in a high-
cavity, including the regime where the emitted photon belongs to a wave packet
that simultaneously covers the areas inside and outside the cavity. For both
continuing atom--field interaction and short-term atom--field interaction, we
have determined the spatio-temporal shape of the excited outgoing wave packet
and calculated the efficiency of the wave packet to carry a one-photon Fock
state. Furthermore, we have made contact with quantum noise theories where the
intracavity field and the field outside the cavity are regarded as
approximately representing independent degrees of freedom such that two
separate Hilbert spaces can be introduced.Comment: 16 pages, 7 eps figures; improved version as submitted to Phys. Rev.
Ground-state topology of the Edwards-Anderson +/-J spin glass model
In the Edwards-Anderson model of spin glasses with a bimodal distribution of
bonds, the degeneracy of the ground state allows one to define a structure
called backbone, which can be characterized by the rigid lattice (RL),
consisting of the bonds that retain their frustration (or lack of it) in all
ground states. In this work we have performed a detailed numerical study of the
properties of the RL, both in two-dimensional (2D) and three-dimensional (3D)
lattices. Whereas in 3D we find strong evidence for percolation in the
thermodynamic limit, in 2D our results indicate that the most probable scenario
is that the RL does not percolate. On the other hand, both in 2D and 3D we find
that frustration is very unevenly distributed. Frustration is much lower in the
RL than in its complement. Using equilibrium simulations we observe that this
property can be found even above the critical temperature. This leads us to
propose that the RL should share many properties of ferromagnetic models, an
idea that recently has also been proposed in other contexts. We also suggest a
preliminary generalization of the definition of backbone for systems with
continuous distributions of bonds, and we argue that the study of this
structure could be useful for a better understanding of the low temperature
phase of those frustrated models.Comment: 16 pages and 21 figure
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