10,127 research outputs found
Adiabatic dynamics in a spin-1 chain with uniaxial single-spin anisotropy
We study the adiabatic quantum dynamics of an anisotropic spin-1 XY chain
across a second order quantum phase transition. The system is driven out of
equilibrium by performing a quench on the uniaxial single-spin anisotropy, that
is supposed to vary linearly in time. We show that, for sufficiently large
system sizes, the excess energy after the quench admits a non trivial scaling
behavior that is not predictable by standard Kibble-Zurek arguments for
isolated critical points or extended critical regions. This emerges from a
competing effect of many accessible low-lying excited states, inside the whole
continuous line of critical points.Comment: 17 pages, 8 figures, published versio
Structural design studies of a supersonic cruise arrow wing configuration
Structural member cross sections were sized with a system of integrated computer programs to satisfy strength and flutter design requirements for several variants of the arrow wing supersonic cruise vehicle. The resulting structural weights provide a measure of the structural efficiency of the planform geometry, structural layout, type of construction, and type of material including composites. The material distribution was determined for a baseline metallic structure and the results indicate that an approximate fatigue constraint has an important effect on the structural weight required for strength but, in all cases, additional material had to be added to satisfy flutter requirements with lighter mass engines with minimum fuel onboard. The use of composite materials on the baseline configuration was explored and indicated increased structural efficiency. In the strength sizing, the all-composite construction provided a lower weight design than the hybrid construction which contained composites only in the wing cover skins. Subsequent flutter analyses indicated a corresponding lower flutter speed
Multiple electron-hole scattering effect on quasiparticle properties in a homogeneous electron gas
We present a detailed study of a contribution of the T matrix accounting for
multiple scattering between an electron and a hole to the quasiparticle
self-energy. This contribution is considered as an additional term to the GW
self-energy. The study is based on a variational solution of the T-matrix
integral equation within a local approximation. A key quantity of such a
solution, the local electron-hole interaction, is obtained at the small
four-momentum transfer limit. Performed by making use of this limit form,
extensive calculations of quasiparticle properties in the homogeneous electron
gas over a broad range of electron densities are reported. We carry out an
analysis of how the T-matrix contribution affects the quasiparticle damping
rate, the quasiparticle energy, the renormalization constant, and the effective
mass enhancement. We find that in comparison with the GW approximation the
inclusion of the T matrix leads to an essential increase of the damping rate, a
slight reduction of the GW band narrowing, a decrease of the renormalization
constant at the Fermi wave vector, and some "weighting" of quasiparticles at
the Fermi surface.Comment: 12 pages, 11 figures, 1 tabl
Spin liquid ground state in a two dimensional non-frustrated spin model
We consider an exchange model describing two isotropic spin-1/2 Heisenberg
antiferromagnets coupled by a quartic term on the square lattice. The model is
relevant for systems with orbital degeneracy and strong electron-vibron
coupling in the large Hubbard repulsion limit, and is known to show a
spin-Peierls-like dimerization in one dimension. In two dimensions we calculate
energy gaps, susceptibilities, and correlation functions with a Green's
Function Monte Carlo. We find a finite spin gap and no evidence of any kind of
order. We conclude that the ground state is, most likely, a spin liquid of
resonating valence bonds.Comment: 4 pages, 4 figures, Revte
Valence-bond states in dynamical Jahn-Teller molecular systems
We discuss a hopping model of electrons between idealized molecular sites
with local orbital degeneracy and dynamical Jahn-Teller effect, for crystal
field environments of sufficiently high symmetry. For the Mott-insulating case
(one electron per site and large Coulomb repulsions), in the simplest two-fold
degenerate situation, we are led to consider a particular exchange hamiltonian,
describing two isotropic spin-1/2 Heisenberg problems coupled by a quartic term
on equivalent bonds. This twin-exchange hamiltonian applies to a physical
regime in which the inter-orbital singlet is the lowest-energy intermediate
state available for hopping. This regime is favored by a relatively strong
electron-phonon coupling. Using variational arguments, a large-N limit, and
exact diagonalization data, we find that the ground state, in the one
dimensional case, is a solid valence bond state. The situation in the two
dimensional case is less clear. Finally, the behavior of the system upon hole
doping is studied in one dimension.Comment: 11 pages, 5 figure
Serum ferritin is an independent risk factor for acute respiratory distress syndrome in COVID-19
Increased ferritin levels could be indicative of a strong inflammatory reaction in COVID-19 and recent studies suggest that increased levels of circulating ferritin levels play a critical role by contributing to the development of a cytokine storm. In this regard, ferritin evaluation could be an early, available and easy to use screening tool to assess the disease severity at the first admission in the emergency department. This test might be of crucial importance for the timely identification of patients at higher risk of an adverse outcome
Melting transition of an Ising glass driven by magnetic field
The quantum critical behavior of the Ising glass in a magnetic field is
investigated. We focus on the spin glass to paramagnet transition of the
transverse degrees of freedom in the presence of finite longitudinal field. We
use two complementary techniques, the Landau theory close to the T=0 transition
and the exact diagonalization method for finite systems. This allows us to
estimate the size of the critical region and characterize various crossover
regimes. An unexpectedly small energy scale on the disordered side of the
critical line is found, and its possible relevance to experiments on metallic
glasses is briefly discussed.Comment: 4 pages, 3 figure
Working group written presentation: Trapped radiation effects
The results of the Trapped Radiation Effects Panel for the Space Environmental Effects on Materials Workshop are presented. The needs of the space community for new data regarding effects of the space environment on materials, including electronics are listed. A series of questions asked of each of the panels at the workshop are addressed. Areas of research which should be pursued to satisfy the requirements for better knowledge of the environment and better understanding of the effects of the energetic charged particle environment on new materials and advanced electronics technology are suggested
Anomalous diffusion in a symbolic model
We address this work to investigate some statistical properties of symbolic
sequences generated by a numerical procedure in which the symbols are repeated
following a power law probability density. In this analysis, we consider that
the sum of n symbols represents the position of a particle in erratic movement.
This approach revealed a rich diffusive scenario characterized by non-Gaussian
distributions and, depending on the power law exponent and also on the
procedure used to build the walker, we may have superdiffusion, subdiffusion or
usual diffusion. Additionally, we use the continuous-time random walk framework
to compare with the numerical data, finding a good agreement. Because of its
simplicity and flexibility, this model can be a candidate to describe real
systems governed by power laws probabilities densities.Comment: Accepted for publication in Physica Script
Spectral Function in Mott Insulating Surfaces
We show theoretically the fingerprints of short-range spiral magnetic
correlations in the photoemission spectra of the Mott insulating ground states
realized in the triangular silicon surfaces K/Si(111)-B and SiC(0001). The
calculated spectra present low energy features of magnetic origin with a
reduced dispersion ~10-40 meV compared with the center-of-mass spectra
bandwidth ~0.2-0:3 eV. Remarkably, we find that the quasiparticle signal
survives only around the magnetic Goldstone modes. Our findings would position
these silicon surfaces as new candidates to investigate non-conventional
quasiparticle excitations.Comment: 5 pages, 4 figures. To be published in Journal of Physics: Condensed
Matte
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