2,237 research outputs found
Magnetic properties of (FeCo)B alloys and the effect of doping by 5 elements
We have explored, computationally and experimentally, the magnetic properties
of \fecob{} alloys. Calculations provide a good agreement with experiment in
terms of the saturation magnetization and the magnetocrystalline anisotropy
energy with some difficulty in describing CoB, for which it is found that
both full potential effects and electron correlations treated within dynamical
mean field theory are of importance for a correct description. The material
exhibits a uniaxial magnetic anisotropy for a range of cobalt concentrations
between and . A simple model for the temperature dependence of
magnetic anisotropy suggests that the complicated non-monotonous temperature
behaviour is mainly due to variations in the band structure as the exchange
splitting is reduced by temperature. Using density functional theory based
calculations we have explored the effect of substitutional doping the
transition metal sublattice by the whole range of 5 transition metals and
found that doping by Re or W elements should significantly enhance the
magnetocrystalline anisotropy energy. Experimentally, W doping did not succeed
in enhancing the magnetic anisotropy due to formation of other phases. On the
other hand, doping by Ir and Re was successful and resulted in magnetic
anisotropies that are in agreement with theoretical predictions. In particular,
doping by 2.5~at.\% of Re on the Fe/Co site shows a magnetocrystalline
anisotropy energy which is increased by 50\% compared to its parent
(FeCo)B compound, making this system interesting, for
example, in the context of permanent magnet replacement materials or in other
areas where a large magnetic anisotropy is of importance.Comment: 15 pages 17 figure
Heavy-Quark Diffusion and Hadronization in Quark-Gluon Plasma
We calculate diffusion and hadronization of heavy quarks in high-energy
heavy-ion collisions implementing the notion of a strongly coupled quark-gluon
plasma in both micro- and macroscopic components. The diffusion process is
simulated using relativistic Fokker-Planck dynamics for elastic scattering in a
hydrodynamic background. The heavy-quark transport coefficients in the medium
are obtained from non-perturbative -matrix interactions which build up
resonant correlations close to the transition temperature. The latter also form
the basis for hadronization of heavy quarks into heavy-flavor mesons via
recombination with light quarks from the medium. The pertinent resonance
recombination satisfies energy conservation and provides an equilibrium mapping
between quark and meson distributions. The recombination probability is derived
from the resonant heavy-quark scattering rate. Consequently, recombination
dominates at low transverse momentum () and yields to fragmentation at
high . Our approach thus emphasizes the role of resonance correlations in
the diffusion and hadronization processes. We calculate the nuclear
modification factor and elliptic flow of - and -mesons for Au-Au
collisions at the Relativistic Heavy Ion Collider, and compare their
decay-electron spectra to available data. We also find that a realistic
description of the medium flow is essential for a quantitative interpretation
of the data.Comment: 16 pages, 14 figure
The QCD confinement transition: hadron formation
We review the foundations and the applications of the statistical and the
quark recombination model as hadronization models.Comment: 45 pages, 16 figures, accepted for publication in Landolt-Boernstein
Volume 1-23
A computational study on altered theta-gamma coupling during learning and phase coding
There is considerable interest in the role of coupling between theta and gamma oscillations in the brain in the context of learning and memory. Here we have used a neural network model which is capable of producing coupling of theta phase to gamma amplitude firstly to explore its ability to reproduce reported learning changes and secondly to memory-span and phase coding effects. The spiking neural network incorporates two kinetically different GABAA receptor-mediated currents to generate both theta and gamma rhythms and we have found that by selective alteration of both NMDA receptors and GABAA,slow receptors it can reproduce learning-related changes in the strength of coupling between theta and gamma either with or without coincident changes in theta amplitude. When the model was used to explore the relationship between theta and gamma oscillations, working memory capacity and phase coding it showed that the potential storage capacity of short term memories, in terms of nested gamma-subcycles, coincides with the maximal theta power. Increasing theta power is also related to the precision of theta phase which functions as a potential timing clock for neuronal firing in the cortex or hippocampus
Aplicação de cálcio alivia parcialmente o efeito deletério da hipoxia em uma cultivar de milho selecionada para tolerância ao encharcamento.
xSuplemento. Edição dos resumos do IX Congresso Brasileiro de Fisiologia Vegetal, 2003, Atibaia, SP
Magnetocaloric effect of gadolinium in high magnetic fields
International audienceThe magnetocaloric effect of gadolinium has been measured directly in pulsed magnetic fields up to 62 T. The maximum observed adiabatic temperature change is T ad = 60.5 K, the initial temperature T 0 being just above 300 K. The field dependence of T ad is found to follow the usual H 2/3 law, with a small correction in H 4/3. However, as H is increased, a radical change is observed in the dependence of T ad on T 0 , at H = const. The familiar caret-shaped peak situated at T 0 = T C becomes distinctly asymmetric, its high-temperature slope becoming more gentle and evolving into a broad plateau. For yet higher magnetic fields, μ 0 H 140 T, calculations predict a complete disappearance of the maximum near T C and an emergence of a new very broad maximum far above T C
Search for the Neutron Decay n X+ where X is a dark matter particle
In a recent paper submitted to Physical Review Letters, Fornal and Grinstein
have suggested that the discrepancy between two different methods of neutron
lifetime measurements, the beam and bottle methods can be explained by a
previously unobserved dark matter decay mode, n X+ where X
is a dark matter particle. We have performed a search for this decay mode over
the allowed range of energies of the monoenergetic gamma ray for X to be a dark
matter particle. We exclude the possibility of a sufficiently strong branch to
explain the lifetime discrepancy with greater than 4 sigma confidence.Comment: 6 pages 3 figure
Hard Probes in Heavy Ion Collisions at the LHC: Jet Physics
We discuss the importance of high-pT hadron and jet measurements in
nucleus-nucleus collisions at the CERN Large Hadron Collider.Comment: The writeup of the working group "Jet Physics" for the CERN Yellow
Report on "Hard Probes in Heavy Ion Collisions at the LHC", 123 pages.
Subgroup convenors: R. Baier, X.N. Wang, U.A. Wiedemann (theory) and I.P.
Lokhtin, A. Morsch (experiment). Editor: U.A. Wiedeman
Enhanced error estimator based on a nearly equilibrated moving least squares recovery technique for FEM and XFEM
In this paper a new technique aimed to obtain accurate estimates of the error
in energy norm using a moving least squares (MLS) recovery-based procedure is
presented. We explore the capabilities of a recovery technique based on an
enhanced MLS fitting, which directly provides continuous interpolated fields,
to obtain estimates of the error in energy norm as an alternative to the
superconvergent patch recovery (SPR). Boundary equilibrium is enforced using a
nearest point approach that modifies the MLS functional. Lagrange multipliers
are used to impose a nearly exact satisfaction of the internal equilibrium
equation. The numerical results show the high accuracy of the proposed error
estimator
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