396 research outputs found
Asymmetry of Strange Sea in Nucleons
Based on the finite-temperature field theory, we evaluate the medium effects
in nucleon which can induce an asymmetry between quarks and antiquarks of the
strange sea. The short-distance effects determined by the weak interaction can
give rise to where is the medium-induced mass of strange quark by a few KeV at
most, but the long-distance effects by strong interaction are sizable. Our
numerical results show that there exists an obvious mass difference between
strange and anti-strange quarks, as large as 10-100 MeV.Comment: 15 latex pages, 3 figures, to appear in PR
A New Model for Void Coalescence by Internal Necking
A micromechanical model for predicting the strain increment required to bring a damaged material element from the onset of void coalescence up to final fracture is developed based on simple kinematics arguments. This strain increment controls the unloading slope and the energy dissipated during the final step of material failure. Proper prediction of the final drop of the load carrying capacity is an important ingredient of any ductile fracture model, especially at high stress triaxiality. The model has been motivated and verified by comparison to a large set of finite element void cell calculations.
New Results for the Correlation Functions of the Ising Model and the Transverse Ising Chain
In this paper we show how an infinite system of coupled Toda-type nonlinear
differential equations derived by one of us can be used efficiently to
calculate the time-dependent pair-correlations in the Ising chain in a
transverse field. The results are seen to match extremely well long large-time
asymptotic expansions newly derived here. For our initial conditions we use new
long asymptotic expansions for the equal-time pair correlation functions of the
transverse Ising chain, extending an old result of T.T. Wu for the 2d Ising
model. Using this one can also study the equal-time wavevector-dependent
correlation function of the quantum chain, a.k.a. the q-dependent diagonal
susceptibility in the 2d Ising model, in great detail with very little
computational effort.Comment: LaTeX 2e, 31 pages, 8 figures (16 eps files). vs2: Two references
added and minor changes of style. vs3: Corrections made and reference adde
Theoretical analysis of neutron scattering results for quasi-two dimensional ferromagnets
A theoretical study has been carried out to analyse the available results
from the inelastic neutron scattering experiment performed on a quasi-two
dimensional spin-1/2 ferromagnetic material . Our formalism is based
on a conventional semi-classical like treatment involving a model of an ideal
gas of vortices/anti-vortices corresponding to an anisotropic XY Heisenberg
ferromagnet on a square lattice. The results for dynamical structure functions
for our model corresponding to spin-1/2, show occurrence of negative values in
a large range of energy transfer even encompassing the experimental range, when
convoluted with a realistic spectral window function. This result indicates
failure of the conventional theoretical framework to be applicable to the
experimental situation corresponding to low spin systems. A full quantum
formalism seems essential for treating such systems.Comment: 16 pages, 6 figures, 1 Table Submitted for publicatio
Finite Temperature Properties of Quantum Antiferromagnets in a Uniform Magnetic Field in One and Two Dimensions
Consider a -dimensional antiferromagnet with a quantum disordered ground
state and a gap to bosonic excitations with non-zero spin. In a finite external
magnetic field, this antiferromagnet will undergo a phase transition to a
ground state with non-zero magnetization, describable as the condensation of a
dilute gas of bosons. The finite temperature properties of the Bose gas in the
vicinity of this transition are argued to obey a hypothesis of ZERO
SCALE-FACTOR UNIVERSALITY for , with logarithmic violations in .
Scaling properties of various experimental observables are computed in an
expansion in , and exactly in .Comment: 27 pages, REVTEX 3.0, 8 Postscript figures appended, YCTP-xyz
On the infrared scaling solution of SU(N) Yang-Mills theories in the maximally Abelian gauge
An improved method for extracting infrared exponents from functional
equations is presented. The generalizations introduced allow for an analysis of
quite complicated systems such as Yang-Mills theory in the maximally Abelian
gauge. Assuming the absence of cancellations in the appropriately renormalized
integrals the only consistent scaling solution yields an infrared enhanced
diagonal gluon propagator in support of the Abelian dominance hypothesis. This
is explicitly shown for SU(2) and subsequently verified for SU(N), where
additional interactions exist. We also derive the most infrared divergent
scaling solution possible for vertex functions in terms of the propagators'
infrared exponents. We provide general conditions for the existence of a
scaling solution for a given system and comment on the cases of linear
covariant gauges and ghost anti-ghost symmetric gauges.Comment: 23 pages, 10 figures; version coincides with version published in
EPJ
Asymmetric nuclear matter:the role of the isovector scalar channel
We try to single out some qualitative new effects of the coupling to the
-isovector-scalar meson introduced in a minimal way in a
phenomenological hadronic field theory. Results for the equation of state
() and the phase diagram of asymmetric nuclear matter () are
discussed. We stress the consistency of the -coupling introduction in a
relativistic approach. New contributions to the slope and curvature of the
symmetry energy and the neutron-proton effective mass splitting appear
particularly interesting. A more repulsive for neutron matter at high
baryon densities is expected. Effects on new critical properties of warm ,
mixing of mechanical and chemical instabilities and isospin distillation, are
also presented. The influence is mostly on the {\it isovectorlike}
collective response.
The results are largely analytical and this makes the physical meaning quite
transparent. Implications for nuclear structure properties of drip-line nuclei
and for reaction dynamics with Radioactive Beams are finally pointed out.Comment: 12 pages, 10 Postscript figure
Relativistic Mean Field Model with Generalized Derivative Nucleon-Meson Couplings
The quantum hadrodynamics (QHD) model with minimal nucleon-meson couplings is
generalized by introducing couplings of mesons to derivatives of the nucleon
field in the Lagrangian density. This approach allows an effective description
of a state-dependent in-medium interaction in the mean-field approximation.
Various parametrizations for the generalized couplings are developed and
applied to infinite nuclear matter. In this approach, scalar and vector
self-energies depend on both density and momentum similarly as in the
Dirac-Brueckner theory. The Schr\"{o}diger-equivalent optical potential is much
less repulsive at high nucleon energies as compared to standard relativistic
mean field models and thus agrees better with experimental findings. The
derivative couplings in the extended model have significant effects on
properties of symmetric nuclear matter and neutron matter.Comment: 35 pages, 1 table, 10 figure
IRF4 and BATF are critical for CD8(+) T-cell function following infection with LCMV.
CD8(+) T-cell functions are critical for preventing chronic viral infections by eliminating infected cells. For healthy immune responses, beneficial destruction of infected cells must be balanced against immunopathology resulting from collateral damage to tissues. These processes are regulated by factors controlling CD8(+) T-cell function, which are still incompletely understood. Here, we show that the interferon regulatory factor 4 (IRF4) and its cooperating binding partner B-cell-activating transcription factor (BATF) are necessary for sustained CD8(+) T-cell effector function. Although Irf4(-/-) CD8(+) T cells were initially capable of proliferation, IRF4 deficiency resulted in limited CD8(+) T-cell responses after infection with the lymphocytic choriomeningitis virus. Consequently, Irf4(-/-) mice established chronic infections, but were protected from fatal immunopathology. Absence of BATF also resulted in reduced CD8(+) T-cell function, limited immunopathology, and promotion of viral persistence. These data identify the transcription factors IRF4 and BATF as major regulators of antiviral cytotoxic T-cell immunity
How to keep it adequate: A protocol for ensuring validity in agent-based simulation
There has so far been no shared understanding of validity in agent-based simulation. We here conceptualise validation as systematically substantiating the premises on which conclusions from simulation analysis for a particular modelling context are built. Given such a systematic perspective, validity of agent-based models cannot be ensured if validation is merely understood as an isolated step in the modelling process. Rather, valid conclusions from simulation analysis require context-adequate method choices at all steps of the simulation analysis including model construction, model and parameter inference, uncertainty analysis and simulation. We present a twelve-step protocol to highlight the (often hidden) premises for methodological choices and their link to the modelling context. It is designed to aid modelers in understanding their context and in choosing and documenting context-adequate and mutually consistent methods throughout the modelling process. Its purpose is to assist reviewers and the community as a whole in assessing and discussing context-adequacy
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