6,700 research outputs found
Gluon Condensates, Chiral Symmetry Breaking and Pion Wave Function
We consider here chiral symmetry breaking in quantum chromodynamics arising
from gluon condensates in vacuum. Through coherent states of gluons simulating
a mean field type of approximation, we show that the off-shell gluon
condensates of vacuum generate a mass-like contribution for the quarks, giving
rise to chiral symmetry breaking. We next note that spontaneous breaking of
global chiral symmetry links the four component quark field operator to the
pion wave function. This in turn yields many hadronic properties in the light
quark sector in agreement with experiments, leading to the conclusion that low
energy hadron properties are primarily driven by the vacuum structure of
quantum chromodynamics.Comment: 25 pages, IP/BBSR/92-76, revte
A Continuous Injection Plasma Model for the X-Ray/Radio Knots in Kpc-Scale Jets of AGN
We consider the evolution of a spherically expanding plasma cloud, where
there is continuous injection of non-thermal electrons. We compute the time
dependent electron distribution and resultant photon spectra taking into
account synchrotron, adiabatic and inverse Compton cooling. This model is
different from previous works where, instead of a continuous injection of
particles, a short injection period was assumed. We apply this model to the
radio/optical knots in the large scale jets of AGN, detected in X-rays by {\it
Chandra} and find that the overall broadband spectral features can be
reproduced. It is shown that for some sources, constraints on the X-ray
spectral index (by a longer {\it Chandra} observation) will be able to
differentiate between the different models. This in turn will put a strong
constraint on the acceleration mechanism active in these sources.Comment: Accepted for publications in the Astrophysical Journal Letter
INTRINSIC MECHANISM FOR ENTROPY CHANGE IN CLASSICAL AND QUANTUM EVOLUTION
It is shown that the existence of a time operator in the Liouville space
representation of both classical and quantum evolution provides a mechanism for
effective entropy change of physical states. In particular, an initially
effectively pure state can evolve under the usual unitary evolution to an
effectively mixed state.Comment: 20 pages. For more information or comments contact E. Eisenberg at
[email protected] (internet)
Spatiotemporal chaos and the dynamics of coupled Langmuir and ion-acoustic waves in plasmas
A simulation study is performed to investigate the dynamics of coupled
Langmuir waves (LWs) and ion-acoustic waves (IAWs) in an unmagnetized plasma.
The effects of dispersion due to charge separation and the density nonlinearity
associated with the IAWs, are considered to modify the properties of Langmuir
solitons, as well as to model the dynamics of relatively large amplitude wave
envelopes. It is found that the Langmuir wave electric field, indeed, increases
by the effect of ion-wave nonlinearity (IWN). Use of a low-dimensional model,
based on three Fourier modes shows that a transition to temporal chaos is
possible, when the length scale of the linearly excited modes is larger than
that of the most unstable ones. The chaotic behaviors of the unstable modes are
identified by the analysis of Lyapunov exponent spectra. The space-time
evolution of the coupled LWs and IAWs shows that the IWN can cause the
excitation of many unstable harmonic modes, and can lead to strong IAW
emission. This occurs when the initial wave field is relatively large or the
length scale of IAWs is larger than the soliton characteristic size. Numerical
simulation also reveals that many solitary patterns can be excited and
generated through the modulational instability (MI) of unstable harmonic modes.
As time goes on, these solitons are seen to appear in the spatially partial
coherence (SPC) state due to the free ion-acoustic radiation as well as in the
state of spatiotemporal chaos (STC) due to collision and fusion in the
stochastic motion. The latter results the redistribution of initial wave energy
into a few modes with small length scales, which may lead to the onset of
Langmuir turbulence in laboratory as well as space plasmas.Comment: 10 Pages, 14 Figures; to appear in Physical Review
Ferromagnetic relaxation by magnon-induced currents
A theory for calculating spin wave relaxation times based on the
magnon-electron interaction is developed. The theory incorporates a thin film
geometry and is valid for a large range of magnon frequencies and wave vectors.
For high conductivity metals such as permalloy, the wave vector dependent
damping constant approaches values as high as 0.2, showing the large magnitude
of the effect, and can dominate experimentally observed relaxation.Comment: 5 pages, 4 figure
Service limit state resistance factors for drilled shafts
This is the published version. Copyrigh 2009 ICE PublishingThe analysis of bored piles, or drilled shafts, at the service limit state is important when foundation settlements are critical to the operation of a structure. The t–z method is a widely used soil–structure interaction model for the analysis of drilled shaft settlement. In current practice, nominal values of soil stiffness and strength parameters are used to determine settlement based upon the t–z method. However, the nominal values can vary from one designer to another, making the results somewhat inconsistent. By considering reliability-based design principles, probabilistic relationships can be incorporated into the settlement analysis of the drilled shaft, and thus design uncertainty can be quantified. Following this approach, load and resistance factor design (LRFD) procedures may be utilised and resistance factors established for use in design. Using a t–z model and the Monte Carlo simulation process, probability distributions are determined for drilled shaft capacity at the service limit state. Resistance factors are calculated based upon these relationships. The drilled shaft geometry and the shaft/soil interface parameters are varied so that their effects on the resistance factors may be understood
Spin contribution to the ponderomotive force in a plasma
The concept of a ponderomotive force due to the intrinsic spin of electrons
is developed. An expression containing both the classical as well as the
spin-induced ponderomotive force is derived. The results are used to
demonstrate that an electromagnetic pulse can induce a spin-polarized plasma.
Furthermore, it is shown that for certain parameters, the nonlinear
back-reaction on the electromagnetic pulse from the spin magnetization current
can be larger than that from the classical free current. Suitable parameter
values for a direct test of this effect are presented.Comment: 4 pages, 2 figures, version accepted for publication in Physical
Review Letter
Quantum Information and Entropy
Thermodynamic entropy is not an entirely satisfactory measure of information
of a quantum state. This entropy for an unknown pure state is zero, although
repeated measurements on copies of such a pure state do communicate
information. In view of this, we propose a new measure for the informational
entropy of a quantum state that includes information in the pure states and the
thermodynamic entropy. The origin of information is explained in terms of an
interplay between unitary and non-unitary evolution. Such complementarity is
also at the basis of the so-called interaction-free measurement.Comment: 21 pages, 3 figure
Spatiotemporal evolution in a (2+1)-dimensional chemotaxis model
Simulations are performed to investigate the nonlinear dynamics of a
(2+1)-dimensional chemotaxis model of Keller-Segel (KS) type with a logistic
growth term. Because of its ability to display auto-aggregation, the KS model
has been widely used to simulate self-organization in many biological systems.
We show that the corresponding dynamics may lead to a steady-state, divergence
in a finite time as well as the formation of spatiotemporal irregular patterns.
The latter, in particular, appear to be chaotic in part of the range of bounded
solutions, as demonstrated by the analysis of wavelet power spectra. Steady
states are achieved with sufficiently large values of the chemotactic
coefficient and/or with growth rates below a critical value .
For , the solutions of the differential equations of the model diverge
in a finite time. We also report on the pattern formation regime for different
values of , and the diffusion coefficient .Comment: 6 pages, 7 figures; To appear in Physica A (2011
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