18,098 research outputs found
2D modeling of electromagnetic waves in cold plasmas
The consequences of sheath (rectified) electric fields, resulting from the different mobility of electrons and ions as a response to radio frequency (RF) fields, are a concern for RF antenna design as it can cause damage to antenna parts, limiters and other in-vessel components. As a first step to a more complete description, the usual cold plasma dielectric description has been adopted, and the density profile was assumed to be known as input. Ultimately, the relevant equations describing the wave-particle interaction both on the fast and slow timescale will need to be tackled but prior to doing so was felt as a necessity to get a feeling of the wave dynamics involved. Maxwell's equations are solved for a cold plasma in a 2D antenna box with strongly varying density profiles crossing also lower hybrid and ion-ion hybrid resonance layers. Numerical modelling quickly becomes demanding on computer power, since a fine grid spacing is required to capture the small wavelengths effects of strongly evanescent modes
Thermally stable electrolytes for rechargeable lithium batteries, phase 2
During the second year of research under NASA SBIR Contract NAS7-967, Covalent Associates and NASA contract monitors at the Jet Propulsion Laboratory agreed to perform an evaluation of the three best electrolytes developed during Phase 2. Due to the extensive period of time required to collect meaningful cycling data, we realized the study would extend well beyond the original formal end of the Phase 2 program (August 31, 1988). The substitution of this effort in lieu of an earlier proposed 20-cell final deliverable is formally documented in Modification No. 1 of Contract NAS7-967 as task 7. This Addendum contains the results of the cycling studies performed at Covalent Associates. In addition, sealed ampoules of each of these three electrolytes were delivered to the Jet Propulsion Laboratory Electrochemical Power Group. Their concurrent evaluation in a different test vehicle has also been recently concluded and their results are also summarized herein
Nonplanar integrability at two loops
In this article we compute the action of the two loop dilatation operator on
restricted Schur polynomials that belong to the su(2) sector, in the displaced
corners approximation. In this non-planar large N limit, operators that
diagonalize the one loop dilatation operator are not corrected at two loops.
The resulting spectrum of anomalous dimensions is related to a set of decoupled
harmonic oscillators, indicating integrability in this sector of the theory at
two loops. The anomalous dimensions are a non-trivial function of the 't Hooft
coupling, with a spectrum that is continuous and starting at zero at large N,
but discrete at finite N.Comment: version to appear in JHE
A double coset ansatz for integrability in AdS/CFT
We give a proof that the expected counting of strings attached to giant
graviton branes in AdS_5 x S^5, as constrained by the Gauss Law, matches the
dimension spanned by the expected dual operators in the gauge theory. The
counting of string-brane configurations is formulated as a graph counting
problem, which can be expressed as the number of points on a double coset
involving permutation groups. Fourier transformation on the double coset
suggests an ansatz for the diagonalization of the one-loop dilatation operator
in this sector of strings attached to giant graviton branes. The ansatz agrees
with and extends recent results which have found the dynamics of open string
excitations of giants to be given by harmonic oscillators. We prove that it
provides the conjectured diagonalization leading to harmonic oscillators.Comment: 33 pages, 3 figures; v2: references adde
The chemical equilibration volume: measuring the degree of thermalization
We address the issue of the degree of equilibrium achieved in a high energy
heavy-ion collision. Specifically, we explore the consequences of incomplete
strangeness chemical equilibrium. This is achieved over a volume V of the order
of the strangeness correlation length and is assumed to be smaller than the
freeze-out volume. Probability distributions of strange hadrons emanating from
the system are computed for varying sizes of V and simple experimental
observables based on these are proposed. Measurements of such observables may
be used to estimate V and as a result the degree of strangeness chemical
equilibration achieved. This sets a lower bound on the degree of kinetic
equilibrium. We also point out that a determination of two-body correlations or
second moments of the distributions are not sufficient for this estimation.Comment: 16 pages, 15 figures, revtex
Crossover transition in bag-like models
We formulate a simple model for a gas of extended hadrons at zero chemical
potential by taking inspiration from the compressible bag model. We show that a
crossover transition qualitatively similar to lattice QCD can be reproduced by
such a system by including some appropriate additional dynamics. Under certain
conditions, at high temperature, the system consist of a finite number of
infinitely extended bags, which occupy the entire space. In this situation the
system behaves as an ideal gas of quarks and gluons.Comment: Corresponds to the published version. Added few references and
changed the titl
Pion and Quark Annihilation Mechanisms of Dilepton Production in Relativistic Heavy-Ion Collisions
We revise the pion-pion and quark-quark annihilation mechanisms of dilepton
production during relativistic heavy-ion collisions. We focus on the
modifications caused by the specific features of intramedium pion states rather
than by medium modification of the rho-meson spectral density. The main
ingredient emerging in our approach is a form-factor of the multi-pion
(multi-quark) system. Replacing the usual delta-function the form-factor plays
the role of distribution which, in some sense, "connects" the 4-momenta of the
annihilating and outgoing particles. The difference between the c.m.s.
velocities attributed to annihilating and outgoing particles is a particular
consequence of this replacement and results in the appearance of a new factor
in the formula for the dilepton production rate. We obtained that the
form-factor of the multi-pion (multi-quark) system causes broadening of the
rate which is most pronounced for small invariant masses, in particular, we
obtain a growth of the rate for the invariant masses below two masses of the
annihilating particles.Comment: 6 pages, 6 figures, LaTex; to appear in Mod. Phys. Lett.
Surprisingly Simple Spectra
The large N limit of the anomalous dimensions of operators in
super Yang-Mills theory described by restricted Schur polynomials, are studied.
We focus on operators labeled by Young diagrams that have two columns (both
long) so that the classical dimension of these operators is O(N). At large N
these two column operators mix with each other but are decoupled from operators
with columns. The planar approximation does not capture the large N
dynamics. For operators built with 2, 3 or 4 impurities the dilatation operator
is explicitly evaluated. In all three cases, in a certain limit, the dilatation
operator is a lattice version of a second derivative, with the lattice emerging
from the Young diagram itself. The one loop dilatation operator is diagonalized
numerically. All eigenvalues are an integer multiple of and there
are interesting degeneracies in the spectrum. The spectrum we obtain for the
one loop anomalous dimension operator is reproduced by a collection of harmonic
oscillators. This equivalence to harmonic oscillators generalizes giant
graviton results known for the BPS sector and further implies that the
Hamiltonian defined by the one loop large dilatation operator is
integrable. This is an example of an integrable dilatation operator, obtained
by summing both planar and non-planar diagrams.Comment: 34 page
Deciphering Deconfinement in Correlations of Conserved Charges
Diagonal and off-diagonal flavor and conserved charge susceptibilities reveal
the prevalent degrees of freedom of heated strongly interacting matter. Results
obtained from lattice simulations are compared with various model estimates in
an effort to weed down various possible pictures of a quark gluon plasma. We
argue that the vanishing of the off-diagonal quark flavor susceptibilities and
its derivatives with respect to chemical potential, at temperatures above
1.5Tc, can only be understood in a picture of a gas or liquid composed of
quasi-particles which carry the same quantum numbers as quarks and antiquarks.
A potential new observable, blind to neutral and non-strange particles, is
introduced and related via isospin symmetry to the ratio of susceptibilities of
baryonic strangeness to strangeness generated in the excited matter created at
RHIC.Comment: 5 pages, 3 figures, LATEX, To appear in the proceedings of the
International Conference on Strangeness in Quark Matter, Los Angeles, CA, Mar
26-31, 200
Orthogonal Bases of Invariants in Tensor Models
Representation theory provides a suitable framework to count and classify
invariants in tensor models. We show that there are two natural ways of
counting invariants, one for arbitrary rank of the gauge group and a second,
which is only valid for large N. We construct bases of invariant operators
based on the counting, and compute correlators of their elements. The basis
associated with finite N diagonalizes the two-point function of the theory and
it is analogous to the restricted Schur basis used in matrix models. We comment
on future lines of investigation.Comment: Two overlapping but independent results are merged to a joint work.
16 pages, 1 tabl
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