9,243 research outputs found
Negative-energy perturbations in cylindrical equilibria with a radial electric field
The impact of an equilibrium radial electric field on negative-energy
perturbations (NEPs) (which are potentially dangerous because they can lead to
either linear or nonlinear explosive instabilities) in cylindrical equilibria
of magnetically confined plasmas is investigated within the framework of
Maxwell-drift kinetic theory. It turns out that for wave vectors with a
non-vanishing component parallel to the magnetic field the conditions for the
existence of NEPs in equilibria with E=0 [G. N. Throumoulopoulos and D.
Pfirsch, Phys. Rev. E 53, 2767 (1996)] remain valid, while the condition for
the existence of perpendicular NEPs, which are found to be the most important
perturbations, is modified. For ( is the
electrostatic potential) and ( is
the total plasma pressure), a case which is of operational interest in magnetic
confinement systems, the existence of perpendicular NEPs depends on ,
where is the charge of the particle species . In this case the
electric field can reduce the NEPs activity in the edge region of tokamaklike
and stellaratorlike equilibria with identical parabolic pressure profiles, the
reduction of electron NEPs being more pronounced than that of ion NEPs.Comment: 30 pages, late
Comprehensive study of Leon-Queretaro area
There are no author-identified significant results in this report
Negative-Energy Perturbations in Circularly Cylindrical Equilibria within the Framework of Maxwell-Drift Kinetic Theory
The conditions for the existence of negative-energy perturbations (which
could be nonlinearly unstable and cause anomalous transport) are investigated
in the framework of linearized collisionless Maxwell-drift kinetic theory for
the case of equilibria of magnetically confined, circularly cylindrical plasmas
and vanishing initial field perturbations. For wave vectors with a
non-vanishing component parallel to the magnetic field, the plane equilibrium
conditions (derived by Throumoulopoulos and Pfirsch [Phys Rev. E {\bf 49}, 3290
(1994)]) are shown to remain valid, while the condition for perpendicular
perturbations (which are found to be the most important modes) is modified.
Consequently, besides the tokamak equilibrium regime in which the existence of
negative-energy perturbations is related to the threshold value of 2/3 of the
quantity , a new
regime appears, not present in plane equilibria, in which negative-energy
perturbations exist for {\em any} value of . For various analytic
cold-ion tokamak equilibria a substantial fraction of thermal electrons are
associated with negative-energy perturbations (active particles). In
particular, for linearly stable equilibria of a paramagnetic plasma with flat
electron temperature profile (), the entire velocity space is
occupied by active electrons. The part of the velocity space occupied by active
particles increases from the center to the plasma edge and is larger in a
paramagnetic plasma than in a diamagnetic plasma with the same pressure
profile. It is also shown that, unlike in plane equilibria, negative-energy
perturbations exist in force-free reversed-field pinch equilibria with a
substantial fraction of active particles.Comment: 31 pages, late
Quantizing Open Spin Chains with Variable Length: an example from Giant Gravitons
We study an XXX open spin chain with variable number of sites, where the
variability is introduced only at the boundaries. This model arises naturally
in the study of Giant Gravitons in the AdS/CFT correspondence. We show how to
quantize the spin chain by mapping its states to a bosonic lattice of finite
length with sources and sinks of particles at the boundaries. Using coherent
states, we show how the Hamiltonian for the bosonic lattice gives the correct
description of semiclassical open strings ending on Giant Gravitons.Comment: 4 pages. v2: updated reference
On local structures of cubicity 2 graphs
A 2-stab unit interval graph (2SUIG) is an axes-parallel unit square
intersection graph where the unit squares intersect either of the two fixed
lines parallel to the -axis, distance ()
apart. This family of graphs allow us to study local structures of unit square
intersection graphs, that is, graphs with cubicity 2. The complexity of
determining whether a tree has cubicity 2 is unknown while the graph
recognition problem for unit square intersection graph is known to be NP-hard.
We present a polynomial time algorithm for recognizing trees that admit a 2SUIG
representation
High magnetic field thermal-expansion and elastic properties of CeRhIn
We report high magnetic field thermal-expansion and magnetostriction results
on CeRhIn single crystals. Several transitions, both first and second
order, are observed when the field is applied perpendicular to the
crystallographic c-axis. The magnetic field dependence of the thermal-expansion
coefficient above 15 K, where the magnetic correlations are negligible, can be
explained supposing an almost pure ground state doublet, in
apparent contradiction with neutron scattering experiments. Although the
spin-lattice interaction is relevant in this compound, the effect of the
magnetic correlations on the elastic properties is relatively weak, as revealed
by resonant ultrasound spectroscopy experiments.Comment: 5 pages, 6 figure
Single gap superconductivity in beta-Bi2Pd
beta-Bi2Pd compound has been proposed as another example of a multi-gap
superconductor [Y. Imai et al., J. Phys. Soc. Jap. 81, 113708 (2012)]. Here, we
report on measurements of several important physical quantities capable to show
a presence of multiple energy gaps on our superconducting single crystals of
beta-Bi2Pd with the critical temperature Tc close to 5 K. The calorimetric
study via a sensitive ac technique shows a sharp anomaly at the superconducting
transition, however only a single energy gap is detected. Also other
characteristics inferred from calorimetric measurements as the field dependence
of the Sommerfeld coefficient and the temperature and angular dependence of the
upper critical magnetic field point unequivocally to standard single s-wave gap
superconductivity. The Hall-probe magnetometry provides the same result from
the analysis of the temperature dependence of the lower critical field. A
single-gapped BCS density of states is detected by the scanning tunneling
spectroscopy measurements. Then, the bulk as well as the surface sensitive
probes evidence a standard conventional superconductivity in this system where
the topologically protected surface states have been recently detected by ARPES
[M. Sakano et al., Nature Comm. 6, 8595 (2015)] .Comment: 7 pages, 4 figures, 1 tabl
Cosmological scenarios from multiquintessence
In this work we derive and analyse cosmological scenarios coming from
multi-component scalar field models. We consider a direct sum of a sine-Gordon
with a Z2 model, and also a combination of those with a BNRT model. Moreover,
we work with a modified version of the BNRT model, which breaks the Z2 x Z2
symmetry of the original BNRT potential, coupled with the sine-Gordon and with
the standard Z2 models. We show that our approach can be straightforwardly
elevated to fields. All the computations are made analytically and some
parameters restriction is put forward in order to get in touch with complete
and realistic cosmological scenarios
Asymptotic Bethe equations for open boundaries in planar AdS/CFT
We solve, by means of a nested coordinate Bethe ansatz, the open-boundaries
scattering theory describing the excitations of a free open string propagating
in , carrying large angular momentum , and ending on
a maximal giant graviton whose angular momentum is in the same plane. We thus
obtain the all-loop Bethe equations describing the spectrum, for finite but
large, of the energies of such strings, or equivalently, on the gauge side of
the AdS/CFT correspondence, the anomalous dimensions of certain operators built
using the epsilon tensor of SU(N). We also give the Bethe equations for strings
ending on a probe D7-brane, corresponding to meson-like operators in an
gauge theory with fundamental matter.Comment: 30 pages. v2: minor changes and discussion section added, J.Phys.A
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