16,390 research outputs found
The Angular Momentum Distribution within Halos in Different Dark Matter Models
We study the angular momentum profile of dark matter halos for a statistical
sample drawn from a set of high-resolution cosmological simulations of
particles. Two typical Cold Dark Matter (CDM) models have been analyzed, and
the halos are selected to have at least particles in order to
reliably measure the angular momentum profile. In contrast with the recent
claims of Bullock et al., we find that the degree of misalignment of angular
momentum within a halo is very high. About 50 percent of halos have more than
10 percent of halo mass in the mass of negative angular momentum . After the
mass of negative is excluded, the cumulative mass function follows
approximately the universal function proposed by Bullock et al., though we
still find a significant fraction of halos () which exhibit
systematic deviations from the universal function. Our results, however, are
broadly in good agreement with a recent work of van den Bosch et al.. We also
study the angular momentum profile of halos in a Warm Dark Matter (WDM) model
and a Self-Interacting Dark Matter (SIDM) model. We find that the angular
momentum profile of halos in the WDM is statistically indistinguishable from
that in the CDM model, but the angular momentum of halos in the SIDM is reduced
by the self-interaction of dark matter.Comment: 23 pages, 10 figures, 2 tables. Revised version, added a new table,
accepted for publication in MNRA
Effect of charged impurities on graphene thermoelectric power near the Dirac point
In graphene devices with a varying degree of disorders as characterized by
their carrier mobility and minimum conductivity, we have studied the
thermoelectric power along with the electrical conductivity over a wide range
of temperatures. We have found that the Mott relation fails in the vicinity of
the Dirac point in high-mobility graphene. By properly taking account of the
high temperature effects, we have obtained good agreement between the Boltzmann
transport theory and our experimental data. In low-mobility graphene where the
charged impurities induce relatively high residual carrier density, the Mott
relation holds at all gate voltages
Fermionic realization of two-parameter quantum affine algebra
We construct all fundamental modules for the two parameter quantum affine
algebra of type using a combinatorial model of Young diagrams. In
particular we also give a fermionic realization of the two-parameter quantum
affine algebra
Growth Tight Actions
We introduce and systematically study the concept of a growth tight action.
This generalizes growth tightness for word metrics as initiated by Grigorchuk
and de la Harpe. Given a finitely generated, non-elementary group acting on
a --space , we prove that if contains a strongly
contracting element and if is not too badly distorted in ,
then the action of on is a growth tight action. It follows
that if is a cocompact, relatively hyperbolic --space, then
the action of on is a growth tight action. This generalizes
all previously known results for growth tightness of cocompact actions: every
already known example of a group that admits a growth tight action and has some
infinite, infinite index normal subgroups is relatively hyperbolic, and,
conversely, relatively hyperbolic groups admit growth tight actions. This also
allows us to prove that many CAT(0) groups, including flip-graph-manifold
groups and many Right Angled Artin Groups, and snowflake groups admit
cocompact, growth tight actions. These provide first examples of non-relatively
hyperbolic groups admitting interesting growth tight actions. Our main result
applies as well to cusp uniform actions on hyperbolic spaces and to the action
of the mapping class group on Teichmueller space with the Teichmueller metric.
Towards the proof of our main result, we give equivalent characterizations of
strongly contracting elements and produce new examples of group actions with
strongly contracting elements.Comment: 29 pages, 4 figures v2 added references v3 40 pages, 6 figures,
expanded preliminary sections to make paper more self-contained, other minor
improvements v4 updated bibliography, to appear in Pacific Journal of
Mathematic
Na/beta-alumina/NaAlCl4, Cl2/C circulating cell
A study was made of a high specific energy battery based on a sodium negative electrode and a chlorine positive electrode with molten AlCl3-NaCl electrolyte and a solid beta alumina separator. The basic performance of a Na beta-alumina NaAlCl4, Cl2/C circulating cell at 200 C was demonstrated. This cell can be started at 150 C. The use of melting sodium chloroaluminate electrolyte overcomes some of the material problems associated with the high working temperatures of present molten salt systems, such as Na/S and LiAl/FeS, and retains the advantages of high energy density and relatively efficient electrode processes. Preliminary investigations were conducted on a sodium-chlorine static cell, material compability, electrode design, wetting, and theoretical calculations to assure a better chance of success before assembling a Na/Cl2 circulating cell. Mathematical models provide a theoretical explanation for the performance of the NaCl2 battery. The results of mathematical models match the experimental results very well. According to the result of the mathematical modeling, an output at 180 mA/sq cm and 3.2 V can be obtained with optimized cell design
A Conjecture about Raising Operators for Macdonald Polynomials
A multivariable hypergeometric-type formula for raising operators of the
Macdonald polynomials is conjectured. It is proved that this agrees with Jing
and Jozefiak's expression for the two-row Macdonald polynomials, and also with
Lassalle and Schlosser's formula for partitions with length three.Comment: 13 page
Quantum entropy of the Kerr black hole arising from gravitational perturbation
The quantum entropy of the Kerr black hole arising from gravitational
perturbation is investigated by using Null tetrad and \'t Hooft\'s brick-wall
model. It is shown that effect of the graviton\'s spins on the subleading
correction is dependent of the square of the spins and the angular momentum per
unit mass of the black hole, and contribution of the logarithmic term to the
entropy will be positive, zero, and negative for different value of .Comment: 8 pages, 1 figure, Latex. to appear in Phys. Rev.
Accurate determination of the Lagrangian bias for the dark matter halos
We use a new method, the cross power spectrum between the linear density
field and the halo number density field, to measure the Lagrangian bias for
dark matter halos. The method has several important advantages over the
conventional correlation function analysis. By applying this method to a set of
high-resolution simulations of 256^3 particles, we have accurately determined
the Lagrangian bias, over 4 magnitudes in halo mass, for four scale-free models
with the index n=-0.5, -1.0, -1.5 and -2.0 and three typical CDM models. Our
result for massive halos with ( is a characteristic non-linear
mass) is in very good agreement with the analytical formula of Mo & White for
the Lagrangian bias, but the analytical formula significantly underestimates
the Lagrangian clustering for the less massive halos $M < M_*. Our simulation
result however can be satisfactorily described, with an accuracy better than
15%, by the fitting formula of Jing for Eulerian bias under the assumption that
the Lagrangian clustering and the Eulerian clustering are related with a linear
mapping. It implies that it is the failure of the Press-Schechter theories for
describing the formation of small halos that leads to the inaccuracy of the Mo
& White formula for the Eulerian bias. The non-linear mapping between the
Lagrangian clustering and the Eulerian clustering, which was speculated as
another possible cause for the inaccuracy of the Mo & White formula, must at
most have a second-order effect. Our result indicates that the halo formation
model adopted by the Press-Schechter theories must be improved.Comment: Minor changes; accepted for publication in ApJ (Letters) ; 11 pages
with 2 figures include
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