2,728 research outputs found
Quark Coalescence with Quark Number Conservation and the Effect on Quark-Hadron Scaling
We develop a new formulation of the quark coalescence model by including the
quark number conservation in order to describe the hadronization of the bulk of
the quark-gluon plasma. The scalings between hadron and quark phase space
distributions are shown to depend on the transverse momentum. For hard quarks,
our general scalings reproduce the usual quadratic scaling relation for mesons
and the cubic scaling relation for baryons. For softer quarks, however, the
inclusion of the quark number conservation leads to a linear scaling for the
hadron species that dominates the quark number of each flavor, while the
scalings of non-dominant hadrons depend on the coalescence dynamics. For charm
mesons, we find that the distribution of soft mesons does not depend on the
light quark distribution but the distribution of soft mesons is
inversely correlated to the light quark distribution.Comment: Added 6 more equations to explain the derivations; added discussions;
final published versio
Impurity State and Variable Range Hopping Conduction in Graphene
The variable range hopping theory, as formulated for exponentially localized
impurity states, does not necessarily apply in the case of graphene with
covalently attached impurities. We analyze the localization of impurity states
in graphene using the nearest-neighbor, tight-binding model of an
adatom-graphene system with Green's function perturbation methods. The
amplitude of the impurity state wave function is determined to decay as a power
law with exponents depending on sublattice, direction, and the impurity
species. We revisit the variable range hopping theory in view of this result
and find that the conductivity depends as a power law of the temperature with
an exponent related to the localization of the wave function. We show that this
temperature dependence is in agreement with available experimental results
Sparse production networks
Firm-to-firm connections in domestic and international production networks play a fundamental role in economic outcomes. Firm heterogeneity and the sparse nature of firm-to-firm connections implicitly discipline network structure. We find that a large group of well-established statistical relationships are not useful in improving our understanding of production networks. We propose an "elementary" model for production networks based on random matching and firm heterogeneity and characterize the families of statistics and data generating processes that may raise underidentification concerns in more complex models. The elementary model is a useful benchmark in developing "instructive" statistics and informing model construction and selection
Fractional quantum Hall effect at : Ground states, non-Abelian quasiholes, and edge modes in a microscopic model
We present a comprehensive numerical study of a microscopic model of the
fractional quantum Hall system at filling fraction , based on the
disc geometry. Our model includes Coulomb interaction and a semi-realistic
confining potential. We also mix in some three-body interaction in some cases
to help elucidate the physics. We obtain a phase diagram, discuss the
conditions under which the ground state can be described by the Moore-Read
state, and study its competition with neighboring stripe phases. We also study
quasihole excitations and edge excitations in the Moore-Read--like state. From
the evolution of edge spectrum, we obtain the velocities of the charge and
neutral edge modes, which turn out to be very different. This separation of
velocities is a source of decoherence for a non-Abelian quasihole/quasiparticle
(with charge ) when propagating at the edge; using numbers obtained
from a specific set of parameters we estimate the decoherence length to be
around four microns. This sets an upper bound for the separation of the two
point contacts in a double point contact interferometer, designed to detect the
non-Abelian nature of such quasiparticles. We also find a state that is a
potential candidate for the recently proposed anti-Pfaffian state. We find the
speculated anti-Pfaffian state is favored in weak confinement (smooth edge)
while the Moore-Read Pfaffian state is favored in strong confinement (sharp
edge).Comment: 15 pages, 9 figures; Estimate of e/4 quasiparticle/hole coherence
length when propagating along the edge modified in response to a recent
revision of Ref. 25, and minor changes elsewher
Topological structure of the many vortices solution in Jackiw-Pi model
We construct an M-solitons solutions in Jackiw-Pi model depends on 5M
parameters(two positions, one scale, one phase per solition and one charge of
each solution). By using \phi -mapping method, we discuss the topological
structure of the self-duality solution in Jackiw-Pi model in terms of gauge
potential decomposition. We set up relationship between Chern-Simons vortices
solution and topological number which is determined by Hopf indices and and
Brouwer degrees. We also give the quantization of flux in this case.Comment: 14 pages, 4 figure
Computational study of structural and elastic properties of random AlGaInN alloys
In this work we present a detailed computational study of structural and
elastic properties of cubic AlGaInN alloys in the framework of Keating valence
force field model, for which we perform accurate parametrization based on state
of the art DFT calculations. When analyzing structural properties, we focus on
concentration dependence of lattice constant, as well as on the distribution of
the nearest and the next nearest neighbour distances. Where possible, we
compare our results with experiment and calculations performed within other
computational schemes. We also present a detailed study of elastic constants
for AlGaInN alloy over the whole concentration range. Moreover, we include
there accurate quadratic parametrization for the dependence of the alloy
elastic constants on the composition. Finally, we examine the sensitivity of
obtained results to computational procedures commonly employed in the Keating
model for studies of alloys
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