29,674 research outputs found
Towards Noncommutative Linking Numbers Via the Seiberg-Witten Map
In the present work some geometric and topological implications of
noncommutative Wilson loops are explored via the Seiberg-Witten map. In the
abelian Chern-Simons theory on a three dimensional manifold, it is shown that
the effect of noncommutativity is the appearance of new knots at the
-th order of the Seiberg-Witten expansion. These knots are trivial homology
cycles which are Poincar\'e dual to the high-order Seiberg-Witten potentials.
Moreover the linking number of a standard 1-cycle with the Poincar\'e dual of
the gauge field is shown to be written as an expansion of the linking number of
this 1-cycle with the Poincar\'e dual of the Seiberg-Witten gauge fields. In
the process we explicitly compute the noncommutative 'Jones-Witten' invariants
up to first order in the noncommutative parameter. Finally in order to exhibit
a physical example, we apply these ideas explicitly to the Aharonov-Bohm
effect. It is explicitly displayed at first order in the noncommutative
parameter, we also show the relation to the noncommutative Landau levels.Comment: 19 pages, 1 figur
Luttinger liquid superlattices: realization of gapless insulating phases
We investigate Luttinger Liquid superlattices, a periodic structure composed
of two kinds of one-dimensional systems of interacting electrons. We calculate
several properties of the low-energy sector: the effective charge and spin
velocities, the compressibility, various correlation functions, the Landauer
conductance and the Drude weight. The low-energy properties are subsumed into
effective parameters, much like homogeneous one-dimensional systems. A generic
result is the weighted average nature of these parameters, in proportion to the
spatial extent of the underlying subunits, pointing to the possibility of
``engineered'' structures. As a specific realization, we consider a
one-dimensional Hubbard superlattice, which consists of a periodic arrangement
of two long Hubbard chains with different coupling constants and different
hopping amplitudes. This system exhibits a rich phase diagram with several
phases, both metallic and insulating. We have found that gapless insulating
phases are present over a wide range of parameters.Comment: 16 pages, 15 figures, RevTeX
Jeans' gravitational instability and nonextensive kinetic theory
The concept of Jeans gravitational instability is rediscussed in the
framework of nonextensive statistics and its associated kinetic theory. A
simple analytical formula generalizing the Jeans criterion is derived by
assuming that the unperturbed self- gravitating collisionless gas is
kinetically described by the -parameterized class of power law velocity
distributions. It is found that the critical values of wavelength and mass
depend explicitly on the nonextensive -parameter. The standard Jeans
wavelength derived for a Maxwellian distribution is recovered in the limiting
case =1. For power-law distributions with cutoff, the instability condition
is weakened with the system becoming unstable even for wavelengths of the
disturbance smaller than the standard Jeans length .Comment: 5 pages, including 3 figures. Accepted for publication in A&
Genetic diversity of Lusitano horse in Brazil using pedigree information
This study aimed to evaluate population parameters and to describe the genetic diversity of the Lusitano
breed in Brazil using pedigree data. Two populations were evaluated: total population (TP) containing
18,922 animals, and reference population (RP) composed of a part of TP containing 8,329 animals, representing
the last generation. The generation interval (10.1 ± 5.1 years) was in the range for horse populations.
Pedigree completeness in RP shows almost 100% filling in the three most recent generations,
indicating improvement in the pedigree data and accuracy of the results, and the inbreeding coefficient
(4.46%) and average relatedness (5.97%) for RP, indicating control on the part of breeders. The effective
population size was 89 (TP) and 90 (RP). The effective number of founders (fe) were 33 and 29, effective
number of ancestors (fa) were 30 and 26, and effective number of founder genomes (fg) were 19 and 15 for
TP and RP, respectively, indicating a reduction of genetic variability in the last generations. The total
number of ancestors that explains 100% of the genetic diversity in the Lusitano breed in Brazil was 427 (TP)
and 341 (RP). The reproductive parameters, probabilities of gene origin showing loss of variability in the
last generations, and the genetic contributions of ancestors suggest the need to monitor genetic diversity
over time in breeding programs to allow control of the next generations and to increase their variability.info:eu-repo/semantics/publishedVersio
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