2,196 research outputs found
Directed abelian algebras and their applications to stochastic models
To each directed acyclic graph (this includes some D-dimensional lattices)
one can associate some abelian algebras that we call directed abelian algebras
(DAA). On each site of the graph one attaches a generator of the algebra. These
algebras depend on several parameters and are semisimple. Using any DAA one can
define a family of Hamiltonians which give the continuous time evolution of a
stochastic process. The calculation of the spectra and ground state
wavefunctions (stationary states probability distributions) is an easy
algebraic exercise. If one considers D-dimensional lattices and choose
Hamiltonians linear in the generators, in the finite-size scaling the
Hamiltonian spectrum is gapless with a critical dynamic exponent . One
possible application of the DAA is to sandpile models. In the paper we present
this application considering one and two dimensional lattices. In the one
dimensional case, when the DAA conserves the number of particles, the
avalanches belong to the random walker universality class (critical exponent
). We study the local densityof particles inside large
avalanches showing a depletion of particles at the source of the avalanche and
an enrichment at its end. In two dimensions we did extensive Monte-Carlo
simulations and found .Comment: 14 pages, 9 figure
Complete spectrum of the infinite- Hubbard ring using group theory
We present a full analytical solution of the multiconfigurational
strongly-correlated mixed-valence problem corresponding to the -Hubbard ring
filled with electrons, and infinite on-site repulsion. While the
eigenvalues and the eigenstates of the model are known already, analytical
determination of their degeneracy is presented here for the first time. The
full solution, including degeneracy count, is achieved for each spin
configuration by mapping the Hubbard model into a set of Huckel-annulene
problems for rings of variable size. The number and size of these effective
Huckel annulenes, both crucial to obtain Hubbard states and their degeneracy,
are determined by solving a well-known combinatorial enumeration problem, the
necklace problem for beads and two colors, within each subgroup of the
permutation group. Symmetry-adapted solution of the necklace
enumeration problem is finally achieved by means of the subduction of coset
representation technique [S. Fujita, Theor. Chim. Acta 76, 247 (1989)], which
provides a general and elegant strategy to solve the one-hole infinite-
Hubbard problem, including degeneracy count, for any ring size. The proposed
group theoretical strategy to solve the infinite- Hubbard problem for
electrons, is easily generalized to the case of arbitrary electron count ,
by analyzing the permutation group and all its subgroups.Comment: 31 pages, 4 figures. Submitte
Thoracic involvement in generalised lymphatic anomaly (or lymphangiomatosis)
Generalised lymphatic anomaly (GLA), also known as lymphangiomatosis, is a rare disease caused by congenital abnormalities of lymphatic development. It usually presents in childhood but can also be diagnosed in adults. GLA encompasses a wide spectrum of clinical manifestations ranging from singleorgan involvement to generalised disease. Given the rarity of the disease, most of the information regarding it comes from case reports. To date, no clinical trials concerning treatment are available. This review focuses on thoracic GLA and summarises possible diagnostic and therapeutic approaches
Closed timelike curves in superfluid He
It is shown that the curved spacetime induced in a thin film of superfluid
He-A by the presence of symmetric vortices with the unbroken symmetry
phase, admits the existence of closed timelike curves through which only
superfluid clusters formed by anti-He atoms can travel and violate
causality.Comment: 7 pages, LaTex, to appear in Phys. Lett.
Percolation on the average and spontaneous magnetization for q-states Potts model on graph
We prove that the q-states Potts model on graph is spontaneously magnetized
at finite temperature if and only if the graph presents percolation on the
average. Percolation on the average is a combinatorial problem defined by
averaging over all the sites of the graph the probability of belonging to a
cluster of a given size. In the paper we obtain an inequality between this
average probability and the average magnetization, which is a typical extensive
function describing the thermodynamic behaviour of the model
B polarization of the CMB from Faraday rotation
We study the effect of Faraday rotation due to a homogeneous magnetic field
on the polarization of the cosmic microwave background (CMB). Scalar
fluctuations give rise only to parity-even E-type polarization of the CMB.
However in the presence of a magnetic field, a non-vanishing parity-odd B-type
polarization component is produced through Faraday rotation. We derive the
exact solution for the E and B modes generated by scalar perturbations
including the Faraday rotation effect of a uniform magnetic field, and evaluate
their cross-correlations with temperature anisotropies. We compute the angular
autocorrelation function of the B-modes in the limit that the Faraday rotation
is small. We find that primordial magnetic fields of present strength around
G rotate E-modes into B-modes with amplitude comparable to those
due to the weak gravitational lensing effect at frequencies around
GHz. The strength of B-modes produced by Faraday rotation scales as
. We evaluate also the depolarizing effect of Faraday rotation upon
the cross correlation between temperature anisotropy and E-type polarization.Comment: 11 pages, 4 figures. Minor changes to match the published versio
Weak-Lensing by Large-Scale Structure and the Polarization Properties of Distant Radio-Sources
We estimate the effects of weak lensing by large-scale density
inhomogeneities and long-wavelength gravitational waves upon the polarization
properties of electromagnetic radiation as it propagates from cosmologically
distant sources. Scalar (density) fluctuations do not rotate neither the plane
of polarization of the electromagnetic radiation nor the source image. They
produce, however, an appreciable shear, which distorts the image shape, leading
to an apparent rotation of the image orientation relative to its plane of
polarization. In sources with large ellipticity the apparent rotation is rather
small, of the order (in radians) of the dimensionless shear. The effect is
larger at smaller source eccentricity. A shear of 1% can induce apparent
rotations of around 5 degrees in radio sources with the smallest eccentricity
among those with a significant degree of integrated linear polarization. We
discuss the possibility that weak lensing by shear with rms value around or
below 5% may be the cause for the dispersion in the direction of integrated
linear polarization of cosmologically distant radio sources away from the
perpendicular to their major axis, as expected from models for their magnetic
fields. A rms shear larger than 5% would be incompatible with the observed
correlation between polarization properties and source orientation in distant
radio galaxies and quasars. Gravity waves do rotate both the plane of
polarization as well as the source image. Their weak lensing effects, however,
are negligible.Comment: 23 pages, 2 eps figures, Aastex 4.0 macros. Final version, as
accepted by ApJ. Additional references and some changes in the introduction
and conclusion
A Search for the Fourth SM Family Fermions and E_6 Quarks at Colliders
The potential of colliders to investigate the fourth SM
family fermions predicted by flavour democracy has been analyzed. It is shown
that muon colliders are advantageous for both pair production of fourth family
fermions and resonance production of fourth family quarkonia. Also isosinglet
quarks production at colliders has been investigated.Comment: 9 pages, 5 table
Tax Administrations’ Capacity in Preventing Tax Evasion and Tax Avoidance
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