1,304 research outputs found
Human leucocyte antigen profile in patients with aids and cytomegalovirus retinitis with and without macular involvement
Introduction: Cytomegalovirus retinitis is one of AIDS ocular manifestations. The objective of the present study was to determine possible associations between class I and II HLA antigens and alleles in patients with AIDS and cytomegalovirus retinitis (CMV-R) with macular involvement.Method: The study population consisted of 22 patients with AIDS and CMV-R with macular involvement (Group I), 19 patients with AIDS and CMV-R without macular involvement (Group II), and 202 individuals with negative serology for human immunodeficiency virus (Group III - control). Class I HLA antigens were typed by classical serology. Class II alleles were identified using sequence-specific oligonucleotide primers hybridized with amplified DNA. Results: HLA-DRB1*14 and HLA-DRB1*10 specificities were more frequent among patients with macular involvement, possibly indicating greater susceptibility to this condition. In contrast, the HLA-B35 antigen may be associated with protection against macular involvement since it was significantly more frequent among patients without this involvement.Conclusions: The HLA-DRB1*14 and HLA-DRB1*10 alleles may favor the development of CMV-R with macular involvement, whereas the HLA-B35 subtype may be associated with protection against macular involvement
Thermodynamics of the S=1 spin ladder as a composite S=2 chain model
A special class of S=1 spin ladder hamiltonians, with second- neighbor
exchange interactions and with anisotropies in the -direction, can be mapped
onto one-dimensional composite S=2 (tetrahedral S=1) models. We calculate the
high temperature expansion of the Helmoltz free energy for the latter class of
models, and show that their magnetization behaves closely to that of standard
XXZ models with a suitable effective spin , such that
, where refers to the
components of spin in the composite model. It is also shown that the specific
heat per site of the composite model, on the other hand, can be very different
from that of the effective spin model, depending on the parameters of the
hamiltonian.Comment: 17 pages, 4 figures. Submitted for publicatio
Structural and optical studies of FeSb2 under high pressure
Nanostructured orthorhombic FeSb2 and an amorphous phase were formed by
mechanical alloying starting from a mixture of high purity elemental Fe and Sb
powders. The effects of high pressures on structural and optical properties
were studied using X-ray diffraction (XRD) and Raman spectroscopy (RS). XRD
patterns showed the presence of the orthorhombic FeSb2 phase up to the maximum
pressure applied (28.2 GPa). The XRD patterns showed also an increase in the
amount of the amorphous phase with increasing pressure up to 23.3 GPa. At 14.3
GPa, together with the former phases, a new phase was observed and indexed to a
tetragonal FeSb2 phase, but its volume fraction is small at least up to 23.3
GPa. For the orthorhombic FeSb2 phase, the pressure dependence of the volume
fitted to a Birch-Murnaghan equation of state gave a bulk modulus = 74.2 +- 3.0
GPa and its pressure derivative = 7.5 +- 0.6. RS measurements were performed
from atmospheric pressure up to 45.2 GPa. For the orthorhombic FeSb2 phase, the
Raman active mode was observed up to the maximum pressure applied, while the
mode disappeared at 16.6 GPa. For pressures higher than 21 GPa, the Raman
active mode of a tetragonal FeSb2 phase was observed, confirming ab initio
calculations reported in the literature.Comment: 31 pages, 11 figures and 2 tables. Already submitted for publicatio
Sporopollenin as an efficient green support for covalent immobilization of a lipase
Sporopollenin exine capsules (SECs), derived from the spores of Lycopodium clavatum, have been functionalised with 1,n-diamines and the resulting aminoalkyl microcapsules used to immobilize Candida antarctica lipase B (Cal B) via a glutaradehyde-based diimine covalent linker. The supported enzyme efficiently catalyzes the esterification of oleic acid with ethanol. Initial rates using the SEC-CalBs were comparable to the commercial enzyme Novozym 435, but displayed up to 20-fold higher specific activity. The supported enzymes could also be recycled and after four cycles displayed only a modest decrease in conversions. In a kinetic resolution the SEC-CalBs efficiently acetylated rac-1-phenylethanol, with conversions up to 37% after 5 hours and product enantiomeric excesses of >99%. Related to this, the dynamic resolution of rac-1-phenylethylamine, in the presence of Pd-BaSO₄ and ammonium formate, led to the acetylated amine with a 94% conversion and >99% ee
Yet on statistical properties of traded volume: correlation and mutual information at different value magnitudes
In this article we analyse linear correlation and non-linear dependence of
traded volume, , of the 30 constituents of Dow Jones Industrial Average at
different value scales. Specifically, we have raised to some real value
or , which introduces a bias for small ()
or large () values. Our results show that small values of
are regularly \emph{anti-correlated} with values at other scales of traded
volume. This is consistent with the high liquidity of the 30 equities analysed
and the asymmetric form of the multi-fractal spectrum for traded volume which
has supported the dynamical scenario presented by us.Comment: 6 pages, 2 figure
The high temperature expansion of the classical chain
We present the -expansion of the Helmholtz free energy of the
classical model, with a single-ion anisotropy term and in the presence of
an external magnetic field, up to order . We compare our results to
the numerical solution of Joyce's [Phys. Rev. Lett. 19, 581 (1967)] expression
for the thermodynamics of the classical model, with neither single-ion
anisotropy term nor external magnetic field. This comparison shows that the
derived analytical expansion is valid for intermediate temperatures such as
. We show that the specific heat and magnetic
susceptibility of the spin-2 antiferromagnetic chain can be approximated by
their respective classical results, up to , within an error
of 2.5%. In the absence of an external magnetic field, the ferromagnetic and
antiferromagnetic chains have the same classical Helmholtz free energy. We show
how this two types of media react to the presence of an external magnetic
field
A set of exactly solvable Ising models with half-odd-integer spin
We present a set of exactly solvable Ising models, with half-odd-integer
spin-S on a square-type lattice including a quartic interaction term in the
Hamiltonian. The particular properties of the mixed lattice, associated with
mixed half-odd-integer spin-(S,1/2) and only nearest-neighbour interaction,
allow us to map this system either onto a purely spin-1/2 lattice or onto a
purely spin-S lattice. By imposing the condition that the mixed
half-odd-integer spin-(S,1/2) lattice must have an exact solution, we found a
set of exact solutions that satisfy the {\it free fermion} condition of the
eight vertex model. The number of solutions for a general half-odd-integer
spin-S is given by . Therefore we conclude that this transformation is
equivalent to a simple spin transformation which is independent of the
coordination number
Generalized Transformation for Decorated Spin Models
The paper discusses the transformation of decorated Ising models into an
effective \textit{undecorated} spin models, using the most general Hamiltonian
for interacting Ising models including a long range and high order
interactions. The inverse of a Vandermonde matrix with equidistant nodes
is used to obtain an analytical expression of the transformation. This
kind of transformation is very useful to obtain the partition function of
decorated systems. The method presented by Fisher is also extended, in order to
obtain the correlation functions of the decorated Ising models transforming
into an effective undecorated Ising models. We apply this transformation to a
particular mixed spin-(1/2,1) and (1/2,2) square lattice with only nearest site
interaction. This model could be transformed into an effective uniform spin-
square lattice with nearest and next-nearest interaction, furthermore the
effective Hamiltonian also include combinations of three-body and four-body
interactions, particularly we considered spin 1 and 2.Comment: 16 pages, 4 figure
A Comment on the beta-expansion of s=1/2 and s=1 Ising Models
The purpose of the present work is to apply the method recently developed in
reference [chain_m] to the spin-1 Ising chain, showing how to obtain analytical
-expansions of thermodynamical functions through this formalism. In this
method, we do not solve any transfer matrix-like equations. A comparison
between the -expansions of the specific heat and the magnetic
susceptibility for the and one-dimensional Ising models is
presented. We show that those expansions have poorer convergence when the
auxiliary function of the model has singularities.Comment: 12 pages, 8 figure
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