649 research outputs found
Stability of 3D Cubic Fixed Point in Two-Coupling-Constant \phi^4-Theory
For an anisotropic euclidean -theory with two interactions [u
(\sum_{i=1^M {\phi}_i^2)^2+v \sum_{i=1}^M \phi_i^4] the -functions are
calculated from five-loop perturbation expansions in
dimensions, using the knowledge of the large-order behavior and Borel
transformations. For , an infrared stable cubic fixed point for
is found, implying that the critical exponents in the magnetic phase
transition of real crystals are of the cubic universality class. There were
previous indications of the stability based either on lower-loop expansions or
on less reliable Pad\'{e approximations, but only the evidence presented in
this work seems to be sufficently convincing to draw this conclusion.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Paper also at
http://www.physik.fu-berlin.de/~kleinert/kleiner_re250/preprint.htm
New approach to Borel summation of divergent series and critical exponent estimates for an N-vector cubic model in three dimensions from five-loop \epsilon expansions
A new approach to summation of divergent field-theoretical series is
suggested. It is based on the Borel transformation combined with a conformal
mapping and does not imply the exact asymptotic parameters to be known. The
method is tested on functions expanded in their asymptotic power series. It is
applied to estimating the critical exponent values for an N-vector field model,
describing magnetic and structural phase transitions in cubic and tetragonal
crystals, from five-loop \epsilon expansions.Comment: 9 pages, LaTeX, 3 PostScript figure
Actualités sur les co-infections VIH–VHC
Objectives
To evaluate the incidence of HIV–HCV co-infections and analyse the outcome in co-infected patients.
Epidemiology. Effects of antivirals
The prevalence of the co-infection by the HCV thus varies from 10 to 14% on subjects who have sexual behaviors at risk at 80 or 90% on users of drug IV. Numerous studies showed that the infection by the HIV made worse the natural history of the infection by the HCV [J Acquir Immune Defic Syndr 6 1993 602–610; J Hepatol 28 1998 945–950]. On the other hand, the studies which endeavoured to appreciate the effect of the antiretroviral therapeutics on the natural history of the chronic hepatitis C, on the co-infected patients, are more discussed. In cohorts of big size, it was demonstrated that the hepatic mortality increased with the exposure to antiretrovirals. However, the duration of the antiretroviral treatment also reports the more important survival of the patients, which distorts credibly the figures. The effect of the infection by the HCV on the progress of the disease with HIV is more discussed. The patients infected by the HIV, in any case, have to benefit from the research for a co-infection by the viruses of hepatitis B and C (HBV and HCV). This screening must be renewed every year, in particular on the drug addicts patients or presenting behaviors at risk.
Viral replication
The research of a viral replication, must be implemented for any confirmed positive HCV serology. The research of the HCV RNA needs ultrasensitive techniques of molecular biology which allow a qualitative detection andor a quantification of the viral genome (viral load). The techniques of last generation of real-time PCR combine both approaches (detection and quantification). The viral load HCV is not correlated to the degree of hepatic disease and does not predict the severity of the hepatic disease, contrary to the correlation demonstrated in the infection by the HIV. On the other hand, it can be a predictive factor in the response to the treatment. The pretherapeutic check-up also includes a determination of the viral genotype because a strong involvement in the response to the treatment was clearly demonstrated.
Hepatic fibrosis
The hepatic fibrosis must be estimated on patients having a chronic hepatitis because it conditions the prognosis and the treatment of the hepatitis. The anatomopathological study after hepatic biopsy (DHB) remains the reference method. Recently, the development of non invasive methods of measure of the hepatic fibrosis improved the care of hepatitis C, notably the blood tests (fibrotest BioPredictive Paris, fibrometer BLS Angers) and physical measures as the impulsional elastometry (Fibroscan® Echosens) which substitutes more and more in practice to the draining hepatic biopsy.
Treatment
Numerous studies now validated the treatment associating interferon pegilated and ribavirine as the reference treatment on the co-infected patients HIV/HCV. This treatment involves a high virological response going from 14 to 36% in the patients infected by a genotype 1 and 2 and from 43 to 73% in the patients infected by a genotype 2 or 3. The duration of the treatment is 48 weeks. As well as usual virological factors on the mono-infected patients (genotype, viral load), the rate of CD4 is one of the best predictive factors with a good response. Many hopes go towards the new molecules in development (inhibitors of protease), inhibitors of polymerase), with promising results on the mono-infected patients. However, the toxicity of these molecules is not very well known at the moment in the co-infected patients. It is thus necessary to perform trials in this group of patient, by watching very carefully the toxicity of the therapeutic associations
Large-Order Behavior of Two-coupling Constant -Theory with Cubic Anisotropy
For the anisotropic [u (\sum_{i=1^N {\phi}_i^2)^2+v \sum_{i=1^N
\phi_i^4]-theory with {} we calculate the imaginary parts of the
renormalization-group functions in the form of a series expansion in , i.e.,
around the isotropic case. Dimensional regularization is used to evaluate the
fluctuation determinants for the isotropic instanton near the space dimension
4. The vertex functions in the presence of instantons are renormalized with the
help of a nonperturbative procedure introduced for the simple g{\phi^4-theory
by McKane et al.Comment: LaTeX file with eps files in src. See also
http://www.physik.fu-berlin.de/~kleinert/institution.htm
Surface critical behavior in fixed dimensions : Nonanalyticity of critical surface enhancement and massive field theory approach
The critical behavior of semi-infinite systems in fixed dimensions is
investigated theoretically. The appropriate extension of Parisi's massive field
theory approach is presented.Two-loop calculations and subsequent Pad\'e-Borel
analyses of surface critical exponents of the special and ordinary phase
transitions yield estimates in reasonable agreement with recent Monte Carlo
results. This includes the crossover exponent , for which we obtain
the values and , considerably
lower than the previous -expansion estimates.Comment: Latex with Revtex-Stylefiles, 4 page
Spin Frustration and Orbital Order in Vanadium Spinels
We present the results of our theoretical study on the effects of geometrical
frustration and the interplay between spin and orbital degrees of freedom in
vanadium spinel oxides VO ( = Zn, Mg or Cd). Introducing an
effective spin-orbital-lattice coupled model in the strong correlation limit
and performing Monte Carlo simulation for the model, we propose a reduced spin
Hamiltonian in the orbital ordered phase to capture the stabilization mechanism
of the antiferromagnetic order. Orbital order drastically reduces spin
frustration by introducing spatial anisotropy in the spin exchange
interactions, and the reduced spin model can be regarded as weakly-coupled
one-dimensional antiferromagnetic chains. The critical exponent estimated by
finite-size scaling analysis shows that the magnetic transition belongs to the
three-dimensional Heisenberg universality class. Frustration remaining in the
mean-field level is reduced by thermal fluctuations to stabilize a collinear
ordering.Comment: 4 pages, 4 figures, proceedings submitted to SPQS200
Critical Exponents of the pure and random-field Ising models
We show that current estimates of the critical exponents of the
three-dimensional random-field Ising model are in agreement with the exponents
of the pure Ising system in dimension 3 - theta where theta is the exponent
that governs the hyperscaling violation in the random case.Comment: 9 pages, 4 encapsulated Postscript figures, REVTeX 3.
Critical adsorption at chemically structured substrates
We consider binary liquid mixtures near their critical consolute points and
exposed to geometrically flat but chemically structured substrates. The
chemical contrast between the various substrate structures amounts to opposite
local preferences for the two species of the binary liquid mixtures. Order
parameters profiles are calculated for a chemical step, for a single chemical
stripe, and for a periodic stripe pattern. The order parameter distributions
exhibit frustration across the chemical steps which heals upon approaching the
bulk. The corresponding spatial variation of the order parameter and its
dependence on temperature are governed by universal scaling functions which we
calculate within mean field theory. These scaling functions also determine the
universal behavior of the excess adsorption relative to suitably chosen
reference systems
Quasispecies evolution in NS5A region of hepatitis C virus genotype 1b during interferon or combined interferon-ribavirin therapy
AIM: To evaluate the implication of substitutions in the hepatitis C virus (HCV) non-structural 5A (NS5A) protein in the resistance of HCV during mono-interferon (IFN) or combined IFN-ribavirin (IFN-R) therapy. Although NS5A has been reported to interact with the HCV RNA-dependent RNA polymerase, NS5B, as well as with many cellular proteins, the function of NS5A in the life cycle of HCV remains unclear.
METHODS: HCV quasispecies were studied by cloning and sequencing of sequential isolates from patients infected by HCV genotype 1b. Patients were treated by IFN-alpha2b for 3 mo followed by IFN-alpha2b alone or combined IFN-R therapy for 9 additional months. Patients were categorized into two groups based on their response to the treatments: 7 with sustained virological response (SVR) (quasispecies = 150) and 3 non-responders (NR) to IFN-R (quasispecies = 106).
RESULTS: Prior to treatment, SVR patients displayed a lower complexity of quasispecies than NR patients. Most patients had a decrease in the complexity of quasispecies during therapy. Analysis of amino acids substitutions showed that the degree of the complexity of the interferon sensitivity-determining region (ISDR) and the V3 domain of NS5A protein was able to discriminate the two groups of patients. Moreover, SVR patients displayed more variability in the NS5A region than NR patients.
CONCLUSION: These results suggest that detailed molecular analysis of the NS5A region may be important for understanding its function in IFN response during HCV 1b infection
Scaling Analysis of Chiral Phase Transition for Two Flavors of Kogut-Susskind Quarks
Report is made of a systematic scaling study of the finite-temperature chiral
phase transition of two-flavor QCD with the Kogut-Susskind quark action based
on simulations on (=8, 12 and 16) lattices at the quark mass of
and 0.01. Our finite-size data show that a phase
transition is absent for , and quite likely also at .
The scaling behavior of susceptibilities as a function of is consistent
with a second-order transition at . However, the exponents deviate from
the O(2) or O(4) values theoretically expected.Comment: Talk presented by M. Okawa at the International Workshop on ``
LATTICE QCD ON PARALLEL COMPUTERS", 10-15 March 1997, Center for
Computational Physics, University of Tsukuba. 7 LaTeX pages plus 5 postscript
figures, uses espcrc2.st
- …