773 research outputs found
A semi-empirical method for prediction of antigenic determinants on protein antigens
AbstractAnalysis of data from experimentally determined antigenic sites on proteins has revealed that the hydrophobic residues Cys, Leu and Val, if they occur on the surface of a protein, are more likely to be a part of antigenic sites. A semi-empirical method which makes use of physicochemical properties of amino acid residues and their frequencies of occurrence in experimentally known segmental epitopes was developed to predict antigenic determinants on proteins. Application of this method to a large number of proteins has shown that our method can predict antigenic determinants with about 75% accuracy which is better than most of the known methods. This method is based on a single parameter and thus very simple to use
Characteristic distributions of finite-time Lyapunov exponents
We study the probability densities of finite-time or \local Lyapunov
exponents (LLEs) in low-dimensional chaotic systems. While the multifractal
formalism describes how these densities behave in the asymptotic or long-time
limit, there are significant finite-size corrections which are coordinate
dependent. Depending on the nature of the dynamical state, the distribution of
local Lyapunov exponents has a characteristic shape. For intermittent dynamics,
and at crises, dynamical correlations lead to distributions with stretched
exponential tails, while for fully-developed chaos the probability density has
a cusp. Exact results are presented for the logistic map, . At
intermittency the density is markedly asymmetric, while for `typical' chaos, it
is known that the central limit theorem obtains and a Gaussian density results.
Local analysis provides information on the variation of predictability on
dynamical attractors. These densities, which are used to characterize the {\sl
nonuniform} spatial organization on chaotic attractors are robust to noise and
can therefore be measured from experimental data.Comment: To be appear in Phys. Rev
A thermodynamic framework to develop rate-type models for fluids without instantaneous elasticity
In this paper, we apply the thermodynamic framework recently put into place
by Rajagopal and co-workers, to develop rate-type models for viscoelastic
fluids which do not possess instantaneous elasticity. To illustrate the
capabilities of such models we make a specific choice for the specific
Helmholtz potential and the rate of dissipation and consider the creep and
stress relaxation response associated with the model. Given specific forms for
the Helmholtz potential and the rate of dissipation, the rate of dissipation is
maximized with the constraint that the difference between the stress power and
the rate of change of Helmholtz potential is equal to the rate of dissipation
and any other constraint that may be applicable such as incompressibility. We
show that the model that is developed exhibits fluid-like characteristics and
is incapable of instantaneous elastic response. It also includes Maxwell-like
and Kelvin-Voigt-like viscoelastic materials (when certain material moduli take
special values).Comment: 18 pages, 5 figure
Interruption of torus doubling bifurcation and genesis of strange nonchaotic attractors in a quasiperiodically forced map : Mechanisms and their characterizations
A simple quasiperiodically forced one-dimensional cubic map is shown to
exhibit very many types of routes to chaos via strange nonchaotic attractors
(SNAs) with reference to a two-parameter space. The routes include
transitions to chaos via SNAs from both one frequency torus and period doubled
torus. In the former case, we identify the fractalization and type I
intermittency routes. In the latter case, we point out that atleast four
distinct routes through which the truncation of torus doubling bifurcation and
the birth of SNAs take place in this model. In particular, the formation of
SNAs through Heagy-Hammel, fractalization and type--III intermittent mechanisms
are described. In addition, it has been found that in this system there are
some regions in the parameter space where a novel dynamics involving a sudden
expansion of the attractor which tames the growth of period-doubling
bifurcation takes place, giving birth to SNA. The SNAs created through
different mechanisms are characterized by the behaviour of the Lyapunov
exponents and their variance, by the estimation of phase sensitivity exponent
as well as through the distribution of finite-time Lyapunov exponents.Comment: 27 pages, RevTeX 4, 16 EPS figures. Phys. Rev. E (2001) to appea
Multicloud solutions with massless and massive monopoles
Certain spontaneously broken gauge theories contain massless magnetic
monopoles. These are realized classically as clouds of non-Abelian fields
surrounding one or more massive monopoles. In order to gain a better
understanding of these clouds, we study BPS solutions with four massive and six
massless monopoles in an SU(6) gauge theory. We develop an algebraic procedure,
based on the Nahm construction, that relates these solutions to previously
known examples. Explicit implementation of this procedure for a number of
limiting cases reveals that the six massless monopoles condense into four
distinct clouds, of two different types. By analyzing these limiting solutions,
we clarify the correspondence between clouds and massless monopoles, and infer
a set of rules that describe the conditions under which a finite size cloud can
be formed. Finally, we identify the parameters entering the general solution
and describe their physical significance.Comment: 58 pages, 5 figure
Non-Abelian Vortices in Supersymmetric Gauge Field Theory via Direct Methods
Vortices in supersymmetric gauge field theory are important constructs in a
basic conceptual phenomenon commonly referred to as the dual Meissner effect
which is responsible for color confinement. Based on a direct minimization
approach, we present a series of sharp existence and uniqueness theorems for
the solutions of some non-Abelian vortex equations governing color-charged
multiply distributed flux tubes, which provide an essential mechanism for
linear confinement. Over a doubly periodic domain, existence results are
obtained under explicitly stated necessary and sufficient conditions that
relate the size of the domain, the vortex numbers, and the underlying physical
coupling parameters of the models. Over the full plane, existence results are
valid for arbitrary vortex numbers and coupling parameters. In all cases,
solutions are unique.Comment: 38 pages, late
Prevalence and risk of hepatitis e virus infection in the HIV population of Nepal
Background: Infection with the hepatitis E virus (HEV) can cause acute hepatitis in endemic areas in immune-competent hosts, as well as chronic infection in immune-compromised subjects in non-endemic areas. Most studies assessing HEV infection in HIV-infected populations have been performed in developed countries that are usually affected by HEV genotype 3. The objective of this study is to measure the prevalence and risk of acquiring HEV among HIV-infected individuals in Nepal. Methods: We prospectively evaluated 459 Human Immunodeficiency Virus (HIV)-positive individuals from Nepal, an endemic country for HEV, for seroprevalence of HEV and assessed risk factors associated with HEV infection. All individuals were on antiretroviral therapy and healthy blood donors were used as controls. Results: We found a high prevalence of HEV IgG (39.4%) and HEV IgM (15.3%) in HIV-positive subjects when compared to healthy HIV-negative controls: 9.5% and 4.4%, respectively (OR: 6.17, 95% CI 4.42-8.61, p < 0.001 and OR: 3.7, 95% CI 2.35-5.92, p < 0.001, respectively). Individuals residing in the Kathmandu area showed a significantly higher HEV IgG seroprevalance compared to individuals residing outside of Kathmandu (76.8% vs 11.1%, OR: 30.33, 95% CI 18.02-51.04, p = 0.001). Mean CD4 counts, HIV viral load and presence of hepatitis B surface antigen correlated with higher HEV IgM rate, while presence of hepatitis C antibody correlated with higher rate of HEV IgG in serum. Overall, individuals with HEV IgM positivity had higher levels of alanine aminotransferase (ALT) than IgM negative subjects, suggesting active acute infection. However, no specific symptoms for hepatitis were identified. Conclusions: HIV-positive subjects living in Kathmandu are at higher risk of acquiring HEV infection as compared to the general population and to HIV-positive subjects living outside Kathmandu
Multiorder coherent Raman scattering of a quantum probe field
We study the multiorder coherent Raman scattering of a quantum probe field in
a far-off-resonance medium with a prepared coherence. Under the conditions of
negligible dispersion and limited bandwidth, we derive a Bessel-function
solution for the sideband field operators. We analytically and numerically
calculate various quantum statistical characteristics of the sideband fields.
We show that the multiorder coherent Raman process can replicate the
statistical properties of a single-mode quantum probe field into a broad comb
of generated Raman sidebands. We also study the mixing and modulation of photon
statistical properties in the case of two-mode input. We show that the prepared
Raman coherence and the medium length can be used as control parameters to
switch a sideband field from one type of photon statistics to another type, or
from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.
- …