3,917 research outputs found
Effect of dipole polarizability on positron binding by strongly polar molecules
A model for positron binding to polar molecules is considered by combining
the dipole potential outside the molecule with a strongly repulsive core of a
given radius. Using existing experimental data on binding energies leads to
unphysically small core radii for all of the molecules studied. This suggests
that electron-positron correlations neglected in the simple model play a large
role in determining the binding energy. We account for these by including
polarization potential via perturbation theory and non-perturbatively. The
perturbative model makes reliable predictions of binding energies for a range
of polar organic molecules and hydrogen cyanide. The model also agrees with the
linear dependence of the binding energies on the polarizability inferred from
the experimental data [Danielson et al 2009 J. Phys. B: At. Mol. Opt. Phys. 42
235203]. The effective core radii, however, remain unphysically small for most
molecules. Treating molecular polarization non-perturbatively leads to
physically meaningful core radii for all of the molecules studied and enables
even more accurate predictions of binding energies to be made for nearly all of
the molecules considered.Comment: 26 pages, 18 figure
Calculations of positron binding and annihilation in polyatomic molecules
A model-potential approach to calculating positron-molecule binding energies
and annihilation rates is developed. Unlike existing ab initio calculations,
which have mostly been applied to strongly polar molecules, the present
methodology can be applied to both strongly polar and weakly polar or nonpolar
systems. The electrostatic potential of the molecule is calculated at the
Hartree-Fock level, and a model potential that describes short-range
correlations and long-range polarization of the electron cloud by the positron
is then added. The Schrodinger equation for a positron moving in this effective
potential is solved to obtain the binding energy. The model potential contains
a single adjustable parameter for each type of atom present in the molecule.
The wave function of the positron bound state may be used to compute the rate
of electron-positron annihilation from the bound state. As a first application,
we investigate positron binding and annihilation for the hydrogen cyanide (HCN)
molecule. Results for the binding energy are found to be in accord with
existing calculations, and we predict the rate of annihilation from the bound
state to be --.Comment: 13 pages, 6 figures, accepted by J. Chem. Phy
Many-body theory for positronium-atom interactions
A many-body-theory approach has been developed to study positronium-atom
interactions. As first applications, we calculate the elastic scattering and
momentum-transfer cross sections and the pickoff annihilation rate
for Ps collisions with He and Ne. The cross section for He is
in agreement with previous coupled-state calculations, and the
momentum-transfer cross section for Ne agrees with available experimental data.
is found to be 0.13 and 0.26 for He and Ne, respectively, in
excellent agreement with the measured values.Comment: Accepted by Phys. Rev. Lett. (V2 contains update to text and Figs. 3
and 5. V3 contains further discussion on the calculation of pickoff
annihilation rates.
Systems analysis of host-parasite interactions.
Parasitic diseases caused by protozoan pathogens lead to hundreds of thousands of deaths per year in addition to substantial suffering and socioeconomic decline for millions of people worldwide. The lack of effective vaccines coupled with the widespread emergence of drug-resistant parasites necessitates that the research community take an active role in understanding host-parasite infection biology in order to develop improved therapeutics. Recent advances in next-generation sequencing and the rapid development of publicly accessible genomic databases for many human pathogens have facilitated the application of systems biology to the study of host-parasite interactions. Over the past decade, these technologies have led to the discovery of many important biological processes governing parasitic disease. The integration and interpretation of high-throughput -omic data will undoubtedly generate extraordinary insight into host-parasite interaction networks essential to navigate the intricacies of these complex systems. As systems analysis continues to build the foundation for our understanding of host-parasite biology, this will provide the framework necessary to drive drug discovery research forward and accelerate the development of new antiparasitic therapies
Positronium collisions with rare-gas atoms
We calculate elastic scattering of positronium (Ps) by the Xe atom using the
recently developed pseudopotential method [I. I. Fabrikant and G. F. Gribakin,
Phys. Rev. A 90, 052717 (2014)] and review general features of Ps scattering
from heavier rare-gas atoms: Ar, Kr, and Xe. The total scattering cross section
is dominated by two contributions: elastic scattering and Ps ionization
(breakup). To calculate the Ps ionization cross sections we use the
binary-encounter method for Ps collisions with an atomic target. Our results
for the ionization cross section agree well with previous calculations carried
out in the impulse approximation. Our total Ps-Xe cross section, when plotted
as a function of the projectile velocity, exhibits similarity with the
electron-Xe cross section for the collision velocities higher than 0.8 a.u.,
and agrees very well with the measurements at Ps velocities above 0.5 a.u.Comment: 7 pages, 7 figures, submitted to J. Phys.
Elevated interferon-stimulated gene transcription in peripheral blood mononuclear cells occurs in patients infected with genotype 1 but not genotype 3 hepatitis C virus
Hepatitis C virus (HCV) can be classified into seven distinct genotypes that are associated with differing pathologies and respond differently to antiviral therapy. In the UK, genotype 1 and 3 are present in approximately equal proportions. Chronic infection with HCV genotype 3 is associated with increased liver steatosis and reduced peripheral total cholesterol levels, which potentially influences peripheral immune responses. To understand these differences, we investigated host gene transcription in peripheral blood mononuclear cells by microarray and quantitative PCR in patients with genotype 1 (n = 22) or genotype 3 infection (n = 22) and matched healthy controls (n = 15). Enrichment of genes involved in immune response and inflammatory pathways were present in patients infected with HCV genotype 1; however, no differences in genes involved in lipid or cholesterol metabolism were detected. This genotype-specific induction of genes is unrelated to IL28B genotype or previous treatment failure. Our data support the hypothesis that genotype 1 infection drives a skewed Type I interferon response and provides a foundation for future investigations into the host–pathogen interactions that underlie the genotype-specific clinical outcomes of chronic HCV infection
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