11,300 research outputs found
Modeling Lepton-Nucleon Inelastic Scattering from High to Low Momentum Transfer
We present a model for inclusive charged lepton-nucleon and
(anti)neutrino-nucleon cross sections at momentum transfer squared, ,
. We quantify the impact of existing low-Q charged-lepton
deep-inelastic scattering (DIS) data on effects due to high-twist operators and
on the extraction of parton distribution functions (PDFs). No evidence is found
for twist-6 contributions to structure functions (SF), and for a twist-4 term
in the logitudinal SF at . We find that DIS data are consistent
with the NNLO QCD approximation with the target mass and phenomenological high
twist corrections. For , we extend extrapolation of the
operator product expansion, preserving the low- current-conservation
theorems. The procedure yields a good description of data down to . An updated set of PDFs with reduced uncertainty and applicable
down to small momentum transfers in the lepton-nucleon scattering is obtained.Comment: 10 pages, 6 figures, proceedings of the 5th International Workshop on
Neutrino-Nucleus Interactions in the Few-GeV Region (NuInt07), Batavia,
Illinois, 30 May - 3 Jun 200
Noise rectification by a superconducting loop with two weak links
We consider a superconducting loop with two weak links that encloses a
magnetic flux. The weak links are unequal and are treated as Josephson
junctions with non-sinusoidal phase dependence. We devise a model that takes
into account the fluctuation of the critical currents, due to the fluctuations
of the order parameter in the weak links. These fluctuations are important near
the onset of superconductivity; in this regime they may significantly weaken
and eventually disconnect the superconducting loop. As a consequence of these
fluctuations and of the resistive noise in the junctions, the average dc
voltage does not vanish. Our model can be easily extended to provide a
qualitative description of a recent experiment.Comment: version accepted by PR
Chemical abundances for the transiting planet host stars OGLE-TR-10, 56, 111, 113, 132 and TrES-1. Abundances in different galactic populations
We used the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolution
spectra of 6 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111,
113, 132 and TrES-1. The spectra are now used to derive and discuss the
chemical abundances for C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni,
Cu and Zn. Abundances were derived in LTE, using 1-D plane-parallel Kurucz
model atmospheres. For S, Zn and Cu we used a spectral synthesis procedure,
while for the remaining cases the abundances were derived from measurements of
line-equivalent widths. The resulting abundances are compared with those found
for stars in the solar neighborhood. Distances and galactic coordinates are
estimated for the stars. We conclude that besides being particularly
metal-rich, with small possible exceptions OGLE-TR-10, 56, 111, 113, 132 and
TrES-1 are chemically undistinguishable from the field (thin disk) stars
regarding their [X/Fe] abundances. This is particularly relevant for the most
distant of the targets, located at up to ~2 Kpc from the Sun. We also did not
find any correlation between the abundances and the condensation temperature of
the elements, an evidence that strong accretion of planetary-like material,
tentatively connected to planetary migration, did not occur.Comment: Accepted for publication in Astronomy & Astrophysics (June 2006
Modeling spontaneous formation of precursor nanoparticles in clear-solution zeolite synthesis
We present a lattice model describing the formation of silica nanoparticles in the early stages of the clear-solution templated synthesis of silicalite-1 zeolite. Silica condensation/hydrolysis is modeled by a nearest-neighbor attraction, while the electrostatics are represented by an orientation-dependent, short-range interaction. Using this simplified model, we show excellent qualitative agreement with published experimental observations. The nanoparticles are identified as a metastable state, stabilized by electrostatic interactions between the negatively charged silica surface and a layer of organic cations. Nanoparticle size is controlled mainly by the solution pH, through nanoparticle surface charge. The size and concentration of the charge-balancing cation are found to have a negligible effect on nanoparticle size. Increasing the temperature allows for further particle growth by Ostwald ripening. We suggest that this mechanism may play a role in the growth of zeolite crystals
Jet Quenching in Non-Conformal Holography
We use our non-conformal holographic bottom-up model for QCD described in
1012.0116 to further study the effect of the QCD trace anomaly on the energy
loss of both light and heavy quarks in a strongly coupled plasma. We compute
the nuclear modification factor for bottom and charm quarks in an
expanding plasma with Glauber initial conditions. We find that the maximum
stopping distance of light quarks in a non-conformal plasma scales with the
energy with a temperature (and energy) dependent effective power.Comment: 4 pages, 1 figure. Proceedings for Quark Matter 201
Frequency of genetic polymorphisms of PXR gene in the Brazilian population
INTRODUCTION: PXR polymorphisms have been implicated in modulating CYP3A4 and PXR expression, potentially accounting for interindividual differences in drug metabolism. The prevalence of PXR polymorphisms varies among ethnic groups and data on the allelic distribution in the highly mixed Brazilian population is lacking. The aim of this study was to analyze genetic variations in the PXR gene in Brazilians and to compare the results to other ethnic groups. METHODS: DNA samples from 117 healthy Brazilians underwent PCR amplification and sequencing. RESULTS: Eleven polymorphisms were identified, 3 of which are highly associated with differences in CYP3A4 expression. We also identified 1 new synonymous variant in 1.3% of the alleles. Among the functional polymorphisms, -25913 C>T and -6994T>C occurred at a higher frequency comparedtothe Africanalleles (p < 0.05) but at a lower frequency compared to Caucasian alleles. The 8055 C>T allele was found at a similar frequency to those described in Caucasians and Africans (p > 0.05). CONCLUSION: We observed that functional variants of the PXR were frequent in our sample of the Brazilian population. Our results suggest that PXR gene variants may be of interest in pharmacogenetic studies involving Brazilians
Frequency of genetic polymorphisms of PXR gene in the Brazilian population
INTRODUCTION: PXR polymorphisms have been implicated in modulating CYP3A4 and PXR expression, potentially accounting for interindividual differences in drug metabolism. The prevalence of PXR polymorphisms varies among ethnic groups and data on the allelic distribution in the highly mixed Brazilian population is lacking. The aim of this study was to analyze genetic variations in the PXR gene in Brazilians and to compare the results to other ethnic groups. METHODS: DNA samples from 117 healthy Brazilians underwent PCR amplification and sequencing. RESULTS: Eleven polymorphisms were identified, 3 of which are highly associated with differences in CYP3A4 expression. We also identified 1 new synonymous variant in 1.3% of the alleles. Among the functional polymorphisms, -25913 C>T and -6994T>C occurred at a higher frequency comparedtothe Africanalleles (p < 0.05) but at a lower frequency compared to Caucasian alleles. The 8055 C>T allele was found at a similar frequency to those described in Caucasians and Africans (p > 0.05). CONCLUSION: We observed that functional variants of the PXR were frequent in our sample of the Brazilian population. Our results suggest that PXR gene variants may be of interest in pharmacogenetic studies involving Brazilians
Direct transition from a disordered to a multiferroic phase on a triangular lattice
Competing interactions and geometric frustration provide favourable
conditions for exotic states of matter. Such competition often causes multiple
phase transitions as a function of temperature and can lead to magnetic
structures that break inversion symmetry, thereby inducing ferroelectricity
[1-4]. Although this phenomenon is understood phenomenologically [3-4], it is
of great interest to have a conceptually simpler system in which
ferroelectricity appears coincident with a single magnetic phase transition.
Here we report the first such direct transition from a paramagnetic and
paraelectric phase to an incommensurate multiferroic in the triangular lattice
antiferromagnet RbFe(MoO4)2 (RFMO). A magnetic field extinguishes the electric
polarization when the symmetry of the magnetic order changes and
ferroelectricity is only observed when the magnetic structure has chirality and
breaks inversion symmetry. Multiferroic behaviour in RFMO provides a
theoretically tractable example of ferroelectricity from competing spin
interactions. A Landau expansion of symmetry-allowed terms in the free energy
demonstrates that the chiral magnetic order of the triangular lattice
antiferromagnet gives rise to a pseudoelectric field, whose temperature
dependence agrees with that observed experimentally.Comment: 16 pages pdf including 3 figure
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