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, $Q^2$, $\sim1 {\rm GeV}^2$. 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 $x\gtrsim0.1$. We find that DIS data are consistent with the NNLO QCD approximation with the target mass and phenomenological high twist corrections. For $Q^2<1 {\rm GeV}^2$, we extend extrapolation of the operator product expansion, preserving the low-$Q$ current-conservation theorems. The procedure yields a good description of data down to $Q^2\sim 0.5 {\rm GeV}^2$. 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 $R_{AA}$ 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

The chemical composition of red giants in 47 Tucanae I: Fundamental parameters and chemical abundance patterns

Context: The study of chemical abundance patterns in globular clusters is of key importance to constrain the different candidates for intra-cluster pollution of light elements. Aims: We aim at deriving accurate abundances for a large range of elements in the globular cluster 47 Tucanae (NGC 104) to add new constraints to the pollution scenarios for this particular cluster, expanding the range of previously derived element abundances. Methods: Using tailored 1D LTE atmospheric models together with a combination of equivalent width measurements, LTE, and NLTE synthesis we derive stellar parameters and element abundances from high-resolution, high signal-to-noise spectra of 13 red giant stars near the tip of the RGB. Results: We derive abundances of a total 27 elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ru, Ba, La, Ce, Pr, Nd, Eu, Dy). Departures from LTE were taken into account for Na, Al and Ba. We find a mean [Fe/H] = $-0.78\pm0.07$ and $[\alpha/{\rm Fe}]=0.34\pm0.03$ in good agreement with previous studies. The remaining elements show good agreement with the literature, but the inclusion of NLTE for Al has a significant impact on the behaviour of this key element. Conclusions: We confirm the presence of an Na-O anti-correlation in 47 Tucanae found by several other works. Our NLTE analysis of Al shifts the [Al/Fe] to lower values, indicating that this may be overestimated in earlier works. No evidence for an intrinsic variation is found in any of the remaining elements.Comment: 22 pages, 16 figures. Accepted for publication in A&