Deformed Complex Hermite Polynomials

We study a class of bivariate deformed Hermite polynomials and some of their properties using classical analytic techniques and the Wigner map. We also prove the positivity of certain determinants formed by the deformed polynomials. Along the way we also work out some additional properties of the (undeformed) complex Hermite polynomials and their relationships to the standard Hermite polynomials (of a single real variable).Comment: 12 page

Complete gluon bremsstrahlung corrections to the process b -> s l+ l-

In a recent paper, we presented the calculation of the order (alpha_s) virtual corrections to b->s l+ l- and of those bremsstrahlung terms which are needed to cancel the infrared divergences. In the present paper we work out the remaining order(alpha_s) bremsstrahlung corrections to b->s l+ l- which do not suffer from infrared and collinear singularities. These new contributions turn out to be small numerically. In addition, we also investigate the impact of the definition of the charm quark mass on the numerical results.Comment: 20 pages including 11 postscript figure

Specific recognition of a multiply phosphorylated motif in the DNA repair scaffold XRCC1 by the FHA domain of human PNK.

Short-patch repair of DNA single-strand breaks and gaps (SSB) is coordinated by XRCC1, a scaffold protein that recruits the DNA polymerase and DNA ligase required for filling and sealing the damaged strand. XRCC1 can also recruit end-processing enzymes, such as PNK (polynucleotide kinase 3'-phosphatase), Aprataxin and APLF (aprataxin/PNK-like factor), which ensure the availability of a free 3'-hydroxyl on one side of the gap, and a 5'-phosphate group on the other, for the polymerase and ligase reactions respectively. PNK binds to a phosphorylated segment of XRCC1 (between its two C-terminal BRCT domains) via its Forkhead-associated (FHA) domain. We show here, contrary to previous studies, that the FHA domain of PNK binds specifically, and with high affinity to a multiply phosphorylated motif in XRCC1 containing a pSer-pThr dipeptide, and forms a 2:1 PNK:XRCC1 complex. The high-resolution crystal structure of a PNK-FHA-XRCC1 phosphopeptide complex reveals the basis for this unusual bis-phosphopeptide recognition, which is probably a common feature of the known XRCC1-associating end-processing enzymes

Tunneling and Non-Universality in Continuum Percolation Systems

The values obtained experimentally for the conductivity critical exponent in numerous percolation systems, in which the interparticle conduction is by tunnelling, were found to be in the range of $t_0$ and about $t_0+10$, where $t_0$ is the universal conductivity exponent. These latter values are however considerably smaller than those predicted by the available ``one dimensional"-like theory of tunneling-percolation. In this letter we show that this long-standing discrepancy can be resolved by considering the more realistic "three dimensional" model and the limited proximity to the percolation threshold in all the many available experimental studiesComment: 4 pages, 2 figure

Matrix Gravity and Massive Colored Gravitons

We formulate a theory of gravity with a matrix-valued complex vierbein based on the SL(2N,C)xSL(2N,C) gauge symmetry. The theory is metric independent, and before symmetry breaking all fields are massless. The symmetry is broken spontaneously and all gravitons corresponding to the broken generators acquire masses. If the symmetry is broken to SL(2,C) then the spectrum would correspond to one massless graviton coupled to $2N^2 -1$ massive gravitons. A novel feature is the way the fields corresponding to non-compact generators acquire kinetic energies with correct signs. Equally surprising is the way Yang-Mills gauge fields acquire their correct kinetic energies through the coupling to the non-dynamical antisymmetric components of the vierbeins.Comment: One reference adde

Investigating the Effect of Stratospheric Radiation on Seed Germination and Growth

Three seed types: bean (Phaseolus vulgaris), corn (Zea mays) and radish (Raphanus sativus) were flown in a high altitude weather balloon into the mid-stratosphere to investigate the effects of high altitude radiation on germination success and seedling growth. After recovering and planting the seeds, the bean seeds showed lower germination success with exposure to high altitude radiation, and consequently stunted seedling growth. Cord and radish seeds experienced a statistically significant positive effect on germination success form radiation exposure compared to control seeds, but negative effect on seedling growth. Overall, the field experiments presented here support laboratory studies that show radiation exposure on vegetable seeds has a mixed effect on the germination success and negative effect on seedling growth on investigated seed types

Nonthermal Laser-Induced Formation of Crystalline Ge Quantum Dots on Si(100)

The effects of laser-induced electronic excitations on the self-assembly of Ge quantum dots on Si (100) - (2×1) grown by pulsed laser deposition are studied. Electronic excitations due to laser irradiation of the Si substrate and the Ge film during growth are shown to decrease the roughness of films grown at a substrate temperature of ∼120 °C. At this temperature, the grown films are nonepitaxial. Electronic excitation results in the formation of an epitaxial wetting layer and crystalline Ge quantum dots at ∼260 °C, a temperature at which no crystalline quantum dots form without excitation under the same deposition conditions.© 2008 American Institute of Physics. [DOI: 10.1063/1.3041493

Melting and Solidification Study of As-Deposited and Recrystallized Bi Thin Films

Melting and solidification of as-deposited and recrystallized Bi crystallites, deposited on highly oriented 002-graphite at 423 K, were studied using reflection high-energy electron diffraction (RHEED). Films with mean thickness between 1.5 and 33 ML (monolayers) were studied. Ex situ atomic force microscopy was used to study the morphology and the size distribution of the formed nanocrystals. The as-deposited films grew in the form of three-dimensional crystallites with different shapes and sizes, while those recrystallized from the melt were formed in nearly similar shapes but different sizes. The change in the RHEED pattern with temperature was used to probe the melting and solidification of the crystallites. Melting started at temperatures below the bulk melting point of Bi, T0=544.5 K, and extended over a temperature range that depended on the size distribution of the crystallites. The as-deposited 1.5 ML film started to melt at T0-50 K and melted completely at T0-20 K. For films with higher coverage, the size distribution was observed to spread over a wider range with a larger mean value, resulting in a shift in the melting temperature range towards higher temperatures. Due to the shift in size distribution to higher values upon recrystallization, the recrystallized Bi crystallites showed a melting temperature range higher than that of the as-deposited crystallites. For the investigated conditions, all films were completely melted below or at T 0 of Bi. The characteristic film melting point, defined as the temperature at which the film melting rate with temperature is the fastest, showed a linear dependence on the reciprocal of the average crystallite radius, consistent with theoretical models. Of these models, the surface-phonon instability model best fits the obtained results. During solidification, the Bi films showed high amount of supercooling relative to T0 of Bi. The amount of liquid supercooling was found to decrease linearly with the reciprocal of the average crystallite size. © 2006 American Institute of Physics. [DOI: 10.1063/1.2208551

Activation Energy of Surface Diffusion and Terrace Width Dynamics During the Growth of in (4×3) on Si (100) - (2×1) by Femtosecond Pulsed Laser Deposition

The nucleation and growth of indium on a vicinal Si (100) - (2×1) surface at high temperature by femtosecond pulsed laser deposition was investigated by in situ reflection high energy electron diffraction (RHEED). RHEED intensity relaxation was observed for the first ∼2 ML during the growth of In (4×3) by step flow. From the temperature dependence of the rate of relaxation, an activation energy of 1.4±0.2 eV of surface diffusion was determined. The results indicate that indium small clusters diffused to terrace step edges with a diffusion frequency constant of (1.0±0.1) × 1011 s-1. The RHEED specular beam split peak spacing, which is characteristic of a vicinal surface, was analyzed with the growth temperature to obtain the average terrace width. Gradual reduction in the terrace width during growth of In (4×3) was observed with In coverage and is attributed to the detachment of In atoms from terrace edges. At a substrate temperature of 405 °C, the average terrace width decreased from 61±10 Å, which corresponds to the vicinal Si(100) surface, to an equilibrium value of 45±7 Å after deposition of ∼23 ML. Further In coverage showed a transition of the RHEED pattern from (4×3) to (1×1) and the growth of rounded In islands (average height of ∼1 nm and width of ∼25 nm), as examined by ex situ atomic force microscopy. © 2008 American Institute of Physics. [DOI: 10.1063/1.2909923