On Orientifold Constructions of Type IIA Dual Pairs

In this paper we analyze the earlier constructions of the type IIA dual pairs through orientifolding. By an appropriate choice of $\Gamma$-matrix basis for the spinor representations of the $U$-duality group, we give an explicit relationship between the orientifold models and their dual pairs.Comment: 11pages, Late

Genus Topology of the Cosmic Microwave Background from the WMAP 3-Year Data

We have independently measured the genus topology of the temperature fluctuations in the cosmic microwave background seen in the Wilkinson Microwave Anisotropy Probe (WMAP) 3-year data. A genus analysis of the WMAP data indicates consistency with Gaussian random-phase initial conditions, as predicted by standard inflation. We set 95% confidence limits on non-linearities of -101 < f_{nl} < 107. We also find that the observed low l (l <= 8) modes show a slight anti-correlation with the Galactic foreground, but not exceeding 95% confidence, and that the topology defined by these modes is consistent with that of a Gaussian random-phase distribution (within 95% confidence).Comment: MNRAS LaTeX style (mn2e.cls), EPS and JPEG figure

Mean encounter times for cell adhesion in hydrodynamic flow: analytical progress by dimensional reduction

For a cell moving in hydrodynamic flow above a wall, translational and rotational degrees of freedom are coupled by the Stokes equation. In addition, there is a close coupling of convection and diffusion due to the position-dependent mobility. These couplings render calculation of the mean encounter time between cell surface receptors and ligands on the substrate very difficult. Here we show for a two-dimensional model system how analytical progress can be achieved by treating motion in the vertical direction by an effective reaction term in the mean first passage time equation for the rotational degree of freedom. The strength of this reaction term can either be estimated from equilibrium considerations or used as a fit parameter. Our analytical results are confirmed by computer simulations and allow to assess the relative roles of convection and diffusion for different scaling regimes of interest.Comment: Reftex, postscript figures include

A Note on Marginally Stable Bound States in Type II String Theory

Spectrum of elementary string states in type II string theory contains ultra-short multiplets that are marginally stable. $U$-duality transformation converts these states into bound states at threshold of $p$-branes carrying Ramond-Ramond charges, and wrapped around $p$-cycles of a torus. We propose a test for the existence of these marginally stable bound states. Using the recent results of Polchinski and of Witten, we argue that the spectrum of bound states of $p$-branes is in agreement with the prediction of $U$-duality.Comment: LaTeX file, 6 page

Covariantes continuas individuales dependientes del tiempo y el modelo de Cormack–Jolly–Seber

The Cormack–Jolly–Seber model provides the basic framework for analyzing the survival of animals in open populations using capture–recapture data. Extensions of this model have already been developed that allow the survival and capture probabilities to vary between individuals based on auxiliary variables, but none can allow for variables that are continuous, time–dependent, and vary among individuals. We summarize a new method for incorporating this type of variable into the Cormack–Jolly–Seber model by modelling the distribution of the unobserved values of the variable conditional on the observed values, given a few basic assumptions about how the variable changes over time. We begin with a hypothetical scenario as motivation for our model and also present the results of two examples used in developing the model.El modelo de Cormack–Jolly–Seber proporciona el marco básico para analizar la supervivencia de animales en poblaciones abiertas utilizando datos de captura–recaptura. Si bien se han desarrollado ampliaciones de este modelo que permiten variar las probabilidades de supervivencia y de captura entre individuos a partir de variables auxiliares, en ninguna de ellas es posible utilizar variables continuas, dependientes del tiempo y que varíen de un individuo a otro. El presente estudio analiza un nuevo método que permite la incorporación de este tipo de variable en el modelo de Cormack–Jolly–Seber mediante la modelación de la distribución de los valores no observados de la variable según los valores observados, tomando como referencia algunas asumciones básicas acerca de cómo la variable cambia con el tiempo. En primer lugar, presentamos un escenario hipotético con objeto de definir el modelo, para posteriormente indicar los resultados de dos ejemplos que utilizamos para su desarrollo

SECOR observations in the Pacific

Geometric adjustment technique for Pacific SECOR observations based on least squares metho

Influence of substrate temperature on lattice strain field and phase transition in MeV oxygen ion implanted GaAs crystals

A detailed study of the influence of substrate temperature on the radiation-induced lattice strain field and crystalline-to-amorphous (c-a) phase transition in MeV oxygen ion implanted GaAs crystals has been made using channeling Rutherford backscattering spectroscopy, secondary ion mass spectrometry, and the x-ray rocking curve technique. A comparison has been made between the cases of room temperature (RT) and low temperature (LT) (about 100 K) implantation. A strong in situ dynamic annealing process is found in RT implantation at a moderate beam current, resulting in a uniform positive strain field in the implanted layer. LT implantation introduces a freeze-in effect which impedes the recombination and diffusion of initial radiation-created lattice damage and defects, and in turn drives more efficiently the c-a transition as well as strain saturation and relaxation. The results are interpreted with a spike damage model in which the defect production process is described in terms of the competition between defect generation by nuclear spikes and defects diffusion and recombination stimulated by electronic spikes. It is also suggested that the excess population of vacancies and their complexes is responsible for lattice spacing expansion in ion-implanted GaAs crystals