Systematic errors and combination of individual CRF solutions in the framework of the international pilot project for the next ICRF

A new international Pilot Project for the re-determination of the ICRF was initiated by the International VLBI Service for Geodesy and Astrometry (IVS) in January 2005. The purpose of this project is to compare the individual CRF solutions and to analyze their systematic and random errors with focus on the selection of the optimal strategy for the next ICRF realization. Eight radio source catalogues provided by the IVS Analysis Centers GA, SHAO, DGFI, GIUB-BKG, JPL, MAO NANU, GSFC, USNO were analyzed. In present study, four analytical models were used to investigate the systematic differences between solutions: solid rotation, rotation and deformation (IERS method), and expansion in orthogonal functions: Legendre-Fourier polynomials and spherical functions. It was found that expansions by orthogonal function describe the differences between individual catalogues better than the two former models. Finally, the combined CRF was generated. Using the radio source positions from this combined catalogue for estimation of EOP has shown improvement of the uncertainty of the celestial pole offset time series.Comment: 9 pages, 8 figures. Presented at the XXVIth IAU General Assembly, JD16, Prague, Czech Republic, 14-25 August 200

A molecular mechanism of symmetry breaking in the early chick embryo

The first obvious sign of bilateral symmetry in mammalian and avian embryos is the appearance of the primitive streak in the future posterior region of a radially symmetric disc. The primitive streak marks the midline of the future embryo. The mechanisms responsible for positioning the primitive streak remain largely unknown. Here we combine experimental embryology and mathematical modelling to analyse the role of the TGFβ-related molecules BMP4 and Vg1/GDF1 in positioning the primitive streak. Bmp4 and Vg1 are first expressed throughout the embryo, and then become localised to the future anterior and posterior regions of the embryo, where they will, respectively, inhibit or induce formation of the primitive streak. We propose a model based on paracrine signalling to account for the separation of the two domains starting from a homogeneous array of cells, and thus for the topological transformation of a radially symmetric disc to a bilaterally symmetric embryo

Robustness and modular design of the Drosophila segment polarity network

Biomolecular networks have to perform their functions robustly. A robust function may have preferences in the topological structures of the underlying network. We carried out an exhaustive computational analysis on network topologies in relation to a patterning function in Drosophila embryogenesis. We found that while the vast majority of topologies can either not perform the required function or only do so very fragilely, a small fraction of topologies emerges as particularly robust for the function. The topology adopted by Drosophila, that of the segment polarity network, is a top ranking one among all topologies with no direct autoregulation. Furthermore, we found that all robust topologies are modular--each being a combination of three kinds of modules. These modules can be traced back to three sub-functions of the patterning function and their combinations provide a combinatorial variability for the robust topologies. Our results suggest that the requirement of functional robustness drastically reduces the choices of viable topology to a limited set of modular combinations among which nature optimizes its choice under evolutionary and other biological constraints.Comment: Supplementary Information and Synopsis available at http://www.ucsf.edu/tanglab

The Large Quasar Reference Frame (LQRF) - an optical representation of the ICRS

The large number and all-sky distribution of quasars from different surveys, along with their presence in large, deep astrometric catalogs,enables the building of an optical materialization of the ICRS following its defining principles. Namely: that it is kinematically non-rotating with respect to the ensemble of distant extragalactic objects; aligned with the mean equator and dynamical equinox of J2000; and realized by a list of adopted coordinates of extragalatic sources. Starting from the updated and presumably complete LQAC list of QSOs, the initial optical positions of those quasars are found in the USNO B1.0 and GSC2.3 catalogs, and from the SDSS DR5. The initial positions are next placed onto UCAC2-based reference frames, following by an alignment with the ICRF, to which were added the most precise sources from the VLBA calibrator list and the VLA calibrator list - when reliable optical counterparts exist. Finally, the LQRF axes are inspected through spherical harmonics, contemplating to define right ascension, declination and magnitude terms. The LQRF contains J2000 referred equatorial coordinates for 100,165 quasars, well represented across the sky, from -83.5 to +88.5 degrees in declination, and with 10 arcmin being the average distance between adjacent elements. The global alignment with the ICRF is 1.5 mas, and the individual position accuracies are represented by a Poisson distribution that peaks at 139 mas in right ascension and 130 mas in declination. It is complemented by redshift and photometry information from the LQAC. The LQRF is designed to be an astrometric frame, but it is also the basis for the GAIA mission initial quasars' list, and can be used as a test bench for quasars' space distribution and luminosity function studies.Comment: 23 pages, 23 figures, 6 tables Accepted for publication by Astronomy & Astrophysics, on 25 May 200

A particle-hole model approach for hypernuclei

A particle-hole model is developed to describe the excitation spectrum of single lambda hypernuclei and the possible presence of collective effects is explored by making a comparison with the mean-field calculations. Results for the spectra of 12C, 16O, 40Ca, 90Zr and 208Pb single lambda hypernuclei are shown. The comparison with the available experimental data is satisfactory. We find that collective phenomena are much less important in hypernuclei than in ordinary nuclei.Comment: 24 pages, 5 eps figures, accepted for publication in Nucl. Phys.

Topologies on Quantum Effects

Quantum effects play an important role in quantum measurement theory. The set of all quantum effects can be organized into an algebraical structure called effect algebra. In this paper, we study various topologies on the Hilbert space effect algebra and the projection lattice effect algebra

Changes in white adipose tissue metabolism induced by resveratrol in rats.

BACKGROUND: A remarkable range of biological functions have been ascribed to resveratrol. Recently, this polyphenol has been shown to have body fat lowering effects. The aim of the present study was to assess some of the potential underlying mechanisms of action which take place in adipose tissue. METHODS: Sixteen male Sprague-Dawley rats were randomly divided into two groups: control and treated with 30 mg resveratrol/kg body weight/d. All rats were fed an obesogenic diet and after six weeks of treatment white adipose tissues were dissected. Lipoprotein lipase activity was assessed by fluorimetry, acetyl-CoA carboxylase by radiometry, and malic enzyme, glucose-6P-dehydrogenase and fatty acid synthase by spectrophotometry. Gene expression levels of acetyl-CoA carboxylase, fatty acid synthase, lipoprotein lipase, hormone-sensitive lipase, adipose triglyceride lipase, PPAR-gamma, SREBP-1c and perilipin were assessed by Real time RT-PCR. The amount of resveratrol metabolites in adipose tissue was measured by chromatography. RESULTS: There was no difference in the final body weight of the rats; however, adipose tissues were significantly decreased in the resveratrol-treated group. Resveratrol reduced the activity of lipogenic enzymes, as well as that of heparin-releasable lipoprotein lipase. Moreover, a significant reduction was induced by this polyphenol in hormone-sensitive lipase mRNA levels. No significant changes were observed in other genes. Total amount of resveratrol metabolites in adipose tissue was 2.66 ± 0.55 nmol/g tissue. CONCLUSIONS: It can be proposed that the body fat-lowering effect of resveratrol is mediated, at least in part, by a reduction in fatty acid uptake from circulating triacylglycerols and also in de novo lipogenesis