Deformation of the Planetary Orbits Caused by the Time Dependent Gravitational Potential in the Universe

In the paper are studied the deformations of the planetary orbits caused by the time dependent gravitational potential in the universe. It is shown that the orbits are not axially symmetric and the time dependent potential does not cause perihelion precession. It is found a simple formula for the change of the orbit period caused by the time dependent gravitational potential and it is tested for two binary pulsars.Comment: 7 page

Gamma-Ray Bursts: The Underlying Model

A pedagogical derivation is presented of the ``fireball'' model of gamma-ray bursts, according to which the observable effects are due to the dissipation of the kinetic energy of a relativistically expanding wind, a ``fireball.'' The main open questions are emphasized, and key afterglow observations, that provide support for this model, are briefly discussed. The relativistic outflow is, most likely, driven by the accretion of a fraction of a solar mass onto a newly born (few) solar mass black hole. The observed radiation is produced once the plasma has expanded to a scale much larger than that of the underlying ``engine,'' and is therefore largely independent of the details of the progenitor, whose gravitational collapse leads to fireball formation. Several progenitor scenarios, and the prospects for discrimination among them using future observations, are discussed. The production in gamma- ray burst fireballs of high energy protons and neutrinos, and the implications of burst neutrino detection by kilometer-scale telescopes under construction, are briefly discussed.Comment: In "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture Notes in Physics, Springer-Verlag (in press); 26 pages, 2 figure

Gravitational Radiation from Compact Binary Pulsars

An outstanding question in modern Physics is whether general relativity (GR) is a complete description of gravity among bodies at macroscopic scales. Currently, the best experiments supporting this hypothesis are based on high-precision timing of radio pulsars. This chapter reviews recent advances in the field with a focus on compact binary millisecond pulsars with white-dwarf (WD) companions. These systems - if modeled properly - provide an unparalleled test ground for physically motivated alternatives to GR that deviate significantly in the strong-field regime. Recent improvements in observational techniques and advances in our understanding of WD interiors have enabled a series of precise mass measurements in such systems. These masses, combined with high-precision radio timing of the pulsars, result to stringent constraints on the radiative properties of gravity, qualitatively very different from what was available in the past.Comment: Short review chapter to appear in "Gravitational Wave Astrophysics" by Springer-Verlag, edited by Carlos F. Sopuerta; v3: a few major corrections and updated references. Comments are welcome

A Kinematical Approach to Conformal Cosmology

We present an alternative cosmology based on conformal gravity, as originally introduced by H. Weyl and recently revisited by P. Mannheim and D. Kazanas. Unlike past similar attempts our approach is a purely kinematical application of the conformal symmetry to the Universe, through a critical reanalysis of fundamental astrophysical observations, such as the cosmological redshift and others. As a result of this novel approach we obtain a closed-form expression for the cosmic scale factor R(t) and a revised interpretation of the space-time coordinates usually employed in cosmology. New fundamental cosmological parameters are introduced and evaluated. This emerging new cosmology does not seem to possess any of the controversial features of the current standard model, such as the presence of dark matter, dark energy or of a cosmological constant, the existence of the horizon problem or of an inflationary phase. Comparing our results with current conformal cosmologies in the literature, we note that our kinematic cosmology is equivalent to conformal gravity with a cosmological constant at late (or early) cosmological times. The cosmic scale factor and the evolution of the Universe are described in terms of several dimensionless quantities, among which a new cosmological variable delta emerges as a natural cosmic time. The mathematical connections between all these quantities are described in details and a relationship is established with the original kinematic cosmology by L. Infeld and A. Schild. The mathematical foundations of our kinematical conformal cosmology will need to be checked against current astrophysical experimental data, before this new model can become a viable alternative to the standard theory.Comment: Improved version, with minor changes. 58 pages, including 7 figures and one table. Accepted for publication in General Relativity and Gravitation (GERG

IBD risk loci are enriched in multigenic regulatory modules encompassing putative causative genes.

GWAS have identified >200 risk loci for Inflammatory Bowel Disease (IBD). The majority of disease associations are known to be driven by regulatory variants. To identify the putative causative genes that are perturbed by these variants, we generate a large transcriptome data set (nine disease-relevant cell types) and identify 23,650 cis-eQTL. We show that these are determined by ∼9720 regulatory modules, of which ∼3000 operate in multiple tissues and ∼970 on multiple genes. We identify regulatory modules that drive the disease association for 63 of the 200 risk loci, and show that these are enriched in multigenic modules. Based on these analyses, we resequence 45 of the corresponding 100 candidate genes in 6600 Crohn disease (CD) cases and 5500 controls, and show with burden tests that they include likely causative genes. Our analyses indicate that ≥10-fold larger sample sizes will be required to demonstrate the causality of individual genes using this approach

A comparison of exit and voice relationships under common uncertainty

Dawid H, Kopel M. A comparison of exit and voice relationships under common uncertainty. JOURNAL OF ECONOMICS & MANAGEMENT STRATEGY. 2003;12(4):531-555.We consider a repeated interaction between a manufacturing firm and a subcontractor. The relationship between the two parties is characterized (1) by moral hazard, and (2) by the fact that they do not have perfect knowledge about the base cost level of the project, which is carried out by a subcontractor (the parties only have identical a priori beliefs). We consider a two-period model where the players can update their estimate of the base cost level according to incoming information. Exit relationships, where the firm signs one-period contracts with different subcontractors, are compared with voice relationships, where both partners commit to a two-period interaction and (due to information sharing and face-to-face communication between the partners) additional information about the base cost level is generated. It is shown that in such a dynamic framework with common uncertainty the quality of the additional information plays a crucial role in determining the characteristics of the optimal relationship: voice-based strategies governed by long-term contracts are preferable if the precision of the additional information about the base cost level is high. If the precision of the additional signal is low, exit strategies with frequent changes of the subcontractors are optimal for the manufacturer