From Taub Numbers to the Bondi Mass

Taub numbers are studied on asymptotically flat backgrounds with Killing symmetries. When the field equations are solved for a background spacetime and higher order functional derivatives (higher order variational derivatives of the Hilbert Lagrangean) are solved for perturbations from the background, such perturbed space-times admit zeroth, first, and second order Taub numbers. Zeroth order Taub numbers are Komar constants (upto numerical factors) or Penrose-Goldberg constants of the background. For a Killing symmetry of the background, first order Taub numbers give the contribution of the linearized perturbation to the associated backgound quantity, such as the perturbing mass. Second order Taub numbers give the contribution of second order perturbations to the background quantity. The Bondi mass is a sum of first and second order Taubs numbers on a Minkowski background.Comment: To appear in the proceedings of the 8th Marcel Grossmann Conferenc

Evaluation of a Phosphate Management Protocol to Achieve Optimum Serum Phosphate Levels in Hemodialysis Patients

Original article can be found at: http://www.sciencedirect.com/science/journal/10512276 Copyright National Kidney Foundation, Inc. DOI: 10.1053/j.jrn.2008.05.003To evaluate the effectiveness of a protocol designed to optimize serum phosphate levels in patients undergoing regular hemodialysis (HD).Peer reviewe

Projectile Δ\Delta Excitations in p(p,n)Nπp(p,n)N\pi Reactions

It has recently been proven from measurements of the spin-transfer coefficients $D_{xx}$ and $D_{zz}$ that there is a small but non-vanishing $\Delta S=0$ component $\sigma_{0}$, in the inclusive $p(p,n)N\pi\,$ reaction cross section $\sigma\,$. It is shown that the dominant part of the measured $\sigma_{0}$ can be explained in terms of the projectile $\Delta$ excitation mechanism. An estimate is further made of contributions to $\sigma_{0}$ from s-wave rescattering process. It is found that s-wave rescattering contribution is much smaller than the contribution coming from projectile $\Delta$ excitation mechanism. The addition of s-wave rescattering contribution to the dominant part, however, improves the fit to the data.Comment: 9 pages, Revtex, figures can be obtained upon reques

Reactions to extreme events: moving threshold model

In spite of precautions to avoid the harmful effects of extreme events, we experience recurrently phenomena that overcome the preventive barriers. These barriers usually increase drastically right after the occurrence of such extreme events, but steadily decay in their absence. In this paper we consider a simple model that mimics the evolution of the protection barriers to study the efficiency of the system's reaction to extreme events and how it changes our perception of the sequence of extreme events itself. We obtain that the usual method of fighting extreme events introduces a periodicity in their occurrence and is generally less efficient than the use of a constant barrier. On the other hand, it shows a good adaptation to the presence of slow non-stationarities.Comment: 14 pages and 7 figure

Ultralow noise performance of an 8.4-GHz maser-feedhorn system

A total system noise temperature of 6.6 K was demonstrated with an 8.4-GHz traveling wave maser and feedhorn operating in a cryogenic environment. Both the maser and feedhorn were inserted in the helium cryostat, with the maser operating in the 1.6-K liquid bath and the feedhorn cooled in the helium gas, with a temperature gradient along the horn ranging from the liquid bath temperature at its lower end to room temperature at its top. The ruby maser exhibited 43 dB of gain with a bandwidth of 76 MHz(-3 dB) centered at 8400 MHz. Discussions of the maser, cooled feedhorn, and cryostat designs are presented along with a discussion of the noise temperature measurements

Tyrosine dephosphorylation of H2AX modulates apoptosis and survival decisions.

Life and death fate decisions allow cells to avoid massive apoptotic death in response to genotoxic stress. Although the regulatory mechanisms and signalling pathways controlling DNA repair and apoptosis are well characterized, the precise molecular strategies that determine the ultimate choice of DNA repair and survival or apoptotic cell death remain incompletely understood. Here we report that a protein tyrosine phosphatase, EYA, is involved in promoting efficient DNA repair rather than apoptosis in response to genotoxic stress in mammalian embryonic kidney cells by executing a damage-signal-dependent dephosphorylation of an H2AX carboxy-terminal tyrosine phosphate (Y142). This post-translational modification determines the relative recruitment of either DNA repair or pro-apoptotic factors to the tail of serine phosphorylated histone H2AX (gamma-H2AX) and allows it to function as an active determinant of repair/survival versus apoptotic responses to DNA damage, revealing an additional phosphorylation-dependent mechanism that modulates survival/apoptotic decisions during mammalian organogenesis

Robustness and Enhancement of Neural Synchronization by Activity-Dependent Coupling

We study the synchronization of two model neurons coupled through a synapse having an activity-dependent strength. Our synapse follows the rules of Spike-Timing Dependent Plasticity (STDP). We show that this plasticity of the coupling between neurons produces enlarged frequency locking zones and results in synchronization that is more rapid and much more robust against noise than classical synchronization arising from connections with constant strength. We also present a simple discrete map model that demonstrates the generality of the phenomenon.Comment: 4 pages, accepted for publication in PR

Research on nonlinear optical materials: an assessment. IV. Photorefractive and liquid crystal materials

This panel considered two separate subject areas: photorefractive materials used for nonlinear optics and liquid crystal materials used in light valves. Two related subjects were not considered due to lack of expertise on the panel: photorefractive materials used in light valves and liquid crystal materials used in nonlinear optics. Although the inclusion of a discussion of light valves by a panel on nonlinear optical materials at first seems odd, it is logical because light valves and photorefractive materials perform common functions

Diffraction-Limited Imaging and Photometry of NGC 1068

The nearby Seyfert 2 Galaxy NGC 1068 was observed with speckle imaging techniques in the near-infrared H-band (1.6 microns) at the Hale 200-inch Telescope and K-band (2.2 microns) at the 10 m Keck I Telescope. Images with diffraction limited or near-diffraction limited resolutions of 0.''05 - 0.''1 were obtained and used to search for structure in the nuclear region. Images of the nucleus of NGC 1068 reveal an extended region of emission which accounts for nearly 50% of the nuclear flux at K-band. This region extends 10 pc on either side of an unresolved point source nucleus which is at most, 0.''02 or 1.4 pc in size. Both the point source and the newly imaged extended emission are very red, with identical H-K colors corresponding to a color temperature of 800 K. While the point source is of a size to be consistent with grains in thermal equilibrium with the nuclear source, the extended emission is not. It must consist either of nuclear emission which has been reflected off an extended dusty disk or of small grains raised to transiently high temperatures by reflected UV photons.Comment: accepted to AJ, AAS LaTeX and epsfig, 22 pages incl. 5 ps figure