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

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

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

Schwarzschild Atmospheric Processes: A Classical Path to the Quantum

We develop some classical descriptions for processes in the Schwarzschild string atmosphere. These processes suggest relationships between macroscopic and microscopic scales. The classical descriptions developed in this essay highlight the fundamental quantum nature of the Schwarzschild atmospheric processes.Comment: to appear in Gen. Rel. Gra

Noise Effects on the Complex Patterns of Abnormal Heartbeats

Patients at high risk for sudden death often exhibit complex heart rhythms in which abnormal heartbeats are interspersed with normal heartbeats. We analyze such a complex rhythm in a single patient over a 12-hour period and show that the rhythm can be described by a theoretical model consisting of two interacting oscillators with stochastic elements. By varying the magnitude of the noise, we show that for an intermediate level of noise, the model gives best agreement with key statistical features of the dynamics.Comment: 4 pages, 4 figures, RevTe

Debris disks around Sun-like stars

We have observed nearly 200 FGK stars at 24 and 70 microns with the Spitzer Space Telescope. We identify excess infrared emission, including a number of cases where the observed flux is more than 10 times brighter than the predicted photospheric flux, and interpret these signatures as evidence of debris disks in those systems. We combine this sample of FGK stars with similar published results to produce a sample of more than 350 main sequence AFGKM stars. The incidence of debris disks is 4.2% (+2.0/-1.1) at 24 microns for a sample of 213 Sun-like (FG) stars and 16.4% (+2.8/-2.9) at 70 microns for 225 Sun-like (FG) stars. We find that the excess rates for A, F, G, and K stars are statistically indistinguishable, but with a suggestion of decreasing excess rate toward the later spectral types; this may be an age effect. The lack of strong trend among FGK stars of comparable ages is surprising, given the factor of 50 change in stellar luminosity across this spectral range. We also find that the incidence of debris disks declines very slowly beyond ages of 1 billion years.Comment: ApJ, in pres

Affinity and dose of TCR engagement yield proportional enhancer and gene activity in CD4+ T cells.

Affinity and dose of T cell receptor (TCR) interaction with antigens govern the magnitude of CD4+ T cell responses, but questions remain regarding the quantitative translation of TCR engagement into downstream signals. We find that while the response of mouse CD4+ T cells to antigenic stimulation is bimodal, activated cells exhibit analog responses proportional to signal strength. Gene expression output reflects TCR signal strength, providing a signature of T cell activation. Expression changes rely on a pre-established enhancer landscape and quantitative acetylation at AP-1 binding sites. Finally, we show that graded expression of activation genes depends on ERK pathway activation, suggesting that an ERK-AP-1 axis plays an important role in translating TCR signal strength into proportional activation of enhancers and genes essential for T cell function

Stellar sources in the ISOGAL intermediate bulge fields

We present a study of ISOGAL sources in the "intermediate" galactic bulge ($|$$l$$|$ $<$ 2$^\circ$, $|$$b$$|$ $\sim$ 1$^\circ$--4$^\circ$), observed by ISOCAM at 7 and 15 $\mu m$. In combination with near-infrared (I, J, K$_{\rm s}$) data of DENIS survey, complemented by 2MASS data, we discuss the nature of the ISOGAL sources, their luminosities, the interstellar extinction and the mass-loss rates. A large fraction of the 1464 detected sources at 15 $\mu m$ are AGB stars above the RGB tip, a number of them show an excess in ([7]-[15])$_{\rm 0}$ and (K$_{\rm s}$-[15])$_{\rm 0}$ colours, characteristic of mass-loss. The latter, especially (K$_{\rm s}$-[15])$_{\rm 0}$, provide estimates of the mass-loss rates and show their distribution in the range 10$^{-8}$ to 10$^{-5}$ M$_{\rm \odot}$/yr.Comment: 16 pages, accepted for publication in Astronomy and Astrophysic

A framework for understanding the factors influencing pair programming success

Pair programming is one of the more controversial aspects of several Agile system development methods, in particular eXtreme Programming (XP). Various studies have assessed factors that either drive the success or suggest advantages (and disadvantages) of pair programming. In this exploratory study the literature on pair programming is examined and factors distilled. These factors are then compared and contrasted with those discovered in our recent Delphi study of pair programming. Gallis et al. (2003) have proposed an initial framework aimed at providing a comprehensive identification of the major factors impacting team programming situations including pair programming. However, this study demonstrates that the framework should be extended to include an additional category of factors that relate to organizational matters. These factors will be further refined, and used to develop and empirically evaluate a conceptual model of pair programming (success)