Maximal Subrings and Covering Numbers of Finite Semisimple Rings

We classify the maximal subrings of the ring of nx n matrices over a finite field, and show that these subrings may be divided into three types. We also describe all of the maximal subrings of a finite semisimple ring, and categorize them into two classes. As an application of these results, we calculate the covering number of a finite semisimple ring

Possible depletion of metals into dust grains in the core of the Centaurus cluster of galaxies

We present azimuthally averaged metal abundance profiles from a full, comprehensive, and conservative re-analysis of the deep ($\sim$800 ks total net exposure) \textit{Chandra}/ACIS-S observation of the Centaurus cluster core (NGC\,4696). After carefully checking various sources of systematic uncertainties, including the choice of the spectral deprojection method, assumptions about the temperature structure of the gas, and uncertainties in the continuum modeling, we confirm the existence of a central drop in the abundances of the `reactive' elements Fe, Si, S, Mg, and Ca, within $r\lesssim$10 kpc. The same drops are also found when analyzing the \textit{XMM-Newton}/EPIC data ($\sim$150 ks). Adopting our most conservative approach, we find that, unlike the central drops seen for Fe, Si, S, Mg and Ca, the abundance of the `nonreactive' element Ar is fully consistent with showing no central drop. This is further confirmed by the significant ($>3\sigma$) central radial increase of the Ar/Fe ratio. Our results corroborate the previously proposed `dust depletion scenario' , in which central metal abundance drops are explained by the deposition of a significant fraction of centrally cooled reactive metals into dust grains present in the central regions of the Centaurus cluster. This is also supported by the previous findings that the extent of the metal abundance drops in NGC\,4696 broadly coincides with the infrared dust emission.Comment: Accepted for publication in A&A; 12 pages, 5 figures, 2 table

A combination of soluble helper factors bypasses the requirement for stimulator cells and induces nonspecific cytotoxic T cell responses

The specificity of cytotoxic T lymphocyte (CTL) responses generated in the presence of lymphokines was studied. Thymic responder cells were activated in the presence of stimulator cells that differed in their metabolic activity. After 5 days of culture, the cytotoxic response was estimated in a 4-h 51Cr-release test. Coculture of thymic responders with irradiated splenic stimulator cells in the presence of interleukin 2(IL 2) led to preferential cytolysis of target cells that expressed the same histocompatibility antigens as the cells used for sensitization. Addition of T cell cytotoxicity-inducing factor 1 (TCF1), however, to those cultures made the presence of stimulator cells unnecessary and induced cytotoxic responses against all target cells tested, including target cells syngeneic to the responder cells. This activation was neither due to contaminating mitogen nor to the effect of heterologous serum in the assay system. The conclusion of these findings was that either polyclonal activation of CTL was induced by TCF1 or that some specific CTL clones differentiated into unrestricted killer cells under the influence of TCF1

A glance beyond the quantum model

One of the most important problems in Physics is how to reconcile Quantum Mechanics with General Relativity. Some authors have suggested that this may be realized at the expense of having to drop the quantum formalism in favor of a more general theory. However, as the experiments we can perform nowadays are far away from the range of energies where we may expect to observe non-quantum effects, it is difficult to theorize at this respect. Here we propose a fundamental axiom that we believe any reasonable post-quantum theory should satisfy, namely, that such a theory should recover classical physics in the macroscopic limit. We use this principle, together with the impossibility of instantaneous communication, to characterize the set of correlations that can arise between two distant observers. Although several quantum limits are recovered, our results suggest that quantum mechanics could be falsified by a Bell-type experiment if both observers have a sufficient number of detectors

Redshift and velocity dispersion of the cluster of galaxies around NGC 326

Redshifts of several galaxies thought to be associated with NGC 326 are determined. The results confirm the presence of a cluster and find a mean redshift of z = 0.0477 +/- 0.0007 and a line-of-sight velocity dispersion sigma_{z} = 599 (+230, -110) km/s. The velocity dispersion and previously measured X-ray gas temperature of kT ~ 1.9 keV are consistent with the cluster sigma_{z}/kT relation, and NGC 326 is seen to be a slowly-moving member of the cluster.Comment: 3 pages, to appear in MNRA