X-Ray Spectroscopy of Stars

(abridged) Non-degenerate stars of essentially all spectral classes are soft X-ray sources. Low-mass stars on the cooler part of the main sequence and their pre-main sequence predecessors define the dominant stellar population in the galaxy by number. Their X-ray spectra are reminiscent, in the broadest sense, of X-ray spectra from the solar corona. X-ray emission from cool stars is indeed ascribed to magnetically trapped hot gas analogous to the solar coronal plasma. Coronal structure, its thermal stratification and geometric extent can be interpreted based on various spectral diagnostics. New features have been identified in pre-main sequence stars; some of these may be related to accretion shocks on the stellar surface, fluorescence on circumstellar disks due to X-ray irradiation, or shock heating in stellar outflows. Massive, hot stars clearly dominate the interaction with the galactic interstellar medium: they are the main sources of ionizing radiation, mechanical energy and chemical enrichment in galaxies. High-energy emission permits to probe some of the most important processes at work in these stars, and put constraints on their most peculiar feature: the stellar wind. Here, we review recent advances in our understanding of cool and hot stars through the study of X-ray spectra, in particular high-resolution spectra now available from XMM-Newton and Chandra. We address issues related to coronal structure, flares, the composition of coronal plasma, X-ray production in accretion streams and outflows, X-rays from single OB-type stars, massive binaries, magnetic hot objects and evolved WR stars.Comment: accepted for Astron. Astrophys. Rev., 98 journal pages, 30 figures (partly multiple); some corrections made after proof stag

Activism and willingness to help in union organizing : who are the activists?

“The original publication is available at www.springerlink.com” Copyright SpringerResearch on union renewal often cites a critical role for lay activism. This study examines determinants of activism and activism intentions among a broadly representative sample of U.S. union members. Hypotheses are developed from theory and previous research on union commitment and participation. Results for current activism are generally consistent with prior work. Extending the model to future intentions to help with organizing, an interesting contrast is that pro-union attitude influences appear much more important than do union instrumentality perceptions. This suggests that “covenant” rather than “exchange” concerns are more salient for this form of activism. Findings for ideological orientation support this interpretation.Peer reviewe

General feelings toward unions and employers as predictors of union voting intent

“The original publication is available at www.springerlink.com” Copyright Springer [Full text of this article is not available in the UHRA]The union voting intention literature shows that many nonunion employees who indicate that they think unions are instrumental in increasing wages, benefits, and working conditions would vote against forming a union. Although American workers have often been characterized as pragmatic with regard to their support for unions, the “disconnect” between union beliefs and union voting intentions just described suggests that more subtle forces are at work. In this paper, it is shown empirically that union instrumentality is a limited predictor of union voting intentions for a recent national cross-section of workers. Rather, more general feelings toward unions and employers are primary. These accounted for a large portion of the variance in union voting intentions, with general feelings towards unions by far the most critical predictor. A concluding section discusses whether the results may reflect changes in union power and changes in employee views of unions. Areas for future research are discussed.Peer reviewe

FcRn: From Molecular Interactions to Regulation of IgG Pharmacokinetics and Functions

The neonatal Fc receptor, FcRn, is related to MHC class I with respect to its structure and association with β2microglobulin (β2m). However, by contrast with MHC class I molecules, FcRn does not bind to peptides, but interacts with the Fc portion of IgGs and belongs to the Fc receptor family. Unlike the 'classical' Fc receptors, however, the primary functions of FcRn include salvage of IgG (and albumin) from lysosomal degradation through the recycling and transcytosis of IgG within cells. The characteristic feature of FcRn is pH-dependent binding to IgG, with relatively strong binding at acidic pH (&lt;6.5) and negligible binding at physiological pH (7.3-7.4). FcRn is expressed in many different cell types, and endothelial and hematopoietic cells are the dominant cell types involved in IgG homeostasis in vivo. FcRn also delivers IgG across cellular barriers to sites of pathogen encounter and consequently plays a role in protection against infections, in addition to regulating renal filtration and immune complex-mediated antigen presentation. Further, FcRn has been targeted to develop both IgGs with extended half-lives and FcRn inhibitors that can lower endogenous antibody levels. These approaches have implications for the development of longer lived therapeutics and the removal of pathogenic or deleterious antibodies.</p