Neutrinos and Gamma Rays from Galaxy Clusters

The next generation of neutrino and gamma-ray detectors should provide new insights into the creation and propagation of high-energy protons within galaxy clusters, probing both the particle physics of cosmic rays interacting with the background medium and the mechanisms for high-energy particle production within the cluster. In this paper we examine the possible detection of gamma-rays (via the GLAST satellite) and neutrinos (via the ICECUBE and Auger experiments) from the Coma cluster of galaxies, as well as for the gamma-ray bright clusters Abell 85, 1758, and 1914. These three were selected from their possible association with unidentified EGRET sources, so it is not yet entirely certain that their gamma-rays are indeed produced diffusively within the intracluster medium, as opposed to AGNs. It is not obvious why these inconspicuous Abell-clusters should be the first to be seen in gamma-rays, but a possible reason is that all of them show direct evidence of recent or ongoing mergers. Their identification with the EGRET gamma-ray sources is also supported by the close correlation between their radio and (purported) gamma-ray fluxes. Under favorable conditions (including a proton spectral index of 2.5 in the case of Abell 85, and sim 2.3 for Coma, and Abell 1758 and 1914), we expect ICECUBE to make as many as 0.3 neutrino detections per year from the Coma cluster of galaxies, and as many as a few per year from the Abell clusters 85, 1758, and 1914. Also, Auger may detect as many as 2 events per decade at ~ EeV energies from these gamma-ray bright clusters.Comment: Accepted for publication in Ap

The dose of hemodialysis and patient mortality

The dose of hemodialysis and patient mortality. The relationship between the delivered dose of hemodialysis and patient mortality remains somewhat controversial. Several observational studies have shown improved patient survival with higher levels of delivered dialysis dose. However, several other unmeasured variables, changes in patient mix or medical management may have impacted on this reported difference in mortality. The current study of a U.S. national sample of 2,311 patients from 347 dialysis units estimates the relationship of delivered hemodialysis dose to mortality, with a statistical adjustment for an extensive list of comorbidity/risk factors. Additionally this study investigated the existence of a dose beyond which more dialysis does not appear to lower mortality. We estimated patient survival using proportional hazards regression techniques, adjusting for 21 patient comorbidity/risk factors with stratification for nine Census regions. The patient sample was 2,311 Medicare hemodialysis patients treated with bicarbonate dialysate as of 12/31/90 who had end-stage renal disease for at least one year. Patient follow-up ranged between 1.5 and 2.4 years. The measurement of delivered therapy was based on two alternative measures of intradialytic urea reduction, the urea reduction ratio (URR) and Kt/V (with adjustment for urea generation and ultrafiltration). Hemodialysis patient mortality showed a strong and robust inverse correlation with delivered hemodialysis dose whether measured by Kt/V or by URR. Mortality risk was lower by 7% (P = 0.001) with each 0.1 higher level of delivered Kt/V. (Expressed in terms of URR, mortality was lower by 11% with each 5 percentage point higher URR; P = 0.001). Above a URR of 70% or a Kt/V of 1.3 these data did not provide statistical evidence of further reductions in mortality. In conclusion, the delivered dose of hemodialysis therapy is an important predictor of patient mortality. In a population of dialysis patients with a very high mortality rate, it appears that increasing the level of delivered therapy offers a practical and efficient means of lowering the mortality rate. The level of hemodialysis dose measured by URR or Kt/V beyond which the mortality rate does not continue to decrease, though not well defined with this study, appears to be above current levels of typical treatment of hemodialysis patients in the U.S

Electrophysiological correlates of high-level perception during spatial navigation

We studied the electrophysiological basis of object recognition by recording scalp\ud electroencephalograms while participants played a virtual-reality taxi driver game.\ud Participants searched for passengers and stores during virtual navigation in simulated\ud towns. We compared oscillatory brain activity in response to store views that were targets or\ud nontargets (during store search) or neutral (during passenger search). Even though store\ud category was solely defined by task context (rather than by sensory cues), frontal ...\ud \u

Chandra Observation of V426 Oph: Weighing the Evidence for a Magnetic White Dwarf

We report the results of a 45 ks Chandra observation of the cataclysmic variable V426 Ophiuchus. The high resolution spectrum from the high-energy transmission grating spectrometer is most consistent with a cooling flow model, placing V426 Oph among the group of CVs including U Gem and EX Hya. An uninterrupted lightcurve was also constructed, in which we detect a significant 4.2 hr modulation together with its first harmonic at 2.1 hrs. Reanalysis of archival Ginga, and ROSAT X-ray lightcurves also reveals modulations at periods consistent with 4.2 and/or 2.1 hrs. Furthermore, optical photometry in V, simultaneous with the Chandra observation, indicates a modulation anti-correlated with the X-ray, and later more extensive R band photometry finds a signal at ~2.1 hrs. The earlier reported X-ray periods at ~0.5 and 1 hrs appear to be only transient and quasi-periodic in nature. In contrast, the 4.2 hr period or its harmonic are stable and persistent in X-ray/optical data from 1988 to 2003. This periodicity is clearly distinct from the 6.85 hr orbit, and could be due to the spin of the white dwarf. If this is the case, V426 Oph would be the first long period intermediate polar with a ratio P_spin/P_orb of 0.6. However, this interpretation requires unreasonable values of magnetic field strength and mass accretion rate.Comment: 11 pages, 7 figures, 5 tables. Accepted for publication in the Astrophysical Journal (to appear August 2004

Books in the News in Cromwellian England

This article offers detailed analysis of the patterns of book advertising in Marchamont Nedham’s government-sponsored newsbook, Mercurius Politicus. It contends that, for a brief period, Politicus was the nearest thing that the mid-seventeenth century had to a literary periodical and contests standard accounts that Politicus was only successful because government monopoly made it so. Instead I show that Politicus was instrumental in creating an image of the Commonwealth and Protectorate as a Republic of Letters; the cheap print of its small advertisements insisted that the publication of a book was an event, that London was a city of the book, and that its inhabitants might respond to the uncertainty of political revolution by eagerly imagining a future comprised of new books as yet unread