The relative and absolute timing accuracy of the EPIC-pn camera on XMM-Newton, from X-ray pulsations of the Crab and other pulsars

Reliable timing calibration is essential for the accurate comparison of XMM-Newton light curves with those from other observatories, to ultimately use them to derive precise physical quantities. The XMM-Newton timing calibration is based on pulsar analysis. However, as pulsars show both timing noise and glitches, it is essential to monitor these calibration sources regularly. To this end, the XMM-Newton observatory performs observations twice a year of the Crab pulsar to monitor the absolute timing accuracy of the EPIC-pn camera in the fast Timing and Burst modes. We present the results of this monitoring campaign, comparing XMM-Newton data from the Crab pulsar (PSR B0531+21) with radio measurements. In addition, we use five pulsars (PSR J0537-69, PSR B0540-69, PSR B0833-45, PSR B1509-58 and PSR B1055-52) with periods ranging from 16 ms to 197 ms to verify the relative timing accuracy. We analysed 38 XMM-Newton observations (0.2-12.0 keV) of the Crab taken over the first ten years of the mission and 13 observations from the five complementary pulsars. All the data were processed with the SAS, the XMM-Newton Scientific Analysis Software, version 9.0. Epoch folding techniques coupled with \chi^{2} tests were used to derive relative timing accuracies. The absolute timing accuracy was determined using the Crab data and comparing the time shift between the main X-ray and radio peaks in the phase folded light curves. The relative timing accuracy of XMM-Newton is found to be better than 10^{-8}. The strongest X-ray pulse peak precedes the corresponding radio peak by 306\pm9 \mus, which is in agreement with other high energy observatories such as Chandra, INTEGRAL and RXTE. The derived absolute timing accuracy from our analysis is \pm48 \mus.Comment: 16 pages, 9 figures. Accepted for publication on A&

High-time Resolution Astrophysics and Pulsars

The discovery of pulsars in 1968 heralded an era where the temporal characteristics of detectors had to be reassessed. Up to this point detector integration times would normally be measured in minutes rather seconds and definitely not on sub-second time scales. At the start of the 21st century pulsar observations are still pushing the limits of detector telescope capabilities. Flux variations on times scales less than 1 nsec have been observed during giant radio pulses. Pulsar studies over the next 10 to 20 years will require instruments with time resolutions down to microseconds and below, high-quantum quantum efficiency, reasonable energy resolution and sensitive to circular and linear polarisation of stochastic signals. This chapter is review of temporally resolved optical observations of pulsars. It concludes with estimates of the observability of pulsars with both existing telescopes and into the ELT era.Comment: Review; 21 pages, 5 figures, 86 references. Book chapter to appear in: D.Phelan, O.Ryan & A.Shearer, eds.: High Time Resolution Astrophysics (Astrophysics and Space Science Library, Springer, 2007). The original publication will be available at http://www.springerlink.co

Cephazolin and Gentamicin are stable in lactate-buffered Fresenius peritoneal Dialysate for seven days at room temperature

Peritoneal dialysis (PD) peritonitis is a common complication of PD and is associated with significant morbidity and mortality (1). Treatment involves intraperitoneal delivery of antibiotics, which, for this condition, is superior to the intravenous route (2). Outpatient treatment involves loading antibiotics into bags of dialysate, which are then self-administered. However, some patients are unable to load the antibiotics themselves and therefore rely on pre-loaded bags provided to them by health care staff. Treatment for PD peritonitis is usually required for no less than 14 days, and it is desirable to pre-load at least several days’ worth of bags for convenient outpatient therapy (3). That pre-loading in turn depends on the stability of the required antibiotic in solution under conditions of home storage. However, relevant data on antibiotic stability is limited to just some of the available PD solutions and containers (4-7). Guidelines, such as those published by the International Society for Peritoneal Dialysis provide information about the stability and compatibility of various antibiotics in peritoneal dialysate, although they note the limited data for specific PD solutions and suggest the need for further study (3). It has also been suggested by others that data obtained from experiments in one solution or system cannot be extrapolated to another (4). A commonly used PD system is the polyvinyl chloride twin-bagged lactate-buffered glucose-based solution from Fresenius (ANDY-Plus/Disc: Fresenius Medical Care, Bad Homburg, Germany). The stability of antibiotics in this system has not been widely studied and cannot be confirmed by the manufacturer. The aim of the present study was therefore to assess the stability of cephazolin and gentamicin in that dialysate under conditions that simulate up to 7 days of home storage, to ensure effective and convenient use for outpatient treatment of PD peritonitis

Poly-γ-glutamylation of biomolecules

Abstract Poly-γ-glutamate tails are a distinctive feature of archaeal, bacterial, and eukaryotic cofactors, including the folates and F420. Despite decades of research, key mechanistic questions remain as to how enzymes successively add glutamates to poly-γ-glutamate chains while maintaining cofactor specificity. Here, we show how poly-γ-glutamylation of folate and F420 by folylpolyglutamate synthases and γ-glutamyl ligases, non-homologous enzymes, occurs via processive addition of L-glutamate onto growing γ-glutamyl chain termini. We further reveal structural snapshots of the archaeal γ-glutamyl ligase (CofE) in action, crucially including a bulged-chain product that shows how the cofactor is retained while successive glutamates are added to the chain terminus. This bulging substrate model of processive poly-γ-glutamylation by terminal extension is arguably ubiquitous in such biopolymerisation reactions, including addition to folates, and demonstrates convergent evolution in diverse species from archaea to humans