The Crab pulsar and its red knot in the near-infrared

We present near-infrared observations obtained with ISAAC on the VLT of the Crab pulsar and its environment. Photometry of the pulsar in Js, H and Ks shows the pulsar spectrum to extend fairly smoothly from the UV/optical regime. PSF subtraction of the pulsar allows us to study its immediate neighborhood in some detail. In particular, the knot positioned just 0.6 arcsec from the pulsar has been revealed in the IR. Using also archival HST data for the knot, we have measured its broad band spectrum to rise steeply into the IR, in contrast to the spectrum of the pulsar itself.Comment: Accepted by A&

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&

Desacetyl-α-melanocyte stimulating hormone and α-melanocyte stimulating hormone are required to regulate energy balance.

OBJECTIVE: Regulation of energy balance depends on pro-opiomelanocortin (POMC)-derived peptides and melanocortin-4 receptor (MC4R). Alpha-melanocyte stimulating hormone (α-MSH) is the predicted natural POMC-derived peptide that regulates energy balance. Desacetyl-α-MSH, the precursor for α-MSH, is present in brain and blood. Desacetyl-α-MSH is considered to be unimportant for regulating energy balance despite being more potent (compared with α-MSH) at activating the appetite-regulating MC4R in vitro. Thus, the physiological role for desacetyl-α-MSH is still unclear. METHODS: We created a novel mouse model to determine whether desacetyl-α-MSH plays a role in regulating energy balance. We engineered a knock in targeted QKQR mutation in the POMC protein cleavage site that blocks the production of both desacetyl-α-MSH and α-MSH from adrenocorticotropin (ACTH1-39). RESULTS: The mutant ACTH1-39 (ACTHQKQR) functions similar to native ACTH1-39 (ACTHKKRR) at the melanocortin 2 receptor (MC2R) in vivo and MC4R in vitro. Male and female homozygous mutant ACTH1-39 (Pomctm1/tm1) mice develop the characteristic melanocortin obesity phenotype. Replacement of either desacetyl-α-MSH or α-MSH over 14 days into Pomctm1/tm1 mouse brain significantly reverses excess body weight and fat mass gained compared to wild type (WT) (Pomcwt/wt) mice. Here, we identify both desacetyl-α-MSH and α-MSH peptides as regulators of energy balance and highlight a previously unappreciated physiological role for desacetyl-α-MSH. CONCLUSIONS: Based on these data we propose that there is potential to exploit the naturally occurring POMC-derived peptides to treat obesity but this relies on first understanding the specific function(s) for desacetyl-α-MSH and α-MSH

Svestka's Research: Then and Now

Zdenek Svestka's research work influenced many fields of solar physics, especially in the area of flare research. In this article I take five of the areas that particularly interested him and assess them in a "then and now" style. His insights in each case were quite sound, although of course in the modern era we have learned things that he could not readily have envisioned. His own views about his research life have been published recently in this journal, to which he contributed so much, and his memoir contains much additional scientific and personal information (Svestka, 2010).Comment: Invited review for "Solar and Stellar Flares," a conference in honour of Prof. Zden\v{e}k \v{S}vestka, Prague, June 23-27, 2014. This is a contribution to a Topical Issue in Solar Physics, based on the presentations at this meeting (Editors Lyndsay Fletcher and Petr Heinzel

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

Direct detection of peptide hormones from single pancreatic islets using MALDI-TOF MS

This presentation describes a novel application of a method based on direct tissue mass spectrometry that has been shown to consistently detect whole peptide secretions from individual isolated rat pancreatic islets. Somewhat surprisingly, the most prominent peaks corresponded to peptides known to be secreted from pancreatic islets and peak intensities corresponded well with expected secretion quantities. Expected islet responses to diabetes were also observed. Possible mechanisms by which these peptides are extracted by laser ionisation will be discussed. This method has potential to provide further insights into the physiology and control of pancreatic islet secretions as well as providing a rapid method for research and clinical assessment of islet function