High Energy Neutrinos and Photons from Curvature Pions in Magnetars

We discuss the relevance of the curvature radiation of pions in strongly magnetized pulsars or magnetars, and their implications for the production of TeV energy neutrinos detectable by cubic kilometer scale detectors, as well as high energy photons.Comment: 19 pages, 4 figures, to appear in JCA

Studies on heavy metal toxicity and accumulation in the catchment area of the Derwent Reservoir

A three year long study has been carried out of the distribution of zinc, lead and cadmium within the water, sediments and submerged plants of the Derwent Reservoir and its catchment These studies have been extended to include detailed field investigations of the accumulation of heavy metals by Lemanea fluviatilis, an alga common in the R. Derwent Further field and laboratory investigations have been carried out of the tolerance to zinc of Stxgeoclonxum tenue. Elevated concentrations of zinc, lead and cadmium were shown to be present, in the water and sediments of the R. Derwent at its point of entry to the Derwent Reservoir. These metals were derived mainly from Bolts Burn, a polluted tributary. This latter stream was found to receive inputs of heavy metals from clearly defined sources within an active fluorspar mine. Although old mine workings were present within the catchment, these had a relatively small effect on the composition of water in Bolts Burn and the R. Derwent. Detailed investigations of the composition of stream and river water enabled various aspects of the behaviour of different fractions of metals to be described and compared in polluted and non-polluted reaches. The concentrations of zinc, lead and cadmium within the water, sediments and submerged plants of the Derwent Reservoir were found to be high when compared with data from other published studies. The pollution of the reservoir with these metals may therefore be regarded as serious. Surveys of the distribution of heavy metals in the water column were carried out at different stages in the filling cycle of the reservoir. These, together with surveys of the composition of sediments and submerged plants, enabled several of the major factors influencing the distribution of metals within the reservoir to be determined. Studies of the accumulation of heavy metals by 47 populations of Lemanea fluviatilis indicated that the alga is a potentially useful 'monitor' of pollution by zinc, lead and cadmium in flowing waters. Although the enrichment ratios for these metals were not constant over a range of concentrations in the water, clear linear relationships were apparent between the concentrations of each metal in the water and in filaments of Lemanea. Intensive sampling from a single population in the R. Derwent demonstrated that a proportion of the zinc content of filaments was sensitive to short term fluctuations in the zinc content of the surrounding water. The results of a series of transplant experiments are also reported. Stigeoclonium tenue was found to be abundant in several streams carrying relatively high concentrations of zinc in the water A study of populations isolated from 35 reaches demonstrated that material growing in higher concentrations of zinc in the field had an enhanced tolerance to zinc. This tolerance was stable during long term culturing, and appeared to have a genetic basis. Assays of populations from harder waters suggested that high concentrations of calcium acted to reduce the toxicity of zinc in the field. Further studies performed in the laboratory demonstrated that increases in pH and the concentrations of magnesium, calcium and phosphate all acted to reduce the toxicity of zinc to Stigeoclonium tenue. However, the effects of these factors on toxicity were found to differ between a zinc sensitive population and a zinc tolerant populatio

Magnetic Photon Splitting: Computations of Proper-time Rates and Spectra

The splitting of photons in the presence of an intense magnetic field has recently found astrophysical applications in polar cap models of gamma-ray pulsars and in magnetar scenarios for soft gamma repeaters. Numerical computation of the polarization-dependent rates of this third order QED process for arbitrary field strengths and energies below pair creation threshold is difficult: thus early analyses focused on analytic developments and simpler asymptotic forms. The recent astrophysical interest spurred the use of the S-matrix approach by Mentzel, Berg and Wunner to determine splitting rates. In this paper, we present numerical computations of a full proper-time expression for the rate of splitting that was obtained by Stoneham, and is exact up to the pair creation threshold. While the numerical results derived here are in accord with the earlier asymptotic forms due to Adler, our computed rates still differ by as much as factors of 3 from the S-matrix re-evaluation of Wilke and Wunner, reflecting the extreme difficulty of generating accurate S-matrix numerics for fields below about \teq{4.4\times 10^{13}}Gauss. We find that our proper-time rates appear very accurate, and exceed Adler's asymptotic specializations significantly only for photon energies just below pair threshold and for supercritical fields, but always by less than a factor of around 2.6. We also provide a useful analytic series expansion for the scattering amplitude valid at low energies.Comment: 13 pages, AASTeX format, including 3 eps figures, ApJ in pres

Use of strategies to improve retention in primary care randomised trials: a qualitative study with in-depth interviews

Objective To explore the strategies used to improve retention in primary care randomised trials.<p></p> Design Qualitative in-depth interviews and thematic analysis.<p></p> Participants 29 UK primary care chief and principal investigators, trial managers and research nurses.<p></p> Methods In-depth face-to-face interviews.<p></p> Results Primary care researchers use incentive and communication strategies to improve retention in trials, but were unsure of their effect. Small monetary incentives were used to increase response to postal questionnaires. Non-monetary incentives were used although there was scepticism about the impact of these on retention. Nurses routinely used telephone communication to encourage participants to return for trial follow-up. Trial managers used first class post, shorter questionnaires and improved questionnaire designs with the aim of improving questionnaire response. Interviewees thought an open trial design could lead to biased results and were negative about using behavioural strategies to improve retention. There was consensus among the interviewees that effective communication and rapport with participants, participant altruism, respect for participant's time, flexibility of trial personnel and appointment schedules and trial information improve retention. Interviewees noted particular challenges with retention in mental health trials and those involving teenagers.<p></p> Conclusions The findings of this qualitative study have allowed us to reflect on research practice around retention and highlight a gap between such practice and current evidence. Interviewees describe acting from experience without evidence from the literature, which supports the use of small monetary incentives to improve the questionnaire response. No such evidence exists for non-monetary incentives or first class post, use of which may need reconsideration. An exploration of barriers and facilitators to retention in other research contexts may be justified.<p></p&gt

ICESat Lidar and Global Digital Elevation Models: Application to DESDynI

Geodetic control is extremely important in the production and quality control of topographic data sets, enabling elevation results to be referenced to an absolute vertical datum. Global topographic data with improved geodetic accuracy achieved using global Ground Control Point (GCP) databases enable more accurate characterization of land topography and its change related to solid Earth processes, natural hazards and climate change. The multiple-beam lidar instrument that will be part of the NASA Deformation, Ecosystem Structure and Dynamics of Ice (DESDynI) mission will provide a comprehensive, global data set that can be used for geodetic control purposes. Here we illustrate that potential using data acquired by NASA's Ice, Cloud and land Elevation Satellite (ICEsat) that has acquired single-beam, globally distributed laser altimeter profiles (+/-86deg) since February of 2003 [1, 2]. The profiles provide a consistently referenced elevation data set with unprecedented accuracy and quantified measurement errors that can be used to generate GCPs with sub-decimeter vertical accuracy and better than 10 m horizontal accuracy. Like the planned capability for DESDynI, ICESat records a waveform that is the elevation distribution of energy reflected within the laser footprint from vegetation, where present, and the ground where illuminated through gaps in any vegetation cover [3]. The waveform enables assessment of Digital Elevation Models (DEMs) with respect to the highest, centroid, and lowest elevations observed by ICESat and in some cases with respect to the ground identified beneath vegetation cover. Using the ICESat altimetry data we are developing a comprehensive database of consistent, global, geodetic ground control that will enhance the quality of a variety of regional to global DEMs. Here we illustrate the accuracy assessment of the Shuttle Radar Topography Mission (SRTM) DEM produced for Australia, documenting spatially varying elevation biases of several meters in magnitude