A New Analysis Method for Reconstructing the Arrival Direction of TeV Gamma-rays Using a Single Imaging Atmospheric Cherenkov Telescope

We present a method of atmospheric Cherenkov imaging which reconstructs the unique arrival direction of TeV gamma rays using a single telescope. The method is derived empirically and utilizes several features of gamma-ray induced air showers which determine, to a precision of 0.12 degrees, the arrival direction of photons, on an event-by-event basis. Data from the Whipple Observatory's 10 m gamma-ray telescope is utilized to test selection methods based on source location. The results compare these selection methods with traditional techniques and three different camera fields of view. The method will be discussed in the context of a search for a gamma-ray signal from a point source located anywhere within the field of view and from regions of extended emission.Comment: 24 pages, 16 figures, accepted for publication in Astroparticle Physics May 11, 200

Beings in their own right? Exploring Children and young people's sibling and twin relationships in the Minority World

This paper examines the contributions that the sociological study of sibship and twinship in the Minority World can make to childhood studies. It argues that, in providing one forum within which to explore children and young people's social relationships, we can add to our understanding of children and young people's interdependence and develop a more nuanced understanding of agency. As emergent subjects, children, young people and adults are in a process of ‘becoming’. However, this does not mean that they can ‘become’ anything they choose to. The notion of negotiated interdependence (Punch 2002) is useful in helping us to grasp the contingent nature of children and young people's agency

Design of light concentrators for Cherenkov telescope observatories

The Cherenkov Telescope Array (CTA) will be the largest cosmic gamma ray detector ever built in the world. It will be installed at two different sites in the North and South hemispheres and should be operational for about 30 years. In order to cover the desired energy range, the CTA is composed of typically 50-100 collecting telescopes of various sizes (from 6 to 24-m diameters). Most of them are equipped with a focal plane camera consisting of 1500 to 2000 Photomultipliers (PM) equipped with light concentrating optics, whose double function is to maximize the amount of Cherenkov light detected by the photo-sensors, and to block any stray light originating from the terrestrial environment. Two different optical solutions have been designed, respectively based on a Compound Parabolic Concentrator (CPC), and on a purely dioptric concentrating lens. In this communication are described the technical specifications, optical designs and performance of the different solutions envisioned for all these light concentrators. The current status of their prototyping activities is also given

A Spectacular VHE Gamma-Ray Outburst from PKS 2155-304 in 2006

Since 2002 the VHE (>100 GeV) gamma-ray flux of the high-frequency peaked BL Lac PKS 2155-304 has been monitored with the High Energy Stereoscopic System (HESS). An extreme gamma-ray outburst was detected in the early hours of July 28, 2006 (MJD 53944). The average flux above 200 GeV observed during this outburst is ~7 times the flux observed from the Crab Nebula above the same threshold. Peak fluxes are measured with one-minute time scale resolution at more than twice this average value. Variability is seen up to ~600 s in the Fourier power spectrum, and well-resolved bursts varying on time scales of ~200 seconds are observed. There are no strong indications for spectral variability within the data. Assuming the emission region has a size comparable to the Schwarzschild radius of a ~10^9 solar mass black hole, Doppler factors greater than 100 are required to accommodate the observed variability time scales.Comment: 4 pages, 3 figures; To appear in the Proceedings of the 30th ICRC (Merida, Mexico

Reanalysis of Data Taken by the CANGAROO 3.8 Meter Imaging Atmospheric Cherenkov Telescope: PSR B1706-44, SN 1006, and Vela

We have reanalyzed data from observations of PSR B1706-44, SN 1006, and the Vela pulsar region made with the CANGAROO 3.8 m imaging atmospheric Cherenkov telescope between 1993 and 1998 in response to the results reported for these sources by the H.E.S.S. collaboration. In our reanalysis, in which gamma-ray selection criteria have been determined exclusively using gamma-ray simulations and OFF-source data as background samples, no significant TeV gamma-ray signals have been detected from compact regions around PSR B1706-44 or within the northeast rim of SN 1006. We discuss reasons why the original analyses gave the source detections. The reanalysis did result in a TeV gamma-ray signal from the Vela pulsar region at the 4.5 sigma level using 1993, 1994, and 1995 data. The excess was located at the same position, 0.13 deg. to the southeast of the Vela pulsar, as that reported in the original analysis. We have investigated the effect of the acceptance distribution in the field of view of the 3.8 m telescope, which rapidly decreases toward the edge of the field of the camera, on the detected gamma-ray morphology. The expected excess distribution for the 3.8 m telescope has been obtained by reweighting the distribution of HESS J0835-455 measured by H.E.S.S. with the acceptance of the 3.8 m telescope. The result is morphologically comparable to the CANGAROO excess distribution, although the profile of the acceptance-reweighted H.E.S.S. distribution is more diffuse than that of CANGAROO. The integral gamma-ray flux from HESS J0835-455 has been estimated for the same region as defined by H.E.S.S. from the 1993-1995 data of CANGAROO to be F(> 4.0 +/- 1.6 TeV) = (3.28 +/- 0.92) x 10^{-12} photons cm^{-2} s^{-1}, which is statistically consistent with the integral flux obtained by H.E.S.S.Comment: Published in ApJ, minor improvement

Generationing development

The articles in this special issue present a persuasive case for accounts of development to recognise the integral and fundamental roles played by age and generation. While the past two decades have witnessed a burgeoning of literature demonstrating that children and youth are impacted by development, and that they can and do participate in development, the literature has tended to portray young people as a special group whose perspectives should not be forgotten. By contrast, the articles collected here make the case that age and generation, as relational constructs, cannot be ignored. Appropriating the term ‘generationing’, the editors argue that a variety of types of age relations profoundly structure the ways in which societies are transformed through development – both immanent processes of neoliberal modernisation and the interventions of development agencies that both respond and contribute to these. Drawing on the seven empirical articles, I attempt to draw some of the ideas together into a narrative that further argues the case for ‘generationing’ but also identifies gaps, questions and implications for further research

Optimizing projectional radiographic imaging of the abdomen of obese patients: an e-Delphi study

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Purpose: Obesity is increasing in prevalence globally, with increased demands placed on radiology departments to image obese patients to assist with diagnosis and management. The aim of this study was to determine perceived best practice techniques currently used in clinical practice for projectional radiography of the abdomen for obese patients with the aim to help elucidate areas for future research and education needs in this field. Experimental Design: A two round e-Delphi study was undertaken to establish a consensus within a reference group of expert Australian clinical educator diagnostic radiographers (CEDRs). Initially, a conceptual map of issues regarding imaging obese patients was undertaken by analysing interview transcripts of 12 CEDRs. This informed an online questionnaire design used in Delphi rounds 1 and 2. A consensus threshold was set <75% “agreement/disagreement”, with 15 and 14 CEDRs participating in rounds 1 and 2, respectively. Results: Seven of the 11 statements reach consensus after round 2. Consensus on using a combination of higher peak kilovoltage (kVp) and milliampere-seconds (mAs) to increase radiation exposure increased source-to-image distance and tighter collimation was achieved. There was no consensus regarding patient positioning practices or patient communication strategies. The expert group reported the importance of personal confidence and treating patients as individuals when applying techniques. Conclusion: Diversity of experts' opinions and current practice may be due to the variations in obese patients’ size and presentation. Therefore, there is a need for extensive empirical evidence to underpin practice and education resources for radiographers when imaging obese patients