Preliminary Results for LP VPE X-Ray Detectors

Thick epitaxial layers have been grown using Low Pressure Vapour Phase Epitaxy techniques with low free carrier concentrations . This type of material is attractive as a medium for X-ray detection, because of its high conversion efficiency for X-rays in the medically interesting energy range.Comment: 4 pages. PS file only - original in WORD. Also available at http://ppewww.ph.gla.ac.uk/preprints/97/07

Basic Scale on Insomnia complaints and Quality of Sleep (BaSIQS): Reliability, initial validity and normative scores in higher education students

Based on successive samples totaling more than 5000 higher education students, we scrutinized the reliability, structure, initial validity and normative scores of a brief self-report seven-item scale to screen for the continuum of nighttime insomnia complaints/perceived sleep quality, used by our team for more than a decade, henceforth labeled the Basic Scale on Insomnia complaints and Quality of Sleep (BaSIQS). In study/sample 1 (n = 1654), the items were developed based on part of a larger survey on higher education sleep-wake patterns. The test-retest study was conducted in an independent small group (n = 33) with a 2-8 week gap. In study/sample 2 (n = 360), focused mainly on validity, the BaSIQS was completed together with the Pittsburgh Sleep Quality Index (PSQI). In study 3, a large recent sample of students from universities all over the country (n = 2995) answered the BaSIQS items, based on which normative scores were determined, and an additional question on perceived sleep problems in order to further analyze the scale's validity. Regarding reliability, Cronbach alpha coefficients were systematically higher than 0.7, and the test-retest correlation coefficient was greater than 0.8. Structure analyses revealed consistently satisfactory two-factor and single-factor solutions. Concerning validity analyses, BaSIQS scores were significantly correlated with PSQI component scores and overall score (r = 0.652 corresponding to a large association); mean scores were significantly higher in those students classifying themselves as having sleep problems (p < 0.0001, d = 0.99 corresponding to a large effect size). In conclusion, the BaSIQS is very easy to administer, and appears to be a reliable and valid scale in higher education students. It might be a convenient short tool in research and applied settings to rapidly assess sleep quality or screen for insomnia complaints, and it may be easily used in other populations with minor adaptations.Projects: LEIES (FCGPortugal); SPASHE (FCT-Portugal); Research Units CCPSF / CIECC (FCT-Portugal)

Recent results on GaAs detectors - 137

The present understanding of the charge collection in GaAs detectors with respect to the materials used and its processing are discussed. The radiation induced degradation of the charge collection efficiency and the leakage current of the detectors are summarised. The status of strip and pixel detectors for the ATLAS experiment are reported along with the latest results from GaAs X-ray detectors for non-high energy physics applications.Comment: 7 pages. 4 postscript figures + 1 postscript preprint logo + 1 LaTeX file + 1 style file. Also available at http://ppewww.ph.gla.ac.uk/preprints/97/05

Test beam Characterizations of 3D Silicon Pixel detectors

3D silicon detectors are characterized by cylindrical electrodes perpendicular to the surface and penetrating into the bulk material in contrast to standard Si detectors with planar electrodes on its top and bottom. This geometry renders them particularly interesting to be used in environments where standard silicon detectors have limitations, such as for example the radiation environment expected in an LHC upgrade. For the first time, several 3D sensors were assembled as hybrid pixel detectors using the ATLAS-pixel front-end chip and readout electronics. Devices with different electrode configurations have been characterized in a 100 GeV pion beam at the CERN SPS. Here we report results on unirradiated devices with three 3D electrodes per 50 x 400 um2 pixel area. Full charge collection is obtained already with comparatively low bias voltages around 10 V. Spatial resolution with binary readout is obtained as expected from the cell dimensions. Efficiencies of 95.9% +- 0.1 % for tracks parallel to the electrodes and of 99.9% +- 0.1 % at 15 degrees are measured. The homogeneity of the efficiency over the pixel area and charge sharing are characterized.Comment: 5 pages, 7 figure

Associations between sleep quality and domains of quality of life in a non-clinical sample: results from higher education students

The association between sleep quality and quality of life (QoL) in clinical samples diagnosed with sleep disorders, mental disorders, or other medical conditions has been widely investigated. However, few studies focused on this relationship in samples of mostly young and healthy adults. This study analyzed the associations between sleep quality and several dimensions of QoL in higher education students and examined whether or not sleep quality would significantly predict QoL after statistically controlling for psychopathological symptoms

Multifunctional Fetishism: Neoliberal Restructuring And The Valorization Of European Agriculture

This thesis conceptualizes the transformation of food from a source of cultural and social reproduction into a commodity for speculation and bargaining as a central component of neoliberal agricultural reforms. Within this framework, I underscore how the emergence of market-based strategies for the valorization of agricultural multifunctionality in Europe has deepened the subjection of agriculture and food to circuits of capital accumulation, rather than promoting the development of ecologically sustainable and socially embedded farming systems. In particular, I analyze how the strategic deployment of a Euro-centric notion of multifunctionality has allowed for the retention of subsidies decoupled from production which are compliant with WTO demands of trade liberalization and benefit large producers and food industries operating on a world scale. Correspondingly, I argue that the discourse of multifunctionality promoted by the EU is closely associated with the deployment of neoliberal concepts of self-help, social capital, and value-adding which seek to justify the contested withdrawal of the state from the provision of public support to small scale producers. As such, the commercialization of agriculture?s multiple functions has become a focal site of resistance for farmers? movements and rural communities across Europe advocating for an alternative model of agricultural development premised on the notion of food sovereignty. In this respect, the thesis concludes by focusing on forms of agrarian politics which seeks to transcend the structural contradictions of the neoliberal project of agricultural restructuring by re-embedding agriculture and food in their social and ecological foundations

First fabrication of full 3D-detectors at SINTEF

3D-detectors, with electrodes penetrating through the entire substrates have drawn great interests for high energy physics and medical imaging applications. Since its introduction by C. Kenney et al in 1995, many laboratories have begun research on different 3D-detector structures to simplify and industrialise the fabrication process. SINTEF MiNaLab joined the 3D collaboration in 2006 and started the first 3D fabrication run in 2007. This is the first step in an effort to fabricate affordable 3D-detectors in small to medium size production volumes. The first run was fully completed in February 2008 and preliminary results are promising. Good p-n junction characteristics have been shown on selected devices at the chip level with a leakage current of less than 0.5 nA per pixel. Thus SINTEF is the second laboratory in the world after the Stanford Nanofabrication Facility that has succeeded in demonstrating full 3D-detectors with active edge. A full 3D-stacked detector system were formed by bump-bonding the detectors to the ATLAS readout electronics, and successful particle hit maps using an Am-241 source were recorded. Most modules, however, showed largely increased leakage currents after assembly, which is due to the active edge and p-spray acting as part of the total chip pn-junction and not as a depletion stop. This paper describes the first fabrication and the encountered processing issues. The preliminary measurements on both the individual detector chips and the integrated 3D-stacked modules are discussed. A new lot has now been started on p-type wafers, which offers a more robust configuration with the active edge acting as depletion stop instead of part of the pn-junction. © 2009 IOP Publishing Ltd and SISSA

Semiconductor Pixel Detectors for Imaging Applications

In this thesis the work is presented as follows: Chapter 1 introduces the ideal detector characteristics for medical imaging. The requirements of the ideal diagnostic method are related to the various types of medical examinations, comparing the existing techniques and discussing results of Monte Carlo simulation studies. A review of existing detectors based on semiconductor microstrip and semiconductor pixel detectors introduces the hybrid Omega family, the pixel readout electronics used by the author for the tests presented in the following chapters. Chapter 2 describes a material defect characterisation study of semi-insulating gallium arsenide using a near-infrared absorption technique. Generally this technique is applied to "as-grown" materials but in this case, using a set-up proposed by the author, the concentration of the deep defect EL2 was monitored in a biased detector for different values of the applied electric field. The results obtained seem to support a theoretical model which predicts the presence of a "quasi"-neutral region inside the detector active volume. The tests performed by the author using silicon and gallium arsenide pixel detectors coupled with the Omega2 and Omega3 read-out electronics are discussed in Chapter 3. The results reported include images of phantoms of different contrasts illuminated by X-ray sources, biological samples traced with beta- emitters and pixel detector characterisation using particle beams. Chapter 4 describes the characterisation made by the author of a photosensitive version of the silicon pixel detector associated with the OmegaD and Omega2 read-out electronics. The tests were performed using light sources at different wavelengths, scintillating plastic fibres and scintillating crystals excited by radioactive sources and particle beams. The aim of this study was the search for a fast, high spatial resolution alternative to CCDs and multi-anodes photomultipliers for scintillating fibre particle tracking and for nuclear medicine based on scintillating crystals. The advantages and limitations of the present system are discussed with possible future improvements The final chapter draws some conclusions about the work reported and offers some considerations for future developments. In particular, a description is given of a new pixel detector electronics chip with single photon counting capabilities, which followed the experience gained with the present versions of the Omega family electronics. The new electronics chip consists of a 64 x 64 array of pixels, each measuring 170 x 170 mum2 and including a 15-bit binary counter. This chip is therefore extremely well-matched to a wide range of X-ray imaging applications, some of which are reviewed here

Photocatalytic oxidation of glucose and cellobiose using TiO2 supported bimetallic nanoparticles.

There is a growing interest in developing new photocatalytic routes for biomass upgrade to chemicals and fuels, but despite of some recent progress this remains an area in infancy. The ultimate aim is to convert hemicellulose, cellulose and lignin into valuable platform chemicals using green processes, there is a need to find model compounds to mimic their properties and obtain fundamental understanding of the chemistry. For this reason, cellobiose is used as model compound for cellulose because of its dimer structure, whilst glucose is cheap, easily sourced, and very abundant as the monomeric unit of cellulose, the most abundant polymer on earth, which presents great potential for commercial applications and its upgrade via selective oxidation reactions is highly desirable. However, for oxidation processes, photocatalysis is typically associated with total mineralisation reactions. In this PhD thesis will be presented for the first time the visible light mediated selective photo-catalytic oxidation of glucose and cellobiose with +98% selectivity to partial oxidation products and a near total suppression of the mineralization pathway. In this study three different experimental set-ups were used. A photoreactor equipped with UVA lamps for a total power of 112 W, a 300 and 1000 W Xenon lamps equipped with visible light filters with a cut-off wavelength of 420 nm. Typically, 40 mg of catalyst were suspended in H2O and exposed to visible light for different reaction times from 2-24h at room temperature. TiO2-P25 displayed significant activity under visible light when glucose and cellobiose were used as substrates. Nonetheless, the decoration of the surface of the support with the metal nanoparticles enhances the overall activity of the catalyst achieving 100% cellobiose conversion in under UVA light in under 2 hours at room temperature. With the addition of the 1 wt% AuAg nanoparticles with different molar ratios to the surface of the TiO2 support, cellobiose conversions of up to 30% were observed. Under UVA light the AuAg catalysts displayed a 100% cellobiose conversion with the presence of the partial oxidation products and the oxidation products coming from the hydrolysis of cellobiose. The reaction conditions were optimized by controlling the catalyst to substrate ratio, the light source power and the wavelength range. The catalysts were recycled 3 times with no significant loss of activity or changes in the product distribution values and were characterized with ICP, XRD, XPS, TEM and solid UV-Vis. This study attempts to apply a systematic approach towards the understanding of photocatalytic reactions, specifically focusing on the possibility of upgrading glucose and cellobiose to valuable chemicals. The reactivity of sugars when exposed to UV light and metal supported catalysts has been reported in the literature, but for the first time, this work tries to combine the production of the gaseous products (H2 and CO2) along with the presence of partially oxidised products in the aqueous phase with a new global reaction mechanism which takes into account what are believed to be the two main competitive reaction pathways, the Ruff degradation, and the alpha scission of sugars. This study can be transferred to other bio-derived molecules to get a better understanding on how to optimize and exploit photoactive materials to upgrade biomass under mild conditions and emphasises the crucial role of the Au and Ag metal nanoparticles present on the surface towards extending the activity range in the visible part of the spectrum