11,193 research outputs found
Ray L. Jones
No full text"Ray L. Jones SX 25250 27th. Aust Inf. Bn(A.I.F) (S.A.Scottish Regiment) Darwin 1941/43 Now of - Burnside S.A."Ray L. Jones SX 25250. 27th. Australian Infantry Battalion (Australian Imperial Forces) (South Australian Scottish Regiment) Darwin 1941/43. Now of - Burnside South Australia
A search for TeV gamma ray emission from X-ray binary stars
No full textThis work is concerned with the detection of pulsed TeV gamma ray emission from a number of X-ray binary systems by the use of the atmospheric Cerenkov technique. Chapters 1 and 2 give an overview of the development of gamma ray astronomy, with emphasis placed on progress made in the detection of TeV gamma rays by their Cerenkov radiation in the atmosphere. Chapters 3 and 4 describe the University of Durham atmospheric Cerenkov telescopes, which were used to make the observations reported in this work, and the standard data processing and analysis procedures adopted. The main part of the thesis deals with the application of these techniques to observations of five X-ray binaries. After a review of the properties of such objects in Chapter 5, Chapters 6 and 7 deal specifically with the results for two of the systems considered to be among the most likely candidates to give a detectable TeV photon flux; Centaurus X-3 and Vela X-1. A study of all data recorded on Cen X-3 over the course of six years suggests the presence of a weak gamma ray flux pulsed at the X-ray period. Previous reports of stronger emission near the ascending node of the orbit are confirmed here. For Vela X-1, the analysis of a dataset recorded during a single dark moon interval reveals evidence for two short outbursts of pulsed TeV gamma ray emission. Chapter 8 reports the series of observations made of SMC X-1, 4U1626-67 and X0G21-72, and upper limits are placed on the TeV gamma ray emission from each. Finally, the results reported here are compared with the predictions of a number of theoretical models, some of which are found to give good agreement with the limits and detections derived in this work. A discussion of the status of this field and future observational prospects is also given
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Enhanced colour encoding of materials discrimination information for multiple view dual-energy x-ray imaging
No full textThis thesis reports an investigation into dual-energy X-ray discrimination techniques. These techniques are designed to provide colour-coded materials discrimination information in a sequence of perspective images exhibiting sequential parallax. The methods developed are combined with a novel 3D imaging technique employing depth from motion or kinetic depth effect (KDE). This technique when applied to X-ray images is termed KDEX imaging and was developed previously by the university team for luggage screening applications at security checkpoints. A primary motivation for this research is that the dual-energy X-ray techniques, which are routinely incorporated into ‘standard’ 2D luggage scanners, provide relatively crude materials discrimination information. In this work it was critical that robust materials discrimination and colour encoding process was implemented as the sequential parallax exhibited by the KDEX imagery may introduce colour changes, due to the different X-ray beam paths associated with each perspective image. Any introduction of ‘colour noise’ into the resultant image sequences could affect the perception of depth and hinder the ongoing assessment of the potential utility of the dual-energy KDEX technique. Two dual-energy discrimination methods have been developed, termed K-II and W-E respectively. Employing the total amount of attenuation measured at each energy level and the weight fraction of layered structures, a combination of the K-II and the W-E techniques enables the computation and extraction of a target objects’ effective atomic number (Zeff) and its surface density (ρS) in the presence of masking layers
Very high energy cosmic gamma rays from radio and x-ray pulsars
No full textThis thesis is concerned with the detection of very high energy cosmic gamma-rays from isolated pulsars and X-ray binary sources using the atmospheric Cerenkov technique. A general introduction to gamma ray detection techniques is followed by adscription of the properties of atmospheric Cerenkov radiation and a discussion of the principles of the atmospheric Cerenkov technique. The Mark I and Mark II gamma-ray telescopes operated in Dugway, Utah by the University of Durham between 1981 and 1984 are briefly described. There follows a discussion of the results from observations at many different wavelengths of Cygnus X-3. This object was observed by the Durham group between 1981 and 1983 in Dugway Utah and also in Durham during autumn 1985. The detection in the Dugway data of the 4.8 hr X-ray period and the possible detection of a19.2 day intensity variation are considered. The discovery of a 12.59 ms pulsar in data taken on Cygnus X-3 in 1983 is described. Evidence is presented which suggests this periodicity is also present at a weaker level in earlier data and also in the data taken in Durham in 1985.Results from observations of PSR1937+21 , PSR1953+29and six radio pulsars , are presented. The design and construction of the Mark III telescope, now operating in Narrabri , N.S.W. , is described in detail. Preliminary results from observations with the Mark III telescope of three objects, LMC X-4, the Vela pulsar and CentaurusX-3, are presented, with particular reference to periodicities inherent in the sources. An observation of the supernova in the Large Magellanic Cloud is discussed. A brief discussion of the mechanisms by which V.H.E. gamma-rays may be produced in isolated pulsars and X-ray binary pulsars is given, followed by a description of the future prospects for the Mark III and Mark IV telescopes
Gamma ray Cerenkov telescope image analysis
No full textThe subject of this thesis is ground based gamma ray astronomy using the imaging atmospheric Cerenkov technique. The first two chapters are introductory, and describe the field of gamma ray astronomy, the generation of extensive air showers in the atmosphere and the Cerenkov radiation they induce. Chapter three describes the atmospheric Cerenkov telescope, including the development of the imaging technique for background discrimination. The characteristics of the three University of Durham atmospheric Cerenkov telescopes and the processing and calibration of their data products are outlined. Chapter four is concerned with periodic sources of gamma ray emission and includes a review of candidate sources and time series analysis techniques. An analysis of the Mark 3 telescope SMC X-1 database is presented. An upper limit of 1.2 x 10(^-11) cm(^-2) s(^-1) above a cosmic ray threshold of 1 TeV is determined for the guard ring analysis of Mark 3 data. For an analysis of medium resolution Mark 3 imaging data, the upper limit is 2 x 10(^-10) cm(^-2) s(^-1) above a cosmic ray threshold of 500 GeV. Chapter five introduces a new method for the parameterisation of Cerenkov images of extensive air showers recorded by atmospheric Cerenkov telescopes. This method, involving the optimization of a bivariate Gaussian fit to the image, is shown to be significantly better than the standard moment based parameterisation using simulated images. In Chapter six, both of these methods are employed in an attempt to enhance the signal to noise ratio for observations of the pulsar PSR 1706-44 made with the Mark 6 telescope and some evidence for steady emission is seen. The implied fluxes are (2.6 ± 0.3 ± 0.1)x 10(^-11) cm(^-2) s(^-1) above 420 GeV for the bivariate Gaussian analysis and (1.7 ± 0.4 ± 0.2)x10(^-11) cm(^-2) s(^-1) above 500 GeV for the moment analysis
Gamma ray astronomy in the low energy range
No full textA low energy gamma ray telescope, and the results of its observations are described. The telescope consisted of four sodium iodide crystals, each of 120 cm2 area, occulted by lead discs. Charged particles are rejected using scintillation, anti-coincidence shields.The telescope was flown from Palestine, Texas in 1974. Gamma rays were observed from the Crab Nebula, the pulsar NP0 532, and the atmospheric background. No evidence for a gamma ray burst was found, giving an upper limit of less than 5.8 x 103 bursts per year of intensity greater than 1.6 x 10-6 ergs cm-2.Various types of existing, and planned, gamma ray detectors, and successful gamma ray observations are reviewed. Detailed calculations of the detection efficiency of a Double Compton telescope are presented and these results led to the development of the MISO low energy gamma ray telescope.Preliminary calculations of the detection efficiency of an Anticollimated Double Compton telescope are presented, which suggest that further, more detailed investigation of this type of detector would prove fruitful
Characterization of Aptamer-Protein Complexes by X-ray Crystallography and Alternative Approaches
No full textAptamers are oligonucleotide ligands, either RNA or ssDNA, selected for high-affinity binding to molecular targets, such as small organic molecules, proteins or whole microorganisms. While reports of new aptamers are numerous, characterization of their specific interaction is often restricted to the affinity of binding (KD). Over the years, crystal structures of aptamer-protein complexes have only scarcely become available. Here we describe some relevant technical issues about the process of crystallizing aptamer-protein complexes and highlight some biochemical details on the molecular basis of selected aptamer-protein interactions. In addition, alternative experimental and computational approaches are discussed to study aptamer-protein interactions.
Anisotropy of the sky distribution of gamma-ray bursts
No full textThe isotropy of gamma-ray bursts collected in current BATSE catalog is studied. It is shown that the quadrupole term being proportional to \sim sin 2b sin l is non-zero with a probability of 99.9%. The occurrence of this anisotropy term is then confirmed by the binomial test even with the probability of 99.97 %. Hence, the sky distribution of all known gamma-ray bursts is anisotropic. It is also argued that this anisotropy cannot be caused exclusively by instrumental effects due to the nonuniform sky exposure of BATSE instrument. Separating the GRBs into short and long subclasses, it is shown that the short ones are distributed anisotropically, but the long ones seem to be distributed still isotropically. The character of anisotropy suggests that the cosmological origin of short GRBs further holds, and there is no evidence for their Galactical origin
High resolution gamma-ray astronomy in the energy range 0.05 to 10 mev
No full textAn analysis of the detection properties of an actively shielded 86cm (^3) germanium detector is given. Results are presented of observations of the Crab Nebula, its associated pulsar PSR0531+21, the Seyfert galaxy NGC1275, and the COS B source 2CG195+5. Evidence is presented for gamma-ray line emission from the Crab at energies of 404.7 and 1049.8 keV with intensities at the top of the atmosphere of (7.2 ± 2.1) x 10(^-3) and (2.03 ± 0.46) X 10(^-2) s (^-1) respectively. A line at 78.9 keV has also been detected at the 4.1o level which shows time variability. The peak flux at the top of the atmosphere was measured to be (1.1 ± 0.26) x 10(^-2) photons cm"(^-2)s(^-1) .We report the detection of redshifted annihilation radiation from the type II Seyfert galaxy, NGC 1275.The measured flux at the top of the atmosphere is (7.1 ± 2.2) x 10(^-3)photons cm(^-2)s(^-1)
Preface to Special Issue: Advanced doping methods in semiconductor devices and nanostructures
No full textImprovements in semiconductor technology and downscaling have required continuous efforts of the scientific community to solve new challenges in the doping of semiconductor materials. Semiconductor devices, as well as their doping needs, are now undergoing profound change, from the introduction of 3D na- nostructured CMOS architectures to new materials and processes for exciting applications in nanoelectronics, quantum technology, optoelectronics, plasmonics, etc.
This special issue, under the valuable and inspiring guidance of Giuliana Impellizzeri, Editor, focuses on the recent progress in the area of doping methodologies for different advanced applications in semiconductor technology. It is composed of fifteen invited review papers and four regular original papers. The review papers address doping strategies for advanced finFET and nanowire FET devices (A. Veloso), applications of ion implantation in advanced silicon devices (M.I. Current), deterministic doping methods for applications in quantum technology (D.N. Jamieson), doping characterization in 3D structures (W. Vandervorst), modeling of doping processes (in reviews by N. Zographos, L. Pelaz and S.F. Lombardo), doping by pulsed laser melting (in reviews by K. Huet and W. Yang) and flash lamp annealing (S. Prucnal), molecular monolayers for conformal doping (L. Ye), doping of nanostructures (in reviews by S.A. Dayeh and E. Arduca), and doping of III–V semiconductors (in reviews by H. Aldridge and P. Pampili).
We would like to gratefully acknowledge all the contributing authors for sharing their valuable knowledge and expertise, as well as reviewers for their insightful comments and suggestions: all have contributed to the success of this special issue. We hope the papers presented here provide a representative overview of the current progress in semiconductor doping across most classes of semiconductors that are driving advanced applications and will stimulate new exciting research in this field, thus enabling even further progress in semiconductor technolog
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