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In this paper the Very High Energy (VHE) gamma-ray astronomy program at the University of Adelaide is described. VHE gamma rays with energies above ~5 × 1011eV are observed using the atmospheric Cerenkov technique. Results from the first three years observations at Woomera and the current upgrading of the telecope are described. The CANGAROO project, a collaboration between the University of Adelaide and a number of Japanese institutions, is also introduced.
A rapid and dramatic change in our views of the Universe which we have witnessed during the past two decades or so is often compared with what happened at the time of Galileo. Revolutionary role of the optical telescope then may be analogized with that of space-astronomy today which has drastically opened the new observational window to the Universe. The revolution is ongoing with a rapid pace or even being accelerated.
The Collaboration of Australia and Nippon for a GAmma Ray Observatory in the Outback operates two large telescopes at Woomera (South Australia), which detect the Čerenkov light images produced in the atmosphere by electronpositron cascades initiated by very high energy (~1 TeV or 1012 eV) gamma rays. These gamma rays arise from a different mechanism than at EGRET energies: inverse Compton (IC) emission from relativistic electrons.
The spoke-like images are recorded by a multi-pixel camera which facilitates the rejection of the large numbers of oblique and ragged cosmic ray images. A field of view ~3.5° is required. The Australian team operates a triple 4 m diameter mirror telescope, BIGRAT, with a 37 photomultiplier tube camera and energy threshold 600 GeV. The Japanese operate a single, highly accurate 3.8 m diameter f/1 telescope and high resolution 256 photomultipler tube camera. In 1998 a new 7 m telescope is planned for Woomera with a design threshold ~;200GeV.
A balloon-borne X-ray instrument with the modulation collimator was designed and constructed to study the structure of solar X-ray flares. The angular resolution was approximately one arc minute. The instrument was used on an occasion of X-ray flare on Sept. 27, 1970.
Cosmic X-rays were observed with three sets of proportional counters covering the energy range between 0.15 and 20 keV. The detector born on a spinning rocket scanned a celestial region in which the galactic latitude bII changed from 30° to −55° across the galactic plane in the Cygnus-Cassiopeia region. The spectrum of Cyg XR-2 thus obtained is represented by a thermal bremsstrahlung of temperature 3.4 keV modified by the interstellar absorption for the hydrogen column density of 3 × 1021 cm−2. The diffuse component showed an interstellar absorption effect, which was however found much weaker than one would expect if the diffuse component were due entirely to be of extragalactic origin. The spectrum obtained in the highest latitude region is represented approximately by a power law E−1.8 but shows a possible trough at about 1 keV.
We performed a couple of balloon experiments to measure the size and the location of Cyg-X-1 using the techniques of the modulation collimator . The angular periods of the modulation collimator were 26′ and 10′ for the respective flights corresponding to the approximate angular resolutions of the size determination and location, 3′ and 1′ respectively. Preliminary results of the experiment with 3′ resolution are reported here.
The present study investigates the indications for transnasal endoscopic surgery in treating post-operative maxillary cysts.
In this retrospective study, the records of 118 patients with post-operative maxillary cysts (88 unilateral and 30 bilateral) consisting of 148 procedures were reviewed.
A transnasal endoscopic approach was performed in 144 lesions (97.3 per cent). A combined endonasal endoscopic and canine fossa (external) approach was performed in 4 of 148 lesions, because the cysts were located distant from the nasal cavity and had a thick bony wall. A ventilation stent was placed in four patients (four cysts) to avoid post-operative meatal antrostomy stenosis. Recurrence was observed in five patients (4.2 per cent), all of whom subsequently underwent transnasal endoscopic revision surgery.
Transnasal endoscopic surgery is an effective treatment for post-operative maxillary cyst with the exception of cysts located distant from the nasal cavity.
We describe an outbreak of simultaneous Clostridium difficile and norovirus infections in a long-term-care facility. Thirty patients experienced acute gastroenteritis, and four had co-infection with identical C. difficile 027 and genotype II.4 New Orleans norovirus strains. Co-occurring infection requires improved understanding of risk factors, clinical impact, and testing strategies.
To determine whether improper high-level disinfection practices during endoscopy procedures resulted in bloodborne viral infection transmission.
Retrospective cohort study.
Four Veterans Affairs medical centers (VAMCs).
Veterans who underwent colonoscopy and laryngoscopy (ear, nose, and throat [ENT]) procedures from 2003 to 2009.
Patients were identified through electronic health record searches and serotested for human immunodeficiency virus (HIV), hepatitis C virus (HCV), and hepatitis B virus (HBV). Newly discovered case patients were linked to a potential source with known identical infection, whose procedure occurred no more than 1 day prior to the case patient's procedure. Viral genetic testing was performed for case/proximate pairs to determine relatedness.
Of 10,737 veterans who underwent endoscopy at 4 VAMCs, 9,879 patients agreed to viral testing. Of these, 90 patients were newly diagnosed with 1 or more viral bloodborne pathogens (BBPs). There were no case/proximate pairings found for patients with either HIV or HBV; 24 HCV case/proximate pairings were found, of which 7 case patients and 8 proximate patients had sufficient viral load for further genetic testing. Only 2 of these cases, both of whom underwent laryngoscopy, and their 4 proximates agreed to further testing. None of the 4 remaining proximate patients who underwent colonoscopy agreed to further testing. Mean genetic distance between the 2 case patients and 4 proximate patients ranged from 13.5% to 19.1%.
Our investigation revealed that exposure to improperly reprocessed ENT endoscopes did not result in viral transmission in those patients who had viral genetic analysis performed. Any potential transmission of BBPs from colonoscopy remains unknown.
Bentonite-water interaction was studied using a simple equilibrium model based on experimental measurements in order to describe bentonite porewater chemistry. Direct pH measurements for highly compacted bentonite and batch-type bentonite-water interaction experiments were performed under anaerobic conditions. In the direct pH measurements, resin particles doped with a pH indicator were sandwiched between a pair of bentonite columns immersed in a test solution. The experimental results showed that the solution compositions in equilibrium with bentonite depended on the bentonite to liquid ratio (B/L) and the initial solution composition. An equilibrium model assuming only fast equilibration processes between the bentonite minerals and the solution could be used to calculate the trends of pH and other ion concentrations with B/L. This study indicates that the surface deprotonation of smectite is a very important factor influencing the porewater chemistry in highly compacted bentonite.
Nano-particles can become one of the best materials for forming thin and fine pitch films at low temperature, if particles are individually dispersed densely in a solvent. Individually dispersed metal(gold, silver, copper) nano-particle(d-nano particle) are formed at a state of suspension in an organic solvent by the modified gas evaporation method where formed particles are covered with an organic surfactant just after their formation. The particle formed by the gas evaporation method are metal impurity free and have a narrow size distribution. This suspension is condensed and used as a formed of solution or paste. D-nano particle solution or paste can be baked at 200-300C to form metal thin films. These has been applied to PDP electrode repairing, coloring of car window glass, a filler of electric conductive resin paste and ULSI interconnection formation.
Self-aligned ultra-high-speed SiGe HBTs were developed by using selective epitaxial growth (SEG) technology. The use of HCl-free SEG, incorporation of C, and optimization of doping profiles significantly improves the performance of the HBT, producing a transistor with a high cutoff frequency of 170 GHz and a maximum oscillation frequency of 204 GHz, for a minimum ECL gate delay time of 4.8 ps. This is applied in a 16:1 MUX with a maximum clock rate of 57 GHz. A 0.13-μm SiGe BiCMOS technology is also realized without any degradation of CMOS due to the high stability of SiGe HBTs. Furthermore, the structure of SiGe HBT is optimized for an emitter scaled down towards 100 nm, mainly through the use of a funnel-shaped emitter electrode to reduce both emitter and base resistances. High-speed operation of a static frequency divider demonstrates the advantage of SiGe HBTs for ultra-high-speed communications systems.
We have studied photoluminescence (PL) of surface oxidized nanocrystalline silicon quantum dots (QDs) for various oxidation periods and temperatures. With increasing oxidation period, the surface oxide grows and the Si QD core shrinks initially, then retardation of the oxidation process occurs which is ascribed to compressive stress at the interface between Si QD core and oxide. Upon oxidation, the PL spectrum peak shifts toward the shorter wavelength side followed by retardation of the blueshift or even manifestation of the redshift. The origin of PL is due to the localized excitons at the interface between Si QD core and oxide or amorphous SiOx (a-SiOx) formed at the interface. The blueshift is associated with the increased quantum con.nement or increased bandgap of a-SiOx. The redshift is due to the stress e.ect of the bandgap of Si QD core or a-SiOx. We have successfully confirmed the effect of compressive stress associated with the self-limiting oxidation by PL measurement.
We prepared a SiO2/nanocrystalline Si (nc-Si)/SiO2 sandwich structure. A clear positive shift in C-V and G-V curves due to electrons trapped in nc-Si dots has been observed at room temperature. The peak in conductance around flat band condition indicates that a trap event had occurred where an electron is stored per nc-Si dot. A logarithmic charge loss function is found and this discharging process is independent of the thermal activation mechanism. The longer memory retention time and logarithmic charge loss in the dots are explained by a “built-in” electric field through the tunnel oxide, which varies with time, resulting in a variable tunneling probability. The electric repulsion induced by the built-in electric field hinders the discharging of electrons remained in the dots.
We have proposed digital plasma processing for the fabrication of silicon quantum dots with grain size less than l0nm. By using the pulsed gas supply of SiH4 and H2 in the very-high frequency (VHF) plasma, we have clarified the role of atomic hydrogen in the nucleation, crystallization of nanocrystalline Si (nc-Si) as well as in the selective etching of amorphous Si to nc-Si. Recently, we have prepared nc-Si by employing an ultra-high-vacuum (UHV) chamber equipped with VHF plasma cells of SiH4 and H2. Flux rate of Si cluster depends significantly on the pressure of the plasma cell and VHF power. Spherical shaped nc-Si clusters less than 6nm in diameter have been observed by transmission electron microscopy (TEM). Infrared absorption measurements have clarified that the surface of nc-Si is covered by hydrogen. In an attempt to control the position of nuclei, we have prepared nc-Si on SiO2 with micro trenches, 40nm wide and 20nm deep, fabricated by electron beam exposure and electron cyclotron resonance (ECR) etching. It has been revealed by TEM observation that nc-Si are formed preferentially along micro trenches.
Systematic studies have been made on preparation of Si thin films from SiF4 under control over the flow of atomic hydrogens. The gas phase reactions taking place in the mixture of fragments (SiFn) resulting from plasma-induced dissociation and atomic hydrogens were widely investigated by a mass spectroscopy. Chemically active species,i.e., SiF2H and SiH2F were found as those related to the growth of films. The growth in the vicinity of substrates involves either endothermic or radical-enhanced reaction for the propagation of the three dimensional Si networks, accompaning release of terminators such as H and F. Accordingly, Si thin films with structures from amorphous to crystalline were obtained by controlling the flow of atomic hydrogen. A marked improvement in the hole-transport was established in the Si films containing hydrogen less than 5–6 at % due to the reduction in the tail states near the valence band.
We have been developing a low energy Ne atom scattering system combined with a time-of-flight spectrometer for insulator surface structural analysis. Insulator surface structure is difficult to study because of charging effects during electron or ion beam bombardment. Structural analyses of insulator surfaces are very important in fundamental research as well as technology fields. In our system, charged ion beams of 2 keV-Ne+ are converted into neutral beams by charge exchange with the same element gas after the primary beam passes through a chopper. Other features of this system are pulsed beams, time-of-flight measurements, and a micochannel plate (MCP) detector is coaxially mounted along the primary beam. This is a home made equipment. We will show the detection systems, as well.
Recently, it was found that semi-insulating behavior of undoped InP can be realized by high pressure annealing of undoped high purity InP. In the present work, studies related with the achievement of the semi-insulating state are reviewed. Purification of raw materials, effect of native defects, effect of high pressure annealing, contamination of Fe are discussed. The semi-insulation mechanism is explained by the Shockley diagram. The semi-insulating state is supposed to be achieved by the annihilation of shallow donors (presumably phosphorus vacancies) and the compensation of the residual donors with a small amount of Fe deep acceptor.
A new method for the formation of nanocrystalline Si (nc-Si) in the SiH4 plasma using pulsed-H2 supply with very-high-frequency (VHF;144MHz) excitation is proposed to control the size of nc-Si. Nanocrystalline Si is formed in the gas phase of SiH4 plasma cell by coalescence of radicals. The principle of size control is based on the separation of nucleation and growth process. Supplying H2 into a SiH4 plasma enhances nucleation of nc-Si and suppresses growth rate of nc-Si. The nucleated nc-Si grows larger in a SiH4 plasma during the off state of the H2 supply. As the newly supplied H2 forces nc-Si grown in the previous cycle out of the plasma cell into the deposition chamber, the next nucleation of nc-Si is enhanced simultaneously. Using this method, we fabricated 8 nm-diameter nc-Si with small dispersion (±1 nm) successfully.
Palladium solubility was measured in a dilute aqueous solution at room temperature in the pH range from 3 to 13 under anaerobic conditions. Crystalline Pd metal was clearly visible and the concentration of palladium in solution decreased gradually with aging time. The palladium concentrations in solution were less than 9.4×10-10M in the pH range from 4 to 10 and increased to 10-7M in the pH range greater than 10. This study suggests that palladium concentrations in certain high-level waste repository environments may be limited by Pd metal and may be less than 10-9M.