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In a series of papers, we have performed N-body simulations of a galaxy collision to reproduce the observed shape, kinematics, and metallicity distribution of a giant stellar stream and shell-like structures in the halo of Andromeda galaxy (M31).
We report on the investigation of GaN(0001)−1×1 using synchrotron radiation x-ray excited photoelectron spectra from the core levels Ga 3p and N 1s, as well as from the contaminants O 1s and C 1s. Measurements were done after outgassing (a) and during three surface treatment methods performed in sequence; (b) ammonia (NH3) flux anneals, (c) Ga deposition with sample held at room temperature followed by vacuum anneal, and (d) Ga deposition on a heated sample followed by Ga desorption during NH3 flux anneal. We have found that the initial NH3 flux anneals increased the amount of present N on the surface and enabled the formation of a well-ordered surface structure, according to the low energy electron diffraction (LEED) pattern. After treatment (b) and (d) the core level spectra of Ga 3p are much improved showing clearly distinct features indicative of increased Ga-N bonding. The Ga to N concentration ratio decreases during the surface treatments from 4.0 to 1.1, hence towards stoichiometry. The amounts of C (and O) present on the surface after outgassing corresponded to 1.1 (0.9) monolayers (ML) but reduced to 0.1 (0.1) ML after the final treatment (d). The Fermi level position in the band gap shifts down by 0.55 eV during the surface treatments, indicating a change of states present in the band gap. We have also found strong support that this Ga-polar sample is initially Ga-terminated.
Amorphous silicon(a-Si) stripe p-i junction photodiode array for contact-type image sensor of a facsimile has been developed and investigated especially with regard to its unsymmetrical electrode structure. This sensor consists of a p-i a-Si stripe layer, Cr separate electrodes, and an ITO common electrode. As a result, it is found that the photosensitive region of a-Si stripe type photodiode exists not only in a-Si sub-region having both upper and lower electrodes but also in a-Si sub-regions having upper or lower one-sided electrode. It is considered that photocarrier collecting mechanisms in the a-Si sub-regions are different and result to the different photodiode characteristics.
The preparation and properties of hydrogenated amorphous silicon thin film transistor arrays for active matrix liquid crystal displays are reported. The effect of amorphous silicon film preparation conditions on the field effect mobility of thin film transistors was investigated. The dry etching rate of silicon nitride film was studied.The thin film transistor arrays have 408 ˜ 640 transistors on the first version and 450 ˜ 640 ˜ 3 transistors on the second version. The liquid crystal panel fabricated using the first version arrays showed good characteristics.
Photoemission spectra (XPS and UPS) of As-covered Si (001) surfaces prepared at high (>600ºC) and low (<450ºC) temperatures and GaAs epilayers subsequently grown on them were measured without exposing to air. It was found that the surface electronic structures of As/Si prepared at the low temperature are different from those of the high temperature sample, the spectra of which can be interpreted as a symmetric dimer model. Differences were also observed between the GaAs epilayers on the As—covered Si surfaces prepared at the high and low temperatures. The temperature dependence of the surface and interface structures are discussed.
In order to fill high quality insulators into narrower spaces in advanced metallizationthe digital CVD (Chemical Vapor Deposition) of multilayer stacked Si oxide and nitride films was studied. Reaction of TES (triethylsilane) with hydrogen (H) atoms was also found to lead to conformal CVD of Si film involving organic species. This reaction took place only on the surface reaction. In-situ FTIR studies reveal that H atoms react with Si-C2H5 bonds in TES and thus generate strong Si-CH3 bonds and weak Si-H bonds, thereby liberating H2 and forming the organic Si film on the surface, and the surface reaction is dominated by the thermal effect from the substrate. Then Si oxide or nitride films were formed by the digitaCVD which repeated a cycle of deposition of this film with subsequent oxidation or nitridation. Oxide film integrity was improved greatly by removing included organic bonds in the TES/H reaction film by exposing the film to H atoms before the oxidation step. Thus electrically excellent multilayer stacked oxide and nitride films were obtained in a deep trench.
Cleaning effects of pure water containing dissolved oxygen of very low concentration (LDO water) to metallic contaminants on silicon wafer surface were confirmed. To maintain the concentration of the dissolved oxygen in water, experiments were performed in a glove box in which ambience was controlled so as to satisfy Henry's law between the water and the ambient gas. In the experiment using intensionally contaminated wafers, residual metal contaminants except copper on Si-surface decreased from 1014 atoms/cm2 to 1011 atoms/cm2 after the 1ppb hot LDO treatment at boiling point. This effect depended on the concentration of dissolve oxygen, treatment temperature, and rinsing time. Contact angle of the wafer surface increased gradually from about 10 [deg] with decrease in the residual metals and jumped up to about 90 [deg]. when the amount of residual metals reached to minimum. Then absorption peak of Si-O bonds in FT-IR-RAS spectra also disappeared. These results therefore show that hot LDO water removed metal contaminants from the wafer surface with etching of the native oxide.
A scanning tunneling microscopy (STM) has revealed an atomic structure of Si(111)-√3× √3R30° which is induced by the hydrogen desorption at about 500 °C. There exist domains with the √3× √3R30° structures, indicating that each domain is formed by rearrangement of Si adatoms around each cluster present at room temperature. Near the domain boundary, the adatoms locate mostly at T4 sites and occasionally at H3 sites. The dynamic nature of the adatoms are predicted.
Some compositions of Ni-Mn-X (X = Ga, In, Sn) ferromagnetic shape memory alloys exhibit a first order magnetostructural phase transition. Magnetic entropy change ΔSm in the vicinity of this transition has been studied by magnetization and heat capacity measurements. Comparison of these results point to a large difference in magnitudes of ΔSm obtained from magnetization and heat capacity data. It is suggested that this discrepancy originates from overestimation of \Delta S_m determined from the magnetization measurements and underestimation of ΔSm obtained from the heat capacity measurements.
The aims of this descriptive study were to confirm the high incidence of subacute sclerosing panencephalitis (SSPE) previously reported from Papua New Guinea (PNG) and to relate SSPE to previous measles vaccination and measles illness. From February 1997 to April 1999 we diagnosed a total of 55 patients with SSPE at Goroka Base General Hospital in Eastern Highlands Province (EHP) of PNG. The diagnosis was based on high cerebrospinal fluid and serum measles virus antibody titres with progressive neurological disorder and myoclonic jerks. Of these 55 patients 42 were from EHP, including 32 whose onset was in the 2-year period 1997–1998. The annual incidence of SSPE in EHP in these 2 years was 98 per million population under 20 years of age, the highest ever reported. This incidence was more than ten times higher than the highest incidence in the prevaccine era reported from elsewhere. The mean age of onset of SSPE was 7·7 years (range 2·8–14·8 years) and the interval between measles and the onset of SSPE, where known, had a mean of 5·9 years and a range of 2·5–11·1 years. Among the SSPE patients 19 had a documented history of measles vaccination. Eight of these 19 also had documentation of previous measles illness; of these, seven were vaccinated after the development of measles and one was vaccinated 20 days before measles illness. Two non-SSPE children received vaccination twice which was documented and subsequently developed measles which was also substantiated by documentation. Two patients with SSPE yielded amplified nucleotide sequences of measles virus that were different from any of the vaccine strains. We found no evidence to implicate measles vaccination in the development of SSPE.
Geoffrey T. Manley, Department of Neurological Surgery, University of California, San Francisco, CA,
Miki Fujimura, Department of Neurosurgery, Stanford University School of Medicine, Stanford, CA,
Tonghui Ma, Departments of Medicine and Physiology, Cardiovascular Research Institute, University of California, San Francisco, CA,
Ferda Filiz, Departments of Medicine and Physiology, Cardiovascular Research Institute, University of California, San Francisco, CA,
Andrew W. Bollen, Department of Pathology, University of California, San Francisco, CA,
Pak H. Chan, Department of Neurosurgery, Stanford University School of Medicine, Stanford, CA,
Alan S. Verkman, Departments of Medicine and Physiology, Cardiovascular Research Institute, University of California, San Francisco, CA
Abnormalities in brain water balance, such as edema and increased intracranial pressure, play an important role in the pathophysiology of acute head trauma, stroke and a variety of neurological disorders. However, little is known about the molecular mechanisms responsible for these alterations in cerebral water balance. Consequently, at present the therapeutic options are limited to neurosurgical decompression, intravenous administration of hyperosmolar agents and steroids, therapies that were introduced more than 40 years ago. There is recent evidence that molecular water channels called aquaporins, which have recently been identified in mammals, may play an important role in brain edema, thus offering therapeutic alternatives.
Aquaporins are small integral membrane proteins that function primarily as bidirectional water-selective transporters in many cell types in the kidney, lung and other fluid-transporting tissues where water flow is driven by osmotic gradients and hydrostatic pressure differences. The brain expresses at least two members of the aquaporin family in areas that are known to participate in the production and absorption of brain fluid. Aquaporin-1 is selectively expressed on the ventricular surface of choroid plexus epithelium where it may play a role in cerebrospinal fluid (CSF) production. Aquaporin-4 (AQP4) is abundantly expressed throughout the brain, particularly at the blood–brain and brain–CSF interfaces. AQP4 is expressed to a much lesser extent in tissue outside of the nervous system.
Plasmas with long life times (∼20 ns) are generated in a cavity target by intense CO2 laser pulses (2 × 1014W/cm2). The plasma life depends on the configuration of irradiation and target, which may infer thermal conduction inhibition by the laser-generated magnetic field. The experimental results agree with those of computer simulations with magnetic inhibition of thermal conduction.
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