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An X-ray transmission method has been developed to obtain a continuous profile of bulk densities of ice cores. Intensities of X-rays transmitted through an ice-core sample were continuously measured by an X-ray detector during translation of the sample across the X-ray beam. A thick section of an ice core with a constant thickness was prepared by band-sawing followed by microtome planing. The X-ray intensity profile obtained was converted to a density profile using a calibration curve for X-ray absorption vs ice thickness. Using this method, spatial resolution of the density profile was down to 1 mm. X-ray radiographs were also taken on a two-dimensional detector imaging plate, in order to observe layer structures of the ice cores.
The method was applied to Dome Fuji (Antarctica) ice cores from the surface to 110 m depth. From the density profile obtained we calculated the power spectrum of the density variation by the discrete Fourier transform, and obtained several peaks at different frequencies. The center period in the spectrum was close to the annual accumulation thickness at the drill site.
A deep ice core drilled to 2503 m depth at Dome Fuji, Antarctica, contains 25 visible tephra layers during the past 340 ka. The thickness of tephra layers is in the range 1-24 mm. The thickness and duration at deposition, determined by a simple ice-flow model, suggests that a violent volcanic eruption caused ash to fall onto the Antarctic ice sheet for ~5 years and to form a ~100 mm thick tephra layer at 117 ka BE Two tephra layers at depths of 573 and 2202 m probably originated from volcanoes in the South Sandwich Islands, Southern Ocean, given the size of tephra shards, >20μm in diameter, and their major chemical composition. Only eight of the 25 tephra layers can also be recognized in the Vostok (Antarctica) ice core, but all correspond to the Vostok tephras if we consider cloudy bands to be volcanic.
We examined microorganisms and pollen in a pit (4.5m deep) and a shallow ice core (25.01m long) from Sofiyskiy glacier in the Altai mountains of Russia for potential use in dating ice cores from a mid-latitude glacier. The ice-core and pit samples contained various green algae, cyanobacteria, bacteria, fungi and pollen. In the vertical profiles of the pit, algal biomass peaks corresponded to high δ18O layers and Pinaceae pollen peaks, suggesting that these algae grew during the melt season. In contrast, the layer with the lowest δ18O contained almost no algal cells. Major peaks of the cyanobacteria, bacteria and a fungus roughly corresponded to those of the algae. However, seasonal changes in these microorganisms became indistinct deeper in the core, as did the seasonal variation in δ18O and major ions, most likely due to heavy meltwater percolation and/or post-depositional decomposition. In contrast, clear seasonal cycles were evident in the algal biomass and pollen in snow samples. Assuming that the peaks of the snow algae and Pinaceae pollen marked summer layers and that the layers with almost no snow algae represented the winter layers, we estimated that the ice core contained 16 annual layers (1985–2001). The mean annual mass balance for the period was estimated to be 1.01mw.e. The value agreed well with those estimated from stake measurements, indicating that snow algae and pollen could provide reliable boundary markers of annual layers in the ice cores of this region.
In 1987 an ice core to the bedrock at a depth of 85.6 m was drilled at the top of Høghetta ice dome in northern Spitsbergen. Chronology of the ice core was examined by tritium and 14C methods showing time gap at about 50 m depth. The age of three bottom ice samples was determined as 4150–5670 year B.P. by 14C method done for frozen bacteria colonies and a frozen petal. This chronology and negative bottom temperature of −9.4°C suggest that glaciers in Spitsbergen shrank considerably during the hypsithermal. The pH of melt-water samples lower than 5.0 corresponds well to large northern hemispheric volcanic eruptions during the last 300 years. Increase of acidity from 30 m depth to the surface may reflect the spread of air pollution to the Arctic during the past 200 years. On the basis of ice-core analyses on electrical conductivity, pH, chemical composition and air bubble pattern, climate and environment in Spitsbergen during the last 6000 years are discussed.
Horizontal and vertical distributions of melt features (ice layers) were examined using two ice cores (206.6 and 101.5 m deep, 1 m apart) from Site J (66°51.9′ N, 46°15.9′W, 2030 m a.s.l.). The temperature at 10 m was −16.3°C. We observed 2804 melt features, with a total thickness of 30.32 m, in the 206.6 m core, corresponding to 16.4% by volume of the ice-equivalent core length. Horizontal distribution of melt features was examined by correlating melt-feature thicknesses in the two cores. The correlation coefficient was 0.71 (n = 514) for each melt feature in the two cores. It was maximum for data passed through 5 and 40 year low-pass filters. A significant relationship (P = 0.005, n = 36) was obtained for the vertical distribution of melt features and the June temperature on the west coast of Greenland (Jakobshavn). Using this, June temperatures at Jakobshavn since 1550 were estimated. There are three periods (1685-1705, 1835-70 and 1933-45) during which mean June temperatures clearly decreased, when they were estimated to he 0.1°, 0.4° and 0.2°C lower than the average for the whole period (1550-1989). The first two “cold” periods have been identified in melt features of the Dye 3 and Devon Island ice cores and in a tree-ring profile from Yukon Territory, Canada. Melt-feature percentages in the Site J ice core have increased since about 1945, probably reflecting summer-temperature warming on the ice sheet.
Lützowholmbukta, East Antarctica, is covered by fast ice except during a short period in April and May, but occasionally the ice cover breaks up and floats out of the bay.
The fast ice was observed every day using NOAA-7, 8 infra-red imagery. The satellite signal was received at Syowa Station, located on Ongul Island. In addition, aerial photographs and video pictures were taken using aircraft every fortnight.
In 1983, before the break-up of the fast ice in April, a distinctive increase of the infra-red radiance (NOAA AVHRR) was observed, even though the aerial observation showed no change. The increase of the radiance was estimated to be 5°C. It was in this area, where the higher infra-red signal was observed, where the fast ice broke up. In December, in the central part of the northern area of the fast ice, the hummock-ice zone formed in a triangular shape. Before the hummock-ice zone floated out, observation of the infra-red radiance showed that the temperature of the ice had decreased by 3°C.
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.
The CANGAROO project incorporates two Čerenkov imaging telescopes at Woomera to obtain stereo images of very high-energy gamma-ray (and cosmic-ray) showers. The first stereo observations, with one imaging system, were made in March 1992, and preliminary stereo imaging observations began in July 1992. This paper describes the stereo imaging technique, the sources under investigation, and the indications from the first data sets.
Spherical nylon projectiles of 7mm diameter and up-to 4km/s velocities were penetrated into three types of targets; aluminum multisheet stacks, foamed polystyrene, and 1-atm air. Penetration depth, recovery rate of the projectiles were determined as a function of projectile velocity and target density, and a new type of dust collector is proposed.
Shiga-toxin-producing Escherichia coli (STEC) infections usually cause haemolytic uraemic syndrome (HUS) equally in male and female children. This study investigated the localization of globotriaosylceramide (Gb3) in human brain and kidney tissues removed from forensic autopsy cases in Japan. A fatal case was used as a positive control in an outbreak of diarrhoeal disease caused by STEC O157:H7 in a kindergarten in Urawa in 1990. Positive immunodetection of Gb3 was significantly more frequent in female than in male distal and collecting renal tubules. To correlate this finding with a clinical outcome, a retrospective analysis of the predictors of renal failure in the 162 patients of two outbreaks in Japan was performed: one in Tochigi in 2002 and the other in Kagawa Prefecture in 2005. This study concludes renal failure, including HUS, was significantly associated with female sex, and the odds ratio was 4·06 compared to male patients in the two outbreaks. From 2006 to 2009 in Japan, the risk factor of HUS associated with STEC infection was analysed. The number of males and females and the proportion of females who developed HUS were calculated by age and year from 2006 to 2009. In 2006, 2007 and 2009 in adults aged >20 years, adult women were significantly more at risk of developing HUS in Japan.
The post-AGB stars rapidly change their spectral energy distribution on their way from the asymptotic giant branch(AGB) to planetary nebula stage. They are generally surrounded by cool and extended dust shells emitting largely in the infrared wavelengths.
A selected sample of the post-AGB candidates were observed using the CCDand IR camera at Kiso and Nishi-Harima Astronomical Observatory. They were classified based on their broad band spectra from B to K’ band and their evolutionary stages have been discussed using the simple model of the dust shell around a star.
The light variation of some of these objects were monitored and their light curves are also presented.
The superbubble (SB) 30 Dor C with the strong non-thermal X-ray emission is one of the best targets for study of the cosmic-ray (CR) acceleration. We investigated X-ray spectral properties of the SB with a high spatial resolution of ~10 pc. Consequently, the spectra in the east regions can be described with a combination of absorbed thermal and non-thermal models while the spectra in the west regions can be fitted with an absorbed non-thermal model. We found that the observed photon index and intensity in 2-10 keV show variations of 2.0-3.5 and (0.6-8.0) × 10−7 erg s−1 cm−2 str−1, respectively. The results are possibly caused by the spatial variation of the CR acceleration efficiency and/or the circumstellar environment.
We report the Eu doping induced improvement on the second harmonic generation (SHG) of ZnO nanowires and correlates with the structural modification and corresponding linear absorption. A non-monotonic enhancement in the SHG emission is observed with the increase of Eu concentration. To understand the underlying mechanism, the effective second order non–linear coefficient (deff) is calculated from the theoretical fitting with considering the absorption effect. The highest deff (19.09±0.11 pm/V) is obtained for the 1 at.% Eu doped ZnO nanowires, which is several times larger than the standard SHG material β-BaB2O4 (BBO). Dependence of the deff with the Eu doping, structural modification and absorption magnitude are systematically discussed.
Effect of high-pressure water vapor (HPV) annealing is discussed from density of state (DOS) by capacitance–voltage (C–V) method and ΔVFB by the cyclic C–V measurement. The DOS of HPV samples were smaller than that of conventional atmosphere (AT) annealing around conduction band minimum (Ec). The ΔVFB of HPV samples were also smaller than that of AT. This suggests that HPV annealing is an effective method to decrease electron trap density as compared with AT condition. Especially, HPV 0.5 MPa sample was lower electron trap density and more stable than the other pressure HPV samples. Therefore, it is considered that the HPV in 0.5 MPa is the most promising condition. In addition, we succeeded in demonstrating the analysis of trap density in thin film by C–V method and cyclic C–V measurement.
For the fabrication of bulk strained Si devices, a thin Si layer is deposited on a virtual substrate consisting of a several μm thick compositionally graded SiGe layer. A simpler approach utilizing H or He implantation to enhance relaxation of a thin SiGe film was recently reported. In this current work, hydrogen implantation is used to enhance the SiGe relaxation; and, relaxation beyond the previous reported limit is demonstrated. Experiments are performed on CVD deposited SiGe films with Ge fractions ranging from 20% to 40 % and thickness in the range of 100nm to about 500nm. After annealing at 800°C, relaxation of more than 80% is achieved. PMOS and NMOS devices are successfully fabricated and much enhanced hole and electron mobilities are demonstrated.