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After completion of the drilling by the US Army Cold Regions Research and Engineering Laboratory (USA-CRREL) at Camp Century, Greenland, in July 1966, the operation was moved to Byrd Station, Antarctica, during the 1966/67 austral summer. The drill employed was an electromechanical cable-suspended drill that used ethylene glycol to dissolve the chips formed, producing a core with an average diameter of 114 mm. A mixture of diesel oil and trichlorethylene was used as a borehole fluid. Ice-core drilling at Byrd Station occurred from 2 to 18 February 1967 and from 12 October 1967 to 2 February 1968 when the ice sheet was penetrated at a depth of 2164 m. During the ensuing 1968/69 season the drill was lost, and ultimately the cable was severed in early 1969/70 at a depth of 1545 m. This brief report reviews the drilling operation and some of the problems encountered primarily during the 1967/68 season, with a focus on the last few days of drilling.
The USA CRREL drill is an 80-kg, electrothermal unit designed for continuous coring in temperate or polar ice or snow. The drill melts a hole approximately 16.3 cm in diameter and retrieves a core approximately 12.2 cm in diameter at rates from 1.9 m h−1 in −28°C ice to 2.3 m h−1 in temperate ice. The melt water formed is removed by a vacuum system and stored in a tank. Additional equipment includes 450 m of armored electrical cable, a hoist, a 6.7-m tower and a gasoline generator. The minimum time required to drill a 450-m hole is 435 h. All of the equipment has been designed to be assembled and operated by two men and has a gross shipping weight of 1180 kg.
The drill hole at “Byrd” station, which was completed in January 1968 to a vertical gerpth of 7 063 ft (2 153 m) below the top of the hole casing, was resurveyed in January 1975 to a vertical gerpth of 4 835 ft (1 474 m)· Inclination and azimuth measurements were mager with a Parsons multiple shoe inclinometer and compared with the earlier measurements mager during drilling. The results indicate a progressively increasing displacement with gerpth to a value of 51.2 ft (15.6 m) or about 7.3 ft/year (2.23 m/year) at the 4 835 ft (1 474 m) level. The direction of movement relative to the surface varies freom south-west at 300 ft (91.5 m) to north-east at 1 100 ft (335 m) to east at 3 368 ft (1 027 m) to north-east at 4835 ft (l 474 m), indicative of a complex twisting motion. An increase in accessible gerpth along the hole axis of 18 ft (549 m) beyond the 1969 gerpth was noted. No attempt was mager to measure hole diameter or vertical strain. It is recommengerd that the hole be resurveyed in 3-5 years if it is still logistically feasible, using a more up-dated inclinometer.
RXJ 13434+0001 is a rare example of radio-quiet type-2 quasars at high redshift. It was discovered through deep ROSAT observations and identified with a galaxy with a strong but narrow Lyα emission line at z = 2.35. In order to constrain the hard-X-ray properties we observed RXJ 13434+0001 with ASCA. The main purpose is to study the origin of the X-ray emission observed with ROSAT. If it is a scattered component from a strongly absorbed AGN, we could see it much brighter in the hard X-ray band.
To reveal the origin of the cosmic X-ray background (CXB) in the hard band, we are now conducting a wide (~ 7 deg2) and deep (~ 1 × 10−13 erg sec−1 cm−2 in the 2-10 keV band) survey with the ASCA (the ASCA Large Sky Survey, hereafter LSS). We have detected 83 sources above 4 sigma level in the 0.7-10 keV band with the GIS and resolved ~30% of the CXB in the 2-10 keV band into discrete sources (Ueda 1996). AGNs (type 1 and type 2) and clusters of galaxies are expected to be major contributers to these X-ray sources.
We are constructing the ASCA GIS source catalog from the ASCA public archive, mainly for extra-galactic sky. The large field of view and the low-background characteristics of the GIS make it suitable for a search for serendipitous sources in a wide energy band of 0.7-10 keV. Sources to be detected by the project will provide valuable information on the log N-log S relation over the entire sensitivity band, which has never been available before. About this project, also refer to Ishisaki et al. (1995), Ueda et al. (1997) and Takahashi et al. (1997). There is the SIS source catalog project, too (Gotthelf et al., 1996). These catalogs are going to appear on the WEB.
Since the discovery of fading X-rays from Gamma-Ray Bursts (GRBs) with BeppoSAX (Piro et al. 1997, Costa et al. 1997), world-wide follow-up observations in optical band have achieved the fruitful results. The case of GRB 970228, there was an optical transient, coincides with the BeppoSAX position and faded (Paradijs et al. 1997, Sahu et al. 1997). These optical observations also confirmed the extended component, which was associated with the optical transient. The new transient are fading with a power-law function in time and the later observation of HST confirmed the extended emission is stable (Fruchter et al. 1997). This extended object seems to be a distant galaxy and strongly suggests to be the host.
There are several regions where a group of quasars are significantly clustered in the physical space. In the “CFHT grens survey” conducted by Crampton et al. (Crampton et al. 1989 and references therein), the 23 quasars between z=1.036 and 1.185 were found to be clustered over ~ 2° × 2° in the region denoted as 1338+27 At the mean redshift zave = 1.113, the angular extent 6000 arcsec (CHH89) of this cluster corresponds to 60 h−1Mpc(q0 = 0.5) and the dispergion of the redshift λz = 0.044 to 45 h−1Mpc.
ASCA DSS was intended to carry out unbiased surveys in wide energy range of 0.5-10 keV. The strategy of this project is to survey small sky region with extremely high sensitivity reaching to the source confusion limit of ASCA XRT, in contrast to the Large Sky Survey project (Ueda 1996) which covers much larger sky area with relatively shallow exposure.
About 10 X-ray binaries in our Galaxy and LMC/SMC are considered to contain black hole candidates (BHCs). Among these objects, Cyg X-1 was identified as the first BHC, and it has led BHCs for more than 25 years(Oda 1977, Liang and Nolan 1984). It is a binary system composed of normal blue supergiant star and the X-ray emitting compact object. The orbital kinematics derived from optical observations indicates that the compact object is heavier than ~ 4.8 M⊙ (Herrero 1995), which well exceeds the upper limit mass for a neutron star(Kalogora 1996), where we assume the system consists of only two bodies. This has been the basis for BHC of Cyg X-1.
The origin of the Cosmic X-ray Background (CXB) radiation has been investigated extensively by soft X-ray deep survey imaging observations with Einstein and ROSAT. In contrast, the lack of telescopes capable of detecting hard X-rays has prevented us from extensive study of the nature of the CXB in the energy range above 2 keV before ASCA.
The X-ray background in the energy range above 2 keV is highly uniform except for an excess component along the Galactic plane. The excess along the plane is considered to be associated with our Galaxy, whereas the rest of the emission is believed to be of extragalactic origin. In this paper, the X-ray background at high Galactic latitude is discussed and is designated as the CXB (cosmic X-ray background) to distinguish it from the Galactic origin.
We made a search of quiescent X-ray counterparts of two Gamma-Ray Bursts (GRBs), GRB930131 and GRB940217. These GRBs were detected with BATSE, EGRET, COMPTEL on board CGRO together with the GRB detector on Ulysses spacecraft, then they were localized in small error regions. These observations showed that the bursts were remarkably bright accompanying delayed high energy gamma-rays. ASCA observations have found a single X-ray source for each GRB on the possible location determined with the above instruments.
GRS1915+105 is an extraordinary X-ray transient which exhibits superluminal radio jets. In this paper, ASCA observations of the GRS1915+105 conducted from 1994 to 1997 are reported. Observations are carried out on the following dates each for ~ 20 ksec exposure; Sep 27 1994, April 20 1995, Oct 23 1996 and Apr 25 1997.
In this work, we have reported the interface characterization of rf sputtered ZnO/HfO2 in thin film transistor structure by dc current-voltage and admittance spectroscopy. The interface state density (Dit) of 1013 eV−1cm−2 was extracted from the Gp/ω vs ω plot was comparable to value obtained from the subthreshold behavior. The grain boundary trap density (NGB) of 9.12×1012 cm−2 was estimated using Levinson’s model. The interface state density distribution below the conduction band edge shows a decreasing trend with energy below the conduction band edge. We also studied the impact of introducing MgO interfacial layer between ZnO and HfO2 interface as an approach towards decreasing the interface state density.
CZT is a semiconductor material that promises to be a good candidate for uncooled gamma radiation detectors. However, to date, technological difficulties in production of large size defect-free CZT crystals are yet to be overcome. The most common problem is accumulation of tellurium precipitates as microscopic inclusions. These inclusions influence the charge collection through charge trapping and electric field distortion. The common work-around solutions are to fabricate pixelated detectors by either grouping together many small volume CZT crystals to act as individual detectors, or to deposit a pixelated grid of electrical contacts on a larger, but defective, crystal, and selectively collect charge. These solutions are satisfactory in an R&D environment, but are unsuitable for mass production and commercial development. Our modeling effort is aimed at quantifying the various contributions of tellurium inclusions in CZT crystals to the charge generation, transport, and collection, as a function of inclusions size, position, and concentration. We model the energy deposition of gamma photons in the sensitive volume of the detector using LANL’s MCNP code. The electron-hole pairs produced at the energy deposition sites are then transported through the defective crystal and collected as integral charge at the electrical contact sites using CERN’s Garfield software package. The size and position distribution of tellurium inclusions is modeled by sampling experimentally measured distributions of such inclusions on a variety of commercially-grown CZT crystals using IR microscopy and image processing software packages.
A single-grained Pb(Zr,Ti)O3 (PZT) was successfully grown for the gate dielectric of polycrystalline-silicon (poly-Si) thin-film transistor (TFT). The total structure was MoW/PZT/HfO2/poly-Si/glass. The giant single-grained PZT was obtained by controlling the artificial nucleation formed by Pt dots in a desirable location and enlarging the nucleated seed until it covers the poly-Si channel. The single-grained diameter size was 40 μm with a (100) dominated texture. The poly-Si memory device with single-grained PZT showed an excellent ferroelectric, electrical and reliability properties comparing with poly-Si memory device with poly-grained PZT. Moreover, eliminating the grain boundary in PZT film showed the fatigue and retention characteristics with only 1.1 % after 1013 cycles and 22 % after 1 month, respectively.
The stability of green phosphorescent OLEDs with different structures was evaluated through constant-current stressing. Through the modifications of the ITO anode by different plasma treatments and the hole transport layer (HTL) by incorporating inorganic dopants, we proved that energy level misalignment at the ITO/HTL interface leads to localized joule heating, accelerating defect generation and luminescence decay. Pulsed current stressing was then employed to suppress the joule-heating effect so as to differentiate the thermal and nonthermal factors governing the device degradation. For OLEDs with a large energy barrier at the ITO/HTL interface, the effective lifetime was markedly increased under pulsed operation, whereas in OLEDs with an appropriate interfacial energy level alignment, pulsed stressing with 10% duty cycle only improved the effective half life by ∼15% as compared to continuous-wave stressing, indicating a minor role played by joule heating.
Pm-Si:H PIN and NIP solar cells structures grown using plasma enhanced chemical vapor deposition (PECVD) technique were analyzed during 400 hrs of light-soaking exposition. The evolution of the structural and optical properties was observed and characterized by Raman spectroscopy, spectroscopic ellipsometry. The effect observed is related to defects creation due to induced hydrogen diffusion, break of Si-H bonds and the generation of dangling bonds that causes less passivated films. The film microstructure, and therefore the optical properties varied with the exposition time. The crystalline fraction of these structures presents a slight decrease and it is observed to be between 15 to 24% for the PIN and 5 to 10% for the NIP. The optical gap increases from 1.66 to 1.68 eV for the PIN structure while for the NIP no significant change is observed during light-soaking. Hydrogen diffusion during lights soaking generates a decrease on the absorption properties of the films which in turn is expected to reduce the device efficiency during operation. In this work we show that long range motion of hydrogen during light-soaking causes a hydrogen rearrangement on the film and microstructure changes. We determined that there is not an pronounced change on the film structure during prolonged light exposition related to the stability of the pm-Si:H films. The PIN structure properties are more affected during light soaking in comparison to the NIP structure which is expected to cause less degradation of its optoelectronic properties under illumination, and a more stable device during operation.
CuxO thin films have been deposited on a quartz substrate by reactive radio frequency (rf) magnetron sputtering at different target powers Pt (140-190 W) while keeping other growth process parameters fixed. Room-temperature photoluminescence (PL) measurements indicate considerable improvement of crystallinity for the films deposited at Pt>170 W, with most pronounced excitonic features being observed in the film grown using Pt=190 W. These results corroborate well with the surface morphology of the films, which was found more flat, smooth and homogeneous for Pt >170 W films in comparison with those deposited at lower powers.