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Thermal analyses of samples of thorium dicarbide in equilibrium with graphite show arrests which indicate phase transitions at 1427 ± 21°C arid 1481 ± 28°C. These thermal effects have been observed on heating and cooling both in standard thermal analysis and in differential thermal analysis using graphite as a reference material. The microstructure of thorium dicarbide samples shows the characteristic “herringbone” pattern of a material which has undergone a martensitic-type transition.
A high-temperature X-ray investigation has revealed that the observed thermal arrests correspond to erystallographic transformations. The monodinic modification found at room temperature is stable to 1427°C, at which temperature a tetragonal modification with a0 = 4.235 ± 0.002Å and c0 = 5.408 ± 0.002Å is formed. At 1481°C, the tetragonal is transformed to cubic with a0 = 5.809 ± 0.002 Å. The best agreement between observed and calculated intensities has been obtained with C-C units of 1.5-Å assumed bond length in space groups P42/mmc and Pa3 for the tetragonal and cubic modifications, respectively.
NGC 7027 is justifiably THE template spectrum for PNe. Its vast range of emission species – from molecular and neutral to ions with ionization potential > 120eV – its high surface brightness and accessibiliy for northern observatories make it the PN laboratory of choice. However the quality of the spectra from the UV to the IR is mixed, many line fluxes and identifications still remaining unchecked from photographic or image tube spectra. Very deep spectra of NGC 7027 (emission line strengths <10-4 of Hβ) in the 0.65 to 1.05μm region (Baluteau et al. 1995) showed the presence of many faint emission lines. Pequignot & Baluteau (1994) showed that heavy elements from the 4th, 5th and 6th rows of the Periodic Table have much higher abundances than Solar, confirming the synthesis of neutron capture elements in low mass stars and providing new constraints on stellar evolution theory.
We report the direct detection of cyclic diameter variations in the Mira variable χ Cygni. Interferometric observations made between 1997 July and 1998 September, using the Cambridge Optical Aperture Synthesis Telescope (COAST) indicate periodic changes in the apparent angular diameter with amplitude 45 per-cent of the smallest value.
The measurements were made in a 50 nm bandpass centred on 905 nm, which is only moderately contaminated by molecular absorption features. To assess the effects of atmospheric stratification on the apparent diameter measured in this band, we have also measured near-infrared diameters for a sample of five Miras, in both the J-band (1.3 μm) and Wing's (1971) 1.04 μm band, which is expected to isolate essentially pure continuum emission. We present J-band visibility curves which indicate that the intensity profiles of the stars in the sample differ greatly from each other.
A geological disposal facility (GDF) will include fissile materials that could, under certain conditions, lead to criticality. Demonstration of criticality safety therefore forms an important part of a GDF's safety case.
Containment provided by the waste package will contribute to criticality safety during package transport and the GDF operational phase. The GDF multiple-barrier system will ensure that criticality is prevented for some time after facility closure. However, on longer post-closure timescales, conditions in the GDF will evolve and it is necessary to demonstrate: an understanding of the conditions under which criticality could occur; the likelihood of such conditions occurring; and the consequences of criticality should it occur.
Work has addressed disposal of all of the UK's higher-activity wastes in three illustrative geologies. This paper, however, focuses on presenting results to support safe disposal of spent fuel, plutonium and highlyenriched uranium in higher-strength rock.
The results support a safety case assertion that post-closure criticality is of low likelihood and, if it was to occur, the consequences would be tolerable.
The discrete source of radio emission in Sagittarius is among the most intense in the whole sky, but its situation in the belt of emission from ionized hydrogen and other sources associated with the galactic plane makes it difficult to observe. The observations described in this paper were made at frequencies of 38, 81·5, 210, and 500 Mc./s.; at these low frequencies it is particularly difficult to obtain sufficient aerial resolving power to distinguish the discrete source from the background. Interferometer aerials were therefore used, and at 38 and 210 Mc./s. spacings up to λ60 were used, sufficient to resolve the source completely. At 81·5 Mc./s. various sections of the large interferometer aerial were used.
Two years ago the Cambridge 4-aerial interferometer  was adapted to work at a frequency of 159 Mc/s, the resolving power thereby being increased by a factor of four over that at the previous frequency, 81.5 Mc/s. The overall beamwidth at 159 Mc/s is 1.2 degrees by 7 degrees but the beam contains interference fringes in two planes at right angles, so that, by phase-switching between the east pair and the west pair of aerials, sources with angular diameters greater than about 7 minutes of arc are eliminated. A survey using this technique has been carried out by Edge and Shakeshaft and may be called a “small diameter” survey. If the phase-switching receiver is connected between the north pair and the south pair of aerials it is possible to record sources with diameters up to about 1 degree and to measure diameters between 2 and 8 minutes of arc. Archer and Baldwin have used the aerial in this way to make a “large diameter” survey. These two surveys will be referred to collectively as the 3C survey.
The boundaries of psychotic illness and the extent to which operational diagnostic categories are distinct in the long term remain poorly understood. Clarification of these issues requires prospective evaluation of diagnostic trajectory, interplay and convergence/divergence across psychotic illness, without a priori diagnostic or other restrictions.
The Cavan-Monaghan First Episode Psychosis Study (CAMFEPS), conducted using methods to attain the closest approximation to epidemiological completeness, incepts all 12 DSM-IV psychotic diagnoses. In this study we applied methodologies to achieve diagnostic reassessments on follow-up, at a mean of 6.4 years after first presentation, for 196 (97%) of the first 202 cases, with quantification of prospective and retrospective consistency.
Over 6 years, the 12 initial psychotic diagnoses were characterized by numerous transitions but only limited convergence towards a smaller number of more stable diagnostic nodes. In particular, for initial brief psychotic disorder (BrP), in 85% of cases this was the harbinger of long-term evolution to serious psychotic illness of diagnostic diversity; for initial major depressive disorder with psychotic features (MDDP), in 18% of cases this was associated with mortality of diverse causality; and for initial psychotic disorder not otherwise specified (PNOS), 31% of cases continued to defy DSM-IV criteria.
CAMFEPS methodology revealed, on an individual case basis, a diversity of stabilities in, and transitions between, all 12 DSM-IV psychotic diagnoses over 6 years; thus, psychotic illness showed longitudinal disrespect to current nosology and may be better accommodated by a dimensional model. In particular, a first episode of BrP or MDDP may benefit from more vigorous, sustained interventions.
Intermediate-level wastes (ILW) include substantial quantities of fissile material and controls are required to ensure that its storage, transport and disposal does not present a nuclear criticality hazard. This paper describes the Radioactive Waste Management Directorate's research to develop package fissile material limits (in the form of screening levels) for four different categories of ILW, defined according to uranium or plutonium composition: (1) irradiated natural and slightly enriched uranium (uranium containing up to 1.9 wt.% 235U); (2) low-enriched uranium (uranium containing up to 4 wt.% 235U); (3) high-enriched uranium (uranium containing up to 100 wt.% 235U); and (4) separated plutonium (plutonium containing up to 100 wt.% 239Pu).
The derivation of package screening levels was supported by neutron transport calculations that addressed conditions during waste package transport to a geological disposal facility (GDF), during the GDF operational phase and after GDF closure. The analysis included consideration of combinations of events and processes that could result in fissile material accumulation and concentration after GDF closure, when waste packages have deteriorated sufficiently for fissile material to be mobilized. The results of the calculations have provided input to Radioactive Waste Management Directorate's decision making on setting waste package screening levels.
The use of psychotropic medication is an important part of most psychiatrists' clinical practice. We propose here that psychiatry needs to give more prominence to psychopharmacology in order to ensure that psychiatric drugs are used effectively and safely. The issue has several ramifications, including the future of psychiatry as a medical discipline.
We have explored the effects of ion beam irradiation on the electrical and structural properties of superconducting thin films of YBa2Cu3O7-δ. Damage created by nuclear energy loss processes degrades the superconducting transitions. In general, the onset temperatures do not vary significantly with ion fluence, but the transition widths broaden until the resistance no longer reaches zero. This behavior is strikingly similar to that observed in granular superconducting films where islands of superconductor are progressively decoupled from each other, destroying the phase coherence. Data from resistance measurements as well as from Rutherford Backscattering and channeling measurements suggest that ion bombardment is not changing the volume fraction of superconducting material substantially.
The production, characterization, and consolidation of Fe3Al-based iron-aluminide powders are described. The consolidated powders were fabricated into sheet. The sheet was tensile tested from room temperature to 800°C and creep tested in the temperature range of 450 to 704°C. Mechanical properties were compared for nitrogen and argon atomized powders. Mechanical properties were also compared for argon atomized powders of Fe3Al alloys containing 2 and 5% Cr.
This paper reports the results of uniaxial and compression tests on IC-218LZr extruded bars at temperatures from 700 to 1000°C in air. Tensile results indicate reduction in ductility at temperatures between 750 to 900°C. However, the results show improvement in ductility above 950°C. Compression test results do not show a decrease in the ductility in the temperature range.
The stresses in Al-0.75w%Si-0.5w%Cu unpatterned metallization on silicon wafers have been measured using substrate curvature and x-ray diffraction techniques after quenching in liquid nitrogen. Stresses were measured with and without phospho-silicate glass overlayers and SiO2 underlayers, and thermal cycling followed by relaxation at room temperature. It was found that cooling the substrates to 77 K and warming to room temperature caused the metallization stress to go from tensile to compressive. Subsequent heating of the substrates to above ∼70°C followed by cooling to room temperature caused the stress to become tensile. Both compressive and tensile stresses were found to relax at room temperature with a time constant of 2.3 ± 0.2 hours. The magnitude of stress relaxation was a function of temperature, being about 20 MPa after heating to 240°C. The metallization exhibited both compressive and tensile flow stresses of ∼100 MPa near room temperature.
The asymmetrical forward versus reverse - bias DC electrical conductivity (macroscopic and also nanoscopic) through Langmuir-Blodgett multilayers and monolayers of γ-(nhexadecyl) quinolinum tricyanoquinodimethanide, C16H33Q-3CNQ (1) is attributable to rectification of electrical current by a single molecule.
The cathodic arc provides a method for depositing extremely hard thin carbon films. These films are potentially useful in a variety of tribological applications including protection of magnetic media and recording heads. Effective application of this technology requires an improved understanding of the influence of process parameters on the microstructure and hardness of the deposited films. In this work, we use a commercially available filtered cathodic arc to deposit tetrahedral amorphous carbon at several deposition angles.