Reversibility of scrapie inactivation is enhanced by copper

The only known difference between the cellular (PrPC) and scrapie-specific (PrPSc) isoforms of the prion protein is conformational. Because disruption of PrPSc structure decreases scrapie infectivity, restoration of the disease-specific conformation should restore infectivity. In this study, disruption of PrPSc (as monitored by the loss of proteinase K resistance) by guanidine hydrochloride (GdnHCl) resulted in decreased infectivity. Upon dilution of the GdnHCl, protease resistance of PrP was restored and infectivity was regained. The addition of copper facilitated restoration of both infectivity and protease resistance of PrP in a subset of samples that did not renature by the simple dilution of the GdnHCl. These data demonstrate that loss of scrapie infectivity can be a reversible process and that copper can enhance this restoration of proteinase K resistance and infectivity.     

Reaction of water vapor and oxygen with liquid uranium

The reactions of water vapor and oxygen with liquid uranium were studied by modulated molecular-beam mass spectrometric methods. Equivalent pressures of the reactant fluxes on the surface ranged from 6×10 ^–6 to 2×10^–4 torr. Temperatures up to 1570 K were investigated. The metal surface was kept clean during reaction by mechanical removal of the oxide formed with a tungsten needle. For the clean liquid uranium surface, a water reaction probability of 0.4 was deduced both from measurement of the reaction-product hydrogen signal and by the temperature dependence of the scattered reactant signal. Based solely on the latter measure, a reaction probability of 0.6 was estimated for oxygen. The reaction probabilities on the clean surface were temperatureindependent. They decreased as the coverage of the surface by islands of oxide increased and, for water, appeared to approach a value of 0.08 for a surface completely covered with an oxide estimated to be 500 Å thick. Bombardment of the surface during reaction with argon ions produced an increase in the reactivity on solid uranium but had a negligible effect on the reaction probability for the liquid.     

Improving the SMAC atmospheric correction code by analysis of Meteosat Second Generation NDVI and surface reflectance data

In order to obtain high quality data, the correction of atmospheric perturbations acting upon land surface reflectance measurements recorded by a space-based sensor is an important topic within remote sensing. For many years the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) radiative transfer model and the Simplified Method for Atmospheric Correction (SMAC) codes have been used for this atmospheric correction, but previous studies have shown that in a number of situations the quality of correction provided by the SMAC is low. This paper describes a method designed to improve the quality of the SMAC atmospheric correction algorithm through a slight increase in its computational complexity. Data gathered from the SEVIRI aboard Meteosat Second Generation (MSG) is used to validate the additions to SMAC, both by comparison to simulated data corrected using the highly accurate 6S method and by comparison to in-situ and 6S corrected SEVIRI data gathered for two field sites in Africa. The additions to the SMAC are found to greatly increase the quality of atmospheric correction performed, as well as broaden the range of atmospheric conditions under which the SMAC can be applied. When examining the Normalised Difference Vegetation Index (NDVI), the relative difference between SMAC and in-situ values decreases by 1.5% with the improvements in place. Similarly, the mean relative difference between SMAC and 6S reflectance values decreases by a mean of 13, 14.5 and 8.5% for Channels 1, 2 and 3 respectively. Furthermore, the processing speed of the SMAC is found to remain largely unaffected, with only a small increase in the time taken to process a full SEVIRI scene. Whilst the method described within this paper is only applicable to SEVIRI data, a similar approach can be applied to other data sources than SEVIRI, and should result in a similar accuracy improvement no matter which instrument supplies the original data.     

Uranium-zirconium hydride fuel properties

Properties of the two-phase hydride U_0.3ZrH_1.6 pertinent to performance as a nuclear fuel for LWRs are reviewed. Much of the available data come from the Space Nuclear Auxiliary Power (SNAP) program of 4 decades ago and from the more restricted data base prepared for the TRIGA research reactors some 3 decades back. Transport, mechanical, thermal and chemical properties are summarized. A principal difference between oxide and hydride fuels is the high thermal conductivity of the latter. This feature greatly decreases the temperature drop over the fuel during operation, thereby reducing the release of fission gases to the fraction due only to recoil. However, very unusual early swelling due to void formation around the uranium particles has been observed in hydride fuels. Avoidance of this source of swelling limits the maximum fuel temperature to ∼650 °C (the design limit recommended by the fuel developer is 750 °C). To satisfy this temperature limitation, the fuel-cladding gap needs to be bonded with a liquid metal instead of helium. Because the former has a thermal conductivity ∼100 times larger than the latter, there is no restriction on gap thickness as there is in helium-bonded fuel rods. This opens the possibility of initial gap sizes large enough to significantly delay the onset of pellet-cladding mechanical interaction (PCMI). The large fission-product swelling rate of hydride fuel (3× that of oxide fuel) requires an initial radial fuel-cladding gap of ∼300 m if PCMI is to be avoided. The liquid-metal bond permits operation of the fuel at current LWR linear-heat-generation rates without exceeding any design constraint. The behavior of hydrogen in the fuel is the source of phenomena during operation that are absent in oxide fuels. Because of the large heat of transport (thermal diffusivity) of H in ZrH_x, redistribution of hydrogen in the temperature gradient in the fuel pellet changes the initial H/Zr ratio of 1.6 to ∼1.45 at the center and ∼1.70 at the periphery. Because the density of the hydride decreases with increasing H/Zr ratio, the result of H redistribution is to subject the interior of the pellet to a tensile stress while the outside of the pellet is placed in compression. The resulting stress at the pellet periphery is sufficient to overcome the tensile stress due to thermal expansion in the temperature gradient and to prevent radial cracking that is a characteristic of oxide fuel. Several mechanisms for reduction of the H/Zr ratio during irradiation are identified. The first is transfer of impurity oxygen in the fuel from Zr to rare-earth oxide fission products. The second is the formation of metal hydrides by these same fission products. The third is by loss to the plenum as H₂.The review of the fabrication method for the hydride fuel suggests that its production, even on a large scale, may be significantly higher than the cost of oxide fuel fabrication.     

Silicone elastomers with controlled surface composition using argon or hydrogen plasma treatment

Plasma treatment of poly(dimethyl siloxane) (PDMS) leads to changes in the surface composition that can be followed by X‐ray photoelectron spectroscopy (XPS). Prolonged plasma treatment in argon or hydrogen leads to an increase in oxygen, a decrease in carbon, and only minor changes in the silicon content. The extent of the change in elemental composition is dependent on the plasma conditions (e.g., the power and pressure during the treatment). We have determined how these parameters influence the surface composition of PDMS exposed to argon and hydrogen microwave plasma as a function of treatment time. A model has been developed describing the extent of change in surface composition under different plasma conditions. The power had a large impact on the rate of change in elemental surface composition, whereas the pressure had only a minor influence. We show that the rate of change in elemental composition can be described by one factor common for all treatments and one factor specific for each plasma condition of power, pressure, and gas. Using this model we can determine the plasma parameters and treatment time to obtain any desired extent of surface modification. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1378–1383, 2003     

The use of computed microtomography to monitor morphological changes in small animals

RATIONALE AND OBJECTIVES: We investigate the methodological aspects of computerised microtomography (Cm 1) for monitoring the development of osteoporosis in male Sprague-Dawley rats. METHODS: 120 Rats were gastrectomized or sham operated. Femurs were prepared and tomograms with spatial resolutions of 5-500 mm were made. Bone diameters, bone areas and moments of inertia were determined from the tomograms. Optimal slice position and the need for spatial resolution for future in vivo applications were investigated. In order to minimise the absorbed dose to the specimen, a theoretical model for determination of optimal irradiation conditions is developed. RESULTS: Gastrectomy caused dramatic changes in the bone architecture. The main features were vaccuolisation of the bone and reduced amounts of compact bone. While the outer diameters of tubular bones were largely unaffected, their inner diameters were greatly increased following gastrectomy. Relative bone area and moment of inertia were greatly reduced. Optimal photon energy was 12 keV. CONCLUSIONS: It is possible to monitor gastrectomy-evoked changes in bone morphology at various sites in rats with computerised microtomography. The changes are suggestive of osteoporosis.     

7.4 Gbit monolithically integrated GaAs/AlGaAs laser diode-laser driver structure

A molecular beam epitaxy (MBE) grown GaAs/AlGaAs multiquantum well laser, monolithically integrated with a laser driver was realised on 2 inch GaAs substrate wafers. In an optical data communication set up, performance up to data rates of 7.4 Gbit/s was demonstrated.<>     

Leucocyte elastase as a marker in the diagnosis of acute appendicitis

OBJECTIVE: To investigate the value of measuring the activity of the leucocyte elastase complex in plasma in the diagnosis of acute appendicitis, either as a single or four-hourly test. DESIGN: Open study. SETTING: Teaching hospital, Sweden. SUBJECTS: 165 consecutive patients admitted with suspected acute appendicitis. MAIN OUTCOME MEASURES: Correlation of concentrations of leucocyte elastase complex (elastase) and total white blood cell count (WBC) with C-reactive protein concentration and histological appearance of the appendix. RESULTS: Of 165 patients, 101 patients had their appendixes removed, and of these 86 had histologically confirmed appendicitis. An elastase value of less than 54 micrograms/l was considered to be the reference range. Elastase activity measured on admission gave a sensitivity of 61% and a specificity of 43% for acute appendicitis compared with the WBC which had a sensitivity of 81% and a specificity of 36%. The above blood tests were taken on two or more occasions four hourly after admission in 29 patients. Appendicitis was found in 25 of the 29 cases (87%), in which repeated tests showed a significant reduction in WBC together with a definite but not significant reduction in the elastase activity during the preoperative period. Repeated tests were of no value. CONCLUSIONS: Measurement of the leucocyte elastase complex in plasma does not increase the accuracy of the diagnosis of acute appendicitis. There was no significant correlation between the leucocyte elastase activity and the total white cell count.     

Thermodynamics of the Zr-H System

The consistencies among the reported univariant hydrogen pressures in the three two-phase regions of the Zr-H system, aZr/δZrH_2-xαZr/βZr, and βRZr/δZrH_2–x, are evaluated with the thermodynamic constraint derived by Speiser.¹⁶ Hydrogen dissolution in αZr is evaluated by checking the consistencies among the Sieverts'law constant, the terminal solubility, and the corresponding two-phase univariant pressures involving this phase. A modified Sieverts'law is proposed for the complicated behavior of hydrogen dissolution in βZr. An analytical compositiontemperature-pressure relationship for δ ZrH_2–x is established by using the quasi-chemical model derived by Arita et al . The thermodynamic constraint of the free energy of formation of ZrH₂ shows that the value measured by Fredricken et al . is the most reliable. In addition, a more accurate free energy of formation of zirconium hydride at the upper phase boundary of αZr/δZrH_2–x two-phase region is suggested.