Far-infrared pump-probe measurement of the lifetime of the 2p−1 shallow donor level in n-GaAs

The low temperature lifetime of electrons excited in the 2p^?1 donor level of n-GaAs has been studied in a far-infrared pump-probe experiment. The measurement has been carried out using a pulsed far-infrared molecular gas laser working at a wavelength of 292µm, with the sample in a magnetic field of 5.1 T, resonant with the 1s_o?2p^?1 transition. Two FIR pulses are sliced from one FIR-laser pulse by means of optical switching techniques using two Q-switched Nd:YAG lasers. The first pulse is used to saturate the transition, while the second pulse probes the return of the population in the excited state towards thermal equilibrium as a function of the time delay after the excitation pulse. The value of 350±50 ns found for the lifetime falls in line with CW saturation results on materials with other doping concentrations.     

Control of lipolysis in intra-abdominal fat cells of nonhuman primates: comparison with humans

The mechanisms that control lipolysis in intra-abdominal fat cells from various primate species, the marmoset (Callithrix jacchus), the baboon (Papio papio), and the macaque (Macaca fascicularis), were compared to those of human intraabdominal fat cells. Selective beta 1- or beta 2-adrenoceptor agonists induced lipolysis in all species. Selective beta 3-agonists (BRL 37344, CL 316243, and SR 58611) acted as partial agonists in marmoset but were inefficient in other primates, including humans. alpha 2-Adrenoceptor number ([3H]RX 8210002 binding) equalized (baboon) or exceeded (other primates) beta 1/beta 2-adrenoceptors ([3H]CGP 12177 binding). Baboon fat cell membranes expressed similar amounts of coupled beta- and alpha 2-adrenoceptors. In all species, norepinephrine- or epinephrine-induced lipolysis did not reach the lipolytic effect of isoproterenol but their effects were enhanced after alpha 2-adrenoceptor blockade. N6-phenylisopropyladenosine (PIA) induced a full antilipolytic effect in baboon, macaque, and human adipocytes through adenosine receptors ([3H]DPCPX binding). Peptide YY (PYY) weakly inhibited lipolysis in baboon. Adrenocorticotropic hormone (ACTH) was inactive whereas parathyroid hormone (PTH) partially stimulated lipolysis in primates. Histamine was partially lipolytic in marmoset only. This study emphasizes the similarities of the mechanisms controlling the lipolysis in nonhuman primate and in human adipocytes and suggests that the baboon and the macaque should provide unique models for the study of the regulation of lipolysis.     

Mixed waste ferrite as a novel sorbent for carbon dioxide derived from flue gases

Ferrite is a potential sorbent for flue gases such as CO₂, H₂S and SO₂. This paper discusses the adsorption and decomposition of CO₂ into carbon by hydrogen-activated waste ferrites prepared from Berkeley Pit acid mine water (Butte, MT). The decomposition effectiveness of these waste ferrites was studied at 300 °C and compared with the synthetic magnetite obtained from ferrous sulfate solution in our laboratory. The decomposition was measured by two methods: indirectly by measuring the adsorption rate of CO₂ and directly by analysing the carbon deposited on the samples. The results indicated that the mixed waste ferrite had good affinity for the adsorption and decomposition. The CO₂ decomposition data of both sorbents fitted the first-order reaction kinetics. Even though the surface area of the magnetite was higher than that of waste ferrite, the CO₂ decomposition rate of the waste ferrite was estimated to be 2.5 times higher than that of magnetite under identical conditions. The carbon analysis deposited on the sample indicated that the CO₂ was 100% decomposed into carbon and other carbon/hydrogen compounds by the waste ferrite, whereas the conversion was 43% by the magnetite. In terms of specific adsorption of carbon, ferrite was three to five times more efficient than magnetite.     

Zirconium recovery from zircaloy shavings

A chlorination process for recovering Zr from zircaloy scrap has been studied. Zircaloy chlorination was possible at temperatures as low as 220 °C. The scale microstructure and its effect on the zircaloy reactivity was analysed using Thermogravimetric analysis (TGA), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS) and scanning electron microscopy (SEM) techniques. A solid-solid phase transformation took place into the oxide scale during the zircaloy chlorination. Zirconium, as ZrCl₄(g), was separated from the oxide scale and chlorides of Cr and Fe. The effect of the reaction temperature was also analysed.     

Occupational stress, social support, and the costs of health care.

Relationships among health care costs, social support, and occupational stress are investigated. Health care cost data were collected over two years for 260 working individuals. Multiple regression analyses were used to control for initial health care costs, age, and gender in predicting later costs; independent variables were stress, strain, social support, and their interactions. Main effects and interactions each accounted for significant proportions of the variance in various health care costs.     

The effect of particle distribution on damage formation in particulate reinforced metal matrix composites deformed in compression

Image analysis results are reported on the generation of damage in particulate reinforced metal matrix composites during compressive deformation. The technique allows the automated collection of data on the incidence of particle fracture and void formation in the matrix as a function of important microstructural parameters such as local particle volume fraction and particle size. There is a strong relationship between damage and the local volume fraction of the reinforcement proving that damage formation is accentuated in regions of particle clustering. With the SiC reinforced materials examined, there was observed to be a change in dominance of damage mechanism from particle fracture at low local volume fractions to void formation in the matrix within strongly clustered regions. The results are compared with finite element (FE) modelling of the compressive deformation of clustered particles using a simple cluster of equi-spaced particles. The FE results suggest that plastic flow is generally inhibited in clustered regions. In certain highly clustered configurations shielding is such that flow does not occur in the heart of the cluster even at high levels of average plastic strain. The modelling suggests that the change in dominance of damage mechanism is related to the dramatic increase in tensile hydrostatic stresses in the matrix with higher levels of particle clustering.     

Low-flow measurements with roller/blade tachometric chamber transducers

Three roller/blade tachometric chamber transducers, with capacities of 2, 10, and 20 cm³/rev, have been designed for measuring low flow rates. Translated from Izmeritel'naya Tekhnika, No. 5, pp. 37–41, May, 1996.