Tunneling through Thin Oxides—New Insights from Microscopic Calculations

In this paper, we summarize our recent efforts to analyze transmission probabilities of extremely thin SiO₂ gate oxides using microscopic models of Si[100]-SiO₂-Si[100] heterojunctions. We predict energy-dependent tunneling masses and their influence on transmission coefficients, discuss tunneling probabilities and analyze effects arising from the violation of parallel momentum conservation. As an application of the present method, gate currents in short bulk MOSFETs are calculated, including elastic defect-assisted contributions.     

Modern electronic and chemical thermometers used in the axilla are inaccurate

Rectal and axillary temperatures were measured simultaneously in 83 children using three different thermometer devices providing 166 pairs of results. In the first series consisting of 22 febrile children (44 measurements) and 20 afebrile children (40 measurements), the rectal mercury measurement was compared to an axillary mercury and axillary Tempa-DOT thermometer. The axillary mercury had sensitivity of 14/22 (64%) and specificity of 20/20 (100%) while the Tempa-DOT had sensitivity of 15/22 (68%) and specificity of 19/20 (95%). In the second series comprising 21 febrile children (42 measurements) and 20 afebrile children (40 measurements) the axillary mercury had sensitivity of 11/21 (52%) and specificity of 20/20 (100%) while the electronic thermometer had sensitivity of 10/21 (48%) and specificity of 20/20 (100%). Regardless of the thermometer used, the axilla is a poor alternative to rectal measurements in the diagnosis of fever. CONCLUSION: Mercury-free thermometers, when used in the axilla are as poor alternatives to rectal measurements as mercury-in-glass thermometers.     

Structure of very early protein folding intermediates: new insights through a variant of hydrogen exchange labelling

BACKGROUND: Hydrogen exchange labelling has been a key method in characterizing the structure of transient folding intermediates. In studies of several proteins, however, there has been clear spectroscopic evidence for partial folding of some kind at very early times, before any protection from exchange was measurable. These results, presumably a consequence of limited stability of specific backbone interactions, have made it difficult to assess the extent of native-like folding in the very early intermediates. We have used a variant of the labelling method to investigate marginally stable structures formed within the first few milliseconds of refolding of two such proteins, hen lysozyme and ubiquitin. RESULTS: In lysozyme, population of a subset of native-like secondary structures on this timescale is revealed, thus reconciling the exchange behaviour with circular dichroism measurements and confirming the significance of the rapidly formed embryonic structure as a foundation for the subsequent folding pathway. In the case of ubiquitin, by contrast, no significantly protective structure was detectable, suggesting that here secondary structural elements can be populated only marginally ahead of the major cooperative folding event; this was also supported by stopped-flow circular dichroism measurements. CONCLUSIONS: The hydrogen exchange approach can be extended to probe the formation of native-like structure formed in very early folding intermediates, even when the stability of specific interactions is marginal. In the case of lysozyme, this has provided a new window on an early stage of organization of the alpha-helical domain.     

The bioconversion of tunisian phosphorite usingAspergillus niger

It is well known that the production of phosphoric fertilizers by traditional methods is connected with certain environmental problems, particularly related to use of acids during the decomposition of natural phosphates. A basic problem is also the fact that only 15 – 20% of the phosphorus contained in superphosphates is assimilated by plants.The development of methods to process natural phosphates without acid precipitation has potential advantages and in this respect biotechnological processing of natural phosphates in order to obtain organo-mineral fertilizers is very promising. The possibility of bioconverting the phosphorus of natural phosphates by usingAspergillus niger fungi through their deep incubation has been investigated. The investigations aim to achieve a high degree of P₂O₅ extraction from the phosphates with conversion from a non-utilizable to a utilizable form. The influence of the fungal strain, the kind of nutritive medium and the time of incubation of the process of biological mobilization of the phosphate rock is examined.It was established that the time of incubation, the kind of micro-organisms of theAspergillus niger group, as well as the kind of nutritive medium, influence significantly the process of bioconversion and the conversion of phosphorus from non-utilizable to water-soluble and utilizable for plants form. A maximum degree 90% of phosphorus extraction in the form of water-soluble and citrate-soluble has been reached for 10-day incubation. Physicochemical examinations have been carried out and they have proved that, as a result of the produced organic acids, a process of decomposition of the initial Tunisian phosphorite takes place.     

38. Generalversammlung von CENELEC

Ohne Zusammenfassung     

Crystal structures of Escherichia coli and Salmonella typhimurium 3-isopropylmalate dehydrogenase and comparison with their thermophilic counterpart from Thermus thermophilus

The basis of protein stability has been investigated by the structural comparison of themophilic enzymes with their mesophilic counterparts. A number of characteristics have been found that can contribute to the stabilization of thermophilic proteins, but no one is uniquely capable of imparting thermostability. The crystal structure of 3-isopropylmalate dehydrogenase (IPMDH) from the mesophiles Escherichia coli and Salmonella typhimurium have been determined by the method of molecular replacement using the known structure of the homologous Thermus thermophilus enzyme. The structure of the E. coli enzyme was refined at a resolution of 2.1 A to an R-factor of 17.3%, that of the S. typhimurium enzyme at 1.7 A resolution to an R-factor of 19.8%. The three structures were compared to elucidate the basis of the higher thermostability of the T. thermophilus enzyme. A mutant that created a cavity in the hydrophobic core of the thermophilic enzyme was designed to investigate the importance of packing density for thermostability. The structure of this mutant was analyzed. The main stabilizing features in the thermophilic enzyme are an increased number of salt bridges, additional hydrogen bonds, a proportionately larger and more hydrophobic subunit interface, shortened N and C termini and a larger number of proline residues. The mutation in the hydrophobic core of T. thermophilus IPMDH resulted in a cavity of 32 A3, but no significant effect on the activity and thermostability of the mutant was observed.     

Sociodemographic factors and the variation in syphilis rates among US counties, 1984 through 1993: an ecological analysis

OBJECTIVES: Syphilis in the United States is focally distributed, with high incidence rates in the South and in metropolitan areas nationwide. In this study an ecological analysis, using the county as the unit of analysis, was performed to generate hypotheses about community-level determinants of syphilis rates. METHODS: Bivariate rank correlations and multivariate, backward stepwise elimination linear regressions were performed. Mean annual incidence of primary- and secondary-stage syphilis in a county was the dependent variable, and county sociodemographic characteristics (from census data) were the independent variables. RESULTS: In the multivariate regression model, sociodemographic characteristics accounted for 71% of the variation in syphilis rates among counties. With other factors accounted for, the most highly correlated characteristics were percentage non-Hispanic Black population, county location in the South, percentage of the population that was urban, percentage Hispanic population, and percentage of births to women younger than 20 years. CONCLUSIONS: Most of the variation in syphilis rates among counties is accounted for by sociodemographic characteristics. Identification and remediation of modifiable health determinants for which these factors are markers are needed to improve the health status of these populations.     

Capacity and power control for CDMA microcells

Capacity and power control issues are considered for urban CDMA microcells that operate on channels characterized by log-normal shadowing and Nakagami fading. The effects of fading on the desired and interfering signals, variations in the shadow standard deviation, imperfect power control, and the requiredE _b /N _o for satisfactory link operation are investigated. It is shown that the reverse channel is relatively insensitive, and the forward channel very sensitive, to shadow and fading variations. Power control error is shown to significantly degrade reverse channel capacity. Twobiased forward channel power control strategies are introduced to enhance existing unbiasedbalancing forward channel power control algorithms.This research has been supported by BNR Inc.