兼作电压监控电路的低压降线性稳压器

很多低压降稳压器都带有一个使能输入脚,它可以用作一个廉价的电压监控IC。虽然使能脚通常是用于切断稳压器的输出以节省功耗,但增加几个分立元件就可以使稳压器输出控制相应输入电压下的通、断。因此,可以将此电路用作一个电压监控器或一个特性受控的线性稳压器。     

Assessment of weighting methodology for the National Comorbidity Survey

The authors studied weighting adjustments for the National Comorbidity Survey (1990-1992), a large-scale national epidemiologic investigation of the prevalence, risk factors, and consequences of psychiatric morbidity and comorbidity in the United States. Weighting adjustments for differential selection within households, new construction, unit nonresponse, and poststratification were examined separately and in combination. Specific issues addressed included the magnitude of the bias incurred from ignoring the weights, the added variance from weighting and how well this was predicted by simple formulae, and the performance of methods for trimming the weights. Weights had quite modest effects on point estimates of prevalences but resulted in major increases in variance unless trimmed. The weights after trimming and poststratification appeared to work well. It is suggested that the added variance from weighting be carefully monitored in similar surveys. Alternatives to the use of trimming for controlling variance are worth exploring.     

60-GHz power performance of ion-implantedInxGa(1-x/)AsGaAs MESFETs

State-of-the-art 60-GHz power performance is reported for ion-implanted InGaAs/GaAs MESFETs with 0.25×200-μm gate length. At output power of 100 mW, a power-added efficiency of 15% and associated gain of 4.2 dB were obtained and a saturated output power of 121 mW was achieved for the same device. These results are comparable to the best reported millimeter-wave power performance of InGaAs/GaAs pseudomorphic HEMTs     

Geostatistical modeling of the spatial distribution of soil dioxin in the vicinity of an incinerator. 2. Verification and calibration study

A key component in any investigation of cause-effect relationships between point source pollution, such as an incinerator, and human health is the availability of measurements and/or accurate models of exposure at the same scale or geography as the health data. Geostatistics allows one to simulate the spatial distribution of pollutant concentrations over various spatial supports while incorporating both field data and predictions of deterministic dispersion models. This methodology was used in a companion paper to identify the census blocks that have a high probability of exceeding a given level of dioxin TEQ (toxic equivalents) around an incinerator in Midland, MI. This geostatistical model, along with population data, provided guidance for the collection of 51 new soil data, which permits the verification of the geostatistical predictions, and calibration of the model. Each new soil measurement was compared to the set of 100 TEQ values simulated at the closest grid node. The correlation between the measured concentration and the averaged simulated value is moderate (0.44), and the actual concentrations are clearly overestimated in the vicinity of the plant property line. Nevertheless, probability intervals computed from simulated TEQ values provide an accurate model of uncertainty: the proportion of observations that fall within these intervals exceeds what is expected from the model. Simulation-based probability intervals are also narrower than the intervals derived from the global histogram of the data, which demonstrates the greater precision of the geostatistical approach. Log-normal ordinary kriging provided fairly similar estimation results for the small and well-sampled area used in this validation study; however, the model of uncertainty was not always accurate. The regression analysis and geostatistical simulation were then conducted using the combined set of 53 original and 51 new soil samples, leading to an updated model for the spatial distribution of TEQ in Midland, MI.     

Half-micrometer gate-length ion-implanted GaAs MESFET with 0.8-dBnoise figure at 16 GHz

Ion-implanted GaAs MESFETs with half-micrometer gate length have been fabricated on 3-in-diameter GaAs substrates. At 16 GHz, a minimum noise figure of 0.8 dB with an associated gain of 6.3 dB has been measured. This noise figure is believed to be the lowest ever reported for 0.5- and 0.25-μm ion-implanted MESFETs, and is comparable to that for 0.25-μm HEMTs at this frequency. By using the Fukui equation and the fitted equivalent circuit model, a K_f factor of 1.4 has been obtained. These results clearly demonstrate the potential of ion-implanted MESFET technology for K-band low-noise integrated circuit applications     

0.25-μm gate millimeter-wave ion-implanted GaAs MESFETs

Quarter-micrometer gated ion-implanted GaAs MESFETs which demonstrate device performance comparable to AlGaAs/InGaAs pseudomorphic HEMTs (high-electron mobility transistors) have been successfully fabricated on 3-in-diameter GaAs substrates. The MESFETs show a peak extrinsic transconductance of 480 mS/mm with a high channel current of 720 mA/mm. From S-parameter measurements, the MESFETs show a peak current-gain cutoff frequency f_t of 68 GHz with an average f_t of 62 GHz across the wafer. The 0.25-μm gate MESFETs also exhibit a maximum-available-gain cutoff frequency f_t greater than 100 GHz. These results are the first demonstration of potential volume production of high-performance ion-implanted MESFETs for millimeter-wave application     

Socioeconomic factors, health behaviors, and mortality: results from a nationally representative prospective study of US adults

CONTEXT: A prominent hypothesis regarding social inequalities in mortality is that the elevated risk among the socioeconomically disadvantaged is largely due to the higher prevalence of health risk behaviors among those with lower levels of education and income. OBJECTIVE: To investigate the degree to which 4 behavioral risk factors (cigarette smoking, alcohol drinking, sedentary lifestyle, and relative body weight) explain the observed association between socioeconomic characteristics and all-cause mortality. DESIGN: Longitudinal survey study investigating the impact of education, income, and health behaviors on the risk of dying within the next 7.5 years. PARTICIPANTS: A nationally representative sample of 3617 adult women and men participating in the Americans' Changing Lives survey. MAIN OUTCOME MEASURE: All-cause mortality verified through the National Death Index and death certificate reviews. RESULTS: Educational differences in mortality were explained in full by the strong association between education and income. Controlling for age, sex, race, urbanicity, and education, the hazard rate ratio of mortality was 3.22 (95% confidence interval [CI], 2.01-5.16) for those in the lowest-income group and 2.34 (95% CI, 1.49-3.67) for those in the middle-income group. When health risk behaviors were considered, the risk of dying was still significantly elevated for the lowest-income group (hazard rate ratio, 2.77; 95% CI, 1.74-4.42) and the middle-income group (hazard rate ratio, 2.14; 95% CI, 1.38-3.25). CONCLUSION: Although reducing the prevalence of health risk behaviors in low-income populations is an important public health goal, socioeconomic differences in mortality are due to a wider array of factors and, therefore, would persist even with improved health behaviors among the disadvantaged.     

Neutron transmutation doping of high purity GaAs

High purity n-type GaAs samples grown by a variety of epitaxial techniques were transmutation doped with a low fluence of thermal neutrons to produce Ge and Se impurities from the host Ga and As atoms, respectively. Samples were chosen having low concentrations of Se and Ge donors and Ge acceptors prior to doping. Photothermal ionization and photoluminescence spectra as well as Hall effect data were recorded before and after doping and subsequent low temperature anneals. The high purity of these samples and low neutron dose, together with the low noise and high resolu-tion of the photothermal ionization measurements, has allowed the precise identification of the Se and Ge donor peaks through an accurate determination of their ls-2p(m=−l) transition energies. Comparison of the relative concentra-tions of shallow donors and acceptors, obtained from the photothermal ionization and photoluminescence spectra, with N_D and N_A determined from the Hall effect data, allowed the activation of Se and Ge to be measured. The observation of Ge_Ass acceptors after doping and of the incomplete activation of Se as donors are interpreted in terms of transmutation induced recoil of the Se and Ge due to γ-pray and e -v_e pair emission.