GaN and AlGaN metal–semiconductor–metal photodetectors

GaN based interdigital metal–semiconductor–metal (MSM) photodetectors have been successfully fabricated. The MSM structures were patterned on highly resistive GaN and the ternary compound, AlGaN. For the highly resistive GaN detector, the lowest dark current is 0.1 nA and the UV responsivity of the device was about 460 A W⁻¹ at a DC bias of 5 V. The AlGaN with 24% Al exhibited larger gains of up to 10⁶ A W⁻¹ at 20 V, but at a very high dark current, 1 mA, and very long detector responses, greater than 60 s. The high gain in this device is not well understood. The preliminary measurements indicate that tunneling occurs at high electric fields since a negative temperature coefficient for the breakdown voltage was observed.     

Sex chromosome meiotic drive in stalk-eyed flies

Meiotically driven sex chromosomes can quickly spread to fixation and cause population extinction unless balanced by selection or suppressed by genetic modifiers. We report results of genetic analyses that demonstrate that extreme female-biased sex ratios in two sister species of stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei, are due to a meiotic drive element on the X chromosome (Xd). Relatively high frequencies of Xd in C. dalmanni and C. whitei (13-17% and 29%, respectively) cause female-biased sex ratios in natural populations of both species. Sex ratio distortion is associated with spermatid degeneration in male carriers of Xd. Variation in sex ratios is caused by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Y-linked polymorphism for resistance to drive exists in C. dalmanni in which a resistant Y chromosome reduces the intensity and reverses the direction of meiotic drive. When paired with Xd, modifying Y chromosomes (Ym) cause the transmission of predominantly Y-bearing sperm, and on average, production of 63% male progeny. The absence of sex ratio distortion in closely related monomorphic outgroup species suggests that this meiotic drive system may predate the origin of C. whitei and C. dalmanni. We discuss factors likely to be involved in the persistence of these sex-linked polymorphisms and consider the impact of Xd on the operational sex ratio and the intensity of sexual selection in these extremely sexually dimorphic flies.     

Estimation of atmospheric transmittance from upper-air humidity

A very simple model of atmospheric transmittance uses as its input regularly observed and archived measures of upper air humidity. The five model parameters were determined empirically to optimize the agreement with radiation measured at six sites in the northwestern contiguous U.S. in summer and winter 1990. The model uses the relative humidity at 500 hPa, the relative humidity at either 950 hPa or 800 hPa depending on the altitude of the station, and the precipitable water.Although the model does not use cloud observations explicitly, it is partitioned into a low-humidity stage and a high-humidity stage with markedly different dependences on relative humidity. In the low-humidity stage the transmittance is approximated as the product of factors for dry air and for water vapor. In the high-humidity stage the transmittance is the product of the transmittances of each of the two layers used; the product is a strongly decreasing function of relative humidity, as a representation of the effect of cloud.A split-sample test using measurements for spring and autumn indicated that the model parameters were not badly distorted by conditions unique to the summer and winter seasons. In terms of the average daily global shortwave radiation received at the surface, the rms errors are 31 W m⁻² in spring, 33 in summer, 30 in autumn, and 18 in winter. The corresponding relative errors are 0.25, 0.17, 0.20, and 0.31. Because of high-frequency temporal variation in the model residuals, the error declines to about half of the daily error for 7-day averages and to about a quarter of the daily error for 30-day averages.     

MEASUREMENTS AND ANALYSIS OF THE PARTICULATE EMISSION FROM A DIRECT INJECTION DIESEL

For five different operating conditions of varying speed and load, measurements have been made of the particulate emissions using a mini-dilution tunnel operated at different dilution ratios and air temperatures. Particles were sized by electron microscopy and employment of interactive computer graphics.

Analysis of results leads to conclusions that the organic fraction of the particulates can be explained by either an adsorption or condensation interaction with the gas phase. Account must be taken of the multi-component nature of the organic species and that adsorption is multilayer in modeling these processes.     

A deterministic model to quantify pathogen loads in drinking water catchments: pathogen budget for the Wingecarribee.

This paper describes the development and testing of a mathematical model as a tool to quantify pathogen loads in Sydney's drinking water catchments. It has been used to identify, quantify and prioritise sources of Cryptosporidium, Giardia and E. coli in the Wingecarribee catchment. The pathogen model promotes understanding of the relative significance of different sources of pathogen risks as well as their fate and transport as they move through the subcatchments. This pathogen model not only enables water utility managers to identify those catchment segments that may contribute the highest load of pathogens, but also where management options will be most effective.     

Lithium polyacrylate as a binder for tin-cobalt-carbon negative electrodes in lithium-ion batteries

A lithium polyacrylate (Li-PAA) binder has been developed by 3M Company that is useful with electrodes comprising alloy anode materials. This binder was used to prepare electrodes made with Sn₃₀Co₃₀C₄₀ material prepared by mechanical attrition. The electrochemical performance of electrodes using Li-PAA binder was characterized and compared to those using sodium carboxymethyl cellulose (CMC) and polyvinylidene fluoride (PVDF) binders. The Sn₃₀Co₃₀C₄₀ electrodes using Li-PAA and CMC binders show much smaller irreversible capacity than the ones using PVDF binder. Poor capacity retention is observed when PVDF binder is used. By contrast, the electrodes using Li-PAA binder show excellent capacity retention for Sn₃₀Co₃₀C₄₀ materials and a specific capacity of 450 mAh/g is achieved for at least 100 cycles. The results suggest that Li-PAA is a promising binder for electrodes made from large-volume change alloy materials.