Sensitivity of 2DEG-based Hall-effect sensors at high temperatures.

The magnetic sensitivity of Hall-effect sensors made of InAlN/GaN and AlGaN/GaN heterostructures was measured between room temperature and 576 °C. Both devices showed decreasing voltage-scaled magnetic sensitivity at high temperatures, declining from 53 mV/V/T to 8.3 mV/V/T for the InAlN/GaN sample and from 89 mV/V/T to 8.5 mV/V/T for the AlGaN/GaN sample, corresponding to the decreasing electron mobility due to scattering effects at elevated temperatures. Alternatively, current-scaled sensitivities remained stable over the temperature range, only varying by 13.1% from the mean of 26.3 V/A/T and 10.5% from the mean of 60.2 V/A/T for the InAlN/GaN and AlGaN/GaN samples, respectively. This is due to the minimal temperature dependence of the electron sheet density on the 2-dimensional electron gas (2DEG). Both devices showed consistency in their voltage- and current-scaled sensitivity over multiple temperature cycles as well as nearly full recovery when returned to room temperature after thermal cycling. Additionally, an AlGaN/GaN sample held at 576 °C for 12 h also showed nearly full recovery at room temperature, further suggesting that GaN-based Hall-effect sensors are a good candidate for use in high temperature applications.

Assessment of the spatial occurrence of childhood leukaemia mortality using standardized rate ratios with a simple linear Poisson model.

Reports of a suspected cluster of childhood leukaemia cases in West Central Phoenix have led to a number of epidemiological studies in the geographical area. We report here on a death certificate-based mortality study, which indicated an elevated rate ratio of 1.95 during 1966-1986, using the remainder of the Phoenix standard metropolitan statistical area (SMSA) as a comparison region. In the process of analysing the data from this study, a methodology for dealing with denominator variability in a standardized mortality ratio was developed using a simple linear Poisson model. This new approach is seen as being of general use in the analysis of standardized rate ratios (SRR), as well as being particularly appropriate for cluster investigations.

Effects of twinning on lactation and days open in Holsteins.

Effects of twinning on lactation and days open in Holsteins were studied from calving records compiled by member surveys of Eastern Artificial Insemination Cooperative. Records of cows with 305-day mature-equivalent records from the Northeast Dairy Records Processing Laboratory were grouped according to whether the twin calving was associated with dystocia. Records of each cow that had a twin calving were paired with records of a single-calving control herdmate. In the twin group of 175 cows associated with dystocia, twin pregnancy had no effect on production; milk and fat production in the lactation initiated by twinning was depressed (137 kg and 7 kg) although not significantly; and days open following twin calving was increased. In the twinning group of 367 cows with no dystocia at twinning, milk and fat production were depressed by 285 kg and 14 kg in the lactation initiated by the twinning. Days open after twinning were increased by about 22 days. These results indicate a negative economic effect of twinning on lactation performance in Holstein cattle. Increased rates of twinning via selection or artificial induction of twinning dairy cattle appear not to be desirable.