Parallel Temperatures in Supersonic Beams: Ultra Cooling of Light Atoms seeded in a Heavier Carrier Gas

We have found recently that, in a supersonic expansion of a mixture of two monoatomic gases, the parallel temperatures of the two gases can be very different. This effect is large if the seeded gas is highly diluted and if its atomic mass is considerably smaller than the one of the carrier gas. In the present paper, we present a complete derivation of our theoretical analysis of this effect. Our calculation is a natural extension of the existing theory of supersonic cooling to the case of a gas mixture, in the high dilution limit. Finally, we describe a set of temperature measurements made on a beam of lithium seeded in argon. Our experimental results are in very good agreement with the results of our calculation.Comment: 24 novembre 200

Succession in AMF communities from early to late season in grassland national park

Non-Peer ReviewedChange of AMF (arbuscular mycorrhizal fungi) community between two seasons in Grassland National Park had been studied in this article. We used FAMEs analysis and PCR-DGGE analysis tested soil samples collected from 3 different ecosystems at two sampling seasons. Based on our study, we found that AMF activity was significantly higher in early (wet) than late (dry) seasons, and in early season, the amount of AMF also showed significant positive linear relationship with amount of P and N in plant tissue. During late season we didn’t find significant result among these variables, which may suggest that seasonal changes could change the activity of AMF and affect relationship between AMF and their host plant nutrient metabolism. Also, AMF species composition differed in early and late season. Most AMF taxa found in the dry season in our study were unknown to the scientific community. This suggests that AMF biodiversity had difference between seasons and these uncommon AMF taxa are adapted to dry conditions. Besides, crested wheatgrass, the dominant species in the park, although didn’t show significantly directly relationship with AMF activity, it may improve soil organic carbon, soil soluble P, and increase the amount of soil bacteria, which are also three important factors that could further affect AMF activity. However, the absence of activity of crested wheatgrass combined with the low biodiversity in the stand and low association with AMF in the dry season, suggests that a prolonged drought period detrimental to crested wheatgrass would leave a prairie of crested wheatgrass vulnerable and depleted

Optimization of Single-Sided Charge-Sharing Strip Detectors

Simulation of the charge sharing properties of single-sided CZT strip detectors with small anode pads are presented. The effect of initial event size, carrier repulsion, diffusion, drift, trapping and detrapping are considered. These simulations indicate that such a detector with a 150 µm pitch will provide good charge sharing between neighboring pads. This is supported by a comparison of simulations and measurements for a similar detector with a coarser pitch of 225 µm that could not provide sufficient sharing. The performance of such a detector used as a gamma-ray imager is discussed

Further studies of single-sided charge-sharing CZT strip detectors

We report progress in the study of a thick CZT strip detector module designed to perform gamma-ray spectroscopy and 3-D imaging. We report preliminary performance measurements of 7.5 mm thick single-sided charge-sharing strip detector prototype devices. This design features both row and column contacts on the anode surface. This electron-only approach addresses problems associated with poor hole transport in CZT that limit the thickness and energy range of double-sided strip detectors. This work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma measurements while minimizing the number and complexity of the electronic readout channels. This is particularly important in space-based coded aperture and Compton telescope instruments that require large area, large volume detector arrays. Such arrays will be required for the NASA Black Hole Finder Probe (BHFP)and Advanced Compton Telescope (ACT). This new design requires an anode pattern with contacts whose dimensions and spacing are roughly the size of the ionization charge cloud. The first prototype devices have 125 μm anode contacts on 225 μm pitch. Our results demonstrate the principle of operation but suggest that even finer anode contact feature sizes will be necessary to achieve the desired performance

Continued Studies of Single-Sided Charge-Sharing CZT Strip Detectors

In this paper, we report progress in the study of thick single-sided charge-sharing cadmium zinc telluride (CZT) strip detector modules designed to perform gammaray spectroscopy and 3-D imaging. We report on continuing laboratory and simulation measurements of prototype detectors with 11×11 unit cells (15×15×7.5mm3 ). We report preliminary measurements of the 3-D spatial resolution. Our studies are aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma measurements while minimizing the number and complexity of the electronic readout channels. This is particularly important in space-based coded aperture and Compton telescope instruments that require large area, large volume detector arrays. Such arrays will be required for the NASA’s Black Hole Finder Probe (BHFP) and Advanced Compton Telescope (ACT). This design requires an anode pattern with contacts whose dimensions and spacing are roughly the size of the ionization charge cloud. The first prototype devices have 125µm anode contacts on 225µm pitch. Our studies conclude that finer pitch contacts will be required to improve imaging efficiency

Depression, quantity of social interaction, reciprocal self-disclosure, and perspective-taking in the elderly

The present research was designed to investigate the relationships among; a) depression, b) the quantity of social interaction and, c) the quality of social interaction in the elderly. Twenty-three residents aged 72 to 98 of a rural senior citizens home were tested. The subjects were administered the Zung Self-Rating Depression Scale and Flavell's (1975) measure of visual perspective-taking. The quantity of social interaction was measured by the subject's self-reports of their frequency of interaction with various groups of people and the number of persons they talked to most frequently. The measure of the quality of social interaction was derived from a round robin procedure based on the subjects' reported self-disclosure to peers. This enabled the identification of subjects who had relationships characterized by reciprocal intimate disclosures - or confidants. The analysis provided partial support for the validity of the quantity and the quality of social interaction measures. Consistent with previous research, depression was negatively correlated with one measure of quantity of social interaction, the number of peers with whom the subject frequently talked. Contrary to expectation, perspective-taking was not significantly correlated with the measures of quantity of social interaction or the measures of reciprocal disclosure. Contrary to the quality of social interaction research, the intimacy of the subject's disclosures and the intimacy of the target's disclosures were not significantly correlated, indicating that disclosure patterns among the elderly were not reciprocal. In addition, having a relationship characterized by reciprocal intimate disclosure was positively, rather than negatively correlated with depression. This indicates that the more depressed an elderly individual is, the more the individual had in objective terms - confidants. One interpretation of this latter finding was advanced, that depressed elderly reciprocate personal information in the form of negative perceptions or complaints