Differential cross sections for elastic scattering of electrons from dimethylsulfide and dimethylsulfoxide in the energy range from 30 to 500 eV are presented. The cross sections have been measured using a crossedbeam-type high-resolution electron spectrometer. The measured cross sections have been put on an absolute scale using the relative flow technique. The measured differential cross sections show an increase in the midangles at 30 and 50 eV for both the molecules that is characteristic of resonant enhanced d-wave scattering. Total and momentum-transfer cross sections were derived by integrating over all angles after extrapolating the data to forward and backward angles using a least-squares fitting procedure based on the Legendre polynomial expansion. Independent-atom-model-based theoretical calculations incorporating static, exchange, and polarization potentials are also reported and compared with the experimental cross sections. For energies lower than 100 eV, it is seen that the independent-atom-model calculations fail to predict the qualitative behavior of the differential cross sections correctly, while at energies greater than 100 eV it seems to describe the data adequately. The effect of polarization and enhancement of cross sections through d-wave scattering at low energies is also analyzed.
We report here the results of experiments on two flows – one on a convex surface and the other on a flat surface – designed to bring out explicitly the influence of streamwise curvature on relaminarization in highly favourable pressure gradients. In both flows, the initial conditions and the streamwise distribution of the Launder pressure-gradient parameter $K$ are virtually identical. The maximum value of $K$ is $6.2\,{\times}\, 10^{-6}$, well above the critical value of about $3.5\,{\times}\, 10^{-6}$ usually advocated for relaminarization. The spatial extent of the acceleration zone is of order 10 initial boundary-layer thicknesses, appreciably shorter than in earlier work in order better to simulate conditions at the leading edge of a typical aircraft wing. The fall in skin friction coefficient is steeper and the rise in shape factor sharper on the convex surface than on the flat surface, indicating that relaminarization on the convex surface is both more rapid and more nearly complete. In the crucial relaminarizing zone, two-layer quasi-laminar theory is found to predict the convex-surface mean-flow parameters more accurately than the flat-surface flow, without any explicit modelling of curvature effects. Thus, experimental results and supporting calculations both indicate that the dominant effect of streamwise convex curvature on the mean flow is to promote more rapid and complete relaminarization in an accelerated turbulent boundary layer, thus enhancing the probability of its occurrence on the leading edge of swept wings where both factors are significantly in operation.
Charge trapping degrades the energy resolution of germanium (Ge) detectors, which require increased experimental sensitivity in searching for dark matter and neutrinoless double-beta decay. We investigate the charge trapping processes utilizing nine planar detectors fabricated from USD-grown crystals with well-known net impurity levels. The charge collection efficiency as a function of charge trapping length is derived from the Shockley–Ramo theorem. Furthermore, we develop a model that correlates the energy resolution with the charge collection efficiency. This model is then applied to the experimental data. As a result, charge collection efficiency and charge trapping length are determined accordingly. Utilizing the Lax model (further developed by CDMS collaborators), the absolute impurity levels are determined for nine detectors. The knowledge of these parameters when combined with other traits such as the Fano factor serve as a reliable indicator of the intrinsic nature of charge trapping within the crystals. We demonstrate that electron trapping is more severe than hole trapping in a p-type detector and the charge collection efficiency depends on the absolute impurity level of the Ge crystal when an adequate bias voltage is applied to the detector. Negligible charge trapping is found when the absolute impurity level is less than 1.0 × 1011 cm−3 for collecting electrons and 2.0 × 1011 cm−3 for collecting holes.
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