Cell design modifications to harden an N-channel power IGBT againstsingle event latchup

A device simulator is used to analyze the heavy ion induced failure mechanism in insulated gate bipolar transistors (IGBTs) and to investigate hardening solutions. Single event latchup was already identified as the failure mechanism. Lateral and vertical modifications of the P⁺ plug are proposed to reduce the efficiency of the parasitic thyristor, responsible for the latchup, and validated by 2D-simulations on a N-channel IGBT cell structure     

A study of apparent apical defects in attenuation corrected cardiacSPECT

There are a number of factors that affect the intensity of the apical region in cardiac SPECT images, which sometime lead to apparent defects in this region. In some patient studies, images reconstructed with non-uniform attenuation correction appear to have a significant decrease of apical intensity, whereas images reconstructed without such correction have only a slight decrease. This phenomenon has been evaluated using a series of simulations, phantom experiments, and a patient study. The effects of a number of factors upon the severity of the apparent apical defects were studied, including: partial volume effect, non-uniform attenuation, and depth-dependent detector response. Simulation and phantom results indicate that (1) since the apex is generally less attenuated than the rest of the heart wall, attenuation correction boosts the intensity of non-apical regions more than that of the apex (by as much as 20%); and (2) partial volume effects due to discretization inadequacies and finite spatial resolution may cause as much as a 26% decrease in reconstructed intensity in the apical region. These two effects, in combination, may partially explain the presence of apparent apical defects when attenuation correction is performed. In addition, detector response compensation consistently reduced the severity of apparent apical defects. These results agree with and help to explain the occurrence of apparent apical defects observed in patient data     

Experimental study of the effect of non-circular flow geometry on the critical heat flux

An experimental study of the effect of flow geometry (circular, rectangular, triangular, and dumb-bell shaped) on the critical heat flux (CHF) was performed using R-134a as a coolant. The CHF is affected by the following geometric parameters: hydraulic-equivalent diameter, heated length, gap size, channel shape, and curvature. It may also be affected by the thermal conductivity of the wall material and wall thickness. The effect of flow geometry on CHF is influenced by flow parameters. The effect of these parameters on CHF was examined, and recommendations for predicting the CHF in non-circular geometries have been made.     

Large deflection beam transport with screened Rutherford scattering

We consider the steady-state monoenergetic searchlight problem involving screened Rutherford scattering. A recently reported formalism is modified to improve upon its accuracy for large beam deflections. Comparisons with benchmark Monte Carlo calculations demonstrate the improved accuracy of this modified formalism.     

Developing utility functions for environmental decision making

The selection of a technology for the cleanup of a contaminated site is complicated by the involvement of multiple stakeholders with conflicting objectives. Multi-attribute decision analysis can be employed to assess the impact of the alternative technologies on a number of performance measures and to rank these alternatives according to the preferences of each stakeholder. In this paper, we present an approach to constructing the utility functions that decision analysis requires using stakeholder input. The proposed approach is based on the Analytic Hierarchy Process and accounts for linguistic imprecision in the stakeholder assessments. The experience from a real case study is reported and discussed.     

Pollution effects on stone benches of the Eagle Warriors Precinct at the Major Temple, Mexico City

During Major Temple archaeological site excavations in Downtown Mexico City, the precinct of one of the most important Mexica military caste, the Eagle Warriors, was discovered. The ceremonial enclosure is composed of three rooms surrounded by paintings on 11 stone benches placed against the walls. Nowadays, these paintings and the stones present the effects of different deterioration processes produced by the underground water level, high humidity, and the presence of soil, water, and air pollutants. Ion beam analysis of samples from the benches and wall paintings was performed using PIXE and RBS techniques. Using enrichment factors of elements relative to iron concentrations, possible contamination by sulfur and chlorine salts was found, as well as airborne zinc scavenged by rain.     

Heat transfer during boiling of a liquid metal during emergency cooldown of a fast-neutron reactor

The physics of the processes, the characteristics, and the stability of different regimes, of boiling (nucleate, projectile, disperse-ring), which are observed in experiments investigating the boiling of liquid-metal coolant in a model of a fuel assembly for a fast-neutron reactor in the emergency cooldown regime with low circulation velocity, are analyzed. The experimental setup, the, methods for performing measurements, and the experimental data on the boiling of a liquid metal are described. A mathematical model of the process of boiling of a liquid-metal, coolant in a natural-circulation loop is described, and the results of test calculations for regimes with an increase in heating and with sharp pressure drop are prresented. 7 figures, 12 references. State Science Center of the Russian Federration–A. I. Leipunskii Physics and Power Engineering Institute. Translated from Atomnaya énergiya, Vol. 87, No. 5, pp. 337–342, November, 1999.     

Observation of atomic steps on single crystal surfaces by a commercial scanning electron microscope.

Atomic steps on (111) and (100) crystal surfaces of Pt were observed using a commercial scanning electron microscope (SEM) in secondary electron mode. By comparing the SEM images and those by reflection electron microscopy (REM), the observed contrast was confirmed to be that from atomic steps on crystal surfaces. The contrast mechanism is briefly discussed. One application of this imaging technique is also shown.