A new punch-through IGBT having a new n-buffer layer

Insulated gate bipolar transistors (IGBTs) based on the non-punch-through (NPT) design approach exhibit excellent safe operating area (SOA) and short-circuit endurance, a positive temperature coefficient of on-state voltage over the operating current range, and low silicon cost. These merits have supported the development and commercialization of NPT IGBTs above the 1200-V class. However, the need for quite thin silicon to obtain competitive on-state losses at 1200-V and below classes has hindered the use of the NPT approach in this area. A new punch-through (PT) IGBT has been developed which exhibits the merits of the NPT approach, rugged SOA and short-circuit endurance, while also having a better tradeoff relation between on-state voltage and turn-off loss than either existing NPT or third-generation PT IGBTs     

Assignment of turn-on and turn-off power and energy losses in a GTO

The authors discuss the turn-on and turn-off losses in a gate turn-off (GTO) thyristor which must be properly accounted for because they can comprise upwards of 60% of the total losses. The authors attempt to discuss and clarify the definitions of power loss and energy per pulse for the turn-on and turn-off intervals. It is shown that prior work defining turn-on and turn-off power and energy losses does not adequately include all losses associated with the turn-on and turn-off events. Thus, it will be difficult to account for all those losses determining the heating effects of the GTO unless improvements are made. An example shows that the error can be substantial (8 to 15%). For this reason, improved definitions that have an underestimation of only 1 to 2% of the switching losses have been proposed. It was also found that the gate losses during the turn-off event must be accounted for and that improved measuring techniques and instrumentation are both necessary and possible     

Precipitation in non-stoichiometric spinel

Precipitation in non-stoichiometric spinel (MgO · 3.5Al₂O₃) single crystals has been investigated in the temperature range 900 to 1600° C. The formation of a coherent intermediate phase precedes precipitation of the equilibriumα-Al₂O₃, and the time-temperature-extent of transformation (T-T-T) curve for the formation of this metastable phase has been determined. Nucleation ofα-Al₂O₃ occurs only at free surfaces, presumably because of the large strain energy accompanying the transformation of the anion sublattice from cubic to hexagonal close-packing. The growth rate ofα-Al₂O₃ from the free surfaces follows a linear law and appears similar to the “autocatalytic reaction” found in some metallic alloys. The following orientation relationship between spinel andα-Al₂O₃ is observed: $$\langle 10\overline 1 0\rangle _{\alpha - {\rm A}l_2 O_3 } \parallel \langle 110\rangle _{spinel} $$ and $$(0001)_{\alpha - {\rm A}l_2 O_3 } \parallel \{ 111\} _{spinel.} $$ .     

Strontium in 19th century Australian children''s teeth

The enamel of teeth from 57 children, who died in the mid to late 1800s, were analysed to investigate strontium (Sr) concentrations in historic teeth. Teeth were analysed using proton induced X-ray emission at the Australian Nuclear Science and Technology Organisation (ANSTO). Where available, multiple teeth were analysed for each individual including permanent (molars and premolars) and deciduous teeth (molars). Preliminary results show that Sr does not appear to be affected by the postmortem environment. Sr levels in permanent molars strongly correlate with levels in the premolars but not with the deciduous molars. Concerns are raised over the large variation seen in Sr levels and the effect it would have on the interpretation of Sr levels in studies with small sample sizes.     

Modeling the age-hardening behavior of Al-Si-Cu alloys

We describe a new approach for modeling the age-hardening behavior of Al-Si-Cu cast alloys, that utilizes recently proposed micromechanical models of precipitation strengthening which connect key microstructural parameters for realistic precipitate morphologies (e.g., {100} plates) with the age-hardening response. This approach is illustrated and tested for a series of 319-type Al alloys (which we refer to as W319), where the microstructural parameters of ϑ′ plates measured by transmission electron microscopy and a first-principles/computational-thermodynamics model of ϑ′ volume fraction are used in the micromechanical model to predict precipitation strengthening. Thus, the precipitation-strengthening contribution contains no free parameters in our approach. An aging temperature- and time-dependent component that describes the strengthening of the Guinier-Preston (GP) zones and solid-solution copper, as well as a constant intrinsic strength, is combined with the calculated precipitation strength to predict the yield strength with a minimum of fitting parameters. This yield-strength model provides a good predictor of the yield strength of W319, and the methodology should be more generally applicable to all industrial cast alloys strengthened primarily by ϑ′. We also discuss limitations of the present approach and point to areas for improvement in future studies.     

Yttrium Segregation and YAG Precipitation at Surfaces of Yttrium- Doped α-A12O3

Auger electron spectroscopy and low-energy ion scattering were used to assess surface composition of yttrium-doped polycrystalline and single-crystal α-aluminas which were heated under vacuum to temperatures above 1500°C. Extensive surface and intergranular precipitation of yttrium aluminum garnet was observed in a compact of nominal Y content of 210 wt ppm, while apparent Y segregation to surface cation sites predominated in a second compact with a Y content of 160 wt ppm. In the latter case, the segregation enthalpy of yttrium to the alumina surface in the temperature range 1700° to 1900°C was estimated to be of the order –44 kJ/mol with a maximum surface cation site occupancy of ∼13%.     

Using sea surface temperature measurements from microwave and infrared satellite measurements

The Tropical Rainfall Mapping Mission Microwave Imager (TMI) instrument Sea Surface Temperature (SST) product (v1.0) is compared with in situ observations obtained in the Atlantic Ocean. The TMI SST has a mean warm bias of 0.25?K±0.7?K when compared to in situ SST at a depth of 7?m. When TMI SST are compared to in situ skin SST measurements, the bias is 0.6?K±0.5?K. A limited global comparison between TMI SST and co-incident ERS-2 Along-Track Scanning Radiometer (ATSR/2) skin SST demonstrates a bias of 0.6?K±0.6?K consistent with the result obtained using in situ observations. These results are consistent with the predicted accuracy of the TMI SST data products. Based on these results, a simple method to merge the TMI and ATSR data is proposed.     

Biotransformation and biodegradation of N-substituted aromatics in methanogenic granular sludge

N-Substituted aromatic compounds are environmental contaminants associated with the production and use of dyes, explosives, pesticides and pharmaceuticals. In this article, we examine the potential of anaerobic granular sludge from anaerobic treatment systems towards the detoxification, transformation, and mineralization of nitroaromatic and azo compounds. Nitroaromatics and azo dyes with strong electron withdrawing are highly inhibitory to acetoclastic methanogenic bacteria. However, nitro and azo substituted aromatics are readily reductively detoxified in methanogenic consortia to their respective aromatic amines, which are several orders of magnitude less toxic. This reductive detoxification has allowed the successful operation of anaerobic reactors for the treatment of highly toxic aromatic compounds. In the course of the experiments it was discovered that some aromatic amines were mineralized. These results indicate that some N-substituted aromatic compounds can be completely mineralized and serve as a carbon and energy source for anaerobic bacteria.