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Abstract: AlGaN/GaN heterostructure field-effect transistor has great potential for use in high voltage, high current and high power device applications. To reduce the gate leakage current, generally oxide layers are employed. Using an Al2O3 layer as a gate oxide layer, effects on the device performances were investigated. Leakage current density and current–voltage characteristics of AlGaN/GaN heterostructure field-effect transistor with Al2O3 layer were measured, the drain current was about 510 mA/mm at V gs =1 V and the gate leakage current density was lowered with Al2O3 layer. [Copyright &y& Elsevier]

Abstract: Nitryl Chloride (ClNO2) mixing ratios above 1 ppbv have been measured off the coast of Southeast Texas. ClNO2 formation, the result of heterogeneous N2O5 uptake on chloride-containing aerosols, has a significant impact on oxidant formation for the Houston area. This work reports on the modeling of ClNO2 formation and describes the sensitivity of ClNO2 formation to key parameters. Model sensitivity analyses found that: (1) Chloride availability limits the formation of nitryl chloride at ground level but not aloft; (2) When excess particulate chloride was assumed to be present at ground level through sea salt, ClNO2 concentrations increased in some locations by a factor of 13, as compared to cases where sea salt chloride was assumed to be limited; (3) Inland formation of ClNO2 seems feasible based on chloride availability and could have a large impact on total ClNO2 formed in the region; and (4) ClNO2 formation is quite sensitive to the assumed yield of ClNO2 from N2O5 uptake. These results demonstrate that there is a need for further field studies to better understand the geographic extent of ClNO2 formation and the atmospheric conditions which control partitioning of chloride into the particle phase. In addition, this work examined the role of ClNO2 in the cycling of chlorine between chloride and reactive chlorine radicals. The modeling indicated that the majority of reactive chlorine in Texas along the Gulf coast is cycled through ClNO2, demonstrating the importance of including ClNO2 into photochemical models for this region. [ABSTRACT FROM AUTHOR]

Abstract: We investigated a two-week episode with high PM concentrations in California Central Valley during the Christmas–New Year of 2000–2001 using a modeling system that consists of a computationally efficient, 3-D photochemical–microphysical transport model, a mesoscale meteorological model, emission models, and an evaluation package. One hundred simulations were conducted with fine resolutions and observational constraints, to reproduce spatial and temporal features of observed PM concentrations and to understand the formation mechanism of the episode. Simulated PM concentrations consist of secondary inorganic components, mainly ammonium nitrate, and total carbon in areas with elevated concentrations in the accumulation mode, and consist of mainly dust and sea salt in the coarse mode. Simulated oxidants and nitrate were significantly elevated over the valley, and the latter showed much less amplitude than the former. Simulated PM concentrations were evaluated with observations systematically with spatially and temporally paired method, a more restrictive multivariate method (NMFROC), and a more flexible “gradient evaluation” method. The paired evaluation shows that high correlation coefficient (R =∼0.8) and low fractional error (FE=∼0.1) could be achieved at stations with elevated 24-h concentration of PM in the accumulation mode in some simulations. The NMFROC method was used to extract useful information from seemingly failed simulations. A “gradient evaluation” method is introduced here to extract additional information from simulations. We found that emission reductions of NO x and AVOC showed similar effects on percentage basis in different areas, and both are more effective than reducing NH3 for abating elevated concentrations of accumulation mode PM in California Central Valley during the winter episode. [Copyright &y& Elsevier]

In this paper, we discuss the theory of adjoint sensitivity analysis and the method of 4D-Var data assimilation in the context of the Sulfur Transport Eulerian Model (STEM). The STEM atmospheric Chemical Transport Model (CTM) is used to perform adjoint sensitivity analysis and data assimilation over the State of Texas. We first demonstrate the use of adjoint sensitivity analysis for a receptor located at ground level in the Dallas Fort Worth (DFW) area. Simulations are carried out for three 36-h intervals in July 2004. One set of simulations focuses on a passive tracer, and illustrates the influence of meteorological conditions. The other results show the areas of influence associated with DFW ground level ozone, i.e. the areas where changes in precursors (O3, NO2, and HCHO) have the maximum impact on DFW ozone. Next, we employ data assimilation to optimize initial conditions of chemical fields and ground level emissions. We optimize the initial conditions for two episodes on 1 and 16 July 2004. Data assimilation makes use of AirNow ground level observations (for both episodes) and SCHIAMACHY NO2 and HCHO observations from ENVISAT (for the 16 July episode). The re-analyzed chemical fields show considerable improved agreement with AirNow observations for non-initial conditions. We also perform inverse modeling of ground level emissions using data assimilation under an additional smoothness constraint. The results indicate higher NO2 emission levels than in the current emission inventory in the DFW area, and lower emission levels in eastern Texas. The formaldehyde emissions are found to be larger than reported in a localized area near the Gulf Coast, and about at the reported level elsewhere. While the results obtained with the current state-of-the-art tools can help guide tuning of emission inventories, better constraints on the inverse problem are needed to obtain more rigorous quantitative estimates. [Copyright &y& Elsevier]

Homozygous deletion or somatic mutations of mitogen-activated protein kinase kinase 4 (MKK4), a candidate tumour suppressor gene located at 17p11, have been observed in many types of human tumours. To explore the likelihood that MKK4 acts as a suppressor in gastric tumorigenesis, we examined the expression and mutation status of MKK4 in 144 gastric tissues and cell line specimens. Expression of the MKK4 transcript was easily detectable in all normal and benign tumour tissues and none of 102 primary carcinomas and cell lines showed an abnormal reduction in MKK4 expression. Expression levels of MKK4 transcript showed no cancer-specific reduction in 43 matched sets and did not correlate with stage, grade and histopathological types of the tumours. Western blot analysis also revealed that MKK4 protein expression in carcinoma tissues and cell lines is comparable to non-cancerous tissues. A significant loss of heterozygosity (LOH) was detected at telomeric markers of the MKK4, locus. However, no allelic deletion of the MKK4 gene or at the centromeric loci was identified. Moreover, no evidences for somatic mutations leading to amino acid substitutions or frameshifts of MKK4 were identified in the carcinoma tissues and cell lines, whereas a substantial fraction of the same set showed allelic loss or mutations of the TP53 gene located at 17p13, suggesting that LOH at telomeric loci or the TP53 locus might not extend into the MKK4 gene in gastric cancers. In this study, we also report the identification of a highly conserved MKK4 processed pseudogene, which shares 95% homology with the coding region of the functional MKK4 transcript. Collectively, our data demonstrate that genomic deletion or somatic mutation of MKK4 is infrequent in gastric cancers, suggesting that MKK4 might not be a critical target of genetic inactivation in gastric tumorigenesis. [Copyright &y& Elsevier]