Reactivity of Pb(II) at the Mn(III,IV) (oxyhydr)oxide--water interface

In this study, the reactivity of lead (Pb(II)) on naturally occurring Mn(III,IV) (oxyhydr)oxide minerals was evaluated using kinetic, thermodynamic, and spectroscopic investigations. Aqueous Pb(II) was more strongly adsorbed to birnessite (delta-MnO1.7) than to manganite (gamma-MnOOH) under all experimental conditions. The isoteric heat of Pb adsorption (delta HT) or birnessite was 94 kJ mol-1 at a surface loading of 1.1 mmol g-1, and decreased with increasing adsorption density. This indicated that adsorption was an endothermic process and that birnessite possessed heterogeneous sites of reactivity for Pb. X-ray absorption fine structure (XAFS) spectra revealed that Pb was adsorbed as inner-sphere complexes on both birnessite and manganite with no evidence to suggest oxidation as an operative sorption mechanism. Lead appeared to coordinate to vacancy sites in the birnessite layer structure with concurrent release of Mn to solution, which resulted in a greater number of second shell Mn scatterers in Pb-birnessite when compared to Pb-manganite samples. The difference in Pb coordination apparently explained the contrasting desorption behavior between the two Mn minerals. These results have significant implications for Pb partitioning in soil environments containing solid-phase Mn(III,IV) (oxyhydr)oxides.     

Effect of annealing on GaN-insulator interfaces characterized by metal-insulator-semiconductor capacitors

GaN metal-oxide-semiconductor (MOS) capacitors have been used to characterize the effect of annealing temperature and ambient on GaN-insulator interface properties. Silicon dioxide was deposited on n-type GaN at 900 /spl deg/C by low-pressure chemical vapor deposition and MOS capacitors were fabricated. The MOS capacitors were used to characterize the GaN-SiO/sub 2/ interface with a low interface-state density of 3 /spl times/ 10/sup 11/ cm/sup -2/eV/sup -1/ at 0.25 eV below the conduction band edge, even after annealing in N/sub 2/ at temperatures up to 1100 /spl deg/C; however, insulator properties were degraded by annealing in NO and NH/sub 3/ at 1100 /spl deg/C.     

Effect of hepatoma on host liver,heart and lung lipids as tumor growth progresses

A large group of rats was transplanted with hepatoma 7288CTC and 4 animals were sacrificed at 3-day intervals for four weeks. Lipid class concentrations, fatty acid class compositions, and the distribution ofcis octadecenoate positional isomers in the major lipid classes were determined for heart, liver and lung at each time period. The hearts of host animals decreased in dry weight as hepatoma growth progressed. At day 30, heart weights were less than two-thirds of initial weights. Lipid class concentrations changed in all three tissues: cholesterol and free fatty acids increased in liver; triglycerides and cholesterol decreased and then increased in heart; and cholesterol, triglycerides and PC decreased in lung as tumor growth progressed. Hexadecenoate percentages exhibited a progressive decrease in all the lipid classes of heart and liver. Although total octadecenoate percentages showed only minor changes, oleate concentrations generally increased and vaccenate levels decreased in heart and liver lipids as tumor growth progressed. Palmitoleate, precursor of vaccenate, exhibited decreased concentrations early that resulted in decreased vaccenate levels. Decreased palmitoleate concentrations suggest inhibition of the Δ9 desaturase system, but normal oleate concentrations complicate this interpretation. Most of the changes in the lipids were detectable 3–6 days after transplantation, indicating the hepatoma affects the lipid metabolism of the host animal early and well in advance of nutritional stresses.     

High-voltage normally off GaN MOSFETs on sapphire substrates

Gallium nitride self-aligned MOSFETs were fabricated using low-pressure chemical vapor-deposited silicon dioxide as the gate dielectric and polysilicon as the gate material. Silicon was implanted into an unintentionally doped GaN layer using the polysilicon gate to define the source and drain regions, with implant activation at 1100/spl deg/C for 5 min in nitrogen. The GaN MOSFETs have a low gate leakage current of less than 50 pA for circular devices with W/L=800/128 /spl mu/m. Devices are normally off with a threshold voltage of +2.7 V and a field-effect mobility of 45 cm/sup 2//Vs at room temperature. The minimum on-resistance measured is 1.9 m/spl Omega//spl middot/cm/sup 2/ with a gate voltage of 34 V (W/L=800/2 /spl mu/m). High-voltage lateral devices had a breakdown voltage of 700 V with gate-drain spacing of 9 /spl mu/m (80 V//spl mu/m), showing the feasibility of self-aligned GaN MOSFETs for high-voltage integrated circuits.     

Geometrical and positional isomer content of the monounsaturated fatty acids from various rat tissues

The percentage distribution of the geometrical and positional isomers in the hexadecenoates and octadecenoates isolated from triglycerides, phosphatidylch olines, and phosphatidylethanolamines of brain, heart, kidney, liver, lung, muscle, spleen, and adipose tissues from normal rats maintained on a laboratory diet has been determined. All of the octadecenoates and most of the hexadecenoates from the lipid classes of all the tissues consisted of more than 95%cis isomers. Generally, palmitoleic was the predominant hexadecenoate, but many of the tissue phospholipids contained relatively high percentages of the Δ6 and Δ7 isomers. Oleate and vaccenate were the predominant octadecenoates in all tissues. Except for brain and adipose tissues, the oleate to vaccenate ratios differed for each lipid class, as well as between most tissues. In contrast to the monoenes of the phospholipids, the triglyceride monoenes exhibited the same approximate: percentage composition; percentage of geometrical isomers; and percentage distribution of hexadecenoate and octadecenoate positional isomers. These data add to our basic information about the percentage distribution of geometrical and positional isomers of naturally occurring unsaturated fatty acids in the major lipid classes of various normal tissues. Some new concepts were advanced as possible explanations to some of the observed positional isomer distributions.     

Determination of Lean Burn Combustion Temperature Using Ultraviolet Emission

Measurements of the ultraviolet emission spectrum emitted from a lean burn premixed natural gas flame were taken over a range of flame temperatures using a fiber-optic/CCD spectrometer. Combustion temperatures were determined by two methods: by measuring the unburned oxygen in the exhaust and by calculating the temperature using the fuel and airflows. These temperatures were correlated to ratios composed of the integrated intensity of the long wavelength region of the OH band between 310 to 340 nm (ratio's numerator) and that between 305 and 310 nm (ratio's denominator). Average local combustor flame temperatures at the end of the combustion zone may then be determined by tracking these ratios during combustor operation. The sensitivity of these ratios yields a 0.8% change in the ratios every 20 degF with a precision of plusmn30 degF or plusmn1% at 3000 degF with 95 % confidence bounds demonstrating the feasibility of this technique for use as a potential control parameter for gas turbine combustors burning natural gas and air mixtures. This method is well suited for the low equivalence ratios (< 1) required to reduce NOx and CO emissions. Other methods using peak ratios of different emission bands exhibit nonlinearity, lower sensitivity and greater uncertainty.     

Positive flatband voltage shift in MOS capacitors on n-type GaN

GaN MOS capacitors were fabricated using silicon dioxide deposited by low-pressure chemical vapor deposition oxide at 900°C. The MOS capacitor flatband voltage shift versus temperature was used to determine a pyroelectric charge coefficient of 3.7 × 10⁹ q/cm²-K, corresponding to a pyroelectric voltage coefficient of 7.0 × 10⁴ V/m-K     

Changes in host animal plasma lipids during hepatoma growth

The concentrations of the major neutral lipid and phospholipid classes in the plasma of rats bearing hepatoma 7288CTC were determined at various times after transplantation. The fatty acid composition of each lipid class was also analyzed quantitatively as tumor growth progressed. Generally, most lipid classes exhibited a slight decrease between the third and sixth day after transplantation, returned to near normal levels by the 15th day, increased dramatically and peaked between the 24th and 27th days before plummeting sharply. At peak concentrations, triglycerides were increased 5 times the normal levels, whereas cholesterol, cholesteryl esters and phosphatidylcholines were increased 3-fold. The percentage of hexadecenoates decreased in all lipid classes as tumor growth progressed and generally, stearate levels increased. In addition to monounsaturated fatty acids, lysophosphatidylcholines and phosphatidylcholines showed relatively large decreases in the percentages of polyunsaturated fatty acids with increased tumor growth. These results indicate that hepatoma 7288CTC can cause perturbation of host animal plasma lipids in the early stages of growth which precedes the massive hyperlipidemia. The interpretation of these results suggests that the early changes in plasma lipids may result from alterations in the normal lipid metabolism of the host, and the hyperlipidemia that develops later may result from the mobilization of lipids to compensate for the altered metabolism. This paper was given by M. Matocha as an Honored Student Award presentation at the AOCS meeting, San Francisco, CA, April 29–May 31, 1979. This work has been submitted in partial fulfillment of the requirement for the M.S. degree.     

Comment on A. Agarwal and S. Haney, “Some Critical Materials and Processing Issues in SiC Power Devices” [J. Electron. Mater. 37, 646 (2008)]

Agarwal and Haney [J. Electron. Mater. 37, 646 (2008)] have recently suggested that bulk defects may limit the inversion-layer mobility in SiC metal oxide semiconductor field-effect transistors. However, we believe that the physics of charge trapping and Coulomb scattering by bulk traps quantitatively contradicts this model.     

Locating group members in a mobile environment

The Internet Engineering Task Force lists multicasting as a desired service for our future mobile computing environment. To provide this service, location management of a group of users involved in a multicasting application needs to be addressed. In this paper, we propose two protocols that can be used by a group of mobile hosts to share their current location with other group members efficiently.