GaAs IC's fabricated with the high-performance, high-yieldmultifunction self-aligned gate process for radar and EW applications

Design and test results are presented for several multiuse GaAs ICs for radar and electronic warfare (EW) applications. The chips described are a redundant switch, a broadband distributed amplifier, a broadband variable-gain amplifier, a 2.5-GHz sample and hold, a 1-GHz analog-to-digital converter, and an L-band buffered prescalar. These ICs, fabricated with the ITT 0.4-μm-gate MESFET multifunction self-aligned gate (MSAG) process, demonstrate excellent performance     

Efficacy of antimicrobial treatment in non-dysenteric persistent diarrhoea in a community setting

OBJECTIVES: To determine the efficacy of antimicrobial treatment in non-dysenteric persistent diarrhoea in a community setting. METHODS: In this double-blind field trial, 156 children aged 4-36 months with persistent diarrhoea not associated with Giardia lamblia infestation seeking treatment in a community outpatient clinic, were randomized to receive a combination of nalidixic acid and metronidazole, metronidazole alone, or placebo for 7 days. RESULTS: In comparison with placebo, metronidazole treatment did not result in a significant reduction in the mean post-enrollment diarrhoeal duration and stool frequency, increase in the proportion of patients recovered by days 3, 5 and 7 of treatment, and increase in weight gain at days 7 and 14. Comparing the combination of nalidixic acid and metronidazole with metronidazole alone, 17.5% more children treated with the combination recovered by day 3 of treatment (p = 0.08) and the mean stool frequency ascertained on day 7 for the previous 24 h was 26.8% less in them (p = 0.05). The weight gains at days 7 and 14 were similar in the two groups. CONCLUSIONS: These findings indicate that metronidazole offers no therapeutic benefit in persistent diarrhoea not associated with Giardia lamblia and nalidixic acid has only a modest clinical benefit, which is not substantial enough to warrant its routine use.     

Synthesis of silicon carbide through the sol-gel process from different precursors

Silicon carbide (SiC) was synthesised from silicon alkoxides and various carbon sources. Tetraethoxysilane (TEOS), methyltriethoxysilane (MTES) and a mixture of TEOS and MTES were hydrolysed in the presence of phenolic resin, ethylcellulose, polyacrylonitrile (PAN) and starch to incorporate the gel into the carbon source in the silica network. The gel thus obtained was carbonized at 800°C in an argon atmosphere to obtain the mixture of silica and carbon which when heated to 1550°C in argon yielded silicon carbide. The characterization of the product by X-ray, FTIR and SEM showed it to be β SiC with different crystallite and grain sizes. The difference in the crystallite and grain sizes is attributed to the nature of the carbon source. The density of the SiC obtained by the sol—gel process was found to be lower than the values reported for SiC and this is ascribed to the porous nature of the products generally obtained by this process.     

Die Aceton-Butanol-Gärung: Grundlage für einen modernen biotechnologischen Prozeß?

Acetone-butanol fermentation: basis of a modern biotechnological process? Acetone-butanol fermentation was performed on a large industrial scale for about forty years. After the Second World War it was unable to compete with petrochemical processes and renewed interest in this fermentation has developed only during the last decade. It has led to a vast increase of our knowledge of the biochemistry of acetone-butanol formation and of the genetics of the producing organism, Clostridium acetobutylicum. Considerable progress was also made in defining optimal fermentation conditions. However, the biotechnological process is not yet economically feasible, primarily because low final product concentrations engender high product recovery costs.     

Elimination of mesa-sidewall gate leakage in InAlAs/InGaAsheterostructures by selective sidewall recessing

Conventional mesa isolation in InAlAs/InGaAs HFETs results in the gate coming in contact with the exposed channel at the mesa sidewall, forming a parasitic gate-leakage path. The authors propose a simple method of recessing the channel edge into the mesa sidewall using a succinic-acid-based selective etchant for InGaAs over InAlAs. SEM photographs confirm the recessing of the channel along the sidewall. Special heterostructure diodes, designed with varying amounts of mesa-sidewall/gate-metal overlap, were fabricated with and without the sidewall isolation step. Electrical measurements confirm the complete elimination of sidewall leakage. for both diodes and HFETs     

Effect of pressure on the coking yields of coal tar pitches

Pyrolysis of five coal tar pitches with wide ranging characteristics, made from the same coal tar precursor, has been studied under nitrogen pressures of 10⁵, 50×10⁵, 90×10⁵ and 160×10⁵ Pa, at a temperature of 550 °C. The residues were further heat-treated to 900 °C to obtain the ultimate normal (10⁵ Pa) and pressure coking yields of these pitches. The literature states that for pitches with relatively lower softening points the carbonization pressure not only increases the coking yield but also lowers the temperature at which the pyrolysis is complete. This is seen to hold true for the present set of pitches, having a much wider range of softening points. Further, one of the pitches, earlier reported by us to be a good preforming pitch for carbon-carbon composites, gave an ultimate coking yield of 88% on subjection to a nitrogen pressure of 160×10⁵ Pa at 550 °C followed by ambient pressure carbonization to 900 °C. It thus appears that a carbonization pressure of 160×10⁵ Pa for a suitable preforming pitch can act as a reasonably good alternative to the expensive hot isostatic pressure impregnation carbonization technique employed in the production of carbon-carbon composites.     

Influence of boric acid on the synthesis of silicon carbide whiskers from rice husks and polyacrylonitrile

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

A relationship for the evaluation o coking values of coal tar pitches from their physical characteristics

A relationship has been proposed to evaluate the coking values of coal tar pitches from the knowledge of their three other characteristics, namely, softening point, benzene insolubles content and quinoline insolubles content. It has been tried on 44 self-prepared coal tar pitches and 18 others obtained from the literature, possessing widely-ranging characteristics, and is found to give coking values comparable to those obtained experimentally. The coefficients of correlation between the theoretical (obtained using the relationship) and experimentally determined coking values for the two lots of pitches have been calculated to be 0.98 and 8.94 respectively, which indicate an excellent validity of the proposed relationship for the evaluation of coking values of coal tar pitches.