A non-destructive analytic tool for nanostructured materials : Raman and photoluminescence spectroscopy

Modern materials science requires efficient processing and characterization techniques for low dimensional systems. Raman spectroscopy is an important non-destructive tool, which provides enormous information on these materials. This understanding is not only interesting in its own right from a physicist's point of view, but can also be of considerable importance in optoelectronics and device applications of these materials in nanotechnology. The commercial Raman spectrometers are quite expensive. In this article, we have presented a relatively less expensive set-up with home-built collection optics attachment. The details of the instrumentation have been described. Studies on four classes of nanostructures - Ge nanoparticles, porous silicon (nanowire), carbon nanotubes and 2D InGaAs quantum layers, demonstrate that this unit can be of use in teaching and research on nanomaterials.Comment: 32 pages, 13 figure

Fermentation of Cellulosic Substrates in Batch and Continuous Culture by Clostridium thermocellum

Fermentation of dilute-acid-pretreated mixed hardwood and Avicel by Clostridium thermocellum was compared in batch and continuous cultures. Maximum specific growth rates per hour obtained on cellulosic substrates were 0.1 in batch culture and >0.13 in continuous culture. Cell yields (grams of cells per gram of substrate) in batch culture were 0.17 for pretreated wood and 0.15 for Avicel. Ethanol and acetate were the main products observed under all conditions. Ethanol:acetate ratios (in grams) were approximately 1.8:1 in batch culture and generally slightly less than 1:1 in continuous culture. Utilization of cellulosic substrates was essentially complete in batch culture. A prolonged lag phase was initially observed in batch culture on pretreated wood; the length of the lag phase could be shortened by addition of cell-free spent medium. In continuous culture with ∼5 g of glucose equivalent per liter in the feed, substrate conversion relative to theoretical ranged from 0.86 at a dilution rate (D) of 0.05/h to 0.48 at a D of 0.167/h for Avicel and from 0.75 at a D of 0.05/h to 0.43 at a D of 0.11/h for pretreated wood. At feed concentrations of <4.5 g of glucose equivalent per liter, conversion of pretreated wood was 80 to 90% at D = 0.083/h. Lower conversion was obtained at higher feed substrate concentrations, consistent with a limiting factor other than cellulose. Free Avicelase activities of 12 to 84 mU/ml were observed, with activity increasing in this order: batch cellobiose, batch pretreated wood < batch Avicel, continuous pretreated wood < continuous Avicel. Free cellulase activity was higher at increasing extents of substrate utilization for both pretreated wood and Avicel under all conditions tested. The results indicate that fermentation parameters, with the exception of free cellulase activity, are essentially the same for pretreated mixed hardwood and Avicel under a variety of conditions. Hydrolysis yields obtained with C. thermocellum cellulase acting either in vitro or in vivo were comparable to those previously reported for Trichoderma reesei on the same substrates

Bioconversion of coal-derived synthesis gas to liquid fuels. Final report, September 29, 1992--December 27, 1994

The proposed research project consists of an integrated, two-stage fermentation and a highly energy-efficient product separation scheme. In the first fermentation, Butyribacterium methylotrophicum converts carbon monoxide (CO) into butyric acid and acetic acids which are then converted into butanol, ethanol, and a small amount of acetone in the second stage fermentation by Clostridium acetobutylicum. An advanced separation system process, based on pervaporation, removes the alcohols from the fermentation broth as they are formed, along with some of the hydrogen sulfide (H{sub 2}S), to minimize possible inhibition of the fermentations. This bioconversion process offers a critical advantage over conventional, catalytic processes for synthesis gas conversion: the microorganisms are several orders of magnitude more sulfur tolerant than metallic catalysts. The catalysts require sulfur removal to the parts per million level, while the microorganisms are unaffected by H{sub 2}S and carbonyl sulfide (COS) at one part per hundred--roughly the composition of sulfur in raw synthesis gas. During the two-year course of this project, the following major objectives have been accomplished: demonstrated long-term cell recycle of continuous fermentation of synthesis gas; demonstrated cell immobilization of Butyribacterium methylotrophicum; identified trickle-bed reactor as a viable alternative fermentation method; modulated metabolic pathways to increase C4 formation during synthesis gas fermentation; recovered carbon and electrons from H{sub 2} and CO{sub 2} with pathway modulation for increased C4 production; developed bacterial strains with improved selectivity for butyrate fermentation; demonstrated two-stage CO to alcohol fermentation; and concentrated alcohol from solventogenic fermentation by pervaporation

Bioconversion of coal-derived synthesis gas to liquid fuels. Annual report, September 29, 1992--September 28, 1993

The overall objective of the project is to develop and optimize a two-stage fermentation process for the conversion of coal derived synthesis gas in an mixture of alcohols. The goals include the development of superior strains with high product tolerance and productivity, optimization of process conditions for high volumetric productivity and product concentrations, integration and optimization of two stage syngas fermentation, evaluation of bioreactor configurations for enhanced mass transfer, evaluation of syngas conversion by a culture of Butyribacterium methyltrophicum and Clostridium acetobutylicum, development of a membrane based pervaporation system for in situ removal of alcohols, and development of a process for reduction of carbon and electron loss. The specific goals for year one (September 1992 - September 1993) were (1) development of a project work plan, (2) development of superior CO-utilizing strains, (3) optimization of process conditions for conversion of synthesis gas to a mixture of acids in a continuously stirred reactor (CSTR), (4) evaluation of different bioreactor configurations for maximization of mass transfer of synthesis gas, (5) development of a membrane based pervaporation system, and (6) reduction of carbon and electron loss via H{sub 2}CO{sub 2} fermentation. Experimentation and progress toward these goals are described in this report