Two-stage Temperature Research Articles

Hybrid process for the conversion of lignocellulosic materials.

Because of the recalcitrant nature of lignocellulosic materials, it is important to pretreat the biomass in order to obtain a suitable material for the bioconversion. In this study, two different types of pretreatments were performed. The first experiment used a 2-gal Parr reactor operated at 140, 150, 160, and 170 degrees C with sulfuric acid concentrations varying from 0.5 to 2%. A second pretreatment was performed with a two-stage low-temperature process. The first-stage pretreatment was performed at 100 or 120 degrees C with sulfuric acid concentrations of 0.5, 2, and 5% followed by a second-stage pretreatment at 120 degrees C with 2% acid concentration. The best residues for enzymatic hydrolysis and simultaneous saccharification and fermentations (SSF) came from the higher temperature pretreatment with the Parr reactor. However, a large portion of the xylose fraction was degraded to furfural and glucose was degraded to HMF. On the contrary, the two-stage low temperature pretreatment resulted in a very low percentage of xylose degradation, and no glucose degradation. The residues from this two-stage pretreatment performed satisfactorily toward the production of ethanol by SSFs. This study discusses the results obtained from these experiments.

Integrated Two-Stage Processing of Microcrystalline Silicon Thin Films on SiO2 and Glass

AbstractA novel two-stage low temperature plasma assisted deposition process, which separates interface formation from bulk film growth, was investigated for deposition of in-situ phosphorous doped microcrystalline silicon (μc-Si) thin films on SiO2 and glass substrates. We find that the bulk layer microstructure, as characterized by reflection high energy electron diffraction and Raman scattering spectroscopy, is the same whether or not a buffer layer is used. However, we find significant differences in the room temperature dark conductivity, and the dark conductivity activation energies.

Simultaneous measurement of phytosterols (campesterol and beta-sitosterol) and 7-ketocholesterol in human lipoproteins by capillary column gas chromatography.

7-Ketocholesterol (a major cholesterol oxidation product) and phytosterols are important indicators of lipoprotein oxidation and lipoprotein metabolism respectively. We describe a simple, sensitive and reproducible method for the simultaneous measurement of these sterols in human lipoprotein samples by capillary column gas liquid chromatography. The method is suitable for clinical studies as small quantities of lipoprotein are required. Sterols are analysed after extraction from lipoprotein samples obtained by sequential flotation ultracentrifugation. The method involves briefly: extraction from lipoprotein samples using chloroform-methanol, saponification of sterol esters using cold potassium hydroxide, purification and derivatisation to trimethylsilyl ethers using BSTFA and 1% TMCS. Oxidation is prevented by drying under nitrogen and the use of powerful antioxidants. Separation is achieved using a DB-1 capillary column and a two-stage temperature ramp from 180-250 degrees C and detection using FID. The identity of sterols can be confirmed by GC-MS. Phytosterols and 7-ketocholesterol are present at low concentration in all the major lipoproteins. Using [3,4-13C]cholesterol and GC-MS we present evidence that cholesterol oxidation does not occur during the processing of lipoproteins using this technique.

Molecular beam epitaxy growth and characterization of thin (

This paper reports the effect of growth parameters and buffer structure on the luminescence electrical and structural characteristics of thin (<2 mu m) GaSb layers grown by molecular beam epitaxy (MBE) on GaAs(100) substrates. A two-stage substrate temperature growth regime has been developed on the basis of a thermodynamic consideration of the growth process, taking into account the additional Gibbs free energy due to the strain at the initial growth. This regime permits the growth of GaSb epilayers with a small Sb/Ga ratio at high substrate temperatures; it provides a greater exciton photoluminescence (PL) intensity and Hall mobility (over 5000 cm2 V-1 s-1 at 77 K) and improves the layer quality. The appearance of a free exciton luminescence line (809 meV) in the PL spectra of MBE GaSb/GaAs is reported for the first time. It is also shown that a (50 AA AlSb/50 AA GaSb)10 short-period superlattice prevents non-radiative recombination centres and carrier scattering centres from propagating in the top GaSb layer but does not bend the misfit dislocation growing through the layer from the GaSb/GaAs interface.

Two-stage temperature rise in a thermoviscoplastic half-plane under impact

A thermoviscoplastic constitutive model is used to treat uniaxial shock wave propagation in a material exhibiting rate-sensitive plasticity and thermal softening. Simple relations are obtained for the pressure jump as a function of the density jump, shock speed as a function of particle velocity, and pressure decay behind the shock front. Also, the model predicts a two-stage temperature rise, involving a jump at the shock front followed by a rise due to plastic dissipation (stress decay). The temperature rise and other quantities are predicted in the case of impact of titanium plates.

Kinetics of texture development and sulfur removal in oriented silicon iron

The kinetics of (110)[001] secondary grain growth, the temperature dependence of selectivity to a (110)[001] texture, and the kinetics of desulfurization in cold rolled-decarburized, thin sheet (semiprocessed 3 pct Si−Fe) were measured as were the parameters requited to produce (110)[001] grain-oriented sheet by high temperature strip annealing. Kinetic studies revealed that (110)[001] grain growth in several semiprocessed sheets exhibited the following characteristics: 1) sigmoidal growth kinetics; 2) an activation energy of ∼64 Kcal; and 3) essentially complete (110)[001] secondary grain growth within 8 min at temperatures of 1000°C and higher. Measurements of magnetic torque properties and pole figures of isothermally annealed semiprocessed sheet showed a degradation in selectivity to a (110)[001] texture above 1050°C. Desulfurization kinetics were in good agreement with a theoretical diffusion model which takes into account sulfur removal in the presence of a dispersed second phase of MnS particles. A two-stage high temperature strip annealing cycle in dry hydrogen produced (110)[001] grain-oriented sheet having magnetic properties comparable to those obtained by conventional box annealing.

Development of High Resolution Pyrolysis-Gas Chromatography for the Identification of Microorganisms

The application of pyrolysis-gas chromatography (PGC) to the rapid identification of medically and economically important microorganisms has increased in the last five years. However, there are major problems concerning the resolution of such complex pyrolyzates and the long term reproducibility of the PGC system. Use of the PGC system described by Shulman et al. (J. Chromatog. Sci. 7, 36, 1969) and optimization of the chromatographic parameters resolved approximately 200 peaks from the pyrolyzates of representative bacteria, yeast, fungus and mycoplasma. Lyophilized samples of 80 µg were accurately weighed in a pyrex pyrolysis tube which was then inserted into the pyrolysis chamber. The samples were heated to 600°C in eight seconds. The entire pyrolysis chamber was disposed of each time, thus eliminating background in subsequent analyses. The pyrolyzate was separated on a 500 ft by 0.03 in. i.d. capillary column coated with 4% Carbowax 20M. Two-stage temperature programming with a helium flow rate of 5.2 cc/min greatly enhanced the resolution. The sensitivity was such that peaks equivalent to 1 ng were readily detected. The reproducibility was excellent initially, but the column exhibited signs of aging after 100 analyses in each direction. Our observations suggested that control of column aging in this system may be aided by use of short disposable precolumns.