PREPARATION AND CHARACTERIZATION OF MAGNESIUM CHROMITE AND MAGNESIUM FERRITE AEROGELS

A supercritical drying process has been used to prepare MgO-Cr₂O₃, and MgO-Fe₂O₃ powders from a mixture of magnesium acetate and the metallic acetylacetonates hydrolyzed in a methanolic solvent. The resultant aerogels have small particle sizes in the range of 10 to 20 nm and high surface areas in the range of 50 to 250 m²sol;g. After removal from the autoclave, characterization by X-ray diffraction (XRD) showed that the MgO-Cr₂O₃, was amorphous and that the MgO-Fe₂O₃ was readily in the form of a spinel structure for magnesioferrite (MgFe₂O₄). Fourier transform infrared spectroscopy (FTIR) and thermogravimetric and differential Ihermal analyses (TG-DTG-DTA) showed a high level of retained surface methoxy and carboxylate species for the MgO-Cr₂O₃ aerogel (lover 40% by weight). The MgO-Fe₂O₄, on the otherhand, had less than 10% organic matter. The differences observed between MgO-Cr₂O₃ and MgO-Fe₂O₄ have been attributed to the formation of Cr⁺⁶ in the former case. After heating in air at 970 K. MgO-Cr₂O₃ crystallized to the spinel structure MgCr₂O₄. The IR transmittance of pressed disks of MgFe204 aerogel showed behavior typical for a n-type semiconductor. The MgCr₂O₄, however, was a p-type semiconductor due to mainly C^r+6 present on the surface. Lewis acid centers were prevalent on both materials. The acid strength was found to be higher on the MgFe₂O₄ compare to the MgCr₂O₄     

Knowledge of partner's ability as a moderator of group motivation gains: An exploration of the K?hler discrepancy effect.

O. K?hler (1926, 1927) found that less able performers tried harder as team members under conjunctive task demands (K?hler motivation gain effect) and that the greatest gain occurred with moderately discrepant coworker abilities (K?hler discrepancy effect). Recent investigations have reproduced K?hler's overall motivation gain but not the discrepancy effect. The present research examined whether workers' foreknowledge of task abilities--present in K?hler's research, absent in contemporary studies--moderates the discrepancy effect. Participants worked alone or in 2-person teams under conjunctive task demands. Exp 1 manipulated foreknowledge of ability. Exp 2 manipulated discrepancy: a (confederate) teammate performed slightly, moderately, or substantially better. Both experiments found (1) overall motivation gains and (2) discrepancy moderation under foreknowledge conditions. Implications for understanding group motivation gains are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aggregated Scheduling of a Multiproduct Batch Plant by Two-Stage Stochastic Integer Programming

We consider the mid-term scheduling of a multiproduct batch plant. Market requirements for the final products are uncertain but given in terms of a probability distribution. We introduce a two-stage stochastic integer programming model for the problem and solve it by a scenario decomposition method based on Lagrangian relaxation. We describe heuristics and preprocessing for both the single- and the multi-scenario models. Preliminary computational results are presented.     

Simulation of batch and continuous reactors with co-immobilized yeast and β-galactosidase

A reaction-diffusion model was used to simulate a co-immobilized system utilizing the numerical method of orthogonal collocation. The production of ethanol from deproteinized whey using β-galactosidase co-immobilized with Saccharomyces cerevisiae in calcium alginate gel beads was chosen as a model system. Calculated concentrations of lactose, glucose, galactose and ethanol were compared with experimental data for a batch reactor and a continuous horizontal packed-bed reactor. The mathematical model has been used to analyse the influence of internal and external mass transfer for the continuous reactor. The external mass transfer was shown to be of minor importance. The introduction of baffles decreased the backmixing in the horizontal packed-bed reactor. Internal mass transfer was found to be the main cause of the reduction in the apparent reaction rate. Thus, much of the expected increase in reaction rate is diminished by mass transfer hindrance when the cell concentration is increased.     

Inhibition of nitric oxide synthesis aggravates reperfusion injury after hepatic ischemia and endotoxemia

The potential role of nitric oxide (NO) was investigated in the pathophysiology of liver injury after priming with 20 min hepatic ischemia-reperfusion and administration of .5 mg/kg Salmonella enteritidis endotoxin. Liver injury during the early reperfusion phase of 4 h was characterized by severe vascular oxidant stress, lipid peroxidation (LPO), neutrophil infiltration, and a 33% reduction of the microvascular blood flow in the liver. Inhibition of NO synthesis with N omega-nitro-L-arginine methyl ester hydrochloride (L-NAME) aggravated liver injury by 90%, reduced LPO, and did not affect liver neutrophils but further impaired microvascular blood flow. Treatment with the NO-donor spermine-NONOate or L-arginine did not affect these parameters in postischemic animals, however, treatment did restore all values of L-NAME-treated animals back to disease control levels. These data suggest that endogenous NO formation is sufficient to limit ischemic liver injury during reperfusion but inhibition of NO synthesis will result in additional ischemic damage. NO may also be involved in scavenging of superoxide in the vasculature and in inducing LPO.     

Analysis of low molecular weight plant phenolics by thermospray liquid chromatography/mass spectrometry

High performance liquid chromatography-mass spectrometry using a thermospray interface and discharge ionisation has been conducted on a group of plant phenolic standards and on a wheat straw acid hydrolysate. Protonated molecules, [M + H]⁺, were observed for the phenolic standards and it was possible to identify several phenolic compounds in the hydrolysate. These results indicate that thermospray HPLC/MS has potential as a technique for determining the presence of useful marker compounds which are indicative of the progress of the lignification during plant growth.     

Rough surface absorption of Nd:YAG laser rods

The rough surface of Nd:YAG-laser rods exhibits a broad spectral absorption due to impurities. The optical density of the investigated surfaces was determined up to several percent in the near infrared and visible spectral range. The characteristics of the rough surface absorption was investigated.