Extracellular carbohydrate polymers from five desert soil algae with different cohesion in the stabilization of fine sand grain

Extracellular polymeric substances (EPS) from four filamentous cyanobacteria Microcoleus vaginatus, Scytonema javanicum, Phormidium tenue and Nostoc sp. and a coccoid single-cell green alga Desmococcus olivaceus that had been separated from desert algal crusts of Tegger desert of China, were investigated for their chemical composition, structure,and physical properties. The EPS contained 7.5-50.3% protein (in polymers ranging from 14 to more than 200 kD, SDS-PAGE) and 16.2-46.5% carbohydrate (110-460 kD, GFC). 6-12 kinds of monosaccharides, including 2-O-methyl rhamnose, 2-O-methyl glucose, and N-acetyl glucosamine were found. The main carbohydrate chains from M. vaginatus and S. javanicum consisted mainly of equal proportion of Man, Gal and Glc, that from P. tenue consisted mainly of arabinose, glucose and rhamnose. Arabinose was present in pyranose form, mainly alpha-L 1 --> 3 linked, with branches on C4 of almost half of the units. Glucose was responsible for the terminal units, in addition of having some units as beta1 --> 3 and some as beta1 --> 4 linked. Rhamnose was mainly 1 --> 3 linked with branches on C2 on half of the units. The carbohydrate polymer from D. olivaceus was composed mainly of beta1 --> 4 linked xylose, galactose and glucose. The galactose part was present both in beta-pyranose and -furanose forms. Arabinose in alpha-L-furanose form was mainly present as 1 --> 2 and 1 --> 2, 5 linked units, rhamnose only as alpha 1 --> 3 and xylose as beta 1 --> 4. The backbone of the polysaccharide from Nostoc sp. was composed of beta-1 --> 4 linked xylose, galactose and glucose. Most of the glucose was branched on position C6, terminal glucose and 2-O-methyl glucose units are also present. The relationship between structure, physical properties and potential biological function is discussed. (C) 2003 Elsevier Ltd. All rights reserved.

Effect of Copassivation of Cl and Cu on CdTe Grain Boundaries

Using a first-principles method, we investigate the structural and electronic properties of grain boundaries (GBs) in polycrystalline CdTe and the effects of copassivation of elements with far distinct electronegativities. Of the two types of GBs studied in this Letter, we find that the Cd core is less harmful to the carrier transport, but is difficult to passivate with impurities such as Cl and Cu, whereas the Te core creates a high defect density below the conduction band minimum, but all these levels can be removed by copassivation of Cl and Cu. Our analysis indicates that for most polycrystalline systems copassivation or multipassivation is required to passivate the GBs.

Effects of grain size on the mosaic tilt and twist in InN films grown on GaN by metal-organic chemical vapor deposition

The structural property of InN films grown on Ga-face GaN layers by metal-organic chemical vapor deposition has been studied by high-resolution x-ray diffraction. The mosaic tilt and twist are found to be strongly dependent on the surface lateral grain size. The twist decreases with increasing grain size and finally approaches to a constant level. On the other hand, the mosaic tilt increases substantially when the grain size becomes large enough and exceeds the width of step terraces on the GaN surface, showing an important mechanism for the defect generation in the InN/GaN system with large out-of-plane lattice mismatch. (c) 2006 American Institute of Physics.

New insight into the origin of twin and grain boundary in InP

X-ray reflectivity curves show bi-crystal (twin) characteristics. Defect segregations at the twin boundary can be seen, whereas stress is relaxed at the edge of the boundary. Relaxation of the stress resulted in the formation of twins and other defects. As a result of the formation of such defects, a defect-free and stress-free zone or low defect density and small stress zone is created around the defects. Stress, chemical stoichiometry deviation and non-homogeneous distribution of impurities are the key factors that cause twins in LEC InP crystal growth. (C) 1999 Elsevier Science Ltd. All rights reserved.

Conversion of Soybean oil to Biodiesel Fuel with Immobilized Candida Lipase on Textile Cloth

The characteristic of biodiesel fuel production from transesterification of soybean oil is studied. The reactant solution is the mixture of soybean oil, methanol, and solvent. A new lipase immobilization method, textile cloth immobilization, was developed in this study. Immobilized Candida lipase sp. 99-125 was applied as the enzyme catalyst. The effect of flow rate of reaction liquid, solvents, reaction time, and water content on the biodiesel yield is investigated. Products analysis shows that the main components in biodiesel are methyl sterate, methyl hexadecanoate, methyl oleate, methyl linoleate, and methyl linolenate. The test results indicate that the maximum yield of biodiesel of 92% was obtained at the conditions of hexane being the solvent, water content being 20 wt%, and reaction time being 24 h.

Novel biodiesel production technology from soybean soapstock

This paper describes an attractive method to make biodiesel from soybean soapstock (SS). A novel recovery technology of acid oil (AO) from SS has been developed with only sulfuric acid solution under the ambient temperature (25 +/- 2 degrees C). After drying, AO contained 50.0% FFA, 15.5% TAG 6.9% DAG 3.1% MAG 0.8% water and other inert materials. The recovery yield of AO was about 97% (w/w) based on the total fatty acids of the SS. The acid oil could be directly converted into biodiesel at 95 degrees C in a pressurized reactor within 5 hours. Optimal esterification conditions were determined to be a weight ratio of 1 : 1.5 : 0.1 of AO/methanol/sulfuric acid. Higher reaction temperature helps to shorten the reaction time and requires less catalyst and methanol. Ester content of the biodiesel derived from AO through one-step acid catalyzed reaction is around 92%. After distillation, the purity of the biodiesel produced from AO is 97.6% which meets the Biodiesel Specification of Korea. The yield of purified biodiesel was 94% (w/w) based on the total fatty acids of the soapstock.