Purification and enzymatic properties of the extracellular and constitutive chitosanase produced by Bacillus subtilis RKY3

BACKGROUND: Purification and enzymatic properties of a chitosanase from Bacillus subtilis RKY3 have been investigated to produce a chitooligosaccharide. The enzyme reported was extracellular and constitutive, which was purified by two sequential steps including ammonium sulfate precipitation and ion exchange chromatography. RESULTS: Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis of the purified chitosanase revealed one single band corresponding to a molecular weight of around 24 kDa. The highest chitosanase activity was found to be at pH 6.0 and at 60 °C. Although the mercaptide forming agents such as Hg²⁺ (10 mmol L^?1) and p‐hydroxymercuribenzoic acid (1 mmol L^?1, 10 mmol L^?1) significantly or totally inhibited the enzyme activity, its activity was enhanced by the presence of 10 mmol L^?1 Mn²⁺. The enzyme showed activity for hydrolysis of soluble chitosan and glycol chitosan, but colloidal chitin, carboxymethyl cellulose, crystalline cellulose, and soluble starch were not hydrolyzed. The analysis of chitosan hydrolysis by thin‐layer chromatography and viscosity variation revealed that the purified enzyme should be endosplitting‐type chitosanase. CONCLUSION: The chitosanase produced by Bacillus subtilis RKY3 was a novel chitosanlytic enzyme with relatively low molecular weight, which is a versatile enzyme for chitosan hydrolysis because it could hydrolyze soluble chitosan into a biofunctional oligosaccharide at a high level. Copyright © 2011 Society of Chemical Industry     

Generation of H2O2 from H2 and O2 over zeolite beta containing Pd and heterogenized organic compounds

The catalytic generation of H₂O₂ from H₂ and O₂ has been studied over zeolite beta-supported Pd and zeolite beta-adsorbed organic compounds such as 1,4-benzoquinone (BQ), hydroquinone (HQ), azobenzene (AB) and hydrazobenzene (HAB). According to catalytic results, zeolite beta-supported Pd catalysts display effective performance relative to those prepared from other types of zeolites reported and Pd-loaded zeolite beta-adsorbed HQ catalysts show enhanced activity compared to zeolite beta-supported Pd catalysts. In situ UV–Vis spectroscopic study indicates that HQ can readily be converted to BQ reversibly under H₂ and air inside zeolite beta only in the presence of Pd. The results suggest that HQ acts as a strong hydrogen transfer agent to promote the production of H₂O₂ from H₂ and O₂ in cooperation with a Pd catalyst. By contrast, adsorption of BQ, AB and HAB induces suppression of the catalytic properties of Pd/zeolite beta.     

Contribution of fuel cell systems to CO2 emission reduction in their application fields

Fuel cells (FCs) and their hybrid systems can play a key role in reducing carbon dioxide (CO₂) emissions. The present paper analyzes the contributions of the FC system to CO₂ emission reduction in three application fields.In the mobile application field, the direct methanol FC system has little or no influence on CO₂ emission reduction.The benefit of the FC in CO₂ emission reduction in the transportation field is directly dependant on the H₂ production method. Pre-combustion technology (with carbon capture) represents one of the best mid-term solutions for H₂ production. If FC vehicles (FCVs) use the H₂ produced by this process, the CO₂ emissions in this field could be decreased to 70–80% of the traditional CO₂ emissions.In the stationary application field, the FC system can be effectively operated as the distributed generation (DG) in terms of CO₂ emission reduction. Among the various types of FC or FC hybrid system used for DG, the solid oxide FC (SOFC) hybrid system with a CO₂ capture unit is the best option as it doubled the electricity efficiency compared to the traditional combustion cycle and decreases the CO₂ emission to 13.4% of the traditional CO₂ emission.However, the FC and carbon capture and sequestration (CCS) technologies need to be fully developed before the FC can contribute to reducing CO₂ emissions.     

Segment-based proxy caching for Internet streaming media delivery

The proliferation of multimedia content on the Internet poses challenges to existing content delivery networks. While proxy caching can successfully deliver traditional text-based static objects, it faces difficulty delivering streaming media objects because of the objects' sizes as well as clients' rigorous continuous delivery demands. We present two techniques supporting segment based proxy caching of streaming media. We evaluated these techniques in simulations and real systems.     

Clinical efficacy of amniotic membrane transplantation in the treatment of various ocular surface diseases.

PURPOSE: To investigate the efficacy of permanent amniotic membrane transplantation (AMT) for the treatment of various ocular surface diseases. METHODS: The medical records of 62 eyes from 58 patients who had undergone permanent AMT were reviewed. The amniotic patches were grafted for the treatment of neurotrophic ulcers (n=15), inflammatory corneal ulcers (n=15), scleral ulcers (n=11), painful bullous keratopathy (n=8) and pterygium as an adjuvant to a conjunctival autograft (n=13). Cryo-preserved or freeze-dried amniotic membrane (AM) were used. The overall success rate, the interval to epithelialization, pain-subsiding time, and complications were evaluated. The pain relief and the full epithelialization interval in the bullous keratopathy patients given the cryo-preserved AM were compared with those given the freeze-dried AM. RESULTS: The success rate in the patients with neurotrophic ulcer, inflammatory corneal ulcer, scleral ulcer and bullous keratopathy were 93.3%, 66.7%, 92.9% and 100%, respectively. A conjunctival autograft with AMT showed a 100% success rate without recurrence. The time to re-epithelialization was 24.4+/-24.2, 20.4+/-5.8, and 16.9+/-7.0 days in patients with neurotrophic, inflammatory and scleral ulcers, respectively (p=0.431). The pain relief interval in the cryo-preserved and freeze-dried AM group was 17.7 and 23.3 days, and the re-epithelialization interval was 29 and 22 days, respectively, which was insignificant. CONCLUSIONS: AMT has a high success in the treatment of neurotrophic, scleral ulcer, bullous keratopathy and pterygium with a low rate of complications but presented only partial success in the treatment of inflammatory corneal ulcers. The clinical efficacy of AMT was not related to the methods used to preserve the AM.     

Coupling effects in bending, buckling and free vibration of generally laminated composite beams

A closed form expression to determine the effective flexural modulus of a laminated composite beam is developed and presented in this contribution. This effective flexural modulus is applied to the bending, buckling and free vibration response of generally laminated composite beams with various boundary supports. The expression was developed using the combination of the Euler–Bernoulli beam and classical lamination theory. In addition the results of an extensive finite element analysis are used to validate the analytical model. The comparison of the analytical results, the finite element results and the experimental results showed good correlation. It is also observed that coupling response is an important variable that must be included in the computation of the effective flexural stiffness of generally laminated beam.     

春之路

这个纪念方案拟建一条道路,以表达对2008年5·12四川大地震遇难者的沉痛哀悼.这条路毗邻四川省的某一河边,那里有一大片可循环利用的建筑废墟地,零星分布着小麦田.独特的场所体验由地下和地上两个项目组成.     

Surface-layer damage and responsivity in sputtered-ITO/p-GaN Schottky-barrier photodiodes

It is postulated that donor-like nitrogen vacancies, caused by the sputtering of a Schottky-barrier metal onto p-type gallium nitride, diffuse into the GaN and form a surface layer in which both the minority-carrier lifetime and mobility are drastically reduced. Such a damaged surface layer is shown to reduce the responsivity of p-GaN Schottky-barrier photodiodes, thereby offering an explanation for the responsivity values in the range of 0.03–0.04 A/W that have been measured in experimental ITO/p-GaN devices. On making allowance for the damaged surface layer, an electron diffusion length of around 300 nm can be inferred for the undamaged p-GaN region.