One‐step production of 2,3‐butanediol from starch by secretory over‐expression of amylase in Klebsiella pneumoniae

BACKGROUND: 2,3‐Butanediol (2,3‐BD) is a valuable chemical that can be biosynthesized from many kinds of substrates. For commercial biological production of 2,3‐BD, it is desirable to use cheap substrate without pretreatment, such as starch. However, there have been few reports on the production of 2,3‐BD directly from starch. RESULTS: In this work, gene malS coding for α‐amylase (EC 3.2.1.1) precursor was inserted into plasmid pUC18K, and secretory over‐expression of α‐amylase was achieved by engineered Klebsiella pneumoniae. The extracellular recombinant amylase accelerated the hydrolyzation of starch, and one‐step production of 2,3‐BD from starch was carried out by engineered K. pneumoniae. A 2,3‐BD concentration of 3.8 g L^?1 and yield of 0.19 g 2,3‐BD g^?1 starch were obtained after 24 h fermentation. CONCLUSION: The one‐step production of 2,3‐BD from starch was achieved by secretory over‐expression of amylase in K. pneumoniae. This would simplify the process and reduce the production cost considerably by enabling use of starch with minimal pretreatment. Copyright © 2008 Society of Chemical Industry     

氧化锌颗粒膜电阻响应-恢复特性研究

测试了氧化锌颗粒膜电阻响应-恢复特性，讨论了颗粒形态，加热电压、环境气氛、气氛浓度和注入方式等因素对电阻响应-恢复特性的影响。结果表明，随着加热电压的升高，电阻响应-恢复的速度和程度明显加大；断续注入时颗粒膜电阻值的响应随着浓度的增加逐步减弱．     

绿色纤维天丝纱（Tencel）的生产实践

文章主要介绍了绿色环保纤维--天丝(Tencel)纤维特点、主要物理指标及特征,同时也详细介绍了该产品生产的工艺流程、各工序实际生产过程中的主要工艺参数、注意方面以及质量指标测试情况,以供大家参考.     

Synthesis of p‐aminophenol from the hydrogenation of nitrobenzene over metal–solid acid bifunctional catalyst

BACKGROUND: A single‐step conversion of nitrobenzene (NB) to p‐aminophenol (PAP) through catalytic hydrogenation is a widely used synthesis route for PAP. The main shortcoming of this route is the use of sulfuric acid for rearrangement of the phenylhydroxylamine (PHA) intermediate. In this paper, S₂O₈^2?/ZrO₂ (PSZ) solid acid and Pt‐S₂O₈^2?/ZrO₂ (Pt‐PSZ) bifunctional catalysts were prepared for the synthesis of PAP in non‐acid medium. RESULTS: Calcination temperature has a substantial effect on the acidity, structure and activity for PHA rearrangement of PSZ. The highest PAP yield was 33.8% over PSZ calcined at 823 K when the reaction was carried out in water at 423 K. A high PAP yield of 23.9% was achieved by a single‐step reaction of nitrobenzene over Pt‐PSZ bifunctional catalysts. CONCLUSION: PSZ solid acid exhibits high activity for PHA rearrangement. Perfect tetragonal ZrO₂ and much stronger acid sites play important roles in catalytic activity. Inhibiting the hydrogenation activity by reducing the amount of Pt loading on Pt‐PSZ can improve the competition of PHA rearrangement on acid sites with hydrogenation of PHA on metal active sites, resulting in better selectivity to PAP. Copyright © 2008 Society of Chemical Industry     

基于遗传算法的工作辊温度场参数优化模型

针对热连轧机工作辊热辊形计算中温度场模型的热交换等参数难以确定的问题 ,建立了基于遗传算法的参数优化模型 ,可以解决复杂条件下的热参数的求解问题。利用优化参数计算的轧辊温度场与实际测量结果一致。     

雏议造价监理工程师在工程建设中的作用

分析了造价监理工程师如何在在施工前期的招投标、施工组织方案技术经济评价和工程施工阶段的签证、索赔、进度款控制等方面对造价进行合理确定和有效控制。     

提高自主创新能力，加速变频器制造业持续快速发展

创新是企业发展不竭的动力，是增强企业竞争力的关键因素。本文就变频器企业在当前激烈的市场矗虿中，如何做好自主创新工作进行了探讨。在简要阐述自主创新的重要意义后，分析了变频器企业目前发展的现状和存在的问题。针对问题提出了变频器企业在开展自主创新时，可供参考的一些基本思路和途径。     

Application of artificial neural networks to the analysis of two‐dimensional fluorescence spectra in recombinant E coli fermentation processes

A two‐dimensional (2D) spectrofluorometer was used to monitor various fermentation processes with recombinant E coli for the production of 5‐aminolevulinic acid (ALA). The whole fluorescence spectral data obtained during a process were analyzed using artificial neural networks, ie self‐organizing map (SOM) and feedforward backpropagation neural network (BPNN). The SOM‐based classification of the whole spectral data has made it possible to qualitatively associate some process parameters with the normalized weights and variances, and to select some useful combinations of excitation and emission wavelengths. Based on the classified fluorescence spectra a supervised BPNN algorithm was used to predict some of the process parameters. It was also shown that the BPNN models could elucidate some sections of the process's performance, eg forecasting the process's performance. Copyright © 2005 Society of Chemical Industry     

砂岩储层渗透率表征方法探讨

渗透率是反映储层渗流能力的重要参数，目前对于单一储层的渗透率表征方法，通常是在岩心分析渗透率或测井解释渗透率的基础上进行厚度加权算术平均。这种方法对于均质的储层来说是适用的，但对于非均质严重的储层，不能准确反映该储层的实际渗流能力。本文提出一种应用可动流体体积权衡表征渗透率的方法，经实际资料验证，能较好地反映储层的实际渗透能力。