Biocompatibility studies of silk fibroin-based artificial nerve grafts in vitro and in vivo

Silk fibroin(SF)has been used extensively in the biomedical field including tissue engineering for the generation of artificial bones,skins or ligaments.We have previously reported on good in vitro biocompatibility of SF fibers with peripheral nerve tissues and cells.In the present study,we developed a novel design of the SF-based artificial nerve graft(SF graft)which was composed of a SF-nerve guidance conduit(NGC)inserted with SF fibers.MTT assay was performed to determine the cytotoxicity of the SF-NGC extract fluid on the cultured L929 cells derived from an immortalized mouse fibroblast cell line.In addition,this SF graft was implanted into adult rats for bridging a 10-mm long sciatic nerve defect.The following-up experiments at initial stage(1-4 week)of nerve regeneration including routine blood tests and histochemical investigation were conducted to evaluate the in vivo biocompatibility of the SF graft with peripheral nerves.The results demonstrated that the SF-NGC graft was biocompatible with the surrounding tissues and cells due to its low inflammatory potential with a grade 0 under the U.S.Pharmacopeia guidelines and it was generally suitable to a certain degree for bridging peripheral nerve defects in virtue of supporting Schwann cell adherence,expansion and migration.Therefore the SF graft is a promising alternative to classical autografts for peripheral nerve repair.     

从《Science》和《Nature》看关于台风研究的热点问题

热带气旋是形成在热带或副热带洋面上,具有有组织的对流和确定的气旋性地面风环流的非锋面性的天气尺度系统.世界气象组织将最大风速在32.7 ms-1以上的热带气旋称为台风或飓风.由台风引起的强风、暴雨、巨浪等气象灾害给人类带来巨大的损失,其影响范围广,发生频率高,使得对台风的研究成为全球关注的气象课题.本文侧重总结了近8年来(1998～2005)Science和Nature杂志中有关台风研究的文章,综合了国际权威科学家对台风关注的最新进展和研究成果.其中在台风观测手段改进方面,如Doppler雷达对于边界层强滚动现象的发现,GPS风廓线仪对于台风中海-气边界层理论拖曳系数的修正;而在动力结构的研究方面,海气相互作用的重要性,特别是对台风强度预报的影响有了新的认识;在全球变暖的大背景下,气候变化对台风活动趋势的影响成为科学家日益关心和争论的话题.     

Microbial communities in microcosm soils treated with battery waste

Battery waste is one of the most destructive hazards to our environment,especially to the soil.In order to understand the effects of the battery waste on the microbial communities in soil,microcosm soils were treated with the powder made from the battery waste.Microbial biomass and respiration were measured after 15,30,45,and 60 days of the treatment,and catabolic capability and Bi- olog profile were determined after 60 days.Microbial biomass was declined by all treatments,while microbial respiration and catabolic ca- pability were enhanced.Although microbial biomass recovered after a period of incubation,microbial respiratory quotient,catabolic capa- bility and community structure remained significantly affected.Our results also suggest that microbial respiratory quotient and Biolog pa- rameters are more sensitive than microbial biomass to the battery stress on bioavailability.     

Comparing the biological coherence of network clusters identified by different detection algorithms

Protein-protein interaction networks serve to carry out basic molecular activity in the cell. Detecting the modular structures from the protein-protein interaction network is important for understanding the organization, function and dynamics of a biological system. In order to identify functional neighbor- hoods based on network topology, many network cluster identification algorithms have been devel- oped. However, each algorithm might dissect a network from a different aspect and may provide dif- ferent insight on the network partition. In order to objectively evaluate the performance of four com- monly used cluster detection algorithms: molecular complex detection (MCODE), NetworkBlast, shortest-distance clustering (SDC) and Girvan-Newman (G-N) algorithm, we compared the biological coherence of the network clusters found by these algorithms through a uniform evaluation framework. Each algorithm was utilized to find network clusters in two different protein-protein interaction net- works with various parameters. Comparison of the resulting network clusters indicates that clusters found by MCODE and SDC are of higher biological coherence than those by NetworkBlast and G-N algorithm.     

Research on the Bit Computation Model for Time Variable Channel Bandwidth

For the encoding bit-rate problem in H.264 wireless video communication,this paper analyzes the bit-rate computation model and the Mean Square Error distortion model,establishes the relation between the quantization parameter of the encoding bit-rate and the intra frame refresh rate of the macro block,and put forward a new ideal about the coding rate on the basis of general binomial computation model theory. Furthermore,this method not only can adaptively adjust the bit allocation and quantization parameter and prevents buffer from overflowing downward or upward under given network bandwidth,but also can apply the rate-distortion to optimize the solution method,control the encoding bits accurately and optimizes the allocation between the intra and inter frame encoding macro block.     

Single grain Rb-Sr dating of euhedral and cataclastic pyrite from the Qiyugou gold deposit in western Henan, central China

The Rb-Sr isotopic dating of pyrite mineral from ore deposits can directly provide mineralization age. However, many geological factors may affect the Rb-Sr isotopic system,which baffles application of this method. Employing ultra-low procedural blank Rb-Sr method,we have dated pyrites separated from the No. 4 breccia pipe of the Qiyugou gold deposit,western Henan Province. Single grains of euhedral pyrite crystal with few microcracks yield an isochron age of 126 ± 11 Ma, which represents time of the main mineralization stage of the deposit. Pyrite grains of cataclastic type show nevertheless scattered Rb-Sr isotopic composition and no reasonable isochron can be defined. Crystal morphology and mineral inclusion studies reveal that Rb and Sr of pyrite mineral probably are preserved mainly in biotite, K-feldspar, and sericite mineral inclusions. The dating results likely suggest that cataclastic pyrite is not suitable for the Rb-Sr dating due to modification of the Rb-Sr isotopic system by later hydrothermal activity of fluid.     

上海中心城区地表灰尘与土壤中重金属累积及污染评价

通过对上海中心城区土壤与地表灰尘和降雨径流样品的取样调查，探讨了城市不同土地利用类型中重金属Cu,Zn,Cr,Pb的累积特征及其环境效应.结果显示：地表灰尘、土壤重金属在不同土地利用类型中的富集程度均高于土壤背景值，且存在显著性差异.相比之下，灰尘重金属污染比土壤严重，同一土地利用类型灰尘重金属P值为土壤的3~4倍.土地利用方式对重金属在地表灰尘和土壤中的积累有较明显的影响.地表灰尘重金属在工业、交通、居住用地中的含量普遍偏高，而在绿地中的含量普遍较低；土壤重金属在交通、商业和绿地中浓度较高，而工业用地中浓度较低.不同土地利用方式对地表径流重金属含量的影响不同，与土壤相比，地表灰尘直接影响到降雨径流重金属含量，两者之间耦合关系明显.工业、交通、居住和商业用地地表径流中，重金属EMC值以工业用地最高，其次为交通用地，商业和居住用地较小，但Cr，Pb，Zn的平均EMC值都超过了国家Ⅴ类水的标准，具有潜在的环境危害.     

基于安全域的输电系统概率安全评估系统框架

针对输电系统概率安全评估问题,提出了一种基于安全域的输电系统概率安全分析系统的模型.介绍了该模型的构成、实用动态安全域和割集电压稳定域在概率安全评估中的应用,以及概率安全评估的计算步骤.该系统应用最新的安全域的研究成果,在能量管理系统数据的基础上,通过对安全域、随机潮流的计算,实现了输电系统在线概率安全评估.给出的动态和静态不安全概率指标,可用于指导运行人员进行预防性控制决策.     

企业战略模式选择对企业关系收益诉求影响的实证研究——以北京高新产业集群为例

先前研究表明,企业组织对关系收益的不同诉求是驱动企业选择其关系实践模式的关键性因素,但对于企业关系收益诉求的决定机制,并未提供系统性的考察与解释。针对这一问题,该文从新的视角详细界定了企业战略模式的四维度框架,详细考察了战略模式的不同维度对于企业对组织关系收益诉求的不同影响,构建起了战略模式和关系收益诉求决定机制间的作用路径。基于北京市高新技术产业集群的企业样本进行了相关实证分析。研究结果表明,企业战略模式的4个导向与企业3类组织关系收益诉求水平间具有显著的正相关关系。     

高职高专英语写作能力培养实践与理论发展综述

在全国高职高专英语写作大赛的推动下，高职院校学生英语写作能力培养的探索实践和理论研究成效显著，实践表明，该项赛事凸显职业教育技能比赛的导向功能，促进职业英语写作理论发展，推动英语写作课程的改革，有助于完善英语专业技能竞赛能力体系的建设。