一株烟草内生拮抗放线菌发酵条件优化

为提高烟草内生放线菌Y12发酵时产生抑菌物质的产量,通过摇瓶正交优化试验,确定了Y12的三角瓶发酵条件.发酵培养基组成为:黄豆粉1.5%,蛋白胨1.5%,葡萄糖1.5%,可溶性淀粉1.5%,MgSO4.7H2O 0.05%,(NH4)SO40.25%,NaCl 0.4%,KH2PO4 0.1%,CaCO3 0.5%;培养基初始pH 7.5,培养温度30℃,发酵时间72 h.经过优化发酵液的抑菌圈直径增加了44.9%.     

我国北方城市暴雨灾害演化过程及风险分析

提出一种基于灾害演化网络的风险分析方法,针对城市暴雨灾害的演化过程进行了风险分析。利用复杂网络理论构建北方城市暴雨灾害演化网络模型,将危机事件分为三个等级,并探讨了事件级别和出入度的关系;分析城市暴雨灾害链演化特点和暴雨危机事件后果蔓延规律,得到关键危机事件和演化链。结果表明,交通堵塞是我国北方城市暴雨灾害系统中关键危机事件;暴雨灾害演化系统存在短链、长直链和循环链三种结构,其中循环链中的危机事件互为因果,可自行激化,是灾害演化网络控制的关键结构。     

矩形和钟形震源时间函数对地震动模拟结果的影响比较

首先介绍了用于地震动数值模拟的国际通用软件COMPSYN程序,并对此进行了二次开发,将其震源时间函数由矩形函数改为钟形函数,通过与全空间的解析解计算结果的对比,验证了修改后程序的正确性.通过对比2种震源时间函数的频谱特点,指出矩形函数的高频成分丰富,不利于地震动的模拟.2种震源时间函数下用COMPSYN程序对同一观测点...     

Off-flavor compounds from decaying cyanobacterial blooms of Lake Taihu

The effect of cyanobacterial bloom decay on water quality and the complete degradation of cyanobacterial blooms in a short period were examined by an enclosure experiment in Gonghu Bay of Lake Taihu,China.Water quality parameters as well as taste and odor compounds during the breakdown of cyanobacterial blooms were measured.Results showed that the decay of cyanobacterial blooms caused anoxic water conditions,decreased pH,and increased nutrient loading to the lake water.The highest concentrations of dimethyl sulfide (DMS),dimethyl trisulfide (DMTS),and β-cyclocitral were observed in the anoxic water,at 62331.8,12413.3,and 1374.9 ng/L,respectively.2-Methylisoborneol was dominant during the live growth phase of cyanobacterial blooms,whereas DMS and DMTS were dominant during the decomposition phase.Dissolved oxygen,pH,and chlorophyll a were negatively correlated with DMS,DMTS,and β-cyclocitral,whereas total phosphorus,total nitrogen,and ammonium (NH4+-N) were positively correlated with DMS,DMTS,β-cyclocitral,and β-ionone.The experimental results suggested that preventing the anaerobic decomposition of cyanobacterial blooms is an important strategy against the recurrence of a malodor crisis in Lake Taihu.     

浙北平原富硒土壤资源区硒来源的定量分离

明确硒元素含量不同来源组分(自然背景组分和外源输入组分)贡献率是评价富硒土地资源是否具有可持续利用性的前提.以嘉兴市秀洲富硒土地资源区为研究区域,通过地学分析和多元统计交互验证,将该区域土壤硒来源定性分离为自然背景组分和含外源输入组分,并采用频数分布函数为工具,对硒含量不同来源组分的贡献率进行定量分离.结果表明,秀洲区富硒土地硒含量来源自然背景组分的贡献率占90%,外源输入组分占10%,表明秀洲区富硒土地资源具有可持续开发利用的潜力.     

The nuchal translucency and the fetal heart: a literature review

In this overview the current knowledge of the relationship between an increased nuchal translucency (NT) measurement and fetal heart structure and function in chromosomally normal fetuses is reviewed. Relevant pathophysiological theories behind the increased NT are discussed. Fetuses with an increased NT have an increased risk for congenital heart disease (CHD) with no particular bias for one form of CHD over another. This risk increases with increasing NT measurement. Although the NT measurement is only a modestly effective screening tool for all CHD when used alone, it may indeed be effective in identifying specific CHD “likely to benefit” from prenatal diagnosis. The combination of an increased NT, tricuspid regurgitation and an abnormal ductus venosus (DV) Doppler flow profile, is a strong marker for CHD. A fetal echocardiogram should be performed at 20 weeks' gestation in fetuses with an NT ≥ 95th percentile but < 99th percentile. When the NT measurement is ≥ 99th percentile, or when tricuspid regurgitation and/or an abnormal DV flow pattern is found along with the increased NT, an earlier echocardiogram is indicated, followed by a repeat scan at around 20 weeks' gestation. The resultant increased demand for early fetal echocardiography and sonographers with this special expertise needs to be planned and provided for. Copyright © 2009 John Wiley & Sons, Ltd.     

Function of Agricultural Land Use and Its Evolvement in Peri-urban Area: A Case Study of Beijing

Rapid urbanization in Beijing stimulates the urban land expansion and diminishes available agricultural land. Monofunctional agricultural land use can not meet the demand of the devel- opment of the multifunctional agriculture and urbanization any more, so multifunctional agricultural land use is going to be promoted in the city. This article proposes the evolvement of the land use change from 1992 to 2004 and discusses some evolvement views.     

Mg2Sn对镁合金耐腐蚀性能影响的计算分析与验证

目的 从计算角度分析镁合金中的主要析出相Mg_(2)Sn对ZA系镁合金耐蚀性能的影响,并采用试验测试的方法对其进行验证。方法 利用第一性原理计算方法对Mg_(2)Sn的表面能与功函数进行计算,通过与构建的Mg基体以及Zn、Al掺杂的Mg表面的表面能、功函数进行对比分析,分析Mg_(2)Sn对ZA系镁合金耐蚀性能的影响。为了验证计算结果,制备Mg-5Zn-3Al-0Sn合金以及Mg-5Zn-3Al-3Sn合金,通过电化学实验对2种合金的耐蚀性能进行对比分析,研究Mg_(2)Sn对ZA系镁合金耐蚀性能的影响。结果 计算了Mg基体表面能与功函数,与其他成果计算结果的符合程度较好。对Mg_(2)Sn不同表面的功函数进行计算,通过与Mg、Mg-Zn、Mg-Al表面的计算结果进行对比,发现Mg_(2)Sn的功函数均要更高。XRD测试结果表明,制备的Mg-5Zn-3Al-3Sn合金中有明显的Mg_(2)Sn相。电化学测试结果表明,Mg-5Zn-3Al-0Sn的耐蚀性能要好于Mg-5Zn-3Al-3Sn的耐蚀性能。结论 通过第一性原理计算发现,Mg_(2)Sn的功函数高于Mg基体表面的功函数,说明在合金中易发生微电偶腐蚀,Mg_(2)Sn充当阴极相促进Mg基体的腐蚀。电化学测试结果说明,当合金中存在明显的Mg_(2)Sn相时,合金的耐蚀性能降低,腐蚀电位达到-1.21 V。     

黑河上游不同植被类型土壤细菌群落多样性、功能及季节动态

土壤微生物群落与植物群落间的作用机制是探究生物地球化学循环过程和维持植被生态系统稳定的关键.黑河上游植被的垂直分布特征明显,选取垫状植被（CV）、灌丛草甸（HM）、森林草原（FS）、山地干草原（MS）和荒漠草原（DG）共5种典型植被样地,运用高通量测序技术分析冬、夏季不同植被类型土壤细菌的群落结构和多样性,基于FAPROTAX数据库进行群落功能预测,运用冗余分析、结构方程模型探讨驱动土壤细菌群落的主要环境因子,并揭示细菌群落变化的作用机制与季节差异.结果表明：①不同植被类型和季节下土壤理化性质差异显著,各指标随土壤深度的变化规律不同,森林草原（FS）的土壤含水率和碳氮养分含量更高;②细菌群落α-多样性指数在季节间的差异（P<0.05）大于植被类型（P>0.05）,冬季群落丰度整体高于夏季,物种多样性在冬季随海拔呈"倒U "型分布,夏季呈" W"型分布;③细菌群落结构和组成在门水平上无显著差异,优势种群为酸杆菌门（Acidobacteria）、变形菌门（Proteobacteria）和放线菌门（Actinobacteria）,但在属水平上随季节有明显不同;④土壤细菌群落的功能随植被类型和季节变化较小,均以化能异养、硝化和氨氧化作用为主;⑤影响细菌群落的关键因子存在季节差异,冬季为土壤温度（ST）、总有机碳（TOC）和pH,夏季为土壤含水率（SWC）、碳氮比（C/N）和pH;⑥土壤细菌群落受彼此关联的环境因子的协同作用,土壤理化性质对细菌群落多样性和功能的影响较植被类型更直接,改善土壤的碳、氮水平有助于提升细菌的物种和功能多样性.研究结果可为探索区域植被退化机制和维持高寒生态系统稳定提供参考.     

三峡库区生态系统服务功能重要性评价及其空间分布研究

以长江上游重点生态脆弱区三峡库区(重庆段)为研究区,结合RS和GIS软件,选取生物多样性维护功能、水源涵养功能和水土保持功能为评价指标,采用植被净初级生产力(vegetation net primary productivity,NPP)定量指标评估法,综合分析研究区2020年生态系统服务功能的重要性程度以及空间分异特...