Influence of gait speed on the control of mediolateral dynamic stability during gait initiation

This study investigated the influence of gait speed on the control of mediolateral dynamic stability during gait initiation. Thirteen healthy young adults initiated gait at three self-selected speeds: Slow, Normal and Fast. The results indicated that the duration of anticipatory postural adjustments (APA) decreased from Slow to Fast, i.e. the time allocated to propel the centre of mass (COM) towards the stance-leg side was shortened. Likely as an attempt at compensation, the peak of the anticipatory centre of pressure (COP) shift increased. However, COP compensation was not fully efficient since the results indicated that the mediolateral COM shift towards the stance-leg side at swing foot-off decreased with gait speed. Consequently, the COM shift towards the swing-leg side at swing heel-contact increased from Slow to Fast, indicating that the mediolateral COM fall during step execution increased as gait speed rose. However, this increased COM fall was compensated by greater step width so that the margin of stability (the distance between the base-of-support boundary and the mediolateral component of the “extrapolated centre of mass”) at heel-contact remained unchanged across the speed conditions. Furthermore, a positive correlation between the mediolateral extrapolated COM position at heel-contact and step width was found, indicating that the greater the mediolateral COM fall, the greater the step width. Globally, these results suggest that mediolateral APA and step width are modulated with gait speed so as to maintain equivalent mediolateral dynamical stability at the time of swing heel-contact.     

西伯利亚地台早寒武世钙藻的发育特征

西伯利亚地台的新元古代到早寒武世间的钙藻化石特别丰富,为研究钙藻化石的发育历史提供了模式。在几次演化事件背景下记录了演化的两次转折,其中一个是藻类的普遍钙化,还有一个是Botomian晚期到Toyonian早期之间在西伯利亚地台缺失钙藻化石记录,而在其它地区包括西伯利亚地台的边缘(Altay—Sayan地区),钙藻的丰度却达到了最大。     

底栖藻对扬子地台西缘晚奥陶世生态危机的改善作用

晚奥陶世的冈瓦纳大陆冰川导致全球性海退和两幕生物灭绝事件,第一幕,也是高潮幕,发生于Rawtheyan期末;第二幕发生于Hirnantian期末。在经历第一幕事件的过程中,扬子地台西缘的四川汉源地区大渡河组浅水相灰岩和硅质灰岩中出现了极其繁盛的底栖藻类,局部层位中可达到造礁的程度。大量底栖藻通过光合作用改善、缓冲了这一浅海地区的低温、缺氧的灾变环境,并成为生态系统重建的先驱群落。局部浅海环境的正常化为后生动物腕足类、三叶虫和海百合在Hirnantian期南郑组的短暂复苏创造了生存条件。当后生动物再度成为生态系统的主体时,啃食压力的增大使底栖藻的居群数量骤然减低。始于Hirnantian后期冰川消融的海进造成第二幕Hirnantia动物群的灭绝。     

扬子台地西北缘志留纪笔石Oktavites spiralis (Geinitz, 1842)发育过程研究

Oktavites spiralis(Geinitz,1842)是志留系特列奇阶(Telychian)的笔石带化石,其形态特征明显,在全球范围内广泛分布,地层对比意义较强。然而,该种宽泛的化石定义以及缺乏居群变异研究,造成了对该化石延限的争议,不利于地层的精确对比。笔者对产自陕西紫阳、岚皋地区特列奇阶Oktavites spiralis带至Cyrtograptus lapworthi笔石带的45个Oktavites spiralis不同发育阶段的幼体标本进行研究,建立了较完整的发育序列,从而对该种的始部特征有了更为深入的了解,增加了描述的精确性。同时,通过始部特征的对比研究,可将Oktavites spiralis和与之共生的Oktavites contortus(Perner,1897)明确区分为2个独立的种。此外,对Oktavites spiralis和Oktavites contortus发育过程的研究,也可成为该属进一步精确厘定的主要依据之一。     

平台化学品短链支链脂肪酸和短链支链醇的微生物代谢工程

短链支链脂肪酸和短链支链醇均为重要的平台化学品,是合成多种高附加值产品的前体物质,市场需求巨大。目前两者的生产主要是利用基于石化原料的化学合成法。化学合成法存在着严重依赖化石燃料、反应效率低以及极易造成环境污染等缺点。微生物代谢工程的快速发展为这些平台化学品的生产提供了一条极具潜力的生物合成路线。利用微生物代谢工程技术构建生产这些平台化学品的微生物细胞工厂具有绿色清洁、可持续发展和经济效益好等独特优势。本文系统综述了近年来微生物代谢工程技术在短链支链脂肪酸和短链支链醇合成方面的研究进展,包括所涉及的宿主菌株、关键酶、代谢途径及其改造等,并探讨了未来的发展前景。     

基于叶缘分析法定量重建中国始新世植物群的年均温

全球气候在始新世总体上经历了由极热逐渐转冷的过程。植物叶片化石作为地质时期的产物,可以用来反映陆地古气候的这一变化历史。文中采用叶缘分析法首次定量重建中国始新世6个植物群的古年均温。分析结果显示,热鲁植物群（年均温17．3±3．7℃）、依兰植物群A段（年均温18．2±2．9℃）和柳区植物群（年均温22．7±2．3℃）反映了早始新世至中始新世早期气温较高。依兰植物群B段（年均温10．1±3．4℃）、石脑植物群（年均温10．1±3．4℃）、抚顺植物群（年均温5．0±1．4℃）和白鹿塬植物群（年均温9．2±3．1℃）则反映了中始新世后期至晚始新世气温明显下降的过程。植物群的古年均温推测值与植物群物种组合代表的气候类型吻合。研究表明,始新世时期中国与全球的气候变化过程基本一致,即早始新世至中始新世早期气温较高,中始新世后期至到晚始新世气温明显降低。     

基因表达谱信息分析软件IDEA与WebGEA

基因芯片具有高通量快速并行检测基因表达水平的功能,是功能基因组研究的有力工具。针对基因芯片常规的信息分析需要,我们初步设计开发了基因表达谱的信息学分析平台,包括基于单机的软件IDKA(Information Digger for Experiments of microArray)与网络应用程序WebGEA(WEB GeneChip Expression Analysis),分别支持用户运行独立程序与在因特网上提交数据运行服务器程序来完成数据采掘分析任务。该平台得到良好的应用,是解决基因芯片常规的信息分析问题的一个方便工具。     

Middle–Late Ordovician chitinozoans from Songliang of Qiaojia,western South China,and their biostratigraphic implications

Ordovician chitinozoans are as yet inadequately documented from the western Yangtze Platform, South China. Here we present a systematic study on chitinozoans from a Middle–Upper Ordovician succession at Songliang of Qiaojia, northestern Yunnan, southwestern China. Altogether 34 species of 12 genera are identified from the upper Hungshihyen and the Huadan formations. The top of the Hungshihyen Formation yields typical Early and Middle Ordovician forms, for instance, Lagenochitina obeligis and Belonechitina chenjiawuensis, with the latter only known from the lower Darriwilian in South China, thus suggesting an early Darriwilian age for this interval. The chitinozoans recovered from the Huadan Formation include Lagenochitina prussica and Spinachitina fossensis, both are mainly confined in Katian and sometimes ranging into younger strata. This indicates an age younger than the middle to late Darriwilian previously determined for the Huadan Formation. However, conflicts exist in age assignment of the Huadan Formation based on chitinozoan and other evidence, and further work is required.     

Effects of general fatigue induced by incremental maximal exercise test on gait stability and variability of healthy young subjects

The purpose of this study was to determine whether general fatigue induced by incremental maximal exercise test (IMET) affects gait stability and variability in healthy subjects. Twenty-two young healthy male subjects walked in a treadmill at preferred walking speed for 4 min prior (PreT) the test, which was followed by three series of 4 min of walking with 4 min of rest among them. Gait variability was assessed using walk ratio (WR), calculated as step length normalized by step frequency, root mean square (RMS_ratio) of trunk acceleration, standard deviation of medial-lateral trunk acceleration between strides (VAR_ML), coefficient of variation of step frequency (SFCV), length (SLCV) and width (SWCV). Gait stability was assessed using margin of stability (MoS) and local dynamic stability (λ_s). VAR_ML, SFCV, SLCV and SWCV increased after the test indicating an increase in gait variability. MoS decreased and λ_s increased after the test, indicating a decrease in gait stability. All variables showed a trend to return to PreT values, but the 20-min post-test interval appears not to be enough for a complete recovery. The results showed that general fatigue induced by IMET alters negatively the gait, and an interval of at least 20 min should be considered for injury prevention in tasks with similar demands.     

Deglacial ocean and climate seasonality in laminated diatom sediments, Mac.Robertson Shelf, Antarctica

The palaeoceanography and climate history of the East Antarctic Margin (EAM) are less well understood than those of West Antarctica. Yet, the EAM plays an important role in deep ocean circulation and the global ocean system and has likely done so in the past. Deglacial-age marine sediments from the EAM provide clues about its past role during this critical period of rapid climate change. Several deep basins across the EAM such as Iceberg Alley (∼67°S, 63°E) on the Mac.Robertson Shelf (MRS) accommodate thick marine sequences that archive the deglaciation in the form of diatom-rich, continuously laminated (varved) sediments. These laminated sediments are pristinely preserved and contain seasonal and long-term information on the cryospheric and palaeoceanographic changes associated with the rapid retreat of the glacial ice sheet across the MRS. We present results of microfabric analysis of the lower ∼2 m of deglacial varves from jumbo piston core JPC43B (Iceberg Alley). Backscattered electron imagery (BSEI) of polished thin sections and scanning electron microscope secondary electron imagery (SEI) of lamina-parallel fracture surfaces are used to analyze the varves. One hundred and ninety-two laminations are investigated and their nature and temporal significance are discussed in terms of seasonal deposition and cyclicity of diatom species. Our high-resolution palaeodata record exceptionally high diatom production and silica flux associated with the retreat of the East Antarctic Ice Sheet, and seasonal sea-ice changes along the EAM. This information is invaluable for assessing cryospheric-oceanographic variation and, therefore, the local and regional response to this period of rapid climate change. Varves are made up of lamina couplets comprising (i) thickly laminated to thinly bedded orange/orange-brown very pure diatom ooze dominated by Hyalochaete Chaetoceros spp. vegetative cells and resting spores, and (ii) brown/blue-grey terrigenous angular quartz sand, silt and clay with an abundant mixed diatom flora. The colour variation between these two types of lamination is striking. Using floristic and textural information we interpret the diatom oozes as spring flux and the terrigenous laminae as summer flux. Each couplet pair represents one annual cycle and reflects seasonal changes in nutrient availability and stratification associated with the cyclical advance and retreat of seasonal sea-ice. The diatom oozes can reach up to ∼7.5 cm in thickness indicating enormous silica flux to the sea floor associated with ice sheet retreat.