Numerical investigation of the active role of the actin cytoskeleton in the compression resistance of cells.

Numerous in-vitro studies have established that cells react to their physical environment and to applied mechanical loading. However, the mechanisms underlying such phenomena are poorly understood. Previous modelling of cell compression considered the cell as a passive homogenous material, requiring an artificial increase in the stiffness of spread cells to replicate experimentally measured forces. In this study, we implement a fully 3D active constitutive formulation that predicts the distribution, remodelling, and contractile behaviour of the cytoskeleton. Simulations reveal that polarised and axisymmetric spread cells contain stress fibres which form dominant bundles that are stretched during compression. These dominant fibres exert tension; causing an increase in computed compression forces compared to round cells. In contrast, fewer stress fibres are computed for round cells and a lower resistance to compression is predicted. The effect of different levels of cellular contractility associated with different cell phenotypes is also investigated. Highly contractile cells form more dominant circumferential stress fibres and hence provide greater resistance to compression. Computed predictions correlate strongly with published experimentally observed trends of compression resistance as a function of cellular contractility and offer an insight into the link between cell geometry, stress fibre distribution and contractility, and cell deformability. Importantly, it is possible to capture the behaviour of both round and spread cells using a given, unchanged set of material parameters for each cell type. Finally, it is demonstrated that stress distributions in the cell cytoplasm and nucleus computed using the active formulation differ significantly from those computed using passive material models.

Templates and anchors for antenna-based wall following in cockroaches and robots

The interplay between robotics and neuromechanics facilitates discoveries in both fields: nature provides roboticists with design ideas, while robotics research elucidates critical features that confer performance advantages to biological systems. Here, we explore a system particularly well suited to exploit the synergies between biology and robotics: high-speed antenna-based wall following of the American cockroach (Periplaneta americana). Our approach integrates mathematical and hardware modeling with behavioral and neurophysiological experiments. Specifically, we corroborate a prediction from a previously reported wall-following template - the simplest model that captures a behavior - that a cockroach antenna-based controller requires the rate of approach to a wall in addition to distance, e.g., in the form of a proportional-derivative (PD) controller. Neurophysiological experiments reveal that important features of the wall-following controller emerge at the earliest stages of sensory processing, namely in the antennal nerve. Furthermore, we embed the template in a robotic platform outfitted with a bio-inspired antenna. Using this system, we successfully test specific PD gains (up to a scale) fitted to the cockroach behavioral data in a "real-world" setting, lending further credence to the surprisingly simple notion that a cockroach might implement a PD controller for wall following. Finally, we embed the template in a simulated lateral-leg-spring (LLS) model using the center of pressure as the control input. Importantly, the same PD gains fitted to cockroach behavior also stabilize wall following for the LLS model. © 2008 IEEE.

Boundary effects on the vibration statistics of a random plate

This paper considers the estimation of statistics of displacement of a vibrating rectangular plate with random wave scatterers. The influence of uncertainty is investigated using point impedance theory. Coherent boundary effects are seen, which decrease when the number of scatterers increases. The boundary effect is investigated using images and the first side and corner reflections are found to be a minimum requirement to estimate the spatial correlation. Statistics for point driven response are investigated under the assumption that the statistics of the natural frequencies follow those of the Gaussian Orthogonal Ensemble (GOE). The estimates are compared with Monte Carlo simulation results, and they show good agreement. © 2012 Elsevier Ltd. All rights reserved.

水样不同处理方式对高锰酸盐指数测定值的影响

研究了水样不同处理方式对三峡水库干流江段高锰酸盐指数(COD_(Mn))测定值的影响。结果表明,悬浮颗粒物浓度(SS)是澄清样和浑样之间、清样和浑样之间、清样和澄清样之间高锰酸盐指数差别的主要影响因子;用非线形回归方法得出了水样不同处理方式下高锰酸盐指数间的经验关系,并用实测数据进行了验证,结果表明,计算值和实测值吻合良好。依据SS和所得经验关系,可计算高锰酸盐指数所表征有机物(COD_(Mn))即OS(COD_(Mn))作为一个整体在水-固两相之间的分配,及其在粗颗粒物和细颗粒物上的赋存比例。河床上覆水

鱼类入侵的过程、机制及研究方法

当前生物入侵问题已成为一个危害自然生态环境、生物多样性及人类社会可持续发展的国际问题,其中鱼类入侵的影响不容忽视.本文在国内外已有研究基础上,从入侵鱼类的自身特性、入侵地的特征、外来种与土著种之间的相互关系、外来种的适应性进化几个角度综合分析了鱼类入侵的机制,并概括了国内外鱼类入侵过程和研究方法的进展.

中山市淡水浮游动物区系调查

2005年6～7月和12月对中山市主要淡水水体的浮游动物区系进行了调查。结果表明,中山市主要淡水水体浮游动物由38目92科129属317种组成。区系特点以原生动物最丰富,有30目82科102属263种,占浮游动物物种总数的83%;其次为轮虫,有4目4科19属37种组成,占12%;枝角类和桡足类物种数最少。各样点浮游动物种类在11～168种之间,种类最少的出现在洪奇沥,最多的出现在逍遥谷。研究结果表明,中山市淡水浮游动物资源比较丰富。各区系浮游动物的分布与水体的营养状态密切相关,污染严重的水体,种类数较少,

三峡水库上游消落区生态渔业模式研究

根据生态渔业系统的需要,结合不同鱼的食性和空间生态位要求,对开县当地常规放养模式的品种和结构进行了合理调整。确定以草鱼为主养鱼,鲢、鳙为配养鱼,由食性相似而价值较高的异育银鲫代替常规的鲤鱼,并套养黄颡鱼,各种鱼的放养比例大致为草鱼45.7%、异育银鲫11%、黄颡鱼0.6%、鲢25%、鳙17.8%。结果表明,该模式单产约7267.5kg/hm2,毛利润约18757.5元/hm2,增产比例为53.7%,经济效益提高143%。

鲤吉陶单极虫免疫原性的研究

以鲤吉陶单极虫孢子的可溶性抗原 ,采用 B淋巴细胞杂交瘤融合技术制备了 4A8、6 B8、7B93株杂交瘤细胞 ,并用该抗原免疫新西兰白兔制备了高免血清。通过对虫体进行抗原检测、定位和 Western- blot试验 ,结果发现 :4A8、6 B8、7B9和多抗经间接 EL ISA可检出抗原的最低质量浓度分别为 0 .14、0 .2 0、0 .32和 0 .86 mg/ L;IFA定位显示 ,单、多抗检出的抗原都定位于虫壁 ,其中 4A8的抗原主要位于虫体后部 (胚核附近 ) ,6 B8和 7B9的抗原主

宽鳍(?)Zacco platypus(Temminck et Schlegel)的形态变异

采用形态度量与框架度量相结合方法测量了13个地理区域的宽鳍鳃标本,并进行了主成分分析。结果表明:宽鳍鳃的形态变异主要表现在躯体纵轴及头部特征上。头部的形态变异大于躯体的形态变异。宽鳍鳃的分布没有明显的地理位置方面的南北和东西变化特点,各地理区域的宽鳍鳃应视为一个种。