胞质分裂力学及其分子生物学机制的研究

胞质分裂通过一系列的形态学变化使母细胞一分为二生成两个子细胞,几乎整个胞质分裂过程都伴随着力学现象.形成刚度或黏弹性互不相同的区域对细胞形态的改变至关重要,特殊肌动蛋白与交联蛋白是导致细胞局部刚度改变的重要因素.因此有必要深入理解细胞如何变形、以及促进细胞变形的材料特性及其分子生物学基础.本文将针对细胞的力学特性、胞质分裂中的力学现象以及分子生物学基础进行讨论.      

基于InSAR的西安地面沉降与地裂缝发育特征研究

哺乳动物细胞胞质分裂过程中伴随着一系列形态学改变,随着分裂沟不断收缩,形成连接两 个子细胞的细胞间桥. 间桥不断拉长、变细,直至断裂、生成两个子细胞. 采用细胞力学 和形态学测量及分析方法,通过施加肌球蛋白II抑制剂,定量研究了NRK细胞间桥变细动力 学; 采用细胞免疫荧光技术, 检测了早期胞质分裂肌动蛋白的分布,揭示肌球蛋白II缺失细 胞胞质分裂可能的机制. 结果表明：施加肌球蛋白II抑制剂的NRK细胞, 其整体形态学和细胞 间桥形态学曲线明显不同于0.3%DMSO组. 根据流体力学特性和所测量的力学参数对曲线 进行模拟发现,表面张力对肌球蛋白II抑制组细胞的间桥动力学曲线轨迹影响很大. 研究结 果提示由细胞力学特性决定的拉普拉斯压力和细胞运动共同参与了肌球蛋白II缺失细胞胞 质分裂的调节.     

肌球蛋白Ⅱ缺失细胞胞质分裂机制研究

哺乳动物细胞胞质分裂过程中伴随着一系列形态学改变,随着分裂沟不断收缩,形成连接两个子细胞的细胞间桥.间桥不断拉长、变细,直至断裂、生成两个子细胞.采用细胞力学和形态学测量及分析方法,通过施加肌球蛋白Ⅱ抑制剂,定量研究了NRK细胞间桥变细动力学;采用细胞免疫荧光技术,检测了早期胞质分裂肌动蛋白的分布,揭示肌球蛋白Ⅱ缺失细胞胞质分裂可能的机制.结果表明:施加肌球蛋白Ⅱ抑制剂的NRK细胞,其整体形态学和细胞间桥形态学曲线明显不同于0.3%DMSO组.根据流体力学特性和所测量的力学参数对曲线进行模拟发现,表面张力对肌球蛋白Ⅱ抑制组细胞的间桥动力学曲线轨迹影响很大.研究结果提示由细胞力学特性决定的拉普拉斯压力和细胞运动共同参与了肌球蛋白Ⅱ缺失细胞胞质分裂的调节.     

一种新型的高分辨率通量差分裂格式

传统的Roe格式不满足熵条件并且在计算激波问题时会遭遇不同形式的不稳定现象,如慢行激波的波后振荡和红玉(carbuncle)现象.基于Zha-Bilgen对流-压力通量分裂方法,构造一种新型的通量差分裂格式.利用约旦标准型理论,通过添加广义特征向量构造通量差分裂方法来计算对流子系统.压力子系统具有一组完备的线性无关特征向量,因此可以构造传统的通量差分裂格式进行计算.为了提高接触间断的分辨率,利用界面变差下降(BVD)算法来重构对流通量耗散项中的密度差.激波稳定性分析表明,新格式可以有效地衰减数值误差,从而抑制不稳定现象的发生.一系列数值实验证明了本文构造的新型通量差分裂格式比Roe格式具有更高的分辨率和更好的鲁棒性.     

微流控通道内细胞及其初级纤毛的力传导行为

细胞处于复杂的生理环境之下,附着在细胞表面的初级纤毛被认为是重要的力学信号传感器,其与细胞的代谢、发育、分裂和增殖等生理活动密切相关.为了研究细胞及其初级纤毛在微流体环境下的力传导行为,本文建立了力-电协同驱动下的矩形微流控通道和含有多孔黏弹性属性的贴壁细胞有限元模型系统.考察了细胞的细胞质和细胞核在振荡层流下的应力、应变、孔隙压力和孔隙流速等力学信号响应,量化研究了初级纤毛作为细胞独特的力学感受器的生物力学行为. 结果表明:细胞在振荡层流下的力学响应表现出和外加力-电驱动载荷相同的震荡规律.渗透率是细胞多孔弹性力学行为的主要影响因素. 初级纤毛是细胞主要的力学感受器,细胞可以通过纤毛长度和直径调节其力学感受敏感性(应力影响区域),随着初级纤毛长度的增大, 其纤毛挠曲刚度减小, 但是敏感性增大.模型的建立为进一步研究微流体剪切作用下的细胞生长、分化等微观机理提供基础,同时也为检测细胞微结构器(纤毛等蛋白链)的力学性能提供了理论技术支持.      

六分裂导线试验线路双摆防舞器防舞效果数值模拟研究

针对真型输电线路综合试验基地六分裂线路段,利用ABAQUS软件建立覆冰六分裂导线有限元模型,数值模拟覆冰导线在风荷载作用下的舞动过程,将数值模拟结果与现场实测结果进行分析比较.进一步建立双摆防舞器数值模型,实现了安装防舞器后导线动力响应的数值模拟方法.数值模拟结果表明,在试验线路上现有双摆防舞器防舞效果差,与现场观测一致.对安装不同双摆防舞器线路的动力响应过程模拟结果表明,通过改进双摆防舞器参数和安装方案,可以对舞动产生有效的抑制效果.     

MECHANOTRANSDUCTION OF THE CELL AND ITS PRIMARY CILIUM IN THE MICROFLUIDIC CHANNEL 1)

细胞处于复杂的生理环境之下,附着在细胞表面的初级纤毛被认为是重要的力学信号传感器,其与细胞的代谢、发育、分裂和增殖等生理活动密切相关.为了研究细胞及其初级纤毛在微流体环境下的力传导行为,本文建立了力-电协同驱动下的矩形微流控通道和含有多孔黏弹性属性的贴壁细胞有限元模型系统.考察了细胞的细胞质和细胞核在振荡层流下的应力、应变、孔隙压力和孔隙流速等力学信号响应,量化研究了初级纤毛作为细胞独特的力学感受器的生物力学行为. 结果表明:细胞在振荡层流下的力学响应表现出和外加力-电驱动载荷相同的震荡规律.渗透率是细胞多孔弹性力学行为的主要影响因素. 初级纤毛是细胞主要的力学感受器,细胞可以通过纤毛长度和直径调节其力学感受敏感性(应力影响区域),随着初级纤毛长度的增大, 其纤毛挠曲刚度减小, 但是敏感性增大.模型的建立为进一步研究微流体剪切作用下的细胞生长、分化等微观机理提供基础,同时也为检测细胞微结构器(纤毛等蛋白链)的力学性能提供了理论技术支持.     

气流式喷雾化过程的分形特征及液滴分裂模型

研究了在雾化等过程中液滴粒度分形特征，提出了一个液滴分裂服从均匀分布概率的数学模型，通过计算机模拟，计算出同代液滴的结构分维和特征分维，并用对异代液滴计算得到的结果，验证粒度分布中的结构分维，结果吻合很好，实验测定了液滴分裂的分形维数，与模拟结果相符。     

二流体系统中界面孤立波的分裂

本文讨论了二流体系统界面上内孤立波的分裂,发现上下层流体密度比对分裂成两个内孤立波的条件没有影响,此时只要孤立波从较深的流体运动到较浅的流体就会发生分裂,但分裂成二个以上孤立波的条件受密度比和上游上下层流体厚度比的影响。     

Z2—对称破缺音叉分歧点的分裂迭代算法

Ｗｒｒｎｅｒ和Ｓｐｅｎｃｅ在（５）中提出了一个正则的扩张系统，用以计算Ｚ２－对称破缺音叉分歧点。这种方法即是直接法。本文将用另一种方法－－分列迭代算法来计算Ｚ２－对称破缺音叉分歧点，分裂迭代算法超线性收敛，并明显地节约计算的工作量和计算所占用的内存。数值例子的计算成功地说明分裂迭代算法的有效笥。     

Effects of polar cortical cytoskeleton and unbalanced cortical surface tension on intercellular bridge thinning during cytokinesis

To probe the contributions of polar cortical cytoskeleton and the surface tension of daughter cells to intercellular bridge thinning dynamics during cytokinesis,we applied cytochalasin D(CD) or colchicine(COLC) in a highly localized manner to polar regions of dividing normal rat kidney(NRK) cells.We observed cellular morphological changes and analyzed the intercellular bridge thinning trajectories of dividing cells with different polar cortical characteristics.Global blebbistatin(BS) application was used to obtain cells losing active contractile force groups.Our results show that locally released CD or colchicine at the polar region caused inhibition of cytokinesis before ingression.Similar treatment at phases after ingression allowed completion of cytokinesis but dramatically influenced the trajectories of intercellular bridge thinning.Disturbing single polar cortical actin induced transformation of the intercellular bridge thinning process,and polar cortical tension controlled deformation time of intercellular bridges.Our study provides a feasible framework to induce and analyze the effects of local changes in mechanical properties of cellular components on single cellular cytokinesis.     

A structural constitutive model for smooth muscle contraction in biological tissues

A structural constitutive model that characterizes the active and passive responses of biological tissues with smooth muscle cells (SMCs) is proposed. The model is formulated under the assumption that the contractile units in SMCs and the connected collagen fibers are the active tissue component, while the collagen fibers not connected to the SMCs are the passive tissue component. An evolution law describing the deformation of the active tissue component over time is developed based on the sliding filament theory. In this evolution law the contraction force is the sum of a motor force that initiates contraction, a viscous force that describes the actin–myosin filament sliding, and an elastic force that accounts for the deformation of the cross-bridges. The mechanical response of the collagen fibers is governed by the fiber recruitment process: collagen fibers support load and behave as a linear elastic material only after becoming taut. The proposed structural constitutive model is tested with published active and passive, uniaxial and biaxial experimental data on pig arteries.     

On the gating of mechanosensitive channels by fluid shear stress

Mechanosensation is an important process in biological fluid–structure interaction. To understand the biophysics underlying mechanosensation, it is essential to quantify the correlation between membrane deformation,membrane tension, external fluid shear stress, and conformation of mechanosensitive(MS) channels. Smoothed dissipative particle dynamics(SDPD) simulations of vesicle/cell in three types of flow configurations are conducted to calculate the tension in lipid membrane due to fluid shear stress from the surrounding viscous flow. In combination with a simple continuum model for an MS channel, SDPD simulation results suggest that shearing adhered vesicles/cells is more effective to induce membrane tension sufficient to stretch MS channels open than a free shear flow or a constrictive channel flow. In addition, we incorporate the bilayer–cytoskeletal interaction in a two-component model to probe the effects of a cytoskeletal network on the gating of MS channels.     

Liquid crystal model of vesicle deformation in alternating electric fields

Considering the effects of osmotic pressure, elastic bending, Maxwell pressure, surface tension, as well as flexo-electric and dielectric properties of phospholipid membrane, the shape equation for sphere vesicle in alternation (AC) electric field is derived based on the liquid crystal model by minimizing the free energy due to coupled mechanical and AC electrical fields. Besides the effect of elastic bending, the influence of osmotic pressure and surface tension on the frequency dependent behavior of vesicle membrane in AC electric field is also discussed. Our theoretical results for membrane deformation are consistent with corresponding experiments. The present model provides the possibility to further disclose the frequency-depended behavior of biological cells in the coupled AC electric and different mechanical fields.     

Migration and deformation of leukocytes in pressure driven flows

Direct numerical simulations (DNS) are used to study the motion and deformation of leukocytes in pressure driven flows in parallel plate channels. The influence of the adhesion force between the leukocytes and the channel wall on such motion and deformation is also investigated. Leukocytes are represented by two composite fluid models, consisting of a membrane, a cytoplasm and a nucleus. The adhesion force is computed using two adhesion force models. In the first model, the adhesion force is given by a potential, and in the second one it is given by Dembo’s kinetic adhesion model. The numerical code is based on the finite element method and the level set technique is used to track the cell membrane position. In the absence of the adhesion force, the leukocyte moves away from the wall to an equilibrium location that depends on the ratio of the cell to plasma viscosities. In presence of the adhesion force, the leukocyte is attracted to the layer of endothelial cells and, as it gets closer, it flattens under the action of hydrodynamic forces. This deformation, in turn, further increases the adhesion force. The leukocyte, however, can be captured only when it is placed sufficiently close to the wall, which for the kinetic model is of the order of 30 nm. We also find that for the normal parameter values and flow rates the adhesive force given by the kinetic model is too small to capture the leukocyte.     

A constitutive model for active–passive transition of muscle fibers

In this paper, we examine the transition of striated muscles between active and passive states. New experimental data of a muscle performing such a transition are provided, allowing for a new model to be developed to capture this mechanical behavior. Specifically, a strain energy function is formulated using the theory of transient networks, introducing an intermediate, stress-free configuration for the active muscle fibers. Additionally, energy dissipation occurring during the unloading is accounted for by specifying a pseudo-energy function. The general three-dimensional case is specialized to uniaxial deformation for comparison with test data, from which material parameters are determined. Finally, numerical results are presented, demonstrating the model's ability to capture the mechanical behavior with changing stimulus.     

Comparison between three-dimensional linear and nonlinear tsunami generation models

The modeling of tsunami generation is an essential phase in understanding tsunamis. For tsunamis generated by underwater earthquakes, it involves the modeling of the sea bottom motion as well as the resulting motion of the water above. A comparison between various models for three-dimensional water motion, ranging from linear theory to fully nonlinear theory, is performed. It is found that for most events the linear theory is sufficient. However, in some cases, more-sophisticated theories are needed. Moreover, it is shown that the passive approach in which the seafloor deformation is simply translated to the ocean surface is not always equivalent to the active approach in which the bottom motion is taken into account, even if the deformation is supposed to be instantaneous.      

介电高弹聚合物理论

软材料受刺激会发生变形, 该变形会引起相应的功能, 这种材料称为活性软材料(soft active material, SAM). 本综述主要讨论介电高弹聚合物这一类活性软材料. 当介电高弹聚合物薄膜受到厚度方向的电压作用时, 薄膜厚度减小同时面积增大, 可导致超过100{\%}的应变. 介电高弹聚合物作为转换器被广泛应用, 包括柔性机器人、智能光学器件、盲文显示屏、发电机等. 本文综述了建立在连续介质力学和热力学框架内的、并且基于分子理论描述和经验观测的介电高弹聚合物理论. 该理论耦合了大变形和电势, 描述了非线性和非平衡行为, 如力电失稳和黏弹性. 采用该理论能够通过有限元方法模拟实际构型的转换器, 计算力电能量转换的效率, 给出电致大变形的可行途径. 该理论有助于材料和器件设计.     

Rheological study of emulsions with cross-linked polymeric interfaces

We study the behaviour of emulsions stabilized by a polymeric interfacial gel in a simple shear flow. We demonstrated that the observed non-Newtonian effects are due to the deformation of the globules. This deformation is not compatible with interfacial tension effects, but implies a membrane elasticity which strongly varies with the degree of polymerization.     

Constitutive analysis of thin biological membranes with application to radial stretching of a hollow circular membrane

The constitutive analysis of the mechanical response of thin elastic membranes under inplane deformation is presented by using the multiplicative decomposition of the deformation gradient into its areal and distortional parts. Specific results are obtained for the Evans-Skalak form of the strain energy function. The solution to the problem of radial stretching of a hollow circular membrane obeying this constitutive model is then derived. The stress concentration factor is determined as a function of the relative hole size and the magnitude of the applied tension. The tension boundary is identified above which no compressive stress appears in the membrane. The limit boundary is introduced below which the membrane cannot support the applied loading without unstable wrinkling. For the loading between the tension and the limit boundary, nonuniformly distributed infinitesimal wrinkles appear within the inner portion of the membrane, carrying radial tension but no circumferential stress (tension field). The specific form of the strain energy function is used to describe this behavior, and to calculate the amount of the membrane area absorbed by infinitesimal wrinkles. The wrinkled portion is surrounded by the outer portion of the membrane carrying both radial and circumferential stresses. The limit boundary is reached when wrinkles spread throughout the membrane. It is shown that for a sufficiently large tension at the outer boundary, the wrinkling does not spread throughout the membrane no matter how large the applied tension at the inner boundary of the membrane is, provided that no rupture takes place. The limiting extent of the tension field in such cases is calculated. The linearized version of the analysis is characterized by a closed form solution.