细胞黏附的力学建模及其力敏感性的机理研究

细胞黏附在机体的生理和病理过程中起着重要的作用。作为细胞内、外信息交流和传递的通道，细胞黏附斑具有独特的力敏感性。实验表明，在力的作用下，黏附斑不仅可以生长、成熟和破坏，而且还能感知外部环境的力学性质，如基底硬度、硬度梯度和形貌等等。细胞黏附如何响应不同的力学刺激，物理机理是什么，如何定量描述这些物理机理？这些问题是细胞生物学和细胞力学中的重要问题。本论文通过在分子和亚细胞尺度上的力学建模研究了黏附斑的力敏感性机理，主要包括以下几方面的内容： (1) 发展了一个非线性的撕裂模型，研究了细胞黏附的稳定性和边缘依赖性。通过引入黏附分子键的非线性本构关系，并考虑黏附分子键的多种分布形式，我们发现黏附分子键的非线性效应对维持细胞黏附的稳定性起着至关重要的作用。黏附分子键的非线性力学性质使黏附分子键可以同时承载，降低了细胞对黏附分子键分布的依赖性，大大提高了细胞的黏附强度。本文的预测结果与实验结果一致。 (2) 建立了细胞黏附的细观力学模型，研究了在力作用下黏附斑生长和失稳的分子机理。在细观力学模型中，引入了“整联蛋白的聚集”和“整联蛋白-配体的反应”两个分子作用机理，并用两个化学反应来描述。通过基于Monte Carlo思想的Gillespie算法模拟了细胞黏附在不同载荷下的响应。我们发现黏附斑只能在一定范围的张力下生长，在这个范围内整联蛋白的聚集机制占主导。而当张力大于某个临界值时，黏附斑将失稳并导致破坏，这时整联蛋白-配体分子键的解离机制占主导。因此，黏附斑对作用力的不同响应，是不同分子作用机制在力作用下相互消长的结果。同时我们还建立了一个唯象的热力学模型中，验证了我们的细观力学模型。 (3) 基于细胞黏附的细观力学模型，研究了周期性载荷下细胞的重排和转向机理。在细观力学模型中，通过黏附块(adhesion plaque)，将整联蛋白-配体分子键和细胞骨架联系起来。基于Monte Calro模拟，我们发现存在一个载荷临界值，当外载大于临界值时，细胞将进行重排。细胞重排的原因是在周期性载荷下黏附斑的失稳。通过引入整联蛋白-配体成键的化学反应动力学和应力纤维的粘弹性性质，解释了细胞黏附稳定性的频率依赖性。本文预测的细胞转向临界载荷和重排方向，与实验结果一致。

The near wall velocity measurements in microchannels with different diameter particles by microPIV/PTV. 8th International symposium on PIV

In near wall measurements with microPIV/PTV, whether seeding particles can be effectively used to detect local fluid velocity is a crucial problem. This talk presents our recent measurements in microchannels [1][2]. Based on measured velocity profiles with 200nm and 50nm in pure water, we found that the measured velocity profiles are agreed with the theoretical values in the middle of channel, but large deviations between measured data and theoretical prediction appear close to wall (0.25mm focal plane thickness and particle concentration distribution near wall on the velocity deviation appeared in shear flows.

Neutron source from thin foil confined by two laser pulses

Neutron production from a thin deuterium-tritium (D-T) foil irradiated by two intense femtosecond laser pulses from opposite sides with zero phase difference is studied analytically and numerically. For the interaction of a laser pulse of amplitude a = 7, focal area 100 mu m(2) and areal density 4.4 x 10(18) cm(-2) with a D-T plasma foil, about 1.17 x 10(21) neutron s(-1) can be obtained, much more than from other methods. The profiles of the ion and electron densities are also calculated.

Reduced deep-tissue image degradation in three-dimensional multiphoton microscopy with concentric two-color two-photon fluorescence excitation

We theoretically demonstrate that enhanced penetration depth in three-dimensional multiphoton microscopy can be achieved using concentric two-color two-photon (C2C2P) fluorescence excitation in which the two excitation beams are separated in space before reaching their common focal spot. Monte Carlo simulation shows that, in comparison with the one-color two-photon excitation scheme, the C2C2P fluorescence microscopy provides a significantly greater penetration depth for imaging into a highly scattering medium. (C) 2008 Optical Society of America.

Micromodification of element distribution in glass using femtosecond laser irradiation

We report micromodification of Eu element distribution in a silicate glass with femtosecond laser irradiation. Elemental analysis shows that the content of Eu decreased at the focal point and increased in a ring-shaped region around the focal point, which indicates migration of Eu ions has been induced by the femtosecond laser irradiation. Confocal fluorescence spectra demonstrate that the fluorescence intensity of Eu3+ ions increased by 20% in the laser-induced, Eu-enriched, ring-shaped region compared with that for nonirradiated glass. The mechanism for the laser induced change in fluorescence properties of Eu3+ has been investigated. (C) 2009 Optical Society of America

Phase-matched high-order harmonic generation in a gas cell with midinfrared femtosecond pulses

We experimentally investigate the generation of high-order harmonics in a 4-mm-long gas cell using midinfrared femtosecond pulses at various wavelengths of 1240 nm, 1500 nm, and 1800 nm. It is observed that the yield and cutoff energy of the generated high-order harmonics critically depend on focal position, gas pressure, and size of the input beam which can be controlled by an aperture placed in front of the focal lens. By optimizing the experimental parameters, we achieve a cutoff energy at similar to 190 eV with the 1500 nm driving pulses, which is the highest for the three wavelengths chosen in our experiment.

Microstructures induced in the bulk of SrTiO3 crystal by a femtosecond laser

Microstructures with the total length of hundreds of mu m were induced by fixing the focal point of the femtosecond laser at a certain depth in the bulk of SrTiO3 crystal. By different combination of the focusing conditions with the laser parameters, different morphologies have been observed, such as void array, necklace-shaped structures, continuous/segmental filaments and etc. The possible mechanism of the formation of those diversiform structures is discussed.

超连续谱干涉方法测量古依相移

利用两束超连续光干涉得到的信号,测量了透镜焦点附近飞秒激光脉冲的古依(Gouy)相移。根据得到的光谱干涉信号,利用傅里叶变换得到相对相位值。激光光束在聚焦透镜后的束腰半径可以由成像方法测得。根据测量得到的激光光束束腰半径,用非线性拟合的方法得到了古依相移曲线,拟合曲线与实验结果符合得非常好。给出了古依相位在焦点前后1 mm区域内的移动量。

Manipulating spectral anomalies of focused pulses in a medium with electromagnetically induced transparency

We study the possibility of manipulating the focusing properties of a medium with electromagnetically induced transparency. In the focal region of focused ultraslow light pulses, the spectral anomalous behaviors can be actively modified by varying the control field intensity. Unlike the case in free space, we find in slow light focusing that the spectrum bandwidth of the incident field needed to produce observable spectral changes can be reduced by several orders. Numerical simulations with accessible parameters clearly show that spectral anomalies of focused mu s pulses are observable.

自由空间激光远距离传输的地面模拟研究

根据透镜的傅里叶变换性质，提出了采用光学傅里叶变换加级联光学成像放大并结合有限口径接收的方法来实现自由空间激光光束远距离传输的实验室模拟。由此原理设计了自由空间激光远距离传输模拟装置，该装置主要由大口径、长焦距的傅里叶变换平行光管和三级成像放大镜所组成，最大等效传输距离达2.4×10^5km，可用于星间激光通信终端综合通信性能的评估，在设定的误码率下测量终端可能的通信距离，或者在设定的作用通信距离下检测通信的误码率。

星间激光通讯中的精跟踪研究

星间激光通讯中，精跟踪起着十分重要的作用，而精密偏转镜（FSM）是精跟踪系统中最为关键的部件．基于光学矢量反射定律，推导得到了FSM的精确光学特性，这一特性为精跟踪控制系统提供了精确的理论依据．设计了基于FSM精确光学特性的精跟踪控制系统，对系统整定所用的单纯形法进行了两点重要改进，并对所设计的精跟踪系统进行了数字模拟，由此实现了对FSM的精确控制，提高了精跟踪系统的精确性；将光学衍射超分辨原理应用到星间激光通讯中．利用三区位相光瞳滤波器的超分辨性能，改变光学系统的点扩散函数，从而改变接收端焦平面上的光强

星间光通信中的APT技术及其控制系统

APT（Acquisition Pointing and Tracking）技术是星间光通信的关键技术。介绍了该技术中的扫描、捕获、指向、跟踪过程及其控制系统，重点论述了实现跟踪的困难性，相应地介绍了一种有效的扰动抑制控制系统。

Extended fractional Fourier transforms

The concept of an extended fractional Fourier transform (FRT) is suggested. Previous PBT's and complex FRT's are only its subclasses. Then, through this concept and its method, we explain the physical meaning of any optical Fresnel diffraction through a lens: It is just an extended FRT; a lens-cascaded system can equivalently be simplified to a simple analyzer of the FRT; the two-independent-parameter FRT of an object illuminated with a plane wave can be readily implemented by a lens of arbitrary focal length; when cascading, the Function of each lens unit and the relationship between the adjacent ones are clear and simple; and more parameters and fewer restrictions on cascading make the optical design easy. (C) 1997 Optical Society of America.

Enlarging the depth of focus by filtering in the phase-space domain

The ambiguity function was employed as a merit function to design an optical system with a high depth of focus. The ambiguity function with the desired enlarged-depth-of-focus characteristics was obtained by using a properly designed joint filter to modify the ambiguity function of the original pupil in the phase-space domain. From the viewpoint of the filter theory, we roughly propose that the constraints of the spatial filters that are used to enlarge the focal depth must be satisfied. These constraints coincide with those that appeared in the previous literature on this topic. Following our design procedure, several sets of apodizers were synthesized, and their performances in the defocused imagery were compared with each other and with other previous designs. (c) 2005 Optical Society of America.

透镜自重变形引起波像差的有限元分析

在用大口径、长焦距平行光管模拟激光远场特性时，其光组透镜在重力作用下的变形不能忽略，为了分析对出射光束质量的影响，采用有限元分析软件“ANSYS”建立了平行光管光组中声400mm平凸透镜的有限元模型，给出一种分析透镜轴向变形引起的波像差的方法，在不同工况下，计算了平凸透镜在重力作用下轴向变形的峰谷值和均方根值，对轴向变形量均方根值最小工况画出了透镜表面变形的等值线图，计算了声350mm通光口径内的波像差峰谷值和均方根值，对平行光管光组的波像差做出估计，验证了设计的合理性。