The Impact of an Anchoring Layer on the Formation of Tethered Bilayer Lipid Membranes on Silver Substrates

Tethered bilayer lipid membranes (tBLMs) have been known as stable and versatile experimental platforms for protein–membrane interaction studies. In this work, the assembly of functional tBLMs on silver substrates and the effect of the molecular chain-length of backfiller molecules on their properties were investigated. The following backfillers 3-mercapto-1-propanol (3M1P), 4-mercapto-1-butanol (4M1B), 6-mercapto-1-hexanol (6M1H), and 9-mercapto-1-nonanol (9M1N) mixed with the molecular anchor WC14 (20-tetradecyloxy-3,6,9,12,15,18,22 heptaoxahexatricontane-1-thiol) were used to form self-assembled monolayers (SAMs) on silver, which influenced a fusion of multilamellar vesicles and the formation of tBLMs. Spectroscopic analysis by SERS and RAIRS has shown that by using different-length backfiller molecules, it is possible to control WC14 anchor molecules orientation on the surface. An introduction of increasingly longer surface backfillers in the mixed SAM may be related to the increasing SAMs molecular order and more vertical orientation of WC14 at both the hydrophilic ethylenoxide segment and the hydrophobic lipid bilayer anchoring alkane chains. Since no clustering of WC14 alkane chains, which is deleterious for tBLM integrity, was observed on dry samples, the suitability of mixed-component SAMs for subsequent tBLM formation was further interrogated by electrochemical impedance spectroscopy (EIS). EIS showed the arrangement of well-insulating tBLMs if 3M1P was used as a backfiller. An increase in the length of the backfiller led to increased defectiveness of tBLMs. Despite variable defectiveness, all tBLMs responded to the pore-forming cholesterol-dependent cytolysin, vaginolysin in a manner consistent with the functional reconstitution of the toxin into phospholipid bilayer. This experiment demonstrates the biological relevance of tBLMs assembled on silver surfaces and indicates their utility as biosensing elements for the detection of pore-forming toxins in liquid samples.     

绳系卫星在轨试验及地面物理仿真进展

通过系绳释放、运行和回收的在轨卫星称为绳系卫星. 绳系卫星功能独特, 在人工重力梯度、空间传送、电动力推进等方面应用广泛. 本文以绳系卫星为对象, 概述了全世界历年来绳系卫星的在轨飞行试验, 包括试验背景、目的、步骤以及结果等; 介绍了近年来绳系卫星的地面物理仿真实验技术, 分析了系统结构、仿真原理以及实验结果; 对未来我国空间绳系卫星技术的发展提出建议.     

Nonlinear dynamics of flexible tethered satellite system subject to space environment

The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J ₂ perturbation, the air drag force, the solar pressure, the heating effect, and the orbital eccentricity. The flexible tether is modeled as a series of lumped masses and viscoelastic dampers so that a finite multidegree-of-freedom nonlinear system is obtained. The stability of equilibrium positions of the nonlinear system is then analyzed via a simplified two-degree-freedom model in an orbital reference frame. In-plane motions of the tethered satellite system are studied numerically, taking the space environments into account. A large number of numerical simulations show that the flexible tethered satellite system displays nonlinear dynamic characteristics, such as bifurcations, quasi-periodic oscillations, and chaotic motions.     

Structure and switching of single-stranded DNA tethered to a charged nanoparticle surface

Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA(ss DNA)tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows: i) when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii)for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii) when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.     

球-地双基地雷达云雨杂波建模与仿真研究

以空地为背景,研究了基于球载发射源,地面接收站的双基地雷达云雨杂波建模与仿真问题。首先给出了球-地双基地椭球与云雨杂波区域的几何关系,并建立了球-地双基地雷达云雨杂波空间几何模型,给出了基于云雨杂波反射特性、杂波的幅度起伏、杂波的频谱分布以及雷达系统参数的球-地双基地雷达杂波建模方法,导出了球-地双基地雷达在指定距离门内云雨杂波模型的表达式,最后仿真分析了球-地双基地雷达云雨杂波的距离方位维杂波强度和距离-多普勒二维谱,为后续球-地双基地雷达云雨杂波区域目标检测问题的研究提供了仿真数据和理论基础。     

系留气球拉力传感器数字滤波算法研究

拉力传感器是系留气球上测量缆绳张力的重要部件,处于系留气球复杂的干扰环境中测量准确度一直很低。本文提出了一种数字滤波算法,基于对拉力传感器信号的分析和滤波验证,证明此算法有很好的滤波效果同时保持了对突变信号的跟随性。     

平流层气球载通信系统

平流层气球（飞艇）通信是近几年来出现的一种通信方式,它利用一个漂浮于地球上空２０～５０公里的平流层气球（飞艇）装载的通信平台,实现信息的传输或转发。由于该通信系统具有适中的覆盖面积、低廉的成本、安全可靠等一系列独特的优点,已经引起了许多国家的注意和重视,应用前景十分诱人。本文简单概述了平流层气球载通信系统在国内外的发展与应用,较详细地描述了该系统的各组成部分、性能特性及系统的应用前景。     

高度对球形气球诱饵及导弹辐射特性的影响研究

为了使导弹拥有方达到突防的目的,在分析背景辐射的基础上,利用空间目标表面温度数学模型计算了不同高度下空间目标表面的温度场分布,并分析讨论了高度对红外辐射特性的影响。结果表明,无论是白天还是夜间,高度都不会成为区分诱饵与弹头的参数,但尽可能在白天部署可以降低击中率,从而达到突防的效果。     

临近空间高空气球地基探测能力分析

基于探测系统背景辐射特性及高空气球辐射特性,建立了探测系统辐射接收模型.考虑大气传输、光学系统成像、探测器及其采样对辐射的影响,精确计算了高空气球辐射及背景辐射在探测器焦平面阵列上产生的信号电子数,推导出用于高空气球探测的信噪比.利用Modtran软件仿真计算了自身辐射、镜背景辐射、漫背景辐射亮度,分析了复杂大气条件下的气球辐射特性,及高空气球镜反射率、漫反射率与积分时间对探测系统信噪比的影响.结果表明:采用光谱滤波技术,在晴朗无云天气下,可见光近红外(0.6~2.4)探测器适合高空气球探测;在复杂大气条件下,长波红外(8~12)探测器适合高空气球探测;在积分时间为0.25s,镜反射率为0.32,漫反射率为0.68时,或积分时间为1s,镜反射率0.43,漫反射率0.57时,探测系统对高空气球探测能力最强.     

Fluorescence Depolarization Due to Excitation Energy Migration in Polymeric Micelles: A Monte Carlo Study

Cores of block copolymer micelles have been studied by Monte Carlo simulation. Core-forming chains have been modeled as self-avoiding chains enclosed in a spherical cavity and tethered to its surface. A fraction of the untethered end segments of chains (18–53%) has been treated as fluorescent probes. The time-dependent solution of the Pauli master equation that describes excitation energy migration among probes has been averaged in an ensemble of 10⁴ simulated cores. We have studied the dependence of the depolarization function G ^S(t), i.e., the probability that the originally excited probe is still excited at time t, on the chain length and on the energy migration critical radius of the probe. Cores with randomly solubilized probes and with clusters of probes have been also studied for comparison.