How the cucumber tendril coils and overwinds

The helical coiling of plant tendrils has fascinated scientists for centuries, yet the underlying mechanism remains elusive. Moreover, despite Darwin's widely accepted interpretation of coiled tendrils as soft springs, their mechanical behavior remains unknown. Our experiments on cucumber tendrils demonstrate that tendril coiling occurs via asymmetric contraction of an internal fiber ribbon of specialized cells. Under tension, both extracted fiber ribbons and old tendrils exhibit twistless overwinding rather than unwinding, with an initially soft response followed by strong strain-stiffening at large extensions. We explain this behavior using physical models of prestrained rubber strips, geometric arguments, and mathematical models of elastic filaments. Collectively, our study illuminates the origin of tendril coiling, quantifies Darwin's original proposal, and suggests designs for biomimetic twistless springs with tunable mechanical responses.     

激光偏振特性在近炸引信中的应用

激光近炸引信容易受到各种有源干扰的影响.在对激光的偏振态能够区分目标和背景的原理进行研究的基础上,将激光的偏振特性应用到激光引信中.通过对激光光束的偏振进行调控,达到测距、目标分类、信息保密的目的.引信在工作时,根据目标和背景对激光散射回波信号的偏振取向进行目标分类与判断,从而可以减小背景光和有源干扰对激光近炸引信的影响,进一步提高了激光近炸引信的抗干扰能力.同时对引信中弹体旋转、测距信息加密等关键技术问题进行了分析和讨论.     

Frequency Dependence of Polarization of Pulsar CP 0328

The circularly polarized emission from the pulsar CP 0328 has an approximately flat spectrum in the 1-megahertz band centered at 113.6 megahertz, whereas the linearly polarized emission varies with frequency and from pulse to pulse. A simple model for the source that has a constant Faraday rotation measure fits some of the linearly polarized spectra observed for individual pulses, but changes in the rotation measure of as much as 30 radians per square meter are required between adjacent pulses. The simple model does not fit the average spectrum of the linearly polarized emission, although the average spectrum had the same form on two nights.     

Polarization of chemoattractant receptor signaling during neutrophil chemotaxis

Morphologic polarity is necessary for chemotaxis of mammalian cells. As a probe of intracellular signals responsible for this asymmetry, the pleckstrin homology domain of the AKT protein kinase (or protein kinase B), tagged with the green fluorescent protein (PHAKT-GFP), was expressed in neutrophils. Upon exposure of cells to chemoattractant, PHAKT-GFP is recruited selectively to membrane at the cell's leading edge, indicating an internal signaling gradient that is much steeper than that of the chemoattractant. Translocation of PHAKT-GFP is inhibited by toxin-B from Clostridium difficile, indicating that it requires activity of one or more Rho guanosine triphosphatases.     

Polarization observations with the Cosmic Background Imager

Polarization observations of the cosmic microwave background with the Cosmic Background Imager from September 2002 to May 2004 provide a significant detection of the E-mode polarization and reveal an angular power spectrum of polarized emission showing peaks and valleys that are shifted in phase by half a cycle relative to those of the total intensity spectrum. This key agreement between the phase of the observed polarization spectrum and that predicted on the basis of the total intensity spectrum provides support for the standard model of cosmology, in which dark matter and dark energy are the dominant constituents, the geometry is close to flat, and primordial density fluctuations are predominantly adiabatic with a matter power spectrum commensurate with inflationary cosmological models.     

Polarization of fucoid eggs by a calcium ionophore gradient

When the eggs of the brown alga Pelvetia were grown in a gradient of the calcium ionophore A23187, they tended to form their rhizoidal outgrowths on the sides that were exposed to the higher concentration of ionophore. This result supports the hypothesis that the formation of an intracellular calcium gradient is an essential step in the polarization of these eggs; the rhizoid forms at the pole that has the higher concentration of calcium.     

典型旱作物极化散射特征分析与应用研究

选择典型旱作物冬小麦为分析对象,利用全极化星载SAR数据分析了其极化特征,并基于极化分解理论分析了冬小麦在不同长势下的响应特征。最后基于极化分析结果,建立了反演冬小麦长势的新参数。研究方法对利用全极化雷达数据分解目标散射特征,提高反演精度和有效性方面具有重要意义。     

Polarization of PAR proteins by advective triggering of a pattern-forming system

In the Caenorhabditis elegans zygote, a conserved network of partitioning-defective (PAR) polarity proteins segregates into an anterior and a posterior domain, facilitated by flows of the cortical actomyosin meshwork. The physical mechanisms by which stable asymmetric PAR distributions arise from transient cortical flows remain unclear. We present evidence that PAR polarity arises from coupling of advective transport by the flowing cell cortex to a multistable PAR reaction-diffusion system. By inducing transient PAR segregation, advection serves as a mechanical trigger for the formation of a PAR pattern within an otherwise stably unpolarized system. We suggest that passive advective transport in an active and flowing material may be a general mechanism for mechanochemical pattern formation in developmental systems.     

混浊介质后向散射的Mueller矩阵的偏振特性分析

对典型混浊介质（Intralipid悬浊液）后向散射的Mueller矩阵进行了试验测量。基于Mueller矩阵计算的保偏度反映散射介质某点的偏振效应：接近光入射点的区域,保偏能力较强;随着距离的增加,保偏能力逐渐减弱而趋向于1;混浊介质浓度加大,将导致介质的保偏能力减弱。     

IBM—PC机控制恒电位仪的自动极化测试系统

An automatic polarization measure system can be made up of a commercial potentiostat and a computer. This paper described a corresponding analog interface circuit and a software consisting of the controlling,sampling and fitting programs with which the da     

3PE管道补口的极化处理技术

国内3PE管道采用辐射交联聚乙烯(PE)热收缩套/带进行补口,存在的主要问题是热收缩套/带边缘开裂,其原因与人工加热热收缩套/带的不均匀性有直接关系。为提高涂料与PE搭接处的粘结力,针对3PE防腐层的技术特点,开发了高密度聚乙烯(HDPE)表面极化处理技术,包括极化处理器和管道表面行走小车在内的极化处理设备。对HDPE防腐层表面进行极化处理、火焰处理、喷砂处理和未处理的对比试验,考核了在不同介质下的老化处理对极化处理后HDPE粘结力的影响,结果表明:HDPE表面经极化处理后,涂料在PE表面的粘结力大幅提高,且老化处理后粘结力没有明显损失。     

中国栽培稻的籼粳分化机理再论

综述前人在不同时期对栽培稻起源演化的代表性观点,并结合近年来对稻种籼粳分化机理的研究结果,重点研究了籼粳分化的机理并提出了自然选择与人工选择对籼粳分化的影响作用,其作用有三:一是确定籼粳分化的方向;二是积累和扩大籼粳分化的范围和程度;三是人工选择加上生态环境的自然选择的作用要明显大于单纯的自然选择。其结果可为进一步研究栽培稻的起源与演化和育种提供参考。     

2014年7月4日降水的双偏振雷达多参量回波分析

为了研究飑线的降水结构和云物理特征,利用南京信息工程大学的C波段双偏振雷达资料,分析了2014年7月4日飑线的双偏振雷达多参量回波。研究发现,雷达回波图中降水回波结构较紧密,降水范围较大,但降水强度并不是很高;相关系数回波图中存在亮度层亮带,相关系数与差分反射率因子成负相关。这项研究有助于增进对飑线天气的云物理结构和回波演变机理的认识。     

群体决策极端化的征兆、成因及其改进策略

群体决策极端化容易使个体和群体丧失理性,最终导致决策偏离正确轨道。文章从分析群体决策极端化的征兆出发,深入研究极端化的影响因素和形成机理,并进一步探讨改进群体决策,防止极端化的措施。     

基于ALOS PALSAR双极化模式数据的森林覆盖识别方法研究

[目的]探讨森林PALSAR双极化模式数据后向散射、极化和干涉相干性等特征,提出一种在异质地区的森林识别方法。[方法]以中国东南部漳浦县为试验区,对试验区不同土地类型PALSAR的后向散射信息、极化比值和相干性信息进行分析。[结果]利用该区林相图及同时相SPOT-5影像进行精度检验,其总体精度、用户精度和制图精度均高于90%。[结论]基于PALSAR双极化模式数据进行森林识别精度较高。