Optoelectronic quotient-selected modified signed-digit division

A novel optoelectronic quotient-selected modified signed-digit division technique is proposed. This division method generates one quotient digit per iteration involving only one shift operation, one quotient selection operation and one addition/subtraction operation. The quotient digit can be selected by observing three most significant digits of the partial remainder independent of the divisor. Two algorithms based on truth-table look-up and binary logic operations are derived. For optoelectronic implementation, an efficient shared content-addressable memory based architecture as well as compact logic array processor based architecture with an electron-trapping device is proposed. Performance evaluation of the proposed optoelectronic quotient-selected division shows that it is faster than the previously reported convergence division approach. Finally, proof-of-principle experimental results are presented to verify the effectiveness of the proposed technique. (C) 2001 Society of Photo-Optical Instrumentation Engineers.

High-efficiency reflective diffraction gratings in fused silica as (de)multiplexers at 1.55 mu m for dense wavelength division multiplexing application

We describe high-efficiency, high-dispersion reflection gratings fabricated in bulk fused Silica illuminated by incident lights in the C + L bands as (de)multiplexers for dense wavelength division multiplexing (DWDM) application. Based on the phenomenon of total internal reflection, gratings with optimized profile parameters exhibit diffraction efficiencies of more than 90% under TM- and TE-polarized incident lights for 101-nm spectral bandwidths (1520-1620 nm) and can reach an efficiency of greater than 97% for both polarizations at a wavelength of 1550 nm. Without loss of metal absorption, without coating of dielectric film layers, and independent of tooth shape, this new kind of grating should be of great interest for DWDM application. (C) 2005 Optical Society of America.

克隆植物对异质性环境的生态适应对策

时空异质性是生境的基本特征。几乎所有植物都是在一定尺度的时空异质性环境中完成其生活史的。在进化过程中，植物可能形成了各种有效利用环境异质性的生态适应对策。克隆生长使得克隆植物在理论上更容易适应于异质性环境。本文以匍匐茎和根状茎型草本为材料，应用实验生态学方法研究了游击型克隆植物对异质性环境的生态适应对策。 在沙丘生境（如毛乌素沙地）中，沙埋是植物常常遭遇的事件。由于沙埋在水平空间表现出非均匀性，克隆植物的基株或克隆片断常常经历局部沙埋。通过温室和野外实验，研究了克隆整合作用对鹅绒委陵菜和沙鞭沙埋分株忍受沙埋能力的影响。结果表明，克隆整合显著提高鹅绒委陵菜和沙鞭沙埋分株的存活。进一步的耗-益分析表明，克隆整合使鹅绒委陵菜沙埋分株显著受益，而对非沙埋分株却没有显著耗损，故整个克隆片断的生长得到显著提高。因此，克隆整合是沙丘生境中克隆植物对局部沙埋胁迫的生态适应对策之一。 通过2个温室实验，研究了金戴戴对光照、基质养分和盐分的克隆可塑性。结果表明：光照强度、基质养分和盐分对金戴戴克隆生长和克隆形态均有十分显著的影响。深度遮光、低养和高盐均显著削弱金戴戴的生长，其生物量、叶面积、分株数、匍匐茎长及叶柄长和根冠比对基质盐分的可塑性大小和格局显示出基株间的差异。在低养分条件下，金戴戴匍匐茎节间显著伸长，而分枝强度显著减弱。这些结果与克隆植物觅食模型相符合，表明当生长于异质性环境，金戴戴可凭借克隆可塑性实现的觅养行为来增加对养分资源的摄取。因此，克隆可塑性是克隆植物利用环境异质性的另一条途径。 在另一温室实验中，研究了三种匍匐茎克隆草本鹅绒委陵菜、金戴戴和绢毛匍匐委陵菜对光照和养分资源交互斑块性环境的反应。当置于高光低养下的分株与低光高养下的分株相连时，高光低养分株、低光高养分株以及克隆片断的生物量均得到显著提高。同时，低光高养下分株的根冠比相对增加，而高光低养下分株的根冠比相对下降。这表明，三种克隆植物发生了环境诱导的克隆内分工行为。这种环境诱导的克隆内分工行为有利于整个基株对资源交互斑块性环境的利用，是克隆植物对异质性环境的生态适应对策。

异质性环境中两种匍匐茎草本植物的克隆可塑性

　　克隆植物常常生长在资源异质性分布的环境中，克隆植物特有的生活史特征使其对环境和资源变化产生的反应规范（Reaction norm）具有特殊的表现和适应意义。本文以匍匐茎草本植物蛇莓(Duchesnea indica)和活血丹(Glechoma longituba)为材料，研究克隆植物在不同异质性环境中的反应规范，即可塑性（plasticity）和克隆分株间相互作用（即克隆整合（clonal integration））对表型的影响及其适应意义。 蛇莓和活血丹是具有不同分枝类型的两种匍匐茎草本植物。对于匍匐茎草本植物而言，生境中光资源分布在时间和空间上的变化极为丰富。本文主要研究在不同环境中，这两种克隆植物克隆分株间的相互作用是如何通过影响其形态特征，从而影响其光资源获取策略。 实验涉及了4种光照条件，分为5个部分，分别在大棚和野外进行。 1．同质光环境中蛇莓和活血丹克隆片段的可塑性 在大棚中，将整个克隆片段（clonal fragment）都放置在光照强度分别为自然光照PPFD（Photosynthetic Photon Flux Density）的100％、50％和10％三种不同的同质光环境中，目标是通过比较不同光照强度同质环境中不同基因型的形态特征，揭示匍匐茎草本克隆植物的反应规范及遗传差异。实验结果发现，当光照强度从100% PPFD 降到 50% PPFD时，活血丹增加对地上部分生物量投资，增加部分多投入到匍匐茎上，用于支持匍匐茎实现觅食行为，叶片和叶柄的变化不大。同样条件下，蛇莓的生物量投资却向根部转移，地上部分叶片和叶柄形态上的变化比匍匐茎的形态变化显著，出现增强对光资源吸收能力的变化。当光照强度从50%降到 10%时，活血丹继续增加对地上部分的生物量投资，但由于光照强度弱，几乎不足以维持新的匍匐茎的发生，所有增加的生物量部分都投入到叶片和叶柄的变化上。这种条件下，蛇莓的生物量投资依然向根部转移，叶片和叶柄为增加对光资源吸收能力而发生了相应变化，匍匐茎的新增数减少，形态变化也不大。实验证明，可能由于匍匐茎的发生方式不同，活血丹的匍匐茎节间长度，叶片和叶柄的关联程度比蛇莓相应性状的关联程度强。不同基因型的蛇莓和活血丹对光照梯度的反应有显著差异。 2．异质光环境中蛇莓克隆片段的可塑性 针对克隆植物分株间在相当长的时间里形体相连，而环境异质性可能存在于分株大小的空间尺度，设置异质环境，将蛇莓的不同相连分株放置在不同的光资源斑块中，研究其整合作用在适应异质性环境过程中的作用及其对表型的影响。首先设置同一种资源（光资源）的梯度差异斑块。 在光斑块中，整合作用发生与否、作用方式与资源梯度、分株自身所处斑块的资源条件和分株的年龄结构有关。在不同的条件下，整合作用可能造成对表型的不同影响，从而可能加剧或削弱分株对本地资源的反应（局部反应，local response）。整合作用对分株局部反应的影响强度和方向，在不同基因型间存在明显差异。这些基因型间的差异暗示，整合作用可能也是具有遗传基础的一种独立性状。 3．光块斑和养分斑块共存环境中活血丹克隆片段的可塑性 设置光和养分的资源互补性斑块。将相连分株种植在不同斑块中。当生长在高光低养斑块中的分株与其互补斑块（低光高养斑块）的分株相连时，其适合度相关性状的值增加，根冠比是可塑的，通过相应的形态变化，高光照斑块中的分株捕获光资源的能力增强，但两种斑块中植株的吸收养分的能力却没有大的变化。收益－损耗分析显示整合作用有益于异质环境中的植株，低光高养斑块中植株的生物量获益。实验结果证明了异质环境中相连分株间存在光合产物和养分传递。在这种环境种，分株形态的变化对本地斑块发生趋富反应，形态的改变有助于对本地丰富资源的吸收。这种反应有利于克隆片段对资源的吸收。 4．野外环境中蛇莓克隆片段的可塑性 基于大棚实验资料，对野外林下蛇莓种群进行监测。首先对单株在林下复杂的光环境中的表现进行了跟踪，结果发现，随着分株数目的增加，适合度相关性状值有所提高，而处于不同位置的相连分株在形态上的差异不显著。大棚实验中发现的显著形态变化在具有显著差异的自然环境条件下没有发生，这可能暗示着在资源条件变化频率较高的环境中整合作用的作用方式。分株不是对某一时刻资源条件进行形态特化，而是通过对所扩展的总体区域的总的环境条件调整表型。这样，从克隆片段的水平上看，资源的吸收可能达到较高水平。在密度增大，植株间互相荫蔽使得光照减弱的情况下，匍匐茎的变化没有表现出觅食行为，叶片和叶柄出现增大增长等增强吸收光能力的相应表型变化，证明叶片叶柄是克服光照不足的主要器官。这些结果与大棚实验结果一致。蛇莓基株对于相连分株内部可能具有密度调节功能，从而通过减弱叶片增大的趋势，增长匍匐茎，分散新生分株，使密度保持在一定程度，不对种群的发展造成阻碍作用。非相连分株间随着密度的增大，相互间的作用方式类似于非克隆植物：出现叶片增大，叶柄增长的现象，同时密度制约了适合度相关性状如分株数目等的增加。 5．野外环境中蛇莓种群格局动态 最后，在进化的单位，种群水平上对蛇莓种群在自然界的动态进行了调查。Spearman相关分析，没有发现光资源和测量指标在量上的相关。在自然界中整合作用使大量分散分布、相互连接的分株相互作用，以促进基株对资源的获取。Moran’s I指数分析显示，随时间的推进，各个指标在相关尺度上有所增加。这暗示了整合作用的存在，分株间联系的加强。大棚实验中观察到的关于各个器官的作用的结论在自然界中得到进一步的验证。蛇莓匍匐茎在遮荫环境中不是作为觅食器官。为了争取对更多光资源的吸收，蛇莓在叶片数和叶形态上发生改变。对分株数、叶片数、匍匐茎数目的分布格局的调查显示出没有一定的规律性，而且处于不断的变化中。这一结果可能暗示种群发展过程中处理异质性分布资源的对策的变化。 此外，本文还揭示了可塑性和整合作用在基因型间的差异，针对所发现的现象，从作用的遗传机制上对可塑性及其适应意义进行了讨论。结合分子生物学和地统计学等学科的研究成果，对进一步的实验提出了方法和路线。

Regulation by hetC of genes required for heterocyst differentiation and cell division in Anabaena sp strain PCC 7120

Unlike those of the wild-type strain, proheterocysts of the Anabaena sp. strain PCC 7120 hetC strain keep dividing. ftsZ, the most critical cell division gene, is up-regulated in hetC proheterocysts. Heterocyst differentiation genes hglD, hglE, patB, nijB, and xisA are no longer expressed in the hetC mutant. hetC also regulates the expression of patA, a pattern formation gene.

Margulis' theory on division of labour in cells revisited

Division of labour is a marked feature of multicellular organisms. Margulis proposed that the ancestors of metazoans had only one microtubule organizing center (MTOC), so they could not move and divide simultaneously. Selection for simultaneous movement and cell division had driven the division of labour between cells. However, no evidence or explanation for this assumption was provided. Why could the unicellular ancetors not have multiple MTOCs? The gain and loss of three possible strategies are discussed. It was found that the advantage of one or two MTOC per cell is environment-dependent. Unicellular organisms with only one MTOC per cell are favored only in resource-limited environments without strong predatory pressure. If division of labour occurring in a bicellular organism just makes simultaneous movement and cell division possible, the possibility of its fixation by natural selection is very low because a somatic cell performing the function of an MTOC is obviously wasting resources. Evolutionary biologists should search for other selective forces for division of labour in cells.

Enhanced fiber Bragg grating sensor demodulation technique using cascade wavelength division multiplex couplers

An enhanced technique for interrogating fiber Bragg grating wavelength shift using cascade wavelength division multiplexer (WDM) couplers was proposed and demonstrated. Three WDM couplers which show a linear filter function over the expected wavelength range are employed and cascaded to track Bragg wavelength shifts. Compared with single WDM demodulator. sharper spectral slope is obtained and considerable linear filter range is kept. The static and dynamic strain sensor demodulation experiments demonstrated that the simple passive technique improves the sensitivity approximately two times and keeps 5nm linear demodulation range based on our devices. The cascade WDM coupler demodulation system has high scan rate which can be used to monitor fast vibration.

克隆植物东方草莓对异质生境的适应对策

克隆植物被认为比非克隆植物更宜于利用异质性环境。在复杂的空间异质环境中，克隆植物可能形成了各种有效利用环境异质性的适应对策。对于克隆植物适应机制的研究，前人已做了大量的工作，特别是从形态和生物量分配等方面对简单异质生境下克隆植物的克隆整合和克隆分工进行了详细的研究。本研究以分布广泛的克隆植物东方草莓（Fragaria orientalis）作为研究对象，应用野外调查和实验生态学方法，采用多对比度单资源模型和不同向双资源模型，从形态和生理生态的角度，研究复杂异质生境下克隆植物的整合和分工及其耗益问题，分析不同类型的生境对克隆植物整合和分工的修饰作用，进而探讨克隆植物对异质生境的适应策略。克隆构型和分株种群特征是植物克隆生长及其生态适应对策研究的基本内容。本文通过野外调查，研究在不同光照条件下东方草莓克隆构型、分株种群特征以及点分布格局。结果表明：东方草莓的克隆构型随光照发生相应的变化，低光照下其匍匐茎节间长和分枝角度均增大而分枝强度减小；随光照减弱，东方草莓分株种群的生物量、根冠比和分株种群密度显著降低；不同光照下东方草莓分株均以随机分布为主但不同尺度下有所差异，其分布格局强度依次为旷地<林缘<林下。结合克隆植物对资源的利用对策，探讨了克隆构型和分株种群特征以及分布格局随环境条件变化的生态适应意义。不同生境斑块条件下克隆植物可能采取不同的适应对策。采用盆栽实验，研究不同水分对比度下克隆整合及其生理生态特征，并对单向和交互资源中东方草莓的克隆整合做了对比研究。结果显示：高的水分对比度能够促进东方草莓的克隆整合，并能刺激相连分株增加光合作用，东方草莓体内的氧化—抗氧化系统也II随对比度做出相应的反应。耗-益分析表明胁迫分株的受益是以供给分株的损耗为代价的，但从克隆片段总体来说是受益的。单向资源中东方草莓生长的绝对值高于交互资源，但耗-益分析表明生长于交互资源下东方草莓的克隆整合获益大于生长于单向资源下东方草莓的克隆整合获益。长期生长于特定生境的克隆植物，在进化过程中其克隆整合和克隆分工在对资源异质性的适应策略方面可能有所侧重。采用盆栽实验对来自不同海拔梯度的东方草莓的克隆整合和克隆分工对异质资源的适应对策进行了研究。实验结果表明，来自高海拔的东方草莓可塑性较差。来自两个海拔的东方草莓对切断匍匐茎的表现有所差异，总体上切断匍匐茎对来自高海拔的东方草莓影响更大些。另外，来自高海拔的东方草莓表现出更高的克隆分工。IIIClonal plants are known to be more suitable for the habitats of heterogeneousresources than nonclonal plants, perhaps due to their well developed adaptivestrategies to environmental heterogeneity. Many studies have been done on theadaptive mechanisms of clonal plants, especially on the clonal integration anddivision of labor with morphology and biomass allocation under simpleheterogeneous habitats. Based on field surveys, laboratory experiments, multi-contrastunidirectional resource model and reciprocal resource model, Fragaria orientalis, aRosaceae stoloniferous herb that widely distributes in China, was used to study thisplant’s morphological and physiological responses to complicated heterogeneoushabitats in terms of its clonal integration, division of labor and cost-benefit, as well astheir modifications by different habitats, so as to better understand the adaptivestrategies of clonal plants under heterogeneous environments.Clonal architecture and ramet population characteristics are of the major concernin the studies on growth and adaptive strategies of clonal plants. Clonal architecture,ramet population characteristics and spatial point pattern of F. orientalis underdifferent light intensity were studied with field observations. The results showed that,clonal architecture changed with light availability: Internode-lengths and branchangels of stolons were larger while branch intensities were smaller under lower lightintensity than those under higher light intensity; Biomass of ramet population,root-shoot ratio and density of ramet population decreased significantly with reduce oflight intensity; Under all light intensities, spatial pattern of ramets was mainlyrandomly distributed but it changed with different scales, with pattern intensity as:open space < forest edge < understory. Adaptation significance of the clonal architecture, the ramet population characteristics and the spatial pattern changing withdifferent environments was discussed according to these results.Clonal plants may take different adaptive strategies under different patches. Withpot culture, clonal integration and physiological parameters of F. orientalis underdifferent water contrasts were studied, and clonal integration under unilateralresources and reciprocal resources were also compared. The results suggested that,high water contrast improve the clonal integration of F. orientalis and increase thephotosynthesis of connected ramets. Oxidative and antioxidative system of F.orientalis also responded with changing water contrasts. According to cost-benefitanalysis, the drought-stressed ramets obtained benefits from the connectedwell-watered ramets, and as a whole, the clonal fragment could also get benefits.Growth of F. orientalis in homogeneous resources was better than that inheterogeneous resources, but the whole plant got more benefit through clonalintegration in heterogeneous resources than in homogeneous resources.Pot culture experiments were also used to study the adaptive strategies inutilizing heterogeneous resources by the plant populations from different altitudes.The results showed that, F. orientalis from alpine zones were shorter and lessexpanded with poorer clonal plasticity than those from middle mountains. F.orientalis from two different altitudes showed different responses to stolon severing,and as a whole, stolon severing had more influence on F. orientalis from alpine zones.In addition, F. orientalis from alpine zones exhibited higher division of labor, whichsuggested that clonal plants from different habitats develop their own adaptivemechanisms in their clonal integration and division of labor in response toenvironmental heterogeneity.

分工式门限认证加密方案

(t,n)门限认证加密方案允许t个以上签名方产生指定接收方的认证加密签名,使得只有指定的接收方能够恢复消息和验证消息的完整性,而其他人却无法做到这一点.最近,在Tseng和Jan的认证加密方案的基础上,Chung等构造了一个(t,n)门限认证加密方案.该方案运用了分工式签名技术,有效地减轻了签名方的负担.然而,该文作者对该方案的安全性仅进行了解释性说明.目前,文献中没有对分工式门限认证加密的形式化刻画,没有出现可证安全分工式门限认证加密方案.事实上,Chung等的分工式门限认证加密方案存在设计上的缺陷.文中给出了分工式门限认证加密方案的形式化模型和安全模型,基于双线性映射构造了一个新的分工式门限认证加密方案.在随机预言机模型下,证明了该方案对于适应性选择密文攻击是语义安全的,该方案对于适应性选择消息攻击是存在性不可伪造的.方案的安全性可规约到计算性Diffie-Hellman(CDH)困难假设和决定性双线性Diffie-Hellman困难假设(DBDH).