Near optimal combination of sensory and motor uncertainty in time during a naturalistic perception-action task.

Most behavioral tasks have time constraints for successful completion, such as catching a ball in flight. Many of these tasks require trading off the time allocated to perception and action, especially when only one of the two is possible at any time. In general, the longer we perceive, the smaller the uncertainty in perceptual estimates. However, a longer perception phase leaves less time for action, which results in less precise movements. Here we examine subjects catching a virtual ball. Critically, as soon as subjects began to move, the ball became invisible. We study how subjects trade-off sensory and movement uncertainty by deciding when to initiate their actions. We formulate this task in a probabilistic framework and show that subjects' decisions when to start moving are statistically near optimal given their individual sensory and motor uncertainties. Moreover, we accurately predict individual subject's task performance. Thus we show that subjects in a natural task are quantitatively aware of how sensory and motor variability depend on time and act so as to minimize overall task variability.

The 1958 pearl oyster fishery, Gulf of Mannar

The continental shelf between the three and twelve fathom lines, off the Ceylon coast in the Gulf of Mannar is popularly known as the Pearl Banks. Though the area of this plateau is extensive the pearl oysters are concentrated on restricted areas known as "paars". The more productive of these are the Cheval Group of paars and the Moderagam Paar. The Peria Paar and Twynam's Paar though covering larger areas are not dependable as oyster beds. The True Vankalai, Peria Paar Karai and Muthuvarathu Paars are small in extent, but have yielded oysters on a commercial scale. Although the Ceylon Pearl Banks has been commercially fished for centuries, the first scientific investigation of its pearl oysters on an intensive scale was started by Herdman in 1902 (1902-06) and later continued by Hornell (1905-41), Shipley (1904-06), Pearson (1911-33), Jameson (1912-13), Southwell (1910-14) and Malpas (1922-39).

Development of design and construction of fishing boats in Uganda

Fishing boats and canoes varied very little in Uganda from the middle of the 19th century umil 1949. types in use being the Dug Out Canoe. up to 40 ft. in length with 4 ft. beam hollowed from trees, and "Sesse" canoes which were used on Lake Victoria; these had an obvious Arab influence. The length of the "Sesse" in recent years as from about 1912 is 28 ft., and it is used as an open fishing craft.

原白蚁的形态变异及其种类厘定商榷(等翅目:草白蚁科)

草白蚁科Hodotermitdae原白蚁亚科Hodotermopsinae目前仅知Zootermopsis,Archotermopsis和Hodotermopsis3个属。前1属分布于西半球的北美洲，后2属分布于东半球的东洋区。原白蚁属Hodotermopsis广泛分布于我国长江以南的丘陵地带，以及越南北部和日本南部的一些岛屿。这类白蚁取食木材，危害多种林木，一般生活在亚热带潮湿森林内，俗称湿木白蚁Dampwoodtermites。原白蚁属Hodotermopsis是N．Holmgren于1911年建立的，属于比较原始的类群。常筑巢于原木内，蚁巢结构比较简单，群体品级的分化亦处于较原始状态。幼蚁担负全巢劳作替代工以职能，故有拟工蚁之称。兵蚁的形态与成虫和幼蚁近似，其头部特别是个体小的头型近圆形，扁平；上颚粗壮，左右内缘多齿；触角节数多于20节；附节5节；尾须分节等。这些性状均保留了原始类型的特点。原白蚁形态变化颇大，有时似呈连续的梯度变异。如果采得少数个体，很容易将不同地方的种群或不同个体误定为不同种。原白蚁的模式种是H．sjbstedtiHolmgren。1912年，H0lmgren又以兵蚁右上颚齿的尖形与...

THE PHYLOGENETIC-RELATIONSHIPS AND CLASSIFICATION OF THE DOUCS AND SNUB-NOSED LANGURS OF CHINA AND VIETNAM

The taxonomy of the douc and snub-nosed langurs has changed several times during the 20th century. The controversy over the systematic position of these animals has been due in part to difficulties in studying them: both the doucs and the snub-nosed langurs are rare in the wild and are generally poorly represented in institutional collections. This review is based on a detailed examination of relatively large numbers of specimens of most of the species of langurs concerned. An attempt was made to draw upon as many types of information as were available in order to make an assessment of the phyletic relationships between the langur species under discussion. Toward this end, quantitative and qualitative features of the skeleton, specific features of visceral anatomy and characteristics of the pelage were utilized. The final data matrix comprised 178 characters. The matrix was analyzed using the program Hennig86. The results of the analysis support the following conclusions: (1) that the douc and snub-nosed langurs are generically distinct and should be referred to as species of Pygathrix and Rhinopithecus, respectively; (2) that the Tonkin snub-nosed langur be placed in its own subgenus as Rhinopithecus (Presbytiscus) avunculus and that the Chinese snub-nosed langur thus be placed in the subgenus Rhinopithecus (Rhinopithecus); (3) that four extant species of Rhinopithecus be recognized: R. (Rhinopithecus) roxellana Milne Edwards, 1870; R. (Rhinopithecus) bieti Milne Edwards, 1897; R. (Rhinopithecus) brelichi Thomas, 1903, and R. (Presbytiscus) avunculus Dollman, 1912; (4) that the Chinese snub-nosed langurs fall into northern and southern subgroups divided by the Yangtze river; (5) that R. lantianensis Hu and Qi, 1978, is a valid fossil species, and (6) the precise affinities and taxonomic status of the fossil species R. tingianus Matthew and Granger, 1923, are unclear because the type specimen is a subadult.

植物活性多糖的研究进展

活性多糖的研究已成为多糖研究领域内的一个热点.对植物活性多糖的研究范围、重要意义及化学结构与构效关系方面的研究进展进行了综述分析,并对其应用前景作了介绍.

鲤科的科下类群及其宗系发生关系

<正> 鲤科为鲤形目中最大的科,拥有275属1600种(Pattern 1975)。早在100多年前Bleeker(1863)已对该科进行了较细的类群划分,嗣后,其他作者也先后做过这方面的工作。Regan(1911)发现某些骨骼性状在宗系发生(phylogeny)上具有一定的重要性,而另一些性状则对划分类群没有意义。Berg(1912,1940)依据较特别的外部形态来规定

鳡鱼的颅骨结构及其对掠食生态的适应性

<正> 鳡鱼Elopichthys bambusa(Richardson)是我国特有的一种鲤科鱼类,生活于江河、湖泊的中上层,游泳非常迅速,经常袭击和追捕其他鱼类,是一种咬捕掠食型的凶猛鱼类。由于这种习性,使它的形态,特别是颅骨的结构产生了某些相应变化。为此,(1912)曾据其上颔骨与前上颌骨相愈合等特征,建立了一个与鲤科其他亚科并列的一个类群——Elopichthyini。但至今未见到鳡鱼颅骨结构的系统描述。作者以两尾性成熟个体(标准长分别为930毫米和890毫米)为材料,对鳡鱼的颅骨结构进行了比较观察

Optical properties of InGaAs/GaAs quantum chains

We have investigated the steady-state and transient optical properties of InGaAs/GaAs quantum chains and found that the photoluminescence (PL) decay time exhibits a strong photon energy dependence. It increases with the decrease of the emission energy. It is also found that the PL decay time increases with the excitation power. When the excitation power is large enough the PL decay time tends to be saturated. All these experimental results show that there is a strong carrier coupling along the chain direction in the quantum dot chain structure. The polarization PL measurements further confirm the carrier transfer process along the chain direction.

RBAC实施中国墙策略及其变种的研究

中国墙策略的目的是防止在有竞争关系的企业间访问信息导致的利益冲突.著名的中国策略模型包括Brewer等人提出的BN模型和Sandhu提出的基于格访问控制模型实施的中国墙模型.然而这些模型都存在严重的缺陷:灵活性不够或者实施不方便.RBAC是目前主流的访问控制模型,该模型的特点是策略中立.基于RBAC模型全面研究了实施中国墙策略及其各种变种策略的方法,利用角色体系和RBAC的约束机制,给出了具体的构造方法,讨论了这些构造中约束的形式化描述方法.与传统的中国墙模型相比,更加灵活,并可在支持RBAC的系统中直接实施.

CONTINUOUSLY CHIRPED DFB GRATINGS BY SPECIALLY BENT WAVE-GUIDES FOR TUNABLE LASERS

We have implemented and studied a new type of tunable multiple-section semiconductor distributed feedback (DFB) laser using tailored chirped DFB gratings. Arbitrarily and continuously chirped DFB gratings are defined by bent waveguides on homogeneous grating fields with ultrahigh spatial precision, The mathematical bending functions are optimized in this case to provide enlarged wavelength tuning ranges. We present the results of model calculations, the technological device realization and experimental results of the DFB laser characterization e.g. a tuning range of 5.5 mm without wavelength gaps and high side mode suppression ratio.

InGaAs/GaAs量子链的光学特性研究

研究了InGaAs/GaAs量子链的稳态和瞬态光谱特性,特别是载流子的动力学过程.实验发现荧光寿命有很强的探测能量依赖关系,荧光寿命随发光能量的增加而减小;实验还发现,当激发功率较小时,荧光寿命随激发功率增大而增大,当激发功率足够大时,荧光寿命趋于饱和.这些结果清楚地表明,在量子链结构中,参与发光的载流子之间存在明显的耦合和输运现象,进一步分析表明,这种输运主要是由于载流子沿量子链方向的耦合造成的.发光的偏振特性研究进一步证实了载流子沿量子链方向输运过程.

一种用于抑制椒盐噪声的多窗口中值滤波器

该文提出了一种用于抑制椒盐噪声的多窗口中值滤波算法。算法在招待过程中根据具体情况采用不同大小的滤波窗口。仿真结果表明，与标准中值滤波算法相比，该方法不仅可以有效去除图像中的椒盐噪声，特别是在噪声密度非常大的情况下，表现了很好的性。

Intercellular calcium wave propagation in linear and circuit-like bone cell networks

In the present study, the mechanism of intercellular calcium wave propagation in bone cell networks was identified. By using micro-contact printing and self-assembled monolayer technologies, two types of in vitro bone cell networks were constructed: open-ended linear chains and looped hexagonal networks with precisely controlled intercellular distances. Intracellular calcium responses of the cells were recorded and analysed when a single cell in the network was mechanically stimulated by nano-indentation. The looped cell network was shown to be more efficient than the linear pattern in transferring calcium signals from cell to cell. This phenomenon was further examined by pathway-inhibition studies. Intercellular calcium wave propagation was significantly impeded when extracellular adenosine triphosphate (ATP) in the medium was hydrolysed. Chemical uncoupling of gap junctions, however, did not significantly decrease the transferred distance of the calcium wave in the cell networks. Thus, it is extracellular ATP diffusion, rather than molecular transport through gap junctions, that dominantly mediates the transmission of mechanically elicited intercellular calcium waves in bone cells. The inhibition studies also demonstrated that the mechanical stimulation-induced calcium responses required extracellular calcium influx, whereas the ATP-elicited calcium wave relied on calcium release from the calcium store of the endoplasmic reticulum.