Age structure, growth and mortality estimates of an endemic Ptychobarbus dipogon (Regan, 1905) (Cyprinidae: Schizothoracinae) in the Lhasa River, Tibet

Ptychobarbus dipogon is an endemic fish in the Yarlung Tsangpo River, but its biology is poorly known. We sampled 582 specimens (total length, TL, between 70.6 and 593.0 mm) from April 2004 to August 2006 in the Lhasa River, Tibet. We estimated ages based on the counts of alternating opaque and translucent zones (annuli) in thin transverse sections of lapilli otoliths. Ages ranged from 1(+) to 23(+) years for males and 1(+) to 44(+) for females. The observed 44(+) years was the oldest reported for schizothoracine fishes. Females attained a larger size than males. The TL weight relationship was W=7.12 x 10(-6)TL(3.006) for combined sexes. The growth parameters fitted von Bertalanffy growth functions were L-infinity = 598.66 mm, k=0.0898 year(-1), t(0)=-0.7261 year and W-infinity = 1585.38 g for females and L-infinity = 494.23mm, k=0.1197 year(-1), t(0)=-0.7296 year and W-infinity = 904.88g for males. The longevities of 32.7 year for females and 24.3 year for males were similar to the observed ages. Using an empirical model we estimated the instantaneous rate of total mortality (Z) at 0.28 per year in the lower reaches. Z in the upper and middle stocks was close to the M because of unexploited or lightly exploited stock. Protracted longevity, slow growth, low natural mortality and large body size were typical characteristics of P. dipogon. The current declining trend of P. dipogon could be prevented by altering fishing regulations.

Antibunching and blinking from a single colloidal CdSe quantum dot

We have investigated the optical properties of single CdSe/ZnS nanocrystals by conducting combinations of experiments on antibunching and photoluminescence intermittence under different experimental conditions. Based on photoluminescence in an antibunching experiment, we analyzed the emission lifetime of QDs by using stretched exponentials. The difference between the parameters obtained from average lifetimes and stretched exponents were analyzed by considering the effect of nonradiative emission. An Auger-assisted tunneling model was used to explain the power law exponents of off time distribution. The power law exponent under high excitation power was correlated with a higher Auger ionization rate. Using the parameters obtained from stretched exponential function and power law, the antibunching phenomena at different time and under different excitation intensity were analyzed.

Unselective regrowth buried heterostructure long-wavelength superluminescent diode realized with MOVPE

A novel unselective regrowth buried heterostructure (BH) long-wavelength superluminescent diode (SLD), which has a grade-strained bulk InGaAs active region, was developed by metalorganic vapor-phase epitaxy (MOVPE). The 3 dB emission spectrum bandwidth of the SLD is about 65 nm with the range from 1596 to 1661 nm at 90 mA and front 1585 to 1650 nm at 150 mA. An output power of 3.5 mW is obtained at 200 mA injection current under CW operation at room temperature. (c) 2006 Elsevier B.V. All rights reserved.

Fabrication of 2 x 2 tapered multimode interference coupler

The authors demonstrate a 3dB 2 x 2 parabolically tapered multimode interference (MMT) coupler with a large cross-section and space between the different ports using silicon-on-insulator technology. The device exhibits a uniformity of < 0.8dB and can be used in the realisation of an MMI-based optical switch with a high extinction ratio.

关于“为设计认证协议的一个简明逻辑”一文的注记

Buttyan等人提出了一个简洁的逻辑 ,他们把它用于改进 Woo- L am协议 ,并且未证明地声称 :改进后的协议是抗协议与自身的交互攻击的 .为表明他们的结论是不正确的 ,找到了改进协议的两个不同的攻击 ,并详细解释如何加以实现 .构造攻击的方式除了要求更细致之外 ,与 Debbabi等人的方式在本质上是相似的 .进一步的分析表明Debbabi等人的逻辑没有足够的能力推理交互攻击 ,该逻辑有待改进

热学微流控系统中瞬态相变传热研究

微尺度相变传热广泛存在于微反应器、微型燃料电池、微蒸发器、微冷凝器、微热管、微汽泡执行器等微流控器件中，研究微流控系统中的相变问题对于微流控器件的设计和运行具有重要的科学意义。本文针对三类典型的微尺度相变问题，即微尺度流动沸腾、微尺度流动凝结以及微加热器上的汽泡动力学进行了深入细致的研究，实验研究中所采用的实验件均为标准MEMS微加工工艺制作，克服了常规机械加工所造成的表面粗糙度的影响。 考虑到微流控系统中大量应用交叉型、弯曲型等复杂结构的微通道，在微尺度流动沸腾研究中，设计了一种具有交错微通道结构的微流控芯片，并以丙酮为工质，对该芯片内的流动沸腾进行了研究。发现了周期为毫秒量级微时间尺度的流型结构，整个周期包括单相液体充液、两相分层流以及部分蒸干的液膜流三个阶段；在单个微通道区域，由于蒸发动量力的作用，液膜沿流动方向呈非均匀分布，蒸干首先发生在上游；由于液相弗劳德数较小，导致微通道中依然存在分层流流型。由于毕渥数较小，芯片背面温度几乎与芯片内壁面温度保持同步变化。虽然红外热像仪的响应频率较低，但仍然可以鉴别出由于流型周期性转换导致的壁面温度脉动。 在微尺度流动凝结换热研究中，为便于获取凝结过程的动态流动特性，设计了一种低高宽比的单微通道，并以水为工质，对该微通道中的流动凝结换热进行了研究。实验中采取了空气自然对流冷却和 水强制对流冷却两种冷却强度。研究发现，该微通道中的凝结换热呈周期性，其周期在毫秒量级。在通道上游入口处，存在一个呈准静止状态的长汽弹，汽弹前端周期性脱离汽泡。增加冷却强度会使汽泡的脱离频率增大，脱离直径减小；长汽弹前端周期性脱离汽泡是由于汽液界面具有较大的韦伯数。汽泡在该微通道内的运动过程中直径基本不变是由于汽泡在通道内的滞留时间远小于汽泡完全冷凝所需的总时间。 为澄清并联通道的多通道效应对微尺度凝结换热的影响，作者设计了由三个矩形通道组成的并联微通道冷凝器。研究发现，通道中的流型结构与单通道凝结过程类似，均为上游呈准静止状态的长汽弹和下游周期性的汽泡脱离。在中间通道和侧通道中，总共发现了三种不同的汽泡脱离模式，即单汽丝断裂模式、双汽丝同步断裂模式以及双汽丝非同步断裂模式。多通道效应主要表现在由于硅基固体导热的影响，三个通道中具有不同的温度分布，中间通道的温度关于其中心线成对称分布，而两侧通道中的高温区域均靠向中间通道。虽然硅具有良好的导热性，整个硅基上的温差很小，但在微尺度下，小温差依然可以导致较大的温度梯度，造成中间通道的双汽丝关于其中心线成对称分布，并且总是发生同步断裂；侧通道中的双汽丝偏向中间通道，并且在靠近中间通道的一侧汽丝总是首先发生断裂。由于温度梯度引起的Maragnoni对流效应，侧通道中的汽泡脱离后便靠向高温侧。 在微汽泡动力学研究中，设计了一种尺寸为 的Pt薄膜微加热器，研究了脉冲控制参数对微加热器上汽泡动力学特性的影响。研究发现在该微加热器上发生汽泡核化时，核化温度均达到液体的过热极限，因此为均质核化过程。在不同的脉冲控制参数下，存在三类不同的汽泡动力学特性，即（1）汽泡爆炸性生长和冷凝以及汽泡二次生长；（2）汽泡爆炸性生长继而分裂、吸引并聚合；（3）汽泡振荡生长而后持续生长并最终达到稳定状态。在第（1）类中，汽泡二次生长是由于脉冲加热过程中在玻璃基片上储存了热量；在第（2）类中，汽泡冷凝过程中的Marangoni效应导致分裂后的汽泡互相吸引并最终聚合。在第（3）类中，汽泡尺寸最终达到稳定是由于汽泡内蒸汽的发生量与汽液界面上蒸汽的凝结量相等。 本文的研究将为微反应器、微型燃料电池、微换热器、微汽泡执行器等相变微流控系统的设计和运行提供科学指导。