贝叶斯联合模型与中国洞穴鱼类分化时间的估算(鲤科:金线鲃属)

金线鲃属分布于中国云贵高原及周边地区,包括10多种适应于洞穴生活、具有不同程度眼睛和色素退化的典型洞穴鱼类.迄今为止,金线鲃属的系统发育关系还存在很大争议.我们获得了34种金线鲃属鱼类及外类群的细胞色素b和ND4基因序列,用贝叶斯联合模型分析数据,重建了金线鲃属的系统发育关系;并用松散分子钟估算了本属及内部分支的起源时间.金线鲃属的单系性得到强烈的支持,本属可分为6个分支.此外,本研究结果还支持洞穴物种的多系起源假说以及季氏金线鲃(Sinocyclocheilus jii)的基部位置.松散分子钟估算表明,

空间飞行和辐射对微藻光合系统影响的观察

目的研究空间飞行及辐射对微藻光合系统的影响。方法利用卫星搭载空间飞行、钴60的γ射线照射及地面对照黑暗培养微藻葛仙米,测定其存活率、光合活性、光合系统色素及观察藻细胞超微结构。结果空间飞行和射线处理后的微藻其存活率、光合活性发生显著降低,捕光色素明显降解、光合片层结构出现异常,同时空间飞行后微藻细胞外诱导出较厚的胶被。结论空间飞行及辐射均对微藻的光合系统产生损伤,但微藻可以通过结构上的改变对其进行适应。

扁担塘两种底栖动物的周年生产量

研究了1996年4月至1997年3月间扁担塘两种底栖动物———幽蚊和圆扁螺的周年生产量,采用体长频率法测算的生产量分别是:幽蚊周年生产量湿质量为0.1419g·m-2·a-1,干质量为0.0114g·m-2·a-1,P/B系数为1.8;圆扁螺的周年生产量带壳湿质量为1.6266g·m-2·a-1,去壳干质量为0.0732g·m-2·a-1,P/B系数为7.1.但与国外数据相比,这些结果比较适中,说明扁担塘并不是幽蚊和圆扁螺的最适生长环境.

alpha-tocopherol is essential for acquired chill-light tolerance in the cyanobacterium Synechocystis sp strain PCC 6803

Unlike Escherichia coli, the cyanobacterium Synechocystis sp. strain PCC 6803 is insensitive to chill (5 degrees C) in the dark but rapidly losses viability when exposed to chill in the light (100 mu mol photons m(-2) s(-1)). Preconditioning at a low temperature (15 degrees C) greatly enhances the chill-light tolerance of Synechocystis sp. strain PCC 6803. This phenomenon is called acquired chill-light tolerance (ACLT). Preconditioned wild-type cells maintained a substantially higher level of alpha-tocopherol after exposure to chill-light stress. Mutants unable to synthesize alpha-tocopherol, such as slr1736, slr1737, slr0089, and slr0090 mutants, almost completely lost ACLT. When exposed to chill without light, these mutants showed no or a slight difference from the wild type. When complemented, the slr0089 mutant regained its ACLT. Copper-regulated expression of slr0090 from P-petE controlled the level of et-tocopherol and ACLT. We conclude that alpha-tocopherol is essential for ACLT of Synechocystis sp. strain PCC 6803. The role of a-tocopherol in ACLT may be based largely on a nonantioxidant activity that is not possessed by other tocopherols or pathway intermediates.

Distribution and bioaccumulation of microcystins in water columns: A systematic investigation into the environmental fate and the risks associated with microcystins in Meiliang Bay, Lake Taihu

For the purpose of understanding the environmental fate of microcystins (MCs) and the potential health risks caused by toxic cyanobacterial blooms in Lake Taihu, a systematic investigation was carried out from February 2005 to January 2006. The distribution of MCs in the water column, and toxin bioaccumulations in aquatic organisms were surveyed. The results suggested that Lake Taihu is heavily polluted during summer months by toxic cyanobacterial blooms (with a maximum biovolume of 6.7 x 10(8) cells/L) and MCs. The maximum concentration of cell-bound toxins was 1.81 mg/g (DW) and the dissolved MCs reached a maximum level of 6.69 mu g/L. Dissolved MCs were always found in the entire water column at all sampling sites throughout the year. Our results emphasized the need for tracking MCs not only in the entire water column but also at the interface between water and sediment. Seasonal changes of MC concentrations in four species of hydrophytes (Eichhornic crassipes, Potamogeton maackianus, Alternanthera philoxeroides and Myriophyllum spicatum) ranged from 129 to 1317, 147 to 1534, 169 to 3945 and 124 to 956 ng/g (DW), respectively. Toxin accumulations in four aquatic species (Carassius auratus auratu, Macrobrachium nipponensis, Bellamya aeruginosa and Cristaria plicata) were also analyzed. Maximum toxin concentrations in the edible organs and non-edible visceral organs ranged from 378 to 730 and 754 to 3629 ng/g (DW), respectively. Based on field studies in Lake Taihu, risk assessments were carried out, taking into account the WHO guidelines and the tolerable daily intake (TDI) for MCs. Our findings suggest that the third largest lake in China poses serious health threats when serving as a source of drinking water and for recreational use. In addition, it is likely to be unsafe to consume aquatic species harvested in Lake Taihu due to the high-concentrations of accumulated MCs. (C) 2007 Elsevier Ltd. All rights reserved.

Multimode resonances in metallically confined square-resonator microlasers

Directional emission InP/AlGaInAs square-resonator microlasers with a side length of 20 mu m are fabricated by standard photolithography and inductively coupled-plasma etching technique. Multimode resonances with about seven distinct mode peaks in a free-spectral range are observed from 1460 to 1560 nm with the free-spectral range of 12.1 nm near the wavelength of 1510 nm, and the mode refractive index versus the photon energy E (eV) as 3.07152+0.18304E are obtained by fitting the laser spectra with an analytical mode wavelength formula derived by light ray method. In addition, mode field pattern is simulated for cold cavity by two dimensional finite-difference time-domain technique.

Relationship between the electric performance and the photoluminescence spectra of resonant tunnelling diodes

Resonant tunnelling diodes with different structures were grown. Their photoluminescence spectra were investigated. By contrast, the luminescence in the quantum well is separated from that of other epilayers. The result is obtained that the exciton of the luminescence in the quantum well is partly come from the cap layer in the experiment. So the photoluminescence spectrum is closely related to the electron transport in the resonant tunnelling diode structure. This offers a method by which the important performance of resonant tunnelling diode could be forecast by analysing the integrated photoluminescence intensities.

Experiment on Qinghai-Tibet railroad subgrade temperature monitoring based on FBG sensors

Qinghai-Tibet Railway is the longest and highest plateau railway in the world. A long term monitoring system of the stability of the subgrade in the permafrost regions should be put forward immediately to prevent damage to the railway. As it's very difficult to set up the long-distance automatic monitoring system which contains a lot of measure points along the 550 kilometers railway in the permafrost area, we present a subgrade temperature monitor system based on fiber Bragg grating (FBG). In this paper the principles of the FBG was presented, and the feasibility of the FBG sensors in the permafrost area of Qinghai-Tibet plateau was analysized. We embedded fifteen FBG temperature sensors and thermal resistance temperature sensors. A contrast experiment is made while the two kinds of sensors are arranged in the same position. The result of the experiment shows that the accuracy of the FBG temperature sensors is less than 0.1 degrees C. and the FBG sensors can do well in the measurement of pattern which the temperature varies with the depth of the permafrost soil. The result also shows the stability of the FBG sensors in the bad environmental condition of Qinghai-Tibet plateau, which proves the feasibility of the application of FBG sensors and our monitoring system on the Qinghai-Tibet railway.

Second-Order Raman Scattering from n- and p-Type 4H-SiC

The results of second-order Raman-scattering experiments on n- and p-type 4H-SiC are presented,covering the acoustic and the optical overtone spectral regions.Some of the observed structures in the spectra are assigned to particular phonon branches and the points in the Brillouin zone from which the scattering originates.There exists a doublet at 626/636cm-1 with energy difference about 10cm-1 in both n- and p-type 4H-SiC,which is similar to the doublet structure with the same energy difference founded in hexagonal GaN,ZnO, and AlN.The cutoff frequency at 1926cm-1 of the second-order Raman is not the overtone of the A1(LO) peak of the n-type doping 4H-SiC,but that of the undoping one.The second-order Raman spectrum of 4H-SiC can hardly be affected by doping species or doping density.