中国美丽尖额溞(甲壳纲:双甲目)的新资料

<正> 美丽尖额溞(Alona pulchella King,1853)是广泛分布于澳大利亚区、埃塞俄比亚区以及新热带区的一种枝角类。据中国动物志淡水枝角类卷的记载,在我国只分布于广东、福建、北京、陕西及西藏,而且并不常见,雄性特征也不明。1989年6月中、下旬,在武汉市的中国科学院水生生物研究所一只曾用于培养本市东湖的水草而后閒弃室外的小水缸中,出现了美丽尖额溞的种群,而且有雌雄两性以及带卵鞍的个体,这在过去的文献中从未报道过。

Bioaccumulative characteristics of hexabromocyclododecanes in freshwater species from an electronic waste recycling area in China

Hexabromocyclododecanes (HBCDs) are now emerging ubiquitous contaminants due to their wide usage, persistence and toxicities. To investigate the bioaccumulative characteristics of HBCDs, sediments, Winkle (Littorina littorea), crucian carp (Carassius carassius) and loach (Misgurnus anguillicaudatus) were collected from two streams near an E-waste dismantling site in China. and HBCD exposure test was then conducted on Chinese rare minnow. The concentration of HBCDs was 14 ng g(-1) dry weight in sediments, 186. 377 and 1791 ng g(-1) lipid weight in winkle, crucian carp and loach, respectively. gamma-HBCD was found to be the dominant diastereoisomer in the sediments (63% of total HBCDs). However, alpha-HBCD was selectively accumulated in the biotic samples and contributed to 77%, 63% and 63% of total HBCDs in winkle, crucian carp and loach, respectively. Moreover, an enrichment of (-)-enantiomers of alpha- and gamma-HBCD were found in the winkle. The reverse results were observed in the crucian carp and loach. Similar observations of diastereoisomeric and enantiomeric composition were obtained in Chinese rare minnow with those found in the crucian carp and loach. These results indicate that the freshwater species from the streams are contaminated by HBCDs. alpha-HBCD can be selectively accumulated in organisms and the accumulative characteristics are enantioselective among species. (C) 2009 Elsevier Ltd. All rights reserved.

The structural and photoluminescence character of InAs quantum dots grown on a combined InAlAs and GaAs strained buffer

The structural and photoluminescence (PL) properties of the InAs quantum dots (QDs) grown on a combined InAlAs and GaAs strained buffer layer have been investigated by AFM and PL measurements. The dependence of the critical thickness for the transition from 2D to 3D on the thickness of GaAs layer is demonstrated directly by RHEED. The effects of the introduced-InAlAs layer on the density and the aspect ratio of QDs have been discussed.

Prediction and suppression of strong dispersive coupling in microracetrack channel drop filters

For a four-port microracetrack channel drop filter, unexpected transmission characteristics due to strong dispersive coupling are demonstrated by the light tunneling between the input-output waveguides and the resonator, where a large dropping transmission at off-resonance wavelengths is observed by finite-difference time-domain simulation. It causes a severe decline of the extinction ratio and finesse. An appropriate decrease of the coupling strength is found to suppress the dispersive coupling and greately increase the extinction ratio and finesse, a decreased coupling strength can be realized by the application of an asymmetrical coupling waveguide structure. In addition, the profile of the coupling dispersion in the transmission spectra can be predicted based on a coupled mode theory analysis of an equivalent system consisting of two coupling straight waveguides. The effects of structure parameters on the transmission spectra obtained by this method agree well with the numerical results. It is useful to avoid the strong dispersive coupling region in the filter design. (c) 2007 Optical Society of America.

Experiments and their analysis for self-assembly growth of GaN quantum dots via MOCVD

In recent years, growth of GaN-based materials-related quantum dots has become a hot topic in semiconductor materials research. Considerable efforts have been devoted to growth of self-assembled quantum dots of GaN-based materials via MOCVD (Metal Organic Chemical Vapor Deposition) and there are a lot of relevant literatures. There is, however, few review papers for the topic. In this paper, different experimental methods for fabrication of quantum dots of GaN-based materials via MOCVD are critically reviewed and the experimental conditions and parameters, which may affect growth of the quantum dots, are analyzed, with an aim at providing some critical reference for the related future experiment research.

用MOCVD法生长GaN基自组装量子点的相关实验及其分析

GaN基相关材料的量子点生长是半导体材料研究的一个热点，尤其是用MOCVD方法生长GaN基自组装量子点占了相当的比例，因此相关的文献较多，但综述性文章却不多见。鉴于此，本文综述了用MOCVD法制备GaN基量子点的不同实验方法，并对影响量子点牛长的实验条件和参数做了简要的分析。希望能够对相关的实验研究工作提供一些参考。