第54届国际宇航大会介绍

<正> 第54届国际宇航大会于2003年9月29～10月3日在德国布莱梅召开.国际宇航大会是国际宇航联合会(IAF)、国际宇航科学院(IAA)和国际空间法律联合会联合主办的国际宇航界盛会,每年举办一届,至今已举办了54届,一直得到国际宇航领域的科学家和工程技术与管理人员的极大重视.来自世界多个国家和地区的超过2000位代表参加了会议,此次国际宇航大会共交流学术论文约 1170篇,分26个专题,分别是:

铒玻璃在1．54μm实现1 Hz下3 J和5 Hz下0．6 J的激光输出

近年来,随着激光告警、激光指示、风速测量、激光雷达尤其是激光美容等方面的需求逐渐增加,要求掺铒激光玻璃能够实现比以往更高重复频率以及更大能量的激光输出,其中对脉冲能量的要求达1～10 J。

不同基因型小麦（Triticum aestivum）京411与小偃54抗光氧化特性及其机理的比较研究

对两种不同基因型小麦京411（北京地区高产小麦品种）和小偃54（在生产上已应用二十年的优良品种）幼苗及旗叶光抑制特性进行了比较研究，着重探讨了它们抗光氧化的差异及其机理，主要结果如下： 1. 强光条件下，同京411相比小偃54能保持较高的光合色素含量和放氧速率。其DCPIP光还原活性也较高。 2. 光谱特性分析表明，强光胁迫下小偃54在红区及蓝区的特征性吸收峰及F683荧光发射峰下降的幅度明显小于京411相应峰位的下降。 3. 色素蛋白复合物分析表明，强光条件下，京411色素蛋白复合物中LHCII聚合体大量的解聚，而小偃54在强光条件下仍能保持较高比例的LHCII聚合体。这可能在一定的程度上有利于小偃54在强光下维持较强的激发能耗散的能力。 4. 多肽SDS-PAGE分析表明，强光对不同基因型小麦中同PSII光抑制敏感性有关的两个外周蛋白23kD和17kD的影响不同。光抑制明显地降低了京411的23kD和17kD的含量，而对于小偃54中这两个外周蛋白23kD和17kD的影响不大。强光条件下小偃54旗叶PSII颗粒中捕光色素蛋白27kD含量提高，而京411捕光色素蛋白27kD含量明显的下降。 5. 上述结果表明，西北地区的优良小麦品种小偃54同北京地区的高产品种京411相比更耐强光的胁迫，其抗光氧化的能力较强。 6. 进一步分析表明，同京411相比，小偃54抗光氧化的主要原因是其不仅含有较大的叶黄素循环的色素库，而且在强光下能维持高的VDE酶活性及高水平的叶黄素循环的脱环化水平。 7. 叶黄素循环色素在两个小麦品种类囊体膜色素蛋白复合体中的分布存在差异，抗光氧化的小偃54大部分的VAZ分布在PSII上，其中绝大部分集中在LHCII聚合体上。LHCII上VAZ的集中分布可能有利于在强光下对过多光能的耗散，减少过多激发能对PSII的损伤。 8. 类囊体膜流动性分析表明，叶黄素循环参与了对类囊体膜流动性的调整，对维持强光下抗光氧化品种小偃54的类囊体膜相对稳定起重要作用。 9. 依赖于叶黄素循环的热耗散是抗光氧化品种小偃54的一个主要的光保护途径。

Solar UV radiation drives CO2 fixation in marine phytoplankton: A double-edged sword

Photosynthesis by phytoplankton cells in aquatic environments contributes to more than 40% of the global primary production (Behrenfeld et al., 2006). Within the euphotic zone (down to 1% of surface photosynthetically active radiation [PAR]), cells are exposed not only to PAR (400-700 nm) but also to UV radiation (UVR; 280-400 nm) that can penetrate to considerable depths (Hargreaves, 2003). In contrast to PAR, which is energizing to photosynthesis, UVR is usually regarded as a stressor (Hader, 2003) and suggested to affect CO2-concentrating mechanisms in phytoplankton (Beardall et al., 2002). Solar UVR is known to reduce photosynthetic rates (Steemann Nielsen, 1964; Helbling et al., 2003), and damage cellular components such as D1 proteins (Sass et al., 1997) and DNA molecules (Buma et al., 2003). It can also decrease the growth (Villafane et al., 2003) and alter the rate of nutrient uptake (Fauchot et al., 2000) and the fatty acid composition (Goes et al., 1994) of phytoplankton. Recently, it has been found that natural levels of UVR can alter the morphology of the cyanobacterium Arthrospira (Spirulina) platensis (Wu et al., 2005b). On the other hand, positive effects of UVR, especially of UV- A (315-400 nm), have also been reported. UV- A enhances carbon fixation of phytoplankton under reduced (Nilawati et al., 1997; Barbieri et al., 2002) or fast-fluctuating (Helbling et al., 2003) solar irradiance and allows photorepair of UV- B-induced DNA damage (Buma et al., 2003). Furthermore, the presence of UV-A resulted in higher biomass production of A. platensis as compared to that under PAR alone (Wu et al., 2005a). Energy of UVR absorbed by the diatom Pseudo-nitzschia multiseries was found to cause fluorescence (Orellana et al., 2004). In addition, fluorescent pigments in corals and their algal symbiont are known to absorb UVR and play positive roles for the symbiotic photosynthesis and photoprotection (Schlichter et al., 1986; Salih et al., 2000). However, despite the positive effects that solar UVR may have on aquatic photosynthetic organisms, there is no direct evidence to what extent and howUVR per se is utilized by phytoplankton. In addition, estimations of aquatic biological production have been carried out in incubations considering only PAR (i. e. using UV-opaque vials made of glass or polycarbonate; Donk et al., 2001) without UVR being considered (Hein and Sand-Jensen, 1997; Schippers and Lurling, 2004). Here, we have found that UVR can act as an additional source of energy for photosynthesis in tropical marine phytoplankton, though it occasionally causes photoinhibition at high PAR levels. While UVR is usually thought of as damaging, our results indicate that UVR can enhance primary production of phytoplankton. Therefore, oceanic carbon fixation estimates may be underestimated by a large percentage if UVR is not taken into account.

Environmental signals: Synthetic humic substances act as xeno-estrogen and affect the thyroid system of Xenopus laevis

According to outdated paradigms humic substances (HS) are considered to be refractory or inert that do not directly interact with aquatic organisms. However, they are taken up and induce biotransformation activities and may act as hormone-like substances. In the present study, we tested whether HS can interfere with endocrine regulation in the amphibian Xenopus laevis. In order to exclude contamination with phyto-hormones, which may occur in environmental isolates, the artificial HS 1500 was applied. The in vivo results showed that HS 1500 causes significant estrogenic effects on X. laevis during its larval development and results of semi-quantitative RT-PCR revealed a marked increase of the estrogenic biomarker estrogen receptor mRNA (ER-mRNA). Furthermore, preliminary RT-PCR results showed that the thyroid-stimulating hormone (TSH beta-mRNA) is enhanced after exposure to HS1500, indicating a weak adverse effect on T3/T4 availability. Hence, HS may have estrogenic and anti-thyroidal effects on aquatic animals, and therefore may influence the structure of aquatic communities and they may be considered environmental signaling chemicals. (c) 2005 Elsevier Ltd. All rights reserved.

Infraciliature and myoneme system of Campanella umbellaria (Protozoa, Ciliophora, Peritrichida)

The infraciliature and myoneme system of Campanella umbellaria were revealed using the protargol impregnation technique. The main characteristics of the infraciliature are the peristomial ciliary rows (haplokinety and polykineties), which make four and a half turns around the peristomial disc before plunging into the infundibulum, and the aboral infraciliature, which is made up of the aboral ciliary wreath (trochal band) and the scopula. The myoneme system is composed of: 1) longitudinal fibers, which include 60-84 (mean 72.3) short longitudinal fibers, 40-56 (mean 45.8) medium-length longitudinal fibers, and numerous long longitudinal fibers; and 2) circular fibers, which include 8-12 (mean 9.3) peristomial ring fibers, linking fibers, support fibers, and peristomial disc fibers. The various fibers in C. umbellaria are interconnected to form a single myoneme system that may act as a cell skeleton as well as providing the mechanism by which the zooid contracts and relaxes. (C) 2004 Wiley-Liss, Inc.

Role of Bi3+ ions for Er3+ ions efficient 1.54 mu m light emission in Er/Bi codoped SiO2 thin film prepared by sol-gel method

Er/Bi codoped SiO2 thin films were prepared by sol-gel method and spin-on technology with subsequent annealing process. The bismuth silicate crystal phase appeared at low annealing temperature while vanished as annealing temperature exceeded 1000 degrees C, characterized by X-ray diffraction, and Rutherford backscattering measurements well explained the structure change of the films, which was due to the decrease of bismuth concentration. Fine structures of the Er3+-related 1.54 mu m light emission (line width less than 7 nm) at room temperature was observed by photoluminescence (PL) measurement. The PL intensity at 1.54 gm reached maximum at 800 degrees C and decreased dramatically at 1000 degrees C. The PL dependent annealing temperature was studied and suggested a clear link with bismuth silicate phase. Excitation spectrum measurements further reveal the role of Bi3+ ions for Er3+ ions near infrared light emission. Through sol-gel method and thermal treatment, Bi3+ ions can provide a perfect environment for Er3+ ion light emission by forming Er-Bi-Si-O complex. Furthermore, energy transfer from Bi3+ ions to Er3+ ions is evidenced and found to be a more efficient way for Er3+ ions near infrared emission. This makes the Bi3+ ions doped material a promising application for future erbium-doped waveguide amplifier and infrared LED

Carrier relaxation and thermal activation of localized excitons in self-organized InAs multilayers grown on GaAs substrates

We have investigated the temperature dependence of photoluminescence (PL) properties of a number of self-organized InAs/GaAs heterostructures with InAs layer thickness ranging from 0.5 to 3 ML. The temperature dependence of InAs exciton emission and linewidth was found to display a significant difference when the InAs layer thickness is smaller or larger than the critical thickness around 1.7 ML. The fast redshift of PL energy and an anomalous decrease of linewidth with increasing temperature were observed and attributed to the efficient relaxation process of carriers in multilayer samples, resulting from the spread and penetration of the carrier wave functions in coupled InAs quantum dots. The measured thermal activation energies of different samples demonstrated that the InAs wetting layer may act as a barrier for the thermionic emission of carriers in high-quality InAs multilayers, while in InAs monolayers and submonolayers the carriers are required to overcome the GaAs barrier to escape thermally from the localized states.

MOCVD生长Al_(0.48)Gao_(0.52)N/Al_(0.54)Ga_(0.36)N多量子阱的结构和光学特性

采用金属有机物化学气相淀积(MOCVD)技术,在蓝宝石衬底上生长了Al_(0.48)Gao_(0.52)N/Al_(0.54)Ga_(0.36)N多量子阱(MQWs)结构.通过双晶X射线衍射(DCXRD)、原子力显微镜(AFM)和阴极荧光(CL)等测试技术,分别对样品的结构和光学特性进行了表征.在DCXRD图谱中,可以观察到明显的MQWs衍射卫星峰,通过拟和,MQWs结构中阱和垒的厚度分别为2.1和9.4 nm,Al组分分别为0.48和0.54.在AFM表面形貌图上,可以观察到清晰的台阶流,表明MQWs获得了二维生长;与此同时,MQWs结构存在一些裂缝,主要原因为AlGaNMQWs结构和下层GaN层间存在很大的应力.CL测试表明,AlGaN MQWs结构的发光波长为295 nm,处于深紫外波段,同时观察到处于蓝光、绿光波段的缺陷发光.

掺铒氢化非晶氧化硅1.54μm发光性质的研究

采用等离子体增强化学汽相沉积技术生长不同氧含量的氢化非晶氧化硅薄膜(a-SiO_x:H),离子注入铒及退火后在室温观察到很强的光致发光。当材料中氧硅含量比约为1和1.76时，分别对应77K和室温测量时最强的1.54μm光致发光。从15到250K的变温实验显示出三个不同的强度与温度变化关系，表明氢化非晶氧化硅中铒离子的能量激发和发光是一个复杂的过程。提出氢化非晶氧化硅薄膜中发生铒离子来自于富氧区，并对实验现象进行了解释。氢化非晶氧化硅中铒发光的温度淬灭效应很弱。从15到250K,光致发光强度减弱约1/2。

氧、硼、磷掺杂对氢化非晶硅中铒1.54μm发光的作用

利用等离子体增强化学气相淀积(PECVD)技术生长氧、硼、磷掺杂的氢化非晶硅薄膜。在室温下注入铒离子后研究三种掺杂元素对铒离子发光的作用。室温下观察到很强的光致发光现象。氧的引入并且和铒离子形成发光中心，提高了铒离子的发光强度。退火实验表明氧、硼、磷的掺杂补偿了材料中的缺陷，提高了氢的逃逸温度，改善材料的热稳定性，使材料的退火温度因掺杂元素的加入而提高，铒的发光得到增强。讨论了铒离子的发光机制。