Generation of optimized wavelength-tunable optical pulse from an uncooled gain-switched Fabry-Perot semiconductor laser using optical amplifier as external light injection

We present a novel system design that can generate the optimized wavelength-tunable optical pulse streams from an uncooled gain-switched Fabry-Perot semiconductor laser using an optical amplifier as external light source. The timing jitter of gain-switched laser has been reduced from about 3 ps to 600 fs and the pulse width has been optimized by using our system. The stability of the system was also experimentally investigated. Our results show that an uncooled gain-switched FP laser system can feasibly produce the stable optical pulse trains with pulse width of 18 ps at the repetition frequency of 5 GHz during 7 h continuous working. We respectively proved the system feasibility under 1 GHz, 2.5 GHz and 5 GHz operation. (c) 2008 Elsevier B.V. All rights reserved.

A High Power Light Emitting Diode Module for Projection Display Application

Electron. Manuf. Packag. Technol. Soc. Chin. Inst. Electron.; IEEE Compon., Packag., Manuf. Technol. Soc. (IEEE-CPMT); Xidian University

Tb3+/Yb3+ heavily-doped tellurite glasses with efficient green light emission

Without introducing concentration quenching phenomenon, a few wt% of Tb3+ and Yb3+ ions were doped into a group of easily-fiberized tellurite glasses characterized by loose polyhedron structures and rich interstitial positions. Intense green upconversion emission from Tb3+ ions centered at 539 nm due to transition 5D4→7F5 was observed by direct excitation of Yb3+ ions with a laser diode at 976 nm. Optimizing the concentration ratio of Tb3+/Yb3+, a tellurite glass with composition of 80TeO2-10ZnO-10Na2O (mol%)+1.0wt% Tb2O3+3.0wt% Yb2O3 was found to present the highest green light intensity and therefore is especially suitable for efficient green fiber laser development.

运用含有偶氮苯的自组装单层膜在光化学条件下可逆地控制细胞黏附

细胞生物学研究的一个重要方向是动态地控制细胞在基底上的黏附。最近，随着表面化学的研究深入，尤其是对烷基硫醇在金基底上形成自组装单层膜（self-assembled monolayers, SAMs）这一体系的研究，使得人们能在分子水平的表面上控制细胞黏附。精氨酸-甘氨酸-天冬氨酸（arginine-glycine-aspartate, RGD）序列首先是从细胞外基质蛋白中分离出来的，能够识别并非共价结合细胞膜表面的整合素受体，从而促进细胞黏附。以前的一些工作已经证实，将含有RGD的肽链连接到SAMs表面之后，能够生物特异性地黏附动物细胞。已有的手段比如光照、电压、加热、微电极、微流控以及表面纳米形貌的梯度变化，都不能真正实现可逆地控制细胞黏附，原因是这些方法所用的化学有限；这些方法也不能得到完全抗拒细胞黏附的表面，原因是这些方法产生的表面缺陷等不完整。用两种不同波长的光（紫外光和可见光）照射偶氮苯，偶氮苯会发生可逆的光致异构变化，因此，偶氮苯的光致异构性质可以用来可逆地控制细胞在表面黏附。运用含有偶氮苯的混合SAMs，偶氮苯的末端连接GRGDS肽，混合SAMs中是以末端为六聚乙二醇的硫醇为背景，该SAMs修饰而成的表面能够黏附或者抗拒细胞黏附，其表面黏附性质取决于SAMs中偶氮苯的构象。该方法提供了一种在分子水平的表面上我们所了解到的唯一能可逆控制细胞黏附的方法，该方法需要用到的光源来自于标准荧光显微镜所配置的汞灯。 为了实现在金基底表面可逆的控制细胞黏附，我们合成了如下三个化合物： 由于化合物1的溶解性很差，几乎在所有溶剂里都不溶，所以不能直接用化合物1制备SAMs；化合物2能高效地抗拒细胞的黏附；化合物3的偶氮苯末端是活化酯，能够连接GRGDS肽，从而控制细胞黏附。 将化合物2和化合物3以一定的比例均匀混合在金基底表面形成SAMs，然后将GRGDS肽连接到偶氮苯(反式)的末端（通过GRGDS肽的甘氨酸上的伯胺基与偶氮苯末端的活化酯反应），从而得到细胞黏附的表面。用紫外光照射该细胞黏附表面5-10小时，随着偶氮苯的构象由反式变为顺式，偶氮苯末端的GRGDS肽淹没在化合物2的六聚乙二醇中，得到抗拒细胞黏附的惰性表面。再用可见光照射该惰性表面1个小时，随着偶氮苯的构象由顺式变为反式，原先埋没在六聚乙二醇中的GRGDS肽伸展至单层膜的末端，又得到了细胞黏附的表面。因此，该表面能完全可逆地控制细胞在金表面黏附。 An important area in cell biology is the dynamic control of cell adhesion on substrates. Recent advancements in surface chemistry, in particular, self-assembled monolayers (SAMs) of alkanethiols on gold substrates, have permitted unprecedented control of cell adhesion via molecularly defined surfaces. The tri-peptide sequence arginine-glycine-aspartate (RGD), initially isolated from the extracellular matrix (ECM) proteins, can recognize and non-covalently bind with integrin receptors on cell membranes to promote cell adhesion. Some previous work has demonstrated that RGD peptide grafted on SAMs can allow bio-specific adhesion of mammalian cells that mimic natural adhesion. Existing technologies such as light, voltage, heat, microelectrodes, microfluidic systems and surface gradient of nanotopography, either cannot realize fully reversible control of cell adhesion, due to the limitation in the chemistry used, or cannot yield a surface completely resistant against cell adhesion, due to the imperfection of surfaces. Azobenzenes undergo reversible photo-induced isomerization rapidly at two different wavelengths of light (UV and visible light), it therefore potentially allows the reversible control of cell adhesion on a surface. By using a mixed SAMs presenting azobenzene groups terminated in GRGDS peptides in a background of hexa(ethylene glycol) groups, the surface can either accommodate or resist cell adhesion depending on the conformation of the azobenzene embedded in SAMs. This method provides the only means we know to control cell adhesion reversibly on a molecularly well-defined surface by using light generated by a mercury lamp equipped on standard fluorescence microscopes. To realize the reversible control of cell adhesion on gold surface, we synthesized three kinds of compounds as following, We found that it was difficult to obtain SAMs directly from compound 1 because of its poor solubility in almost all kinds of solvents; compound 2 can resist cell adhesion efficiently; compound 3 presents an azobenzene terminated with NHS-activated ester, which can couple with a GRGDS peptide to control cell adhesion. After coating a gold surface with compound 2 and 3 in appropriate ratios to form a SAM followed by coupling the GRGDS peptides with NHS-activated esters at the end of azobenzene (E configuration) resulted in a cell-adhesive SAM. Irradiating this cell-adhesive SAM with UV light for 5-10 h converted the E configuration of azobenzene into the Z form, the GRGDS peptides becoming masked in the PEG, resulting in a cell-resistant surface. These SAM could again support cell adhesion as a result of the conformational switch of azobenzene from Z to E with the irradiation of visible light for 1 h. This surface, therefore, allows completely reversible control of cell adhesion on a gold surface.

三种豆科灌木对干旱胁迫的响应与适应

干旱胁迫是全球范围内影响植物生存、生长和分布的重要环境因子。岷江上游干旱河谷区，由于生态环境的脆弱性和长期人类活动的干扰和过度利用，导致植被严重退化，水土流失加剧，山地灾害频繁，干旱化和荒漠化趋势明显。这种趋势若不能遏制，将严重阻碍区域社会经济的快速协调发展，并且威胁成都平原地区的发展和长江中下游地区的生态安全。因而开展干旱河谷生态恢复研究成为解决这些问题的关键。水分匮乏是限制干旱河谷生态恢复的关键因子，在全球气候变化的背景下，干旱胁迫在区域尺度上可能会更加严重，并使干旱河谷的生态环境更加恶化。因此，深入研究干旱河谷乡土植物对干旱胁迫的响应和适应机理，具有非常重要的理论和实践意义。 本论文以岷江上游干旱河谷的三种乡土豆科灌木，白刺花（Sophora davidii）、小马鞍羊蹄甲（Bauhinia faberi var. microphylla）和小雀花（Campylotropics polyantha）理论和实践意义。为研究对象，在人工控制条件下设计了4-5个连续性干旱胁迫处理，系统地研究了灌木幼苗的生长、生物量积累和水分利用效率（WUE）、形态结构和生理过程等对干旱胁迫的反应，揭示了幼苗的干旱适应能力及种间差异。主要研究结论如下： 1) 灌木生长和繁殖对干旱胁迫的反应 在干旱胁迫下，幼苗生长速率显著减小，叶片衰老和脱落比率增大，这些变化随着胁迫强度的增加具有累积效应。叶片比茎对干旱胁迫的反应更敏感。在严重干旱胁迫下，幼苗的有性繁殖被限制，但在中等程度干旱胁迫下，幼苗的有性繁殖能力被提高。 2) 灌木生物量积累及其分配和WUE对干旱胁迫的反应 在干旱胁迫下，灌木各器官的生物量都显著减小，但是生物量的分配侧重于地下部分，使得根茎比在干旱条件下增大。幼苗的耗水量（WU）随着干旱胁迫的增加而显著减少。白刺花和小马鞍羊蹄甲WUE在干旱胁迫下降低；小雀花的WUE在中等干旱胁迫下升高。 3) 灌木叶片结构特征对干旱胁迫反应 白刺花叶片具有较为典型的旱生型结构，而小马鞍羊蹄甲和小雀花则为中生型结构。在1至2年的干旱胁迫下，灌木叶片结构组成未发生本质性的改变，主要是细胞大小的变化。在中等和严重干旱胁迫下，叶肉组织厚度明显减小；并且气孔和表皮细胞面积也显著减小，气孔和表皮细胞密度显著增大；叶肉细胞层数、P/S值、表皮厚度等无显著变化。 4) 灌木对干旱胁迫的生理响应 气体交换参数和叶片相对含水量（RWC）在中等干旱胁迫下发生了明显的改变，而叶绿素荧光参数和光合色素含量在严重干旱胁迫下才发生显著变化。在干旱胁迫下，净光合作用速率（Pn）、气孔导度（gs）和RWC呈下降趋势，而叶片温度（Tl）呈增加趋势，蒸腾速率（Tr）的变化不明显。除了日最大Pn减小以外，干旱胁迫对气体交换参数的日变化无显著影响，但是对光合-光响应曲线有显著的影响，使有效光合时间缩短。在严重干旱胁迫下光系统受到损害而代谢减弱，PSⅡ中心的内禀光能转换效率（Fv/Fm）、量子产量（Yield）、光化学淬灭参数（qP）显著降低，而非光化学淬灭参数（NPQ）明显增加。气孔限制和非气孔限制对Pn的影响与干旱胁迫强度有关。在中度胁迫下，气孔限制起主导作用，在严重胁迫下非气孔限制起主导作用，40% FC水分条件可能是灌木由气孔限制向非气孔限制的转折点。 5) 灌木对干旱胁迫的适应能力及其种间差异 三种灌木对干旱胁迫具有较好的适应能力，即使在20% FC，幼苗未因干旱胁迫III而死亡；80% FC适宜于幼苗生长。白刺花生长速率慢，耗水量较少，具有较强的耐旱和耐贫瘠能力，并具有干旱忍受机制，能够在较干旱的环境中定居和生长。小马鞍羊蹄甲和小雀花，生长快，水分消耗量较大，尤其是小雀花，对干旱胁迫的忍受能力较弱，具有干旱回避机制，因而适宜于在较为湿润的生境中生长。综合分析表明，生长速率较慢的物种抗旱能力较强，其更适宜于作为干旱地区植被恢复物种。 Drought is often a key factor limiting plant establishment, growth and distribution inmany regions of the world. The harsh environmental conditions and long-termanthropogenic disturbance had resulted in habitat destruction in the dry valley ofMinjiang river, southwest China. Recently, it tended to be more severe on the vegetationdegradation, soil erosion and water loss, natural disaster, as well as desertification, whichimpact on regional booming economy and harmonious development, and would be verydangerous to the environmental security in the middle and lower reaches of Yangzi River.Therefore, ecological restoration in the dry valley is one of the vital tasks in China. Waterdeficit is known to affect adversely vegetation restoration in this place. Moreover, in thecontext of climate change, an increased frequency of drought stress might occur at aregional scale in the dry valleys of Minjiang River. The selection of appropriate plantingspecies for vegetation restoration in regard to regional conditions is an important issue atpresent and in further. The research on responses of indigenous species to drought stresscould provide insights into the improvement of the vegetation restoration in the dry valleys of Minjiang River. In this paper, the responses of three indigenous leguminous shrubs, Sophora davidii,Bauhinia faberi var. microphylla and Campylotropics polyantha, to various soil watersupplies were studied in order to assess drought tolerance of seedlings, and to compare interspecific differences in seedlings’ responses to drought stress. The results were as follows: 1 Growth and reproduction of shrubs in response to drought stress Seedling growth reduced significantly while leaf senescence accelerated underdrought stress, the cumulative responses to prolonged drought were found. The capacityfor reproduction was limited by severe drought stress, and improved by moderate droughtstress. Leaf responses were more sensitive than shoot to various water supplies. 2 WUE, biomass production and its partitioning of shrubs in response to drought stress Drought stress reduced significantly the total dry mass and their components ofseedlings, and altered more biomass allocation to root system, showing higher R/S ratiounder drought. Water use (WU) and water-use efficiency (WUE) of both S. davidii and B.faberi var. microphylla declined strongly with drought stress. The WU C. polyantha ofalso declined with drought stress, but WUE improved under moderate drought stress. 3 Anatomical characteristics and ultrastructures of leaves in response to drought stress There were xeromorphic for S. davidii leaves and mesomorphic for B. faberi var.microphylla and C. polyantha at the all water supplies. The foundational changes in leafstructures were not found with drought stress. However, mesophyll thickness, the areas ofstomatal and epidermis reduced slightly while the densities of stomatal and epidermisincreased under severe drought stress. Variations in these parameters could mainly be duoto cell size. Other structures did not displayed significant changes with drought stress. 4 Physiological responses of shrubs to drought stress The gas exchange parameters and leaf relative water content (RWC) were affectedby moderate stress, while chlorophyll fluorescence and chlorophyll content were onlyaffected by severe stress. Drought stress decreased net photosynthesis rate (Pn), stomatalconductance, light-use efficiency and RWC, and increased leaf temperature. Therespiration rates (Tr) were kept within a narrower range than Pn, resulting in aprogressively increased instantaneous water use effiecency (WUEi) under drought stress.Moreover, drought stress also affected the response curve of Pn to RAR, there was adepression light saturation point (Lsat) and maximum Pn (Pnmax) for moderate andsevere stressed seedling. However, diurnal changes of gas exchange parameters did notdiffer among water supplies although maximum daily Pn declined under severe stress.VISevere stress reduced Fv/Fm, Yield and qP while increased NPQ and chlorophyll content.Photosynthetic activity decreased during drought stress period due to stomatal andnon-stomatal limitations. The relative contribution of these limitations was associatedwith the severity of stress. The limitation to Pn was caused mainly by stomatal limitationunder moderate drought stress, and by the predominance of non-stomatal limitation undersevere stress. In this case, 40% FC water supply may be a non-stomatal limitation 5 Interspecific differences in drought tolerance of shrubs Three shrubs exhibited good performance throughout the experiment process, evenif at 20% FC treatment there were no any seedlings died, 80% FC water supply wassuitable for their establishment and growth. S. davidii minimized their water loss byreducing total leaf area and growth rate, as well as maintained higher RWC and Pncompared to the other two species under drought stress, thus they might be more tolerantto the drought stress than the other two species. On the contrary, it was found that C.polyantha and B. faberi var. microphylla had higher water loss because of their stomatalconductance and higher leaf area ratios. They reduced water loss with shedding theirleaves and changing leaf orientation under drought stress. Based on their responses, thestudied species could be categorized into two: (1) S. davidii with a tolerance mechanismin response to drought stress; (2) C. polyantha and B. faberi var. microphylla withdrought avoidance mechanism. These results indicated that slow-growing shrub speciesare better adapted to drought stress than intermediate or fast-growing species in present orpredicted drought conditions. Therefore, selecting rapid-growing species might leavethese seedlings relatively at a risk of extreme drought.