Long-wavelength monolithic mode-locked diode lasers

A detailed study of the design issues relevant to long-wavelength monolithic mode-locked lasers is presented. Following a detailed review of the field, we have devised a validated travelling wave model to explore the limits of mode-locking in monolithic laser diodes, not only in terms of pulse duration and repetition rate, but also in terms of stability. It is shown that fast absorber recovery is crucial for short pulse width, that the ratio of gain to absorption saturation is key in accessing ultrashort pulses and that low alpha factors give only modest benefit. Finally, optimized contact layouts are shown to greatly enhance pulse stability and the overall operational success. The design rules show high levels of consistency with published experimental data.

内蒙古退化草原对不同类型干扰的响应研究

本文结合野外调查、野外实验和模型模拟方法研究了内蒙古退化草原在继续放牧和啮齿类动物活动干扰下，植物多样性、种群空间格局、种间空间关联、小尺度鼠丘和小尺度空斑（Gap）上植被发展动态的生态响应。研究结果如下： （1）经过长期不同强度的放牧干扰后，无牧条件下植被盖度显著低于其它三个放牧（轻牧、中牧、重牧）条件下的植被盖度，而其它三个放牧条件之间的植被盖度差异不显著;无牧条件下羊草成为群落的优势种，轻牧和中牧条件下冷蒿依然是群落的优势种，这三种条件下寸草苔的种群盖度最大;重牧条件下优势种变为星毛委陵菜，并且其种群盖度最大;不同放牧退化阶段指示植物的种群盖度随放牧强度增大的变化趋势是：冷蒿为先增大后减小，而星毛委陵菜为先急剧增大，然后平缓增大，最后再急剧增大;植物多样性和均匀度指数在中牧条件下最大，在无牧条件下最小，说明中牧条件下群落的多样性最高，无牧条件下群落的多样性最小，而优势度指数的变化趋势和它们正相反。 （2）放牧对星毛委陵菜（或糙隐子草）种群空间格局有显著影响，即使在同一放牧强度下其种群在不同尺度上的空间格局存在显著差异。在小尺度上，植物种群主要呈现为集聚分布;同一放牧强度下随着尺度的增大，集聚分布趋向于随机和均匀分布;随着放牧强度的增大，物种的集聚分布消失的空间尺度缩短。 （3）不同放牧强度下，冷蒿和星毛委陵菜之间的空间关联存在显著的差异。在无牧和轻牧条件下，冷蒿和星毛委陵菜在小尺度（0-100cm）上主要呈负关联的空间关系，而在中牧和重牧条件下除了呈负关联的空间关系外，两个物种在空间上还是相互独立的。同时，放牧强度的增大缩小了负关联程度的峰值（最小值）。放牧强度越大，两物种之间的空间关系由负关联转变为相互独立的空间尺度越小（距离越短）。 （4）草原黄鼠鼠丘干扰显著降低了植物物种的丰富度（24种），同样，减少了不同功能组内的物种数，特别是多年生非禾本科草类减少的物种数最多;和周围的未受鼠丘干扰的植被比较，鼠丘上植物多样性减少了1.42，优势度减少了4.21，而均匀度增加了0.06;鼠丘上，多年生植物出现频率(0.37)大约是一年生植物出现频率(0.13)的四倍。具有高抗埋藏性的物种（寸草苔）和抗埋藏性的物种（冷蒿、冰草和糙隐子草）具有相对较高的出现频率。对于功能组来说，多年生非禾本科草类(PF, EF=0.51)具有最大的出现频率，接下来依次是多年生根茎禾草(PR, EF=0.46)、灌木和半灌木(SS, EF=0.32)、多年生丛生禾草(PB, EF=0.25)、一年生和两年生植物(AB, EF=0.13);鼠丘上，寸草苔的密度最大（244.43 个体/米2)。多年生非禾本科草类的密度(130.74个体/米2)远大于其他功能组的密度（PR，34.76个体/米2;PB，16.52个体/米2;AB，14.31个体/米2;SS，12.39个体/米2）;鼠丘上植被地上生物量(35.90克/米2)远远小于外围对照植被地上生物量(211.54克/米2)。冷蒿的地上生物量最大，其次是寸草苔。对于功能组，SS最大 (8.44克/米2) ，其次是PF (7.17克/米2)，这两个功能组的地上生物量远大于其他三个功能组的地上生物量（PR, PB和 AB分别是 3.23克/米2、1.40克/米2和2.49克/米2）。 （5）干扰产生空斑的拓殖受空斑大小和放牧历史的影响，植物拓殖空斑的方式随空斑形成后的时间而变化。空斑直径越大，其被拓殖的机会越大;具有高强度放牧历史群落中的空斑更易被植物拓殖;第一年对空斑的拓殖主要通过种子萌发;第二年，种子萌发方式（特别是一年生植物）拓殖空斑的比例有所降低，而通过地下根茎的克隆繁殖拓殖空斑的比例有所增加。

Present status and future scope of fisheries in the Andaman group of islands

The coastal area of approximately 2000 km and the water-bodies in between the Andaman and Nicobar islands are rich in fishery potential which range from 0.012-0.47 million tonnes. The fishery is dominated by catches of sardines, perches, carangids, mackerels, Leiognathus elasmobranchs, seerfish, mullets and tunas. About 2050 fishermen, with 1150 country craft, 113 mechanised boats and 1367 different kinds of nets and lines are engaged in active fishing in the island. Numerous bays, lagoons and creeks are available among the group of islands for mariculture activities. The mangroves of these islands provide feeding and nursery grounds for juveniles of penaeid prawns, crabs and finfishes.

Modelling and predictive control: Enabling technologies for reconfiguration

An approach to reconfiguring control systems in the event of major failures is advocated. The approach relies on the convergence of several technologies which are currently emerging: Constrained predictive control, High-fidelity modelling of complex systems, Fault detection and identification, and Model approximation and simplification. Much work is needed, both theoretical and algorithmic, to make this approach practical, but we believe that there is enough evidence, especially from existing industrial practice, for the scheme to be considered realistic. After outlining the problem and proposed solution, the paper briefly reviews constrained predictive control and object-oriented modelling, which are the essential ingredients for practical implementation. The prospects for automatic model simplification are also reviewed briefly. The paper emphasizes some emerging trends in industrial practice, especially as regards modelling and control of complex systems. Examples from process control and flight control are used to illustrate some of the ideas.

国际合作与生物多样性研究

<正> 生物多样性不依国界而分布,这一特点决定了完整的生物多样性研究必须通过国际合作才能实现。虽然我们国家的生物多样性资源十分丰富,但是,如果我们的研究仅仅局限于我国特有的材料,势必影响到科学问题的选择与解决。同时,由于我们课题组所研究的是基因组多样性与进化,这是一个新兴的交叉学科,涉及诸多的领域,如进化生物学、