A NEW TYPE OF SILICON-ON-INSULATOR WITH A PERFECT SURFACE SILICON LAYER

A novel silicon structure consisting of a silicon-on-defect layer (SODL), with enhanced surface Hall mobility in the surface layer on a buried defect layer (DL), has been discovered [J. Li, Nucl. Instr. and Meth. B59/60 (1991) 1053]. SODL material was formed by using proton implantation and subsequent two-step annealing. The implantation was carried out with a Varian 350D ion implanter. Based on the discovery, a standard measurement method (current-voltage curve method) was adopted to measure the true resistivity value of the DL in order to replace the spreading resistivity measurement by which the true resistivity in seriously defective silicon cannot be obtained. By adopting the current-voltage current method, the true resistivity value of the DL is measured to be 4.2 x 10(9) OMEGA cm. The SODL material was proved to be a silicon-on-insulator substrate.

川西云杉(Picea balfouriana)天然群体的遗传变异

青藏高原东南缘由于特殊的生态地理条件，有着丰富的森林资源，这些资源是长江上游涵养水源、保持水土的生态屏障，是生物多样性的资源宝库。但随着过量的森林采伐，使该区曾经丰富的生物多样性资源遭受了前所未有的破坏，天然林的质量严重下降，生态系统退化，功能减弱。与此同时，许多物种的种群规模正在锐减，物种的遗传多样性也严重丧失。川西云杉是西部地区分布最广的云杉树种之一，在较高海拔的地区有着重要的生态学功能，是一种适应性很强的乡土树种。本项目采用简单序列重复标记(SSR)和特定序列位点(STS)研究不同生境条件下川西云杉群体的遗传变异及其时空分布格局，考察遗传变异与复杂的山地生态环境间的潜在联系，系统地揭示川西云杉天然群体与环境系统相互作用的生态适应与分子进化机制。研究成果能有效地为该树种遗传资源的科学保护与合理利用提供理论依据和科学指导，可为中国西南部亚高山天然林的可持续经营及退化生态系统的恢复与重建提供依据。主要研究结果如下： 1 STS和SSR两种分子标记的研究结果表明：川西云杉群体拥有中等水平的遗传多样性(基于SSR标记，平均He = 0.640；基于STS标记，平均He = 0.553)。造成这种中等水平的遗传多样性，可能是由于历史原因，川西云杉天然林被大量采伐，导致了遗传多样性的丧失。两种方法都检测出群体BT有着最高水平的遗传多样性。 2 两种标记的结果都一致说明：检测的10个川西云杉群体间遗传分化比较高，其存在群体间的遗传变异比例要明显地高于广泛分布的挪威云杉、横贯大陆的黑云杉以及兼有连续分布和不连续分布的西加云杉等，但要低于分布范围狭窄且呈不连续分布的粗枝云杉。青藏高原东南部的片段化生境可能是导致高水平遗传分化的主要原因。 3 基于两种标记的UPGMA 聚类和PCA分析结果，以及基于SSR标记的FCA分析结果都显示：群体BY遗传上明显区别于其它群体，其可能原因是青藏高原东南缘山脉阻隔而导致的生殖隔离的结果。 4 根据软件Bottleneck 1.2.02的检测以及不依赖哈迪一温伯格平衡的M比率检测结果：川西云杉种群很有可能经历了近期的遗传瓶颈效应。在本研究中遗传瓶颈效应并没有显著影响到物种的遗传多样性。然而，在这些片断化群体未来的子代群体中很可能出现遗传瓶颈导致的遗传多样性下降的效应。 Due to the extremely complex topography and climatic conditions, the southeast of the Qinghai-Tibet Plateau is region abundant in forest resource, which is benefit to the upper reaches of the Yangtze River water conservation, and protecting natural environment and biodiversity resources. However, by the reason of a plenty of trees were cut in these yeas, the biodiversity resource was destroy with degraded ecosystem and imperfect funcation. Picea balfouriana is one of the regionally distributed conifer species in the southeast of the Qinghai-Tibet Plateau and considered as a constructive species within its distribution area. It is an optimal species for the production of biomass. Moreover, it is well adapted to stressful environments at high altitude, especially to cold and drought conditions which are generally harsh for other trees. In our study, two types of molecular markers (SSR and STS) were used to estimate the genetic diversity and genetic structure of P. balfouriana populations originating from the southeast of the Qinghai-Tibet Plateau with varying climatic and geographical conditions. The results will not only provide a deep insight into its genetic diversity and population genetic structure but also valuable information for further management and breeding programs in P. balfouriana. In summary, the results obtained in this study revealed that: 1 A moderate degree of genetic variation is present in P. balfouriana in the southeast of the Qinghai-Tibet Plateau and it may caused by many trees were cut in the past. Population BT owns the highest level of genetic diversity by both two types of markers. 2 Considerable population differentiation exists among the ten P. balfouriana populations based on both SSR and STS markers, possibly caused by habitat fragmentation and heterogeneous environments. 3 The UPGMA clustering and PCA analyses based on SSR and STS marker, and FCA analyses based on SSR marker congruously separated population BY from other populations, which is likely due to the presence of mountain barriers. 4 The results of bottleneck analysis indicated that P. balfouriana populations that have undergone recent declines. In our research, the bottleneck effect don’t have a significant impact on the genetic diversity of species, however, the level of genetic diversity of P. balfouriana offspring populations growing in the fragmented habitats will decline in the future.

Biopotentials of marine sponges from China oceans: past and future

An extensive literature survey of over 17 Journals was carried out on Chinese sponges and their natural products in the period from 1980 to 2001. This review is thus intended to provide the first thorough overview of research on marine sponges from China Ocean territories. Information is provided about the rather-limited taxonomic study of Chinese marine sponges, with an analysis on their distribution and diversity. Research findings on the natural products and their bioactivity screening from Chinese sponges are summarized. The weaknesses, gaps and problems in the past R&D program of Chinese sponges are identified, which point to the future opportunities in exploiting these huge untapped sponge resources. The report is expected to serve as an entry point for understanding Chinese sponges and for furthering R&D on their bioactive compounds for new drug development. (C) 2003 Elsevier Science B.V. All rights reserved.

Further study on double-melting endotherms of isotactic polypropylene

The origins of the single- and double-melting endotherms of isotactic polypropylene crystallized at different temperatures were studied carefully by differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering. The experimental data show that spontaneous crystallization occurs when the crystallization temperature is lower than 117 degrees C; thus the lamellae formed are imperfect. At a lower heating rate, the recrystallization or reorganization of these imperfect lamellae leads to double endotherms. On the other hand, when the crystallization temperature is higher than 136 degrees C, two major kinds of lamellae with different thickness are developed during the isothermal process, which also results in the double-melting endotherms. In the intermediate temperature range the lamellae formed are perfect, and there is only a single peak in the distribution of lamellar thickness. This explains the origin of the single-melting endotherm. (C) 2000 John Wiley & Sons, Inc.

Morphology and structure of micro-fibrillar crystal of nylon 10 10

The nanoscale and microscale fibrillar crystals of nylon 10 10 were obtained by atomizing the very dilute formic acid solution. The length-diameter ratio of these fibrillar crystals increases as the concentration of the atomizing solution increases. Electron diffraction (ED) analysis showed that the hydrogen-bonded sheet in these solution-grown fibrillar crystals was imperfect and had a lower order. Both electron diffraction and characteristic morphology show that melt-crystallized fibrillar crystals always possess perfect packing order and stable structure. A rather perfect ED pattern of the triclinic form of nylon 10 10 along the [001] zone was obtained by tilting the specimen 41 degrees along the elongated direction of the crystal. Fibrillar crystals from bulk have a great tendency to aggregate with parallel packing to form crystal clusters, which look like shish kebabs in morphology. Spherulite is observed occasionally in the domains with very rich sample. (C) 2001 Elsevier Science Ltd. All rights reserved.

The double-melting behavior of poly(ether diphenyl ether ketone)

Poly(ether diphenyl ether ketone) (PEDEK) synthesized by the nucleophilic route has the following chemical structure: [GRAPHICS] At some given temperatures for a given time isothermally crystallized PEDEK sample exhibits two endothermic peaks which are similar to PEEK and PEEKK The melting behavior of PEDEK crystallized from the glassy state is investigated through differential scanning calorimeter (DSC). We consider that the high-melting peak is related to the perfect crystals and the low-melting peak is associated with a few imperfect crystals. (C) 1997 John Wiley & Sons, Inc.