First charge collection and position-precision data on the medium-resistivity silicon strip detectors before and after neutron irradiation up to 2x10(14) n/cm(2)

Test strip detectors of 125 mu m, 500 mu m, and 1 mm pitches with about 1 cm(2) areas have been made on medium-resistivity silicon wafers (1.3 and 2.7 k Ohm cm). Detectors of 500 mu m pitch have been tested for charge collection and position precision before and after neutron irradiation (up to 2 x 10(14) n/cm(2)) using 820 and 1030 nm laser lights with different beam-spot sizes. It has been found that for a bias of 250 V a strip detector made of 1.3 k Ohm cm (300 mu m thick) can be fully depleted before and after an irradiation of 2 x 10(14) n/cm(2). For a 500 mu m pitch strip detector made of 2.7 k Ohm cm tested with an 1030 nm laser light with 200 mu m spot size, the position reconstruction error is about 14 mu m before irradiation, and 17 mu m after about 1.7 x 10(13) n/cm(2) irradiation. We demonstrated in this work that medium resistivity silicon strip detectors can work just as well as the traditional high-resistivity ones, but with higher radiation tolerance. We also tested charge sharing and position reconstruction using a 1030 nm wavelength (300 mu m absorption length in Si at RT) laser, which provides a simulation of MIP particles in high-physics experiments in terms of charge collection and position reconstruction, (C) 1999 Elsevier Science B.V. All rights reserved.

长白植物区维管束植物多样性及其格局研究

本文应用植物区系分析、数量分类（TWINSPAN）、相似性比较和生物多样性指数评估等方法对长白植物区维管束植物多样性及其格局进行了比较系统的研究。 本文对长白植物区维管束植物区系研究表明，本区共有维管束植物142科624属1881种，此区系属于温带性质，地理联系广泛，与东亚其它地区特别是与日本的联系最为密切。 通过对本区物种多样性的水平分布格局研究，提出了全区86县市的植物组成、分化指数、Shannon-Wiener指数、G－F指数和物种重要值IM的分布格局，并着重对本区六大山地和二大平原的物种多样性进行了分析，指出本区长白山植物分布最为集中。长白山、辽东山地、小兴安岭和张广才岭是本区植物多样性较高的地区。长白山、辽东山地和小兴安岭是本区物种分化中心。 对本区代表性山地长白山的物种多样性垂直分布格局研究表明，各植被垂直带的物种多样性指数（G-F指数）随海拔升高而递减。随海拔增高，温带性质的区系成分逐渐减弱，寒带亚寒带性质成分逐渐增强。热带性质的成分只影响到阔叶红松林带和暗针叶林带。 本文的对长白植物区重要山地阔叶红松林的物种多样性做了对比研究，提出长白山的阔叶红松林物种丰富度最高。各主要山地的多样性指数没有随纬度变化而呈单一升降关系。TWINSPAN 以属为单位的聚类结果表明，本区阔叶红松林的24个样地可以分为7个类型，阔叶红松林中的33个乔木树种划分为8个关联组。 本文提出了一种用于大尺度多样性评估的方法——物种重要值比较法。这种方法计算简便，结果可靠，对于改善目前大尺度生物多样性评价方法较少的状况有积极意义。此外本文首次将G－F指数引入植物多样性研究领域，并对G－F指数、Shannon-Wiener指数和IM值的测度结果进行评估，确认F指数和IM值的测度结果最令人满意。