鄂尔多斯东胜地区土地覆盖的景观格局

利用ETM影像数据,通过遥感软件、地理信息系统软件进行多通道合成、几何校正和空间分析,并运用景观指数对鄂尔多斯东胜地区土地覆盖景观格局进行定量分析和评判.结果表明:研究区的植被景观类型可划分为18种.典型草原丘陵区的斑块数为921,平均斑块面积18km2,分维数为2.7125,景观分离度指数为4.4208;典型草原丘陵区受人为干扰和其他外力作用最小,存在优势景观类型;典型草原沙化区平均斑块面积10km2,分维数为4.1421,景观分离度指数为7.1829,最大缀块指数0.0153;荒漠草原区平均斑块面积13km2,分维数变动范围为-166.58～25.36,景观分离度指数为10.2243,最大缀块指数0.0156;城镇区分维数为1.91,景观分离度指数为0.10,最大缀块指数为0.8545.典型草原沙化区的景观多样性、景观破碎度最大,景观形状指数、景观隔离度和景观均匀度最高,景观优势度最低;荒漠草原区的景观优势度最大,景观均匀度最小;典型草原丘陵区景观破碎度和景观隔离度最小;典型草原平原区的景观多样性和景观形状指数最低.土地利用和土地覆盖变化是影响景观结构、功能及动态的主导因素之一.该结果可为生态脆弱区生物修复和生态保育提供案例借鉴.     

Structural basis for specific cleavage of Lys 63-linked polyubiquitin chains

Deubiquitinating enzymes (DUBs) remove ubiquitin from conjugated substrates to regulate various cellular processes. The Zn(2+)-dependent DUBs AMSH and AMSH-LP regulate receptor trafficking by specifically cleaving Lys 63-linked polyubiquitin chains from internalized receptors. Here we report the crystal structures of the human AMSH-LP DUB domain alone and in complex with a Lys 63-linked di-ubiquitin at 1.2 A and 1.6 A resolutions, respectively. The AMSH-LP DUB domain consists of a Zn(2+)-coordinating catalytic core and two characteristic insertions, Ins-1 and Ins-2. The distal ubiquitin interacts with Ins-1 and the core, whereas the proximal ubiquitin interacts with Ins-2 and the core. The core and Ins-1 form a catalytic groove that accommodates the Lys 63 side chain of the proximal ubiquitin and the isopeptide-linked carboxy-terminal tail of the distal ubiquitin. This is the first reported structure of a DUB in complex with an isopeptide-linked ubiquitin chain, which reveals the mechanism for Lys 63-linkage-specific deubiquitination by AMSH family members.     

中美在城市水源地供水过程中生态补偿的差异性(英文)

饮用水源保护是确保饮用水安全的重要保障.为了深入探讨不同国家生态补偿的经验教训,以城市供水系统为案例,分析美国纽约州与中国北京密云水库在城市供水过程中生态服务付费的差异性.结果表明:虽然美国和中国之间的生态补偿制度具有一定的独特性,但美国在市郊水库为纽约市政供水过程中的补偿效应值得中国借鉴.中国的生态补偿中的关键步骤必须包括生态效益评价的数量化和货币化.此外,现有研究结果认为,美国在公众参与生态补偿全过程的做法值得中国效法,而中国的退耕还林工程的生态效率和效益值得美国借鉴.