Global positioning system measurements for crustal deformation: precision and accuracy

Analysis of 27 repeated observations of Global Positioning System (GPS) position-difference vectors, up to 11 kilometers in length, indicates that the standard deviation of the measurements is 4 millimeters for the north component, 6 millimeters for the east component, and 10 to 20 millimeters for the vertical component. The uncertainty grows slowly with increasing vector length. At 225 kilometers, the standard deviation of the measurement is 6, 11, and 40 millimeters for the north, east, and up components, respectively. Measurements with GPS and Geodolite, an electromagnetic distance-measuring system, over distances of 10 to 40 kilometers agree within 0.2 part per million. Measurements with GPS and very long baseline interferometry of the 225-kilometer vector agree within 0.05 part per million.     

Global distribution of crustal magnetization discovered by the mars global surveyor MAG/ER experiment

Vector magnetic field observations of the martian crust were acquired by the Mars Global Surveyor (MGS) magnetic field experiment/electron reflectometer (MAG/ER) during the aerobraking and science phasing orbits, at altitudes between approximately 100 and 200 kilometers. Magnetic field sources of multiple scales, strength, and geometry were observed. There is a correlation between the location of the sources and the ancient cratered terrain of the martian highlands. The absence of crustal magnetism near large impact basins such as Hellas and Argyre implies cessation of internal dynamo action during the early Naochian epoch ( approximately 4 billion years ago). Sources with equivalent magnetic moments as large as 1.3 x 10(17) ampere-meter2 in the Terra Sirenum region contribute to the development of an asymmetrical, time-variable obstacle to solar wind flow around Mars.     

Production of isotopic variability in continental basalts by cryptic crustal contamination

Regional variations in the Nd, Sr, and Pb isotopic compositions of Neogene basalts from the western United States are commonly interpreted to originate in the subcontinental mantle. In southern California, isotopic variability is restricted to lavas that lack mantle-derived xenoliths; xenolith-bearing basalts have uniform isotopic compositions similar to those of ocean-island basalts (OIBs). Combined with available geochemical data, these observations suggest that isotopic variability at these volcanoes results from subtle crustal contamination, locally by mafic crust, of primitive OIB-like magma. Recognition of such cryptic contamination may help to reconcile local discrepancies between tectonic and isotopic views of the subcontinental mantle.     

GRACE measurements of mass variability in the Earth system

Monthly gravity field estimates made by the twin Gravity Recovery and Climate Experiment (GRACE) satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers. The annual cycle in the geoid variations, up to 10 millimeters in some regions, peaked predominantly in the spring and fall seasons. Geoid variations observed over South America that can be largely attributed to surface water and groundwater changes show a clear separation between the large Amazon watershed and the smaller watersheds to the north. Such observations will help hydrologists to connect processes at traditional length scales (tens of kilometers or less) to those at regional and global scales.     

利用mtDNA d-loop分析石迁野生鸳鸯在系统发育中的定位

采用PCR产物直接测序主法测定鸳鸯线粒体DNA(mtDNA)控制区的全序列,测定其与GenBank上已知雁形目28个物种的遗传距离,并构建系统发育树 结果表明,试验样品鸳鸯(采白贵州石阡县)mtDNA d-loop序列全长为1 035 bp,与欧洲鸳鸯(GenBank登录号AY112953)的遗传距离最近、为0.002,NJ分子系统树也显示两者同属一个分支,即鸳鸯为雁形目鸭科柄鸭族鸳鸯属,这与传统分类学方法一致.     

中国花卉业发展现状及方向

本文从我国花卉生产的面积、产值、区域布局、管理体制、政策、标准、新品种和技术的应用与推广和园林市场的发展阐述了中国花卉业发展的现状；从世界花卉业生产布局的调查和我国花卉生产、花卉品种的优势、潜力、花卉延伸开发产业分析了我国花卉业的发展方向；认为我国花卉业将成为国民经济中的又一具有活力的支柱产业。     

全球金融危机对我国大学生就业的影响

金融危机严重影响了中国大学生就业,通过对全国1万多名大学生和几百家企业进行认真的实地调研,深入了解了当前我国大学生就业的真实情况,并对调研结果进行了认真总结和细致分析,从政府、企业、高校、大学生等角度提出了解决大学生就业难的措施.     

Hardening by annealing and softening by deformation in nanostructured metals

We observe that a nanostructured metal can be hardened by annealing and softened when subsequently deformed, which is in contrast to the typical behavior of a metal. Microstructural investigation points to an effect of the structural scale on fundamental mechanisms of dislocation-dislocation and dislocation-interface reactions, such that heat treatment reduces the generation and interaction of dislocations, leading to an increase in strength and a reduction in ductility. A subsequent deformation step may restore the dislocation structure and facilitate the yielding process when the metal is stressed. As a consequence, the strength decreases and the ductility increases. These observations suggest that for materials such as the nanostructured aluminum studied here, deformation should be used as an optimizing procedure instead of annealing.     

Devon Acres CSA: local struggles in a global food system

This paper focuses on examining the dynamic nature of community supported agriculture (CSA) and the real-world experiences which mark its contours, often making it distinct from the early idealized CSA “model.” Specifically, our study examines the narratives of the farmers of Devon Acres CSA over its duration, in tandem with a survey of recent shareholders in order to understand and explain its evolution. The framework we develop here shows that this CSA is largely characterized by instrumental and functional beliefs and practices, with some elements in the collaborative mode. A key contribution of this research is the development of a framework which helps to highlight the relative fluidity and patchwork quality of CSA participant positions over time. At Devon Acres, the real-world factors and issues influencing CSA evolution are seen to be products of both the local and larger contexts, evident in such areas as shifts in farmer learning and adaptation, differences between beliefs and practices in member volunteer efforts, and changes in farm and resource conditions. With respect to CSA more broadly, we argue that the reality of dominant food system context and site-specific influences on CSA development compels us to rework our attachment to early idealized “model” traits. Expansion in CSA numbers, evidence of adaptation and situated learning, and retention of the local and organic as core traits, speak to the pragmatic yet transformative potential of CSA contribution to food system change.

Using global organic markets to pay for ecologically based agricultural development in China

The traditional command and control approach and the more recent free market have proven inadequate for promoting ecological agricultural development in China. Organic certification represents a regulated market mechanism with the potential to stimulate ecologically based agricultural research, extension, and investment. Recent linkages between the global organic food industry and local agricultural development in China provide an opportunity to test this potential. The article examines Chinas two largest organic certification systems for their potential to promote the adoption of integrated pest management (IPM) as a key component of ecological agriculture. Organic certification is providing a format for research, extension, and implementation of IPM principles and practices, and has the potential to do much more. However, possible contradictions between ecological and market rationality, inherent in organic certification and marketing systems, may be exacerbated by the authoritarian political economy of rural China.Paul Thiersis an assistant professor of Political Science at Washington State University Vancouver where he teaches comparative politics, political economy, and environmental policy in the Program in Public Affairs. His research focuses on the environmental, social, and political dynamics of globalization in rural China, with a particular emphasis on Chinas integration into global food trade and food standards.     

我国证券信息披露制度研究

信息披露制度起源于英国,完善发展于美国,已成为现代证券市场的核心内容。目前,我国已建立了基本的信息披露制度,但由于利益驱使、监管不力等因素,违法信息披露行为时有发生,严重阻碍了证券市场的健康发展。因此从我国证券信息披露制度存在的问题入手,分析原因,为完善信息披露制度提出合理的建议。     

建设社会主义新农村统计制度探索

本文阐述了统计工作在建设社会主义新农村中的意义,分析了目前统计工作存在的不足,最后就如何完善新农村建设中统计制度提出若干措施。     

植物生态系统中的植硅体闭蓄有机碳及其在全球土壤碳汇中的重要作用

植硅体闭蓄有机碳（phytolith—occluded organiccarbon,PhytOC）是封存在植硅体中的有机碳。在土壤环境中受到具有高度抗分解能力的植硅体的保护,它可以长期（数千年至万年以上）封存在土壤剖面中,从而成为陆地土壤长期（万年尺度）固碳的重要机制之一。以千年的时间尺度来衡量,估计全球土壤有机碳的平均积累率为2．4g·m^-2．a^-1,其中PhytOC积累贡献了15．0％～37．0％。通过选择种植高产PhytOC的植物物种来增加短期和长期碳汇的途径是存在的。大多数的农作物如大麦Hordeumvulgare,玉米Zeamays,水稻Oryzasativa,高粱Sorghumvulgare,甘蔗Saccharumofficinarum和小麦Triticumaestivum已知是植硅体的生产者。估计全球上述作物每年生产的PhytOC高达（5．08～12．01）×10^6t.a^-1。综述了植物生态系统中PhytOC的形成机制与特征、积累率、提高土壤PhytOC积累率的农学措施及其在全球土壤碳汇中的重要作用。     

2种常用的全球土地利用/覆被历史数据集在中国区域的精度评价

【目的】分析全球土地利用/覆被历史数据集在中国区域的精度。【方法】分别搜集耕地、草地的统计资料和空间数据以及林地的统计资料,采用升尺度方法对耕地和草地的空间数据进行处理,分析全球土地利用/覆被历史数据集SAGE和HYDE 3.1与我国统计资料中耕地、林地和草地面积的差异。【结果】SAGE数据集中耕地、草地和林地面积与我国统计数据相差较大,HYDE 3.1数据集中耕地和草地面积与我国统计数据虽然相近,但其反映的耕地和草地面积变化趋势以及空间分布与我国实际情况存在较大差距。【结论】鉴于全球土地利用/覆被历史数据集SAGE和HYDE 3.1在我国的精度较低,因此有必要依据国内的历史统计资料,重建一套适用于中国的高精度土地利用数据集,以服务于我国气候变化研究。     

专家系统在我国农业上的应用

本文概述了农业专家系统的研究发展过程、结构框架和设计基础,分析了进入新世纪以来我国农业专家系统应用的现状和存在的问题,并对农业专家系统的进一步发展进行了讨论。     

中国节水农作制度发展趋势探讨

建立有区域特色的节水农作制度,将工程节水技术、农艺节水技术、生物节水技术和管理节水技术进行有机结合与集成,提高节水农业的综合效益,是当前国内外节水农业发展的普遍趋势.本研究重点对节水农作制度的概念、基本特征、研究框架等进行了探讨,总结分析了国外节水农作制度发展的模式、技术、政策及其效果.在此基础上,结合我国节水农作制度发展的趋势和问题,提出了我国节水农作制度发展的重点方向,包括:1)从区域多样化出发,构建区域节水型和适水型的农业生产结构;2)加强节水技术标准规范化、技术模式多样化及区域性的综合节水农作制配套技术体系等关键技术研究;3)进一步深化缺水条件下作物需耗水量特征及节水优化灌溉指标体系与模式研究以及区域主导性节水优化种植模式评价与筛选等共性理论问题研究;4)加强研究农民参与的旱作节水技术推广模式,建立相应的管理制度和政策支持措施,制定区域节水农作制度预案.     

中国湿地分类编码系统研究

湿地分类是湿地科学研究中最复杂的问题之一,直到现在还没有一个能为研究者们广泛认同的分类原则和分类系统.我国湿地资源丰富,种类多样,为了方便湿地资源的管理,必须确立一个科学而全面的分类系统,并在此分类系统的基础上进行编码,这是实现湿地资源信息化以及科学管理湿地的前提和基础.该文从湿地所处的行政区划、地貌、气候、植被等自然要素出发,结合《湿地公约》对湿地的分类标准,对我国的湿地进行了分类编码研究      

论我国律师辩护制度的完善

律师刑事辩护制度的科学化程度是衡量一个国家法治文明与司法公正的一个重要标志。针对我国律师参与刑事辩护越来越低的现状和我国律师辩护制度的不足，应以控辩平衡为理论基础，借鉴国外的有益经验，从辩护律师的身份定位、准入门槛及执业权利三方面来完善我国的辩护律师制度。     

我国农业信息化与网络化发展概况

信息化(Informatization)起源于60年代的日本，西方70年代后期开始使用这一概念，我国80年代才开始使用。 关于信息化有几种表述：①信息化就是计算机、通信和网络技术的现代化；②信息化就是从物质生产占主导地位的社会向信息产业占主导地位社会转变的发展过程；③信息化就是从工业社会向信息社会演进的过程。 至于信息化和国家信息化，一般认为：①信息化是指培育、发展以智能化工具为代表的新的生产力并使之造福于社会的历史过程。②国家信息化就是在国家统一规划和组织下，在农业、工业、科学技术、国防及社会生活各个方面应用现代信息…