The inner solar system cratering record and the evolution of impactor populations

We review previously published and newly obtained crater size-frequency distributions in the inner solar system. These data indicate that the Moon and the terrestrial planets have been bombarded by two populations of objects. Population 1,dominating at early times, had nearly the same size distribution as the present-day asteroid belt, and produced heavily cratered surfaces with a complex, multi-sloped crater size-frequency distribution. Population 2, dominating since about 3.8–3.7 Gyr,had the same size distribution as near-Earth objects(NEOs) and a much lower impact flux, and produced a crater size distribution characterized by a differential –3single-slope power law in the crater diameter range 0.02 km to 100 km. Taken together with the results from a large body of work on age-dating of lunar and meteorite samples and theoretical work in solar system dynamics, a plausible interpretation of these data is as follows. The NEO population is the source of Population 2 and it has been in near-steady state over the past ～ 3.7–3.8 Gyr; these objects are derived from the main asteroid belt by size-dependent non-gravitational effects that favor the ejection of smaller asteroids. However, Population 1 was composed of main belt asteroids ejected from their source region in a size-independent manner, possibly by means of gravitational resonance sweeping during orbit migration of giant planets;this caused the so-called Late Heavy Bombardment(LHB). The LHB began some time before ～3.9 Gyr, peaked and declined rapidly over the next ～ 100 to 300 Myr,and possibly more slowly from about 3.8–3.7 Gyr to ～2 Gyr. A third crater population(Population S) consisted of secondary impact craters that can dominate the cratering record at small diameters.     

新一代天气雷达台站环境监控系统设计与实施

根据雷达站运行环境因素、附属设备等,设计并实施了新一代天气雷达台站环境监控平台,实现了新一代天气雷达站级环境状态远程在线监控,对环境恶化、附属设备运行参数超限或不正常等问题进行及时手机报警,从而保证雷达运行环境设备能够稳定可靠运行,有效消除雷达故障隐患,减少雷达故障发生.     

双基地雷达系统探测椭球雨滴群时主站仰角对探测性能的影响

为了提高双基地偏振雷达的探测精度,从旋转椭球粒子散射和衰减的理论出发,推导出基于椭球雨滴群的双基地偏振雷达方程,并利用此方程探讨了旋转椭球雨滴群一致垂直取向情况下,主站雷达发射仰角、目标粒子群位置等因素对双基地偏振雷达探测能力的影响程度.结果表明,随着仰角的抬高,几何因子值和两种偏振状态下的回波功率比均出现了高值区和低值区面积减少的变化特征;散射截面因子值也随着仰角的抬高在水平偏振时增加,垂直偏振时减少.     

吉林省主汛期典型多雨年和少雨年成因对比分析

将1951-2011年吉林省主汛期降水量排名的前、后6位分别定义为多、少雨年,利用NCEP（2.5°×2.5°）再分析资料计算主汛期平均高度场、温度场、风场及比湿、涡度等物理量场;根据天气学原理和常规天气预报经验,对比分析主汛期典型多雨与少雨天气系统结构形态、分布位置、中心强度等特征。结果表明：500 hPa多雨年568等高线较少雨年平均偏南3个纬度,副热带高压588等高线较少雨年平均偏西7个经度偏北1个纬度;低层辐合高层辐散是多雨年的重要特征;850 hPa和700 hPa平均水汽含量多雨年明显多于少雨年;典型多雨年850 hPa风场贝加尔湖附近为单辐合中心,少雨年为双辐合中心。     

奥长花岗岩和奥陶纪Ammonoosuc火山岩系的变质石英角斑凝灰岩——新罕布什尔州西部和邻近的佛蒙特州和马萨诸塞州

奥陶纪Ammouoosuc火山岩及相当的岩石沿着新罕布什尔州北部和康涅狄格州南部之间的BronsonHill复背斜(BHA)分布的OLiverian穹窿出露。在新罕布什尔和相邻佛蒙特和马萨诸塞州,岩系的下部以镁铁质斜长角闪岩为主,上部以长英质变质石英角斑凝灰岩为主。在局部地区两种岩性呈互层,且两者都被奥长花岗岩岩床、岩墙及岩颈侵入。奥长花岗岩还构成若干小穹窿或深成岩体内部的片麻状“核心”。奥长花岗岩高硅(SiO_2=73—81％),低Al_2O_3(11.3—13.5％),一般K_2O<1％,从而类似于某些岛弧或大陆边缘环境的奥长花岗岩。奥长花岗岩和Ammonoosuc火山岩两者化学成分变化基本属于钙—碱性趋势。几个穹窿中的奥长花岗岩的主要元素和微量元素的变化,反映沿Brinson Hill复背斜有些不同的物质来原。可是,从总体上看,奥长花岗岩的主要元素和次要元素组成都很类似于Ammonoosuc石英角斑凝灰岩。由玄武质源岩的部分熔融或分离结晶作用都能够产生这些岩石,但根据该区存在大规模双模式玄武岩-石英角斑岩的Ammonoosuc组合,其中实际上缺少安山岩和其它中性成分的岩石,故部分熔融模式比较合理。正如对纽芬兰的非常相似的奥长花岗岩-角闪岩组合(Twillingate奥长花岗岩,Little Port杂岩)所假定的那样,比较簿的Ammonoosuc剖面似乎排除了奥长花岗岩在目前暴露出的岛弧底部产生。而正如现代板块构造模型所主张的那样,长英质Ammonoosuc岩石的形成更可能发生在BHA以下,沿着向东倾斜的俯冲带的较深部位。硅铝地壳与Ammonoosuc火山岩在时间和空间上紧密并置。可以解释后者的钙-碱趋势,并揭示古构造环境为收敛型的海洋-大陆板块边缘,可能横跨该岛弧有明显的地壳缩短。     

培育土地有形市场

丹阳市国土资源局在认真贯彻执行国务院<关于加强国有土地资产管理的通知>精神,切实做好土地批租专项治理工作中,加强土地资产管理和土地市场建设,土地使用制度改革取得了显著的成效.     

Resource Flows of Villages with Contrasting Lifestyles in Nanda Devi Biosphere Reserve, Central Himalaya, India

Resource use efficiency analyses of village ecosystem are necessary for effective and efficient planning of resource utilization. This paper deals with economic and energy input-output analyses of different components of village ecosystem in representative buffer zone villages, which are practicing transhumance and settled way of lifestyles in Nanda Devi Biosphere Reserve （NDBR） of Garhwal Himalaya. While the villages practicing transhumance used various natural resources spatially segregated,the villages practicing settled way of lifestyle have to manage resources from a limited spatial area through rotation and varied extraction intensities. Forests subsidized the production activity in both type of villages and the per capita resource extractions were found to be greater in tran~humance village than settled village. Though crops provided maximum energy, in terms of economic criteria, animal husbandry played important role in both settled and transhumance villages. As villages representing both the situations showed different ways of adjustments to the conservation oriented land use changes, management authority needs to address the eco-development plans fulfilling the aspirations of all people traditionally using the resources of the Reserve to reduce the conflicts and encourage their participation in the conservation of the area.