非线性方程的极限环问题

本文首先研究非线性方程x=φ(y)-F(x),y=-g(x)的极限环存在问题,放弃了φ(±∞)=±∞的条件,包含了[3—7]的有关定理。然后对形如x F(x,x) g(x)h(x)=0的二阶非线性方程,利用[8]及本文§1的结果,给出了若干存在极限环的条件,包含了[9]的定理2及[10]p.374的Reissig定理。     

The return of subducted continental crust in Samoan lavas

Substantial quantities of terrigenous sediments are known to enter the mantle at subduction zones, but little is known about their fate in the mantle. Subducted sediment may be entrained in buoyantly upwelling plumes and returned to the Earth's surface at hotspots, but the proportion of recycled sediment in the mantle is small, and clear examples of recycled sediment in hotspot lavas are rare. Here we report remarkably enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures in Samoan lavas from three dredge locations on the underwater flanks of Savai'i island, Western Samoa. The submarine Savai'i lavas represent the most extreme 87Sr/86Sr isotope compositions reported for ocean island basalts to date. The data are consistent with the presence of a recycled sediment component (with a composition similar to the upper continental crust) in the Samoan mantle. Trace-element data show affinities similar to those of the upper continental crust--including exceptionally low Ce/Pb and Nb/U ratios--that complement the enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures. The geochemical evidence from these Samoan lavas significantly redefines the composition of the EM2 (enriched mantle 2; ref. 9) mantle endmember, and points to the presence of an ancient recycled upper continental crust component in the Samoan mantle plume.     

Livestock and vegetation responses to rotational grazing in short-grass steppe

There is a paucity of information concerning livestock and vegetation responses to rotational grazing in short-grass steppe. We compared effects between 1995 and 2003 of time-controlled, short-duration rotational grazing against season-long continuous grazing, at a moderate stocking rate (1.95 ha ? animal unit month –1 ), on livestock gains and on foliar and basal cover in short-grass steppe. Livestock average daily gains, grazing-season gains, and beef production did not differ between grazing systems. We observed no relationship between precipitation (annual or growing-season) and average daily gain. In contrast, both grazing-season gains and beef production exhibited a significant curvilinear response to both growing-season and annual precipitation. Basal and foliar cover of all plant functional groups (C 3 annual grasses, C 3 perennial grasses and grass-likes, C 4 perennial grasses, cactus, annual forbs, perennial forbs, and shrubs/subshrubs) did not differ between grazing systems. Litter and bare ground were also unaffected by grazing system, with litter increasing and bare ground decreasing over the duration of this experiment. Land managers in shortgrass steppe who are implementing rotational grazing at moderate stocking rates should not expect increased livestock gains or changes in basal and foliar cover of the plant community. Rotational grazing may be a useful management tool for achieving conservation goals through modifications of seasonality and intensity of use in paddocks within larger management units to accommodate spatial variability in vegetation and temporal variation in precipitation.     

一种基于视频水印技术的数字视频节目监控系统设计

为了实现特定电视节目的监控,设计完成了一种基于视频水印技术的电视节目监控系统．视频水印技术对具体的节目内容进行标识,通过在双向机顶盒中完成水印的检测和TS信息的处理,从而完成对特定节目的版权所有者、播出时间、长度等信息的捕获,并由机顶盒的回传模块完成到前端数据服务器的信息传送．视频水印方案的实验结果表明,对于电视广播中采用的MPEG-2压缩具有较好的鲁棒性．设计的节目监控软件,通过对TS流中相关信息的实时显示和保存达到了电视节目监控的目的．     

Geology and palaeontology of the Late Miocene Middle Awash valley, Afar rift, Ethiopia.

The Middle Awash study area of Ethiopia's Afar rift has yielded abundant vertebrate fossils (approximately 10,000), including several hominid taxa. The study area contains a long sedimentary record spanning Late Miocene (5.3-11.2 Myr ago) to Holocene times. Exposed in a unique tectonic and volcanic transition zone between the main Ethiopian rift (MER) and the Afar rift, sediments along the western Afar rift margin in the Middle Awash provide a unique window on the Late Miocene of Ethiopia. These deposits have now yielded the earliest hominids, described in an accompanying paper and dated here to between 5.54 and 5.77 Myr. These geological and palaeobiological data from the Middle Awash provide fresh perspectives on hominid origins and early evolution. Here we show that these earliest hominids derive from relatively wet and wooded environments that were modulated by tectonic, volcanic, climatic and geomorphic processes. A similar wooded habitat also has been suggested for the 6.0 Myr hominoid fossils recently recovered from Lukeino, Kenya. These findings require fundamental reassessment of models that invoke a significant role for global climatic change and/or savannah habitat in the origin of hominids.     

Triterpenes of toxic and non-toxic taxa of Lantana camara.

The taxa of Lantana camara toxic to animals contain lantadene A lantadene B, whereas in two non-toxic taxa other triterpenes predominate. Several new triterpenes have been characterized. Contrary to earlier claims, lantadene A and to a lesser extent lantadene B are toxic when administered intraruminally to sheep.