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A sea surface temperature (SST) record based on planktonic foraminiferal magnesium/calcium ratios from a site in the western equatorial Pacific warm pool reveals that glacial-interglacial oscillations in SST shifted from a period of 41,000 to 100,000 years at the mid-Pleistocene transition, 950,000 years before the present. SST changes at both periodicities were synchronous with eastern Pacific cold-tongue SSTs but preceded changes in continental ice volume. The timing and nature of tropical Pacific SST changes over the mid-Pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time. 相似文献
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Today's ice cover (2 to 4 meters thick) over the Arctic Ocean provides a shadow that prevents coccolithophorids (photosynthetic, planktonic algae) from living there. Sparse, low-diversity, but indigenous coccolith assemblages in late Pliocene to mid-Pleistocene (but not Holocene) sediments imply deep penetrating warm currents or an ice-free Arctic Ocean, or both, as those layers were being deposited. 相似文献
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Hominin fossils from the African mid-Pleistocene are rare despite abundant Acheulean tools in Africa and apparently African-derived hominins in Eurasia between 1.0 and 0.5 million years ago (Ma). Here we describe an African fossil cranium constrained by 40Ar/39Ar analyses, magnetostratigraphy, and sedimentary features to 0.97 to 0.90 Ma, and stratigraphically associated with Acheulean handaxes. Although the cranium represents possibly the smallest adult or near-adult known between 1.7 and 0.5 Ma, it retains features observed in larger Homo erectus individuals, yet shows a distinct suite of traits indicative of wide population variation in the hominins of this period. 相似文献
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Yamei H Potts R Baoyin Y Zhengtang G Deino A Wei W Clark J Guangmao X Weiwen H 《Science (New York, N.Y.)》2000,287(5458):1622-1626
Stone artifacts from the Bose basin, South China, are associated with tektites dated to 803,000 +/- 3000 years ago and represent the oldest known large cutting tools (LCTs) in East Asia. Bose toolmaking is compatible with Mode 2 (Acheulean) technologies in Africa in its targeted manufacture and biased spatial distribution of LCTs, large-scale flaking, and high flake scar counts. Acheulean-like tools in the mid-Pleistocene of South China imply that Mode 2 technical advances were manifested in East Asia contemporaneously with handaxe technology in Africa and western Eurasia. Bose lithic technology is associated with a tektite airfall and forest burning. 相似文献
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JAAS:灵活的Java安全机制 总被引：2，自引：0，他引：2
Java Authentication Authorization Service(JAAS,Java验证和授权API)提供了根据验证主题身份来验证主题和授权资源访问的标准方法。本文介绍Java验证和授权的概论,核心JAAS类,配置文件及如何开发登录模块。 相似文献
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H Elderfield P Ferretti M Greaves S Crowhurst IN McCave D Hodell AM Piotrowski 《Science (New York, N.Y.)》2012,337(6095):704-709
Earth's climate underwent a fundamental change between 1250 and 700 thousand years ago, the mid-Pleistocene transition (MPT), when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing. Over this time, an increase occurred in the amplitude of change of deep-ocean foraminiferal oxygen isotopic ratios, traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep-ocean temperature. We have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios. Our results suggest that the MPT was initiated by an abrupt increase in Antarctic ice volume 900 thousand years ago. We see no evidence of a pattern of gradual cooling, but near-freezing temperatures occur at every glacial maximum. 相似文献
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C＋＋支持类的多继承,Java采用类的单继承。Java中引入了接口,它定义了一组协议规范,即方法原型,将方法的实现部分放到类中完成,从而将接口继承与实现继承分开。接口继承可以间接替代多继承,具有多继承的优点,而且使用简单。 相似文献
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Java中基于TCP/IP的Socket编程 总被引：3，自引：0，他引：3
Socket是基于TCP／IP的网络上运行的两个程序间双向通讯的一端,java net包中包含Socket类,用以快速地开发网络通信程序。通过实例模型探讨基于Java的Socket通信程序的一般结构对开发一般性的通信软件,有一定的参考价值。 相似文献
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Java是一种面向对象的程序设计语言,Java的异常处理非常出色。Java把异常封装到类里,运用“try/catch/finally”异常处理机制,最终得到的是更为“健壮”的异常处理代码。结合开发实践,用实例说明了Java异常处理如何具体应用。 相似文献
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Java实践教学是Java程序设计能力的训练,它的内容包括三个阶段:基础语言实践,核心API应用实践,项目开发实践.按照实践教学内容建立实验平台:Java教学实验平台和Java应用软件开发平台. 相似文献
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二进制是计算机中所采用的数据表示形式,在文章中介绍了基于VRML与JAVA的虚拟动态交互技术,分析了利用Java或JavaScript语言创建出新的内插节点和传感节点来驱动和控制整个虚拟空间的方法,研究了利用VRML和Java的技术去设计动态交互的场景,实现了二进制与十进制之间的动态交互显示,最后指出该系统已被成功运用于教学,文章的创新点在于利用PRO/E优化建模。 相似文献
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We propose that from approximately 3 to 1 million years ago, ice volume changes occurred in both the Northern and Southern Hemispheres, each controlled by local summer insolation. Because Earth's orbital precession is out of phase between hemispheres, 23,000-year changes in ice volume in each hemisphere cancel out in globally integrated proxies such as ocean delta18O or sea level, leaving the in-phase obliquity (41,000 years) component of insolation to dominate those records. Only a modest ice mass change in Antarctica is required to effectively cancel out a much larger northern ice volume signal. At the mid-Pleistocene transition, we propose that marine-based ice sheet margins replaced terrestrial ice margins around the perimeter of East Antarctica, resulting in a shift to in-phase behavior of northern and southern ice sheets as well as the strengthening of 23,000-year cyclicity in the marine delta18O record. 相似文献
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线程是现代操作系统的一个重要机制,重点介绍线程的基本思想和Java的实现方法,并且用Java的线程机制实现了生产者-消费者之间的通信. 相似文献
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刘杰 《仲恺农业技术学院学报》2005,18(3):34-38
以Java技术为背景对模型-视图-控制器(Model-View-Controller,MVC)体系结构进行了分析,并结合Struts架构,给出Web应用开发的方法实例. 相似文献