生物灭绝与化石记录

化石记录中有丰富的生物灭绝证据。海洋动物中平均寿命大约只有4Ma。生物种的这个寿命转换成平均更新率为每百万年25％。如果这种计算用于整个生物群的话,并假设地球上大约有1000万个物种,那么平均每年有2～3个物种会自然灭绝。这种逻辑是简单的,但有点使人误解,因为有些平均年份可以极少发生灭绝。化石记     

追求速度 永不满足

哪一种高速技术用于您的未来——或者现在?从前，10-Mbps Ethemet居于王位，甚至被认为是这间时代技术。当计算机技术     

自由电子激光放大器为真空紫外及X射线研究带来新的科学机遇

自由电子激光将成为第四代辐射源的基础，这一事实已在同步辐射学术界成成共识。通过相干辐射产生自由电子激光所能提供的峰值功率将比第三代储存环装置亢１２个数量级，其工作波长范围可以扩展到远远超出固体激光技术所能达到的极限。自由电子激光有可能产生脉仅几个飞秒的超短脉冲，单脉冲能量达到毫焦耳量级。由于存在上述优点，皮长自由电子激光在化学、表面和固体物理、生物和材料等领域实验研究中的应用已经引起广泛的兴趣。本     

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运用稳定氧同位素（δ^18O)、Mg/Ca比值、碳酸盐胶结物和岩盐流体包裹体等方法，能够获得古环境温度或盐度参数，但这些方法本身存在各自缺陷，因而在实际应用中受到一定限制。文章首次检测到不同地区、不同层位和不同沉积环境中石英碎屑颗粒继承性裂纹和空隙胶结物捕获近地表同生流体包裹体均一温度和盐度。在成因上，它属于同沉积期或近地表捕获与古环境相关的次生（裂纹中）和原生（硅质胶结物中）盐水包裹体。因此，鉴别和测定这种类型的流体包裹体，为建立沉积环境古温度和古盐度的连续记录来了解古气候变迁而提供了一种可能的新途径。根据北海West Lewis和Shetland盆地、渤海渤中地区和南海莺歌海盆地钻井取心样品测定，证实了该方法的可靠性和实用性。     

合理设计电源电路

设计DC/DC转换器需要计算许多元件的参数,需要细心选择控制器芯片。它们对线路板的布置、元件的寄生参数都非常敏感,因此,整个设计过程比较复杂。一些电子技术教科书论述了有     

集群技术该成熟了

当仔细对Intel、Microsoft和Compaq公司共同提出的新的集群技术规范进行考察时,你就会想到:集群技术该是成熟的时候了。新的集群技术规范名为虚拟接口结构(Virtual Interface Architecture)规范,或简称为VIA。该规范自去年4月以来就开始制订了,现在终于正式成为可用的规范。我尤其不理解Microsoft公司在集群技术的开发方面显得如此没有生气,许多WindOWS NT开发人员被Digital公司挖走,在其     

Lotus StreamCam——通过Web流式播放演示内容

流式技术已经问世“很长”一段时间了,它不再是本月的热门话题。因此,当Lotus宣布推出一种用于在Web环境中流式播放ScreenCam电影的基于服务器的附加模块StreamCam时,我们的反应是:“正是时候！”我们在Windows NT 4.0环境下对该产品的一个beta版本进行了测试,在读者阅读本文时,该产品应该已经问世。 StreamCam是捆绑在ScreenCam for Windows NT4.0     

粮食及粮食制品中有机磷、拟除虫菊酯和氨基甲酸酯杀虫剂的提取、净化及色谱测定(综述)

1.前言由于粮食及其成品如面包和米饭构成了人类膳食及家庭动物饲料的主要部分,因而粮食中农药残留的分析尤为重要。尽管分析此类储藏商品及其制品中的杀虫剂具有明显意义,但目前对此问题似乎尚无一致评价。基于此,我们在此篇综述中为满足该需要做了尝试。     

A reusable surface-enhanced Raman scattering (SERS) substrate prepared by atomic layer deposition of alumina on a multi-layer gold and silver film

A thermally stable, reusable surface-enhanced Raman scattering (SERS) substrate consisting of a gold/silver bi-layer film with a protective alumina coating is reported. The film is synthesized by thermally evaporating sequential layers of gold and silver followed by coating an ultra-thin alumina layer using atomic layer deposition. The use of gold as the foundational layer improves the thermal stability of the metal bi-layer film while providing the additional ability to tune the SERS response. Deposition of the thin alumina overlayer on the bi-layer film creates a SERS substrate capable of enduring multiple high-temperature exposures to 400 °C with minimal loss of enhancement capabilities. We demonstrate the multi-use capability of the substrate by measuring the SERS spectrum of rhodamine 6G followed by a thermal treatment at 400 °C to remove the analyte. A representative substrate was used to acquire SERS spectra of rhodamine 6G up to five repeat measurements, thus establishing the reusability of this relatively simple, inexpensive, and stable substrate.     

Mutual diffusion occurring at the interface between La₀.₆Sr₀.₄Co₀.₈Fe₀.₂O₃ cathode and Gd-doped ceria electrolyte during IT-SOFC cell preparation

The microstructure and local chemistry of the interface between the screen-printed La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3) (LSCF) thin film cathode and Gd-doped ceria (GDC) electrolyte substrate have been investigated. Elemental distribution analyses, by energy-dispersive X-ray spectroscopy operated in scanning transmission electron microscopy (STEM) mode, illustrate that all constituent elements in GDC and LSCF mutually diffuse across the LSCF/GDC interface, with equal diffusion length. This leads to the formation of mutual diffusion zones at the LSCF/GDC interfaces, with the resultant mixture of diffusing ions being associated with specific valence state changes, as verified by STEM electron energy loss spectroscopy analyses. Moreover, this mutual diffusion can result in microstructural changes, where superstructure formation is accompanied by enhancement of oxygen vacancy ordering at this region. Such mutual diffusion and associated microstructure evolution is considered to be detrimental to fuel cell efficiency and should be suppressed by lowering cell fabrication temperatures.