Climate change in the North Pacific region over the past three centuries

The relatively short length of most instrumental climate records restricts the study of climate variability, and it is therefore essential to extend the record into the past with the help of proxy data. Only since the late 1940s have atmospheric data been available that are sufficient in quality and spatial resolution to identify the dominant patterns of climate variability, such as the Pacific North America pattern and the Pacific Decadal Oscillation. Here we present a 301-year snow accumulation record from an ice core at a height of 5,340 m above sea level-from Mount Logan, in northwestern North America. This record shows features that are closely linked with the Pacific North America pattern for the period of instrumental data availability. Our record extends back in time to cover the period from the closing stages of the Little Ice Age to the warmest decade in the past millennium. We find a positive, accelerating trend in snow accumulation after the middle of the nineteenth century. This trend is paralleled by a warming over northwestern North America which has been associated with secular changes in both the Pacific North America pattern and the Pacific Decadal Oscillation.     

A cat cloned by nuclear transplantation

Sheep, mice, cattle, goats and pigs have all been cloned by transfer of a donor cell nucleus into an enucleated ovum, and now we add the successful cloning of a cat (Felis domesticus) to this list. However, this cloning technology may not be readily extendable to other mammalian species if our understanding of their reproductive processes is limited or if there are species-specific obstacles.     

一种用于结构动态过程数值模拟的广义有限元法

提出了一种能同时处理连续体和离散体动态过程的有限元法. 该法通过构造接触力模型, 将传统的离散元当做标准的一节点有限单元来看待. 新构造的一节点单元与常规有限单元具有同样物理特征, 包括应力和应变. 从而, 将离散元算法与有限元算法紧密结合在一起, 形成了统一的、与现有有限元系统兼容的广义有限元计算模型. 这种模型不仅简化了计算过程, 还可最大限度地发挥现有有限元代码的功能. 数值算例表明, 新方法可以更加有效地模拟大量离散体与连续体相互作用的复杂动力学过程.