Dynamos in asymptotic-giant-branch stars as the origin of magnetic fields shaping planetary nebulae

Planetary nebulae are thought to be formed when a slow wind from the progenitor giant star is overtaken by a subsequent fast wind generated as the star enters its white dwarf stage. A shock forms near the boundary between the winds, creating the relatively dense shell characteristic of a planetary nebula. A spherically symmetric wind will produce a spherically symmetric shell, yet over half of known planetary nebulae are not spherical; rather, they are elliptical or bipolar in shape. A magnetic field could launch and collimate a bipolar outflow, but the origin of such a field has hitherto been unclear, and some previous work has even suggested that a field could not be generated. Here we show that an asymptotic-giant-branch (AGB) star can indeed generate a strong magnetic field, having as its origin a dynamo at the interface between the rapidly rotating core and the more slowly rotating envelope of the star. The fields are strong enough to shape the bipolar outflows that produce the observed bipolar planetary nebulae. Magnetic braking of the stellar core during this process may also explain the puzzlingly slow rotation of most white dwarf stars.     

Potassium channel receptor site for the inactivation gate and quaternary amine inhibitors

Many voltage-dependent K+ channels open when the membrane is depolarized and then rapidly close by a process called inactivation. Neurons use inactivating K+ channels to modulate their firing frequency. In Shaker-type K+ channels, the inactivation gate, which is responsible for the closing of the channel, is formed by the channel's cytoplasmic amino terminus. Here we show that the central cavity and inner pore of the K+ channel form the receptor site for both the inactivation gate and small-molecule inhibitors. We propose that inactivation occurs by a sequential reaction in which the gate binds initially to the cytoplasmic channel surface and then enters the pore as an extended peptide. This mechanism accounts for the functional properties of K+ channel inactivation and indicates that the cavity may be the site of action for certain drugs that alter cation channel function.     

A role for MLH3 in hereditary nonpolyposis colorectal cancer

We investigated a possible role of the mismatch-repair gene MLH3 in hereditary nonpolyposis colorectal cancer by scanning for mutations in 39 HNPCC families and in 288 patients suspected of having HNPCC. We identified ten different germline MLH3 variants, one frameshift and nine missense mutations, in 12 patients suspected of HNPCC. Three of the 12 also carried a mutation in MSH6.     

核燃料循环后端研究进展和一体化新思路

最近的《参考消息》以“处理核废料研究取得突破”为题，转载了英国《观察家报》的报道，介绍说欧洲科学家设计了一个能安全处理放射性废料的反应堆，能“把反应堆产生的各种没用的东西都拿过来，并将它们投入到我们设计的反应堆的实体模型中，所有的东西都分解成低放射性的无害垃圾”。这确实是一个突破性的成果，如果原型反应堆能够建成并最终取得成功的话，将带来核能应用的又一个“春天”进入80年代以来，特别是前苏联发生了切尔诺贝利事故以后，除东亚等少数地区外，世界范围内的核电发展基本处于停滞状态。从1991年到1996年的5年间，…     

水工金属结构可靠性综合评估方法

通过剖析水工金属结构的失事原因，确定影响水工金属结构的主要因素是设计问题、制造安装问题和运行管理问题.在此基础上，建立水工金属结构安全评估体系，拟定评估等级，计算评估指标.综合评估方法应用于实际工程，可操作性较强，评估结果可信.