Observation of the two-channel Kondo effect

Some of the most intriguing problems in solid-state physics arise when the motion of one electron dramatically affects the motion of surrounding electrons. Traditionally, such highly correlated electron systems have been studied mainly in materials with complex transition metal chemistry. Over the past decade, researchers have learned to confine one or a few electrons within a nanometre-scale semiconductor 'artificial atom', and to understand and control this simple system in detail(3). Here we combine artificial atoms to create a highly correlated electron system within a nano-engineered semiconductor structure. We tune the system in situ through a quantum phase transition between two distinct states, each a version of the Kondo state, in which a bound electron interacts with surrounding mobile electrons. The boundary between these competing Kondo states is a quantum critical point-namely, the exotic and previously elusive two-channel Kondo state, in which electrons in two reservoirs are entangled through their interaction with a single localized spin.     

Abrupt onset of a second energy gap at the superconducting transition of underdoped Bi2212

The superconducting gap--an energy scale tied to the superconducting phenomena--opens on the Fermi surface at the superconducting transition temperature (T(c)) in conventional BCS superconductors. In underdoped high-T(c) superconducting copper oxides, a pseudogap (whose relation to the superconducting gap remains a mystery) develops well above T(c) (refs 1, 2). Whether the pseudogap is a distinct phenomenon or the incoherent continuation of the superconducting gap above T(c) is one of the central questions in high-T(c) research. Although some experimental evidence suggests that the two gaps are distinct, this issue is still under intense debate. A crucial piece of evidence to firmly establish this two-gap picture is still missing: a direct and unambiguous observation of a single-particle gap tied to the superconducting transition as function of temperature. Here we report the discovery of such an energy gap in underdoped Bi2Sr2CaCu2O8+delta in the momentum space region overlooked in previous measurements. Near the diagonal of Cu-O bond direction (nodal direction), we found a gap that opens at T(c) and has a canonical (BCS-like) temperature dependence accompanied by the appearance of the so-called Bogoliubov quasi-particles, a classical signature of superconductivity. This is in sharp contrast to the pseudogap near the Cu-O bond direction (antinodal region) measured in earlier experiments.     

Ecology: diversity and stability in plant communities

The relationship between species diversity and ecosystem stability is controversial. Tilman et al. analyse biomass patterns over a decade in a grassland experiment with artificial plant communities, and provide evidence for a positive relationship between the number of plant species and the temporal stability of the ecosystem. Here we use data from a long-term biodiversity experiment with plant communities that were not controlled by weeding in order to show that diverse systems can be both stable and unstable.     

供热设计方案综合评价与优选研究

多目标综合效果测度法是一种非常有效的系统优化评价方法。从方案的经济性、技术性及对环境的影响等角度,对5种供热方案进行分析,运用多目标综合效果测度法对备选方案进行评价,确定污水源热泵系统为最佳方案。     

电磁阻尼器性能参数试验研究

电磁阻尼器性能与多种因素有关,在电磁阻尼器基本性能试验研究基础上,制作了一个电磁阻尼器模型,进行了涡流板厚度参数影响的试验研究:做了3种厚度涡流板在不同频率、不同位移情况下的试验,得到了涡流板厚度对阻尼器性能影响的定性结论。     

粘土基防渗浆材的实验研究

针对目前常用浆材的局限性和工程应用的需要,采用正交优化的实验方法研究一种以粘土为主的粘土基防渗浆材,浆材具有良好的稳定性和可灌性,其结石体具有低渗透性和较低强度,适用于非加固型的防渗注浆工程。     

QY25起重机行星变速箱优化设计

根据产品要求,对起重机起升机构中的行星变速箱进行优化设计,主要对变速箱中的齿轮进行高度变位计算,从而达到减轻整机的重量和体积,合理地确定已有参数,以期达到最佳设计的目的。     

一种包边模边界缩进控制方法

 将确定性优化方法用于板料包边设计.汽车板料包边仿真中变形区域小导致有限元模型在变形区域的网格很小,模型计算时间太长.本文针对影响板料包边后边界缩进较大的3个参数,建立目标函数的径向基函数近似模型,并用确定性优化方法对近似模型进行优化,近似模型计算效率高,提高了优化方法计算效率,使板料包边的优化设计成为可能,并为生产中的汽车板料控制包边后的边界缩进提供了一种新的思路.     

某类重特大火灾数值模拟研究

某酒吧火灾、深圳舞王俱乐部火灾和福建长乐拉丁酒吧火灾的发生场所和火灾原因类似,且短时间就造成大量人员伤亡,研究这类火灾防控措施有较好的意义。本文利用FDS软件构造某酒吧的火灾模型,合理分析场所的人员情况设定疏散模拟参数,根据火场情况设定合适的火灾场景,分析热辐射、烟气温度、烟气毒性、烟气能见度等参数的变化过程,并得到可用疏散时间。结合CFE软件进行人员疏散过程模拟,模拟的预期火灾人员伤亡与实际情况较好相符;并对不同的可燃物类型、消防设施状况和待疏散人数进行火灾后果分析,可燃物分析结果说明装修用聚氨酯泡沫吸音棉是造成火灾极速蔓延的直接原因,这类材料产生大量的有毒浓烟,很快就造成人员伤亡;不同消防设施模拟分析的结果体现了自动消防设施的重要作用,公共娱乐场所的自动喷水灭火系统应推广快速响应喷头,未按国家标准安装自动消防设施是造成重大火灾人员伤亡的成灾原因;对酒吧不同待疏散人数的火灾预期伤亡数定量分析证明了公共娱乐场所定员管理的重要意义;模拟分析的结果可用于此类火灾成因分析和火灾防控措施研究。