Resonance as a measure of pairing correlations in the high-Tc superconductor YBa2Cu3O6.6

One of the most striking properties of the high-transition-temperature (high-Tc) superconductors is that they are all derived from insulating antiferromagnetic parent compounds. The intimate relationship between magnetism and superconductivity in these copper oxide materials has intrigued researchers from the outset, because it does not exist in conventional superconductors. Evidence for this link comes from neutron-scattering experiments that show the unambiguous presence of short-range antiferromagnetic correlations (excitations) in the high-Tc superconductors. Even so, the role of such excitations in the pairing mechanism for superconductivity is still a subject of controversy. For YBa2Cu3O(6+x), where x controls the hole-doping level, the most prominent feature in the magnetic excitation spectrum is a sharp resonance (refs 6-11). Here we show that for underdoped YBa2Cu3O6.6, where x and Tc are below their optimal values, modest magnetic fields suppress the resonance significantly, much more so for fields approximately perpendicular to the CuO2 planes than for parallel fields. Our results indicate that the resonance measures pairing and phase coherence, suggesting that magnetism plays an important role in high-Tc superconductivity. The persistence of a field effect above Tc favours mechanisms in which the superconducting electron pairs are pre-formed in the normal state of underdoped copper oxide superconductors, awaiting transition to the superconducting state.     

One-dimensional nature of the magnetic fluctuations in YBa2Cu3O6.6

There is increasing evidence that inhomogeneous distributions of charge and spin--so-called 'striped phases'--play an important role in determining the properties of the high-temperature superconductors. For example, recent neutron-scattering measurements on the YBa2Cu3O(7-x) family of materials show both spin and charge fluctuations that are consistent with the striped-phase picture. But the fluctuations associated with a striped phase are expected to be one-dimensional, whereas the magnetic fluctuations observed to date appear to display two-dimensional symmetry. We show here that this apparent two-dimensionality results from measurements on twinned crystals, and that similar measurements on substantially detwinned crystals of YBa2Cu3O6.6 reveal the one-dimensional character of the magnetic fluctuations, thus greatly strengthening the striped-phase interpretation. Moreover, our results also suggest that superconductivity originates in charge stripes that extend along the b crystal axis, where the superfluid density is found to be substantially larger than for the a direction.     

“拉丁字母”和“罗马字母”

ABCD……这26个字母,既称“拉丁字母”,又称“罗马字母”。两个名称有什么不同?什么时候用“拉丁字母”,什么时候用“罗马字母”,有什么规律?本文从这套字母的发展史谈起,通过考察两个名称在中国及英语国家的使用情况,得出“罗马字母”应该取代“拉丁字母”的结论。     

Cloned pigs derived from somatic cell nuclear transfer embryos cultured in vitro at low oxygen tension

Great progress have been made in animal cloning in China, as evidenced by the live births of cloned cat- tle[1,2], goats[3,4], and sheep[5]. In contrast, pig cloning is still in its infancy though limited fundamental studieshave been conducted[6]. It is g…     

Properties of PbLa（Zr,Sn, Ti）O3 ceramics near ferroelectric-antiferroelectric phase boundary

Shirane found in the middle of the 20th century that the solid solution PZT had a lot of fine characteristics and carried out detailed researches[1]. The critical phase transition field of antiferroelectric decreased by adding titanate. Titanate expands t…     

凸多边形最小面积四边形包围盒算法

针对凸多边形的最小面积四边形包围盒问题进行研究,通过数学推导证明,得出了凸多边形的最小面积四边形包围盒的四边都是多共点边,或三边是多共点边而另一边(单共点边)中点与凸多边形的一顶点重合等一系列结论.依据此结论设计了时间复杂度为O(n4)的算法,依据本算法可以构造出凸多边形面积最小的凸四边形包围盒,而且其算法的复杂度仅与凸多边形的边数n相关,是多项式级的复杂度.运算实例表明了算法的正确性和有效性.     

电磁流量计使用中常见故障诊断

文章将电磁流量计在使用中发生的故障进行归纳分类，并按产生的原因从安装、环境条件和流体特性等方面作了分析。     

银行支付网络操作可靠性增长的研究

银行现代支付系统是电子资金划拨的物质基础，其平稳性的运营有赖于支付网络的可靠性及对支付网络操作的可靠性．将可靠性增长的思想和方法引入银行支付网络操作可靠性的研究，针对实际存在的操作人员的培训与操作实践两个时期的学习模式，用顺序约束模型描述培训时期操作可靠性的分布，导出了培训期末操作失效率的预计模型；用时间函数模型描述操作实践可靠性的增长，给出了支付网络运行时刻操作可靠性的推断方法．     

因子分析模式识别法在乙苯生产调优中的应用

模式识别方法是一种具有独到之处的多元统计处理方法。本文运用因子分析模式识别法,研究乙苯烃化装置的生产调优。自编了相应的计算机程序,建立了数学模式,找到了优化控制条件,获得了十分明显的经济效益。     

管内竖直向上固液两相流固相非均匀分布及其机理分析

根据粒径和流量的不同，管内竖直向上固液两相流动可能会出现四种基本流型，即固定床模式、局部流化模式、充分流化模式和水力输送模式．在充分流化模式中，固相存在着明显的轴向分布不均匀性．通过对轴向分布不均匀性现象的详尽的观察与分析，提出了逐层流化-壁面效应机理模型，给出了床体膨胀曲线的测量结果，并指出，稳定流化的流量操作范围窄是固液流化床的固有特性。