Spontaneous skyrmion ground states in magnetic metals

Since the 1950s, Heisenberg and others have addressed the problem of how to explain the appearance of countable particles in continuous fields. Stable localized field configurations were searched for an ingredient for a general field theory of elementary particles, but the majority of nonlinear field models were unable to predict them. As an exception, Skyrme succeeded in describing nuclear particles as localized states, so-called 'skyrmions'. Skyrmions are a characteristic of nonlinear continuum models ranging from microscopic to cosmological scales. Skyrmionic states have been found under non-equilibrium conditions, or when stabilized by external fields or the proliferation of topological defects. Examples are Turing patterns in classical liquids, spin textures in quantum Hall magnets, or the blue phases in liquid crystals. However, it has generally been assumed that skyrmions cannot form spontaneous ground states, such as ferromagnetic or antiferromagnetic order, in magnetic materials. Here, we show theoretically that this assumption is wrong and that skyrmion textures may form spontaneously in condensed-matter systems with chiral interactions without the assistance of external fields or the proliferation of defects. We show this within a phenomenological continuum model based on a few material-specific parameters that can be determined experimentally. Our model has a condition not considered before: we allow for softened amplitude variations of the magnetization, characteristic of, for instance, metallic magnets. Our model implies that spontaneous skyrmion lattice ground states may exist generally in a large number of materials, notably at surfaces and in thin films, as well as in bulk compounds, where a lack of space inversion symmetry leads to chiral interactions.     

基于磁弛豫原理的磁化学传感器研究进展

基于磁性纳米粒子的磁化学传感器是集纳米/微米技术、化学反应、生物技术及核磁共振技术于一体的多学科交叉、多技术集成的传感器.利用这一传感器可以检测各种金属离子、蛋白质、小分子、细菌、病毒、DNA、分子间的相互作用、细胞、肿瘤以及癌症.首先简要概述磁化学传感器的传感原理,然后重点介绍在检测方面的应用.     

Bose-Einstein condensation of the triplet states in the magnetic insulator TlCuCl3

Bose-Einstein condensation denotes the formation of a collective quantum ground state of identical particles with integer spin or intrinsic angular momentum. In magnetic insulators, the magnetic properties are due to the unpaired shell electrons that have half-integer spin. However, in some such compounds (KCuCl3 and TlCuCl3), two Cu2+ ions are antiferromagnetically coupled to form a dimer in a crystalline network: the dimer ground state is a spin singlet (total spin zero), separated by an energy gap from the excited triplet state (total spin one). In these dimer compounds, Bose-Einstein condensation becomes theoretically possible. At a critical external magnetic field, the energy of one of the Zeeman split triplet components (a type of boson) intersects the ground-state singlet, resulting in long-range magnetic order; this transition represents a quantum critical point at which Bose-Einstein condensation occurs. Here we report an experimental investigation of the excitation spectrum in such a field-induced magnetically ordered state, using inelastic neutron scattering measurements of TlCuCl3 single crystals. We verify unambiguously the theoretically predicted gapless Goldstone mode characteristic of the Bose-Einstein condensation of the triplet states.     

悬浮式磁流体惯性传感黏阻与量程可控机理

实现悬浮式磁流体惯性传感的量程控制关键在于分析基于经典黏性流体力学理论的动态黏度特性和流固系统运动特性.在质量块作简谐运动下,建立惯性传感结构中间隙的流动模型并对理论方程进行求解.在不同动力黏度下,对作简谐运动的传感运动块进行流阻力进行数值计算,结果表明:质量块所受黏阻力主要是两侧压力差,压力差随时间呈现简谐特性,幅值与磁流体动力黏度有较好的线性关系;在选定实验参数后研究结果为压差相位超前22°～40°,剪切应力超前在15°以内,且随着动力黏度增大而减少,当运动黏度达到75 pma·s时,相位超前量变化趋缓.     

Megagauss sensors

Magnetic fields change the way that electrons move through solids. The nature of these changes reveals information about the electronic structure of a material and, in auspicious circumstances, can be harnessed for applications. The silver chalcogenides, Ag2Se and Ag2Te, are non-magnetic materials, but their electrical resistance can be made very sensitive to magnetic field by adding small amounts--just 1 part in 10,000--of excess silver. Here we show that the resistance of Ag2Se displays a large, nearly linear increase with applied magnetic field without saturation to the highest fields available, 600,000 gauss, more than a million times the Earth's magnetic field. These characteristics of large (thousands of per cent) and near-linear response over a large field range make the silver chalcogenides attractive as magnetic-field sensors, especially in physically tiny megagauss (10(6) G) pulsed magnets where large fields have been produced but accurate calibration has proved elusive. High-field studies at low temperatures reveal both oscillations in the magnetoresistance and a universal scaling form that point to a quantum origin for this material's unprecedented behaviour.     

不同应力状态下金属磁记忆检测信号特征

文章介绍利用金属磁记忆无损检测技术研究了构件在单向拉伸应力状态和纯剪切应力状态下的磁记忆检测信号特征,并对此进行了对比和分析。通过试验发现,磁记忆检测信号与构件的损伤状态之间具有明显的相关性,通过检测法向磁场的过零点可以实现对构件早期损伤的检测。     

氟硼铍酸钾晶体深紫外区域倍频的非共线匹配

根据氟硼铍酸钾(KBe2BO3F2,简称KBBF)晶体最新的色散方程以及非共线匹配的条件,采用FORTAN语言变精度数值计算方法,计算了入射波长为400nm的KBBF晶体的类非共线倍频相位匹配角、有效非线性系数和允许角.计算结果显示:在第1象限内存在2个匹配方向,第1个匹配方向对应的基频o光和倍频e光的匹配角范围为51.00°~90.00°,50.83°~66.32°,52.68°~78.16°;第2个匹配方向对应的基频o光和倍频e光匹配角范围分别为51.00°~66.00°,60.41°~89.59°,55.71°~77.79°.第1个匹配方向的相位匹配角范围和相应的有效非线性系数比第2个匹配方向大,第1个匹配方向对应的允许角比第2个匹配方向小.因此非共线相位匹配结构下KBBF晶体的Ⅰ类倍频采用第1个匹配方向.     

光流控传感器及其应用

 基于光流控技术,通过设计不同的芯片结构,可以制造出性能优异的光流控传感器。根据光流控传感器的芯片结构,可以将其分为4大类：前2类为基于光子晶体谐振腔的光流控传感器和基于回音壁模式的光流控传感器,流体在流经这2种传感器中的腔体结构时,产生的折射率改变会引起腔体耦合模式的变化,从而使光响应信号产生改变,起到传感作用;第3类为基于光波导模式的光流控传感器,光在波导中全反射产生的條逝场会与流体发生相互作用,令光信号产生变化;第4类为基于表面等离子体共振的光流控传感器,它利用表面等离子共振对金属表面区域折射率的敏感性实现传感功能,流体带来的折射率变化会令共振峰发生偏移。本文综述了以上4类光流控传感器芯片的结构、原理及应用。光流控传感器对于微小的折射率变化十分敏感,具有很高的灵敏度和精准度,同时,光流控系统本身具有低成本、小型化、结构简洁及实时调控的特征。随着未来被探测物体趋于微观,光流控传感器在物质探测和生物物质探测领域将发挥越来越强大的作用。     

可燃气体传感器研究综述

可燃气体传感器作为检测工业气体的标准工具之一,是实现"智慧地球,感知中国"的基础.研究了可燃气体传感器的发展情况,介绍了4种检测原理特点:催化燃烧式具有计量准确、响应快的特点,但无选择性;半导体式价格低廉、普及广,但受环境影响大,不适用计量准确的场所;电化学式选择性强、温度性能好,但寿命低;红外线式测量范围宽、精准度高,但价格昂贵.近半个世纪以来传感器在可燃气体检测方面逐步实现低功耗、小型化、智能化、一体化,进一步向跨学科的横向领域突破,集管理数据化、应急主动化、设备智能化于一身的传感器将是打造智慧城市、智慧园区的关键.     

光纤电流传感器小波信号处理系统

为了减少光纤电流传感器的噪声影响,提高传感器的信噪比,提出了一个基于小波变换理论的数字信号处理系统。文中简介了小波变换的优点及特性,设计了基于小波变换的带通滤波器,组建了一套光纤电流传感器带通滤波系统。该系统能实现１ Ｈｚ 的带通滤波特性,并能根据需要经改变软件参数很方便地实现不同频率、不同带宽的信号提取。这个系统及分析方法对其他参数测量用光纤传感器及其他类型的传感器信号处理系统也是适用的     

Sweep Coverage中的节点移动控制

作为无线传感器网络中一种新的覆盖类型,Sweep Coverage与其他覆盖类型相比,可以使用较少的节点满足特定区域的监控需求.为了改进Sweep Coverage机制的性能,本文以Vehicle Routing Problem with Time Windows问题的模型,对Sweep coverage问题进行了分析,提出了一种基于模拟退火算法的Sweep Coverage机制(VRP-Sweep).实验结果表明,在相同的网络场景下,VRP-Sweep机制较以往的Sweep Coverage机制取得更好的性能表现.     

CFRP预警传感器的研究

利用碳纤维增强复合材料(CFRP)的导电性和压电效应,根据碳纤维断裂时所形成的电阻阶跃信号,分别采用直接铺层和预先铺层2种方法制成对结构不同状态进行监测的CFRP预警传感器,该预警传感器具有造价低、耐腐蚀、监测信号易于获取等优点,并将此传感器应用于5根钢筋混凝土梁的试验研究.结果表明,CFRP预警传感器对于钢筋混凝土梁宏观行为的预测具有较好的效果,在混凝土开裂、钢筋屈服等关键时刻,其电阻信号发生突变,触发预警信号,该传感器对于钢筋混凝土类构件的监测具有实用性.     

用电容式传感器进行变压器绝缘纸板微水分在线测量

介绍一种绝缘纸板微水分检测系统,它可用于大型电力变压器器身整体干燥过程中绝缘纸板水的质量分数在线实时检测,专门设计的电容式传感器十几米以外的干燥罐中器身的微水分变化;其输出信号经放大、变换后,由微机处理数据并显示水含量。同时给出了传感器的工作原理、结构形式,以及相关软梗件组成。     

Stochastic sensors inspired by biology

Sensory systems use a variety of membrane-bound receptors, including responsive ion channels, to discriminate between a multitude of stimuli. Here we describe how engineered membrane pores can be used to make rapid and sensitive biosensors with potential applications that range from the detection of biological warfare agents to pharmaceutical screening. Notably, use of the engineered pores in stochastic sensing, a single-molecule detection technology, reveals the identity of an analyte as well as its concentration.     

TRP channels as cellular sensors

TRP channels are the vanguard of our sensory systems, responding to temperature, touch, pain, osmolarity, pheromones, taste and other stimuli. But their role is much broader than classical sensory transduction. They are an ancient sensory apparatus for the cell, not just the multicellular organism, and they have been adapted to respond to all manner of stimuli, from both within and outside the cell.     

煤矿井下长巷道瓦斯传感器间距设计

为了解决瓦斯传感器空间布设位置标准问题,为煤矿安全的规范提供理论依据,采用了理论推导和示例相结合的方法,研究了瓦斯涌出源稳定情况下,依据相似原理求出了瓦斯与空气的混合距离.结果表明:巷道瓦斯平均浓度与风速、巷道截面积、瓦斯涌出强度、传感器间距之间存在一定的函数关系,矿井监控系统所需要的最短响应时间是目前迫切需要解决的问题.该成果对提高瓦斯监控系统运行效率,节省经济成本,有着重要的参考价值和指导意义.