磁场对La2-x-yNdySrxCuO4体系电荷条纹相的影响

最近的研究结果表明在La2-x-yNdySrxCuO4体系中,静态电荷条纹的形成以及动态电荷条纹的运动都和晶格有一定的耦合.基于此,我们通过超声衰减测量研究了磁场对La2-x-yNdySrxCuO4(x=0.12, y=0, 0.4 and x=0.04, y=0)体系中电荷条纹的影响.对La1.48Nd0.4Sr0.12CuO4,我们发现70 K附近对应于静态电荷条纹形成的超声衰减峰以及此温度以下超声声速的异常硬化在零场和14T的强磁场下基本没有变化,说明静态电荷有序非常稳定,磁场对其没有影响.但是对La1.88Sr0.12CuO4样品,由于超导电性占主导地位,静态电荷序的形成被压制在很低的温度(10 K以下).我们发现低温下的超声衰减峰及声速硬化随磁场的增加而逐渐向高温方向移动,同时低温下的声速硬化加强.这意味着磁场能够钉扎La1.88Sr0.12CuO4中的动态电荷条纹.这一实验结果为La系超导体中静态电荷有序与超导电性之间的竞争提供了了进一步的证据.随着磁场的加强,超导序逐渐被压制,静态电荷序得以显现.La1.96Sr0.04CuO4的超声衰减特性测量结果显示,在团簇玻璃态下由于作为团簇畴壁的电荷条纹的运动而导致的超声能量损耗不随磁场发生变化.     

La2CuO4型超导体中电荷有序行为的超声衰减特性研究

本文系统研究了La2CuO4型超导体中电荷有序行为相关的超声衰减特性。在La1．88-y，NdySr0．12CuO4系列样品中观察到由于动态及静态的电荷条纹与晶格之间耦合而导致的超声声速和衰减异常。不同磁场下La1.88Sr0.12-xBaxCuO4系列样品的超声衰减特性表明x≤0．04的样品中存在局域的电荷条纹有序，外加磁场压制超导电性后能够导致局域电荷条纹序的增强。实验结果表明电声子相互作用在铜氧化物超导体的电荷有序现象中扮演着重要的角色。     

La2CuO4型超导体中电荷有序行为的超声衰减特性研究

本文系统研究了La2CuO4型超导体中电荷有序行为相关的超声衰减特性.在La1.88-yNdySr0.12CuO4系列样品中观察到由于动态及静态的电荷条纹与晶格之间耦合而导致的超声声速和衰减异常.不同磁场下La1.88Sr0.12-xBaxCuO4系列样品的超声衰减特性表明x≤0.04的样品中存在局域的电荷条纹有序,外加磁场压制超导电性后能够导致局域电荷条纹序的增强.实验结果表明电声子相互作用在铜氧化物超导体的电荷有序现象中扮演着重要的角色.     

La1.88-yNdySr0.12CuO4中电荷有序的超声衰减研究

通过对La1.88-yNdySr0.12CuO4系列多晶样品电阻率的测量,发现y=0.3,0.4,0.5,0.6样品的电阻率随着温度降低在50～80K之间出现一个小于5%的跳跃转变,转变前其导电行为呈金属性,转变后呈半导体性,暗示了体系中静态电荷有序的产生.随着Nd掺杂量y的增加,转变温度Tc0升高,跳跃转变宽度变窄.进一步的超声衰减测量显示,对应电荷有序温度Tc0,声速随温度降低开始出现异常硬化,衰减系数也出现峰值,随y的增加,衰减峰明显加强.实验结果表明, Nd掺杂的增加利于钉扎体系中的动态电荷关联而形成静态的电荷有序.这种作用可能主要是由于Nd掺杂引起体系局域结构畸变,低温四方相(LTT)结构畴比例增加并得以稳定引起的,说明LTT相利于静态电荷有序条纹的形成.     

Ultrasonic Study on Jahn-Teller Distortions in La1=3Sr2=3CoO3

系统研究了La1=3Sr2=3CoO3单相多晶样品在低温下的电磁输运性质和超声特性．电阻率测量表明，La1=3Sr2=3CoO3在整个温区内都表现出金属特性，并且在235 K处电阻率-温度曲线的斜率发生了变化，同时伴随着铁磁相变．超声声速在铁磁相变温度以下出现软化，并在120 K附近达到最小，之后，随着温度的进一步降低，声速开始硬化，同时出现了一个宽大的超声衰减峰．分析认为，该超声异常可能起源于中等自旋态Co3+的Jahn-Teller效应．     

La1．85Sr0．15CuO4纳米线阵列的微结构与超导电性

采用溶胶凝胶结合多孔氧化铝硬模板约束的方法，成功制备出直径约30nm的La1．85Sr0．15CuO4纳米线阵列，用XRD与X-ray EDX测定了所制备纳米线的物相与成分；FE-SEM与TEM表征了其形貌特征；由HRTEM与SAKD测量分析了其微结构；磁化强度的测量结果表明样品具有L-30K的超导电性，比块材La1．85Sr0．15CuO4的Tc稍低．分析表明所制各的样品中存在一种α，b轴拉伸，c轴压缩的结构畸变，减弱了铜氧面内Cu3d和O2p轨道的杂化程度，减小了α，b面内的态密度，从而压制了体系的超导电性．     

内耗测量在钙钛矿结构Mn基氧化物研究中的应用

运用内耗测量技术系统地研究了空穴型和电子型掺杂锰氧化物的相分离行为。对于La0．67，Ca0．33MnO3样品，在铁磁金属区，内耗温度曲线Q^-1（T）上观察到与电子相分离有关的内耗峰。此外，我们在顺磁区观察到与磁团簇形成有关的内耗峰。磁测量的结果也证明了在顺磁区Griffiths相的存在。采用内耗、电阻和杨氏模量原位测量的方法研究了La5／8-yPryCa3／8MnO3（y=0．35）中电流对电荷有序相的影响。较大的电流破坏了电荷有序态，导致电阻率降低，同时杨氏模量也有相应的变化。通过分析表明，在La5／8-yPryCa3／8MnO3（y=0．35）中存在相分离行为，即电荷有序相和铁磁金属相共存。对于电子型掺杂的Sr0．8Ce0．2MnO3和Bi0.4Ca0．5MnO3样品，通过内耗实验同样给出了相分离的证据。在外加磁场下的内耗实验表明，Sr0．8Ce0．2MnO3顺磁区的内耗峰起源于非关联的磁团簇的形成。对于电荷有序体系Bi0.4Ca0．5MnO3由于电荷有序和电荷无序畴壁运动而导致的内耗峰被观测到。研究表明，对于空穴型和电子型掺杂锰氧化物，实验中观察到的相分离行为可能是由于MnO3八面体的Jahn-Teller畸变所导致。实验结果显示了内耗测量技术对研究强关联电子体系Mn基氧化物相分离行为是十分有效的工具。     

La1．48Nd0．4Sr0．12CuO4的结构相变研究

用高分辨电镜观察了室温下La1．48Nd0．4Sr0．12CuO4和La1.88Sr0.12CuO4样品的原子结构像，观察到了其中的La2O2层和CuO2层沿c轴方向交叉堆砌．这两个样品的微结构非常相似，说明Nd掺杂没有造成周期性的调制结构．用变温X射线研究了La1．48Nd0．4Sr0．12CuO4样品中低温正交（LTO）到低温四方（LTT）结构相变，给出了晶格常数随温度的演化过程．     

高温超导体的电子结构、反铁磁交换和磁性超导机制

高温超导体中电子的自旋和电荷一样重要。文章对高温超导体的电子结构、磁性相互作用和关于单胞层La1.85Sr0.15CuO4存在超导态的最新实验结果作了扼要的介绍，并指出，电子的有效自旋耦合应当是产生高温超导电性的原因。     

La1.85Sr0.15CuO4纳米线阵列的微结构与超导电性

采用溶胶-凝胶结合多孔氧化铝硬模板约束的方法,成功制备出直径约30nm的La1.85Sr0.15CuO4纳米线阵列,用XRD与X-ray EDX测定了所制备纳米线的物相与成分;FE-SEM与TEM表征了其形貌特征;由HRTEM与SAED测量分析了其微结构;磁化强度的测量结果表明样品具有Tc= 30 K的超导电性,比块材La1.85Sr0.15CuO4的Tc稍低.分析表明所制备的样品中存在一种a,b轴拉伸,c轴压缩的结构畸变,减弱了铜氧面内Cu3d和O2p轨道的杂化程度,减小了a,b面内的态密度,从而压制了体系的超导电性.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.     

Real-time, continuous-wave terahertz imaging by a pyroelectric camera

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped farinfrared laser is used as the illumination source, and a 124 × 124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.