含Chern-Simons项的(2+1)维标量量子电动力学

本文用一种方便的微扰展开方法,将一个含有Chem-Simons项的(2+1)维标量量子电动力学(QED)模型中的标量场φ量子化,在一圈图近似下,导出矢量场A_μ的等效作用量,从而证明有两支(不稳定的)元激发谱。Chern-Simons项的耦合系数不受φ场量子化的影响。     

(Nd1-x Erx)3 Fe25 Cr4.0(0≤x≤1.0)化合物的结构与磁性

合成了 (Nd1 -xErx) 3Fe2 5Cr4 . 0 (0≤x≤ 1 .0 )系列化合物并采用x射线衍射和磁测量等手段研究了它们的结构和磁性 .发现当 0≤x≤ 0 . 8时化合物保持Nd3(Fe,Ti) 2 9型结构 ,属于单斜晶系 ,A2 m空间群 ,当 0 8相似文献   

Nb掺杂导致LaMnO_3绝缘体-金属转变的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理计算,系统研究了Nb掺杂LaMn_(1-x)Nb_xO_3(x=0,0. 25,0. 5,0. 75)的结构和电磁性质.计算结果表明,所有的LaMn_(1-x)Nb_xO_3都稳定在正交结构. LaMn_(1-x)Nb_xO_3当x 0. 5时为A型反铁磁绝缘体,在x=0. 5和0. 75时为G型反铁磁金属.随着Nb掺杂量增加,当x=0. 5时掺杂电子占据导带的底部,系统产生绝缘体-金属转变.这意味着LaMn_(1-x)Nb_xO_3在电子器件上可能有重要的应用.另外,LaMn_(1-x)Nb_xO_3在x=0. 25和0. 75时出现了自旋玻璃行为.     

Ti1－xCoxO2铁磁性半导体薄膜研究

利用射频磁控反应溅射制备了Ti1-xCoxO2薄膜样品.超导量子干涉仪(SQUID)测量了样品在常温，低温下的磁特性.结果显示样品在常温下已经具有明显的铁磁性.常温时其矫顽力32×103A/m,饱和磁化强度55emu／cm3磁性元素的磁矩达0679μB／Co.饱和场12×104A/m.x射线衍射(XRD)和x射线光电子能谱(XPS)实验分析初步表明样品中没有钴颗粒. 关键词： 铁磁半导体 TiO2 薄膜     

(Nd1－xErx)3Fe25Cr4.0(0≤x≤1.0) 化合物的结构与磁性

合成了(Nd1-xErx)3Fe25Cr4.0(0≤x≤1.0)系列化合物并采用x射线衍射和磁测量等手段研究了它们的结构和磁性.发现当0≤x≤0.8时化合物保持Nd3(Fe,Ti)29型结构,属于单斜晶系,A2/m空间群,当0.8＜x≤1.0时,化合物形成一种哑铃对Fe-Fe无序替代Th2Ni17结构,P63/mmc空间群.随着Er含量的增加,化合物的居里温度TC和饱和磁化强度Ms单调下降.当x=0时,Nd3Fe25Cr4.0化合物的易磁化方向非常靠近[040]方向,仅略微偏离15结构的基面,但随Er含量的增加,(Nd1-xErx)3Fe25Cr4.0化合物的易磁化方向从靠近[040]方向转向靠近[4 0 2]方向,同时与15结构的基面所成的倾角也增大.通过测量交流磁化率发现,x=0-0.4和x=1.0的化合物在低温下出现自旋重取向.在x=0-0.4的化合物中,自旋重取向温度Tm随Er含量增加单调升高.用高达13T的磁场测量难磁化方向的磁化曲线发现,在0≤x≤0.8的化合物中发生了一级磁化过程(FOMP),其临界场Bcr随Er含量的增加而降低.     

类富勒烯纳米晶CNx薄膜及其场致电子发射特性

利用微波等离子体增强化学气相沉积技术制备出了CNx薄膜,并利用x射线光电子能谱、x射线衍射、扫描电子显微镜和Raman光谱等测试手段对所制备的CNx薄膜的微结构和成分进行了分析.研究了其场致电子发射特性.发现薄膜的结构和场发射特性与反应系中的甲烷、氮气及氢气的流量比有关,当甲烷、氢气及氮气流量比为8/50/50sccm时,制备的薄膜具有弯曲层状的纳米石墨晶体结构(类富勒烯结构)和很好的场发射特性.场发射阈值电场降低至1.1V/μm.当电场为5.9V/μm时,平均电流密度达70μA/cm2,发射点密度大于1×104cm-2.     

零质量玻色场,自发破缺与Goldstone定理

本文讨论零质量玻色场φ(x)在动量空间的零频部分,它不是动量趋于零时的极限,所以并不代表粒子的产生和湮灭算符。由于正则量子化得到一连续量子数,因此所有物理态都不能归一。真空变成一个无穷宽能带中的任意一个态。当φ(x)是厄米场时,真空并不存在简并,因此没有真空自发破缺;当φ(x)是复数场时,每一真空都是无穷地分立简并,因此也没有连续对称的自发破缺。利用这些态容易验证 Goldstone 定理证明中所插入的零动量零能量中间态并非代表不同数目的 Goldstone 粒子的相干迭加,也不一定与原来的真空态正交。文章亦讨论了φ(x)→φ(x)+η的生成元,它作用在φ(x)上的真空平均值及作用在真空态上的结果。     

少量Mn替代对Gd2Co17化合物结构与磁性的影响

通过X射线衍射和磁性测量研究了Gd2Co17-xMnx(x=0—1)化合物的结构和磁性.X射线衍射表明样品均为Th2Zn17型菱方结构.晶胞体积随Mn含量x线性增大,居里温度TC单调下降,饱和磁化强度Ms单调增加,化合物的磁晶各向异性场μ0Ha先随Mn含量减少,当x=0.6时达到最小,然后再增大 关键词： 2∶17型化合物 晶体结构 磁性     

RCo12-xTix(R=Y，Sm)化合物的结构与磁性研究

通过x射线衍射分析和磁性测量研究了RCo12-xTix(R=Y，Sm)化合物的结构与磁性，所有化合物全部具有ThMn12型结构.常规取向样品的x射线衍射谱表明，SmCo12-xTix化合物具有室温面磁晶各向异性，而YCo12-xTix化合物具有室温单轴磁晶各向异性.随着Ti含量的增加，SmCo12-xTix和YCo12-xTix化合物的居里温度TC及饱和磁化强度Ms均单调降低.YCo12-xTix化合物的磁晶各向异性场μ0Ha随Ti含量的增加而降低，而SmCo12-xTix化合物的磁晶各向异性场μ0Ha在x=1.74时出现一极大值，这可以用双次晶格模型来解释.     

具有Eckart势的Schrdinger方程的任意l波解析解

使用完全量子化规则计算了具有离心项的Eckart势,根据动量积分∫xBxAk(x)dx-∫x0Bx0Ak0(x)dx=nπ和Greene-Aldrich近似化条件,得到了系统的任意l波Schrdinger方程的解析解.讨论了:(1)基态和激发态下,势能范围参数λ和势阱深度η对具有不同角动量量子数的能量本征值的影响;(2)径向量子数n和角动量量子数l与能量本征值的关系.     

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.     

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.     

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.     

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].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

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.