Quantum phase transition in the Dzyaloshinskii–Moriya interaction with inhomogeneous magnetic field: Geometric approach

In this paper, we generalize the results of Oh (Phys Lett A 373:644–647, 2009) to Dzyaloshinskii–Moriya model under non-uniform external magnetic field to investigate the relation between entanglement, geometric phase (or Berry phase) and quantum phase transition. We use quaternionic representation to relate the geometric phase to the quantum phase transition. For small values of DM parameter, the Berry phase is more appropriate than the concurrence measure, while for large values, the concurrence is a good indicator to show the phase transition. On the other hand, by increasing the DM interaction the phase transition occurs for large values of anisotropy parameter. In addition, for small values of magnetic field the concurrence measure is appropriate indicator for quantum phase transition, but for large values of magnetic field the Berry phase shows a sharp changes in the phase transition points. The results show that the Berry phase and concurrence form a complementary system from phase transition point of view.     

The structured phase margin for robust stability analysis of linear systems with phase and time delay uncertainties

In this paper, we introduce the notion of the structured phase margin for characterising stability margins for a dynamical system with block-structured phase uncertainty. Since the structured phase margin may in general be difficult to compute, we derive an easily computable lower bound in terms of a generalised eigenvalue problem. This bound is constructed by choosing stability multipliers that are tailored to the structure of the phase uncertainty. The results in this paper complement and generalise phase information results presented in the literature involving principal phases, multivariable phase margin, phase spread, phase envelope, phase matching, and phase-sensitive structured singular value. Finally, using the structured phase margin, we present new and improved delay-dependent stability criteria for stability analysis of time-delay systems.     

A Two-Phase BMAP|G|1|N → PH|1|M – 1 System with Blocking

The stationary probability distribution of a two-phase queueing system with a finite or an infinite buffer for the first phase and a finite buffer for the second phase is derived. The input flow of the system is a batch Markov arrival process. Both phases have single-servers. The service time distribution is arbitrary for the first phase and of phase-type for the second phase. If the buffer of the second phase is full at the instant of completion of service at the first phase, the first server is blocked until the buffer is freed.     

Models for the determination of kinetic phase diagrams and kinetic phase separation domains

Several theoretical models for the determination of kinetic phase diagrams for solid solution growth from the liquid phase are presented and compared to each other. These models include a Monte Carlo simulation model, used as a reference model, a previously defined analytical model, based on linear non-equilibrium thermodynamics, and a new model, rooted in the kinetics at kink sites.All models have in common that the composition of the growing solid phase tends to the liquid phase composition for increasing undercooling, enhancing mixing even for systems with a strong tendency to phase separation. However, depending on the system parameters considerable quantitative differences can occur between the results from the model based on non-equilibrium thermodynamics and the MC model. Instead, the new model follows very well the trends of the MC simulations, both for well-mixing systems and for phase separating systems.For phase separating systems the analytical models predict kinetic phase separation domains, zones in the kinetic phase diagram yielding steady state growth of more than one solid phase with different compositions. According to MC simulations such domains in phase space correspond to domain formation in real space. Also in this case the new model is consistent with the MC results.     

Differential phase shifters based on Schiffman type‐C and type‐F networks with wide phase shift range

This study proposes a class of differential phase shifters based on the Schiffman type‐C and type‐F networks with wide phase shift range. After the phase and bandwidth properties of these two distinct networks are numerically analyzed, two unique advantages of wide phase shift range and wide phase shift bandwidth are revealed. Next, the optimal design parameters for different phase shift values up to 405° are presented to allow for a quick design process. To verify the proposed approach, a 180° differential phase shifter is designed, fabricated and measured. Good performance is achieved with an impedance ratio of 1.959 and 3.7° phase deviation over a phase shift bandwidth of 61%.     

Phenomenological calculation of phase equilibria in the Fe---Ni system

In order to seek inexpensive substituting elements for Pd in an Fe---Pd based L1₀ ordered phase, a phenomenological calculation based on the cluster variation method combined with a Lennard-Jones type pair-wise atomic interaction energies has been attempted for a Fe---Ni binary system. The phase equilibria for FeNi₃-disorder and FeNi-disorder are investigated. In particular, a tetragonal distortion is explicitly considered for the FeNi L1₀ ordered phase. The calculated FeNi₃-disorder phase boundary shows good agreements with an experimental result. An FeNi L1₀ ordered phase which does not appear in a conventional Fe---Ni binary phase diagram is predicted as a stable phase, implying that Ni is a potential substituting element for Pd in an Fe---Pd based L1₀ ordered phase.     

基于QPSO的震动传感器片上相位补偿器设计方法

震动传感器的系统相位非一致性会对地震波到时时差提取产生很大的误差,严重影响震源定位精度;针对这一问题,提出了一种基于量子粒子群优化算法（QPSO）的震动传感器片上相位补偿器设计方法。首先对震动传感器进行相位标定,获得传感器与参考传感器的相位差;其次设计基于QPSO算法的相位补偿滤波器对相位差进行修正,使其无限趋近于0;最后,将相位补偿滤波器封装成FPGA软核部署于FPGA上,完成对震动传感器的相位片上实时补偿。为了验证该方法的性能,将相位补偿滤波器部署于自研的多通道震动信号采集系统上,对8个相同型号震动传感器进行相位一致性校准。试验结果表明,在震动传感器频响范围内,该方法可以将2.5°内的传感器相位差实时修正至0.0044°以下,实现了震动传感器阵列的相位一致性实时校准。该成果在地下浅层震源定位领域具有较强的应用价值。     

混沌分量对相位噪声测量的影响

针对在相位噪声测量过程中,存在测得的振荡器相位噪声比实际中使用时的相位噪声要好一些的问题,考虑到非线性系统中,混沌现象的普遍存在,提出修正振荡器的输出表达式,使其中含有弱混沌分量。采用常用的鉴相测量法,通过仿真得出混沌分量对振荡器相位噪声测量的影响结果。讨论了为减小混沌信号对振荡器相位噪声的影响所需研究的一些问题。     

基于融合相位特征的视网膜血管分割算法

针对相位一致性特征对血管中心检测不足问题,提出基于融合相位特征的眼底视网膜血管分割算法。首先,预处理原始的视网膜图像;然后,对图像中每个像素构造4D的特征向量（包括Hessian矩阵、Gabor变换、条带选择组合位移滤波响应（B-COSFIRE）滤波、相位特征）;最后,采用支持向量机（SVM）进行像素分类,实现眼底视网膜血管的分割。其中,相位特征是将分别提取的相位一致性特征与Hessian矩阵特征进行小波融合后得到的一种新的融合相位特征。该特征既保留了相位一致性特征良好的血管边缘信息,又克服了相位一致性特征对血管中心检测的不足。在用于血管提取的数字视网膜图像（DRIVE）数据库上测得基于融合相位特征的视网膜血管分割算法的平均准确率（Acc）为0.9574,平均受试者工作曲线面积（AUC）为0.9702;且在单一特征进行像素分类提取血管的实验中,与使用相位一致性特征相比,使用融合相位特征进行像素分类提取血管的Acc由0.9191提高到0.9478,AUC由0.9359提高到0.9578。实验结果表明,融合相位特征比相位一致性特征更适用于基于像素分类的眼底视网膜血管分割算法。     

一种改进的模拟退火算法的相位恢复

首先对传统的模拟退火算法进行改进,然后由独立变量分析方法对纯相位复波的数字全息图进行零级项消除,得到其共轭项,获取未解压的共轭复波相位,最后利用改进的模拟退火算法对未解压的共轭复波相位进行了相位恢复。结果表明,利用以上方法能较好的解决数字全息重构中的零级项和相位恢复问题。     

一种三相同步器鉴相式采集及分区间解算方法

针对三相同步器信号采集过程中偏差较大且剧烈跳动的问题,提出一种三相同步鉴相式采集及分区间解算方法,该方法首先通过鉴相方式判断励磁与三相电压相位关系,再进行A/D转换,最后通过分区间解算获取三相同步器角度值.为恶劣工业现场、机载环境等三相同步器信号的处理提供了一种低功耗、低成本、高精度解决方案.     

Gain optimization for millimeter wave reflectarray antennas based on a phase gradient approach

This paper is concerned with reflectarray antenna design with multiple unit cells in order to enhance the gain at the design frequency, while keeping an acceptable bandwidth to work for 5-G mobile base station applications. The design is based on five unit cells. The design begins with an investigation of the phase responses of all unit cells. It is required to choose a unit cell that can span 360° with linear characteristics. Unfortunately, none of the unit cells has perfectly linear phase characteristics. Each of them has a limited linear phase region. The proposed reflectarray design method selects the most linear region from each phase curve for selecting the appropriate unit cell with the appropriate size for each required phase using a phase gradient approach. With this approach, piece-wise linear phase characteristics are adopted for the design of the reflectarray to enhance the gain at the design frequency.     

Comparison of different gaits with rotation of the feet for a planar biped

Fast human walking includes a phase where the stance heel rises from the ground and the stance foot rotates about the stance toe. This phase where the biped becomes under-actuated is not present during the walk of humanoid robots. The objective of this study is to determine if this phase is useful to reduce the energy consumed in the walking. In order to study the efficiency of this phase, six cyclic gaits are presented for a planar biped robot. The simplest cyclic motion is composed of successive single support phases with flat stance foot on the ground. The most complex cyclic motion is composed of single support phases that include a sub-phase of rotation of the stance foot about the toe and of finite time double support phase. For the synthesis of these walking gaits, optimal motions with respect to the torque cost, are defined by taking into account given performances of actuators. It is shown that for fast motions a foot rotation sub-phase is useful to reduce the criteria cost. In the optimization process, under-actuated phase (foot rotation phase), fully-actuated phase (flat foot phase) and over-actuated phase (double support phase) are considered.     

The theorem of corresponding relation between neighboring phase regions and their boundaries in phase diagrams (I)

Several fundamental concepts in phase diagrams have been discussed. The theorem of corresponding relation between the number of different phases in the neighboring phase regions Φ and the dimension R₁ of their phase boundary in the phase diagrams is derived from the phase rule. The five corollaries of this theorem for isobaric phase diagrams are derived also. By applying this theorem and its corollaries, the following results can be obtained. Both the boundary rule and contact rule of phase regions in phase diagrams may be deduced. The ten empirical rules for constructing the complex ternary isobaric phase diagrams from phase diagram units may be put on a theoretical basis. The relation between neighboring phase regions and their boundary in phase diagrams of one-, two-, three- and four-components of all types and in the different horizontal and vertical sections of ternary phase diagrams may be explained without introducing any supplementary concept.     

计算机仿真在研究变频器制动中的应用

为解决异步电机在电压型变频器驱动下制动困难的问题，试验一种新型的异步电机三相／二相制动方法。根据异步电动机本身非线性的动态数学模型，构造出两相静止坐标系下基于MATLAB环境的异步电机三相／二相制动仿真模型。通过对异步电机三相／二相制动的动态过程仿真，详细分析了电压型变频器驱动下的异步电机能进行三相／二相制动的原因，同时验证了这一仿真模型的正确性。     

一种基于灰度级相位的指纹图像增强方法

图像增强是指纹识别系统中非常重要的一个步骤。本文提出了灰度级相位的概念,并实现了一个根据灰度级相位增强指纹图像的方法。该方法首先计算指纹区域内每个像素点的灰度级相位,然后对灰度级相位进行滤波,最后根据滤波后的灰度级相位构建指纹图像。测试结果表明该方法对低质量的指纹图像增强效果好。     

高精度微波矢量移相器研究

针对相控阵系统对微波信号相位高精度调整的要求,提出了一种基于I／Q调制器的微波矢量移相器的设计方法。通过理论推导,对影响移相器相位精度的幅度、相位不平衡因素进行了分析。介绍了幅度、相位不平衡引入的误差校正和如何提高微波宽带电路的幅度、相位平衡方法。将分析结果用于微波矢量移相器设计,使移相器相位精度控制在±1．5°内。     

Phase measurements in MAESTRO polarimetric data from the U.K. test sites

Tests using MAESTRO data from the Reedham and Feltwell test sites suggest that the assumptions of a multi-variate complex zero-mean Gaussian distribution for scattering am litudes and a linear distortion model for polarimetric data lead to a viable model for C-band observations, though with some deviations between theory and measurements. P·band observations arc in general not consistent with this data model. When viable, the Gaussian model provides a basis for defining phase information, and has implications for the statistical measures which should be used to do so. The usual mean and standard deviation sta istics arc shown to have undesirable characteristics when applied to phase measurements. The effects of calibration and noise on phase measurements from distributed targets arc discussed, and other system effects on phase arc noted. Analysis of phase data from fields at the Feltwell test site shows that at C band the copolarized phase difference can discriminate between different crop types, but not at P band.     

Theoretical and experimental study of the U-Pu-Zn system

A method for analyzing binary phase diagrams developed by L. Brewer for a desk top calculator is applied to determining lattice stability and excess free energy parameters for the U-Pu, Pu-Zn, and U-Zn binary systems. These data were used to calculate a ternary phase diagram. Several experimental U-Pu-Zn melts were prepared. The results of the computer generated phase diagrams prepared with the calculator generated parameters and with regular solution theory constants are compared with each other and with the experimental data. Although the regular solution theory constants gave better agreement, we believe that the desk top calculator program provides a valuable method for analysis of binary phase systems. The computer generated phase diagram was very valuable in guiding experimentation and in interpreting the results.     

PXI总线幅相一致性测试模块设计

幅相一致性是单脉冲体制相控阵雷达的重要指标,其对雷达测角精度影响很大。采用虚拟仪器技术、自适应处理技术设计了基于PXI总线的幅相一致性测试模块,实现了幅相一致性的快速同步自动测试。试验结果表明,该模块在测试精度、测试方便性和实用性方面与专业矢量电压表测试结果相当。对雷达性能测试能力的提高具有很大的实用价值和指导意义。