Comparison of performance between bipolar and unipolar double-frequency sinusoidal pulse width modulation in a digitally controlled H-bridge inverter system

By deriving the discrete-time models of a digitally controlled H-bridge inverter system modulated by bipolar sinu- soidal pulse width modulation （BSPWM） and unipolar double-frequency sinusoidal pulse width modulation （UDFSPWM） respectively, the performances of the two modulation strategies are analyzed in detail. The circuit parameters, used in this paper, are fixed. When the systems, modulated by BSPWM and UDFSPWM, have the same switching frequency, the stabil- ity boundaries of the two systems are the same. However, when the equivalent switching frequencies of the two systems are the same, the BSPWM modulated system is more stable than the UDFSPWM modulated system. In addition, a convenient method of establishing the discrete-time model of piecewise smooth system is presented. Finally, the analytical results are confirmed by circuit simulations and experimental measurements.

Differences in Non-suicidal Self-injury Behaviors between Unipolar Depression and Bipolar Depression in Adolescent Outpatients

Objective Non-suicidal self-injury(NSSI)has a higher prevalence in adolescents with depressive disorders than in community adolescents.This study examined the differences in NSSI behaviors between adolescents with unipolar depression(UD)and those with bipolar depression(BD).Methods Adolescents with UD or BD were recruited from 20 general or psychiatric hospitals across China.The methods,frequency,and function of NSSI were assessed by Functional Assessment of Self-Mutilation.The Beck Suicide Ideation Scale was used to evaluate adolescents’suicidal ideation,and the 10-item Kessler Psychological Distress Scale to estimate the anxiety and depression symptoms.Results The UD group had higher levels of depression(19.16 vs.17.37,F=15.23,P<0.001)and anxiety symptoms(17.73 vs.16.70,F=5.00,P=0.026)than the BD group.Adolescents with BD had a longer course of NSSI than those with UD(2.00 vs.1.00 year,Z=−3.39,P=0.001).There were no statistical differences in the frequency and the number of methods of NSSI between the UD and BD groups.Depression(r=0.408,P<0.01)and anxiety(r=0.391,P<0.01)were significantly and positively related to NSSI frequency.Conclusion Adolescents with BD had a longer course of NSSI than those with UD.More importantly,NSSI frequency were positively and strongly correlated with depression and anxiety symptoms,indicating the importance of adequate treatment of depression and anxiety in preventing and intervening adolescents’NSSI behaviors.

Reduction of Unipolar Leakage Flux and Torque Ripple in Consequent-pole PM Vernier Machine

This paper proposes a new consequent-pole permanent magnet vernier machine(CPMVM),which can be regarded as a combination of two conventional CPMVM with opposite polarities.Based on the simplified axial magnetic circuit model,it is verified that the proposed CPMVM can reduce the unipolar leakage flux.In order to reduce the torque ripple of machine and improve the output torque of machine,the flux barrier is placed on the rotor of the proposed machine.Then,the parameters of the proposed CPMVM are optimized and determined.Moreover,the electromagnetic performance,including no-load air-gap flux density,average torque and torque ripple,flux linkage,back-electromotive force,cogging torque,average torque,torque ripple,power factor and loss,is compared with conventional surface-mounted permanent magnet vernier machine(SPMVM)and CPMVM.Finally,it is demonstrated that proposed CPMVM with flux barrier can effectively reduce the unipolar leakage flux and greatly reduce the torque ripple of machine.Also,compared with the SPMVM,the proposed CPMVM with flux barrier saves more than 45%of the permanent magnet material without reducing output torque.

手持式心电采集仪的使用技巧

手持式心电采集仪是一款简易的双极单导联心电图记录设备,只需双手拇指紧捏正、负两极,就能方便地记录出标准Ⅰ导联心电图,多用于监测心律失常。它属于家用医疗器械,颇受广大中老年朋友的欢迎。基于单极导联与双极导联的本质及其内在联系,本文衍生出标准导联与加压单极导联的记录方法;同时,在深入探究CR导联与Wilson导联内在联系的基础上,创造性地提出了手持式心电采集仪直采CR胸导联心电图的方法。理论和实践均表明,加压单极肢体导联的等效记录法与CR胸导联的双极记录法不仅能满足临床需要,而且还有其独到之处。该方法能充分发挥家用医疗器械的医用价值,值得推广普及。

Coexistence of unipolar and bipolar modes in Ag/ZnO/Pt resistive switching memory with oxygen-vacancy and metal-Ag filaments

In this study, the unipolar resistive switching （URS） and bipolar resistive switching （BRS） are demonstrated to be coexistent in the Ag/ZnO/Pt memory device, and both modes are observed to strongly depend on the polarity of forming voltage. The mechanisms of the URS and BRS behaviors could be attributed to the electric-field-induced migration of oxygen vacancies （Vo） and metal-Ag conducting filaments （CFs） respectively, which are confirmed by investigating the temperature dependences of low resistance states in both modes. Furthermore, we compare the resistive switching （RS） characteristics （e.g., forming and switching voltages, reset current and resistance states） between these two modes based on Vo- and Ag-CFs. The BRS mode shows better switching uniformity and lower power than the URS mode. Both of these modes exhibit good RS performances, including good retention, reliable cycling and high-speed switching. The result indicates that the coexistence of URS and BRS behaviors in a single device has great potential applications in future nonvolatile multi-level memory.

PHOTOACOUSTIC GENERATION OF FOCUSED QUASI-UNIPOLAR PRESSURE PULSES

The photoacoustic effect was employed to generate short-duration quasi-unipolar acoustic pressure pulses in both planar and spherically focused geometries.In the focal region,the temporal profile of a pressure pulse can be approximated by the first derivative of the temporal profile near the front transducer surface,with a time-averaged value equal to zero.This approximation agreed with experimental results acquired from photoacoustic transducers with both rigid and free boundaries.For a free boundary,the acoustic pressure in the focal region is equal to the sum of a positive pressure that follows the spatial profile of the optical energy deposition in the medium and a negative pressure that follows the temporal profile of the laser pulse.

Coexistence of Bipolar and Unipolar Resistive Switching Behavior in Ag/ZnMn_2O_4/p^+-Si Device

ZnMnOthin films were deposited by a sol-gel technique onto a p+-Si substrate, and a RRAM device with the Ag/ZnMnO/p~+-Si structure was fabricated. The microstructure of ZnMnOfilms and the resistive switching behavior of Ag/ZnMnO/p~+-Si device were investigated. ZnMnOthin films had a spinel structure after annealing at 650 °C for 1 h. The Ag/ZnMnO/p~+-Si device showed unipolar and/or bipolar resistive switching behavior, exhibiting different ION/IOFF ratio and switching endurance properties. In bipolar resistive switching, high-resistance-state(HRS) conduction was dominated by the space-charge-limited conduction mechanism, whereas the filament conduction mechanism dictated the low resistance state(LRS). For unipolar resistive switching, HRS and LRS were controlled by the filament conduction mechanism. For bipolar resistive switching, the conduction process can be explained by the space-charge region of the p-n junction.

SPICE modeling of flux-controlled unipolar memristive devices

Unipolar memristive devices are an important kind of resistive switching devices. However, few circuit models of them have been proposed. In this paper, we propose the SPICE modeling of flux-controlled unipolar memristive devices based on the memristance versus state map. Using our model, the flux thresholds, ON and OFF resistance, and compliance current can easily be set as model parameters. We simulate the model in HSPICE using model parameters abstracted from real devices, and the simulation results show that the proposed model caters to the real device data very well, thus demonstrating that the model is correct. Using the same modeling methodology, the SPICE model of charge-controlled unipolar memristive devices could also be developed. The proposed model could be used to model resistive memory cells, logical gates as well as synapses in artificial neural networks.

A "Superpower" instead of "Unipolarity"

The power position and influence of a country depend on its comprehensive national power based on economics. While addressing to the press in Kansas on July 6, 1971, President Nixon noted: "Comparing to our overwhelming position at the end of World War II, the United States is now facing immense challenges that we have never expected before. " He added, "In terms of economics, the United States is no longer a dominant power or an overwhelming global power. At present, there exist not only two superpowers. In consideration of eco-

Bias polarity-dependent unipolar switching behavior in NiO/SrTiO_3 stacked layer

The identification of the switching location has been a key technology to tune the physical properties of unipolar resistive switching（RS） cells.Here we report the RS properties of Au/Ni O/Sr Ti O3（STO）/Pt memory cells.The switching repeatability is closely related to the applied bias polarity,which is different from the scenario of the Au/STO/Pt cells reported in our previous researches.The high resistance in positive bias is greater than that in negative bias.The R（T）–R0I^2 R（T） plot of the on-state I–V curve shows a regular shape only with a slight bend and an abnormal shape with an abrupt increase and decrease under negative and positive bias,respectively.These comparative experimental results reveal that the conductance filament consisting of oxygen vacancies grows from the cathode to the anode.The spatial RS location is identified with the weaker part along the conductance filament length direction,which should be near the Ni O/STO interface and STO/Pt interface under positive and negative bias,respectively.

Healthy individuals vs patients with bipolar or unipolar depression in gray matter volume

BACKGROUND Previous studies using voxel-based morphometry(VBM)revealed changes in gray matter volume(GMV)of patients with depression,but the differences between patients with bipolar disorder(BD)and unipolar depression(UD)are less known.AIM To analyze the whole-brain GMV data of patients with untreated UD and BD compared with healthy controls.METHODS Fourteen patients with BD and 20 with UD were recruited from the Mental Health Center of Shantou University between August 2014 and July 2015,and 20 nondepressive controls were recruited.After routine three-plane positioning,axial T2WI scanning was performed.The connecting line between the anterior and posterior commissures was used as the scanning baseline.The scanning range extended from the cranial apex to the foramen magnum.Categorical data are presented as frequencies and were analyzed using the Fisher exact test.RESULTS There were no significant intergroup differences in gender,age,or years of education.Disease course,age at the first episode,and Hamilton depression rating scale scores were similar between patients with UD and those with BD.Compared with the non-depressive controls,patients with BD showed smaller GMVs in the right inferior temporal gyrus,left middle temporal gyrus,right middle occipital gyrus,and right superior parietal gyrus and larger GMVs in the midbrain,left superior frontal gyrus,and right cerebellum.In contrast,UD patients showed smaller GMVs than the controls in the right fusiform gyrus,left inferior occipital gyrus,left paracentral lobule,right superior and inferior temporal gyri,and the right posterior lobe of the cerebellum,and larger GMVs than the controls in the left posterior central gyrus and left middle frontal gyrus.There was no difference in GMV between patients with BD and UD.CONCLUSION Using VBM,the present study revealed that patients with UD and BD have different patterns of changes in GMV when compared with healthy controls.

Reversible alternation between bipolar and unipolar resistive switching in La-SrTiO_3 thin films

The alternation from bipolar to unipolar resistive switching is observed in perovskite La0.01Sr0.99TiO3 thin films. These two switching modes can be activated separately depending on the compliance current （Icomp） during the electroforming process： with a higher Icomp （5 mA） the unipolar resistance switching behavior is measured, while the bipolar resistance switching behavior is observed with a lower Icomp （1 mA）. On the basis of I–V characteristics, the switching mechanisms for the URS and BRS modes are considered as being a change in the Schottky-like barrier height and/or width at the Pt/La-SrTiO3 interface and the formation and disruption of conduction filaments, respectively.

三相三状态无刷直流电机的系统模型及其仿真

根据三相三状态无刷直流电机的运行规律，建立了包括电机、驱动线路在内的整个系统的数学模型，利用该模型对样机进行起动过程暂态仿真，仿真结果与样机实测数据基本吻合。

单极性偏差控制算法在矿井提升机机械制动系统中的应用

提出一种单极性偏差控制算法,并将其应用到矿井提升机机械制动系统中。该算法可将一个反馈控制系统从无差变为有差,利于提高系统的稳定性,简化系统设计;可在不改变系统结构的基础上,提高系统动态性能。在矿井提升机机械制动系统中,通过改变给定形式即可实现该算法,具有简单、实用等优点。

单极结构下的体系效应与国家行为——兼论中国的战略选择

尽管冷战后形成的单极体系已存在20年之久,但是学术界对这一特殊国际结构的研究尚不充分。本文考察了单极结构的基本含义与特征、单极结构在体系层面的基本性质,以及这种结构在单元层面造成的影响,尤其关注单极体系的稳定性及这种结构下主要国家的行为倾向。进而根据现实主义有关国际体系变迁的理论论述,对目前美国主导的单极结构的基本方向进行了预测。本文认为,单极体系正处于弱化过程中,而无政府状态下大国竞争的压力和政治经济发展不平衡规律是削弱这一结构的基本因素,单极体系下中国外交战略应作出相应的选择。

伪随机脉位调制与单极性伪码调相复合体制引信

伪码调相引信抗干扰能力较差,伪随机脉位调制与单极性伪码调相复合引信是伪码复合体制引信发展的一个重要方向,有必要对该体制引信进行研究。首先给出了伪随机脉位调制与单极性伪码调相复合引信的数学模型,得出了相应的模糊函数、绘制了模糊图的中心部分,接着设计了基于FPGA/CPLD的系统实现原理框图,论证了单极性伪码应用及二次混频法抑制多普勒频率两个关键技术的可行性,并简单介绍了数字相关的思想及其实施。研究表明,该体制引信有良好的整体性能和现实的工程应用前景。

PWM功率放大器在直流伺服系统中的应用

介绍了PWM功率放大器的基本概念和分类,详细说明了H型双极可逆PWM系统的工作原理及其与单极、受限单极的区别。研制了基于智能功率模块PM75CES060的H型可逆PWM功率放大器,实验结果表明该系统具有高可靠性和较好的实用价值。

超高压直流输电系统关键技术探讨

对两端超高压直流输电系统构成的单极系统、双极系统和背靠背直流系统等三种类型及其应用场合进行了分析和探讨,同时还讨论超高压直流输电系统换流站直流侧特征谐波和谐波抑制装置的选择以及功率因数的补偿等,最后给出超高压直流输电系统的主要优缺点以及重点需要解决的主要问题,并提出直流输电系统未来的发展前景。

信息化进程中国际体系与秩序特征探析

人类文明正在从工业化社会迈向信息化社会,世界各国立足于不同的国情,秉持迥异的发展理念与施政方略,在国际舞台上共同演奏了民族国家竞争角逐、合作互惠、兴衰失衡并存的交响曲,共同造就了当代国际战略格局与世界秩序的全新态势。美国作为信息化浪潮的发源地与最为积极踊跃的推动者,赢得了信息化时代全球博弈的最大红利,依托厚重的经济基础和强大的军事实力,成为短期内难以逾越的单极霸权;而其他从两极格局中分离出来的诸强国以及为信息化、全球化浪潮所催生的多种国际行为体在把握机遇、发展实力、蓄势待发的同时,也于不同的领域与层次上对美国霸权形成一定的平衡与制约。单极主导、多元并存无疑成为步入信息化时代之初国际政治体系最显著的标志,但随着信息化浪潮在深度与广度上进一步拓展,在飞跃与调整的交替中不断前行,世界格局多极化、国际关系民主化、国际社会行为体多元化、从传统的"国家间政治"向世界政治乃至"全球政治"转变等趋势初现端倪,作为未来世界的可能性蓝图正逐渐呈现于世人眼前。从美国全球扩张战略的周期看,从20世纪80年代以来经过近30年持续的攻势态势,已经呈现出疲惫的征兆,在次贷危机和金融危机的影响下,美国很可能要进入一个战略休整期,美国在国际体系中的主导地位也将受到一定程度的削弱。

单相多模块电压源型逆变器

为实现低压直流到高压交流的变换,提出一种适用于低输入电压场合的单相多模块电压源型逆变器拓扑。产生同样大小的交流电压,电压源型逆变器(VSI)的直流侧电压仅需为传统H桥逆变器的1/3,因而更加适用于新能源发电系统和电池储能系统。介绍单相多模块VSI拓扑结构及工作原理,详细分析单极性PWM下电路运行特性,在此基础上完成电容器参数的设计,最后通过PSIM软件对该电路结构进行仿真,并搭建一个2k W的实验系统,对带有稳态负荷、阶跃负荷及感性负荷时的工作特性进行验证。仿真和实验结果表明,电容参数设计合理,提出的VSI具有较大的升压能力,并在阶跃负荷、感性负荷下依然具有良好的运行特性。