Pressure Evolution of the Magnetism and Fermi Surface of YbPtBi Probed by a Tunnel Diode Oscillator Based Method

A central research topic in condensed matter physics is the understanding of the evolution of various phases and phase transitions under different tuning parameters such as temperature, magnetic field and pressure. To explore the pressure-induced evolution of the magnetism and Fermi surface of the heavy fermion antiferromagnet Yb Pt Bi, we performed tunnel diode oscillator based measurements under pressure at low temperatures in high magnetic fields. Our results reveal that the magnetic order strengthens and the Fermi surface shrinks as the pressure increases, which are consistent with typical observations for Yb-based heavy fermion compounds. In addition, an anomalous change in the quantum oscillation amplitudes is observed above 1.5 GPa, and determining the origin requires further study.

考虑用电和馈电模式的变流器电驱系统建模与稳定性分析

由大量异步电机驱动设备构成的电力电子化交流配用电系统存在严重的次/超同步振荡问题。电驱系统正常工作时具有用电和馈电2种运行模式,现场振荡现象表明不同的运行模式对系统的稳定性影响也不同。建立了含机侧系统的电驱系统详细阻抗模型,利用阻抗分析法揭示了电驱系统接入电网的次/超同步振荡机理,分析了运行模式、电网强度、控制参数、交流电压幅值等因素对系统次/超同步稳定性的影响,并基于相位裕度灵敏度明确了主导影响因素。基于实际系统数据,搭建了时域仿真模型,仿真复现了振荡现象,并验证了理论分析的正确性。

Steady and oscillatory plasma properties in the near-field plume of a hollow cathode

Hollow cathodes serve as electron sources in Hall thrusters,ion thrusters and other electric propulsion systems.One of the vital problems in their application is the cathode erosion.However,the basic erosion mechanism and the source of high-energy ions cause of erosion are not fully understood.In this paper,both potential measurements and simulation analyses were performed to explain the formation of high-energy ions.A high-speed camera,a single Langmuir probe and a floating emissive probe were used to determine the steady and oscillatory plasma properties in the near-field plume of a hollow cathode.The temporal structure,electron temperature,electron density,and both static and oscillation of plasma potentials of the plume have been obtained by the diagnostics mentioned above.The experimental results show that there exists a potential hill（about 30 V） and also severe potential oscillations in the near-plume region.Moreover,a simple 2 D particle-in-cell model was used to analyze the energy transition between the potential hill and/or its oscillations and the ions.The simulation results show that the energy of ions gained from the static potential background is about 20 e V,but it could reach to 60 e V when the plasma oscillates.

向量血流技术在腹部凸阵超声探头上的应用研究

向量血流成像是一种新型的超声血流测量技术。相对于传统的彩色多普勒和频谱多普勒,它具有不依赖角度校正、可直接获取血流的实时幅值和方向(血流速度矢量)等优势。横向振荡法(transverse oscillation,TO)是实现向量血流成像的有效方法之一。然而,对于结构更加复杂的凸阵探头,目前仍然缺乏基于商用超声机的完整且详细的算法验证过程。该研究先介绍了TO成像过程和成像原理,然后通过仿真实验,计算设定速度值与测量速度值之间的误差,再通过多普勒体模实验,验证设定速度值与测量速度值之间的误差。其中仿真实验中TO向量血流技术测得的速度值为0.48 m/s,与预设值0.50 m/s的误差为−4%;多普勒体模实验中测得的速度值为8.33、11.14、14.44、16.67 cm/s,与实际速度值7.97、10.78、14.06、17.34 cm/s的误差均在±5%内。2个实验都验证了向量血流技术在腹部凸阵探头上应用的可行性。

Effects of Probe Support on the Stall Characteristics of a Low-Speed Axial Compressor

In order to investigate the effects of probe support on the stall characteristics of micro compressors, an experiment was carried out on a large-scale low-speed research compressor according to the principle of geometric similarity. A cylindrical probe support intruding to 50% blade span was mounted at 50% chord upstream from the rotor blade leading edge. The static pressure rise characteristic of the compressor is measured, with and without the probe support respectively. The dynamic compressor behavior from pre-stall to full stall was also measured. The results indicate that the stability margin of the compressor is lowered after installing the probe support. The stall inception is aroused by modal wave disturbances. The disturbances developed into two stall cells smoothly before installing the probe support, while the disturbances first developed into a single stall cell then splitting into two stall cells after installing the probe support. The presence of probe support lowers the initial intensity of the rotating stall of the compressor, while it doesn't alter the intensity of the rotation stall after the compressor enters into full stall.

Nanosensitive Silicon Microprobes for Mechanical Detection and Measurements

Nanosensitive mechanical microprobes with CMOS transistors, inverters, inverters cascades and ring oscillators, integrated on the thin silicon cantilevers are presented. Mechanical stress shifts linear, steep switching fragment of the inverters’ electrical characteristics. Microprobes were fabricated with use of the standard CMOS technology (3.5 μm design rules, one level polysilicon gate and one level of the metal interconnections) and relief MEMS technique. Control of the silicon cantilever thickness was satisfactory in the range above the few micrometers. Several computer simulations were done to analyze and optimize transistors location on the cantilever, in respect to the mechanical stress distribution. Results of the microprobes electromechanical tests confirm high deflection sensitivity 1.2 - 1.8 mV/nm and force sensitivity 2.0 - 2.4 mV/nN, both in nano ranges. Microprobes, with the ring oscillators revealed sensitivities 5 - 8 Hz/nm. These microprobes seem to be appropriate for applications in precise chemical and biochemical sensing.

Quantization of the 1-D Forced Harmonic Oscillator in the Space (<i>x</i>, <i>v</i>)

The quantization of the forced harmonic oscillator is studied with the quantum variable (x, v∧), with the commutation relation , and using a Schrödinger’s like equation on these variable, and associating a linear operator to a constant of motion K (x, v, t) of the classical system, The comparison with the quantization in the space (x, p) is done with the usual Schrödinger’s equation for the Hamiltonian H(x, p, t), and with the commutation relation . It is found that for the non-resonant case, both forms of quantization bring about the same result. However, for the resonant case, both forms of quantization are different, and the probability for the system to be in the exited state for the (x, v∧) quantization has fewer oscillations than the (x, p∧) quantization, the average energy of the system is higher in (x, p∧) quantization than on the (x, v∧) quantization, and the Boltzmann-Shannon entropy on the (x, p∧) quantization is higher than on the (x, v∧) quantization.

基于频域无源性的并网逆变器前馈相位补偿策略

针对基于频域无源性设计的LCL型并网逆变器接入弱电网后可能会引发高频段谐波振荡问题,设计一种改进的并网逆变器前馈相位补偿策略。首先对LCL型并网逆变器的无源性及并网系统的相角裕度进行分析;然后提出一种改进的并网逆变器控制策略,通过附加超前相位补偿的PCC点电压前馈策略,保证系统无源性以及输出阻抗的相角裕度,避免发生高频段的谐波振荡,提高弱电网条件下并网逆变器系统的稳定性;最后通过仿真验证了所提方法的有效性。

后牙邻面壁提升术对牙周探诊出血的影响

目的:应用不同龈壁处理方式及成形系统对龈下深龋行邻面边缘提升术,观察充填后对牙周探诊出血的影响,为龈下深龋充填提供参考。方法:将36例龈下深龋病例分别采用排龈术、电刀切龈术、翻瓣术,将龈下缺损提升至龈上,完成复合树脂直接充填。术后3个月复查牙周探诊出血(bleeding on probing,BOP)。通过单因素分析及最优标度初步判断性别、年龄、牙齿类型、成形片种类、牙髓活力、处理方式对BOP的影响,建立非条件Logistic回归模型筛选影响BOP的因素。结果:成形片种类影响BOP(P=0.009),个性化修剪的Ivory型成形片比分段式成形片的探诊出血率高。年龄、性别、牙齿类型、牙髓活力及处理方式对BOP均无显著影响(P>0.05)。结论:成形片种类影响BOP,排龈术、电刀切龈术、翻瓣术3种龈壁暴露技术未对BOP造成明显影响。

一种可有效提高临界增益的改进型电力系统稳定器

目前,实际电力系统中广泛使用电力系统稳定器（power system stabilizer,PSS）进行低频振荡阻尼控制。但是,PSS在低频振荡控制中有一定的局限性,可能使其增益整定值难以同时满足系统阻尼水平以及《电力系统稳定器整定试验导则》规定的增益必须小于临界增益1/3的投运要求。该文通过分析,发现自并励条件下,PSS临界增益主要受励磁模式限制,而励磁模式是由励磁–PSS回路在3~8 Hz频段的固有特性形成。在上述分析的基础上,提出在励磁–PSS回路外环引入一个功率增量软反馈,形成一种带有并联环节的改进型PSS模型,改善了回路相位特性,提高了PSS临界增益,解决了上述问题。最后,以锡盟火电集中外送仿真系统为例,验证了所提方案的有效性。

交/直流电压下气体绝缘变电站盆式绝缘子表面电荷对闪络电压的影响

在气体绝缘变电站(GIS)中,盆式绝缘子表面电荷的存在会使局部电场发生畸变,严重时还会降低沿面闪络电压。为此,研制了一种用于实际252 k V GIS盆式绝缘子表面电荷的3维测量装置,可以对盆式绝缘子表面电荷进行全径向、全角度测量。参考实际盆式绝缘子的绝缘设计裕度及其沿面闪络特性,设计了闪络试验模型,分别针对直流、交流电压作用下绝缘子表面电荷对沿面闪络电压的影响开展了研究。结果表明:在交流电压和直流电压作用下,随着表面电荷积累量的增加,绝缘子沿面闪络电压有所减小;相比于交流电压50 k V作用1 h工况下,在53 k V交流电压作用3 h工况下,盆式绝缘子的沿面闪络电压降低了10.2%,而直流电压下,绝缘子的沿面闪络电压最大可降低23.0%,这说明了绝缘子表面电荷的存在对其沿面闪络电压具有明显的影响,在绝缘设计时需予以重视。研究结果可为GIS及气体绝缘输电线路(GIL)绝缘子的绝缘设计提供参考。

基于Overhauser效应的磁场梯度探测器

为提高单探头磁力仪在自然环境中的抗干扰能力,设计了一种基于Overhauser效应的双探头磁场梯度探测器。文中介绍了Overhauser效应的基本原理,对仪器的射频激发系统、信号调理系统和频率计做了详细的描述。论文分析了射频系统的不稳定因素,并给出解决方案。针对拉莫尔旋进信号,提出一种基于FPGA的多通道测频算法,并对比测试使用该算法前后的结果,分析了实验数据。同时对仪器双探头的数据一致性进行比对,给出了测试方法和测试结果。最后将该仪器和商用仪器进行室内、室外以及磁异常探测等对比试验,结果表明,其性能接近商用仪器水平,具有野外操作便捷、测量磁场精度高、抗干扰能力强等优点,证明了所研制的基于Overhauser效应的磁场梯度探测器在梯度测量中的有效性。

重复控制系统的稳定性分析

在非圆数控车削加工等场合,需要伺服驱动单元执行重复性的工作,其输入为周期性的信号或指令,其输出要求能稳定无静差地跟踪这种周期性的输入信号.而重复控制对于周期性的信号和周期性的干扰具有较好的跟踪效果和抑制作用.从时域和频域两个角度对基于内模原理的重复控制系统的原理及稳定性进行了分析,同时对改进的重复控制系统的原理及稳定性也进行了剖析,揭示了重复控制的实质,最后对设计实例进行了稳定性分析,验证了重复控制系统以及改进的重复控制系统的稳定性.

基于能量函数的低频振荡新型预警指标

提出可用于实际分析的断面潮流分析模型,通过选择观测断面,将对全网的分析转化为对每个观测断面的分析,从而实现全网的分散解耦分析。在该模型的基础上,简化了基于惯性中心的传统能量函数,对传统的稳定裕度指标进行改进,提出了稳定裕度增量指标,该指标建立于电力系统联络线观测断面的基础上,计算简单方便,可对多重扰动下的低频振荡进行预警,且能应用于扰动严重性的判断。New England 10机系统和实际系统的仿真算例验证了该方法的有效性。

关于大陆与陆缘的深部地震探查的进展──1994、1996年两届国际学术讨论会综述

连续两届国际深部地震讨论会成果累累。对深部地震的资料采集、处理、解释技术以及几类专门地质地球物理问题的研究进行了综述。研究成果在理论、方法方面是该领域的世界先进水平：在地震学应用于陆缘、陆壳与壳幔过渡带等地质问题方面有明显的提高。提出了值得讨论的问题。

从核磁共振仪到电子自旋共振实验仪的改装

介绍了将核磁共振仪改装成电子自旋共振实验仪的制作过程．实验弃用了原有的HZ811小型核磁共振中的永磁体，改用螺线管，并增加了专供电源，同时改变了边线振荡器的频率范围，实现了磁场强度从0·4T到0．0005T、对应频率从12～18MHz的范围到21～31MHz的转变，从而满足了电子自旋共振实验仪的实验要求．

永久磁铁核磁共振实验仪如何获得清晰的共振信号

用永久磁铁作为外场的核磁共振实验仪观察共振吸收信号和测量1H、19F的g因子时,如果仪器没有处于最佳状态,将找不到清晰的共振信号。如何对仪器进行适当的调整和技术处理,得到清晰的核磁共振吸收信号,本文对几个相关问题作了探讨和说明。

基于互补式电导探针阵列传感器设计与静态实验

互补式电导探针阵列传感器设计是在以前所研究仪器基础上进行创新,采用轴向及周向互补的方式将电导探针传感器均匀分布,是一种主要应用于测量水平井油水两相含水率的电导成像方法,通过测量等效阻抗的变化来判断探针所处的位置,从而实现在水平状态下对油水界面位置的判别,同时给出持水率,并接通过探针所测量阻抗变化的规律判断油水界面附近的流型和流态。通过验证内外环之间互相补充,使得测量的精确率达到了理想的效果。

开关电源反馈环路稳定性分析与设计研究

文章首先对开关电源反馈环路的基本原理以及常用反馈补偿方式及特点进行阐述,然后以反激式开关电源设计为例,对反馈环路和补偿的关键电路进行计算设计后,对反馈环路在PCB布局方面给出一定的建议,具有一定的参考价值。

风电机组接入对内蒙古电网低频振荡的影响分析

根据内蒙古电网风电运行现状,研究了内蒙古电网风机接入带来的动态交互问题及改善措施。利用PSD-BPA软件,分析了将原有风电机组替换为同步机组对内蒙古电网-山东电网振荡模式的影响;再将原来存在的振荡机组替换为风电机组,观察对内蒙古电网-山东电网振荡模式的影响情况,认为替换西侧区域部分风电机组为同步机会恶化系统稳定性,替换东侧区域部分风电机组为同步机,对系统稳定性的恶化程度较小。基于矢量裕度法分析了风电机组的接入对于电力系统低频振荡的影响,认为靠近西部盟市的双馈风机均对系统稳定性起帮助作用,而对于靠近中、东侧盟市的双馈风机则起恶化作用。并基于矢量裕度法,研究了内蒙古电网低频振荡的改善措施。