Absolute Wall Thickness Measurement of Conducting Plates Using Pulsed Eddy Currents

The method using pulsed eddy currents to determine the thickness of a conduction plate is extended to enable the simultaneous measurement of the plate thickness and material properties. For optimal performance, a probe must be designed depending on the thickness range that should be accessible. The need for a calibration of the material properties of a conducting plate to enable the measurement of its thickness has been removed. All that is needed is a probe with known dimensions and suitable hardware to create a current pulse and measure a transient magnetic induction.

Effect of wall friction on oscillation of velocity at the head of the gravity current

Velocity oscillations at the head of the gravity current were investigated in experiments and numerical simulations of a locked-exchange flow.A comparison of the experimental and numerical simulations showed that the depth and volume of the released fluid affected the oscillations in the velocity of the gravity current.At the initial stage,the head moved forward at a constant velocity,and velocity oscillations occurred.The head maximum thickness increased at the same time as the head,which did not have a round,and accumulated buoyant fluid due to the buoyancy effect intrusion force.The period of accumulation and release of the buoyant fluid was almost the same as that observed for the head movement velocity;the head movement velocity was faster when the buoyant fluid accumulated and slower when it was released.At the viscous stage,the forward velocity decreased proportionally to the power of 1/2 of time,since the head was not disturbed from behind.As the mass concentration at the head decreased,the gravity current was slowed by the viscous stage in its effect.At the viscous stage,the mass concentration at the head was no longer present,and the velocity oscillations also decreased.

Study on the formation of arc plasma on the resistive wall liquid metal current limiter

Due to its significant attributes,the liquid metal current limiter(LMCL)is considered a new strategy for limiting short-circuit current in the power grid.A resistive wall liquid metal current limiter(RWLMCL)is designed to advance the starting current-limiting time.Experiments are performed to investigate the dynamic behaviors of liquid metal,and the influence of different currents on the liquid metal self-shrinkage effect is compared and analyzed.Furthermore,the liquid metal self-shrinkage effect is mathematically modeled,and the reason for the formation of arc plasma is obtained by simulation.The laws of arc plasma formation and the current transfer in the cavity are revealed,and the motion mechanisms are explained by physical principles.The simulations are in accordance with the test data.It is demonstrated that the sudden change of the current density at both ends of the wall causes the liquid metal to shrink and depress under the electromagnetic force,and the current starts to transfer from the liquid metal path to the wall resistance path.The RWLMCL can effectively advance the starting current-limiting time.

Nonmonotonic effects of perpendicular magnetic anisotropy on current-driven vortex wall motions in magnetic nanostripes

In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy（PMA） on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations.The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current.

Effect of Droop Phenomenon in InGaN/GaN Blue Laser Diodes on Threshold Current

Electroluminescence （EL） and temperature-dependent photolumineseenee measurements are performed to study the internal quantum efficiency droop phenomenon of blue laser diodes （LDs） before lasing. Based on the ABC mode, the EL result demonstrates that non-radiative recombination rates of LDs with threshold current densities of 4 and 6kA/cm2 are similar, while LD with threshold current density of 4kA/cm2 exhibits a smaller auger- like recombination rate compared with the one of 6kA/cm2. The internal quantum efficiency droop is more serious for LD with higher threshold current density. temperature-dependent photoluminescence is consistent The internal quantum efficiency value estimated from with EL measurements.

Interaction of Streamwise and Wall-Normal Velocities in Combined Wave-Current Motion

The aim of this paper is to present an analytical expression for the streamwise velocity distribution in a non-uniform flow in the presence of waves; the correlation between the horizontal and vertical velocity components has been compreheusively examined. Different from previous researches which attributed the deviation of velocity from the classical log-law to the wave Reynolds stress, i.e. - ρ uv^- only, this study demonstrates that the momentum flux caused by mean velocities, i.e., u^- and v^-, is also responsible for the velocity deviation, and it is found that the streamwise velocity for a flow in the presence of non-zero wall-normal velocity does not follow the classical log-law, but the modified log-law proposed in this study based on simplified mixing-length theorem. The validity of the modified log-law has been verified by use of available experimental data from published sources for combined wave-current flows, and good agreement between the predicted and observed velocity profiles has been achieved.

Inverse problem of pulsed eddy current field of ferromagnetic plates

To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters,it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate.

Curvature and Zeeman effects on persistent currents in a multi-walled carbon nanotorus

Taking into account both the intrinsic curvature and Zeeman effects, persistent currents in a multi-walled carbon nanotorus are explored by using a supercell method, within the tight-binding formalism. It is shown that in the absence of the Zeeman effect, the intrinsic curvature induces some dramatic changes in energy spectra and thus changes in the shape of the flux-dependent current. A paramagnetism diamagnetism transition is observed. With consideration of the Zeeman splitting energy, the period of persistent current is destroyed, and a diamagnetism-paramagnetism transition is obtained at high magnetic field. In addition, we further explore the effect of external electric field energy （Eef） on persistent current, indicating that it changes unmonotonously with Eef.

Anomalous Josephson current in quantum anomalous Hall insulator-based superconducting junctions with a domain wall structure

We theoretically study the Josephson effect in a quantum anomalous Hall insulator(QAHI)nanoribbon with a domain wall structure and covered by the superconductor.The anomalous Josephson current,the nonzero supercurrent at the zero superconducting phase difference,appears with the nonzero magnetization and the suitable azimuth angle of the domain wall.Dependent on the configuration of the domain wall,the anomalous current peaks in the Bloch type but disappears in the Néel type because the y-component of magnetization is necessary to break symmetry to arouse the anomalous current.The phase shift of the anomalous current is tunable by the magnetization,the azimuth angle,or the thickness of the domain wall.By introducing a bare QAHI region in the middle of the junction which is not covered by the superconductor,the anomalous Josephson effect is enhanced such that the phase shift can exceedπ.Thus,a continuous change between 0 andπjunctions is realized via regulating the configuration of the domain wall or the magnetization strength.As long as an s-wave superconductor is placed on the top of the QAHI with a domain wall structure,this proposal can be experimentally fabricated and useful for the phase battery or superconducting quantum bit.

Current-Driven Domain Wall Motion: Velocity, Current and Phase Transition

The relation between domain wall motion and intensity of driven current is examined in a phenomenological theory where the kinetic energy is expanded as a series of polynomial function of current density just as the Landau phase transition theory. The dependency of velocity on current density is square root which degenerates into linear if the current is much higher than the critical value. The theory result is consistent with several previous experiments and also can explain the change of critical current in the presence of temperature. The role of temperature playing in the dynamics of domain wall motion is also discussed. The phase transition theory in terms of current density is employed to explain the critical behavior of domain wall motion.

Development of a high current short pulse electron gun

Dielectric wall accelerator(DWA), towards high gradient acceleration field(30 MeV/m–100 MeV/m), is under development at Institute of Modern Physics. A prototype was designed and constructed to prove the principle. This needs a short pulse high current electron source to match the acceleration field generated by the Blumlein-type pulse forming lines(PFLs). In this paper, we report the design and test of a new type short pulse high current electron gun based on principle of vacuum arc discharge. Electron beams of 100 mA with pulse width of 10 ns were obtained.

直角凸壁面附近非对称位置的空泡动力学行为实验研究

空化破坏现象在核电厂中广泛存在。为了更深入地揭示空化破坏的机理,本文借助高速摄影实验系统,研究了直角凸壁面附近非对称位置空泡的动力学行为。具体分析了空泡的轮廓变形,形心的移动距离和方向,以及空泡射流的方向随着空泡与壁面相对位置d、h的变化规律。本文主要结论如下:(1)空泡的变形与空泡和固体壁面的相对位置d、h有关。随着空泡与右壁面的距离d的增大,空泡的非对称性越来越弱。随着空泡与上壁面的距离h的增大,在整个空泡的动力学过程中空泡的非球形特征逐渐减弱。(2)在空泡的溃灭和再生长过程中,空泡形心会持续地向左下方移动,且形心向左移动的距离随着d和h的增大而明显减小。(3)当空泡与上壁面的距离h适当时,会产生明显的斜向左下方的射流现象,且射流方向角θ随着d的增大而增大。

铁磁畴壁中自旋极化电流诱导的左旋极化自旋波

极化指的是波偏振的方式,是波的一个基本性质.利用波的极化可以进行信息的编码,这一编码方式在光学和声学中得到广泛应用.利用自旋波进行信息的传递和处理是磁子学的主要研究课题.然而在铁磁材料中,由于只存在右旋极化的自旋波,利用波的极化进行信息的编码在铁磁自旋波器件中始终没有实现.前期研究发现,通过自旋极化电流可以在铁磁体中产生左旋极化自旋波,从而有望实现利用极化编码的自旋波器件.然而在一个均匀磁化铁磁体中产生左旋极化自旋波所需的电流密度过大,实验上难以实现.磁畴壁可作为自旋波波导,且畴壁中自旋波的截止频率趋近于零.本文从朗道-栗弗席兹方程出发,研究了在自旋极化电流存在的条件下磁畴壁中自旋波的色散关系和传播特性,证明只需要很小的自旋极化电流就可在畴壁中产生稳定的左旋极化自旋波.微磁学模拟证明了理论分析结果.该项研究为研制基于极化编码信息的自旋波器件提供了一个实际可行的方案.

三相PWM整流器离散空间矢量无模型预测电流控制策略

针对PWM整流器模型预测控制对系数参数准确性高度依赖的问题,提出一种基于离散空间矢量的无模型预测电流控制(MFPCC)策略。该策略通过矢量合成,在每个控制周期应用两个基本矢量,提高了预测电流的准确性;通过峰谷采样,分别测量并存储上一控制周期两个基本矢量作用下的电流梯度;并建立电流梯度方程,从而根据应用矢量的电流梯度进一步更新剩余6个未应用矢量的电流梯度,结合当前时刻的电流采样值,实现未来时刻的电流预测,得到下一时刻最优的虚拟矢量。该方法不依赖于任何系统参数,且消除了传统MFPCC策略中电流梯度更新停滞现象,降低了输出电流谐波。最后,通过实验和仿真验证了所提方法的有效性和优越性。

炸高对线性聚能装药射流毁伤混凝土墙体效果的影响

采用一种新型线性聚能装药结构,研究了不同炸高时线性聚能装药射流对混凝土墙体的毁伤效应。数值模拟发现,药型罩锥角为80°与50°时,能较好地避免拉断现象。得到了线性聚能装药结构的射流头部速度、侵彻深度随炸高的变化规律。炸高为60 mm时,最佳侵彻深度达130.6 mm。对炸高为60 mm与100 mm时的线性聚能装药进行试验研究。结果表明,炸高100 mm时,侵彻深度达到125.0 mm,与仿真结果吻合较好。验证了该线性聚能装药结构对混凝土墙体的毁伤效果较好。可为线性聚能装药结构的设计与试验研究提供参考。

仿生锯齿形壁面对压缩机排气噪声的影响

针对活塞式压缩机在排气过程中,排气阀压紧块壁面产生涡流导致噪声过大的问题,以某活塞式压缩机为研究对象,基于Fluent对活塞式压缩机内部流场进行模拟,确定涡流产生的壁面位置,对压紧块壁面进行仿生锯齿形结构正交设计,得到16组正交试验方案,对16组方案进行流场分析与声学仿真,得到8号试验的降噪效果最为明显。结果表明,采用仿生锯齿形壁面设计的压紧块可以降低气体的湍流动能和速度,最大气体速度降低了8.314 m/s,最大湍流动能下降了25.413 m^(2)/s^(2),最大压力减小了0.53 Pa,减少涡流的产生和对压缩机出口流域壁面的冲击;齿高为2.2 mm,齿宽为2.3 mm,齿距为1.0 mm的方案降噪效果最优,噪声降低3.92 dB,降噪率为4.5%。研究结果为压缩机排气噪声的降低提供了指导和参考。

显微镜下精索内静脉-腹壁下静脉逆行转流术治疗男性少精弱精症型精索静脉曲张并胡桃夹现象的临床分析

目的:探讨男性少精弱精症型精索静脉曲张(VC)并胡桃夹现象(NCP)行显微镜下精索内静脉-腹壁下静脉逆行转流术(简称“精索静脉转流术”)治疗的效果。方法:选择2021年1月—2023年1月就诊于赣州市人民医院的70例男性少弱精症VC并NCP患者,按随机数字表法分为试验组和对照组,各35例。试验组运用显微镜下精索静脉转流术治疗,对照组运用显微镜下左侧精索静脉高位结扎治疗。对比两组左肾静脉彩超检查结果、精液质量参数、左侧阴囊疼痛情况、左侧VC严重程度。结果:术后,试验组受压段内径D1较对照组高,受压段流速V1慢于对照组,精索静脉曲张内径D3、扩张段内径D2均较对照组低,差异均有统计学意义(P<0.05)。术后,试验组精子密度、向前运动精子百分率均较对照组高,左侧阴囊疼痛评分较对照组低,差异均有统计学意义(P<0.05)。术后,试验组左侧VC严重程度较对照组轻,差异有统计学意义(P<0.05)。结论:显微镜下精索静脉转流术可改善男性少精弱精症型VC并NCP患者左肾静脉内径、血流速度,提高精液质量,减轻左侧阴囊疼痛程度。

脉冲涡流检测在核电厂管道的应用

[目的]为了提高换热效率,核电厂的凝结水管线、主给水管线、疏水管线及部分抽气管线管道外侧均加装了包覆层,目前对于铁磁性管道的检测手段主要为常规超声技术及超声导波技术。上述检测技术受限于检测环境及前提条件,检测难度较大。文章旨在提高带保温层管道的检测效率,丰富技术手段,缩短检修工期,提高核电厂经济效益。[方法]通过研究核电站低频电磁干扰下脉冲涡流检测方法的可行性和可靠性,利用感应电压测量值与计算值建立最优化参数反演问题,并结合参数之间的耦合关系式,根据管道脉冲涡流场时域解析解的基础上,建立感应电压测量值与计算值特定关系式,建立最优化参数反演问题,并结合参数之间的耦合关系式,提出1种针对核电厂带保温管道在役运维的脉冲涡流检测技术。[结果]利用文章提出的铁磁管道相对壁厚脉冲涡流检测方法对核电厂在役样管进行检测,并将检测结果与常规超声检测结果进行对比,得出二者检测结果误差在5%左右。[结论]脉冲涡流检测结果可靠,适用于核电厂铁磁管道壁厚腐蚀减薄的无损检测与评估。

大容量多层陶瓷电容器的充测特性与测试方法研究

智能驾驶时代的到来使得新能源汽车得到了巨大发展,大容量、高耐压、多层陶瓷电容的市场需求与日俱增。这类电容属于Ⅱ类陶瓷电容,具有介电常数大、充放电时间长的特点,测试分选这类电容需提出更高要求。为满足这类电容的测试分选需求,为相关行业研发人员解惑,分析了电容的介电特性、吸收电特性、充放电特性、双峰现象以及在线测试等。通过相关产品测试得出:在额定电压电流条件下,改变充电时间、充电次数、空位间隔等相关参数,可延长充电时间和充电后空置时间,减小漏电流。

连接件对夹心墙板热性能和能耗的影响

为解决连接件因热桥现象而产生大量能耗问题,又能为连接件设计提供研究基础,文中采用有限元模拟方法,研究了不同连接件材料、类型对夹心墙板热性能和五个热工区能耗的影响。结果表明热桥影响随连接件断桥尺寸的增加而降低,连接件产生的能耗主要受连接件属性和环境影响。研究结论有助于区分热桥影响和能耗差异,对指导连接件的工程应用具有较大价值。