Symbolic Computation and Graphic Presentation of Magneto-Static Field and Its Associated Vector Potential for a Steady Looping Current

With the advent of Computer Algebra System (CAS) such as Mathematica [1], challenging symbolic longhand calcula-tions can effectively be performed free of error and at ease. Mathematica’s integrated features allow the investigator to combine the needed symbolic, numeric and graphic modules all in one interactive environment. This assists the author to focus on interpreting the output rather than exerting the efforts of relating the scattered separate modules. In this note the author, utilizing these three features, explores the magneto-static field and its associated vector potential of a steady looping current. In particular by deploying the numeric features of Mathematica the exact value of the vector potential of the looping current conducive to its 3D graph is presented.

Application of computational fluid dynamics simulation for submarine oil spill

Computational fluid dynamics （CFD） codes are being increasingly used in the simulation of submarine oil spills. This study focuses on the process of oil spills, from damaged submarine pipes, to the sea surface, using numerical models. The underwater oil spill model is developed, and a description of the governing equations is proposed, along with modifications required for the particalization of the control volume. Available experimental data were introduced to evaluate the validity of the CFD predictions, the results of which proved to be in good agreement with the experimental data. The effects of oil leak rate, leak diameter, current velocity, and oil density are investigated, by the validated CFD model, to estimate the undersea leakage time, the lateral migration distance, and surface diffusion range when the oil reaches the sea surface. Results indicate that the leakage time and lateral migration distance increase with decreasing leak rates and leak diameter, and increase with increasing current velocity and oil density. On the other hand, a large leak diameter, high density, high leak rate, or fast currents result in a greater surface diffusion range. The findings and analysis presented here will provide practical predictions of oil spills, and guidance for emergency rescues.

Calculation of Eddy Current Loss and Short-circuit Force in SSZ11-50000/110 Power Transformer

The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.

A Computational Study of Interaction of Main Channel and Floodplain: Open Channel Flows

The assumption of steady uniform flow permits the computation of the velocity isoline, secondary current and turbulent statistics in open channel flows. However, it becomes important to choose appropriate turbulence models to capture the length scale of turbulence near the interfacial zone of compound channels. This paper not only focusses on capturing the longitudinal vortex and primary mean velocity but also extrapolates the results of numerical analysis to understand the interaction between the main channel and floodplain in asymmetric compound channels. The results of computational fluid dynamics simulation showed that the velocity isoline bulging near the bed of the floodplain and sidewall at the junction, due to high-momentum transport by secondary current, can be captured with Reynolds stress model. Furthermore, by applying the three different cases of channels with varying geometrical aspects, the maximum velocity simulated showed similar results to the experiments where the structure of primary mean velocity is seen to be influenced by momentum transport due to the secondary current.

Chiral current regulation and detection of Berry phase in triangular triple quantum dots

Based on the hierarchical equations of motion(HEOM)calculation,we theoretically investigate the corresponding control of a triangular triple-quantum-dots(TTQD)ring which is connected to two reservoirs.We initially demonstrate by adding bias voltage and further adjusting the coupling strength between quantum dots,the chiral current induced by bias will go through a transformation of clockwise to counterclockwise direction and an unprecedented effective Hall angle will be triggered.The transformation is very rapid,with a corresponding characteristic time of 80-200 ps.In addition,by adding a magnetic flux to compensate for the chiral current in the original system,we elucidate the relationship between the applied magnetic flux and the Berry phase,which can realize direct measurement of the chiral current and reveal the magnetoelectric coupling relationship.

Nano-scale Bias-scalable CMOS Analog Computational Circuits Using Margin Propagation

Approximation techniques are useful for implementing pattern recognizers, communication decoders and sensory processing algorithms where computational precision is not critical to achieve the desired system level performance. In our previous work, we had proposed margin propagation (MP) as an efficient piece-wise linear (PWL) approximation technique to a log-sum-exp function and had demonstrated its advantages for implementing probabilistic decoders. In this paper, we present a systematic and a generalized approach for synthesizing analog piecewise-linear (PWL) computing circuits using the MP principle. MP circuits use only addition, subtraction and threshold operations and hence can be implemented using universal conservation principles like the Kirchoff's current law. Thus, unlike the conventional translinear CMOS current-mode circuits, the operation of the MP circuits are functionally similar in weak, moderate and strong inversion regimes of the MOS transistor making the design approach bias-scalable. This paper presents measured results from MP circuits prototyped in a 0.5μm standard CMOS process verifying the bias-scalable property. As an example, we apply the synthesis approach towards designing linear classifiers and verify its performance using measured results.

低复杂度永磁同步电机三矢量固定开关频率模型预测电流控制策略

针对传统永磁同步电机(permanent magnet synchronous motor,PMSM)三矢量模型预测电流控制(three-vector model predictive current control,TV-MPCC)存在开关频率不固定和计算复杂的问题,提出一种固定开关频率TV-MPCC策略。利用前一周期的零电压矢量和参考电压矢量所在扇区来快速筛选所需最优电压矢量和次优电压矢量,避免了无效枚举计算,从而降低了开关频率和计算复杂度。引入系统d和q轴电流差参数,计算各电压矢量的作用时间,确保电压矢量作用时间恒大于零和开关频率固定。以三相两电平电压型逆变器驱动的表贴式PMSM为被控对象,通过仿真和实验对传统TV-MPCC策略和所提三矢量固定开关频率模型预测电流控制策略进行对比研究,仿真和实验结果表明,所提策略在保证系统稳态和动态性能的基础上,在固定和降低开关频率的同时,降低了计算复杂度。

宽电压增益CLLLC谐振变换器的改进型电流解析方法

对谐振电流的精确解析是计算CLLLC谐振变换器损耗的重要环节。针对宽电压增益CLLLC谐振变换器励磁电感与谐振电感比值较小的特点,基于电流拟合近似法提出了一种改进型谐振电流解析方法。首先通过分析变换器在三元谐振期间的等效拓扑,列写出谐振电流的阶段解析式,其次在考虑到三角函数未知量求解计算复杂的情况下,提出了修正系数的概念以简化计算,最终根据谐振电流的波形特点得出谐振电流初始解,并进一步通过分段迭代的方法逐步逼近谐振电流真实值。仿真结果表明,所提出的改进型电流解析式相比于传统方法,在三元谐振期间能够更加准确地描述谐振电流的变化过程,验证了所提方法的正确性。

期望扇区三矢量模型预测电流控制

三矢量模型预测电流控制需要依次计算6扇区电压矢量的作用时间,再由价值函数选取期望电压矢量,存在计算量大的缺点。本文提出一种基于期望扇区的三矢量模型预测电流控制,以快速确定期望电压矢量。首先,建立d-q轴的三矢量电流模型,给出其三矢量作用时间;然后,令预测电流为期望电流,可以获得期望电压矢量,并利用Clark变换得到α-β轴的期望电压矢量;最后,利用反正切函数求得期望电压矢量角度,确定期望电压矢量所在的期望扇区,得到期望三矢量及其作用时间。仿真和实验表明,该方法能够保持很好的控制系统性能。同时,该方法只需一次计算期望电压矢量角度即可确定期望三矢量及其作用时间,比传统三矢量方法有效缩短了算法执行时间约60%。

永磁同步电机新型模型预测电流控制

为降低传统多矢量模型预测电流控制(MPCC)算法的计算量和复杂度,并保证良好的控制性能,提出了快速筛选第二电压矢量的新型多矢量MPCC算法。根据电流无差拍控制原则,通过直交轴电流差值定义直交轴电流判定因数,简化了第二电压矢量选择过程,减轻了控制芯片的计算量,并保持了低电流脉动的优势。在新型双矢量MPCC算法基础上,提出了结合直交轴电流判定因数和有效电压矢量表用以直接选择第二电压矢量的新型三矢量MPCC算法。实验结果表明,新型多矢量MPCC算法在保持传统多矢量MPCC算法控制性能的同时,新型双矢量MPCC算法的计算量减少33.96%,新型三矢量MPCC算法的计算量减少48.7%。

结构参数对固体氧化物电解槽性能的影响

SOEC(固体氧化物电解槽)的流道结构及电极厚度等结构参数对其性能具有重要影响。基于SOEC三维计算流体力学模型建立预测电流密度与温差的ANN(人工神经网络)模型,研究结构参数对SOEC电化学性能和温度场的影响规律。结果表明:ANN代理模型具有较高的精度和低的计算成本;温度分布均匀性与电解性能负相关;减小节距、肋宽和电极厚度会引起欧姆损耗的降低,电解槽的电流密度提高。与阳极肋宽相比,阴极肋宽对电流密度的影响更为显著,导致两者对温差的影响规律有所不同。当阳极厚度<40μm,阳极厚度减小导致反应活性面积急剧减小,电流密度因此降低。在参数研究范围内,当节距为1.8 mm,电解质厚度为8μm,阳极肋宽为0.6 mm,阴极肋宽为1.2 mm,阴极厚度为600μm时,能够保持高电流密度(>3700 A/m^(2))的同时获得最佳的温度均匀度。研究结果为固体氧化物电解槽的结构优化设计提供一种便捷可行的方法,具有重要指导意义。

基于视听觉和运动反馈的脑机接口结合经颅直流电刺激对脑卒中患者上肢功能的效果

目的 探讨基于视听觉和运动反馈的脑机接口(BCI)结合经颅直流电刺激(tDCS)对脑卒中患者上肢功能的疗效。方法 2023年3月至10月,徐州医科大学附属徐州康复医院和徐州市中心医院住院的脑卒中患者45例,随机分为BCI组、tDCS组和联合组,每组15例。3组均接受常规康复治疗,BCI组增加BCI,tDCS组增加tDCS治疗,联合组先行tDCS治疗,然后立即进行BCI,共4周。治疗前后采用Fugl-Meyer评定量表上肢部分(FMA-UE)、上肢动作研究量表(ARAT)和改良Barthel指数(MBI)进行评定,测量脑电图δ-α比(DAR)和功率比指数(PRI)。结果 治疗后,3组FMA-UE、ARAT和MBI评分均较治疗前显著提高(|t|> 5.350, P <0.001),联合组最优(F>3.366, P <0.05),DAR和PRI均较治疗前显著减小(|t|> 2.208, P <0.05),联合组最优(F> 5.224, P <0.01)。结论 基于视听觉和运动反馈的BCI结合tDCS可进一步改善脑卒中患者上肢运动功能,提高日常生活活动能力。

Characteristics of Bi-2223 HTS Tapes Under Short-Circuit Current Impacts in Hybrid Energy Transmission Pipelines

A hybrid energy transmission pipeline is proposed with the aim of long-distance cooperative transmission of electricity and chemical fuels, which is composed of an inner high-temperature superconducting (HTS) power cable and outer liquefied natural gas (LNG) pipeline. The flowing LNG could maintain the operating temperature of the inner HTS power cable within the range of 85 K-90 K, thus the Bi-2223 superconductors in the HTS power cable produce little Joule loss with the transmission current below the critical current. Owing to the advantages of high power density, low transmission losses and economical manufacturing costs, the hybrid energy transmission pipeline is expected to be widely utilized in the near future. In order to ensure the safety of the HTS power cable and explosive LNG in case of short-circuit faults, this paper tests and analyzes the characteristics of Bi-2223 HTS tapes of the Type HT-CA, Type HT-SS and Type H models under short-circuit current impacts at the LNG cooling temperature (85 K-90 K). An experimental platform is designed and established for the ampacity tests of HTS tapes above LN2 cooling temperature (77 K). The AC over-current impact tests at 85 K-90 K are carried out on each sample of Bi-2223 tapes respectively, and the experimental results are analyzed and compared to evaluate their performances under different operating conditions. The results indicate that the Type HT-CA tape can withstand 50 Hz short-circuit current impact with the amplitude of 1108 A (10 times of critical current Ic ) for 100 ms at 90 K, and its resistance is the smallest of the three tested samples under similar current impacts. Therefore, the Type HT-CA Bi-2223 tape is the optimal superconductor of the HTS power cable in the hybrid energy transmission pipeline.

Modelling dynamic pantograph loads with combined numerical analysis

Appropriate interaction between pantograph and catenary is imperative for smooth operation of electric trains.Changing heights of overhead lines to accommodate level crossings,overbridges,and tunnels pose significant challenges in maintaining consistent current collection performance as the pantograph aerodynamic profile,and thus aerodynamic load changes significantly with operational height.This research aims to analyse the global flow characteristics and aerodynamic forces acting on individual components of an HSX pantograph operating in different configurations and orientations,such that the results can be combined with multibody simulations to obtain accurate dynamic insight into contact forces.Specifically,computational fluid dynamics simulations are used to investigate the pantograph component loads in a representative setting,such as that of the recessed cavity on a Class 800 train.From an aerodynamic perspective,this study indicates that the total drag force acting on non-fixed components of the pantograph is larger for the knuckle-leading orientation rather than the knuckle-trailing,although the difference between the two is found to reduce with increasing pantograph extension.Combining the aerodynamic loads acting on individual components with multibody tools allows for realistic dynamic insight into the pantograph behaviour.The results obtained show how considering aerodynamic forces enhance the realism of the models,leading to behaviour of the pantograph-catenary contact forces closely matching that seen in experimental tests.

载人月球探测飞行器综合电子系统技术发展研究

针对载人月球探测飞行器数据种类多、数据量大、数据分布远的特点和高可靠性数据通信要求,通过调研国内外航天器综合电子系统发展趋势和系统分析载人月球探测任务的研制需求和技术特点,秉承网络一体化、计算通用化、执行集成化、软件APP化的设计理念,提出了全新的“统一管理-区域执行”两层分级控制综合电子系统架构,对高性能计算、时间触发网络、高集成采集驱动、分时分区操作系统等关键技术的研究目标和实施途径进行了详细阐述,应用于载人月球探测飞行器综合电子系统设计后,将有效提升自主健康管理和任务规划能力、功能密度、设计可靠性及有人参与的闭环控制能力。

基于BLDC的气象温度传感器设计与实验研究

针对自然通风温度传感器受太阳辐射影响后测量精度较差,而强制通风温度传感器功耗大、能耗浪费严重等问题,设计了一种基于无刷直流电机(BLDC),将自然通风与强制通风相结合的新型温度传感器。首先利用计算流体动力学(CFD)方法量化传感器在不同环境变量及电机转速下的辐射误差,并基于此制定电机转速的控制策略。其次利用粒子群优化的神经网络算法对仿真数据进行训练学习,并拟合成辐射误差修正方程。最后搭建户外测试平台验证新型温度传感器的测温精度以及修正方程的修正效果。实验结果表明,新型温度传感器具有较高的温度测量精度,其修正值与基准值的差值的平均绝对误差(MAE)和均方根误差(RMSE)分别为0.035℃和0.043℃。

基于等效电流密度模型的多层有限长螺线管轴线磁场分析

为了解决短杆轴向霍尔磁场探头现场校准的难题,提出了采用便携式有限长螺线管作为标准磁场发生器的方法。建立圆柱坐标系下螺线管线圈模型,并提出等效电流密度(ECD)法,结合Biot-Savrt定理及磁场叠加原理,计算其轴线磁场强度,获得多层有限长螺线管轴线磁场的分布规律。同时,建立了多层有限长螺线管静磁场有限元模型,仿真计算获得给定激励电流条件下的空间磁场分布情况。根据理论分析结果,设计了中心磁场100 mT的螺线管试验样机,对ECD模型理论计算结果、仿真分析结果和样机测试数据进行对比。结果显示,在螺线管中心处,理论计算与仿真结果偏差在0.1%以内,试验测试结果与理论计算偏差在0.8%以内。分析结果验证了ECD法分析螺线管轴线磁场的有效性。该方法对于提高螺线管结构设计效率、优化设计参数等具有重要意义。

公共信用信息交换与共享浅析

公共信用信息的交换与共享在促进社会经济发展和提升金融服务效率上发挥着重要作用,公共信用信息系统的有效运行对促进区域经济增长、维护金融市场稳定、降低信贷风险、营造良好营商环境具有至关重要的作用。文中浅析了公共信用信息交换与共享的现状和存在的问题,提出了加强隐私保护和数据安全的解决方案。通过文中分析可以了解公共信用信息交换与共享的重要性和作用,为其应用和发展提供参考。

心房颤动患者导管消融术不同管电流CT扫描方案对患者辐射剂量影响研究

目的研究心房颤动患者导管消融术不同管电流电子计算机断层扫描(CT)扫描方案对患者辐射剂量的影响。方法回顾性分析2020年7月至2022年11月于我院进行导管消融术治疗的133例心房颤动患者临床资料,根据患者胸部CT扫描管电流水平将其分为微管电流组(管电流为30mAs)、低管电流组(管电流为50mAs)、中管电流组(管电流为100mAs)和高管电流组(管电流为200mAs),四组例数分别为30例、37例、34例、32例。记录四组患者辐射剂量[CT剂量指数(CTDI)、CT剂量长度乘积(DLP)、有效辐射剂量(ED)]、客观图像质量[CT值、对比噪声比(CNR)、信噪比(SNR)]、主观图像质量[解剖结构显示、噪声、图像清晰度]、左心房(LA)直径、LA憩室显示率、肺静脉(PV)解剖变异显示率。结果四组辐射剂量比较差异有统计学意义(P<0.05),其中微管电流组CTDI、DLP、ED均低于低、中、高管电流组(P<0.05),低管电流组CTDI、DLP、ED均低于中、高管电流组(P<0.05),中管电流组CTDI、DLP、ED均低于高管电流组(P<0.05)。微管电流组LA、左上肺静脉(LSPV)及右上肺静脉(RSPV)的CT值、SNR、CNR均低于低、中、高管电流组(P<0.05),低、中、高管电流组LA、LSPV及RSPV的CT值、SNR、CNR比较差异均无统计学意义(P>0.05)。微管电流组解剖结构显示、噪声及图像清晰度评分均低于低、中、高管电流组(P<0.05),低、中、高管电流组解剖结构显示、噪声及图像清晰度比较差异均无统计学意义(P>0.05)。微管电流组LA直径、LA憩室显示率及PV解剖变异显示率均低于其他三组(P<0.05),低、中、高管电流组LA直径、LA憩室显示率及PV解剖变异显示率比较差异均无统计学意义(P>0.05)。结论与100mAs、200mAs管电流相比,心房颤动患者导管消融术采用50mAs管电流CT扫描辐射剂量明显较少,所获图像质量也能够达到相关标准。

应用于忆阻器阵列存内计算的低延时低能耗新型感知放大器

存内计算(Computing In Memory,CIM)在人工智能神经网络的卷积运算方面具有巨大的应用潜力。基于忆阻器阵列的多位存内计算由于具备写入速度快、与互补金属氧化物半导体(Complementary Metal Oxide Semiconductor,CMOS)工艺兼容等特点,有望成为解决“内存墙”的有效手段。然而,当前多位存内计算电路架构面临输出延时高和能耗大的问题,主要原因为传统感知放大器的性能制约,为此本文提出了一种低延时低能耗多位电流型感知放大器(Low-delay Low-power Multi-bit Current-mode Sense Amplifier,LLM-CSA),通过减少传统CSA电路工作状态数量、简化工作时序来优化功能;采用新型低位检测模块的电路设计思路,来多层次系统性地降低输出延时并优化能耗。使用中芯国际40 nm低漏电逻辑工艺(SMIC40 nm LL),利用Cadence电路设计平台,仿真验证所提LLM-CSA的功能和延时-能耗性能。通过对比分析发现:LLM-CSA比传统CSA输出延时降低1.42倍,能量消耗降低1.56倍。进一步地,以一种4 bit输入、4 bit权重、11 bit输出的忆阻器阵列多位存内计算架构为应用,对比验证所提LLM-CSA的性能:与基于传统CSA的存内计算系统相比,新架构延时降低1.18倍,能耗降低1.03倍。LLM-CSA的提出对促进感知放大器设计思路和忆阻器阵列存内计算架构的发展,具有一定的理论和现实意义。