基于空间三维非均匀SISO阵列雷达的介质目标快速成像算法

近年来,随着高精度定位系统的迅猛发展,基于手持式毫米波雷达的阵列成像技术在无损检测和医疗成像等涉及介质内部结构成像的领域中引起了广泛关注.与常见的二维(Two-Dimensional,2D)平面单发单收(SingleInput-Single-Output,SISO)阵列不同的是,基于手持式毫米波雷达的阵列,其阵元通常非均匀分布于三维(Three-Dimensional,3D)空间中,导致现有的基于平面SISO阵列的对介质目标内部结构进行快速成像重构的算法无法适用.为此,本文提出了一种适用于空间3D非均匀SISO阵列雷达的半空间介质目标快速成像算法.该算法将空间3D非均匀SISO阵列的每一个阵元扩展为一个的虚拟阵列,然后将所有虚拟阵列的回波数据变换至波数域后进行相干累加,最后通过3D逆傅里叶变换(Inverse Fourie Transform,IFT)实现快速成像.数值仿真和实验测量表明,与同样适用于该场景的改进后向投影(Improved Backward Projection,IBP)算法相比,在本文给定的成像参数条件下,所提算法可以在保证成像质量的同时,将成像时间缩短94%以上.

基于谐波状态空间的高压直流输电系统SISO阻抗建模及稳定性分析

近年来,电网换相换流器型高压直流输电(line commutated converter based on high voltage direct current,LCC-HVDC)系统的稳定性问题得到广泛关注,多位专家学者建议采用谐波状态空间(harmonic state space,HSS)等线性周期时变建模方法对其分析。然而,HSS不可避免地提高了建模的复杂度与维数,在面对大规模交直流系统时具有局限性。同时,LCC-HVDC包含多类型谐波耦合,各部分耦合对稳定性的影响大小尚未得到充分论证。为此,文中以HSS为底层理论建立LCC-HVDC的耦合阻抗矩阵,揭示高压直流输电系统内部的谐波耦合机理。进一步,通过多频电路等效思想,提出三相系统多维阻抗的降维方法,将耦合阻抗矩阵无损降维成单入单出阻抗,以此分析不同次数的谐波耦合对阻抗特性与稳定性的影响。结果表明,考虑到13次谐波截断可以有效提升高压直流输电系统阻抗模型精度,但对稳定性分析结果的影响小于忽略工况变化、简化逆变侧带来的误差。

A chaotic hierarchical encryption/watermark embedding scheme for multi-medical images based on row-column confusion and closed-loop bi-directional diffusion

Security during remote transmission has been an important concern for researchers in recent years.In this paper,a hierarchical encryption multi-image encryption scheme for people with different security levels is designed,and a multiimage encryption(MIE)algorithm with row and column confusion and closed-loop bi-directional diffusion is adopted in the paper.While ensuring secure communication of medical image information,people with different security levels have different levels of decryption keys,and differentiated visual effects can be obtained by using the strong sensitivity of chaotic keys.The highest security level can obtain decrypted images without watermarks,and at the same time,patient information and copyright attribution can be verified by obtaining watermark images.The experimental results show that the scheme is sufficiently secure as an MIE scheme with visualized differences and the encryption and decryption efficiency is significantly improved compared to other works.

Evaluation of hybrid closed-loop insulin delivery system in type 1 diabetes in real-world clinical practice:One-year observational study

BACKGROUND In 2016,the Food and Drug Administration approved the first hybrid closed-loop(HCL)insulin delivery system for adults with type 1 diabetes(T1D).There is limited information on the impact of using HCL systems on patient-reported outcomes(PROs)in patients with T1D in real-world clinical practice.In this independent study,we evaluated glycemic parameters and PROs over one year of continuous use of Medtronic’s 670G HCL in real-world clinical practice.AIM To assess the effects of hybrid closed loop system on glycemic control and quality of life in adults with T1D.METHODS We evaluated 71 patients with T1D(mean age:45.5±12.1 years;59%females;body weight:83.8±18.7 kg,body mass index:28.7±5.6 kg/m2,A1C:7.6%±0.8%)who were treated with HCL at Joslin Clinic from 2017 to 2019.We measured A1C and percent of glucose time-in-range(%TIR)at baseline and 12 months.We measured percent time in auto mode(%TiAM)for the last two weeks preceding the final visit and assessed PROs through several validated quality-of-life surveys related to general health and diabetes management.RESULTS At 12 mo,A1C decreased by 0.3%±0.1%(P=0.001)and%TIR increased by 8.1%±2.5%(P=0.002).The average%TiAM was only 64.3%±32.8%and was not associated with A1C,%TIR or PROs.PROs,provided at baseline and at the end of the study,showed that the physical functioning submodule of 36Item Short-Form Health Survey increased significantly by 22.9%(P<0.001).Hypoglycemia fear survey/worry scale decreased significantly by 24.9%(P<0.000);Problem Areas In Diabetes reduced significantly by-17.2%(P=0.002).The emotional burden submodules of dietary diversity score reduced significantly by-44.7%(P=0.001).Furthermore,analysis of Clarke questionnaire showed no increase in awareness of hypoglycemic episodes.WHO-5 showed no improvements in subject’s wellbeing among participants after starting the 670G HCL system.Finally,analysis of Pittsburgh Sleep Quality Index showed no difference in sleep quality,sleep latency,or duration of sleep from baseline to 12 mo.CONCLUSION The use of HCL in real-world clinical practice for one year was associated with significant improvements in A1C,%TIR,physical functioning,hypoglycemia fear,emotional distress,and emotional burden related to diabetes management.However,these changes were not associated with time in auto mode.

基于SISO序阻抗的直驱风场经柔直输电系统中频振荡机理分析及抑制

直驱风场可通过柔性直流实现大容量、远距离输电。目前已有诸多研究表明直驱风场经柔直输电系统面临着次同步或高频振荡问题。然而,也可能存在一种频段介于两者之间的中频振荡现象,值得进一步研究。为此,该文基于直驱风场经柔直输电系统的单输入单输出(singleinputsingle output,SISO)等效序阻抗模型研究该互联系统的中频振荡机理。然后,据此分析直驱风场和柔直换流站参数对该中频振荡特性的影响,分析结果得到了仿真验证。最后,该文还提出基于虚拟阻抗的阻抗重塑控制,并通过仿真验证所提控制策略对抑制直驱风场经柔直输电系统中频振荡的有效性,对于实际工程具有参考意义。

Informative Property of the Data Set in a Single-input Single-output (SISO) Closed-loop System with a Switching Controller

Closed-loop identification is important and necessary to various model-based advanced process control strategies, whose performance depends greatly on the informative property of the data set. Switching control is an important method in process control. Therefore, this paper studies the informative property of a data set in a single-input single-output (SISO) closed-loop system with a switching controller. It is proved that this data set is informative if the controller switches among at least two modes (i.e., feedback laws). Our result does not require any assumption on the way of switch and removes the constraints on the switching manner required in some classical literature. Finally, simulation case studies based on a continuous stirred-tank reactor (CSTR) process are given to validate the results.

A compact and closed-loop spin-exchange relaxation-free atomic magnetometer for wearable magnetoencephalography

Atomic magnetometers operated in the spin-exchange relaxation-free(SERF)regime are the promising sensor to replace superconducting quantum interference devices(SQUIDs)in the biomagnetism field.The SERF magnetometer with compact size and good performance is crucial to the new generation of wearable magnetoencephalography(MEG)system.In this paper,we developed a compact and closed-loop SERF magnetometer with the dimensions of 15.0×22.0×30.0 mm^(3)based on a single-beam configuration.The bandwidth of the magnetometer was extended to 675 Hz while the sensitivity was maintained at 22 f T/Hz^(1/2).A nearly 3-fold enhancement of the bandwidth was obtained in comparison with the open-loop control.The implementation of the closed-loop control also greatly improved the dynamic range,enabling the magnetometer to be robust against the disturbance of the ambient field.Moreover,the magnetometer was successfully applied for the detection of humanα-rhythm and auditory evoked fields(AEFs),which demonstrated the potential to be extended to multi-channel MEG measurements for future neuroscience studies.

Subspace Identification for Closed-Loop Systems With Unknown Deterministic Disturbances

This paper presents a subspace identification method for closed-loop systems with unknown deterministic disturbances.To deal with the unknown deterministic disturbances,two strategies are implemented to construct the row space that can be used to approximately represent the unknown deterministic disturbances using the trigonometric functions or Bernstein polynomials depending on whether the disturbance frequencies are known.For closed-loop identification,CCF-N4SID is extended to the case with unknown deterministic disturbances using the oblique projection.In addition,a proper Bernstein polynomial order can be determined using the Akaike information criterion(AIC)or the Bayesian information criterion(BIC).Numerical simulation results demonstrate the effectiveness of the proposed identification method for both periodic and aperiodic deterministic disturbances.

Type Synthesis of Fully Decoupled Three Translational Parallel Mechanism with Closed-Loop Units and High Stifness

In order to solve the problem of weak stifness of the existing fully decoupled parallel mechanism, a new synthesis method of fully decoupled three translational (3T) parallel mechanisms (PMs) with closed-loop units and high stifness is proposed based on screw theory. Firstly, a new criterion for the full decoupled of PMs is presented that the reciprocal product of the transmission wrench screw matrix and the output twist screw matrix of PMs is a diagonal matrix, and all elements on the main diagonal are nonzero constants. The forms of the transmission wrench screws are determined by the criterion. Secondly, the forms of the actuated and unactuated screws can be obtained according to their relationships with the transmission wrench screws. The basic decoupled limbs are generated by combination of the above actuated and unactuated screws. Finally, a closed-loop units construction method is investigated to apply the decoupled mechanisms in a better way on the high stifness occasion. The closed-loop units are constructed in the basic decoupled limbs to generate a high-stifness fully decoupled 3T PM. Kinematic and stifness analyses show that the Jacobian matrix is a diagonal matrix, and the stifness is obviously higher than that of the coupling mechanisms, which verifes the correctness of the proposed synthesis method. The mechanism synthesized by this method has a good application prospect in vehicle durability test platform.

Closed-Loop System Identification Approach of the Inertial Models

The mathematical model that approximates the dynamics of the industrial process is essential for the efficient synthesis of control algorithms in industrial applications. The model of the process can be obtained according to the identification procedures in the open-loop, or in the closed-loop. In the open-loop, the identification methods are well known and offer good process approximation, which is not valid for the closed-loop identification, when the system provides the feedback output and doesn’t permit it to be identified in the open-loop. This paper offers an approach for experimental identification in the closed-loop, which supposes the approximation of the process with inertial models, with or without time delay and astatism. The coefficients are calculated based on the values of the critical transfer coefficient and period of the underdamped response of the closed-loop system with P controller, when system achieves the limit of stability. Finally, the closed-loop identification was verified by the computer simulation and the obtained results demonstrated, that the identification procedure in the closed-loop offers good results in process of estimation of the model of the process.

采用MATLAB中的SISO工具设计PID控制系统

新版MATLAB软件中SISO Tool图形化工具箱功能强大,可以实现以控制理论为基础的PID、最优化、LQG和内模控制校正等多种线性系统校正和补偿;通过实例对控制系统PID进行了校正设计,使用SISO工具既可以避免繁杂的计算和MATLAB函数的重复调用,方便模拟参数调整过程,也可以实时显示设计和控制结果。

单输入单输出系统分数阶预测函数控制

基于分数阶微积分理论和预测函数控制理论,针对一类单输入单输出分数阶线性系统提出了一种分数阶预测函数控制方法。用Oustaloup近似法对分数阶系统近似的整数阶系统建立预测输出模型,并根据GL定义在代价函数中引入分数阶算子。该控制方法通过将控制输入结构化简化了控制器设计,引入分数阶算子增加了控制器的自由度。仿真结果表明:与传统预测控制器相比,分数阶预测函数控制器具有调节时间短、抗干扰能力强及鲁棒性强等优点,在模型失配的情况下也有较好的跟踪效果。

SISO系统的鲁棒性能设计

本文讨论了SISO系统的鲁棒性能设计问题 .根据具有乘性不确定性SISO系统鲁棒性能指标 μ的显式表达式 ,分析了 μ综合中权函数的选择 .

一种改进的SISO多用户检测算法

根据信道译码器所提供的发送比特的先验信息,对数据联合算法(PDA)进行了改进,在仅有较小性能损失的前提下,进一步降低了PDA算法的计算复杂度.

基于SISO Design Tool设计系统的PID整定

本文介绍了基于Matlab中的RTW实验平台,利用三容水箱进行观测二阶系统的动态响应曲线。阐述了如何根据Matlab中的SISO Design Tool设计系统(即单输入单输出设计工具)对系统进行PID整定。重点分析利用SISO Design Tool对对象进行PID参数的整定。实践证明,采用SISO系统进行PID整定,会节省大量的时间,而且过程清晰、直观。

SISOTOOL在自动控制系统校正中的应用

本文介绍了SISO系统图形交互式设计工具SISOTOOL,并以小功率角度跟踪位置随动系统为例,用简洁、直观的方式设计出校正装置,给出仿真曲线和相应的时域、频域性能指标,对自动控制系统的设计有一定的参考意义。

应用MATLAB中的SISO设计工具对线性系统进行校正

介绍了如何以MATLAB中的SISO设计工具箱为计算工具,以经典控制理论为基础对线性系统进行校正和补偿。通过一个简单的实例证明应用该工具箱对SISO线性系统进行校正和补偿是十分有效的。

SISO系统混合灵敏度的鲁棒性能设计

讨论ＳＩＳＯ系统鲁棒性能设计问题，指出只要适当修改不确定性权函数和性能权函数，就可以用混合灵敏度进行鲁棒性能设计。示例说明此设计所得系统的鲁棒性能较好。

无模型SISO时滞系统的PID参数稳定域研究

针对无精确模型的单输入单输出(SISO)时滞系统,利用频率响应数据,给出确定PID参数稳定域的解析方法.首先通过继电反馈频域辨识法得到系统的频率响应数据,然后基于该数据确定控制参数的奇异边界线和非奇异边界线,并判断边界线的哪一侧具有更少的不稳定极点,从而给出能使闭环系统稳定的控制参数区域.该方法避免了模型辨识的复杂计算过程,为无模型SISO时滞系统的PID控制器设计和调节提供了一条简单有效的途径.仿真结果验证了方法的有效性。

SISO-CMAC算法在传感器非线性误差补偿中应用

研究了一种单输入单输出的小脑神经网络(SISO-CMAC),并对SISO-CMAC的收敛性进行了证明.SISO-CMAC具有收敛速度快、算法简单和函数逼近精度高等优点,可以在单片机上实现.将SISO-CMAC直接用于传感器误差非线性补偿中,提高了测量系统的精度,并通过试验验证了该方法的有效性.