Complementary Sliding Mode Speed Control with Saturation Function Boundary Layer Optimization

A simple method is proposed to optimize the thickness parameter of the boundary layer of the saturation function in the Complementary Sliding Mode Control (CSMC). A pair of complementary sliding surfaces are constructed. And the Taylor series is used to estimate the steady state error of CSMC system to optimize the parameter value for the boundary layer of the saturation function without artificial settings. This proposed CSMC strategy is applied to the speed regulation in permanent magnet synchronous motor with lump uncertainties. The experimental results show that the proposed CSMC strategy can obtain an optimal value for the boundary layer parameter effectively suppressing the chattering and keep an excellent system performance.

Spreading Speed for a Periodic Reaction-diffusion Model with Nonmonotone Birth Function

A reaction-diffusion model for a single species with age structure and nonlocal reaction for periodic time t is derived. Some results about the model with monotone birth function are firstly introduced, and then by constructing two auxiliary equations and squeezing method, the spreading speed for the system with nonmonotone birth function is obtained.

全膝关节置换前膝关节伸屈肌肌肉力量与置换后步态功能的关系

背景:步态功能障碍是导致全膝关节置换后患者不满的重要原因之一,临床研究中发现术前股四头肌和腘绳肌的肌肉力量与术后步态功能障碍有关,但其相关性目前尚不完全清楚。目的:探讨全膝关节置换前以股四头肌为主的伸肌、以腘绳肌为主的屈肌肌肉力量与置换后步态功能等的相关性。方法:回顾性分析70例接受单侧初次全膝关节置换患者的纵向数据,术前测量伸屈肌的峰力矩、峰力矩体质量比、总功数据,术后6个月测量起立-步行计时测试结果和步态速度。使用岭回归分析确定术后步态功能的影响因素。结果与结论:①术前伸肌峰力矩、峰力矩体质量比、总功以及屈肌峰力矩、总功与术后步态速度呈非常强正相关(P<0.001),术前屈肌峰力矩体质量比与术后步态速度呈强正相关(P<0.001);术前伸肌、屈肌峰力矩、峰力矩体质量比、总功与术后起立-步行计时测试结果呈非常强负相关(P<0.001);②岭回归分析中,94.2%可能性可说明术前伸肌峰力矩、峰力矩体质量比、总功及屈肌峰力矩、总功对全膝关节置换后患者的步态速度具有正向影响(P<0.001),术前屈肌峰力矩体质量比对术后步态速度具有负向影响(P<0.001);87.7%可能性说明术前伸肌峰力矩、峰力矩体质量比、总功及屈肌峰力矩、总功对术后起立-步行计时测试具有负向影响(P<0.05),而屈肌峰力矩体质量比对术后起立-步行计时测试无影响(P>0.05);③提示全膝关节置换前股四头肌、腘绳肌肌肉力量的大小与置换后步态速度、起立-步行计时测试结果相关,可预测术后步态功能结果;加强置换前膝关节肌肉锻炼可能是减缓全膝关节置换后步态障碍发生的途径。

Extreme Values of Wind Speed over the Kara Sea Based on the ERA5 Dataset

Extreme values of wind speed were studied based on the highly detailed ERA5 dataset covering the central part of the Kara Sea. Cases in which the ice coverage of the cells exceeded 15% were filtered. Our study shows that the wind speed extrema obtained from station observations, as well as from modelling results in the framework of mesoscale models, can be divided into two groups according to their probability distribution laws. One group is specifically designated as black swans, with the other referred to as dragons (or dragon-kings). In this study we determined that the data of ERA5 accurately described the swans, but did not fully reproduce extrema related to the dragons;these extrema were identified only in half of ERA5 grid points. Weibull probability distribution function (PDF) parameters were identified in only a quarter of the pixels. The parameters were connected almost deterministically. This converted the Weibull function into a one-parameter dependence. It was not clear whether this uniqueness was a consequence of the features of the calculation algorithm used in ERA5, or whether it was a consequence of a relatively small area being considered, which had the same wind regime. Extremes of wind speed arise as mesoscale features and are associated with hydrodynamic features of the wind flow. If the flow was non-geostrophic and if its trajectory had a substantial curvature, then the extreme velocities were distributed according to a rule similar to the Weibull law.

Rapid environmental assessment in the South China Sea:Improved inversion of sound speed profile using remote sensing data

Complex perturbations in the profile and the sparsity of samples often limit the validity of rapid environmental assessment(REA)in the South China Sea(SCS).In this paper,the remote sensing data were used to estimate sound speed profile(SSP)with the self-organizing map(SOM)method in the SCS.First,the consistency of the empirical orthogonal functions was examined by using k-means clustering.The clustering results indicated that SSPs in the SCS have a similar perturbation nature,which means the inverted grid could be expanded to the entire SCS to deal with the problem of sparsity of the samples without statistical improbability.Second,a machine learning method was proposed that took advantage of the topological structure of SOM to significantly improve their accuracy.Validation revealed promising results,with a mean reconstruction error of 1.26 m/s,which is 1.16 m/s smaller than the traditional single empirical orthogonal function regression(sEOF-r)method.By violating the constraints of linear inversion,the topological structure of the SOM method showed a smaller error and better robustness in the SSP estimation.The improvements to enhance the accuracy and robustness of REA in the SCS were offered.These results suggested a potential utilization of REA in the SCS based on satellite data and provided a new approach for SSP estimation derived from sea surface data.

Executive function impairments in high IQ children and adolescents with ADHD

Objective: To demonstrate that high IQ children and adolescents diagnosed with ADHD tend to suffer from executive function (EF) impairments that: a) can be identified with a combination of standardized measures and normed self-report data;and b) occur more frequently in this group than in the general population. Method: From charts of 117 children and adolescents aged 6 to 17 years with high IQ ( ≥ 120) who fully met DSM-IV diagnostic criteria for ADHD, data on 8 normed measures of executive function (EF) were extracted: IQ index scores for working memory and processing speed, a standardized measure of auditory verbal memory, and 5 clusters of the Brown ADD Scale, a normed, age-graded rating scale for ADHD-related executive function impairments in daily life. Significant impairment was computed for each individual relative to age-appropriate norms for each measure and comparisons were made to base-line rates in the general population. Results: Sixty-two percent of participants were significantly impaired on at least 5 of these 8 markers of EF. Chi-square comparisons of scores from these high IQ participants were significantly different (p < 0.001) from standardization norms for each of the eight EF measures. Conclusions: High IQ children and adolescents with ADHD, despite their cognitive strengths, tend to suffer from significant impairments of executive functions that can be assessed with these measures;incidence of these impairments is significantly greater than in the general population. These results are fully consistent with data on high IQ adults diagnosed with ADHD.

Image-Based Ultrasound Speed Estimation: Phantom and Human Liver Studies

Purpose: A novel image-based method for speed of sound (SoS) estimation is proposed and experimentally validated on a tissue-mimicking ultrasound phantom and normal human liver in vivo using linear and curved array transducers. Methods: When the beamforming SoS settings are adjusted to match the real tissue’s SoS, the ultrasound image at regions of interest will be in focus and the image quality will be optimal. Based on this principle, both a tissue-mimicking ultrasound phantom and normal human liver in vivo were used in this study. Ultrasound image was acquired using different SoS settings in beamforming channels ranging from 1420 m/sec to 1600 m/sec. Two regions of interest (ROIs) were selected. One was in a fully developed speckle region, while the other contained specular reflectors. We evaluated the image quality of these two ROIs in images acquired at different SoS settings in beamforming channels by using the normalized autocorrelation function (ACF) of the image data. The values of the normalized ACF at a specific lag as a function of the SoS setting were computed. Subsequently, the soft tissue’s SoS was determined from the SoS setting at the minimum value of the normalized ACF. Results: The value of the ACF as a function of the SoS setting can be computed for phantom and human liver images. SoS in soft tissue can be determined from the SoS setting at the minimum value of the normalized ACF. The estimation results show that the SoS of the tissue-mimicking phantom is 1460 m/sec, which is consistent with the phantom manufacturer’s specification, and the SoS of the normal human liver is 1540 m/sec, which is within the range of the SoS in a healthy human liver in vivo. Conclusion: Soft tissue’s SoS can be determined by analyzing the normalized ACF of ultrasound images. The method is based on searching for a minimum of the normalized ACF of ultrasound image data with a specific lag among different SoS settings in beamforming channels.

Investigations into Some Simple Expressions of the Gamma Function in Wind Power Theoretical Estimate by the Weibull Distribution

The Weibull distribution is a probability density function (PDF) which is widely used in the study of meteorological data. The statistical analysis of the wind speed v by using the Weibull distribution leads to the estimate of the mean wind speed , the variance of v around and the mean power density in the wind. The gamma function Γ is involved in those calculations, particularly Γ (1+1/k), Γ (1+2/k) and Γ (1+3/k). The paper reports the use of the Weibull PDF f(v) to estimate the gamma function. The study was performed by looking for the wind speeds related to the maximum values of f(v), v2 f(v) and v3 f(v). As a result, some approximate relationships were obtained for Γ (1+1/k), Γ (1+2/k) and Γ (1+3/k), that use some fitting polynomial functions. Very good agreements were found between the exact and the estimated values of Γ (1+n/k) that can be used for the estimation of the mean wind speed , the variance σ2 of the wind speed v;around the mean speed and the average wind power density.

基于动态理论模型的电液伺服加载前馈补偿复合控制系统

针对一般电液伺服系统存在的非预期负载扰动和非线性干扰等问题,为了提高系统的自适应能力和动态响应的品质,减小系统跟踪和输出响应的误差,提出了一种基于动态理论模型的电液伺服加载前馈补偿复合控制方法。首先,阐释了电液伺服试验台的结构组成及其数学模型,分析了系统力矩控制和位置控制的结构关系;然后,论证了自适应前馈补偿复合控制的伺服原理,阐述了以调速理论模型和实际模型的误差函数作为调速依据的前馈补偿和复合控制的原理和方法;最后,进行了系统仿真,同时为了验证基于动态理论模型的自适应前馈补偿复合控制策略的合理性和有效性,对伺服系统进行了加载试验。研究结果表明:采用该复合控制策略可以精确算出对伺服马达进行转速补偿的基准值和调整参数,系统动态响应速度比采用传统闭环控制算法提高了8%以上;系统控制器自适应能力和抗扰动性能也明显优于采用传统PI闭环控制及模糊PI闭环控制算法的系统;通过对比分析0.2 Hz和0.5 Hz的正弦响应曲线可知,该系统的位置跟踪曲线性能最优,控制精度最高,实际输出值的误差也最小。

Fracture Analysis of Composites in High-speed Tension

In this paper the results of a high-speed tension experiment of the SiC_w/Al composite have been reported and a simplified theoretical model has been developed to study the fracture mechanism of composites in high-speed tension. This theoretical model provides a new explanation for the increase of dynamic fracture strength of composites in high-speed tension.

北京社区55~75岁高、低痴呆风险人群身体素质及其认知功能特点

目的分析预测社区中处于生命中期健康老年人痴呆风险因素。方法2021年7月至2023年4月招募北京市两个社区常住1年以上的55~75岁中老年人175例,收集心血管危险因素、衰老和痴呆(CAIDE)相关危险因素和其他一般人口资料,CAIDE风险评分≥9分为高危组,<9分为低危组。采用Stroop色词测验(SCWT)、两元素1-back任务范式、连线测验(TMT)进行评估;测量握力、30 s前臂屈曲测验和5次坐站试验;记录平地步行10 m的平均步速和步长。结果高危组CAIDE总分平均9.86分,低危组4.95分。两组年龄无显著性差异(P=0.188)。男性,受教育程度<7年、收缩压>140 mmHg、胆固醇>6.5 mmol/L、体质量指数>30 kg/m^(2)和缺乏体力活动人群CAIDE痴呆风险评分更高(χ^(2)>3.116,P<0.05)。高危组握力(t=-4.174)、步速(t=-2.414)、SCWT正确率(Z=-2.684)均差于低危组(P<0.05)。Logistic回归分析显示,步速(OR=25.483)、握力(OR=1.133),SCWT正确率(OR=37.430)是痴呆的独立危险因素(P<0.05)。结论握力弱、步速慢、抑制控制能力差可能预示痴呆风险增加。

Constraint-induced movement therapy promotes brain functional reorganization in stroke patients with hemiplegia

Stroke patients with hemiplegia exhibit flexor spasms in the upper limb and extensor spasms in the lower limb, and their movement patterns vary greatly. Constraint-induced movement therapy is an upper limb rehabilitation technique used in stroke patients with hemiplegia; however, studies of lower extremity rehabilitation are scarce. In this study, stroke patients with lower limb hemiplegia underwent conventional Bobath therapy for 4 weeks as baseline treatment, followed by constraint-induced movement therapy for an additional 4 weeks. The 10-m maximum walking speed and Berg balance scale scores significantly improved following treatment, and lower extremity motor function also improved. The results of functional MRI showed that constraint-induced movement therapy alleviates the reduction in cerebral functional activation in patients, which indicates activation of functional brain regions and a significant increase in cerebral blood perfusJon. These results demonstrate that constraint-induced movement therapy promotes brain functional reorganization in stroke patients with lower limb hemiplegia.

Model of Traffic Speed-Flow Relationship at Signal Intersections

Speed-flow relationship is the fundamental for the traffic simulation and traffic volume forecast. Traditional quadratic polynomial model can’t reflect the saturate flow at signal intersections. In order to determine the speed-flow relationship at signal intersections, the speed and time-headway of vehicles at two signal intersections were investigated and the accuracy of software used to get the speed was tested. After vehicle starting-up from queuing, the time-headway reduces gradually with the increase of speed. The relationship of power exponential function between speed and time-headway is formulated. Traffic volume can be calculated by the vehicle time-headway. Then the speed-flow relationship was developed and an S-shaped curve model was built in this paper. In the S-shaped curve model, traffic flow approaches to the saturate when the speed doesn’t increase. Thus, S-shaped curve model is better to describe the speed-flow relationship at signal intersection. The results can provide a reference to determine the parameters in traffic simulation and for the study of level of service of intersections.

3D打印速度对铸造蜡成型翘曲变形的影响

通过快速模具制造可打印熔模铸造用的蜡模,缩短生产周期,提高生产效率。但在实际成型过程中,由于制件不同位置的温度分布不均,会造成内应力差异,导致制件翘曲变形,进而对制件的成型质量产生较大的影响;而且,受3D打印速度和沉积层数等成型参数的制约,较难在降低制件翘曲变形程度的同时提高成型效率。有鉴于此,文中通过建立成型制件翘曲变形的数学模型,并结合实验设计与数学计算等方法,探究打印速度对铸造蜡直写成型翘曲变形程度与打印效率的影响机制。实验结果显示:在一定打印速度下,试样翘曲值随沉积层数的增加而减小,且随着打印速度的不断增加翘曲值逐渐变大;成型打印速度越高,不同试样的打印耗时越接近于某一稳定值,表明打印速度对成型效率的影响随打印速度的增加而降低。文中还通过对成型翘曲变形和打印效率分别赋予权重系数,建立了表面轮廓最佳打印速度连续函数模型,并验证了模型的有效性。研究结果表明,基于铸造蜡成型翘曲变形建立的最佳打印速度连续函数模型可在降低翘曲变形的同时提高打印效率。

信号交叉口车辆生态驾驶速度优化策略

为提高交叉口车辆通行效率,降低车辆因频繁启停造成的能耗及污染物排放,提出一种考虑排队长度动态变化的信号交叉口车辆生态驾驶速度优化策略。首先,根据排队长度预测目标车辆与排队队列的碰撞时间(TTC)。其次,将目标车辆通行策略分为匀速、加速、减速三种情况建立通行决策模型,结合改进的三角函数速度优化模型计算最优通行速度,确保车辆以平滑的速度顺利通过信号交叉口。最后,在不同排队长度场景下进行仿真实验,对比分析速度优化策略与无速度优化策略的时空轨迹。仿真结果表明,提出的速度优化策略既可以提高绿灯利用率,又可以降低目标车辆的燃油消耗,相较于无速度优化策略驾驶,燃油消耗最多可降低19.5%,对信号交叉口处车辆生态驾驶有积极作用。

基于改进蚁群优化算法的AUV三维路径规划

针对蚁群算法在三维路径规划时收敛速度慢且难以收敛至最优的缺点,提出一种新的改进蚁群算法,并将其应用于自主式水下机器人(autonomous underwater vehicle,AUV)三维路径规划。与现有算法相比,改进算法优点主要体现在3个方面:首先,引进伪随机状态转移概率提升算法全局搜索能力;其次,将距离和轨迹限定因子引入启发式函数,距离因子保证搜索不断趋近目标点,在轨迹限定因子约束下,轨迹累计转角更小,以此提升收敛速度和精度;最后,通过扩大信息素增量差距并逐步提高信息素衰减系数,进一步提高路径规划效率。实验结果表明,改进蚁群算法能够获得累计转角更小路径,且路径长度更小,收敛速度更快。

复杂环境下DWA与RRT算法融合的AUV局部路径规划

针对复杂水下环境下的自主水下航行器(autonomous underwater vehicle,AUV)局部路径规划问题,传统动态窗口法(dynamic window approach,DWA)存在复杂障碍物中陷入局部停滞,动态避障性能不佳等问题,本文提出了一种基于DWA与快速随机搜索树(rapid-exploration random tree,RRT)算法融合的路径规划算法。改进的DWA算法速度空间根据整个动态窗口的周期生成,重设了评价函数并结合AUV任务环境引入洋流能耗评价函数;改进的RRT算法在局部已知空间内规划导引点,帮助DWA脱离局部停滞状态并实现更安全的动态避障。将2种算法融合,实现了AUV在复杂水下环境中的局部路径规划。仿真表明,该融合算法能够降低AUV在洋流中的能耗代价,解决了DWA在复杂障碍物中陷入局部停滞的问题,能够安全有效地躲避动态避障物。

基于小样本迁移代理模型的高速永磁电机应力优化

针对目前电机代理模型样本空间计算效率低的问题,该文提出迁移径向基函数神经网络代理模型。该模型的样本信息源于足量可快速获取或先验积累的低可信度数据和少量高可信度的数据。基于高速永磁电机应力优化问题,研究该模型对小样本的学习能力、对电机相似拓扑结构的学习能力以及基函数对迁移模型精度的影响,证明该模型在工程优化中的效率优势。最后展望迁移学习技术在电机优化中的发展趋势。

一种加加速度连续平滑的新型柔性加减速控制算法

针对数控机床加工微小线段时因加加速度突变而导致精度和效率下降等问题,提出一种新型柔性加减速控制算法。该算法基于正弦函数构建了加加速度连续平滑的运动控制曲线,并通过分析数控机床加工线段的长度和初末速度,实现新型柔性加减速算法的速度规划。仿真与实验测试结果表明:与传统S形算法相比,该算法能有效地降低因加加速度突变引起的振动,提高数控加工过程中的平稳性与效率。

异地独立董事与上市公司高质量发展——基于高铁通车与独立董事履职的视角

独立董事的尽责履职对推动上市公司高质量发展具有重要意义。文章以2004—2020年我国A股上市公司为样本,从独立董事履职的视角,对异地独立董事如何影响上市公司高质量发展进行了实证研究,并考察了高铁通车在其中的调节作用。研究发现,异地独立董事对上市公司高质量发展具有显著负向影响,高铁通车则有效缓解了这一影响。机制检验发现,异地独立董事因为监督、咨询和决策无效而不利于上市公司高质量发展,高铁通车则主要通过改善监督和咨询职能的发挥,缓解上述不利影响。进一步研究发现,高铁通车后不同背景特征的异地独立董事对上市公司高质量发展存在差异化影响。具体而言,高铁开通后,具有行业专长、学术背景、海外背景的异地独立董事比例与上市公司高质量发展显著正相关;而不论高铁是否开通,具有法律、财务背景的异地独立董事比例与上市公司高质量发展显著负相关。