STATISTIC MODELING OF THE CREEP BEHAVIOR OF METAL MATRIX COMPOSITES BASED ON FINITE ELEMENT ANALYSIS

The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep behavior and the material micro geometric parameters. The unit cell models were used to calculate the macroscopic creep behavior with different micro geometric parameters of fibers on different loading directions. The influence of the geometric parameters of the fibers and loading directions on the macroscopic creep behavior had been obtained, and described quantitatively. The matrix/fiber interface had been considered by a third layer, matrix/fiber interlayer, in the unit cells with different creep properties and thickness. Based on the numerical results of the unit cell models, a statistic model had been presented for the plane randomly-distributed-fiber MMCs. The fiber breakage had been taken into account in the statistic model for it starts experimentally early in the creep life. With the distribution of the geometric parameters of the fibers, the results of the statistic model agree well with the experiments. With the statistic model, the influence of the geometric parameters and the breakage of the fibers as well as the properties and thickness of, the interlayer on the macroscopic steady creep rate have been discussed.

考虑颗粒形貌的干砂热传导特性研究

为揭示颗粒形貌对干砂热导率的影响规律,通过砂颗粒形貌测量和室内热探针试验,研究不同天然河砂的二维颗粒形貌统计分布特征以及颗粒形貌特征参数与热导率的相关关系,同时从细观尺度探讨砂颗粒接触传热的内在机制。结果表明:天然河砂颗粒圆度和球度值的统计分布具有正态分布特征,期望值可作为定量表征颗粒形貌的参数;干砂热导率随孔隙率增加而减小,在半对数坐标中两者具有良好的线性关系,直线斜率与“平均形貌因子”Am呈线性减小关系;相同孔隙率下,浑圆颗粒的干砂热导率值较大,不同干砂间热导率值的差异随孔隙率的增加而逐渐减小;提出的热导率计算新模型综合考虑了颗粒形貌和矿物组分的影响,相比于传统Côté和Konrad模型,具有更好的适用性和先进性;颗粒形貌对干燥状态下无黏性土热传导特性的作用受多因素综合影响,与应力环境、颗粒刚度等密切相关。

问题与思考:我国旅游统计的困境与出路

近年来,随着互联网、大数据等新技术在文旅领域的加速应用,以及旅游业的不断融合,供需双方发生了根本性变化,出现了新的经济形态、业态和商业模式,这进一步拓展了旅游产业的边界,并引起了广泛的关注,尤其是对旅游统计工作的关注日益增加。作为衡量旅游发展和评估旅游经济影响的关键工具,目前旅游统计数据的全面性、准确性与真实性情况存在出入,长期面临着国家层面和地方层面统计口径不一致、抽样调查存在局限性以及国际上无法与全球标准对接等问题。文章以旅游人数统计面临的问题为切入点,深入探讨我国旅游统计的困境,通过引入旅游者行为视角,提出大数据运用于我国旅游统计体系的优化思路,以期为如何判别旅游活动的边界等问题提供补充性参考。

典型事故形态下驾驶人工作记忆与应激反应研究

为探究事故发生时的不同形态和工作记忆与驾驶人应激反应能力及视觉行为的关系,本文对31名驾驶人分别开展城市道路中侧面碰撞、追尾碰撞和刮撞行人这3种典型事故形态下的驾驶模拟器实验。根据摄像机和眼动仪的输出视频,采用动态聚类将驾驶人的注视区域划分成7类,同时,基于单因素方差分析,Mann-Whitney U检验和Kruskal-Wallis检验,分析事故形态的类型、不同工作记忆容量的人群避险时的应激反应能力和视觉行为的影响。结果表明:事故形态和驾驶人的应激反应能力显著相关,在前车紧急制动事件中驾驶人的反应时间最短,较侧面碰撞减少了25.46%;在面对危险时的反应时间受到驾驶人工作记忆容量的影响,即相比于低工作记忆容量,高工作记忆容量的驾驶人反应时间短;此外,注视总持续时间、平均扫视时间和瞳孔直径均与工作记忆容量相关。研究结果可为车辆安全针对性预警提供理论支持。

Detection of Nonlinear Behavior Induced by Hard Limiting in Voltage Source Converters in Wind Farms Based on Higher-order Spectral Analysis

In recent years, sub-synchronous oscillation accidents caused by wind power integration have received extensive attention. The recorded constant-amplitude waveforms can be induced by either linear or nonlinear oscillation mechanisms. Hence, the nonlinear behavior needs to be distinguished prior to choosing the analysis method. Since the 1960s, the higher-order statistics(HOS) theory has become a powerful tool for the detection of nonlinear behavior(DNB) in production quality control wherein it has mainly been applied to mechanical condition monitoring and fault diagnosis. This study focuses on the hard limiters of the voltage source converter(VSC) control systems in the wind farms and attempts to detect the nonlinear behavior caused by bi-or uni-lateral saturation hard limiting using the HOS analysis. First, the conventional describing function is extended to obtain the detailed frequency domain information on the bi-and uni-lateral saturation hard limiting. Furthermore, the bi-and tri-spectra are introduced as the HOS, which are extended into bi-and tri-coherence spectra to eliminate the effects of the linear parts on the harmonic characteristics of hard limiting in the VSC control system, respectively. The effectiveness of the HOS in the DNB and the classification of the hard-limiting types is proven, and its detailed derivation and estimation procedure is presented. Finally, the quadratic and cubic phase coupling in the signals is illustrated, and the performance of the proposed method is evaluated and discussed.

开放教育学生学习行为差异化的计算机统计研究

基于国家开放大学学习网平台学习数据和调查问卷结果,运用计算机统计技术,本文研究了台州开放大学在开放教育下对学生学习行为差异化的影响因素。详细地分析了影响学生学习行为的6个因素,其中可分为个人因素和环境因素,此外还分析了学习行为过程与学习行为效果的相关性,并在此基础上提出了一系列优化开放教育和学习支持服务的方法与措施。

基于OBD数据采集的驾驶员驾驶平稳性分析

驾驶员驾驶平稳性分析对研究交通安全影响因素起着至关重要的作用。为此提出基于车载自动诊断系统(OBD)采集数据,利用多项式回归进行短时间内车辆速度预测研究。首先分析影响车辆驾驶速度的客观因素,如地势、天气、行驶路径等。其次通过控制客观因素不变,整合有效驾驶速度数据进行多项式回归预测,得到模型的参数。通过真实值与预测值的比对,得到均方差MSE与拟合优度,进而得到最优参数。最后通过大量的实验数据,验证了该模型在此次研究中取得了很好的预测结果。

Assessing gray matter volume in patients with idiopathic rapid eye movement sleep behavior disorder

Idiopathic rapid eye movement sleep behavior disorder(iRBD) is often a precursor to neurodegenerative disease. However, voxel-based morphological studies evaluating structural abnormalities in the brains of iRBD patients are relatively rare. This study aimed to explore cerebral structural alterations using magnetic resonance imaging and to determine their association with clinical parameters in iRBD patients. Brain structural T1-weighted MRI scans were acquired from 19 polysomnogram-confirmed iRBD patients(male:female 16:3; mean age 66.6 ± 7.0 years) and 20 age-matched healthy controls(male:female 5:15; mean age 63.7 ± 5.9 years). Gray matter volume(GMV) data were analyzed based on Statistical Parametric Mapping 8, using a voxel-based morphometry method and two-sample t-test and multiple regression analysis. Compared with controls, iRBD patients had increased GMV in the middle temporal gyrus and cerebellar posterior lobe, but decreased GMV in the Rolandic operculum, postcentral gyrus, insular lobe, cingulate gyrus, precuneus, rectus gyrus, and superior frontal gyrus. iRBD duration was positively correlated with GMV in the precuneus, cuneus, superior parietal gyrus, postcentral gyrus, posterior cingulate gyrus, hippocampus, lingual gyrus, middle occipital gyrus, middle temporal gyrus, and cerebellum posterior lobe. Furthermore, phasic chin electromyographic activity was positively correlated with GMV in the hippocampus, precuneus, fusiform gyrus, precentral gyrus, superior frontal gyrus, cuneus, inferior parietal lobule, angular gyrus, superior parietal gyrus, paracentral lobule, and cerebellar posterior lobe. There were no significant negative correlations of brain GMV with disease duration or electromyographic activity in iRBD patients. These findings expand the spectrum of known gray matter modifications in iRBD patients and provide evidence of a correlation between brain dysfunction and clinical manifestations in such patients. The protocol was approved by the Ethics Committee of Huashan Hospital(approval No. KY2013-336) on January 6, 2014. This trial was registered in the ISRCTN registry(ISRCTN18238599).

Virtual ballistic impact testing of Kevlar soft armor:Predictive and validated finite element modeling of the V0-V100 probabilistic penetration response

This works presents the first fully validated and predictive capability to model the V_0-V_(100) probabilistic penetration response of a woven fabric using a yarn-level fabric finite element model. The V_0-V_(100) curve describes the probability of complete fabric penetration as a function of projectile impact velocity. The exemplar case considered in this paper comprises of a single-layer, fully-clamped, plain-weave Kevlar fabric impacted at the center by a 17-gr, 0.22 cal FSP or fragment-simulating projectile. Each warp and fill yarn in the fabric is individually modeled using 3 D finite elements and the virtual fabric microstructure is validated in detail against the experimental fabric microstructure. Material and testing sources of statistical variability including yarn strength and modulus, inter-yarn friction, precise projectile impact location, and projectile rotation are mapped into the finite element model. A series of impact simulations at varying projectile impact velocities is executed using LS-DYNA on the fabric models, with each model comprising unique mappings. The impact velocities together with the outcomes(penetration, nonpenetration) are used to generate the numerical V_0-V_(100) curve which is then validated against the experimental V_0-V_(100) curve. The numerical Vi-Vrdata(impact, residual velocities) is also validated against the experimental Vi-Vrdata. For completeness, this paper also reports the experimental characterization data and its statistical analysis used for model input, viz. the Kevlar yarn tensile strengths, moduli, and inter-yarn friction, and the experimental ballistic test data used for model validation.

PROPAGATION OF SHORT FATIGUE CRACKS IN STEEL 16Mn

Small bar speeimens of steel 16Mn with blind-holes were fatigued under constant amplitude Ioadings on a rotathing bending fatigue machie.Short crack propagation emanating from the blind-holes was obtained.Based on the experimental results,an expression of average propa- gation rate of short cracks was proposed.Statistical behavior of short crack propagation was discussed and the evoluation of sutrface sizes of short cracks with fatigue cycle number was al- so given.

Symbolic Macromodeling for Statistical Simulation of Operational Amplifiers

Symbolic circuit simulator is traditionally applied to the small-signal analysis of analog circuits. This paper establishes a symbolic behavioral macromodeling method applicable to both small-signal and large-signal analysis of general two-stage operational amplifiers （op-amps）. The proposed method creates a two-pole parametric macromodel whose parameters are analytical functions of the circuit element parameters generated by a symbolic circuit simulator. A moment matching technique is used in deriving the analytical model parameter. The created parametric behavioral model can be used for op-amps performance simulation in both frequency and time domains. In particular, the parametric models are highly suited for fast statistical simulation of op-amps in the time-domain. Experiment results show that the statistical distributions of the op-amp slew and settling time characterized by the proposed model agree well with the transistor-level results in addition to achieving significant speedup.

Dark count in single-photon avalanche diodes:A novel statistical behavioral model

Dark count is one of the inherent noise types in single-photon diodes,which may restrict the performances of detectors based on these diodes.To formulate better designs for peripheral circuits of such diodes,an accurate statistical behavioral model of dark current must be established.Research has shown that there are four main mechanisms that contribute to the dark count in single-photon avalanche diodes.However,in the existing dark count models only three models have been considered,thus leading to inaccuracies in these models.To resolve these shortcomings,the dark current caused by carrier diffusion in the neutral region is deduced by multiplying the carrier detection probability with the carrier particle current at the boundary of the depletion layer.Thus,a comprehensive dark current model is constructed by adding the dark current caused by carrier diffusion to the dark current caused by the other three mechanisms.To the best of our knowledge,this is the first dark count simulation model into which incorporated simultaneously are the thermal generation,trap-assisted tunneling,band-to-band tunneling mechanisms,and carrier diffusion in neutral regions to evaluate dark count behavior.The comparison between the measured data and the simulation results from the models shows that the proposed model is more accurate than other existing models,and the maximum of accuracy increases up to 31.48%when excess bias voltage equals 3.5 V and temperature is 50℃.

计划行为理论在旅游研究中的应用回顾

计划行为理论对个人行为意向的选择具有良好的解释和预测能力,近年来在旅游研究中的应用也越来越多。文章以计划行为理论和旅游为关键词,检索了中国知网和Web of Science共440篇文献,运用VOSviewer 1.6.11对文献的关键词与聚类特征进行了统计分析,讨论计划行为理论的发展演进,回顾了国内外计划行为理论模型在旅游研究中的应用,分析了国内外计划行为理论模型在旅游研究中的研究方法。研究发现:计划行为理论作为旅游研究领域的重要理论之一,在旅游研究中具有良好的解释力;学者在运用该理论时,应当兼顾三大维度的范畴以及变量间的相互关系;计划行为理论具有良好的拓展性,采用新的方法或变量可能导致结果的不可靠,改进该理论时应当形成相对一致的研究范式。文章提出了计划行为理论的应用方式,为旅游研究的拓展提供了参考。

基于数据挖掘的大学生消费行为数据聚类统计研究

为精准统计大学生消费行为,并分析环境因素对学生消费能力的影响,基于数据挖掘方法聚类统计大学生消费行为数据。按照数据挖掘原则,提取数据簇中心,挖掘数据并进行数据集转换。确定大学生的主要消费方式,联合采集到的数据样本,求解聚类参数与统计学向量。实验结果表明,家庭环境是影响大学生消费能力的主要因素,大多数学生在商品价格不超过个人经济负担能力的情况下,能够进行理性消费。

基于PigsTrack跟踪器的群养生猪多目标跟踪

基于视频的生猪行为跟踪和识别对于实现精细化养殖具有重要价值。为了应对群养生猪多目标跟踪任务中由猪只外观相似、遮挡交互等因素带来的挑战,研究提出了基于PigsTrack跟踪器的群养生猪多目标跟踪方法。PigsTrack跟踪器利用高性能YOLOX网络降低目标误检与漏检率,采用Transformer模型获取具有良好区分特性的目标外观特征;基于OC-SORT(observation-centric sort)的思想,通过集成特征匹配、IoU匹配和遮挡恢复匹配策略实现群养生猪的准确跟踪。基于PBVD(pigs behaviours video dataset)数据集的试验结果表明,PigsTrack跟踪器的HOTA(higher order tracking accuracy),MOTA(multiple object tracking accuracy)和IDF1得分(identification F1 score)分别为85.66%、98.59%和99.57%,相较于现有算法的最高精度,分别提高了3.71、0.03和2.05个百分点,证明了PigsTrack跟踪器在解决外观相似和遮挡交互引起的跟踪过程中身份跳变问题方面的有效性。随后,利用Slowfast网络对PigsTrack跟踪器的跟踪结果进行了典型行为统计,结果显示PigsTrack在群养生猪个体行为统计方面更准确。此外,通过在ABVD(aggressive-behavior video)数据集上的试验,PigsTrack跟踪器的HOTA、MOTA和IDF1得分分别为69.14%、94.82%和90.11%,相对于现有算法的最高精度,提高了5.33、0.57和8.60个百分点,验证了PigsTrack跟踪器在群养生猪跟踪任务中的有效性。总而言之,PigsTrack跟踪器能够有效应对外观相似和遮挡交互等挑战,实现了准确的生猪多目标跟踪,并在行为统计方面展现出更高的准确性,为生猪养殖领域的研究和实际应用提供了有价值的指导。

融合可视化教学的高校智慧课堂互动行为研究

集成丰富信息技术的智慧课堂让可视化教学形式变得丰富、高效,为分析该课堂环境下的高校师生互动行为特点,以湖北大学智慧课堂9节课程教学案例为研究对象,基于自主设计的课堂互动分类指标对教学视频进行量化编码与统计,从教学行为整体、学科性质比较与视觉表征差异3个层面对融合可视化教学的智慧课堂师生互动行为特点进行深入分析。研究发现,在此教学环境下,学生的“主体性”地位得到提升,对于可视化技术或工具的应用还有待适应;教师在进行言语教学的同时运用可视化教学进行知识表示,有助于提高理工类课堂的学生互动率;智慧课堂下的可视化教学流畅度高,且学生的参与氛围更浓厚,各种动态视频动画、可视化工具的使用能够进一步调动学生的学习积极性。

Universal behaviors of magnon-mediated spin transport in disordered nonmagnetic metalferromagnetic insulator heterostructures

We numerically investigate magnon-mediated spin transport through nonmagnetic metal/ferromagnetic insulator(NM/FI)heterostructures in the presence of Anderson disorder,and discover universal behaviors of the spin conductance in both one-dimensional(1D)and 2D systems.In the localized regime,the variance of logarithmic spin conductanceσ2(lnGγ)shows a universal linear scaling with its average(lnGγ),independent of Fermi energy,temperature,and system size in both 1D and 2D cases.In 2D,the competition between disorder-enhanced density of states at the NM/FI interface and disorder-suppressed spin transport leads to a non-monotonic dependence of average spin conductance on the disorder strength.As a result,in the metallic regime,average spin conductance is enhanced by disorder,and a new linear scaling between spin conductance fluctuation rms(GT)and average spin conductance GT is revealed which is universal at large system width.These universal scaling behaviors suggest that spin transport mediated by magnon in disordered 2D NM/FI systems belongs to a new universality class,different from that of charge conductance in 2D normal metal systems.

医院防止非法统方的对策探讨

非法统方是非正常商业行为得以实现的关键一环,近年来,非法统方涉嫌违法犯罪案件频繁公之于众,引发公众对医药领域乱象的持续关注和担忧,且患者在就医过程中,往往对疾病的治疗结果报以不合理的期望,在一定程度上加剧了医患之间的不信任,给医院带来了不良的影响,甚至引发医疗纠纷。医院如何有效地防止医疗工作人员的统方行为,斩断伸向非法获取数据的“黑手”,从而遏制暗中收受回扣的贿赂行为,唯有跳出单一依靠防统方系统来监控非法统方行为的方法,从事前、事中、事后三个节点不断加大非法统方的监控力度,实现抑制“开药提成”等不正之风。

谢林模型的统计物理学

社会性隔离是人类社会作为复杂系统涌现的典型现象之一.托马斯·谢林(Thomas C.Schelling,1921—2016)在1971年提出了解释种族隔离现象的著名模型——谢林模型.半个多世纪以来,谢林模型吸引了相当数量的研究,由此产生了许多重要结论.本文旨在对谢林模型的统计物理以及晚近的进展做一概要介绍,以阐明统计物理和社会动力学之间的深层关系.