Validation of a videogrammetry technique for analysing American football helmet kinematics     

Ann Bailey  James Funk  David Lessley  Chris Sherwood  Jeff Crandall  William Neale 《Sports biomechanics / International Society of Biomechanics in Sports》2020,19(5):678-700

ABSTRACT

Professional American football games are recorded in digital video with multiple cameras, often at high resolution and high frame rates. The purpose of this study was to evaluate the accuracy of a videogrammetry technique to calculate translational and rotational helmet velocity before, during and after a helmet impact. In total, 10 football impacts were staged in a National Football League (NFL) stadium by propelling helmeted 50th percentile male crash test dummies into each other or the ground at speeds and orientations representative of concussive impacts for NFL players. The tests were recorded by experienced sports film crews to obtain video coverage and quality typically available for NFL games. A videogrammetry procedure was used to track the position and rotation of the helmet throughout the relevant time interval of the head impact. Compared with rigidly mounted retroreflective marker three dimensional (3-D) motion tracking that was concurrently collected in the experiments, videogrammetry accurately calculated changes in translational and rotational velocity of the helmet using high frame rate (two cameras at 240 Hz) video (7% and 15% error, respectively). Low frame rate (2 cameras at 60 Hz) video was adequate for calculating pre-impact translational velocity but not for calculating the translational or rotational velocity change of the helmet during impact.  相似文献   

基于曲线匹配的星载激光测高仪无场在轨几何定标方法     

陈林生  周梅  腾格尔  陈玖英  李传荣  唐伶俐 《中国科学院大学学报》2020,37(1):113-119

星载激光测高技术的快速发展急需有效的在轨几何定标方法来校正测高数据中的系统误差。探索一种基于曲线匹配的测高仪无场在轨几何定标方法。该方法利用激光足印高程曲线与DEM进行匹配获得激光足印控制点进而实现定标参数求解，无需到野外布设探测器定标场地。采用资源三号02星激光测高数据进行定标方法验证，并对定标结果进行精度评估。实验表明，经本文的定标方法校正后的测高数据的精度得到显著提升，验证了本方法的有效性。  相似文献   

College course scarcity and time to degree     

《Economics of Education Review》2014

College students are taking longer to earn baccalaureate degrees now than ever before, but little is known about institutional factors that may contribute to this trend. In this paper we investigate an important institutional constraint—course scarcity—that we hypothesize may be associated with increased time to degree. We employ a unique administrative dataset from a large, moderately selective, public institution and use an instrumental variables approach, identifying off the random registration times assigned to students. Results suggest that course scarcity does not delay students’ graduation. We explore alternative explanations for our findings and discuss a variety of other factors correlated with time to baccalaureate completion.  相似文献   

Is academic tracking related to gains in learning competence? Using propensity score matching and differential item change functioning analysis for better understanding of tracking implications     

《Learning and Instruction》2020

This study analyzes gains in cognitive components of learning competence with respect to cohorts based on ability tracking in a Czech longitudinal study. Propensity score matching is used to form parallelized samples of academic and non-academic track students and to eliminate the effect of selective school intake. We applied regression models on the total scores to test for the overall track effect. Furthermore, we analyze scores and gains on the subscores and check for differential item functioning in Grade 6 and in change to Grade 9. While after 3 years, no significant difference between the two tracks was apparent in the total learning competence score, we did, however, find significant differences in some subscores and in the functioning of some items. We argue that item-level analysis is important for deeper understanding of the tracking implications and may provide the basis for more precise evidence-based decisions regarding the tracking policy.  相似文献   

中国体育产业与旅游产业发展耦合关联性测度及空间相关分析     

许金富  陈海春 《山东体育学院学报》2020,(1):9-16

体育产业和旅游产业的互动融合发展是当前经济发展的客观需求,基于耦合协调度模型、探索性空间数据分析方法,构建体育产业和旅游产业发展耦合协调评价指标体系,探讨中国大陆31个省、直辖市、自治区体育产业和旅游产业综合水平及耦合协调度时序、空间分异特征。结果显示:我国体育产业和旅游产业综合水平均表现出增长态势,空间分布呈东中西阶梯分布,旅游产业综合水平好于体育产业水平;耦合协调度发展缓慢,整体处于较低水平;两个产业的耦合协调度在空间上呈正向聚集特征,且聚集程度逐年递增;东部沿海地区耦合协调度好于中部和西部地区。并提出如下建议:建立区域协同发展机制,促进体育产业均衡发展;挖掘体育产业与旅游产业的关联性,完善体育产业发展体系;协同发挥体育产业与旅游产业融合进程中的政府引导作用和企业创新管理能力。  相似文献   

关中带高新技术供求的配套潜力与机制研究   总被引：2，自引：0，他引：2  

杨锁强  韩骁  张鹏柱 《科学学研究》2003,21(2):171-175

在对陕西省关中高新技术产业开发带高新技术资源、生产潜力优势与企业对高新技术需求分析的基础上 ,本文研究了高新技术生产与需求相互配套的潜力、重点与具体方案 ,并建立了高新技术生产与需求的配套机制 ,提出了关中带配套机制运行中需要解决的主要问题与具体的对策。  相似文献   

同类产品(服务)竞争优势变动趋势——基于客户满意度的动态分析框架     

高江舟  李常洪 《科技与管理》2007,9(3):76-78

为了能更深入地考察同类产品（服务）在消费者市场中的长期稳定状态,采用独立增量过程——马尔可夫链,基于客户满意度建立动态优势测度分析模型,并结合算例加以分析。预测同类产品（服务）在消费市场中客户满意度的变化及长期稳定状态,使得企业能够掌握及预测本企业产品（服务）在提供同类产品的所有企业中客户满意度的竞争地位,为企业决策提供依据。  相似文献   

供应链上信息流集成的实现和优化分析     

员巧云  刘斌  陈剑 《科学学与科学技术管理》2007,28(7):14-17

研究有效的供应链信息共享模式,寻求供应链信息流集成的实现途径和优化手段。通过网络数据结构建立信息流网络模型,并构建信息流集成块,求顶点间的最小路径以确定两两信息共享成本最小的信息流集成块,利用信息共享能力指标体系和信息共享度来测量和确定信息流集成中心,提出了优化供应链信息流集成的方法和途径。  相似文献   

山东省产业结构优化升级中的人力资本适配性研究     

靳卫东 《科学与管理》2011,(4):60-63

产业结构的优化升级需要与人力资本基础相互协同。这种协同关系决定了产业结构优化升级的阶段、重点、路径和方式。山东省产业结构正在实现由"二、三、一"向"三、二、一"模式的转化,人力资本的数量和结构对这一转化的进程具有决定性作用。首先,人力资本水平决定了劳动力在三次产业之间的优化配置能力;其次,人力资本决定了技术进步的类型,从而也就决定了产业结构调整的速度和方式。三次产业区位商值的变化表明,山东省第一产业的比较优势正在丧失,而第三产业的比较优势开始逐步形成。所以,增加高层次人力资本投资,大力发展高新技术产业,已经成为山东省产业结构优化升级的内在要求。  相似文献   

基于熵权的大型项目决策影响因素模糊分析   总被引：13，自引：0，他引：13  

陈黎明  邱菀华 《预测》2003,22(3):65-67

在分析大型社会公共项目决策影响因素的基础上，我们建立了基于熵权的模糊决策分析模型。结合模糊数学和熵的思想，运用多属性决策分析中的双基点法，该模型对大型社会公共项目决策的影响因素进行模糊分析，可为项目开发商分析关键影响因素提供决策参考，有一定的实际应用指导意义。  相似文献