网络资源命名及用户命名行为的分析

网络资源是指通过互联网传播共享、以文件目录为主要存储组织结构的内容,如书、讲义、音乐等.每个资源的内容具有完整独立性.它们是数字图书馆、教学资源库、专业内容库藏的重要组成.网络资源的一大特点是命名模式不规范,给检索利用带来极大不便.本文以2003～2006年间搜集的61万文件构成的16 284个网络资源为对象,用统计的方法考察网络资源命名特点及其中体现的用户命名习惯.包括资源及其内部子目录、文件的名字长度分布,字符类型熵、常用符号、高频片段模式、语义类型等,并分析无序命名中蕴含的用户命名习惯.本文的意义一方面有助于从混乱命名中净化和提取对检索查询有用的信息,另一方面有助于揭示网络用户参与海量网络资源共享的行为习惯.     

中国大学生龙舟男子500m直道途中坐姿划桨技术的运动学分析

对2006年首届、2009年第三届、2011年第四届中国大学生龙舟锦标赛男子直道500m前3名运动队途中划桨三次现场双机同步二维平面拍摄,运用SIMImotion7．50生物力学解析系统解析,拟揭示途中划桨技术的运动学特征。结果表明：抓水阶段是动力阶段,该阶段桨的入水角度小,抓水猛、稳、准,桨面与舟前进法线的夹角减小;拉水阶段的动作特点是拉桨快而深,划距增大,该阶段需要调整合理浆频和划距;提桨要巧,动作要快,幅度要小;外摆阶段空中划摆快,举桨、撑桨幅度增大;举插阶段桨摆动角速度变小,舟速从最小舟速开始增加;整个途中划姿不变,桨频为中桨频;人体在垂直方向的变化很小,主要为水平方向上近匀速的运动,平均速度为6．02m／s,T抓水：T拉水：Tl提浆：T外摆：T举插＝5：6：4：6：4,节奏分明,周期0．71s。旨在为龙舟划桨技术改进提供参考。     

The nature of force depression and force enhancement in skeletal muscle contraction

Here, we review the history-dependent phenomena associated with muscle force production. Specifically, the depression of the steady-state isometric force following muscle shortening, and the enhancement of the steady-state isometric force following muscle stretching are discussed. First, we describe the observations that have been made experimentally, then we introduce the primary proposed mechanisms for force depression and force enhancement. Next, in view of the available results, we critically evaluate specific hypotheses based on these mechanisms. Finally, we recommend further discussion about some of the proposed mechanisms.     

Forefoot running requires shorter gastrocnemius fascicle length than rearfoot running

ABSTRACT

This study aimed to investigate the influence of foot strike patterns on the behaviour of the triceps surae muscle-tendon unit, including the Achilles tendon whose length nearly corresponds to force of the triceps surae, and the medial gastrocnemius muscle (MG) during running. Seven male volunteers ran with forefoot and rearfoot strikes at 10, 14 and 18 km h^?1 on a treadmill. The MG fascicle length was measured using ultrasonography. The in vivo length of the curved Achilles tendon was quantified by combining ultrasonography with optical motion capture of reflective markers on the right lower limb and an ultrasound probe. The forefoot strike resulted in a significantly shorter MG fascicle length at the initial contact, at Achilles tendon peak elongation, and at toe-off, than the rearfoot strike. The Achilles tendon length at initial contact was greater during the forefoot strike than during the rearfoot strike at 18 km h^?1, while its peak elongation was not significantly different during forefoot and rearfoot running. These results indicate that the MG, with a shorter length during forefoot running, manages to address demands for a similar peak force of the triceps surae than during rearfoot running.     

Ball launch conditions for skilled golfers using drivers of different lengths in an indoor testing facility

Abstract

The displacement of the golf ball struck by a driving club is affected by several player characteristics and equipment parameters and their interrelationships. Some modelling and simulation studies have shown a relationship between shaft length and clubhead speed, supported by a few experimental studies. The aim of the present study was to examine the relationship between driver length and ball launch conditions in an indoor test facility using a ball launch monitor. Nine males considered to be skilled golfers participated in the study. Four driving clubs of total length 117, 119, 124, and 132 cm were assembled from commercially available components and were used to strike golf shots while initial ball velocity, backspin rate, and launch angles were measured. Statistical analysis identified a significant difference in initial launch speed due to club length, a significant difference between participants, but no difference between the trials for a given golfer. A positive trend was noted between backspin and launch angle for all four clubs, and significant inverse associations between initial launch speed and backspin rate and launch angle. However, the combined launch conditions associated with increasing length were not considered optimal, with uncontrolled swingweight and moment of inertia effects considered to be limiting factors.     

Improved sentence retrieval using local context and sentence length

In this paper we propose improved variants of the sentence retrieval method TF–ISF (a TF–IDF or Term Frequency–Inverse Document Frequency variant for sentence retrieval). The improvement is achieved by using context consisting of neighboring sentences and at the same time promoting the retrieval of longer sentences. We thoroughly compare new modified TF–ISF methods to the TF–ISF baseline, to an earlier attempt to include context into TF–ISF named tfmix and to a language modeling based method that uses context and promoting retrieval of long sentences named 3MMPDS. Experimental results show that the TF–ISF method can be improved using local context. Results also show that the TF–ISF method can be improved by promoting the retrieval of longer sentences. Finally we show that the best results are achieved when combining both modifications. All new methods (TF–ISF variants) also show statistically significant better results than the other tested methods.     

中美航线飞越北极最短时间

利用把不定长转化为定长和建立数学模型的方法,借助空间立体图形、函数、控制测量学、计算机编程及物体间相互运动等知识,解决了从北京到底特律飞行航线最短,应用于实际中。     

Computation of average run length for residual-based T 2 control chart for multivariate autocorrelated processes

The expression of residual is obtained according to its dynamic response to mean shift,then the distribution of T 2 statistic applied to the residual is derived,thus the probability of the T 2 statistic lying outside the control limit is calculated.The above-mentioned results are substituted into the infinite definition expression of the average run length(ARL),and then the final finite ARL expression is obtained.An example is used to demonstrate the procedures of the proposed method.In the comparative study,eight autocorrelated processes and four different mean shifts are performed,and the ARL values of the proposed method are compared with those obtained by simulation method with 50,000 replications.The accuracy of the proposed method can be illustrated through the comparative results.     

3～6岁幼儿数守恒和长度守恒的发展特点

不同年龄阶段的幼儿在数守恒和长度守恒方面具有不同的发展水平。小班幼儿极易受物体排列形式的影响,部分中班幼儿仍摆脱不了物体排列形式的影响,大班幼儿初步形成了数的守恒。幼儿长度守恒的发展落后于数守恒的发展,其发展顺序与皮亚杰的研究结果一致,但形成年龄略微提前。     

队列管理机制QOS性能仿真

队列管理机制是网络拥塞控制和网络服务质量的基础,采用NS2仿真工具基=JaQOS性能评价指标对主、被动队列的代表算法RED、DropTail进行仿真分析,得出两种算法性能差异及各自的特点,为进一步研究提供依据．