换热器尺寸过大的隐患

通过分析换热器实际应用中存在的问题,说明换热器的尺寸不是越大越好。根据实践经验总结了提高管壳程流速的方法,指出在换热器的设计计算中,流速是换热器的重要参数。在压力降允许的范围内尽量保持高流速,才能提高换热器的传热效果,确保换热器运行可靠。     

发电厂厂用快速切换技术的应用

以东大金智公司生产的MFC2000—2型快切装置为例,详细介绍了快切装置的应用及运行规程的要求,归纳了厂用快切在实际运用中需解决好的三点关键问题,分析了微机厂用快切的构成及工作原理,最后提出了快切的定值整定方法。     

Talent identification and selection process of outfield players and goalkeepers in a professional soccer club

Abstract

The aim of this study was to analyse the talent identification process of a professional soccer club. A preselection of players (n = 64) aged 9–10 years and a final selection (n = 21) were performed by the technical staff through the observation during training sessions and matches. Also, 34 age-matched players of an open soccer camp (CampP) acted as controls. All participants underwent anthropometric, maturity and performance measurements.

Preselected outfield players (OFs) were older and leaner than CampP (P < 0.05). Besides, they performed better in velocity, agility, endurance and jump tests (P < 0.05). A discriminant analysis showed that velocity and agility were the most important parameters. Finally, selected OFs were older and displayed better agility and endurance compared to the nonselected OFs (P < 0.05). Goalkeepers (GKs) were taller and heavier and had more body fat than OFs; also, they performed worse in the physical tests (P < 0.05). Finally, selected GKs were older and taller, had a higher predicted height and advanced maturity and performed better in the handgrip (dynamometry) and jump tests (P < 0.05).

Thus, the technical staff selected OFs with a particular anthropometry and best performance, particularly agility and endurance, while GKs had a different profile. Moreover, chronological age had an important role in the whole selection process.     

跑台速度与坡度对步态的影响

旨在通过对不同速度和不同坡度的控制,比较受试者在步态跑台上步态参数的异同。为使步态跑台更好地应用于健身、训练及康复提供参考和建议。采集并比较14名健康大学生以三种不同速度、三种不同坡度走时的时空和动力学参数。结果发现:步幅、步长与速度正相关,双支撑时长、单脚支撑时长、每步时长、步态周期与速度呈负相关。支撑力、触地受力时长、推动力随着速度增加而减小。在不同坡度的条件下行走,步长随着坡度的上升而增加,步态周期则相反。随着坡度的增加,触底受力时长、推动力、支撑力均变小。X轴方向平均力值与速度和坡度均呈正相关。     

第12届全运会男、女20km竞走运动员速度特征分析

竞走速度是所有关于竞走运动技术和特征研究的首要问题,也是所有竞速项目最终要解决的问题。运用文献资料法、数理统计法、逻辑分析法对12运会男子、女子20km前8名运动员的速度特征进行分析,探求中国竞走运动员速度发展的趋势以及存在的问题,为中国竞走运动员参加2015世界田径锦标赛和2016里约奥运会提供参考。     

纤维素手性拆分剂的研究进展

文章介绍了几种纤维素类手性拆分剂以及其制备方法相关分离机理,综述了纤维素手性拆分剂的分离机理及其应用,重点地介绍纤维素手性固定相和纤维素膜的应用。     

Exhaled breath condensate – from an analytical point of view

Over the past three decades, the goal of many researchers is analysis of exhaled breath condensate (EBC) as noninvasively obtained sample. A total quality in laboratory diagnostic processes in EBC analysis was investigated: pre-analytical (formation, collection, storage of EBC), analytical (sensitivity of applied methods, standardization) and post-analytical (interpretation of results) phases. EBC analysis is still used as a research tool. Limitations referred to pre-analytical, analytical, and post-analytical phases of EBC analysis are numerous, e.g. low concentrations of EBC constituents, single-analyte methods lack in sensitivity, and multi-analyte has not been fully explored, and reference values are not established. When all, pre-analytical, analytical and post-analytical requirements are met, EBC biomarkers as well as biomarker patterns can be selected and EBC analysis can hopefully be used in clinical practice, in both, the diagnosis and in the longitudinal follow-up of patients, resulting in better outcome of disease.     

Different centre of pressure patterns within the golf stroke II: Group-based analysis

Abstract

Although the golf coaching literature stresses the importance of weight transfer during the swing, research has been conflicting or lacking statistical support. A potential problem with previous studies is that no attempt was made to account for different movement strategies in the golf swing. This study evaluated the relationship between centre of pressure measures and club head velocity within two previously identified swing styles, the “Front Foot” and “Reverse” styles. Thirty-nine Front Foot golfers and 19 Reverse golfers performed swings with a driver while standing on two force plates. From the force plate data, centre of pressure displacement, velocity, range, and timing parameters were calculated. Correlation and regression analysis indicated that a larger range of centre of pressure and a more rapid centre of pressure movement in the downswing was associated with a larger club head velocity at ball contact for the Front Foot group. For the Reverse golfers, positioning the centre of pressure further from the back foot at late backswing and a more rapid centre of pressure transfer towards the back foot at ball contact was associated with a larger club head velocity at ball contact. This study has highlighted the importance of identifying different movement strategies before evaluating performance measures, as different parameters were found to be important for the Front Foot and Reverse styles.     

Fatigue in a simulated cross-country skiing sprint competition

Abstract

The aim of this study was to assess fatigue during a simulated cross-country skiing sprint competition based on skating technique. Sixteen male skiers performed a 30-m maximal skiing speed test and four 850-m heats with roller skies on a tartan track, separated by 20 min recovery between heats. Physiological variables (heart rate, blood lactate concentration, oxygen consumption), skiing velocity, and electromyography (EMG) were recorded at the beginning of the heats and at the end of each 200-m lap during the heats. Maximal skiing velocity and EMG were measured in the speed test before the simulation. No differences were observed in skiing velocity, EMG or metabolic variables between the heats. The end (820–850 m) velocities and sum-iEMG of the triceps brachii and vastus lateralis in the four heats were significantly lower than the skiing velocity and sum-iEMG in the speed test. A significant correlation was observed between mean oxygen consumption and the change in skiing velocity over the four heats. Each single heat induced considerable neuromuscular fatigue, but recovery between the heats was long enough to prevent accumulation of fatigue. The results suggest that the skiers with a high aerobic power were less fatigued throughout the simulation.     

Interpersonal coordination tendencies shape 1-vs-1 sub-phase performance outcomes in youth soccer

Abstract

This study investigated the influence of interpersonal coordination tendencies on performance outcomes of 1-vs-1 sub-phases in youth soccer. Eight male developing soccer players (age: 11.8 ± 0.4 years; training experience: 3.6 ± 1.1 years) performed an in situ simulation of a 1-vs-1 sub-phase of soccer. Data from 82 trials were obtained with motion-analysis techniques, and relative phase used to measure the space-time coordination tendencies of attacker-defender dyads. Approximate entropy (ApEn) was then used to quantify the unpredictability of interpersonal interactions over trials. Results revealed how different modes of interpersonal coordination emerging from attacker-defender dyads influenced the 1-vs-1 performance outcomes. High levels of space-time synchronisation (47%) and unpredictability in interpersonal coordination processes (ApEn: 0.91 ± 0.34) were identified as key features of an attacking player's success. A lead-lag relation attributed to a defending player (34% around ?30° values) and a more predictable coordination mode (ApEn: 0.65 ± 0.27, P < 0.001), demonstrated the coordination tendencies underlying the success of defending players in 1-vs-1 sub-phases. These findings revealed how the mutual influence of each player on the behaviour of dyadic systems shaped emergent performance outcomes. More specifically, the findings showed that attacking players should be constrained to exploit the space-time synchrony with defenders in an unpredictable and creative way, while defenders should be encouraged to adopt postures and behaviours that actively constrain the attacker's actions.