后张法预应力构件施工改进及质量控制

广东省茂名学院图书馆工程主梁采用有粘结预应力混凝土结构和目前国内最先进的HVM系列锚具及高强度钢绞线。并在施工方法上作了改进。经济效果更加明显。工程质量进一步提高。     

从范式转型看现代艺术的张力

现代艺术是一种包含否定性力量的艺术,它的自反性以它的对立面为前提。这种包含矛盾的整体性就是张力。必须通过范式理论,分析现代艺术的多重张力结构,考察它得以发生的内在和外在的机制。所谓现代艺术的自反性,源于社会的危机和对危机的反叛;它对主体内在性的强调,对现实与大众的疏离,人为缔造了破碎、荒凉的世界,有被现实重新整合的危险。     

冷连轧实验轧机自动控制系统

实验平台基于现代化冷连轧机自动控制系统的性能要求,针对多变量控制系统高速通信和高速控制的特点,满足可靠性、快速性和工艺适应性的需要。通过采用西门子多CPU控制器SIMATIC TDC,系统实现了主电机速度控制、压下机构位置控制和带钢张力控制等功能。该实验平台既可用来开发冷连轧控制算法,也可用来实现轧制过程的物理模拟,为工业生产提供实验数据。     

村组合并背景下组合竞选制的张力与调适

村组合并一定程度地改变了村委会选举的政治生态。不同村委会选举模式的适应性和承受力不尽相同。相比较而言,村委会"组合竞选制"更具张力弹性。为了适应村委会选举生态的改变,村委会组合竞选制在提名、候选人的审查、组合等环节和程序上需要进行调适和改进。     

加拿大基础教育体制改革兴盛背后暗藏的压力与危机

20世纪90年代,加拿大对基础教育体制进行的全面改革,使加拿大基础教育呈现出了繁荣的景象,然而兴盛表象的背后,市场机制这面双刃剑,给当代基础教育体制带来的压力和危机已经逐渐浮出水面.     

肌肉放松能力在青少年速度滑冰训练中的作用及提高途径探讨

速度滑冰技术是高度协调的周期性运动项目,需要运动员在滑跑过程动作高度自动化、肌肉协调放松以达到高度节能效果。因此,肌肉的协调放松能力对于提高青少年运动员的滑跑成绩具有重要作用。试图从肌肉放松的生理机制;运动员滑跑肌肉放松能力训练的主要途径等,运用人体科学理论及速度滑冰专项训练等理论,来探讨肌肉放松能力对提高青少年速度滑冰运动员成绩的影响,以期为速度滑冰青少年训练提供理论与实践的参考。     

Elite tennis player sensitivity to changes in string tension and the effect on resulting ball dynamics

Eighteen elite male tennis players were tested to determine their ability to identify string tension differences between rackets strung from 210 N (47 lb) to 285 N (64 lb). Each player impacted four tennis balls projected from a ball machine before changing rackets and repeating the test. Eleven participants (61%) could not correctly detect a 75 N (17 lb) difference between rackets. Only two participants (11%) could correctly detect a 25 N (6 lb) difference. To establish whether varying string tensions affected ball rebound dynamics, the ball’s rebound speed and landing position were analysed. The mean rebound ball speed was 117 km h⁻¹, with only the trials from the 210 N racket producing significantly lower (P < 0.05) rebound speeds than the 235 N and 260 N rackets. This is contrary to previous laboratory-based tests where higher rebound speeds are typically associated with low-string tensions. The anomaly may be attributable to lower swing speeds from participants as they were not familiar with such a low string tension. Ball placement did not appear related to string tension, with the exception of more long errors for the 235 N racket and fewer long errors for the 285 N racket. It was concluded that elite male tennis players display limited ability to detect changes in string tension, impact the ball approximately 6% faster than advanced recreational tennis players during a typical rallying stroke, and that ball placement is predominantly unrelated to string tension for elite performers.     

Antioxidant-rich beetroot juice does not adversely affect acute neuromuscular adaptation following eccentric exercise

This study examined the effects of beetroot juice on the repeated bout effect (RBE) to eccentric exercise. Twenty-nine recreationally active males performed two bouts of 100-drop jumps, separated by 14–21 days. Using a double-blind, independent groups design, participants consumed either a higher dose beetroot juice (H-BT; 250 ml, n = 10), a lower dose beetroot juice (L-BT; 125 ml, n = 9) or an isocaloric placebo (PLA; 250 ml, n = 10) for 3 days after bout 1; no drinks were consumed after bout 2. Maximal isometric voluntary contraction (MIVC), countermovement jump (CMJ), pressure-pain threshold (PPT) and creatine kinase (CK) were measured pre, post, 24, 48 and 72 h following both bouts. In bout 2, CMJ and MIVC recovered quicker and CK activity was attenuated (versus bout 1) (P < 0.05) in all groups, demonstrating an RBE. At 24 h post bout 1, MIVC was 84.1 ± 16.1, 83.6 ± 11.6, 79.7 ± 15.1% relative to baseline values in the H-BT, L-BT and PLA groups, respectively; at 24 h post bout 2, MIVC recovered to 90.7 ± 13.7, 92.9 ± 6.9, 87.8 ± 6.9, in the H-BT, L-BT and PLA groups, respectively. These findings suggest that supplementation with antioxidant-rich beetroot juice does not adversely affect acute adaptations to a bout of eccentric exercise.     

The relationship between strength asymmetries and jumping performance in professional volleyball players

Knee peak torque (PT) is associated to jump performance in volleyball players. It is not clear whether muscle strength imbalances of the knee joint can influence jump performance. The purpose of study was to analyse the association between PT and knee muscular imbalances with jump performance in professional volleyball players. Eleven elite male volleyball players (90.3 ± 9.7 kg body mass and 1.94 ± 0.06 m height) were evaluated in an isokinetic dynamometer at speeds of 60, 180 and 300 deg/s. Muscle strength imbalances were obtained through calculation of contralateral deficit between limbs and the conventional ratio (hamstrings/quadriceps). Countermovement jump (CMJ) was performed on a force plate to calculate mechanical power and height. Association was found between knee extensor PT at 180 deg/s with CMJ power (r = 0.610, p = 0.046). Conventional ratio at 300 deg/s showed negative association with CMJ (r = ?0.656, p = 0.029). The optimal ratio between knee extensors PT in relation to the flexors PT is associated with the greater mechanical power in CMJ. Contralateral deficit does not seem to be associated with the CMJ performance. Considering the knee extensor PT is associated with CMJ power, our findings suggest that strength-based training in volleyball athletes should not omit the conventional muscle ratio.     

强磁场对导电流体热毛细流动和换热影响的实验研究

核聚变装置限制器有效地屏蔽来自器壁的杂质,排出来自中心等离子体的粒子流和热流。液态金属可以较好地完成这一任务。液态金属具有导热性强、液相温度范围大和易于补充等特性,是未来聚变反应堆面向等离子体部件的主要备选材料之一。限制器的不同位置存在较大的温差,在表面张力驱动下液态金属自由表面形成热毛细对流。该热毛细对流受到聚变堆强磁场的影响。通过建立导电流体自由表面热毛细对流实验系统获得可视化的实验结果,研究温差变化和强磁场参数对导电流体自由表面热毛细对流的影响规律,深入分析该过程对液态金属在未来聚变堆面向等离子体部件的成功应用具有重要意义。