一种直流力矩电机精确控制的新方法

针对直流力矩的闭环调速控制,提出一种渐近调速算法,主要解决调速过程的快速、平稳、精确控制问题.介绍算法,并给出实现这一算法的技术方案.方案以数字信号处理器为核心,与集成马达控制器和锁相倍频测速单元共同组成闭环随动控制系统.给出驱动控制通道设计和速度反馈通道设计,并对测速单元的测量方法做出精度分析.     

任意有限阶循环群的整群环的极大Z-序

讨论了有限阶循环群整群环ZG在QG中的极大Z-序Γ,给出了Γ的具体表达式。     

加权模不等式和Schrodinger算子的特征值估计

本文应用二进极大算子的加权模不等式和I_1算子的性质。估计了广义Schrodinger算子H=-A-U+V的最小特征值,并与龙瑞麟先生对某些H=-A-U型算子的特征值估计进行了比较。     

一种减小无刷直流电机转矩脉动的广角波控制方法

In order to deal with torque pulsation problem caused by traditional control method for brushless DC （BLDC） motor and to achieve high precision and good stability, a novel control strategy is proposed. Compared with the traditional control scheme, by using phase voltage as a control objective and making waveform of phase current approximately quasi-sinusoidal, torque ripple of BLDC motor is reduced from the original 14% to 3.4%, while toque is increased by 3.8%. Furthermore, by detecting zero-crossings of back electromotive force （BEMF） with non-conducting phases, sensorless control is realized. The new control strategy is simple. It can minimize torque ripple, increase torque, and realize sensorless control for BLDC motor. Simulation and experiments show good performance of BLDC motor by using the new control method.     

表面磁钢永磁无刷电机电磁转矩的解析法分析

With the air gap magnetic field distribution of surface mounted permanent magnet (PM) motors obtained using an analytical technique, the instantaneous electromagnetic torque and its corresponding components are investigated with the Maxwell stress tensor method. Accurate results can easily be achieved using the proposed method without using the tedious finite element analysis (FEA). In this paper, the electromagnetic torque of a surface mounted PM motor with two phases energized is decomposed into four torque components. This technique is useful not only for the design and optimization of the permanent magnet motor, but also for the choice of control strategy.     

进气凸轮移相对发动机性能的影响分析

利用AMESim软件建立了春风152MI小型单缸内燃机模型,基于发动机原始数据对发动机模型参数进行了设置,并验证了模型的正确性;利用VVT凸轮移相原理改变模型中进气凸轮相位,研究其扭矩及功率的变化。结果表明：随转速的升高,进气迟闭角越大扭矩越大,功率也越大。     

Mining direct antagonistic communities in signed social networks

Social networks provide a wealth of data to study relationship dynamics among people. Most social networks such as Epinions and Facebook allow users to declare trusts or friendships with other users. Some of them also allow users to declare distrusts or negative relationships. When both positive and negative links co-exist in a network, some interesting community structures can be studied. In this work, we mine Direct Antagonistic Communities (DACs) within such signed networks. Each DAC consists of two sub-communities with positive relationships among members of each sub-community, and negative relationships among members of the other sub-community. Identifying direct antagonistic communities is an important step to understand the nature of the formation, dissolution, and evolution of such communities. Knowledge about antagonistic communities allows us to better understand and explain behaviors of users in the communities.     

Science and the Gaelic sports: Gaelic football and hurling

Abstract

The two major sports indigenous to Ireland are Gaelic football and hurling. Both are 15-a-side field games played on a pitch 40% longer than a soccer field. They are firmly linked to a nationalist tradition and have by far the highest participation rates in sports in the country. Both games make multiple demands on participants due to their free-flowing nature and quick movement of play from end to end of the pitch. Hurling calls for hand–eye coordination and skilled use of the hurling stick in hitting and blocking the ball. Fitness characteristics mirror game demands. Participants at elite level in both games display high aerobic power, the footballers tending to be stronger in the upper body and better in vertical jumping. Gaelic footballers in particular match the fitness characteristics of professional soccer players, except for sprinting speed. Less attention has been paid to female participants, especially in camogie, the female version of hurling. Despite their amateur status, and due to the popularity of the sports and the training regimens adopted by players, the games have garnered sports science support systems for elite performers. Support personnel benefit from a generic knowledge base as well as a burgeoning research agenda targeted at the Gaelic games.     

Strength,power, and postural control in seniors: Considerations for functional adaptations and for fall prevention

Abstract

The ageing neuromuscular system is affected by structural and functional changes that lead to a general slowing down of neuromuscular performance and an increased risk of falling. As a consequence, the process of ageing results in a reduced ability to develop maximal and explosive force, as well as in deficits in static and dynamic postural control. A decrease in the number and size of type II fibres in particular accounts for the age-related decline in muscle mass (sarcopaenia) and strength performance. Multiple denervation and re-innervation processes of muscle fibres seem to be responsible for the reduced number of muscle fibres. Recently, it has been suggested that it is not the decline in motoneurons that accounts for the loss in number of muscle fibres but the disturbed potential of fibre regeneration and re-innervation. Furthermore, an age-related reduction in the number of satellite cells has also been associated with sarcopaenia. The ability to compensate for platform and gait perturbations deteriorates with ageing as reflected in longer onset latencies and inefficient postural responses. All sites within the somatosensory system are affected by ageing and therefore contribute to postural instability. However, morphological changes of muscle spindles appear primarily to be responsible for the impaired ability to compensate for balance threats in old age. Given these neuromuscular limitations in old age, it is important to apply adequate training interventions that delay or even reverse the onset of these constraints. Strength training has the potential to enhance maximal as well as explosive force production capacity. This is accomplished by neural factors, including an improved recruitment pattern, discharge rate, and synchronization of motor units. Furthermore, an increase in number of satellite cells most likely accounts for training-induced muscle hypertrophy. Recent studies have investigated the impact of balance training in old age on the ability to develop maximal and explosive force. In addition, the effects of balance training on reflex activity during gait perturbations were also examined. Increases in maximal and explosive force production capacity and an improved ability to compensate for gait perturbations were observed. It is evident from the literature that researchers are increasingly studying the effects of more specifically designed training programmes on performance in populations of older adults. Thus, in the near future, strength training could be replaced by high-velocity forms of power training and balance training by perturbation-based training programmes. It is hypothesized that this new approach is more efficient in terms of fall prevention than the traditional approach.     

The time course of muscle-tendon properties and function responses of a five-minute static stretching exercise

Abstract

The purpose of this study was to investigate the time course of the changes of muscle-tendon mechanical properties and the function responses of the plantar flexor muscles following 5?×?60?s of static stretching.

Fourteen healthy volunteers were tested on four separate days in a random order with three different rest times (0, 5, 10?min) after 5?×?60?s of stretching or following a control period without stretching. During each test, the dorsiflexion range of motion (RoM), passive resistive torque (PRT), and maximum voluntary contraction (MVC) were measured with a dynamometer. Ultrasonography of the gastrocnemius medialis (GM) muscle-tendon junction displacement and motion capture allowed us to determine the length changes in the tendon and muscle, respectively, and hence to calculate their stiffness.

We observed an increase in RoM and decrease in MVC at 0, 5, and 10?min post-stretching. This could be attributed to an increase in muscle elongation which lasted at least 10?min. A decrease in muscle-tendon stiffness was observed immediately, but not 5 or 10?min after the stretching. A decrease in PRT and muscle stiffness was observed up to 5?min after the stretching. No changes were detected in tendon stiffness or in any variable in the control group.

The effects of a 5?×?60?s static stretching exercise changes the muscle-tendon functions (RoM, MVC), which are related to mechanical changes of the muscle but not the tendon structure, respectively. Although the functional changes last for at least 10?min, changes in muscle stiffness were only observed up to 5?min after the stretching exercise.