Use-dependent plasticity of the human motor cortex in health and disease.

The adult brain can reorganize to accommodate environmental modifications and to compensate for lost function, a process known as plasticity. The last few years have provided extraordinary evidence regarding the mechanisms underlying plastic changes and have spurred the development of new strategies to modulate these processes. The ability of the mature brain to constantly reorganize has gained further credibility with the advent of transcranial magnetic stimulation (TMS). Plasticity is thought to be influenced by neurotransmitters and decreases substantially with normal aging. TMS has demonstrated that remarkable plastic changes occur in response to pharmacological agents and peripheral or central nervous system injury. Plastic changes are also associated with intense motor training such as constraint-induced therapy (CIT). For instance, premedication with amphetamine resulted in faster induction, increased magnitude, and prolonged duration of plasticity elicited by motor training compared to a placebo. Similarly, peripheral sensory stimulation resulted in enhancement of plastic changes. Finally, TMS cortical motor maps enlarge after CIT in stroke patients. This work discusses the potential of TMS as a useful tool to probe novel strategies to enhance plasticity in humans.     

Non-linear self-driven spectral tuning of Extreme Ultraviolet Femtosecond Pulses in monoatomic materials

Self-action nonlinearity is a key aspect–either as a foundational element or a detrimental factor–of several optical spectroscopies and photonic devices. Superc...     

Impact of TMS on the primary motor cortex and associated spinal systems.

Repetitive transcranial magnetic stimulation (rTMS) is able to modulate corticospinal and intracortical motor cortex excitability, depending on the stimulation parameters. In the present study, we explored the effects of highand low-frequency rTMS on spinal reflex monosynaptic responses (H waves or H reflexes) in humans recorded from the flexor carpi radialis (FCR) muscle. After 1-Hz rTMS, H-wave minimal and optimal thresholds were decreased by 14-22% of their pre-rTMS values. The maximal H-wave and H/M amplitude ratio were both significantly increased by 52-54%, whereas direct muscle responses (M waves) remained unchanged. The area under the H-wave recruitment curve was also significantly increased by 86 /spl plusmn/ 21% of its pre-rTMS baseline values. Conversely, after 20-Hz rTMS, H-wave minimal and optimal thresholds were both increased by 15-26%. The maximal H wave and H/M amplitude ratio were significantly decreased by -37 /spl plusmn/ 11%, whereas M responses remained unchanged. The area under the H-response recruitment curve was also significantly decreased by -45/spl plusmn/5%. Neither 20-Hz nor 1-Hz sham rTMS induced noticeable changes in M or H responses. We conclude that 1-Hz rTMS applied to primary motor areas increases the monosynaptic spinal cord H reflex, whereas 20-Hz rTMS induces the opposite effect, presumably by modulating inhibitory descending conicospinal projections onto spinal motoneurons. These results offer an opportunity to influence the level of spinal excitability and modify descending corticospinal influences in a controlled manner using noninvasive approaches that could prove useful in the study of the pathophysiology and eventual treatment of spasticity.     

Neural ensemble activity from multiple brain regions predicts kinematic and dynamic variables in a multiple force field reaching task.

In everyday life, we reach, grasp, and manipulate a variety of different objects all with their own dynamic properties. This degree of adaptability is essential for a brain-controlled prosthetic arm to work in the real world. In this study, rats were trained to make reaching movements while holding a torque manipulandum working against two distinct loads. Neural recordings obtained from arrays of 32 microelectrodes spanning the motor cortex were used to predict several movement related variables. In this paper, we demonstrate that a simple linear regression model can translate neural activity into endpoint position of a robotic manipulandum even while the animal controlling it works against different loads. A second regression model can predict, with 100% accuracy, which of the two loads is being manipulated by the animal. Finally, a third model predicts the work needed to move the manipulandum endpoint. This prediction is significantly better than that for position. In each case, the regression model uses a single set of weights. Thus, the neural ensemble is capable of providing the information necessary to compensate for at least two distinct load conditions.     

Reliability of signals from a chronically implanted, silicon-based electrode array in non-human primate primary motor cortex.

Multiple-electrode arrays are valuable both as a research tool and as a sensor for neuromotor prosthetic devices, which could potentially restore voluntary motion and functional independence to paralyzed humans. Long-term array reliability is an important requirement for these applications. Here, we demonstrate the reliability of a regular array of 100 microelectrodes to obtain neural recordings from primary motor cortex (MI) of monkeys for at least three months and up to 1.5 years. We implanted Bionic (Cyberkinetics, Inc., Foxboro, MA) silicon probe arrays in MI of three Macaque monkeys. Neural signals were recorded during performance of an eight-direction, push-button task. Recording reliability was evaluated for 18, 35, or 51 sessions distributed over 83, 179, and 569 days after implantation, respectively, using qualitative and quantitative measures. A four-point signal quality scale was defined based on the waveform amplitude relative to noise. A single observer applied this scale to score signal quality for each electrode. A mean of 120 (+/- 17.6 SD), 146 (+/- 7.3), and 119 (+/- 16.9) neural-like waveforms were observed from 65-85 electrodes across subjects for all recording sessions of which over 80% were of high quality. Quantitative measures demonstrated that waveforms had signal-to-noise ratio (SNR) up to 20 with maximum peak-to-peak amplitude of over 1200 microv with a mean SNR of 4.8 for signals ranked as high quality. Mean signal quality did not change over the duration of the evaluation period (slope 0.001, 0.0068 and 0.03; NS). By contrast, neural waveform shape varied between, but not within days in all animals, suggesting a shifting population of recorded neurons over time. Arm-movement related modulation was common and 66% of all recorded neurons were tuned to reach direction. The ability for the array to record neural signals from parietal cortex was also established. These results demonstrate that neural recordings that can provide movement related signals for neural prostheses, as well as for fundamental research applications, can be reliably obtained for long time periods using a monolithic microelectrode array in primate MI and potentially from other cortical areas as well.     

磁钢充磁方式对表贴式永磁电机磁场影响分析

针对永磁电机中不同充磁方式时磁场的分布和强度不同,分析了径向、平行和Halbach 3种磁体结构,建立了内转子和外转子永磁电机的有限元分析模型,对比3种充磁方式时永磁电机气隙磁场的分布特点,明确了3种充磁方式的适用场合,给出了极对数和永磁体厚度对电机气隙磁场分布影响的变化规律.结果表明;采用平行充磁的内转子永磁电机有更...     

超导同步电动机温度场计算与分析

为判断高温超导电机超导体及永磁体运行的稳定性,准确计算电机内的温度场十分必要.以全超导样机热性能为研究对象,首先利用时步有限元方法建立二维正弦时变电磁场模型,得到了电机定转子损耗分布.根据传热学原理,通过数值分析给出定子表面散热系数的计算方法.然后计算分析高温超导电机的温度场.通过计算结果与实测数据的对比分析,验证所给...     

Quench in high-temperature superconducting motor field coils: experimental results

The results of quench tests on high-temperature superconducting motor coils are presented. These results clearly demonstrate that the quench process is characterized by a current level, referred to as the "quench current", above which the cooling system cannot maintain the winding temperature. The result will be an unstable growth in winding temperature in a process commonly referred to as a winding quench.     

Numerical approach to field fluctuations and spectral lineshape in InGaAsP laser diodes

This paper reports on a numerical approach to model the field fluctuations, spectral lineshape and linewidth in semiconductor lasers. The approach is based on numerical solution of the laser rate equations augmented by Langevin noise sources that account for fluctuations in the lasing field. The paper newly examines contributions of intensity and frequency noises to the spectral characteristics of the lineshape and its linewidth over a wide range of injection current. The model is applied to InGaAsP lasers emitting in a wavelength of 1.5 μm as the most representative light sources in optical communication systems. Accuracy of approximated models of calculating linewidth from low‐frequency components of the frequency noise is checked. Effect of non‐linear gain suppression on the lineshape is also explored. The spectral lineshape promotes and the linewidth decreases as the laser is injected far from the near‐threshold region. The lineshape changes mainly with changes in the frequency noise spectrum while the linewidth is sensitive to variation in the low‐frequency levels of both intensity and frequency noises. Copyright © 2004 John Wiley & Sons, Ltd.     

在现代家用电器中电机的应用和商机

时下各种电机在现代家用电器中的应用十分广泛,而且随着科技发展和人们生活水平的提高,对现代家用电器中的电机要求不断提高,更新换代也快。家电用电机主要是小功率电机,凡家庭中有转动件的,都是由电机来驱动的,如空调用的室内机风扇电机、室外机的风扇电机、压缩机、室内机转叶电机等。家用电器性能与所匹配的小功率电机有着直接的关系,电机的效率、功率因数、调速范围及噪声直接与家用电器的节能环保有着密切的关系。1家电用电机的特点(1)品种多,用途广由于小电机在家用电器中使用场合不一致,各种家用电器对小电机的使用要求也不尽相同,因…     

防爆型水冷电机内换热与温度场计算

采煤机电机安装空间严格受限,随着电机设计容量的提升,使单位体积损耗(发热率)增大.为了研究该类电机的发热与冷却问题,在对防爆型水冷电机的结构、材料以及换热机理进行分析的基础上,建立了防爆型水冷电机的传热数学物理模型.采用有限元法对电机定、转子及水套的温度场进行了计算与分析.通过计算结果与实测值对比,验证所建传热模型可以真实反映实际传热过程.分析计算结果表明电机定子最高温度点位于定子上层绕组近气隙侧;定子齿是热量传递的主要通道,热流密度最大;选用适当的冷却水流速,可以用最小的代价获取所需的冷却效果.研究结果可以为采煤机电机热控制和优化设计提供理论依据.     

Nonlinear analysis of field distribution in electric motor with periodicity conditions

Contents Numerical analysis of electromagnetic field distribution in linear motion tubular electric motor has been performed with the aid of finite element method. Two Fortran programmes for the solution of DBBF and BF large linear symmetric equation systems have been developed for purposes of this analysis. A new iterative algorithm, taking into account iron nonlinearity and periodicity conditions, has been introduced. Final results of the analysis in the form of induction diagrammes and motor driving force and directly useful for motor designers.

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Nichtlineare Analyse der Feldverteilung im Elektrischen Motor mit Berücksichtigung der Periodizitätsbedingungen

Übersicht Es wurde eine numerische Analyse der Verteilung des elektromagnetischen Feldes im linearen röhrenförmigen elektrischen Motor mittels der Methode der Finiten Elemente durchgeführt. Zwei Fortran-Programmen zur Lösung großer Systeme der Lineargleichungen mit DBBF und BF Koeffizientmatrizen wurden für diese Analyse entwickelt. Ein neuer Iterationsalgorithmus berücksichtigt die Nichtlinearität des Eisens und die Periodizitätsbedingungen. Resultate der Analyse — d. h. Diagramme der magnetischen Induktion und der Schubkraft des Motors-sind unmittelbar anwendbar beim Entwurf elektrischer Motore.

     

DSP在基于想象动作电位的脑-机接口中的应用

应用数字信号处理器设计了一个基于想象动作电位的脑-机接口系统,通过模拟滤波与数字信号器处理相结合的方法,实现了对想象动作电位信息的有效采集和处理.系统在硬件上设计了脑电信号放大器,DSP开发板;对脑电信号放大、AD转换后,通过分类特征提取处理后,完成动作识别与控制命令的输出.将数字信号处理器应用在脑-机接口中,利用数字信号处理器优异的处理能力和丰富的外设资源,实现了一个嵌入式、微型化的脑-机接口构建,实现了脑-机接口实时处理与微型化.     

Difference method in integral technique in field analysis of doubly salient switched reluctance motor

Contents The paper presents a method of calculation of the switched reluctance motor torque on the basis of the calculated electromagnetic field distribution while the difference method in integral technique has been employed.The analysis of the electromagnetic field distribution has been performed for the model motor, with the effect of magnetic nonlinearity of the medium taken into account.The obtained SR motor torque curves gives evidence of the torque as a function of the rotor position.

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Die Differenzmethode in der integralen Auffassung zur Feldanalyse in einem geschalteten Doppelreluktanzmotor

Übersicht Der Artikel betrifft die auf die Verteilung des elektromagnetischen Feldes gestützte Berechnungsmethode des Drehmoments eines geschalteten Doppelreluktanzmotors. Die magnetischen Berechnungen wurden nach der Differenzenmethode in der integralen Auffassung durchgeführt.Die Analyse der Verteilung des elektromagnetischen Feldes wurde für einen Modellmotor bei Berücksichtigung der nichtlinearen Eigenschaften der Medien dargestellt.Die Momentenkennlinie des Reluktanzmotors zeigt die Abhängigkeit des Drehmoments von der Rotorstellung.

     

An inverter-fed self-controlled commutatorless series motor withthe field winding in the DC link

This paper examines the basic operation of a self-controlled synchronous motor driven by a three-phase MOSFET inverter with the field winding located in the DC link, yielding inherent series characteristics like a DC series motor. A new approach to the analytical and experimental study of the drive with the switches conducting for both 120° and 180° is presented, and typical results, both simulation and experimental, are shown and the performance characteristics compared. The effect of shifting the rotor position sensor is studied for both cases, as well as for four-quadrant operation. It is observed that the resulting drive system is simple, able to operate with reduced torque ripples and voltage spikes, and the characteristics of the drive are well suited for traction/transit propulsion applications and battery/flywheel energy storage systems     

动态环境下基于人工势场的足球机器人路径规划

人工势场法是足球机器人路径规划中常用的方法,传统人工势场法在静态环境中取得了很好的效果,但它不能够满足复杂的动态环境下实时规划的要求。本文将相对速度矢量引入人工势场,对势场函数进行改进,推导出基于速度矢量的引力函数和斥力函数。在新的势场函数作用下,机器人能够快速躲避障碍物并迅速到达目标位置,仿真结果验证了方法的有效性。     

Robot-enhanced motor learning: accelerating internal model formation during locomotion by transient dynamic amplification.

When adapting to novel dynamic environments the nervous system learns to anticipate the imposed forces by forming an internal model of the environmental dynamics in a process driven by movement error reduction. Here, we tested the hypothesis that motor learning could be accelerated by transiently amplifying the environmental dynamics. A novel dynamic environment was created during treadmill stepping by applying a perpendicular viscous force field to the leg through a robotic device. The environmental dynamics were amplified by an amount determined by a computational learning model fit on a per-subject basis. On average, subjects significantly reduced the time required to predict the applied force field by approximately 26% when the field was transiently amplified. However, this reduction was not as great as that predicted by the model, likely due to nonstationarities in the learning parameters. We conclude that motor learning of a novel dynamic environment can be accelerated by exploiting the error-based learning mechanism of internal model formation, but that nonlinearities in adaptive response may limit the feasible acceleration. These results support an approach to movement training devices that amplify rather than reduce movement errors, and provide a computational framework for both implementing the approach and understanding its limitations.     

变频调速同步电机转子三维温度场数值模拟

为使所研发的某变频调速同步电机转子通风结构合理,温度场分布较均匀,且安全运行,建立该电机转子风路最长的6号槽半轴向段整体结构模型,根据CFD原理,基于Fluent软件,数值模拟额定负荷和护环下部分顶匝风路堵塞时转子内部冷却空气以及绕组温度场分布,并分析其特点.结果表明:转速不同时,绕组峰值温度及位置均发生变化.结果对变...