A serial functional connectivity MRI study in healthy individuals assessing the variability of connectivity measures: reduced interhemispheric connectivity in the motor network during continuous performance

To date, little data is available on the reproducibility of functional connectivity MRI (fcMRI) studies. Here, we tested the variability and reproducibility of both the functional connectivity itself and different statistical methods to analyze this phenomenon. In the main part of our study, we repeatedly examined two healthy subjects in 10 sessions over 6 months with fcMRI. Cortical areas involved in motor function were examined under two different cognitive states: during continuous performance (CP) of a flexion/extension task of the fingers of the right hand and while subjects were at rest. Connectivity to left primary motor cortex (lSM1) was calculated by correlation analysis. The resulting correlation coefficients were transformed to z-scores of the standard normal distribution. For each subject, multisession statistical analyses were carried out with the z-score maps of the resting state (RS) and the CP experiments. First, voxel based t tests between the two groups of fcMRI experiments were performed. Second, ROI analyses were carried out for contralateral right SM1 and for supplementary motor area (SMA). For both ROI, mean and maximum z-score were calculated for each experiment. Also, the fraction of significantly (P<.05) correlated voxels (FCV) in each ROI was calculated. To evaluate the differences between the RS and the CP condition, paired t tests were performed for the mean and maximum z-scores, and Wilcoxon signed ranks tests for matched pairs were carried out for the FCV. All statistical methods and connectivity measures under investigation yielded a distinct loss in left–right SM1 connectivity under the CP condition. For SMA, interindividual differences were apparent. We therefore repeated the fcMRI experiments and the ROI analyses in a group of seven healthy subjects (including the two subjects of the main study). In this substudy, we were able to verify the reduction of left–right SM1 connectivity during unilateral performance. Still, the direction of SMA to lSM1 connectivity change during the CP condition remained undefined as four subjects showed a connectivity increase and three showed a decrease. In summary, we were able to demonstrate a distinct reduction in left–right SM1 synchrony in the CP condition compared to the RS both in the longitudinal and in the multisubject study. This effect was reproducible with all statistical methods and all measures of connectivity under investigation. We conclude that despite intra- and interindividual variability, serial and cross-sectional assessment of functional connectivity reveals stable and reliable results.     

高压变频器同步切换技术在12MW高压同步电动机软起动中的应用

本文分析了同步电动机的应用特点并讨论了大型同步电动机的起动过程;介绍了几种常见的高压同步电动机软起动方案并进行了比较和分析:并以某钢厂12MW同步电动机软起动项目为例,介绍了静止变频软起动技术在大容量高压同步电动机中的实际应用,阐明了技术原理并对调试过程碰到的一些技术问题给出了相应的工程解决方法。     

Origins of intersubject variability of blood oxygenation level dependent and arterial spin labeling fMRI: implications for quantification of brain activity

Accurate localization of brain activity using blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) has been challenged because of the large BOLD signal within distal veins. Arterial spin labeling (ASL) techniques offer greater sensitivity to the microvasculature but possess low temporal resolution and limited brain coverage. In this study, we show that the physiological origins of BOLD and ASL depend on whether percent change or statistical significance is being considered. For BOLD and ASL fMRI data collected during a simple unilateral hand movement task, we found that in the area of the contralateral motor cortex the centre of gravity (CoG) of the intersubject coefficient of variation (CV) of BOLD fMRI was near the brain surface for percent change in signal, whereas the CoG of the intersubject CV for Z-score was in close proximity of sites of brain activity for both BOLD and ASL. These findings suggest that intersubject variability of BOLD percent change is vascular in origin, whereas the origin of inter-subject variability of Z-score is neuronal for both BOLD and ASL. For longer duration tasks (12 s or greater), however, there was a significant correlation between BOLD and ASL percent change, which was not evident for short duration tasks (6 s). These findings suggest that analyses directly comparing percent change in BOLD signal between pre-defined regions of interest using short duration stimuli, as for example in event-related designs, may be heavily weighted by large-vessel responses rather than neuronal responses.     

分光光度法测定车用甲醇汽油中的甲醇

建立了可见分光光度法测定甲醇汽油中甲醇含量的方法.实验结果表明,当甲醇含量在0-2.0mL/L时,吸光度与浓度能很好地遵循朗伯-比耳定律,相关系数为0.9934,该方法的平均加标回收率为96.9％,精密度实验M15和M20甲醇汽油的变异系数CV分别为1.1％和1.0％.     

Performances and design of ironless loudspeaker motor structures

This paper presents several kinds of structures of ironless loudspeaker motors. The proposed devices go from simple structures, in terms of manufacturing process, to structures in which the magnet rings can be stacked, with different magnetization directions or values. The structures are studied and compared according to their created induction level and uniformity across the coil displacement range, which are directly linked to the loudspeaker performances (force factor). The model used is the coulombian model of magnets to calculate the magnetic field created, therefore all the calculations are analytical. The paper shows that no structure is universal when it comes to the loudspeaker design: some are well adapted to micro displacements of the coil while other structures are adapted to large displacements.     

一种高效全桥功率驱动器/放大器的设计

设计了一种高效全桥功率驱劝器／放大器，介绍了它的设计原理。该功率驱劝器／放大器可广泛应用于刷式电机控制、D类音频放大、无功(电抗性)负载、MRI、振劝取消等系统中。     

浅谈软起动器在铝箔厂水泵上的应用

本文首先提出水泵系统采用传统起动方式的弊端,阐述利用软起动器控制水泵系统的原理,具体分析笼型交流异步电动机起动要求,通过选择合理的软起动器和安装措施,提出了铝箔厂污水处理水泵采用软起动器实际应用的可行性。     

浅谈软起动器在铝箔厂水泵上的应用

本文首先提出水泵系统采用传统起动方式的弊端,阐述利用软起动器控制水泵系统的原理,具体分析笼型交流异步电动机起动要求,通过选择合理的软起动器和安装措施,提出了铝箔厂污水处理水泵采用软起动器实际应用的可行性。     

采用固态软起动器降低供电设施容量

在上海宜山路泵站的设计和建设中，通过采用中压固态软起动器起动大功率水泵，从而减少了供电设施的容器，达到减少投资和减少运行电费的效果，本文对此进行了分析和总结，并比较了固态软起动器与水电阻两种方案。降低供电设施容量使之与用电设备容量接近，也是降低单位国内生产总值的能源消耗的一项重要措施。     

Energy transformation in biological molecular motors

Biological molecular motors transform the metabolic free energy into the directed movement. The physical principles governing this transformation are very different from the principles underlying the manmade macroscopic motors. Theoretical analysis shows that the internal thermal diffusion in motor proteins is a key element of the process, and the chemical energy performs no mechanical work directly but instead it is used for rectifying the diffusion. A few specific motor systems are considered to illustrate the general principle. The principle of rectified thermal diffusion has recently received a great support from the single-molecule studies.