Tests for a difference in timing of physiological response between two brain regions measured by using functional magnetic resonance imaging

Summary.  Functional magnetic resonance imaging (FMRI) measures the physiological response of the human brain to experimentally controlled stimulation. In a periodically designed experiment it is of interest to test for a difference in the timing (phase shift) of the response between two anatomically distinct brain regions. We suggest two tests for an interregional difference in phase shift: one based on asymptotic theory and one based on bootstrapping. Whilst the two procedures differ in some of their assumptions, both tests rely on employing the large number of voxels (three-dimensional pixels) in non-activated brain regions to take account of spatial autocorrelation between voxelwise phase shift observations within the activated regions of interest. As an example we apply both tests, and their counterparts assuming spatial independence, to FMRI phase shift data that were acquired from a normal young woman during performance of a periodically designed covert verbal fluency task. We conclude that it is necessary to take account of spatial autocovariance between voxelwise FMRI time series parameter estimates such as the phase shift, and that the most promising way of achieving this is by modelling the spatial autocorrelation structure from a suitably defined base region of the image slice.     

基于投影的fMRI时间序列图像配准方法研究

利用投影技术,针对功能磁共振时间序列图像,介绍了一种新的自动图像配准方法。该方法将序列图像二值化后沿着水平方向或垂直方向进行投影,根据投影向量元素的位置和大小,快速地计算出图像的旋转、平移运动的变化参数。仿真实验和实际的功能磁共振应用证实了该方法的有效性。     

长直螺线管中的交变磁场

长直螺线管中变化的磁场是产生涡旋电场的源，涡旋电场也将反作用于磁场．在一般情况下，磁场的分布不是均匀的。文中指出了一般教材中假定磁场均匀分布的条件，推导出了一般情况下的磁场分布曲线，并进一步讨论了交变电磁场用频率及导休时磁场分布的影响。     

快速循环热处理对(Co_(0.35)Fe_(0.65))_(99)O_1薄膜磁性能的影响

针对(Co0.35Fe0.65)99O1薄膜,研究了两种不同热处理工艺对其磁性能的影响。结果表明:快速循环热处理可以改善高磁矩(Co0.35Fe0.65)99O1薄膜磁性能,在450°C几个快速循环热处理后,沉积薄膜的矫顽力从105下降到3Oe,电阻率下降到70%,a-Fe(Co)相晶粒尺寸可以减小到15～35nm,该处理方法较以往的热处理更能改善软磁薄膜的性能。     

三维涡流场基于有限元法的电磁位对

介绍了用有限元法解决三维涡流场问题时电磁位对的优选问题,分析了其适应情况和优缺点.对目前基于有限元法的三维涡流场数值分析方法的国内外现状作了综合评述.     

无波蕩器自由电子激光非线性分析

本文对低导引场无波荡器自由电子激光进行了非线性数值计算分析。结果表明,这种自由电子激光工作在毫米波段时,电子束在纵向及横向均有净动能交给信号波,具有很高的互作用效率(32％);而且,腔体长度较短,腔体直径较大,易于加工制作。     

具有复合周期磁场的电子回旋脉塞

本文从降低回旋脉塞中直流磁场的角度出发,利用线性伏拉索夫——麦克斯韦方程组,对通过静态复合周期磁场的弱相对论电子注与缓变圆波导中沿纵向作任意缓变的TE_(mn)模式之间的互作用机理,在理论上进行了详细的分析和讨论,导出了色散方程并作了数值计算。分析和计算表明,由于采用了静态复合周期磁场,其电子注与波互作用的不稳定性产生在电子回旋共振条件下,从而可以在不同的电子回旋空间谐波上工作而大大地降低直流磁场。     

粒子的镜象对称理论

本文证明了平均自旋和磁物同向,提出了恢复镜象对称的两个方案,并对它们进行了分析比较,发现它们是根本对立的,从而对CP联合反演提出了异议。     

Leukemia Attributable to Residential Magnetic Fields: Results from Analyses Allowing for Study Biases

Nearly every epidemiologic study of residential magnetic fields and childhood leukemia has exhibited a positive association. Nonetheless, because these studies suffer from various methodologic limitations and there is no known plausible mechanism of action, it remains uncertain as to how much, if any, of these associations are causal. Furthermore, because the observed associations are small and involve only the highest and most infrequent levels of exposure, it is believed that the public health impact of an effect would be small. We present some formal analyses of the impact of power-frequency residential magnetic-field exposure (as measured by attributable fractions), accounting for our uncertainties about study biases as well as uncertainties about exposure distribution. These analyses support the idea that the public health impact of residential fields is likely to be limited, but both no impact and a substantial impact remain possibilities in light of the available data.     

磁处理对豌豆幼苗生长及生理的效应

用磁感应强度为0．01T的磁场处理豌豆种子或用该磁场处理的水浸种显著促进豌豆幼苗的营养生长，增加干物质累积量，而用同样磁场处理的水浇灌胚根已经伸出的种子则显著抑制幼苗生长及干物质积累。