环结构中的若干新成果(一)

代数结构的理论发展起来后,Artin,E.在环中引进极小条件,建立了具极小条件的半单纯环与单纯环的结构理论,被誉为是抽象代数中仅次于Galois理论的工作。对称地,Goldie与Lesieur and Croisot等又建立了具极大条件的半质环的结构理论,其结果也是很漂亮的。     

基于F-P标准具的固体激光可调线宽控制技术

钠导星激光研制需激光线宽在一定范围内可调节。开展了F-P标准具压窄线宽数值模拟,设计一台高光束质量基横模线偏振激光输出全固态1064 nm激光器作为实验装置,结合激光器输出光谱特性进行计算。根据计算结果采用不同规格的单标准具、组合双标准具实现了激光线宽在0.75 ~2.83 GHz范围内的离散调节控制。在标准具未控温情况下,不同线宽时激光中心波长保持1064.58 nm,30 min内波长漂移量小于3 pm。     

TEM喇叭天线脉冲辐射特性

采用时域有限积分法（FIT）对相同几何口径尺寸下不同长度TEM喇叭天线的主轴辐射特性进行了研究,分析了有限长TEM喇叭天线与理想（无限长）TEM喇叭天线主轴辐射场存在差异的原因,导出了有限长TEM喇叭天线主轴辐射场在接近理想TEM喇叭天线辐射场条件下天线长度与激励脉冲宽度（或脉冲上升时间）之间的关系。在此基础上,根据文献中的研究结果,并结合激励脉冲波形,给出了TEM喇叭天线几何参数的优化设计方法。     

Measuring causality by taking the directional symbolic mutual information approach

We propose a novel measure to assess causality through the comparison of symbolic mutual information between the future of one random quantity and the past of the other.This provides a new perspective that is different from the conventional conceptions.Based on this point of view,a new causality index is derived that uses the definition of directional symbolic mutual information.This measure presents properties that are different from the time delayed mutual information since the symbolization captures the dynamic features of the analyzed time series.In addition to characterizing the direction and the amplitude of the information flow,it can also detect coupling delays.This method has the property of robustness,conceptual simplicity,and fast computational speed.     

The quantum nonthermal radiation and horizon surface gravity of an arbitrarily accelerating black hole with electric charge and magnetic charge

Using a new tortoise coordinate transformation,we discuss the quantum nonthermal radiation characteristics near an event horizon by studying the Hamilton-Jacobi equation of a scalar particle in curved space-time,and obtain the event horizon surface gravity and the Hawking temperature on that event horizon.The results show that there is a crossing of particle energy near the event horizon.We derive the maximum overlap of the positive and negative energy levels.It is also found that the Hawking temperature of a black hole depends not only on the time,but also on the angle.There is a problem of dimension in the usual tortoise coordinate,so the present results obtained by using a correct-dimension new tortoise coordinate transformation may be more reasonable.     

相对论速调管中间腔与调制电子束间的非线性互作用

在强流相对论电子束驱动的相对论速调管放大器中, 由于强流和高场强的影响, 尤其是中间腔具有高Q值, 微波腔与电子束之间的非线性作用很明显, 严重影响器件性能. 根据麦克斯韦方程组以及电子在微波场作用下运动方程给出了中间腔的束-波互作用自洽方程. 从这些方程出发, 研究了调制深度和调制频率对间隙电压幅度和相位的影响. 对比常规速调管的等效电路模型, 自洽公式给出的间隙电压幅值同粒子模拟结果更接近, 尤其是较高调制深度的情况. 同时器件带宽随调制深度的增加而变宽, 这也同粒子模拟结果一致. 由此设计了一个S波段高增益相对论放大器, 在LTD (长脉冲螺旋线)加速器上开展了相应的实验工作, 实验上获得了1.1 GW的输出功率, 器件增益49 dB. 关键词： 相对论速调管 非线性互作用 自洽方程     

快速多极边界元法用于扩散光学断层成像研究

在求解扩散光学断层成像中的正向问题时, 目前普遍采用有限元法, 但是随着实际模型规模的增大, 有限元法的计算量问题日益显著, 而边界元法则由于可以降低计算维度使计算量减少而备受关注. 本文以均匀的高散射介质为模型, 研究了将快速多极边界元法用于扩散光学断层成像的正向问题. 快速多极边界元法利用核函数的多极展开, 将常规边界元法中系数矩阵和迭代矢量的乘积项等价为相应四叉树结构的一次递归, 再结合广义最小残量法进行迭代求解. 将计算结果和蒙特卡罗法的模拟结果进行了比较, 表明利用快速多极边界元法的模拟结果和蒙特卡罗法的结果有很好的一致性. 研究结果验证了快速多极边界元法可以用于扩散光学断层成像, 为其大规模和实时成像带来可观的前景. 关键词： 扩散光学断层成像 边界元法 快速多极边界元法     

Pigment identification and decoration analysis of a 5th century Chinese lacquer painting screen: a micro‐Raman and FTIR study

To investigate the pigments and decoration applied to a wood‐based lacquer painting screen from the tomb of Si‐ma Jin‐long, Shanxi Province, central China, made by Chinese craftsmen in the 5th century, a combination of micro‐Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), wavelength dispersive X‐ray fluorescence (WDXRF), and microscopic examination was used. The obtained results are as follows: (1) the black, yellow, and red colors are identified as carbon black, orpiment and realgar, and cinnabar, respectively, by using micro‐Raman spectroscopy. The FTIR result shows that the white pigment filled in the leaves is not lead white, as assumed in the literature, but gypsum. Whether lead white was used at other locations remains unanswered and requires more samples for further work; (2) the thickness of each discernable pigment layer, as observed under the microscope, is approximately equal and the differences among them are small, suggesting a superfine painting skill; besides, a noticeable smooth interface between wood and the red grounding substance indicates that a polishing process might have been applied before the painting; (3) the red background was proved to contain cinnabar, but further FTIR analyses found no evidence for the presence of Chinese wood oil; and (4) the most interesting finding, rarely reported before, is that white grains of different sizes are found in both pigment layers and the grounding substance, which are perhaps an intentional addition. Further, in situ XRF and Raman analyses indicate that they are sourced from hydroxyapatite, coming probably from the intentional addition of animal bone ash to the lacquer. But how such a process could be finished and what purpose it served have not yet been answered. Copyright © 2009 John Wiley & Sons, Ltd.     

铁磁/有机半导体/铁磁系统的电流自旋极化性质研究

根据有机半导体中的电流自旋极化注入和输运实验现象，理论上研究了铁磁/有机半导体/铁磁系统的电流自旋极化性质.考虑到有机半导体的具体特性，从自旋扩散理论和欧姆定律出发，得到了系统的电流自旋极化率.假设自旋极化子和不带自旋的双极化子为有机半导体中的载流子.通过计算发现，极化子为实现有机半导体中电流极化注入和输运的有效自旋载流子，即使它只占总载流子很少一部分.还进一步研究了自旋相关界面电阻和电导率匹配以及有机半导体长度等因素对系统电流自旋极化的影响. 关键词： 自旋电子学 自旋注入 有机半导体 极化子     

Tunneling magnetoresistance of the double spin-filter junctions at nonzero bias

A recent theoretical estimation indicated that the NM/FI/FI/NM double spin-filter junction (DSFJ, here the NM and FI represent the nonmagnetic electrode and the ferromagnetic insulator (semiconductor) spacer, respectively) could have very high tunneling magnetoresistance (TMR) at zero bias. To meet the requirement in research and application of the magnetoresistance devices, we have calculated the dependences of tunneling magnetoresistance of DSFJ on the bias (voltage), the thicknesses of ferromagnetic insulators (semiconductors) and the average barrier height. Our results show that except its very high value, the TMR of DSFJ does not decrease monotonously and rapidly with rising bias, but increase slowly at first and decrease then after having reached a maximum value. This feature is in distinct contrast to the ordinary magnetic tunnel junction FM/NI/FM (FM and NI denote the ferromagnetic electrode and the nonmagnetic insulator (semiconductor) spacer, respectively), and is of benefit to the use of DSFJ as a magnetoresistance device.