应用于ROF系统中的单边带调制微波毫米波生成技术研究

介绍了单边带调制微波毫米波生成技术研究的背景及意义,综述了几种主要的单边带调制微波毫米波生成技术方案,包括移相法、滤波法、非线性效应法,以及在此基础上的改进方法,如应用于ROF系统中基于谐波抑制的新型单边带调制方案、应用超窄双传输峰光纤光栅实现光学单边带调制等。还介绍了两种新型单边带调制生成微波毫米波技术,包括基于极性反转电光调制器的单边带调制技术以及新型光学注入锁定单边带调制实验系统     

一种改进人工蜂群的分数阶PID控制器优化算法

摘 要：针对分数阶PID控制器参数整定过程参数多复杂性大,传统靠经验试凑的方法不易实现且优化效果差的问题,提出了一种改进的人工蜂群算法,实现分数阶PID控制器参数的整定.该算法通过改进人工蜂群算法中搜索方程,并引入一个淘汰机制,对分数阶控制器参数进行群智能搜索,将搜索到的参数送至分数阶PID控制器中反复迭代,以带有权值的误差绝对值积分指标（AIE）作为人工蜂群寻优的目标函数,最后得出控制器.本文以非线性系统为被控对象,经过实例仿真,验证了该算法实现的控制器比传统整数阶控制器和未改进的人工蜂群算法实现的分数阶控制器的动态性能和稳态性能都有所提高,在超调、上升时间、振荡性方面都优于未改进算法.     

新试剂苯并噻唑重氮氨基偶氮苯与锌的显色反应的研究

研究了新显色剂苯并噻唑重氮氨基偶氮苯(BTDAB)与锌的显色反应.结果表明,在TritonX-100存在下,于pH11.0～11.8的硼砂-氢氧化钠介质中,该试剂与锌可形成稳定的橙红色络合物,其最大吸收波长位于525nm处,表观摩尔吸光系数为1.6×10~5L·mol~(-1)·cm~(-1),锌量在0～12μg/25ml范围内符合比耳定律.     

光纤布拉格光栅型全光纤声光调制器的特性研究

将光纤光栅的傅里叶模式耦合理论应用于光纤布拉格光栅型全光纤声光调制器的理论分析中. 与现有的分析方法相比, 该模型算法简单、 求解容易, 能够快速有效地获得调制器的传输特性. 基于该模型, 理论分析了超声波频率及声致应变幅度对调制器特性的影响. 仿真结果表明, 该调制器反射谱的主反射峰与次反射峰的波长间隔与超声波频率成正比, 反射峰的反射率随着声致应变幅度的改变而发生周期性的变化. 另外, 在同一声致应变幅度下, 低频超声波调制的光栅反射中存在更多的次反射, 光栅反射能量的周期性变化更加明显. 实验中, 使用频率为885.5 kHz的超声波对光纤布拉格光栅进行调制. 实验结果与仿真结果相一致.     

描述人体内水分子扩散各向异性特征的新方法

通过核磁共振扩散张量成像(DTI)得到的特定值域的扩散各向异性指数(DAI) 可用于揭示水分子扩散椭球的形态学特征, 定量反映被成像物体内部水分子扩散的优势方向和强度, 间接得到被成像物体内部的组织结构信息. DAI的可靠性直接影响对DTI数据的分析和理解. 本文基于扩散张量椭球的几何学信息, 提出利用扩散椭球几何比(EGR)定量描述水分子扩散的各向异性程度. 通过蒙特卡罗模拟实验和对人脑DTI数据进行分析, 并与当前广泛应用的水分子扩散各向异性分数(FA)和近期文献提出的扩散椭球面积比(EAR)进行对比. 实验发现EGR在不同级别噪声影响下的对比度效果和抗噪性都优于FA及EAR. 而且EGR 加入了体积修正, 增强了盘形扩散张量情况下的敏感性, 能够更好地鉴别神经纤维束交叉情况, 对于各向异性扩散程度较高的白质深层和相对均质的表层都有较好的量化区分结果. 关键词： 扩散系数 各向异性扩散 扩散张量成像 扩散椭球几何比     

Bifurcation phenomena of photodetached electron flux in parallel external fields

A semiclassical method based on the closed-orbit theory is applied to analysing the dynamics of photodetached electron of H$^- $ in the parallel electric and magnetic fields. By simply varying the magnetic field we reveal spatial bifurcations of electron orbits at a fixed emission energy, which is referred to as the fold caustic in classical motion. The quantum manifestations of these singularities display a series of intermittent divergences in electronic flux distributions. We introduce semiclassical uniform approximation to repair the electron wavefunctions locally in a mixed phase space and obtain reasonable results. The approximation provides a better treatment of the problem.     

QGP中反应过程的内线统计效应

用热场动力学方法研究了QGP中的反应过程,发现内线的统计效应不能忽略.并具体计算了热真空极化对双轻子产生率的贡献.     

非拓扑孤子模型的袋常数与退禁闭相变

用有限温度场论方法,通过计算非拓扑孤子袋模型中与温度和密度相关的有效势,进而得到了袋常数随温度和化学势的变化关系,相应地讨论了退禁闭相变的性质.     

Accuracy and effectiveness of self-gating signals in free-breathing three-dimensional cardiac cine magnetic resonance imaging

Conventional multiple breath-hold two-dimensional(2D) balanced steady-state free precession(SSFP) presents many difficulties in cardiac cine magnetic resonance imaging(MRI). Recently, a self-gated free-breathing three-dimensional(3D) SSFP technique has been proposed as an alternative in many studies. However, the accuracy and effectiveness of selfgating signals have been barely studied before. Since self-gating signals are crucially important in image reconstruction, a systematic study of self-gating signals and comparison with external monitored signals are needed.Previously developed self-gated free-breathing 3D SSFP techniques are used on twenty-eight healthy volunteers. Both electrocardiographic(ECG) and respiratory bellow signals are also acquired during the scan as external signals. Self-gating signal and external signal are compared by trigger and gating window. Gating window is proposed to evaluate the accuracy and effectiveness of respiratory self-gating signal. Relative deviation of the trigger and root-mean-square-deviation of the cycle duration are calculated. A two-tailed paired t-test is used to identify the difference between self-gating and external signals. A Wilcoxon signed rank test is used to identify the difference between peak and valley self-gating triggers.The results demonstrate an excellent correlation(P = 0, R 0.99) between self-gating and external triggers. Wilcoxon signed rank test shows that there is no significant difference between peak and valley self-gating triggers for both cardiac(H = 0, P 0.10) and respiratory(H = 0, P 0.44) motions. The difference between self-gating and externally monitored signals is not significant(two-tailed paired-sample t-test: H = 0, P 0.90).The self-gating signals could demonstrate cardiac and respiratory motion accurately and effectively as ECG and respiratory bellow. The difference between the two methods is not significant and can be explained. Furthermore, few ECG trigger errors appear in some subjects while these errors are not found in self-gating signals.