速调管离子噪声特性的模拟分析

 离子噪声已成为影响现代微波管性能的一个重要因素，采用一维混合模型研究了速调管的离子噪声，用自编的1维粒子模拟程序对速调管的离子噪声特性进行了分析。采用小信号近似，从理论上推导出了速调管离子噪声与相位畸变关系的表达式，表明微波管相位噪声直接来源于管内离子量的变化。模拟了有离子噪声时速调管的相位特性，对模拟过程做了离子诊断并与实验结果进行比较，证明了模拟过程的正确性。探讨了电子束电流、电压以及聚焦磁场对离子噪声的影响规律，束电流与束电压改变后，离子噪声的周期与大小相应改变，增大束电流，离子噪声幅度会下降，并趋于稳定，而在束电流不变的情况下，离子噪声存在一个最小值。束电流与束电压确定，存在最佳的磁场使离子噪声幅度最小。     

Surface Polaritons in a Wire Medium with Spatial Dispersion

The dispersion relations of the surface polariton in a semi-infinite wire medium with spatial dispersion are analysed. In comparison with the traditional spatial dispersive medium there only exists one branch instead of multibranch for the dispersion curve. The possibility of the experimentally observing the surface polaritons by attenuated total reflection is simulated numerically.     

Study on the pre-chopper in CSNS LEBT

Physical designing of the pre-chopper in CSNS LEBT is carried out,which includes the deflecting voltage,the length and the width of the deflecting plates,and the gap between the deflecting plates.The most outstanding feature of the design is that both the gap and the width vary with the beam envelope size.So both the requried deflecting voltage and the loaded capacitance are lowered.In order to avoid destruction of the space charge neutralization by the pre-chopper in the whole LEBT,an electron-trapping electrode is arranged to confine the electrostatic field of the pre-chopper to the local area.To examine the reliability of the pre-chopping design in CSNS LEBT,a similar pre-chopping design in ADS RFQ LEBT is set up and an experiment on the pre-chopper is prepared.3-dimensional simulations are carried out to determine the loaded capacitance and the applied voltage of the electron-trapping electrode.     

Electronic,Vibrational, and Superconducting Properties of High-Pressure Metallic SiH4： ab initio Calculations

We extensively explore the experimentally proposed metallic structure of hcp P63 for the hydrogen rich compound, SiH4. It is found that the lattice dynamic of this structure is severely unstable. By freezing the soften mode, an orthorhombic Pbcn structure is discovered to be dynamically stable up to 226GPa. Within the conventional BCS theory, the calculated critical temperature Tc within the proposed Pbcn structure is 16.5K at 188GPa, in good agreement with the experimental result （17.5K）. Thus, we propose that the current predicted orthorhombic phase is a better candidate for the metallic phase of SiH4.     

External Electric Field Effect on Hydrogenic Donor Impurity in Zinc-Blende InGaN Quantum Dot

The binding energy of a hydrogenic donor impurity in zinc-blende (ZB) InGaN quantum dot (QD) is calculated in the framework of effective-mass envelope-function theory using the plane wave basis. It is shown that the donor binding energy is highly dependent on the impurity position, QD size and the external electric field. The symmetry of the electron probability distribution is broken and the maximum of the donor binding energy is shifted from the centre of QD in the presence of the external electric field. The degenerating energy levels for symmetrical positions with respect to the centre of QD are split. The splitting increases with the increase of QD height while the splitting increases up to a maximum value and then decreases with the increase of QD radius.     

5—25keV刻度用X射线发生器

利用轫致辐射激发原子产生X射线荧光,经吸收边过滤,研制成单色低中能X射线发生器。实验给出5—25keV能区的4个单能点的强度、纯度以及相应的剂量率,可供刻度使用。     

类凸向量均衡问题解的最优性条件

在实的局部凸的Hausdorff拓扑线性空间中,考虑带约束的向量均衡问题,利用凸集分离定理,给出了带约束的类凸向量均衡问题的弱有效解,Henig有效解,全局有效解和超有效解的充分必要条件,并通过举例说明了锥类凸映射是比锥凸映射更弱的映射。     

激光磁共振用于对NO_2分子的定量测量

本文叙述了采用CO激光磁共振方法对NO_2分子作定量测量,给出了激光磁共振信号幅度的数学表达式以及信号与分子浓度、激光功率等实验参数之间的依赖关系,实验结果与理论分析一致。     

超导临界温度理论(Ⅲ)

本文定出超导临界温度T_c级数公式(1)的前几项系数。对于形式为α²F(ω)=(λω)/2[a₁δ(ω-ω₁)+(1-a₁)δ(ω-ω₂)]的双δ型有效声子谱及若干具体材料的谱,将级数公式计算的T_c与Allen-Dynes公式(以下简称A-D公式)及Eliashberg方程的数值解作了比较。计算表明,当级数(1)收敛时,级数公式计算的结果较A-D公式更接近于数值解。此外,本文还给出了一个近似的T_c级数公式,得到了估计该T_c级数收敛半径的方法,并计算了若干材料的收敛半径值。因此,可估计级数公式(1)的适用范围。 关键词：     

黄颡鱼属SSR分子鉴定及其遗传多样性

利用13对SSR引物对黄颡鱼属进行遗传多样性和分类研究。结果显示,13对SSR引物中有10对为有效引物,获得93条多态性条带,每对引物扩增条带的数目范围为8~11,扩增片段大小在90~400bp之间,SSR获得的多态性条带所构成各物种的特异性谱系能够用于黄颡鱼属的区分。聚类结果显示,5种黄颡鱼之间的遗传相似系数范围为0.670~1.000,瓦氏黄颡鱼、长须黄颡鱼和中间黄颡鱼亲缘关系较近,之后与光泽黄颡鱼聚为一支,普通黄颡鱼与其它物种差异最大。黄颡鱼属遗传多样性分析结果显示5种黄颡鱼遗传多样性处于水平较高,这将有助于后续深入对黄颡鱼属各物种亲缘关系和系统演化进行分析和理论研究。