二阶Y环频率选择表面的设计研究

利用分形结构的自相似性将分形理论应用于频率选择表面(FSS)领域即可使在单屏FSS上具有多频段带通滤波的特性,结合Floquet周期边界条件,采用矩量法研究了二阶Y环分形FSS在不同入射角度下迭代比例因子F及单元排布方式对频率响应特性的影响规律,给出谐振频率的经验估算值.计算及实验结果表明,FSS的谐振频率主要由迭代比例因子及起始单元尺寸决定,而透过率及-3 dB带宽则对排布方式的改变较敏感.实验结果与理论分析一致.     

杂质对量子环上荷负电激子的影响

讨论了在杂质电荷的电场影响下,量子环上荷负电激子X-的能-光谱及其Aharonov-Bohm振荡.当轨道总角动量不守恒的情况下,提出如何按轨道角动量分类构成基矢组并用典型的对角化方法求解体系的本征值和本征矢的方案.该方案计算简单,计算结果令人满意.还讨论了运用等效电荷变换公式和变换图,把位于三维空间的杂质简化为二维平面(或x轴上)的杂质处理,使计算变得更简单,对结果的分析也更明晰.     

CCl自由基A 2Δ←X 2Π跃迁REMPI光谱研究

在271-279 nm波长范围内采用REMPI技术研究CCl自由基的A 2Δ光谱。实验观察到12C35Cl以及同位素分子12C37Cl 的A 2Δ←X 2Π1/2,0-0,1-0和2-1跃迁谱带,其中2-1的跃迁为新观察到谱带。A 2Δ同三个排斥态2Π,2Σ-和4Π交叉,自旋轨道相互作用使得A 2Δ为预解离态。实验结果揭示υ"＝0态预解离要快于υ"＝1,2振动态。     

Nb掺杂对γ-TiAl抗氧化能力影响的第一性原理研究

添加Nb被证实是提高TiAl合金抗氧化能力最有效的途径之一,但对于其机理仍然存在一些相互矛盾的解释.运用第一性原理方法对γ-TiAl氧化过程中存在的几种重要点缺陷杂质进行了系统的研究.在确定杂质的稳定结构基础之上,研究发现：γ-TiAl中Nb掺杂的形成能随着含量的增加而升高,导致γ-TiAl相的稳定性降低,对抗氧化性能造成不利影响;而间隙O和Ti空位的形成能随Nb掺杂量的增加而显著升高,因此Nb能有效地降低氧扩散及空位缺陷的进入,从而提高γ-TiAl的抗氧化性能;Nb掺杂对降低杂质含量的作用存在明显的局域特性,是一种近程作用,因此Nb在γ-TiAl中的作用与其含量和分布有关. 关键词： γ-TiAl 高温氧化 Nb掺杂 形成能     

氩气/空气介质阻挡放电自组织超六边形斑图实验研究

采用双水电极介质阻挡放电装置,在氩气/空气混合气体放电中,在三种边界条件下得到了一种新型的超六边形斑图.给出了超六边形斑图的傅里叶变换及其不同模强度随旋转角的变化.实验测量了超六边形斑图随空气含量和外加电压变化的相图.研究了超六边形斑图的时空动力学,发现超六边形斑图是由两套子结构嵌套而成.在四边形边界条件下,研究了放电面积的大小对斑图模式选择的影响.发现超四边形斑图的形成受边界条件影响很大,而超六边形斑图则是自组织的结果. 关键词： 介质阻挡放电 超六边形斑图 时空动力学 边界条件     

基片对交替溅射制备的MnZn铁氧体薄膜结构和磁性的影响

使用成分分别为MnFe₂O₄和ZnFe₂O₄的靶,使用射频溅射交替沉积制备了成分不同的Mn_1-xZn_xFe₂O₄薄膜,沉积薄膜所用基片分别为单晶硅Si（100）,氧化的单晶硅SiO₂/Si（100）, ZnFe₂O₄为衬底的单晶硅ZnFe< 关键词： MnZn铁氧体 纳米晶 软磁性 磁性薄膜     

Density and impurity profile behaviours in HL-2A tokamak with different gas fuelling methods

The electron density profile peaking and the impurity accumulation in the HL-2A tokamak plasma are observed when three kinds of fuelling methods are separately used at different fuelling particle locations. The density profile becomes more peaked when the line-averaged electron density approaches the Greenwald density limit n_G and, consequently, impurity accumulation is often observed. A linear increase regime in the density range n_e< 0.6n_G and a saturation regime in n_e > 0.6n_G are obtained. There is no significant difference in achieved density peaking factor f_ne between the supersonic molecular beam injection (SMBI) and gas puffing into the plasma main chamber. However, the achieved f_ne is relatively low, in particular, in the case of density below 0.7n_G, when the working gas is puffed into the divertor chamber. A discharge with a density as high as 1.2n_G, i.e. n_e = 1.2n_G, can be achieved by SMBI just after siliconization as a wall conditioning. The metallic impurities, such as iron and chromium, also increase remarkably when the impurity accumulation happens. The mechanism behind the density peaking and impurity accumulation is studied by investigating both the density peaking factor versus the effective collisionality and the radiation peaking versus density peaking.     

界面生长中断对GaAs (111)衬底上AlGaAs/GaAs量子阱电子自旋寿命的影响

用固源分子束外延技术(SSMBE)在GaAs(111)衬底上,采用不同的界面中断时间生长了多组AlGaAs/GaAs多量子阱样品(MQWs),通过室温发光光谱和时间分辨克尔旋转谱(TRKR)研究了界面生长中断对发光光谱半峰全宽(FWHM)和量子阱中电子自旋弛豫时间(自旋寿命)的影响,发现了自旋寿命随着界面生长中断时间的增加呈现先减小后增加的趋势,此变化趋势与荧光光谱半峰全宽表征的材料质量随中断时间的变化一致,适当的界面生长中断时间能有效的增加GaAs (111)衬底上AlGaAs/GaAs 多量子阱中电子自旋寿命。     

Cs nuclear magnetic resonance study in CsZnCl3 single crystals of perovskite ABX3 type

CsZnCl₃ single crystals were grown by the slow evaporation method, and the spin-lattice relaxation rates and resonance lines of the ¹³³Cs nuclei in the resulting crystals were investigated using FT NMR spectrometry. The temperature dependence of the relaxation rate of the ¹³³Cs nuclei in the CsZnCl₃ crystals was found to be continuous near T_C (=366 K), and was not affected by this phase transition. Our results for CsZnCl₃ are compared with those obtained previously for other CsBCl₃ (B=Mn, Cu, and Cd) perovskite crystals. The Cs relaxation time of CsCdCl₃ is longer than that of CsMnCl₃. The differences between the atomic weights of Mn, Cu, Zn, and Cd are responsible for the differences between the spin-lattice relaxation times of these single crystals. The influence of paramagnetic ions is also important in these crystals. The differences between the spin-lattice relaxation times of these crystals could also be due to differences between the electron structures of their metal ions, in particular the structures of the d electrons.     

以“问题”为主线的多元化教学方法和模式的研究

简要介绍了在物理实验的"教"与"学"过程中,改变教学模式,以"问题"为主线,开展多元化的教学方法和模式. 实践表明,该教学模式促进了学生自主创新意识和综合实验研究能力的提升.