Model for spontaneous frequency sweeping of an Alfvén wave in a toroidal plasma

We study the frequency chirping signals arising from spontaneously excited toroidial Alfvén eigenmode (TAE) waves that are being driven by an inverted energetic particle distribution whose free energy is tapped from the generic particle/wave resonance interaction. Initially a wave is excited inside the Alfvén gap with a frequency determined from the linear tip model of Rosenbluth, Berk and Van dam (RBV) [1]. Hole/clumps structures are formed and are observed to chirp towards lower energy states. We find that the chirping signals from clump enter the Alfvén continuum which eventually produce more rapid chirping signals. The accuracy of the adiabatic approximation for the mode evolution is tested and verified by demonstrating that a WKB-like decomposition of the time response for the field phase and amplitude agree with the data. Plots of the phase space structure correlate well with the chirping dependent shape of the separatrix structure. A novel aspect of the simulation is that it performed close to the wave frame of the phase space structure, which enables the numerical time step to remain the same during the simulation, independent of the rest frame frequency.     

阿尔芬波加热研究的进展

本文概述了阿尔芬波加热的理论和实验情况。讨论了阿尔芬波加热的基本物理问题,并介绍了某些重要的实验结果。对在大托卡马克上采用阿尔芬波加热的可能性进行了全面论述。     

柠檬醛对黄曲霉质膜物理损伤机制的研究

通过反射干涉对比显微技术和快速图像分析技术,捕获细胞质膜外光晕变化和细胞周边边缘激发变化的信息,并采用闪烁本征模式分解测定柠檬醛作用于黄曲霉质膜前后各模式（m=0,1,2）所对应的平均平方振幅<δn2m>、剪切弹性μ和弹性弯曲模量Kc,与理论模式光谱相比,研究柠檬醛损伤质膜的物理机制.结果表明,m=1的平动模式主导了光晕波谱,其平均平方振幅呈双指数衰变,该模式几乎与剪切弹性无关,即μ=0;弹性弯曲模量Kc的最小和最大值分别为9.45×10-18J和5.43×10-17J,与柠檬醛的浓度成正相关性.揭示该醛对黄曲霉质膜的损伤,除改变膜的选择通透性和电导率外,同时使质膜平动模式的平均平方振幅呈双指数衰变,弹性弯曲模量Kc增加,从而降低膜伸缩的弹性.     

Diffusion Lattice Boltzmann Scheme on a Orthorhombic Lattice

We present a diffusion lattice Boltzmann (DLB) scheme which is derived from first principles. As opposed to the traditional lattice BGK schemes the DLB is valid for orthorhombic lattices and it has two eigenvalues of the collision operator. It is shown that the diffusion coefficient depends only on one eigenvalue of the collision operator. Hence, the DLB scheme can be optimized with means of the additional eigenvalue of the collision operator and with different lattice spacing along the principal axes. The properties of the DLB scheme concerning consistency, stability, and accuracy are studied with eigenmode analysis. This analysis shows that the DLB scheme is consistent with diffusion for a wide range of diffusion coefficients, it has unconditional stability, and that it has third-order accuracy. Furthermore, it is shown that accuracy is improved by setting the additional eigenvalue to zero and by densifying the lattice spacing along the direction of the density gradient.     

Dual-band left-handed metamaterials fabricated by using tree-shaped fractal

<正>A method of fabricating dual-band left-handed metematerials(LHMs) is investigated numerically and experimentally by single-sided tree-like fractals.The resulting structure features multiband magnetic resonances and two electric resonances.By appropriately adjusting the dimensions,two left-handed(LH) bands with simultaneous negative permittivity and permeability are engineered and are validated by full-wave eigenmode analysis and measurement as well in the microwave frequency range.To study the multi-resonant mechanism in depth,the LHM is analysed from three different perspectives of field distribution analysis,circuit model analysis,and geometrical parameters evaluation.The derived formulae are consistent with all simulated results and resulting electromagnetic phenomena,indicating the effectiveness of the established theory.The method provides an alternative to the design of multi-band LHM and has the advantage of not requiring two individual resonant particles and electrically continuous wires,which in turn facilitates planar design and considerably simplifies the fabrication.     

Relationship between group velocity and symmetry of photonic crystals

Group velocity (GV) of eigenmode is a crucial parameter to explain the extraordinary phenomena about light propagation in photonic crystals (PhCs). To study relationships between group velocity and symmetry of PhCs, a new general expression of GV in PhCs made up of non-dispersive material is introduced. Based on this, the GVs of eigenmodes of PhCs, especially those of degenerate eigenmodes at highly symmetric points in the first Brillouin zone, are discussed. Some interesting results are obtained. For example, the summation of degenerate eigenmodes' GVs is invariant under the operations of wave vector ${{\bm K}}$-group $M_{{\bm K}} $. In addition, some numerical results are presented to verify them.     

Optical modelling of photonic crystals and VCSELs using eigenmode expansion and perfectly matched layers

We present a modelling approach for photonic crystal structures and vertical-cavity surface-emitting lasers (VCSELs). This method is based on vectorial eigenmode expansion combined with perfectly matched layer (PML) boundary conditions. Compared to other methods, a relatively small computational effort is required, while at the same time accurate results are obtained, even in the presence of strong scattering and diffraction losses.     

Some mathematical aspects of Anderson localization: boundary effect,multimodality, and bifurcation

Anderson localization is a famous wave phenomenon that describes the absence of diffusion of waves in a disordered medium. Here we generalize the landscape theory of Anderson localization to general elliptic operators and complex boundary conditions using a probabilistic approach, and further investigate some mathematical aspects of Anderson localization that are rarely discussed before. First, we observe that under the Neumann boundary condition, the low energy quantum states are localized on the boundary of the domain with high probability. We provide a detailed explanation of this phenomenon using the concept of extended subregions and obtain an analytical expression of this probability in the one-dimensional case. Second, we find that the quantum states may be localized in multiple different subregions with high probability in the one-dimensional case and we derive an explicit expression of this probability for various boundary conditions. Finally, we examine a bifurcation phenomenon of the localization subregion as the strength of disorder varies. The critical threshold of bifurcation is analytically computed based on a toy model and the dependence of the critical threshold on model parameters is analyzed.     

单层石墨烯带传输模式及其对气体分子振动谱的传感特性研究

自2004年石墨烯被成功制备以来, 相关研究引起了广泛关注, 其中, 传感应用是一个重要方向. 目前, 有关石墨烯传感特性的研究都集中在低频, 即根据分子附着引起的电导率变化来实现检测. 然而, 由于大部分分子吸附都会使电导率发生变化, 因此该方法难以区分不同分子的特征. 论文基于Kubo公式, 结合数值仿真方法研究了单层石墨烯带的传输模式, 分析了有效模式指数与模式传输特性的关联, 证实了波导模的局域性和宽带特性. 同时, 利用一阶波导模与气体作用引起的传输强度的变化反演分子振动谱. 以SO₂, CO和C₇H₈气体的传感为例, 基于本征分析验证了方法的有效性. 结果表明, 传输模式与分子作用能够产生耦合共振增强, 并且其变化趋势与气体分子振动谱一致; 在传输方向上, 分子与传输模式的作用范围越大, 则模式传输强度的变化越大. 该研究为实现气体分子指纹的识别和检测奠定了理论基础.