Probing (topological) Floquet states through DC transport

We consider the differential conductance of a periodically driven system connected to infinite electrodes. We focus on the situation where the dissipation occurs predominantly in these electrodes. Using analytical arguments and a detailed numerical study we relate the differential conductances of such a system in two and three terminal geometries to the spectrum of quasi-energies of the Floquet operator. Moreover these differential conductances are found to provide an accurate probe of the existence of gaps in this quasi-energy spectrum, being quantized when topological edge states occur within these gaps. Our analysis opens the perspective to describe the intermediate time dynamics of driven mesoscopic conductors as topological Floquet filters.     

Role of inter-tube coupling and quantum interference on electrical transport in carbon nanotube junctions

Due to excellent transport properties, Carbon nanotubes (CNTs) show a lot of promise in sensor and interconnect technology. However, recent studies indicate that the conductance in CNT/CNT junctions are strongly affected by the morphology and orientation between the tubes. For proper utilization of such junctions in the development of CNT based technology, it is essential to study the electronic properties of such junctions. This work presents a theoretical study of the electrical transport properties of metallic Carbon nanotube homo-junctions. The study focuses on discerning the role of inter-tube interactions, quantum interference and scattering on the transport properties on junctions between identical tubes. The electronic structure and transport calculations are conducted with an Extended Hückel Theory-Non Equilibrium Green's Function based model. The calculations indicate conductance to be varying with a changing crossing angle, with maximum conductance corresponding to lattice registry, i.e. parallel configuration between the two tubes. Further calculations for such parallel configurations indicate onset of short and long range oscillations in conductance with respect to changing overlap length. These oscillations are attributed to inter-tube coupling effects owing to changing π orbital overlap, carrier scattering and quantum interference of the incident, transmitted and reflected waves at the inter-tube junction.     

山地城市轻轨沿线典型地段声环境研究*

重庆作为典型山地城市,独特的城市空间形态产生了轻轨系统与其沿线建筑特有的空间关系,使得轻轨噪声的影响变得更为复杂。本文以重庆市轻轨建设现状与空间形态特征的分析研究为基础,选取了轻轨2、3号线沿线的三处典型地段进行声环境测试,测试结果表明,轻轨通过时噪声会增加10-25 dB(A),而山地城市多轻轨线路多弯道,列车通过400m以下小半径弯道时噪声平均比直行状态高2-3 dB(A),同时轻轨在进出隧道时,其噪声的持续影响时间平均增加10-12s。     

Switching of transmission resonances in a two-channels coupler: A Boundary Wall Method scattering study

In this work, we study the transmission characteristics of a two-channels coupler model system using the Boundary Wall Method (BWM) to determine the solution of the corresponding scattering problem of an incident plane wave. We show that the BWM provides detailed information regarding the transmission resonances. In particular, we focus on the case of single channel input aiming to explore the energy switching performance of the coupler. We show that the coupler geometry can be tailored to allow for the first transmission resonances to be predominantly transmitted on specific output channels, an important characteristic for the realization of logical operations.     

部分相干平顶高斯光束通过球差透镜的聚焦特性

 基于部分相干光的传输理论,研究了部分相干平顶高斯光束通过球差透镜聚焦后轴上点的光强分布。数值计算表明:轴上最佳聚焦点随着球差从负到正的变化而向几何焦点方向移动;光束阶数越大,实现最佳聚焦点越过几何焦点所需的正球差值越小;正负球差对应的最佳聚焦点始终分居于无球差时最佳聚焦点的两侧;轴上最佳聚焦点的光强随着球差从负到正的变化而变小;当正负球差绝对值较大时,光强随球差的变化较为缓慢,而在球差值为0附近,光强随球差的变化比较剧烈。     

梯度折射率微球回归反射材料的研究

提出一种回归反射面材的新结构,以梯度折射率微球代替传统的超高折射率匀质玻璃微球.利用四阶Runge-Kutta方法进行光线追迹的理论计算,确定了制作新型回归反射面材的工艺参数.结果表明,按此条件制作回归反射面材可大幅度降低原先对折射率的过高要求,并显著提高回归反射的性能.     

A simple method for evaluation of optical scattering effect on the Raman signal of a sample beneath an Intralipid layer

Optical scattering by biological tissues largely deteriorates the efficiency of the Raman analysis of these tissues. To evaluate the effect of scattering on Raman depth profiles (RDPs), we developed a simple method using a thin-layered sample mimicking real tissues and a conventional Raman microscope. The sample comprised three layers: a silicon wafer, a thin aqueous film containing Intralipid particles as scatters, and a fused silica window; this design was used to mimic real skin tissues quantitatively. The multi-scattering effect, which deteriorates spatial resolution, was clearly observed as broadening of RDPs. Decrease in Raman intensity was also systematically examined as a function of both the concentration of the Intralipid particles and depth of the film, and evaluated using Lambert-Beer's law. The abovementioned observations can be quantitatively explained on the basis of the scattering cross-section and concentration of the Intralipid particles, indicating that the method is useful for the quantification of the deterioration of Raman measurements due to optical scattering.     

Design and simulation of nano-antenna with tunable direction of radiation

A new concept for tuning direction of radiation in nano-antenna with negative and positive polarizability is introduced and evaluated by numerical simulation. It has shown that such a configuration consisted of an array of nanoparticles can tune the direction of radiation pattern successfully. Increasing the number of nanoparticles exhibits more directivity at special direction. Variation in position of nanoparticles is used to tune the angle of maximum radiation. The maximum tunability for special geometry of three particles is about 40°. Angle of maximum radiation pattern for four particles is shifted from interval 150–180° to 0–30°.     

The physics of quantum gravity

Quantum gravity is still very mysterious and far from being well understood. In this text we review the motivations for the quantification of gravity, and some expected physical consequences. We discuss the remarkable relations between scattering processes in quantum gravity and in Yang–Mills theory, and the role of string theory as a unifying theory.