The effect of two ferromagnetic metal stripes on valley polarization of electrons in a graphene

As the key factor for designing the valleytronic devices is to well understand the valley-dependent transport mechanism in graphene, we investigate, in this work, the effect of two ferromagnetic (FM) metal stripes on the valley polarization in a graphene nanostructure with a strain. The nearly 100% valley polarization is observed at certain energy windows and it can be easily controlled through changing the width and the position of the FM stripe as well as the strength of the magnetic field induced by the FM stripe. Our interesting findings reveal the valley-dependent transport mechanism of electrons and promote the realization of the new types of valleytronic devices modulated by the FM stripe and the strain.     

Broadband topological valley-projected edge-states transport in composite structure phononic crystal

The topological valley transport, realized in phononic crystals, has aroused tremendous interest in these years. Many previous researches have further promoted the development of this transport phenomenon. Crucially, the bandwidth of the valley-projected edge mode has been an essential research topic. As is well known, the broadband will improve the adaptability of the acoustic edge-states, which will be more conducive to the transmission of information. Therefore, in this paper, we present a composite structure, composed of the atoms with different shapes forming a hexagonal lattice, which can achieve larger bandwidth than a single structure. Meanwhile, the results demonstrate that the topological protected edge states are also observed in our structure. Furthermore, the backscattering suppressions from associated valley-protected edge states under certain perturbations have also been investigated and demonstrated. Our work can provide a new idea for designing acoustic devices based on valley degree of freedom.     

V型河谷地应力研究

介绍了河谷地应力研究现状 ,利用弹性理论和变分原理 ,研究了V型河谷岩体地应力问题 ,得到了河谷岩体中由于自重应力和构造应力引起的复杂应力场。应用本文结果 ,不仅可以方便绘制各种应力图件 ,而且可以较为精确地得到河谷区域任意指定点的应力值 ,从而为区域稳定性和岩体稳定性评价 ,为水电工程、地下硐室设计以及边坡工程等提供必要的岩体力学资料。本文方法数值实现简单 ,编程容易 ,计算快 ,精度高 ,可应用推广.     

Selective Excitation of Band Extrema in Valley Photonic Crystals

Flexible control of building blocks of photonic crystals enables achieving desirable band structures. Exploration of photonic band extrema has brought many fantastic features to design artificial optical materials, such as Brillouin‐zone‐corner extrema for valley photonic materials and zone‐center extremum for zero‐index metamaterials. However, two such kinds of extrema are always found independently in different photonic crystals. In this work, a kind of valley photonic crystals possessing both zone‐center and zone‐corner band extrema almost at the same frequency is proposed. Inspired by antennas theory, a three‐antenna array (TAA) source is devoted to individually manipulate each extremum. The correlation coefficient is given to determine the coupling efficiency between the TAA source and extrema eigenmodes. By using a source with a high correlation coefficient, these extrema bulk states are selectively excited consistent with their eigenfields. Furthermore, three control cases are shown that multiple extrema points are simultaneously excited, in order to confirm the validity of the correlation coefficient. Finally, a potential application of a beam‐steering device is proposed through selective excitation of ternary extrema. This work develops binary valley states into ternary mix states, rendering more degrees of freedom for on‐chip optical information transport, particularly for beam steering and mode division multiplexing.     

声子角动量与手性声子

在经典的物理学理论中,声子广泛地被认为是线极化的、不具有角动量的.最近的理论研究发现,在具有自旋声子相互作用的磁性体系(时间反演对称性破缺)中,声子可以携带非零的角动量,在零温时声子除了具有零点能以外还带有零点角动量;非零的声子角动量将会修正通过爱因斯坦-德哈斯效应测量的回磁比.在非磁性材料中,总的声子角动量为零,但是在空间反演对称性破缺的六角晶格体系中,其倒格子空间的高对称点上声子具有角动量,并具有确定的手性;三重旋转对称操作给予声子量子化的赝角动量,赝角动量的守恒将决定电子谷间散射的选择定则;此外还理论预测了谷声子霍尔效应.     

谷值V~2控制Boost变换器的精确建模与动力学分析

建立了谷值V2控制Boost变换器的离散迭代映射模型,在此基础上得到了输入电压、输出电容及其等效串联电阻(equivalent series resistance,ESR)变化时的分岔图,推导了不动点处的雅可比矩阵,利用特征值和最大Lyapunov指数对系统进行了稳定性分析,并验证了分岔图的正确性.重点研究了输入电压和输出电容及其ESR对谷值V2控制Boost变换器的动力学特性的影响.研究结果表明,输入电压增大时,变换器从周期1态经历1次倍周期分岔和边界碰撞分岔进入混沌状态;输出电容及其ESR具有相同的分岔路由,随着输出电容及其ESR的逐渐减小,变换器具有从周期1态经历周期2态、周期4态、周期8态、逐渐演变到混沌态的动力学行为.最后,用仿真和实验结果验证了本文理论分析的正确性.     

New mechanistic insights into the Claisen rearrangement of chorismate – a Unified Reaction Valley Approach study

ABSTRACT

The Bacillus subtilis chorismate mutase catalysed Claisen rearrangement of chorismate to prephenate is one of the few pericyclic processes in biology, and as such provides a rare opportunity for understanding how Nature promotes such rearrangements so successfully. The major focus of this work is on (i) Exploring the hypothesis that the mechanism of the chorismate rearrangement is the same in the gas phase, in the aqueous solution and in the enzyme; (ii) Investigating current suggestions that the enzyme lowers the barrier via transition state stabilisation rather than via space confinement; and (iii) A comparison of Nature's way of catalysing the reaction with a gold(I) catalysed chorismate rearrangement. Based the Unified Reaction Valley Approach (URVA), for the first time, a detailed one-to-one comparison of the rearrangement in the gas phase, in the aqueous solution and in the enzyme is presented. URVA confirms that the actual chemical process of CO bond breaking and CC bond forming is the same for all media and unravels the unique catalytic function of the enzyme as a combination of shortening the process of positioning the enolpyruvyl side chain over the cyclohexadienyl ring by space confinement in concert with facilitating CO cleavage by enhanced charge polarisation. The transition state does not play a signifiant role for the rearrangement. In contrast, the gold catalyst changes the chemical process. The rearrangement is split into two steps by switching between Au[I]-π and Au[I]-σ complexation, thus avoiding the energy consuming CO breakage in the first step. Suggestions are made for metalloenzyme analogues combining both strategies.