Electronic structure,Dirac points and Fermi arc surface states in three-dimensional Dirac semimetal Na_3Bi from angle-resolved photoemission spectroscopy

The three-dimensional(3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A_3Bi(A = Na, K, Rb). Here we report comprehensive high-resolution angle-resolved photoemission(ARPES) measurements on the two cleaved surfaces,(001) and(100), of Na_3Bi. On the(001) surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the k_x–k_y plane and by varying the photon energy to get access to different out-of-plane k_zs. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the(100) surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the(100) plane. We directly observe two isolated 3D Dirac nodes on the(100) surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ~150 me V before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na_3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the3 D Dirac cones, on the possible formation of surface reconstruction of the(001) surface, and on the issue of basic Brillouin zone selection for the(100) surface.     

反套路 重计算 孕思想——2023年全国甲卷数学理科试题评析与反思

<正>2023年高考早已落下帷幕,笔者作为一线数学教师,结合自己和部分同行做全国甲卷理科数学试题的感受,以及笔者的学生在考场上和考后的感受,对2023年全国甲卷数学理科试题进行评析与反思.笔者所在学校的学生大致处于中等及中等偏上的水平,对试卷整体的感受有一定的代表性.     

基于报表数据的上市公司顾客资产测量与提升——中国联通公司的应用研究

顾客资产体现企业在市场竞争中获取顾客资源的能力,本研究旨在利用报表数据对上市公司的顾客资产进行测量,并依据测量结果提出提升策略。首先,运用Matlab编程模拟上市公司的每期期末顾客存量适用的技术替代模型,进而求得顾客资产。其次,依据β转换模型原理估算企业现有顾客的终身价值总和,在同时考虑顾客的获取与流失的前提下求得顾客资产可持续比率。再次,依据顾客资产可持续比率和顾客资产的计算结果构建二维坐标图,以分析企业顾客资产的时间序列特征,作为提升顾客资产的依据。最后,将该方法在中国联通公司进行了应用。研究结果表明,该方法对上市公司的顾客资产测量和提升具有较好的适用性和可操作性。研究结果对于上市公司的顾客资产管理具有一定的参考价值。     

用丝网印刷技术制备薄膜微电极的方法研究

对丝网印刷术在微电极制备方面的应用作了系统和详尽的描述,对绷网、制阳图底板、涂布感光胶、晒网、显影、坚膜、印刷等印制各步骤中所需注意事项和技巧作了总结。考察了标记方式、曝光时间、显影时间等的影响,并在优化条件下制成了微电极。用1mmol／L铁氰化钾在微电极上进行循环伏安扫描实验。结果表明,所制得的微电极条具有良好的电化学性能。用此方法可大批量制得廉价的适用于电化学研究和应用的微电极条。     

中医药现代化对分析化学的机遇与挑战

综述了多种分析方法在中医药现代化中的重要作用,内容包括中药面临的机遇与挑战,中药市场及所存在的问题,当前在中药鉴别、分离、提纯以及复方药效的研究常用的分析方法,中药指纹图谱以及残留农药的检测。引用文献183篇。     

Collision-Induced Coherence Effect on Coherent Population Transfer

We investigate the effect of collision-induced coherence on coherent population transfer with the stimulated Raman adiabatic passage technique in a double A-type four-level system with a widely separated excited doublet. It is shown that when the two pulsed lasers with Rabi frequencies nearly comparable to the energy separation of the doublet are tuned to the particular frequency where the condition for quantum interference is satisfied, the very low transfer efficiency due to the nonadiabatic coupling between the two degenerate adiabatic states could be enhanced significantly with the increase of the collisional decay rates in a moderate range. The enhanced transfer efficiency results from the weakening of the nonadiabatic coupling between the two degenerate adiabatic states realized through collision-induced destructive quantum interference.     

Ni-Ru-Ir氧化物阴极涂层的析氢活性

应用热分解氧化法制备Ni-Ru-Ir氧化物活性阴极.循环伏安、Tafel曲线及计时电流测试表明,在90℃、30%(bymass)的NaOH溶液中,电流密度0.3A·cm-2条件下,Ru∶Ir质量比为1∶1的Ni-Ru-Ir氧化物电极的析氢过电位比Ni电极低300mV;表面粗糙度是Ni网电极的32倍;交换电流密度是Ni网电极的4倍;其析氢性能显然远优于Ni网电极,有望应用于氯碱工业以期降低能耗.     

基于遗传算法的统一混沌系统比例-积分-微分神经网络解耦控制研究

提出了采用改进的遗传算法优化比例-积分-微分(PID)神经网络解耦控制器的连接权值，从而实现PID控制器参数的优化及非线性多变量系统的解耦控制. 改进的遗传算法优于基本遗传算法，它使寻优过程中的计算量减少，计算效率提高，收敛速度加快. 将优化后的PID神经网络解耦控制器应用于统一混沌系统的控制中，仿真实验收到良好的控制效果，证明了PID控制器应用于统一混沌系统控制的有效性. 关键词： 混沌系统 遗传算法 比例-积分-微分 神经网络     

一道新高考题的解法探究与背景推广

从一题多解、考题溯源、试题推广和背景分析等角度对2022年新高考Ⅰ卷的解析几何试题进行深度探究.     

用于丝网印刷电极条上几种固定酶方法的比较研究

对几种酶固定方法:电极表面简单物理吸附、单分子层自组装固定酶法、光敏胶酶固定法、牛血清白蛋白-戊二醛分子交联固定法进行了比较研究,并把这几种方法用于乙酰胆碱酯酶在丝网印刷电极上的固定,在此基础上,提出了在丝网印刷电极上固定乙酰胆碱酯酶的新方法———由Nafion加固的蛋白-戊二醛分子交联法,实际使用中取得了很好的固定效果和良好的酶稳定性。用此法制成的生物传感器对敌敌畏农药进行了测定,经0.1 mg.kg-1农药抑制后,乙酰胆碱酯酶的活性被有效抑制(抑制率达到10%左右)。实验结果表明,Nafion-蛋白-戊二醛交联是一种行之有效的丝网印刷电极上的酶固定方法。