基于石墨烯的太赫兹漫反射表面快速设计方法

漫反射电磁表面能够提高目标被探测的难度,实现电磁消隐的功能.太赫兹漫反射电磁表面有望在下一代雷达与通信场景中作为一种智能隐身蒙皮使用,具有广阔的应用前景.本文利用石墨烯在太赫兹频段优异的电磁可调特性,并基于谐振模式的开关机理设计了一种反射场具有反相位的石墨烯/金属协同单元结构.且相位的切换由偏置电压动态控制.另一方面,不同于金属材料,石墨烯具有不可忽略的损耗特性,导致了所设计的结构在谐振/非谐振两种反相位状态对应的反射幅度不一致,根据场的干涉与叠加原理,其不利于远场相干相消,难以获得理想的漫反射效果.本文提出了一种将反相位单元结构进行二次组合形成"分子"结构的方法,并将其作为反射表面的基本元素,进而运用粒子群算法,优化"分子"结构的排布方式.计算结果表明,使用这种方法设计的动态漫反射表面,具有收敛速度快、远场峰值小的优势.     

β-Ga2O3晶体金刚石线锯切割的表面质量研究

本文探究了往复式金刚石线锯的工艺参数对β-Ga₂O₃单晶沿(001)晶面切片时表面质量的影响,从压痕断裂力学理论角度探究了金刚石线锯切割β-Ga₂O₃单晶过程中磨粒行为和材料去除机理。实验从各向异性角度分析了切割方向对(001)面β-Ga₂O₃单晶切割片表面质量的影响,并采用SEM和SJ-210粗糙度测试仪探究了工艺参数对金刚石线锯切割后的晶片表面质量的影响。实验结果表明,增大锯丝速度或减小材料进给速度都能降低亚表面损伤层深度及表面粗糙度,有效改善晶片表面质量。     

供应链成本“减压”

成本上升已经成为近些年来中国制造业企业供应链主管们热议的话题,也成为提升企业竞争力所必须解决的问题。中国制造业企业成本的持续上升,使得企业在现阶段供应链运营管理时面临着更加复杂的挑战。要找到应对成本上升的办法,首先要了解近些年影响成本上升的关键因素。     

新型近红外超长余辉材料Zn_3Al_2Ge_2O_(10)∶Cr~(3+)的发光性能

采用高温固相法制备了新型近红外长余辉材料Zn3Al2Ge2O10∶Cr3+,利用X射线衍射、荧光光谱和余辉衰减曲线等对合成的样品进行了分析。结果表明:样品Zn3Al2Ge2O10∶Cr3+是Ge4+取代ZnAl2O4∶Cr3+尖晶石中的部分Al3+而形成的固溶体。在397 nm光的激发下,发射光谱主要由两个明显的窄峰叠加在Cr3+离子的自旋允许跃迁4T2→4A2辐射的宽发射带上。发光强度随着Cr3+离子掺杂浓度的增大和煅烧温度的升高而出现浓度猝灭及温度猝灭现象。当Zn3Al2-xGe2O10∶xCr3+中的Cr3+离子掺杂量x为2%且煅烧温度为1 350℃时,样品的近红外发光及余辉强度最大。材料的余辉持续时间超过300 h,余辉发射谱峰位与荧光发射光谱中的N线一致,均位于697 nm附近。最后分析了煅烧温度对样品余辉性能的影响,并对材料的余辉机制进行了探讨。     

利用金属贴片电磁带隙结构在金属波导中创建准横电磁波

为解决准横电磁(TEM)模波导工作带宽较窄的问题,提出采用金属贴片电磁带隙(EBG)结构在金属波导中创建准TEM波.通过理论分析和数值计算,研究金属贴片EBG结构创建准TEM波导对展宽带宽、改善传输特性和增强准TEM波电场分布均匀性的作用.模拟结果表明,在频率14 GHz附近,金属贴片EBG将TE₁₀模成功转换成准TEM模,转换带宽达到1.7 GHz,且在波导横截面83.9%的面积上电场分布均匀性达到84.7%. 关键词： 电磁带隙 金属贴片电磁带隙结构 磁导体 准横电磁模波导     

On-surface synthesis of one-dimensional carbyne-like nanostructures with sp-carbon

Carbyne is an infinite one-dimensional carbon chain comprising of sp-hybridized carbons. Due to its high chemical reactivity and extreme instability, the synthesis and structural diversity of carbyne have been much less investigated in the past decades compared to carbon allotropes built with sp² hybridized carbons, such as fullerenes, carbon nanotubes, and graphene. The emerging on-surface synthesis strategy provides an extremely promising approach for the fabrication of novel carbyne-like nanostructures with atomic precision. Herein, we summarize recent exciting progress in the synthesis of carbyne-like nanostructures with one-dimensional sp-carbon on surfaces, including polyynes, cumulenes, and organometallic polyynes. We also point out the scientific challenges and prospects, encouraging scientists to explore the fabrication and characterization of single strands of carbyne in this young and promising research field.     

紫杉醇C_(13)侧链的硒代合成及其结构性质

用Se元素修饰紫杉醇C13侧链合成硒代C13类拟物.以手性薄荷醇为原料,通过Darzen缩合、叠氮化、还原、胺解、水解等,合成含硒酰胺的C13侧链,目标物用IR、元素分析、原子荧光等手段进行结构表征.同时采用密度泛函B3LYP方法,6-31+G*水平基组对目标物的微观结构及其性质进行气态、溶液模拟计算.分析比较实验、计算的IR光谱吻合较好.并对目标物微观性质进行理论预测,为典型的两性试剂,Se的取代可增加活性部位,增强溶解性.本研究成果为该类化合物的定量构效关系研究和药效团模型的建立以及先导化合物的化学结构修饰改造提供理论依据及实验基础.     

Bending localization of nitrous oxide under anharmonicity and Fermi coupling: the dynamical potential approach

This paper studies the vibrational nonlinear dynamics of nitrous oxide with Fermi coupling between the symmetric stretching and bending coordinates by classical dynamical potential approach.This is a global approach in the sense that the overall dynamics is evidenced by the classical nonlinear variables such as the fixed points and the focus are on a set of levels instead of individual ones.The dynamics of nitrous oxide is demonstrated to be not so much dependent on the excitation energy.Moreover,the localized bending mode is shown to be ubiquitous in all the energy range studied.     

Transformation of Sign of Nonlinear Refraction between Mo（W）/S/Cu Planar Metal Clusters

Optical nonlinear refractive properties of a series of Mo（W）/S/Cu planar square clusters are investigated using the Z-scan technique with the ns laser pulses at the wavelength of 532 nm. The result shows that the planar metal clusters containing the halogen ligands demonstrate the self-focusing effect, and the other planar metal dusters demonstrate the self-defocusing effect. These facts indicate that the halogen ligands can act as crucial factors in determining the sign of the nonlinear refraction of the Mo（W）/S/Cu planar metal clusters. The analysis of the experimental data shows that the planar clusters with halogen ligands possess greater refraction volume of the excited state than that of the ground state, while the other planar clusters possess the smaller refraction volume of the excited state than that of the ground state.     

声速不均匀介质热声成像的声场仿真

为了精确表示声速不均匀介质热声成像的声场,提出了一种时域有限差分(FDTD)仿真方法.先用FDTD将热声成像的基本方程离散化,给出描述热声成像的离散差分方程;再对电磁波脉冲进行两次修正,以消除高频电磁波引入的计算误差.计算机仿真研究的结果表明:当介质声速不均匀时,FDTD仿真方法其准确度高于目前常用的飞行时间法.在仿真实验条件下,当介质的声速差异大于50%时,FDTD法的误差比飞行时间法小十倍以上.可见,FDTD方法是一种有效的热声成像声场仿真方法,可以为声速不均匀介质热声成像算法的研究提供理论基础.