Electronic and optical properties of quaternary selenides for optoelectronic applications: Insights from DFT+U-computations

The optical properties, electronic charge density, electronic structure of the new layered selenides materials, BaGdCuSe₃, CsUCuSe₃, CsZrCuSe₃, and CsGdZnSe₃ compounds have been calculated by using the full potential and linear augmented plane wave (FP-LAPW) methods as applied in the WIEN2k package, which is based on the density functional theory. The ALnMSe3 compound's structure of these was (A = Cs, Ba; Ln = Zr, Gd, U; M = Cu, Zn) is composed of (n = 1, 2) layers, which might be separated by A atoms. It is to be observed that there is strong hybridization between the s, p, and d states of Zr, Gd, and Cu atoms. Around the gadolinium atom, the charge density contours are completely circular, but the Gadolinium “Gd” atom shows an ionic nature. To calculate the refractive index, we used Kramer's Kronig correlations with the imaginary part dielectric function. The decrease in the refractive index is due to the lack of probability for direct excitation of the electrons, resulting in a loss of energy. The value of the static refractive index for all reference compounds is about 1.75–2.25, which is indication that the material used in optoelectronic devices.     

Component reconstruction in the primary space of spectra and concentrations. Alternating regression and related direct methods

A set of methods that extract the spectral components in a chromatographic run is considered. The methods do not need libraries of previously known spectra or retention times. The methods have been developed for two-dimensional spectra but they can also be used for chromatographic analyses with a single-channel detector. The methods are direct; they do not use principal components as the starting point. Alternating regression (AR) remains in the primary space of spectra and concentrations during the calculations. Random numbers are used as the starting spectra. Regression is used to solve first for the concentrations, then for the spectra. The method uses two kinds of constraints: all spectra and concentrations are forced to be positive; and all concentration profiles are forced to a unimodal shape with a single local maximum. It is assumed that all observations are a linear sum of components. Compact alternating regression (CAR) is a new variant of the basic AR. The idea is to replace multiplication of a large matrix by two multiplications of smaller matrices. This typically speeds up the iterations by a factor of ten. AR and CAR have been successfully used with combined techniques such as gas chromatography—mass spectrometry and liquid chromatography with UV—visible detection. The reliability of the solution is checked by repeatedly injecting noise and performing the analysis several times. This produces estimates of confidence intervals. AR and CAR have recently been extended to handle single-dimensional signals. Examples are single-channel detectors such as the flame ionization detector in gas or liquid chromatography with a fixed-wavelength UV detector. A batch of samples is used as the observation matrix. As a result, one obtains both the concentrations and the elution shapes of individual chromatographic peaks.     

HS-6顶空进样器的性能考察及其应用

考察了连接在Sigmal气相色谱仪上的HS-6顶空分析器的性能,特别注意考察了样品的体积,平衡所需时间和分流比等对保留时间和峰高的影响,研究结果还表明增加样品的加热温度和稀释样品的浓度会改善测定的灵敏度,文章还给出了一系列不同类型样品的应用结果,包括香烟、茶叶、啤酒、中药等。     

结构相角二阶代数式的应用：Ⅱ.正交空间群二阶式及其应用

以作者在前文中提出的单相角二阶代数式的推导方法为依据,在完成三斜、单斜空间群推导结果的基础上,进而又完成了正交晶系59个空间群二阶式的推导,从而提供了低级晶系(三斜、单斜和正交)全部74个空间群的简明、完备的二阶代数式运算用表。对三个晶体结构进行了相角估算,结果较好。文中提出了代数法应用的新特点,即“一种类型相角可用多种二阶式求得,多种类型相角也可用一种二阶式求算”。     

DCE-MRI定量参数对子宫内膜癌的诊断价值及与临床病理因素的相关性

本文选取了子宫内膜癌患者108例作为观察组,另选取子宫内膜良性病变患者105例作为对照组,均行DCE-MRI检查后发现,观察组容量转移常数(Ktrans)、速率常数(Kep)、血管外细胞外间隙容积比值(Ve)高于对照组(P＜0.05);Ktrans、Kep、Ve值联合诊断子宫内膜癌的曲线下面积(AUC)为0.841;K...     

氧化石墨阳离子交换容量测定过程中结构的变化

氧化石墨(GO)结构层上的碳羟基(―C―OH)和边缘羧基(―COOH)在水介质中发生质子化反应解离出的H+具有阳离子可交换性。实验采用甲醛缩合法测量了GO的阳离子交换容量(CEC),用X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱和X射线光电子能谱(XPS)分析测试手段对GO阳离子交换过程中间产物的结构变化进行了分析。结果表明,GO的CEC高达541.48 mmol/100 g。NH_4~+和Ca~(2+)交换后的GO,保持稳定的层状结构,c轴方向层间距分别增大了0.1499和0.2905 nm。NH_4+和Ca~(2+)主要以层间可交换阳离子形式存在于层间域中,并与水分子形成可交换水化阳离子层,部分以[NH_4(H_2O)_6]+和[Ca(H_2O)_6]_2+的形式存在于结构层的边缘附近,共同平衡结构层水解产生的负电荷。     

老年人彩度对比敏感度函数研究及滤波应用

为研究老年人彩色视觉频率响应特性，获取彩度对比敏感度与空间频率之间的函数关系，本文在LCH均匀颜色空间基础上，固定明度和色调角值，以彩度作为变量，设计人眼彩度对比敏感度实验，进行人眼视觉观察实验。获得彩度对比敏感度与空间频率的关系，并构建指数型对比敏感度函数模型。经分析表明老年人眼彩度对比敏感度随着空间频率的增加，产生先升高再缓慢降低的变化，各色调角下彩度对比度存在差异。经分析人眼对比敏感度差异与人眼视觉辨色特性有很大的相关性。并且，将构建的对比敏感度函数模型用于实现基于人眼视觉系统的滤波处理。     

非典型发光化合物的簇聚诱导发光

不含大共轭结构的非典型发光化合物因其理论研究的重要性和潜在应用前景引起研究者的广泛关注。非典型发光化合物的结构通常含有N、O、S、P等杂原子,C≡N、C=O、C=C等不饱和单元,及相应的组合功能团(如羟基、胺基、酯基、酐、酰胺、脲基、肟基、砜基等)。近年来,尽管这一领域正快速发展,其发光机理仍存争议。前期,我们提出了簇聚诱导发光(CTE)机理,即含π电子和/或孤对(n)电子的非典型生色团的簇聚及其带来的空间共轭使体系离域扩展,构象刚硬化;同时,其他分子内/间相互作用也有利于簇生色团的刚硬化,从而易于受激发射。基于CTE机理,本文综述了非典型发光化合物的发光特性,包括浓度增强发光、聚集诱导发光(AIE)、激发波长依赖性及磷光发射。CTE机理可合理解释天然产物、合成化合物、生物分子等不同体系的光物理行为,并可用来指导发现和设计新的非典型发光化合物。本文总结了上述不同体系的发展,并对未来研究进行了展望。     

Atomic electron-pair distances and subshell radii in position and momentum space

For the 53 neutral atoms from He to Xe in their ground states, the average distances < u> _{n l , n ′ l ′} in position space and < v> _{n l , n ′ l ′} in momentum space between an electron in a subshell nl and another electron in a subshell n ^′ l ^′ are studied, where n and l are the principal and azimuthal quantum numbers of an atomic subshell, respectively. Analysis of 1700 subshell pairs shows that the electron-pair distances < u> _{n l , n ′ l ′} in position space have an empirical but very accurate linear correlation with a one-electron quantity U _{n l , n ′ l ′}≡L _r +S _r ²/(3L _r ), where L _r and S _r are the larger and smaller of subshell radii < r> _{n l} and < r> _{n ′ l ′}, respectively. The correlation coefficients are never smaller than 0.999 for the 66 different combinations of two subshells appearing in the 53 atoms. The same is also true in momentum space, and the electron-pair momentum distances < > _{n l , n ′ l ′} have an accurate linear correlation with a one-electron momentum quantity V _{n l , n ′ l ′}≡L _p +S _p ²/(3L _p ), where L _p and S _p are the larger and smaller of average subshell momenta < p> _{n l} and < p> _{n ′ l ′}, respectively. Trends in the proportionality constants between < u> _{n l , n ′ l ′} and U _{n l , n ′ l ′} and between < > _{n l , n ′ l ′} and V _{n l , n ′ l ′} are discussed based on a hydrogenic model for the subshell radial functions. Received: 8 April 1998 / Accepted: 6 July 1998 / Published online: 18 September 1998