Understanding the Effect of Crystalline Structural Transformation for Lead-Free Inorganic Halide Perovskites

Lead-free inorganic halide perovskites have triggered appealing interests in various energy-related applications including solar cells and photocatalysis. However, why perovskite-structured materials exhibit excellent photoelectric properties and how the unique crystalline structures affect the charge behaviors are still not well elucidated but essentially desired. Herein, taking inorganic halide perovskite Cs₃Bi₂Br₉ as a prototype, the significant derivation process of silver atoms incorporation to induce the structural transformation from Cs₃Bi₂Br₉ to Cs₂AgBiBr₆, which brings about dramatic differences in photoelectric properties is unraveled. It is demonstrated that the silver incorporation results in the co-operated orbitals hybridization, which makes the electronic distributions in conduction and valence bands of Cs₂AgBiBr₆ more dispersible, eliminating the strong localization of electron–hole pairs. As consequences of the electronic structures derivation, exhilarating changes in photoelectric properties like band structure, exciton binding energy, and charge carrier dynamics are verified experimentally and theoretically. Using photocatalytic hydrogen evolution activity under visible light as a typical evaluation, such crystalline structure transformation contributes to a more than 100-fold enhancement in photocatalytic performances compared with pristine Cs₃Bi₂Br₉, verifying the significant effect of structural derivations on the exhibited performances. The findings will provide evidences for understanding the origin of photoelectric properties for perovskites semiconductors in solar energy conversion.     

open GL几何变换与Windows屏幕坐标转换的研究

分析openGL三维图形显示流程,讨论其坐标变换过程,推导了openGL坐标与Windows屏幕坐标的转换关系,给出了在MFC下实现openGL图形编程的方法。     

Euclidism and Theory of Architecture

Michele Sbacchi examines the impact of the discipline of Euclidean geometry upon architecture and, more specifically, upon theory of architecture. Special attention is given to the work of Guarino Guarini, the seventeenth century Italian architect and mathematician who, more than any other architect, was involved in Euclidean geometry. Furthermore, the analysis shows how, within the realm of architecture, a complementary opposition can be traced between what is called “Pythagorean numerology” and “Euclidean geometry”. These two disciplines epitomized two overlapping ways of conceiving architectural design.     

基于AutoCAD平台的六自由度并联机器人

本文研究基于AutoCAD平台的六自由度并联机器人在姿态给定情况下工作空间(即位置工作空 间)的几何确定方法,该方法以机器人的运动学反解为基础,得出Stewart并联机器人和6-R TS并联机器人位置工作空间的边界方程,从而得出Stewart并联机器人的位置工作空 间是6个球体的交集,6-RTS并联机器人在姿态给定时其工作空间是6个相同的规则曲面体 的交集．基于AutoCAD平台,其交集以及交集的容积可以很容易的得出,该方法是确定六自 由度并联机器人工作空间的一种简单、有效方法．     

Recursive operations in image algebra

The image algebra, developed by Ritter et al. at the University of Florida, is an algebraic structure for image processing. The three commonly used high-level image-template operations provided by the image algebra are the generalized convolution , the additive maximum or generalized lattice convolution {ie23-1}, and the multiplicative maximum {ie23-2}. These are used to realize various nonrecursive image transformations, including morphological transformations. Along with nonrecursive transformations, a class of recursive transformations, such as IIR filters, adaptive dithering, and predictive coding, are also widely used in signal and image processing. In this paper the notions of recursive templates and recursive template operations are introduced; these allow the image algebra to express a set of linear and nonlinear recursive transformations. Algebraic properties of these recursive operations are given, providing a mathematical basis for recursive template composition and decomposition. Finally, applications of recursive template operations in specifying some image processing algorithms are presented.     

Cubic-to-Tetragonal (t') Transformation in Zirconia-Containing Systems

The coexistence of the cubic fluorite and tetragonal phases in rapidly quenched samples was studied in the ZrO₂-MO_1.5 systems for M = Sc, In, Y, and rare earths (R). Spontaneous transformation from metastable cubic phase was triggered at room temperature by a mechanical force. Isolated tetragonal platelets in the cubic matrix were bounded by [101] habit planes and contained anti-phase boundaries. The tetragonality decreased with stabilizer content and vanished at around 18 mol% for M = Y and R, 23 mol% for M = Sc, and 25 mol% for M = In, all at room temperature. With increasing temperature, the tetragonality initially increased because of anisotropic thermal expansion, then decreased rapidly, after reaching a maximum, as the temperature for the tetragonal-to-cubic transformation was approached. Being a first-order martensitic transformation, the cubic-to-tetragonal transformation is accompanied by a discontinuous change of tetragonality and a hysteresis loop as the temperature or composition passes through the equilibrium value.