Dielectric properties Ca-substituted barium strontium titanate ferroelectric ceramics

The dielectric and ferroelectric properties of Ba_1−xSr_xTiO₃ (BST) (x=0.10,0.20,0.30,0.40 and 0.60) ceramics and Ba_1−2xSr_xCa_xTiO₃ (BSCT) (x=0.10,0.20,0.30) ceramics have been investigated. The low temperature phase transitions of BST ceramics vanish after Ca²⁺ substitution while the high temperature transition is diffused and relaxed, which becomes more obvious with increasing x. Ca²⁺ substitution obviously decreases the dielectric constant maximum, K_m, of BST ceramics and changes the temperature of dielectric constant maximum, T_m, of BST ceramics. The shift of T_m in BST is attributed mainly to the Sr²⁺ and Ba²⁺ concentration. BST ceramics exhibit almost normal ferroelectric characteristics, while a typical relaxor behavior was observed in BSCT ceramics. The relaxor behavior observations may be understood by a random electric field induced domain state.     

Spatial symmetry of head-related transfer function

Methods for analyzing the spatial symmetry of head-related transfer function (HRTF) are proposed. The influences of anatomical structures on the symmetry of HRTF are investigated using HRTFs measured on KEMAR mannequin and human subjects. Results show that for KEMAR mannequin, pinnae destroy the front-back symmetry of HRTF above 5 to 6 kHz, while for human subjects the frequency reduces to 2.5 kHz because of the locations of ears. Furthermore, at low and median frequencies, HRTF is approximately left-right symmetrical. While as frequencies increase, the asymmetry caused by the fine anatomical leftright differences appears. The starting frequency and the extent of the left-right asymmetry in HRTF depend on individuals. The analyses demonstrate the spatial symmetrical characteristics of HRTF and the frequency ranges in which the current binaural models are valid.     

Synthesis and Characterization of Heterobimetallic Aluminum‐Germanium(IV) Disulfides

Three heterobimetallic aluminum‐germanium(IV) disulfides are synthesized. The reaction of {LAl[(SLi)₂(THF)₂]}₂ ( 1 ) (L = HC(CMeNAr)₂, Ar = 2,6‐iPr₂C₆H₃) with Ph₂GeCl₂, Me₂GeCl₂, and GeCl₄, respectively, in THF afforded LAl(μ‐S)₂GePh₂ ( 2 ), LAl(μ‐S)₂GeMe₂ ( 3 ) and LAl(μ‐S)₂Ge(μ‐S)₂AlL ( 4 ) in good yields. Compounds 2 , 3 and 4 were investigated by elemental analysis, NMR, EI‐MS and 3 was also characterized by single crystal X‐ray structural analysis.     

Assessing the Apparent Effective Thickness of the Supported Hybrid Bilayer Membranes Consisting of Octadecanethiol and Phospholipid by ac Impedance Spectroscopy

The electrochemical behavior of the gold electrode modified by hybrid bilayer membranes in different concentrations of Fe(CN)₆^3?/Fe(CN)₆^4? was investigated by electrochemical impedance spectroscopy and cyclic voltammetry technology. The electron transfer between gold and the redox species separated by the hybrid bilayers assembly was completed by an electron tunneling process. A detailed equivalent circuit for electron transport across the HBMs is proposed. It was found that the apparent effective thickness of the hybrid bilayer membranes was lower than that of the sum of the chain length of octadecanethiol and phospholipid so some possible collapsed sites might exist at the hybrid bilayer membranes.     

计算机辅助教学在分析化学课堂上的应用

利用PowerPoint、Flash软件制作电子课件，谈计算机辅助课堂教学的几种技巧。     

CE with Field-Enhanced Stacking for Rapid and Sensitive Determination of Umbelliferone, Rutin and Aesculetin in Prunella vulgaris

A new capillary electrophoresis procedure with field-enhanced stacking concentration for the analysis of umbelliferone, rutin and aesculetin in Prunella vulgaris is established for the first time. After optimization of the separation and concentration conditions, the three analytes can be separated within 6 min and quantified with high sensitivity. The method was useful for qualitative and quantitative analysis of umbelliferone, rutin and aesculetin in Prunella vulgaris with recovery of 97.5 to 105.3%.     

Electrochemistry of Mitochondria: A New Way to Understand Their Structure and Function

In this article, electrochemistry of mitochondria is achieved. Cyclic voltammograms of freshly prepared mitochondria were obtained by immobilizing mitochondria together with glutaraldehyde and bovine serum albumin on the surface of a pyrolytic graphite electrode. Two pairs of redox peaks could be observed which were ascribed to the electron transfer reactions of cytochrome c and FAD/FADH₂. Study of submitochondrial particles was also conducted, which could confirm the results of the study of the entire mitochondria. The redox wave of NADH could be obtained due to the destruction of the membrane of mitochondria. We have also checked the function of succinate in mitochondria by employing the electrochemical method. This work is not only the first to be able to obtain the direct electrochemistry of mitochondria, but is also beneficial to the further understanding of the structure and function of mitochondria in vitro.     

根据性质对误差进行分类的一种新观点

根据误差的性质，针对仍广泛使用的“偶然误差和系统误差”、“随机误差和系统误差”等分类方法，本文提出了新的“随机误差和非随机误差”的误差分类方法     

Reaction mechanism of hydrogen cyanide catalyzed by gas‐phase titanium

To explore the details of the reaction mechanism of Ti atom with HCN, the reactive site and reactivity have been predicted first, the potential energy surfaces have been systematically studied at different theoretical levels. Four different reaction pathways and product distribution are discussed by means of the activation strain model and Curtin–Hammett principle. In addition, the structures, bonding properties and the frontier molecular orbital interaction diagrams of main stationary points were analyzed by atoms in molecules and natural bond orbital. The results show that for this system, there are four reaction pathways, in which path b (HCN＋Ti→IM1→TS1→IM2→T2b→IM4) is the most favorable pathway.     

Crystal Structures of Bacterial (6‐4) Photolyase Mutants with Impaired DNA Repair Activity

PhrB from Agrobacterium fabrum is the first prokaryotic photolyase which repairs (6‐4) UV DNA photoproducts. The protein harbors three cofactors: the enzymatically active FAD chromophore, a second chromophore, 6,7‐dimethyl‐8‐ribityllumazine (DMRL) and a cubane‐type Fe‐S cluster. Tyr424 of PhrB is part of the DNA‐binding site and could provide an electron link to the Fe‐S cluster. The PhrB_Y424F mutant showed reduced binding of lesion DNA and loss of DNA repair. The mutant PhrB_I51W is characterized by the loss of the DMRL chromophore, reduced photoreduction and reduced DNA repair capacity. We have determined the crystal structures of both mutants and found that both mutations only affect local protein environments, whereas the overall fold remained unchanged. The crystal structure of PhrB_Y424F revealed a water network extending to His366, which are part of the lesion‐binding site. The crystal structure of PhrB_I51W shows how the bulky Trp leads to structural rearrangements in the DMRL chromophore pocket. Spectral characterizations of PhrB_I51W suggest that DMRL serves as an antenna chromophore for photoreduction and DNA repair in the wild type. The energy transfer from DMRL to FAD could represent a phylogenetically ancient process.