In this paper we study invariant (α, β)-metrics on homogeneous spaces. We first give a method to construct invariant (α, β)-metrics
on homogeneous spaces. Then we obtain some conditions for some special type of (α, β)-metrics to be of Berwald type and Douglas
type. At last, we give a rigidity result concerning the Randers metrics and Matsumoto metrics of Berwald type on homogeneous
spaces.
Members of LPMC and supported by NSFC (no. 10671096) and NCET of China.
Second author was corresponding author.
Authors’ address: Huihui An and Shaoqiang Deng, School of Mathematical Sciences, Nankai University, Tianjin, 300071, People’s
Republic of China 相似文献
Structural and infrared-to-visible upconversion fluorescence properties of Er3+/Yb3+-codoped oxychloride lead-germanium-bismuth glass have been studied. The Raman spectrum investigation indicates that PbCl2 plays an important role in the formation of glass network, and has an important influence on the upconversion luminescence owing to lower phonon energy. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2, respectively, were observed at room temperature. The quadratic dependence of the 525, 546, and 657 nm emissions on excitation power indicates that a two-photon absorption process occurs under 975 nm excitation. 相似文献
Novel structures of H2C?C?CLiX (X ? F, Cl) were determined using HF/STO-3G gradient method. Both of the carbenoids have two equilibrium structures, askew and linear forms, at the level of calculation. In the case X?F, the former is more stable, but in the case X=Cl, the latter is more stable. The frontier MOs are given and analyzed. 相似文献
Though siRNA-based therapy has achieved great progress, efficient siRNA delivery remains a challenge. Here, we synthesized a copolymer PAsp(-N=C-PEG)-PCys-PAsp(DETA) consisting of a poly(aspartate) block grafted with comb-like PEG side chains via a pH-sensitive imine bond (PAsp(-N=C-PEG) block), a poly(l-cysteine) block with a thiol group (PCys block), and a cationic poly(aspartate) block grafted with diethylenetriamine (PAsp(DETA) block). The cationic polymers efficiently complexed siRNA into polyplexes, showing a sandwich-like structure with a PAsp(-N=C-PEG) out-layer, a crosslinked PCys interlayer, and a complexing core of siRNA and PAsp(DETA). Low pH-triggered breakage of pH-sensitive imine bonds caused PEG shedding. The disulfide bond-crosslinking and pH-triggered PEG shedding synergistically decreased the polyplexes’ size from 75 nm to 26 nm. To neutralize excessive positive charges and introduce the targeting ligand, the polyplexes without a PEG layer were coated with an anionic copolymer modified with the targeting ligand lauric acid. The resulting polyplexes exhibited high transfection efficiency and lysosomal escape capacity. This study provides a promising strategy to engineer the size and surface of polyplexes, allowing long blood circulation and targeted delivery of siRNA. 相似文献
A series of Cr-doped Li3V2 − xCrx(PO4)3 (x = 0, 0.1, 0.25, and 0.5) samples are prepared by a sol–gel method. The effects of Cr doping on the physical and chemical characteristics of Li3V2(PO4)3 are investigated. Compared with the XRD pattern of the undoped sample, the XRD patterns of the Cr-doped samples have no extra reflections, which indicates that Cr enters the structure of Li3V2(PO4)3. As indicated by the charge–discharge measurements, the Cr-doped Li3V2 − xCrx(PO4)3 (x = 0.1, 0.25, and 0.5) samples exhibit lower initial capacities than the undoped sample at the 0.2 C rate. However, both the discharge capacity and cycling performance at high rates (e.g., 1 and 2 C) are enhanced with proper amount of Cr doping (x = 0.1). The highest discharge capacity and capacity retention at the rates of 1 and 2 C are obtained for Li3V1.9Cr0.1(PO4)3. The improvement of the electrochemical performance can be attributed to the higher crystal stability and smaller particle size induced by Cr doping.
Isomerizations of cyclobutylidene 1 to methylenecyclopropane 2 , cyclobutene 3 and bicyclobutane 4 have been studied using ab initio method. Equilibrium and transition structures are fully optimized with 3–21G basis set. The reaction barriers are 78, 75 and 110 kJ/mol at 6–31 G**, respectively, 1→2 occurs via the outward disrotation of two end C-C bonds, 1→3 via the attack of an exo hydrogen to the carbene p AO before the transition state, and 1→4 is unable to compete with 1→2 and 1→3 for its higher barrier. 相似文献