北京及河北植物新记录(Ⅲ)

报道了北京植物新记录共计14种,它们是西伯利亚滨藜(Atriplex sibirica)、球序卷耳(Cerastium glomeratum)、细叶地榆(Sanguisorba tenuifolia)、大地锦(Euphorbia nutans)、宽苞水柏枝(Myricaria bracteata)、蒙山附地菜(Trygonotis tenera)、刺萼龙葵(Solanum rostratum)、墨苜蓿(Richardia scabra)、盖裂果(Mitracarpus villosus)、伞房花耳草(Hedyotis corymbosa)、钻形紫菀(Aster sublatus)、野塘蒿(Coniza bonariensis)、龙爪茅(Datyloctenium aegypticum)和虮子草(Leptochloa panicea),其中水柏枝属(Myricaria)、墨苜蓿属(Richardia)和盖裂果属(Mitracarpus)为北京新纪录属,除西伯利亚滨藜、宽苞水柏枝外有12种也为河北植物区系新记录.     

Structure determination of homoleptic AuI, AgI, and CuI aryl/alkylethynyl coordination polymers by X-ray powder diffraction

This article describes the structure determination of five homoleptic d(10) metal-aryl/alkylacetylides [RC triple bond CM] (M=Cu, R=tBu 1, nPr 2, Ph 3; R=Ph, M=Ag 4; Au 5) by using X-ray single-crystal and powder diffraction. Complex 1.C6H6 reveals an unusual Cu20 catenane cluster structure that has various types of tBuC triple bond C-->Cu coordination modes. By using this single-crystal structure as a starting model for subsequent Rietveld refinement of X-ray powder diffraction data, the structure of the powder synthesized from CuI and tBuC triple bond CH was found to have the same structure as 1. Complex 2 has an extended sheet structure consisting of discrete zig-zag Cu4 subunits connected through bridging nPrC triple bond C groups. Complex 3 forms an infinite chain structure with extended Cu-Cu ladders (Cu-Cu=2.49(4)-2.83(2) A). The silver(I) congener 4 is iso-structural to 3 (average Ag-Ag distance 3.11 A), whereas the gold(I) analogue 5 forms a Au...Au honeycomb network with PhC triple bond C pillars (Au-Au=2.98(1)-3.26(1) A). Solid-state properties including photoluminescence, nu(C triple bond C) stretching frequencies and thermal stability of these polymeric systems are discussed in the context of the determined structures.     

Structure and superconductivity in FexCu1−xBa2YCu2O7+y superconductors synthesized by high pressure

Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Mössbauer effect have been made on Fe_xCu_1−xBa₂YCu₂O_7+y superconductors (0.00≤x≤0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Mössbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuO_x chains have fivefold-oxygen coordination. These are important reasons for the enhancement of T_c in the HP-samples.     

ZnSe/SiO2复合薄膜光学常数与荧光光谱的研究

采用溶胶-凝胶工艺与原位生长技术，制备了ZnSe/SiO₂复合薄膜.X射线衍射分 析表明薄膜中ZnSe晶体呈立方闪锌矿结构.X射线荧光分析结果显示薄膜中Zn与Se摩尔比为1 ∶1.01—1∶1.19.利用场发射扫描电子显微镜观察了复合薄膜的表面形貌，结果表明复合薄 膜表面既存在尺寸约为400nm的ZnSe晶粒，也存在尺寸小于100nm的ZnSe晶粒.利用椭偏仪测 量了薄膜椭偏角Ψ，Δ与波长λ的关系，采用Maxwell-Garnett有效介质理论对薄膜的光学 常数、厚度、气孔率、ZnS 关键词： 2复合薄膜')" href="#">ZnSe/SiO₂复合薄膜 光学性质 椭偏光度法 荧光光谱     

Recent progress and new challenges in isospin physics with heavy-ion reactions

The ultimate goal of studying isospin physics via heavy-ion reactions with neutron-rich, stable and/or radioactive nuclei is to explore the isospin dependence of in-medium nuclear effective interactions and the equation of state of neutron-rich nuclear matter, particularly the isospin-dependent term in the equation of state, i.e., the density dependence of the symmetry energy. Because of its great importance for understanding many phenomena in both nuclear physics and astrophysics, the study of the density dependence of the nuclear symmetry energy has been the main focus of the intermediate-energy heavy-ion physics community during the last decade, and significant progress has been achieved both experimentally and theoretically. In particular, a number of phenomena or observables have been identified as sensitive probes to the density dependence of nuclear symmetry energy. Experimental studies have confirmed some of these interesting isospin-dependent effects and allowed us to constrain relatively stringently the symmetry energy at sub-saturation densities. The impact of this constrained density dependence of the symmetry energy on the properties of neutron stars have also been studied, and they were found to be very useful for the astrophysical community. With new opportunities provided by the various radioactive beam facilities being constructed around the world, the study of isospin physics is expected to remain one of the forefront research areas in nuclear physics. In this report, we review the major progress achieved during the last decade in isospin physics with heavy ion reactions and discuss future challenges to the most important issues in this field.     

二维正方格子磁性光子晶体的界面传导模

采用平面波展开加超元胞方法计算了二维正方格子磁性光子晶体的光子带隙结构，其中散射子的形状分别为长方形，正方形，六角形和圆形.结果表明绝对带隙宽度和其宽高比远大于同种结构的非磁性光子晶体.在此基础上，构成了混合型异质结，并计算了相应的传导模，发现了理想的界面传导模，而且当磁性散射子为长方形、圆形、六角形散射子时产生传导模都不需要晶格畸变，这也是磁性光子晶体异质结所具备的优点. 关键词： 光子晶体 光子带隙结构 传导模     

Tetradentate Gold(III) Complexes as Thermally Activated Delayed Fluorescence (TADF) Emitters: Microwave-Assisted Synthesis and High-Performance OLEDs with Long Operational Lifetime

Structurally robust tetradentate gold(III)-emitters have potent material applications but are rare and unprecedented for those displaying thermally activated delayed fluorescence (TADF). Herein, a novel synthetic route leading to the preparation of highly emissive, charge-neutral tetradentate [C^C^N^C] gold(III) complexes with 5-5-6-membered chelate rings has been developed through microwave-assisted C−H bond activation. These complexes show high thermal stability and with emission origin (³IL, ³ILCT, and TADF) tuned by varying the substituents of the C^C^N^C ligand. With phenoxazine/diphenylamine substituent, we prepared the first tetradentate gold(III) complexes that are TADF emitters with emission quantum yields of up to 94 % and emission lifetimes of down to 0.62 μs in deoxygenated toluene. These tetradentate Au^III TADF emitters showed good performance in vacuum-deposited OLEDs with maximum EQEs of up to 25 % and LT₉₅ of up to 5280 h at 100 cd m⁻².     

Infrared characterization of hydroxyl groups on MgO: a periodic and cluster density functional theory study

The infrared OH stretching frequencies of the various types of hydroxyl groups on MgO surfaces have been calculated by periodic (VASP) and cluster (Gaussian) DFT simulations. Surface irregularities (mono and diatomic steps, corners, step divacancies, and kinks) have been considered to model the IR spectra of hydroxylated MgO powders. A good correspondence between calculated and experimental frequencies is obtained with the B3LYP functional. Hydrogen-bonding is the parameter which influences most the IR frequency of OH groups, followed by location of OH groups in concave or convex areas of the surface and then oxygen coordination. The evolution of experimental IR spectra upon evacuation at increasing temperature can be rationalized on the basis of calculated thermal stabilities of each kind of OH groups. A new model is finally proposed to help assign the experimental bands, in terms of hydrogen-bonding, local topology of the hydroxylated sites, and coordination of oxygen.     

Structures, photoluminescence, and reversible vapoluminescence properties of neutral platinum(II) complexes containing extended pi-conjugated cyclometalated ligands

Reacting K2PtCl4 with the tridentate R-C(wedge)N(wedge)C-H2 ligands 2,6-di-(2'-naphthyl)-4-R-pyridine (R = H, 1a; Ph, 1b; 4-BrC6H4, 1c; 3,5-F2C6H3, 1d) in glacial acetic acid, followed by heating in dimethyl sulfoxide (DMSO), gave complexes [(R-C(wedge)N(wedge)C)Pt(DMSO)] (2a-d). In the crystal structures of 2a-c, the molecules are paired in a head-to-tail orientation with Pt...Pt separations >6.3 A, and there are extensive close C-H...pi (d = 2.656-2.891 A), pi...pi (d = 3.322-3.399 A), and C-H...O=S (d = 2.265-2.643 A) contacts. [(Ph-C(wedge)N(wedge)C)Pt(PPh3)] (3) was prepared by reacting 2b with PPh3. Reactions of 2a-d with bis(diphenylphosphino)methane (dppm) gave [(R-C(wedge)N(wedge)C)2Pt2(mu-dppm)] (4a-d). Both head-to-head (syn) and head-to-tail (anti) conformations were found for 4a.6CHCl3.C5H12, whereas only one conformation was observed for 4b.2CHCl3 (syn), 4c.3CH2Cl2 (syn), and 4d.2CHCl3 (anti). In the crystal structures of 4a-d, there are close intramolecular Pt...Pt contacts of 3.272-3.441 A in the syn conformers, and long intramolecular Pt...Pt separations of 5.681-5.714 A in the anti conformers. There are weak C-H...X (d = 2.497-3.134 A) and X...X (X = Cl or Br; d = 2.973-3.655 A) interactions between molecules 4a-d and occluded CHCl3/CH2Cl2 molecules, and their solvent channels are of varying diameters (approximately 9-28 A). Complexes 2a-d, 3, and 4a-d are photoluminescent in the solid state, with emission maxima at 602-643 nm. Upon exposure to volatile organic compounds, 4a shows a fast and reversible vapoluminescent response, which is most intense with volatile halogenated solvents (except CCl4). Powder X-ray diffraction analysis of desolvated 4a revealed a more condensed molecular packing of syn and anti complexes than crystal 4a.6CHCl3.C5H12.