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排序方式: 共有302条查询结果,搜索用时 15 毫秒
1.
J. Kircher M. Cardona M. Alouani S. Gopalan O. Jepsen O. K. Andersen
E. Kaldis
J. Karpinski S. Rusieki 《Physica C: Superconductivity and its Applications》1992,200(3-4):413-417We report results of ellipsometric measurements of the dielectric tensor of YBa2Cu4O8 as well as calculations employing density functional theory in the local density approximation (LDA). For the computation of the one-electron eigenvalues and states the linear-muffin-tin-orbital method (LMTO) was used. Measured and calculated results show good agreement. In particular, the calculation predicts different band structures for YBa2Cu3O7 and YBa2Cu4O8 in the vicinity of the Fermi energy which lead to significant differences in the optical spectra. One such difference is a region of small ε2 in the near infrared which is a fingerprint of the high (relative to the top of the highest fully occupied band) Fermi energy as compared to the situation in YBa2Cu3O7. Our experimental results confirm the theoretical findings. 相似文献
2.
3.
Padma Gopalan Xuefa Li Mingqi Li Christopher K. Ober Chad P. Gonzales Craig J. Hawker 《Journal of polymer science. Part A, Polymer chemistry》2003,41(22):3640-3656
A modular approach has been developed for the synthesis of rod–coil block copolymers involving the initial preparation of a macroinitiator based on the rod block followed by the growth of the coil segment with living free-radical procedures. The key feature of this strategy is the utilization of an alkoxyamine group from the beginning of the synthesis, which serves as a solubilizing group and ensures that each rod block contains a single initiating fragment. Using this approach permits block copolymers based on insoluble biphenyl ester oligomers to be conveniently prepared with coil segments that range from styrenes to acrylates to 1,3-dienes. The tendency of the rod segments to crystallize is strongly dependent on the weight fraction of the rod segment and the chemical nature of the coil segment. Rod–coil molecules containing at least 25–35 wt % polystyrene or poly(n-butyl acrylate) coil segments show a two-dimensional hexagonal arrangement of rod aggregates, as characterized by transmission electron microscopy and small-angle X-ray scattering. Polyisoprene block copolymers exhibit a lamellar microstructure with short rigid domains in which the rod units lie in an interdigitated smectic C arrangement. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3640–3656, 2003 相似文献
4.
A. Gopalan S. Paulrajan S. Vaidyanathan K. Venkatarao N.R. Subbaratnam 《European Polymer Journal》1984,20(10):971-973
The kinetics of polymerization of acrylamide initiated by potassium peroxomonosulphate, in the presence and absence of Ag+, were studied. Rates of polymerization and oxone disappearance were followed. From the rate law for the polymerization, a mechanism has been proposed. 相似文献
5.
Santhosh P Gopalan A Vasudevan T 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(7):1427-1439
UV-visible spectroelectrochemical studies on copolymerization of diphenylamine (DPA) with ortho-methoxy aniline (OMA) were carried out for different feed ratios of DPA and OMA using indium tin oxide (ITO)-coated glass as working electrode. The UV-visible spectra show clear dependencies on the molar feed composition of DPA or OMA used in electropolymerization. Derivative cyclic voltabsorptogram (DCVA) was deduced at the wavelengths corresponding to the absorption by the intermediate species and used to confirm the intermediates generated during the electropolymerization. The composition of DPA and OMA in the copolymer for the copolymers synthesized with different molar feed ratios of DPA and OMA was determined by UV-visible spectroscopy. Reactivity ratios of DPA and OMA were deduced by using Fineman-Ross and Kelen-Tudos methods and correlated with spectroelectrochemical results. 相似文献
6.
L. Mandelkern J. Michael Price M. Gopalan J. G. Fatou 《Journal of Polymer Science.Polymer Physics》1966,4(3):385-400
Replicas of fracture surfaces of fractions of linear polyethylene, which were crystallized at elevated temperatures for extended time periods, were examined by electron microscopy. Striated. lamella-type crystallites were observed for all molecular weights over the range 3.2 × 103?5.7 × 105. In agreement with Anderson's previous report, for molecular weights of 12,000 or less, the crystallite thicknesses were comparable to the extended chain length. As the molecular weight increased above this level, however, the crystallite sizes increased only slightly and hence at high molecular weights were very much smaller than the extended chain length. From the measured melting temperatures, crystallite interfacial free energies were calculated from the theory for the melting of finite size crystals comprised of chains of finite length. The crystallite interfacial free energy was found to increase with molecular weight. Based on these results, a crystallization process is outlined which allows for the formation of either extended chain crystallites, or crystallites whose size is much smaller than the extended chain length without any change in nucleation mechanism or arbitrary adjustment in growth mechanism with molecular weight. 相似文献
7.
Methods for concentrating dilute fluids using adsorption followed by partial thermal regeneration were studied using the simulation package ADSIM. The systems studied were NaCl in liquid water on Amberlite XD-2 resin and benzene vapor in nitrogen on activated carbon. Cycles studied included counter-current regeneration with pure hot fluid, co-current regeneration with pure hot fluid, a new process called Hot Feed Addition (HFA) consisting of co-current regeneration with pure hot fluid followed by hot feed, and cycling zone adsorption (co-current alternating hot and cold feeds with no pure regeneration fluid). The optimum system depends upon the conditions of the system and the value function chosen to evaluate the systems. For example, for benzene in nitrogen with hot regeneration gas at 467.4 K, cycling zone adsorption used no carrier gas, had the most concentrated benzene stream and a very pure nitrogen product, but the energy use was greater than the other processes. For liquid systems counter-current operation could produce the purest product, but regenerant requirements were high. With slightly lower purity requirements HFA reduced solvent usage and increased the concentration of the concentrated waste stream. For the liquid system all processes used approximately 3% or less of the energy that would be required for evaporation. 相似文献
8.
Star-shaped azo-based dipolar chromophores: design, synthesis, matrix compatibility, and electro-optic activity 总被引:1,自引:0,他引:1
Gopalan P Katz HE McGee DJ Erben C Zielinski T Bousquet D Muller D Grazul J Olsson Y 《Journal of the American Chemical Society》2004,126(6):1741-1747
Three new azo-benzene-based push-pull chromophores with dendritic architecture were synthesized as active materials for electro-optic applications. These chromophores were synthesized in six or seven synthetic steps with an overall yield of around 80% per step and high purity. UV-vis spectroscopy showed significant influence of the transient dipole moment on the observed r(33) values. The chromophores were stable to photochemical oxidation in ambient light and air. The electrical poling conditions were optimized for each chromophore as the T(g) of the composite material varied significantly. The highest EO coefficient achieved was 22-25 pm/V at 1550 nm wavelength. STEM analysis of the blends enabled the correlation of the activity of these large chromophores with the blend morphology. An amorphous polycarbonate host effectively disperses the chromophores in 2-20 nm aggregates in the active materials. However, macrophase separation into 200-500 nm aggregates was observed in a methacrylate host matrix. 相似文献
9.
2-{[1-(3,4-Dihydroxyphenyl)methylidene]amino}benzoic acid (DMABA) was loaded on Amberlite XAD-16 (AXAD-16) via azo linker and the resulting resin AXAD-16-DMABA explored for enrichment of Zn(II), Mn(II), Ni(II), Pb(II), Cd(II), Cu(II), Fe(III) and Co(II). The optimum pH values for extraction are 6.5-7.0, 5.0-6.0, 5.5-7.5, 5.0-6.5, 6.5-8.0, 5.5-7.0, 4.0-5.0 and 6.0-7.0, respectively. The sorption capacity was found between 97 and 515 μmol g−1 and the preconcentration factors from 100 to 450. Tolerance limits for foreign species are reported. The kinetics of sorption is fast as t1/2 is ≤5 min. The chelating resin can be reused for 50 cycles of sorption-desorption without any significant change (<1.5%) in the sorption capacity. The limit of detection values (blank +3 s) are 1.12, 1.38, 1.76, 0.67, 0.77, 2.52, 5.92 and 1.08 μg L−1 for Zn(II), Mn(II), Ni(II), Pb(II), Cd(II), Cu(II), Fe(III) and Co(II), respectively. The enrichment on AXAD-16-DMABA coupled with monitoring by flame atomic absorption spectrometry (FAAS) is used to determine all the metal ion ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples. 相似文献
10.
A novel series of complexes of the type [M(TML)X2]; where TML is a tetradentate macrocyclic ligand; M = Co(II), Ni(II), Cu(II) or Zn(II); X = Cl−, CH3COO− or NO
3
−
have been synthesized by template condensation of benzil and thiocarbohydrazide in the presence of divalent metal salts in
methanolic medium. The complexes have been characterized with the help of elemental analyses, conductance measurements, molecular
weight determination, magnetic measurements, electronic, NMR, infrared and far infrared spectral studies. Electronic spectra
along with magnetic moments suggest the six coordinate octahedral geometry for these complexes. The low value of molar conductance
indicates them to be non-electrolytes. The biological activities of metal complexes have been tested in vitro against a number of pathogenic bacteria to assess their inhibiting potential. 相似文献