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181.
William M. Baker 《International Journal of Theoretical Physics》2006,45(12):2257-2273
We study theories of gravitation that are based on the Einstein – Hilbert action that are not projectively invariant and can therefore completely determine their connections. We are thus lead to the conclusion that the geometry is necessarily Riemann – Cartan and at least the trace part of a torsion field must be present. We examine the consequence of including these torsion fields in cosmological models. Our results differ from those obtained earlier in the Einstein – Cartan – Sciama – Kibble theory. We also consider a model that includes a series of quadratic torsion terms. This series leads to a potential function that has the effect of “turning on” the cosmological constant. This potential function then acts like dark energy. This model also shows that the torsion field can produce an inflationary period.
PACS: 04.02 Cv, 95.30 Sf, 98.80-k 相似文献
182.
Laura L. Tomasevich Stephen M. Zitelli Chelsey R. Gillen Neal J. Baker Jason M. Conley Mari Lynne Starr Patrick J. Carroll 《Tetrahedron letters》2007,48(4):599-602
Condensation of ninhydrin with tryptamide or tryptamine followed by Lewis acid-induced rearrangement provided yohimbanones that were readily converted to β-carbolines via oxidative ring cleavage. The analogous condensation-rearrangement with 3,4-dimethoxyphenethylamine and ninhydrin afforded an oxyprotoberberine, which was further oxygenated at the 13a position. 相似文献
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The structure of the N‐heterocyclic gallium hydride complex, [GaH2I{CN(Mes)C2H2N(Mes)}], Mes = mesityl, shows both hydride ligands to be bonded to the distorted tetrahedral gallium centre. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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187.
Barrie M. Baker 《The Journal of the Operational Research Society》1992,43(10):1009-1012
A recent publication reported improved solutions to two of the standard test problems for vehicle routeing. A modification to an interactive heuristic is reported here, leading to further improvements to the best solutions given for two of these test problems. 相似文献
188.
T. M. Liu H. Q. Xie K. J. O'callaghan A. Rudin W. E. Baker 《Journal of Polymer Science.Polymer Physics》1993,31(10):1347-1362
Blends of t-butylaminoethyl methacrylate grafted polyethylene (PE-g-tBAEMA) with methyl methacrylate-methacrylic acid copolymer (PMMA-MAA) and polymethyl methacrylate (PMMA) were prepared in a Banbury type batch mixer. The effects of component proportions and processing conditions on the melt flow index, morphology, impact, and tensile properties of the resulting polymer blends were investigated. The interfacial chemical reaction was studied using Fourier transform infrared (FTIR) technique. It was observed that the melt index of the blends was reduced with increasing melt processing temperature and mixing time, indicating the formation of PE-g-PMMA block copolymer. New IR bands at 1554, 1628, 1800, and 1019 cm?1 were observed only for PE-g-tBAEMA/PMMA-MAA, the reactive blends, but not for PE-g-tBAEMA/PMMA, the nonreactive blend. These IR bands were attributed to the amide, carboxylate anion and methacrylimide formation resulting from the chemical reaction between the secondary amine on the PE-g-tBAEMA/PMMA moiety and the carboxylic acid on PMMA-MAA segment. The morphology of the blends in various compositions was examined using scanning electron microscopy (SEM) and related to their mechanical properties. All of the blends have a domain structure whose morphology is strongly dependent on the concentration of the dispersed phase. Furthermore, the PE-g-tBAEMA/PMMA-MAA reactive blends were shown to have much finer morphology than the corresponding nonreactive blends. For the reactive polymer blends consisting of brittle particles dispersed in the ductile matrices, the PE-g-tBAEMA/PMMA-MAA, impact and tensile result higher than predicted by the additivity rule were observed. The toughening of polyethylene by PMMA was explained by a “cold-drawing” mechanism. The Young's modulus of the blends and the extent of interfacial adhesion were analyzed with Takayanagi and Sato-Furukawa's theories. © 1993 John Wiley & Sons, Inc. 相似文献
189.
François Cheviré Charles F. Baker Olivier Larcher Christophe Colbeau-Justin 《Journal of solid state chemistry》2006,179(10):3184-3190
A new fluorite-type solid solution domain has been evidenced in the system (1−x) CeO2−x/7 Y6WO12□2 using the amorphous citrate route. All the studied phases (0?x?1) crystallize in a cubic-type symmetry. Diffuse reflectance spectra reveal a strong optical absorption between 380 and 400 nm. All substituted compositions spectral selectivities are estimated suitable for application as inorganic UV absorbers. The non linear variation observed in the optical gap values between Y6WO12 and CeO2 is attributed to the presence of the cerium 4f-block band. Additionally, Time Resolved Microwave Conductivity (TRMC) experiment and phenol photodegradation analyses carried out on the Ce0.81Y0.16W0.03O1.95□0.05 (x=0.19) composition do not indicate any photocalatytic activity for this material. 相似文献
190.
C. W. Baker 《Acta Mathematica Hungarica》2002,94(1-2):45-52
A new weak form of both slight continuity and precontinuity, called slight precontinuity, is developed. It is shown that slight precontinuity is strictly weaker than faint precontinuity and slight continuity. Relationships between slightly precontinuous functions and preconnected sets are investigated. In particular, it is shown that the slightly precontinuous image of a preconnected space is connected. This strengthens a result in the literature. Also, additional properties of these functions are investigated 相似文献