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91.
Social permutation invariant coordinates are introduced describing the bond network around a given atom. They originate from the largest eigenvalue and the corresponding eigenvector of the contact matrix, are invariant under permutation of identical atoms, and bear a clear signature of an order-disorder transition. Once combined with ab initio metadynamics, these coordinates are shown to be a powerful tool for the discovery of low-energy isomers of molecules and nanoclusters as well as for a blind exploration of isomerization, association, and dissociation reactions. 相似文献
92.
A simple variational method is used to determine the modal properties of single-mode couplers and Y junctions when the cores are close together or coalesce. The results complement the well-known perturbation expressions for large core separation. Together the two approximation methods provide accurate approximations over the complete range of separation from infinite separation to complete coalescence. 相似文献
93.
Wawrzyniec Podkoscielny Wanda Kowalewska 《Journal of polymer science. Part A, Polymer chemistry》1984,22(5):1025-1033
Several polythioesters by interfacial polycondensation of 1,4-di(mercaptomethyl)-2,3,5,6-tetramethylbenzene with oxalyl, succinyl, adipoyl, suberoyl, and sebacoyl chlorides were obtained. To determine the optimal conditions for interfacial polycondensation, the influence of the following factors on yield and value of reduced viscosity were studied: type of organic phase, concentration of hydrogen chloride acceptor, the quantitative ratio of aqueous to organic phase, molar ratio of reagents; temperature of reaction, rate of acid chloride addition, and contribution of catalyst. Thorough studies were carried out only for polycondensation of the dithiol with adipoyl and sebacoyl chlorides. The structure of all polythioesters obtained under the model conditions was determined by elementary analysis and infrared spectra. Initial decomposition temperature, mass loss in percentage at the same temperature, maximum rate of decomposition, and mass loss percentage at 100–400°C were defined by thermogravimetric analyses. Chemical resistance of the polythioesters was determined by treatment with some organic solvents, mineral acids (concentrated and 10%), and sodium hydroxide (10 and 50%). Some mechanical and electrical properties of the polythioesters obtained from dithiol and adipoyl and sebacoyl chlorides were determined. The molecular weight was not measured because of the low solubility of the polythioesters. 相似文献
94.
95.
Summary
The behavior of the solutions of a class of perturbed nonlinear second order differential equations is studied where the perturbation term may be unbounded in each of its arguments. Upper and lower bounds for solutions and a nonoscillation theorem are included in the results.Research supported by the Mississippi State University Biological and Physical Sciences Research Institute. 相似文献
96.
Ichimura AS Lew W Allara DL 《Langmuir : the ACS journal of surfaces and colloids》2008,24(6):2487-2493
Infrared reflection spectroscopy (IRS), single wavelength ellipsometry, and density functional theory were used to elucidate the structure of a molecular tripod self-assembled monolayer (SAM) on polycrystalline gold{111} substrates. The tripod SAM was formed by the reaction of SiCl4 with a densely packed monolayer of 2-mercaptoethanol, 6-mercaptohexanol, and 16-mercaptohexadecanol under inert atmosphere. After reaction with SiCl4, IRS spectra show an intense absorption at approximately 1112 cm(-1) that is attributed to Si-O-C asymmetric stretching vibration of a molecular tripod structure. Harmonic vibrational frequencies computed at the B3LYP/6-311+g** level of theory for the mercaptoethanol tripod SAM closely match the experimental IRS spectra, giving further support for the tripod structure. When rinsed with methanol or water, the Si-Cl-terminated SAM becomes capped with Si-OMe or Si-OH. The silanol-terminated tripod SAM is expected to find use in the preparation of thin zeolite and silica films on gold substrates. 相似文献
97.
The first guaian-12-oic acid glucopyranosyl ester was isolated from the roots of Picris rhagadioloides (L.) Desf. (Asteraceae), in addition to five costuslactone-type guaianolides, four germacranolides and three phenolic compounds. This is the first time that the known phenolics syringaldehyde and syringaresinol, as well as the known sesquiterpene lactones glucozaluzanin C, cichorioside C and hypochoeroside A have been described from a Picris species. The compounds were characterized on the basis of physicochemical, 1D- and 2D-NMR spectroscopic, and mass spectrometric data. 相似文献
98.
Wanda Ziemkowska Anna Kubiak Szymon Kucharski Robert Woźniak Romana Anulewicz-Ostrowska 《Polyhedron》2007
Reactions of Me5Al3[OC(C6H5)2C(C6H5)2O]2 (1) with alcohols ROH (R = Me, Et, tBu) in a 1:1 molar ratio afforded the compound Me2Al2[OC(C6H5)2C(C6H5)2O]2(C4H8O) (2) and a mixture of methylaluminum alkoxides. The alcohols acted as the factor formally eliminating a molecule of Me3Al (as a methylaluminum alkoxide) from compound 1. tBu3Al reacted with an equimolar amount of benzopinacol to form the monomeric complex tBuAl[OC(C6H5)2C(C6H5)2O](C4H8O) (3). Reactions of Me3Ga and Me3In with benzopinacol yielded trinuclear complexes Me5M3[OC(C6H5)2C(C6H5)2O]2 (4 (M = Ga), 5 (M = In)), isostructural to compound 1. In the presence of water and alcohols, compounds 4 and 5 underwent a decomposition reaction to benzopinacol and a mixture of metalloxanes and alkoxides. An unusual methylmethoxo indium benzopinacolate Me6In4[OC(C6H5)2C(C6H5)2O]2(OCH3)2 (6) was obtained in the reaction of benzopinacol with Me3In and Me2InOMe in a 1:1:1 molar ratio. Molecular structures of the compounds 3, 4 and 6 were determined by X-ray crystallography. 相似文献
99.
100.
Adamson P Auty DJ Ayres DS Backhouse C Barr G Barrett WL Bishai M Blake A Bock GJ Boehnlein DJ Bogert D Bower C Budd S Cavanaugh S Cherdack D Childress S Choudhary BC Coelho JA Cobb JH Coleman SJ Corwin L Cravens JP Cronin-Hennessy D Danko IZ de Jong JK Devenish NE Diwan MV Dorman M Escobar CO Evans JJ Falk E Feldman GJ Frohne MV Gallagher HR Gomes RA Goodman MC Gouffon P Gran R Grant N Grzelak K Habig A Harris D Harris PG Hartnell J Hatcher R Himmel A Holin A Huang X Hylen J Ilic J Irwin GM 《Physical review letters》2010,105(15):151601
We searched for a sidereal modulation in the MINOS far detector neutrino rate. Such a signal would be a consequence of Lorentz and CPT violation as described by the standard-model extension framework. It also would be the first detection of a perturbative effect to conventional neutrino mass oscillations. We found no evidence for this sidereal signature, and the upper limits placed on the magnitudes of the Lorentz and CPT violating coefficients describing the theory are an improvement by factors of 20-510 over the current best limits found by using the MINOS near detector. 相似文献