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21.
Tibor Novák Péter Bakó György Keglevich András Dobó Károly Vékey László Tóke 《Journal of inclusion phenomena and macrocyclic chemistry》2001,40(3):207-212
Five chiral -D-glucose-based monoaza-15-crown-5 ethers with phosphinoxidoalkyl side chains of one to five carbon atoms (5a–e)have been synthesised. The cation binding ability of the new lariat ethers was evaluated bythe picrate extraction method. The substituents at the nitrogen atom were not a major influenceon the cation extraction ability of the azacrown ether; the compounds showed, however, a significant asymmetric induction as phase transfer catalysts in the Michael addition of2-nitropropane to chalcone (95% ee). 相似文献
22.
Fires in the one-dimensional Bak-Chen-Tang forest fire model propagate as solitons, resembling shocks in Burgers turbulence. The branching of solitons, creating new fires, is balanced by the pairwise annihilation of oppositely moving solitons. Two distinct, diverging length scales appear in the limit where the growth rate of trees, p, vanishes. The width of the solitons, w, diverges as a power law, 1/p, while the average distance between solitons diverges much faster as d approximately exp(pi2/12p). 相似文献
23.
L. de Arcangelis H. J. Herrmann M. Kolb René Thomas C. Amitrano L. Peliti M. Saber G. Weisbuch Sara A. Solla F. Bagnoli A. Francescato R. Livi S. Ruffo Pablo Tamayo Michel Droz Peter Jörg Plath S. Romano Yves Pomeau Stéphane Zaleski D. Stauffer Luciano R. da Silva Alex Hansen Stéphane Roux Antonio Coniglio B. Derrida Henrik Flyvbjerg Naeem Jan Dietrich Stauffer Peter Grassberger A. Zippelius K. E. Kurten Werner Krauth Jean -Pierre Nadal Marc Mézard Per Bak Chao Tang Itzhak Webman M. L. Martins H. F. V. Resende C. Tsallis A. C. N. Magalhaes 《Journal of statistical physics》1989,55(5-6):1333-1359
24.
Electrical properties of TiO<Subscript>2</Subscript>: equilibrium vs dynamic electrical conductivity
The present work reports semiconducting properties of high purity TiO2 determined in the gas/solid equilibrium, as well as during controlled heating and cooling in the range 300–1,273 K. The activation
energy of the electrical conductivity is considered in terms of the activation enthalpy of the formation of ionic defects
and the activation enthalpy of the mobility of electronic defects. These data, determined from the dynamic electrical conductivity
experiments, are compared to the electrical conductivity data determined in equilibrium. It is shown that only the equilibrium
electrical conductivity data for high-purity TiO2 are well defined. It is shown that the activation energy of the electrical conductivity determined in equilibrium differs
substantially from that for the dynamic electrical conductivity data during cooling and heating. It is concluded that the
formation enthalpy term determined from the dynamic conductivity data is determined by the heating/cooling rate rather than
materials’ properties. 相似文献
25.
26.
This paper reports the results of work function and EPR studies of yttria-stabilized zirconia (10Y-ZrO2). The experimental data are considered in terms of the formation of oxygen chemisorbed species and subsequent oxygen incorporation
as well as related charge transfer. It is concluded that oxygen chemisorption on 10Y-ZrO2 at room temperature in its initial stage results in the formation of O
2
−
species. These species are then transformed into O
2
2−
, O− species and, finally, are slowly incorporated into the oxide lattice. These processes take place without presence of Pt or
any other electrode material. 相似文献
27.
28.
B. Bak 《Molecular physics》2013,111(4):373-375
By means of microwave spectra of six isotopic pyridines and dipole moment and proton magnetic resonance data the magnitude of the charges on the carbon atoms of pyridine is estimated. Each of the ortho carbon atoms has a charge of ca. +0·08 e, the meta atoms are uncharged, while the para carbon atom has a charge of ca. 0·04 e. The result is in rough agreement with quantum-mechanical estimates. 相似文献
29.
Attila Makó Zsolt Rapi György Keglevich Áron Szöllősy László Drahos László Hegedűs Péter Bakó 《Tetrahedron: Asymmetry》2010,21(8):919-925
The chiral monoaza-15-crown-5 lariat ethers annellated to methyl-4,6-O-benzylidene-α-d-glucopyranoside-1 or mannopyranoside 2 have been applied as phase-transfer catalysts in the epoxidation of substituted chalcones and chalcone analogues with tert-butylhydroperoxide resulting in significant asymmetric induction. It was found that the position of the substituents in the aromatic ring of the chalcone had an influence both on the chemical yields and enantiomeric excesses. The lowest enantioselectivities (62–83% ee) were found in the case of ortho-substituted model compounds. The highest ee values (ee of 83–97%) were obtained in the case of para-substituted models. From among the chalcone analogues, the maximum ee (90–92%) was detected for the model compound having α-tert-butyl- and β-aryl groups. Using glucose-based crown ether 1, formation of the (?)-enantiomer was preferred, while applying mannose-based 2 as the catalyst, the (+)-enantiomer was in excess. 相似文献
30.
This paper concerns verification of the defect chemistry models of La1−xSrxCoO3−δ (LSC), involving the random defect model and the cluster defect model, against empirical data of oxygen nonstoichiometry.
It appears that the experimental data may well be explained within the random defect model. 相似文献