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61.
Daniele Bartoli Giorgio Faina Stefano Marcugini Fernanda Pambianco 《Journal of Geometry》2013,104(3):409-419
The minimum size of a complete arc in the planes PG(2, 31) and PG(2, 32) and of a 1-saturating set in PG(2, 17) and PG(2, 19) is determined. Also, the minimal 1-saturating sets in PG(2, 9) and PG(2, 11) are classified. In addition, the minimal 1-saturating sets of the smallest size in PG(2, q) are classified for 16 ≤ q ≤ 23. These results have been found using a computer-based exhaustive search that exploits projective equivalence properties. 相似文献
62.
Lifshitz A Tamburu C Suslensky A Dubnikova F 《The journal of physical chemistry. A》2006,110(41):11677-11683
Isomerization and decomposition of 1,2-benzisoxazole were studied behind reflected shock waves in a pressurized driver, single-pulse shock tube. It isomerizes to o-hydroxybenzonitrile, and no fragmentation is observed up to a temperature where the isomerization is almost complete (approximately 1040 K at 2 ms reaction time). The isomerization experiments in this investigation covered the temperature range 900-1040 K. The lack of fragmentation is in complete contrast to the thermal behavior of isoxazole, where no isomerization was observed and the main decomposition products over the same temperature range were carbon monoxide and acetonitrile. In a series of experiments covering the temperature range 1190-1350 K, a plethora of fragmentation products appear in the post shock samples of 1,2-benzisoxazole. The product distribution is exactly the same regardless of whether the starting material is 1,2-benzisoxazole or o-hydroxybenzonitrile, indicating that over this temperature range the 1,2-benzisoxazole has completely isomerized to o-hydroxybenzonitrile prior to fragmentation. Two potential energy surfaces that lead to the isomerization were evaluated by quantum chemical calculations. One surface with one intermediate and two transition states has a high barrier and does not contribute to the process. The second surface is more complex. It has three intermediates and four transition states, but it has a lower overall barrier and yields the isomerization product o-hydroxybenzonitrile at a much higher rate. The unimolecular isomerization rate constants kinfinity at a number of temperatures in the range of 900-1040 K were calculated from the potential energy surface using transition-state theory and then expressed in an Arrhenius form. The value obtained is kfirst=4.15x10(14) exp(-51.7x10(3)/RT) s-1, where R is expressed in units of cal/(K mol). The calculated value is somewhat higher than the one obtained from the experimental results. When it is expressed in terms of energy difference it corresponds of ca. 2 kcal/mol. 相似文献
63.
Giorgio Faina 《Journal of Combinatorial Theory, Series A》1984,36(3):307-314
The object of this paper is to classify all the Buekenhout ovals of order q ? 8. The close relationship between Buekenhout ovals of even order q = 2t ? 2 and partial geometries pg(t, 2t ? 3, t ? 2) is pointed out. 相似文献
64.
N. M. Vitkovskaya V. B. Kobychev N. Yu. Matveenko F. S. Dubnikova O. Yu. Dolgunicheva B. A. Trofimov 《Russian Chemical Bulletin》1990,39(8):1624-1627
Within the framework of the ab initio method SCF MO LCAO, using a model potential, the influence of alkali metal cations on the reactivity of the acetylene molecule has been investigated. Activation of acetylene with respect to a nucleophile is favored by a lowering of energy of the vacant * orbital upon coordination, a change in its form as a consequence of sufficiently free motion of the cation along the triple bond, and stabilization of the transdistorted form of acetylene in the complex. In the acetylene/alkali/DMSO system, the activating capability of cations is related to the ease of replacement of a solvent molecule in the solvate complex of the acetylene molecule, this capability increasing in the series Li < Na< K.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1793–1797, August, 1990. 相似文献
65.
Faina Gelman Jochanan Blum Herbert Schumann David Avnir 《Journal of Sol-Gel Science and Technology》2003,26(1-3):43-46
Silica sol-gel entrapped acids, bases and organometallic catalysts are used successfully in one-pot reactions without interfering with each other. Both physically and covalently entrapped acids and bases were employed in these processes, including polystyrene sulfonic acid, 1-propane sulfonic acid, molybdosilicic acid (SiO2-MoO3), poly[(vinylbenzyltrimethyl)ammonium] hydroxide and 1,5,7-triazabicyclo[4.4.0]decene. The entrapped metal-based catalysts are Rh2Co2(CO)12 and RuCl2(PPh3)3. The one-pot reactions carried out with these heterogenized reagents and catalysts include formation of alkenes under acidic and basic conditions, C—C bond formation by condensation reactions with an -carbon to a carbonyl, hydroformylation and hydrogenation. 相似文献
66.
Frank J. Millero Faina Vinokurova Marino Fernandez J. Peter Hershey 《Journal of solution chemistry》1987,16(4):269-284
The sound velocities of aqueous NaCl, Na2SO4, MgCl2, and MgSO4 solutions were measured from 25 to 95°C in 10o intervals from dilute to saturated solutions. The results were combined with our earlier data and fitted to functions of molality and temperature to within ±0.4 m-sec–1. The adiabatic compressibilities S were calculated from sound speeds and used to calculate the adiabatic apparent molal compressibilities . Isothermal compressibilities and isothermal apparent molal compressibilities were calculated from S using literature values for the expansibilities and heat capacities. The values of were extrapolated to infinite dilution using the Debye-Huckel limiting law to determine partial molal compressibilities. The apparent molal compressibilities were fitted to Pitzer's equations. The Pitzer parameters for the concentration dependence of were determined as a function of temperature. Correlations of and V at various temperatures were found for the electrolytes. 相似文献
67.
68.
Sergey V. Avgustinovich Olof Heden Faina I. Solov'eva 《Designs, Codes and Cryptography》2004,31(3):313-318
Perfect 1-error correcting codes C in Z
2
n
, where n=2
m–1, are considered. Let
; denote the linear span of the words of C and let the rank of C be the dimension of the vector space
. It is shown that if the rank of C is n–m+2 then C is equivalent to a code given by a construction of Phelps. These codes are, in case of rank n–m+2, described by a Hamming code H and a set of MDS-codes D
h
, h
H, over an alphabet with four symbols. The case of rank n–m+1 is much simpler: Any such code is a Vasil'ev code. 相似文献
69.
70.