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991.
Tetra(3-pyridyl)porphyrazine is soluble in trifluoroethanol yielding intense blue solutions. The electronic spectra exhibit the characteristic Soret and Q bands around 330 and 610 nm, respectively; however, the absorption profile is strongly dependent on the concentration, reflecting the occurrence of an association process. The system has been elucidated by solving the equilibrium and the absorbance-concentration equations for all the wavelengths in the spectral range, according to a variational procedure. In this way the consistent spectra of the individual species have been generated. The study has also been extended to the luminescence properties of the porphyrazine molecule, and discussed in terms of the ground state association and the exciplex formation involving the monomeric species. 相似文献
992.
Diver Sellanes Ivana Núñez Pablo Espósito Jenny Saldaña Eduardo Manta 《Tetrahedron》2010,66(29):5384-5395
The synthesis of key fragments of scleritodermin A, their assembly, and their biological evaluation as cytotoxic and anthelmintic were performed. Highlights of the synthetic route include formation of the α-ketoamide linkage and use of stereocontrolled reactions. Open analogs of this natural product were obtained using a convergent strategy. 相似文献
993.
María Isabel González Vasco Angel L. Pérez del Pozo Pedro Taborda Duarte 《Designs, Codes and Cryptography》2010,55(2-3):189-200
In this paper, we study the recently proposed encryption scheme MST 3, focusing on a concrete instantiation using Suzuki-2-groups. In a passive scenario, we argue that the one wayness of this scheme may not, as claimed, be proven without the assumption that factoring group elements with respect to random covers for a subset of the group is hard. As a result, we conclude that for the proposed Suzuki 2-groups instantiation, impractical key sizes should be used in order to prevent more or less straightforward factorization attacks. 相似文献
994.
995.
Adriana da Silva Fontes Walter Sano Luiz Henrique Dall’ Antonia Eduardo Di Mauro 《Applied magnetic resonance》2010,39(4):381-390
The aim of this study was to assess the relation between the number of free radicals generated and the polymerization depth
in two different commercial brands of resin composites with different colors and translucence. Electron paramagnetic resonance
quantified the radical populations through relative intensity (I
r) of free radicals generated, and radical decay was monitored. Sample translucence and the classical polymerization depth
were measured. The analysis indicated that resin with more color pigments (MA4, I
r = 0.73 a.u) or more opacity components (ODA2, I
r = 0.84 a.u) generated smaller populations of free radicals and have the lower polymerization depth than clearer (M, I
r = 1.20 a.u and MA2, I
r = 1.02) or more translucent (OEA2, I
r = 1.00 a.u) composites for the same light-curing time. It seems that irradiation doses have to be adequate to more colored
and less translucent resins. 相似文献
996.
To define a metric or a similarity relation with good properties is a crucial issue in most analogy and rule induction oriented methods for multicriteria sorting. Here, we propose a valued indifference (closeness) relation which is inspired on concordance and discordance measures. The criterion “weights” are obtained from the preferential information embedded in a reference set. This proposal performs very well in several practical problems. 相似文献
997.
Semiempirical calculations have been carried out on the interactions of [R2Sn(H2O)2]2+, [R = H(CH2)n: n = 1–8], mainly with five nucleotides, 5′‐adenosine monophosphate (5′‐AMP), but also with guanosine 5′‐monophosphate (5′‐GMP), cytidine 5′‐monophosphate (5′‐CMP), uridine‐5′‐monophosphate (5′‐UMP) and inosine 5′‐monophosphate (5′‐IMP). The preferred sites of interaction were calculated to be the ribose O2 and O3 hydroxyl oxygens and/or the phosphate oxygens, with the nitrogen sites in the bases the least attractive to the tin compounds. This is in general agreement with experimental findings. Structures of the 1:1 coordination complexes vary from distorted tetrahedral, to distorted trigonal pyramidal to distorted octahedral geometries. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
998.
We consider the geometry of a special family of curves associated with the motion of a two-fluid interface in a rotating Hele-Shaw cell. This family of stationary exact solutions with surface tension consists of interface shapes which balance exactly the competing capillary and centrifugal forces. The result is the formation of patterned structures presenting fingers that eventually assume a teardrop-like shape, and tend to be detached from the main body of the rotating fluid (occurrence of a pinch-off event). By using the vortex-sheet formalism, we approach the problem analytically, and show that the curvature of these particular curves can be very simply expressed as a function of the radial distance to the rotation axis. Motivated by this fact, and through a simple geometric interpretation, we show that the exact solutions for the rotating Hele-Shaw problem satisfy a first-order ordinary differential equation which is readily solved, so that the shape solutions are determined up to quadratures. The ability to probe a number of key morphological features of such solutions analytically is demonstrated, and a gallery of plots is provided to highlight these findings. The possibility of accessing a criterion to predict the occurrence of pinch-off is also discussed. Finally, we prove that the general solutions are dense, and use this fact to guarantee the very existence of the neat, highly symmetric physical patterns. 相似文献
999.
Eduardo Rodriguez-Tello Jin-Kao Hao Jose Torres-Jimenez 《European Journal of Operational Research》2008
In this paper, a simulated annealing algorithm is presented for the bandwidth minimization problem for graphs. This algorithm is based on three distinguished features including an original internal representation of solutions, a highly discriminating evaluation function and an effective neighborhood. The algorithm is evaluated on a set of 113 well-known benchmark instances of the literature and compared with several state-of-the-art algorithms, showing improvements of some previous best results. 相似文献
1000.
Fátima Duarte Freire Cícero Flávio Soares Aragão Túlio Flávio Accioly de Lima e Moura Fernanda Nervo Raffin 《Journal of Thermal Analysis and Calorimetry》2009,97(1):333-336
Rifampicin–Isoniazid mixture is a frequently used product in the treatment of tuberculosis. Rifampicin exhibits polymorphism
and exists in two polymorphic forms: the stable form I and the metastable form II. The aim of this work was to evaluate the
thermal behavior of the binary mixtures of polymorphs I and II of rifampicin and isoniazid by using DSC. Mixtures of different
forms (rifampicin form I and II) showed interaction with isoniazid indicating that the mixtures are less stable compared to
the drug alone. Interaction was observed in case of both polymorphs of rifampicin. 相似文献