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991.
Ana M. Gonzlez‐Noya M. Isabel Fernndez Marcelino Maneiro M. Jesús Rodríguez Rosa Pedrido Miguel Vzquez Manuel R. Bermejo 《无机化学与普通化学杂志》2005,631(11):2167-2173
Interaction of asymmetrical Schiff base ligands H3Ln [where H3Ln are substituted 3–aza–4–(2–hydroxyphenyl)–N– (2–hydroxyphenyl)but–3–enamide] with Mn(acac)3 (acac = acetylacetonate) has been investigated. Two different type of manganese(III) complexes have been obtained depending on the nature of the substituents on the ligand. We have found that ligands containing donor substituents drives to the formation of two different kinds of complexes from the same reaction: Mn(Ln)(H2O)x ( 1a–5a ) and [Mn(HLn)(acac)](H2O)y ( 1b–5b ) (where Ln and HLn signify the ligand in its trianionic and dianionic form, respectively). However, when the substituents are electron withdrawing or poor donor only compounds of the type [Mn(HLn)(acac)](H2O)y ( 6–10 ) are obtained. All these compounds have been characterized by elemental analyses, IR and 1H NMR spectroscopy, FAB mass spectrometry, magnetic measurements and molar conductivities. The electrochemical behaviour of these complexes has also been studied. 相似文献
992.
Classical (Heisenberg) simulations show that the total magnetization of the lowest-energy states of clusters made of antiferromagnetically
coupled chromium atoms is planar, rather than collinear, depending on the arrangement of the atoms. Although the model Hamiltonian
is not restrictive, many cluster configurations of various numbers of atoms do not use all three directions for the spins.
This result confirms the conclusion drawn from the local-spin DFT calculation by Kohl and Bertsch that clusters of N≤13 have non-collinear magnetic moments. The present simulations show non-collinear spin ordering also for bigger clusters,
designed to be as spherical as possible following the bcc arrangement, when atoms interact both with the nearest and next-nearest neighbours. Depending on the signs of the coupling
constants frustration appears. The advantage of the discrete model, despite the simplicity, is that very large clusters and
magnetization at finite temperatures can be studied. This model predicts that clusters with specific numbers of atoms interacting
only with the nearest neighbours have collinear spins as in the bulk. We also apply the model to simulate the destruction
of the anti-ferromagnetic ordering by thermal fluctuations. This model shows no unique magnetization of mixed Fe
0.33
Cr
0.67, which is consistent with experimental observations. 相似文献
993.
The ground state rotational spectrum of the 14NF3 and 15NF3 isotopic species of nitrogen fluoride has been observed in the ∼450-810 GHz frequency range. This investigation allowed us to improve the rotational parameters for both isotopologues. In particular, for the first time the K = 3 line splitting parameter and the sextic centrifugal distortion constants have been determined for 15NF3. 相似文献
994.
The generation of standard reference frequencies close to the ITU channels is essential for the calibration and maintenance of DWDM systems. This work describes a method to synthesize frequency references in the range from 187.1 to 205.1 THz (1462-1602 nm). The method is based on the generation of four equispaced frequencies (by the process of four-wave mixing in a semiconductor amplifier) of which two are locked to absorption lines of the acetylene 12C2H2 (1511-1542 nm). 相似文献
995.
Vinyl p-aminophenylsulfone and methyl vinyl sulfone were shown to react, as Michael acceptors, with a broad range of secondary and primary amines using Amberlyst as catalyst. The reactions occurred, generally, with high yields and in a short time. 相似文献
996.
J. J. Barroso P. J. Castro R. A. Corrêa 《International Journal of Infrared and Millimeter Waves》1996,17(5):921-932
A study of the electrodynamical properties of open coaxial cylindrical resonators using a partially conical inner rod is made along with experimental verification. On the basis of a geometrical criterion for the occurrence of high-Q resonances, it turns out to be possible to discriminate certain classes of TE modes by keeping to a minimum value their diffrationQ factors. In particular, for an especially designed cavity only TE0.2 and TE1.3 modes appear to have strong resonance in the 6 · 14GH
z
range as a result of the action of the coaxial insert. 相似文献
997.
M.A. López-Manchado J.L. Valentín J. Carretero F. Barroso M. Arroyo 《European Polymer Journal》2007,43(10):4143-4150
The influence of inorganic nanoparticles on crosslinking mechanism of elastomers has been evaluated by applying the tube model on equilibrium statistical mechanics. The results have shown that a highly ordered structure with a huge amount of entanglements, wherein the polymer is nanoscopically confined, is formed by the addition of nanoparticles. These physical links exhibit freedom of movement under stretching, but in a lower volume because of confinement. That is, network molecular parameters such as lateral tube dimensions or average molecular mass of the chains decreased in presence of nanoparticles. 相似文献
998.
Cristina Bazgan W. Fernandez de la Vega Marek Karpinski 《Random Structures and Algorithms》2003,23(1):73-91
It is known that large fragments of the class of dense Minimum Constraint Satisfaction (MIN‐CSP) problems do not have polynomial time approximation schemes (PTASs) contrary to their Maximum Constraint Satisfaction analogs. In this paper we prove, somewhat surprisingly, that the minimum satisfaction of dense instances of kSAT ‐formulas, and linear equations mod 2, Ek‐LIN2, do have PTASs for any k. The MIN‐Ek‐LIN2 problems are equivalent to the k‐ary versions of the Nearest Codeword problem, the problem which is known to be exceedingly hard to approximate on general instances. The method of solution of the above problems depends on the development of a new density sampling technique for k‐uniform hypergraphs which could be of independent interest. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 73–91, 2003 相似文献
999.
In this paper we explore the usefulness of induced-order statistics in the characterization of integrated series and of cointegration
relationships. We propose a non-parametric test statistic for testing the null hypothesis of two independent random walks
against wide cointegrating alternatives including monotonic nonlinearities and certain types of level shifts in the cointegration
relationship. We call our testing device the induced-order Kolmogorov–Smirnov cointegration test (KS), since it is constructed
from the induced-order statistics of the series, and we derive its limiting distribution. This non-parametric statistic endows
the test with a number of desirable properties: invariance to monotonic transformations of the series, and robustness for
the presence of important parameter shifts. By Monte Carlo simulations we analyze the small sample properties of this test.
Our simulation results show the robustness of the induced order cointegration test against departures from linear and constant
parameter models.
This paper is an extension of the work of Aparicio and Granger (1995) and Aparicio and Escribano (1998). 相似文献
1000.
The isosceles three body problem consists of three point masses located on the vertices of an isosceles triangle on the plane.
The two masses on the asymmetric edge are equal. This problem has been extensively studied but not as a perturbation of the
Kepler problem. In this case we arrive at a differential inclusion as a natural formulation when we regularize the problem.
We also derive an extension of the vectorfield that allows us to consider orbits across singular sets.
相似文献