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921.
Some sequences of matrix polynomials have been introduced recently as solutions of certain second-order differential equations,
which can be seen as appropriate generalizations, to the matrix setting, of classical orthogonal polynomials. In this paper,
we consider families (in a complex parameter) of matrix-valued special functions of Hermite type, which arise as natural extensions
of the aforementioned matrix polynomials of the same type. We show that such families are solutions of corresponding differential
equations and enjoy several structural properties. In particular, they satisfy a Rodrigues formula expressed in terms of the
Weyl fractional calculus. We also show that, unlike the scalar case, a second-order differential operator having such a family
as a set of joint eigenfunctions need not be unique. 相似文献
922.
We give a method to compute all nonnegative integer solutions of a homogeneous system of linear equations. We use this method to provide an algorithm to compute all nonnegative integer solutions of homogeneous systems of equations having some of the equations in congruences. 相似文献
923.
LetG be a connected semi-simple Lie group with finite center andS⊄G a subsemigroup with interior points. LetG/L be a homogeneous space. There is a natural action ofS onG/L. The relationx≤y ify ∈Sx, x, y ∈G/L, is transitive but not reflexive nor symmetric. Roughly, a control set is a subsetD ⊄G/L, inside of which reflexivity and symmetry for ≤ hold. Control sets are studied inG/L whenL is the minimal parabolic subgroup. They are characterized by means of the Weyl chambers inG meeting intS. Thus, for eachw ∈W, the Weyl group ofG, there is a control setD
w
.D
1 is the only invariant control set, and the subsetW(S)={w:D
w
=D
1} turns out to be a subgroup. The control sets are determined byW(S)/W. The following consequences are derived: i)S=G ifS is transitive onG/H, i.e.Sx=G/H for allx ∈G/H. HereH is a non discrete closed subgroup different fromG andG is simple. ii)S is neither left nor right reversible ifS #G iii)S is maximal only if it is the semigroup of compressions of a subset of some minimal flag manifold.
Research partially supported by CNPq grant no 50.13.73/91-8 相似文献
924.
The Babichev–Dokuchaev–Eroshenko model for the accretion of dark energy onto black holes has been extended to deal with black holes with non-static metrics. The possibility that for an asymptotic observer a black hole with large mass will rapidly increase and eventually engulf the Universe at a finite time in the future has been studied by using reasonable values for astronomical parameters. It is concluded that such a phenomenon is forbidden for all black holes in quintessential cosmological models. 相似文献
925.
Juan Pedro Milaszewicz 《Applications of Mathematics》2004,49(2):165-184
Given two initial points generating monotone convergent Brown iterations in the context of the monotone Newton theorem (MNT), it is proved that if one of them is an upper bound of the other, then the same holds for each pair of respective terms in the Brown sequences they generate. This comparison result is carried over to the corresponding Brown-Fourier iterations. An illustration is discussed. 相似文献
926.
927.
Pedro E. M. Lopes Guillaume Lamoureux Alexander D. Mackerell 《Journal of computational chemistry》2009,30(12):1821-1838
The polarizable empirical CHARMM force field based on the classical Drude oscillator has been extended to the nitrogen‐containing heteroaromatic compounds pyridine, pyrimidine, pyrrole, imidazole, indole, and purine. Initial parameters for the six‐membered rings were based on benzene with nonbond parameter optimization focused on the nitrogen atoms and adjacent carbons and attached hydrogens. In the case of five‐member rings, parameters were first developed for imidazole and transferred to pyrrole. Optimization of all parameters was performed against an extensive set of quantum mechanical and experimental data. Ab initio data were used for the determination of initial electrostatic parameters, the vibrational analysis, and in the optimization of the relative magnitudes of the Lennard‐Jones (LJ) parameters, through computations of the interactions of dimers of model compounds, model compound‐water interactions, and interactions of rare gases with model compounds. The absolute values of the LJ parameters were determined targeting experimental heats of vaporization, molecular volumes, heats of sublimation, crystal lattice parameters, and free energies of hydration. Final scaling of the polarizabilities from the gas‐phase values by 0.85 was determined by reproduction of the dielectric constants of pyridine and pyrrole. The developed parameter set was extensively validated against additional experimental data such as diffusion constants, heat capacities, and isothermal compressibilities, including data as a function of temperature. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 相似文献
928.
929.
Conceio Fonseca M. Rosrio M. Domingues Cludia Simes Francisco Amado Pedro Domingues 《Journal of mass spectrometry : JMS》2009,44(5):681-693
The exposure of peptides and proteins to reactive hydroxyl radicals results in covalent modifications of amino acid side‐chains and protein backbone. In this study we have investigated the oxidation the isomeric peptides tyrosine–leucine (YL) and leucine–tyrosine (LY), by the hydroxyl radical formed under Fenton reaction (Fe2+/H2O2). Through mass spectrometry (MS), high‐performance liquid chromatography (HPLC‐MS) and electrospray tandem mass spectrometry (HPLC‐MSn) measurements, we have identified and characterized the oxidation products of these two dipeptides. This approach allowed observing and identifying a wide variety of oxidation products, including isomeric forms of the oxidized dipeptides. We detected oxidation products with 1, 2, 3 and 4 oxygen atoms for both peptides; however, oxidation products with 5 oxygen atoms were only present in LY. LY dipeptide oxidation leads to more isomers with 1 and 2 oxygen atoms than YL (3 vs 5 and 4 vs 5, respectively). Formation of the peroxy group occurred preferentially in the C‐terminal residue. We have also detected oxidation products with double bonds or keto groups, dimers (YL–YL and LY–LY) and other products as a result of cross‐linking. Both amino acids in the dipeptides were oxidized although the peptides showed different oxidation products. Also, amino acid residues have shown different oxidation products depending on the relative position on the dipeptide. Results suggest that amino acids in the C‐terminal position are more prone to oxidation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
930.
Prado Martín-Moruno Az-Eddine L. Marrakchi Salvador Robles-Pérez Pedro F. González-Díaz 《General Relativity and Gravitation》2009,41(12):2797-2811
In this paper we study the accretion of dark energy onto a black hole in the cases that dark energy is equipped with a positive
cosmological constant and when the space-time is described by a Schwarzschild-de Sitter metric. While the first case is the
same as the usual accretion procedure for a more complicated fluid, the second one give rise to a consistent cosmic scenario
for the mentioned phenomenon. 相似文献