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991.
We show that every Gromov hyperbolic group Γ admits a quasi-isometric embedding into the product of n+1 binary trees, where n=dim∂∞Γ is the topological dimension of the boundary at infinity of Γ. 相似文献
992.
Sandra Reemers Petra Mela Ahmed Mourran Sergei Magonov Helmut Keul Martin Möller 《Journal of polymer science. Part A, Polymer chemistry》2007,45(4):614-628
First‐generation dendritic macromonomers with a methacryloyl end group on one side, long alkyl chains on the other side, and a biuret system with two urethane groups in the core have been synthesized. The synthesis comprises three steps with hexamethylene diisocyanate uretdione as the starting material. The branching points were introduced via biuret groups and the prepared macromonomers were polymerized by free and controlled radical polymerization. Depending on the reaction conditions linear dendronized polymers as well as branched dendronized polymers and microgels with long alkyl chains were obtained. Scanning force microscopy was used to visualize high molecular weight molecules spincoated on highly oriented pyrolytic graphite. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 614–628, 2007 相似文献
993.
Marina Chugunova Illya M. Karabash Sergei G. Pyatkov 《Integral Equations and Operator Theory》2009,65(3):319-344
We study the Cauchy problem with periodic initial data for the forward-backward heat equation defined by a J-self-adjoint
linear operator L depending on a small parameter. The problem originates from the lubrication approximation of a viscous fluid film on the
inner surface of a rotating cylinder. For a certain range of the parameter we rigorously prove the conjecture, based on numerical
evidence, that the complete set of eigenvectors of the operator L does not form a Riesz basis in L2(-p, p)\mathcal{L}^2(-\pi, \pi). Our method can be applied to a wide range of evolution problems given by PT-symmetric operators. 相似文献
994.
995.
This paper is concerned with a new class of graded algebras naturally uniting within a single framework various deformations
of the Witt, Virasoro and other Lie algebras based on twisted and deformed derivations, as well as color Lie algebras and
Lie superalgebras.
Presented at the International Colloquium “Integrable Systems and Quantum Symmetries”, Prague, 16–18 June 2005.
Supported by the Liegrits network
Supported by the Crafoord foundation 相似文献
996.
We discuss a choice of weight in penalization methods. The motivation for the use of penalization in computational mathematics
is to improve the conditioning of the numerical solution. One example of such improvement is a regularization, where a penalization
substitutes an ill-posed problem for a well-posed one. In modern numerical methods for PDEs a penalization is used, for example,
to enforce a continuity of an approximate solution on non-matching grids. A choice of penalty weight should provide a balance
between error components related with convergence and stability, which are usually unknown. In this paper we propose and analyze
a simple adaptive strategy for the choice of penalty weight which does not rely on a priori estimates of above mentioned components.
It is shown that under natural assumptions the accuracy provided by our adaptive strategy is worse only by a constant factor
than one could achieve in the case of known stability and convergence rates. Finally, we successfully apply our strategy for
self-regularization of Volterra-type severely ill-posed problems, such as the sideways heat equation, and for the choice of
a weight in interior penalty discontinuous approximation on non-matching grids. Numerical experiments on a series of model
problems support theoretical results. 相似文献
997.
998.
Pd complexes of tetrabenzoporphyrins (PdTBPs) are strong near infra-red phosphors, suitable for tissue oxygen imaging by phosphorescence quenching. For in vivo use, PdTBP phosphors have to be water-soluble and protected from interactions with biomacromolecules in the blood. An approach to the construction of biologically compatible PdTBP-phosphors based on dendritic encapsulation is proposed. A series of polyglutamic PdTBP-dendrimers was synthesized and their optical and quenching properties were studied. While retaining the excellent optical characteristics (λmax Q=630 nm, φphos=12%) of basic PdTBPs and in addition being highly water soluble, PdTBP-dendrimers still exhibit excessively high oxygen quenching constants (2000-3000 mmHg−1 s−1) and form complexes with lipophilic proteins, such as serum albumin. Modification of the dendrimer periphery with polyethyleneglycol chains somewhat reduces the quenching constants but does not prevent binding of the phosphors to albumin. 相似文献
999.
1000.
Sergei A. JerebetsMingqin Zou Roger D. Willett 《Journal of Physics and Chemistry of Solids》2002,63(5):793-799
The compound (Me4P)2ZnBr4, a member of the β-K2SO4 structure class, undergoes a phase transition at 84°C from the room temperature space group P121/c1 to the parent Pmcn structure. The room temperature structure corresponds to a ferrodistortive transition of B1g symmetry at the zone center. At room temperature, the compound has lattice constants a=9.501(1), b=16.055(2), c=13.127(2) Å and β=90.43(1)°. For the high temperature phase, the orthorhombic cell has dimensions a=9.466(2), b=16.351(3) and c=13.284(2) Å. The structures consist of two crystallographically independent Me4P+ cations and the ZnBr42− anions. In the room temperature phase, all three ionic species show substantial displacement from the mirror plane perpendicular to the a-axis that exists in the high temperature phase, as well as rotations out of that plane. The thermal parameters of the cations are indicative of substantial librational motion. Measurements of lattice parameters have been made at 2-5°C intervals over the temperature range 40-140°C. The changes in the lattice constants appear continuous at Tc (within experimental limits) indicating that the phase transition is likely second-order. The a lattice constant shows an anomalous shortening as Tc is approached. Thermal expansion coefficients are calculated from this data. An application of Landau theory is used to derive the temperature dependencies of spontaneous shear strain and corresponding elastic stiffness constants associated with the primary order parameter. 相似文献