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891.
This brief paper presents an A-stability result for operator splitting type time integration methods applied to advection–diffusion–reaction equations with possibly indefinite source terms. These results extend our earlier work on diffusion–reaction systems [D.L. Ropp, J.N. Shadid, Stability of operator splitting methods for systems with indefinite operators: reaction–diffusion systems, J. Comput. Phys. 203 (2) (2005) 449–466]. The A-stability result presents sufficient conditions that control both low and high wave number instabilities. A corollary shows that if L-stable methods are used for the diffusion term the high wave number instability will be controlled more easily. Numerical results are presented that verify second-order convergence for the operator splitting methods and demonstrate control of instabilities on a chemotaxis problem by use of an L-stable diffusion integrator. 相似文献
892.
Using the single-crystal adsorption calorimeter (SCAC), coverage-dependent heats of adsorption and sticking probabilities are reported for O2 and NO on Pt{1 1 1}, Pt{2 1 1} and Pt{4 1 1} at 300 K. At low coverage, oxygen adsorption is dissociative for all Pt surfaces. The highest initial heat of adsorption is found on Pt{2 1 1}, with a value of 370 kJ/mol, followed by those on Pt{4 1 1} (310 kJ/mol) and Pt{1 1 1} (300 kJ/mol). We attribute this relatively large difference in the dissociative heat of adsorption at low coverage to the step character of the {2 1 1} surface. Initial sticking probabilities, so, are similar for the three surfaces, 0.22 on Pt{1 1 1}, 0.17 on Pt{2 1 1} and 0.18 on Pt{4 1 1}, rapidly decreasing as the oxygen coverage increases. For nitric oxide, the initial heats of adsorption are very similar and consistent with either dissociative or molecular adsorption, with values of 182 kJ/mol on Pt{1 1 1}, 192 kJ/mol on Pt{2 1 1} and 217 kJ/mol on Pt{4 1 1}. The so value is virtually identical for all three systems, with values ranging from 0.82 to 0.85, suggesting that the initial sticking probability is insensitive to the surface structure and adsorption is intrinsically precursor mediated. SCAC data are also used to evaluate pre-exponential factors, ν, for first-order desorption at high coverage where adsorption is non-dissociative. Values of 3 × 1018, 6 × 1018 and 2 × 1018 s?1 for O2, and 4 × 1019, 6 × 1017 and 2 × 1020 s?1 for NO on Pt{1 1 1}, Pt{2 1 1} and Pt{4 1 1}, respectively, are found. These unexpectedly high values are rationalised in terms of conventional transition state theory entropy changes. 相似文献
893.
We describe a phase retrieval approach for intensity point-spread functions of high-numerical-aperture optical systems such as light microscopes. The method calculates a generalized pupil function defined on a spherical shell, using measured images at several defocus levels. The resultant pupil functionsreproduce measured point-source images significantly better than does an ideal imaging model. Availability of pupil function information will facilitate new approaches to aberration correction in such systems. 相似文献
894.
The logarithmic conformal field theory describing critical percolation is further explored using Watts' determination of the probability that there exists a cluster connecting both horizontal and vertical edges. The boundary condition changing operator which governs Watts' computation is identified with a primary field which does not fit naturally within the extended Kac table. Instead a “shifted” extended Kac table is shown to be relevant. Augmenting the previously known logarithmic theory based on Cardy's crossing probability by this field, a larger theory is obtained, in which new classes of indecomposable rank-2 modules are present. No rank-3 Jordan cells are yet observed. A highly non-trivial check of the identification of Watts' field is that no Gurarie–Ludwig-type inconsistencies are observed in this augmentation. The article concludes with an extended discussion of various topics related to extending these results including projectivity, boundary sectors and inconsistency loopholes. 相似文献
895.
Christopher M. Tollan Jon Echeberria Rebeca Marcilla José A. Pomposo David Mecerreyes 《Journal of nanoparticle research》2009,11(5):1241-1245
The synthesis and characterisation of gold nanorods have been carried out by reduction of the gold salt HAuCl4. This has been done using a single reducing agent, acetylacetone, rather than the two reducing agents, sodium borohydride
and ascorbic acid, normally required by standard wet chemistry methods of gold nanorod formation. Using this novel method,
the nanorods were synthesised at several different pH values which were found to greatly affect both the rate at which the
nanorods form and their physical dimensions. The concentrations of acetylacetone and silver nitrate used relative to the gold
salt were found to alter the aspect ratio of the nanorods formed. Rods with an average length of 42 nm and an aspect ratio
of 4.6 can be easily and reproducibly formed at pH 10 using this method. Nanorods formed under optimum conditions were investigated
using TEM.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
896.
David Cox 《Journal of Pure and Applied Algebra》2008,212(7):1787-1796
Let a,b,c be linearly independent homogeneous polynomials in the standard Z-graded ring R?k[s,t] with the same degree d and no common divisors. This defines a morphism P1→P2. The Rees algebra of the ideal I=〈a,b,c〉 is the graded R-algebra which can be described as the image of an R-algebra homomorphism h: . This paper discusses one result concerning the structure of the kernel of the map h and its relation to the problem of finding the implicit equation of the image of the map given by a, b, c. In particular, we prove a conjecture of Hong, Simis and Vasconcelos. We also relate our results to the theory of adjoint curves and prove a special case of a conjecture of Cox. 相似文献
897.
898.
899.
Loran V. Akopyan Vladimir I. Man’ko David K. Udumyan 《Journal of Russian Laser Research》2010,31(1):61-69
Tomographic entropies of multiqudit systems are studied. A comparison of Shannon and von Neumann entropic inequalities with
analogous inequalities for tomographic entropies is presented. An attempt to associate the violation of these and Bell-type
inequalities of multipartite states is done within the framework of tomographic probability theory. 相似文献
900.
Oswin Aichholzer Thomas Hackl David Orden Pedro Ramos Günter Rote André Schulz Bettina Speckmann 《Graphs and Combinatorics》2013,29(6):1577-1593
We study flip graphs of triangulations whose maximum vertex degree is bounded by a constant k. In particular, we consider triangulations of sets of n points in convex position in the plane and prove that their flip graph is connected if and only if k > 6; the diameter of the flip graph is O(n 2). We also show that, for general point sets, flip graphs of pointed pseudo-triangulations can be disconnected for k ≤ 9, and flip graphs of triangulations can be disconnected for any k. Additionally, we consider a relaxed version of the original problem. We allow the violation of the degree bound k by a small constant. Any two triangulations with maximum degree at most k of a convex point set are connected in the flip graph by a path of length O(n log n), where every intermediate triangulation has maximum degree at most k + 4. 相似文献