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1.
A Geometric Characterization of Automatic Monoids 总被引:1,自引:0,他引:1
2.
In this paper, a generalized anti–maximum principle for the second order differential operator with potentials is proved. As an application, we will give a monotone iterative scheme for periodic solutions of nonlinear second order equations. Such a scheme involves the Lp norms of the growth, 1 ≤ p ≤ ∞, while the usual one is just the case p = ∞. 相似文献
3.
The big trip is a cosmological process thought to occur in the future by which the entire universe would be engulfed inside a gigantic wormhole and might travel through it along space and time. In this Letter we discuss different arguments that have been raised against the viability of that process, reaching the conclusions that the process can actually occur by accretion of phantom energy onto the wormholes and that it is stable and might occur in the global context of a multiverse model. We finally argue that the big trip does not contradict any holographic bounds on entropy and information. 相似文献
4.
5.
Pedro Ontaneda 《Geometriae Dedicata》2004,104(1):25-35
We study the following question: does a compact nonpositively curved space have a totally geodesic core? 相似文献
6.
Pedro lvarez‐Boo Jos Sergio Casas Alfonso Castieiras María Delfina Couce Eduardo Freijanes Eva Novoa Jos Sordo 《应用有机金属化学》2003,17(9):725-729
Reaction of dichloro‐ and dibromodimethyltin(IV) with 2‐(pyrazol‐1‐ylmethyl)pyridine (PMP) afforded [SnMe2Cl2(PMP)] and [SnMe2Br2(PMP)] respectively. The new complexes were characterized by elemental analysis and mass spectrometry and by IR, Raman and NMR (1H, 13C) spectroscopies. Structural studies by X‐ray diffraction techniques show that the compounds consist of discrete units with the tin atom octahedrally coordinated to the carbon atoms of the two methyl groups in a trans disposition (Sn? C = 2.097(5), 2.120(5) Å and 2.110(6), 2.121(6) Å in the chloro and in the bromo compounds respectively), two cis halogen atoms (Sn? Cl = 2.4908(16), 2.5447(17) Å; Sn? Br = 2.6875(11), 2.7464(9) Å) and the two donor atoms of the ligand (Sn? N = 2.407(4), 2.471(4) Å and 2.360(5), 2.455(5) Å). In both cases, the Sn? N(pyridine) bond length is markedly longer than the Sn? N(pyrazole) distance. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
H.D. Fonseca Filho R. Prioli M.P. Pires A.S. Lopes P.L. Souza F.A. Ponce 《Applied Physics A: Materials Science & Processing》2007,89(4):945-949
Atomic-force nanolithography was used to control the nucleation sites of InAs nanostructures on InP substrates. Indentations
with a wide range of dimensions were produced on InP. InAs nanostructures were selectively grown by metal organic vapor phase
epitaxy. It is shown that the number of active nucleation sites depends on the normal force applied during nanoindentation.
Crystalline defects introduced by nanoindentation are shown to be nucleation sites for these nanostructures. The presence
of screw dislocations within the grown nanostructures further supports this observation.
PACS 81.07.-b; 68.37.Ps; 81.16.Nd 相似文献
8.
Pedro Traar 《Tetrahedron letters》2006,47(30):5293-5296
The synthesis of (R)-2′,3′-dihydroxypropyl 5-deoxy-5-dimethylarsinoyl-β-d-riboside, (S)-2′-hydroxy-3′-sulfonylpropyl 5-deoxy-5-dimethylarsinoyl-β-d-riboside and (S)-2′-hydroxy-3′-sulfooxypropyl 5-deoxy-5-dimethylarsinoyl-β-d-riboside, common naturally-occurring arsenicals in algae and molluscs, is reported. 相似文献
9.
Jaime Pfretzschner Pedro Cobo Francisco Simón María Cuesta Alejandro Fernández 《Applied Acoustics》2006,67(1):62-73
Microperforated panels (MPPs) coupled to a rigid wall have been proposed recently as an alternative to porous absorbers in situations having concerns with bacterial contamination and small particles discharge, like food, pharmaceutical and microelectronic industries. There exists also an increasing interest for MPP absorbers in the transportation industry and civil engineering. In general, an optimally designed MPP with good broadband absorption requires many submillimetric holes distributed over a panel of also submillimetric thickness. Such thin plates or foils become so fragile that they need to be protected from mechanical damage. In this paper, an alternative strategy is investigated which allows the design of MPPs with panels of millimetric thickness while maintaining their acoustic performance. These absorbers, named microperforated insertion units (MIUs), avoid the structural problems of the classical MPPs. An assessment of the sound absorption properties of these structures is presented. Comparisons between calculations and measurements are also made under two experimental conditions: plane waves at normal incidence (impedance tube) and free field (anechoic room). 相似文献
10.
Pedro Freitas 《Journal of Functional Analysis》2007,251(1):376-398
We study the asymptotic expansion of the first Dirichlet eigenvalue of certain families of triangles and of rhombi as a singular limit is approached. In certain cases, which include isosceles and right triangles, we obtain the exact value of all the coefficients of the unbounded terms in the asymptotic expansion as the angle opening approaches zero, plus the constant term and estimates on the remainder. For rhombi and other triangle families such as isosceles triangles where now the angle opening approaches π, we have the first two terms plus bounds on the remainder. These results are based on new upper and lower bounds for these domains whose asymptotic expansions coincide up to the orders mentioned. Apart from being accurate near the singular limits considered, our lower bounds for the rhombus improve upon the bound by Hooker and Protter for angles up to approximately 22° and in the range (31°,54°). These results also show that the asymptotic expansion around the degenerate case of the isosceles triangle with vanishing angle opening depends on the path used to approach it. 相似文献