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91.
Energy conservation of numerical integrators is well understood for symplectic one-step methods. This article provides new insight into energy conservation with non-symplectic methods. Sufficient conditions and counter-examples are presented.
AMS subject classification (2000) 65L06, 65P10, 37J99.Submitted June 2004. Accepted October 2004. Communicated by Syvert Nørsett. 相似文献
92.
93.
Wuxia Li Georgi Lalev Stefan Dimov Hao Zhao D.T. Pham 《Applied Surface Science》2007,253(7):3608-3614
A dual-beam scanning electron microscopy (SEM)/focused-ion-beam (FIB) system was used to pattern fused silica substrates coated with a 15 nm thin Cr layer. The dimensions of fabricated features together with their surface morphology and profiles were investigated by SEM and atomic force microscopy (AFM). The study demonstrated that with the increase of the ion beam fluence the sputtering rate of the fused silica decreased non-linearly. Also, it was found that initially the sputtering rate increased with the increase of the beam current, after reaching a maximum value, it started decreasing when further beam current increment was performed. Compared with unprocessed areas, the surface finish of the features fabricated by FIB exhibited a significant improvement, and the ion fluence influence on the surface roughness of trenches with low aspect ratios could be considered as negligible. Using a fine beam probe, nano-gratings in the form of grooves with a width down to 54 nm and an aspect ratio higher than three were fabricated. The study showed that FIB machining could be an alternative technology to e-beam lithography for producing fused silica templates for UV nanoimprinting. 相似文献
94.
Although they are simple techniques from the early days of timetabling research, graph colouring heuristics are still attracting
significant research interest in the timetabling research community. These heuristics involve simple ordering strategies to
first select and colour those vertices that are most likely to cause trouble if deferred until later. Most of this work used
a single heuristic to measure the difficulty of a vertex. Relatively less attention has been paid to select an appropriate
colour for the selected vertex. Some recent work has demonstrated the superiority of combining a number of different heuristics
for vertex and colour selection. In this paper, we explore this direction and introduce a new strategy of using linear combinations
of heuristics for weighted graphs which model the timetabling problems under consideration. The weights of the heuristic combinations
define specific roles that each simple heuristic contributes to the process of ordering vertices. We include specific explanations
for the design of our strategy and present the experimental results on a set of benchmark real world examination timetabling
problem instances. New best results for several instances have been obtained using this method when compared with other constructive
methods applied to this benchmark dataset. 相似文献
95.
It has been shown in an earlier paper [G. Navarro, Pham Huu Tiep, Rational Brauer characters, Math. Ann. 335 (2006) 675-686] that, for any odd prime p, every finite group of even order has a non-trivial rational-valued irreducible p-Brauer character. For p=2 this statement is no longer true. In this paper we determine the possible non-abelian composition factors of finite groups without non-trivial rational-valued irreducible 2-Brauer characters. We also prove that, if p≠q are primes, then any finite group of order divisible by q has a non-trivial irreducible p-Brauer character with values in the cyclotomic field Q(exp(2πi/q)). 相似文献
96.
Houxiang Sean Tang Theresa J. Hermel‐Davidock Stephen F. Hahn Dan J. Murray Robert C. Cieslinski Nikhil E. Verghese Ha Q. Pham 《Journal of Polymer Science.Polymer Physics》2009,47(4):393-406
Microdeformation behavior in nanostructured block copolymer‐toughened epoxy resins, or templated epoxy thermosets, was studied using an in situ tensile deformation technique performed directly in a transmission electron microscope. The observed microdeformation modes were found to correlate well with the macroscopic mechanical properties of the materials. In the order of decreasing macroscopic fracture toughness, the microdeformation modes were observed to change from large uniform plastic deformation over an extensive area, to localized plastic deformation bands, to little plastic deformation observed in the most brittle material. A similar trend was also observed when samples of the same material were tested at different temperatures, reflecting changes in the deformation mechanism as a function of temperature. Structural defects were observed in nanotoughening phases when plastic deformation was observed. The implication of the observed microdeformation modes to the macroscopic toughening mechanisms is discussed in the context of the micromorphology of the nanometer sized toughening phases and parameters of the epoxy matrix chemistry such as bromination, molecular weight, and interfacial miscibility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 393–406, 2009 相似文献
97.
98.
Yohann Catel Michel Degrange Loïc Le Pluart Pierre‐Jean Madec Thi‐Nhàn Pham Fei Chen Wayne D. Cook 《Journal of polymer science. Part A, Polymer chemistry》2009,47(20):5258-5271
Four new monomers, 3‐(N‐methylacrylamido)propylidenebisphosphonic acid, 3‐(N‐propyl‐acrylamido)propylidenebisphosphonic acid, 3‐(N‐hexylacrylamido)propylidenebisphosphonic acid, and 3‐(N‐octylacrylamido)propylidenebisphosphonic acid, have been synthesized in good yields and fully characterized by 1H, 13C, 31P NMR, and HRMS. The copolymerization of these monomers with N,N′‐diethyl‐1,3‐bis(acrylamido)propane (DEBAAP) has been investigated with differential scanning calorimetry. These mixtures show a higher reactivity than DEBAAP. New self‐etch dental primers, based on these acrylamide monomers, have been formulated. Dentin shear bond strength measurements have shown that primers based on these bisphosphonic acids assure a strong bond between the tooth substance and a dental composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5258–5271, 2009 相似文献
99.
Ngoc Binh Vo Le Anh Nguyen Tung Lam Pham Duy Tien Doan Thanh Binh Nguyen Quoc Anh Ngo 《Tetrahedron letters》2017,58(25):2503-2506
A procedure to exclusively obtain 3′S-cyanoanhydrovinblastine 12 from two naturally occurring vinca-alkaloids (catharanthine and vindoline) in one step with good yield is described. Stereoselective reductions of 12, providing straightforward access to three new vinca-alkaloids, including two diastereomers 3′S-cyano-(4′R,5′-dihydro)-anhydrovinblastine and 3′S-cyano-(4′S,5′-dihydro)-anhydrovinblastine as well as (3′S-aminomethyl)-(4′S,5′-dihydro)-anhydrovinblastine in good yields is also reported. 相似文献
100.
An efficient procedure for synthesizing oxazines was developed by the palladium(0)-catalyzed intramolecular cyclization of a benzamide through a π-allylpalladium (II) complex. Interestingly, the diastereoselectivity of oxazine ring formation was dominantly controlled by the bulkiness of various protecting groups on the secondary alcohols. 相似文献