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61.
62.
63.
Elvira Vidović Doris Klee Hartwig Höcker 《Journal of polymer science. Part A, Polymer chemistry》2007,45(19):4536-4544
Poly(D ,L ‐lactide) and poly(D ,L ‐lactide‐co‐glycolide) with various composition and with one methacrylate and one carboxylate end group were synthesized and grafted onto poly(vinyl alcohol) (PVA) via the carboxylate group. The graft copolymers were crosslinked via the methacrylate groups using a free radical initiator. The polymer networks were characterized by means of NMR and studied qualitatively by means of IR spectroscopy. The influence of the glycolide content in the polyester grafts and of the number of ester units in the grafts on thermal properties and swellability were studied as well. The high swellability in water is characteristic of all hydrogels. Differential scanning calorimetry (DSC) showed a single glass transition temperature that occurs in the range between 51 and 69 °C. Thermogravimetric analysis (TGA) of the networks showed the main loss in weight in the temperature range between 290 and 370 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4536–4544, 2007 相似文献
64.
This study compared the fracture strength of Class II slot cavities restored with polymerizable restorative materials. Sixty, caries-free, posterior teeth were divided into five groups of 12 teeth. The Class II slot cavities were prepared. The teeth were restored with two packable composites (Filtek P60, Surefil), a microhybrid composite (Filtek Z250)and two ormocer (Definite, Admira). The restorations were then subjected to fracture resistance tests. The marginal ridges of the restorations were loaded at an angle of 13.5° to the long axis of the tooth in an Universal Testing Machine until failure. Analysis of mean forces indicated that, Filtek P60, Surefil and Filtek Z250 exhibited better performance than Definite and Admira. The tested resin composites differed in their mechanical properties. This study suggested that fracture behavior were highly influenced by the filler system. Overall, Filtek P60, Surefil, Filtek Z250, demonstrated good fracture resistance. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
65.
Finding Robust Solutions Using Local Search 总被引:1,自引:0,他引:1
Kenneth Sörensen 《Journal of Mathematical Modelling and Algorithms》2004,3(1):89-103
This paper investigates how a local search metaheuristic for continuous optimisation can be adapted so that it finds broad
peaks, corresponding to robust solutions. This is relevant in problems in which uncertain or noisy data is present. When using
a genetic or evolutionary algorithm, it is standard practice to perturb solutions once before evaluating them, using noise
from a given distribution. This approach however, is not valid when using population-less techniques like local search and
other heuristics that use local search. For those algorithms to find robust solutions, each solution needs to be perturbed
and evaluated several times, and these evaluations need to be combined into a measure of robustness. In this paper, we examine
how many of these evaluations are needed to reliably find a robust solution. We also examine the effect of the parameters
of the noise distribution. Using a simple tabu search procedure, the proposed approach is tested on several functions found
in the literature.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
66.
Jessica Strömbro Peter Gudmundson 《International Journal of Solids and Structures》2008,45(22-23):5765-5787
In this paper a simplified network model for mechano-sorptive creep is presented, which is a further development of an earlier paper [Strömbro, J., Gudmundson, P., 2008. Mechano-sorptive creep under compressive loading – a micromechanical model. International Journal of Solids and Structures 45 (9), 2420–2450.]. It is assumed that the anisotropic hygroexpansion of the fibres leads to large stresses at the fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive effects in compression than in tension. Moisture dependent material parameters and anisotropy in the fibre distribution have been introduced. Theoretical predictions based on the model are compared to experimental results for an anisotropic paper both under tensile and compressive loading at varying moisture content and it is found that the important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined. 相似文献
67.
Earlier measurements in large synchronous generators indicate the existence of backward whirling motion, and also relatively large deviations of shape in both the rotor and the stator. These non-symmetric geometries produce an attraction force between the rotor and the stator, called unbalanced magnetic pull (UMP). The target of this paper is to analyse the whirling frequencies and amplitude of the response for large synchronous generators with a high number of poles, due to deviations of shape in the rotor and stator. A mathematical model is developed to describe the shapes of the rotor and stator, and the corresponding UMP is obtained by using the law of energy conservation. The UMP is analysed due to different deviations of shape. The result gives the average angular frequency and the magnitude of the UMP for certain deviations of shape. From this result, the whirling frequency and the amplitude of the corresponding response can be approximated. Simulations of the response of a Jeffcott rotor model show good agreement with the theoretical results of the UMP for some generator geometries. The conclusion is that different whirling frequencies, both backward and forward whirling, can occur in these machines due to deviations in shape of the generator. Therefore, the shape of the generator can excite resonance vibrations on several other frequencies than the rotation frequency. During maintenance of hydropower generators the shapes of the rotor and stator are frequently measured. The results from this paper can be used to evaluate such measurements and to explain the existence of complicated whirling motion. 相似文献
68.
69.
P.R. Willmott R. Herger M.C. Falub L. Patthey M. Döbeli C.V. Falub M. Shi M. Schneider 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1199-1201
A new ablation target geometry is presented that was used to produce thin films of La1-xSrxMnO3 grown heteroepitaxially on SrTiO3 by pulsed reactive crossed-beam laser ablation. The films were grown in order to perform angle-resolved photoelectron spectroscopy, which demands that the surface be atomically flat. In situ and ex situ analysis shows that this condition was met, even after depositing to a thickness of over 100 nm. PACS 61.10.-i; 61.18.Bn; 68.47.Gh; 71.27.+a; 81.15.Fg 相似文献
70.
D. V. Isakov T. R. Volk L. I. Ivleva K. Betzler C. David A. Tunyagi M. Wöhlecke 《JETP Letters》2004,80(4):258-262
Measurements of 90°-scattering of weak laser light are used to investigate pulsed domain switching in ferroelectrics. The studies were performed on strontium-barium niobate (SBN) single crystals. A good agreement of the switching parameters estimated from the optical measurements with those obtained by means of conventional electrical methods proves the validity of the optical method for switching studies. Due to the limited scattering volume in all three spatial dimensions, the method facilitates local probing of the switching within the crystal bulk. In particular, local specialities of the domain density can be detected. Furthermore, the excellent time resolution inherent in optical probing techniques allows for a comprehensive study of the dynamics. 相似文献