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排序方式: 共有661条查询结果,搜索用时 31 毫秒
51.
José R. Fonseca Michael I. Friswell John E. Mottershead Arthur W. Lees 《Journal of sound and vibration》2005,288(3):587-599
To incorporate uncertainty in structural analysis, a knowledge of the uncertainty in the model parameters is required. This paper describes efficient techniques to identify and quantify variability in the parameters from experimental data by maximising the likelihood of the measurements, using the well-established Monte Carlo or perturbation methods for the likelihood computation. These techniques are validated numerically and experimentally on a cantilever beam with a point mass at an uncertain location. Results show that sufficient accuracy is attainable without a prohibitive computational effort. The perturbation approach requires less computation but is less accurate when the response is a highly nonlinear function of the parameters. 相似文献
52.
53.
Luigi Ambrosio Irene Fonseca Paolo Marcellini Luc Tartar 《Archive for Rational Mechanics and Analysis》1999,149(1):23-47
. Existence of minimizers for a volume-constrained energy $ E(u) := \int_{\Omega} W(\nabla u)\, dx Existence of minimizers for a volume-constrained energy E(u) : = òW W(?u) dx E(u) := \int_{\Omega} W(\nabla u)\, dx where LN({u = zi}) = ai, i = 1, ?, P, {\cal L}^N(\{u = z_i\}) = \alpha_i, i = 1, \ldots, P, is proved for the case in which ziz_i are extremal points of a compact, convex set in \Bbb Rd\Bbb R^d and under suitable assumptions on a class of quasiconvex energy densities W. Optimality properties are studied in the scalar-valued problem where d=1d=1, P=2P=2, W(x)=|x|2W(\xi)=|\xi|^2, and the &-limit as the sum of the measures of the 2 phases tends to \L(W)\L(\Omega) is identified. Minimizers are fully characterized when N=1N=1, and candidates for solutions are studied for the circle and the square in the plane. 相似文献
54.
Pedro Silva Sofia M. Fonseca Cláudia T. Arranja Hugh D. Burrows Ana M. Urbano Abilio J. F. N. Sobral 《Photochemistry and photobiology》2010,86(5):1147-1153
A new 5,10,15,20-tetra-(phenoxy-3-carbonyl-1-amino-naphthyl)-porphyrin was prepared by an isocyanate condensation reaction and its photophysical properties fully evaluated, both in terms of photostability and singlet oxygen production. It shows considerably enhanced photostability when compared with the parent 5,10,15,20-tetra-(3-hydroxy-phenyl)-porphyrin, with the photodegradation quantum yields for T(NAF)PP and T(OH)PP being 4.65 × 10−4 and 5.19 × 10−3, respectively. Its photodynamic effect in human carcinoma HT-29 cells was evaluated. The new porphyrin showed good properties as a sensitizer in photodynamic therapy with an in vitro cytotoxicity IC50 value of 6.80 μg mL−1 for a 24 h incubation. In addition to the potential of this compound, the synthetic route used provides possibilities of extension to a wide range of new sensitizers. 相似文献
55.
Manuel J. S. Monte Luís M. N. B. F. Santos José M. S. Fonseca Carlos A. D. Sousa 《Journal of Thermal Analysis and Calorimetry》2010,100(2):465-474
The vapour pressures of six para-substituted benzoic acids were measured using the Knudsen effusion method within the pressure range (0.1–1 Pa) in the following
temperature intervals: 4-hydroxybenzoic acid (365.09–387.28) K; 4-cyanobenzoic acid (355.14–373.28) K; 4-(methylamino)benzoic
acid (359.12–381.29) K; 4-(dimethylamino)benzoic acid (369.29–391.01) K; 4-(acetylamino)benzoic acid (423.10–443.12) K; 4-acetoxybenzoic
acid (351.28–373.27) K. From the temperature dependence of the vapour pressure, the standard molar enthalpy, entropy and Gibbs
energy of sublimation, at the temperature 298.15 K, were derived for each of the studied compounds using estimated values
of the heat capacity differences between the gaseous and the crystalline phases. Equations for estimating the vapour pressure
of para substituted benzoic acids at the temperature of 298.15 K are proposed. 相似文献
56.
Célia Fonseca Guerra Tushar van der Wijst Jordi Poater Marcel Swart F. Matthias Bickelhaupt 《Theoretical chemistry accounts》2010,125(3-6):245-252
We have investigated the performance of the dispersion-corrected density functionals (BLYP-D, BP86-D and PBE-D) and the widely used B3LYP functional for describing the hydrogen bonds and the stacking interactions in DNA base dimers. For the gas-phase situation, the bonding energies have been compared to the best ab initio results available in the literature. All dispersion-corrected functionals reproduce well the ab initio results, whereas B3LYP fails completely for the stacked systems. The use of the proper functional leads us to find minima for the adenine quartets, which are energetically and structurally very different from the C4h structures, and might explain why adenine has to be sandwiched between guanine quartets to form planar adenine quartets. 相似文献
57.
58.
A. L. F. Briso M. S. M. Fonseca L. C. A. G. de Almeida S. J. Mauro P. H. dos Santos 《Laser Physics》2010,20(12):2066-2069
This study evaluated the color alteration of teeth subjected to the action of different bleaching agents and the influence
of light sources commonly used in association with these products, In GI, the specimens remained immersed in artificial saliva.
The specimens in GII were bleached with a 10% carbamide peroxide gel 4 hours/day during 3 weeks; the teeth in the other three
groups were subjected to three sessions of three 10-min applications of 35% hydrogen peroxide gel at 7-day intervals. In GIII,
no light was used, while in GIV and GV the gel was associated with a quartz-tungsten-halogen light and a LED/laser source,
respectively. The teeth color was evaluated before and 7 days after the bleaching sessions by reflectance spectrophotometry.
Data were analyzed statistically by ANOVA and Fisher’s test (α = 0.05), and showed that a significant color change was obtained
in all treated groups. After the first week of treatment and at the end of it, the bleaching protocols showed similar results.
The results of the present study indicate that association of a light source is not necessary to obtain the bleaching effect
and that optimal bleaching can be achieved with all techniques tested. 相似文献
59.
Nattascha Kyaw Rafael Fonseca de Mesquita Etel Kameda João Crisósthomo de Queiroz Neto Marta Antunes Pereira Langone Maria Alice Zarur Coelho 《Applied biochemistry and biotechnology》2010,161(1-8):171-180
Drilling fluid has many functions, such as carry cuttings from the hole permitting their separation at the surface, cool and clean the bit, reduce friction between the drill pipe and wellbore, maintain the stability of the wellbore, and prevent the inflow of fluids from the wellbore and form a thin, low-permeable filter cake. Filter cake removal is an important step concerning both production and injection in wells, mainly concerning horizontal completion. The drilling fluids are typically comprised of starch, the most important component of the filter cake. A common approach to remove this filter cake is the use of acid solutions. However, these are non-specific reactants. A possible alternative is the use of enzymatic preparations, like amylases, that are able to hydrolyze starch. Wells usually operate in drastic conditions for enzymatic preparations, such as high temperature, high salt concentration, and high pressure. Thus, the main objective of this work was to characterize four enzymatic preparations for filter cake removal under open hole conditions. The results showed that high salt concentrations (204,000 ppm NaCl) in completion fluid decreased amylolytic activity. All enzymatic preparations were able to catalyze starch hydrolysis at all temperatures tested (30, 65, 80, and 95 °C). An increase of amylolytic activity was observed with the increase of pressure (100, 500 and 1,000 psi) for one commercial amylase. 相似文献
60.
Renato M. Fonseca Jorge C. Rom?o Ana M. Teixeira 《The European Physical Journal C - Particles and Fields》2012,72(11):1-16
We present a generator for single top-quark production via flavour-changing neutral currents. The MEtop event generator allows for Next-to-Leading-Order direct top production pp??t and Leading-Order production of several other single top processes. A?few packages with definite sets of dimension six operators are available. We discuss how to improve the bounds on the effective operators and how well new physics can be probed with each set of independent dimension six operators. 相似文献