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81.
A. Bayón F. Gascón R. Medina F.J. Nieves F.J. Salazar 《Journal of sound and vibration》2012,331(10):2315-2333
The flexural vibration of a homogeneous isotropic linearly elastic cylinder of any aspect ratio is analysed in this paper. Natural frequencies of a cylinder under uniformly distributed axial loads acting on its bases are calculated numerically by the Ritz method with terms of power series in the coordinate directions as approximating functions. The effect of axial loads on the flexural vibration cannot be described by applying infinitesimal strain theory, therefore, geometrically nonlinear strain–displacement relations with second-order terms are considered here. The natural frequencies of free–free, clamped–clamped, and sliding–sliding cylinders subjected to axial loads are calculated using the proposed three-dimensional Ritz approach and are compared with those obtained with the finite element method and the Bernoulli–Euler theory. Different experiments with cylinders axially compressed by a hydraulic press are carried out and the experimental results for the lowest flexural frequency are compared with the numerical results. An approach based on the Ritz formulation is proposed for the flexural vibration of a cylinder between the platens of the press with constraints varying with the intensity of the compression. The results show that for low compressions the cylinder behaves similarly to a sliding–sliding cylinder, whereas for high compressions the cylinder vibrates as a clamped–clamped one. 相似文献
82.
J. de Jong L. Cao S. H. Woodward J. P. L. C. Salazar L. R. Collins H. Meng 《Experiments in fluids》2009,46(3):499-515
Measuring the turbulent kinetic energy dissipation rate in an enclosed turbulence chamber that produces zero-mean flow is
an experimental challenge. Traditional single-point dissipation rate measurement techniques are not applicable to flows with
zero-mean velocity. Particle image velocimetry (PIV) affords calculation of the spatial derivative as well as the use of multi-point
statistics to determine the dissipation rate. However, there is no consensus in the literature as to the best method to obtain
dissipation rates from PIV measurements in such flows. We apply PIV in an enclosed zero-mean turbulent flow chamber and investigate
five methods for dissipation rate estimation. We examine the influence of the PIV interrogation cell size on the performance
of different dissipation rate estimation methods and evaluate correction factors that account for errors related to measurement
uncertainty, finite spatial resolution, and low Reynolds number effects. We find the Re
λ
corrected, second-order, longitudinal velocity structure function method to be the most robust method to estimate the dissipation
rate in our zero-mean, gaseous flow system. 相似文献
83.
Mary C. Salazar José L. Paz Antonio J. Hernández Carlos I Manzanares Eduardo V. Ludeña 《Theoretical chemistry accounts》2001,106(3):218-222
In the present contribution we report a study of the weakly bound van der Waals N2–He molecule in the framework of the supermolecule approach by means of the PWPW and mPW1PW exchange–correlation functionals,
using density functional theory local-spin-optimized atom-centered basis sets complemented with bond functions optimized at
the mPW1PW level of theory. Calculations show that the mPW1PW functional using bond functions gives a realistic representation
of the interaction-energy potentials for this van der Waals dimer, comparable to reference M?ller–Plesset perturbation theory
calculations. In contrast, the PWPW functional is unable to describe the bonding properties of this system and all values
of the bonding properties obtained at different geometries with this functional are considered out-of-scale compared with
the rest of the calculations presented in this study.
Received: 30 October 2000 / Accepted: 3 January 2001 / Published online: 3 April 2001 相似文献
84.
L. Z. Meneghini C. A. Junqueira F. R. Salazar M. Brandalise P. E. Fröehlich A. M. Bergold 《Journal of Analytical Chemistry》2013,68(9):772-780
A set of experimental designs was applied to develop and validate a spectrophotometric method using derivative transformation coupled with zero-crossing methodology for the quantification of darifenacin hydrobromide in extended-release tablet form. In the presence of the matricial interference, a central composite (face-centered) design was necessary to reach the best condition without interference in the quantification. The optimal system was confirmed using the function named Derringer’s desirability to assess high precision and low quantification limit. The best condition pointed was the first order to derivative transformation, Δλ = 4, scale factor 150, scanning speed 280 nm/s and anulation point in 239.4 nm as wavelength. From these parameters it was possible to perform the method validation resulting in R 2 = 0.999, concentration ranging from 0.10 to 2.50 μg/mL, recovery 98.65% and mean precision 97.67% (RSD = 0.0136). Additionally, robustness was assessed by a Plackett-Burman design, and no significant variability was obtained. The spectrophotometric method was compared with high-performance liquid chromatography method, resulting in no significant difference between the methods. 相似文献
85.
U. Wagner F. E. Wagner A. Stockklauser R. Salazar J. Riederer F. Kauffmann-Doig 《Hyperfine Interactions》1986,29(1-4):1113-1116
A large number of ceramic sherds from Chavin, Peru, as well as recent clay samples from the same region have been studied by Mössbauer spectroscopy. The changes of the Mössbauer spectra of the clay were studied as a function of firing temperature and atmosphere. From a comparison of these data with those form the sherds one can make estimates of the precolumbian firing conditions. 相似文献
86.
U. Wagner F. E. Wagner B. Marticorena R. Salazar R. Schwabe J. Riederer 《Hyperfine Interactions》1986,29(1-4):1117-1120
To obtain information on the firing of inca ceramics, 7 samples from different locations were studied by Mössbauer spectroscopy including a detailed laboratory refiring procedure. The glaze typical for the surface of this ware was studied by Mössbauer scattering. 相似文献
87.
U. Wagner W. Knorr A. Forster E. Murad R. Salazar F. E. Wagner 《Hyperfine Interactions》1988,41(1):855-858
An illite separated from mylonites from the southern rim of the Bohemian massif was studied by Mössbauer spectroscopy at temperatures between 300 and 1.8 K. The iron is mainly contained in oxides associated with the illite. Only 13% of the iron are structural Fe3+ and Fe2+ within the clay mineral matrix. The transformations of the oxidic iron during heating at temperatures up to 1250°C were followed by Mössbauer measurements at 300 and 4.2 K. 相似文献
88.
Loreto Salazar Julia Rubido Modesta Espada Carmen Pedregal Gregorio Trigo Jos Elguero 《Journal of heterocyclic chemistry》1986,23(2):481-485
N3-Substituted hydantoins have been to undergo lithium aluminum hydride reduction (THF, room temperature, 5 hours) to give 4-hydroxy-2-imidazolidinones in good yields. 相似文献
89.
Salazar MR 《The journal of physical chemistry. A》2005,109(50):11515-11520
A novel way of assembling the total potential for performing molecular dynamical studies of complex gas-phase reactive chemical systems is introduced. The method breaks the calculation of the total potential and gradients of the potential into time-dependent groups that are governed by spatial cutoffs. These groups evolve during the course of the simulation and their number may increase or diminish as the dynamics of the system determine. In an effort to extend the simulation time of these complex reactive processes and to use high levels of theory when necessary, multiple levels of theory may be used over the groups for the calculation of both the intragroup and intergroup interactions. Representative simulations are performed to illustrate the method and a computationally facile method of obtaining the groups of a simulation are also discussed. 相似文献
90.