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排序方式: 共有251条查询结果,搜索用时 234 毫秒
21.
Silke C. Wenzel Holger Hoffmann Jidong Zhang Laurent Debussche Sabine Haag‐Richter Michael Kurz Frederico Nardi Peer Lukat Irene Kochems Heiko Tietgen Dietmar Schummer Jean‐Paul Nicolas Loreley Calvet Valerie Czepczor Patricia Vrignaud Agnes Mühlenweg Stefan Pelzer Rolf Müller Mark Brnstrup 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(51):15781-15785
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23.
Paulo B. Gonçalves Frederico M. A. Silva Zenón J. G. N. Del Prado 《Nonlinear dynamics》2007,50(1-2):121-145
In the present study, the large-amplitude vibrations and stability of a perfect circular cylindrical shell subjected to axial
harmonic excitation in the neighborhood of the lowest natural frequencies are investigated. Donnell's shallow shell theory
is used and the shell spatial discretization is obtained by the Ritz method. An efficient low-dimensional model presented
in previous publications is used to discretize the continuous system. The main purpose of this work is to discuss the use
of basins of attraction as a measure of the reliability and safety of the structure. First, the nonlinear behavior of the
conservative system is discussed and the basin structure and volume is understood from the topologic structure of the total
energy and its evolution as a function of the system parameters. Then, the behavior of the forced oscillations of the harmonically
excited shell is analyzed. First the stability boundaries in force control space are obtained and the bifurcation events connected
with these boundaries are identified. Based on the bifurcation diagrams, the probability of parametric instability and escape
are analyzed through the evolution and erosion of basin boundaries within a prescribed control volume defined by the manifolds.
Usually, basin boundaries become fractal. This together with the presence of catastrophic subcritical bifurcations makes the
shell very sensitive to initial conditions, uncertainties in system parameters, and initial imperfections. Results show that
the analysis of the evolution of safe basins and the derivation of appropriate measures of their robustness is an essential
step in the derivation of safe design procedures for multiwell systems. 相似文献
24.
Pham VT Penfold TJ van der Veen RM Lima F El Nahhas A Johnson SL Beaud P Abela R Bressler C Tavernelli I Milne CJ Chergui M 《Journal of the American Chemical Society》2011,133(32):12740-12748
Picosecond and femtosecond X-ray absorption spectroscopy is used to probe the changes of the solvent shell structure upon electron abstraction of aqueous iodide using an ultrashort laser pulse. The transient L(1,3) edge EXAFS at 50 ps time delay points to the formation of an expanded water cavity around the iodine atom, in good agreement with classical and quantum mechanical/molecular mechanics (QM/MM) molecular dynamics (MD) simulations. These also show that while the hydrogen atoms pointed toward iodide, they predominantly point toward the bulk solvent in the case of iodine, suggesting a hydrophobic behavior. This is further confirmed by quantum chemical (QC) calculations of I(-)/I(0)(H(2)O)(n=1-4) clusters. The L(1) edge sub-picosecond spectra point to the existence of a transient species that is not present at 50 ps. The QC calculations and the QM/MM MD simulations identify this transient species as an I(0)(OH(2)) complex inside the cavity. The simulations show that upon electron abstraction most of the water molecules move away from iodine, while one comes closer to form the complex that lives for 3-4 ps. This time is governed by the reorganization of the main solvation shell, basically the time it takes for the water molecules to reform an H-bond network. Only then is the interaction with the solvation shell strong enough to pull the water molecule of the complex toward the bulk solvent. Overall, much of the behavior at early times is determined by the reorientational dynamics of water molecules and the formation of a complete network of hydrogen bonded molecules in the first solvation shell. 相似文献
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27.
Valfredo Azevedo Lemos Moacy Selis Santos Márcio José Silva dos Santos Daniel Rodrigues Vieira Cleber Galvão Novaes 《Mikrochimica acta》2007,157(3-4):215-222
Cloud point extraction employing the new reagent 6-[2′-(6′-methyl-benzothiazolylazo)]-1,2-dihydroxy-3,5-benzenedisulfonic
acid as complexing agent and Triton X-114 as the surfactant is proposed for copper determination. A sample volume of 10 mL
was used. Dilution of the surfactant-rich phase with acidified methanol was performed after phase separation, and the copper
contents were measured by flame atomic absorption spectrometry. Variables affecting the system were optimized using factorial
design and Doehlert matrix. Signals were measured as peak height using an instrument software. Using the experimental conditions
defined in the optimization, the method allowed copper determination with a detection limit of 1.5 μg L−1. The calculated enrichment factor is 14. The effects of foreign ions are reported. The accuracy of the procedure was tested
by analyzing certified reference material. The method was successfully applied to copper determination in natural and drinking
water samples. 相似文献
28.
29.
S.K. Adhikari T. Frederico 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):219-222
It is shown that the appearance of a fixed-point singularity in the kernel of the two-electron Cooper problem is responsible
for the formation of the Cooper pair for an arbitrarily weak attractive interaction between two electrons. This singularity
is absent in the problem of three and few superconducting electrons at zero temperature on the full Fermi sea. Consequently,
such three- and few-electron systems on the full Fermi sea do not form Cooper-type bound states for an arbitrarily weak attractive
pair interaction.
Received: 9 February 1998 / Revised and Accepted: 13 May 1998 相似文献
30.
Frederico Xavier 《Mathematische Annalen》1984,269(2):179-182