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Isabel Cristina S. F. Jardim Kenneth E. Collins Carol H. Collins 《Microchemical Journal》2004,77(2):191-198
Polysiloxanes immobilized onto the surfaces of porous silica particles have proven to be good stationary phases for the separation of multiresidues of pesticides and their metabolic/degradation products by reversed-phase high-performance liquid chromatography (RP-HPLC). Similar materials have proven effective for pre-concentration and clean-up procedures using solid phase extraction. The present paper describes the preparation and some applications of several of these packing materials. 相似文献
23.
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
24.
Colin J. Thompson Keith M. Briggs Peter Farrell Anthony Fleming Bruce Hocking Kenneth Joyner Vitas Anderson Andrew W. Wood 《Physica A》1995,220(3-4):471-484
A nonlinear Lorenz model describing interactions between charged particles and combined ac-dc electromagnetic fields is studied for various combinations of frequencies, field strengths and relative angle (θ) between the ac and dc magnetic fields. Strong directional effects on the magnitude and location of resonant particle motion are observed when θ is varied and the regular resonance windows in the aligned field (θ = 0) and linear version of the model studied previously by Durney etaal., break up to form irregular and less well pronounced regions of large and small particle displacements when nonlinearities are taken into account. The length of time takne to achieve resonant behaviour also becomes larger and more variable when nonlinearities are present. The possible relevance of these effects to interactions between electromagnetic fields and biological media is briefly discussed. 相似文献
25.
Xinyu Huang Roham Solasi Yue Zou Matthew Feshler Kenneth Reifsnider David Condit Sergei Burlatsky Thomas Madden 《Journal of Polymer Science.Polymer Physics》2006,44(16):2346-2357
The life of proton exchange membrane fuel cells (PEMFC) is currently limited by the mechanical endurance of polymer electrolyte membranes and membrane electrode assemblies (MEAs). In this paper, the authors report recent experimental and modeling work toward understanding the mechanisms of delayed mechanical failures of polymer electrolyte membranes and MEAs under relevant PEMFC operating conditions. Mechanical breach of membranes/MEAs in the form of pinholes and tears has been frequently observed after long‐term or accelerated testing of PEMFC cells/stacks. Catastrophic failure of cell/stack due to rapid gas crossover shortly follows the mechanical breach. Ex situ mechanical characterizations were performed on MEAs after being subjected to the accelerated chemical aging and relative humidity (RH) cycling tests. The results showed significant reduction of MEA ductility manifested as drastically reduced strain‐to‐failure of the chemically aged and RH‐cycled MEAs. Postmortem analysis revealed the formation and growth of mechanical defects such as cracks and crazing in the membranes and MEAs. A finite element model was used to estimate stress/strain states of an edge‐constrained MEA under rapid RH variations. Damage metrics for accelerated testing and life prediction of PEMFCs are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2346–2357, 2006 相似文献
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David P. Dobkin Steven J. Friedman Kenneth J. Supowit 《Discrete and Computational Geometry》1990,5(1):399-407
LetS be any set ofN points in the plane and let DT(S) be the graph of the Delaunay triangulation ofS. For all pointsa andb ofS, letd(a, b) be the Euclidean distance froma tob and let DT(a, b) be the length of the shortest path in DT(S) froma tob. We show that there is a constantc (≤((1+√5)/2) π≈5.08) independent ofS andN such that $$\frac{{DT(a,b)}}{{d(a,b)}}< c.$$ 相似文献
28.
Gerald J. Smith Kenneth R. Markham W. Hugh Melhuish 《Photochemistry and photobiology》1994,60(3):196-198
Abstract Solvent-cleaned Merino wool, which was enzymatically digested with protease K, displayed a fluorescence maximum at 500 nm when excited at 430 nm. The yield of this emission was approximately 15 times greater for a fiber tips digest than for a digest of the mid-length region of the same fibers.
Separation of the components in the wool tip digest by silica gel thin-layer chromatography revealed the presence of several fluorescent species. The chromatographic mobility of these species was similar to the behavior observed in a preparation of authentic 1-methyltetrahydro-P-carboline, 1,3-dicarboxylic acid.
Mass spectroscopy of the fluorescent compounds in the wool tip digest displayed molecular ions, [M + H]+ with m/z = 273.0890 and 257.0560, and molecular weights that define the formulae C14 H12 N2 O4 and C11 H8 O4 N2 , respectively, which correspond to β-carboline 1,3-dicarboxylic acids. Mass spectral evidence also indicates the presence of two other β-carbolines. 相似文献
Separation of the components in the wool tip digest by silica gel thin-layer chromatography revealed the presence of several fluorescent species. The chromatographic mobility of these species was similar to the behavior observed in a preparation of authentic 1-methyltetrahydro-P-carboline, 1,3-dicarboxylic acid.
Mass spectroscopy of the fluorescent compounds in the wool tip digest displayed molecular ions, [M + H]
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