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61.
In this paper we consider a class of systems described by singular integrodifferential equations. This type of systems appear, for example, in the modeling of certain aeroelastic control problems. We study these systems in frequency domain framework and show the existence of finite-dimensional stabilizing controllers. An algorithmic procedure is outlined for the construction of such controllers. In order to illustrate the numerical aspects of this algorithm, we present an example involving the classical Theodorsen model of an airfoil, which fits in the class of systems considered here.This work was supported in part by the National Science Foundation under Grants DMS-8907019 and MSS-9203418. 相似文献
62.
We study the derivation of a Langevin equation from a microscopic basis in order to elucidate the nature of the random force. We arrive at the conclusion that the consistent interpretation of the microscopic Langevin equation in terms of a stochastic differential equation (SDE) is according to I
o rules. In addition, the random force is in general not Gaussian, and it is hence not completely characterized by its second moments. 相似文献
63.
α-Aspartame (L-α-aspartyl-L-phenylalanine methyl ester) is increasingly being used in wide variety of commonly consumed food products. This structure contains ester and peptide bonds. The ester linkage may hydrolyze to produce L-α-aspartyl-L-phenylalanine or cyclohydrolyze to produce the corresponding diketopiperazine ring. This ring can open to form L-α-aspartyl-L-phenylalanine and ultimately this compound can hydrolyze to L-phenylalanine and L-aspartic acid. The pH, buffer type, concentration, the presence of water and temperature are other important factors affecting its stability. Because α-aspartame can lose its sweetness under these conditions determination of aspartame and its breakdown products is extremely important for diet foods quality. The optimum mobile phase for the chromatographic separation was found to be acetonitrile-water (20:80, ν/ν) with 5.10?3 M hexanesulfonic acid and a pH of 2.6. 相似文献
64.
A. Baştuğ Ö. Söğüt Y. Şahin M. Ertuğrul 《Journal of Radioanalytical and Nuclear Chemistry》2002,251(2):323-327
La and Lb X-ray fluorescence cross sections in Er, Ta, W and Au at excitation energies of 16.896, 22.581, 25.770, 32.890, 38.184, 43.949, 50.214 and 59.5 keV were investigated. Measurements were made using a low energy Si(Li) detector coupled to a model 4096 computerized multi-channel analyser. The experimental results were compared with the theoretically calculated values of L X-rays fluorescence cross sections and other experimental results. Good agreement was observed between experimental and theoretical values. 相似文献
65.
Summary A fully integrated chromatographic system was developed for the determination of leukotrienes in biological samples using
photodiode-array detection (PDAD), which eliminates time consuming manual sample handling steps. A special solid phase extraction,
(SPE) methodology for leucotriene metabolite stability was developed which increased the recoveries and eliminates the contamination
risk of biological samples. The inherent instability (autooxidation) of many of the leukotriene mediators, and the adsorption
effects onto exposed surfaces in vials and in the chromatographic system were found to be very important parameters to control
in order to circumvent high loss of sample analytes. By binding the cell supernatants to the functionalities of the SPE support
stabilised these mediators. Cell culture samples were eluted through a disposable C18 SPE column. The SPE columns were allowed to thaw and deposited in an automated sample handling unit (ASPEC XL). Desorption
of the analytes was followed by a second on-line SPE step, to eliminate remaining interfering matrix compounds. Typical recoveries
when stored at −70°C were in-between 55–97% except for (LTE4) which was found to be around 40% after 72 days of storage. Seven reversed-phase packings were studied. Selectivity factors,
as well as the separation efficiencies, were found to differ for the various C18 bonded silica stationary phases. This integrated on-line column liquid chromatographic system was applied to the determination
of leukotriene B4, leukotriene C4, leukotriene D4, leukotriene and E4 in human cell extracts using prostaglandin B2 as the internal standard. More than 1500 biological samples were analysed. Some validation data are presented for unattended
operations. 相似文献
66.
Pierre-Alain Blane Fazil O. Gülaar Armand Buchst 《Journal of mass spectrometry : JMS》1980,15(4):198-201
The mechanisms of formation of the ionized acid and the protonated acid fragments in the electron impact induced fragmentation of the title compounds were investigated. The well known mechanisms of hydrogen transfer through mono- and bicyclic transition states that occur in the molecular ions of carboxylic esters are not the main pathways giving rise to these fragments. The major component of the m/z 172 peak corresponding formally to ionized p-toluenesulfonic acid in fact has a different structure; its formation involves a complex mechanism including a double hydrogen transfer reaction. 相似文献
67.
The densities of ethanol and ethanol–water mixtures were measured with a vibrating tube densimeter at 25.0, 50.0 and 75.0 °C in the pressure range from 0.10 to 40.00 MPa. Densities were correlated using an empirical model. Partial molar volumes, excess molar volumes, isothermal compressibilities, cubic expansion coefficients and internal pressures were calculated from obtained densities. This study reports the dependence of densities, partial molar volumes, excess molar volumes, isothermal compressibilities, cubic expansion coefficients and internal pressures on composition, temperature and pressure. 相似文献
68.
Compton scattering normalization method is described for the analysis of uranium bearing ore respect to the usage of K X-rays of uranium. Minimum backscatter energy is obtained at a scatter angle of 180° with fixed point source geometry and collimation in appropriate conclusions. By normalizing the intensities of uranium K-lines to the Compton profile in the measured spectra, the results do not depend on several measuring parameters such as primary radiation intensity, matrix, composition, mass of the sample and measuring time. The method presented in this study indicates the convenience of uranium K-lines analysis for thick targets with an adequate measuring geometry. 相似文献
69.
Gürses A Karaca S Doğar C Bayrak R Açikyildiz M Yalçin M 《Journal of colloid and interface science》2004,269(2):310-314
In this study, adsorption of methylene blue onto clay was investigated. The effect of adsorption time and temperature on the adsorption process was studied. To reveal the adsorptive characteristics of the clay studied, porosity and BET surface area measurements were made. It was observed that the adsorption capacity decreases with increasing temperature, and adsorption equilibrium was attained within 1 h. It was found that the data fit well to Langmuir, Halsey, Henderson, and Harkins-Jura models but experimental data deviate significantly from BET and Freundlich models at especially high concentrations. Furthermore, isosteric adsorption enthalpy and entropy are calculated as -7.99 kJ mol(-1) and 25.41 JK(-1)mol(-1), respectively. 相似文献
70.
Süleyman Özçeli Hakan Sezgin 《Journal of inclusion phenomena and macrocyclic chemistry》2003,45(3-4):185-190
New Hofmann-diaminohexane(dahxn)-type clathrates of the form M(1,6-dahxn)Ni(CN)4.G (M = Co, Ni or Cd; G = chlorobenzene, 1,2-, 1,3 or 1,4-dichlorobenzene) were prepared inpowder form and their infrared spectra are reported. The spectral data suggest that these compounds are similar in structure to those of the Hofmann-diam-type clathrates. Their structure consists of planar polymeric layers, {M–Ni(CN)4}, formedfrom Ni(CN)4 anions coordinated to the bridging 1,6-diaminohexane molecules bound directly to the metal (M). The M atoms are bound to four N atoms of the CN ions and, the Ni atoms are surrounded by four C atoms of the CN groups in a square-planar layer. 相似文献