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The flow behind a vibrating flexible cable at low Reynolds numbers can exhibit complex wake structures such as lace-like patterns,
vortex dislocations and frequency cells. These structures have been observed in experiments and numerical simulations, and
are predicted by a previously developed low-order coupled map lattice (CML). The discrete (in time and space) CML models consist
of a series of diffusively coupled circle map oscillators along the cable span. Motivated by a desire to modify the complex
wake patterns behind flexible vibrating cables we have studied the addition of control terms into the highly efficient CML
models and explored the resulting dynamics. Proportional, adaptive proportional and discontinuous non-linear (DNL) control
methods were used to derive the control laws. The first method employed occasional proportional feedback. The adaptive method
used spatio-temporal feedback control. The DNL method used a discontinuous feedback linearization procedure, and the controller
was designed for the resulting linearized system using eigenvalue assignment. These techniques were applied to a modeled vortex
dislocation structure in the wake of a vibrating cable in uniform freestream flow. Parallel shedding patterns were achieved
for a range of forcing frequency-forcing amplitude combinations studied to validate the control theory. The adaptive proportional
and DNL methods were found to be more effective than the proportional control method due to the incorporation of a spatially
varying feedback gain across the cylinder span. The DNL method was found to be the most efficient controller of the low-order
CML model. The required control level across the cable span was correlated to the 1/1 lock-on behavior of the temporal circle
map. 相似文献
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The response of giant magnetoresistance (GMR) devices depends critically on the film microstructure, with parameters such
as layer thickness and interfacial abruptness being crucial. This paper presents results obtained using high resolution electron
microscopy (HREM), chemical mapping and atom probe microanalysis. Local variations in the magnetic properties are induced
by the microstructure and also when the films are patterned to form small elements. These lead to changes in the magnetization
reversal mechanism. Some results of the studies of the magnetization reversal carried out using in situ in Lorentz transmission electron microscopy (LTEM) magnetizing experiments are also included. 相似文献
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Liu XM Maziarz EP Heiler DJ Grobe GL 《Journal of the American Society for Mass Spectrometry》2003,14(3):195-202
In this study we compare on-line gel permeation chromatography (GPC) electrospray ionization (ESI) time-of-flight (TOF) mass spectrometry (MS) to automated GPC matrix assisted laser desorption ionization (MALDI) TOF MS for poly (dimethylsiloxane) (PDMS) analysis. Average mass values for a hydroxyl-terminated PDMS (OH-PDMS) sample were obtained and compared to traditional GPC that was calibrated with narrow polystyrene standards, by direct ESI and MALDI MS analysis, by a summation of mass spectra of all GPC fractions, and also by the recalibration method determined by both mass spectrometric methods. Quantitatively, the difference noted here between these hyphenated techniques is that GPC-ESI-TOF MS effectively reports the low-mass oligomers and underestimates the high-mass oligomers, while GPC-MALDI-TOF MS effectively reports the high-mass oligomers and underestimates the low-mass oligomers. In the GPC-ESI-TOF MS experiments, ion current suppression was observed in the high molecular weight region. The suppression effect was confirmed by repeatable sample runs and by injecting different PDMS samples. Higher chromatographic resolution was observed for GPC-ESI-TOF MS compared to GPC-MALDI-TOF MS. In fact, truly mono-disperse oligomers were observed in the low molecular weight range from GPC-ESI MS experiments. 相似文献
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Summary In order to investigate the matrix effects of a hazardous waste landfill leachate in the analysis of priority pollutants by headspace gas chromatography, spiking experiments were performed (a) with the untreated leachate, (b) with the leachate after separation of oil and (c) with blanc water samples as a reference. A standard mixture containing volatile chlorinated hydrocarbons, benzene and alkylated benzenes (100–200 g) were spiked into 50 ml-samples of (a)–(c). The samples were thermostated at 40°C for 20 min and analyzed by headspace GC. Serious matrix effects were observed for all reference compounds, resulting in significant enhancement or depression of the corresponding peak areas compared with the spiked water control samples. The data sets are discussed with respect to the contents of leachate oil and chloride. From the findings of this study, recommendations for the application of headspace analysis to leachates are given. 相似文献
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A. Partheil J. von Velsen Beckurts Heiler M. Mansfeld A. Halenke F. Oelze R. Hefelmann J. H. Long und K. Dieterich 《Fresenius' Journal of Analytical Chemistry》1901,40(6):423-428
Ohne Zusammenfassung 相似文献
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We consider dependence structures in multivariate time series that are characterized by deterministic trends. Results from spectral analysis for stationary processes are extended to deterministic trend functions. A regression cross covariance and spectrum are defined. Estimation of these quantities is based on wavelet thresholding. The method is illustrated by a simulated example and a three-dimensional time series consisting of ECG, blood pressure and cardiac stroke volume measurements. 相似文献
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