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Frequency Effect (frequency + effect)
Selected AbstractsDepth of detection of highly conducting and volume polarizable targets using induced polarizationGEOPHYSICAL PROSPECTING, Issue 5 2000A. Apparao We define the apparent frequency effect in induced polarization (IP) as the relative difference between apparent resistivities measured using DC excitation on the one hand and high-frequency excitation (when the IP effect vanishes) on the other. Assuming a given threshold for the minimum detectable anomaly in the apparent frequency effect, the depth of detection of a target by IP can be defined as that depth below which the target response is lower than the threshold for a given electrode array. Physical modelling shows that for the various arrays, the depth of detection of a highly conducting and volume polarizable target agrees closely with the depth of detection of an infinitely conducting and non-polarized body of the same shape and size. The greatest depth of detection is obtained with a two-electrode array, followed by a three-electrode array, while the smallest depth of detection is obtained with a Wenner array when the array spread is in-line (i.e. perpendicular to the strike direction). The depth of detection with a Wenner array improves considerably and is almost equal to that of a two-electrode array when the array spread is broadside (i.e. along the strike direction). [source] Adaptive predistortion of COFDM signals for a mobile satellite channelINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2003Nibaldo Rodriguez Abstract In this paper, we consider the optimization of the performance of QPSK and 16-QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non-linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non-linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non-linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10,3 when compared to QPSK COFDM without the predistortion scheme and 16-QAM COFDM provides a gain of 0.5 dB output back-off and 1.2 dB signal to noise ratio at a BER of 3×10,5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10,4 for QPSK and 16-QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd. [source] Long time investigation of the effect of fouling on the super-heaters in a circulating fluidized biomass boilerINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2006Jan Sandberg Abstract The present investigation involves measurements and theories on the mechanisms of the forming of deposit layers on super-heater tubes in a biomass-fired CFD boiler. The deposit layer thickness and the soot-blowing frequency effect on the super-heaters heat transfer are the main subject of the study that has been conducted over a 3-year period. The measurements show a deposit growth rate on the super-heaters of approximately 4 g m,2 h,1. The distribution of the deposit material varies significantly between the windward and the leeward side of the tubes, with the thickest layers on the windward side. Further down stream of the first super-heater, the fouling problem on the super-heater and re-heater tubes are not so severe. A theoretical model shows that a deposit layer of 20 mm will decrease the heat transfer rate of the first super-heater by nearly 40%. The soot-blowing system shows a strong positive effect on the heat transfer rate of the super-heater a few hours after a soot-blowing sequence has been completed. However in the long run, the varied soot-blowing frequency does not have a significant influence on the deposit layer growth rate. Copyright © 2006 John Wiley & Sons, Ltd. [source] The ,heuristics and biases' bias in expert elicitationJOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES A (STATISTICS IN SOCIETY), Issue 1 2008Mary Kynn Summary., In the early 1970s Tversky and Kahneman published a series of papers on ,heuristics and biases' describing human inadequacies in assessing probabilities, culminating in a highly popular article in Science. This seminal research has been heavily cited in many fields, including statistics, as the definitive research on probability assessment. Curiously, although this work was debated at the time and more recent work has largely refuted many of the claims, this apparent heuristics and biases bias in elicitation research has gone unremarked. Over a decade of research into the frequency effect, the importance of framing, and cognitive models more generally, has been almost completely ignored by the statistical literature on expert elicitation. To remedy this situation, this review offers a guide to the psychological research on assessing probabilities, both old and new, and gives concrete guidelines for eliciting expert knowledge. [source] A new analytical method to extract the small-signal equivalent circuit of high frequency FET transistorsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2008J. L. Olvera Cervantes Abstract A new set of simply analytical equations is proposed as an alternative method to calculate the intrinsic transistor elements of an extended model for microwave FET's. This method is based on Y-parameters as well as on a new process to determine the differential resistances Rfs and Rfd, including the frequency effect, in such way that measurements at very low frequencies are not required and long iterative methods are avoided. The method was applied to FET's transistors and the validity of the model is certified by direct comparison with measured data from 1 to 45 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 453,457, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23130 [source] Dynamics of the ion cyclotron resonance effect on amino acids adsorbed at the interfacesBIOELECTROMAGNETICS, Issue 1 2006N. Comisso Abstract In this study we show a reproduction of the Zhadin experiment, which consists of the transient increase of the electrolytic current flow across an aqueous solution of L -arginine and L -glutamic acid induced by a proper low frequency alternating magnetic field superimposed to a static magnetic field of higher strength. We have identified the mechanisms that were at the origin of the so-far poor reproducibility of the above effect: the state of polarization of the electrode turned out to be a key parameter. The electrochemical investigation of the system shows that the observed phenomenon involves the transitory activation of the anode due to ion cyclotron frequency effect, followed again by anode passivation due to the adsorption of amino acid and its oxidation products. The likely occurrence of similar ion cyclotron resonance (ICR) phenomena at biological membranes, the implications on ion circulation in living matter, and the consequent biological impact of environmental magnetic fields are eventually discussed. Bioelectromagnetics 27:16,25, 2006. © 2005 Wiley-Liss, Inc. [source] | ||||||||||