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RISS 인기검색어
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- 저자 : McEwan, (검색결과 18 건)
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Measurement and Explanation of DC/RF Power Loci of an Active Patch Antenna
Neil J. McEwan,Nazar T. Ali,Kahtan A. Mezher,Elmahdi A. El-Khazmi,Raed A. Abd-Alhameed 한국전자통신연구원 2011 ETRI Journal Vol.33 No.1
A case study of an active transmitting patch antenna revealed a characteristic loop locus of DC power versus RF output power as drive frequency was varied, with an operational bandwidth substantially smaller than the impedance bandwidth of the radiator. An approximate simulation technique, based on separation of the output capacitance of the power transistor, yielded easily visualized plots of power dependence on internal load impedance, and a simple interpretation of the experimental results in terms of a near-resonance condition between the output capacitance and output packaging inductance.
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A comparison of two EIT systems suitable for imaging impedance changes in epilepsy
Fabrizi, L,McEwan, A,Oh, T,Woo, E J,Holder, D S IOP Pub 2009 PHYSIOLOGICAL MEASUREMENT Vol.30 No.6
<P>Electrical impedance tomography (EIT) has the potential to produce functional images of the conductivity changes associated with epilepsy to help localization of epileptic foci. Scalp voltage changes associated with internal conductivity changes due to focal seizures have been shown at the limit of detectability for present EIT systems. The performances of two EIT systems, which may be employed in clinical recordings during presurgical assessment of intractable epilepsy, were compared. Those were the 32-channel serial UCH Mk2.5 and the 16-channel semi-parallel KHU Mk1. Images of three conductivity perturbations, simulating epileptic foci, in a head-shaped saline tank without and with a real human skull were recorded using 31-channel and 16-channel protocols with the UCH Mk2.5, while only 16-channel protocols with the KHU Mk1. The UCH Mk2.5 employing the 31-channel protocol had better overall performance with a localization error of 12.7% of the tank diameter, which would be sufficient for lateralization of the epileptic activity. More blurred images, but with similar localization, were obtained using 16 electrodes.</P>
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Fabrizi, L,McEwan, A,Woo, E,Holder, D S IOP Pub 2007 PHYSIOLOGICAL MEASUREMENT Vol.28 No.7
<P>Electrical impedance tomography measurements in clinical applications are limited by an undesired noise component. We have investigated the noise in three systems suitable for imaging epileptic seizures, the UCH Mark1b, UCH Mark2.5 and KHU Mark1 16 channel, at applied frequencies in three steps from 1 to 100 kHz, by varying load impedance, single terminal or multiplexed measurements, and in test objects of increasing complexity from a resistor to a saline filled tank and human volunteer. The noise was white, and increased from about 0.03% rms on the resistor to 0.08% on the human; it increased with load but was independent of use of the multiplexer. The KHU Mark1 delivered the best performance with noise spectra of about 0.02%, which could be further reduced by averaging to a level where reliable imaging of changes of about 0.1% estimated during epileptic seizures appears plausible.</P>
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Fabrizi, L,McEwan, A,Oh, T,Woo, E J,Holder, D S IOP Pub 2009 PHYSIOLOGICAL MEASUREMENT Vol.30 No.6
<P>Electrical impedance tomography of brain function poses special problems because applied current is diverted by the resistive skull. In the past, image resolution was maximized with the use of an electrode addressing protocol with widely spaced drive electrode pairs and use of a multiplexer so that many electrode pairs could be flexibly addressed. The purpose of this study was to develop and test an electrode protocol for a 16-channel semi-parallel system which uses parallel recording channels with fixed wiring, the Kyung Hee University (KHU) Mk1. Ten protocols were tested, all addressing pairs of electrodes for recording or current drive, based on recording with a spiral, spiral with suboccipital electrodes (spiral s-o) and zig-zag configurations, and combinations of current injection from electrode pairs at 180°, 120° and 60°. These were compared by assessing the image reconstruction quality of five simulated perturbations in a homogenous model of the human head and of four epileptic foci in an anatomically realistic model in the presence of realistic noise, in terms of localization error, resolution, image distortion and sensitivity in the region of interest. The spiral s-o with current injection at 180°+ 120°+ 60° gave the best image quality and permitted reconstruction with a localization error of less than 10% of the head diameter. This encourages the view that it might be possible to obtain satisfactory images of focal abnormalities in the human brain with 16 scalp electrodes and improved instrumentation avoiding multiplexers on recording circuits.</P>
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Kwon, Hyeuknam,McEwan, Alistair L.,Oh, Tong In,Farooq, Adnan,Woo, Eung Je,Seo, Jin Keun Hindawi Publishing Corporation 2013 Computational and mathematical methods in medicine Vol.2013 No.-
<P>Electrical Impedance Tomography (EIT) is a very attractive functional imaging method despite the low sensitivity and resolution. The use of internal electrodes with the conventional reconstruction algorithms was not enough to enhance image resolution and accuracy in the region of interest (ROI). We propose a local ROI imaging method with internal electrodes developed from careful analysis of the sensitivity matrix that is designed to reduce the sensitivity of the voxels outside the local region and optimize the sensitivity of the voxel inside the local region. We perform numerical simulations and physical measurements to demonstrate the localized EIT imaging method. In preliminary results with multiple objects we show the benefits of using an internal electrode and the improved resolution due to the local ROI image reconstruction method. The sensitivity is further increased by allowing the surface electrodes to be unevenly spaced with a higher density of surface electrodes near the ROI. Also, we analyse how much the image quality is improved using several performance parameters for comparison. While these have not yet been studied in depth, it convincingly shows an improvement in local sensitivity in images obtained with an internal electrode in comparison to a standard reconstruction method.</P>
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Natural Products as Manipulators of Rumen Fermentation
Wallace, R. John,McEwan, Neil R.,McIntosh, Freda M.,Teferedegne, Belete,Newbold, C. James Asian Australasian Association of Animal Productio 2002 Animal Bioscience Vol.15 No.10
There is increasing interest in exploiting natural products as feed additives to solve problems in animal nutrition and livestock production. Essential oils and saponins are two types of plant secondary compounds that hold promise as natural feed additives for ruminants. This paper describes recent advances in research into these additives. The research has generally concentrated on protein metabolism. Dietary essential oils caused rates of NH$_3$ production from amino acids in ruminal fluid taken from sheep and cattle receiving the oils to decrease, yet proteinase and peptidase activities were unchanged. Hyper-ammonia-producing (HAP) bacteria were the most sensitive of ruminal bacteria to essential oils in pure culture. Essential oils also slowed colonisation and digestion of some feedstuffs. Ruminobacter amylophilus may be a key organism in mediating these effects. Saponin-containing plants and their extracts appear to be useful as a means of suppressing the bacteriolytic activity of rumen ciliate protozoa and thereby enhancing total microbial protein flow from the rumen. The effects of some saponins seems to be transient, which may stem from the hydrolysis of saponins to their corresponding sapogenin aglycones, which are much less toxic to protozoa. Saponins also have selective antibacterial effects which may prove useful in, for example, controlling starch digestion. These studies illustrate that plant secondary compounds, of which essential oils and saponins comprise a small proportion, have great potential as 'natural' manipulators of rumen fermentation, to the potential benefit of the farmer and the environment.
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Hun Wi,Sohal, Harsh,McEwan, Alistair Lee,Eung Je Woo,Tong In Oh IEEE 2014 IEEE transactions on biomedical circuits and syste Vol.8 No.1
<P>Electrical Impedance Tomography (EIT) is a safe medical imaging technology, requiring no ionizing or heating radiation, as opposed to most other imaging modalities. This has led to a clinical interest in its use for long-term monitoring, possibly at the bedside, for ventilation monitoring, bleeding detection, gastric emptying and epilepsy foci diagnosis. These long-term applications demand auto-calibration and high stability over long time periods. To address this need we have developed a new multi-frequency EIT system called the KHU Mark2.5 with automatic self-calibration and cooperation with other devices via a timing signal for synchronization with other medical instruments. The impedance measurement module (IMM) for flexible configuration as a key component includes an independent constant current source, an independent differential voltmeter, and a current source calibrator, which allows automatic self-calibration of the current source within each IMM. We installed a resistor phantom inside the KHU Mark2.5 EIT system for intra-channel and inter-channel calibrations of all voltmeters in multiple IMMs. We show the deterioration of performance of an EIT system over time and the improvement due to automatic self-calibration. The system is able to maintain SNR of 80 dB for frequencies up to 250 kHz and below 0.5% reciprocity error over continuous operation for 24 hours. Automatic calibration at least every 3 days is shown to maintain SNR above 75 dB and reciprocity error below 0.7% over 7 days at 1 kHz. A clear degradation in performance results with increasing time between automatic calibrations allowing the tailoring of calibration to suit the performance requirements of each application.</P>
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