The Experts below are selected from a list of 179625 Experts worldwide ranked by ideXlab platform
Bronwyn Fox - One of the best experts on this subject based on the ideXlab platform.
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a novel carbon nanofibre phenolic nanocomposite coated polymer system for tailoring thermal behaviour
Composites Part A-applied Science and Manufacturing, 2013Co-Authors: Ehsan Bafekrpour, George P Simon, Chunhui Yang, Mircea Chipara, Jana Habsuda, Bronwyn FoxAbstract:Carbon nanofibre (CNF)/phenolic nanocomposite coatings were applied to the phenolic substrate for tailoring thermal behaviour under rapid temperature changes. A finite element (FE) model was developed in this work for transient thermal analysis of coated samples. The effects of thickness and CNF content of the CNF/phenolic nanocomposite coating on reducing temperature Gradient Field within the samples as well as transient time to steady state were investigated. Temperature-dependent thermal properties including thermal conductivity and heat capacity of phenolic and its nanocomposites containing 2, 4 and 16 wt% CNF were experimentally determined and employed in the FE analysis. The results showed that the temperature Gradient Field and transient time within the polymers can significantly be decreased by using a CNF/phenolic nanocomposite coating.
Bei Yan - One of the best experts on this subject based on the ideXlab platform.
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A Gradient-Field Pulsed Eddy Current Probe for Evaluation of Hidden Material Degradation in Conductive Structures Based on Lift-Off Invariance
Sensors, 2017Co-Authors: Yong Li, Haoqing Jing, Ilham Mukriz Zainal Abidin, Bei YanAbstract:Coated conductive structures are widely adopted in such engineering Fields as aerospace, nuclear energy, etc. The hostile and corrosive environment leaves in-service coated conductive structures vulnerable to Hidden Material Degradation (HMD) occurring under the protection coating. It is highly demanded that HMD can be non-intrusively assessed using non-destructive evaluation techniques. In light of the advantages of Gradient-Field Pulsed Eddy Current technique (GPEC) over other non-destructive evaluation methods in corrosion evaluation, in this paper the GPEC probe for quantitative evaluation of HMD is intensively investigated. Closed-form expressions of GPEC responses to HMD are formulated via analytical modeling. The Lift-off Invariance (LOI) in GPEC signals, which makes the HMD evaluation immune to the variation in thickness of the protection coating, is introduced and analyzed through simulations involving HMD with variable depths and conductivities. A fast inverse method employing magnitude and time of the LOI point in GPEC signals for simultaneously evaluating the conductivity and thickness of HMD region is proposed, and subsequently verified by finite element modeling and experiments. It has been found from the results that along with the proposed inverse method the GPEC probe is applicable to evaluation of HMD in coated conductive structures without much loss in accuracy.
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Gradient Field pulsed eddy current probes for imaging of hidden corrosion in conductive structures
Sensors and Actuators A-physical, 2016Co-Authors: Bei Yan, Deqiang ZhouAbstract:Abstract Pulsed eddy current testing (PEC) has been found advantageous over other non-destructive evaluation (NDE) techniques particularly in detection and characterization of subsurface defects in conductive structures. The measurement of net magnetic Field for acquisition of transient signals is normally employed in traditional PEC during inspection of conductors. In this paper, PEC in conjunction with Gradient Field measurement is investigated in an effort to enhance the inspection sensitivity to hidden corrosion in conductors and accuracy of corrosion imaging. Closed-form expressions of Gradient Field and its sensitivity to hidden corrosion are formulated via the extended truncated region eigenfunction expansion (ETREE) modeling. A series of simulations are subsequently conducted to analyze the characteristics of Gradient Field signals and inspection sensitivity to hidden corrosion. Following this, experiments of Gradient-Field PEC (GPEC) for evaluation and imaging of hidden corrosion are carried out. Through theoretical and experimental investigation, it has been found that the GPEC probe is advantageous over that based on traditional PEC in terms of inspection sensitivity and accuracy of corrosion imaging.
Gary H. Glover - One of the best experts on this subject based on the ideXlab platform.
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generalized reconstruction of phase contrast mri analysis and correction of the effect of Gradient Field distortions
Magnetic Resonance in Medicine, 2003Co-Authors: Michael Markl, Gary H. Glover, Roland Bammer, Marcus T Alley, Christopher J Elkins, Mary T Draney, Alan S Barnett, Michael E Moseley, Norbert J PelcAbstract:To characterize Gradient Field nonuniformity and its effect on velocity encoding in phase contrast (PC) MRI, a generalized model that describes this phenomenon and enables the accurate reconstruction of velocities is presented. In addition to considerable geometric distortions, inhomogeneous Gradient Fields can introduce deviations from the nominal Gradient strength and orientation, and therefore spatially-dependent first Gradient moments. Resulting errors in the measured phase shifts used for velocity encoding can therefore cause significant deviations in velocity quantification. The true magnitude and direction of the underlying velocities can be recovered from the phase difference images by a generalized PC velocity reconstruction, which requires the acquisition of full three-directional velocity information. The generalized reconstruction of velocities is applied using a matrix formalism that includes relative Gradient Field deviations derived from a theoretical model of local Gradient Field nonuniformity. In addition, an approximate solution for the correction of one-directional velocity encoding is given. Depending on the spatial location of the velocity measurements, errors in velocity magnitude can be as high as 60%, while errors in the velocity encoding direction can be up to 45°. Results of phantom measurements demonstrate that effects of Gradient Field nonuniformity on PC-MRI can be corrected with the proposed method. Magn Reson Med 50:791–801, 2003. Published 2003 Wiley-Liss, Inc.
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generalized reconstruction of phase contrast mri analysis and correction of the effect of Gradient Field distortions
Magnetic Resonance in Medicine, 2003Co-Authors: Michael Markl, Gary H. Glover, Roland Bammer, Marcus T Alley, Christopher J Elkins, Mary T Draney, Alan S Barnett, Michael E Moseley, Norbert J PelcAbstract:To characterize Gradient Field nonuniformity and its effect on velocity encoding in phase contrast (PC) MRI, a generalized model that describes this phenomenon and enables the accurate reconstruction of velocities is presented. In addition to considerable geometric distortions, inhomogeneous Gradient Fields can introduce deviations from the nominal Gradient strength and orientation, and therefore spatially-dependent first Gradient moments. Resulting errors in the measured phase shifts used for velocity encoding can therefore cause significant deviations in velocity quantification. The true magnitude and direction of the underlying velocities can be recovered from the phase difference images by a generalized PC velocity reconstruction, which requires the acquisition of full three-directional velocity information. The generalized reconstruction of velocities is applied using a matrix formalism that includes relative Gradient Field deviations derived from a theoretical model of local Gradient Field nonuniformity. In addition, an approximate solution for the correction of one-directional velocity encoding is given. Depending on the spatial location of the velocity measurements, errors in velocity magnitude can be as high as 60%, while errors in the velocity encoding direction can be up to 45 degrees. Results of phantom measurements demonstrate that effects of Gradient Field nonuniformity on PC-MRI can be corrected with the proposed method.
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analysis and generalized correction of the effect of spatial Gradient Field distortions in diffusion weighted imaging
Magnetic Resonance in Medicine, 2003Co-Authors: Roland Bammer, Gary H. Glover, Michael Markl, Marcus T Alley, Alan S Barnett, Norbert J Pelc, Burak Acar, Michael E MoseleyAbstract:Nonuniformities of magnetic Field Gradients can cause serious artifacts in diffusion imaging. While it is well known that nonlinearities of the imaging Gradients lead to image warping, those imperfections can also cause spatially dependent errors in the direction and magnitude of the diffusion encoding. This study shows that the potential errors in diffusion imaging are considerable. Further, we show that retrospective corrections can be applied to reduce these errors. A general mathematical framework was formulated to characterize the contribution of Gradient nonuniformities to diffusion experiments. The Gradient Field was approximated using spherical harmonic expansion, and this approximation was employed (after geometric distortions were eliminated) to predict and correct the errors in diffusion encoding. Before the corrections were made, the experiments clearly revealed marked deviations of the calculated diffusivity for Fields of view (FOVs) generally used in diffusion experiments. These deviations were most significant farther away from the magnet's isocenter. For an FOV of 25 cm, the resultant errors in absolute diffusivity ranged from approximately -10% to +20%. Within the same FOV, the diffusion-encoding direction and the orientation of the calculated eigenvectors can be significantly altered if the perturbations by the Gradient nonuniformities are not considered. With the proposed correction scheme, most of the errors introduced by Gradient nonuniformities can be removed.
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Characterization of spatial distortion in magnetic resonance imaging and its implications for stereotactic surgery
Neurosurgery, 1994Co-Authors: Thilaka S. Sumanaweera, Sandy Napel, John R Adler, Gary H. GloverAbstract:The different sources of spatial distortion in magnetic resonance images are reviewed from the point of view of stereotactic target localization. The extents of the two most complex sources of spatial distortion, Gradient Field nonlinearities and magnetic Field inhomogeneities, are discussed both qualitatively and quantitatively. Several ways by which the spatial distortion resulting from these sources can be minimized are discussed. The clinical relevance of the spatial distortion along with some strategies to minimize the localization errors in magnetic resonance-guided stereotaxy are presented.
Ehsan Bafekrpour - One of the best experts on this subject based on the ideXlab platform.
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a novel carbon nanofibre phenolic nanocomposite coated polymer system for tailoring thermal behaviour
Composites Part A-applied Science and Manufacturing, 2013Co-Authors: Ehsan Bafekrpour, George P Simon, Chunhui Yang, Mircea Chipara, Jana Habsuda, Bronwyn FoxAbstract:Carbon nanofibre (CNF)/phenolic nanocomposite coatings were applied to the phenolic substrate for tailoring thermal behaviour under rapid temperature changes. A finite element (FE) model was developed in this work for transient thermal analysis of coated samples. The effects of thickness and CNF content of the CNF/phenolic nanocomposite coating on reducing temperature Gradient Field within the samples as well as transient time to steady state were investigated. Temperature-dependent thermal properties including thermal conductivity and heat capacity of phenolic and its nanocomposites containing 2, 4 and 16 wt% CNF were experimentally determined and employed in the FE analysis. The results showed that the temperature Gradient Field and transient time within the polymers can significantly be decreased by using a CNF/phenolic nanocomposite coating.
Norbert J Pelc - One of the best experts on this subject based on the ideXlab platform.
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generalized reconstruction of phase contrast mri analysis and correction of the effect of Gradient Field distortions
Magnetic Resonance in Medicine, 2003Co-Authors: Michael Markl, Gary H. Glover, Roland Bammer, Marcus T Alley, Christopher J Elkins, Mary T Draney, Alan S Barnett, Michael E Moseley, Norbert J PelcAbstract:To characterize Gradient Field nonuniformity and its effect on velocity encoding in phase contrast (PC) MRI, a generalized model that describes this phenomenon and enables the accurate reconstruction of velocities is presented. In addition to considerable geometric distortions, inhomogeneous Gradient Fields can introduce deviations from the nominal Gradient strength and orientation, and therefore spatially-dependent first Gradient moments. Resulting errors in the measured phase shifts used for velocity encoding can therefore cause significant deviations in velocity quantification. The true magnitude and direction of the underlying velocities can be recovered from the phase difference images by a generalized PC velocity reconstruction, which requires the acquisition of full three-directional velocity information. The generalized reconstruction of velocities is applied using a matrix formalism that includes relative Gradient Field deviations derived from a theoretical model of local Gradient Field nonuniformity. In addition, an approximate solution for the correction of one-directional velocity encoding is given. Depending on the spatial location of the velocity measurements, errors in velocity magnitude can be as high as 60%, while errors in the velocity encoding direction can be up to 45 degrees. Results of phantom measurements demonstrate that effects of Gradient Field nonuniformity on PC-MRI can be corrected with the proposed method.
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generalized reconstruction of phase contrast mri analysis and correction of the effect of Gradient Field distortions
Magnetic Resonance in Medicine, 2003Co-Authors: Michael Markl, Gary H. Glover, Roland Bammer, Marcus T Alley, Christopher J Elkins, Mary T Draney, Alan S Barnett, Michael E Moseley, Norbert J PelcAbstract:To characterize Gradient Field nonuniformity and its effect on velocity encoding in phase contrast (PC) MRI, a generalized model that describes this phenomenon and enables the accurate reconstruction of velocities is presented. In addition to considerable geometric distortions, inhomogeneous Gradient Fields can introduce deviations from the nominal Gradient strength and orientation, and therefore spatially-dependent first Gradient moments. Resulting errors in the measured phase shifts used for velocity encoding can therefore cause significant deviations in velocity quantification. The true magnitude and direction of the underlying velocities can be recovered from the phase difference images by a generalized PC velocity reconstruction, which requires the acquisition of full three-directional velocity information. The generalized reconstruction of velocities is applied using a matrix formalism that includes relative Gradient Field deviations derived from a theoretical model of local Gradient Field nonuniformity. In addition, an approximate solution for the correction of one-directional velocity encoding is given. Depending on the spatial location of the velocity measurements, errors in velocity magnitude can be as high as 60%, while errors in the velocity encoding direction can be up to 45°. Results of phantom measurements demonstrate that effects of Gradient Field nonuniformity on PC-MRI can be corrected with the proposed method. Magn Reson Med 50:791–801, 2003. Published 2003 Wiley-Liss, Inc.
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analysis and generalized correction of the effect of spatial Gradient Field distortions in diffusion weighted imaging
Magnetic Resonance in Medicine, 2003Co-Authors: Roland Bammer, Gary H. Glover, Michael Markl, Marcus T Alley, Alan S Barnett, Norbert J Pelc, Burak Acar, Michael E MoseleyAbstract:Nonuniformities of magnetic Field Gradients can cause serious artifacts in diffusion imaging. While it is well known that nonlinearities of the imaging Gradients lead to image warping, those imperfections can also cause spatially dependent errors in the direction and magnitude of the diffusion encoding. This study shows that the potential errors in diffusion imaging are considerable. Further, we show that retrospective corrections can be applied to reduce these errors. A general mathematical framework was formulated to characterize the contribution of Gradient nonuniformities to diffusion experiments. The Gradient Field was approximated using spherical harmonic expansion, and this approximation was employed (after geometric distortions were eliminated) to predict and correct the errors in diffusion encoding. Before the corrections were made, the experiments clearly revealed marked deviations of the calculated diffusivity for Fields of view (FOVs) generally used in diffusion experiments. These deviations were most significant farther away from the magnet's isocenter. For an FOV of 25 cm, the resultant errors in absolute diffusivity ranged from approximately -10% to +20%. Within the same FOV, the diffusion-encoding direction and the orientation of the calculated eigenvectors can be significantly altered if the perturbations by the Gradient nonuniformities are not considered. With the proposed correction scheme, most of the errors introduced by Gradient nonuniformities can be removed.
