The Experts below are selected from a list of 174 Experts worldwide ranked by ideXlab platform
Wuge H. Briscoe - One of the best experts on this subject based on the ideXlab platform.
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Friction at nanopillared polymer surfaces beyond Amontons' laws: Stick-slip Amplitude Coefficient (SSAC) and multiparametric nanotribological properties.
Journal of colloid and interface science, 2020Co-Authors: Mohd I. Ishak, Illia Dobryden, Per M. Claesson, Wuge H. BriscoeAbstract:Frictional and nanomechanical properties of nanostructured polymer surfaces are important to their technological and biomedical applications. In this work, poly(ethylene terephthalate) (PET) surfaces with a periodic distribution of well-defined nanopillars were fabricated through an anodization/embossing process. The apparent surface energy of the nanopillared surfaces was evaluated using the Fowkes acid-base approach, and the surface morphology was characterized using scanning electron microscope (SEM) and atomic force microscope (AFM). The normal and lateral forces between a silica microparticle and these surfaces were quantified using colloidal probe atomic force microscopy (CP-AFM). The friction-load relationship followed Amonton's first law, and the friction Coefficient appeared to scale linearly with the nanopillar height. Furthermore, all the nanopillared surfaces showed pronounced frictional instabilities compared to the smooth sliding friction loop on the flat control. Performing the stick-slip Amplitude Coefficient (SSAC) analysis, we found a correlation between the frictional instabilities and the nanopillars density, pull-off force and work of adhesion. We have summarised the dependence of the nanotribological properties on such nanopillared surfaces on five relevant parameters, i.e. pull-off force fp, Amontons' friction Coefficient μ, RMS roughness Rq, stick-slip Amplitude friction Coefficient SSAC, and work of adhesion between the substrate and water Wadh in a radar chart. Whilst demonstrating the complexity of the frictional behaviour of nanopillared polymer surfaces, our results show that analyses of multiparametric nanotribological properties of nanostructured surfaces should go beyond classic Amontons' laws, with the SSAC more representative of the frictional properties compared to the friction Coefficient.
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sustained frictional instabilities on nanodomed surfaces stick slip Amplitude Coefficient
ACS Nano, 2013Co-Authors: Benoit Quignon, Per M. Claesson, Georgia A Pilkington, Esben Thormann, Michael N R Ashfold, Davide Mattia, Hannah Leese, Sean A Davis, Wuge H. BriscoeAbstract:Understanding the frictional properties of nanostructured surfaces is important because of their increasing application in modern miniaturized devices. In this work, lateral force microscopy was used to study the frictional properties between an AFM nanotip and surfaces bearing well-defined nanodomes comprising densely packed prolate spheroids, of diameters ranging from tens to hundreds of nanometers. Our results show that the average lateral force varied linearly with applied load, as described by Amontons’ first law of friction, although no direct correlation between the sample topographic properties and their measured friction Coefficients was identified. Furthermore, all the nanodomed textures exhibited pronounced oscillations in the shear traces, similar to the classic stick–slip behavior, under all the shear velocities and load regimes studied. That is, the nanotextured topography led to sustained frictional instabilities, effectively with no contact frictional sliding. The Amplitude of the stick–sl...
Patrick Wheeler - One of the best experts on this subject based on the ideXlab platform.
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Research on the Amplitude Coefficient for Multilevel Matrix Converter Space Vector Modulation
IEEE Transactions on Power Electronics, 2012Co-Authors: Xu Lie, Li Yongdong, Wang Kui, Jon Clare, Patrick WheelerAbstract:This paper presents an improved space vector modulation (SVM) using Amplitude Coefficient on a capacitor-clamped multilevel matrix converter (MMC). The MMC utilizes a multilevel structure on a conventional matrix converter, which allows direct ac-ac power conversion without large energy store elements. This structure features, in high-voltage application, staircase out- put voltage with less voltage step, better harmonic issue, and compact design. In this paper, the MMC structure and the relative SVM is first introduced. Furthermore, the improved modulation strategy based on Amplitude Coefficient is employed to improve the MMC performance in terms of modulation precision. The theoretical analysis of the Amplitude Coefficient is discussed in detail. A comparison between the traditional SVM and the improved SVM is given to demonstrate the theoretical findings. Results from SABER simulation and experimental prototype are presented to validate the method.
Per M. Claesson - One of the best experts on this subject based on the ideXlab platform.
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Friction at nanopillared polymer surfaces beyond Amontons' laws: Stick-slip Amplitude Coefficient (SSAC) and multiparametric nanotribological properties.
Journal of colloid and interface science, 2020Co-Authors: Mohd I. Ishak, Illia Dobryden, Per M. Claesson, Wuge H. BriscoeAbstract:Frictional and nanomechanical properties of nanostructured polymer surfaces are important to their technological and biomedical applications. In this work, poly(ethylene terephthalate) (PET) surfaces with a periodic distribution of well-defined nanopillars were fabricated through an anodization/embossing process. The apparent surface energy of the nanopillared surfaces was evaluated using the Fowkes acid-base approach, and the surface morphology was characterized using scanning electron microscope (SEM) and atomic force microscope (AFM). The normal and lateral forces between a silica microparticle and these surfaces were quantified using colloidal probe atomic force microscopy (CP-AFM). The friction-load relationship followed Amonton's first law, and the friction Coefficient appeared to scale linearly with the nanopillar height. Furthermore, all the nanopillared surfaces showed pronounced frictional instabilities compared to the smooth sliding friction loop on the flat control. Performing the stick-slip Amplitude Coefficient (SSAC) analysis, we found a correlation between the frictional instabilities and the nanopillars density, pull-off force and work of adhesion. We have summarised the dependence of the nanotribological properties on such nanopillared surfaces on five relevant parameters, i.e. pull-off force fp, Amontons' friction Coefficient μ, RMS roughness Rq, stick-slip Amplitude friction Coefficient SSAC, and work of adhesion between the substrate and water Wadh in a radar chart. Whilst demonstrating the complexity of the frictional behaviour of nanopillared polymer surfaces, our results show that analyses of multiparametric nanotribological properties of nanostructured surfaces should go beyond classic Amontons' laws, with the SSAC more representative of the frictional properties compared to the friction Coefficient.
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sustained frictional instabilities on nanodomed surfaces stick slip Amplitude Coefficient
ACS Nano, 2013Co-Authors: Benoit Quignon, Per M. Claesson, Georgia A Pilkington, Esben Thormann, Michael N R Ashfold, Davide Mattia, Hannah Leese, Sean A Davis, Wuge H. BriscoeAbstract:Understanding the frictional properties of nanostructured surfaces is important because of their increasing application in modern miniaturized devices. In this work, lateral force microscopy was used to study the frictional properties between an AFM nanotip and surfaces bearing well-defined nanodomes comprising densely packed prolate spheroids, of diameters ranging from tens to hundreds of nanometers. Our results show that the average lateral force varied linearly with applied load, as described by Amontons’ first law of friction, although no direct correlation between the sample topographic properties and their measured friction Coefficients was identified. Furthermore, all the nanodomed textures exhibited pronounced oscillations in the shear traces, similar to the classic stick–slip behavior, under all the shear velocities and load regimes studied. That is, the nanotextured topography led to sustained frictional instabilities, effectively with no contact frictional sliding. The Amplitude of the stick–sl...
Khalid S. Essa - One of the best experts on this subject based on the ideXlab platform.
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Magnetic Data Interpretation Using a New R-Parameter Imaging Method with Application to Mineral Exploration
Natural Resources Research, 2020Co-Authors: Salah Mehanee, Khalid S. Essa, Zein E. DiabAbstract:A new imaging method has been developed for elucidating the observed magnetic data gauged along profile. The method is based on the calculation of the correlation factor (the R-parameter) between the analytic signal of the measured magnetic anomaly and the analytic signal of the calculated response of some geometrically simple interpretive models in the confined category of sheets, cylinders, and spheres. The characteristic parameters (Amplitude Coefficient, depth, location, approximative shape of the buried structure, and effective angle of magnetization) of the interpretive model correspond to the maximum R-parameter value. The scheme has been verified on a number of noise-free synthetic examples and recovered the actual model parameters. Prior to applying the developed scheme to real-field examples, the accuracy of it has been carefully investigated on synthetic examples which are contaminated with realistic noise levels, interference effects, and regional field. Finally, the method has been successfully applied to three real-field data examples from the USA, Senegal, and Egypt for mineral exploration, and it is found that the obtained results are in good concordance with those obtained from drilling and/or the published literature.
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pso particle swarm optimization for interpretation of magnetic anomalies caused by simple geometrical structures
Pure and Applied Geophysics, 2018Co-Authors: Khalid S. Essa, Mahmoud ElhusseinAbstract:A new efficient approach to estimate parameters that controlled the source dimensions from magnetic anomaly profile data in light of PSO algorithm (particle swarm optimization) has been presented. The PSO algorithm has been connected in interpreting the magnetic anomaly profiles data onto a new formula for isolated sources embedded in the subsurface. The model parameters deciphered here are the depth of the body, the Amplitude Coefficient, the angle of effective magnetization, the shape factor and the horizontal coordinates of the source. The model parameters evaluated by the present technique, generally the depth of the covered structures were observed to be in astounding concurrence with the real parameters. The root mean square (RMS) error is considered as a criterion in estimating the misfit between the observed and computed anomalies. Inversion of noise-free synthetic data, noisy synthetic data which contains different levels of random noise (5, 10, 15 and 20%) as well as multiple structures and in additional two real-field data from USA and Egypt exhibits the viability of the approach. Thus, the final results of the different parameters are matched with those given in the published literature and from geologic results.
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2.5D regularized inversion for the interpretation of residual gravity data by a dipping thin sheet: numerical examples and case studies with an insight on sensitivity and non-uniqueness
Earth Planets and Space, 2015Co-Authors: Salah A. Mehanee, Khalid S. EssaAbstract:A new two-and-a-half dimensional (2.5D) regularized inversion scheme has been developed for the interpretation of residual gravity data by a dipping thin-sheet model. This scheme solves for the characteristic inverse parameters (depth to top z , dip angle θ , extension in depth L , strike length 2 Y , and Amplitude Coefficient A ) of a model in the space of logarithms of these parameters (log( z ), log( θ ), log( L ), log( Y ), and log(| A |)). The developed method has been successfully verified on synthetic examples without noise. The method is found stable and can estimate the inverse parameters of the buried target with acceptable accuracy when applied to data contaminated with various noise levels. However, some of the inverse parameters encountered some inaccuracy when the method was applied to synthetic data distorted by significant neighboring gravity effects/interferences. The validity of this method for practical applications has been successfully illustrated on two field examples with diverse geologic settings from mineral exploration. The estimated inverse parameters of the real data investigated are found to generally conform well with those yielded from drilling. The method is shown to be highly applicable for mineral prospecting and reconnaissance studies. It is capable of extracting the various characteristic inverse parameters that are of geologic and economic significance, and is of particular value in cases where the residual gravity data set is due to an isolated thin-sheet type buried target. The sensitivity analysis carried out on the Jacobian matrices of the field examples investigated here has shown that the parameter that can be determined with the superior accuracy is θ (as confirmed from drilling information). The parameters z , L , Y , and A can be estimated with acceptable accuracy, especially the parameters z and A . This inverse problem is non-unique. The non-uniqueness analysis and the tabulated inverse results presented here have shown that the parameters most affected by the non-uniqueness are L and Y . It has also been shown that the new scheme developed here is advantageous in terms of computational efficiency, stability and convergence than the existing gravity data inversion schemes that solve for the characteristic inverse parameters of a sheet/dike.
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Three Least-Squares Minimization Approaches to Interpret Gravity Data Due to Dipping Faults
Pure and Applied Geophysics, 2014Co-Authors: El-sayed M. Abdelrahman, Khalid S. EssaAbstract:We have developed three different least-squares minimization approaches to determine, successively, the depth, dip angle, and Amplitude Coefficient related to the thickness and density contrast of a buried dipping fault from first moving average residual gravity anomalies. By defining the zero-anomaly distance and the anomaly value at the origin of the moving average residual profile, the problem of depth determination is transformed into a constrained nonlinear gravity inversion. After estimating the depth of the fault, the dip angle is estimated by solving a nonlinear inverse problem. Finally, after estimating the depth and dip angle, the Amplitude Coefficient is determined using a linear equation. This method can be applied to residuals as well as to measured gravity data because it uses the moving average residual gravity anomalies to estimate the model parameters of the faulted structure. The proposed method was tested on noise-corrupted synthetic and real gravity data. In the case of the synthetic data, good results are obtained when errors are given in the zero-anomaly distance and the anomaly value at the origin, and even when the origin is determined approximately. In the case of practical data (Bouguer anomaly over Gazal fault, south Aswan, Egypt), the fault parameters obtained are in good agreement with the actual ones and with those given in the published literature.
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a fast interpretation method for inverse modeling of residual gravity anomalies caused by simple geometry
Journal of Geological Research, 2012Co-Authors: Khalid S. EssaAbstract:An inversion technique using a fast method is developed to estimate, successively, the depth, the shape factor, and the Amplitude Coefficient of a buried structure using residual gravity anomalies. By defining the anomaly value at the origin and the anomaly value at different points on the profile, the problem of depth estimation is transformed into a problem of solving a nonlinear equation of the form
Xu Lie - One of the best experts on this subject based on the ideXlab platform.
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Research on the Amplitude Coefficient for Multilevel Matrix Converter Space Vector Modulation
IEEE Transactions on Power Electronics, 2012Co-Authors: Xu Lie, Li Yongdong, Wang Kui, Jon Clare, Patrick WheelerAbstract:This paper presents an improved space vector modulation (SVM) using Amplitude Coefficient on a capacitor-clamped multilevel matrix converter (MMC). The MMC utilizes a multilevel structure on a conventional matrix converter, which allows direct ac-ac power conversion without large energy store elements. This structure features, in high-voltage application, staircase out- put voltage with less voltage step, better harmonic issue, and compact design. In this paper, the MMC structure and the relative SVM is first introduced. Furthermore, the improved modulation strategy based on Amplitude Coefficient is employed to improve the MMC performance in terms of modulation precision. The theoretical analysis of the Amplitude Coefficient is discussed in detail. A comparison between the traditional SVM and the improved SVM is given to demonstrate the theoretical findings. Results from SABER simulation and experimental prototype are presented to validate the method.
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The application of Amplitude Coefficient in an improved multilevel matrix converter space vector modulation
2011 International Conference on Electrical Machines and Systems, 2011Co-Authors: Xu Lie, Li Yongdong, Ma Hongwei, Zheng ZedongAbstract:The AC-AC converters (such as matrix converter) gains increasingly attention in recent years due to their merit in compact design, regeneration capability and no large energy store elements. These advantages make the matrix converter attractive in industrial applications. The multilevel topologies are advantages in high voltage, large volume, high power application with better harmonic characteristics and less dv/dt features. The multilevel matrix converter topology and its modulation method has already been discussed in previous papers and this paper concentrates on developing the concepts of Amplitude Coefficient for multilevel matrix converter space vector modulation (SVM) to optimize the modulation accuracy and output precision. The Amplitude Coefficient is discussed in detail and demonstrated by the SABER simulation results to validate the algorithm.