The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Deborah D.l. Chung - One of the best experts on this subject based on the ideXlab platform.
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A critical review of piezoresistivity and its application in electrical-resistance-based strain sensing
Journal of Materials Science, 2020Co-Authors: Deborah D.l. ChungAbstract:Piezoresistivity is an electromechanical effect characterized by the reversible Change in the electrical resistivity with strain. It is useful for electrical-resistance-based strain/stress sensing. The resistivity can be the volumetric, interfacial or surface resistivity, though the volumetric resistivity is most meaningful scientifically. Because the irreversible resistivity Change (due to damage or an irreversible microstructural Change) adds to the reversible Change that occurs at lower strains, the inclusion of the irreversible effect makes the piezoresistivity appear stronger than the inherent effect. This paper focuses on the inherent piezoresistivity that occurs without irreversible resistivity Changes. The effect is described by the gage factor (GF), which is defined as the Fractional Change in resistance per unit strain. The GF can be positive or negative. Strong piezoresistivity involves the magnitude of the Fractional Change in resistivity much exceeding the strain magnitude. The reversible effect of strain on the electrical connectivity is the primary piezoresistivity mechanism. Giant piezoresistivity is characterized by GF ≥ 500. This critical review with 209 references covers the theory, mechanisms, methodology and status of piezoresistivity, and provides the first review of the emerging field of giant piezoresistivity. Piezoresistivity is exhibited by electrically conductive materials, particularly metals, carbons and composite materials with conductive fillers and nonconductive matrices. They include functional and structural materials. Piezoresistivity enables structural materials to be self-sensing. Unfortunately, GF was incorrectly or unreliably reported in a substantial fraction of the publications, due to the pitfalls systematically presented here. The most common pitfall involves using the two-probe method for the resistance measurement.
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through thickness piezoresistivity in a carbon fiber polymer matrix structural composite for electrical resistance based through thickness strain sensing
Carbon, 2013Co-Authors: Daojun Wang, Deborah D.l. ChungAbstract:Piezoresistivity (Change of the volume electrical resistivity with strain) in continuous carbon fiber polymer-matrix structural composites allows electrical-resistance-based strain/stress sensing. Uniaxial through-thickness compression is encountered in fastening. As shown for a 24-lamina quasi-isotropic epoxy-matrix composite, compression results in (i) strain-induced reversible decreases in through-thickness and longitudinal volume resistivities, due to increase in the degree of through-thickness fiber–fiber contact, and (ii) minor-damage-induced irreversible Changes in these resistivities, due to a microstructural Change involving an irreversible through-thickness resistivity increase and an irreversible longitudinal resistivity decrease. The Poisson effect plays a minor role. The effects in the longitudinal resistivity are small compared to those in the through-thickness direction, but longitudinal resistance measurement is more practical. The through-thickness gage factor (reversible Fractional Change in resistance per unit strain) ranges from 2.6 to 5.1 and the reversible Fractional Change in through-thickness resistivity per unit through-thickness strain ranges from 1.5 to 4.0, both quantities decreasing with increasing strain magnitude from 0.19% to 0.73% due to the increasing irreversible effect. The irreversible Fractional Change in through-thickness resistivity per unit through-thickness strain ranges from −1.0 to −1.3 and is strain independent. The effects are consistent with the surface resistance Changes previously reported for the same material under flexure.
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self sensing of flexural damage and strain in carbon fiber reinforced cement and effect of embedded steel reinforcing bars
Carbon, 2006Co-Authors: Sihai Wen, Deborah D.l. ChungAbstract:Self-sensing of flexural damage and strain in carbon fiber reinforced cement is attained by measuring the volume or surface resistance with the four-probe method and electrical contacts on the compression and/or tension surfaces. The oblique resistance (volume resistance in a direction between the longitudinal and through-thickness directions) increases upon loading and is a good indicator of damage and strain in combination. The surface resistance on the compression side decreases upon loading and is a good indicator of strain. The surface resistance on the tension side increases upon loading and is a good indicator of damage. The effectiveness for the self-sensing of flexural strain in carbon fiber reinforced cement is enhanced by the presence of embedded steel rebars on the tension side. For the same midspan deflection, the Fractional Change in surface electrical resistance is increased in magnitude, whether the surface resistance is that of the tension side or the compression side. The Fractional Change in resistance of the tension surface is increased by 40%, while the magnitude of the Fractional Change in resistance of the compression surface is increased by 70%, due to the steel.
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Microstructural effect of the shrinkage of cement-based materials during hydration, as indicated by electrical resistivity measurement
Cement and Concrete Research, 2004Co-Authors: Deborah D.l. ChungAbstract:The shrinkage of cement-based materials during hydration is a cause of defects (such as cracks) in these materials. The extent of microstructural Change (which precedes an event such as cracking) and the evolution of the microstructure as shrinkage occurs are important for understanding the shrinkage process. This article reports on a study in which the effect of shrinkage during hydration on the microstructural Change in cement-based materials was evaluated by measuring electrical resistivity and shrinkage strain. Results show that the microstructural Change caused by shrinkage is diminished with silica fume and increased with sand. The Fractional Change in resistivity per unit shrinkage strain is much larger than the Fractional Change in resistivity per unit compressive strain in the cured state.
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Effect of Stress on the Electrical Resistivity of Solder
Journal of Electronic Materials, 2001Co-Authors: Taejin Kim, Deborah D.l. ChungAbstract:The electrical resistivity of tin-lead eutectic solder was found to increase upon tension. The effect was partially reversible. The Fractional Change in resistance per unit strain was 60. The irreversible part of the effect was due to plastic deformation.
Peter R. Couchman - One of the best experts on this subject based on the ideXlab platform.
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Cell Theory Calculation of Surface Tension of Simple Liquids Solely from Bulk Properties
Journal of Colloid and Interface Science, 1996Co-Authors: Kenneth Van Ness, Peter R. CouchmanAbstract:A cell theory for the prediction of the surface tension of simple liquids is modified to account correctly for the Fractional Change in the potential energy zero term due to missing nearest neighbors of order greater than one. A measure of the surface width is obtained directly from bulk data. Theory and experiment are in good agreement without any adjustable surface parameters.
Michal Chodorowski - One of the best experts on this subject based on the ideXlab platform.
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Influence of the Local Void on measurements of the clustering dipole
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Maciej Bilicki, Michal ChodorowskiAbstract:In measurements of the clustering dipole from all-sky surveys, an important problem is the lack of information about galaxy distribution in the so-called zone of avoidance (ZoA). The existence of the Local Void (LV) has a systematic effect on these measurements. If the ZoA is randomly filled with mock galaxies, then the calculated acceleration of the Local Group (LG) of galaxies has a spurious component, resulting from the lack of real galaxies in the intersection of the LV with the ZoA. This component affects both the misalignment angle between the clustering dipole and the CMB dipole, and the inferred value of mean matter density Ω m . We calculate the amplitude of the spurious acceleration acting on the LG due to the LV. Its value depends on the geometry and size of the LV, as well as on its density contrast. However, under the simplest assumption of the LV being spherical and completely empty, within the linear theory this amplitude amounts only to about 45 km s -1 in units of velocity. The resulting Change in the misalignment angle is smaller than 1°, and the Fractional Change in the deduced value of Ω m is about 5 per cent. Accounting for observationally indicated elongation of the LV and maintaining the maximizing assumption of a complete lack of galaxies inside increases these numbers only moderately. Specifically, the amplitude of the spurious acceleration rises to about 60 km s -1 , the misalignment angle remains still smaller than 1° and the Fractional Change in the deduced value of Ω m is enhanced to about 7 per cent. Thus, despite the overall importance of the LV for the motion of the LG, the influence of the intersection of the LV with the ZoA on measurements of the clustering dipole is found to be only a minor systematic effect.
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Influence of the Local Void on measurements of the clustering dipole
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Maciej Bilicki, Michal ChodorowskiAbstract:In measurements of the clustering dipole from all-sky surveys, an important problem is the lack of information about galaxy distribution in the so-called Zone of Avoidance (ZoA). The existence of the Local Void (LV) has a systematic effect on these measurements. If the ZoA is randomly filled with mock galaxies, then the calculated acceleration of the Local Group of galaxies (LG) has a spurious component, resulting from the lack of real galaxies in the intersection of the LV with the ZoA. This component affects both the misalignment angle between the clustering dipole and the CMB dipole, and the inferred value of mean matter density Omega_m. We calculate the amplitude of the spurious acceleration acting on the LG due to the LV. Its value depends on the geometry and size of the LV, as well as on its density contrast. However, under the simplest assumption of the LV being spherical and completely empty, within the linear theory this amplitude amounts only to about 45 km/s in units of velocity. The resulting Change in the misalignment angle is smaller than 1 degree, and the Fractional Change in the deduced value of Omega_m is about 5%. Accounting for observationally indicated elongation of the LV and maintaining the maximising assumption of a complete lack of galaxies inside increases these numbers only moderately. Specifically, the amplitude of the spurious acceleration rises to about 60 km/s, the misalignment angle remains still smaller than 1 degree, and the Fractional Change in the deduced value of Omega_m is enhanced to about 7%. Thus, despite the overall importance of the Local Void for the motion of the Local Group, the influence of the intersection of the LV with the ZoA on measurements of the clustering dipole is found to be only a minor systematic effect.Comment: 6 pages, 2 figures; revised version, slightly expanded, accepted for publication in MNRAS
Se-hee Lee - One of the best experts on this subject based on the ideXlab platform.
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Pd-Pt alloy as a catalyst in gasochromic thin films for hydrogen sensors
Solar Energy Materials and Solar Cells, 2009Co-Authors: Jae Young Shim, Jae Dong Lee, Jung Mo Jin, Hyeonsik Cheong, Se-hee LeeAbstract:We have used Pd–Pt alloy as the catalyst in the hydrogen sensor thin film. Palladium and platinum were co-sputtered on top of a tungsten oxide layer grown by reactive sputtering. Both the sensitivity and the durability were dramatically improved over the case of a palladium single-component catalyst. The Fractional Change in the optical absorption on exposure to 1% hydrogen gas was increased by a factor larger than 2, and the Fractional Change decreased only a little after more than 1000 cycles of repeated exposure to 1% hydrogen and air. Moreover, the sensor film exhibited good selectivity to other organic vapors.
Luis F. Razon - One of the best experts on this subject based on the ideXlab platform.
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A methodology for criticality analysis in integrated energy systems
Clean Technologies and Environmental Policy, 2015Co-Authors: Michael Francis D. Benjamin, Luis F. RazonAbstract:Integrated energy systems (IES) such as polygeneration plants and bioenergy-based industrial symbiosis (BBIS) networks offer the prospect of increased efficiency and reduced carbon emissions. However, these highly-integrated systems are also characterized by the strong interdependence among component units. This interdependency results in the risk of propagation of cascading failures within such networks, where disturbances in the operation of one component results in ripple effects that affect the other units in the system. In this work, a novel criticality index is proposed to quantify the effects of a component unit’s failure to run at full capacity within an IES. This index is defined as the ratio of the Fractional Change in the net output to the Fractional Change in capacity of the component causing the failure. The component units in the entire system can then be ranked based on this index. Such risk-based information can thus be used as an important input for developing risk mitigation measures and policies. Without this information, risk management based only on network topology could result to counterintuitive results. A simple polygeneration plant and two BBIS case studies are presented to demonstrate the computation of the criticality index.
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A Methodology for Criticality Analysis in Symbiotic Bioenergy Parks
Energy Procedia, 2014Co-Authors: Michael Francis D. Benjamin, Raymond R. Tan, Luis F. RazonAbstract:Abstract The environmental performance of biomass processing plants can be enhanced through industrial symbiosis in bioenergy parks which utilize synergistic exChanges to ensure more sustainable operations. However, symbiosis will also increase the interdependence of plants, such that when one plant fails, there will be a cascading effect in the entire network. In this work, a criticality index is proposed to quantify the effects of a plant's failure to run at full capacity. This index is the ratio of the Fractional Change in the net output to the Fractional Change in capacity of the plant causing the failure. The plants in the entire bioenergy park can then be ranked based on this index. Such information can then be used for developing risk mitigation measures, such us planning for system redundancy. A case study is presented to demonstrate how the method determines the criticality of plants within a bioenergy park.
