Nearly two billion air-conditioning (AC) units are currently being used for space cooling worldwide. The majority of these ACs use R134a as the working fluid, a greenhouse gas (GHG) with a global warming potential (GW...
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With the adoption of the damage tolerance design principle, the health monitoring system has become an integral part of the operation of engineering structures. For the system to work, a damage indicator that describe...
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With the adoption of the damage tolerance design principle, the health monitoring system has become an integral part of the operation of engineering structures. For the system to work, a damage indicator that describes the structural integrity level should be established and monitored. The damage indicator is usually derived from structural responses. Many quantities have been proposed for damage indicator including natural frequency, mode shape, curvature, strain energy, and t-, F-, and z-statistics. In this paper, we propose a new damage indicator in the time and frequency domains derived from the Euler-Bernoulli beam theory. We evaluate the method by using data obtained from a numerical simulation of a cracked beam. The beam deformation is nonlinear due to the contact between the crack faces during vibration. The proposed damage index is estimated in the domains for various observation points on the beam. Besides, the existence of the crack is also predicted by the widely used traditional method based on the change of the natural frequency and mode shape. A comparison is made between the present method and the existing ones. We conclude the present proposal is more sensitive to detect the crack.
When the war is finished, the unexploded mines continue to kill or injure individuals, most of them civilians. These mines represent a particularly acute problem in developing countries, problem that has become a very...
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When the war is finished, the unexploded mines continue to kill or injure individuals, most of them civilians. These mines represent a particularly acute problem in developing countries, problem that has become a very serious international issue, with many people striving to find a solution. This paper will discuss the use of robotic systems for humanitarian demining purposes.
The field of tissue engineering has been growing in the recent years as more products have made it to the market and as new uses for the engineered tissues have emerged, motivating many researchers to engage in this m...
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Powder bed fusion of metals with laser beam (PBF-LB/M) using Ti-6Al-4V (Ti64) has enabled delicate fabrication of biocompatible medical implants. This research focuses on how the spatial uniformity of laser irradiatio...
Powder bed fusion of metals with laser beam (PBF-LB/M) using Ti-6Al-4V (Ti64) has enabled delicate fabrication of biocompatible medical implants. This research focuses on how the spatial uniformity of laser irradiation affects material under continuous wave (CW) and pulse width modulated (PWM) laser conditions, using a self-developed PBF-LB/M system. The volumetric energy density (VED) was used as a reference parameter in order to accurately compare the effects of CW and PWM lasers, but limitations of VED, which does not include spatial and kinetic factors, which are reinforced in the PWM laser process, were also considered. Results revealed that the uniform distribution of energy irradiation across the entire region brought similar porosities and Vickers hardness tendencies for CW and PWM laser processes. In contrast, the spatially nonuniform energy transfer resulted in a significantly higher porosity in the specimen fabricated using the PWM laser than that produced using the CW laser at the same VED, reducing compressive yield strength. The electron backscattered diffraction analysis showed no significant differences in the average grain size, phase distribution, and misorientation angle of the samples produced using CW and PWM lasers under the same VED. However, sharper grains with an aspect ratio of less than 0.3 were 7 % higher in specimens produced using the PWM laser. This study highlights the possibility of controlling the microstructure and mechanical properties in a wider range when using the PWM laser with spatially nonuniform irradiation.
Layer-by-layer (LbL) assembly was used to deposit transparent, highly conductive thin films using aqueous solutions of nanotubes stabilized by deoxycholate (DOC) and poly(diallyl-dimethylammonium chloride) (PDDA). Thr...
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Layer-by-layer (LbL) assembly was used to deposit transparent, highly conductive thin films using aqueous solutions of nanotubes stabilized by deoxycholate (DOC) and poly(diallyl-dimethylammonium chloride) (PDDA). Three different types of carbon nanotubes (CNTs) were used: (1) multi-walled carbon nanotubes (MWNTs), (2) a mixture of single, di- and tri-walled nanotubes (XM grade) and (3) purified HiPCO single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (> 85 %T across visible spectrum) and electrically conductive (˜ 150 S/cm) 20-bilayer films with 42 nm thickness. Moreover, optoelectronic performance of SWNT-based thin films was improved with heat treatment due to the removal of PDDA. A 20-bilayer SWNT LbL film achieved a conductivity of 369 S/cm with a 5 min exposure to 400 °C. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films, which may be useful for a variety of large area electronics applications.
An experimental and analytical approach were performed to study the biomechanics of a self-expanding, nitinol transcatheter aortic valve (TAV) stent device deployed in porcine heart tissue. The radial force, pullout f...
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An experimental and analytical approach were performed to study the biomechanics of a self-expanding, nitinol transcatheter aortic valve (TAV) stent device deployed in porcine heart tissue. The radial force, pullout force, and coefficient of friction (COF) were quantified, and the interacting device tissue response was investigated. The preliminary data generated from this study may provide a useful measure for determining an adequate valve oversize in aiding against device migration.
Edge-to-edge repair (ETER) technique alters mitral valve inflow in the diastolic phase and thus the stress distribution on each leaflet, especially the area near sutured edges. In the present study, we performed finit...
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Edge-to-edge repair (ETER) technique alters mitral valve inflow in the diastolic phase and thus the stress distribution on each leaflet, especially the area near sutured edges. In the present study, we performed finite element simulations of ETER mitral valve during the diastolic phase under different pressures. We conducted planar biaxial mechanical testing to obtain the material properties of native mitral leaflets. The test data were characterized by the Fung-elastic model. Fung-elastic model with material parameters from experiments was implemented into FE models of ETER mitral valve to study leaflet deformation. The simulation results indicate the high stress regions occurred in the areas near sutured edges and the vicinity of commissures.
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