Capacitive energy storage devices are essential components in modern electronics for power conditioning, conversion and renewable integration. The state-of-the-art bi-axially oriented polypropylene dielectric film has...
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Capacitive energy storage devices are essential components in modern electronics for power conditioning, conversion and renewable integration. The state-of-the-art bi-axially oriented polypropylene dielectric film has a breakdown strength of >730 MV/m and low dielectric loss of
The impact and airborne sound transmission characteristics of interior wall and floor components in traditional timber-framed dwellings (Ankara, Turkey) were examined by in-situ acoustical measurements and simulation ...
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Phonon transmission across interfaces of dissimilar materials has been studied intensively in recent years by using atomistic simulation tools due to its importance in determining the effective thermal conductivity of...
Phonon transmission across interfaces of dissimilar materials has been studied intensively in recent years by using atomistic simulation tools due to its importance in determining the effective thermal conductivity of nanostructured materials. The atomistic Green's function method with interatomic force constants from the first-principles calculations has evolved to be a promising approach to study phonon transmission in many material systems that have not been well studied. However, the direct first-principles calculation for interatomic force constants becomes infeasible when the system involves atomic disorder. Mass approximation is usually used, but its validity has not been tested. In this paper, we employ the higher-order force constant model to extract harmonic force constants from the first-principles calculations, which originates from the virtual crystal approximation but considers the local force-field difference. As a feasibility demonstration of the proposed method that integrates higher-order force constant model from the first-principles calculations with the atomistic Green's function, we study the phonon transmission in the Mg2Si/Mg2Si1−xSnx systems. When integrated with the atomistic Green's function, the widely used mass approximation is found to overpredict phonon transmission across the Mg2Si/Mg2Sn interface. The difference can be attributed to the absence of local strain field-induced scattering in the mass approximation, which makes the high-frequency phonons less scattered. The frequency-dependent phonon transmission across an interface between a crystal and an alloy, which often appears in high-efficiency “nanoparticle in alloy” thermoelectric materials, is studied. The interfacial thermal resistance across Mg2Si/Mg2Si1−xSnx interface is found to be weakly dependent on the composition of Sn when the composition of x is less than 40% but increases rapidly when it is larger than 40% due to the transition of high-frequency phonon DOS in Mg2Si1−
Ductile tensile failure of tantalum is examined through large scale non-equilibrium molecular dynamics simulations. Several loading schemes including flyer plate impact, decaying shock loading via a frozen piston, and...
Ductile tensile failure of tantalum is examined through large scale non-equilibrium molecular dynamics simulations. Several loading schemes including flyer plate impact, decaying shock loading via a frozen piston, and quasi-isentropic (constant strain-rate) expansion are employed to span tensile strain-rates of 108 to 1014 per second. Single crystals of 〈001〉 orientation are specifically evaluated to eliminate grain boundary effects. Heterogeneous void nucleation occurs principally at the intersection of deformation twins in single crystals. At high strain rates, multiple spall events occur throughout the material and voids continue to nucleate until relaxation waves arrive from adjacent events. At ultra-high strain rates, those approaching or exceeding the atomic vibrational frequency, spall strength saturates near the maximum theoretical spall strength.
Microcellular metal foam (MMF) is a new class of metallic material with many potential applications such as solar energy storage. In this study we present a sphere template electrodeposition process for bulk MMF fabri...
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Our existing Ultrasonic Broken Rail Detection system detects complete breaks and primarily uses a propagating mode with energy concentrated in the head of the rail. Previous experimental studies have demonstrated that...
Our existing Ultrasonic Broken Rail Detection system detects complete breaks and primarily uses a propagating mode with energy concentrated in the head of the rail. Previous experimental studies have demonstrated that a mode with energy concentrated in the head of the rail, is capable of detecting weld reflections at long distances. Exploiting a mode with energy concentrated in the web of the rail would allow us to effectively detect defects in the web of the rail and could also help to distinguish between reflections from welds and cracks. In this paper, we will demonstrate the analysis of a piezoelectric transducer attached to the rail web. The forced response at different frequencies is computed by the Semi-Analytical Finite Element (SAFE) method and compared to a full three-dimensional finite element method using ABAQUS. The SAFE method only requires the rail track cross-section to be meshed using two-dimensional elements. The ABAQUS model in turn requires a full three-dimensional discretisation of the rail track. The SAFE approach can yield poor predictions at cut-on frequencies associated with other modes in the rail. Problematic frequencies are identified and a suitable frequency range identified for transducer design. The forced response results of the two methods were found to be in good agreement with each other. We then use a previously developed SAFE-3D method to analyse a practical transducer over the selected frequency range. The results obtained from the SAFE-3D method are in good agreement with experimental measurements.
Here we report the influence of substrate temperature (300-500 °C) on the deposition and growth of ZnO over a Flexible polyimide film. Owing to its simplicity, large area deposition capability and Cost effectivit...
Here we report the influence of substrate temperature (300-500 °C) on the deposition and growth of ZnO over a Flexible polyimide film. Owing to its simplicity, large area deposition capability and Cost effectivity Spray Pyrolysis technique was used. We have modified the conventional process of Spray pyrolysis by spraying for shorter durations and repeating the process which in turn reduced the Island formation of ZnO. Moreover, this technique helped in maintaining the constant temperature and uniformity during the deposition as prolonged spraying reduces the temperature of the heating plate drastically. Photoluminescence (PL) reveals that at 350 and 400° C the defect have reduced. XRD reveals the crystallinity and Impurities present. FE-SEM reveals the structure morphology changes with the change in the substrate temperature. TGA was done to ensure that substrate does not undergoes dissociation at high temperature. It was observed at the film deposited at 400 °C was found to be more uniform, defect free and crystalline. Hence, IV characterization of the film deposited at 400 °C was done which showed good rectification behaviour of the Schottky diodes.
Abstract:The paper proposes mechanism of electrochemical discharge ECD based on the results of experiments in stagnant electrolyte cell (SEC). The experiments conducted in SEC have demonstrated that the physical chara...
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This paper focuses on the multiscale mechanism of collapse of hemicylindrical annular surface macrocavities in steel caused by high-strain, high-strain rate plastic flow of copper. Experiments and simulations revealed...
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This paper focuses on the multiscale mechanism of collapse of hemicylindrical annular surface macrocavities in steel caused by high-strain, high-strain rate plastic flow of copper. Experiments and simulations revealed that a two-stage process is responsible for the observed microjetting phenomena: the formation of lateral copper microjets from the localized shear flow in copper at the interface during the filling of the cavity, and their subsequent collision at the apex of the macrocavity generating two additional horizontal microjets. The lengths of these microjets were an order of magnitude smaller than the cavity size but linearly scaled with the cavity radius. This process of microjet development is sensitive to the cavity geometry and is unlike the previously observed jetting phenomena in cavitation, impact crater collapse, or shock-induced cavity collapse.
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