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Abstract In this work, we propose an acoustic energy harvesting metamaterial consisting of an array of silicone rubber pillars and a PZT patch deposited on an ultrathin aluminum plate with several holes based on locally resonant mechanism. The resonance is formed by removing four pillars, drilling a few of holes and attaching the PZT patch on the aluminum plate. The strain energy originating from an incident acoustic wave is centralized in the resonant region, and the PZT patch is used to convert the elastic strain energy into electrical power. Numerical analysis and experimental results show that the proposed millimeter-scale harvester with holes obviously improves the effect of acoustic energy harvesting while performing at the subwavelength scale for sonic low-frequency environment (less than 1150 Hz). In addition, the experimental results demonstrate that the maximum output voltage and power of the proposed acoustic energy harvesting system with 16 holes of 2 mm radius are 3 and 10 times higher than those without holes at the resonant mode for 2 Pa of incident acoustic pressure. Both the number and size of holes have a significant effect on the performance of acoustic energy harvesting. The advantages of the proposed structure are easy-to-machine and full of practicality, and it can be used in broad applications for low-frequency acoustic energy harvesting.

A new approach for the electromagnetic control and propulsion of a current carrying electric arc plasma ring is described. The essence of the approach is to form and manipulate the arc plasma outside rather than inside a magnetic field producing coil so that pulsed plasma thrusts can be produced in a choice of different directions. The interaction of the electric arc, formed in atmospheric pressure air, with such a magnetic field has been investigated. It has been shown that a stable azimuthal plasma ring can be rapidly produced by the simple process of separating two annular contacts. Pulsed plasma propulsion is obtained when the arc plasma and B-field sustaining current is reduced to zero whereby the constraining electromagnetic forces are removed and, as a consequence, the resulting plasma ring expands radially outwards. Several different measurement techniques have been deployed for investigating the behavior of the plasma ring. These include electrical probing, B-field probing and high-speed plus video photography. The results suggest that the plasma control and propulsion is governed by a combination of effects including ablation of the material around which the plasma ring is formed and self-pressurization related to the device geometry, as well as the electromagnetic forces. Preliminary results indicate that through the use of appropriate device geometries, the arc plasma may be propelled in axially opposite directions as well as radially.

Swirl combustors have proven as effective flame stabilisers over a wide range of operation conditions thanks to the formation of well-known swirl coherent structures. However, employment of swirl combustors to work on lean premixed combustion modes while introducing alternative fuels such as high hydrogen blends result in many combustion instabilities. Under these conditions, flame flashback has been considered as one of the major instability problems that have the potential of causing considerable damages of the combustion systems hardware in addition to the significant increase in pollutant levels. Combustion Induced Vortex Breakdown (CIVB) is considered a very particular mode of flashback mechanism in swirling flows as this type of flashback occurs even when the fresh mixture’s velocity is higher than the flame speed, consequence of the interaction between swirl structures and swirl burner geometries. Improvements of burner geometries and manipulation of swirl flows can produce good resistance against this type of flashback. However, increase flame flashback resistance against CIVB can lead to an increase in the propensity of another flashback mechanism, Boundary Layer Flashback (BLF). Thus this paper presents an experimental and numerical approach that allows the increase in CIVB resistance by using diffusive air injection and simultaneously avoid BLF by changing the wall boundary layer characteristics using microsurface grids as a liner for the nozzle wall. Results show that using those two techniques together has promising potentials regarding wider stable operation for swirl combustors, enabling them to burn a great variety of fuel blends safely.

Abstract We single out the role of fully coherent induced gluon radiation on light hadron production in pA collisions. The effect has the same general features as for quarkonium production, however with a richer color structure as the induced radiation depends on the global color charge of the partonic subprocess final state. Baseline predictions for light hadron nuclear suppression in pPb collisions at the LHC are provided, taking into account only the effect of fully coherent energy loss, which proves to be of the same order of magnitude as gluon shadowing or saturation. This underlines the need to include fully coherent energy loss in phenomenological studies of hadron production in pA collisions.

En este trabajo, se ha investigado el impacto de seis capas diferentes de recubrimiento antirreflectante (ARC) utilizando el software de simulación PC1D. La simulación muestra que el rango de 500–700 nm sería adecuado para diseñar un ARCO. Diseñando un ARCO de nitruro de silicio de una sola capa (Si3N4) para una longitud de onda de 600 nm y con un espesor de 74.257 nm, se ha simulado una célula solar de silicio con una eficiencia del 20.35%. Le sigue muy de cerca una célula solar de silicio con una eficiencia del 20,34% con una capa de ARCO de óxido de zinc (ZnO) de 74,87 nm de espesor. Se ha observado un aumento significativo en la eficiencia al aplicar ARC con respecto a no aplicar ningún tipo de ARC. Después de un modelado eficiente de las células solares, se está logrando una eficiencia óptima del 20,67% mediante el uso de la pasivación superficial de SiO2 y la capa de ARCO de Si3N4. Los efectos sobre la tensión, la corriente, la eficiencia fotovoltaica, la reflectividad y la eficiencia cuántica externa debidos a los ARC también están representados en este trabajo. Dans ce travail, l'impact de six couches différentes de revêtement antireflet (ARC) a été étudié à l'aide du logiciel de simulation PC1D. La simulation montre que la plage de 500–700 nm serait appropriée pour concevoir un ARC. En concevant un ARC de nitrure de silicium monocouche (Si3N4) pour une longueur d'onde de 600 nm et une épaisseur de 74,257 nm, une cellule solaire en silicium avec une efficacité de 20,35% a été simulée. Très étroitement suivie par une cellule solaire en silicium à 20,34 % d'efficacité avec une couche d'ARC en oxyde de zinc (ZnO) de 74,87 nm d'épaisseur. Une augmentation significative de l'efficacité a été observée en appliquant L'ARC par rapport à l'absence d'application de tout type d'ARC. Après une modélisation efficace des cellules solaires, une efficacité optimale de 20,67 % est obtenue en utilisant la passivation de surface SiO2 et la couche D'ARC Si3N4. Les effets sur la tension, le courant, l'efficacité photovoltaïque, la réflectivité et l'efficacité quantique externe dus aux ARC sont également représentés dans ce travail. In this work, the impact of six different anti-reflection coating (ARC) layers has been investigated using PC1D simulation software. Simulation shows that the range of 500–700 nm would be suitable for designing an ARC. Designing a single-layer silicon nitride (Si3N4) ARC for 600 nm wavelength and with a thickness of 74.257 nm, a silicon solar cell with 20.35% efficiency has been simulated. Very closely followed by a 20.34% efficient silicon solar cell with 74.87 nm thick zinc oxide (ZnO) ARC layer. Significant increase in efficiency has been observed by applying ARC in respect to not applying any kind of ARC. After efficient solar cell modeling, optimum efficiency of 20.67% is being achieved by using SiO2 surface passivation and Si3N4 ARC layer. The effects on voltage, current, photovoltaic efficiency, reflectivity and external quantum efficiency due to ARCs are also represented in this work. في هذا العمل، تم التحقيق في تأثير ست طبقات مختلفة من الطلاء المضاد للانعكاس (ARC) باستخدام برنامج محاكاة PC1D. تظهر المحاكاة أن النطاق من 500–700 نانومتر سيكون مناسبًا لتصميم القوس. تصميم قوس نيتريد السيليكون أحادي الطبقة (Si3N4) بطول موجي 600 نانومتر وبسمك 74.257 نانومتر، تمت محاكاة خلية شمسية من السيليكون بكفاءة 20.35 ٪. تليها عن كثب خلية شمسية من السيليكون فعالة بنسبة 20.34 ٪ مع طبقة قوسية من أكسيد الزنك بسماكة 74.87 نانومتر (ZnO). لوحظت زيادة كبيرة في الكفاءة من خلال تطبيق القوس فيما يتعلق بعدم تطبيق أي نوع من القوس. بعد نمذجة الخلايا الشمسية بكفاءة، يتم تحقيق الكفاءة المثلى بنسبة 20.67 ٪ باستخدام تخميل سطح SiO2 وطبقة Si3N4 القوسية. يتم تمثيل التأثيرات على الجهد والتيار والكفاءة الكهروضوئية والانعكاسية والكفاءة الكمية الخارجية بسبب ARCs أيضًا في هذا العمل.

Based on the existing acknowledgment that space charge modulates AC and DC breakdown of insulating materials, this investigation promotes the related investigation into the situations of more complex electrical stress, i.e., AC-DC combined voltages. Experimentally, the AC-DC breakdown characteristics of oil impregnated paper insulation were systematically investigated. The effects of pre-applied voltage waveform, AC component ratio, and sample thickness on AC-DC breakdown characteristics were analyzed. After that, based on an improved bipolar charge transport model, the space charge profiles and the space charge induced electric field distortion during AC-DC breakdown were numerically simulated to explain the differences in breakdown characteristics between the pre-applied AC and pre-applied DC methods under AC-DC combined voltages. It is concluded that large amounts of homo-charges are accumulated during AC-DC breakdown, which results in significantly distorted inner electric field, leading to variations of breakdown characteristics of oil impregnated paper insulation. Therefore, space charges under AC-DC combined voltages must be considered in the design of converter transformers. In addition, this investigation could provide supporting breakdown data for insulation design of converter transformers and could promote better understanding on the breakdown mechanism of insulating materials subjected to AC-DC combined voltages.

Before lower purity, lower cost silicon (Si) materials, such as compensated Si, can play a role in the terawatt-level (TW) capacity of photovoltaics, a better understanding of the fundamental properties of impurities in compensated Si is essential. In this work, high-resolution photoluminescence (PL) has been used to study the charge carrier radiative recombination through Donor-Acceptor pairs (DAPs) in phosphorus (P) and gallium (Ga) co-doped Si material grown for solar cell applications. The high spectral resolution of our PL system, 0.06 meV, enables us to overcome hitherto prior issues of overlapping spectral lines, giving access to extremely fine structures associated with DA pair (DAP) recombination. Our results confirm the presence of three broad bands and a discrete line structure related to DAP luminescence. The comparison of the discrete line structure due to DAPs recombination in the PL spectra with the theoretically predicted one allows the accurate determination of the Ga ionization energy. Temperature-dependent PL is then used to understand the thermally-induced changes in the DAP luminescence. In particular, we observe that the radiative recombination channel remains active for distant DAPs up to ∼40 K, unlike that for close-range DAPs for which the radiative channel is quenched after only slight increases in the temperature range 10–25 K. Furthermore, the analysis of the temperature dependent changes in the PL intensity of the broad DAP bands up to ∼200 K is used to derive the ionization energy of P donors in compensated Si material. In light of this important information, the significance of using high resolution PL to analyse spectral features in compensated Si is demonstrated.