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Phase change materials (PCMs) are used to cool high-power-density electronic devices because of their high latent heat and chemical stability. However, their low thermal conductivity limits the application of PCMs. To solve this problem, a double-porosity porous aluminum skeleton/paraffin phase change materials (DPAS/PCM) was prepared via additive manufacturing and the water-bath method. The thermal performance of the DPAS/PCM heat sink (HS) was experimentally investigated to examine the effects of the positive- and reverse-gradient porosity structures of the DPAS/PCM. The results show that a positive-gradient porosity arrangement is more conducive to achieving a low-temperature cooling target for LED operation. In particular, the temperature control time for the positive gradient porosity structure increased by 4.6–13.7% compared with the reverse gradient porosity structure. Additionally, the thermal performances of uniform porous aluminum skeleton/paraffin (UAS) and DPAS/PCMs were investigated. The temperature control effect of the DPAS/PCM was better than that of the UAS/PCM HS at high critical temperatures. Compared with the UAS/PCM HS, the temperature control time of the DPAS/PCM HS is increased by 7.8–12.5%. The results of this work show that the prepared DPAS/PCM is a high-potential hybrid system for thermal management of high-power electronic devices. [ABSTRACT FROM AUTHOR]

Broad-area lasers (BALs) have found applications in a variety of crucial fields on account of their high output power and high energy transfer efficiency. However, they suffer from poor spatial beam quality due to multi-mode behavior along the waveguide transverse direction. In this paper, we propose a novel metasurface waveguide structure acting as a transverse mode selective back-reflector for BALs. In order to effectively inverse design such a structure, a digital adjoint algorithm is introduced to adapt the considerably large design area and the high degree of freedom. As a proof of the concept, a device structure with a design area of 40 × 20 μm2 is investigated. The simulation results exhibit high fundamental mode reflection (above 90%), while higher-order transverse mode reflections are suppressed below 0.2%. This is, to our knowledge, the largest device structure designed based on the inverse method. We exploited such a device and the method and further investigated the device's robustness and feasibility of the inverse method. The results are elaborately discussed. [ABSTRACT FROM AUTHOR]

The generation mechanism of cutting force in ultrasonic vibration assisted turning (UAT), with the composition and decomposition of cutting force is discussed in this paper, and the model of cutting force in UAT is established based on the mechanism of UAT. The force measuring test system is designed on the basis of the established machining system of UAT. The contrast experiments for turning the workpiece of 304 austenitic stainless steel are conducted with and without ultrasonic vibration under different technological parameters. Furthermore, the relational model and correlation between technological parameters and cutting force is obtained by regression analysis and variance analysis. Thereby, the mutual relation among these technological parameters is effectively controlled, which contributes to achieving the high quality and high efficient processing. Simultaneously, the influences of single technological parameter with the interaction between technological parameters on cutting force are researched and analyzed. The results prove that the cutting force is reduced significantly with the aid of ultrasonic vibration in turning and the choice of the proper ultrasonic amplitude, there is an optimal range of ultrasonic amplitudes as well. Meanwhile, the cutting parameters have great influence on cutting force, among which depth of cut has the superior influence, then the cutting speed, and feed rate has the minimal influence. Moreover, cutting parameters should not be too large, UAT is mainly used for semi-finishing or finishing at medium-low speed. UAT will get more ideal machining effect if cutting parameters are chosen properly. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present an experimental investigation of the cutting forces, surface quality, tool wear and chip shape in ultrasonic vibration assisted turning (UAT) of 304 austenitic stainless steel (ASS 304) in comparison to conventional turning (CT). This study focuses on the solution of the machining difficulties of ASS 304 and high demands for the processing quality and efficiency. The machining system of UAT is schemed out to assure the desired machining effect by utilizing ultrasonic vibration method. Meanwhile, a series of systematic experiments are performed with and without ultrasonic vibration using the designed machining system of UAT with cemented carbide coated cutting tool. The results obtained from the UAT and CT experiments demonstrate that the cutting effect of UAT is much better than that of CT. Furthermore, the results of this research indicate that the ultrasonic amplitude, cutting speed, feed rate and depth of cut in UAT of ASS 304 have visible influence on the cutting forces, surface quality and tool wear. And reasonable selection of various technological variables in UAT can obtain lower cutting forces, more superior surface roughness, advantageous surface topography, slow and less tool wear, thin and smooth chips. [ABSTRACT FROM AUTHOR]