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In this paper, the skin-core combined with the triple contour method is proposed to solve the density and roughness problems of selective laser melting. Based on the skin-core strategy, the surface roughness is optimized by laser parameter adjustment, and the high-quality side-surface formation is achieved by the triple contour method. The results showed that the relative density increases first and then decreases with increasing in-skin energy density, and surface roughness decreases with increasing up-skin energy density. The effects of the skin-core parameters have been analyzed. In addition, a triple contour scanning strategy was also conducted, and the variation of surface roughness caused by the different number of contours has been analyzed, along with the fabrication of the Ti6Al4V denture bracket. Results showed that the inclined surface roughness could be improved by the triple contour method to an average roughness (Ra) of 3.5 µm. An average surface roughness of less than 4.3 µm and a relative density of 99.8% have been achieved at the same time using the skin-core and triple contour strategy. The curved surface and overhanging structure quality of the denture bracket was also improved. This work provided a novel approach for the additive manufacturing of a medical titanium alloy. [ABSTRACT FROM AUTHOR]

A strategy is developed to modulate the fluorescent color of carbon nanodots (CNDs) through regulating photon reabsorption and carbonization degree. On the one hand, the emission color is tuned through enhancing the photon reabsorption via the concentration increase. Essentially, the emitted photon of short wavelengths is supposed to be reabsorbed by a neighboring CND, subsequently resulting in a photon emission of long wavelengths. On the other hand, by reaction time control, a higher carbonization degree of CNDs is obtained, which renders larger sizes and less oxygen related groups of CNDs, giving rise to narrower bandgaps, e.g., emissions of longer wavelengths. Through cooperatively managing the carbonization degree and photon reabsorption, a single ultraviolet light can be converted into multi-color luminescence across the entire visible range by using our one-pot-pyrolysis CNDs. [ABSTRACT FROM AUTHOR]

The effects of a collector plasma in a relativistic backward wave oscillator are investigated using a numerical simulation. Analyzing mainly the diffusion process, the results show a fast plasma diffusion occurring as one of the most important reasons for pulse shortening. In this process, the fast plasma affects the modulation of the intense relativistic electron beams, leads to drifting of the microwave frequency, absorbs gigawatts of microwave power, and finally causes pulse shortening. Here, the mechanism underpinning fast diffusion is mainly attributed to the standing wave pattern of the microwave field in the interaction region and the space charge effect. This paper reveals the change in the system after pulse shortening caused by fast diffusion and suggests a measure to control this process by restraining the collector plasma. [ABSTRACT FROM AUTHOR]

(001) textured Fe16N2 thin film with Ag under layer is successfully grown on GaAs substrate using a facing target sputtering (FTS) system. After post annealing, chemically ordered Fe16N2 phase is formed and detected by X-ray diffraction (XRD). High saturation magnetization (Ms) is measured by a vibrating sample magnetometer (VSM). In comparison with Fe16N2 with Ag under layer on MgO substrate and Fe16N2 with Fe under layer on GaAs substrate, the current layer structure shows a higher Ms value, with a magnetically softer feature in contrast to the above cases. In addition, X-ray photoelectron spectroscopy (XPS) is performed to characterize the binding energy of N atoms. To verify the role of strain that the FeN layer experiences in the above three structures, Grazing Incidence X-ray Diffraction (GIXRD) is conducted to reveal a large in-plane lattice constant due to the in-plane biaxial tensile strain. [ABSTRACT FROM AUTHOR]

A dual-cavity TM02-TM01 mode converter is designed for a dual-mode operation over-moded relativistic backward-wave oscillator. With the converter, the fundamental mode output is achieved. Particle-in-cell simulation shows that the efficiency of beam-wave conversion was over 46% and a pureTM01 mode output was obtained. Effects of end reflection provided by the mode converter were studied. Adequate TM01 mode feedback provided by the converter enhances conversion efficiency. The distance between the mode converter and extraction cavity critically affect the generation of microwaves depending on the reflection phase of TM01 mode feedback. [ABSTRACT FROM AUTHOR]