Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 6 Articles
To expand field of view (FOV) of telescope, the method of special scanning often is used, but, for some telescopes with special\nstructure in optics and machine, the conventional scanning methods are unsuitable. This paper proposes a novel scanning method\nbased on autoguiding system so as to expand the FOV of fiber array solar optical telescope (FASOT) in possession of the special\nstructure in optics and machine. Meanwhile, corresponding experiments are conducted in the FASOT prototype, FASOT-1B, in\norder to demonstrate that, for both FASOT and FASOT-1B, the proposed scanning method is feasible. First of all, on the basis of the\nsoftware and hardware characteristics of FASOTand FASOT-1B, the three key technologies related to the proposed scanningmethod\nare described: quickly locating and pointing the first scanning step, the closed-loop controlling of multistep scanning, and the\ndisturbance suppression of every scanning step based on Kalman filter. Afterwards, experiments are conducted and corresponding\nresults show that the proposed scanning method is robust for the random disturbances forced on every scanning step and able to\nmeet the scanning requirement of both FASOT and FASOT-1B ....
This paper presents findings of synchrotron diffraction measurements on tubular specimens\nwith a thermal barrier coating (TBC) system applied by electron beam physical vapor deposition\n(EB-PVD), having a thermally grown oxide (TGO) layer due to aging in hot air. The diffraction\nmeasurements were in situ while applying a thermal cycle with high temperature holds at 1000 ..C and varying internal air cooling mass flow and mechanical load. It was observed that, during high\ntemperature holds at 1000 ..C, the TGO strain approached zero if no mechanical load or internal\ncooling was applied. When applying a mechanical load, the TGO in-plane strain (e22) changed to\ntensile and the out of plane TGO strain (e11) became compressive. The addition of internal cooling\ninduced a thermal gradient, yielding a competing effect, driving the e22 strain to compressive and\ne11 strain to tensile. Quantifying TGO strain variations in response to competing factors will provide\na path to controlling the TGO strain, and further improving the lifetime assessment and durability\ndesign strategies for TBC systems....
Quantum-dot (QD) photonic-crystal (PC) surface-emitting laser (SEL) devices with bottom\ndistributed Bragg reflector (DBR) were fabricated based on vertical-cavity SEL structure with top DBR\ncompletely removed. Two-dimensional (2D) PCs were deeply etched through QD multilayers to yield\nstrong diffraction coupling. Room-temperature optically pumped lasing emissions at 1194 nm and\n1296 nm were demonstrated for two lattice periods of 360 nm and 395 nm, respectively. Two lasing\nwavelengths separated over 100 nm; however, there were less than two times difference in threshold\npower densities while slope efficiencies were comparable. The unique spectral gain characteristics of\nQDs were considered in interpretation of gain-cavity detuning. Moreover, simulation revealed the\nsub-cavity should be designed so that its resonant wavelength is in phase with lasing wavelength....
Forward modeling of diffraction peaks is a potential way to compare the results of\ntheoretical mechanical simulations and experimental X-ray diffraction (XRD) data recorded during\nin situ experiments. As the input data are the strain or displacement field within a representative\nvolume of the material containing dislocations, a computer-aided efficient and accurate method to\ngenerate these fields is necessary. With this aim, a current and promising numerical method is based\non the use of the fast Fourier transform (FFT)-based method. However, classic FFT-based methods\npresent some numerical artifacts due to the Gibbs phenomenon or â??aliasingâ? and to â??voxelizationâ?\neffects. Here, we propose several improvements: first, a consistent discrete Green operator to\nremove â??aliasingâ? effects; and second, a method to minimize the voxelization artifacts generated by\ndislocation loops inclined with respect to the computational grid. Then, we show the effect of these\nimprovements on theoretical diffraction peaks....
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The stellar winds of the central stars of planetary nebulae play an essential role in the shaping of\nplanetary nebulae. In the interacting stellar winds model, the fast stellar wind injects energy and\nmomentum, which are transferred to the nebular envelope through an X-ray-emitting hot bubble.\nTogether with other physical processes, such as the ionization of the nebular envelope, the asymmetrical\nmass-loss in the asymptotic giant branch (AGB), and the action of collimated outflows and magnetic\nfields, the pressurized hot gas determines the expansion and evolution of planetary nebulae. Chandra and\nXMM-Newton have provided us with detailed information of this hot gas. Here in this talk I will review\nour current understanding of the effects of the fast stellar wind in the shaping and evolution of planetary\nnebulae and give some hints of the promising future of this research....
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