32,505 research outputs found

    Very deep spectroscopy of the bright Saturn Nebula NGC 7009 -- I. Observations and plasma diagnostics

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    We present very deep CCD spectrum of the bright, medium-excitation planetary nebula NGC 7009, with a wavelength coverage from 3040 to 11000 A. Traditional emission line identification is carried out to identify all the emission features in the spectra, based on the available laboratory atomic transition data. Since the spectra are of medium resolution, we use multi-Gaussian line profile fitting to deblend faint blended lines, most of which are optical recombination lines (ORLs) emitted by singly ionized ions of abundant second-row elements such as C, N, O and Ne. Computer-aided emission-line identification, using the code EMILI developed by Sharpee et al., is then employed to further identify all the emission lines thus obtained. In total about 1200 emission features are identified, with the faintest ones down to fluxes 10^{-4} of H_beta. The flux errors for all emission lines, estimated from multi-Gaussian fitting, are presented. Plots of the whole optical spectrum, identified emission lines labeled, are presented along with the results of multi-Gaussian fits. Plasma diagnostics using optical forbidden line ratios are carried out. Also derived are electron temperatures and densities from the H I, He I and He II recombination spectrum.Comment: 66 pages, 16 figures, 7 tables, paper accepted by MNRAS in Marc

    Laser ignition of an optically sensitised secondary explosive by a diode laser

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    As a green technology, laser ignition of a relatively insensitive secondary explosive has been experimentally investigated. The explosive, hexanitrostilbene (HNS), was doped with one of two optical sensitizers, carbon black or a laser absorbing dye, and a continuous-wave (CW) infrared diode laser was used as the igniting source. The ignition sensitivities of HNS with each of the two optical sensitizers were analysed and compared in terms of: optical power threshold for ignition, ignition delay and full burn delay at various laser powers. The results have shown that both the chemical dye and carbon black optically sensitize the explosive with similar efficiencies. In contrast to the carbon black, the dye provides wavelength specificity and selectivity in the laser ignition process and its solubility in some specific solvents improves the coating of the explosive material. It was therefore concluded that the laser absorbing dye is a better candidate for optical sensitization in laser ignition than the commonly used carbon black. The combination of laser ignition sensitivity with wavelength selectivity potentially offers higher reliability and safety at a low optical power for future ignitors of secondary explosives

    Lost and Found In Translation

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    „Lost and found in translation‟ explores gaps in communication and mistranslations between languages and cultural identities. My art practice has evolved from traditional printmaking in Shanghai to installations and screenprints as a student in the U.S., to my doctoral work which draws from my research and my experiences and encounters in London. My research centres on three generations of Chinese artists who brought their own culture to bear on the experience of living and making work in the West. The first generation was led by Xu Beihong in the 1920s. The second generation was led by Xu Bing, Ai Weiwei and Tan Dun, who lived together in New York in the 1980s. The third generation, which includes myself, Yang Yuanyuan and Liu Yefu, were born in the 1990s and 2000s and studied abroad. This generation uses multiple media, including social media, in a globalized art world where their identity as „Chinese‟ artists is less central. My own artwork is located also in the context of contemporary artists who use text in their work, such as Jenny Holzer and Jens Haaning. When facing the clash of cultural and linguistic environments, my aim is to find a balance between inclusive and exclusive language systems. What seems to be „lost‟ in translation can be used creatively in art practice, through hybridized forms and often through humour, to „find‟ new meanings for myself, and hopefully for the audiences of my work

    Coherent control of Snell's law

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    We demonstrate coherent control of the generalized Snell's law in ultrathin gradient metasurfaces constructed by an array of V-shaped slot nanoantennas

    An investigation of air and water dual adjustment decoupling control of surface heat exchanger

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    The terminal equipment of central cooling system accounts for a significant proportion of the total system's energy consumption. Therefore, it is important to reduce the terminal equipment energy consumption in central air conditioning system. In this study, the difference of the effect of the chilled water flow rate and air supply rate on the surface cooler during the heat transfer process is taken into full account. Matlab/Simulink simulation software is used to model and simulate the heat transfer of surface cooler of the main terminal equipment of air conditioning system. Simulation tests and experimental validations are conducted by using variable chilled water flow rate and variable air supply rate control mode separately. The experiment results show that the simulation model can effectively predict the heat transfer performance of heat exchanger. Further, the study introduced a dual feedback control mode, which synchronously regulates the chilled water flow rate and air supply rate. Also, under certain conditions, the complex heat transfer process of the surface cooler can be decoupled, and single variable control pattern is used to separately regulate the chilled water flow rate and air supply rate. This can effectively shorten the system regulation time, reduce overshoot and improve control performance