45,322 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

    Control of lasing in fully chaotic open microcavities by tailoring the shape factor

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    We demonstrate experimentally that lasing in a semiconductor microstadium can be optimized by controlling its shape. Under spatially uniform optical pumping, the first lasing mode in a GaAs microstadium with large major-to-minor-axis ratio usually corresponds to a high-quality scar mode consisting of several unstable periodic orbits. Interference of waves propagating along the constituent orbits may minimize light leakage at particular major-to-minor-axis ratio. By making stadium of the optimum shape, we are able to maximize the mode quality factor and align the mode frequency to the peak of the gain spectrum, thus minimizing the lasing threshold. This work opens the door to control chaotic microcavity lasers by tailoring the shape factor

    Summary of my innovation and contributions to research on cultural productivity, contemporary literature and art, and strategic planning of culture construction

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    This statement summarizes my academic achievements in the professional research of humanity and social sciences, my contributions to academy and society, my innovations in theoretical construction and application of the project, and the outlook on my future academic development. The whole text is divided into six parts: an overview of my major works; comprehensive and detailed summary of my research on cultural productivity, its creative breakthroughs and social influence; my academic contribution to research on contemporary literature and art in China; my substantial contribution to the formulation of strategic plans for culture construction and the relevant investigation and study (generally in Hebei Province in China); academic innovations and social influence of some of my specific projects (e.g. information aesthetics); and my plan and prospect for future academic work

    Type I X-ray Bursts at Low Accretion Rates

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    Neutron stars, with their strong surface gravity, have interestingly short timescales for the sedimentation of heavy elements. Recent observations of unstable thermonuclear burning (observed as X-ray bursts) on the surfaces of slowly accreting neutron stars (<0.01< 0.01 of the Eddington rate) motivate us to examine how sedimentation of CNO isotopes affects the ignition of these bursts. We further estimate the burst development using a simple one-zone model with a full reaction network. We report a region of mass accretion rates for weak H flashes. Such flashes can lead to a large reservoir of He, the unstable burning of which may explain some observed long bursts (duration 1000\sim 1000 s).Comment: 6 pages, 2 figures, submitted to the proceedings of the conference "The Multicoloured Landscape of Compact Objects and Their Explosive Origins'', 2006 June 11--24, Cefalu, Sicily (Italy), to be published by AI

    Design Patterns for Fusion-Based Object Retrieval

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    We address the task of ranking objects (such as people, blogs, or verticals) that, unlike documents, do not have direct term-based representations. To be able to match them against keyword queries, evidence needs to be amassed from documents that are associated with the given object. We present two design patterns, i.e., general reusable retrieval strategies, which are able to encompass most existing approaches from the past. One strategy combines evidence on the term level (early fusion), while the other does it on the document level (late fusion). We demonstrate the generality of these patterns by applying them to three different object retrieval tasks: expert finding, blog distillation, and vertical ranking.Comment: Proceedings of the 39th European conference on Advances in Information Retrieval (ECIR '17), 201