612,941 research outputs found

    Evaluation of ASTER GDEM ver2 using GPS measurements and SRTM ver4.1 in China

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    The freely available ASTER GDEM ver2 was released by NASA and METI on October 17, 2011. As one of the most complete high resolution digital topographic data sets of the world to date, the ASTER GDEM covers land surfaces between 83°N and 83°S at a spatial resolution of 1 arc-second and will be a useful product for many applications, such as relief analysis, hydrological studies and radar interferometry. The stated improvements in the second version of ASTER GDEM benefit from finer horizontal resolution, offset adjustment and water body detection in addition to new observed ASTER scenes. This study investigates the absolute vertical accuracy of the ASTER GDEM ver2 at five study sites in China using ground control points (GCPs) from high accuracy GPS benchmarks, and also using a DEM-to-DEM comparison with the Consultative Group for International Agriculture Research Consortium for Spatial Information (CGIAR-CSI) SRTM DEM (Version 4.1). And then, the results are separated into GlobCover land cover classes to derive the spatial pattern of error. It is demonstrated that the RMSE (19m) and mean (-13m) values of ASTER GDEM ver2 against GPS-GCPs in the five study areas is lower than its first version ASTER GDEM ver1 (26m and -21m) as a result of the adjustment of the elevation offsets in the new version. It should be noted that the five study areas in this study are representative in terms of terrain types and land covers in China, and even for most of mid-latitude zones. It is believed that the ASTER GDEM offers a major alternative in accessibility to high quality elevation data

    Charged Higgs Production at Linear Colliders in Large Extra Dimensions

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    In the Two-Higgs-Doublet Model(2HDM) with large extra dimensions(LED), we study the contributions of virtual Kaluza-Klein(KK) gravitons to 2HDM charged Higgs production, especially in the two important production processes e+eH+He^+e^-\to H^+H^- and e+eHtbˉe^+e^-\to H^-t\bar{b}, at future linear colliders (LC). We find that KK graviton effects can significantly modify these total cross sections and also their differential cross sections compared to their respective 2HDM values and, therefore, can be used to probe the effective scale ΛT\Lambda_T up to several TeV. For example, at s=2\sqrt{s}=2 TeV, the cross sections for e+eH+He^+e^-\to H^+H^- and e+eHtbˉe^+e^-\to H^-t\bar{b} in the 2HDM are 7.4fb for mH=150m_{H^-}=150 GeV and 0.003fb for mH=1.1m_{H^-}=1.1 TeV and tanβ=40\tan\beta=40, while in LED they are 12.1fb and 0.01fb, respectively, for ΛT=4\Lambda_T=4 Tev.Comment: 18 pages, 11 figures; a version to appear in PR

    Enhanced collectivity in neutron-deficient Sn isotopes in energy functional based collective Hamiltonian

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    The low-lying collective states in Sn isotopes are studied by a five-dimensional collective Hamiltonian with parameters determined from the triaxial relativistic mean-field calculations using the PC-PK1 energy density functional. The systematics for both the excitation energies of 21+2^+_1 states and B(E2;01+21+)B(E2;0^+_1\to 2^+_1) values are reproduced rather well, in particular, the enhanced E2 transitions in the neutron-deficient Sn isotopes with N<66. We show that the gradual degeneracy of neutron levels 1g7/2 and 2d5/2 around the Fermi surface leads to the increase of level density and consequently the enhanced paring correlations from N=66 to 58. It provokes a large quadrupole shape fluctuation around the spherical shape, and leads to an enhanced collectivity in the isotopes around N=58.Comment: 5 pages, 4 figures, accepted for publication in Physics Letters

    On symmetric commutator subgroups, braids, links and homotopy groups

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    In this paper, we investigate some applications of commutator subgroups to homotopy groups and geometric groups. In particular, we show that the intersection subgroups of some canonical subgroups in certain link groups modulo their symmetric commutator subgroups are isomorphic to the (higher) homotopy groups. This gives a connection between links and homotopy groups. Similar results hold for braid and surface groups.Comment: 24 pages, 1 figur