224,593 research outputs found
Evaluation of ASTER GDEM ver2 using GPS measurements and SRTM ver4.1 in China
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
The Coupled Cluster Method Applied to Quantum Magnets: A New LPSUB Approximation Scheme for Lattice Models
A new approximation hierarchy, called the LPSUB scheme, is described for
the coupled cluster method (CCM). It is applicable to systems defined on a
regular spatial lattice. We then apply it to two well-studied prototypical
(spin-1/2 Heisenberg antiferromagnetic) spin-lattice models, namely: the XXZ
and the XY models on the square lattice in two dimensions. Results are obtained
in each case for the ground-state energy, the ground-state sublattice
magnetization and the quantum critical point. They are all in good agreement
with those from such alternative methods as spin-wave theory, series
expansions, quantum Monte Carlo methods and the CCM using the alternative
LSUB and DSUB schemes. Each of the three CCM schemes (LSUB, DSUB
and LPSUB) for use with systems defined on a regular spatial lattice is
shown to have its own advantages in particular applications
Controlling diffusive transport in confined geometries
We analyze the diffusive transport of Brownian particles in narrow channels
with periodically varying cross-section. The geometrical confinements lead to
entropic barriers, the particle has to overcome in order to proceed in
transport direction. The transport characteristics exhibit peculiar behaviors
which are in contrast to what is observed for the transport in potentials with
purely energetic barriers. By adjusting the geometric parameters of the channel
one can effectively tune the transport and diffusion properties. A prominent
example is the maximized enhancement of diffusion for particular channel
parameters. The understanding of the role of channel-shape provides the
possibility for a design of stylized channels wherein the quality of the
transport can be efficiently optimized.Comment: accepted for publication in Acta Physica Polonica
Stellar mass versus stellar velocity dispersion: which is better for linking galaxies to their dark matter halos?
It was recently suggested that, compared to its stellar mass (M*), the
central stellar velocity dispersion (sigma*) of a galaxy might be a better
indicator for its host dark matter halo mass. Here we test this hypothesis by
estimating the dark matter halo mass for central alaxies in groups as function
of M* and sigma*. For this we have estimated the redshift-space
cross-correlation function (CCF) between the central galaxies at given M* and
sigma* and a reference galaxy sample, from which we determine both the
projected CCF, w_p(r_p), and the velocity dispersion profile (VDP) of
satellites around the centrals. A halo mass is then obtained from the average
velocity dispersion within the virial radius. At fixed M*, we find very weak or
no correlation between halo mass and sigma*. In contrast, strong mass
dependence is clearly seen even when sigma* is limited to a narrow range. Our
results thus firmly demonstrate that the stellar mass of central galaxies is
still a good (if not the best) indicator for dark matter halo mass, better than
the stellar velocity dispersion. The dependence of galaxy clustering on sigma*
fixed M*, as recently discovered by Wake et al. (2012), may be attributed to
satellite galaxies, for which the tidal stripping occurring within halos has
stronger effect on stellar mass than on central stellar velocity dispersion.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letters, minor
revisions in the tex
Transverse Magnetic Susceptibility of a Frustrated Spin- ---- Heisenberg Antiferromagnet on a Bilayer Honeycomb Lattice
We use the coupled cluster method (CCM) to study a frustrated
spin- ---- Heisenberg antiferromagnet
on a bilayer honeycomb lattice with stacking. Both nearest-neighbor (NN)
and frustrating next-nearest-neighbor antiferromagnetic (AFM) exchange
interactions are present in each layer, with respective exchange coupling
constants and . The two layers are
coupled with NN AFM exchanges with coupling strength . We calculate to high orders of approximation within the CCM
the zero-field transverse magnetic susceptibility in the N\'eel phase.
We thus obtain an accurate estimate of the full boundary of the N\'eel phase in
the plane for the zero-temperature quantum phase diagram. We
demonstrate explicitly that the phase boundary derived from is fully
consistent with that obtained from the vanishing of the N\'eel magnetic order
parameter. We thus conclude that at all points along the N\'eel phase boundary
quasiclassical magnetic order gives way to a nonclassical paramagnetic phase
with a nonzero energy gap. The N\'eel phase boundary exhibits a marked
reentrant behavior, which we discuss in detail
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