176,016 research outputs found
The gravitational field of a global monopole
We present an exact solution to the non-linear equation which describes a
global monopole in the flat space. We re-examine the metric and the geodesics
outside the global monopole. We will see that a global monopole produces a
repulsive gravitational field outside the core in addition to a solid angular
deficit. The lensing property of the global monopole and the global
monopole-antimonopole annihilation mechanism are studied.Comment: 8 pages, no figure
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
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Effect factors of part-load performance for various Organic Rankine cycles using in engine waste heat recovery
The Organic Rankine Cycle (ORC) is regarded as one of the most promising waste heat recovery technologies for electricity generation engines. Since the engine usually operates under different working conditions, it is important to research the part-load performance of the ORC. In order to reveal the effect factors of part-load performance, four different forms of ORCs are compared in the study with dynamic math models established in SIMULINK. They are the ORC applying low temperature working fluid R245fa with a medium heat transfer cycle, the ORCs with high temperature working fluid toluene heated directly by exhaust condensing at low pressure and high pressure, and the double-stage ORC. It is regarded that the more slowly the system output power decreases, the better part-load performance it has. Based on a comparison among the four systems, the effects of evaporating pressure, condensing condition, working fluid, and system structure on part-load performance are revealed in the work. Further, it is found that the system which best matches with the heat source not only performs well under the design conditions, but also has excellent part-load performance
Adiabatic passage of collective excitations in atomic ensembles
We describe a theoretical scheme that allows for transfer of quantum states
of atomic collective excitation between two macroscopic atomic ensembles
localized in two spatially-separated domains. The conception is based on the
occurrence of double-exciton dark states due to the collective destructive
quantum interference of the emissions from the two atomic ensembles. With an
adiabatically coherence manipulation for the atom-field couplings by stimulated
Ramann scattering, the dark states will extrapolate from an exciton state of an
ensemble to that of another. This realizes the transport of quantum information
among atomic ensembles.Comment: 7 pages, 2 figure
Intersections of homogeneous Cantor sets and beta-expansions
Let be the -part homogeneous Cantor set with
. Any string with
such that is called a code of . Let
be the set of having a unique code,
and let be the set of which make the intersection a
self-similar set. We characterize the set in a
geometrical and algebraical way, and give a sufficient and necessary condition
for . Using techniques from beta-expansions, we
show that there is a critical point , which is a
transcendental number, such that has positive
Hausdorff dimension if , and contains countably
infinite many elements if . Moreover, there exists a
second critical point
such that
has positive Hausdorff dimension if
, and contains countably infinite many elements if
.Comment: 23 pages, 4 figure
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