719 research outputs found
Aspect ratio dependence of heat transport by turbulent Rayleigh-B\'{e}nard convection in rectangular cells
We report high-precision measurements of the Nusselt number as a
function of the Rayleigh number in water-filled rectangular
Rayleigh-B\'{e}nard convection cells. The horizontal length and width
of the cells are 50.0 cm and 15.0 cm, respectively, and the heights ,
25.0, 12.5, 6.9, 3.5, and 2.4 cm, corresponding to the aspect ratios
, , ,
, , and . The measurements were carried out
over the Rayleigh number range and the
Prandtl number range . Our results show that for
rectangular geometry turbulent heat transport is independent of the cells'
aspect ratios and hence is insensitive to the nature and structures of the
large-scale mean flows of the system. This is slightly different from the
observations in cylindrical cells where is found to be in general a
decreasing function of , at least for and larger. Such a
difference is probably a manifestation of the finite plate conductivity effect.
Corrections for the influence of the finite conductivity of the top and bottom
plates are made to obtain the estimates of for plates with
perfect conductivity. The local scaling exponents of are calculated and found to increase from 0.243 at
to 0.327 at .Comment: 15 pages, 7 figures, Accepted by Journal of Fluid Mechanic
Density-driven higher-order topological phase transitions in amorphous solids
Amorphous topological states, which are independent of the specific spatial
distribution of microscopic constructions, have gained much attention.
Recently, higher-order topological insulators, which are a new class of
topological phases of matter, have been proposed in amorphous systems. Here, we
propose a density-driven higher-order topological phase transition in a
two-dimensional amorphous system. We demonstrate that the amorphous system
hosts a topological trivial phase at low density. With an increase in the
density of lattice sites, the topological trivial phase converts to a
higher-order topological phase characterized by a quantized quadrupole moment
and the existence of topological corner states. Furthermore, we confirm that
the density-driven higher-order topological phase transition is size dependent.
In addition, our results should be general and equally applicable to
three-dimensional amorphous systems. Our findings may greatly enrich the study
of higher-order topological states in amorphous systems
Highly Efficient White Organic Light-Emitting Diodes with Controllable Excitons Behavior by a Mixed Interlayer between Fluorescence Blue and Phosphorescence Yellow-Emitting Layers
A highly efficient hybrid white organic light-emitting diode (HWOLED) has been demonstrated with a mixed interlayer between fluorescent blue and phosphorescent yellow-emitting layers. The device structure is simplified by using a controllable fluorescence-mixed interlayer-phosphorescence emission layer structure. The electroluminance (EL) performance can be modulated easily by adjusting the ratio of the hole-predominated material to the electron-predominated material in the interlayer. It is found that the HWOLED with a ratio of 3 : 2 exhibits a current efficiency of 34 cd/A and a power efficiency of 29 lm/W at 1000 cd/m2 with warm white Commission Internationale de l’Eclairage (CIE1931) coordinates of (0.4273, 0.4439). The improved efficiency and adaptive CIE coordinates are attributed to the controllable mixed interlayer with enhanced charge carrier transport, optimized excitons distribution, and improved harvestings of singlet and triplet excitons
Topological surface electronic states in candidate nodal-line semimetal CaAgAs
We investigate systematically the bulk and surface electronic structure of
the candidate nodal-line semimetal CaAgAs by angle resolved photoemission
spectroscopy and density functional calculations. We observed a metallic,
linear, non--dispersive surface band that coincides with the
high-binding-energy part of the theoretical topological surface state, proving
the topological nontriviality of the system. An overall downshift of the
experimental Fermi level points to a rigid-band-like -doping of the samples,
due possibly to Ag vacancies in the as-grown crystals.Comment: 6 pages, 5 figure
THE IMPACTS OF GOVERNMENT R&D EXPENDITURE ON INNOVATION IN CHINESE PROVINCES: WHAT’S THE ROLE OF CORRUPTION
This study aims to investigate the moderating role of corruption on the effect of government R&D expenditure on enterprise innovation in China, using the annually data over the period 2002-2013 in a panel of 30 provinces. A dynamic panel system GMM model was used to explore the relationship among government R&D expenditure, corruption, and innovation. Our finding shows that though government R&D expenditure has no significant effects on patent applications, it does exhibit significantly positive effects on patents granted. However, when considering official corruption, the interaction term of government R&D expenditure and corruption has a statistically significantly positive effect on patent applications and patents granted, with corruption presenting significantly positive effects on the ratio of the number of patents granted to patent applications. It demonstrates that corruption is still a shortcut for overcoming red tapes and administrative intervention, especially in an economy in transition with lower institution quality and anti-corruption
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