1,638 research outputs found
Electronic, dielectric and optical properties of two dimensional and bulk ice: a multi-scale simulation study
The intercalated water into nanopores exhibits anomalous properties such as
ultralow dielectric constant.~Multi-scale modeling and simulations are used to
investigate the dielectric properties of various crystalline two-dimensional
ices and bulk ices. Although, the structural properties of two-dimensional
(2D-) ices have been extensively studied, much less is known about their
electronic and optical properties. First, by using density functional theory
(DFT) and density functional perturbation theory (DFPT), we calculate the key
electronic, optical and dielectric properties of 2D-ices. Performing DFPT
calculations, both the ionic and electronic contributions of the dielectric
constant are computed. The in-plane electronic dielectric constant is found to
be larger than the out-of-plane dielectric constant for all the studied
2D-ices. The in-plane dielectric constant of the electronic response is found
to be isotropic for all the studied ices. Secondly, we determined the dipolar
dielectric constant of 2D-ices using molecular dynamics simulations (MDS) at
finite temperature. The total out-of-plane dielectric constant is found to be
larger than 2 for all the studied 2D-ices. Within the framework of the
random-phase approximation (RPA), the absorption energy ranges for 2D-ices are
found to be in the ultraviolet spectra. For the comparison purposes, we also
elucidate the electronic, dielectric and optical properties of four crystalline
ices (ice VIII, ice XI, ice Ic and ice Ih) and bulk water
Fast spectral solutions of the double-gyre problem in a turbulent flow regime
Several semi-analytical models are considered for a double-gyre problem in a turbulent flow regime for which a reference fully numerical eddy-resolving solution is obtained. The semi-analytical models correspond to solving the depth-averaged Navier–Stokes equations using the spectral Galerkin approach. The robustness of the linear and Smagorinsky eddy-viscosity models for turbulent diffusion approximation is investigated. To capture essential properties of the double-gyre configuration, such as the integral kinetic energy, the integral angular momentum, and the jet mean-flow distribution, an improved semi-analytical model is suggested that is inspired by the idea of scale decomposition between the jet and the surrounding flow
Blocked All-Pairs Shortest Paths Algorithm on Intel Xeon Phi KNL Processor: A Case Study
Manycores are consolidating in HPC community as a way of improving
performance while keeping power efficiency. Knights Landing is the recently
released second generation of Intel Xeon Phi architecture. While optimizing
applications on CPUs, GPUs and first Xeon Phi's has been largely studied in the
last years, the new features in Knights Landing processors require the revision
of programming and optimization techniques for these devices. In this work, we
selected the Floyd-Warshall algorithm as a representative case study of graph
and memory-bound applications. Starting from the default serial version, we
show how data, thread and compiler level optimizations help the parallel
implementation to reach 338 GFLOPS.Comment: Computer Science - CACIC 2017. Springer Communications in Computer
and Information Science, vol 79
Excitation of the Earth's Chandler wobble by a turbulent oceanic double-gyre
We develop a layer-averaged, multiple-scale spectral ocean model and show how an oceanic double-gyre can communicate with the Earth's Chandler wobble. The overall transfers of energy and angular momentum from the double-gyre to the Chandler wobble are used to calibrate the turbulence parameters of the layer-averaged model. Our model is tested against a multilayer quasi-geostrophic ocean model in turbulent regime, and base states used in parameter identification are obtained from mesoscale eddy resolving numerical simulations. The Chandler wobble excitation function obtained from the model predicts a small role of North Atlantic ocean region on the wobble dynamics as compared to all oceans, in agreement with the existing observations
Star Formation in the vicinity of Nuclear Black Holes: Young Stellar Objects close to Sgr A*
It is often assumed that the strong gravitational field of a super-massive
black hole disrupts an adjacent molecular cloud preventing classical star
formation in the deep potential well of the black hole. Yet, young stars have
been observed across the entire nuclear star cluster of the Milky Way including
the region close (0.5~pc) to the central black hole, Sgr A*. Here, we focus
particularly on small groups of young stars, such as IRS 13N located 0.1 pc
away from Sgr A*, which is suggested to contain about five embedded massive
young stellar objects (1 Myr). We perform three dimensional hydrodynamical
simulations to follow the evolution of molecular clumps orbiting about a
black hole, to constrain the formation and the physical
conditions of such groups. The molecular clumps in our models assumed to be
isothermal containing 100 in 0.2 pc radius. Such molecular
clumps exist in the circumnuclear disk of the Galaxy. In our highly
eccentrically orbiting clump, the strong orbital compression of the clump along
the orbital radius vector and perpendicular to the orbital plane causes the gas
densities to increase to values higher than the tidal density of Sgr A*, which
are required for star formation. Additionally, we speculate that the infrared
excess source G2/DSO approaching Sgr A* on a highly eccentric orbit could be
associated with a dust enshrouded star that may have been formed recently
through the mechanism supported by our models.Comment: 18 pages, 11 figures, accepted for publication in MNRA
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