25,082 research outputs found
Dynamic Atomic Snapshots
Snapshots are useful tools for monitoring big distributed and parallel systems. In this paper, we adapt the well-known atomic snapshot abstraction to dynamic models with an unbounded number of participating processes. Our dynamic snapshot specification extends the API to allow changing the set of processes whose values should be returned from a scan operation. We introduce the ephemeral memory model, which consists of a dynamically changing set of nodes; when a node is removed, its memory can be immediately reclaimed. In this model, we present an algorithm for wait-free dynamic atomic snapshots
Disorder Correlation Frequency Controlled Diffusion in the Jaynes-Cummings-Hubbard Model
We investigate time-dependent stochastic disorder in the one-dimensional
Jaynes-Cummings-Hubbard model and show that it gives rise to diffusive
behaviour. We find that disorder correlation frequency is effective in
controlling the level of diffusivity. In the defectless system the mean squared
displacement (MSD), which is a measure of the diffusivity, increases with
increasing disorder frequency. Contrastingly, when static defects are present
the MSD increases with disorder frequency only at lower frequencies; at higher
frequencies, increasing disorder frequency actually reduces the MSD
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Unraveling the Role of Interfaces on the Spall Failure of Cu/Ta Multilayered Systems.
Molecular dynamics (MD) simulations are carried out to investigate the effects of the type and spacing of FCC/BCC interfaces on the deformation and spall behavior. The simulations are carried out using model Cu/Ta multilayers with six different types of interfaces. The results suggest that interface type can significantly affect the structure and intensity of the incoming shock wave, change the activated slip systems, alter dislocation slip and twinning behavior, affect where and how voids are nucleated during spallation and the resulting spall strength. Moreover, the above aspects are significantly affected by the interface spacing. A transition from homogeneous to heterogeneous dislocation nucleation occurs as the interface spacing is decreased to 6 nm. Depending on interface type and spacing, damage (voids) nucleation and spall failure is observed to occur not only at the Cu/Ta interfaces, but also in the weaker Cu layer interior, or even in the stronger Ta layer interior, although different mechanisms underlie each of these three distinct failure modes. These findings point to the fact that, depending on the combination of interface type and spacing, interfaces can lead to both strengthening and weakening of the Cu/Ta multilayered microstructures
Learning from Ontology Streams with Semantic Concept Drift
Data stream learning has been largely studied for extracting knowledge
structures from continuous and rapid data records. In the semantic Web, data is
interpreted in ontologies and its ordered sequence is represented as an
ontology stream. Our work exploits the semantics of such streams to tackle the
problem of concept drift i.e., unexpected changes in data distribution, causing
most of models to be less accurate as time passes. To this end we revisited (i)
semantic inference in the context of supervised stream learning, and (ii)
models with semantic embeddings. The experiments show accurate prediction with
data from Dublin and Beijing
Quantum Monte Carlo and exact diagonalization study of a dynamic Hubbard model
A one-dimensional model of electrons locally coupled to spin-1/2 degrees of
freedom is studied by numerical techniques. The model is one in the class of
that describe the relaxation of an atomic orbital
upon double electron occupancy due to electron-electron interactions. We study
the parameter regime where pairing occurs in this model by exact
diagonalization of small clusters. World line quantum Monte Carlo simulations
support the results of exact diagonalization for larger systems and show that
kinetic energy is lowered when pairing occurs. The qualitative physics of this
model and others in its class, obtained through approximate analytic
calculations, is that superconductivity occurs through hole undressing even in
parameter regimes where the effective on-site interaction is strongly
repulsive. Our numerical results confirm the expected qualitative behavior, and
show that pairing will occur in a substantially larger parameter regime than
predicted by the approximate low energy effective Hamiltonian.Comment: Some changes made in response to referees comments. To be published
in Phys.Rev.
Structural disjoining potential for grain boundary premelting and grain coalescence from molecular-dynamics simulations
We describe a molecular dynamics framework for the direct calculation of the
short-ranged structural forces underlying grain-boundary premelting and
grain-coalescence in solidification. The method is applied in a comparative
study of (i) a Sigma 9 120 degress twist and (ii) a Sigma 9 {411}
symmetric tilt boundary in a classical embedded-atom model of elemental Ni.
Although both boundaries feature highly disordered structures near the melting
point, the nature of the temperature dependence of the width of the disordered
regions in these boundaries is qualitatively different. The former boundary
displays behavior consistent with a logarithmically diverging premelted layer
thickness as the melting temperature is approached from below, while the latter
displays behavior featuring a finite grain-boundary width at the melting point.
It is demonstrated that both types of behavior can be quantitatively described
within a sharp-interface thermodynamic formalism involving a width-dependent
interfacial free energy, referred to as the disjoining potential. The
disjoining potential for boundary (i) is calculated to display a monotonic
exponential dependence on width, while that of boundary (ii) features a weak
attractive minimum. The results of this work are discussed in relation to
recent simulation and theoretical studies of the thermodynamic forces
underlying grain-boundary premelting.Comment: 24 pages, 8 figures, 1 tabl
Stone-Wales Transformation Paths in Fullerene C60
The mechanisms of formation of a metastable defect isomer of fullerene C60
due to the Stone-Wales transformation are theoretically studied. It is
demonstrated that the paths of the "dynamic" Stone-Wales transformation at a
high sufficient for overcoming potential barriers) temperature can differ from
the two "adiabatic" transformation paths discussed in the literature. This
behavior is due to the presence of a great near-flat segment of the
potential-energy surface in the neighborhood of metastable states. Besides, the
sequence of rupture and formation of interatomic bonds is other than that in
the case of the adiabatictransformation.Comment: 10 pages, 6 figure
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