7,375 research outputs found
Entanglement entropy of integer Quantum Hall states
We compute the entanglement entropy, in real space, of the ground state of
the integer Quantum Hall states for three different domains embedded in the
torus, the disk and the sphere. We establish the validity of the area law with
a vanishing value of the topological entanglement entropy. The entropy per unit
length of the perimeter depends on the filling fraction, but it is independent
of the geometry.Comment: 5 pages, 2 figures, minor changes, one reference adde
Testing the equation of state for viscous dark energy
Some cosmological scenarios with bulk viscosity for the dark energy fluid are considered. Based on
some considerations related to hydrodynamics, two different equations of state for dark energy are
assumed, leading to power-law and logarithmic effective corrections to the pressure. The models are tested
with the latest astronomical data from type Ia supernovae (Pantheon sample), measurements of the Hubble
parameter HðzÞ, baryon acoustic oscillations and cosmic microwave background radiation. In comparison
with the ΛCDM model, some different results are obtained and their viability is discussed. The power-law
model shows some modest results, achieved under negative values of bulk viscosity, while the logarithmic
scenario provide good fits in comparison to the ΛCDM model.Ministerio de Economía, Industria y Competitividad (project FIS2016-76363-P)Agencia de Gestión de Ayudas Universitarias y de Investigación (project 2017 SGR 247)CANTATA COST action (grant CA15117
The effect of Fe atoms on the adsorption of a W atom on W(100) surface
We report a first-principles calculation that models the effect of iron (Fe)
atoms on the adsorption of a tungsten (W) atom on W(100) surfaces. The
adsorption of a W atom on a clean W(100) surface is compared with that of a W
atom on a W(100) surface covered with a monolayer of Fe atoms. The total energy
of the system is computed as the function of the height of the W adatom. Our
result shows that the W atom first adsorbs on top of the Fe monolayer. Then the
W atom can replace one of the Fe atoms through a path with a moderate energy
barrier and reduce its energy further. This intermediate site makes the
adsorption (and desorption) of W atoms a two-step process in the presence of Fe
atoms and lowers the overall adsorption energy by nearly 2.4 eV. The Fe atoms
also provide a surface for W atoms to adsorb facilitating the diffusion of W
atoms. The combination of these two effects result in a much more efficient
desorption and diffusion of W atoms in the presence of Fe atoms. Our result
provides a fundamental mechanism that can explain the activated sintering of
tungsten by Fe atoms.Comment: 9 pages, 2 figure
Integrated design optimization research and development in an industrial environment
An overview is given of a design optimization project that is in progress at the GE Research and Development Center for the past few years. The objective of this project is to develop a methodology and a software system for design automation and optimization of structural/mechanical components and systems. The effort focuses on research and development issues and also on optimization applications that can be related to real-life industrial design problems. The overall technical approach is based on integration of numerical optimization techniques, finite element methods, CAE and software engineering, and artificial intelligence/expert systems (AI/ES) concepts. The role of each of these engineering technologies in the development of a unified design methodology is illustrated. A software system DESIGN-OPT has been developed for both size and shape optimization of structural components subjected to static as well as dynamic loadings. By integrating this software with an automatic mesh generator, a geometric modeler and an attribute specification computer code, a software module SHAPE-OPT has been developed for shape optimization. Details of these software packages together with their applications to some 2- and 3-dimensional design problems are described
Is exponential gravity a viable description for the whole cosmological history?
Here we analysed a particular type of gravity, the so-called
exponential gravity which includes an exponential function of the Ricci scalar
in the action. Such term represents a correction to the usual Hilbert-Einstein
action. By using Supernovae Ia, Barionic Acoustic Oscillations, Cosmic
Microwave Background and data, the free parameters of the model are well
constrained. The results show that such corrections to General Relativity
become important at cosmological scales and at late-times, providing an
alternative to the dark energy problem. In addition, the fits do not determine
any significant difference statistically with respect to the CDM
model. Finally, such model is extended to include the inflationary epoch in the
same gravitational Lagrangian. As shown in the paper, the additional terms can
reproduce the inflationary epoch and satisfy the constraints from Planck data.Comment: 20 pages, 6 figures, analysis extended, version published in EPJ
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