9,192 research outputs found
Role of Strain on Electronic and Mechanical Response of Semiconducting Transition-Metal Dichalcogenide Monolayers: an ab-initio study
We characterize the electronic structure and elasticity of monolayer
transition-metal dichalcogenides MX2 (M=Mo, W, Sn, Hf and X=S, Se, Te) with 2H
and 1T structures using fully relativistic first principles calculations based
on density functional theory. We focus on the role of strain on the band
structure and band alignment across the series 2D materials. We find that
strain has a significant effect on the band gap; a biaxial strain of 1%
decreases the band gap in the 2H structures, by as a much 0.2 eV in MoS2 and
WS2, while increasing it for the 1T materials. These results indicate that
strain is a powerful avenue to modulate their properties; for example, strain
enables the formation of, otherwise impossible, broken gap heterostructures
within the 2H class. These calculations provide insight and quantitative
information for the rational development of heterostructures based on these
class of materials accounting for the effect of strain.Comment: 16 pages, 4 figures, 1 table, supplementary materia
Shape evolution in Yttrium and Niobium neutron-rich isotopes
The isotopic evolution of the ground-state nuclear shapes and the systematics
of one-quasiproton configurations are studied in neutron-rich odd-A Yttrium and
Niobium isotopes. We use a selfconsistent Hartree-Fock-Bogoliubov formalism
based on the Gogny energy density functional with two parametrizations, D1S and
D1M. The equal filling approximation is used to describe odd-A nuclei
preserving both axial and time reversal symmetries. Shape-transition signatures
are identified in the N=60 isotopes in both charge radii and spin-parities of
the ground states. These signatures are a common characteristic for nuclei in
the whole mass region. The nuclear deformation and shape coexistence inherent
to this mass region are shown to play a relevant role in the understanding of
the spectroscopic features of the ground and low-lying one-quasiproton states.
Finally, a global picture of the neutron-rich A=100 mass region from Krypton up
to Molybdenum isotopes is illustrated with the systematics of the nuclear
charge radii isotopic shifts.Comment: 21 pages, 14 figures. To be published in Phys. Rev.
Systematics of one-quasiparticle configurations in neutron-rich Sr, Zr, and Mo odd isotopes with the Gogny energy density functional
The systematics of one-quasiparticle configurations in neutron-rich Sr, Zr,
and Mo odd isotopes is studied within the Hartree-Fock-Bogoliubov plus Equal
Filling Approximation method preserving both axial and time reversal
symmetries. Calculations based on the Gogny energy density functional with both
the standard D1S parametrization and the new D1M incarnation of this functional
are included in our analysis. The nuclear deformation and shape coexistence
inherent to this mass region are shown to play a relevant role in the
understanding of the spectroscopic features of the ground and low-lying
one-quasineutron states.Comment: 11 page
Signatures of shape transition in odd-A neutron-rich Rubidium isotopes
The isotopic evolution of the ground-state nuclear shapes and the systematics
of one-quasiproton configurations are studied in odd-A Rubidium isotopes. We
use a selfconsistent Hartree-Fock-Bogoliubov formalism based on the Gogny
energy density functional with two parametrizations, D1S and D1M, and
implemented with the equal filling approximation. We find clear signatures of a
sharp shape transition at N=60 in both charge radii and spin-parity of the
ground states, which are robust, consistent to each other, and in agreement
with experiment. We point out that the combined analysis of these two
observables could be used to predict unambiguously new regions where shape
transitions might develop.Comment: 6 pages, 7 figures. To appear in Phys. Rev. C (Rapid Communications
Microscopic description of quadrupole-octupole coupling in Sm and Gd isotopes with the Gogny Energy Density Functional
The interplay between the collective dynamics of the quadrupole and octupole
deformation degree of freedom is discussed in a series of Sm and Gd isotopes
both at the mean field level and beyond, including parity symmetry restoration
and configuration mixing. Physical properties like negative parity excitation
energies, E1 and E3 transition probabilities are discussed and compared to
experimental data. Other relevant intrinsic quantities like dipole moments,
ground state quadrupole moments or correlation energies associated to symmetry
restoration and configuration mixing are discussed. For the considered
isotopes, the quadrupole-octupole coupling is found to be weak and most of the
properties of negative parity states can be described in terms of the octupole
degree of freedom alone.Comment: 31 pages, 11 figure
Gravitational cooling of self-gravitating Bose-Condensates
Equilibrium configurations for a self-gravitating scalar field with
self-interaction are constructed. The corresponding Schr\"odinger-Poisson (SP)
system is solved using finite differences assuming spherical symmetry. It is
shown that equilibrium configurations of the SP system are late-time attractor
solutions for initially quite arbitrary density profiles, which relax and
virialize through the emission of scalar field bursts; a process dubbed
gravitational cooling. Among other potential applications, these results
indicate that scalar field dark matter models (in its different flavors)
tolerate the introduction of a self-interaction term in the SP equations. This
study can be useful in exploring models in which dark matter in galaxies is not
point-like.Comment: 10 aastex pages, 12 eps figures. Accepted for publication in Ap
Tracing the magnetic field of IRDC G028.23-00.19 using NIR polarimetry
The importance of the magnetic (B) field in the formation of infrared dark clouds (IRDCs) and massive stars is an ongoing topic of investigation. We studied the plane-of-sky B field for one IRDC, G028.23-00.19, to understand the interaction between the field and the cloud. We used near-IR background starlight polarimetry to probe the B field and performed several observational tests to assess the field importance. The polarimetric data, taken with the Mimir instrument, consisted of H-band and K-band observations, totaling 17,160 stellar measurements. We traced the plane-of-sky B-field morphology with respect to the sky-projected cloud elongation. We also found the relationship between the estimated B-field strength and gas volume density, and we computed estimates of the normalized mass-to-magnetic flux ratio. The B-field orientation with respect to the cloud did not show a preferred alignment, but it did exhibit a large-scale pattern. The plane-of-sky B-field strengths ranged from 10 to 165 μG, and the B-field strength dependence on density followed a power law with an index consistent with 2/3. The mass-to-magnetic flux ratio also increased as a function of density. The relative orientations and relationship between the B field and density imply that the B field was not dynamically important in the formation of the IRDC. The increase in mass-to-flux ratio as a function of density, though, indicates a dynamically important B field. Therefore, it is unclear whether the B field influenced the formation of G28.23. However, it is likely that the presence of the IRDC changed the local B-field morphology.We thank J. Montgomery, T. Hogge, and I. Stephens for constructive discussions on the analysis. We are grateful to R. Crutcher for permission to include his Zeeman data. This research was conducted in part using the Mimir instrument, jointly developed at Boston University and Lowell Observatory and supported by NASA, NSF, and the W.M. Keck Foundation. This research made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology (Caltech), under contract with NASA. This publication made use of data products from the Two Micron All Sky Survey, which was a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/Caltech, funded by NASA and NSF. This work is based in part on data obtained as part of the UKIRT Infrared Deep Sky Survey. The ATLAS-GAL project is a collaboration between the Max-PlanckGesellschaft, the European Southern Observatory (ESO), and the Universidad de Chile. It includes projects E-181.C-0885, E-078.F-9040(A), M-079.C-9501(A), M-081.C-9501(A), and Chilean data. This publication makes use of molecular line data from the Boston University-FCRAO Galactic Ring Survey (GRS). The GRS is a joint project of Boston University and Five College Radio Astronomy Observatory, funded by the National Science Foundation under grants AST-9800334, 0098562, 0100793, 0228993, and. 0507657. A.E.G. acknowledges support from FONDECYT 3150570. This work was supported under NSF grants AST 09-07790 and 14-12269 and NASA grant NNX15AE51G to Boston University. We thank the anonymous referee for valuable feedback, which improved the quality of this work. (NASA; NSF; W.M. Keck Foundation; E-181.C-0885 - Max-Planck-Gesellschaft; E-078.F-9040(A) - Max-Planck-Gesellschaft; M-079.C-9501(A) - Max-Planck-Gesellschaft; M-081.C-9501(A) - Max-Planck-Gesellschaft; E-181.C-0885 - European Southern Observatory (ESO); E-078.F-9040(A) - European Southern Observatory (ESO); M-079.C-9501(A) - European Southern Observatory (ESO); M-081.C-9501(A) - European Southern Observatory (ESO); E-181.C-0885 - Universidad de Chile; E-078.F-9040(A) - Universidad de Chile; M-079.C-9501(A) - Universidad de Chile; M-081.C-9501(A) - Universidad de Chile; AST-9800334 - National Science Foundation; 0098562 - National Science Foundation; 0100793 - National Science Foundation; 0228993 - National Science Foundation; 0507657 - National Science Foundation; 3150570 - FONDECYT; AST 09-07790 - NSF; 14-12269 - NSF; NNX15AE51G - NASA
Modelling the rotational curves of spiral galaxies with a scalar field
In a previous work (Mbelek 2001), we modelled the rotation curves (RC) of
spiral galaxies by including in the equation of motion of the stars the
dynamical terms from an external real self-interacting scalar field, ,
minimally coupled to gravity and which respects the equivalence principle in
the weak fields and low velocity approximation. This model appeared to have
three free parameters : the turnover radius, , the maximum tangential
velocity, , plus a strictly positive
integer, . Here, we propose a new improved version where the coupling of the
-field to dark matter is emphasized at the expense of its
self-interaction. This reformulation presents the very advantageous possibility
that the same potential is used for all galaxies. Using at the same time a
quasi-isothermal dark matter density and the scalar field helps to better fit
the RC of spiral galaxies. In addition, new correlations are established.Comment: Latex, 5 pages with 3 Postscript figure
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