1,647 research outputs found
Coexisting orders in the quarter-filled Hubbard chain with elastic deformations
The electronic properties of the quarter-filled extended
Peierls-Holstein-Hubbard model that includes lattice distortions and molecular
deformations are investigated theoretically using the bosonization approach. We
predict the existence of a wide variety of charge-elastic phases depending of
the values of the Peierls and Holstein couplings. We include the effect of the
Peierls deformation in the nearest-neighbor repulsion V, that may be present in
real materials where Coulomb interactions depend strongly on the distance, and
we show that the phase diagram changes substantially for large V when this term
is taken into account.Comment: 6 pages, 3 figure
Diffusion and mixing in gravity-driven dense granular flows
We study the transport properties of particles draining from a silo using
imaging and direct particle tracking. The particle displacements show a
universal transition from super-diffusion to normal diffusion, as a function of
the distance fallen, independent of the flow speed. In the super-diffusive (but
sub-ballistic) regime, which occurs before a particle falls through its
diameter, the displacements have fat-tailed and anisotropic distributions. In
the diffusive regime, we observe very slow cage breaking and Peclet numbers of
order 100, contrary to the only previous microscopic model (based on diffusing
voids). Overall, our experiments show that diffusion and mixing are dominated
by geometry, consistent with fluctuating contact networks but not thermal
collisions, as in normal fluids
Magnetic-field effects on transport in carbon nanotube junctions
Here we address a theoretical study on the behaviour of electronic states of
heterojunctions and quantum dots based on carbon nanotubes under magnetic
fields. Emphasis is put on the analysis of the local density of states, the
conductance, and on the characteristic curves of current versus voltage. The
heterostructures are modeled by joining zigzag tubes through single
pentagon-heptagon pair defects, and described within a simple tight binding
calculation. The conductance is calculated using the Landauer formula in the
Green functions formalism. The used theoretical approach incorporates the
atomic details of the topological defects by performing an energy relaxation
via Monte Carlo calculation. The effect of a magnetic field on the conductance
gap of the system is investigated and compared to those of isolated constituent
tubes. It is found that the conductance gap of the studied CNHs exhibits
oscillations as a function of the magnetic flux. However, unlike the pristine
tubes case, they are not Aharonov-Bohm periodic oscillations
Measuring primality in numerical semigroups with embedding dimension three
Electronic version of an article published as Journal of Algebra and Its Applications, 15, 1, 2016, 1650007. DOI:10.1142/S0219498816500079 © World Scientific Publishing Company https://www.worldscientific.com/doi/abs/10.1142/S0219498816500079In this paper, we find the ω-value of the generators of any numerical semigroup with embedding dimension three. This allows us to determine all possible orderings of the ω-values of the generators. In addition, we relate the ω-value of the numerical semigroup to its catenary degree.The first and third authors received National Science Foundation support under DMS-1262897. The second author is supported by the projects MTM2010-15595, FQM-343, FQM-5849, NSF-1061366 and FEDER funds
Velocity profile of granular flows inside silos and hoppers
We measure the flow of granular materials inside a quasi-two dimensional silo
as it drains and compare the data with some existing models. The particles
inside the silo are imaged and tracked with unprecedented resolution in both
space and time to obtain their velocity and diffusion properties. The data
obtained by varying the orifice width and the hopper angle allows us to
thoroughly test models of gravity driven flows inside these geometries. All of
our measured velocity profiles are smooth and free of the shock-like
discontinuities ("rupture zones") predicted by critical state soil mechanics.
On the other hand, we find that the simple Kinematic Model accurately captures
the mean velocity profile near the orifice, although it fails to describe the
rapid transition to plug flow far away from the orifice. The measured diffusion
length , the only free parameter in the model, is not constant as usually
assumed, but increases with both the height above the orifice and the angle of
the hopper. We discuss improvements to the model to account for the
differences. From our data, we also directly measure the diffusion of the
particles and find it to be significantly less than predicted by the Void
Model, which provides the classical microscopic derivation of the Kinematic
Model in terms of diffusing voids in the packing. However, the experimental
data is consistent with the recently proposed Spot Model, based on a simple
mechanism for cooperative diffusion. Finally, we discuss the flow rate as a
function of the orifice width and hopper angles. We find that the flow rate
scales with the orifice size to the power of 1.5, consistent with dimensional
analysis. Interestingly, the flow rate increases when the funnel angle is
increased.Comment: 17 pages, 8 figure
MUSE Reveals a Recent Merger in the Post-starburst Host Galaxy of the TDE ASASSN-14li
We present MUSE integral field spectroscopic observations of the host galaxy
(PGC 043234) of one of the closest (, Mpc) and
best-studied tidal disruption events (TDE), ASASSN-14li. The MUSE integral
field data reveal asymmetric and filamentary structures that extend up to
kpc from the post-starburst host galaxy of ASASSN-14li. The
structures are traced only through the strong nebular [O III] 5007, [N
II] 6584, and H emission lines. The total off nuclear [O III]
5007 luminosity is luminosity is erg s and
the ionized H mass is . Based on the BPT
diagram, the nebular emission can be driven by either AGN photoionization or
shock excitation, with AGN photoionization favored given the narrow intrinsic
line widths. The emission line ratios and spatial distribution strongly
resemble ionization nebulae around fading AGNs such as IC 2497 (Hanny's
Voorwerp) and ionization "cones" around Seyfert 2 nuclei. The morphology of the
emission line filaments strongly suggest that PGC 043234 is a recent merger,
which likely triggered a strong starburst and AGN activity leading to the
post-starburst spectral signatures and the extended nebular emission line
features we see today. We briefly discuss the implications of these
observations in the context of the strongly enhanced TDE rates observed in
post-starburst galaxies and their connection to enhanced theoretical TDE rates
produced by supermassive black-hole binaries.Comment: Accepted for publication in ApJ
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