5,546 research outputs found
Collinear versus non-collinear magnetic order in Pd atomic clusters: ab-initio calculations
We present a thorough theoretical assessment of the stability of
non-collinear spin arrangements in small palladium clusters. We generally find
that ferromagnetic order is always preferred, but that antiferromagnetic and
non-collinear configurations of different sorts exist and compete for the first
excited isomers. We also show that the ground state is insensitive to the
choice of atomic configuration for the pseudopotential used and to the
approximation taken for the exchange and correlation potential. Moreover, the
existence and relative stability of the different excited configurations also
depends weakly on the approximations employed. These results provide strong
evidence on the transferability of pseudopotential and exchange and correlation
functionals for palladium clusters as opposed to the situation found for the
bulk phases of palladium.Comment: 5 pages, 4 figure
Fast connected component labeling algorithm: a non voxel-based approach
This paper presents a new approach to achieve connected component labeling on both binary images and volumes by using the Extreme Vertices Model (EVM), a representation model for orthogonal
polyhedra, applied to digital images and volume datasets recently. In contrast with previous techniques, this method does not use a voxel-based approach but deals with the inner sections of the object.Postprint (published version
Clock spectroscopy of interacting bosons in deep optical lattices
We report on high-resolution optical spectroscopy of interacting bosonic
Yb atoms in deep optical lattices with negligible tunneling. We prepare
Mott insulator phases with singly- and doubly-occupied isolated sites and probe
the atoms using an ultra-narrow "clock" transition. Atoms in singly-occupied
sites undergo long-lived Rabi oscillations. Atoms in doubly-occupied sites are
strongly affected by interatomic interactions, and we measure their inelastic
decay rates and energy shifts. We deduce from these measurements all relevant
collisional parameters involving both clock states, in particular the intra-
and inter-state scattering lengths
Non-linear Relaxation of Interacting Bosons Coherently Driven on a Narrow Optical Transition
We study the dynamics of a two-component Bose-Einstein condensate (BEC) of
Yb atoms coherently driven on a narrow optical transition. The
excitation transfers the BEC to a superposition of states with different
internal and momentum quantum numbers. We observe a crossover with decreasing
driving strength between a regime of damped oscillations, where coherent
driving prevails, and an incoherent regime, where relaxation takes over.
Several relaxation mechanisms are involved: inelastic losses involving two
excited atoms, leading to a non-exponential decay of populations; Doppler
broadening due to the finite momentum width of the BEC and inhomogeneous
elastic interactions, both leading to dephasing and to damping of the
oscillations. We compare our observations to a two-component Gross-Pitaevskii
(GP) model that fully includes these effects. For small or moderate densities,
the damping of the oscillations is mostly due to Doppler broadening. In this
regime, we find excellent agreement between the model and the experimental
results. For higher densities, the role of interactions increases and so does
the damping rate of the oscillations. The damping in the GP model is less
pronounced than in the experiment, possibly a hint for many-body effects not
captured by the mean-field description.Comment: 7 pages, 4 figures; supplementary material available as ancillary
fil
Magneto--thermal evolution of neutron stars
We study the mutual influence of thermal and magnetic evolution in a neutron
star's crust in axial symmetry. Taking into account realistic microphysical
inputs, we find the heat released by Joule effect consistent with the
circulation of currents in the crust, and we incorporate its effects in 2D
cooling calculations. We solve the induction equation numerically using a
hybrid method (spectral in angles, but a finite--differences scheme in the
radial direction), coupled to the thermal diffusion equation. We present the
first long term 2D simulations of the coupled magneto-thermal evolution of
neutron stars. This substantially improves previous works in which a very crude
approximation in at least one of the parts (thermal or magnetic diffusion) has
been adopted. Our results show that the feedback between Joule heating and
magnetic diffusion is strong, resulting in a faster dissipation of the stronger
fields during the first million years of a NS's life. As a consequence, all
neutron stars born with fields larger than a critical value (about 5 10^13 G)
reach similar field strengths (approximately 2-3 10^{13} G) at late times.
Irrespectively of the initial magnetic field strength, after years the
temperature becomes so low that the magnetic diffusion timescale becomes longer
than the typical ages of radio--pulsars, thus resulting in apparently no
dissipation of the field in old NS. We also confirm the strong correlation
between the magnetic field and the surface temperature of relatively young NSs
discussed in preliminary works. The effective temperature of models with strong
internal toroidal components are systematically higher than those of models
with purely poloidal fields, due to the additional energy reservoir stored in
the toroidal field that is gradually released as the field dissipates.Comment: 10 pages, 5 figures, accepted for publication in A&
Low-cost technology for the integration of micro- and nanochips into fluidic systems on printed circuit board: fabrication challenges
Nowadays, micro- and nanochips are usually\ud
fabricated with Silicon and/or glass. A simple, low-cost and\ud
reliable integration packaging method that provides flexibility\ud
to the incorporation of electronic and fluidic devices into a\ud
system has not been fully developed yet. The use of Printed\ud
Circuit Board material as substrate to create dry film resist\ud
microfluidic channels is the core technology to provide such an\ud
integration method. The feasibility and potential of the\ud
proposed packaging method is demonstrated in this wor
Revisiting neutron starquakes caused by spin-down
Pulsars show a steady decrease in their rotational frequency, occasionally
interrupted by sudden spin-ups called glitches, whose physical origin is still
a mystery. One suggested explanation for at least the small glitches are
starquakes, that is, failures of the solid neutron star crust, in which the
progressive reduction in the centrifugal force deforms the star, stressing the
solid until it breaks. This produces a spin-up, dissipating energy inside the
star. We analyze the deformations produced by the decreasing centrifugal force,
modeling the star with a fluid core and a solid crust, each with uniform
density and with the core possibly denser than the crust, as a simple
approximation to the strong density gradient present in real neutron stars. The
deformation is qualitatively different from the previously studied case of
equal densities. The former more closely resembles the behavior of a fluid
star, in which the core-crust interface is a surface of constant gravitational
plus centrifugal potential. Regardless of the uncertain breaking strain, the
glitch activity in this model is several orders of magnitude smaller than
observed, even if only small glitches are considered. For a large breaking
strain, suggested by simulations, glitches due to starquakes could be roughly
of the correct size but much less frequent than observed glitches. The energy
released in each glitch is much larger than in the model of angular momentum
transfer from a faster rotating superfluid in the inner crust. On the other
hand, we cannot rule out that the heating produced by small starquakes could
trigger glitches by allowing neutron superfluid vortices to move. We also
confirm that stresses in the neutron star crust can in principle support an
ellipticity much larger than some observational upper limits from pulsar timing
and continuous gravitational wave searches.Comment: 17 pages, 11 figure
CorrecciĂłn de consolidaciĂłn viciosa diafisaria de fĂ©mur: osteotomĂa en caparazĂłn. A propĂłsito de dos casos.
La adecuada alineaciĂłn del miembro inferior es esencial para el adecuado reparto de cargas que
permita una deambulaciĂłn sin alteraciones. Por lo que a la hora del tratamiento de fracturas de huesos largos del
miembro inferior, fundamentalmente fémur y tibia, habrå que evitar cualquier deformidad angular que a medio
plazo provoque fenĂłmenos degenerativos en las articulaciones adyacentes. Se presentan dos casos clĂnicos complejos,
en los que se corrigieron sendas consolidaciones viciosas de fracturas diafisarias de fémur satisfactoriamente,
mediante osteotomĂa tipo caparazĂłn o clamshellThe lower limb alignment is essential to share correctly the bearing weight of the body to allow
a suitable gait. We should take it into account when treating femoral and tibial diaphyseal fractures, in order to
avoid angular deformities which could lead to degenerative changes in adjacent joints. We report two complex
cases, with femoral shaft malunions corrected satisfactorily by using a clamshell osteotom
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