5,140 research outputs found
Electronic properties of emergent topological defects in chiral -wave superconductivity
Chiral -wave superconductors in applied magnetic field can exhibit more
complex topological defects than just conventional superconducting vortices,
due to the two-component order parameter (OP) and the broken time-reversal
symmetry. We investigate the electronic properties of those exotic states, some
of which contain clusters of one-component vortices in chiral components of the
OP and/or exhibit skyrmionic character in the \textit{relative} OP space, all
obtained as a self-consistent solution of the microscopic Bogoliubov-de Gennes
equations. We reveal the link between the local density of states (LDOS) of the
novel topological states and the behavior of the chiral domain wall between the
OP components, enabling direct identification of those states in scanning
tunneling microscopy. For example, a skyrmion always contains a closed chiral
domain wall, which is found to be mapped exactly by zero-bias peaks in LDOS.
Moreover, the LDOS exhibits electron-hole asymmetry, which is different from
the LDOS of conventional vortex states with the same vorticity. Finally, we
present the magnetic field and temperature dependence of the properties of a
skyrmion, indicating that this topological defect can be surprisingly large in
size, and can be pinned by an artificially indented non-superconducting closed
path in the sample. These features are expected to facilitate the experimental
observation of skyrmionic states, thereby enabling experimental verification of
chirality in emerging superconducting materials
A simple and objective method for reproducible resting state network (RSN) detection in fMRI
Spatial Independent Component Analysis (ICA) decomposes the time by space
functional MRI (fMRI) matrix into a set of 1-D basis time courses and their
associated 3-D spatial maps that are optimized for mutual independence. When
applied to resting state fMRI (rsfMRI), ICA produces several spatial
independent components (ICs) that seem to have biological relevance - the
so-called resting state networks (RSNs). The ICA problem is well posed when the
true data generating process follows a linear mixture of ICs model in terms of
the identifiability of the mixing matrix. However, the contrast function used
for promoting mutual independence in ICA is dependent on the finite amount of
observed data and is potentially non-convex with multiple local minima. Hence,
each run of ICA could produce potentially different IC estimates even for the
same data. One technique to deal with this run-to-run variability of ICA was
proposed by Yang et al. (2008) in their algorithm RAICAR which allows for the
selection of only those ICs that have a high run-to-run reproducibility. We
propose an enhancement to the original RAICAR algorithm that enables us to
assign reproducibility p-values to each IC and allows for an objective
assessment of both within subject and across subjects reproducibility. We call
the resulting algorithm RAICAR-N (N stands for null hypothesis test), and we
have applied it to publicly available human rsfMRI data (http://www.nitrc.org).
Our reproducibility analyses indicated that many of the published RSNs in
rsfMRI literature are highly reproducible. However, we found several other RSNs
that are highly reproducible but not frequently listed in the literature.Comment: 54 pages, 13 figure
Genetic variability and heterogeneity of venezuelan equine encephalitis virus vector Ochlerotatus taeniorhynchus (Diptera : Culicidae) populations of the Colombian Atlantic coast, based on microsatellite loci
In Colombia, the mosquito Ochlerotatus taeniorhynchus has been identified as an efficient vector of the epidemic-epi-zootic Venezuelan equine encephalitis virus. We evaluated the genetic variability and heterogeneity of this mosquito in Colombian populations using eight microsatellite DNA loci. Two hundred and ten mosquito specimens collected from seven populations of the Colombian Atlantic coast (San Bernardo del Viento, Coveñas, Carta-gena, Barranquilla, Ciénaga, Dibulla, and Riohacha) were analyzed. We found five polymorphic microsatellite loci, with 19 alleles giving 62.5% polymorphism; the mean number of alleles per locus was 3.8. The mean expected heterogeneity ranged from 0.568 to 0.660. Most of the polymorphic microsatellite loci were in Hardy-Wein-berg disequilibrium, due to both deficit and excess of heterozygotes. The Fst statistic gave a total value of 0.0369, reflecting low genetic differentiation among the populations and, as a consequence, a low degree of structuring among them, while gene flow was high (Nm = 6.52); these findings point to genetic homogeneity among these populations. There was no significant linkage disequilibrium between genotype pairs of the various populations. We concluded that this mosquito is distributed in local populations along the Colombian Atlantic coast; these findings will be useful for developing strategies for controlling this vector. © FUNPEC-RP
Generation of optimal trajectories for Earth hybrid pole sitters
A pole-sitter orbit is a closed path that is constantly above one of the Earth's poles, by means of continuous low thrust. This work proposes to hybridize solar sail propulsion and solar electric propulsion (SEP) on the same spacecraft, to enable such a pole-sitter orbit. Locally-optimal control laws are found with a semi-analytical inverse method, starting from a trajectory that satisfies the pole-sitter condition in the Sun-Earth circular restricted three-body problem. These solutions are subsequently used as first guess to find optimal orbits, using a direct method based on pseudospectral transcription. The orbital dynamics of both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows savings on propellant mass fraction. Finally, it is shown that for sufficiently long missions, a hybrid pole-sitter, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft
Displaced geostationary orbit design using hybrid sail propulsion
Because of an increase in the number of geostationary spacecraft and the limits imposed by east–west spacing
requirements, the geostationary orbit is becoming congested. To increase its capacity, this paper proposes to create
new geostationary slots by displacing the geostationary orbit either out of or in the equatorial plane by means of
hybrid solar sail and solar electric propulsion. To minimize propellant consumption, optimal steering laws for the
solar sail and solar-electric-propulsion thrust vectors are derived and the performance in terms of mission lifetime is
assessed. For comparison, similar analyses are performed for conventional propulsion, including impulsive and pure
solar electric propulsion. It is shown that hybrid sails outperform these propulsion techniques and that out-of-plane
displacements outperform in-plane displacements. The out-of-plane case is therefore further investigated in a
spacecraft mass budget to determine the payload mass capacity. Finally, two transfers that enable a further
improvement of the performance of hybrid sails for the out-of-plane case are optimized using a direct pseudospectral
method: a seasonal transit between orbits displaced above and below the equatorial plane and a transit to a parking
orbit when geostationary coverage is not needed. Both transfers are shown to require only a modest propellant
budget, outweighing the improvements they can establish
Topological charge, spin and heat transistor
Spin pumping consists in the injection of spin currents into a non-magnetic
material due to the precession of an adjacent ferromagnet. In addition to the
pumping of spin the precession always leads to pumping of heat, but in the
presence of spin-orbital entanglement it also leads to a charge current. We
investigate the pumping of charge, spin and heat in a device where a
superconductor and a quantum spin Hall insulator are in proximity contact with
a ferromagnetic insulator. We show that the device supports two robust
operation regimes arising from topological effects. In one regime, the pumped
charge, spin and heat are quantized and related to each other due to a
topological winding number of the reflection coefficient in the scattering
matrix formalism -- translating to a Chern number in the case of Hamiltonian
formalism. In the second regime, a Majorana zero mode switches off the pumping
of currents owing to the topologically protected perfect Andreev reflection. We
show that the interplay of these two topological effects can be utilized so
that the device operates as a robust charge, spin and heat transistor.Comment: Final accepted versio
OptimizaciĂłn integral del centro de mantenimiento de intendencia
Las exigencias de la vida moderna, obligan a las instituciones pĂşblicas y privadas, a involucrarse en los avances y desarrollos tecnolĂłgicos, a fin de alcanzar un alto rendimiento en su producto o servicio que les permita el ingreso a nuevos mercados locales e internacionales, los cuales se vuelven cada vez más exigentes y competitivos. La GlobalizaciĂłn, los cambios vertiginosos en los cuales se desenvuelve las organizaciones, son tan rápidos que han inducido a que instituciones como Fuerzas Armadas, y dentro de esta a la industria metalmecánica, opten por un cambio de filosofĂa en su cultura organizacional, en donde no existe otra alternativa que aprender a competir y buscar nuevas oportunidades para mejorar su potencial operativo tanto interno como externo en busca de un constante crecimiento y desarrollo institucional
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A kinetic isotope effect (kD/kH) of 7.4 has been found for the reaction of chlorosilylene with trimethysilane (Me3SiD vs Me3SiH). Such a value can be accounted for by theoretical modelling, but only if an internal rearrangement of the initially form complex is included in the mechanism. This provides the first concrete evidence for such complexes
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