4,916 research outputs found
Non-equilibrium Transport in the Anderson model of a biased Quantum Dot: Scattering Bethe Ansatz Phenomenology
We derive the transport properties of a quantum dot subject to a source-drain
bias voltage at zero temperature and magnetic field. Using the Scattering Bethe
Anstaz, a generalization of the traditional Thermodynamic Bethe Ansatz to open
systems out of equilibrium, we derive exact results for the quantum dot
occupation out of equilibrium and, by introducing phenomenological spin- and
charge-fluctuation distribution functions in the computation of the current,
obtain the differential conductance for large U/\Gamma. The Hamiltonian to
describe the quantum dot system is the Anderson impurity Hamiltonian and the
current and dot occupation as a function of voltage are obtained numerically.
We also vary the gate voltage and study the transition from the mixed valence
to the Kondo regime in the presence of a non-equilibrium current. We conclude
with the difficulty we encounter in this model and possible way to solve them
without resorting to a phenomenological method.Comment: 20 pages, 20 figures, published versio
A new species of Liolaemus related to L. nigroviridis from the Andean highlands of Central Chile (Iguania, Liolaemidae)
Indexación: Web of Science; Scopus.The Liolaemus nigroviridis group is a clade of highland lizards endemic to Chile. These species are distributed from northern to central Chile, and currently there are no cases of sympatric distribution. This study describes a new species, Liolaemus uniformis sp. n., from this group, and provides a detailed morphological characterization and mitochondrial phylogeny using cytochrome-b. Liolaemus uniformis was found in sympatry with L. nigroviridis but noticeably differed in size, scalation, and markedly in the color pattern, without sexual dichromatism. This new species has probably been confused with L. monticola and L. bellii, both of which do not belong to the nigroviridis group. The taxonomic issues of this group that remain uncertain are also discussed.https://zookeys.pensoft.net/articles.php?id=601
Electronic Structure of gated graphene and graphene ribbons
We study the electronic structure of gated graphene sheets. We consider both
infinite graphene and finite width ribbons. The effect of Coulomb interactions
between the electrically injected carriers and the coupling to the external
gate are computed self-consistently in the Hartree approximation. We compute
the average density of extra carriers, , the number of occupied
subbands and the density profiles as a function of the gate potential . We
discuss quantum corrections to the classical capacitance and we calculate the
threshold above which semiconducting armchair ribbons conduct. We find
that the ideal conductance of perfectly transmitting wide ribbons is
proportional to the square root of the gate voltage.Comment: 8 pages, 6 figure
Evolution of small-scale magnetic elements in the vicinity of granular-size swirl convective motions
Advances in solar instrumentation have led to a widespread usage of time
series to study the dynamics of solar features, specially at small spatial
scales and at very fast cadences. Physical processes at such scales are
determinant as building blocks for many others occurring from the lower to the
upper layers of the solar atmosphere and beyond, ultimately for understanding
the bigger picture of solar activity. Ground-based (SST) and space-borne
(Hinode) high-resolution solar data are analyzed in a quiet Sun region
displaying negative polarity small-scale magnetic concentrations and a cluster
of bright points observed in G-band and Ca II H images. The studied region is
characterized by the presence of two small-scale convective vortex-type plasma
motions, one of which appears to be affecting the dynamics of both, magnetic
features and bright points in its vicinity and therefore the main target of our
investigations. We followed the evolution of bright points, intensity
variations at different atmospheric heights and magnetic evolution for a set of
interesting selected regions. A description of the evolution of the
photospheric plasma motions in the region nearby the convective vortex is
shown, as well as some plausible cases for convective collapse detected in
Stokes profiles.Comment: 9 figure
Gestión de Déchets Miniers
L'objet de mon travail concerne l'exploitation minière et plus particulièrement du
Drainage Minier Acide (DMA).
Le premier travail expérimental est organisé autour de deux axes :
- des essais de terrain mettant en lumière la présence de DMA sur le site même
avec la mise en évidence des eaux acides contenant du fer (sous forme d'ions
ferreux) sortant du dépôt d'anciens déchets miniers ou stérile à l'aide de mesures
ou d'essais sommaires (pH, neutralisation à la soude, ajout d'oxydant)
- des essais de lixiviation d'échantillons (sables "blanc" ou "gris") prélevés sur le
site pour simuler le drainage et étudier certains paramètres comme le rôle de
l'oxygène, de la granulométrie ou des bactéries lors de l'acidification du lixiviat.
Les résultats préliminaires obtenus (voir annexe 1) confirment le phénomène
d'acidification des eaux observé sur le terrain, le rôle probable de l'oxygène, de
certaines bactéries sur la vitesse d'acidification des lixiviats. L'approche
normalisée a permis de préparer des échantillons de matériau plus représentatifs et
d'expliciter l'influence de la granulométrie des particules, garantissant à priori, une
approche plus rigoureuse du modèle simulant, ici, le drainage. Pouvoir simuler ce
phénomène, le modéliser permet de mieux prévoir son impact environnemental et le
processus de lixiviation industrielle dans le cas où il s'agira d'une application de type
hydrométallurgique pour extraire un métal par exemple
Organic vs Conventional Suckling Lamb Production: Product Quality and Consumer Acceptance
Samples of suckling lambs (n=40) of two breeds reared under conventional and organic conditions were analysed to asses physico-chemical characteristics, including instrumental texture, and nutritional quality in terms of fatty acid composition. Consumer acceptance was also studied using the home-use test. Results revealed that organic suckling lamb meat is healthier as shown by the lower saturated fatty acid levels, the higher polyunsaturated fatty acid contents and the higher 6/3 ratiko. The organic meat had lower instrumental hardness, received higher scores in all sensory parameters, and had statistically better fat sensation and higher ratings for overall liking. These results lend support to the notion among consumers that organic products are healthier and tastier
Consumer Appreciation of Carcass Quality of Organic vs Conventional Suckling Lamb Production
Carcass characteristics of sucking lambs (n= 40) of two breeds reared under conventional and organic conditions were analysed including objective and subjective parameters for fatness and conformation, meat and fat colour. Consumer acceptance was also studied using the home-use test. Results showed that the characteristics of the carcass of suckling lamb were similar for both types of production systems pointing out that organic production system did not affect fatness or muscle development. However, organic meat was darker (higher L* and a* values) probably related with the higher amount of exercise, although fat was not more yellow. In contrast consumers did not consider organic meat darker and there were not significant differences in appearance related with the similar conformation. These results reflect that consumer perceive organic meat as at least as good as conventional production not only regarding environmental quality but also regarding carcass quality
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