3,806 research outputs found
Functional renormalization group approach to the singlet-triplet transition in quantum dots
We present a functional renormalization group approach to the zero bias
transport properties of a quantum dot with two different orbitals and in
presence of Hund's coupling. Tuning the energy separation of the orbital
states, the quantum dot can be driven through a singlet-triplet transition. Our
approach, based on the approach by Karrasch {\em et al} which we apply to
spin-dependent interactions, recovers the key characteristics of the quantum
dot transport properties with very little numerical effort. We present results
on the conductance in the vicinity of the transition and compare our results
both with previous numerical renormalization group results and with predictions
of the perturbative renormalization group.Comment: 15 pages, 9 figure
Spin-orbit coupled cold exciton condensates
We analyze theoretically the dynamics of degenerate condensate of cold
indirect excitons. We account for both linear spin dependent terms arising from
spin-orbit interaction of Rashba and Dresselhaus types and non-linear terms
transforming a pair of bright excitons into a pair of dark ones. We show that
both terms should lead to the qualitative changes in the dynamics of cold
exciton droplets in the real space and time.Comment: 14 pages, 7 figure
Density-matrix approach for an interacting polariton system
Using the Lindblad approach we develop a general formalism for theoretical
description of a spatially inhomogeneous bosonic system with dissipation
provided by the interaction of bosons with a phonon bath. We apply our results
to model the dynamics of an interacting one-dimensional polariton system in
real space and time, analyzing in detail the role of polariton-polariton and
polariton-phonon interactions.Comment: 7 pages + 3 figures. arXiv admin note: text overlap with
arXiv:1103.1336 by other author
Bistability phenomena in one-dimensional polariton wires
We investigate the phenomena of bistability and domain wall propagation in
polaritonic systems with dissipation provided by the interaction with
incoherent phonon bath. The results on the temperature dependence of the
polariton bistability behavior and polariton neuron switching are presented.Comment: 6 pages + 4 figures. Continuation of the work published in Phys. Rev.
B 83, 165316 (2011
Phonon-mediated Josephson oscillations in excitonic and polaritonic condensates
We analyze theoretically the role of the exciton-phonon interactions in
phenomena related to the Josephson effect between two spatially separated
exciton and exciton-polariton condensates. We consider the role of the
dephasing introduced by phonons in such phenomena as Josephson tunneling,
self-trapping and spontaneous polarization separation. In the regime of cw
pumping we find a remarkable bistability effect arising from exciton- exciton
interactions as well as regimes of self- sustained regular and chaotic
oscillations.Comment: 10 pages, Submitted to Phys. Rev.
Clustering of vacancy defects in high-purity semi-insulating SiC
Positron lifetime spectroscopy was used to study native vacancy defects in
semi-insulating silicon carbide. The material is shown to contain (i) vacancy
clusters consisting of 4--5 missing atoms and (ii) Si vacancy related
negatively charged defects. The total open volume bound to the clusters
anticorrelates with the electrical resistivity both in as-grown and annealed
material. Our results suggest that Si vacancy related complexes compensate
electrically the as-grown material, but migrate to increase the size of the
clusters during annealing, leading to loss of resistivity.Comment: 8 pages, 5 figure
Optical properties of carbon nanofiber photonic crystals
Carbon nanofibers (CNF) are used as components of planar photonic crystals.
Square and rectangular lattices and random patterns of vertically aligned CNF
were fabricated and their properties studied using ellipsometry. We show that
detailed information such as symmetry directions and the band structure of
these novel materials can be extracted from considerations of the polarization
state in the specular beam. The refractive index of the individual nanofibers
was found to be n_CNF = 4.1.Comment: 10 pages, 4 figure
Preventive herd management practices and their effect on lamb mortality in Ethiopia.
According to previous studies, lamb mortality is high in the Ethiopian highlands. The present study aims to evaluate the execution of preventive sheep herd health management practices with respect to if, and how, such practices are linked to occurrence of lamb mortality. Interviews were performed with 74 sheep-owning households participating in a capacity development program on livestock and 69 households not participating in such program. To evaluate the impact of combinations of performed practices, a scoring system was developed-the households retrieved a higher score the more desired routines were accomplished. To identify which practices had the highest impact on lamb mortality, a similar score was calculated for each phase of the sheep reproductive year, creating sub-scores for each phase. The results showed a significant (p < 0.05) negative correlation between the total number of performed practices and occurrence of lamb mortality, indicating a lower occurrence of lamb mortality the more desired practices implemented. Further analysis of sub-scores showed significant (p < 0.05) negative correlations between a higher number of performed desired practices during gestation period and during lambing. Conclusively, the study indicates that preventive herd management routines are beneficial for lamb survival, foremost when enforced during the gestation period and around lambing-hence, this is where to focus future interventions
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