2,080 research outputs found
Tuning of heat and charge transport by Majorana fermions
We investigate theoretically thermal and electrical conductances for the
system consisting of a quantum dot (QD) connected both to a pair of Majorana
fermions residing the edges of a Kitaev wire and two metallic leads. We
demonstrate that both quantities reveal pronounced resonances, whose positions
can be controlled by tuning of an asymmetry of the couplings of the QD and a
pair of MFs. Similar behavior is revealed for the thermopower, Wiedemann-Franz
law and dimensionless thermoelectric figure of merit. The considered geometry
can thus be used as a tuner of heat and charge transport assisted by MFs
Star Formation Towards The Galactic H Ii Region Rcw 120 - Herschel Observations Of Compact Sources
The expansion of H ii regions can trigger the formation of stars. An overdensity of young stellar objects is observed at the edges of H ii regions but the mechanisms that give rise to this phenomenon are not clearly identified. Moreover, it is difficult to establish a causal link between H ii -region expansion and the star formation observed at the edges of these regions. A clear age gradient observed in the spatial distribution of young sources in the surrounding might be a strong argument in favor of triggering
Efeito de genĂłtipos de sorgo sobre o predador Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) alimentado com Schizaphis graminum (Rondani) (Hemiptera: Aphididae).
O trabalho objetivou avaliar o efeito indireto da resistĂȘncia de genĂłtipos de soro sobre o predador Chrysoperla externa (Hagen) usando o pulgĂŁo Schizaphis graminum (Rondani) como presa. Os genĂłtipos usados no estudo foram: GR 11111 e TX 430 x GR 111 (resistentes), GB 3B (moderadamente resistente) e BR 007B (suscetĂvel). Larvas recĂ©m-eclodidas foram confinadas individualmente em recipientes de vidro e alimentadas com S. graminum, criados separadamente em cada um dos quatro genĂłtipos. apĂłs a emergĂȘncia, os adultos obtidos de cada tratamento foram sexados e agrupados aos casais, colocados em gaiolas contendo dieta Ă base de levedo de cerveja e mel. Os insetos foram observados diariamente da fase jovem atĂ© o perĂodo de 60 dias apĂłs a emergĂȘncia do adulto. GenĂłtipos com maior grau de resistĂȘncia proporcionaram maior consumo de pulgĂ”es pelo predador, porĂ©m menor peso a este. Quando os pulgĂ”es foram criados no genĂłtipo resistente GR 11111, o peso das larvas, sobrevivĂȘncia da prĂ©-pupa e longevidade da fĂȘmea do predador foram inferiores. As associaçÔes positivas observadas entre o predador, C. externa, e o genĂłtipo resistente, TX 430 x GR 111, e entre o predador e o genĂłtipo moderadamente resistente GB 3B, evidenciaram a possibilidade de integração entre os dois mĂ©todos de controle: resistĂȘncia de plantas e controle biolĂłgico
Classical and quantum-mechanical treatments of nonsequential double ionization with few-cycle laser pulses
We address nonsequential double ionization induced by strong, linearly
polarized laser fields of only a few cycles, considering a physical mechanism
in which the second electron is dislodged by the inelastic collision of the
first electron with its parent ion. The problem is treated classically, using
an ensemble model, and quantum-mechanically, within the strong-field and
uniform saddle-point approximations. In the latter case, the results are
interpreted in terms of "quantum orbits", which can be related to the
trajectories of a classical electron in an electric field. We obtain highly
asymmetric electron momentum distributions, which strongly depend on the
absolute phase, i.e., on the phase difference between the pulse envelope and
its carrier frequency. Around a particular value of this parameter, the
distributions shift from the region of positive to that of negative momenta, or
vice-versa, in a radical fashion. This behavior is investigated in detail for
several driving-field parameters, and provides a very efficient method for
measuring the absolute phase. Both models yield very similar distributions,
which share the same physical explanation. There exist, however, minor
discrepancies due to the fact that, beyond the region for which electron-impact
ionization is classically allowed, the yields from the quantum mechanical
computation decay exponentially, whereas their classical counterparts vanish.Comment: 12 pages revtex, 12 figures (eps files
Quantum phase transition triggering magnetic BICs in graphene
Graphene hosting a pair of collinear adatoms in the phantom atom
configuration has pseudogap with cubic scaling on energy,
which leads to the appearance of
spin-degenerate bound states in the continuum (BICs) [Phys. Rev. B 92, 045409
(2015)]. In the case when adatoms are locally coupled to a single carbon atom
the pseudogap scales linearly with energy, which prevents the formation of
BICs. In this Letter, we explore the effects of non-local coupling
characterized by the Fano factor of interference tunable by changing
the slope of the Dirac cones in the graphene band-structure. We demonstrate
that three distinct regimes can be identified: i) for (critical
point) a mixed pseudogap appears
yielding a phase with spin-degenerate BICs; ii) near when
the system undergoes a quantum phase
transition in which the new phase is characterized by magnetic BICs and iii) at
a second critical value the cubic scaling of the pseudogap with
energy characteristic to the phantom atom
configuration is restored and the phase with non-magnetic BICs is recovered.
The phase with magnetic BICs can be described in terms of an effective
intrinsic exchange field of ferromagnetic nature between the adatoms mediated
by graphene monolayer. We thus propose a new type of quantum phase transition
resulting from the competition between the states characterized by
spin-degenerate and magnetic BICs
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