932 research outputs found
Anomalous quantum chaotic behavior in nanoelectromechanical structures
It is predicted that for sufficiently strong electron-phonon coupling an
anomalous quantum chaotic behavior develops in certain types of suspended
electro-mechanical nanostructures, here comprised by a thin cylindrical quantum
dot (billiard) on a suspended rectangular dielectric plate. The deformation
potential and piezoelectric interactions are considered. As a result of the
electron-phonon coupling between the two systems the spectral statistics of the
electro-mechanic eigenenergies exhibit an anomalous behavior. If the center of
the quantum dot is located at one of the symmetry axes of the rectangular
plate, the energy level distributions correspond to the Gaussian Orthogonal
Ensemble (GOE), otherwise they belong to the Gaussian Unitary Ensemble (GUE),
even though the system is time-reversal invariant.Comment: 4 pages, pdf forma
Quantum chaos in nanoelectromechanical systems
We present a theoretical study of the electron-phonon coupling in suspended
nanoelectromechanical systems (NEMS) and investigate the resulting quantum
chaotic behavior. The phonons are associated with the vibrational modes of a
suspended rectangular dielectric plate, with free or clamped boundary
conditions, whereas the electrons are confined to a large quantum dot (QD) on
the plate's surface. The deformation potential and piezoelectric interactions
are considered. By performing standard energy-level statistics we demonstrate
that the spectral fluctuations exhibit the same distributions as those of the
Gaussian Orthogonal Ensemble (GOE) or the Gaussian Unitary Ensemble (GUE),
therefore evidencing the emergence of quantum chaos. That is verified for a
large range of material and geometry parameters. In particular, the GUE
statistics occurs only in the case of a circular QD. It represents an anomalous
phenomenon, previously reported for just a small number of systems, since the
problem is time-reversal invariant. The obtained results are explained through
a detailed analysis of the Hamiltonian matrix structure.Comment: 14 pages, two column
Avaliação genĂ©tica de indivĂduos de erva-mate (Ilex paraguariensis St. Hil.) na RegiĂŁo de CaarapĂł, MS, pelo procedimento REML/BLUP.
Control of Dephasing and Phonon Emission in Coupled Quantum Dots
We predict that phonon subband quantization can be detected in the non-linear
electron current through double quantum dot qubits embedded into nano-size
semiconductor slabs, acting as phonon cavities. For particular values of the
dot level splitting , piezo-electric or deformation potential
scattering is either drastically reduced as compared to the bulk case, or
strongly enhanced due to phonon van Hove singularities. By tuning via
gate voltages, one can either control dephasing, or strongly increase emission
into phonon modes with characteristic angular distributions.Comment: 4 pages, 3 figures, accepted for publication as Rapid Comm. in Phys.
Rev.
Genetic evaluation of Hevea brasiliensis [(Willd ex Adr. de Juss.) MĂĽell. Arg.] for juvenile vigour using the Reml/Blup method.
This paper intended to estimate genetic values and parameters for plant height, diameter at the base of the plant and leaf-storey number of rubber tree [Hevea brasiliensis (Willd ex Adr. de Juss.) MĂĽell, Arg.] halfsib progenies using the mĂxed-model methodology (Reml/Blup procedure). The rubber tree progenies were obtained from a second generation population produced from the recombination of 30 original parents, pertaining to the Instituto AgronĂ´mico de Campinas (IAC) in SĂŁo Paulo state. At the age of eight months the variables were evaluated. Results demonstrated the existence of significant genetic variability among the progenies for the studied traits. The estimates of the heritability coefficient showed moderate values for both height and leaf-storey number, and low values for plant diameter at the base of the plant. There are good possibilities of genetic gain for these main traits in the context of the improvement program that was started in Mato Grosso do Sul state
Panorama geral da produção extrativista de castanha-da-amazônia no Estado de Rondônia.
Este documento tem como objetivo apresentar uma análise da cadeia e da produção extrativista da castanha-da-amazônia no Estado de Rondônia, com base nos estudos do MapCast feitos nos anos de 2014 e 2015, seguindo a metodologia conhecida como bola de neve.bitstream/item/201939/1/DOC1661.pd
Avaliação genĂ©tica de progĂŞnies de leucena: contribuição para estabelecimento de SAF´S na reserva indĂgena Kaiowá e Guarani, em CaarapĂł, MS.
Generalized thermodynamics of q-deformed bosons and fermions
We study the thermostatistics of q-deformed bosons and fermions obeying the
symmetric algebra and show that it can be built on the formalism of q-calculus.
The entire structure of thermodynamics is preserved if ordinary derivatives are
replaced by an appropriate Jackson derivative. In this framework, we derive the
most important thermodynamic functions describing the q-boson and q-fermion
ideal gases in the thermodynamic limit. We also investigate the semi-classical
limit and the low temperature regime and demonstrate that the nature of the
q-deformation gives rise to pure quantum statistical effects stronger than
undeformed boson and fermion particles.Comment: 8 pages, Physical Review E in pres
Giant Thermoelectric Effect from Transmission Supernodes
We predict an enormous order-dependent quantum enhancement of thermoelectric
effects in the vicinity of a higher-order `supernode' in the transmission
spectrum of a nanoscale junction. Single-molecule junctions based on
3,3'-biphenyl and polyphenyl ether (PPE) are investigated in detail. The
nonequilibrium thermodynamic efficiency and power output of a thermoelectric
heat engine based on a 1,3-benzene junction are calculated using many-body
theory, and compared to the predictions of the figure-of-merit ZT.Comment: 5 pages, 6 figure
Study of Thermal Properties of Graphene-Based Structures Using the Force Constant Method
The thermal properties of graphene-based materials are theoretically
investigated. The fourth-nearest neighbor force constant method for phonon
properties is used in conjunction with both the Landauer ballistic and the
non-equilibrium Green's function techniques for transport. Ballistic phonon
transport is investigated for different structures including graphene, graphene
antidot lattices, and graphene nanoribbons. We demonstrate that this particular
methodology is suitable for robust and efficient investigation of phonon
transport in graphene-based devices. This methodology is especially useful for
investigations of thermoelectric and heat transport applications.Comment: 23 pages, 9 figures, 1 tabl
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