2,465 research outputs found
Caracterização das condições climáticas na Amazônia.
bitstream/item/220361/1/CPAF-AP-2020-cap-2-Caracterizacao-das-condicoes-climaticas.pd
Dynamic instabilities in resonant tunneling induced by a magnetic field
We show that the addition of a magnetic field parallel to the current induces
self sustained intrinsic current oscillations in an asymmetric double barrier
structure. The oscillations are attributed to the nonlinear dynamic coupling of
the current to the charge trapped in the well, and the effect of the external
field over the local density of states across the system. Our results show that
the system bifurcates as the field is increased, and may transit to chaos at
large enough fields.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Letter
Time Dependent Current Oscillations Through a Quantum Dot
Time dependent phenomena associated to charge transport along a quantum dot
in the charge quantization regime is studied. Superimposed to the Coulomb
blockade behaviour the current has novel non-linear properties. Together with
static multistabilities in the negative resistance region of the I-V
characteristic curve, strong correlations at the dot give rise to
self-sustained current and charge oscillations. Their properties depend upon
the parameters of the quantum dot and the external applied voltages.Comment: 4 pages, 3 figures; to appear in PR
A mesoscopic ring as a XNOR gate: An exact result
We describe XNOR gate response in a mesoscopic ring threaded by a magnetic
flux . The ring is attached symmetrically to two semi-infinite
one-dimensional metallic electrodes and two gate voltages, viz, and
, are applied in one arm of the ring which are treated as the inputs of
the XNOR gate. The calculations are based on the tight-binding model and the
Green's function method, which numerically compute the conductance-energy and
current-voltage characteristics as functions of the ring-to-electrode coupling
strength, magnetic flux and gate voltages. Our theoretical study shows that,
for a particular value of () (, the elementary
flux-quantum), a high output current (1) (in the logical sense) appears if both
the two inputs to the gate are the same, while if one but not both inputs are
high (1), a low output current (0) results. It clearly exhibits the XNOR gate
behavior and this aspect may be utilized in designing an electronic logic gate.Comment: 8 pages, 5 figure
Características físico-químicas dos principais solos na Amazônia.
bitstream/item/220362/1/CPAF-AP-2020-cap-3-Caracteristicas-fisico.pd
Physics and chemistry of hydrogen in the vacancies of semiconductors
Hydrogen is well known to cause electrical passivation of lattice vacancies in semiconductors. This effect follows from the chemical passivation of the dangling bonds. Recently it was found that H in the carbon vacancy of SiC forms a three-center bond with two silicon neighbors in the vacancy, and gives rise to a new electrically active state. In this paper we examine hydrogen in the anion vacancies of BN, AlN, and GaN. We find that three-center bonding of H is quite common and follows clear trends in terms of the second-neighbor distance in the lattice, the typical (two-center) hydrogen-host-atom bond length, the electronegativity difference between host atoms and hydrogen, as well as the charge state of the vacancy. Three-center bonding limits the number of H atoms a nitrogen vacancy can capture to two, and prevents electric passivation in GaAs as well
Charge and spin configurations in the coupled quantum dots with Coulomb correlations induced by tunneling current
We investigated the peculiarities of non-equilibrium charge states and spin
configurations in the system of two strongly coupled quantum dots (QDs) weakly
connected to the electrodes in the presence of Coulomb correlations. We
analyzed the modification of non-equilibrium charge states and different spin
configurations of the system in a wide range of applied bias voltage and
revealed well pronounced ranges of system parameters where negative tunneling
conductivity appears due to the Coulomb correlations.Comment: 10 pages, 6 figure
Transport through a quantum wire with a side quantum-dot array
A noninteracting quantum-dot array side-coupled to a quantum wire is studied.
Transport through the quantum wire is investigated by using a noninteracting
Anderson tunneling Hamiltonian. The conductance at zero temperature develops an
oscillating band with resonances and antiresonances due to constructive and
destructive interference in the ballistic channel, respectively. Moreover, we
have found an odd-even parity in the system, whose conductance vanishes for an
odd number of quantum dots while becomes for an even number. We
established an explicit relation between this odd-even parity, and the
positions of the resonances and antiresonances of the conductivity with the
spectrum of the isolated QD arrayComment: 5 pages, 4 figures, submitted to PR
Language and cultural capital in school experience of Polish children in Scotland
This article addresses the complex relationship between migration and education in the context of recent intra-European labour mobility. It considers how this mobility impacts the education and life chances of migrant students attending schools in Scotland, UK. By examining the experiences of Polish migrant children and youth at schools in Scotland, the article engages with the issues of language, cultural capital transferability and social positioning. Drawing on qualitative data from 65 in-depth interviews with school children aged 5–17 years, their parents and teachers, as well as observations in the contexts of school and home, the article points to a range of factors affecting the transition of migrant pupils to new schools and social environments
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