4,666 research outputs found
Non-Markovian Dynamics of Charge Carriers in Quantum Dots
We have investigated the dynamics of bound particles in multilevel
current-carrying quantum dots. We look specifically in the regime of resonant
tunnelling transport, where several channels are available for transport.
Through a non-Markovian formalism under the Born approximation, we investigate
the real-time evolution of the confined particles including transport-induced
decoherence and relaxation. In the case of a coherent superposition between
states with different particle number, we find that a Fock-space coherence may
be preserved even in the presence of tunneling into and out of the dot.
Real-time results are presented for various asymmetries of tunneling rates into
different orbitals.Comment: 9 pages, 3 figures, International Workshop on Physics-Based
Mathematical Models for Low-Dimensional Semiconductor Nanostructures. BIRS,
November 18-23, 200
Reflection and Transmission at the Apparent Horizon during Gravitational Collapse
We examine the wave-functionals describing the collapse of a self-gravitating
dust ball in an exact quantization of the gravity-dust system. We show that
ingoing (collapsing) dust shell modes outside the apparent horizon must
necessarily be accompanied by outgoing modes inside the apparent horizon, whose
amplitude is suppressed by the square root of the Boltzmann factor at the
Hawking temperature. Likewise, ingoing modes in the interior must be
accompanied by outgoing modes in the exterior, again with an amplitude
suppressed by the same factor. A suitable superposition of the two solutions is
necessary to conserve the dust probability flux across the apparent horizon,
thus each region contains both ingoing and outgoing dust modes. If one
restricts oneself to considering only the modes outside the apparent horizon
then one should think of the apparent horizon as a partial reflector, the
probability for a shell to reflect being given by the Boltzmann factor at the
Hawking temperature determined by the mass contained within it. However, if one
considers the entire wave function, the outgoing wave in the exterior is seen
to be the transmission through the horizon of the interior outgoing wave that
accompanies the collapsing shells. This transmission could allow information
from the interior to be transferred to the exterior.Comment: 19 pages, no figures. To appear in Phys. Rev.
The Quantum Stress-Tensor in Self-Similar Spherical Dust Collapse
We calculate the quantum stress tensor for a massless scalar field in the 2-d
self-similar spherical dust collapse model which admits a naked singularity. We
find that the outgoing radiation flux diverges on the Cauchy horizon. This may
have two consequences. The resultant back reaction may prevent the naked
singularity from forming, thus preserving cosmic censorship through quantum
effects. The divergent flux may lead to an observable signature differentiating
naked singularities from black holes in astrophysical observations.Comment: Latex File, 19 page
Non-Newtonian Mechanics
The classical motion of spinning particles can be described without employing
Grassmann variables or Clifford algebras, but simply by generalizing the usual
spinless theory. We only assume the invariance with respect to the Poincare'
group; and only requiring the conservation of the linear and angular momenta we
derive the zitterbewegung: namely the decomposition of the 4-velocity in the
newtonian constant term p/m and in a non-newtonian time-oscillating spacelike
term. Consequently, free classical particles do not obey, in general, the
Principle of Inertia. Superluminal motions are also allowed, without violating
Special Relativity, provided that the energy-momentum moves along the worldline
of the center-of-mass. Moreover, a non-linear, non-constant relation holds
between the time durations measured in different reference frames. Newtonian
Mechanics is re-obtained as a particular case of the present theory: namely for
spinless systems with no zitterbewegung. Introducing a Lagrangian containing
also derivatives of the 4-velocity we get a new equation of the motion,
actually a generalization of the Newton Law a=F/m. Requiring the rotational
symmetry and the reparametrization invariance we derive the classical spin
vector and the conserved scalar Hamiltonian, respectively. We derive also the
classical Dirac spin and analyze the general solution of the Eulero-Lagrange
equation for Dirac particles. The interesting case of spinning systems with
zero intrinsic angular momentum is also studied.Comment: LaTeX; 27 page
Phase-Dependent Properties of Extrasolar Planet Atmospheres
Recently the Spitzer Space Telescope observed the transiting extrasolar
planets, TrES-1 and HD209458b. These observations have provided the first
estimates of the day side thermal flux from two extrasolar planets orbiting
Sun-like stars. In this paper, synthetic spectra from atmospheric models are
compared to these observations. The day-night temperature difference is
explored and phase-dependent flux densities are predicted for both planets. For
HD209458b and TrES-1, models with significant day-to-night energy
redistribution are required to reproduce the observations. However, the
observational error bars are large and a range of models remains viable.Comment: 8 pages, 7 figures, accepted for publication in the Astrophysical
Journa
O acervo raro da biblioteca Milton de Albuquerque, da Embrapa Amazônia Oriental.
bitstream/item/63592/1/Oriental-Doc187.PD
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