44,583 research outputs found
The self-consistent quantum-electrostatic problem in strongly non-linear regime
The self-consistent quantum-electrostatic (also known as
Poisson-Schr\"odinger) problem is notoriously difficult in situations where the
density of states varies rapidly with energy. At low temperatures, these
fluctuations make the problem highly non-linear which renders iterative schemes
deeply unstable. We present a stable algorithm that provides a solution to this
problem with controlled accuracy. The technique is intrinsically convergent
including in highly non-linear regimes. We illustrate our approach with (i) a
calculation of the compressible and incompressible stripes in the integer
quantum Hall regime and (ii) a calculation of the differential conductance of a
quantum point contact geometry. Our technique provides a viable route for the
predictive modeling of the transport properties of quantum nanoelectronics
devices.Comment: 28 pages. 14 figures. Added solution to a potential failure mode of
the algorith
Optimal Trajectories for Near-Earth-Objects Using Solar Electric Propulsion (SEP) and Gravity Assisted Maneuver
The future interplanetary missions will probably use the conventional chemical rockets to leave the sphere of influence of the Earth, and solar electric propulsion (SEP) to accomplish the other maneuvers of the mission. In this work the optimization of interplanetary missions using solar electric propulsion and Gravity Assisted Maneuver to reduce the costs of the mission, is considered. The high specific impulse of electric propulsion makes a Gravity Assisted Maneuver 1 year after departure convenient. Missions for several Near Earth Asteroids will be considered. The analysis suggests criteria for the definition of initial solutions demanded for the process of optimization of trajectories. Trajectories for the asteroid 2002TC70 are analyzed. Direct trajectories, trajectories with 1 gravity assisted from the Earth and with 2 gravity assisted from the Earth and either Mars are present. An indirect optimization method will be used in the simulations
Inductive learning spatial attention
This paper investigates the automatic induction of spatial attention
from the visual observation of objects manipulated
on a table top. In this work, space is represented in terms of
a novel observer-object relative reference system, named Local
Cardinal System, defined upon the local neighbourhood
of objects on the table. We present results of applying the
proposed methodology on five distinct scenarios involving
the construction of spatial patterns of coloured blocks
Magnetic Properties of the Metamagnet Ising Model in a three-dimensional Lattice in a Random and Uniform Field
By employing the Monte Carlo technique we study the behavior of Metamagnet
Ising Model in a random field. The phase diagram is obtained by using the
algorithm of Glaubr in a cubic lattice of linear size with values ranging
from 16 to 42 and with periodic boundary conditions.Comment: 4 pages, 6 figure
Conservation of Orbital Angular Momentum in Stimulated Down-Conversion
We report on an experiment demonstrating the conservation of orbital angular
momentum in stimulated down-conversion. The orbital angular momentum is not
transferred to the individual beams of the spontaneous down-conversion, but it
is conserved when twin photons are taken individually. We observe the
conservation law for an individual beam of the down-conversion through
cavity-free stimulated emission.Comment: Submitted for publication in Phys. Rev. Let
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