7,088 research outputs found
Trajectory generation for road vehicle obstacle avoidance using convex optimization
This paper presents a method for trajectory generation using convex optimization to find a feasible, obstacle-free path for a road vehicle. Consideration of vehicle rotation is shown to be necessary if the trajectory is to avoid obstacles specified in a fixed Earth axis system. The paper establishes that, despite the presence of significant non-linearities, it is possible to articulate the obstacle avoidance problem in a tractable convex form using multiple optimization passes. Finally, it is shown by simulation that an optimal trajectory that accounts for the vehicle’s changing velocity throughout the manoeuvre is superior to a previous analytical method that assumes constant speed
High magnetic field thermal-expansion and elastic properties of CeRhIn
We report high magnetic field thermal-expansion and magnetostriction results
on CeRhIn single crystals. Several transitions, both first and second
order, are observed when the field is applied perpendicular to the
crystallographic c-axis. The magnetic field dependence of the thermal-expansion
coefficient above 15 K, where the magnetic correlations are negligible, can be
explained supposing an almost pure ground state doublet, in
apparent contradiction with neutron scattering experiments. Although the
spin-lattice interaction is relevant in this compound, the effect of the
magnetic correlations on the elastic properties is relatively weak, as revealed
by resonant ultrasound spectroscopy experiments.Comment: 5 pages, 6 figure
Current jets, disorder, and linear magnetoresistance in the silver chalcogenides
The inhomogeneous distribution of excess or deficient silver atoms lies behind the large and linear transverse magnetoresistance displayed by Ag_(2±δ)Se and Ag_(2±δ)Te, introducing spatial conductivity fluctuations with length scales independent of the cyclotron radius. We report a negative, nonsaturating longitudinal magnetoresistance up to at least 60 T, which becomes most negative where the bands cross and the effect of conductivity fluctuations is most acute. Thinning samples down to 10 μm suppresses the negative response, revealing the essential length scale in the problem and paving the way for designer magnetoresistive devices
Optimal control technique for Many Body Quantum Systems dynamics
We present an efficient strategy for controlling a vast range of
non-integrable quantum many body one-dimensional systems that can be merged
with state-of-the-art tensor network simulation methods like the density Matrix
Renormalization Group. To demonstrate its potential, we employ it to solve a
major issue in current optical-lattice physics with ultra-cold atoms: we show
how to reduce by about two orders of magnitudes the time needed to bring a
superfluid gas into a Mott insulator state, while suppressing defects by more
than one order of magnitude as compared to current experiments [1]. Finally, we
show that the optimal pulse is robust against atom number fluctuations.Comment: 5 pages, 4 figures, published versio
An earth pole-sitter using hybrid propulsion
In this paper we investigate optimal pole-sitter orbits using hybrid solar sail and solar electric propulsion (SEP). A pole-sitter is a spacecraft that is constantly above one of the Earth's poles, by means of a continuous thrust. Optimal orbits, that minimize propellant mass consumption, are found both through a shape-based approach, and solving an optimal control problem, using a direct method based on pseudo-spectral techniques. Both the pure SEP case and the hybrid case are investigated and compared. It is found that the hybrid spacecraft allows consistent savings on propellant mass fraction. Finally, is it shown that for sufficiently long missions (more than 8 years), a hybrid spacecraft, based on mid-term technology, enables a consistent reduction in the launch mass for a given payload, with respect to a pure SEP spacecraft
The spin-half Heisenberg antiferromagnet on two Archimedian lattices: From the bounce lattice to the maple-leaf lattice and beyond
We investigate the ground state of the two-dimensional Heisenberg
antiferromagnet on two Archimedean lattices, namely, the maple-leaf and bounce
lattices as well as a generalized - model interpolating between both
systems by varying from (bounce limit) to (maple-leaf
limit) and beyond. We use the coupled cluster method to high orders of
approximation and also exact diagonalization of finite-sized lattices to
discuss the ground-state magnetic long-range order based on data for the
ground-state energy, the magnetic order parameter, the spin-spin correlation
functions as well as the pitch angle between neighboring spins. Our results
indicate that the "pure" bounce () and maple-leaf () Heisenberg
antiferromagnets are magnetically ordered, however, with a sublattice
magnetization drastically reduced by frustration and quantum fluctuations. We
found that magnetic long-range order is present in a wide parameter range and that the magnetic order parameter varies only
weakly with . At a direct first-order transition to
a quantum orthogonal-dimer singlet ground state without magnetic long-range
order takes place. The orthogonal-dimer state is the exact ground state in this
large- regime, and so our model has similarities to the Shastry-Sutherland
model. Finally, we use the exact diagonalization to investigate the
magnetization curve. We a find a 1/3 magnetization plateau for and another one at 2/3 of saturation emerging only at large .Comment: 9 pages, 10 figure
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