4,168 research outputs found
Cooperative look-ahead control for fuel-efficient and safe heavy-duty vehicle platooning
The operation of groups of heavy-duty vehicles (HDVs) at a small
inter-vehicular distance (known as platoon) allows to lower the overall
aerodynamic drag and, therefore, to reduce fuel consumption and greenhouse gas
emissions. However, due to the large mass and limited engine power of HDVs,
slopes have a significant impact on the feasible and optimal speed profiles
that each vehicle can and should follow. Therefore maintaining a short
inter-vehicular distance as required by platooning without coordination between
vehicles can often result in inefficient or even unfeasible trajectories. In
this paper we propose a two-layer control architecture for HDV platooning aimed
to safely and fuel-efficiently coordinate the vehicles in the platoon. Here,
the layers are responsible for the inclusion of preview information on road
topography and the real-time control of the vehicles, respectively. Within this
architecture, dynamic programming is used to compute the fuel-optimal speed
profile for the entire platoon and a distributed model predictive control
framework is developed for the real-time control of the vehicles. The
effectiveness of the proposed controller is analyzed by means of simulations of
several realistic scenarios that suggest a possible fuel saving of up to 12%
for the follower vehicles compared to the use of standard platoon controllers.Comment: 16 pages, 16 figures, submitted to journa
Security Proof for Quantum Key Distribution Using Qudit Systems
We provide security bounds against coherent attacks for two families of
quantum key distribution protocols that use -dimensional quantum systems. In
the asymptotic regime, both the secret key rate for fixed noise and the
robustness to noise increase with . The finite-key corrections are found to
be almost insensitive to .Comment: 5 pages, 1 figure, version 3 corrects equations (9) and (11), and
slightly modifies the figure to reflect the change to equation (11
The Zagier polynomials. Part II: Arithmetic properties of coefficients
The modified Bernoulli numbers \begin{equation*} B_{n}^{*} = \sum_{r=0}^{n}
\binom{n+r}{2r} \frac{B_{r}}{n+r}, \quad n > 0 \end{equation*} introduced by D.
Zagier in 1998 were recently extended to the polynomial case by replacing
by the Bernoulli polynomials . Arithmetic properties of the
coefficients of these polynomials are established. In particular, the 2-adic
valuation of the modified Bernoulli numbers is determined. A variety of
analytic, umbral, and asymptotic methods is used to analyze these polynomials
Thermohaline circulation stability: a box model study - Part II: coupled atmosphere-ocean model
A thorough analysis of the stability of a coupled version of an
inter-hemispheric 3-box model of Thermohaline Circulation (THC) is presented.
This study follows a similarly structured analysis on an uncoupled version of
the same model presented in Part I. We study how the strength of THC changes
when the system undergoes forcings representing global warming conditions. Each
perturbation to the initial equilibrium is characterized by the total radiative
forcing realized, by the rate of increase, and by the North-South asymmetry.
The choice of suitably defined metrics allows us to determine the boundary
dividing the set of radiative forcing scenarios that lead the system to
equilibria characterized by a THC pattern similar to the present one, from
those that drive the system to equilibria where the THC is reversed. We also
consider different choices for the atmospheric transport parameterizations and
for the ratio between the high latitude to tropical radiative forcing. We
generally find that fast forcings are more effective than slow forcings in
disrupting the present THC pattern, forcings that are stronger in the northern
box are also more effective in destabilizing the system, and that very slow
forcings do not destabilize the system whatever their asymmetry, unless the
radiative forcings are very asymmetric and the atmospheric transport is a
relatively weak function of the meridional temperature gradient. The changes in
the strength of the THC are primarily forced by changes in the latent heat
transport in the hemisphere, because of its sensitivity to temperature that
arises from the Clausius-Clapeyron relation.Comment: 34 pages, 10 figure
The Hawking temperature of expanding cosmological black holes
In the context of a debate on the correct expression of the Hawking
temperature of an expanding cosmological black hole, we show that the correct
expression in terms of the Hawking-Hayward quasi-local energy m of the hole is
T=1/(8\pi m(t)). This expression holds for comoving black holes and agrees with
a recent proposal by Saida, Harada, and Maeda.Comment: 5 latex pages, to appear in Phys. Rev. D. Some references adde
Ab initio GW electron-electron interaction effects in Quantum Transport
We present an ab initio approach to electronic transport in nanoscale systems
which includes electronic correlations through the GW approximation. With
respect to Landauer approaches based on density-functional theory (DFT), we
introduce a physical quasiparticle electronic-structure into a non-equilibrium
Green's function theory framework. We use an equilibrium non-selfconsistent
self-energy considering both full non-hermiticity and dynamical
effects. The method is applied to a real system, a gold mono-atomic chain. With
respect to DFT results, the conductance profile is modified and reduced by to
the introduction of diffusion and loss-of-coherence effects. The linear
response conductance characteristic appear to be in agreement with experimental
results.Comment: 5 pages, 4 figures, refused by PR
On cosmological observables in a swiss-cheese universe
Photon geodesics are calculated in a swiss-cheese model, where the cheese is
made of the usual Friedmann-Robertson-Walker solution and the holes are
constructed from a Lemaitre-Tolman-Bondi solution of Einstein's equations. The
observables on which we focus are the changes in the redshift, in the
angular-diameter--distance relation, in the luminosity-distance--redshift
relation, and in the corresponding distance modulus. We find that redshift
effects are suppressed when the hole is small because of a compensation effect
acting on the scale of half a hole resulting from the special case of spherical
symmetry. However, we find interesting effects in the calculation of the
angular distance: strong evolution of the inhomogeneities (as in the approach
to caustic formation) causes the photon path to deviate from that of the FRW
case. Therefore, the inhomogeneities are able to partly mimic the effects of a
dark-energy component. Our results also suggest that the nonlinear effects of
caustic formation in cold dark matter models may lead to interesting effects on
photon trajectories.Comment: 25 pages, 21 figures; replaced to fit the version accepted for
publication in Phys. Rev.
A Lemaitre-Tolman-Bondi cosmological wormhole
We present a new analytical solution of the Einstein field equations
describing a wormhole shell of zero thickness joining two
Lema{\i}tre-Tolman-Bondi universes, with no radial accretion. The material on
the shell satisfies the energy conditions and, at late times, the shell becomes
comoving with the dust-dominated cosmic substratum.Comment: 5 pages, latex, no figures, to appear in Phys. Rev.
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