4,185 research outputs found
Robust visual odometry using uncertainty models
In dense, urban environments, GPS by itself cannot be relied on to provide accurate positioning information. Signal reception issues (e.g. occlusion, multi-path effects) often prevent the GPS receiver from getting a positional lock, causing holes in the absolute positioning data. In order to keep assisting the driver, other sensors are required to track the vehicle motion during these periods of GPS disturbance. In this paper, we propose a novel method to use a single on-board consumer-grade camera to estimate the relative vehicle motion. The method is based on the tracking of ground plane features, taking into account the uncertainty on their backprojection as well as the uncertainty on the vehicle motion. A Hough-like parameter space vote is employed to extract motion parameters from the uncertainty models. The method is easy to calibrate and designed to be robust to outliers and bad feature quality. Preliminary testing shows good accuracy and reliability, with a positional estimate within 2 metres for a 400 metre elapsed distance. The effects of inaccurate calibration are examined using artificial datasets, suggesting a self-calibrating system may be possible in future work
Black hole thermodynamics from simulations of lattice Yang-Mills theory
We report on lattice simulations of 16 supercharge SU(N) Yang-Mills quantum
mechanics in the 't Hooft limit. Maldacena duality conjectures that in this
limit the theory is dual to IIA string theory, and in particular that the
behavior of the thermal theory at low temperature is equivalent to that of
certain black holes in IIA supergravity. Our simulations probe the low
temperature regime for N <= 5 and the intermediate and high temperature regimes
for N <= 12. We observe 't Hooft scaling and at low temperatures our results
are consistent with the dual black hole prediction. The intermediate
temperature range is dual to the Horowitz-Polchinski correspondence region, and
our results are consistent with smooth behavior there. We include the Pfaffian
phase arising from the fermions in our calculations where appropriate.Comment: 4 pages, 4 figure
Perturbative dynamics of fuzzy spheres at large N
We clarify some peculiar aspects of the perturbative expansion around a
classical fuzzy-sphere solution in matrix models with a cubic term. While the
effective action in the large-N limit is saturated at the one-loop level, we
find that the ``one-loop dominance'' does not hold for generic observables due
to one-particle reducible diagrams. However, we may exploit the one-loop
dominance for the effective action and obtain various observables to all orders
from one-loop calculation by simply shifting the center of expansion to the
``quantum solution'', which extremizes the effective action. We confirm the
validity of this method by comparison with the direct two-loop calculation and
with Monte Carlo results in the 3d Yang-Mills-Chern-Simons matrix model. From
the all order result we find that the perturbative expansion has a finite
radius of convergence.Comment: 21 pages, 9 figures, (v2) all order analyses added, (v3) some typos
correcte
Mycophenolate mofetil inhibits lymphocyte binding and the upregulation of adhesion molecules in acute rejection of rat kidney allografts.
Mycophenolate mofetil (MMF) interacts with purine metabolism and possibly with the expression of adhesion molecules. In the present study, we analysed the expression of these molecules in transplanted kidney allografts treated with RS LBNF1 kidneys were orthotopically transplanted into Lewis rats and either treated with RS (20 mg/kg/day) or vehicle. Rats were harvested 3, 5 and 7 days following transplantation. For binding studies, fresh-frozen sections of transplanted kidneys were incubated with lymph node lymphocytes (LNL) derived from transplanted rats. Additionally, immunohistology was performed with various monoclonal antibodies. In general, MMF resulted in better preservation of graft structure by 7 days. Cellular infiltration and tubular atrophy were less pronounced. At day 3, macrophages were diminished in MMF-treated animals to a high extent, while the number of T cells was almost identical to that of controls. In addition, the number of cells positive for MHC class II and LFA-1 was reduced in the MMF-treated animals. These findings correlated with the binding results. Three days following engraftment, LNL bound to MMF-treated kidneys to a lesser extent compared to controls. In conclusion, MMF resulted in a markedly reduced leucocytic infiltrate, presumably based on a reduced expression of lymphocytic adhesion molecules and an interaction with macrophages
Swift Highly Charged Ion Channelling
We review recent experimental and theoretical progress made in the scope of
swift highly charged ion channelling in crystals. The usefulness of such
studies is their ability to yield impact parameter information on charge
transfer processes, and also on some time related problems. We discuss the
cooling and heating phenomena at MeV/u energies, results obtained with
decelerated H-like ion beams at GSI and with ions having an excess of electrons
at GANIL, the superdensity effect along atomic strings and Resonant Coherent
Excitation.Comment: to be published in Journal of Physics
Spin wave dispersion softening in the ferromagnetic Kondo lattice model for manganites
Spin dynamics is calculated in the ferromagnetic (FM) state of the
generalized Kondo lattice model taking into account strong on-site correlations
between e_g electrons and antiferromagnetic (AFM) exchange among t_{2g} spins.
Our study suggests that competing FM double-exchange and AFM super-exchange
interaction lead to a rather nontrivial spin-wave spectrum. While spin
excitations have a conventional Dq^2 spectrum in the long-wavelength limit,
there is a strong deviation from the spin-wave spectrum of the isotropic
Heisenberg model close to the zone boundary. The relevance of our results to
the experimental data are discussed.Comment: 6 RevTex pages, 3 embedded PostScript figure
Hedgehog black holes and the Polyakov loop at strong coupling
In N=4 super-Yang-Mills theory at large N, large \lambda, and finite
temperature, the value of the Wilson-Maldacena loop wrapping the Euclidean time
circle (the Polyakov-Maldacena loop, or PML) is computed by the area of a
certain minimal surface in the dual supergravity background. This prescription
can be used to calculate the free energy as a function of the PML (averaged
over the spatial coordinates), by introducing into the bulk action a Lagrange
multiplier term that fixes the (average) area of the appropriate minimal
surface. This term, which can also be viewed as a chemical potential for the
PML, contributes to the bulk stress tensor like a string stretching from the
horizon to the boundary (smeared over the angular directions). We find the
corresponding "hedgehog" black hole solutions numerically, within an
SO(6)-preserving ansatz, and derive part of the free energy diagram for the
PML. As a warm-up problem, we also find exact solutions for hedgehog black
holes in pure gravity, and derive the free energy and phase diagrams for that
system.Comment: 25 pages, 11 figures; v2: minor clarifications, published versio
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