6,123 research outputs found
Camera motion estimation through planar deformation determination
In this paper, we propose a global method for estimating the motion of a
camera which films a static scene. Our approach is direct, fast and robust, and
deals with adjacent frames of a sequence. It is based on a quadratic
approximation of the deformation between two images, in the case of a scene
with constant depth in the camera coordinate system. This condition is very
restrictive but we show that provided translation and depth inverse variations
are small enough, the error on optical flow involved by the approximation of
depths by a constant is small. In this context, we propose a new model of
camera motion, that allows to separate the image deformation in a similarity
and a ``purely'' projective application, due to change of optical axis
direction. This model leads to a quadratic approximation of image deformation
that we estimate with an M-estimator; we can immediatly deduce camera motion
parameters.Comment: 21 pages, version modifi\'ee accept\'e le 20 mars 200
Numerical study of the lattice vacancy effects on the single-channel electron transport of graphite ribbons
Lattice vacancy effects on electrical conductance of nanographite ribbon are
investigated by means of the Landauer approach using a tight binding model. In
the low-energy regime ribbons with zigzag boundary provide a single conducting
channel whose origin is connected with the presence of edge states. It is found
that the chemical potential dependence of conductance strongly depends on the
difference () of the number of removed A and B sublattice sites. The
large lattice vacancy with shows zero-conductance dips
in the single-channel region, however, the large lattice vacancy with
has no dip structure in this region. The connection between this
conductance rule and the Longuet-Higgins conjecture is also discussed
Dynamical Jahn-Teller Effect and Berry Phase in Positively Charged Fullerene I. Basic Considerations
We study the Jahn-Teller effect of positive fullerene ions C
and C. The aim is to discover if this case, in analogy with the
negative ion, possesses a Berry phase or not, and what are the consequences on
dynamical Jahn-Teller quantization. Working in the linear and spherical
approximation, we find no Berry phase in C, and
presence/absence of Berry phase for coupling of one hole to an
/ vibration. We study in particular the special equal-coupling case
(), which is reduced to the motion of a particle on a 5-dimensional
sphere. In the icosahedral molecule, the final outcome assesses the
presence/absence of a Berry phase of for the hole coupled to
/ vibrations. Some qualitative consequences on ground-state symmetry,
low-lying excitations, and electron emission from C are spelled out.Comment: 31 pages (RevTeX), 3 Postscript figures (uuencoded
Square Patterns and Quasi-patterns in Weakly Damped Faraday Waves
Pattern formation in parametric surface waves is studied in the limit of weak
viscous dissipation. A set of quasi-potential equations (QPEs) is introduced
that admits a closed representation in terms of surface variables alone. A
multiscale expansion of the QPEs reveals the importance of triad resonant
interactions, and the saturating effect of the driving force leading to a
gradient amplitude equation. Minimization of the associated Lyapunov function
yields standing wave patterns of square symmetry for capillary waves, and
hexagonal patterns and a sequence of quasi-patterns for mixed capillary-gravity
waves. Numerical integration of the QPEs reveals a quasi-pattern of eight-fold
symmetry in the range of parameters predicted by the multiscale expansion.Comment: RevTeX, 11 pages, 8 figure
Skin antisepsis: it's not only what you use, it's the way that you use it
International audienc
Chronic performance of Riata 1580 and Endotak 0158 ICD leads: A single center 10-year experience
BACKGROUND: The long term performance of the Riata family of leads has recently come under increasing scrutiny. We aimed to determine the long term performance of the Riata 1580 leads compared with Endotak 0158 leads. METHODS: All patients with Riata 1580 or Endotak 0158 leads implanted from 2003-2008 at the Heart Hospital, UCLH were analysed. Significant electrical changes were: threshold increase >1V at a set pulse width between pacing checks, persistent R wave fall to 50%, noise, pacing impedance change to 1500 Ω, HV change to 200Ω, HV change ± 15Ω, pacing impedance change > 400Ω over 12 months. RESULTS: 333 Riata and 356 Endotak leads were implanted. Median follow up time + interquartile range, after exclusion of censored events including loss to follow up: Riata 3652 + 655 days, Endotak 3730 + 810 days. A total of 51 (15.9%) Riata leads and 21 (6.3%) Endotak leads were affected. A greater risk of failure was found for the Riata lead compared with the Endotak lead (p = 0.0001). An additional time-dependent effect was found, with the Riata lead 1.9 times more likely to fail in the first 6 years following lead implantation and 5.3 times more likely to fail after 6 years. CONCLUSIONS: Riata leads have a higher risk of failure compared to Endotak leads over time. The importance of careful ongoing performance surveillance late in the leads' lifetime is reflected in this ten year follow up study. This article is protected by copyright. All rights reserved
Introduction to RISC-KIT: Resilience-increasing strategies for coasts
Recent and historic low-frequency, high-impact events have demonstrated the flood risks faced by exposed coastal areas in Europe and beyond. These coastal zone risks are likely to increase in the future which requires a re-evaluation of coastal disaster risk reduction (DRR) strategies and a new mix of PMP (prevention, e.g., dike protection; mitigation, e.g., limiting construction in flood-prone areas and eco-system based solutions; and preparedness, e.g., Early Warning Systems, EWS) measures.
In response to these challenges, the RISC-KIT project has delivered a set of open-source and openaccess methods, tools and management approaches to reduce risk and increase resilience to lowfrequency, high-impact hydro-meteorological events in the coastal zone (the âRISC-toolKITâ). These products enhance forecasting, prediction and early warning capabilities, improve the assessment of long-term coastal risk and optimise the mix of PMP-measures.
In this paper an introduction is provided to the objectives, products, applications and lessonslearned of the RISC-KIT project, which are the subjects of this Special Issue. Subsequent papers provide details on the tools and their application on 10 case study sites in Europe
Viscoelastic Depinning of Driven Systems: Mean-Field Plastic Scallops
We have investigated the mean field dynamics of an overdamped viscoelastic
medium driven through quenched disorder. The model introduced incorporates
coexistence of pinned and sliding degrees of freedom and can exhibit continuous
elastic depinning or first order hysteretic depinning. Numerical simulations
indicate mean field instabilities that correspond to macroscopic stick-slip
events and lead to premature switching. The model is relevant for the dynamics
of driven vortex arrays in superconductors and other extended disordered
systems.Comment: 4 pages, 2 figure
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