1,433 research outputs found
Wigner-Moyal description of free variable mass Klein-Gordon fields
A system of coupled kinetic transport equations for the Wigner distributions
of a free variable mass Klein-Gordon field is derived. This set of equations is
formally equivalent to the full wave equation for electromagnetic waves in
nonlinear dispersive media, thus allowing for the description of broadband
radiation-matter interactions and the associated instabilities. The standard
results for the classical wave action are recovered in the short wavelength
limit of the generalized Wigner-Moyal formalism for the wave equation.Comment: 9 pages, accepted for publication in Journal of Mathematical Physic
Acetylene–argon plasmas measured at an rf-biased substrate electrode for diamond-like carbon deposition: II. Ion energy distributions
Are chronic pain syndromes associated with a unique cytokine profile? A systematic review and meta-analysis
Passivity-Based Trajectory Tracking and Formation Control of Nonholonomic Wheeled Robots Without Velocity Measurements
This note proposes a passivity-based control method for trajectory tracking and formation control of nonholonomic wheeled robots without velocity measurements. Coordinate transformations are used to incorporate the nonholonomic constraints, which are then avoided by controlling the front end of the robot rather than the center of the wheel axle into the differential equations. Starting from the passivity-based coordination design, the control goals are achieved via an internal controller for velocity tracking and heading control and an external controller for formation in the port-Hamiltonian framework. This approach endows the resulting controller with a physical interpretation. To avoid unavailable velocity measurements or unreliable velocity estimations, we derive the distributed control law with only position measurements by introducing a dynamic extension. In addition, we prove that our approach is suitable not only for acyclic graphs but also for a class of non-acyclic graphs, namely, ring graphs. Simulations are provided to illustrate the effectiveness of the approach
A Geometric Observer for Scene Reconstruction Using Plenoptic Cameras
This paper proposes an observer for generating depth maps of a scene from a
sequence of measurements acquired by a two-plane light-field (plenoptic)
camera. The observer is based on a gradient-descent methodology. The use of
motion allows for estimation of depth maps where the scene contains
insufficient texture for static estimation methods to work. A rigourous
analysis of stability of the observer error is provided, and the observer is
tested in simulation, demonstrating convergence behaviour.Comment: Full version of paper submitted to CDC 2018. 11 pages. 12 figure
A connexin/ifi30 pathway bridges HSCs with their niche to dampen oxidative stress
Reactive oxygen species (ROS) represent a by-product of metabolism and their excess is toxic for hematopoietic stem and progenitor cells (HSPCs). During embryogenesis, a small number of HSPCs are produced from the hemogenic endothelium, before they colonize a transient organ where they expand, for example the fetal liver in mammals. In this study, we use zebrafish to understand the molecular mechanisms that are important in the caudal hematopoietic tissue (equivalent to the mammalian fetal liver) to promote HSPC expansion. High levels of ROS are deleterious for HSPCs in this niche, however this is rescued by addition of antioxidants. We show that Cx41.8 is important to lower ROS levels in HSPCs. We also demonstrate a new role for ifi30, known to be involved in the immune response. In the hematopoietic niche, Ifi30 can recycle oxidized glutathione to allow HSPCs to dampen their levels of ROS, a role that could be conserved in human fetal liver
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Modelling and Analysis of Vibrations in a UAV Helicopter with a Vision System
The analysis of the nature and damping of unwanted vibrations on Unmanned Aerial Vehicle (UAV) helicopters are important tasks when images from on‐board vision systems are to be obtained. In this article, the authors model a UAV system, generate a range of vibrations originating in the main rotor and design a control methodology in order to damp these vibrations. The UAV is modelled using VehicleSim, the vibrations that appear on the fuselage are analysed to study their effects on the on‐board vision system by using Simmechanics software. Following this, the authors present a control method based on an Adaptive Neuro‐Fuzzy Inference System (ANFIS) to achieve satisfactory damping results over the vision system on board
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