arXiv subjects

Paul Moran

Publications and source records attributed to Paul Moran.

6 recordsLinked to original sources

arXiv2021

2.5D Vehicle Odometry Estimation

It is well understood that in ADAS applications, a good estimate of the pose of the vehicle is required. This paper proposes a metaphorically named 2.5D odometry, whereby the planar odometry derived from the yaw rate sensor and four wheel speed sensors is augmented by a linear model of suspension. While the core of the planar odometry is a yaw rate model that is already understood in the literature, we augment this by fitting a quadratic to the incoming signals, enabling interpolation, extrapolation, and a finer integration of the vehicle position. We show, by experimental results with a DGPS/IMU reference, that this model provides highly accurate odometry estimates, compared with existing methods. Utilising sensors that return the change in height of vehicle reference points with changing suspension configurations, we define a planar model of the vehicle suspension, thus augmenting the odometry model. We present an experimental framework and evaluations criteria by which the goodness of the odometry is evaluated and compared with existing methods. This odometry model has been designed to support low-speed surround-view camera systems that are well-known. Thus, we present some application results that show a performance boost for viewing and computer vision applications using the proposed odometry

cs.RO↗

arXiv2021

A 2.5D Vehicle Odometry Estimation for Vision Applications

This paper proposes a method to estimate the pose of a sensor mounted on a vehicle as the vehicle moves through the world, an important topic for autonomous driving systems. Based on a set of commonly deployed vehicular odometric sensors, with outputs available on automotive communication buses (e.g. CAN or FlexRay), we describe a set of steps to combine a planar odometry based on wheel sensors with a suspension model based on linear suspension sensors. The aim is to determine a more accurate estimate of the camera pose. We outline its usage for applications in both visualisation and computer vision.

cs.RO↗

arXiv2020

Mediation effects that emulate a target randomised trial: Simulation-based evaluation of ill-defined interventions on multiple mediators

Many epidemiological questions concern potential interventions to alter the pathways presumed to mediate an association. For example, we consider a study that investigates the benefit of interventions in young adulthood for ameliorating the poorer mid-life psychosocial outcomes of adolescent self-harmers relative to their healthy peers. Two methodological challenges arise. Firstly, mediation methods have hitherto mostly focused on the elusive task of discovering pathways, rather than on the evaluation of mediator interventions. Secondly, the complexity of such questions is invariably such that there are no existing data on well-defined interventions (i.e. actual treatments, programs, etc.) capturing the populations, outcomes and time-spans of interest. Instead, researchers must rely on exposure (non-intervention) data to address these questions, such as self-reported substance use and employment. We address the resulting challenges by specifying a target trial addressing three policy-relevant questions, regarding the impacts of hypothetical (rather than actual) interventions that would shift the mediators' distributions (separately, jointly or sequentially) to user-specified distributions that can be emulated with the observed data. We then define novel interventional effects that map to this trial, emulating shifts by setting mediators to random draws from those distributions. We show that estimation using a g-computation method is possible under an expanded set of causal assumptions relative to inference with well-defined interventions. These expanded assumptions reflect the lower level of evidence that is inevitable with ill-defined interventions. Application to the self-harm example using data from the Victorian Adolescent Health Cohort Study illustrates the value of our proposal for informing the design and evaluation of actual interventions in the future.

stat.ME↗

arXiv2015

A recent change in the optical and γ-ray polarization of the Crab nebula and pulsar

We report on observations of the polarization of optical and γ-ray photons from the Crab nebula and pulsar system using the Galway Astronomical Stokes Polarimeter (GASP), the Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) and the International Gamma-Ray Astrophysics Laboratory satellite (Integral). These, when combined with other optical polarization observations, suggest that the polarized optical emission and γ-ray polarization changes in a similar manner. A change in the optical polarization angle has been observed by this work, from 109.5 \pm 0.7°in 2005 to 85.3 \pm 1.4 °in 2012. On the other hand, the γ-ray polarization angle changed from 115 \pm 11 °in 2003-2007 to 80 \pm 12 °in 2012-2014. Strong flaring activities have been detected in the Crab nebula over the past few years by the high energy γ-ray missions Agile and Fermi, and magnetic reconnection processes have been suggested to explain these observations. The change in the polarized optical and γ-ray emission of the Crab nebula/pulsar as observed, for the first time, by GASP and Integral may indicate that reconnection is possibly at work in the Crab nebula. We also report, for the first time, a non-zero measure of the optical circular polarization from the Crab pulsar+knot system.

astro-ph.HE↗

arXiv2013

Optical Polarimetry of the Inner Crab Nebula and Pulsar

Time-resolved polarisation measurements of pulsars offer an unique insight into the geometry of their emission regions. Such measure\ ments provide observational constraints on the different models proposed for the pulsar emission mechanisms. Optical polarisation data of the Crab Nebula was obtained from the HST archive. The data set consists of a series of observations of the nebula taken with the HST/ACS. We produced polarisation vector maps of the inner nebula and measured, for the first time, the degree of linear polarisation (P.D.) and the position angle (P.A.) of the pulsar's integrated pulse beam, and of its nearby synchrotron knot. This yielded $\rm P.D.=5.2\pm0.3%$ and $\rm P.A.=105.1\pm1.6\degr$ for the pulsar, and $\rm P.D.=59.0\pm1.9%$ and $\rm P.A.=124.7\pm1.0\degr$ for the synchrotron knot. This is the first high-spatial resolution multi-epoch study of the polarisation of the inner nebula and pulsar. None of the main features in the nebula show evidence of significant polarisation evolution in the period covered by these observations. The results for the pulsar are consistent with those obtained by Słowikowska et al (2009) using the high-time resolution photo-polarimeter OPTIMA, once the DC component has been subtracted. Our results clearly prove that the knot is the main source of the DC component.

astro-ph.HE↗

arXiv2013

INTEGRAL/IBIS and optical observations of the Crab nebula/pulsar polarisation

Previous INTEGRAL/IBIS observations have shown that the gamma-ray radiation of the Crab Nebula is highly polarised and remarkably aligned along the axis of rotation of the pulsar (Forot et al. 2008). Their study was based on the first four years of operation of the satellite. Here we present an analysis based upon nearly ten years of operation. This new analysis allows a better characterisation of the polarisation fraction and position angle, as well as a measure of spectral energy distribution of the polarised component. These results are then compared to the known optical polarisation of the pulsar and nearby synchrotron knot. In the future we shall compare the gamma-ray polarisation with the phase-resolved optical polarisation using instruments such as GASP (Kyne et al. 2010).

astro-ph.HE↗