571 research outputs found
Calibrating a Robot Camera
This paper addresses the problem of calibrating a camera mounted on a robot arm. The objective is to estimate the camera's intrinsic and extrinsic parameters. These include the relative position and orientation of camera with respect to robot base as well as the relative position and orientation of the camera with respect to a pre-defined world frame. A calibration object with a known 3D shape is used together with two known movements of the robot. A method is presented to find calibration parameters within an opti-misation framework. This method differs from existing methods in that 1) it fully exploits information from different displacements of the camera to produce an optimal calibration estimate, and 2) it uses an evolutionary algo-rithm to attain the optimal solution. Experimental results on both synthetic and real data are presented.
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The potential of 1 h refractivity changes from an operational C-band magnetron-based radar for numerical weather prediction validation and data assimilation
Refractivity changes (ΔN) derived from radar ground clutter returns serve as a proxy for near-surface humidity changes (1 N unit ≡ 1% relative humidity at 20 °C). Previous studies have indicated that better humidity observations should improve forecasts of convection initiation. A preliminary assessment of the potential of refractivity retrievals from an operational magnetron-based C-band radar is presented. The increased phase noise at shorter wavelengths, exacerbated by the unknown position of the target within the 300 m gate, make it difficult to obtain absolute refractivity values, so we consider the information in 1 h changes. These have been derived to a range of 30 km with a spatial resolution of ∼4 km; the consistency of the individual estimates (within each 4 km × 4 km area) indicates that ΔN errors are about 1 N unit, in agreement with in situ observations. Measurements from an instrumented tower on summer days show that the 1 h refractivity changes up to a height of 100 m remain well correlated with near-surface values. The analysis of refractivity as represented in the operational Met Office Unified Model at 1.5, 4 and 12 km grid lengths demonstrates that, as model resolution increases, the spatial scales of the refractivity structures improve. It is shown that the magnitude of refractivity changes is progressively underestimated at larger grid lengths during summer. However, the daily time series of 1 h refractivity changes reveal that, whereas the radar-derived values are very well correlated with the in situ observations, the high-resolution model runs have little skill in getting the right values of ΔN in the right place at the right time. This suggests that the assimilation of these radar refractivity observations could benefit forecasts of the initiation of convection
Simplifying the Development, Use and Sustainability of HPC Software
Developing software to undertake complex, compute-intensive scientific
processes requires a challenging combination of both specialist domain
knowledge and software development skills to convert this knowledge into
efficient code. As computational platforms become increasingly heterogeneous
and newer types of platform such as Infrastructure-as-a-Service (IaaS) cloud
computing become more widely accepted for HPC computations, scientists require
more support from computer scientists and resource providers to develop
efficient code and make optimal use of the resources available to them. As part
of the libhpc stage 1 and 2 projects we are developing a framework to provide a
richer means of job specification and efficient execution of complex scientific
software on heterogeneous infrastructure. The use of such frameworks has
implications for the sustainability of scientific software. In this paper we
set out our developing understanding of these challenges based on work carried
out in the libhpc project.Comment: 4 page position paper, submission to WSSSPE13 worksho
Data fusion in ubiquitous networked robot systems for urban services
There is a clear trend in the use of robots
to accomplish services that can help humans. In this
paper, robots acting in urban environments are considered
for the task of person guiding. Nowadays, it is
common to have ubiquitous sensors integrated within
the buildings, such as camera networks, and wireless
communications like 3G or WiFi. Such infrastructure
can be directly used by robotic platforms. The paper
shows how combining the information from the robots
and the sensors allows tracking failures to be overcome,
by being more robust under occlusion, clutter, and
lighting changes. The paper describes the algorithms
for tracking with a set of fixed surveillance cameras
and the algorithms for position tracking using the signal
strength received by a wireless sensor network (WSN).
Moreover, an algorithm to obtain estimations on the positions of people from cameras on board robots is
described. The estimate from all these sources are then
combined using a decentralized data fusion algorithm
to provide an increase in performance. This scheme is
scalable and can handle communication latencies and
failures. We present results of the system operating in
real time on a large outdoor environment, including 22
nonoverlapping cameras, WSN, and several robots.Universidad Pablo de Olavide. Departamento de Deporte e InformáticaPostprin
Binding of more than one Tva800 molecule is required for ASLV-A entry
BACKGROUND: Understanding the mechanism by which viruses enter their target cell is an essential part of understanding their infectious cycle. Previous studies have focussed on the multiplicity of viral envelope proteins that need to bind to their cognate receptor to initiate entry. Avian sarcoma and leukosis virus Envelope protein (ASLV Env) mediates entry via a receptor, Tva, which can be attached to the cell surface either by a phospholipid anchor (Tva800) or a transmembrane domain (Tva950). In these studies, we have now investigated the number of target receptors necessary for entry of ASLV Env-pseudotyped virions. RESULTS: Using titration and modelling experiments we provide evidence that binding of more than one receptor, probably two, is needed for entry of virions via Tva800. However, binding of just one Tva950 receptor is sufficient for successful entry. CONCLUSIONS: The different modes of attachment of Tva800 and Tva950 to the cell membrane have important implications for the utilisation of these proteins as receptors for viral binding and/or uptake
Unhappy families: using tabletop games as a technology to understand play in education
In this article, we argue that tabletop games provide a helpful means of rethinking the affordances of digital games in pedagogy. We argue that tabletop games offer a distinctive technology from digital games in exploring the idea of play as experience, providing a sociable, accessible and tactile platform that can easily be adapted by players to suit their needs. At a workshop session at an international conference on play in education, we used tabletop games to enable discussion and observation of play. This workshop suggested that, rather than a singular definition, tabletop play means different things to different people, and what is ‘counted as’ play depends upon both individual and group interactions. Building upon this discussion, in this article, we return to both tabletop and digital games to discuss the idea of play as experience, especially with regard to the use of technology in educational settings, and how games might be seen as less ‘predictable’ than other technologies. We hope that this discussion provides future inspiration to other scholars who are considering the use of tabletop games in both pedagogical and technological research
The HST Key Project on the Extragalactic Distance Scale XXVI. The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant
A Cepheid-based calibration is derived for four distance indicators that
utilize stars in the old stellar populations: the tip of the red giant branch
(TRGB), the planetary nebula luminosity function (PNLF), the globular cluster
luminosity function (GCLF) and the surface brightness fluctuation method (SBF).
The calibration is largely based on the Cepheid distances to 18 spiral galaxies
within cz =1500 km/s obtained as part of the HST Key Project on the
Extragalactic Distance Scale, but relies also on Cepheid distances from
separate HST and ground-based efforts. The newly derived calibration of the SBF
method is applied to obtain distances to four Abell clusters in the velocity
range between 3800 and 5000 km/s, observed by Lauer et al. (1998) using the
HST/WFPC2. Combined with cluster velocities corrected for a cosmological flow
model, these distances imply a value of the Hubble constant of H0 = 69 +/- 4
(random) +/- 6 (systematic) km/s/Mpc. This result assumes that the Cepheid PL
relation is independent of the metallicity of the variable stars; adopting a
metallicity correction as in Kennicutt et al. (1998), would produce a (5 +/-
3)% decrease in H0. Finally, the newly derived calibration allows us to
investigate systematics in the Cepheid, PNLF, SBF, GCLF and TRGB distance
scales.Comment: Accepted for publication in the Astrophysical Journal. 48 pages
(including 13 figures and 4 tables), plus two additional tables in landscape
format. Also available at http://astro.caltech.edu/~lff/pub.htm K' SBF
magnitudes have been update
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