11,419 research outputs found
Floppy swimming: Viscous locomotion of actuated elastica
Actuating periodically an elastic filament in a viscous liquid generally
breaks the constraints of Purcell's scallop theorem, resulting in the
generation of a net propulsive force. This observation suggests a method to
design simple swimming devices - which we call "elastic swimmers" - where the
actuation mechanism is embedded in a solid body and the resulting swimmer is
free to move. In this paper, we study theoretically the kinematics of elastic
swimming. After discussing the basic physical picture of the phenomenon and the
expected scaling relationships, we derive analytically the elastic swimming
velocities in the limit of small actuation amplitude. The emphasis is on the
coupling between the two unknowns of the problems - namely the shape of the
elastic filament and the swimming kinematics - which have to be solved
simultaneously. We then compute the performance of the resulting swimming
device, and its dependance on geometry. The optimal actuation frequency and
body shapes are derived and a discussion of filament shapes and internal
torques is presented. Swimming using multiple elastic filaments is discussed,
and simple strategies are presented which result in straight swimming
trajectories. Finally, we compare the performance of elastic swimming with that
of swimming microorganisms.Comment: 23 pages, 6 figure
Using the Aesop's fable paradigm to investigate causal understanding of water displacement by New Caledonian crows.
Understanding causal regularities in the world is a key feature of human cognition. However, the extent to which non-human animals are capable of causal understanding is not well understood. Here, we used the Aesop's fable paradigm--in which subjects drop stones into water to raise the water level and obtain an out of reach reward--to assess New Caledonian crows' causal understanding of water displacement. We found that crows preferentially dropped stones into a water-filled tube instead of a sand-filled tube; they dropped sinking objects rather than floating objects; solid objects rather than hollow objects, and they dropped objects into a tube with a high water level rather than a low one. However, they failed two more challenging tasks which required them to attend to the width of the tube, and to counter-intuitive causal cues in a U-shaped apparatus. Our results indicate that New Caledonian crows possess a sophisticated, but incomplete, understanding of the causal properties of displacement, rivalling that of 5-7 year old children
'A habitual disposition to the good': on reason, virtue and realism
Amidst the crisis of instrumental reason, a number of contemporary political philosophers including Jürgen Habermas have sought to rescue the project of a reasonable humanism from the twin threats of religious fundamentalism and secular naturalism. In his recent work, Habermas defends a post-metaphysical politics that aims to protect rationality against encroachment while also accommodating religious faith within the public sphere. This paper contends that Habermas’ post-metaphysical project fails to provide a robust alternative either to the double challenge of secular naturalism and religious fundamentalism or to the ruthless instrumentalism that underpins capitalism. By contrast with Habermas and also with the ‘new realism’ of contemporary political philosophers such as Raymond Geuss or Bernard Williams, realism in the tradition of Plato and Aristotle can defend reason against instrumental rationality and blind belief by integrating it with habit, feeling and even faith. Such metaphysical–political realism can help develop a politics of virtue that goes beyond communitarian thinking by emphasising plural modes of association (not merely ‘community’), substantive ties of sympathy and the importance of pursuing goodness and mutual flourishing
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Exploiting granular electrical energy data and the challenges a utility company faces with an ageing asset base
Thames Water; Brunel University London
A Standardised Modular Approach for Site SCADA Applications within a Water Utility
Any large water treatment/production utility that employs autonomous plant as part of its processes will utilise supervisory control and data acquisition systems. These systems will generally be isolated from each other and will exist solely to serve the site they control and visualise. More often, they are delivered and developed organically through cost driven maintenance regimes, that prioritise on process risk rather than asset lifecycles. In some cases, this has led to variations in installed software and hardware applications, not only across a business enterprise, but also down to a site level. This is usually based on favoured products at the time of supply, and in turn requires a broader range of engineering skills to maintain and update. The previous adoption of a ‘fit and forget’ model has also led to large areas of unsupported computer assets within an organisation that further introduces ‘data risk’. As regulatory bodies start to impose stricter compliance measures on the water industry, so to the suppliers become more reliant upon their process data. This paper presents how a water utility has employed a modular approach and has set to standardise its SCADA assets across all business sectors. It reviews the hardware the systems are installed on, the software applications used to deliver the integration, and discusses how the software devices have been modelled and tagged in search of a common information model. All in line with their respective field assets. It also discusses some of the human factors surrounding the replacement of control systems
Probing the distribution of dark matter in the Abell 901/902 supercluster with weak lensing
We present a weak shear analysis of the Abell 901/902 supercluster, composed
of three rich clusters at z=0.16. Using a deep R-band image from the 0.5 x 0.5
degree MPG/ESO Wide Field Imager together with supplementary B-band
observations, we build up a comprehensive picture of the light and mass
distributions in this region. We find that, on average, the light from the
early-type galaxies traces the dark matter fairly well, although one cluster is
a notable exception to this rule. The clusters themselves exhibit a range of
mass-to-light (M/L) ratios, X-ray properties, and galaxy populations. We
attempt to model the relation between the total mass and the light from the
early-type galaxies with a simple scale-independent linear biasing model. We
find M/L_B=130h for the early type galaxies with zero stochasticity, which, if
taken at face value, would imply Omega_m < 0.1. However, this linear relation
breaks down on small scales and on scales equivalent to the average cluster
separation (approximately 1 Mpc), demonstrating that a single M/L ratio is not
adequate to fully describe the mass-light relation in the supercluster. Rather,
the scatter in M/L ratios observed for the clusters supports a model
incorporating non-linear biasing or stochastic processes. Finally, there is a
clear detection of filamentary structure connecting two of the clusters, seen
in both the galaxy and dark matter distributions, and we discuss the effects of
cluster-cluster and cluster-filament interactions as a means to reconcile the
disparate descriptions of the supercluster.Comment: 23 pages, 19 figures. ApJ, accepte
A method to implement the reservoir-wave hypothesis using phase-contrast magnetic resonance imaging
The reservoir-wave hypothesis states that the blood pressure waveform can be usefully divided into a “reservoir pressure” related to the global compliance and resistance of the arterial system, and an “excess pressure” that depends on local conditions. The formulation of the reservoir-wave hypothesis applied to the area waveform is shown, and the analysis is applied to area and velocity data from high-resolution phase-contrast cardiovascular magnetic resonance (CMR) imaging. A validation study shows the success of the principle, with the method producing largely robust and physically reasonable parameters, and the linear relationship between flow and wave pressure seen in the traditional pressure formulation is retained. The method was successfully tested on a cohort of 20 subjects (age range: 20–74 years; 17 males). This paper: • Demonstrates the feasibility of deriving reservoir data non-invasively from CMR. • Includes a validation cohort (CMR data). • Suggests clinical applications of the method
Radio Polarimetry of the ELAIS N1 Field: Polarized Compact Sources
We present deep polarimetric observations at 1420 MHz of the European Large
Area ISO Survey North 1 region (ELAIS N1) as part of the Dominion Radio
Astrophysical Observatory Planck Deep Fields project. By combining closely
spaced aperture synthesis fields, we image a region of 7.43 square degrees to a
maximum sensitivity in Stokes Q and U of 78 microJy/beam, and detect 786
compact sources in Stokes I. Of these, 83 exhibit polarized emission. We find
that the differential source counts (log N - log p) for polarized sources are
nearly constant down to p > 500 microJy, and that these faint polarized radio
sources are more highly polarized than the strong source population. The median
fractional polarization is (4.8 +/- 0.7)% for polarized sources with Stokes I
flux density between 1 and 30 mJy; approximately three times larger than
sources with I > 100 mJy. The majority of the polarized sources have been
identified with galaxies in the Spitzer Wide Area Infrared Extragalactic Survey
(SWIRE) image of ELAIS N1. Most of the galaxies occupy regions in the IRAC
5.8/3.6 micron vs. 8.0/4.5 micron color-color diagram associated with dusty
AGNs, or with ellipticals with an aging stellar population. A few host galaxies
have colors that suggests significant PAH emission in the near-infrared. A
small fraction, 12%, of the polarized sources are not detected in the SWIRE
data. None of the polarized sources in our sample appears to be associated with
an actively star-forming galaxy.Comment: 28 pages, 8 Figures. Figures 2 and 3 as separate gif images. Accepted
for publication in the Astrophysical Journa
Not in my back yard! Sports stadia location and the property market
In recent years sports stadia have been built in the UK, not only for their intended sporting purpose but with the twin aim of stimulating economic and physical regeneration. However, proposals to locate stadia in urban areas often prompt a negative reaction from local communities, fearing a decline in property prices. This paper will use a case study of the Millennium Stadium in Cardiff and the City of Manchester Stadium to illustrate that in contrast to this widely held belief, sports stadia can actually enhance the value of residential property. Furthermore, it will argue that stadia also contribute indirectly to property value through the creation of pride, confidence and enhanced image of an area.</p
Radio polarimetric imaging of the interstellar medium: magnetic field and diffuse ionized gas structure near the W3/W4/W5/HB3 complex
We have used polarimetric imaging to study the magneto-ionic medium of the
Galaxy, obtaining 1420 MHz images with an angular resolution of 1' over more
than 40 square-degrees of sky around the W3/W4/W5/HB3 HII region/SNR complex in
the Perseus Arm. Features detected in polarization angle are imposed on the
linearly polarized Galactic synchrotron background emission by Faraday rotation
arising in foreground ionized gas having an emission measure as low as 1
cm^{-6} pc. Several new remarkable phenomena have been identified, including:
mottled polarization arising from random fluctuations in a magneto-ionic screen
that we identify with a medium in the Perseus Arm, probably in the vicinity of
the HII regions themselves; depolarization arising from very high rotation
measures (several times 10^3 rad m^{-2}) and rotation measure gradients due to
the dense, turbulent environs of the HII regions; highly ordered features
spanning up to several degrees; and an extended influence of the HII regions
beyond the boundaries defined by earlier observations. In particular, the
effects of an extended, low-density ionized halo around the HII region W4 are
evident, probably an example of the extended HII envelopes postulated as the
origin of weak recombination-line emission detected from the Galactic ridge.
Our polarization observations can be understood if the uniform magnetic field
component in this envelope scales with the square-root of electron density and
is 20 microG at the edge of the depolarized region around W4, although this is
probably an over-estimate since the random field component will have a
significant effect.Comment: 18 pages, 8 figures (7 jpeg and 1 postscript), accepted for
publication in the Astrophysical Journa
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