181 research outputs found
Review of the pilot flood protection grant scheme in a recently flooded area
In 2007, Defra launched a pilot grant scheme that provided funding for property-level flood protection surveys and measures in six locations in England. In November 2009, in what was probably the first flood event to affect any of these areas subsequent to the implementation of the pilot, the River Eden overtopped its banks and flooded one of the principal streets of Appleby-in-Westmorland.
Six months later, this research was commissioned by Defra to discover what difference the government-funded measures had made to the people of the town, what factors had affected the implementation and effectiveness of the grant scheme and how the experience of the flood had changed attitudes towards this approach to flood risk management.
This report details the findings of that research and is therefore of relevance to any local, regional or national bodies that are considering the introduction of similar schemes
Radiation-hydrodynamical simulations of massive star formation using Monte Carlo radiative transfer - I. Algorithms and numerical methods
Copyright © 2015 The Author Published by Oxford University Press on behalf of the Royal Astronomical SocietyWe present a set of new numerical methods that are relevant to calculating radiation pressure terms in hydrodynamics calculations, with a particular focus on massive star formation. The radiation force is determined from a Monte Carlo estimator and enables a complete treatment of the detailed microphysics, including polychromatic radiation and anisotropic scattering, in both the free-streaming and optically thick limits. Since the new method is computationally demanding we have developed two new methods that speed up the algorithm. The first is a photon packet splitting algorithm that enables efficient treatment of the Monte Carlo process in very optically thick regions. The second is a parallelization method that distributes the Monte Carlo workload over many instances of the hydrodynamic domain, resulting in excellent scaling of the radiation step. We also describe the implementation of a sink particle method that enables us to follow the accretion on to, and the growth of, the protostars. We detail the results of extensive testing and benchmarking of the new algorithms.Science & Technology Facilities Council (STFC
Radial and rotational velocities of young brown dwarfs and very low-mass stars in the Upper Scorpius OB association and the rho Ophiuchi cloud core
We present the results of a radial velocity (RV) survey of 14 brown dwarfs
(BDs) and very low-mass (VLM) stars in the Upper Scorpius OB association
(UScoOB) and 3 BD candidates in the rho Ophiuchi dark cloud core. We obtained
high-resolution echelle spectra at the Very Large Telescope using Ultraviolet
and Visual Echelle Spectrograph (UVES) at two different epochs for each object,
and measured the shifts in their RVs to identify candidates for binary/multiple
systems in the sample. The average time separation of the RV measurements is
21.6d, and our survey is sensitive to the binaries with separation < 0.1 au. We
found that 4 out of 17 objects (or 24^{+16}_{-13} per cent by fraction) show a
significant RV change in 4-33d time scale, and are considered as
binary/multiple `candidates.' We found no double-lined spectroscopic binaries
in our sample, based on the shape of cross-correlation curves. The RV
dispersion of the objects in UScoOB is found to be very similar to that of the
BD and VLM stars in Chamaeleon I (Cha I). We also found the distribution of the
mean rotational velocities (v sin i) of the UScoOB objects is similar to that
of the Cha I, but the dispersion of v sin i is much larger than that of the Cha
I objects.Comment: 10 pages, 5 figures, accepted for publication in MNRA
Spectropolarimetry of single and binary stars
Spectropolarimetry is a photon-hungry technique that will reach fruition in
the 8-m telescope age. Here I summarize some of the stellar spectropolarimetric
research that my collaborators and I have undertaken, with particular emphasis
on the circumstellar environment of massive stars, symbiotic binaries, and star
formation.Comment: 12 pages, 8 Figures, to appear in "Stellar Astrophysics with the
World's Largest Telescopes", J. Mikolajewska (ed), to be published by AI
Indirect Detection of Forming Protoplanets via Chemical Asymmetries in Disks
We examine changes in the molecular abundances resulting from increased
heating due to a self-luminous planetary companion embedded within a narrow
circumstellar disk gap. Using 3D models that include stellar and planetary
irradiation, we find that luminous young planets locally heat up the parent
circumstellar disk by many tens of Kelvin, resulting in efficient thermal
desorption of molecular species that are otherwise locally frozen out.
Furthermore, the heating is deposited over large regions of the disk, AU
radially and spanning azimuthally. From the 3D chemical
models, we compute rotational line emission models and full ALMA simulations,
and find that the chemical signatures of the young planet are detectable as
chemical asymmetries in observations. HCN and its isotopologues are
particularly clear tracers of planetary heating for the models considered here,
and emission from multiple transitions of the same species is detectable, which
encodes temperature information in addition to possible velocity information
from the spectra itself. We find submillimeter molecular emission will be a
useful tool to study gas giant planet formation in situ, especially beyond
AU.Comment: 14 pages, 14 figures, accepted for publication in Ap
Walking as a social practice: dispersed walking and the organisation of everyday practices
This paper uses social practice theory to study the interweaving of walking into everyday practices and considers how greater awareness of everyday walking can influence its position within the organisation and scheduling of everyday life. Walking is of policy interest because of its perceived benefits for health. This paper asserts that increased awareness of everyday walking allows users to become more active without having to reschedule existing activities. Using Schatzki’s distinction between dispersed and integrative practices, it argues that by increasing awareness of dispersed walking can enlist walking into the teleoaffective organisation of some social practices and prompt the performance of new ‘health practices’ within everyday domains of life such as shopping and employment. While this analysis offers useful insights for the design of behaviour change strategies, it also points to some unintended consequences of using digital feedback to increase walking awareness. In directing the gaze of participants at one particular element of their daily practices, the paper suggests, digital walking feedback provides a ‘partial’ view of practices: in highlighting the exercise value of walking at the expense of other values it can prompt feedback recipients to pass moral judgements on themselves based on this partial view
Linear spectropolarimetry of young and other emission line stars
The aim of this article is to demonstrate the useful role that can be played
by spectropolarimetric observations of young and evolved emission line stars
that analyse the linearly polarized component in their spectra. At the time of
writing, this demonstration has to be made on the basis of optical data since
there is no common-user infrared facility, in operation, that offers the
desired combination of spectral resolution and sensitivity. Here we focus on
what can be learned from linear spectropolarimetry alone at reasonably high
spectral resolution and at S/N. And we remind that the near
infrared (1--2 micron) has the potential to out-perform the optical as a domain
to work in because of the greatly reduced interstellar obscuration at these
wavelengths. This point has been reached at a time when theory, exploiting
flexible Monte Carlo methods, is fast becoming a powerful tool. In short we
have the complex phenomena, and the rise of the modelling capability to match
-- good data are the missing link.Comment: 11 pages, ESO Conference on High Resolution Infrared Spectroscop
Radiation hydrodynamics of triggered star formation: the effect of the diffuse radiation field
We investigate the effect of including diffuse field radiation when modelling
the radiatively driven implosion of a Bonnor-Ebert sphere (BES).
Radiation-hydrodynamical calculations are performed by using operator splitting
to combine Monte Carlo photoionization with grid-based Eulerian hydrodynamics
that includes self-gravity. It is found that the diffuse field has a
significant effect on the nature of radiatively driven collapse which is
strongly coupled to the strength of the driving shock that is established
before impacting the BES. This can result in either slower or more rapid star
formation than expected using the on-the-spot approximation depending on the
distance of the BES from the source object. As well as directly compressing the
BES, stronger shocks increase the thickness and density in the shell of
accumulated material, which leads to short, strong, photo-evaporative ejections
that reinforce the compression whenever it slows. This happens particularly
effectively when the diffuse field is included as rocket motion is induced over
a larger area of the shell surface. The formation and evolution of 'elephant
trunks' via instability is also found to vary significantly when the diffuse
field is included. Since the perturbations that seed instabilities are smeared
out elephant trunks form less readily and, once formed, are exposed to enhanced
thermal compression.Comment: Accepted for publication in MNRAS. 19 pages, 14 figures, 8 table
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