20,452 research outputs found
Recommended from our members
Implications of HGV charging for the UK
Road transport taxation in Europe is undergoing a major and radical shift away from fixed charges and fuel duties towards pricing according to distance travelled and externalities produced. Implementation is underway in some states, change being led by national schemes for the freight sector only. The UK is considering such a system for implementation by 2008, to use global positioning system technology.
The paper reviews the current developments and considers charging scenarios, including a scenario for covering the full external costs of the UK freight industry. Implications for taxation policy are considered, including whether the doctrine of revenue neutrality is consistent with 'sustainable mobility'. Consideration is given to a transition strategy which could bridge between the current level and structure of prices and a future, more economically efficient approach
The Einstein Ring 0047-2808 Revisited: A Bayesian Inversion
In a previous paper, we outlined a new Bayesian method for inferring the
properties of extended gravitational lenses, given data in the form of resolved
images. This method holds the most promise for optimally extracting information
from the observed image, whilst providing reliable uncertainties in all
parameters. Here, we apply the method to the well studied optical Einstein ring
0047-2808. Our results are in broad agreement with previous studies, showing
that the density profile of the lensing galaxy is aligned within a few degrees
of the light profile, and suggesting that the source galaxy (at redshift 3.6)
is a binary system, although its size is only of order 1-2 kpc. We also find
that the mass of the elliptical lensing galaxy enclosed by the image is
(2.910.01) M_{\sun}. Our method is able to achieve
improved resolution for the source reconstructions, although we also find that
some of the uncertainties are greater than has been found in previous analyses,
due to the inclusion of extra pixels and a more general lens model.Comment: Accepted for publication in Ap
The sialate O-acetylesterase EstA from gut Bacteroidetes species enables sialidase-mediated cross-species foraging of 9-O-acetylated sialoglycans
A Conservation of Resources Approach to Blackberry Use, Work-Family Conflict and Well-Being: Job Control and Psychological Detachment from Work as Potential Mediators
Decomposition of the visible and dark matter in the Einstein ring 0047-2808 by semi-linear inversion
We measure the mass density profile of the lens galaxy in the Einstein ring
system 0047-2808 using our semi-linear inversion method developed in an earlier
paper. By introducing an adaptively gridded source plane, we are able to
eliminate the need for regularisation of the inversion. This removes the
problem of a poorly defined number of degrees of freedom, encountered by
inversion methods that employ regularisation, and so allows a proper
statistical comparison between models. We confirm the results of Wayth et al.
(2004), that the source is double, and that a power-law model gives a
significantly better fit that the singular isothermal ellipsoid model. We
measure a slope alpha=2.11+/-0.04. We find, further, that a dual-component
constant M/L baryonic + dark halo model gives a significantly better fit than
the power-law model, at the 99.7% confidence level. The inner logarithmic slope
of the dark halo profile is found to be 0.87^{+0.69}_{-0.61} (95% CL),
consistent with the predictions of CDM simulations of structure formation. We
determine an unevolved B-band mass to light ratio for the baryons (only) of
3.05^{+0.53}_{-0.90} h_65 M_sol/L_Bsol (95% CL). This is the first measurement
of the baryonic M/L of a single galaxy by purely gravitational lens methods.
The baryons account for 65^{+10}_{-18}% (95% CL) of the total projected mass,
or, assuming spherical symmetry, 84^{+12}_{-24}% (95% CL) of the total
three-dimensional mass within the mean radius of 1.16'' (7.5 h_65^{-1} kpc)
traced by the ring. Finally, at the level of >3sigma, we find that the halo
mass is rounder than the baryonic distribution and that the two components are
offset in orientation from one another.Comment: 17 pages, 5 figures, accepted by ApJ on 17/12/05. This version
corrects various typo
Raising the Dead: Clues to Type Ia Supernova Physics from the Remnant 0509-67.5
We present Chandra X-ray observations of the young supernova remnant (SNR)
0509-67.5 in the Large Magellanic Cloud (LMC), believed to be the product of a
Type Ia supernova (SN Ia). The remnant is very round in shape, with a distinct
clumpy shell-like structure. Our Chandra data reveal the remnant to be rich in
silicon, sulfur, and iron. The yields of our fits to the global spectrum
confirm that 0509-67.5 is the remnant of an SN Ia and show a clear preference
for delayed detonation explosion models for SNe Ia. We study the spectrum of
the single brightest isolated knot in the remnant and find that it is enhanced
in iron by a factor of roughly two relative to the global remnant abundances.
This feature, along with similar knots seen in Tycho's SNR, argues for the
presence of modest small-scale composition inhomogeneities in SNe Ia. The
presence of both Si and Fe, with abundance ratios that vary from knot to knot,
indicates that these came from the transition region between the Si- and
Fe-rich zones in the exploded star, possibly as a result of energy input to the
ejecta at late times due to the radioactive decay of 56Ni and 56Co. Two cases
for the continuum emission from the global spectrum were modeled: one where the
continuum is dominated by hydrogen thermal bremsstrahlung radiation; another
where the continuum arises from non-thermal synchrotron radiation. The former
case requires a relatively large value for the ambient density (~1 cm^-3).
Another estimate of the ambient density comes from using the shell structure of
the remnant in the context of dynamical models. This requires a much lower
value for the density (<0.05 cm^-3) which is more consistent with other
evidence known about 0509-67.5. We therefore conclude that the bulk of the
continuum emission from 0509-67.5 has a non-thermal origin.Comment: 34 pages, 9 figures (1 color), accepted to ApJ (10 June 2004 issue);
correction made to calculation of magnetic field, small sentence change
pH-Independent, 520 mV Open-Circuit Voltages of Si/Methyl Viologen^(2+/+) Contacts Through Use of Radial n^+p-Si Junction Microwire Array Photoelectrodes
The effects of introducing an n^+-doped emitter layer have been evaluated for both planar Si photoelectrodes and for radial junction Si microwire-array photoelectrodes. In contact with the pH-independent, one-electron, outer-sphere, methyl viologen redox system (denoted MV^(2+/+)), both planar and wire array p-Si photoelectrodes yielded open-circuit voltages, V_(oc), that varied with the pH of the solution. The highest V_(oc) values were obtained at pH = 2.9, with V_(oc) = 0.53 V for planar p-Si electrodes and V_(oc) = 0.42 V for vapor−liquid−solid catalyzed p-Si microwire array samples, under 60 mW cm^(−2) of 808 nm illumination. Increases in the pH of the electrolyte produced a decrease in V_(oc) by approximately −44 mV/pH unit for planar electrodes, with similar trends observed for the Si microwire array electrodes. In contrast, introduction of a highly doped, n^+ emitter layer produced V_(oc) = 0.56 V for planar Si electrodes and V_(oc) = 0.52 V for Si microwire array electrodes, with the photoelectrode properties in each system being essentially independent of pH over six pH units (3 < pH < 9). Hence, formation of an n^+ emitter layer not only produced nearly identical photovoltages for planar and Si microwire array photoelectrodes, but decoupled the band energetics of the semiconductor (and hence the obtainable photovoltage) from the value of the redox potential of the solution. The formation of radial junctions on Si microwire arrays thus provides an approach to obtaining Si-based photoelectrodes with high-photovoltages that can be used for a variety of photoelectrochemical processes, including potentially the hydrogen evolution reaction, under various pH conditions, regardless of the intrinsic barrier height and flat-band properties of the Si/liquid contact
- …