37,641 research outputs found
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Higher education academic salaries in the UK
It is widely believed that higher education academic salaries are too low, and that this may lead to a ‘brain drain’ and also lower quality in higher education, as universities fail to attract the ‘brightest and the best’. We compare the salaries of Higher Education teaching professionals in the UK with those of other comparable professionals. We compare academic salaries to a range of occupational groupings that one might view as similar, in terms of unobserved characteristics, to academics. We conclude that HE teaching professionals earn lower earnings than most public sector graduates and do particularly poorly compared to most other comparable professionals. In particular, academic earnings compare poorly to those in the legal professions, consultant physicians and dental practitioners (across both the public and private sectors). On the other hand, some public sector workers do worse than HE academics, e.g. FE teachers
Optimal Prandtl number for heat transfer in rotating Rayleigh-Benard convection
Numerical data for the heat transfer as a function of the Prandtl (Pr) and
Rossby (Ro) numbers in turbulent rotating Rayleigh-Benard convection are
presented for Rayleigh number Ra = 10^8. When Ro is fixed the heat transfer
enhancement with respect to the non-rotating value shows a maximum as function
of Pr. This maximum is due to the reduced efficiency of Ekman pumping when Pr
becomes too small or too large. When Pr becomes small, i.e. for large thermal
diffusivity, the heat that is carried by the vertical vortices spreads out in
the middle of the cell, and Ekman pumping thus becomes less efficient. For
higher Pr the thermal boundary layers (BLs) are thinner than the kinetic BLs
and therefore the Ekman vortices do not reach the thermal BL. This means that
the fluid that is sucked into the vertical vortices is colder than for lower Pr
which limits the efficiency of the upwards heat transfer.Comment: 5 pages, 6 figure
Heat transport and flow structure in rotating Rayleigh-B\'enard convection
Here we summarize the results from our direct numerical simulations (DNS) and
experimental measurements on rotating Rayleigh-B\'enard (RB) convection. Our
experiments and simulations are performed in cylindrical samples with an aspect
ratio \Gamma varying from 1/2 to 2. Here \Gamma=D/L, where D and L are the
diameter and height of the sample, respectively. When the rotation rate is
increased, while a fixed temperature difference between the hot bottom and cold
top plate is maintained, a sharp increase in the heat transfer is observed
before the heat transfer drops drastically at stronger rotation rates. Here we
focus on the question of how the heat transfer enhancement with respect to the
non-rotating case depends on the Rayleigh number Ra, the Prandtl number Pr, and
the rotation rate, indicated by the Rossby number Ro. Special attention will be
given to the influence of the aspect ratio on the rotation rate that is
required to get heat transport enhancement. In addition, we will discuss the
relation between the heat transfer and the large scale flow structures that are
formed in the different regimes of rotating RB convection and how the different
regimes can be identified in experiments and simulations.Comment: 12 pages, 10 figure
A concurrent precursor inflow method for Large Eddy Simulations and applications to finite length wind farms
In order to enable simulations of developing wind turbine array boundary
layers with highly realistic inflow conditions a concurrent precursor method
for Large Eddy Simulations is proposed. In this method we consider two domains
simultaneously, i.e. in one domain a turbulent Atmospheric Boundary Layer (ABL)
without wind turbines is simulated in order to generate the turbulent inflow
conditions for a second domain in which the wind turbines are placed. The
benefit of this approach is that a) it avoids the need for large databases in
which the turbulent inflow conditions are stored and the correspondingly slow
I/O operations and b) we are sure that the simulations are not negatively
affected by statically swept fixed inflow fields or synthetic fields lacking
the proper ABL coherent structures. Sample applications are presented, in
which, in agreement with field data a strong decrease of the power output of
downstream wind-turbines with respect to the first row of wind-turbines is
observed for perfectly aligned inflow.Comment: 13 pages, 5 figure
Radial boundary layer structure and Nusselt number in Rayleigh-Benard convection
Results from direct numerical simulations for three dimensional
Rayleigh-Benard convection in a cylindrical cell of aspect ratio 1/2 and Pr=0.7
are presented. They span five decades of Ra from to . Good numerical resolution with grid spacing Kolmogorov
scale turns out to be crucial to accurately calculate the Nusselt number, which
is in good agreement with the experimental data by Niemela et al., Nature, 404,
837 (2000). In underresolved simulations the hot (cold) plumes travel further
from the bottom (top) plate than in the fully resolved case, because the
thermal dissipation close to the sidewall (where the grid cells are largest) is
insufficient. We compared the fully resolved thermal boundary layer profile
with the Prandtl-Blasius profile. We find that the boundary layer profile is
closer to the Prandtl Blasius profile at the cylinder axis than close to the
sidewall, due to rising plumes in that region.Comment: 10 pages, 6 figure
Sidewall effects in Rayleigh-B\'enard convection
We investigate the influence of the temperature boundary conditions at the
sidewall on the heat transport in Rayleigh-B\'enard (RB) convection using
direct numerical simulations. For relatively low Rayleigh numbers Ra the heat
transport is higher when the sidewall is isothermal, kept at a temperature
(where is the temperature difference between the
horizontal plates and the temperature of the cold plate), than when the
sidewall is adiabatic. The reason is that in the former case part of the heat
current avoids the thermal resistance of the fluid layer by escaping through
the sidewall that acts as a short-circuit. For higher Ra the bulk becomes more
isothermal and this reduces the heat current through the sidewall. Therefore
the heat flux in a cell with an isothermal sidewall converges to the value
obtained with an adiabatic sidewall for high enough Ra ().
However, when the sidewall temperature deviates from the heat
transport at the bottom and top plates is different from the value obtained
using an adiabatic sidewall. In this case the difference does not decrease with
increasing Ra thus indicating that the ambient temperature of the experimental
apparatus can influence the heat transfer. A similar behavior is observed when
only a very small sidewall region close to the horizontal plates is kept
isothermal, while the rest of the sidewall is adiabatic. The reason is that in
the region closest to the horizontal plates the temperature difference between
the fluid and the sidewall is highest. This suggests that one should be careful
with the placement of thermal shields outside the fluid sample to minimize
spurious heat currents.Comment: 27 pages, 16 figure
X-ray absorbed QSOs and the QSO evolutionary sequence
Unexpected in the AGN unified scheme, there exists a population of broad-line
z~2 QSOs which have heavily absorbed X-ray spectra. These objects constitute
10% of the population at luminosities and redshifts characteristic of the main
producers of QSO luminosity in the Universe. Our follow up observations in the
submm show that these QSOs are often embedded in ultraluminous starburst
galaxies, unlike most QSOs at the same redshifts and luminosities. The
radically different star formation properties between the absorbed and
unabsorbed QSOs implies that the X-ray absorption is unrelated to the torus
invoked in AGN unification schemes. Instead, these results suggest that the
objects represent a transitional phase in an evolutionary sequence relating the
growth of massive black holes to the formation of galaxies. The most puzzling
question about these objects has always been the nature of the X-ray absorber.
We present our study of the X-ray absorbers based on deep (50-100ks) XMM-Newton
spectroscopy. We show that the absorption is most likely due to a dense ionised
wind driven by the QSO. This wind could be the mechanism by which the QSO
terminates the star formation in the host galaxy, and ends the supply of
accretion material, to produce the present day black hole/spheroid mass ratio.Comment: 4 pages, to appear in conference proceedings "Studying Galaxy
Evolution with Spitzer and Herschel
Estimating population cardinal health state valuation models from individual ordinal (rank) health state preference data
Ranking exercises have routinely been used as warm-up exercises within health state valuation surveys. Very little use has been made of the information obtained in this process. Instead, research has focussed upon the analysis of health state valuation data obtained using the visual analogue scale, standard gamble and time trade off methods.
Thurstone’s law of comparative judgement postulates a stable relationship between ordinal and cardinal preferences, based upon the information provided by pairwise choices. McFadden proposed that this relationship could be modelled by estimating conditional logistic regression models where alternatives had been ranked. In this paper we report the estimation of such models for the Health Utilities Index Mark 2 and the SF-6D. The results are compared to the conventional regression models estimated from standard gamble data, and to the observed mean standard gamble health state valuations.
For both the HUI2 and the SF-6D, the models estimated using rank data are broadly comparable to the models estimated on standard gamble data and the predictive performance of these models is close to that of the standard gamble models. Our research indicates that rank data has the potential to provide useful insights into community health state preferences. However, important questions remain
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