16,007 research outputs found
Effects on Amorphous Silicon Photovoltaic Performance from High-temperature Annealing Pulses in Photovoltaic Thermal Hybrid Devices
There is a renewed interest in photovoltaic solar thermal (PVT) hybrid
systems, which harvest solar energy for heat and electricity. Typically, a main
focus of a PVT system is to cool the photovoltaic (PV) cells to improve the
electrical performance, however, this causes the thermal component to
under-perform compared to a solar thermal collector. The low temperature
coefficients of amorphous silicon (a-Si:H) allow for the PV cells to be
operated at higher temperatures and are a potential candidate for a more
symbiotic PVT system. The fundamental challenge of a-Si:H PV is light-induced
degradation known as the Staebler-Wronski effect (SWE). Fortunately, SWE is
reversible and the a-Si:H PV efficiency can be returned to its initial state if
the cell is annealed. Thus an opportunity exists to deposit a-Si:H directly on
the solar thermal absorber plate where the cells could reach the high
temperatures required for annealing.
In this study, this opportunity is explored experimentally. First a-Si:H PV
cells were annealed for 1 hour at 100\degreeC on a 12 hour cycle and for the
remaining time the cells were degraded at 50\degreeC in order to simulate
stagnation of a PVT system for 1 hour once a day. It was found that, when
comparing the cells after stabilization at normal 50\degreeC degradation, this
annealing sequence resulted in a 10.6% energy gain when compared to a cell that
was only degraded at 50\degreeC
The impact of the graduated driver licence scheme on road traffic accident youth mortality in New Zealand
This paper examines the impact of the introduction of New Zealand’s Graduated Driving Licence System (GDLS) on patterns of road traffic accident mortality amongst the young driving population from 1980 to 2001. Results show that the mortality rate has declined, but that rates in New Zealand are three times greater than in England and Wales and twice those of Scotland. When the data is adjusted to take account of differences in the minimum driving age, rates remain consistently higher in New Zealand and the proportional reduction in road traffic accident youth mortality is not significantly better than that experienced in Great Britain
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Possible crater-based pingos, paleolakes and periglacial landscapes in the high latitudes of Utopia Planitia, Mars
Simulation of associative learning with the replaced elements model
Associative learning theories can be categorised according to whether they treat the representation of stimulus compounds in an elemental or configural manner. Since it is clear that a simple elemental approach to stimulus representation is inadequate there have been several attempts to produce more elaborate elemental models. One recent approach, the Replaced Elements Model (Wagner, 2003), reproduces many results that have until recently been uniquely predicted by Pearce’s Configural Theory (Pearce, 1994). Although it is possible to simulate the Replaced Elements Model using “standard” simulation programs the generation of the correct stimulus representation is complex. The current paper describes a method for simulation of the Replaced Elements Model and presents the results of two example simulations that show differential predictions of Replaced Elements and Pearce’s Configural Theor
The Role of Projection in the Control of Bird Flocks
Swarming is a conspicuous behavioural trait observed in bird flocks, fish
shoals, insect swarms and mammal herds. It is thought to improve collective
awareness and offer protection from predators. Many current models involve the
hypothesis that information coordinating motion is exchanged between neighbors.
We argue that such local interactions alone are insufficient to explain the
organization of large flocks of birds and that the mechanism for the exchange
of long-ranged information necessary to control their density remains unknown.
We show that large flocks self-organize to the maximum density at which a
typical individual is still just able to see out of the flock in many
directions. Such flocks are marginally opaque - an external observer can also
just still see a substantial fraction of sky through the flock. Although
seemingly intuitive we show that this need not be the case; flocks could easily
be highly diffuse or entirely opaque. The emergence of marginal opacity
strongly constrains how individuals interact with each other within large
swarms. It also provides a mechanism for global interactions: An individual can
respond to the projection of the flock that it sees. This provides for faster
information transfer and hence rapid flock dynamics, another advantage over
local models. From a behavioural perspective it optimizes the information
available to each bird while maintaining the protection of a dense, coherent
flock.Comment: PNAS early edition published online at
http://www.pnas.org/cgi/doi/10.1073/pnas.140220211
A Comparison of Semi-Analytic and Smoothed Particle Hydrodynamics Galaxy Formation
We compare the statistical properties of galaxies found in two different
models of hierarchical galaxy formation: the semi-analytic model of Cole et al.
and the smoothed particle hydrodynamics (SPH) simulations of Pearce et al.
Using a `stripped-down' version of the semi-analytic model which mimics the
resolution of the SPH simulations and excludes physical processes not included
in them, we find that the two models produce an ensemble of galaxies with
remarkably similar properties, although there are some differences in the gas
cooling rates and in the number of galaxies that populate halos of different
mass. The full semi-analytic model, which has effectively no resolution limit
and includes a treatment of star formation and supernovae feedback, produces
somewhat different (but readily understandable) results. Agreement is
particularly good for the present-day global fractions of hot gas, cold dense
(i.e. galactic) gas and uncollapsed gas, for which the SPH and stripped-down
semi-analytic calculations differ by at most 25%. In the most massive halos,
the stripped-down semi-analytic model predicts, on the whole, up to 50% less
gas in galaxies than is seen in the SPH simulations. The two techniques
apportion this cold gas somewhat differently amongst galaxies in a given halo.
This difference can be tracked down to the greater cooling rate in massive
halos in the SPH simulation compared to the semi-analytic model. (abridged)Comment: 19 pages, 13 figures, to appear in MNRAS. Significantly extended to
explore galaxy progenitor distributions and behaviour of models at high
redshift
Peculiar Velocities of Galaxy Clusters
We investigate the peculiar velocities predicted for galaxy clusters by
theories in the cold dark matter family. A widely used hypothesis identifies
rich clusters with high peaks of a suitably smoothed version of the linear
density fluctuation field. Their peculiar velocities are then obtained by
extrapolating the similarly smoothed linear peculiar velocities at the
positions of these peaks. We test these ideas using large high resolution
N-body simulations carried out within the Virgo supercomputing consortium. We
find that at early times the barycentre of the material which ends up in a rich
cluster is generally very close to a high peak of the initial density field.
Furthermore the mean peculiar velocity of this material agrees well with the
linear value at the peak. The late-time growth of peculiar velocities is,
however, systematically underestimated by linear theory. At the time clusters
are identified we find their rms peculiar velocity to be about 40% larger than
predicted. Nonlinear effects are particularly important in superclusters. These
systematics must be borne in mind when using cluster peculiar velocities to
estimate the parameter combination .Comment: 8 pages, 4 figures; submitted to MNRA
Overcoming supply disruptions during pandemics by utilizing found hardware for open source gentle ventilation
This article details the design of an open source emergency gentle ventilator (gentle-vent) framework that can be used in periods of scarcity. Although it is not a medical device, the system utilizes a wide range of commonly-available components that are combined using basic electronics skills to achieve the desired performance. The main function of the gentle-vent is to generate a calibrated pressure wave at the pump to provide support to the patient\u27s breathing. Each gentle-vent permutation was tested using a DIY manometer as it would be utilized in the field in low-resource settings and validated with an open source VentMon. The most rudimentary implementation costs less than $40
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