11,113 research outputs found
The Virtual Runner Learning Game
A learning game has been developed which allows learners to study and learn about the significance of three important variables in human physiology (lactate, glycogen, and hydration) and their influence on sports performance during running. The player can control the speed of the runner, and as a consequence the resulting physiological processes are simulated in real-time. The performance degradation of the runner due to these processes requires that different strategies for pacing the running speed are applied by the player, depending on the total length of the run. The game has been positively evaluated in a real learning context of academic physiology teaching
RS Ophiuchi: Thermonuclear Explosion or Disc Instability?
Sokoloski et al (2008) have recently reported evidence that the recurrent
nova RS Ophiuchi produced a pair of highly collimated radio jets within days of
its 2006 outburst. This suggests that an accretion disc must be present during
the outburst. However in the standard picture of recurrent novae as
thermonuclear events, any such disc must be expelled from the white dwarf
vicinity, as the nuclear energy yield greatly exceeds its binding energy. We
suggest instead that the outbursts of RS Oph are thermal--viscous instabilities
in a disc irradiated by the central accreting white dwarf. The distinctive
feature of RS Oph is the very large size of its accretion disc. Given this, it
fits naturally into a consistent picture of systems with unstable accretion
discs. This picture explains the presence and speed of the jets, the brightness
and duration of the outburst, and its rise time and linear decay, as well as
the faintness of the quiescence. By contrast, the hitherto standard picture of
recurrent thermonuclear explosions has a number of severe difficulties. These
include the presence of jets, the faintness of quiescence, and the fact the the
accretion disc must be unstable unless it is far smaller than any reasonable
estimate.Comment: MNRAS, in pres
Addressing the speed-accuracy simulation trade-off for adaptive spiking neurons
The adaptive leaky integrate-and-fire (ALIF) model is fundamental within
computational neuroscience and has been instrumental in studying our brains
. Due to the sequential nature of simulating these neural
models, a commonly faced issue is the speed-accuracy trade-off: either
accurately simulate a neuron using a small discretisation time-step (DT), which
is slow, or more quickly simulate a neuron using a larger DT and incur a loss
in simulation accuracy. Here we provide a solution to this dilemma, by
algorithmically reinterpreting the ALIF model, reducing the sequential
simulation complexity and permitting a more efficient parallelisation on GPUs.
We computationally validate our implementation to obtain over a
training speedup using small DTs on synthetic benchmarks. We also obtained a
comparable performance to the standard ALIF implementation on different
supervised classification tasks - yet in a fraction of the training time.
Lastly, we showcase how our model makes it possible to quickly and accurately
fit real electrophysiological recordings of cortical neurons, where very fine
sub-millisecond DTs are crucial for capturing exact spike timing.Comment: 15 pages, 5 figure
Amplification of Primordial Magnetic Fields by Anisotropic Gravitational Collapse
If a magnetic field is frozen into a plasma that undergoes spherical
compression then the magnetic field B varies with the plasma density \rho
according to B \propto \rho^{2/3}. In the gravitational collapse of
cosmological density perturbations, however, quasi-spherical evolution is very
unlikely. In anisotropic collapses the magnetic field can be a much steeper
function of gas density than in the isotropic case. We investigate the
distribution of amplifications in realistic gravitational collapses from
Gaussian initial fluctuations using the Zel'dovich approximation. Representing
our results using a relation of the form B\propto \rho^{\alpha}, we show that
the median value of \alpha can be much larger than the \alpha=2/3 resulting
from spherical collapse, even if there is no initial correlation between
magnetic field and principal collapse directions. These analytic arguments go
some way towards understanding the results of numerical simulations.Comment: 9 pages, 4 figures. Submitted to MNRA
Hierarchical temporal prediction captures motion processing along the visual pathway
Visual neurons respond selectively to features that become increasingly complex from the eyes to the cortex. Retinal neurons prefer flashing spots of light, primary visual cortical (V1) neurons prefer moving bars, and those in higher cortical areas favor complex features like moving textures. Previously, we showed that V1 simple cell tuning can be accounted for by a basic model implementing temporal prediction – representing features that predict future sensory input from past input (Singer et al., 2018). Here, we show that hierarchical application of temporal prediction can capture how tuning properties change across at least two levels of the visual system. This suggests that the brain does not efficiently represent all incoming information; instead, it selectively represents sensory inputs that help in predicting the future. When applied hierarchically, temporal prediction extracts time-varying features that depend on increasingly high-level statistics of the sensory input
XMM-Newton and optical follow-up observations of three new polars from the Sloan Digital Sky Survey
We report follow-up XMM-Newton and optical observations of three new polars
found in the Sloan Digital Sky Survey. Simple modeling of the X-ray spectra,
and consideration of the details of the X-ray and optical lightcurves
corroborate the polar nature of these three systems and provide further
insights into their accretion characteristics. During the XMM-Newton
observation of SDSS J072910.68+365838.3, X-rays are undetected apart from a
probable flare event, during which we find both the typical hard X-ray
bremsstrahlung component and a very strong line O VII (E=0.57 keV), but no
evidence of a soft blackbody contribution. In SDSS J075240.45+362823.2 we
identify an X-ray eclipse at the beginning of the observation, roughly in phase
with the primary minimum of the optical broad band curve. The X-ray spectra
require the presence of both hard and soft X-ray components, with their
luminosity ratio consistent with that found in other recent XMM-Newton results
on polars. Lastly, SDSS J170053.30+400357.6 appears optically as a very typical
polar, however its large amplitude optical modulation is 180 degrees out of
phase with the variation in our short X-ray lightcurve.Comment: 9 pages, 9 figures, accepted for publication in the ApJ (January
2005
Theoretical and numerical studies of chemisorption on a line with precursor layer diffusion
We consider a model for random deposition of monomers on a line with
extrinsic precursor states. As the adsorbate coverage increases, the system
develops non-trivial correlations due to the diffusion mediated deposition
mechanism. In a numeric simulation, we study various quantities describing the
evolution of the island structure. We propose a simple, self-consistent theory
which incorporates pair correlations. The results for the correlations, island
density number, average island size and probabilities of island nucleation,
growth and coagulation show good agreement with the simulation data.Comment: 17 pages(LaTeX), 11 figures(1 PS file, uuencoded), submmited to Phys.
Rev.
Dodging the crisis of folding proteins with knots
Proteins with nontrivial topology, containing knots and slipknots, have the
ability to fold to their native states without any additional external forces
invoked. A mechanism is suggested for folding of these proteins, such as YibK
and YbeA, which involves an intermediate configuration with a slipknot. It
elucidates the role of topological barriers and backtracking during the folding
event. It also illustrates that native contacts are sufficient to guarantee
folding in around 1-2% of the simulations, and how slipknot intermediates are
needed to reduce the topological bottlenecks. As expected, simulations of
proteins with similar structure but with knot removed fold much more
efficiently, clearly demonstrating the origin of these topological barriers.
Although these studies are based on a simple coarse-grained model, they are
already able to extract some of the underlying principles governing folding in
such complex topologies.Comment: 29 pages, 11 figures, 1 tabl
The C-Band All-Sky Survey: Instrument design, status, and first-look data
The C-Band All-Sky Survey (C-BASS) aims to produce sensitive, all-sky maps of
diffuse Galactic emission at 5 GHz in total intensity and linear polarization.
These maps will be used (with other surveys) to separate the several
astrophysical components contributing to microwave emission, and in particular
will allow an accurate map of synchrotron emission to be produced for the
subtraction of foregrounds from measurements of the polarized Cosmic Microwave
Background. We describe the design of the analog instrument, the optics of our
6.1 m dish at the Owens Valley Radio Observatory, the status of observations,
and first-look data.Comment: 10 pages, 11 figures, published in Proceedings of SPIE MIllimeter,
Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy V
(2010), Vol. 7741, 77411I-1 - 77411I-1
Pressure induced high-spin to low-spin transition in FeS evidenced by x-ray emission spectroscopy
We report the observation of the pressure-induced high-spin to low-spin
transition in FeS using new high-pressure synchrotron x-ray emission
spectroscopy techniques. The transition is evidenced by the disappearance of
the low-energy satellite in the Fe K emission spectrum of FeS. Moreover,
the phase transition is reversible and closely related to the structural phase
transition from a manganese phosphide-like phase to a monoclinic phase. The
study opens new opportunities for investigating the electronic properties of
materials under pressure.Comment: ReVTeX, 4 pages, 3 figures inserted with epsfig. minor modifications
before submission to PR
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