840 research outputs found
Learning in stochastic neural networks for constraint satisfaction problems
Researchers describe a newly-developed artificial neural network algorithm for solving constraint satisfaction problems (CSPs) which includes a learning component that can significantly improve the performance of the network from run to run. The network, referred to as the Guarded Discrete Stochastic (GDS) network, is based on the discrete Hopfield network but differs from it primarily in that auxiliary networks (guards) are asymmetrically coupled to the main network to enforce certain types of constraints. Although the presence of asymmetric connections implies that the network may not converge, it was found that, for certain classes of problems, the network often quickly converges to find satisfactory solutions when they exist. The network can run efficiently on serial machines and can find solutions to very large problems (e.g., N-queens for N as large as 1024). One advantage of the network architecture is that network connection strengths need not be instantiated when the network is established: they are needed only when a participating neural element transitions from off to on. They have exploited this feature to devise a learning algorithm, based on consistency techniques for discrete CSPs, that updates the network biases and connection strengths and thus improves the network performance
Convectively driven shear and decreased heat flux
We report on direct numerical simulations of two-dimensional, horizontally
periodic Rayleigh-B\'enard convection, focusing on its ability to drive
large-scale horizontal flow that is vertically sheared. For the Prandtl numbers
() between 1 and 10 simulated here, this large-scale shear can be induced
by raising the Rayleigh number () sufficiently, and we explore the
resulting convection for up to . When present in our simulations,
the sheared mean flow accounts for a large fraction of the total kinetic
energy, and this fraction tends towards unity as . The shear helps
disperse convective structures, and it reduces vertical heat flux; in parameter
regimes where one state with large-scale shear and one without are both stable,
the Nusselt number of the state with shear is smaller and grows more slowly
with . When the large-scale shear is present with , the
convection undergoes strong global oscillations on long timescales, and heat
transport occurs in bursts. Nusselt numbers, time-averaged over these bursts,
vary non-monotonically with for . When the shear is present with
, the flow does not burst, and convective heat transport is
sustained at all times. Nusselt numbers then grow roughly as powers of ,
but the growth rates are slower than any previously reported for
Rayleigh-B\'enard convection without large-scale shear. We find the Nusselt
numbers grow proportionally to when and to when
. Analogies with tokamak plasmas are described.Comment: 25 pages, 12 figures, 5 video
Assimilation of nearly turbulent Rayleigh-B\'enard flow through vorticity or local circulation measurements: a computational study
We introduce a continuous (downscaling) data assimilation algorithm for the
2D B\'enard convection problem using vorticity or local circulation
measurements only. In this algorithm, a nudging term is added to the vorticity
equation to constrain the model. Our numerical results indicate that the
approximate solution of the algorithm is converging to the unknown reference
solution (vorticity and temperature) corresponding to the measurements of the
2D B\'enard convection problem when only spatial coarse-grain measurements of
vorticity are assimilated. Moreover, this convergence is realized using data
which is much more coarse than the resolution needed to satisfy rigorous
analytical estimates
A Comparison of Turbulent Thermal Convection Between Conditions of Constant Temperature and Constant Flux
We report the results of high resolution direct numerical simulations of
two-dimensional Rayleigh-B\'enard convection for Rayleigh numbers up to
\Ra=10^{10} in order to study the influence of temperature boundary
conditions on turbulent heat transport. Specifically, we considered the extreme
cases of fixed heat flux (where the top and bottom boundaries are poor thermal
conductors) and fixed temperature (perfectly conducting boundaries). Both cases
display identical heat transport at high Rayleigh numbers fitting a power law
\Nu \approx 0.138 \times \Ra^{.285} with a scaling exponent indistinguishable
from above \Ra = 10^{7}. The overall flow dynamics for both
scenarios, in particular the time averaged temperature profiles, are also
indistinguishable at the highest Rayleigh numbers. The findings are compared
and contrasted with results of recent three-dimensional simulations.Comment: 4 page, two column RevTex4 format, 5 figure
Tendering for low cost generics in Australia
An Australian federal government committee recently proposed, as a cost-saving measure, the introduction of sealed-bid competitive tendering to exclusively supply the Pharmaceutical Benefits Scheme with specific generic medicines. A similar plan involved an open tender to supply generic products below a government set price, also linked with a reduced patient co-payment as an incentive. These proposals represented an opportunity to encourage the price of generic pharmaceuticals to move closer to the marginal cost of production—a process that could be subsequently applied to innovative (or brand-name) patented medicines in a therapeutic class with many competitors. This article examines these tendering proposals, particularly in relation to the potential for increased involvement of generic pharmaceutical manufacturers in the Australian market.<br /
Dynamical Confirmation of SDSS Weak Lensing Scaling Laws
Galaxy masses can be estimated by a variety of methods; each applicable in
different circumstances, and each suffering from different systematic
uncertainties. Confirmation of results obtained by one technique with analysis
by another is particularly important. Recent SDSS weak lensing measurements of
the projected-mass correlation function reveal a linear relation between galaxy
luminosities and the depth of their dark matter halos (measured on 260 \hinv
kpc scales). In this work we use an entirely independent dynamical method to
confirm these results. We begin by assembling a sample of 618 relatively
isolated host galaxies, surrounded by a total of 1225 substantially fainter
satellites. We observe the mean dynamical effect of these hosts on the motions
of their satellites by assembling velocity difference histograms. Dividing the
sample by host properties, we find significant variations in satellite velocity
dispersion with host luminosity. We quantify these variations using a simple
dynamical model, measuring \mtsd a dynamical mass within 260 \hinv kpc. The
appropriateness of this mass reconstruction is checked by conducting a similar
analysis within an N-body simulation. Comparison between the dynamical and
lensing mass-to-light scalings shows reasonable agreement, providing some
quantitative confirmation for the lensing results.Comment: 7 pages, 3 figures, accepted for publication in ApJ Letter
Effects of Topically Applied Acitretin in Reconstructed Human Epidermis and the Rhino Mouse
Oral acitretin is currently indicated for the treatment of severe psoriasis in adults, but its use is limited by systemic side effects and teratogenicity. Topical administration of acitretin may lessen the risk of systemic toxicity while increasing local bioavailability in the skin. The effects of topical acitretin on reconstructed human epidermis (RHE) and Rhino mice were investigated and compared to those of currently marketed topical retinoids: tretinoin and tazarotene. In acitretin-treated RHE cultures, there was a reduction in keratohyalin granules and filaggrin expression in the stratum granulosum, a loss of keratin 10 expression in the stratum spinosum, and an increase in keratin 19 expression in all viable cell layers. All retinoids showed similar signs of activity in RHE cultures. Furthermore, the release of pro-inflammatory cytokines IL-1α and IL-8 in RHE cultures was less pronounced with acitretin compared to tretinoin- and tazarotene-containing formulations, suggesting that acitretin may be less irritating. In Rhino mice, acitretin induced a local, dose-dependent reduction in utricle diameter after seven daily dermal doses. A similar effect was observed in tretinoin- and tazarotene-treated mice. Our data suggest that topical application of acitretin may have a therapeutic benefit in the local management of keratinization disorders
Short paroxysms of impure auricular flutter probably induced by normal sinus beats
Electrocardiograms of a patient with transient auricular fibrillation and flutter and complete A-V heart block are presented. Further tracings, taken immediately after the resumption of normal sinus activity, show short paroxysms of what is believed to be impure flutter induced by normal sinus beats. Some experimental evidence tending to support this view is mentioned.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32598/1/0000738.pd
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