9,051 research outputs found
Public health and landfill sites
Landfill management is a complex discipline, requiring very high levels of organisation, and considerable investment. Until the early 1990âs most Irish landfill sites were not managed to modern standards. Illegal landfill sites are,
of course, usually not managed at all. Landfills are very active. The traditional idea of âput it in the ground and forget about itâ is entirely misleading. There is a lot of chemical and biological activity underground. This produces complex changes in the chemistry of the landfill, and of the emissions from the site.
The main emissions of concern are landfill gases and contaminated water (which is known as leachate). Both of these emissions have complex and changing chemical compositions, and both depend critically on what has been
put into the landfill. The gases spread mainly through the atmosphere, but also through the soil, while the leachate (the water) spreads through surface waters and the local groundwater. Essentially all unmanaged landfills will discharge large volumes of leachate into the local groundwater. In sites where the waste accepted has been
properly regulated, and where no hazardous wastes are present, there is a lot known about the likely composition of this leachate and there is some knowledge of its likely biological and health effects. This is not the case for
poorly regulated sites, where the composition of the waste accepted is unknown.
It is possible to monitor the emissions from landfills, and to reduce some of the adverse health and environmental effects of these. These emissions, and hence the possible health effects, depend greatly on the content of the landfill, and on the details of the local geology and landscape.
There is insufficient evidence to demonstrate a clear link between cancers
and exposure to landfill, however, it is noted that there may be an association
with adverse birth outcomes such as low birth weight and birth defects. It
should be noted, however, that modern landfills, run in strict accordance with
standard operation procedures, would have much less impact on the health of
residents living in proximity to the site
The Specific Heat of a Ferromagnetic Film.
We analyze the specific heat for the vector model on a -dimensional
film geometry of thickness using ``environmentally friendly''
renormalization. We consider periodic, Dirichlet and antiperiodic boundary
conditions, deriving expressions for the specific heat and an effective
specific heat exponent, \alpha\ef. In the case of , for , by
matching to the exact exponent of the two dimensional Ising model we capture
the crossover for \xi_L\ra\infty between power law behaviour in the limit
{L\over\xi_L}\ra\infty and logarithmic behaviour in the limit
{L\over\xi_L}\ra0 for fixed , where is the correlation length in
the transverse dimensions.Comment: 21 pages of Plain TeX. Postscript figures available upon request from
[email protected]
Training a Spiking Neural Network with Equilibrium Propagation
Backpropagation is almost universally used to train artificial neural networks. However, there are several reasons that backpropagation could not be plausibly implemented by biological neurons. Among these are the facts that (1) biological neurons appear to lack any mechanism for sending gradients backwards across synapses, and (2) biological âspikingâ neurons emit binary signals, whereas back-propagation requires that neurons communicate continuous values between one another. Recently, Scellier and Bengio [2017], demonstrated an alternative to backpropagation, called Equilibrium Propagation, wherein gradients are implicitly computed by the dynamics of the neural network, so that neurons do not need an internal mechanism for backpropagation of gradients. This provides an interesting solution to problem (1). In this paper, we address problem (2) by proposing a way in which Equilibrium Propagation can be implemented with neurons which are constrained to just communicate binary values at each time step. We show that with appropriate step-size annealing, we can converge to the same fixed-point as a real-valued neural network, and that with predictive coding, we can make this convergence much faster. We demonstrate that the resulting model can be used to train a spiking neural network using the update scheme from Equilibrium propagation
The Influence of Thermal Pressure on Equilibrium Models of Hypermassive Neutron Star Merger Remnants
The merger of two neutron stars leaves behind a rapidly spinning hypermassive
object whose survival is believed to depend on the maximum mass supported by
the nuclear equation of state, angular momentum redistribution by
(magneto-)rotational instabilities, and spindown by gravitational waves. The
high temperatures (~5-40 MeV) prevailing in the merger remnant may provide
thermal pressure support that could increase its maximum mass and, thus, its
life on a neutrino-cooling timescale. We investigate the role of thermal
pressure support in hypermassive merger remnants by computing sequences of
spherically-symmetric and axisymmetric uniformly and differentially rotating
equilibrium solutions to the general-relativistic stellar structure equations.
Using a set of finite-temperature nuclear equations of state, we find that hot
maximum-mass critically spinning configurations generally do not support larger
baryonic masses than their cold counterparts. However, subcritically spinning
configurations with mean density of less than a few times nuclear saturation
density yield a significantly thermally enhanced mass. Even without decreasing
the maximum mass, cooling and other forms of energy loss can drive the remnant
to an unstable state. We infer secular instability by identifying approximate
energy turning points in equilibrium sequences of constant baryonic mass
parametrized by maximum density. Energy loss carries the remnant along the
direction of decreasing gravitational mass and higher density until instability
triggers collapse. Since configurations with more thermal pressure support are
less compact and thus begin their evolution at a lower maximum density, they
remain stable for longer periods after merger.Comment: 20 pages, 12 figures. Accepted for publication in Ap
Candidates for giant lobes projecting from the LBV stars P Cygni and R 143
Deep, wide-field, continuum-subtracted, images in the light of the
Halpha+[NII] 6548 & 6584 A and [O III] 5007 A nebular emission lines have been
obtained of the environment of the Luminous Blue Variable (LBV) star P Cygni. A
previously discovered, receding, nebulous filament along PA 50 deg has now been
shown to extend up to 12' from this star. Furthermore, in the light of [O III]
5007 A, a southern counterpart is discovered as well as irregular filaments on
the opposite side of P Cygni.
Line profiles from this nebulous complex indicate that this extended
nebulosity is similar to that associated with middle-aged supernova remnants.
However, there are several indications that it has originated in P Cygni and is
not just a chance superposition along the same sight-line. This possibility is
explored here and comparison is made with a new image of the LBV star R 143 in
the LMC from which similar filaments appear to project.
The dynamical age of the P Cygni giant lobe of ~5x10^{4} yr is consistent
with both the predicted and observed durations of the LBV phases of 50M stars
after they have left the main sequence. Its irregular shape may have been
determined by the cavity formed in the ambient gas by the energetic wind of the
star, and shaped by a dense torus, when on the main sequence.
The proper motion and radial velocity of P Cygni, with respect to its local
environment, could explain the observed angular and kinematical shifts of the
star compared with the giant lobe.Comment: 7 pages, 3 figures, accepted for publication in A&
Relaxation and Localization in Interacting Quantum Maps
We quantise and study several versions of finite multibaker maps. Classically
these are exactly solvable K-systems with known exponential decay to global
equilibrium. This is an attempt to construct simple models of relaxation in
quantum systems. The effect of symmetries and localization on quantum transport
is discussed.Comment: 32 pages. LaTex file. 9 figures, not included. For figures send mail
to first author at '[email protected]
Modular Invariance of Finite Size Corrections and a Vortex Critical Phase
We analyze a continuous spin Gaussian model on a toroidal triangular lattice
with periods and where the spins carry a representation of the
fundamental group of the torus labeled by phases and . We find the
{\it exact finite size and lattice corrections}, to the partition function ,
for arbitrary mass and phases . Summing over phases gives
the corresponding result for the Ising model. The limits and
do not commute. With the model exhibits a {\it vortex
critical phase} when at least one of the is non-zero. In the continuum or
scaling limit, for arbitrary , the finite size corrections to are
{\it modular invariant} and for the critical phase are given by elliptic theta
functions. In the cylinder limit the ``cylinder charge''
is a non-monotonic function of that ranges from
for to zero for .Comment: 12 pages of Plain TeX with two postscript figure insertions called
torusfg1.ps and torusfg2.ps which can be obtained upon request from
[email protected]
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