1,443 research outputs found
SKA HI end2end simulation
The current status of the HI simulation efforts is presented, in which a self
consistent simulation path is described and basic equations to calculate array
sensitivities are given. There is a summary of the SKA Design Study (SKADS) sky
simulation and a method for implementing it into the array simulator is
presented. A short overview of HI sensitivity requirements is discussed and
expected results for a simulated HI survey are presented.Comment: 7 pages, 6 figues, need skads2009.cls file to late
Heat transport in ultra-thin dielectric membranes and bridges
Phonon modes and their dispersion relations in ultrathin homogenous
dielectric membranes are calculated using elasticity theory. The approach
differs from the previous ones by a rigorous account of the effect of the film
surfaces on the modes with different polarizations. We compute the heat
capacity of membranes and the heat conductivity of narrow bridges cut out of
such membranes, in a temperature range where the dimensions have a strong
influence on the results. In the high temperature regime we recover the
three-dimensional bulk results. However, in the low temperature limit the heat
capacity, , is proportional with (temperature), while the heat
conductivity, , of narrow bridges is proportional to , leading
to a thermal cut-off frequency .Comment: 6 pages and 6 figure
The Future of Incretin-Based Approaches for Neurodegenerative Diseases in Older Adults: Which to Choose? A Review of their Potential Efficacy and Suitability
The current treatment options for neurodegenerative diseases in older adults rely mainly on providing symptomatic relief. Yet, it remains imperative to identify agents that slow or halt disease progression to avoid the most disabling features often associated with advanced disease stages. A potential overlap between the pathological processes involved in diabetes and neurodegeneration has been established, raising the question of whether incretin-based therapies for diabetes may also be useful in treating neurodegenerative diseases in older adults. Here, we review the different agents that belong to this class of drugs (GLP-1 receptor agonists, dual/triple receptor agonists, DPP-4 inhibitors) and describe the data supporting their potential role in treating neurodegenerative conditions including Parkinson’s disease and Alzheimer’s disease. We further discuss whether there are any distinctive properties among them, particularly in the context of safety or tolerability and CNS penetration, that might facilitate their successful repurposing as disease-modifying drugs. Proof-of-efficacy data will obviously be of the greatest importance, and this is most likely to be demonstrable in agents that reach the central nervous system and impact on neuronal GLP-1 receptors. Additionally, however, the long-term safety and tolerability (including gastrointestinal side effects and unwanted weight loss) as well as the route of administration of this class of agents may also ultimately determine success and these aspects should be considered in prioritising which approaches to subject to formal clinical trial evaluations
Efficient Cosmological Parameter Estimation with Hamiltonian Monte Carlo
Traditional Markov Chain Monte Carlo methods suffer from low acceptance rate,
slow mixing and low efficiency in high dimensions. Hamiltonian Monte Carlo
resolves this issue by avoiding the random walk. Hamiltonian Monte Carlo (HMC)
is a Markov chain Monte Carlo (MCMC) technique built upon the basic principle
of Hamiltonian mechanics. Hamiltonian dynamics allows the chain to move along
trajectories of constant energy, taking large jumps in the parameter space with
relatively inexpensive computations. This new technique improves the acceptance
rate by a factor of 4 and boosts up the efficiency by at least a factor of D in
a D-dimensional parameter space. Therefor shorter chains will be needed for a
reliable parameter estimation comparing to a traditional MCMC chain yielding
the same performance. Besides that, the HMC is well suited for sampling from
non-Gaussian and curved distributions which are very hard to sample from using
the traditional MCMC methods. The method is very simple to code and can be
easily plugged into standard parameter estimation codes such as CosmoMC. In
this paper we demonstrate how the HMC can be efficiently used in cosmological
parameter estimation
Quantum statistical effects in nano-oscillator arrays
We have theoretically predicted the density of states(DOS), the low
temperature specific heat, and Brillouin scattering spectra of a large, free
standing array of coupled nano-oscillators. We have found significant gaps in
the DOS of 2D elastic systems, and predict the average DOS to be nearly
independent of frequency over a broad band f < 50GHz. At low temperatures, the
measurements probe the quantum statistics obeyed by rigid body modes of the
array and, thus, could be used to verify the quantization of the associated
energy levels. These states, in turn, involve center-of mass motion of large
numbers of atoms, N > 1.e14, and therefore such observations would extend the
domain in which quantum mechanics has been experimentally tested. We have found
the required measurement capability to carry out this investigation to be
within reach of current technology.Comment: 1 tex file, 3 figures, 1 bbl fil
Herschel-ATLAS: The angular correlation function of submillimetre galaxies at high and low redshift
Original article can be found at: http://www.aanda.org/ Copyright The European Southern ObservatoryWe present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 μm-selected sample we detect no significant clustering, consistent with the expectation that the 250 μm-selected sources are mostly normal galaxies at z 1. For our 350 μm and 500 μm-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z~2–3 we detect significant strong clustering, leading to an estimate of r0 ~ 7–11 h-1 Mpc. The slope of our clustering measurements is very steep, δ ~ 2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxies.Peer reviewe
A comparison of Eulerian and Lagrangian schemes for the simulation of an incompressible planar jet
In this investigation solutions have been obtained using an Eulerian time accurate fractional step Direct Numerical Simulation (DNS) scheme for a homogeneous incompressible planar jet and the results compared with those obtained using a Lagrangian Direct Simulation Monte-Carlo (DSMC) method. Comparisons were made of various flow features using plots constructed from instantaneous and ensemble averaged data. Details of the schemes, computational requirements and the accuracy obtained with each of the methods will be presented
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