7,728 research outputs found
Generalised additive multiscale wavelet models constructed using particle swarm optimisation and mutual information for spatio-temporal evolutionary system representation
A new class of generalised additive multiscale wavelet models (GAMWMs) is introduced for high dimensional spatio-temporal evolutionary (STE) system identification. A novel two-stage hybrid learning scheme is developed for constructing such an additive wavelet model. In the first stage, a new orthogonal projection pursuit (OPP) method, implemented using a particle swarm optimisation(PSO) algorithm, is proposed for successively augmenting an initial coarse wavelet model, where relevant parameters of the associated wavelets are optimised using a particle swarm optimiser. The resultant network model, obtained in the first stage, may however be a redundant model. In the second stage, a forward orthogonal regression (FOR) algorithm, implemented using a mutual information method, is then applied to refine and improve the initially constructed wavelet model. The proposed two-stage hybrid method can generally produce a parsimonious wavelet model, where a ranked list of wavelet functions, according to the capability of each wavelet to represent the total variance in the desired system output signal is produced. The proposed new modelling framework is applied to real observed images, relative to a chemical reaction exhibiting a spatio-temporal evolutionary behaviour, and the associated identification results show that the new modelling framework is applicable and effective for handling high dimensional identification problems of spatio-temporal evolution sytems
Effective thermal conductivity determination for low-density insulating materials
That nonlinear least squares can be used to determine effective thermal conductivity was demonstrated, and a method for assessing the relative error associated with these predicted values was provided. The differences between dynamic and static determination of effective thermal conductivity of low-density materials that transfer heat by a combination of conduction, convection, and radiation were discussed
Mapping of interstellar clouds with infrared light scattered from dust: TMC-1N
Mapping of near-infrared (NIR) scattered light is a recent method for the
study of interstellar clouds, complementing other, more commonly used methods,
like dust emission and extinction. Our goal is to study the usability of this
method on larger scale, and compare the properties of a filament using NIR
scattering and other methods. We also study the radiation field and differences
in grain emissivity between diffuse and dense areas. We have used scattered J,
H, and K band surface brightness WFCAM-observations to map filament TMC-1N in
Taurus, covering an area of 1dx1d corresponding to ~(2.44 pc)^2. We have
converted the data into optical depth and compared the results with NIR
extinction and Herschel observations of submm dust emission. We see the
filament in scattered light in all three NIR bands. We note that our WFCAM
observations in TMC-1N show notably lower intensity than previous results in
Corona Australis using the same method. We show that 3D radiative transfer
simulations predict similar scattered surface brightness levels as seen in the
observations. However, changing the assumptions about the background can change
the results of simulations notably. We derive emissivity by using optical depth
in the J band as an independent tracer of column density. We obtain opacity
sigma(250um) values 1.7-2.4x10^-25 cm^2/H, depending on assumptions of the
extinction curve, which can change the results by over 40%. These values are
twice as high as obtained for diffuse areas, at the lower limit of earlier
results for denser areas. We show that NIR scattering can be a valuable tool in
making high resolution maps. We conclude, however, that NIR scattering
observations can be complicated, as the data can show relatively low-level
artefacts. This suggests caution when planning and interpreting the
observations.Comment: abstract shortened and figures reduced for astrop
Solvent mediated interactions close to fluid-fluid phase separation: microscopic treatment of bridging in a soft core fluid
Using density functional theory we calculate the density profiles of a binary
solvent adsorbed around a pair of big solute particles. All species interact
via repulsive Gaussian potentials. The solvent exhibits fluid-fluid phase
separation and for thermodynamic states near to coexistence the big particles
can be surrounded by a thick adsorbed `wetting' film of the coexisting solvent
phase. On reducing the separation between the two big particles we find there
can be a `bridging' transition as the wetting films join to form a fluid
bridge. The potential between the two big particles becomes long ranged and
strongly attractive in the bridged configuration. Within our mean-field
treatment the bridging transition results in a discontinuity in the solvent
mediated force. We demonstrate that accounting for the phenomenon of bridging
requires the presence of a non-zero bridge function in the correlations between
the solute particles when our model fluid is described within a full mixture
theory based upon the Ornstein-Zernike equations.Comment: 28 pages, 8 figure
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