5,364 research outputs found
A Kernel-Based Calculation of Information on a Metric Space
Kernel density estimation is a technique for approximating probability
distributions. Here, it is applied to the calculation of mutual information on
a metric space. This is motivated by the problem in neuroscience of calculating
the mutual information between stimuli and spiking responses; the space of
these responses is a metric space. It is shown that kernel density estimation
on a metric space resembles the k-nearest-neighbor approach. This approach is
applied to a toy dataset designed to mimic electrophysiological data
Pulse analysis of acoustic emission signals
A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio were examined in the frequency domain analysis, and pulse shape deconvolution was developed for use in the time domain analysis. Comparisons of the relative performance of each analysis technique are made for the characterization of acoustic emission pulses recorded by a measuring system. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameters values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emissions associated with: (1) crack propagation, (2) ball dropping on a plate, (3) spark discharge and (4) defective and good ball bearings. Deconvolution of the first few micro-seconds of the pulse train are shown to be the region in which the significant signatures of the acoustic emission event are to be found
Development and use of an extensometer for determining the mechanical compliance of crack toughness test specimens
Extensometer for determining mechanical compliance of crack toughness test specimen
Pulse analysis of acoustic emission signals
A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio were examined in the frequency domain analysis and pulse shape deconvolution was developed for use in the time domain analysis. Comparisons of the relative performance of each analysis technique are made for the characterization of acoustic emission pulses recorded by a measuring system. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameter values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emission associated with (a) crack propagation, (b) ball dropping on a plate, (c) spark discharge, and (d) defective and good ball bearings. Deconvolution of the first few micro-seconds of the pulse train is shown to be the region in which the significant signatures of the acoustic emission event are to be found
The most massive galaxies in clusters are already fully grown at
By constructing scaling relations for galaxies in the massive cluster
MACSJ0717.5 at and comparing with those of Coma, we model the
luminosity evolution of the stellar populations and the structural evolution of
the galaxies. We calculate magnitudes, surface brightnesses and effective radii
using HST/ACS images and velocity dispersions using Gemini/GMOS spectra, and
present a catalogue of our measurements for 17 galaxies. We also generate
photometric catalogues for galaxies from the HST imaging. With
these, we construct the colour-magnitude relation, the fundamental plane, the
mass-to-light versus mass relation, the mass-size relation and the
mass-velocity dispersion relation for both clusters. We present a new, coherent
way of modelling these scaling relations simultaneously using a simple physical
model in order to infer the evolution in luminosity, size and velocity
dispersion as a function of redshift, and show that the data can be fully
accounted for with this model. We find that (a) the evolution in size and
velocity dispersion undergone by these galaxies between and is mild, with and , and (b) the stellar populations are old, Gyr,
with a Gyr dispersion in age, and are consistent with evolving purely
passively since with . The implication is that these galaxies formed their stars early and
subsequently grew dissipationlessly so as to have their mass already in place
by , and suggests a dominant role for dry mergers, which may have
accelerated the growth in these high-density cluster environments.Comment: 20 pages; accepted for publication in MNRA
Pulse analysis of acoustic emission signals
A method for the signature analysis of pulses in the frequency domain and the time domain is presented. Fourier spectrum, Fourier transfer function, shock spectrum and shock spectrum ratio are examined in the frequency domain analysis, and pulse shape deconvolution is developed for use in the time domain analysis. To demonstrate the relative sensitivity of each of the methods to small changes in the pulse shape, signatures of computer modeled systems with analytical pulses are presented. Optimization techniques are developed and used to indicate the best design parameters values for deconvolution of the pulse shape. Several experiments are presented that test the pulse signature analysis methods on different acoustic emission sources. These include acoustic emissions associated with: (1) crack propagation, (2) ball dropping on a plate, (3) spark discharge and (4) defective and good ball bearings
Symmetric Skyrmions
We present candidates for the global minimum energy solitons of charge one to
nine in the Skyrme model, generated using sophisticated numerical algorithms.
Assuming the Skyrme model accurately represents the low energy limit of QCD,
these configurations correspond to the classical nuclear ground states of the
light elements. The solitons found are particularly symmetric, for example, the
charge seven skyrmion has icosahedral symmetry, and the shapes are shown to fit
a remarkable sequence defined by a geometric energy minimization (GEM) rule. We
also calculate the energies and sizes to within at least a few percent
accuracy. These calculations provide the basis for a future investigation of
the low energy vibrational modes of skyrmions and hence the possibility of
testing the Skyrme model against experiment.Comment: latex, 9 pages, 1 figure (fig1.gif
A photometric analysis of Abell 1689: two-dimensional multi-structure decomposition, morphological classification, and the Fundamental Plane
We present a photometric analysis of 65 galaxies in the rich cluster Abell
1689 at , using the Hubble Space Telescope Advanced Camera for Surveys
archive images in the rest-frame -band. We perform two-dimensional
multi-component photometric decomposition of each galaxy adopting different
models of the surface-brightness distribution. We present an accurate
morphological classification for each of the sample galaxies. For 50 early-type
galaxies, we fit both a de Vaucouleurs and S\'ersic law; S0s are modelled by
also including a disc component described by an exponential law. Bars of SB0s
are described by the profile of a Ferrers ellipsoid. For the 15 spirals, we
model a S\'ersic bulge, exponential disc, and, when required, a Ferrers bar
component. We derive the Fundamental Plane by fitting 40 early-type galaxies in
the sample, using different surface-brightness distributions. We find that the
tightest plane is that derived by S\'ersic bulges. We find that bulges of
spirals lie on the same relation. The Fundamental Plane is better defined by
the bulges alone rather than the entire galaxies. Comparison with local samples
shows both an offset and rotation in the Fundamental Plane of Abell 1689.Comment: 53 pages, 71 figures, MNRAS in pres
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