149 research outputs found
Automatic imitation and associative learning.
Human body movements are especially effective in eliciting imitative responses. This thesis aims to establish why this is the case, and fundamentally, what this suggests about the mechanisms mediating imitation. Chapter 1 outlines theories which can account for this imitative bias, and highlights issues upon which these theories can be distinguished. Chapter 2 establishes whether the finding that responses are executed faster in response to stimuli of the same action type reflects an automatic tendency to imitate observed actions. On the basis of evidence to support this hypothesis, Chapters 3 and 4 use this reaction time measure to investigate imitation mechanisms. Chapter 3 addresses whether the human imitative bias emerges through top-down modulation of imitation mechanisms, on the basis of knowledge about whether stimuli are of human origin, or through perceptual properties of stimuli. These experiments suggest that automatic imitation effects are larger with human stimuli than robotic stimuli, but are unaffected by beliefs about stimulus identity, indicating that the imitative bias is driven by perceptual properties of stimuli. Chapter 4 asks why the perceptual properties of human stimuli are especially effective in eliciting imitative responses. On the basis of evidence suggesting that training can modulate imitation of robotic stimuli, this chapter supports the hypothesis that the imitative bias results from greater opportunity for associative learning with human stimuli. Chapter 5 investigates whether visuotactile integration can be modulated through training, in a similar way to visuomotor integration. By recording event-related brain potentials in response to tactile stimulation following visuotactile training, Chapter 5 indicates that visuotactile integration is modulated following training, but there are some differences in the influences of training with human and non-human visual stimuli. In summary, the results of the experiments reported in this thesis support the hypothesis that the human imitative bias emerges because of perceptual properties of human stimuli and greater opportunity to form associations between these stimuli and matching responses. These findings are consistent with the Associative Sequence Learning model of imitation. Visuotactile integration may also be understood with reference to associative learning
Hawking Radiation from a (4+n)-Dimensional Rotating Black Hole on the Brane
We study the emission of Hawking radiation in the form of scalar fields from
a (4+n)-dimensional, rotating black hole on the brane. We perform a numerical
analysis to solve both the radial and angular parts of the scalar field
equation, and derive exact results for the radial wavefunction and angular
eigenvalues, respectively. We then determine the Hawking radiation energy
emission rate, and find that, as the angular momentum increases, it is
suppressed in the low-energy regime but enhanced in the intermediate and
high-energy regimes. Our results agree with previous analytical studies,
derived in the low-angular momentum and low-energy approximation, and
generalize them to include angular momentum and energy regimes that were until
now unexplored. We also investigate the energy amplification due to
super-radiance and we find that, in the presence of extra dimensions, the
effect is significantly enhanced.Comment: 9 pages, Latex file, 5 figures, a new figure and a paragraph have
been added along with some clarifying comments, version to appear in Phys.
Lett.
Brane decay of a (4+n)-dimensional rotating black hole: spin-0 particles
In this work, we study the `scalar channel' of the emission of Hawking
radiation from a (4+n)-dimensional, rotating black hole on the brane. We
numerically solve both the radial and angular part of the equation of motion
for the scalar field, and determine the exact values of the absorption
probability and of the spheroidal harmonics, respectively. With these, we
calculate the particle, energy and angular momentum emission rates, as well as
the angular variation in the flux and power spectra -- a distinctive feature of
emission during the spin-down phase of the life of the produced black hole. Our
analysis is free from any approximations, with our results being valid for
arbitrarily large values of the energy of the emitted particle, angular
momentum of the black hole and dimensionality of spacetime. We finally compute
the total emissivities for the number of particles, energy and angular momentum
and compare their relative behaviour for different values of the parameters of
the theory.Comment: 24 pages, 13 figure
Brane Decay of a (4+n)-Dimensional Rotating Black Hole. II: spin-1 particles
The present works complements and expands a previous one, focused on the
emission of scalar fields by a (4+n)-dimensional rotating black hole on the
brane, by studying the emission of gauge fields on the brane from a similar
black hole. A comprehensive analysis of the particle, energy and angular
momentum emission rates is undertaken, for arbitrary angular momentum of the
black hole and dimensionality of spacetime. Our analysis reveals the existence
of a number of distinct features associated with the emission of spin-1 fields
from a rotating black hole on the brane, such as the behaviour and magnitude of
the different emission rates, the angular distribution of particles and energy,
the relative enhancement compared to the scalar fields, and the magnitude of
the superradiance effect. Apart from their theoretical interest, these features
can comprise clear signatures of the emission of Hawking radiation from a
brane-world black hole during its spin-down phase upon successful detection of
this effect during an experiment.Comment: 35 pages, 19 figures, Latex fil
Brane Decay of a (4+n)-Dimensional Rotating Black Hole. III: spin-1/2 particles
In this work, we have continued the study of the Hawking radiation on the
brane from a higher-dimensional rotating black hole by investigating the
emission of fermionic modes. A comprehensive analysis is performed that leads
to the particle, power and angular momentum emission rates, and sheds light on
their dependence on fundamental parameters of the theory, such as the spacetime
dimension and angular momentum of the black hole. In addition, the angular
distribution of the emitted modes, in terms of the number of particles and
energy, is thoroughly studied. Our results are valid for arbitrary values of
the energy of the emitted particles, dimension of spacetime and angular
momentum of the black hole, and complement previous results on the emission of
brane-localised scalars and gauge bosons.Comment: Latex file, JHEP style, 34 pages, 16 figures Energy range in plots
increased, minor changes, version published in JHE
Numerical verification of universality for the Anderson transition
We analyze the scaling behavior of the higher Lyapunov exponents at the
Anderson transition. We estimate the critical exponent and verify its
universality and that of the critical conductance distribution for box,
Gaussian and Lorentzian distributions of the random potential
Electronic Structures of Quantum Dots and the Ultimate Resolution of Integers
The orbital angular momentum L as an integer can be ultimately factorized as
a product of prime numbers. We show here a close relation between the
resolution of L and the classification of quantum states of an N-electron
2-dimensional system. In this scheme, the states are in essence classified into
different types according to the m(k)-accessibility, namely the ability to get
access to symmetric geometric configurations. The m(k)-accessibility is an
universal concept underlying all kinds of 2-dimensional systems with a center.
Numerical calculations have been performed to reveal the electronic structures
of the states of the dots with 9 and 19 electrons,respectively. This paper
supports the Laughlin wave finction and the composite fermion model from the
aspect of symmetry.Comment: Two figure
Granulomatous enteritis in rainbow trout (Oncorhynchus mykiss) associated with soya bean meal regardless of water dissolved oxygen level
This study investigated morphological changes associated with soya bean meal-induced enteritis (SBMIE) in distal intestine (DI) of rainbow trout (Oncorhynchus mykiss) fed a soya bean meal (SBM)-based diet and exposed to normoxia or hypoxia created by optimal and low water flow rates, respectively. A 28-day adaption period was followed by a 42-day challenge period where 600 fish were subjected to dietary challenge and/or hypoxia. Twelve tanks each containing 50 juvenile trout were assigned randomly in triplicate to each treatment. Histopathological and immunohistochemical evaluation revealed pathological features that have not previously been described in association with SBMIE. Vacuolar degeneration of epithelial cells mainly at the base of mucosal folds, epithelial cysts, epithelial dysplasia, necrosis, shedding of necrotic cells, and granulomatous inflammation including infiltration of enlarged, sometimes finely vacuolated or “foamy” macrophages, multinucleated giant cells and increased proliferation of fibroblasts were observed. Acid-fast bacteria were not detected in enlarged macrophages; however, these cells contained AB-PAS- and sometimes cytokeratin-positive material, which was interpreted to be of epithelial/goblet cell origin. Hypoxia did not affect the morphological changes in DI. These results suggest that SBM was associated with a granulomatous form of enteritis in DI of rainbow trout regardless of water oxygen level
Foreground removal from CMB temperature maps using an MLP neural network
One of the main obstacles in extracting the Cosmic Microwave Background (CMB)
signal from observations in the mm-submm range is the foreground contamination
by emission from galactic components: mainly synchrotron, free-free and thermal
dust emission. Due to the statistical nature of the intrinsic CMB signal it is
essential to minimize the systematic errors in the CMB temperature
determinations. Following the available knowledge of the spectral behavior of
the galactic foregrounds simple, power law-like spectra have been assumed. The
feasibility of using a simple neural network for extracting the CMB temperature
signal from the combined CMB and foreground signals has been investigated. As a
specific example, we have analysed simulated data, like that expected from the
ESA Planck Surveyor mission. A simple multilayer perceptron neural network with
2 hidden layers can provide temperature estimates, over more than 80 percent of
the sky, that are to a high degree uncorrelated with the foreground signals. A
single network will be able to cover the dynamic range of the Planck noise
level over the entire sky.Comment: Accepted for publication in Astrophysics and Space Scienc
Modeling the variability of shapes of a human placenta
While it is well-understood what a normal human placenta should look like, a
deviation from the norm can take many possible shapes. In this paper we propose
a mechanism for this variability based on the change in the structure of the
vascular tree
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