3,462 research outputs found
Noise, transient dynamics, and the generation of realistic interspike interval variation in square-wave burster neurons
First return maps of interspike intervals for biological neurons that
generate repetitive bursts of impulses can display stereotyped structures
(neuronal signatures). Such structures have been linked to the possibility of
multicoding and multifunctionality in neural networks that produce and control
rhythmical motor patterns. In some cases, isolating the neurons from their
synaptic network revealsirregular, complex signatures that have been regarded
as evidence of intrinsic, chaotic behavior.
We show that incorporation of dynamical noise into minimal neuron models of
square-wave bursting (either conductance-based or abstract) produces signatures
akin to those observed in biological examples, without the need for fine-tuning
of parameters or ad hoc constructions for inducing chaotic activity. The form
of the stochastic term is not strongly constrained, and can approximate several
possible sources of noise, e.g. random channel gating or synaptic bombardment.
The cornerstone of this signature generation mechanism is the rich,
transient, but deterministic dynamics inherent in the square-wave
(saddle-node/homoclinic) mode of neuronal bursting. We show that noise causes
the dynamics to populate a complex transient scaffolding or skeleton in state
space, even for models that (without added noise) generate only periodic
activity (whether in bursting or tonic spiking mode).Comment: REVTeX4-1, 18 pages, 9 figure
A multi-wavelength study of the dwarf galaxies NGC 2915 and NGC 1705 : star formation, gas dynamics and dark matter
Includes bibliographical references (p. 233-242).This thesis presents the results of a detailed multi-wavelength study of the nearby blue compact dwarf galaxies NGC 2915 and NGC 1705. The primary data set (nearly 100 hours of on-source data) for each galaxy consists of new observations of the neutral hydrogen (Hi) line obtained with the Australia Telescope Compact Array, October 2006 - May 2007. The stellar disk of NGC 1705 is host to an intense star-bursting core which is rapidly depleting the galaxy's central Hi reservoir. This galaxy can be used to rigorously test theories of star formation. Detailed studies of the distribution and kinematics of the neutral inter- stellar medium (ISM) within each galaxy are carried out. A suite of star formation recipes and models are examined for each galaxy to quantify the relationship between the observed star formation activity and the distribution and kinematics of the ISM
Illumination uniformity in endoscopic imaging
Standardised endoscopic digital images were taken and analysed using an image analysis software (National Instruments Vision Assistant version 7.1.1). The luminance plane was extracted and the pixel intensity distribution was determined along a horizontal line at the position of highest average intensity (centroid). The data was exported to MS Excel and the pixel intensity (y-axis) was plotted against pixel position (x-axis). A trendline using a 2nd order polynomial curve was fitted to each data set. The resultant equation for each curve was compared with equations obtained from other images taken under various illumination conditions and settings
An algorithm for clock synchronization with the gradient property in sensor networks
We introduce a distributed algorithm for clock synchronization in sensor
networks. Our algorithm assumes that nodes in the network only know their
immediate neighborhoods and an upper bound on the network's diameter.
Clock-synchronization messages are only sent as part of the communication,
assumed reasonably frequent, that already takes place among nodes. The
algorithm has the gradient property of [2], achieving an O(1) worst-case skew
between the logical clocks of neighbors. As in the case of [3,8], the
algorithm's actions are such that no constant lower bound exists on the rate at
which logical clocks progress in time, and for this reason the lower bound of
[2,5] that forbids constant skew between neighbors does not apply
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