12,031 research outputs found
Toward a dynamical systems analysis of neuromodulation
This work presents some first steps toward a
more thorough understanding of the control systems
employed in evolutionary robotics. In order
to choose an appropriate architecture or to construct
an effective novel control system we need
insights into what makes control systems successful,
robust, evolvable, etc. Here we present analysis
intended to shed light on this type of question
as it applies to a novel class of artificial neural
networks that include a neuromodulatory mechanism:
GasNets.
We begin by instantiating a particular GasNet
subcircuit responsible for tuneable pattern generation
and thought to underpin the attractive
property of “temporal adaptivity”. Rather than
work within the GasNet formalism, we develop an
extension of the well-known FitzHugh-Nagumo
equations. The continuous nature of our model
allows us to conduct a thorough dynamical systems
analysis and to draw parallels between this
subcircuit and beating/bursting phenomena reported
in the neuroscience literature.
We then proceed to explore the effects of different
types of parameter modulation on the system
dynamics. We conclude that while there are
key differences between the gain modulation used
in the GasNet and alternative schemes (including
threshold modulation of more traditional synaptic
input), both approaches are able to produce
tuneable pattern generation. While it appears, at
least in this study, that the GasNet’s gain modulation
may not be crucial to pattern generation ,
we go on to suggest some possible advantages it
could confer
Host-Source Country linkages as determinants of foreign acquisitions by Indian MNEs
This experimental paper explains foreign acquisitions by Indian multinational enterprises by reference to location specific factors in both the source country (India) and host countries together with variables required designed to capture the distance between India and the host country, both geographic and psychic. The paper finds that country specific advantages play an important role in explaining Indian foreign acquisitions. The general model performs well and Indian institutional and domestic capital variables add explanatory value
Optical studies of two LMC X-ray transients : RX J0544.1-7100 and RX J0520.5-6932
We report observations which confirm the identities of the optical
counterpart to the transient sources RX J0544.1-7100 and RX J0520.5-6932. The
counterparts are suggested to be a B-type stars. Optical data from the
observations carried out at ESO and SAAO, together with results from the OGLE
data base, are presented. In addition, X-ray data from the RXTE all-sky monitor
are investigated for long term periodicities. A strong suggestion for a binary
period of 24.4d is seen in RX J0520.5-6932 from the OGLE data.Comment: 6 pages, 7 figure
Exploring emotions and cognitions in hoarding: a Q-methodology analysis
Background:
The cognitions and emotions of people prone to hoarding are key components of the dominant cognitive behavioural model of hoarding disorder.
Aims:
This study sought to use Q-methodology to explore the thoughts and feelings of people that are prone to hoarding, to identify whether distinct clusters of participants could be found.
Method:
A 49-statement Q-set was generated following thematic analysis of initial interviews (n = 2) and a review of relevant measures and literature. Forty-one participants with problematic hoarding met various study inclusion criteria and completed the Q-sort (either online or offline). A by-person factor analysis was conducted and subsequent participant clusters compared on psychometric measures of mood, anxiety, hoarding and time taken on the online task as proxy for impulsivity.
Results:
Four distinct participant clusters were found constituting 34/41 (82.92%) of the participants, as the Q-sorts of n = 7 participants failed to cluster. The four clusters found were ‘overwhelmed’ (n = 11 participants); ‘aware of consequences’ (n = 13 participants); ‘object complexity’ (n = 6 participants) and ‘object–affect fusion’ (n = 4 participants). The clusters did not markedly differ with regard to hoarding severity, anxiety, depression or impulsivity.
Conclusions:
Whilst the participant clusters reflect extant research evidence, they also reveal significant heterogeneity and so prompt the need for further research investigating emotional and cognitive differences between people prone to hoarding
Particle methods for a virtual patient
The particle systems approach is a well known technique in computer graphics for modelling fuzzy objects such as fire and clouds. The algorithm has also been applied to different biomedical applications and this paper presents two such methods: a charged particle method for soft tissue deformation with integrated haptics; and a blood flow visualization technique based on boids. The goal is real time performance with high fidelity results
Computational requirements of the virtual patient
Medical visualization in a hospital can be used to aid training, diagnosis, and pre- and intra-operative planning. In such an application, a virtual representation of a patient is needed that is interactive, can be viewed in three dimensions (3D), and simulates physiological processes that change over time. This paper highlights some of the computational challenges of implementing a real time simulation of a virtual patient, when accuracy can be traded-off against speed. Illustrations are provided using projects from our research based on Grid-based visualization, through to use of the Graphics Processing Unit (GPU)
Relic Abundance of Asymmetric Dark Matter
We investigate the relic abundance of asymmetric Dark Matter particles that
were in thermal equilibrium in the early universe. The standard analytic
calculation of the symmetric Dark Matter is generalized to the asymmetric case.
We calculate the asymmetry required to explain the observed Dark Matter relic
abundance as a function of the annihilation cross section. We show that
introducing an asymmetry always reduces the indirect detection signal from WIMP
annihilation, although it has a larger annihilation cross section than
symmetric Dark Matter. This opens new possibilities for the construction of
realistic models of MeV Dark Matter.Comment: 20 pages, 11 figures, Accepted by JCA
Outbursts of EX Hydrae Revisited
We present optical spectroscopy of EX Hya during its 1991 outburst. This
outburst is characterised by strong irradiation of the front face of the
secondary star by the white dwarf, an overflowing stream which is seen strongly
in HeII and by a dip in the light curves, which extends from 0.1-0.6 in the
binary and spin phases. Strong irradiation of the accretion curtain and that of
the inner regions of the disc led to strong emission of HeII and to the
suppression of the Hg and Hb emission.
Disc overflow was observed in quiescence in earlier studies, where the
overflow stream material was modulated at high velocities close to 1000 km/s.
In outburst, the overflowing material is modulated at even higher velocities
(~1500 km/s). These are streaming velocities down the field lines close to the
white dwarf. Evidence for material collecting near the outer edge of the disc
and corotating with the accretion curtain was observed. In decline, this
material and the accretion curtain obscured almost all the emission near binary
phase 0.4, causing a dip. The dip minimum nearly corresponds with spin pulse
minimum. This has provided additional evidence for an extended accretion
curtain, and for the corotation of material with the accretion curtain at the
outer edge of the disc. From these observations we suggest that a mechanism
similar to that of Spruit & Taam, where outbursts result due to the storage and
release of matter outside the magnetosphere, triggers the outbursts of EX Hya.
This is followed by the irradiation of the secondary star due to accretion
induced radiation.Comment: 12 pages, 14 figures, 1 table. Figures 6, 7, 8 and 11 at low
resolution. Paper accepted by the Monthly Notices of the Royal Astronomical
Societ
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