553 research outputs found
Transient localized wave patterns and their application to migraine
Transient dynamics is pervasive in the human brain and poses challenging
problems both in mathematical tractability and clinical observability. We
investigate statistical properties of transient cortical wave patterns with
characteristic forms (shape, size, duration) in a canonical reaction-diffusion
model with mean field inhibition. The patterns are formed by a ghost near a
saddle-node bifurcation in which a stable traveling wave (node) collides with
its critical nucleation mass (saddle). Similar patterns have been observed with
fMRI in migraine. Our results support the controversial idea that waves of
cortical spreading depression (SD) have a causal relationship with the headache
phase in migraine and therefore occur not only in migraine with aura (MA) but
also in migraine without aura (MO), i.e., in the two major migraine subforms.
We suggest a congruence between the prevalence of MO and MA with the
statistical properties of the traveling waves' forms, according to which (i)
activation of nociceptive mechanisms relevant for headache is dependent upon a
sufficiently large instantaneous affected cortical area anti-correlated to both
SD duration and total affected cortical area such that headache would be less
severe in MA than in MO (ii) the incidence of MA is reflected in the distance
to the saddle-node bifurcation, and (iii) the contested notion of MO attacks
with silent aura is resolved. We briefly discuss model-based control and means
by which neuromodulation techniques may affect pathways of pain formation.Comment: 14 pages, 11 figure
Dependence of radio halo properties on star formation activity and galaxy mass
We investigate the relation between the existence and size of radio halos,
which are believed to be created by star formation (SF) related energy input
into the interstellar medium, and other galaxy properties, most importantly
star formation activity and galaxy mass. Based on radio continuum and H-alpha
observations of a sample of seven late-type spiral galaxies we find a direct,
linear correlation of the radial extent of gaseous halos on the size of the
actively star-forming parts of the galaxy disks. Data of a larger sample of 22
galaxies indicate that the threshold energy input rate into the disk ISM per
unit surface area for the creation of a gaseous halo depends on the mass
surface density of the galaxy, in the sense that a higher threshold must be
surpassed for galaxies with a higher surface density. Because of the good
prediction of the existence of a radio halo from these two parameters, we
conclude that they are important, albeit not the only contributors. The
compactness of the SF-related energy input is also found to be a relevant
factor. Galaxies with relatively compact SF distributions are more likely to
have gaseous halos than others with more widespread SF activity. These results
quantify the so-called "break-out" condition for matter to escape from galaxy
disks, as used in all current models of the interstellar medium and first
defined by Norman and Ikeuchi (1989).Comment: accepted for publication in Astronomy & Astrophysic
The quest for hot gas in the halo of NGC 1511
XMM-Newton observations of the starburst galaxy NGC 1511 reveal the presence
of a previously unknown extended hot gaseous phase of its ISM, which partly
extends out of the disk plane. The emission distribution is asymmetric, being
brightest in the eastern half of the galaxy, where also radio continuum
observations suggest the highest level of star formation. Spectral analysis of
the integral 0.2-12 keV X-ray emission from NGC 1511 indicates a complex
emission composition. A model comprising a power law plus thermal plasma
component, both absorbed by foreground gas, cannot explain all details of the
observed spectrum, requiring a third spectral component to be added. This
component can be a second thermal plasma, but other spectral models can be
fitted as well. Its X-ray properties characterize NGC 1511 as a starburst
galaxy. The X-ray-to-infrared luminosity ratio is consistent with this result.
Together with the X-ray data, XMM-Newton obtained UV images of NGC 1511,
tracing massive stars heating the ambient gas, which is then seen in H\alpha
emission. UV, H\alpha and near-infrared imagery suggest that NGC 1511 is
disturbed, most likely by its two small companions, NGC 1511a and NGC 1511b.Comment: 7 pages, 7 figures, accepted for publication in A&
Time-delayed feedback in neurosystems
The influence of time delay in systems of two coupled excitable neurons is
studied in the framework of the FitzHugh-Nagumo model. Time-delay can occur in
the coupling between neurons or in a self-feedback loop. The stochastic
synchronization of instantaneously coupled neurons under the influence of white
noise can be deliberately controlled by local time-delayed feedback. By
appropriate choice of the delay time synchronization can be either enhanced or
suppressed. In delay-coupled neurons, antiphase oscillations can be induced for
sufficiently large delay and coupling strength. The additional application of
time-delayed self-feedback leads to complex scenarios of synchronized in-phase
or antiphase oscillations, bursting patterns, or amplitude death.Comment: 13 pages, 13 figure
Students Arts Participation Increases STEM Motivation via Self-Efficacy
This work found that there exists a correlation between student motivation in science, technology, engineering and mathematics (STEM) and student participation in the arts during high school with self-efficacy being a mediator. STEM is an important component of student success from a broad, national, perspective, as well as from a domain-specific point of view. The results of this work may provide aid to teachers, parents, administrators, and even students seeking to find ways to increase student motivation and performance in the STEM subjects. Additionally, this work may be of interest to advocates of the arts. This quantitative correlational study was done using Hayes’ PROCESS via data resampling via bootstrapping 5,000 times with a 95% confidence interval at a statistical significance at the a = 0.05 level. The results of this study found an indirect effect of the predictor variable of arts participation on the dependent variable of STEM motivation of b = 0.003, 95% CI [ 0.000, 0.009], and a direct effect of b = 0.003 p \u3c 0.05. Additionally, this study found the predictor variable of arts participation was correlated to the mediator variable of self-efficacy. b = 0.006 at p \u3c 0.05
The variable radio counterpart and possible large-scale jet of the new Z-source XTE J1701-462
We report radio observations, made with the Australia Telescope Compact
Array, of the X-ray transient XTE J1701-462. This system has been classified as
a new `Z' source, displaying characteristic patterns of behaviour probably
associated with accretion onto a low magnetic field neutron star at close to
the Eddington limit. The radio counterpart is highly variable, and was detected
in six of sixteen observations over the period 2006 January -- April. The
coupling of radio emission to X-ray state, despite limited sampling, appears to
be similar to that of other `Z' sources, in that there is no radio emission on
the flaring branch. The mean radio and X-ray luminosities are consistent with
the other Z sources for a distance of 5--15 kpc. The radio spectrum is
unusually flat, or even inverted, in contrast to the related sources, Sco X-1
and Cir X-1, which usually display an optically thin radio spectrum. Deep
wide-field observations indicate an extended structure three arcminutes to the
south which is aligned with the X-ray binary. This seems to represent a
significant overdensity of radio sources for the field and so, although a
background source remains a strong possibility, we consider it plausible that
this is a large-scale jet associated with XTE J1701-462.Comment: Accepted for publication as a Letter in MNRA
ECoG-based short-range recurrent stimulation techniques to stabilize tissue at risk of progressive damage: Theory based on clinical observations
We introduce theoretical concepts based on chaos control to stabilize in acute stroke the tissue at risk of progressive damage by preventing adverse effects of waves of mass neuronal depolarization. Moreover, we present clinical electrocorticography (ECoG) recordings of relevant signals suggested for the feedback control. The recordings are performed in combination with novel subdural opto-electrode technology for simultaneous laser-Doppler flowmetry in patients with aneurysmal subarachnoid haemorrhage (aSAH). In aSAH patients waves of spreading depolarization (SD) have a high incidence and cause hypoxia in tissue at risk, and, importantly, the haemodynamic response is the inverse of that seen in healthy tissue. In previous clinical studies, clusters of prolonged SDs have been measured in aSAH patients in close proximity to structural brain damage as assessed by neuroimaging, and, in theoretical studies, a mechanism was presented, suggesting how a failure of internal feedback could be a putative mechanism of such SD cluster patterns in acute stroke. 

This failing internal feedback control is now suggested to be replaced by ECoG-based short-range recurrent functional stimulation that initiates the normal hyperperfusion haemodynamic response in a demand-controlled way and stabilizes the tissue at risk during the critical phase of SD passage. The suggested method has three key features: (i) it is short-range, i.e., in the order of the distance of the ECoG electrode strip, (ii) it is demand-controlled, and (iii) it uses no prior knowledge of the target state, in particular, it adapts to conditions in the healthy physiological range. On-demand type stimulation provides minimal invasive feedback as the control force is off when the target state is reached, i.e., the tissue at risk is without SD or it is back to the physiological range (out of risk). These last two features (ii-iii) are shared with classical methods of chaos control, where major progress was made in the last years with respect to extensions for spatio-temporal wave patterns. A detailed bifurcation analysis of the nonlinear model is presented, in particular, the SD cluster forming cortical state is suggested to be caused by a delay-induced saddle-node bifurcation.

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