Institut für Theoretische Physik
Start / Aktuell
September  2014
Di
16.09.2014
MPS Equuleus + Fornax
MPI für Sonnensystemforschung
16:00
Rosetta-Seminar

Marco Fulle
Osservatorio Astronomico di Trieste

67P Dust environment from GIADA and OSIRIS data

GIADA is continuously collecting dust since 11 August 2014. Although designed to work at comet distances much closer than those actually planned, thanks to dust loss rates higher than predicted, GIADA is measuring the impact momentum of about a dust grain per day. For the biggest samples, the grain cross section, bulk density and velocity vector has been also determined. These observations have been complemented by 48 OSIRIS single grain detections performed on 4 August 2014, allowing us to complete the dust size distribution up to the largest ejected sizes (actually, some cm). I will discuss results, dust-to-gas ratio and cross section distribution, with comparisons of predictions by the GIADA dust model (2010).

Di
16.09.2014
Ludwig-Prandtl Lecture Hall, Am Fassberg 11, 37077 Goettingen
Nichtlineare Dynamik
17:15
AG-Seminar: MPI für Dynamik und Selbstorganisation - Bernstein Center for Computational Neuroscience/ Bernstein Focus Neurotechnology

Dr. Luc Berthouze
University of Sussex, School of Engineering and Informatics, Falmer, UK

Identification of criticality in neuronal avalanches

The notion that the brain may operate at, or close to, a critical state is receiving much attention in the neuroscience community. Much of the work to date has been focused on finding empirical evidence of operation at this regime through the characterisation of power law in some observable of the system, e.g., avalanche size, fluctuation of amplitude, inter-burst interval. Such characterisation is fraught with difficulties, however. In the first part of my presentation, I will describe our study of a simple model of a purely excitatory non-driven neural network that, by construction, operates at a critical point. This model allows us to consider various markers of criticality and illustrate how they should perform in a finite-size system. By calculating the exact distribution of avalanche sizes we are able to show that, over a limited range of avalanche sizes which we precisely identify, the distribution has scale free properties but is not a power law. We consider other possible markers, such as the divergence of susceptibility as the critical point of the system is approached. In the second part, I will present results when the same network is driven by a continuous external input, i.e., when the model does not have a separation of timescales. Derivation of the distributions of waiting times between neuronal avalanches shows that as the system approaches the critical state by two alternative `routes', different markers of criticality (partial scale-free behaviour and long-range temporal correlations) are displayed. This suggests that signatures of criticality exhibited by a particular system in close proximity to a critical state are dependent on the region in parameter space at which the system (currently) resides.

Kontakt: Dr. Viola Priesemann, mailto:viola@nld.ds.mpg.de
Mi
17.09.2014
MPS-Auditorium
MPI für Sonnensystemforschung
10:00
MPS-Seminar

Victor Silva
Aarhus University, Denmark

Asteroseismology



Kontakt: Saskia Hekker
Mi
17.09.2014
MPS Equuleus + Fornax
MPI für Sonnensystemforschung
16:00
Discussion on Comets

Marco Fulle
Osservatorio Astronomico di Trieste

Bound grains orbiting 67P: are we sure of that?



Kontakt: Pedro Lacerda, Klaus Jockers

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