Veranstaltungen

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Montag, 26.06.2017, 15.15 Uhr (WIAS-ESH)
Seminar Nichtlineare Optimierung und Inverse Probleme
Prof. Dr. M. Hanss, Universität Stuttgart:
Fuzzy arithmetic and probability theory in uncertainty analysis -- Unity in diversity
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Dienstag, 27.06.2017, 10.15 Uhr (WIAS-ESH)
Seminar Nichtlineare Optimierung und Inverse Probleme
M. Mäck, Universität Stuttgart:
Numerical implementation of Fuzzy arithmetic in uncertainty analysis
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin
Dienstag, 27.06.2017, 15.00 Uhr (WIAS-406)
Seminar Modern Methods in Applied Stochastics and Nonparametric Statistics
C. Uebel, Humboldt-universtiät zu Berlin:
Variable selection with hamming loss
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, 4. Etage, Weierstraß-Hörsaal (Raum: 406)

Veranstalter
WIAS Berlin
Dienstag, 27.06.2017, 15.15 Uhr (WIAS-ESH)
Oberseminar Nonlinear Dynamics
I. Franovic, University of Belgrade, Serbia:
Bistability, rate oscillations and slow rate fluctuations in networks of noisy neurons with coupling delay
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
Spontaneous activity of cortical neurons is typically characterized as a doubly-stochastic process, underlying two distinct forms of variability. While the local spike-train variability is reflected on the fast timescale, the variability associated with much longer timescales involves macroscopic irregular fluctuations of the firing rate. The latter fluctuations apparently emerge by coherent switching of neurons between the ?up? and ?down? states of membrane potential, and are believed to play important functional roles. In order to gain qualitative insight into the mechanisms behind such switching phenomena, we consider a random network of rate-based neurons influenced by external and internal noise, as well as the coupling delay. The network behavior is analyzed by deriving the second-order stochastic mean-field model, which describes the network dynamics in terms of the mean-rate and the associated variance. The mean-field model is used to study the stability and bifurcations in the thermodynamic limit, as well as the fluctuations due to the finite-size effect. For the thermodynamic limit, it is established that (i) the network may exhibit coexistence between two stationary levels in a wide range of parameters, whereby the two types of noise affect the levels in a fundamentally different fashion, and (ii) coupling delay may give rise to oscillations of the mean-rate. The slow rate fluctuations are demonstrated to emerge via two distinct scenarios. In the delay-free case, the leading mechanism can be seen as noise-induced transitions between two metastable states, quite reminiscent to fluctuations of a particle in a double-well potential. In the second scenario, which involves the cooperative action of noise and delay, the fluctuations can be interpreted as stochastic mixing between two different oscillatory regimes.

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Oberseminar Nonlinear Dynamics

Veranstalter
Freie Universität Berlin
WIAS Berlin
Mittwoch, 28.06.2017, 10.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Statistik
Prof. B. Sturmfels, Max Planck Institute for Mathematics in the Sciences Leipzig, Germany:
Geometry of log-concave density estimation
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Abstrakt
We present recent work with Elina Robeva and Caroline Uhler that establishes a new link between geometric combinatorics and nonparametric statistics. It concerns shape-constrained densities on d-space that are log-concave, with focus on the maximum likelihood estimator (MLE) for weighted samples. Cule, Samworth, and Stewart showed that the logarithm of the optimal log-concave density is piecewise linear and supported on a regular subdivision of the samples. This defines a map from the space of weights to the set of regular subdivisions of the samples, i.e. the face poset of their secondary polytope. We prove that this map is surjective. In fact, every regular subdivision arises in the MLE for some set of weights with positive probability, but coarser subdivisions appear to be more likely to arise than finer ones. To quantify these results, we introduce a continuous version of the secondary polytope, whose dual we name the Samworth body.

Veranstalter
WIAS Berlin
Humboldt-Universität zu Berlin
Universität Potsdam
Donnerstag, 29.06.2017, 16.00 Uhr (WIAS-ESH)
Forschungsseminar Mathematische Modelle der Photonik
Dr. A. Pimenov, WIAS Berlin:
Efficient simulation and analysis of multi-mode laser dynamics using time-delay models
mehr ... Veranstaltungsort
Weierstraß-Institut, Mohrenstr. 39, 10117 Berlin, Erdgeschoss, Erhard-Schmidt-Hörsaal

Veranstalter
WIAS Berlin