Fast and robust learning by reinforcement signals: explorations in the insect brain

We propose a model for pattern recognition in the insect brain. Departing from a well-known body of knowledge about the insect brain, we investigate which of the potentially present features may be useful to learn input patterns rapidly and in a stable manner. The plasticity underlying pattern recognition is situated in the insect mushroom bodies and requires an error signal to associate the stimulus with a proper response. As a proof of concept, we used our model insect brain to classify the well-known MNIST database of handwritten digits, a popular benchmark for classifiers. We show that the structural organization of the insect brain appears to be suitable for both fast learning of new stimuli and reasonable performance in stationary conditions. Furthermore, it is extremely robust to damage to the brain structures involved in sensory processing. Finally, we suggest that spatiotemporal dynamics can improve the level of confidence in a classification decision. The proposed approach allows testing the effect of hypothesized mechanisms rather than speculating on their benefit for system performance or confidence in its responses

Emergent Properties in Structurally Dynamic Disordered Cellular Networks

We relate structurally dynamic cellular networks, a class of models we developed in fundamental space-time physics, to SDCA, introduced some time ago by Ilachinski and Halpern. We emphasize the crucial property of a non-linear interaction of network geometry with the matter degrees of freedom in order to emulate the supposedly highly erratic and strongly fluctuating space-time structure on the Planck scale. We then embark on a detailed numerical analysis of various large scale characteristics of several classes of models in order to understand what will happen if some sort of macroscopic or continuum limit is performed. Of particular relevance in this context is a notion of network dimension and its behavior in this limit. Furthermore, the possibility of phase transitions is discussed.Comment: 20 pages, Latex, 6 figure

Probing the dynamics of identified neurons with a data-driven modeling approach

In controlling animal behavior the nervous system has to perform within the operational limits set by the requirements of each specific behavior. The implications for the corresponding range of suitable network, single neuron, and ion channel properties have remained elusive. In this article we approach the question of how well-constrained properties of neuronal systems may be on the neuronal level. We used large data sets of the activity of isolated invertebrate identified cells and built an accurate conductance-based model for this cell type using customized automated parameter estimation techniques. By direct inspection of the data we found that the variability of the neurons is larger when they are isolated from the circuit than when in the intact system. Furthermore, the responses of the neurons to perturbations appear to be more consistent than their autonomous behavior under stationary conditions. In the developed model, the constraints on different parameters that enforce appropriate model dynamics vary widely from some very tightly controlled parameters to others that are almost arbitrary. The model also allows predictions for the effect of blocking selected ionic currents and to prove that the origin of irregular dynamics in the neuron model is proper chaoticity and that this chaoticity is typical in an appropriate sense. Our results indicate that data driven models are useful tools for the in-depth analysis of neuronal dynamics. The better consistency of responses to perturbations, in the real neurons as well as in the model, suggests a paradigm shift away from measuring autonomous dynamics alone towards protocols of controlled perturbations. Our predictions for the impact of channel blockers on the neuronal dynamics and the proof of chaoticity underscore the wide scope of our approach

Phase transitions and multifractal properties of random field Ising models

In dieser Arbeit werden Zufallsfeld-Ising-Modelle mit einem eingefrorenen dichotomen symmetrischen Zufallsfeld für den eindimensionalen Fall und das Bethe-Gitter untersucht. Dabei wird die kanonische Zustandssumme zu der eines einzelnen Spins in einem effektiven Feld umformuliert. Im ersten Teil der Arbeit werden das mulktifraktale Spektrum dieses effektiven Feldes untersucht, Übergänge im Spektrum erklärt und Ungleichungen zwischen lokalen und globalen Dimensionsbegriffen bewiesen, die eine weitgehend vollständige Charakterisierung des multifraktalen Spektrums durch eine Reihe von Schranken erlauben. Ein weiterer Teil der Arbeit beschäftigt sich mit einer ähnlichen Charakterisierung des Maßes der lokalen Magnetisierung, das aus dem Maß des effektiven Feldes durch Faltung hervorgeht. In diesem Zusammenhang wird die Faltung von Multifraktalen in einem allgemeineren Rahmen behandelt und Zusammenhänge zwischen den multifraktalen Eigenschaften der Faltung und denen der gefalteten Maße bewiesen. Im dritten Teil der Dissertation wird der Phasenübergang von Ferro- zu Paramagnetismus im Modell auf dem Bethe Gitter untersucht. Neben verbesserten exakten Schranken für die Eindeutigkeit des paramagnetischen Zustands werden im wesentlichen drei Kriterien für die tatsächliche Lage des Übergangs angegeben und numerisch ausgewertet. Die multifraktalen Eigenschaften des effektiven Felds im Modell auf dem Bethe-Gitter schließlich erweisen sich als trivial, da die interessanten Dimensionen nicht existieren.In this work random field Ising models with quenched dichotomous symmetric random field are considered for the one-dimensional case and on the Bethe lattice. To this end the canonical partition function is reformulated to the partition function of one spin in an effective field. In the first part of the work the multifractal spectrum of this effective field is investigated, transitions in the spectrum are explained and inequalities between local and global generalized fractal dimensions are proven which allow to characterize the multifractal spectrum bei various bounds. A further part of the work is dedicated to the characterization of the measure of the local magnetization which is obtained by convolution of the measure of the effective field with itself. In this context the convolution of multifractals is investigated in a more general setup and relations between the multifractal properties of the convolution and the multifractal properties of the convoluted measures are proven. The phase transition from ferro- to paramagnetismus for the model on the Bethe lattice is investigated in the third part of the thesis. Apart from improved exact bounds for the uniqueness of the paramagnetic state essentially three criteria for the transition are developped and numerically evaluated to determine the transition line. The multifractal properties of the effective field for the model on the Bethe lattice finally turn out to be trivial because the interesting dimensions do not exist

Markets, democracy and social capital

'Entgegen seinen Versprechungen hat der Kommunismus wirtschaftliche Entwicklung und Modernisierung nicht beschleunigt. Die von ihm betroffenen Zentral-/ Osteuropäischen Staaten sind in ihrer Entwicklung vielmehr hinter jenen Staaten zurückgeblieben, die vor 70 Jahren noch gleich arm wie sie waren, die sich aber inzwischen dem europäischen Durchschnitt angenähert haben. In der Transformationskrise nach 1990 ist diese Kluft sogar noch breiter geworden. Es gibt keinen Anhaltspunkt für die These, dass die große Dauer und Tiefe dieser Transformationskrise durch eine vorschnelle und zu vollständige Demokratisierung verursacht worden wäre. Im Gegenteil: jene Staaten mit den höchsten demokratischen Standards sind auch jene, die ihre Wirtschaft am wirksamsten umgestaltet haben. Erfolgreiche Demokratisierung und erfolgreiche Wirtschaftsreform scheinen also die selbe tieferliegende Ursache zu haben: funktionierende gemeinschaftliche Einrichtungen sind in beiden Bereichen unerlässlich. Gut funktionieren können solche Einrichtungen aber nur dann, wenn sie sich auf ausreichendes und passendes 'Sozialkapital' von wechselseitigem Vertrauen und Bereitschaft zur Zusammenarbeit stützen können. Die Zerstörung dieses Kapitals zählt zu den schädlichsten Erbstücken, die der Kommunismus hinterlassen hat. Je weiter entfernt ein exkommunistisches Land von den traditionellen Zentren der europäischen Modernisierung, desto drückender die Last dieses Erbes.' (Autorenreferat)'Communism fell short by far of its goal of accelerating modernisation and economic development. Under Communism, Central/Eastern European countries have fallen back even further behind the European average; whereas countries that had been equally poor before World War Two, all have moved closer to the European average by now. In the first half of the Nineties with its 'post-transition' crises, this distance to the rest of Europe had become wider still. Some suggest that the severity of this post-Communist crises would have been a consequence of too rapid and complete democratisation. Empirical data do not support this proposition. Economic development and democratic consolidation do not substitute for one another; but are closely correlated. Countries that successfully consolidate their democratic system are also the ones that score best in economic reform. Both the pace of democratisation and of economic transformation therefore seem to depend on the same underlying causes. In both spheres, well functioning institutions are essential. Yet these institutions can only perform as expected if they are sustained by trust and by the general social routine of a co-operation; that is if they are based on sufficient and appropriate 'social capital'. The dearth of such 'social capital' ranks amongst the most damaging legacies of Communism. The farther removed a country from the original centres European modernisation, the worse this deficiency.' (author's abstract

Metal Laminated Tooling - A Quick and Flexible Tooling Concept

For the fast manufacturing of complex formed tools Fraunhofer IWS works together with partners from the industry on a constant automation solution for cutting, packaging and adding steel sheet cutouts. With the selection of the most suitable connecting technology, also requirements must be considered to quality, surface quality and the production costs. Deep drawing or stamping tools do not require a complete connection of the single metal sheets. Here, a fast and economical connection is the main objective. Due to simple automation, laser beam welding offers itself as joining process. On the other hand, a temperature-steady connection of the sheet metal lamellas is necessary for injection molds, which can resist the injection pressures.Mechanical Engineerin

Flexible neuronal network simulation framework using code generation for NVidia® CUDA™

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Pregeometric Concepts on Graphs and Cellular Networks as Possible Models of Space-Time at the Planck-Scale

Starting from the working hypothesis that both physics and the corresponding mathematics have to be described by means of discrete concepts on the Planck-scale, one of the many problems one has to face is to find the discrete protoforms of the building blocks of continuum physics and mathematics. In the following we embark on developing such concepts for irregular structures like (large) graphs or networks which are intended to emulate (some of) the generic properties of the presumed combinatorial substratum from which continuum physics is assumed to emerge as a coarse grained and secondary model theory. We briefly indicate how various concepts of discrete (functional) analysis and geometry can be naturally constructed within this framework, leaving a larger portion of the paper to the systematic developement of dimensional concepts and their properties, which may have a possible bearing on various branches of modern physics beyond quantum gravity.Comment: 16 pages, Invited paper to appear in the special issue of the Journal of Chaos, Solitons and Fractals on: "Superstrings, M, F, S ... Theory" (M.S. El Naschie, C. Castro, Editors