An Analytical Study of Coupled Two-State Stochastic Resonators

The two-state model of stochastic resonance is extended to a chain of coupled two-state elements governed by the dynamics of Glauber's stochastic Ising model. Appropriate assumptions on the model parameters turn the chain into a prototype system of coupled stochastic resonators. In a weak-signal limit analytical expressions are derived for the spectral power amplification and the signal-to-noise ratio of a two-state element embedded into the chain. The effect of the coupling between the elements on both quantities is analysed and array-enhanced stochastic resonance is established for pure as well as noisy periodic signals. The coupling-induced improvement of the SNR compared to an uncoupled element is shown to be limited by a factor four which is only reached for vanishing input noise.Comment: 29 pages, 5 figure

Epigenetic Control of the foxp3 Locus in Regulatory T Cells

Compelling evidence suggests that the transcription factor Foxp3 acts as a master switch governing the development and function of CD4(+) regulatory T cells (Tregs). However, whether transcriptional control of Foxp3 expression itself contributes to the development of a stable Treg lineage has thus far not been investigated. We here identified an evolutionarily conserved region within the foxp3 locus upstream of exon-1 possessing transcriptional activity. Bisulphite sequencing and chromatin immunoprecipitation revealed complete demethylation of CpG motifs as well as histone modifications within the conserved region in ex vivo isolated Foxp3(+)CD25(+)CD4(+) Tregs, but not in naïve CD25(−)CD4(+) T cells. Partial DNA demethylation is already found within developing Foxp3(+) thymocytes; however, Tregs induced by TGF-β in vitro display only incomplete demethylation despite high Foxp3 expression. In contrast to natural Tregs, these TGF-β–induced Foxp3(+) Tregs lose both Foxp3 expression and suppressive activity upon restimulation in the absence of TGF-β. Our data suggest that expression of Foxp3 must be stabilized by epigenetic modification to allow the development of a permanent suppressor cell lineage, a finding of significant importance for therapeutic applications involving induction or transfer of Tregs and for the understanding of long-term cell lineage decisions

Initiierung und Begleitung unterrichtlicher Lernprozesse als Beitrag zum Gelingen einer inklusiven Schule

Hagedorn U, Siewert J. Initiierung und Begleitung unterrichtlicher Lernprozesse als Beitrag zum Gelingen einer inklusiven Schule. Schulpädagogik-heute. 2014;10(2014)

2.2 Echo State Property.......................... 5

Echo State Networks (ESNs) is a recent simple and powerful approach to training recurrent neural networks (RNNs). In this report we present a modification of ESNs- time warping invariant echo state networks (TWIESNs) that can effectively deal with time warping in dynamic pattern recognition. The standard approach to classify time warped input signals is to align them to candidate prototype patterns by a dynamic programming method and use the alignment cost as a classification criterion. In contrast, we feed the original input signal into specifically designed ESNs which intrinsically are invariant to time warping in the input. For this purpose, ESNs with leaky integrator neurons are required, which are here presented for the first time, too. We then explain the TWIESN architecture and demonstrate their functioning on very strongly warped, synthetic data sets

A Glauber-Dynamics Approach to Coupled Stochastic Resonators

. We derive analytical expressions for the signal-to-noise ratio of a periodically driven chain of coupled spins placed into a heat bath. The analysis closely follows the pioneering work of Glauber for the stochastic Ising model. We find optimal bath temperatures and coupling constants where the SNR maximises. Special attention is given to a wavy excitation of the chain where we discuss the dependence of the SNR on the wave number. 1 Introduction Stochastic resonance (SR) occurs when bistable or threshold systems are driven by noise and a mono-frequent 'signal'. In this case the state variable of the system under consideration typically exhibits a continuous spectrum with sharp peaks at multiples of the signal frequency. The point is that the spectral power amplification (SPA), which is the height of the first peak scaled in units of the driving amplitude, as well as the signal-to-noise ratio (SNR) at the first peak, may resonance-like pass (in general not simultaneously) through a ma..

An Analytical Study of Coupled Two-State Stochastic Resonators

The two-state model of stochastic resonance is extended to a chain of coupled two-state elements governed by the dynamics of Glauber's stochastic Ising model. Appropriate assumptions on the model parameters turn the chain into a prototype system of coupled stochastic resonators. In a weak-signal limit analytical expressions are derived for the spectral power amplification and the signal-to-noise ratio of a two-state element embedded into the chain. The effect of the coupling between the elements on both quantities is analysed and array-enhanced stochastic resonance is established for pure as well as noisy periodic signals. The coupling-induced improvement of the SNR compared to an uncoupled element is shown to be limited by a factor four which is only reached for vanishing input noise. PACS numbers: 5.40.+j, 05.50+q Typeset using REVT E X I. INTRODUCTION The essential point of stochastic resonance [1] is the following: If a stochastic resonator is subjected to an external influence, ..

Initiierung und Begleitung unterrichtlicher Lernprozesse als Beitrag zum Gelingen einer inklusiven Schule

Siewert J, Hagedorn U. Initiierung und Begleitung unterrichtlicher Lernprozesse als Beitrag zum Gelingen einer inklusiven Schule. In: Siedenbiedel C, Theurer C, eds. Grundlagen inklusiver Bildung. Teil 2. Entwicklung zur inklusiven Schule und Konsequenzen für die Lehrerbildung. Theorie und Praxis der Schulpädagogik. Vol 29. Kassel: Prolog-Verlag; 2015: 310-325

Learning optimal features for visual pattern recognition

The optimal coding hypothesis proposes that the human visual system has adapted to the statistical properties of the environment by the use of relatively simple optimality criteria. We here (i) discuss how the properties of different models of image coding, i.e. sparseness, decorrelation, and statistical independence are related to each other (ii) propose to evaluate the different models by verifiable performance measures (iii) analyse the classification performance on images of handwritten digits (MNIST data base). We first employ the SPARSENET algorithm (Olshausen, 1998) to derive a local filter basis (on 13 × 13 pixels windows). We then filter the images in the database (28 × 28 pixels images of digits) and reduce the dimensionality of the resulting feature space by selecting the locally maximal filter responses. We then train a support vector machine on a training set to classify the digits and report results obtained on a separate test set. Currently, the best state-of-the-art result on the MNIST data base has an error rate of 0,4%. This result, however, has been obtained by using explicit knowledge that is specific to the data (elastic distortion model for digits). We here obtain an error rate of 0,55 % which is second best but does not use explicit data specific knowledge. In particular it outperforms by far all methods that do not use data-specific knowledge

Differentially Methylated, Conserved Element of the <i>foxp3</i> Locus Possesses Transcriptional Activity

<p>RLM-11–1 cells were transfected with control vector (pGL3 promoter) or Foxp3-CE vector containing the conserved element (CE). Cells were stimulated with PMA for 24 h. Control cells were left unstimulated. Results given are relative luciferase light units (RLUs) normalized for Renilla luciferase activity (mean ± standard deviation; <i>n</i> = 3). Results are representative for two independent experiments.</p