Rescaling, thinning or complementing? On goodness-of-fit procedures for point process models and Generalized Linear Models

Generalized Linear Models (GLMs) are an increasingly popular framework for modeling neural spike trains. They have been linked to the theory of stochastic point processes and researchers have used this relation to assess goodness-of-fit using methods from point-process theory, e.g. the time-rescaling theorem. However, high neural firing rates or coarse discretization lead to a breakdown of the assumptions necessary for this connection. Here, we show how goodness-of-fit tests from point-process theory can still be applied to GLMs by constructing equivalent surrogate point processes out of time-series observations. Furthermore, two additional tests based on thinning and complementing point processes are introduced. They augment the instruments available for checking model adequacy of point processes as well as discretized models.Comment: 9 pages, to appear in NIPS 2010 (Neural Information Processing Systems), corrected missing referenc

Advanced Multi-Channel SAR Imaging - Measured Data Demonstration

Synthetic Aperture Radar (SAR) is a well-established technique for remote sensing of the Earth. However, conventional SAR systems relying on only a single transmit and receive aperture are not capable of imaging a wide swath with high spatial resolution. Multi-channel SAR concepts, such as systems based on multiple receive apertures in azimuth, promise to overcome these restrictions, thus enabling high-resolution wide-swath imaging. Analysis revealed that these systems imperatively require sophisticated digital processing of the received signals in order to guarantee full performance independently of the spatial sample distribution imposed by the applied pulse repetition frequency (PRF). A suitable algorithm to cope with these challenges of multi-channel data is given by the “multi-channel reconstruction algorithm”, which demonstrated in comprehensive analysis and system design examples its potential for high perform-ance SAR imaging. In this context, various optimization strategies were investigated and aspects of operating multi-channel systems in burst modes such as ScanSAR or TOPS were discussed. Furthermore, a first proof-of-principle showed the algorithm’s applicability to measured multi-channel X-band data gathered by the German Aerospace Cen-ter’s (DLR) airborne F-SAR system. As a next step in the framework of multi-channel azimuth processing, this paper builds on the results recalled above and continues two paths. Firstly, focus is turned to further optimization of the proc-essing algorithm by investigating the classical Space-Time Adaptive Processing (STAP) applied to SAR. Secondly, attention is turned to the analysis of the measured multi-channel data by elaborating the impact and compensation of channel mismatch and by verifying the derived theory

A simple Hidden Markov Model for midbrain dopaminergic neurons

Poster presentation: Introduction Dopaminergic neurons in the midbrain show a variety of firing patterns, ranging from very regular firing pacemaker cells to bursty and irregular neurons. The effects of different experimental conditions (like pharmacological treatment or genetical manipulations) on these neuronal discharge patterns may be subtle. Applying a stochastic model is a quantitative approach to reveal these changes. ..

Real-time phasefront detector for heterodyne interferometers

We present a real-time differential phasefront detector sensitive to better than 3 mrad rms, which corresponds to a precision of about 500 pm. This detector performs a spatially resolving measurement of the phasefront of a heterodyne interferometer, with heterodyne frequencies up to approximately 10 kHz. This instrument was developed as part of the research for the LISA Technology Package (LTP) interferometer, and will assist in the manufacture of its flight model. Due to the advantages this instrument offers, it also has general applications in optical metrology

LISA Phasemeter development

The baseline concept of LISA had been developed within an industrial investigation by Astrium/EADS and is being reviewed since 2005 in an ongoing formulation phase. One of the most important key technology development issues remains the demonstration of the interferometric readout of the main science measurement. This includes the hardware development of an appropriate Phase Measurement System (PMS). We present the status of our work concerning the design and implementation of a LISA-like PMS with particular emphasis on the hardware development based on Field Programmable Gate Arrays (FPGA's) as main technology platform and we report on our first results demonstrating the performance of the PMS with synthetic signals

Individual skyrmion manipulation by local magnetic field gradients

Magnetic skyrmions are topologically protected spin textures, stabilised in systems with strong Dzyaloshinskii-Moriya interaction (DMI). Several studies have shown that electrical currents can move skyrmions efficiently through spin-orbit torques. While promising for technological applications, current-driven skyrmion motion is intrinsically collective and accompanied by undesired heating effects. Here we demonstrate a new approach to control individual skyrmion positions precisely, which relies on the magnetic interaction between sample and a magnetic force microscopy (MFM) probe. We investigate perpendicularly magnetised X/CoFeB/MgO multilayers, where for X = W or Pt the DMI is sufficiently strong to allow for skyrmion nucleation in an applied field. We show that these skyrmions can be manipulated individually through the local field gradient generated by the scanning MFM probe with an unprecedented level of accuracy. Furthermore, we show that the probe stray field can assist skyrmion nucleation. Our proof-of-concepts results pave the way towards achieving current-free skyrmion control

Extraction of Network Topology From Multi-Electrode Recordings: Is there a Small-World Effect?

The simultaneous recording of the activity of many neurons poses challenges for multivariate data analysis. Here, we propose a general scheme of reconstruction of the functional network from spike train recordings. Effective, causal interactions are estimated by fitting generalized linear models on the neural responses, incorporating effects of the neurons’ self-history, of input from other neurons in the recorded network and of modulation by an external stimulus. The coupling terms arising from synaptic input can be transformed by thresholding into a binary connectivity matrix which is directed. Each link between two neurons represents a causal influence from one neuron to the other, given the observation of all other neurons from the population. The resulting graph is analyzed with respect to small-world and scale-free properties using quantitative measures for directed networks. Such graph-theoretic analyses have been performed on many complex dynamic networks, including the connectivity structure between different brain areas. Only few studies have attempted to look at the structure of cortical neural networks on the level of individual neurons. Here, using multi-electrode recordings from the visual system of the awake monkey, we find that cortical networks lack scale-free behavior, but show a small, but significant small-world structure. Assuming a simple distance-dependent probabilistic wiring between neurons, we find that this connectivity structure can account for all of the networks’ observed small-world ness. Moreover, for multi-electrode recordings the sampling of neurons is not uniform across the population. We show that the small-world-ness obtained by such a localized sub-sampling overestimates the strength of the true small-world structure of the network. This bias is likely to be present in all previous experiments based on multi-electrode recordings

Balões de notícias: a infografia e o jornalismo em quadrinhos

Examina a gramática e o vocabulário visual dos quadrinhos, avaliando as interseções entre esta mídia e o jornalismo, com foco no jornalismo literário, que subverte o modelo tradicional da notícia, e na infografia, que utiliza elementos de arte sequencial para construir textos jornalísticos. Obras como Desvendando quadrinhos, de Scott McCloud e Quadrinhos e arte sequencial, de Will Eisner, servem de alicerces teóricos para o funcionamento dos quadrinhos, enquanto obras como Palestina, de Joe Sacco, e Maus, de Art Spiegelman, traçam uma ponte entre a arte sequencial e a prática jornalística, também presente no uso de infográficos e diagramas na imprensa escrita. O estudo busca mostrar que o jornalismo em quadrinhos não é apenas um revival do jornalismo literário, mas que a arte sequencial é uma plataforma já utilizada na construção de notícias e reportagens

¿Vamos a la feria? Un estudio sobre las motivaciones para frecuentar las ferias libres

This work aims to develop and validate a scale to measure the reasons whyconsumers frequent flea markets, alternative markets that grow and prevail;nonetheless, they are forgotten by the area of consumer bahavior. The studywas carried out in two flea markets, in the region of Santiago and Temuco,Chile. The data were subjected to Exploratory Factor Analysis and, subsequently,the obtained structure was tested by using Confirmatory FactorAnalysis. The differences of location and socioeconomic levels were also exploredby using ANOVA. The results indicate that the scale reached satisfactorylevels of reliability and validity as the variables were grouped into twoconstructs related to hedonic and utilitarian motivations. Although in all sociallevels is observed the predominance of utilitarian reasons as motivationsto attend the fairs, in despite the hedonic reasons, the lower socioeconomiclevels show stronger hedonic motivations. Similar result is observed at regionallevel, where the Fair of Temuco presents higher hedonic outcomes thanthe Fair of Santiago.Este trabajo tiene como objetivo la construcción y validación de una escalapara medir las razones por las cuales los consumidores frecuentan las feriaslibres, mercados alternativos que crecen y prevalecen, no obstante son unpoco olvidados por el área de la conducta del consumidor. El estudio fue realizadoen dos ferias libres de la región de Santiago y Temuco, Chile. Los datosfueron sometidos a Análisis Factorial Exploratoria y, posteriormente, la estructuraobtenida fue testada mediante uso de Análisis Factorial Confirmatorio.También fueron exploradas las diferencias por localidad y de nivelessocioeconómicos con uso de ANOVA. Los resultados indican que la escalaalcanzó índices de confiabilidad y validez satisfactorios agrupándose en dosconstructos relacionados a motivaciones hedónicas y utilitarias. A pesar deque en todos los niveles socioeconómicos predominan las razones utilitarias,por sobre las hedónicas, como motivaciones para frecuentar la feria, los nivelessocioeconómicos más bajos presentan motivaciones hedónicas más fuertes.Resultado similar se observa a nivel regional, donde la Feria de Temucopresenta resultados hedónicos mayores que la de Santiago