Search results for "GEP"

2013

The motion energy sensor has been shown to account for a wide range of physiological and psychophysical results in motion detection and discrimination studies. It has become established as the standard computational model for retinal movement sensing in the human visual system. Adaptation effects have been extensively studied in the psychophysical literature on motion perception, and play a crucial role in theoretical debates, but the current implementation of the energy sensor does not provide directly for modelling adaptation-induced changes in output. We describe an extension of the model to incorporate changes in output due to adaptation. The extended model first computes a space-time r…

The EM imaging reconstruction method in γ-ray astronomy

1998

Abstract The simpler imaging reconstruction methods used for γ-ray coded mask telescopes are based on correlation methods, very fast and simple-to-use but with limitations in the reconstructed image. To improve these results, other reconstruction methods have been developed, such as the maximum entropy methods or the Iterative Removal Of Sources (IROS). However, such kind of methods are slower and can be impracticable for very complex telescopes. In this paper we present an alternative image reconstruction method, based on an iterative maximum likelihood algorithm called the EM algorithm, easy to implement and that can be successfully used for not very complex coded mask systems, as is the …

One-shot color digital holography based on the fractional talbot effect

2010

We present a simple method for recording on-axis color digital holograms in a single shot. Our system performs parallel phase-shifting interferometry by using the fractional Talbot effect for every chromatic channel simultaneously. Experimental results are also shown.

Ultra-low material pixel layers for the Mu3e experiment

2016

The upcoming Mu3e experiment will search for the charged lepton flavour violating decay of a muon at rest into three electrons. The maximal energy of the electrons is 53 MeV, hence a low material budget is a key performance requirement for the tracking detector. In this paper we summarize our approach to meet the requirement of about 0.1 % of a radiation length per pixel detector layer. This includes the choice of thinned active monolithic pixel sensors in HV-CMOS technology, ultra-thin flexible printed circuits, and helium gas cooling.

Software Timing Calibration of the ARGO-YBJ Detector

2009

The ARGO-YBJ experiment is mainly devoted to search for astronomical gamma sources. The arrival direction of air showers is reconstructed thanks to the times measured by the pixels of the detector. Therefore, the timing calibration of the detector pixels is crucial in order to get the best angular resolution and pointing accuracy. Because of the large number of pixels a hardware timing calibration is practically impossible. Therefore an off-line software calibration has been adopted. Here, the details of the procedure and the results are presented. (C) 2008 Elsevier B.V. All rights reserved.

A computer-assisted experiment to study the influence of the point spread function in the image formation process

2018

[EN] We present a new open experimental setup assisted with LabView to be used to teach the concept of the point spread function (PSF). The PSF describes the response of an image-forming system to a point object. The PSF concept is of fundamental importance in optics since the output of an image-forming system can be simulated as the convolution of the PSF with the input object. In this work, a new graphical user interface has been developed to obtain a real-time measure of the PSF and the corresponding images provided by different lenses and pupils with different sizes and shapes. From a didactical point of view, the proposed method allows students to interpret the results in a visual and …

Fractals and multifractals in the description of the cosmic structure

1990

Abstract The concepts of fractals and multifractals are applied to describe the large scale galaxy distribution. It is shown how the Universe fits the fractal geometry on small scales (several Mpc), but that there exists some cut-off where the scale invariance is broken. Even in the scaling region the cosmic structure is not a simple fractal, and the task is to introduce more complex and complete clustering descriptors. At this stage, the concept of multifractals appears to be more efficient to describe the texture of the Universe.

Opto-digital tomographic reconstruction of the Wigner distribution function of complex fields.

2008

An optical-digital method has been developed to obtain the Wigner distribution function of one-dimensional complex fields. In this technique an optical setup is employed to experimentally achieve the Radon-Wigner spectrum of the original signal through intensity measurements. Digital tomographic reconstruction is applied to the experimental spectrum to reconstruct the two-dimensional Wigner distribution function of the input. The validity of our proposal is demonstrated with experimental data, and the results are compared with computer simulations.

Temporal ghost imaging with photon pairs

2017

International audience; We present an experiment of temporal ghost imaging based on the spatial properties of twin photons. The retrieval of a binary time signal of 8 bits is performed with an error rate of 0.70%.

Parallel Phase-Shifting Digital Holography Based on the Fractional Talbot Effect

2010

Digital holography allows us to record and process digitally the complex amplitude distribution associated to diffracted light beams and therefore has offered new possibilities for a variety of applications such as 3D microscopy, interferometry, or information security (see, for example, review [1]). In principle, phase-shifting techniques are the most efficient in terms of spatial resolution to record digital holograms [2]. However, a sequential acquisition of several interference patterns with different phase retardations of the reference beam is necessary, preventing dynamic measurements. Different techniques for time-resolved dynamic interferometry have been developed allowing one-shot …