Search results for "Estimation"

Image-based MRI Gradient Estimation

2017

In order to reduce geometric distortion phenomena in MR images, every MRI system main magnet undergoes a shimming process. Since this process aims at optimizing magnetic field homogeneity within a so-called uniformity sphere, image quality outside this sphere is neglected. Since the fields vary smoothly in space, MR signal-to-noise ratio is still non-zero just outside the uniformity region, but correction of MR image distortion fails due to lack of magnetic field knowledge outside it. We propose a novel algorithm for measuring all the fields involved in the generation of images. Our proposal is based on exploitation of the distortion which can be observed in images of a known phantom. The p…

Regularization operators for natural images based on nonlinear perception models.

2006

Image restoration requires some a priori knowledge of the solution. Some of the conventional regularization techniques are based on the estimation of the power spectrum density. Simple statistical models for spectral estimation just take into account second-order relations between the pixels of the image. However, natural images exhibit additional features, such as particular relationships between local Fourier or wavelet transform coefficients. Biological visual systems have evolved to capture these relations. We propose the use of this biological behavior to build regularization operators as an alternative to simple statistical models. The results suggest that if the penalty operator take…

An implicitly parallel EDA based on restricted boltzmann machines

2014

We present a parallel version of RBM-EDA. RBM-EDA is an Estimation of Distribution Algorithm (EDA) that models dependencies between decision variables using a Restricted Boltzmann Machine (RBM). In contrast to other EDAs, RBM-EDA mainly uses matrix-matrix multiplications for model estimation and sampling. Hence, for implementation, standard libraries for linear algebra can be used. This allows an easy parallelization and leads to a high utilization of parallel architectures. The probabilistic model of the parallel version and the version on a single core are identical. We explore the speedups gained from running RBM-EDA on a Graphics Processing Unit. For problems of bounded difficulty like …

Visual motion integration controls attractiveness of objects in walking flies and a mobile robot

2008

Walking fruit flies are attracted by near-by objects. They estimate the distance to these objects by the parallax motion of their images on the retina. Here we provide evidence from robot simulations that distance is assessed by motion integration over large parts of the visual field and time periods of 0.5 s to 2 s. The process in flies is not selective to image motion created by the self-motion of the fly but also sensitive to object motion and to the pattern contrast of objects. Added visual motion (e.g. oscillations) makes objects more attractive than their stationary counterparts. Front-to-back motion, the natural parallax motion on the eyes of a forward-translating fly, is preferred. …

Frequency-Sliding Generalized Cross-Correlation: A Sub-Band Time Delay Estimation Approach

2020

The generalized cross correlation (GCC) is regarded as the most popular approach for estimating the time difference of arrival (TDOA) between the signals received at two sensors. Time delay estimates are obtained by maximizing the GCC output, where the direct-path delay is usually observed as a prominent peak. Moreover, GCCs play also an important role in steered response power (SRP) localization algorithms, where the SRP functional can be written as an accumulation of the GCCs computed from multiple sensor pairs. Unfortunately, the accuracy of TDOA estimates is affected by multiple factors, including noise, reverberation and signal bandwidth. In this paper, a sub-band approach for time del…

Spatio-Temporal Modeling of Zika and Dengue Infections within Colombia

2018

The aim of this study is to estimate the parallel relative risk of Zika virus disease (ZVD) and dengue using spatio-temporal interaction effects models for one department and one city of Colombia during the 2015&ndash

A New Method of Velocity Estimation Based on Variable Temporal Basis Using Incremental Encoder

1997

Abstract This paper deals with analysis and synthesis of algorithms for digital conditioning of signals generated by incremental encoders to estimate velocity of rotating devices for control purposes. Main objectives are to obtain high accuracy at low and high velocity and low tracking delays during accelerations. A digital conditioning method is described, Which uses a polynomial of order n whose coefficients are updated so as to fit the n+1 most recent velocity data acquired on a variable temporal basis. Digital sinlulations and experimental findings are shown with the ainl to validate the proposed estimation method and compare it with other methods.

Long term effect of teenage birth on earnings: Evidence from a British cohort study

2016

We use data from the 1970 British Cohort Study and evaluate the effect of teenage motherhood on hourly earnings at age 30, 34, 38, and 42 using alternative non-experimental estimation methods including linear regression, matching methods, and Heckman sample selection models. We conclude that teenage motherhood has a significant negative long-term effect on hourly wages. At age 42, teenage mothers earn 12% less than other women and 29% less than women who have not had any children. When compared to non-teenage mothers, the pay penalty reduces over time and becomes insignificant on the long term.

Revista electrónica de investigación y evaluación educativa

2014

Resumen basado en el de la publicación Título, resumen y palabras clave en inglés y español Se analiza el estatus del género existente en los equipos o consejos editoriales de las revistas científicas españolas de Educación. A priori, se indaga el estatus de la eminencia científica en el campo de la Educación; con el fin de detectar los posibles sesgos de género. Como análisis complementario se considera la nacionalidad o procedencia de los miembros de los consejos editoriales de las revistas de Educación. El hallazgo principal testimonia un fuerte sesgo contra las mujeres cuando éstas son consideradas editoras. Valencia ESP

Improvement of BEST (Beerkan Estimation of Soil Transfer parameters) method for soil hydraulic characterization

Interpreting and modeling soil hydrological processes require the determination of the soil hydraulic characteristic curves, i.e. the relationships between volumetric soil water content, pressure head, and hydraulic conductivity. Using traditional methods to determine these properties is expensive and time consuming. Haverkamp et al. (1996) pioneered a specific method for soil hydraulic characterization known as the “Beerkan method”. An improved version of this methodology, called the Beerkan Estimation of Soil Transfer parameters (BEST) procedure, was developed by Lassabatère et al. (2006) to simplify soil hydraulic characterization. BEST considers certain analytic formulae for hydraulic c…