Centroid

About: Centroid is a research topic. Over the lifetime, 4110 publications have been published within this topic receiving 53637 citations. The topic is also known as: barycenter (geometry) & geometric center of a plane figure.

Application of stability region centroids in robust PI stabilization of a class of second-order systems

Abstract: In this paper we offer a tuning method for the design of stabilizing PI controllers that utilizes the stability region centroid in the controller parameter space. To this end, analytical formulas are derived to describe the stability boundaries of a class of relative-degree-one linear time invariant second-order systems, the stability region of which has a closed convex shape. The so-called centroid stable point is then calculated analytically and the resultant set of algebraic formulas are utilized to tune the controller parameters. The freedom to choose the surface density function in the calculation of centroid stable point provides the designer with the possibility to incorporate optimal or robustness requirements in the controller design process. The proposed method uses the stability regions in the controller parameter space to ensure closed-loop stability, and, while offering robust stability properties, it does not rely on predetermined information with regard to the nature or range of parameter v...

Improved Iteratively Weighted Centroiding for accurate spot detection in Laser Guide Star based Shack Hartmann Sensor

Abstract: A hybrid centroiding technique involving Iteratively Weighted Center of Gravity (IWCoG) algorithm and corre-lation technique for a Laser Guide Star (LGS) based Shack Hartmann wavefront sensor is proposed. A simplemethod for simulating LGS elongated spots with photon noise and read out noise is demonstrated. The problemsassociated with IWCoG are addressed (a) Error saturation is minimized by adding random numbers iterativelyto centroid positions, (b) non uniform convergence of Centroid Estimation Error (CEE) is reduced by usingthe hypothesis that the iteration number with maximum correlation between the weighting function and theactual spot image function is the iteration with minimum error, (c) convergence rate is improved by shifting theweighting function to the point of maximum intensity in “rst iteration. The novelty of the algorithm is testedby comparing with other centroiding algorithms.Keywords: Shack Hartmann wavefront sensor, iteratively weighted center of gravity algorithm, adaptive optics,laser guide star

The Metabolic Centroid Method for PET Brain Image Analysis

Abstract: The method of centroids is an approach to the analysis of three-dimensional whole-brain positron emission tomography (PET) metabolic images It utilizes the brain's geometric centroid and metabolic centroid so as to objectively characterize the central tendency of the distribution of metabolic activity in the brain The method characterizes the three-dimensional PET metabolic image in terms of four parameters: the coordinates of the metabolic centroid and the mean metabolic rate of the whole brain These parameters are not sensitive to spatially uniform random noise or to the position of the subject's head within a uniform PET camera field of view The method has been applied to 40 normal subjects, 22 schizophrenics who were treated with neuroleptics, and 20 schizophrenics who were neuroleptic-free The mean metabolic centroid of the normal subjects was found to be superior to the mean geometric centroid of the brain The mean metabolic centroid of chronic schizophrenics is lower and more posterior to the

The location of centroids in photon and electron maps of solar flares

Abstract: We explore the use of centroid coordinates as a means to identify the "locations" of electron-proton bremsstrahlung hard X-ray sources in solar flares. Differences between the coordinates of the electron and photon centroids are derived and explained. For electron propagation in a collision-dominated target, with either a uniform or an exponential density profile, the position of the electron centroid can be calculated analytically. We compare these analytic forms to data from a flare event on 2002 February 20. We first spectrally invert the native photon visibility data to obtain "electron visibilities," which are in turn used to construct electron flux images at various electron energies E. Centroids of these maps are then obtained by straightforward numerical integration over the electron maps. This comparison allows us to infer the density structure in the two compact sources visible, and we discuss the (somewhat unexpected) results thus obtained.

Dislocation group dynamics II. general solutions of the n-body problem

Abstract: The general motion of n dislocations under their mutual repulsion and an applied stress field is considered. When the applied field is a linear function of position and an arbitrary function of time, it is shown that a Stieitjes transformation turns the nonlinear equations of motion into a set of linear differential equations which are integrable to give an exact specification of the general motion. The motion of the centroid of the dislocation group and the mean square deviation about the centroid are shown to have particularly simple properties.