Design of a fractional control using performance contours. Application to an electromechanical system

The article proposes a frequency-based method to design a controller ensuring dynamic behavior of a closed-loop control: the first overshoot of the step response in the tracking mode or in the regulation mode, the damping ratio and the natural frequency of its dominant oscillatory mode. This method uses two contours called “performance contours” and constructed on the Nichols diagram. The first contour is the common Nichols magnitude contour which can be considered as an iso-overshoot contour. The second contour, whose construction and analytic expression are given in this article, is a new contour defined on the Nichols diagram and parameterized by the damping ratio. The proposed method uses complex non-integer (or fractional) differentiation to compute a transfer function whose open-loop Nichols locus tangents both performance contours, thus ensuring stability margins (or stability degree). The method is applied to a DC motor whose speed is controlled

3D galaxy clustering with future wide-field surveys: Advantages of a spherical Fourier-Bessel analysis

Upcoming spectroscopic galaxy surveys are extremely promising to help in addressing the major challenges of cosmology, in particular in understanding the nature of the dark universe. The strength of these surveys comes from their unprecedented depth and width. Optimal extraction of their three-dimensional information is of utmost importance to best constrain the properties of the dark universe. Although there is theoretical motivation and novel tools to explore these surveys using the 3D spherical Fourier-Bessel (SFB) power spectrum of galaxy number counts $C_\ell(k,k^\prime)$, most survey optimisations and forecasts are based on the tomographic spherical harmonics power spectrum $C^{(ij)}_\ell$. We performed a new investigation of the information that can be extracted from the tomographic and 3D SFB techniques by comparing the forecast cosmological parameter constraints obtained from a Fisher analysis in the context of planned stage IV wide-field galaxy surveys. The comparison was made possible by careful and coherent treatment of non-linear scales in the two analyses. Nuisance parameters related to a scale- and redshift-dependent galaxy bias were also included for the first time in the computation of both the 3D SFB and tomographic power spectra. Tomographic and 3D SFB methods can recover similar constraints in the absence of systematics. However, constraints from the 3D SFB analysis are less sensitive to unavoidable systematics stemming from a redshift- and scale-dependent galaxy bias. Even for surveys that are optimised with tomography in mind, a 3D SFB analysis is more powerful. In addition, for survey optimisation, the figure of merit for the 3D SFB method increases more rapidly with redshift, especially at higher redshifts, suggesting that the 3D SFB method should be preferred for designing and analysing future wide-field spectroscopic surveys.Comment: 12 pages, 6 Figures. Python package for cosmological forecasts available at https://cosmicpy.github.io . Updated figures. Matches published versio

Las redes sociales como impulsoras de la radio web

Las redes sociales y la radio web están vinculadas por la interacción que las redes le aportan al desarrollo de ésta última. A partir de la interactividad que brindan las redes sociales, es que la radio web ha recuperado la conversación, el oyente, que además es consumidor, puede participar e inclusive producir contenido. Este artículo parte del análisis de la radio web en Argentina, entendida como un nuevo formato de comunicación que recoge las características de la radio tradicional, pero las modifica para convertirlas en modelos distintos, al plantear un nuevo esquema de comunicación radiofónica a partir de incorporar las especificidades que brinda Internet. A partir de allí, es que luego de categorizar a las radios web en Argentina en tres grupos de distintos grados de profundización en la utilización de las herramientas tecnológicas que otorga Internet, es que se puede afirmar que las redes sociales se transformaron en el principal modo de producción de las radios web.Social networks and web radio are linked by the interaction that networks bring to the development of the latter. From the interactivity provided by social networks, the web radio has recovered the conversation, the listener, who is also a consumer, can participate and even produce content. This article is part of the analysis of the web radio in Argentina, understood as a new format of communication that gathers the characteristics of the traditional radio, but modifies them to turn them into different models, when proposing a new scheme of radio communication from incorporating the Specificities that the internet provides. From there, it is that after categorizing the web radios in Argentina in three groups of different degrees of deepening in the use of the technological tools provided by the Internet, it is possible to affirm that social networks became the main mode ff production of the web radios

Stability of closed-loop fractional-order systems and definition of damping contours for the design of controllers

Fractional complex order integrator has been used since 1991 for the design of robust control-systems. In the CRONE control methodology, it permits the parameterization of open loop transfer function which is optimized in a robustness context. Sets of fractional order integrators that lead to a given damping factor have also been used to build iso-damping contours on the Nichols plane. These iso-damping contours can also be used to optimize the third CRONE generation open-loop transfer function. However, these contours have been built using non band-limited integrators, even if such integrators reveal to lead to unstable closed loop systems. One objective of this paper is to show how the band-limitation modifies the left half-plane dominant poles of the closed loop system and removes the right half-plane ones. It is also presented how to obtain a fractional order open loop transfer function with a high phase slope and a useful frequency response. It is presented how the damping contours can be used to design robust controllers, not only CRONE controllers but also PD and QFT controllers

Las redes sociales como herramientas para repensar la teoría de los dos escalones

La teoría de los dos escalones de Lazarsfeld establecía que los medios de comunicación habían perdido de manera relativa cierto poder de influencia sobre la ciudadanía. Para justificarlo se identificó la figura del líder de opinión local que actuaba como intermediario entre el medio y la opinión pública en general. Actualmente, las redes sociales se han transformado en una nueva herramienta de comunicación que reconfiguró la relación entre los medios de comunicación y la opinión pública. En ese sentido, surgen los llamados influenciadores, sujetos que por proximidad o empatía son capaces de incidir en la opinión de gran cantidad de personas en las redes sociales. Estos pueden tener algunas similitudes con el líder de opinión identificado por la teoría de los dos pasos, aunque con funciones distintas. Al repensar dicha noción teórica desde la actualidad puede identificarse una vigencia relativa, ya que los escalones son fácilmente salteados por el constante flujo de comunicación existente entre los medios y la sociedad, a tal punto que las redes sociales logran hoy que los ciudadanos puedan imponer sus temas de agenda en la de los medios masivos, rompiendo con la linealidad del esquema anterior dado que el flujo informativo corre en ambas direcciones

Input-output linearization and fractional robust control of a non-linear system

This article deals with the association of a linear robust controller and an input-output linearization feedback for the control of a perturbed and non-linear system. This technique is applied to the control of a hydraulic system whose actuator is non-linear and whose load is time-variant. The piston velocity of the actuator needs to be controlled and a pressure-difference inner-loop is used to improve the performance. To remove the effect of the non-linearity, an input-output linearization under diffeomorphism and feedback is achieved. CRONE control, based on complex fractional differentiation, is applied to design a controller for piston-velocity loop even when parametric variations occu

Study of two robust controls for an hydraulic actuator

Two robust control design methodologies are analyzed and compared in this article: the H-infinity control system design and the CRONE control system design. The aim of this article is to give practical considerations that will help a designer to choose between these two methodologies. The example of an electrohydraulic actuator is given in order to evaluate the implementation of each methodology and to compare the final performance

Crone control of a nonlinear hydraulic actuator

The CRONE control (fractional robust control) of a hydraulic actuator whose dynamic model is nonlinear is presented. An input-output linearization under diffeomorphism and feedback is first achieved for the nominal plant. The relevance of this linearization when the parameters of the plant vary is then analyzed using the Volterra input-output representation in the frequency domain. CRONE control based on complex fractional differentiation is finally applied to control the velocity of the input-output linearized model when parametric variations occur