2,590 research outputs found
Velocity-sensorless tracking control and identification of switched-reluctance motors
International audienceWe present a solution to the speed sensorless control problem for switched-reluctance motors under parametric uncertainty. Our main results guarantee velocity tracking control for velocity references with constant reference acceleration under the assumption that the load torque, the rotor inertia, the resistance and inductances are unknown. Under a persistency of excitation condition on a function which depends only on reference trajectories, we guarantee uniform global asymptotic stability therefore, we establish conditions for the identification of the physical parameters of the system. Our theoretical findings are supported by illustrative simulation results
Exponential stabilization of switched-reluctance motors via speed-sensorless feedback
International audienceWe solve the control problem of switched-reluctance motors without velocity measurements. Our controller is composed of a loop in the mechanical dynamics which consists of a PI2 D controller and a "tracking" controller closing an inner loop with the stator currents dynamics. The PI2 D controller consists in a linear proportional derivative controller in which the measurement of velocities is replaced by approximate derivatives of angular position. Then a double integrator is added, composed of an integral of the angular position errors and a second integral correction term in function of the approximate derivative. We show global exponential stability and illustrate the performance of our controller in numerical simulations
Self-organization of ultrasound in viscous fluids
We report the theoretical and experimental demonstration of pattern formation
in acoustics. The system is an acoustic resonator containing a viscous fluid.
When the system is driven by an external periodic force, the ultrasonic field
inside the cavity experiences different pattern-forming instabilities leading
to the emergence of periodic structures. The system is also shown to possess
bistable regimes, in which localized states of the ultrasonic field develop.
The thermal nonlinearity in the viscous fluid, together with the
far-from-equilibrium conditions, are is the responsible of the observed
effects
Banks’ Net Interest Margin in the 2000s: A Macro-Accounting International Perspective
This paper re-examines the determinants of Net Interest Margin (NIM) in the banking industries
of 15 developed and emerging economies. It presents three main contributions
with respect to previous studies: first, we analyze the determinants of NIM in the years
leading to the 2008 financial crisis; second, we account for the role of different accounting
standards across countries; third, we use multi-way cluster estimation methodologies
which control for cross-sectional and time-series dependence in macroeconomic and
banking variables. We find that the introduction of International Financial Reporting
Standards (IFRSs) contributed to lower NIM variations unexplained by standard accounting
variables. Interest rate volatility is found to be positively and strongly related to
NIM dynamics, whereas inflation risk is often found to be a relevant driver of NIM crosscountry
differences
Lista patrĂłn de los tiburones, rayas y quimeras (Chondrichthyes, Elasmobranchii, Holocephali) de MĂ©xico
Llista patrĂł dels taurons, rajades i quimeres (Chondrichthyes, Elasmobranchii, Holocephali) de Mèxic Es presenta una relaciĂł de les espècies de taurons, rajades i quimeres (condrictis) que han estat registrades a les aigĂĽes territorials de Mèxic, basada en revisions de bases de dades, literatura, examen fĂsic dels espècimens de col·leccions cientĂfiques i registres d’exemplars recol·lectats en treballs de camp durant els darrers quatre anys i que no han estat publicats. La relaciĂł contĂ© informaciĂł de 214 espècies de condrictis que, com a mĂnim, han estat registrades a les aigĂĽes marines i salobroses de Mèxic, pertanyents a 84 gèneres, 40 famĂlies i 14 ordres. S’hi inclouen vuit espècies de quimeres, 95 de batoĂŻdeus i 111 de taurons. La condrictiofauna mexicana Ă©s una de les mĂ©s riques del mĂłn, amb el 17,3% o mĂ©s de les espècies conegudes. A mĂ©s a mĂ©s, s’ hi inclouen 16 espècies que Ă©s probable que siguin presents a Mèxic atesos els seus patrons de distribuciĂł.Checklist of sharks, rays and chimaeras (Chondrichthyes, Elasmobranchii, Holocephali) from Mexico We present an annotated checklist of the species of sharks, rays and chimaeras (chondrichthyan fishes) occurring in Mexican waters, based on a thorough review of the literature and electronic database searches, examination of museum collection specimens, and unpublished records obtained during fieldwork conducted in the last four years. The checklist contains information of at least 214 species of chondrichthyan fishes that occur in Mexican marine and brackish waters, assigned to 84 genera, 40 families and 14 orders. It includes eight species of chimaeras, 95 batoids and 111 sharks. Condrichthyan fauna in Mexico is one of the richest in the world, with almost 17.3% of the known species. An additional  16 species are included  as their occurrence in Mexican marine waters is probable according to distributional patterns.Se presenta un listado anotado de las especies de tiburones, rayas y quimeras (Condrictios) que han sido registrados en las aguas territoriales de MĂ©xico, basado en revisiones de bases de datos, literatura, examinaciĂłn fĂsica de los especĂmenes de colecciones cientĂficas y de registros de ejemplares recolectados en campo durante los Ăşltimos cuatro años y que no han sido publicados. El listado contiene informaciĂłn de al menos 214 especies de condrictios que se han registrado en las aguas marinas y salobres de MĂ©xico, pertenecientes a 84 gĂ©neros, 40 familias y 14 Ăłrdenes. Se incluyen ocho especies de quimeras, 95 de batoideos y 111 de tiburones. La condrictiofauna mexicana es una de las más ricas a nivel mundial, con al menos 17.3% de las especies conocidas. Adicionalmente, 16 especies, se incluyen como especies probables que ocurran en MĂ©xico debido a sus patrones de distribuciĂłn.Palabras clave: Condrictios, Elasmobranquios, Batoideos, Quimeras, MĂ©xico
Stability Analysis of Single-Phase Low-Voltage AC Microgrids With Constant Power Terminals
This express brief presents the stability analysis of single-phase microgrids (SP-MG) operating under master-slave connection with constant power terminals. The SP-MG is composed of linear elements, nonlinear loads and distributed generators modeled as P Q constant terminals interconnected through power electronic converters. A Lyapunov?s direct method through a Hamiltonian representation of the grid is used to demonstrate stability. The non-autonomous model of the SP-MG is transformed into an autonomous equivalent model based on the dynamics of the error. The proposed analysis shows that if there exists an admissible trajectory x * solution of the power flow equations then the SP-MG is stable in the sense of Lyapunov.Fil: Montoya, O. D.. Universidad Tecnologica de Bolivar; ColombiaFil: Garces, A.. Universidad TecnolĂłgica de Pereira; ColombiaFil: Avila Becerril, S.. Universidad Nacional AutĂłnoma de MĂ©xico; MĂ©xicoFil: Espinosa PĂ©rez, G.. Universidad Nacional AutĂłnoma de MĂ©xico; MĂ©xicoFil: Serra, Federico Martin. Universidad Nacional de San Luis. Facultad de IngenierĂa y Ciencias Agropecuarias. Laboratorio de Control Automático; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - San Luis. Instituto de Investigaciones en TecnologĂa QuĂmica. Universidad Nacional de San Luis. Facultad de QuĂmica, BioquĂmica y Farmacia. Instituto de Investigaciones en TecnologĂa QuĂmica; Argentin
Characterization of AGN and their hosts in the Extended Groth Strip: a multiwavelength analysis
We have employed a reliable technique of classification of Active Galactic
Nuclei (AGN) based on the fit of well-sampled spectral energy distributions
(SEDs) with a complete set of AGN and starburst galaxy templates. We have
compiled ultraviolet, optical, and infrared data for a sample of 116 AGN
originally selected for their X-ray and mid-infrared emissions (96 with single
detections and 20 with double optical counterparts). This is the most complete
compilation of multiwavelength data for such a big sample of AGN in the
Extended Groth Strip (EGS). Through these SEDs, we are able to obtain highly
reliable photometric redshifts and to distinguish between pure and
host-dominated AGN. For the objects with unique detection we find that they can
be separated into five main groups, namely: Starburst-dominated AGN (24 % of
the sample), Starburst-contaminated AGN (7 %), Type-1 AGN (21 %), Type-2 AGN
(24 %), and Normal galaxy hosting AGN (24 %). We find these groups concentrated
at different redshifts: Type-2 AGN and Normal galaxy hosting AGN are
concentrated at low redshifts, whereas Starburst-dominated AGN and Type-1 AGN
show a larger span. Correlations between hard/soft X-ray and ultraviolet,
optical and infrared luminosities, respectively, are reported for the first
time for such a sample of AGN spanning a wide range of redshifts. For the 20
objects with double detection the percentage of Starburst-dominated AGN
increases up to 48%.Comment: 38 pages, 8 figures, 5 tables. Accepted by A
Multitemporal distribution analysis of Dodonaea viscosa (L.) Jacq. by remote sensing in Durango, Mexico
Objective: To determine the distribution of D. viscosa at the Guadalupe Victoria dam for the years 1990, 2010 and 2017.
Design/methodology/approach: Landsat satellite images were processed in order to perform a supervised classification using an artificial neural network. The ground cover of pastures, crops, shrubs and oak forest was estimated from images for the years 1990, 2010 and 2017 at sites where the presence of D. viscosa had been recorded. These data were used to calculate the expansion of D. viscosa in the study area.
Results: Limitations on study/implications: The supervised classification of the artificial neural network was optimal after 400 iterations, obtaining the best overall precision, 84.5%, for 2017. This contrasted with 1990, where overall precision was low, at 45%, because there were few training sites (fewer than 100) recorded for each of the land cover classes.
Findings/conclusions: In 1990, D. viscosa was found on only five hectares, while by 2017 it had increased to 147 hectares. If the disturbance caused by overgrazing continues, the potential distribution projected for D. viscosa shows it invading half the study area, occupying agricultural, forested and scrub areas.Objective: to determine the distribution of D. viscosa in the vicinity of the Guadalupe Victoria Dam in Durango, Mexico, for the years 1990, 2010 and 2017.Design/Methodology/Approach: Landsat satellite images were processed in order to carry out supervised classifications using an artificial neural network. Images from the years 1990, 2010 and 2017 were used to estimate ground cover of D. viscosa, pastures, crops, shrubs, and oak forest. This data was used to calculate the expansion of D. viscosa in the study area.Results/Study Limitations/Implications: the supervised classification with the artificial neural network was optimal after 400 iterations, obtaining the best overall precision of 84.5 % for 2017. This contrasted with the year 1990, when overall accuracy was low at 45 % due to less training sites (fewer than 100) recorded for each of the land cover classes.Findings/Conclusions: in 1990, D. viscosa was found on only five hectares, while by 2017 it had increased to 147 hectares. If the disturbance caused by overgrazing continues, and based on the distribution of D. viscosa, it is likely that in a few years it will have the ability to invade half the study area, occupying agricultural, forested, and shrub area
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