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Humanity has suffered throughout its history from different types of pandemics caused by deadly infectious diseases. Mathematical models are very useful tools to understand the dynamics of the behavior and propagation of these. Among these models are those known as SIS, SIR and SEIR. This paper presents a brief explanation of the structure of these models and its use in some pandemics. In particular, some SIR-type models without and with delays are analyzed with special interest, as well as their applications to the current pandemic caused by the SARS-CoV-2 virus. To determine the correspondence between some of the models analyzed and the data of Infectious and Recovered from Mexico reported by the World Health Organization (WHO), simulations are presented in three different time periods between the years 2020-2021. In addition, an unpublished SIR-type mathematical model with three delays is proposed as a main contribution. Finally, a discussion is given on the application of numerical algorithms to identify some parameters of mathematical models, such as ordinary least squares. [ABSTRACT FROM AUTHOR]

Copyright of Ecologia Austral is the property of Asociacion Argentina de Ecologia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acción Psicológica is the property of Editorial UNED and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper proposes a desing of a boost-type DC-DC converter, based on a state space model and calculation of a controller with multiplicative unstructured uncertainty. Performance of the converter at low frequencies was analyzed; as well, weight of the weighting function was adjusted, to reduce noise at certain frequencies. Results of system simulation, in open loop and closed loop, demostrate that the designed controller allows modifying cutoff frequency, through the variation of weighting functions. It is concluded that this technique optimizes dynamics behavior of the system. [ABSTRACT FROM AUTHOR]

Copyright of Geominas is the property of FUNDA-GEOMINAS. (Fundacion de Egresados d Amigos de la Escuela de Ingenieria Geologica y de Minas) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wind generated waves are a very random phenomenon and it is one of the main environmental disturbances that affect the operation of Autonomous Underwater Vehicles (AUV) navigating in shallow waters and coastal zones. In order to attenuate the undesirable effect of the ocean waves on the control system of AUVs, the measurements from the sensors need to be filtered out, using the estimated wave encounter frequency. Developing an estimator capable of providing the encounter frequency in real time using the Algebraic Identification method, is fully reported in this paper. In the design of the proposed algebraic estimator, a linear differential equation to represent the waves spectrum is used, which simplifies the mathematical procedure. The simulations carried out with simulated data and with real data from an experiment at sea, show the excellent results of the estimator in terms of precision in the final value and estimation time. In addition, its show the use of the wave encounter frequency estimation to adjust the filtering techniques previously implemented for the vehicle in a proper way, which results in a reduction of vibrations and energy consumption of the vehicle's rudder system. [ABSTRACT FROM AUTHOR]

Copyright of Revista Facultad de Ingeniería Universidad de Antioquia is the property of Universidad de Antioquia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Informador Técnico is the property of Servicio Nacional de Aprendizaje SENA and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Monthly wage series with quarterly periodicity between December 1994 and December 2004 for thirteen regions in Chile are presented in this paper. These series are based on the information gathered by the Superintendencia de Fondos de Pensiones (Pensions Fund Superintendence), but are corrected for truncation and censoring bias. The comparative analysis of corrected and non-corrected series indicates that the series show a statistically differentiated behavior. The non-corrected wage series are not good predictors of the corrected series. Thus, to develop regional wage analysis based on this information source, it is preferable to use the corrected series presented in this paper. [ABSTRACT FROM AUTHOR]

Copyright of Trabajos de Estadística is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper we analyze the results and processes used by third-year secondary students and prospective elementary teachers in estimation tasks of continuous quantities of length, surface, capacity and mass. The results show no differences between both groups of students. Both are good estimators of length and surface but underestimate capacity and mass. No big differences are detected in the processes and strategies used, except a higher and more effective use of formulas in the case of prospective teachers. [ABSTRACT FROM AUTHOR]

The methodology for estimating shelf life of food proposes the use of one of the two most widely used estimation methods depending on the nature and expected shelf life of the particular product: Weibull analysis or hazard techniques and accelerated shelf life tests for temperature abuse. In this paper the steps to apply both estimation methods and examples are presented. [ABSTRACT FROM AUTHOR]

A shelf-life study is an objective and methodical means to determine or estimate such time, for this estimation it is necessary for food producers and developers to have a methodology that will help them to perform reliable and accurate shelf life studies. The proposed methodology is based on the general procedure for estimating shelf life consisting of three steps: preliminary analysis of the product packaging environment system, storage and characterization tests and application of the appropriate estimation technique. In this paper, we discuss, in a general way, some methodological and practical considerations that must be taken into account for the execution of the first two steps. [ABSTRACT FROM AUTHOR]

Copyright of Revista Tecno Lógicas is the property of Instituto Tecnologico Metropolitano and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Ingeniería Agrícola is the property of Instituto de Investigaciones de Ingenieria Agricola and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista Logos Ciencia & Tecnologia is the property of Policia Nacional and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Avances de Investigación en Educación Matemática is the property of Sociedad Espanola de Investigacion en Educacion Matematica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Ensayos de Economia is the property of Universidad Nacional de Colombia and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Cuadernos de Administración is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)