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This article belongs to the Special Issue Optimization of Motion Planning and Control for Automatic Machines, Robots and Multibody Systems. ; This work presents and discusses a general approach for the dynamic modeling and analysis of a passive biped walking robot, with a particular focus on the feet-ground contact interaction. The main purpose of this investigation is to address the supporting foot slippage and viscoelastic dissipative contact forces of the biped robot-walking model and to develop its dynamics equations for simple and double support phases. For this investigation, special attention has been given to the detection of the contact/impact between the legs of the biped and the ground. The results have been obtained with multibody system dynamics applying forward dynamics. This study aims at examining and comparing several force models dealing with different approaches in the context of multibody system dynamics. The normal contact forces developed during the dynamic walking of the robot are evaluated using several models: Hertz, Kelvin-Voight, Hunt and Crossley, Lankarani and Nikravesh, and Flores. Thanks to this comparison, it was shown that the normal force that works best for this model is the dissipative Nonlinear Flores Contact Force Model (hysteresis damping parameter - energy dissipation). Likewise, the friction contact/impact problem is solved using the Bengisu equations. The numerical results reveal that the stable periodic solutions are robust. Integrators and resolution methods are also purchased, in order to obtain the most efficient ones for this model. ; This work was financially supported by the Spanish Government through the MCYT project "RETOS2015: sistema de monitorización integral de conjuntos mecánicos críticos para la mejora del mantenimiento en el transporte-maqstatus"

Numerous theorists of social sciences and humanities have analyzed the types of government that human civilization experienced for centuries; this would mean that with the development of ideas, the styles of governing would be adapted to the contexts to perfect themselves with practice. In 2018, we can say, almost certainly, that we are far from this ideal of perfection in political and social interactions. While there has been enough talk of the shaky democracy that Mexico has as a nation and the probable failed state in which we live, the small interactions in terms of politics and democracy that take place in this country have not received enough attention. This text analyzes one of the 2446 political interactions at municipal level that occur in the Mexican territory. Focusing on the form and quality in which the governments of a municipality of Hidalgo have affected positively or negatively its population, and then analyze the solutions that have been tried to give from the citizenship, and rounding up giving an answer from the perspective and axiomatic point of view of the authors of the present essay. ; Un sinnúmero de teóricos de las ciencias sociales y humanidades han analizado los tipos de gobierno que la civilización humana experimentó a través de los siglos, esto supondría que con el paso de las ideas, las formas de gobierno se irían adecuando a los contextos para perfeccionarse en la práctica. En el 2018 podemos decir, casi con certeza, que se está muy lejos de este ideal de perfección en las interacciones políticas y sociales. Si bien se ha hablado suficiente de la democracia tambaleante que tiene México como nación y del probable Estado fallido en el que vivimos, no se ha puesto suficiente atención a las pequeñas interacciones que suceden en este país en cuanto a política y democracia. El presente texto analiza una de las 2446 interacciones políticas a escala municipal que suceden en el territorio mexicano, enfocándose en la forma y calidad en la que los gobiernos de un municipio de Hidalgo han afectado positiva o negativamente a la población de éste, para luego analizar las soluciones que se han intentado dar desde la ciudadanía, y redondear dando una respuesta desde la óptica y punto de vista axiomático de los autores del presente ensayo.

Having accurate and timely data on confirmed active COVID-19 cases is challenging, since it depends on testing capacity and the availability of an appropriate infrastructure to perform tests and aggregate their results. In this paper, we propose methods to estimate the number of active cases of COVID-19 from the official data (of confirmed cases and fatalities) and from survey data. We show that the latter is a viable option in countries with reduced testing capacity or suboptimal infrastructures. ; Regional Government of Madrid ; TRUE ; pub