Estudio y modelizado 3D de la máquina de movimiento alterno que Leonardo da Vinci diseñó en el folio 30 verso del Códice Atlántico

Se ha realizado una investigación sobre el contexto en el que se concibe la máquina de movimiento alterno, dejando una pequeña recopilación de maquinarias y estudios que Leonardo realizó en relación con la transmisión del movimiento y la elevación vertical de cargas pesadas. Esta máquina de movimiento alterno será la base de estudio en la que nos centraremos, realizando un análisis funcional en el que llegaremos a conclusiones de nivel constructivo para proponer cambios o mejoras a la invención para perfeccionar el mecanismo. A nivel de interés general destacaremos el sistema de representación de vista explosionada que Leonardo aplica en este folio, convirtiendo este boceto en pionero histórico en usar este tipo de representación. Una vez aclarado el funcionamiento, nos apoyaremos en el software SolidWorks para realizar un modelo 3D que nos permita realizar renderizados, vistas explosionadas y simulaciones de movimiento que nos ayudará a mostrar al mundo de manera clara cómo funciona la máquina de movimiento alterno diseñada por Leonardo Da Vinci en el folio 0030 verso del Códice Atlántico

Experimental investigation and modelling of biodiesel combustion in engines with late direct injection strategy

The combination of alternate fuels, such as biodiesel, and low-temperature combustion (LTC) constitutes a promising solution to reduce pollutant emission and to avoid dependence on fossil fuels. However, this concept requires additional research to optimise LTC of biodiesel over wider operating ranges, specifically including the implementation of numerical models to assist in the development of these engines. In this work, an experimental analysis was carried out assessing both thermal performance and emissions derived from the LTC of diesel/biodiesel blends with late direct injection. Furthermore, this analysis allowed implementing a predictive tool to characterise in-cylinder pressure trace under this operation strategy. This model was coupled with an empirical law to simulate heat release during the combustion process. Least squares method was applied to fit this empirical law to experimental data involving different conditions in terms of percentages of rapeseed biodiesel in the fuel blend, rotational speed, fuel/air equivalence ratio and percentages of external exhaust gas recirculation. To build the predictive model, a multiple regression methodology was used to correlate the law parameters with the operating conditions. Finally, a validation process based on the simulation of in-cylinder pressure trace was developed, revealing that the predictions agreed well with the experimental data. This suggests that the proposed model is able to satisfactorily predict the LTC of diesel/biodiesel blends within the test range.Junta de Andalucía - Consejería de Economía AT17-5934-USUniversidad de Cádiz PB2022-04

Preliminary study on the performance of biomorphic silicon carbide as substrate for diesel particulate filters

This paper presents the results of a preliminary experimental study to assess the performance of biomorphic silicon carbide when used for the abatement of soot particles in the exhaust of Diesel engines. Given its optimal thermal and mechanical properties, silicon carbide is one of the most popular substrates in commercial diesel particulate filters. Biomorphic silicon carbide is known for having, besides, a hierarchical porous microstructure and the possibility of tailoring that microstructure through the selection of a suitable wood precursor. An experimental rig was designed and built to be integrated within an engine test bench that allowed to characterizing small lab-scale biomorphic silicon carbide filter samples. A particle counter was used to measure the particles distribution before and after the samples, while a differential pressure sensor was used to measure their pressure drop during the soot loading process. The experimental campaign yielded promising results: for the flow rate conditions that the measuring devices imposed (1 litre per minute; space velocity = 42,000 L/h), the samples showed initial efficiencies above 80%, pressure drops below 20 mbar, and a low increase in the pressure drop with the soot load which allows to reach almost 100% efficiency with an increase in pressure drop lower than 15%, when the soot load is still less than 0.01 g/L. It shows the potential of this material and the interest for advancing in more complex diesel particle filter designs based on the results of this workMinisterio de Economía y Competitividad (España) MAT2013-41233-R DPI2013-46485-C3-3-RFondos FEDER MAT2013-41233-R DPI2013-46485-C3-3-RUniversidad de Sevilla VI Plan Propio I.3B - C.I. 24/05/2017 MAT2016-76526-

Mechanical analysis of Genoa 03 stirling engine

Due to the new technologies development based on renewable sources of energy, in recent years Stirling engines have become very important in the energetic sector. Many of them do not allow the use of fluid lubricants and, thus, the effect of friction losses is important. For this purpose, a mathematical model has been developed based on the force balance in the crankshaft using the pressure distribution in the cylinders. The aim of this work is to characterize the mechanical losses in a Genoa 03 Stirling engine using a numerical model and experimentally via the drag method. The results of this model have been compared with those obtained experimentally on Genoa 03 Stirling engine. In the experimental results, a proportional increase in friction torque due to the average pressure and the speed of the crankshaft is observed. The first of these is caused by an increase of dry friction forces and the second, by the viscous friction between the working fluid and the inner walls of the engine. Also in this paper, irreversible processes in a beta type Stirling engine have been investigated in order to highlight the impact of losses on mechanical power and its performance. This article develops the first study of the mechanical losses of Genoa 03 experimental Stirling engine, which has an output power of 3 kW. Although the model response follows the same trends as the experiments, those simplifications provide errors which become more significant as the engine speed increases.Ministerio de Economía y Competitividad ENE2013-43465-

New five stars hotels in Madrid: future according to Altman tests

La expansión de las entidades hoteleras en España sufrió una gran expansión desde la década de los noventa En caso concreto de Madrid se han creado en Madrid 13 hoteles nuevos de cinco estrellas, Dada la actual situación del turismo en Madrid con un descenso continúo de alojados y pernoctaciones desde el año 2008, cabe preguntarse por su viabilidad futura de los anteriores hoteles y más concretamente su posibilidad de quiebra Para responder a la anterior pregunta se puede ejecutar los test de Altman conocidos como Z1 y Z2 utilizando la información contable de estos hoteles desde 2007 y contrastar sus resultados con su situación patrimonial en años posteriores. De esta forma se va a conseguir un doble objetivo: a) Contrastar la calidad de la situación financiera de los nuevos hoteles. b) Confirmar la utilidad o no de los test de Altman para estos hoteles y abrir el debate sobre la necesidad o no de crear un modelo de predicción de la quiebra propio

Prediction of hydrogen-heavy fuel combustion process with water addition in an adapted low speed two stroke diesel engine: Performance improvement

Article number 117250Despite their high thermal efficiency (>50%), large two-stroke (2 T) diesel engines burning very cheap heavy fuel oil (HFO) produce a high level of carbon dioxide (CO2). To achieve the low emission levels of greenhouse gases (GHG) that will be imposed by future legislation, the use of hydrogen (H2) as fuel in 2 T diesel engines is a viable option for reducing or almost eliminate CO2 emissions. In this work, from experimental data and system modelling, an analysis of dual combustion is carried out considering different strategies to supply H2 to the engine and for different H2 fractions in energy basis. Previously, a complete thermodynamic model of a 2 T diesel engine with an innovative scavenging model is developed and validated. The most important drawbacks of this type of engines are controlled in this work using dual combustion and water injection, reducing nitrogen oxides emissions (NOx), self-ignition and combustion knocking. The results show that the developed model matches engine performance data in diesel mode, achieving a higher efficiency and mean effective pressure (MEP) in hydrogen mode of 53% and 14.62 bar respectively.Consejería de Economía, Conocimiento, Empresas y Universidad(Junta de Andalucía) AT17_5934_U

Longitudinal study of low and high achievers in early mathematics

Background. Longitudinal studies allow us to identify, which specific maths skills are weak in young children, and whether there is a continuing weakness in these areas throughout their school years. Aims. This 2-year study investigated whether certain socio-demographic variables affect early mathematical competency in children aged 5–7 years. Sample. A randomly selected sample of 127 students (64 female; 63 male) participated. At the start of the study, the students were approximately 5 years old (M = 5.2; SD = 0.28; range = 4.5–5.8). Method. The students were assessed using the Early Numeracy Test and then allocated to a high (n = 26), middle (n = 76), or low (n = 25) achievers group. The same children were assessed again with the Early Numeracy Test at 6 and 7 years old, respectively. Eight socio-demographic characteristics were also evaluated: family model, education of the parent(s), job of the parent(s), number of family members, birth order, number of computers at home, frequency of teacher visits, and hours watching television. Results. Early Numeracy Test scores were more consistent for the high-achievers group than for the low-achievers group. Approximately 5.5% of low achievers obtained low scores throughout the study. A link between specific socio-demographic characteristics and early achievement in mathematics was only found for number of computers at home. Conclusions. The level of mathematical ability among students aged 5–7 years remains relatively stable regardless of the initial level of achievement. However, early screening for mathematics learning disabilities could be useful in helping low-achieving students overcome learning obstacles.This material is based on work supported by the Spanish Ministry of Science & Technology grant no. SEJ2007-62420/EDUC and Junta de Andalucia grant no. P09-HUM-4918

Tasas de interés pasivas y activas de tarjetas de crédito de instituciones financieras mexicanas y de otros países. Un análisis comparativo

1 archivo PDF (18 páginas). magyefsEste artículo tiene como objetivo comparar las tasas de interés activas de Instituciones Financieras en México y otros países, particularmente las referidas a tarjetas de crédito, buscando probar la hipótesis que México está entre los países cuyos bancos comerciales cobran las tasas de interés activas más altas en tarjeta de crédito, destacando las Instituciones Financieras con participación mayoritariamente mexicana. Se realizó un análisis multivariante que consiste en comparar: 1) Las tasas de interés activas cobradas en México y otros países en el año 2013, 2) El número de tarjetas emitidas por los diferentes bancos comerciales en México en el año 2013, 3) El Índice de Capitalización Bancaria (ICAP), y la variable cuatro describe aquellas instituciones financieras con inversión mayoritariamente extranjera en México y aquellas instituciones bancarias con inversión mayoritariamente mexicana en el mercado doméstico. ABSTRACT: Deposit and lending rates for interest credit cards of Mexican financial Institutions and other countries. A comparative analysis. This article aims to compare the lending rates of financial institutions in Mexico and other countries, particularly those related to credit cards, seeking to test the hypothesis that Mexico is among the countries whose commercial banks charge interest rates higher in active credit card, highlighting financial institutions with majority Mexican ownership. A multivariate analysis was performed to compare: 1) the lending rates charged in Mexico and other countries in 2013, 2) The number of cards issued by different commercial banks in Mexico in 2013, 3) Bank Capitalization Ratio (BCR) and variable four describes those financial institutions with majority foreign investment in Mexico and those banks with majority investment in the Mexican domestic market. PALABRAS CLAVE: tasas de interés activas, tarjetas de crédito, bancos comerciales. KEYWORDS: rates for interest, credit cards, commercial banks

Methodology for the estimation of cylinder inner surface temperature in an air-cooled engine

A methodology for the estimation of the mean temperature of the cylinder inner surface in an air-cooled internal combustion engine is proposed. Knowledge of this temperature is necessary to determine the heat flux from the combustion chamber to the cylinder wall. Along with the heat transfer coefficient this parameter also allows almost 50% of engine heat losses to be determined. The temperature is relatively easy to determine for water-cooled engines but this is not in the case for air-cooled engines. The methodology described here combines numerical and experimental procedures. Simulations were based on FEM models and experiments were based on the use of thermocouples and infrared thermography. The methodology avoids the use of data or correlations developed for other engines, providing more reliable results than extrapolating models from one engine to another. It also prevents from taking measurements from inside the combustion chamber, reducing invasion and experiments complexity. The proposed methodology has been successfully applied to an air-cooled four-stroke direct-injection diesel engine and it allows the cylinder mean inner surface temperature and cylinder-cooling air heat transfer coefficient to be estimated.Ministerio de Eduación y Ciencia CTQ2007-68026-CO2-02/PP