Ecologically Designed Sanitary Sewer Based on Constructed WetlandsTechnology – Case Study in Managua (Nicaragua)

In developed countries the sanitation and treatment of urban wastewater is well sustained and technically solved by means of conventional pipe networksandsubsequentcentralizedtreatments.However,developingcountries lack these infrastructures and are in need of sustainable, decentralized and economically viable solutions for the disposal of their urban wastewaters. In addition to this, there are situations where the demands of conservation of naturalspacesdonotallowintensiveconstructiveproceduresandwhichforce the implementation of sanitary engineering with less environmental impact. We present the Ecological Wastewater Sewer (EWS), an ecological urban sewerage system that simultaneously transports wastewater and improves its quality.Thisinnovativetechnologyisanalternativetoconventionalsanitation piping that has minimal environmental impact. It is based on a successful previous work for the improvement of artificial wetlands in a pilot scheme andatfull-scaleonatestsite.TheEWSisachannel-shapeddevicethatrelies on the application of two key developments: a carefully designed cornered stones layout, and the creation of a natural aeration system. This way, it acts as a separating sewage system that guarantees the presence of a chamber of circulating air within the transportation unit, favouring permanent aerobic conditions in the upper levels of the mass of wastewater. Furthermore, its capacity to set tle suspended solids allows the EWS to be used as a sedimentor in water purification processes. A real-life application of this system proved successful in the sanitation of a district of Managua (Nicaragua). Working with a 100-metre-long street of 20 one-story houses, the system is reported to still be in full operating order after six years. The conclusions and results drawn from its monitoring are meticulously explained in our paper, as well astherecommendations&guidelinesforthedesignofmoreEWSunits,with aim to the popularization of this affordable, efficient and green approach to wastewater sanitation.Andalusian International School of Water Engineering, City hall of SevilleCooperation Office at the University of Sevill

Effect of soil properties on the dynamic response of simply-supported bridges under railway traffic through coupled boundary element-finite element analyses

Railway induced vibrations on short-to-medium span simply-supported (SS) bridges is addressed in this contribution. Such structures may experience high levels of vertical acceleration at the platform, leading to adverse consequences such as a premature degradation of the ballast layer and passenger discomfort. In the present study, the evolution of the bridge dynamic response when soil-structure interaction (SSI) is taken into account is investigated. To this end a coupled three-dimensional (3D) Boundary Element-Finite Element model (BEM-FEM) formulated in the time domain is implemented to reproduce the soil and structural behaviour, respectively. First, a set of soil-bridge systems of interest is defined, covering a wide range of lengths and natural frequencies for the structures, and an interval of expectable elastic properties and damping levels for the soil. Then, different types of analyses are performed on the soil-bridge systems extracting conclusions regarding the effect of including SSI in numerical models for predicting the bridge behaviour under railway traffic. In particular natural frequencies and modal damping levels are identified, and the structure amplification after the passage of a moving load in free vibration is investigated. Conclusions regarding how resonance and cancellation conditions may be affected by soil properties are extracted. Finally, the dynamic response of a real bridge, belonging to the Spanish railway network, is evaluated under the circulation of trains that induce second and third resonances of the bridge fundamental mode. The effect of the soil flexibility, soil material damping and the bridge resonance order are evaluated. Conclusions regarding the appropriateness of the results provided by common models which do not include SSI effects are extractedMinisterio de Economía y Competitividad BIA2013-43085-PMinisterio de Economía y Competitividad BIA2016-75042-C2Centro Informático Científico de Andalucía (CICA

Transición de la aritmética al álgebra: Un estudio con estudiantes universitarios de Nicaragua

The following article presents the results of an investigation on the main difficulties affecting the transition from arithmetic to algebra in students of the National Autonomous University of Nicaragua, Managua (UNAN-MANAGUA), specifically in the Regional Multidisciplinary Faculty of Chontales (FAREM -Chontales). It is a permanent issue today in Mathematics Education. In the review of the literature some important concepts were found that allow to improve these difficulties. The type of sampling used was non-probabilistic, since it is a mixed-focus study, it was defined voluntarily, taking as criteria the way students responded to the test, giving their opinions and expressing their ideas in the interview. Important aspects on how to improve the difficulties presented in the development of the contents of the arithmetic and algebra units were analyzed. It is concluded that the knowledge that students acquire in the development of the contents of the arithmetic and algebra unit is essential for the following subjects as well as in their professional field.El siguiente artículo presenta los resultados de una investigación sobre las principales dificultades que afectan la transición de la aritmética al álgebra en los estudiantes de la Universidad Nacional Autónoma de Nicaragua, Managua (UNAN-MANAGUA), específicamente en la Facultad Regional Multidisciplinaria de Chontales (FAREM-Chontales). Es un tema de actualidad permanente en la Didáctica de la Matemática. En la revisión de la literatura se encontraron algunos conceptos importantes que permiten mejorar estas dificultades. El tipo de muestreo utilizado fue el no probabilístico, por tratarse de un estudio de enfoque mixto, el mismo se definió de forma voluntaria, tomando como criterio la forma que los estudiantes respondían el test, opinando y expresando sus ideas en la entrevista. Se analizaron los aspectos importantes sobre cómo mejorar las dificultades presentadas en el desarrollo de los contenidos de las unidades de aritmética y álgebra. Se concluye que el conocimiento que los estudiantes adquieren en el desarrollo de los contenidos de la unidad de aritmética y de álgebra es fundamental para las asignaturas siguientes al igual que en su ámbito profesional

Finding the principal points of a random variable

The p-principal points of a random variable X with finite second moment are those p points in R minimizing the expected squared distance from X to the closest point. Although the determination of principal points involves in general the resolution of a multiextremal optimization problem, existing procedures in the literature provide just a local optimum. In this paper we show that standard Global Optimization techniques can be applied.Ministerio de Ciencia y Tecnologí

Maximum resonance and cancellation phenomena in orthotropic plates traversed by moving loads: Application to railway bridges

The vibrational response of railway bridges is an issue of main concern, especially since the advent of High-Speed traffic. In the case of short-to-medium lengths and simply-supported spans excessive transverse acceleration levels may be induced at the platform, with detrimental consequences for passengers and infrastructures. The orthotropic plate has proven to be an appropriate model for the prediction of the response of certain typologies in the aforementioned cases such as multiple girder decks, solid or voided slabs or filler-beam multiple-track decks. In this contribution, the vibrational response of orthotropic plates, simply and elastically supported, circulated by vertical moving loads is investigated. First, maximum free vibration and cancellation conditions are derived analytically. From these, bridge span length-characteristic distance ratios leading to maximum and minimum resonances under series of equidistant loads are depicted. Second, the applicability of these ratios in oblique decks is analysed for the most common first three mode shapes: first longitudinal bending, first torsion and first transverse bending modes, and the errors in relation to the straight reference case are bounded. To this end, an extensive bridge catalogue of girder bridges is designed in the range of lengths of interest, covering flexural stiffnesses typical from both conventional and High-Speed railway lines. Finally, the applicability of the previous theoretical results is exemplified with experimental measurements performed on a bridge from the Spanish railway network.Spanish Ministries of Economy and Competitiveness (Ministerio de Economía y Competitividad, España) BIA2016-75042-C2Spanish Ministries of Education (Ministerio de Educación, España) CAS18/00080Generalitat Valenciana (España) AICO/2019/17

Computational study of the cavitation phenomenon and its interaction with the turbulence developed in diesel injector nozzles by Large Eddy Simulation (LES)

Firstly, the code has been validated at real operating diesel engine conditions with experimental data in terms of mass flow, momentum flux and effective velocity, showing that the model is able to predict with a high level of confidence the behavior of the internal flow at cavitating conditions. Once validated, the code has allowed to study in depth the turbulence developed in the discharge orifices and its interaction with cavitation phenomenon. (C) 2011 Elsevier Ltd. All rights reserved.This work was partly sponsored by "Vicerrectorado de Investigacion, Desarrollo e Innovacion'' of the "Universitat Politecnica de Valencia'' in the frame of the project "Estudio numerico de la cavitacion en toberas de inyeccion Diesel mediante Grid Computing (Cavigrid)'', reference No. 2597 and by "Ministerio de Ciencia e Innovacion'' in the frame of the project "Estudio teorico-experimental sobre la influencia del tipo de combustible en los procesos de atomizacion y evaporacion del chorro Diesel (PROFUEL)'', reference TRA2011-26293. This support is gratefully acknowledged by the authors.Salvador Rubio, FJ.; Martínez López, J.; Romero Bauset, JV.; Roselló Ferragud, MD. (2013). Computational study of the cavitation phenomenon and its interaction with the turbulence developed in diesel injector nozzles by Large Eddy Simulation (LES). Mathematical and Computer Modelling. 57(7-8):1656-1662. https://doi.org/10.1016/j.mcm.2011.10.050S16561662577-

OMW spillage control tool based on tracking p-Coumaric acid degradation by HPLC

Olive mill wastewater (OMW) is a major watercourse pollutant agent with a high concentration of phenolic compounds. It is estimated that 30 million OMW m3 are released into rivers every year. Protecting the health of these courses against the uncontrolled discharges implies establishing an adequate legislation, where spillage control tools play a fundamental role. In this paper, a new tool for OMW spillage control is discussed. It is based on the use of a RP-HPLC-UV protocol to track p-Coumaric acid (pCA), a characteristic OMW phenolic compound, and its derivative compounds through their chemical oxidation and biological anaerobic degradation. Laboratory assays and real-life experiences allowed to determine degradation routes and apparition times for every pCA derivative, making it possible to detect an OMW spill and assess its age. Moreover, this RP-HPLC-UV introduces solid advantages over previous detection procedures, namely, quicker response times and smaller costs than HPLC methods and superior specificity than colorimetric methods. Finally, this tool was put to test in an actual OMW-polluted watercourse. In all scenarios, the tool demonstrated solid reliabilit

Bioparticles consisting of olive mill wastewater (OMW)-adapted bacteria and OMW-polluted soil as carrier– An application in an anaerobic fluidized bed bioreactor

The world olive oil production represents a very significant sector of the alimentary industry. Nonetheless, the spillages associated to the sector –olive mill wastewater (OMW)– imply serious environmental risks due to their difficult treatments. This study showcases the use of bioparticles from a soil that has repeatedly been contaminated by OMW, to treat water also polluted by OMW. The bacterial biomass that develops overtime within a OMW-polluted course becomes adapted to its conditions and proves effective in its treatment. Water and soil samples were taken from a watercourse that has been suffering from periodic OMW discharges during the last 25 years. Two main factors were identified as the causes of the efficiency of these soils as a means of biological treatment: high concentrations and extended adaptation of active biomass to the pollutants present in the watercourse. The start-up times of the biological processes are reduced since no adaptation period is necessary. This makes it possible to eschew pre-treatment procedures in biological processes. A guide for the design of a continuous flow anaerobic fluidized bed bioreactor (AnFBR) is provided. A stream of 300 m3 d−1 and 5000 mg L−1 COD generates an electrical and thermal energy of 1654 kW h d−1 and 2341 kW h d−1 respectively

Estudio del riesgo de erosión potencial en la cuenca alta del Río Hozgarganta

En el presente trabajo se analiza el riesgo de erosión potencial del suelo en la cuenca alta del río Hozgarganta. Para ello se ha utilizado el método propuesto por PAP/RAC (1997) y modificado posteriormente por Jordán y Martínez-Zavala (Jordán, 2000; Martínez-Zavala, 2001; Martínez-Zavala et al., 2002). Mediante este sistema se ha dividido el área de estudio en unidades de territorio con diferente grado de susceptibilidad a la erosión hídrica (estado erosivo). Se ha evaluado el riesgo de erosión actual y el riesgo de erosión potencial, planteando tres escenarios posibles de cobertura de la vegetación. De esta forma, se puede concluir que el riesgo de pérdida de suelo en la cuenca del Hozgarganta es bajo. Sin embargo, el sistema se halla en un equilibrio inestable, ya que pequeños cambios en la cobertura de la vegetación pueden originar grandes cambios en la intensidad de los procesos erosivos.Potential soil erosion risk in the high basin of Hozgarganta river is analyzed in this paper. We have used the methodology proposed by PAP/RAC (1997), as modified Jordán and Martínez-Zavala (Jordán, 2000; Martínez-Zavala, 2001; MartínezZavala et al., 2002). Using this method, the study area has been divided in terrain units with different level of susceptibility to rainfall-induced erosion risk (erosive status). An assesment of actual and potential erosion risk is carried out, suposing three posible situations, acording to different percentages of canopy. As a conclusion, the actual soil erosion risk is low for the Hozgarganta Basin. However, the equilibrium of the system is unstable, so that little changes in the vegetation cover may originate great changes in the intensity of the erosive processe

Study of the influence of the needle eccentricity on the internal flow in diesel injector nozzles by computational fluid dynamics calculations

In the present paper, a computational study has been performed in order to clarify the effects of the needle eccentricity in a real multihole microsac nozzle. This nozzle has been simulated at typical operating conditions of a diesel engine, paying special attention to the internal flow development and cavitation appearance within the discharge orifices. For that purpose, a multiphase flowsolver based on a homogeneous equilibrium model with a barotropic equation of state has been used, introducing the turbulence effects by Reynolds-averaged Navier Stokes methods with a re-normalization group k-eps model. The results obtained from this investigation have demonstrated the huge influence of the needle position on the flow characteristics, showing important hole to hole differences.This work was partly sponsored by 'Vicerrectorado de Investigacion, Desarrollo e Innovacion' of the 'Universitat Politecnica de Valencia' in the frame of the project 'Estudio de la influencia del uso de combustibles alternativos sobre el proceso de inyeccion mediante GRID computing (FUELGRID)', and by 'Ministerio de Ciencia e Innovacion' in the frame of the project 'Estudio teorico-experimental sobre la influencia del tipo de combustible en los procesos de atomizacion y evaporacion del chorro Diesel (PROFUEL), reference TRA2011-26293. This support is gratefully acknowledged by the authors.Salvador Rubio, FJ.; Martínez López, JE.; Romero Bauset, JV.; Roselló Ferragud, MD. (2014). Study of the influence of the needle eccentricity on the internal flow in diesel injector nozzles by computational fluid dynamics calculations. International Journal of Computer Mathematics. 91(1):24-31. https://doi.org/10.1080/00207160.2013.770483S2431911Alajbegovic, A., Meister, G., Greif, D., & Basara, B. (2002). Three phase cavitating flows in high-pressure swirl injectors. Experimental Thermal and Fluid Science, 26(6-7), 677-681. doi:10.1016/s0894-1777(02)00179-6Bermúdez, V., Payri, R., Salvador, F. J., & Plazas, A. H. (2005). Study of the influence of nozzle seat type on injection rate and spray behaviour. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 219(5), 677-689. doi:10.1243/095440705x28303Desantes, J. M., Payri, R., Garcia, J. M., & Salvador, F. J. (2007). A contribution to the understanding of isothermal diesel spray dynamics. Fuel, 86(7-8), 1093-1101. doi:10.1016/j.fuel.2006.10.011Faeth, G. ., Hsiang, L.-P., & Wu, P.-K. (1995). Structure and breakup properties of sprays. International Journal of Multiphase Flow, 21, 99-127. doi:10.1016/0301-9322(95)00059-7F. P. Kärrholm, H. Weller, N. Nordin, Modelling injector flow including cavitation effects for diesel applications. Proceedings of FEDSM, 5th Joint ASME/JSME Fluids Engineering Conference, San Diego, California, July 30–August 2 2007Lee, J. W., Min, K. D., Kang, K. Y., Bae, C. S., Giannadakis, E., Gavaises, M., & Arcoumanis, C. (2006). Effect of piezo-driven and solenoid-driven needle opening of common-rail diesel injectors on internal nozzle flow and spray development. International Journal of Engine Research, 7(6), 489-502. doi:10.1243/14680874jer00806T. Oda, M. Hiratsuka, Y. Goda, S. Kanaike, and K. Ohsawa,Experimental and numerical investigation about internal cavitating flow and primary atomization of a large-scaled vco diesel injector with eccentric needle. ILASS-Europe 2010, 23rd Annual Conference on Liquid Atomization and Spray Systems, Brno, Czech Republic, September 2010.Park, S. H., Suh, H. K., & Lee, C. S. (2009). Effect of Bioethanol−Biodiesel Blending Ratio on Fuel Spray Behavior and Atomization Characteristics. Energy & Fuels, 23(8), 4092-4098. doi:10.1021/ef900068aPAYRI, R., GARCIA, J., SALVADOR, F., & GIMENO, J. (2005). Using spray momentum flux measurements to understand the influence of diesel nozzle geometry on spray characteristics. Fuel, 84(5), 551-561. doi:10.1016/j.fuel.2004.10.009Payri, F., Payri, R., Salvador, F. J., & Martínez-López, J. (2012). A contribution to the understanding of cavitation effects in Diesel injector nozzles through a combined experimental and computational investigation. Computers & Fluids, 58, 88-101. doi:10.1016/j.compfluid.2012.01.005Payri, R., Salvador, F. J., Gimeno, J., & de la Morena, J. (2009). Effects of nozzle geometry on direct injection diesel engine combustion process. Applied Thermal Engineering, 29(10), 2051-2060. doi:10.1016/j.applthermaleng.2008.10.009Payri, R., Salvador, F. J., Martí-Aldaraví, P., & Martínez-López, J. (2012). Using one-dimensional modeling to analyse the influence of the use of biodiesels on the dynamic behavior of solenoid-operated injectors in common rail systems: Detailed injection system model. Energy Conversion and Management, 54(1), 90-99. doi:10.1016/j.enconman.2011.10.004Salvador, F. J., Gimeno, J., De la Morena, J., & Carreres, M. (2012). Using one-dimensional modeling to analyze the influence of the use of biodiesels on the dynamic behavior of solenoid-operated injectors in common rail systems: Results of the simulations and discussion. 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