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Search Results: 1 - 10 of 472426 matches for " Miguel A.; "
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Late surgical correction of anomalous left coronary artery from pulmonary trunk in children, using autogenous aortic and pulmonary endotheliazed tube  [PDF]
Miguel A. Maluf
World Journal of Cardiovascular Diseases (WJCD) , 2012, DOI: 10.4236/wjcd.2012.23022
Abstract: Background: Direct re-implantation of an anomalous left coronary artery into the aorta is the preferred surgical option for creating a dual coronary arterial system in patients in whom the anomalous artery originated from the pulmonary trunk. This technique, however, is applicable only when the anomalous ar- tery arises from the left posterior pulmonary sinus. We report the successfully late follow-up of series of patients employing a new technique using combined autogenous aortic and pulmonary endotheliazed tube. Patients and Methods: We have treated 3 patients, aged 2 months, 6 months and 8 months respectively, who presented with anomalous origin of the left coronary artery from the left posterior pulmonary sinus and moderated mitral valve insufficiency by left ventricle dysfunction. We used a trapdoor like coronary artery elongation with autogenous aortic and pulmonary endotheliazed tube to connect the left coronary ostium to ascending aorta, avoiding the mitral valve intervention. Results: There was no early or late death. All patients are in functional class I, with good biventricular function and competent mitral valve at a median follow-up of 94 months, ranged from 108 to 132 months. Postoperative Computerized tomogramphy of aorta in our 1st patient showed good arterial flow, without any distortion. A local and distal stenosis of the left pulmonary artery was observed and submitted to stent treatment. Conclusions: The potential benefits of the trapdoor like and its modification technique are excellent operative exposure. The use of autogenous endothelized tube is a viable tissue capable of further growth, avoidance of injury to the aortic and pulmonary valvar apparatus or production of obstruction within the right ventricular outflow tract.
Internal Vibration and Synchronization of Four Coupled Self-Excited Elastic Beams  [PDF]
Miguel A. Barron
Open Journal of Applied Sciences (OJAppS) , 2016, DOI: 10.4236/ojapps.2016.68050
Abstract: The vibration behavior and the synchronization between some internal points of four coupled self-excited beams are numerically studied. Coupling through the root of the beams is considered. The transverse displacements of the internal points and the beam tips are monitored, and the power spectra of the resulting time series are employed to determine the oscillation frequencies. The synchronization between beams is analyzed using phase portraits and correlation coefficients. Numerical results show multiple frequencies in the vibration pattern, and complex patterns of synchronization between pairs of beams.
Numerical Simulation of Pesticide Transport and Fate for Water Management in the Fucino Plain, Italy  [PDF]
Journal of Water Resource and Protection (JWARP) , 2010, DOI: 10.4236/jwarp.2010.21004
Abstract: A three-phase pesticide transport model is used to verify by numerical simulation, the influence of different parameters on infiltration through soil and/or surface runoff processes. Simulations are performed for a typical sandy loam potato field of Italy’s Fucino Plain, to explain the occurrence of measured concentrations of pesticides (mainly Linuron) in both surface waters and groundwater. Simulations take into account agricultural practices, climatic conditions, and soil characteristics. Results focus on the role of rainfall events and irrigation, of related infiltration amount and distribution, and of root zone thickness in influencing pesticide fate and its possible concentration increase through the years. Modeling results positively fit with the background knowledge of the Plain hydrology, showing the prevalence of surface transport and a scarce possibility for pesticides to reach groundwater in an average rainfall/irrigation scenario. Meanwhile, specific water management strategies are suggested to limit the occurrence of local groundwater pollution, related to high aquifer vulnerability zones, controlling inappropriate irrigation and pesticide application.
Numerical Simulation of an Argon Stirred Ladle with Top and Bottom Injection  [PDF]
Sofia Torres, Miguel A. Barron
Open Journal of Applied Sciences (OJAppS) , 2016, DOI: 10.4236/ojapps.2016.613075
Abstract: The stirring of a molten steel ladle with argon injection through a top submerged lance and a bottom nozzle is numerically studied here through Computational Fluid Dynamics (CFD) simulations. Three lance submergence depths and three injection velocities are considered in the CFD numerical experiments. The turbulent dissipation rate is employed to characterize the stirring phenomenon. The mixing times are determined from the gas flow rate, ladle geometry and bath depth using an empirical correlation.
A Feedforward Controller to Regulate the Chemical Composition of Molten Steel in a Continuous Casting Tundish  [PDF]
Miguel A. Barron, Dulce Yolotzin, Isaias Hilerio
Intelligent Control and Automation (ICA) , 2013, DOI: 10.4236/ica.2013.43029

A feedforward controller for the automatic regulation of chemical composition of molten steel in the tundish of a continuous casting machine is proposed in this work. The flow of molten steel inside the tundish is modeled as a distributed parameter system, and the resulting partial differential equation is transformed into a set of ordinary differential equations by means of the finite differences technique. From the above set and using a proper boundary condition, a feedforward control law is synthesized. No experimental tests are reported, however, the dynamic performance of the controller is illustrated by means of numerical simulations.

Inverter-Based Diesel Generator Emulator for the Study of Frequency Variations in a Laboratory-Scale Autonomous Power System  [PDF]
Miguel Torres, Luiz A. C. Lopes
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.53027

This paper presents the modeling, simulation and practical implementation of an inverter-based diesel generator emulator. The main purpose of this emulator is for the study of frequency variations in diesel-based autonomous power systems in a laboratory environment where the operation of a real diesel generator is not possible. The emulator basically consists in a voltage source inverter with a second order output filter which voltage references are given by the model of the diesel generator. The control of the emulator is based on the digital signal processor TMS320F2812, where the mathematical models of the diesel generator and the control of the inverter are computed in real-time. Parameters for the model were obtained from commercially available components. Experimental results for different values of speed droop showed that the emulator achieves a satisfactory performance in the transient and stationary response. For the stationary response, the measured frequency deviates from theoretical values with a mean absolute error of: 0.06 Hz for 0% droop, 0.037 Hz for 3% droop, and 0.087 Hz for 5% droop. For the transient response, the measured frequency nadir deviates from simulations in: 0.05 Hz for 0% droop, 0.02 Hz for 3% droop, and 0.1 Hz for 5% droop.

Virtual Synchronous Generator: A Control Strategy to Improve Dynamic Frequency Control in Autonomous Power Systems  [PDF]
Miguel Torres, Luiz A. C. Lopes
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.52A005

Ideally, diesel hybrid autonomous power systems would operate with high penetration of renewable energy sources such as wind and photovoltaic to minimize fuel consumption. However, since these are inherently intermittent and fluctuating, the grid-forming diesel engine generator sets are usually required to operate with larger amounts of spinning reserve, often at low loading conditions what tends to increases operating and maintenance costs. Frequency stability is of great concern in “small” systems, such as mini-grids, where any individual generator in-feed represents a substantial portion of the total demand. There, the initial rate of change of frequency is typically larger and a lower value of frequency can be reached in a shorter time than in conventional systems with all generation supplied by rotating machines, possibly resulting in under-frequency load shedding and tripping of renewable energy generators. The first part of this paper, discusses some general concepts regarding frequency stability in a diesel hybrid mini-grid and how energy storage systems can be used to enhance system performance. Then, a particular technique based on a virtual synchronous generator is presented and its effectiveness is demonstrated with simulation results.

A Virtual Synchronous Machine to Support Dynamic Frequency Control in a Mini-Grid That Operates in Frequency Droop Mode  [PDF]
Miguel Torres, Luiz A. C. Lopes
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.53025

This paper addresses the problem of dynamic frequency control in a diesel-based mini-grid. It is shown that a virtual synchronous machine (VSM) can support dynamic frequency control by adding virtual inertia and damping to the system. However, it is found that the typical formulation of damping power does not work properly when the grid forming gen-set operates in droop mode because of the unknown stabilization value of the grid frequency. As a solution to this problem, an estimator for the stabilization frequency that works in conjunction with the damping function of the VSM is proposed. Theoretical and experimental results provide evidence of a satisfactory performance of the proposed VSM with estimator for different values of the gen-set droop factor. The estimated stabilization frequency converges in approximately 2 s and the maximum frequency deviation during the transient is reduced in 34%, on average.

eHealth Management Platform for Screening and Prediction of Down’s Syndrome in the Republic of Panama  [PDF]
Juan Salda?a, Miguel Vargas-Lombardo
E-Health Telecommunication Systems and Networks (ETSN) , 2014, DOI: 10.4236/etsn.2014.33005
Abstract: Through engineering projects, we have integrated software engineering, geographical information systems and HL7 standard to propose a model of an eHealth management platform for Down’s syndrome screening, replicable in all the country. It will use real time sample information acquired from the local population and will geographically reference this information in the territory of Panama for future research.
Numerical Analysis of Slag Carry-Over during Molten Steel Draining  [PDF]
Daniel Flores-Sanchez, Miguel A. Barron
Open Journal of Applied Sciences (OJAppS) , 2017, DOI: 10.4236/ojapps.2017.711044
Abstract: Slag carry-over during the draining of molten steel from a teeming ladle is numerically studied here. Two-phase isothermal transient 3D Computational Fluid Dynamics simulations were employed to simulate the draining process. Two nozzle diameters, two nozzle positions and three slag heights were considered. From mass balances, the slag carry-over in terms of mass flow rate was obtained for each of the above variables. Besides, the draining times of the teeming ladle were estimated from theoretical considerations and CDF simulations, and compared.
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