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Moncada M.V.,National University of Engineering of Nicaragua | Uturbey W.,Federal University of Minas Gerais
GHTC 2016 - IEEE Global Humanitarian Technology Conference: Technology for the Benefit of Humanity, Conference Proceedings | Year: 2016

Most of the distributed generation (DG) systems in Nicaragua are based on micro hydroelectric and photovoltaic systems (less than 1.5 MW). Their main purpose is to provide energy to rural communities, which are not profitable business for utilities due to their socioeconomic characteristics and the high cost of extension of the national grid. This paper provides an analysis of the Nicaraguan legal framework related to DG connected to the electrical grid. The point of view of the electrical market agents is included. Laws are analyzed based on how they were designed to support the particular use of rural electrification by incorporating renewable energies. Findings reveal that while DG is considered in different laws, aspects such as tax exemptions and financial incentives are not properly addressed. Furthermore, grid interconnection standards and commercial regulation are not included at all. These facts represent a real threat to the sustainability model of small energy producers. Additionally, a comparative analysis of the Nicaraguan DG regulatory framework with that of Costa Rica is carried out in order to identify lessons learned as well as failure and success factors. Finally, we provide recommendations for improving Nicaraguan regulation, to support small producers of energy, serving rural communities. © 2016 IEEE.

Picado A.,KTH Royal Institute of Technology | Picado A.,National University of Engineering of Nicaragua | Martinez J.,KTH Royal Institute of Technology
Drying Technology | Year: 2012

A mathematical model for the drying of grain in a continuous vibrating fluidized bed dryer was developed. Simple equipment and material models were applied to describe the process. In the plug-flow equipment model, a thin layer of particles moving forward and well mixed in the direction of the gas flow was examined. Mass and heat transfer within a single wet particle was described by effective transport coefficients. Assuming constant effective mass transport coefficient and thermal conductivity, analytical solutions of the mass and energy balances were obtained. The variation in both transport coefficients along the dryer was taken into account by a stepwise application of the analytical solution in space intervals with averaged coefficients from previous locations in the dryer. Calculation results were in fairly good agreement with experimental data from the literature. However, the results depend strongly on relationships used to determine the heat and mass transfer coefficients; because the results from correlations found in the literature vary considerably, the correlations should be adapted to the specific equipment in order to obtain reliable results. © 2012 Copyright Taylor and Francis Group, LLC.

Gamero R.,National University of Engineering of Nicaragua | Martinez J.,KTH Royal Institute of Technology
Chemical Engineering Research and Design | Year: 2012

The effective thermal conductivity of a porous solid containing multicomponent liquid mixtures has been studied. To achieve this, the liquid composition, liquid content and temperature distributions have been measured in a cylindrical sample dried by convection from the open upper side and heated by contact with a hot source at the bottom side. A quasi-steady state reached at high source temperatures permits to calculate the total heat flux from temperatures measured on the surface and the gas stream. The simulations performed and compared with experimental data made it possible to estimate the adjusting geometric parameter of Krischer's model for the effective thermal conductivity. The effective thermal conductivity has been widely studied for two-phase systems, mostly with regard to thermal insulation elements. The calculation of this transport parameter includes the contribution to heat transfer of the evaporation-diffusion-condensation mechanism undergone by the multicomponent mixture. The influence of liquid composition and temperature on the thermal conductivity due to the evaporation-diffusion-condensation mechanism and the effective thermal conductivity is described. The results reveal that in this case the resistance to heat transfer seems to correspond to a parallel arrangement between the phases. © 2012 The Institution of Chemical Engineers.

Benavente M.,National University of Engineering of Nicaragua | Benavente M.,KTH Royal Institute of Technology | Moreno L.,KTH Royal Institute of Technology | Martinez J.,KTH Royal Institute of Technology
Journal of the Taiwan Institute of Chemical Engineers | Year: 2011

This study is concerned with the use of chitosan produced from shrimp shell waste for the removal of Cu(II), Hg(II), Pb(II) and Zn(II) from gold ore tailing solutions containing cyanide. This work involved the study of equilibrium and kinetic adsorption, the physicochemical characterization of mining effluents and desorption using different regenerating solutions. The experimental results showed that the adsorption capacity of chitosan is a function of the solution pH and that the optimum pH for these metallic ions is 6, except for Hg (pH 4). The equilibrium data were described using the Langmuir, Freundlich, Redlich-Peterson and SIPS isotherm models. The Langmuir equation was used to find the maximum adsorption capacity for Cu (79.94mg/g), Hg (109.55mg/g), Pb (58.71mg/g) and Zn (47.15mg/g). To determine the rate-controlling mechanism for metallic ion adsorption, pseudo-first-order, pseudo-second-order and the Elovich equation kinetic models were tested with experimental adsorption kinetic data. Tests conducted with gold ore tailing solutions indicated that chitosan is effective to remove these metallic ions above 70%. Desorption studies revealed that the regeneration of chitosan saturated with these metallic ions depends on the type and concentration of the regenerating solution ((NH4)2SO4, H2SO4, HCl, NaOH and NaCl). © 2011 Taiwan Institute of Chemical Engineers.

Tercero M.,KTH Royal Institute of Technology | Tercero M.,National University of Engineering of Nicaragua | Sung K.W.,KTH Royal Institute of Technology | Zander J.,KTH Royal Institute of Technology
2011 IEEE Wireless Communications and Networking Conference, WCNC 2011 | Year: 2011

In this paper, we investigate the impact of aggregate interference in a secondary spectrum access system. Particularly, meteorological radar operating in 5.6 GHz band is considered to be a primary user. Secondary users are WLAN devices spreading in a large area which induce aggregate interference to the radar. We develop a mathematical model to derive the probability distribution function (PDF) of the aggregate interference. The derivation considers dynamic frequency selection (DFS) mechanism for the protection of the radar such that the transmission of each WLAN is regulated by an interference threshold. Numerical experiments are performed with various propagation environments and densities of WLAN devices. It is observed that the effect of aggregate interference is severe in a rural environment. The interference threshold for individual WLAN should be much lower than the maximum tolerable interference at the radar. Thus, only a limited number of WLANs can transmit at the same time. On the other hand, adverse effect of the aggregate interference is not shown in an urban environment, where up to 10 WLANs per square kilometer can use the radar spectrum without considering the aggregate interference. The framework discussed in this paper can readily be adapted to assess the aggregate interference for other types of radars. © 2011 IEEE.

Munguia M.M.,National University of Engineering of Nicaragua
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2011

In this paper, the vascular sounds of the arteriovenous fistula at the anastomosis and five centimeters downstream the anastomosis were analyzed. The analysis of the sounds was based on features extracted from the power spectral density (PSD) and wavelet decomposition. The database consists of 15 recordings at the anastomosis and 15 reference recordings obtained from 15 patients. The results showed that the vascular sounds at the anastomosis can be characterized as an extra energy in the higher frequencies (200-1000 Hz) i.e. higher mean frequency of the PSD than the reference recordings. Moreover, the wavelet decomposition of the anastomosis recordings showed a similar energy pattern, in the finer scales, to that found in studies of arterial and venous stenosis.

Vasquez P.,National University of Engineering of Nicaragua
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2010

The Empirical Mode Decomposition (EMD) is a method to decompose non linear, non stationary time series into a sum of different modes, named Intrinsical Mode Functions each one having a characteristic frequency. In the present work we used the EMD to investigate the properties of the recorded sounds from the Arteriovenous fistula on hemodialysis patients. Phonoangiographic signals coming from two different vessel conditions, stenotic and non-stenotic, were analyzed by using EMD, the mean energy and mean instantaneous frequency per IMF proved to be good features for classification. Three types of classification schemes were tested on data from the first IMf features achieving good results.

Munguia M M.,National University of Engineering of Nicaragua
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2010

In this paper, a feature extraction method based on principal component analysis was developed for classification of the vascular access's condition in hemodialysis patients. The assessment of the method was carried out by discriminating between before and after angioplasty sound recordings as well as before angioplasty and reference recordings. The results showed that when before and after angioplasty recordings were compared by patient, the classification agreed with the result of angioplasty procedure. When all the available before and after angioplasty recordings were compared, it was still possible to discriminate them at a good rate. On the other hand, when the reference recordings substituted the after angioplasty recordings, almost a perfect discrimination was achieved.

Obando P.V.,National University of Engineering of Nicaragua | Mandersson B.,Lund University
Proceedings - 2012 IEEE International Conference on Bioinformatics and Biomedicine Workshops, BIBMW 2012 | Year: 2012

In this work we study in time-frequency domain what has been termed 'tea-kettle' sounds found in audio recordings of arteriovenous fistulas with severe stenosis. These sounds appears as frequency modulated signals (chirps) in the time-frequency plots. We first developed a simple model for generating synthetic bruits containing chirps. Then we performed tracking of the time-varying frequency signals using an Extended Kaiman filter (EKF). Finally we analyzed a data base of recordings from 5 patients suffering from venous stenosis EKF frequency tracker, the results shows the chirps mean frequencies (fundamental) can vary in a rather wide range of frequencies from about 200 Hz to 600 Hz and that up to two harmonics can also be found in the considered cases. © 2012 IEEE.

Espinoza-Cuadra J.,CONACyT Mexico | Gallegos-Acevedo P.,Technological University of Mixteca | Mancha-Molinar H.,CIFUNSA | Picado A.,National University of Engineering of Nicaragua
Materials and Design | Year: 2010

An experimental study was carried out to determine the effect of strontium (Sr) on the characteristic of intermetallic phases, particularly the Al5FeSi phase which present morphology of platelets or needle-like. The results showed that within the range of variables studied, the modification process caused the disappearance of the needles and only occur the precipitation of phase α (chinese script-like). Refinement of the intermetallic phases occurs in conjunction with the refinement in grain size. Both parameters depend strongly on local cooling rate (T), temperature gradient (G) and apparent rate of solidification front (V). In the case of equiaxed structures the refinement of grain size and intermetallic occurs with increasing local cooling rate and temperature gradient and decrease the apparent rate of solidification front. In the case of columnar structures, refinement of grains and intermetallic requires the increase in values of the three variables indicated. Moreover, the addition of Sr resulted in the modification of silicon eutectic, as noted in others research works. © 2009 Elsevier Ltd. All rights reserved.

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