Trend analysis in two standard growth models

This paper analyzes the trend processes characterized by two standard growth models using simple econometrics. The first model is the basic neoclassical growth model that postulates a deterministic trend for output. The second model is the Uzawa-Lucas model that postulates a stochastic trend for output. The aim is to understand how the different trend processes for output assumed by these two standard growth models determine the ability of each model to explain the observed trend processes of other macroeconomic variables such as consumption and investment. The results show that the two models reproduce the output trend process. Moreover, the results show that the basic growth model captures properly the consumption trend process, but fails in characterizing the investment trend process. The reverse is true for the Uzawa-Lucas model.Uzawa-Lucas model, basic neoclassical growth model, trend process, cointegration

Cyclical Features of Uzawa-Lucas Endogenous Growth Model

This paper analyzes the cyclical properties of a generalized version of Uzawa-Lucas endogenous growth model. We study the dynamic features of different cyclical components of this model characterized by a variety of decomposition methods. The decomposition methods considered can be classified in two groups. On the one hand, we consider three statistical filters: the Hodrick-Prescott filter, the Baxter-King filter and Gonzalo-Granger decomposition. On the other hand, we use four model-based decomposition methods. The latter decomposition procedures share the property that the cyclical components obtained by these methods preserve the log-linear approximation of the Euler-equation restrictions imposed by the agent’s intertemporal optimization problem. The paper shows that both model dynamics and model performance substantially vary across decomposition methods. A parallel exercise is carried out with a standard real business cycle model. The results should help researchers to better understand the performance of Uzawa-Lucas model in relation to standard business cycle models under alternative definitions of the business cycle.endogenous growth, decomposition methods, cyclical features

Diseño de front-end de receptor óptimo de alta ganancia y eficiencia de potencia en 0.13 μm de tecnología CMOS de RF para aplicaciones de 10GBPS

Este artículo presenta dos versiones de una RF frontend completa para un receptor óptico de 10Gbps. El RF frontend consiste de un amplificador de transimpedancia y amplificador limitador. Se proponen dos versiones de amplificadores TIA. La primera topología tiene una ganancia de transimpedancia de 54 dB, ancho de banda de 11.5 GHz y una salida de densidad de ruido de corriente de solamente 6.8 pA/√ Hz. La segunda topología esta compuesta de una cascada de dos invertores. Esta topología tiene una ganancia de 48 dB de transimpedancia. El amplificador limitador para ambos receptores ópticos es un amplificador de cinco etapas cherry-hooper con inductores activos optimizados para potencia baja. El amplificador principal tiene 38 dB de ganancia, 9.8 GHz de ancho de banda, 69 mW de consumo de potencia y solamente 0.171 mm2 de área muerta. Esta completa fachada de RF está integrada y tiene 10GHz de ancho de banda. Los circuitos fueron diseñados en 0.13 μm de tecnología CMOS de RF

Providing behaviour awareness in collaborative project courses

Several studies show that awareness mechanisms can contribute to enhance the collaboration process among students and the learning experiences during collaborative project courses. However, it is not clear what awareness information should be provided to whom, when it should be provided, and how to obtain and represent such information in an accurate and understandable way. Regardless the research efforts done in this area, the problem remains open. By recognizing the diversity of work scenarios (contexts) where the collaboration may occur, this research proposes a behaviour awareness mechanism to support collaborative work in undergraduate project courses. Based on the authors previous experiences and the literature in the area, the proposed mechanism considers personal and social awareness components, which represent metrics in a visual way, helping students realize their performance, and lecturers intervene when needed. The trustworthiness of the mechanisms for determining the metrics was verified using empirical data, and the usability and usefulness of these metrics were evaluated with undergraduate students. Experimental results show that this awareness mechanism is useful, understandable and representative of the observed scenarios.Peer ReviewedPostprint (published version

Providing behaviour awareness in collaborative project courses

Several studies show that awareness mechanisms can contribute to enhance the collaboration process among students and the learning experiences during collaborative project courses. However, it is not clear what awareness information should be provided to whom, when it should be provided, and how to obtain and represent such information in an accurate and understandable way. Regardless the research efforts done in this area, the problem remains open. By recognizing the diversity of work scenarios (contexts) where the collaboration may occur, this research proposes a behaviour awareness mechanism to support collaborative work in undergraduate project courses. Based on the authors previous experiences and the literature in the area, the proposed mechanism considers personal and social awareness components, which represent metrics in a visual way, helping students realize their performance, and lecturers intervene when needed. The trustworthiness of the mechanisms for determining the metrics was verified using empirical data, and the usability and usefulness of these metrics were evaluated with undergraduate students. Experimental results show that this awareness mechanism is useful, understandable and representative of the observed scenarios.Peer ReviewedPostprint (published version

Understanding collaboration in volunteer computing systems

Volunteer computing is a paradigm in which devices participating in a distributed environment share part of their resources to help others perform their activities. The effectiveness of this computing paradigm depends on the collaboration attitude adopted by the participating devices. Unfortunately for software designers it is not clear how to contribute with local resources to the shared environment without compromising resources that could then be required by the contributors. Therefore, many designers adopt a conservative position when defining the collaboration strategy to be embedded in volunteer computing applications. This position produces an underutilization of the devices’ local resources and reduces the effectiveness of these solutions. This article presents a study that helps designers understand the impact of adopting a particular collaboration attitude to contribute with local resources to the distributed shared environment. The study considers five collaboration strategies, which are analyzed in computing environments with both, abundance and scarcity of resources. The obtained results indicate that collaboration strategies based on effort-based incentives work better than those using contribution-based incentives. These results also show that the use of effort-based incentives does not jeopardize the availability of local resources for the local needs.Peer ReviewedPostprint (published version

A Simplified Electro-Mechanical Model of a DFIG-based Wind Turbine for Primary Frequency Control Studies

In recent years, world-wide power systems are experiencing a steadily growth of wind power penetration. A common concern in the operation of such systems is related to the frequency stability. Modern variable speed wind turbines have a limited capacity in providing ancillary services, such as fast-frequency response and primary frequency regulation. Recent developments in wind plant controllers allow performing active power control from all its units to respond to system frequency deviations. It is thus important to study the effects of the presence of these plants in the system frequency response. Existing detailed models of wind turbines are not suitable to this goal because their complexity makes them impractical for system-wide studies. This paper presents a simplified model of a wind turbine with Doubly-Fed Induction Generator specifically conceived for such studies, along with its validation with a detailed mode

Contribution of DFIG wind turbines to Primary Frequency Control

In recent years, worldwide power systems are experiencing a steadily growth in wind power penetration. A common concern in the operation of such systems is related to the frequency stability. Modern variable speed wind turbines have a limited capacity in providing ancillary services, such as: fastfrequency response and primary frequency regulation. This thesis aims at developing a new methodology for the analysis of frequency dynamics in largescale power systems with high level of wind energy share. Firstly, a simplified electromechanical model of a doubly fed induction generator (DFIG) based wind turbine has been proposed. In addition, a virtual inertia controller version of the optimized power point tracking method (OPPT) has been adapted for this kind of wind turbines. In this method, the maximum power point tracking curve (MPPT) is shifted to drive variations in the active power injection as a function of the grid frequency deviation, by exploiting the available inertial resources. The proposed methodology integrates the model in a primary frequency control scheme to assess the interaction with the rest of the plants in the power system

A role-based software architecture to support mobile service computing in IoT scenarios

The interaction among components of an IoT-based system usually requires using low latency or real time for message delivery, depending on the application needs and the quality of the communication links among the components. Moreover, in some cases, this interaction should consider the use of communication links with poor or uncertain Quality of Service (QoS). Research efforts in communication support for IoT scenarios have overlooked the challenge of providing real-time interaction support in unstable links, making these systems use dedicated networks that are expensive and usually limited in terms of physical coverage and robustness. This paper presents an alternative to address such a communication challenge, through the use of a model that allows soft real-time interaction among components of an IoT-based system. The behavior of the proposed model was validated using state machine theory, opening an opportunity to explore a whole new branch of smart distributed solutions and to extend the state-of-the-art and the-state-of-the-practice in this particular IoT study scenario.Peer ReviewedPostprint (published version

Eletrificação por microrredes em áreas rurais da província de Azuay, Equador

The electrification of rural areas is an increasingly relevant issue, since in some cases they do not have access to the traditional electricity grid. For this reason, the use of renewable energy microgrids applied to these areas is being studied. It is important to consider the available energy resource in order to adequately size the microgrid system, since certain systems may not be viable. In this study, two renewable energy generation microgrid systems are proposed: the first is a wind/photovoltaic system that works with the indirect radiation of the sun [kWh/m^2/day] and the average wind speed [m/s]; the second is a purely photovoltaic system that uses the indirect radiation and the temperature of the sun, both systems are isolated and have an energy storage system (battery bank), also have as load a rural residential consumer of 160 kWh/month. The systems are simulated and modeled in HOMER Pro software. The results indicate that the photovoltaic microgrid system is the most viable, since the site has low wind speeds and therefore a wind system is not viable.La electrificación de zonas rurales es un tema cada vez más relevante, debido a que en ciertos casos no se dispone de la red eléctrica tradicional. Es por ello, que es motivo de estudio el uso de microrredes de energías renovables aplicadas a estas zonas. Es importante considerar el recurso energético disponible para así poder dimensionar adecuadamente el sistema de microrred, ya que ciertos sistemas no pueden ser viables. En este estudio, se proponen dos sistemas de microrredes de generación de energías renovables: el primero es un sistema eólico/fotovoltaico que trabaja con la radiación indirecta del sol [kWh/m^2/día] y la velocidad promedio del viento [m/s]  ; el segundo es un sistema netamente fotovoltaico que utiliza la radiación indirecta y la temperatura del sol, ambos sistemas son aislados y cuentan con un banco de almacenamiento energético (baterías), además tienen como carga a un consumidor rural residencial de 160 kWh/mes. Los sistemas son simulados y modelados en el software HOMER Pro. Los resultados indican que el sistema de microrred fotovoltaico es el más viable, ya que el lugar cuenta con bajas velocidades de viento y por lo tanto un sistema eólico no es viable.A eletrificação das zonas rurais é um tema cada vez mais relevante, pelo facto de em certos casos a rede elétrica tradicional não estar disponível. É por isso que o uso de microrredes de energia renovável aplicadas a essas áreas é motivo de estudo. É importante considerar o recurso energético disponível para dimensionar adequadamente o sistema de microrrede, uma vez que determinados sistemas podem não ser viáveis. Neste estudo são propostos dois sistemas de microrrede de geração de energia renovável: o primeiro é um sistema eólico/fotovoltaico que trabalha com a radiação indireta do sol [kWh/m^2/dia] e a velocidade média do vento [m/s]; o segundo é um sistema puramente fotovoltaico que utiliza a radiação indireta e a temperatura do sol, ambos os sistemas são isolados e possuem banco de armazenamento de energia (baterias), também cobram de um consumidor rural residencial 160 kWh/mês. Os sistemas são simulados e modelados no software HOMER Pro. Os resultados indicam que o sistema de microrrede fotovoltaica é o mais viável, pois o local possui baixas velocidades de vento e portanto um sistema eólico não é viável