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Latin America Transactions, IEEE (Revista IEEE America Latina)

Issue 6 • Date Dec. 2010

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Displaying Results 1 - 18 of 18
  • Design and Implementation of an Arithmetic Processor Unit Based on the Logarithmic Number System

    Page(s): 605 - 617
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (653 KB)  

    This paper presents the design and implementation of an arithmetic processing unit based on the logarithmic number system. The proposed implementation is supported in a new set of linear equations, which allows calculating the approximation of the logarithm and antilogarithm binary functions and leads to a maximum relative error of 1×10-3% and 5×10-3%, respectively. Furthermore, the impact of the logarithmic number system on FPGA for implementing hardware modules to execute multiplication, division, and square root arithmetic operations is also presented and analyzed. In this regards, the analysis takes into account physical resources available on the FPGA, number of clock cycles per arithmetic operation and maximum clock frequency. Experimental results show that using the proposed architecture implemented on the FPGA allows computing multiplication, division and square root operations in only 2 cycles and up to 290.87MHz, obtaining a maximum relative error of 0.015%, 0.018%, and 0.008%, respectively for each one of these arithmetic operations. View full abstract»

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  • Heating within Spheres of Different Size Irradiated by an Electromagnetic Plane Wave

    Page(s): 618 - 622
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (497 KB)  

    This paper presents the results obtained by multiphysics (electromagnetic and thermal) numerical simulations which show the influence of the size in two different spheres that are irradiated by an electromagnetic plane wave. Each sphere is constituted by a series of concentric layers that emulate the tissues in the head. A 10 mW/cm2 plane wave is used as source, and the frequency is setup to 1.8 GHz. The power absorbed per unit volume by the tissues (W/m3) is calculated by using the 3-D Finite Difference Time Domain (FDTD) method. Then, temperature inside the spheres is calculated by using a Finite Differences (FD) formulation of the heat diffusion equation. Two different ways of calculating the power-loss density are presented, and validated with analytical results. It is observed that the increase of temperatures inside a 66 mm sphere, in diameter, is higher than inside a 100 mm sphere. However, the power absorbed per unit volume in the brain zone is six times higher in the 100 mm sphere. View full abstract»

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  • Spectral Fields in Anisotropic Planar Multilayer Structures

    Page(s): 623 - 630
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (587 KB)  

    A new systematic procedure for calculating the electromagnetic fields in anisotropic planar multilayer structures is presented. Working in the Fourier domain and utilizing the symbolic computation capability of the Mathematica package, closed-form expressions for the transformed electromagnetic fields are derived in a straightforward, error-free way. Therefore, spectral Green's functions can be determined in compact, closed form, with considerable reduction of the calculation time. Using this new procedure, Green's functions for anisotropic grounded layer and also for biaxial microstrip multilayer structures are derived. View full abstract»

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  • Comparison Between Voltage Control Structures of Synchronous Machines

    Page(s): 631 - 636
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1345 KB)  

    This paper compares the behaviour of two different control structures of automatic voltage regulators of synchronous machines equipped with static excitation systems. These systems have a fully controlled thyristor bridge that supplies DC current to the rotor winding. The rectifier bridge is fed by the stator terminals through a step-down transformer. The first control structure, named “Direct Control”, has a single proportional-integral (PI) regulator that compares stator voltage setpoint with measured voltage and acts directly on the thyristor bridge's firing angle. This control structure is usually employed in commercial excitation systems for hydrogenerators. The second structure, named “Cascade Control”, was inspired on control loops of commercial DC motor drives. Such drives employ two PIs in a cascade arrangement, the external PI deals with the motor speed while the internal one regulates the armature current. In the adaptation proposed, the external PI compares setpoint with the actual stator voltage and produces the setpoint to the internal PI-loop which controls the field current. View full abstract»

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  • Determination of the Earth Fault Factor in Power Systems for Different Earthed Neutrals

    Page(s): 637 - 645
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (655 KB)  

    This paper proposes an analytical method to calculate the earth fault factor (EFF) in power systems, under different neutral earthed possibilities. The magnitude of the EFF depends on the way the neutrals of a system are earthed and influences some important aspects in power systems as the sensitivity and selectivity of relays, the value of short-circuit currents, the overvoltage between lines and earth, the determination of arrester rating and the system insulation level. The obtained results are compared with the values of EFF referred in International Standards. View full abstract»

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  • Development of a Tool that Integrates the Design Processes of a Switched Reluctance Motor

    Page(s): 646 - 652
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    This paper consists in developing a software that simplifies the design processes of a regular 6/4 switched reluctance motor (SRM) or its multiples, so that the problems involved when using the conventional procedures can be avoided. We wrote this software so that it could generate a set of machines satisfying the entrance parameters. Then, an inner cycle chooses the one which better fits the user's requirements and sends it to finite element analysis. The model developed for the FEA allows the analysis of any regular SRM and includes a windings' model that differ from those commonly used because it represents the windings' cross section exactly. Finally, we compared the results with those presented by T. J. E. Miller on “Switched Reluctance Motors and Their Control”, to verify the correct performance of the tool. View full abstract»

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  • Mechanical analysis of silicone rubber used on the cover of polymeric insulators

    Page(s): 653 - 657
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (706 KB)  

    This paper deals with the thermal degradation of silicone rubber that is used on the cover of polymeric insulators. To carry out this research three samples were previously aged at different temperatures and a fourth one was kept at room temperature. Afterwards, a study was done by means of a tensile test on the silicone rubber. The tensile properties were evaluated by means of the graphs obtained from the tensile-strain, where the straight part of the graphs corresponds to the elastic modulus of the material, called modulus of elasticity. View full abstract»

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  • Mixed-Integer Nonlinear Programming Approach for Short-Term Hydro Scheduling

    Page(s): 658 - 663
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (594 KB)  

    This paper is on the problem of short-term hydro scheduling, particularly concerning a head-sensitive hydro chain. A novel mixed-integer nonlinear programming approach is proposed for optimizing power generation efficiency. The proposed approach considers not only the nonlinear dependence between power generation, water discharge and head, but also start-up costs for the hydro units and discontinuous operating regions, in order to obtain more realistic and feasible results. Numerical results based on one of the main Portuguese cascaded hydro systems illustrate the proficiency of the proposed approach. View full abstract»

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  • Potential Energy of Water

    Page(s): 664 - 669
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (646 KB)  

    In the present paper the importance of the water as resource for hydropower, his sub appraisement in the electrical market, and the function of the state as regulatory entity, to demand the rational use in hydroelectric power station. View full abstract»

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  • Restoring Solution of Electric Network Equations: An Approach Using the Augmented Lagrangean Algorithm

    Page(s): 670 - 677
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    This paper presents and discuss a new, robust approach to restore the solution of electric network equations in electric power systems. The unsolvable power flow is modelled as an constrained optimization problem. The objective function is the sum of squared real and reactive power mismatches at the system buses that are available to load shedding. The equality constraints are the real and reactive power mismatches at null injection buses and/or at buses whose power demands must be integrality supplied due to technical and/or economical criteria. The mathematical model is solved using an algorithm based on Augmented Lagrangean method that considers the special structure of the proposed problem. The inner iterations of the proposed approach are solved using the Levenberg-Marquardt algorithm. Numerical results for both IEEE test systems and a real equivalent power system from South-Southeast region of Brazil are presented to analyze and the performance of the proposed methodology. View full abstract»

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  • Selection of Asymmetrical Transformers Banks with Emphasis in Losses and Efficiency

    Page(s): 678 - 684
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    In many power distribution systems when three-phases and single-phase loads are combined is common to use asymmetrical transformers banks. Although different connections can be used, the most usual for mixes loads, is the wye/delta-grounded three elements transformer bank where one of the transformers, the one with the higher capacity, is called the lighting transformer and the other two power transformers. The lighting transformer in the secondary side is grounded and also supplies the single-phase loads. In rural and low load systems the open-delta and open-wye connections are frequently used. This paper show an optimization process based on artificial intelligence technique; genetic algorithm, to determinate the most adequate capacity of each transformers of the asymmetrical bank based on losses and life cycle cost reduction. The goal is to increase the efficiency and reduce cost of power transformers banks operating in field conditions. This article exposed as a study case a transformer bank supplying Cienfuegos's University in Cuba. The procedure can be applied to other transformers configuration as well as to three phase power transformers. The result obtained show increased efficiency and reduced cost of the Cienfuegos's installation. View full abstract»

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  • A Web-based Tool for Automatizing the Software Process Improvement Initiatives in Small Software Enterprises

    Page(s): 685 - 694
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2028 KB)  

    Top-down process improvement approaches provide a high-level model of what the process of a software development organization should be. Such models are based on the consensus of a designated working group upon how software should be developed or maintained. They are very useful in the sense that they provide general guidelines on where to start improving, and in which order to people who do not know. However, the majority had only worked in scenarios within large companies. We aim to help small software development organizations adopt an iterative approach by providing a Process Improvement Web-based Tool. This paper presents research into the proposal that a small organization may use this tool to define and implement a set of agile project management practices that can be strengthened using the CMMI-DEV 1.2 model as reference. View full abstract»

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  • An Virtual Environment Learning of Low Cost for the Instruction of Electric Circuits

    Page(s): 695 - 702
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (619 KB)  

    In recent years, a proliferation of learning environments has been observed, with positive impacts at the construction of learning. This paper presents a virtual learning environment intended for the teaching of physics in the field of electrical circuits, for high school students. The motivation of this work concerns the small access that these students have the laboratories of this discipline in their schools. Using virtual reality techniques, based on Internet technology, the system simulates a virtual environment for physics experiments, with a low computational cost and financial. In addition, to ensure an educational sustainable environment, the paradigm of conceptual maps was used to help students to organize and adapt the concepts worked. The article highlights the development strategy of the system, presents an application of the laboratory in the creation/analysis of electrical circuits and presents the evaluation of the system. View full abstract»

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  • Experiences in Planning and Implantation of Security at Next Generation Networks

    Page(s): 703 - 707
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1013 KB)  

    In this article some elements are exposed about security in Next Generation Networks (NGN). Important aspects of the accumulated experience in tasks of security Planning and Implantation for different NGN solutions are summarized. In these tasks a Security Architecture and a Management System, obtained in previous works for this type of networks, has been used. This allows presenting many theoretical-practical results, with the objective that it can be generalized in similar environments. View full abstract»

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  • Image Compression via a Fast DCT Approximation

    Page(s): 708 - 713
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1281 KB)  

    Discrete transforms play an important role in digital signal processing. In particular, due to its transform domain energy compaction properties, the discrete cosine transform (DCT) is pivotal in many image processing problems. This paper introduces a numerical approximation method for the DCT based on round-off techniques. The proposed method is a multiplierless technique with low arithmetic complexity. Emphasis was given to approximating the 8-point DCT. A fast algorithm for the introduced 8-point approximate transform was derived. An application in image compression was examined. In several scenarios, the utilization of the proposed method for image compression resulted in comparable or better performances, when compared to the usual DCT-based methodology. View full abstract»

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  • Integration of Tracking Systems for the Development of Virtual Reality Applications

    Page(s): 714 - 721
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (811 KB)  

    The use of intuitive interaction in virtual reality (VR) systems is a factors that affect the sense of immersion of the users in virtual environments. Difficulties related to the incorporation of devices and their costs has motivated research using low-cost devices and high-level tools such as frameworks to development of VR applications. This paper presents the design and integration of a module for spatial tracking in a framework for development of virtual reality applications. The module provides ways to incorporate several tracking techniques and low-cost devices used to obtain the spatial position of objects. View full abstract»

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  • Similarity Join of XML Documents Stored in File Systems

    Page(s): 722 - 727
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (534 KB)  

    Joining XML documents, in a data integration environment, is not a trivial task because besides data are stored in several representations (abbreviated, incomplete, or misspelled), XML data are usually organized as collection of values, which requires a different implementation of the join operation. In this paper, we present two similarity join operators, which are used over XML documents stored in file system. The operators have been implemented in a tool, called SimJoiX, which assists in the task of joining data stored in XML files. View full abstract»

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  • Visualization System Integrated for Electric Power Distribution Networks

    Page(s): 728 - 733
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1129 KB)  

    In this project a system computational was developed for data visualization and making decision based on a geographical information system (GIS). This system was developed for electric power distribution area. The integrated interface is constituted by three graphic environment that present data related to the network of electric power distribution of a city and their electric elements, besides the context regarding the territorial administration that it uses maps 2D and models 3D for making decision. A differential of the system is in the adoption of a Human-Computer Interface that contemplates the synchronization of the three visualization environments and the tool of integrated information. View full abstract»

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Aims & Scope

IEEE Region 9 provides IEEE Latin America Transactions to enable the publication of non-published and technically excellent papers from Latin American engineers, in Spanish or Portuguese languages.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
José Antonio Jardini (Brasil)
IEEE Fellow Member