Pressure field in the cathode-anode region of a high-power klystron amplifier

The pressure field of a high-power klystron amplifier in the cathode and anode region was investigated. The investigation was performed using a 1.3 GHz, 100 A and 240 kV high-power klystron with five reentrant coaxial cavities, assembled in cylindrical drift tube 1.2 m long. The diffusion equation in mathematical model was also solved by using a 3-D finite element method code, in order to obtain pressure profile in region of interest. The results show that density profile of molecules between cathode-anode region was determined, where cathode pressure is approximately 10% higher than anode pressure.

Using cubic splines to mitigate systematic errors in GPS relative positioning

Systematic errors can have a significant effect on GPS observable. In medium and long baselines the major systematic error source are the ionosphere and troposphere refraction and the GPS satellites orbit errors. But, in short baselines, the multipath is more relevant. These errors degrade the accuracy of the positioning accomplished by GPS. So, this is a critical problem for high precision GPS positioning applications. Recently, a method has been suggested to mitigate these errors: the semiparametric model and the penalised least squares technique. It uses a natural cubic spline to model the errors as a function which varies smoothly in time. The systematic errors functions, ambiguities and station coordinates, are estimated simultaneously. As a result, the ambiguities and the station coordinates are estimated with better reliability and accuracy than the conventional least square method.

GPS performance in the quantification of integrated water vapor in Amazonian regions

The Amazonian regions are characterized by large space-time variability in the humidity fields due to the intense convective process in those areas associated with the great humidity potential generated by high temperatures. An experiment denominated RACCI/DRY-TO-WET (RAdiation, Cloud, and Climate Interactions in the Amazonia during the DRY-TO-WET Transition Season) was carried out in the Brazilian Amazonian Region in 2002. The IWV values from GPS and other techniques, such as radiosondes, radiometer and humidity sounding satellites were used in this experiment to supply subsidies to evaluate the aerosols influence in the associated processes modifications to seasonality of atmospheric water vapor. Those regions are one of the most humid of the planet, where IWV (Integrated Water Vapor) average values are in the order of 50 kg/m2. As according the literature the IWV quantification using GPS has not been explored in those circumstances, the objective this paper is to present the preliminary results obtained in the evaluation of the GPS performance in Amazonian Regions when comparing with other techniques. The tendency measurement values indicated that the IWV values from GPS tend to be larger than those from radiosondes and smaller than those from radiometer. On the other hand, IWV values from GPS are very close of the average values supplied by radiosondes and radiometer. Due to the great amount of atmospheric water vapor existent in this region, the results obtained in the experiment in percentile terms are quite better than those found in the literature, which are around of 10%.

Nonlinear absorption spectrum in perylene derivatives

Knowledge about nonlinear absorption spectra of materials used in photonic devices is of paramount importance in determining their optimum operation wavelengths. In this work, we have investigated the two-photon absorption (2PA) degenerate cross-section spectrum for perylene derivatives using the Z-scan technique with femtosecond laser pulses. All perylene derivatives studied present large 2PA cross-sections, only comparable to the best ones reported in the literature. The results achieved in the present investigation indicate perylene derivatives as promising materials for two-photon applications. ©2005 Optical Society of America.

Installation of a getter vacuum pump in cathode-anode region of a high-power klystron amplifier - Propose and feasible

The possibility to install a getter vacuum pump and its feasible in the anode of a high-power klystron amplifier is investigated in order to decrease of the pressure in the gun and consequently increasing its lifetime. The study is conducted using a 1.3 GHz, 100 A and 240 kV high-power klystron with five reentrant coaxial cavities, assembled in a cylindrical drift tube 1.2 m long. This work takes into account the specific conductance of components of gun and all important gas sources, like the degassing of the drift tube, the cavity walls, the cathode, the anode, and the collector, as well the position and pumping speed of the getter vacuum pump in anode region. © 2006 IEEE.

Ultrafast reflectivity dynamics in bis (n-butylimido) perylene thin films

Using pump-probe reflectometry, we study the ultrafast excited-state dynamics in thin films of BuPTCD, an organic semiconductor, deposited on gold nanoparticles. We observe depletion of the ground state and excited state absorption after photo-excitation. © 2008 Optical Society of America.

Virtual simulator for mobile robots navigation systems

This paper presents the virtual environment implementation for project simulation and conception of supervision and control systems for mobile robots, that are capable to operate and adapting in different environments and conditions. This virtual system has as purpose to facilitate the development of embedded architecture systems, emphasizing the implementation of tools that allow the simulation of the kinematic conditions, dynamic and control, with real time monitoring of all important system points. For this, an open control architecture is proposal, integrating the two main techniques of robotic control implementation in the hardware level: systems microprocessors and reconfigurable hardware devices. The implemented simulator system is composed of a trajectory generating module, a kinematic and dynamic simulator module and of a analysis module of results and errors. All the kinematic and dynamic results shown during the simulation can be evaluated and visualized in graphs and tables formats, in the results analysis module, allowing an improvement in the system, minimizing the errors with the necessary adjustments optimization. For controller implementation in the embedded system, it uses the rapid prototyping, that is the technology that allows, in set with the virtual simulation environment, the development of a controller project for mobile robots. The validation and tests had been accomplish with nonholonomics mobile robots models with diferencial transmission. © 2008 IEEE.

Environment mapping for mobile robots navigation using hierarchical neural network and omnivision

Autonomous robots must be able to learn and maintain models of their environments. In this context, the present work considers techniques for the classification and extraction of features from images in joined with artificial neural networks in order to use them in the system of mapping and localization of the mobile robot of Laboratory of Automation and Evolutive Computer (LACE). To do this, the robot uses a sensorial system composed for ultrasound sensors and a catadioptric vision system formed by a camera and a conical mirror. The mapping system is composed by three modules. Two of them will be presented in this paper: the classifier and the characterizer module. The first module uses a hierarchical neural network to do the classification; the second uses techiniques of extraction of attributes of images and recognition of invariant patterns extracted from the places images set. The neural network of the classifier module is structured in two layers, reason and intuition, and is trained to classify each place explored for the robot amongst four predefine classes. The final result of the exploration is the construction of a topological map of the explored environment. Results gotten through the simulation of the both modules of the mapping system will be presented in this paper. © 2008 IEEE.

Foreign Investment in Latin America and the Caribbean 2006

Includes bibliography

Placement and sizing evaluation of distributed generation in electric power systems

This paper presents a methodology for the placement and sizing evaluation of distributed generation (DG) in electric power systems. The candidate locations for DG placement are identified on the bases of Locational Marginal Prices (LMP's) obtained from an optimal power flow solution. The problem is formulated for two different objectives: social welfare maximization and profit maximization. For each DG unit an optimal placement is identified for each of the objectives.

Latest Enhancements in the Brazilian Active Control Network

The Brazilian Network for Continuous Monitoring of GPS - RBMC, since its foundation in December of 1996, has been playing an essential role for the maintenance and user access of the fundamental geodetic frame in the country. It provides to users a direct link to the Brazilian Geodetic System. Its role has become more relevant with the increasing use of space navigation technology in the country. Recently, Brazil adopted a new geodetic frame, SIRGAS2000, in February 2005, fully compatible with GNSS technology. The paper provides an overview of the recent modernization phases the RBMC network has undergone highlighting its future steps. From its current post-mission mode, the RBMC will evolve into a real-time network, providing real-time data and real-time correction to users. The network enhanced with modern GPS receivers and the addition of atomic clocks will be used to compute WADGPS-type corrections to be transmitted, in real time, to users in Brazil and surrounding areas. It is estimated that users will be able to achieve a horizontal accuracy around 0.5 m (1 σ) in static and kinematic positioning and better for dual frequency users. The availability of the WADGPS service will allow users to tie to the new SIRGAS2000 frame in a more rapid and transparent way for positioning and navigation applications. It should be emphasized that support to post-mission static positioning, will continue to be provided to users interested in higher accuracy levels. In addition to this, a post-mission Precise Point Positioning (PPP) service will be provided based on the one currently provided by the Geodetic Survey Division of NRCan (CSRS-PPP). The modernization of the RBMC is under development based on a cooperation signed at the end of 2004 with the University of New Brunswick, supported by the Canadian International Development Agency and the Brazilian Cooperation Agency. The Geodetic Survey Division of NRCan is also participating in this modernization effort under the same project. © Springer-Verlag Berlin Heidelberg 2009.

HPF boost interleaved operating in discontinuous conduction mode for trolleybus application

This paper deals with results of a research and development (R&D) project in cooperation with Electric Power Distribution Company in São Paulo (Brazil) regarding the development and experimental analysis of a new concept of power drive system suitable for application in traction systems of electrical vehicles pulled by electrical motors, which can be powered by urban DC or AC distribution networks. The proposed front-end structure is composed by five boost power cells in interleaving connection, operating in discontinuous conduction mode as AC-DC converter, or as DC-DC converter, in order to provide the proper DC output voltage range required by DC or AC adjustable speed drivers. Therefore, when supplied by single-phase AC distribution networks, and operating as AC-DC converter, it is capable to provide high power factor, reduced harmonic distortion in the input current, complying with the restrictions imposed by the IEC 61000-3-4 standards resulting in significant improvements for the trolleybuses systems efficiency and for the urban distribution network costs. Considering the compliance with input current restrictions imposed by IEC 61000-3-4 standards, two digital control strategies were evaluated. The digital controller has been implemented using a low cost FPGA (XC3S200) and developed totally using a hardware description language VHDL and fixed point arithmetic. Experimental results from a 15 kW low power scale prototype operating in DC and AC conditions are presented, in order to verify the feasibility and performance of the proposed system. © 2009 IEEE.

Modeling approach based on experimental results for prediction of measurement errors in energy meters

This paper presents a general modeling approach to investigate and to predict measurement errors in active energy meters both induction and electronic types. The measurement error modeling is based on Generalized Additive Model (GAM), Ridge Regression method and experimental results of meter provided by a measurement system. The measurement system provides a database of 26 pairs of test waveforms captured in a real electrical distribution system, with different load characteristics (industrial, commercial, agricultural, and residential), covering different harmonic distortions, and balanced and unbalanced voltage conditions. In order to illustrate the proposed approach, the measurement error models are discussed and several results, which are derived from experimental tests, are presented in the form of three-dimensional graphs, and generalized as error equations. © 2009 IEEE.

ENCORE: Enhanced code Galileo receiver for land management applications in Brazil

Taking benefit of the new Galileo ranging signals, the ENCORE (Enhanced Code Galileo Receiver) project aims to develop a low-cost Land Management Application to cover needs of the Brazilian market in terms of geo-referencing and rural/urban cadastre, using a low-cost Enhanced Galileo Code Receiver as baseline. Land management applications require precision and accuracy levels from a few to several decimetres that are under-met with current pseudorange-based receiver and over-met with phase observations. This situation leads either to a waste of resources, or to lack of accuracy. In this project, it is proposed to fill this gap using the new possibilities of the Galileo ranging signals, in particular E5 AltBOC and E1 CBOC. This approach reduces the cost of the end-user solution, helping the rapid penetration of Galileo technology outside Europe. ©2010 IEEE.