Planning and Deployment of WiMAX Networks

Incorporation of measurement based techniques in Worldwide Interoperability for Microwave Access (WiMAX) are required to improve IEEE 802.16 engineering methodologies. Wireless planning methodologies are presented, supported by a planning tool which facilitates the design and implementation of WiMAX networks. Propagation models available for WiMAX still need to be tuned and further validated. By comparing IEEE 802.16-2004 measurement results at 3.5 GHz with computed values using the modified Friis and the Stanford University Interim (SUI) models, for a suburban area, we found that the use of the modified Friis equation with a propagation exponent ~3 is more appropriate than the use of the SUI model, although, for coverage distances between 275 and 475 m, the SUI-B and mainly SUI-C models may still be used. From the analysis of the carrier-to-noise-plus-interference ratio, it is clear that both noise and interference present a strong limitation to the cellular reuse performance of fixed WiMAX mainly for higher order modulation and coding schemes. With a reuse pattern K = 7, cell throughputs near the maximum are only achieved in the uplink if sub-channelisation is used together with sectorization. The planning tool provides planners with practical and useful information through quick coverage/capacity based procedures, and outputs the number and position of the base stations and an estimation of the total cost of implementation, based on data provided by different equipment manufacturers. WiMAX cellular planning exercises are presented for the zone of Covilhã, Portugal, where Geographic Information Systems are used for representation of rural and sparse urban areas. One of the main conclusions is the strong need to use sector antennas in order to guarantee an adequate coverage, and higher system capacity whilst mitigating interference for several terrain types and environments, including hilly terrain.     

Modulation of a photoswitchable dual-color quantum dot containing a photochromic FRET acceptor and an internal standard

Photoswitchable semiconductor nanoparticles, quantum dots (QDs), couple the advantages of conventional QDs with the ability to reversibly modulate the QD emission, thereby improving signal detection by rejection of background signals. Using a simple coating methodology with polymers incorporating a diheteroarylethene photochromic FRET acceptor as well as a spectrally distinct organic fluorophore, photoswitchable QDs were prepared that are small, biocompatible, and feature ratiometric dual emission. With programmed irradiation, the fluorescence intensity ratio can be modified by up to ～100%.     

Hydrogen Spillover in Ga2O3–Pd/SiO2 Catalysts for Methanol Synthesis from CO2/H2

The hydrogenation of CO₂ was investigated on Ga₂O₃-promoted Pd/SiO₂ catalyts and mechanical mixtures of Ga₂O₃/SiO₂ and Pd/SiO₂ catalysts (H₂/CO₂ = 3; P = 3.0 MPa; T = 523 K). By means of the latter it was possible to demonstrate that atomic hydrogen, H_s, can be generated by Pd⁰ far from Ga₂O₃, and move (spill-over) there to reach the other reactive species (formates) and complete the reaction cycle. The reaction results indicate that (as also evidenced by in situ FTIR) the Ga₂O₃-Pd/SiO₂ catalyst works as a true bi-functional system. The metal-promoter intimacy is not decisive in terms of the catalytic chemistry of the system, but the closeness between the Pd crystallites and the Ga₂O₃ surface patches boost the activity, owing to a minimized effort in the H_s supply to the latter.     

Scheduling in sports: An annotated bibliography

Sports have worldwide appeal. Professional sport leagues involve significant investments in players. Events such as the Olympics Games, the Football World Cup and the major golf and tennis tournaments generate huge worldwide television audiences and many sports are multi-million dollar industries. A key aspect of sporting events is the ability to generate schedules that optimize logistic issues and that are seen as fair to all those who have an interest. This is not just restricted to generating the fixtures, but also to other areas such as assigning officials to the games in the competitions. This paper provides an annotated bibliography for sports scheduling articles. This area can be traced back over 40 years. It is noticeable that the number of papers has risen in recent years, demonstrating that scientific interest is increasing in this area.     

Predicting student failure at school using genetic programming and different data mining approaches with high dimensional and imbalanced data

Predicting student failure at school has become a difficult challenge due to both the high number of factors that can affect the low performance of students and the imbalanced nature of these types of datasets. In this paper, a genetic programming algorithm and different data mining approaches are proposed for solving these problems using real data about 670 high school students from Zacatecas, Mexico. Firstly, we select the best attributes in order to resolve the problem of high dimensionality. Then, rebalancing of data and cost sensitive classification have been applied in order to resolve the problem of classifying imbalanced data. We also propose to use a genetic programming model versus different white box techniques in order to obtain both more comprehensible and accuracy classification rules. The outcomes of each approach are shown and compared in order to select the best to improve classification accuracy, specifically with regard to which students might fail.     

Analysis of plate drawing processes by the upper bound method using theoretical work-hardening materials

The present paper analyses the plate drawing processes carried out in converging dies using theoretical work-hardening materials. The analysis has been carried out by the upper bound method (UBM), modelling the plastic deformation zone by triangular rigid zones (TRZ) and considering that the processes occur under plane strain and partial friction conditions. Explicit expressions for the calculation of the necessary power and the non-dimensional total energy to carry out the process using theoretical work-hardening materials have been established. The results have been compared with those obtained using rigid-perfectly plastic materials. In spite of the fact that the energy involved in the process using a work-hardening material is higher than when a rigid-perfectly plastic material is used, the number of possible sets of variables (die geometries, cross-sectional area reductions and partial friction coefficients) increases, since the stability limit of the process increases as well.     

A Performance Comparison of Different FEC System Architectures for ATM over Wireless Multi-Carrier Modulation

In multi-carrier modulation (MCM) systems multiple relatively narrowband sub-carriers are used to alleviate the undesirable influence of frequency selective fading. This paper analyses the performance of MCM data links when forward error correction is employed either in each sub-carrier or in the main stream of bits. The influences on system performance of interleaving and suppression of the poorest sub-carriers are also analysed. José Marcos C. Brito received his diploma in electrical engineering from the National Institute of Telecommunications (Inatel), Brazil, in 1986, his M.Sc. degree in electrical engineering from State University of Campinas, Brazil, in 1998, and his Ph.D. degree in electrical engineering from State University of Campinas in 2003. Since 1986 he has been a professor at Inatel, where he has held several management positions, including vice-principal and director for research. Currently he is a Full Professor at Inatel. He has worked as a consultant for several telecommunications companies in Brazil and has published several papers in international conferences in the telecommunications area. He is the editor-in-chief of the Telecommunications Journal edited by Inatel and has served as a program committee member in some international conferences. His current research interests include computer communications networks, multiple access systems, modeling and performance evaluation of communication systems, wireless networks and error control schemes. Ivanil S. Bonatti was born in Mogi-Mirim, SP, Brazil, in 1951. He received the B.Sc. (1973) and M.Sc. (1975) degrees in Electrical Engineering from the University of Campinas, UNICAMP, Brazil, and the “Doctorat en Automatique” degree from the University Paul Sabatier, Toulouse, France, in 1981. He joined the School of Electical and computer Engineering of the University of Campinas in 1975, where he is currently a professor. His main interests are circuit theory, simulation analysis and telecommunication.     

Gas–liquid mass transfer to single bubbles: Effect of surface contamination

The dissolution of single bubbles of gases of low solubility kept stationary in a downward stream of water was studied. In “clean” water, two regimes are identified. Initially, the process is fast, consistent with the theory for circulating bubbles. Then, the mass-transfer rate falls sharply to that predicted for solid spheres. Transition times and transition diameters vary widely with experimental conditions. In untreated water, only the second regime is found. Results are explained in terms of the kinetics of trace surfactant accumulation at the interface. An adaptation of the stagnant-cap model is proposed, with surface immobilization expressed in terms of interface dynamics. The model yields good prediction of the transition point for a very large set of conditions, including different gases at various concentrations in the liquid stream and a wide range of initial bubble diameters.     

Microbial fuel cell application in landfill leachate treatment

The feasibility of using microbial fuel cells (MFCs) in landfill leachate treatment and electricity production was assessed under high levels of nitrogen concentration (6033 mg NL(-1)) and conductivity (73,588 μS cm(-1)). An air-cathode MFC was used over a period of 155 days to treat urban landfill leachate. Up to 8.5 kg COD m(-3)d(-1) of biodegradable organic matter was removed at the same time as electricity (344 m Wm(-3)) was produced. Nitrogen compounds suffered transformations in the MFC. Ammonium was oxidized to nitrite using oxygen diffused from the membrane. However, at high free ammonia concentrations (around 900 mg N-NH(3)L(-1)), the activity of nitrifier microorganisms was inhibited. Ammonium reduction was also resulted from ammonium transfer through the membrane or from ammonia loss. High salinity content benefited the MFC performance increasing power production and decreasing the internal resistance.