Discrete Dynamical Systems: A Brief Survey

Dynamical system is a mathematical formalization for any fixed rule that is described in time dependent fashion. The time can be measured by either of the number systems - integers, real numbers, complex numbers. A discrete dynamical system is a dynamical system whose state evolves over a state space in discrete time steps according to a fixed rule. This brief survey paper is concerned with the part of the work done by José Sousa Ramos [2] and some of his research students. We present the general theory of discrete dynamical systems and present results from applications to geometry, graph theory and synchronization

On Colorful Bin Packing Games

We consider colorful bin packing games in which selfish players control a set of items which are to be packed into a minimum number of unit capacity bins. Each item has one of $m\geq 2$ colors and cannot be packed next to an item of the same color. All bins have the same unitary cost which is shared among the items it contains, so that players are interested in selecting a bin of minimum shared cost. We adopt two standard cost sharing functions: the egalitarian cost function which equally shares the cost of a bin among the items it contains, and the proportional cost function which shares the cost of a bin among the items it contains proportionally to their sizes. Although, under both cost functions, colorful bin packing games do not converge in general to a (pure) Nash equilibrium, we show that Nash equilibria are guaranteed to exist and we design an algorithm for computing a Nash equilibrium whose running time is polynomial under the egalitarian cost function and pseudo-polynomial for a constant number of colors under the proportional one. We also provide a complete characterization of the efficiency of Nash equilibria under both cost functions for general games, by showing that the prices of anarchy and stability are unbounded when $m\geq 3$ while they are equal to 3 for black and white games, where $m=2$. We finally focus on games with uniform sizes (i.e., all items have the same size) for which the two cost functions coincide. We show again a tight characterization of the efficiency of Nash equilibria and design an algorithm which returns Nash equilibria with best achievable performance

Experimental comparison of single-phase active rectifiers for EV battery chargers

An experimental comparison of single-phase active rectifiers for electric vehicle (EV) battery chargers is presented and discussed. Active rectifiers are used in on-board EV battery chargers as front-end converters to interface the power grid aiming to preserve the power quality. In this paper, four topologies of active rectifiers are compared: traditional power-factor-correction; symmetrical bridgeless; asymmetrical bridgeless; and full-bridge full-controlled. Such comparison is established in terms of the requirements for the hardware structure, the complexity of the digital control system, and the power quality issues, mainly the grid current total harmonic distortion and the power factor. Along the paper these comparisons are presented and verified through experimental results. A reconfigurable laboratorial prototype of an on-board EV battery charger connected to the power grid was used to obtain the experimental results.This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013. This work is financed by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation - COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT - Fundação para a Ciência e a Tecnologia, within project SAICTPAC/0004/2015- POCI- 01-0145-FEDER-016434.info:eu-repo/semantics/publishedVersio

A novel architecture of a bidirectional bridgeless interleaved converter for EV battery chargers

This paper presents a novel architecture of a bidirectional bridgeless interleaved converter for battery chargers of electric vehicles (EVs). The proposed converter is composed by two power stages: an ac-dc converter that is used to interface the power grid and the dc-link, and a dc-dc converter that is used to interface the dc-link and the batteries. The ac-dc converter is an interleaved bridgeless bidirectional boost-type converter and the dc-dc converter is a bidirectional buck-boost-type converter. The proposed converter works with sinusoidal grid current and with high power factor for all operating power levels, and in both grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operation modes. In the paper is described in detail the proposed converter for EV battery chargers: the circuit topology, the principle of operation, the power control theory, and the current control strategy. Several simulation results for both G2V and V2G operation modes are presented.Fundação para a Ciência e Tecnologia (FCT

A comparative study of austenitic structure in NiTi and Fe based shape memory alloys after severe plastic deformation

The effect of high speed high pressure torsion (HS-HPT) was studied in NiTi and FeMnSiCr SMAs, by comparison. Severe plastic deformation was performed in austenite state for both types of alloys. The alloys subjected to HS-HPT, reduced their grain size due to microstructure fragmentation by compression and torsion. The active elements were achieved being able to support variable ranges of processing parameters like force, pressure, rotation speed and time of torsion. The evolution of microstructural refinement in the samples subjected to different deformation by HS-HPT, were studied by optical and scanning electron microscopy observation and the thermal effect was reveled using differential scanning calorimetry (DSC). (C) 2015 The Authors. Published by Elsevier Ltd.publishersversionpublishe

New opportunities and perspectives for the electric vehicle operation in smart grids and smart homes scenarios

New perspectives for the electric vehicle (EV) operation in smart grids and smart homes context are presented. Nowadays, plugged-in EVs are equipped with on-board battery chargers just to perform the charging process from the electrical power grid (G2V – grid-to-vehicle mode). Although this is the main goal of such battery chargers, maintaining the main hardware structure and changing the digital control algorithm, the on-board battery chargers can also be used to perform additional operation modes. Such operation modes are related with returning energy from the batteries to the power grid (V2G- vehicle-to-grid mode), constraints of the electrical installation where the EV is plugged-in (iG2V – improved grid-tovehicle mode), interface of renewables, and contributions to improve the power quality in the electrical installation. Besides the contributions of the EV to reduce oil consumption and greenhouse gas emissions associated to the transportation sector, through these additional operation modes, the EV also represents an important contribution for the smart grids and smart homes paradigms. Experimental results introducing the EV through the aforementioned interfaces and operation modes are presented. An on-board EV battery charger prototype was used connected to the power grid for a maximum power of 3.6 kW.This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013. This work is financed by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation Ǧ COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT - Fundação para a Ciência e a Tecnologia, within project SAICTPAC/0004/2015- POCI- 01-0145-FEDER-016434.info:eu-repo/semantics/publishedVersio

Produtividade de leguminosas em sistema agroflorestal.

O experimento foi conduzido para avaliar a produtividade de leguminosas de sub-bosque em sistema agroflorestal. Foi adotado um esquema de parcelas subdivididas no espaço, no delineamento em blocos casualizados com três repetições. A parcela principal foi o espaçamento do eucalipto e a subparcela espécies de leguminosas. Foram encontradas diferenças de produtividade de MS do subbosque em função do espaçamento de plantio com 100 dias de rebrota das leguminosas e não foram encontradas diferenças de produtividade entre leguminosas de sub-bosque. O maior valor de produtividade (5.984 kg de MS/ha) de leguminosas para sub-bosque foi obtido no espaçamento 12x3. As produtividades das leguminosas estilosantes, calopogônio e amendoim foram, respectivamente, de 5.031; 2.923 e 5.494 kg de MS/ha. Os resultados encontrados são importantes para escolher tanto o espaçamento de plantio de eucalipto como a espécie de sub-bosque em sistemas agroflorestais no Cerrado brasileiro. Productivity of legumes in agroforestry system. Abstract: The work was carried out to evaluate the productivity of understory?s legumes in agroforestry system. A split plot arrangement, with three replicates in the randomized block design, was utilized. Main plot was eucalyptus spacing and sub-plots legumes species. Differences were found to productivity of understory in function of planting spacing with 100 days of regrowth of legumes and there was not difference of productivity between understory?s legumes. The highest productivity (5,984 kg of DM/ha) of legumes to understory was found in 12x3 spacing. The yields of legumes Stylosanthes, Calopogonium and Arachis were respectively 5,031; 2,923 and 5,494 kg of DM/ha. Results found are important to choose as planting spacing to eucalyptus as specie of understory in agroforestry system in Brazilian Cerrado