Browsing by Issue Date, starting with "2011-07"
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- Literatura infantil: proposta para o 1.º ciclo do ensino básicoPublication . Dias, Maria do Carmo Nogal; Sardinha, Maria da Graça Guilherme de AlmeidaA Literatura Infantil é hoje uma presença cada vez mais constante na sala de aula do 1.º Ciclo do Ensino Básico, das escolas portuguesas. Sendo que algumas das obras estudadas poderão ser mais adequadas do que outras, ao seleccionar as nossas tivemos em conta os quadros presentes em Cerrilho, Larronaga e Yubero, cujos parâmetros apontam para além da idade das crianças, sugestões sobre os temas, estrutura literária e o desenho das obras. Seguidamente apresentamos um conjunto de actividades onde o mediador/professor é alguém atento que conhece os passos da didáctica da Literatura Infantil. Duas das obras foram leccionadas na nossa turma, onde recolhemos dados que nos permitiram uma avaliação sobre a eficácia da nossa prática.
- Performance assessment of vehicular delay-tolerant networksPublication . Soares, Vasco Nuno da Gama de Jesus; Rodrigues, Joel José Puga CoelhoVehicular networks have attracted considerable attention in the last few years, both in academia and industry. One of the main reasons for their growing popularity can be attributed to the various applications that they make possible. Road safety, traffic monitoring, driving assistance, entertainment, and delivering connectivity to rural/remote communities or catastrophe-hit areas are just a few examples of the many applications envisioned for these networks. Nevertheless, the special characteristics of vehicular networks such as high mobility, highly dynamic network topology, short contact durations, disruption, intermittent connectivity, significant loss rates, variable node density, and network partitioning introduce unique challenges, which greatly impact the deployment of these networks. Such challenges make data dissemination and routing interesting research topics within the vehicular networking area, which are addressed by this research. The work presented in this thesis is motivated by the need to find new solutions to the communication problems arising in disconnected opportunistic vehicular networking scenarios. A new network architecture for vehicular communications is therefore proposed in this work, called vehicular delay-tolerant network (VDTN). Its layered structure is introduced and the corresponding performance analysis is conducted. This architecture differs from other proposals in the literature in several respects. Briefly, it adopts a store-carry-and-forward paradigm combined with an IP over VDTN approach and out-of-band signaling with control and data plane separation. This thesis presents studies on the impact of stationary relay nodes, node density, vehicles movement patterns, and storage constraints on the VDTN network performance, in terms of bundle delivery probability and bundle average delivery delay. Of particular interest to this thesis is the performance improvement of these networks. In particular, node localization information is exploited to improve and optimize the use of data plane resources. It is demonstrated the performance gains attainable in a VDTN through the cooperation between network nodes, in terms of bundle delivery probability and bundle average delivery delay. These performance metrics are also used to investigate the impact of non-priority and priority-based queueing disciplines. Finally, a detailed analysis is performed with the proposed routing protocol for VDTNs, called GeoSpray, against popular single-copy (Direct Delivery, First Contact, GeOpps), and multiplecopy (Epidemic, Spray and Wait, PRoPHET) routing protocols. Such protocols are considered reference in the literature of DTN networks and were deployed in VDTNs. It is shown that GeoSpray yields significant performance gains in terms of the bundle delivery probability and the bundle average delivery delay. The proposed protocol proves to be efficient in terms of storage and bandwidth resources utilization. The results presented in this thesis are based on computer simulations and testbed experiments. The lack of a simulator specialized for VDTN layered network architecture, created the necessity to propose, develop, and implement a simulation tool for VDTNs, called VDTNsim. VDTNsim was used as a basis for the creation of a prototype of a VDTN laboratory testbed, named VDTN@Lab. This thesis aims to contribute to the advance of the state-of-the-art on techniques for tackling the challenges that arise from the unique properties of vehicular networks. Further, this thesis highlights important guidelines for the improvement and design of new protocols, algorithms, services, and applications for vehicular delay-tolerant networks.
- Fixed WiMAX Profit Maximisation with Energy Saving through Relay Sleep Modes and Cell ZoomingPublication . Velez, Fernando J.; del Camino Noguera, Maria; Holland, Oliver; Aghvami, A. HamidIn Fixed WiMAX, the cost/revenue optimisation function for radio and network planning incorporates the cost of building and maintaining the infrastructure and the impact of the available resources on revenues. Supported throughput typically decreases with larger cells due to the implied greater average distance of users from the base station, although the use of subchannelisation can keep throughput steady with a larger cell radius. The use of sectored base stations facilitates selection of higher order modulation and coding schemes in the cell and can improve throughput; however, sectored equipment is more expensive. Fortuitously, using Relay Stations (RSs) can reduce the deployment cost of such systems. In such a context, if RSs are put into sleep mode during the night and at weekends when they are not necessary, important energy savings can be achieved. With relays, only the consideration of tri-sectored Base Station (BS) antennas with K = 3 (at the cost of extra channels, where nine channels corresponds to a bandwidth of 31.5 MHz) obtains values of system throughput comparable to those without using relays. This is due to the more favourable frame format that is employed under the use of tri-sectored BS antennas. This paper shows that the application of cell zooming in conjunction with relays going into sleep mode at times of low load achieves a notable power saving, corresponding to 10% saving in operation and maintenance cost on average. Moreover, as it is assumed that the DL sub-frame format cannot be changed to a more favourable one, economic performance is better when RSs are deployed. It is however important to highlight that in the absence of RSs, economic performance is still reasonable (for tri-sectored and omnidirectional BSs, 700–800% and 400–450% profit, respectively), compared with the case where RSs are deployed (∼1000 and ∼900% profit, respectively).
- Numerical Study of the Mixing Co-Axial JetsPublication . Neves, Fernando M. S. P.; Barata, Jorge M M; Silva, AndréThis paper presents a numerical study of the effect of the turbulence intensity in the turbulent mixing of coaxial confined jets. The objective of this work is to study the effect of the initial levels of turbulence of each coaxial jet in the process of turbulent mixing for diameter ratios less than 2, which is the case of very low bypass turbofan engines. The computational method was tested using the available experimental data, and revealed good capabilities for the simulation of this kind of flows. The effect of the velocity ratio of the two streams is presented for velocity ratios of the two streams of 0.3, 1.5, and 6, and turbulence intensity ratios between 10 -5 and 10 5. The results revealed that for relatively high turbulence intensities of the outer jet a vortex is always present for velocity ratios of 6 or larger, and this is independent of the turbulence intensity ratio. When the turbulence intensity of the inner jet is kept constant and the ratio of turbulence intensities is increased, the recirculation zone decreases in size, its center moves further upstream until it disappears completely. The existence of a favorable pressure gradient as a similar effect, revealing that this is an additional parameter to be taken into consideration together with the velocity ratio and turbulence intensity ratio as far as the recirculation zone is concerned.