Browsing by Issue Date, starting with "2009-02"
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- Implementation of Multi-service IEEE 802.11e Block Acknowledgement PoliciesPublication . Cabral, Orlando Manuel Brito; Segarra, Alberto; Velez, Fernando J.Optimisation of IEEE 802.11e MAC protocol performance can be performed by modifying several parameters left open in the standard, like buffer size and acknowledgement policies. In this work, an event driven simulator was developed, and a comparison of the results between the case of standalone services and several services supported simultaneously was addressed. With only a single service, higher values for the goodput are obtained for video and background (BK) traffics, while the lowest ones are found for the voice application. Besides, the number of supported users is higher for voice. With mixtures of traffic, when the number of station is small the goodput is lower for voice. However, for higher number of station, the lowest values of the goodput occur for background traffic. By using the Block Acknowledgement procedure, for video and background traffics in a single service situation, the capacity was improved in the case when the number of stations is equal or higher than 16 and 12, respectively. However, for lower values of the number of stations, the use of Block Acknowledgements leads to a slightly worst system performance. In a scenario with mixture of services the most advised block size is 12 (less delay in a highly loaded scenario). The total number of supported user increases from 30 to 35.
- Ocular injectable formulation assessment for oxidized dextran-based hydrogelsPublication . Maia, João; Ribeiro, MP.; Ventura, Carla; Carvalho, Rui; Correia, Ilídio Joaquim Sobreira; Gil, MariaInitiator-free injectable hydrogels are very interesting for drug and/or cell delivery applications, since they can be administered in a minimally invasive way, and avoid the use of potentially harmful chemical initiators. In the current work, oxidized dextran crosslinked with adipic acid dihydrazide hydrogels were further characterized and tuned to produce formulations, with the aim of producing an injectable formulation for the possible treatment of posterior eye diseases. The gelation rate and the hydrogel dissolution profile were shown to be dependent on the balance between the degree of dextran oxidation, and the concentration of both components. For the in vitro studies, rabbit corneal endothelial cells were seeded on the hydrogels to assess cytotoxicity. Hydrogels prepared with low oxidized dextrans were able to promote cell adhesion and proliferation to confluence in just 24 h, while more highly oxidized samples promoted cell adhesion and proliferation, but without achieving confluence. Cell viability studies were performed using MTS assays to verify the non-cytotoxicity of hydrogels and their degradation byproducts, rendering these formulations attractive for further in vivo studies.