Browsing by Issue Date, starting with "2009-01"
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- Investigations of nitrogen removal pathways in a biological packed bed reactor using elementary mass balancesPublication . Albuquerque, Antonio; Makinia, Jacek; Pagilla, KrishnaNitrogen cycle involves a complex set of potential biochemical pathways with reactions catalyzed by different microorganisms. Elementary mass balances for COD, DO, NH4-N and alkalinity were conducted and stoichiometric relationships were investigated to explain possible pathways of the nitrogen removal mechanisms in a lab-scale submerged down flow biological packed bed (BPB) reactor. Four sets of experiments were performed by modifying the organic loading and C/N ratio in comparison with steady-state conditions. Approximately 90% of COD and NH4-N removal occurred in two upper sections occupying 1/5 of the reactor height. The elementary mass balances could not explain all the experimental results with respect to nitrogen removal and oxygen consumption by known mechanisms. The mass balance calculations, excluding the possibility of nitrification, were in general in accordance with the observations indicating no or minimal NO3-N production. The theoretical stoichiometric requirements for nitrification reaction were satisfied in 6 experiments and in another 8 experiments nitrification may have occurred, but stoichiometry was not satisfied. Using C/N ratio as the variable, only at C/N ratio = 10, the predictions confirmed the possibility of nitrification in the same 3 (out of 4) assays as observed in practice. The results of this study reveal that the nitrogen transformations occurring in the studied reactor are complex and cannot be explained by simple mechanisms of microbial assimilation and nitrification
- Optimization of Multi-Service IEEE 802.11e Block AcknowledgementPublication . Cabral, Orlando; Velez, Fernando José; Mihovska, Albena Dimitrova; Prasad, NeeliOptimization of IEEE 802.11e MAC protocol performance is addressed by modifying several parameters left open in the standard, like block size and acknowledgement policies in order to improve the channel efficiency. The use of small block sizes leads to a high overhead caused by the negotiation on the other hand, the use of large block sizes causes long delays, which can affect negatively real-time applications (or delay sensitive applications). An event driven simulator was developed, and results with a single service and several services running simultaneously were extracted. By using the Block Acknowledgement (BA) 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 BA 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 number of supported user (total) increases from 30 to 35.
- Isolation and culture of human umbilical artery smooth muscle cells expressing functional calcium channelsPublication . Cairrão, Elisa; Santos-Silva, António; Alvarez, Ezequiel; Correia, Ilídio Joaquim Sobreira; Verde, IgnacioThe human umbilical cord is a biological sample that can be easily obtained just after birth. A methodology was developed to perform cultures of human umbilical artery smooth muscle cells (HUASMC) expressing contractile proteins and functional ionic channels. To avoid fibroblast and endothelial cell contamination, we mechanically separated the tunica media, which only contains HUASMC and matrix proteins. To isolate the cells, collagenase V and elastase were used as hydrolyzing enzymes. The isolated cells were plated in collagen-coated dishes to obtain cultures of HUASMC. The cells obtained after different passages (1 to 6) exhibit the characteristic vascular smooth cell morphology and express smooth muscle alpha-2 actin, myosin heavy chain SM1, and alpha subunits of L- and T-type calcium channels (Cav 1.2, Cav 1.2, and Cav 3.2). Electrophysiology recordings for L- and T-type calcium channels were made, indicating that these channels are functional in the cultured cells. In conclusion, the procedure developed allows obtaining cultures of HUASMC expressing contractile proteins and also functional ionic channels. These cells could be used to study cellular and molecular aspects about the regulation of the vascular function.
- Electroepoxidation of natural and synthetic alkenes mediated by sodium bromidePublication . Inês, Massuquinini; Mendonça, António; Esteves, Ana P.; Mendonça, Dina; Medeiros, Maria J.Electroepoxidation of synthetic alkenes (styrene, trans-stilbene and trans-b-methylstyrene) and of some natural terpenes (limonene, terpinolene, geraniol, a-terpinene, g-terpinene and a-terpineol) mediated by sodium bromide was performed in MeCN:H2O (4:1) at platinum electrodes. The indirect electrochemical oxidation of the olefins led to the corresponding epoxides in yields ranging from 23% to 79%.