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- Artigo de eventoRanking strategies for stormwater management under uncertainty: Sensitivity analysisReda A.L.L.; Beck M.B. (1997)The disadvantageous consequences of stormwater perturbations of receiving water quality in urban environments can be attenuated by exercising control at various locations across the sewer network, wastewater treatment plant, and the stream itself. As part of a long-standing programme of research on developing an integrated approach to the management and real-time control of water quality in river basins, the paper examines the sensitivity of the associated strategies to model uncertainty. Specifically, results are presented for a case study based on a 10 km stretch of the River Cam as it passes through the city of Cambridge in eastern England. The options for control are restricted to design and operational features of the wastewater treatment facility. Assessment is according to maximum and cumulative values of mass flows of ammonium-N and biochemical oxygen demand, together with the duration of dissolved oxygen concentration below 4.0 gm-3, at the downstream boundary of the system. A straightforward analysis of the sensitivity of these criteria to changes in the parameterization of a model for receiving water quality shows that the ranking of strategies is robust in the face of model uncertainty. Minor differences in ranking occur as a function of whether judgement is based on ammonium-N or the other two attributes of water quality and whether attention is focused on the treatment plant in isolation or performance across the system as a whole. However, such conclusions must be qualified by noting that our analysis has been limited in its scope and elementary in its treatment of uncertainty.The disadvantageous consequences of stormwater perturbations of receiving water quality in urban environments can be attenuated by exercising control at various locations across the sewer network, wastewater treatment plant, and the stream itself. As part of a long-standing programme of research on developing an integrated approach to the management and real-time control of water quality in river basins, the paper examines the sensitivity of the associated strategies to model uncertainty. Specifically, results are presented for a case study based on a 10km stretch of the River Cam as it passes through the city of Cambridge in eastern England. The options for control are restricted to design and operational features of the wastewater treatment facility. Assessment is according to maximum and cumulative values of mass flows of ammonium-N and biochemical oxygen demand, together with the duration of dissolved oxygen concentration below 4.0 gm-3, at the downstream boundary of the system. A straightforward analysis of the sensitivity of these criteria to changes in the parameterisation of a model for receiving water quality shows that the ranking of strategies is robust in the face of model uncertainty. Minor differences in ranking occur as a function of whether judgement is based on ammonium-N or the other two attributes of water quality and whether attention is focused on the treatment plant in isolation or performance across the system as a whole. However, such conclusions must be qualified by noting that our analysis has been limited in its scope and elementary in its treatment of uncertainty.
- Artigo de eventoEnvironmental benefits of replacing fuel oil by natural gas in the metropolitan region of Sao Paulo - BrazilKondo Sohati; de Assuncao Joao Vicente (1998)The Metropolitan Region of Sao Paulo (Brazil) with a population 16.322 million people (1995 estimate)(2) living a in a area of 8,051 km2 and most of them concentrated in the city of Sao Paulo with 9.8 million people and 4.6 million cars, although with an air quality better than some other Latin American megacities such Mexico and Santiago do Chile is still under an air quality that exceeds the national air quality standards (1, 2, 3). In 2/17/1993 Brazilian Petroleum Company (PETROBRAS) and the Bolivian Petroleum Company (Yacimientos Petroliferos Fiscales Bolivianos - YPFB) signed an agreement to bring natural gas from Bolivia to the south and southeast of Brazil (6). The end of the construction of the gas pipeline will be in 1999, and it will deliver 4 million Nm3/day of natural gas to COMGAS - Sao Paulo State Gas Company. This amount will increase to 8.1 million Nm3/day by the year 2006, that will be sufficient to supply the Sao Paulo Metropolitan Region market need at that time (6). In this study an estimate of the influence in the air quality was performed supposing the substitution of fuel oil by natural gas in industry and also in diesel buses. The results showed that there will be benefits in relation to sulfur dioxide, PM10, greenhouse gases and trace elements, and negligible effects in relation to NOx, NMTOC and carbon monoxide.
- Artigo de eventoROBUST CONNECTED WORD SPEECH RECOGNITION USING WEIGHTE VITERBI ALGORITHM AND CONTEXT-DEPENDENT TEMPORAL CONSTRAINTSYoma N.B.; Ling L.L.; Stump S.D. (1999)© 1999 6th European Conference on Speech Communication and Technology, EUROSPEECH 1999. All rights reserved.This paper addresses the problem of connected word speech recognition with signals corrupted by additive and convolutional noise. Context-dependent temporal constraints are proposed and compared with the ordinary temporal restrictions, and used in combination with the weighted Viterbi algorithm which had been tested with isolated word recognition experiments in previous papers. Connected-word recognition tests show that the weighted Viterbi algorithm depends on the accuracy of the state duration modelling and the approach here covered can lead to reductions as high as 90 or 95% in the error rate at moderate SNR using spectral subtraction, an easily implemented technique, even with a poor estimation for noise and without using any information about the speaker. It is also shown that the weighting procedure can reduce the error rate when cepstral mean normalization is also used to cancel both additive and convolutional noise.
- Artigo de eventoTEMPORAL CONSTRAINTS IN VITERBI ALIGNMENT FOR SPEECH RECOGNITION IN NOISEYoma N.B.; Ling L.L.; Stump S.D. (1999)© 1999 6th European Conference on Speech Communication and Technology, EUROSPEECH 1999. All rights reserved.This paper addresses the problem of temporal constraints in the Viterbi algorithm using conditional transition probabilities. The results here presented suggest that in a speaker dependent small vocabulary task the statistical modelling of state durations is not relevant if the max and min state duration restrictions are imposed, and that truncated probability densities give better results than a metric previously proposed [1]. Finally, context dependent and context independent temporal restrictions are compared in a connected word speech recognition task and it is shown that the former leads to better results with the same computational load.
- Artigo de eventoSimulation model for real-time decision support in controlling the impacts of storm sewage dischargesReda A.L.L.; Beck M.B. (1999)The impacts of combined sewage discharges on river water quality are studied using the MCSTR (Multiple Continuously Stirred Tank Reactor) dynamic model. The potential for applying this model in a real-time context is demonstrated as a tool to support decisions regarding treatment plant operation during storm events, when it is often not possible to sustain full treatment of the incoming sewage flow. Discharges to the River Cam of treated and untreated urban wastewaters from Cambridge and the Cambridge Sewage Works are addressed as a hypothetical case study. Alternative treatment strategies are defined for improving receiving water quality and assessed through simulated water quality downstream of the discharge; the state variables of the model include the concentrations of biochemical oxygen demand, ammoniacal- and nitrate-nitrogen, and dissolved oxygen (chlorophyll-a concentrations are also calculated, but not considered herein). Strategies are assessed and ranked according to the reduction in maximum pollutant concentration (or the increase in minimum concentration, in the case of dissolved oxygen) promoted by each alternative, relative to conventional operation. The consequences of discharging overflows at an alternative position in the river, rather than together with the treatment-plant effluent, are also evaluated. Run times for the MCSTR model are of the order of just a few minutes (at most), thus allowing the potential for its use in real time as decision-support aid.