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São José dos Campos, Brazil

Oliveira A.V.M.,Aeronautics Institute of Technology | Lohmann G.,Griffith University | Costa T.G.,Virtus BR Partners
Journal of Transport Geography | Year: 2016

This paper empirically investigates the main drivers of airline network concentration in an air transport market subject to rapid growth. We consider the Brazilian air transport industry of the 2000s, in which network concentration rapidly increased and was followed by a period of massive flight delays and cancelations, which resulted in the "big blackout" of 2006-2007. We develop an econometric model of network concentration, accounting for demand, cost and competition variables that may affect the propensity of carriers to concentrate flights and passenger connections on a few airports of a network. The main focus of the paper is on the relation between networks leading to the problems of the blackout episode. We investigate the dynamic pattern of the evolution of concentration before and after the abnormal period of operations and find that concentration began to rise at least six quarters before, and persisted at a high level until two quarters after the blackout - and then plunged steeply toward the end of the decade. We believe that our analysis contributes to an improved understanding of the behavior of air transport systems subject to network concentration and congestion. With respect to methodology, we suggest and employ the use of alternative measures of network concentration to check the robustness and validity of our results. © 2015 Elsevier Ltd. Source

Hemsi P.S.,Aeronautics Institute of Technology | Shackelford C.D.,Colorado State University | Figueroa L.A.,Colorado School of Mines
Journal of Environmental Engineering | Year: 2010

Experimental data pertaining to two pairs of solid-substrate sulfate-reducing biocolumns for remediation of mine drainage were used for calibrating and testing new reactive transport models based on sulfate reduction and sulfide precipitation linked to rate-limiting solid-substrate hydrolysis. First-order (F) and Contois (C) kinetics for decomposition as well as different numbers of pools of decomposable materials were proposed in different models (F1-F3 and C1-C3). Effluent sulfate concentrations for one of the columns were used as the basis for calibrating the different models and, due to limitations in the calibration data set, the number of adjustable model parameters was limited using parameter tying. Calibrated models were ranked using Akaike information criterion, and Model C2, followed by Model C1, based on Contois kinetics, emerged as the models that were supported to a greater extent by the data. For an independent experimental data set, model testing was performed using Models C2 and C1 with parameters from the previous calibration resulting in good approximations of effluent sulfate. For the calibration data set, longer-term model predictions for effluent sulfate, decomposable substrates, and microbial populations also were performed. The reactive transport models represent a potentially valuable tool for the design of solid-substrate bioreactors used for the treatment of mining influenced water, although future model validation using longer-term field data sets will be necessary to confirm the model predictions. © 2010 ASCE. Source

Bastos G.S.,Federal University of Itajuba | Souza L.E.,Federal University of Itajuba | Ramos F.T.,University of Sydney | Ribeiro C.H.C.,Aeronautics Institute of Technology
IEEE Conference on Intelligent Transportation Systems, Proceedings, ITSC | Year: 2011

Material transportation is one of the most important aspects of open-pit mine operations. The problem usually involves a truck dispatching system in which decisions on truck assignments and destinations are taken in real-time. Due to its significance, several decision systems for material transportation in open-pit mining have been developed in the last few years, improving productivity and reducing operational costs. This paper presents a single-dependent agent approach based on Time-dependent Markov Decision Processes (TiMDPs) to model the truck dispatching problem in an example mine. The uncertainty is present in the model as stochastic path selections by the truck driver. Simulations are executed using the SimEvents™framework, and the results compared to other dispatching heuristics commonly used in the mining industry show the superiority of the proposed approach. © 2011 IEEE. Source

Theodoro F.R.F.,Aeronautics Institute of Technology | Reis M.L.C.D.C.,Brazilian Technological Institute of Aeronautics | Souto C.D.,Brazilian Technological Institute of Aeronautics | Barros E.D.,Brazilian Technological Institute of Aeronautics
Measurement: Journal of the International Measurement Confederation | Year: 2016

In this paper we analyses the time response of a pressure sensor submitted to dynamic pressure step signals produced in a shock tube. The sensor is modeled as a linear second-order system and the mathematical modeling of the input signal is supplied by shock tube theory. The description of the sensor parameters is given and the experimental data are compared to the expected sensor response. The law of propagation of uncertainty and a Monte Carlo method are employed to estimate the uncertainty of the step input signal and uncertainties associated with the sensor parameters. Two approaches for estimate the damping were analyzed, one considering the first peak and other using the values of two consecutive peaks of the signal. The time response obtained by using the second approach showed a better agreement to the experimental output signal of the sensor and therefore seems to be more appropriate for the sensor characterization. © 2016 Elsevier Ltd. All rights reserved. Source

Bendinelli W.E.,Aeronautics Institute of Technology | Bettini H.F.A.J.,Aeronautics Institute of Technology | Bettini H.F.A.J.,University of Sao Paulo | Oliveira A.V.M.,Aeronautics Institute of Technology
Transportation Research Part A: Policy and Practice | Year: 2016

This paper develops an econometric model of flight delays to investigate the influence of competition and dominance on the incentives of carriers to maintain on-time performance. We consider both the route and the airport levels to inspect the local and global effects of competition, with a unifying framework to test the hypotheses of 1. airport congestion internalization and 2. the market competition-quality relationship in a single econometric model. In particular, we examine the impacts of the entry of low cost carriers (LCC) on the flight delays of incumbent full service carriers in the Brazilian airline industry. The main results indicate a highly significant effect of airport congestion self-internalization in parallel with route-level quality competition. Additionally, the potential competition caused by LCC presence provokes a global effect that suggests the existence of non-price spillovers of the LCC entry to non-entered routes. © 2016 Elsevier Ltd. Source

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