João Frederico da Costa Azevedo Meyer

Climate change effects on Antarctic benthos: a spatially explicit model approach

The Antarctic Peninsula is one of the regions on the Earth with the clearest evidence of recent and fast air warming. This air temperature rise has caused massive glacier retreat leading to an increased influx of glacier meltwater which entails hydrological changes in coastal waters, increasing sediment input and ice-scouring impact regime. It has been hypothesized that an increase of sediment load due to glacier retreat resulted in a remarkable benthic community shift in Potter Cove, a small inlet of the South Shetland Islands. In order to test this hypothesis, we developed an explicit spatial model to explore the link between sedimentation and ice-scouring increase upon four of the most conspicuous benthic species. This is a valuable novel approach since disturbances are strongly dependent of the space. The model takes into account sediment and population dynamics with Lotka-Volterra competition, a sediment-dependent mortality term and a randomized ice-scouring biomass removal. With the developed algorithm, and using a MATLAB environment, numerical simulations for scenarios with different sedimentation and ice-impact rates were undertaken in order to evaluate the effect of this phenomenon on biological dynamics. Comparing simulation results with biological data, the model not only recreates the spatial community distribution pattern but also seems to be able to recreate the shifts in abundance under sedimentation enhancement, pointing out its importance as a structuring factor of polar benthic communities. Considering the challenges of Antarctic field work, this model represents a powerful tool for assessing, understanding, and predicting the effects of climate change on threatened Antarctic coastal ecosystems.

Development of Rigorous and Reduced Heterogeneous Dynamic Models for Fixed Bed Catalytic Reactor and Three-Phase Catalytic Slurry Reactor

In this work, the dynamic behavior of two chemical reactors (Fixed Bed Catalytic Reactor and the Three-Phase Reactor), in which different reactions of great industrial interest take place, is presented. Rigorous and reduced models were developed and their capabilities to adequately predict the dynamic behavior of these reactors were compared, indicating which model is more suitable for a specific application (design, optimization and control). Different approaches [Classic, Hermite, Finlayson, Pirkle, Dixion, Generic and Orthogonal collocation (one point)] were used to obtain the reduced models. With these techniques, a mathematical order reduction was carried out, which eliminates the spatial co-ordinate (of the catalyst particle or of the reactor) and promotes radially lumped-differential formulations. The proposed rigorous models were able to predict the main characteristics of the dynamic behavior of the fixed bed catalytic reactor as well as of the three-phase reactor, including the inverse response phenomena and the hot spot present in the former. This knowledge is essential to design and control these reactors. The computational time demanded for the solution of the rigorous models is high in comparison to the reduced ones, which restricts the use of the rigorous models to cases where time is not a limiting factor. Otherwise, when on-line applications are required, the reduced models are more adequate. The models based on reduction techniques overcame computational burden with a faster and easier numerical solution, as well as other difficulties found in rigorous heterogeneous models, especially related to the large number of parameters and sophisticated numerical procedures required by the solution.

“And Now We’re in 2018…”

In this chapter, having been part of IMECC during its 50 years, I try to register, but not officially, of course, stories that make up the history of the Institute, as well as pointing out special moments, highlighting some of these. Some names are mentioned, but many other names do not appear since what I register is, mostly, the result of collective actions. The first years of IMECC are seen through the eyes (and feelings) of an undergraduate student and the remaining 46 years are described—and quite subjectively!—with the observation of a professor. The objective of this chapter, therefore, is to give an idea of where we came from and what made us who we are….

Keystone Species, Forest and Landscape: A Model to Select Protected Areas

The selection of forest fragments for conservation is usually based on spatial parameters as forest size and canopy integrity. This strategy assumes that chosen fragments present high conservation status, ensuring biodiversity and ecological functions. We argue that a well-preserved forest fragment that remains connected by the landscape structure, does not necessarily hold attributes that ensure the presence of keystone species. We also discuss that the presence of keystone species does not always mean that it has the best conditions for its occurrence and maintenance. We developed a model to select areas in forest landscapes to be prioritized for protection based on suitability curves that unify and compare spatial indicators of three categories: forest fragment quality, landscape quality, and environmental conditions for the occurrence of a keystone species. We use a case study to compare different suitability degrees for Euterpe edulis presence, considered an important functional element in Atlantic Forest (São Paulo, Brazil) landscapes and a forest resource for local people. The results show that the identification of medium or advanced stage fragments as singular indicator of forest quality does not guarantee the existence or maintenance of this keystone species. Even in some well-preserved forest fragments, connected to others and with palm presence, the reverse J-shaped distribution of the population size structure is not sustained and these forests continue to be threatened due to human disturbances.

Collective Production with Mathematical Modelling in Digital Culture

In our learning collective, we established the Nucleus for Research in Media in Education including teams from computing, education and science. This research group presents the role of mathematical modelling in the production of Learning Objects, from the interweaving of theoretical and experimental knowledge from individuals implicated in this process. In the production of learning objects involving mathematical models, we note the existence of the following phases of construction: (1) obtaining a mathematical model; (2) describing the reality of the model; (3) the user accesses the application of the information; (4) deciding on how to present the history of the mathematical model; (5) programming the mathematical model; and (6) analysing the interaction between users and their learning via a simulation model. This context shows that the construction of learning objects requires firstly, a process of mathematical modelling.

Rigorous and Reduced Dynamic Models of the Fixed Bed Catalytic Reactor for Advanced Control Strategies

Abstract Rigorous and reduced heterogeneous dynamic models for fixed bed catalytic reactor were developed in this work. The models consist on mass and heat balance equations for the catalyst particles as well as for the bulk phase of gas. They also consider the variations in the physical properties and in the heat and mass transfer coefficients, the continuity equation for the fluid phase as well as the heat exchange through the jacket of the reactors. The models were used to describe the dynamic behaviour of the ethanol oxidation to acetaldehyde over Fe-Mo catalyst. The proposed models were able to predict the main characteristics of the dynamic behaviour of the reactors, and it was possible to compare the results obtained in simulations of models with different degrees of formulation complexity, thus indicating which model is more suitable for a specific application. This information is important for the real time integration implementation procedure.