Patchwork in an interconnected world: the challenges of transport networks in Sub-Saharan Africa*

Sub-Saharan Africa has recently undergone, or still do in many countries, a period of transport infrastructure expansion. Current policies are centred on the development of international links, which require large capital-intensive projects and are sometimes economically dubious. This paper reviews the past policies and transport functions since colonial times by placing them in their economic and political context. We find that present strategies have similarities to the ones prevailing in previous periods, where expansion phases dominated by transport-led economic growth theories were followed by a stagnation of Africa’s infrastructure development. In view of the challenges in translating findings from empirical research into right policies, we identify the potential of more balanced and sustainable strategic investments, notably by reinforcing the existing secondary transport networks converging into urban centres.     

Ability of a “minimum” microbial food web model to reproduce response patterns observed in mesocosms manipulated with N and P, glucose, and Si

We compared an idealised mathematical model of the lower part of the pelagic food web to experimental data from a mesocosm experiment in which the supplies of mineral nutrients (nitrogen and phosphorous), bioavailable dissolved organic carbon (BDOC, as glucose), and silicate were manipulated. The central hypothesis of the experiment was that bacterial consumption of BDOC depends on whether the growth rate of heterotrophic bacteria is limited by organic-C or by mineral nutrients. In previous work, this hypothesis was examined qualitatively using a conceptual food web model. Here we explore the extent to which a “simplest possible” mathematical version of this conceptual model can reproduce the observed dynamics. The model combines algal–bacterial competition for mineral nutrients (phosphorous) and accounts for alternative limitation of bacterial and diatom growth rates by organic carbon and by silicate, respectively. Due to a slower succession in the diatom–copepod, compared to the flagellate–ciliate link, silicate availability increases the magnitude and extends the duration of phytoplankton blooms induced by mineral nutrient addition. As a result, Si interferes negatively with bacterial consumption of BDOC consumption by increasing and prolonging algal–bacterial competition for mineral nutrients. In order to reproduce the difference in primary production between Si and non-Si amended treatments, we had to assume a carbon overflow mechanism in diatom C-fixation. This model satisfactorily reproduced central features observed in the mesocosm experiment, including the dynamics of glucose consumption, algal, bacterial, and mesozooplankton biomass. While the parameter set chosen allows the model to reproduce the pattern seen in bacterial production, we were not able to find a single set of parameters that simultaneously reproduces both the level and the pattern observed for bacterial production. Profound changes in bacterial morphology and stoichiometry were reported in glucose-amended mesocosms. Our “simplest possible” model with one bacterial population with fixed stoichiometry cannot reproduce this, and we suggest that a more elaborate representation of the bacterial community is required for more accurate reproduction of bacterial production.     

Manoeuvring and hotelling external costs: enough for alternative energy sources?

Local air pollution is the most relevant externality of maritime transport, and its effects are more acute in urban areas as a result of manoeuvring, hotelling and load/unload activities at ports. This article is intended to assess ships’ local air pollution impact in generally densely populated harbour areas to decide whether alternative power supply measures are feasible. First, an optimized infrastructure investment model is developed to ease implementation and maximize the efficiency of alternative power supply projects. Once target harbours and traffic (ship types) within a national port network have been chosen, a vessel traffic analysis (ship type, tonnage, manoeuvring, and hotelling times) is carried out to quantify and evaluate annual polluting emissions (PM_2,5, SO₂, NOx, and VOCs) and their externalities. Finally, the assessment model is applied and results of the Spanish port network case study are discussed. The results obtained are significant and bring the possibility of further controlling the ship’s environmental performance at berth.     

Environmental causes of the fluctuations of red shrimp (Aristeus antennatus) landings in the Catalan Sea

The fluctuations of catches of the deep-sea shrimp Aristeus antennatus (Risso, 1816) were analysed in the 6 ports of Catalonia where production is concentrated, based on monthly landings from 1988 to 2004. The 6 selected ports produced 300 t of red shrimp in 2004, or 80% of the total production in Catalonia. The series for each port showed clear interannual variability, with peaks of production in the early 1990s and more recently from 2001 to 2003. The time periods of the monthly data series, estimated by frequency analysis based on Fourier transform, varied around 7–8 years in the four central ports and 12–13 years in the two northern ports. Additionally, the different curves were not in phase: even in nearby ports, the maximum production is observed in different years. Since the North Atlantic Oscillation (NAO) index is an excellent proxy for long-term series of environmental variables, we aimed to explore relationships between the fluctuation of the NAO index and A. antennatus landings in the Catalan Sea. The correlation between the mean annual NAO index and the annual catches in each port was positive and significant with some time lags (from 1 to 3 years). The existence of clear patterns linking the NAO with marine ecological processes has been demonstrated in many studies, but the underlying ecological mechanisms are far from being well understood. The variations in environmental parameters linked to the NAO may act on biological organisms at different levels (individual, population) through physiology (metabolic and reproductive processes) or through trophic relationships, including ecological cascade effects. We propose that NAO-induced environmental variability may enhance food supply to A. antennatus and hence strengthen the reproductive potential of particular year classes, which result in increased catches 1 to 3 years later, although other possible effects of environmental variability on the population dynamics of this species are worth investigating.     

Planning strategies for promoting environmentally suitable pedestrian pavements in cities

This paper examines the relevance of incorporating comprehensive life-cycle environmental data into the design and management of pedestrian pavements to minimize the impact on the built environment. The overall primary energy demand and global warming potential of concrete, asphalt and granite sidewalks are assessed. A design with a long functional lifetime reduces its overall primary energy demand and global warming potential due to lower maintenance and repair requirements. However, long-lived construction solutions do not ensure a lower life-cycle primary energy demand and global warming potential than for shorter-lived designs; these values depend on the environmental suitability of the materials chosen for paving. Asphalt sidewalks reduce long-term global warming potential under exposure conditions where the functional lifetime of the pavements is less than 15 years. In places where it is known that a concrete sidewalk can have a life of at least 40 years, a concrete sidewalk is the best for minimizing both long-term primary energy demand and global warming potential. Granite sidewalks are the largest energy consumers and greenhouse gas contributors.     

Model course to revalidate deck officers’ competences using simulators

In accordance with Part A, Chapter I, Section I/11 Revalidation of Certificates of the Standards of Training, Certification and Watchkeeping for Seafarers (STCW) 2010 Convention, continued evaluation of professional competence shall be established, among others, by successfully completing an approved training course or courses. Every master, officer and radio operator holding a certificate issued or recognised under any chapter of the convention other than chapter VI, who is serving at sea or intends to return to sea after a period ashore, shall be required, at intervals not exceeding 5 years, to demonstrate continued professional competence, in order to continue to qualify for seagoing service. The main objective of this research is to design a model course using simulation technology to train and demonstrate seafarers’ competence in accordance with the provisions of STCW Code for existing seafarers who need to revalidate their professional maritime certificates also in accordance with the standards governing the use of simulators, Reg I/12 of 2010 STCW Code. The purpose of this revalidation simulation-based model course is to assist maritime training institutes and their teaching staff in organising and introducing specific training courses for revalidation of certificates of competence (CoCs) as well as enhancing, updating or supplementing existing training material where the quality and effectiveness of the training courses may thereby be improved. Only those STCW competences relating to ship bridge simulators will be considered for the model course scenario development and testing.     

Accessible pre-design calculation tool to support the definition of EV components

The new freedoms in design that electric powertrains offer lead to a wide variety of configurations to consider when developing an electric vehicle (EV) from scratch. Furthermore, the strong relation of the battery size with vehicle weight, range and performances leads to a set of interrelated dependencies that can result in many design loops to fulfil the vehicle targets, market constraints and regulations simultaneously. The paper presents a pre-design tool to assist the electric vehicle development process by representing the different constraints and the possible feasible solutions in a single plot with the need of a small amount of inputs accesible to assess at pre-design phase. As a result, the tool depicts a set of feasible vehicle configurations that could fulfil the targets easing the interaction and loops among different expertise areas. To better assist selection, it also provides a sensitivity analysis of the performances to selected inputs and the user can introduce a cost function depending on vehicle weight and battery size. The tool is based on the vehicle longitudinal dynamics equations and equations that model the market and regulations constraints. It is aimed at providing an overview of the main specifications for component selection avoiding detailed vehicle modelling in the early pre-design phase at which the vehicle characteristics and even powertrain architecture are unknown. Finally, the tool results quality is evaluated by further developing one of its solutions for passenger car in four different vehicle configurations with the simulation software vemSim and AVL Cruise. The results of the simulations are compared to the solution of the pre-design tool to evaluate the level of fidelity and the deviations in the final result that can appear depending on the final architecture, components characteristics and control strategy.     

Aging characterization of metals for exhaust systems

The mechanical characteristics of four materials used in automotive exhaust systems have been compared after an aging treatment to evaluate the combined effects of thermo-mechanical fatigue and corrosion. For this purpose, an experimental aging procedure has been developed. This procedure is composed of chemical, thermal and mechanical cycles, which are combined and repeated to simulate the actual operating conditions of automotive exhaust systems. Three austenitic steels (AISI 309, AISI 316Ti, and AISI 321) and a nickel-based alloy (Inconel 625) are tested. The results show that Inconel 625 and AISI 309 are less affected by the aging process than the other materials.