Ballast Water Treatment systems: “Old” and “New” ones

This paper offers an overview of the currently available Ballast Water Treatment systems, their efficacy in reducing the number of organisms in relation with the IMO and other, future standards, and explores potentially new and promising technologies and current gaps.     

Tail-Equivalent Linearization Method in frequency domain and application to marine structures

An extension of the Tail-Equivalent Linearization Method (TELM) to the frequency domain is presented. The extension defines the Tail-Equivalent Linear System in terms of its frequency-response function. This function is obtained by matching the design point of the nonlinear response with that of the linearized response, thus guaranteeing the equivalence of the tail probability of the latter and the first-order approximation of the tail probability of the nonlinear response. The proposed approach is particularly suitable when the input and response processes are stationary, as is usually the case in the analysis of marine structures. When linear waves are considered, the Tail-Equivalent Linear System possesses a number of important properties, such as the capability to account for multi-support excitations and invariance with respect to scaling of the excitation. The latter property significantly enhances the computational efficiency of TELM for analysis with variable sea states. Additionally, the frequency-response function of the Tail-Equivalent Linear System offers insights into the geometry of random vibrations discretized in the frequency domain and into the physical nature of the response process. The proposed approach is applied to the analysis of point-in-time and first-passage statistics of the random sway displacement of a simplified jack-up rig model.     

Les systèmes de vélos en libre-service expliquent-ils le retour du vélo en ville ?

Many French and European cities have developed a bike sharing system since 2005. This policy may be explained in a great part by the success of the Velo??v in Lyon, which contributed to improve the image of cycling in the city. If bicycles, however, appear to find a new place in the city, one can wonder whether this is really due to bike sharing systems? What are the real uses of bicycles in contemporary cities, with or without such a system? To answer these questions, the paper starts with a literature review on bicycle in the city, to draw lessons from recent experiences of bike sharing systems. It then discusses the two cases of Lyon and Lille, which never had a bike sharing system on its own. The evolution of bicycle use is measured with a comparison of household transportation surveys in Lyon (1995 and 1998) and Lille (1998 and 2006). In both cities, the analysis reveals a rise in the proportion of healthiest citizens among urban bikers, as well as a return of bikes in dense areas. Bike sharing systems are part of such tendencies. They support them, but should not become a panacea for policies supporting bike use in the city.     

Implementing green supply chain practices: an empirical investigation in the shipbuilding industry

ABSTRACT

Environmental concerns have become important in the shipbuilding industry. Governmental expectations about environmental and social performance are much higher than in the past. Public authorities penalize companies that do not comply with the rules. Shipbuilding companies face these challenges by introducing new technologies into their business processes. They do not only start initiatives to green their own business processes but also those of their supply chain partners. This form of environmental management is called Green Supply Chain Management (GrSCM) and its importance is increasingly recognized. Although GrSCM is growing, companies are experiencing difficulties engaging suppliers in environmental activities.

This empirical study analyses drivers for supply chain participation of suppliers in the shipbuilding industry. We explain the participations of suppliers in GrSCM practice by investigating influencing factors including governmental involvement in greening the supply chain, customer requirements towards green issues, feeling of social responsibility, competitive advantage by going green, and GrSCM readiness. Hypotheses are tested with partial least squares, using survey data of 93 suppliers of two leading shipbuilding companies. We found GrSCM readiness, competitive advantage, and social responsibility to be significant drivers in supplier participation. No significant support was found for governmental involvement and customer requirements.     

Analysis of travel activity determinants using robust statistics

This study investigates travel behavior determinants based on a multiday travel survey conducted in the region of Ghent, Belgium. Due to the limited data reliability of the data sample and the influence of outliers exerted on classical principal component analysis, robust principal component analysis (ROBPCA) is employed in order to reveal the explanatory variables responsible for most of the variability. Interpretation of the results is eased by utilizing ROSPCA. The application of ROSPCA reveals six distinct principal components where each is determined by a few variables. Among others, our results suggest a key role of variable categories such as journey purpose-related impedance and journey inherent constraints. Surprisingly, the variables associated with journey timing turn out to be less important. Finally, our findings reveal the critical role of outliers in travel behavior analysis. This suggests that a systematic understanding of how outliers contribute to observed mobility behavior patterns, as derived from travel surveys, is needed. In this regard, the proposed methods serve for processing raw data typically used in activity-based modelling.     

Determining bicycle infrastructure preferences – A case study of Dublin

This paper examines infrastructure preferences for cyclists and determines the factors that have the greatest influence on the correlation between the level of cycling confidence and preferred types of infrastructure and route characteristics. A stated preference survey is used to gauge preferences for a range of infrastructure types and route characteristics in Dublin. Facilities that were segregated from traffic are the preferred form of cycling infrastructure, regardless of cycling confidence. Routes through residential streets and parks are the second choice, where no specific infrastructure is provided with the exception of improvements in way-finding.     

On the key role of nutrient data to constrain a coupled physical–biogeochemical assimilative model of the North Atlantic Ocean

A sequential assimilative system has been implemented into a coupled physical–biogeochemical model (CPBM) of the North Atlantic basin at eddy-permitting resolution (1/4°), with the long-term goal of estimating the basin scale patterns of the oceanic primary production and their seasonal variability. The assimilation system, which is based on the SEEK filter [Brasseur, P., Verron, J., 2006. The SEEK filter method for data assimilation in oceanography: a synthesis. Ocean Dynamics. doi: 10.1007/s10236-006-0080-3], has been adapted to this CPBM in order to control the physical and biogeochemical components of the coupled model separately or in combination. The assimilated data are the satellite Topex/Poseidon and ERS altimetric data, the AVHRR Sea Surface Temperature observations, and the Levitus climatology for salinity, temperature and nitrate.In the present study, different assimilation experiments are conducted to assess the relative usefulness of the assimilated data to improve the representation of the primary production by the CPBM. Consistently with the results obtained by Berline et al. [Berline, L., Brankart, J-M., Brasseur, P., Ourmières, Y., Verron, J., 2007. Improving the physics of a coupled physical–biogeochemical model of the North Atlantic through data assimilation: impact on the ecosystem. J. Mar. Syst. 64 (1–4), 153–172] with a comparable assimilative model, it is shown that the assimilation of physical data alone can improve the representation of the mixed layer depth, but the impact on the ecosystem is rather weak. In some situations, the physical data assimilation can even worsen the ecosystem response for areas where the prior nutrient distribution is significantly incorrect. However, these experiments also show that the combined assimilation of physical and nutrient data has a positive impact on the phytoplankton patterns by comparison with SeaWiFS ocean colour data, demonstrating the good complementarity between SST, altimetry and in situ nutrient data. These results suggest that more intensive in situ measurements of biogeochemical nutrients are urgently needed at basin scale to initiate a permanent monitoring of oceanic ecosystems.     

Nutrient dynamics and phytoplankton development along an estuary–coastal zone continuum: A model study

This study presents a first attempt to quantify the biogeochemical transformations and fluxes of carbon and nutrients along the entire mixing zone of the shallow, tidally-dominated estuary–coastal zone continuum of the Scheldt (Belgium/The Netherlands). A fully transient, two-dimensional, nested-grid hydrodynamic model of the continuum is coupled to the biogeochemical MIRO model for the coastal zone and the CONTRASTE model for the estuary. Transient model simulations are performed with a high spatial (80–750 m) and temporal (30 min) resolution over a period of one year (January–December 1995). The high temporal resolution allows including the short-term variability triggered by the tides, the freshwater discharge and the wind stress. System scale simulations provide time series of nutrient transformations and fluxes along the entire estuary–coastal zone continuum, as well as highly resolved nutrient inventories for the estuarine and the coastal zone sub-domains. Simulation results reveal that the balance between highly variable estuarine nutrient inputs and physical constrains set by the unsteady residual transport field exert an important control on the magnitude and succession of phytoplankton blooms and the ecosystem structure in the coastal zone. In addition, they suggest that the poorly surveyed estuarine–coastal zone interface plays a central role in the continuum. In this dynamic area, marked spatial concentration gradients develop and episodically lead to a reversal of material fluxes from the coast into the estuary. During distinct episodes of the productive period, euryhaline coastal diatoms intrude far upstream into the saline estuary. This intrusion reduces the estuarine nutrient concentrations and export fluxes, thereby reinforcing the nutrient limitation in the coastal area. As a consequence, the estuarine filter does not operate independently from the processes in the coastal zone. The dynamic interplay between the two ecosystems and the intense process rates operating at their transition, therefore, strongly supports our continuum approach.     

Bacterial production and microbial food web structure in a large arctic river and the coastal Arctic Ocean

Globally significant quantities of organic carbon are stored in northern permafrost soils, but little is known about how this carbon is processed by microbial communities once it enters rivers and is transported to the coastal Arctic Ocean. As part of the Arctic River-Delta Experiment (ARDEX), we measured environmental and microbiological variables along a 300 km transect in the Mackenzie River and coastal Beaufort Sea, in July–August 2004. Surface bacterial concentrations averaged 6.7 × 10⁵ cells mL^− 1 with no significant differences between sampling zones. Picocyanobacteria were abundant in the river, and mostly observed as cell colonies. Their concentrations in the surface waters decreased across the salinity gradient, dropping from 51,000 (river) to 30 (sea) cells mL^− 1. There were accompanying shifts in protist community structure, from diatoms, cryptophytes, heterotrophic protists and chrysophytes in the river, to dinoflagellates, prymnesiophytes, chrysophytes, prasinophytes, diatoms and heterotrophic protists in the Beaufort Sea.Size-fractionated bacterial production, as measured by ³H–leucine uptake, varied from 76 to 416 ng C L^− 1 h^− 1. The contribution of particle-attached bacteria (> 3 µm fraction) to total bacterial production decreased from > 90% at the Mackenzie River stations to < 20% at an offshore marine site, and the relative importance of this particle-based fraction was inversely correlated with salinity and positively correlated with particulate organic carbon concentrations. Glucose enrichment experiments indicated that bacterial metabolism was carbon limited in the Mackenzie River but not in the coastal ocean. Prior exposure of water samples to full sunlight increased the biolability of dissolved organic carbon (DOC) in the Mackenzie River but decreased it in the Beaufort Sea.Estimated depth-integrated bacterial respiration rates in the Mackenzie River were higher than depth-integrated primary production rates, while at the marine stations bacterial respiration rates were near or below the integrated primary production rates. Consistent with these results, P_CO2 measurements showed surface water supersaturation in the river (mean of 146% of air equilibrium values) and subsaturation or near-saturation in the coastal sea. These results show a well-developed microbial food web in the Mackenzie River system that will likely convert tundra carbon to atmospheric CO₂ at increasing rates as the arctic climate continues to warm.     

A dual control approach for repeated anticipatory traffic control with estimation of network flow sensitivity

This paper investigates a strategic signal control, which anticipates travelers' route choice response and determines signal timings to optimize network‐wide objectives. In general traffic assignment models are used for anticipating this route choice response. However, model‐reality mismatch usually brings suboptimal solutions to the real system. A repeated anticipatory control resolves the suboptimality and addresses the modeling error by learning from information on model bias. This paper extends the repeated control approach and focuses on the estimation of flow sensitivity as well as its influence on control, which is a crucial issue in implementation of model bias correction. The main objective of this paper is first to analyze the estimation error in the real flow derivative that is estimated from noisy measurements. A dual control method is then presented, improving both optimization objective function and derivative estimation during the control process. The proposed dual algorithm is tested on a simple network as well as on a midsize network. Numerical examples confirm the reliable performance of the new reality‐tracking control strategy and its ability to identify (local) optimal solutions on real traffic networks. Copyright © 2016 John Wiley & Sons, Ltd.