Motion planning for cooperative unicycle-type mobile robots with limited sensing ranges: A distributed receding horizon approach

This paper presents a decentralized motion planner for a team of nonholonomic mobile robots subject to constraints imposed by sensors and the communication network. The motion planning scheme consists of decentralized receding horizon planners that reside on each vehicle to achieve coordination among flocking agents. The advantage of the proposed algorithm is that each vehicle only requires local knowledge of its neighboring vehicles. The main requirement for designing an optimal conflict-free trajectory in a decentralized way is that each robot does not deviate too far from its presumed trajectory designed without taking the coupling constraints into account. A comparative study between the proposed algorithm and other existing algorithms is provided in order to show the advantages, especially in terms of computing time. Finally, experiments are performed on a team of three mobile robots to demonstrate the validity of the proposed approach.     

Optimized Evolutionary Strategies in Conformational Sampling

Novel genetic algorithm (GA)-based strategies, specifically aimed at multimodal optimization problems, have been developed by hybridizing the GA with alternative optimization heuristics, and used for the search of a maximal number of minimum energy conformations (geometries) of complex molecules (conformational sampling). Intramolecular energy, the targeted function, describes a very complex nonlinear response hypersurface in the phase space of structural degrees of freedom. These are the torsional angles controlling the relative rotation of fragments connected by covalent bonds. The energy surface of cyclodextrine, a macrocyclic sugar molecule with N = 65 degrees of freedom served as model system for testing and tuning the herein proposed multimodal optimization strategies. The success of GAs is known to depend on the peculiar hypotheses used to simulate Darwinian evolution. Therefore, the conformational sampling GA (CSGA) was designed such as to allow an extensive control on the evolution process by means of tunable parameters, some being classical GA controls (population size, mutation frequency, etc.), while others control the herein designed population diversity management tools or the frequencies of calls to the alternative heuristics. They form a large set of operational parameters, and a (genetic) meta-optimization procedure was used to search for parameter configurations maximizing the efficiency of the CSGA process. The specific impact of disabling a given hybridizing heuristics was estimated relatively to the default sampling behavior (with all the implemented heuristics on). Optimal sampling performance was obtained with a GA featuring a built-in tabu search mechanism, a “Lamarckian” (gradient-based) optimization tool, and, most notably, a “directed mutations” engine (a torsional angle driving procedure generating chromosomes that radically differ from their parents but have good chances to be “fit”, unlike offspring from spontaneous mutations). “Biasing” heuristics, implementing some more elaborated random draw distribution laws instead of the ‘flat’ default rule for torsional angle value picking, were at best unconvincing or outright harmful. Naive Bayesian analysis was employed in order to estimated the impact of the operational parameters on the CSGA success. The study emphasized the importance of proper tuning of the CSGA. The meta-optimization procedure implicitly ensures the management, in the context of an evolving operational parameterization, of the repeated GA runs that are absolutely mandatory for the reproducibility of the sampling of such vast phase spaces. Therefore, it should not be only seen as a tuning tool, but as the strategy for actual problem solving, essentially advocating a parallel exploration of problem space and parameter space.     

City Blueprints: 24 Indicators to Assess the Sustainability of the Urban Water Cycle

Climate change, population growth and increased consumption, coupled with urbanization, are all placing increased pressure on water management. This global challenge can often best be addressed at the local level, e.g. in cities by optimizing the role of civil society. Although there are approaches for assessing the sustainability of countries and cities, there is no dedicated framework for the assessment of the sustainability of urban water management. We have therefore compiled a comprehensive list of indicators (the city blueprint) for this. The city blueprint is proposed as a first step towards gaining a better understanding and addressing the challenges of integrated urban water management (IUWM). City blueprints will enable the IUWM of cities to be compared, and stimulate the exchange of success stories (good practices) between cities to address the enormous IUWM challenges which lie ahead. The city blueprint provides a quick scan and baseline assessment. It comprises elements from a variety of methodologies, such as water footprint, urban metabolism and ecosystem services. The indicators have been subdivided into eight broad categories, i.e. (1) water security following the water footprint approach developed by Hoekstra and Chapagain (2007), (2) water quality, which includes surface water and groundwater, (3) drinking water, (4) sanitation, (5) infrastructure, (6) climate robustness, (7) biodiversity and attractiveness and (8) governance. Experience using city blueprints for the cities of Rotterdam, Maastricht and Venlo (in the Netherlands) have been included as practical examples. It was concluded that simplicity (ease of calculation and data availability), transparency and ease of communication makes the blueprint a valuable tool for policy makers, decision makers and resource managers as a first step in the process of understanding, envisioning, developing and implementing measures to transform the water management of cities. The best results are obtained when all the stakeholders are involved and connected right from the start.     

Legislation reduces exposure to second-hand tobacco smoke in New Zealand bars by about 90%

Aim

To measure exposure to second‐hand smoke (SHS) in New Zealand bars before and after comprehensive smoke‐free legislation enacted on 10 December 2004.

Methods

Cotinine is the main specific metabolite of nicotine and a well‐established biomarker for SHS exposure. We measured cotinine levels in saliva of non‐smoking volunteers before and after a 3 h visit to 30 randomly selected bars in 3 cities across the country. Two measures of cotinine before the smoke‐free law change during winter and spring 2004, and two follow‐up measurements in the same volunteers and venues during winter and spring 2005, were included.

Results

Before the smoke‐free law change, in all bars and in all volunteers, exposure to SHS was evident with an average increase in saliva cotinine of 0.66 ng/ml (SE 0.03 ng/ml). Increases in cotinine correlated strongly with the volunteers'' subjective observation of ventilation, air quality and counts of lit cigarettes. However, even venues that were judged to be “seemingly smoke free” with “good ventilation” produced discernable levels of SHS exposure. After the law change, there remained some exposure to SHS, but at much lower levels (mean saliva cotinine increase of 0.08 ng/ml, SE 0.01 ng/ml). Smoking indoors in bars was almost totally eliminated: in 2005 only one lit cigarette was observed in 30 visits.

Conclusions

Comprehensive smoke‐free legislation in New Zealand seems to have reduced exposure of bar patrons to SHS by about 90%. Residual exposures to SHS in bars do not result from illicit smoking indoors.Before December 2004, smoking was prohibited in most, but not all, workplaces in New Zealand. Bars, restaurants and hotels were not required to be smoke free. This changed on 10 December 2004 when the Smokefree Environments Amendment Act 2003 came into force. Since that time, smoking is not permitted in any indoor place of work. After Ireland, which passed its legislation in March 2004, New Zealand was one of the first countries to introduce national, comprehensive smoke‐free legislation.The purpose of this study was to measure the impact of this legislation on personal exposures to second‐hand smoke (SHS) in New Zealand bars. Previous papers^1,2,3 have described exposures of bar workers in Ireland, New York and Scotland before and after legislation. The effects of reduced exposures to SHS on the respiratory health of employees in this industry have also been documented.^3,4 However, we know of no other study that has examined the effects of smoke‐free laws on exposures of the patrons of bars and hotels. In an earlier publication,⁵ we have described in greater detail the analytical methods and findings at baseline.     

The microstructure of foamed maltodextrin/sodium caseinate powders: a comparative study by microscopy and physical techniques

Microscopy followed by image analysis is combined with physical characterisation techniques in order to obtain information about the structure of solid foams consisting of maltodextrin DE12 and sodium caseinate (10–30% w/w) processed under varying foaming conditions. Thin sections of solid foam were analysed by microscopy and image analysis for closed porosity, bubble size distribution and bubble connectivity. The bubble size distribution in the range up to about 25 μm was found to be largely independent of the degree of foaming. The total porosity of the solid foams, as determined by image analysis, was in very good agreement with the results from helium pycnometry and a direct relationship between the porosity and surface area as measured by BET nitrogen adsorption is obtained. Mercury intrusion porosimetry was found to be of limited use for the analysis of the open pore structure because of the fragility of the powders and the overlap in size between bubbles and interstitial spaces between the powder particles.