Shared control of robotic friction stir welding in the presence of imperfect joint fit-up

In this paper a shared control strategy is presented that allows a skilled operator to identify irregularities that occur during robotic friction stir welding (FSW) and assist the robotic system in producing an appropriate response. Human operators are adept at identifying disturbances; however, the complexity of the friction stir welding process makes it difficult for the operator to respond. While examining the capabilities of shared control in friction stir welding, this paper focuses on responding to defects that are caused by a lack of workpiece material during butt welding, such as gaps. A compensation strategy is presented that combines the human operator's perceptual strengths with an automated procedure for adjustment of the process parameters (i.e. travel angle and plunge depth). Experiments comparing four control strategies are performed while welding 5083-H116 aluminum. Through our experiments we demonstrate that if the FSW control task is appropriately shared between the human operator and the computer control system, the weld quality (strength) can be improved (from 9 ksi to 31 ksi for a gap size of 2.5 mm) as compared with the nominal case in which no corrections are made.     

The species flocks of East African cichlid fishes: recent advances in molecular phylogenetics and population genetics

With more than 3,000 species, the fish family Cichlidae is one of the most species-rich families of vertebrates. Cichlids occur in southern and central America, Africa, Madagascar, and India. The hotspot of their biodiversity is East Africa, where they form adaptive radiations composed of hundreds of endemic species in several lakes of various sizes and ages. The unparalleled species richness of East African cichlids has been something of a conundrum for evolutionary biologists and ecologists, since it has been in doubt whether these hundreds of species arose by allopatric speciation or whether it is necessary to invoke somewhat less traditional models of speciation, such as micro-allopatric, peripatric, or even sympatric speciation or evolution through sexual selection mediated by female choice. Ernst Mayrs analyses of these evolutionary uniquely diverse species assemblages have contributed to a more direct approach to this problem and have led to a deeper understanding of the patterns and processes that caused the formation of these huge groups of species. We review here recent molecular data on population differentiation and phylogenetics, which have helped to unravel, to some extent, the patterns and processes that led to the formation and ecological maintenance of cichlid species flocks. It is becoming apparent that sexually selected traits do play an important role in speciation in micro-allopatric or even sympatric settings. Species richness seems to be roughly correlated with the surface area, but not the age, of the lakes. We observe that the oldest lineages of a species flock of cichlids are often less species-rich and live in the open water or deepwater habitats. While the species flocks of the Lake Malawai and the Lake Victoria areas were shown to be monophyletic, the cichlid assemblage of Lake Tanganyika seems to consist of several independent species flocks. Cichlids emerge as an evolutionary model system in which many fundamental questions in evolution and ecology can be tested successfully, yet for other fish species flocks the relative importance of alternative mechanisms of speciation is likely to differ from that in cichlid fish.Dedicated to Prof. Ernst Mayr     

Mitigation Options for Enteric Methane Emissions from Dairy Animals: An Evaluation for Potential CDM Projects in India

Enteric fermentation in livestock is an important source of anthropogenic methane emission. India, with its large livestock population, is estimated to contribute 10.8 Tg of methane annually from this source. An evaluation of various methane mitigation options indicate that some of the available technologies like, diet supplementation with feed additive and molasses urea product are highly cost effective in reducing enteric methane emissions. The gross cost of methane abatement from use of feed additive monensin premix ranges from €0.6 to €1.8/ton CO₂ equivalent, for buffaloes and indigenous cows, respectively. The gross cost of enteric methane mitigation from supplementing molasses urea products and dietary manipulation through increased concentrate feeding is much higher. But, as the monetary value of the increased milk production on application of these technologies was higher than the annual cost of reduction strategy for buffaloes and crossbred cows, the net costs of the former mitigation option was negative for buffaloes (€-28.1/ton CO₂) and of the latter for crossbred cows (€-7.0/ton CO₂,). The availability of cost-effective technologies suggest that the methane mitigation projects under CDM, can be planned in the Indian dairy sector to the mutual benefit of countries with emission targets and India. The vast dairy animal population of India and resulting methane emissions provide good opportunity these countries to buy reasonable quantum of emission credits from projects in India. Such projects will work to the benefit to India by providing a tool for technology transfer to increase animal productivity and attract capital that assists in more prosperous and environmental friendly milk production in the country.     

Distribution and sources of polyfluoroalkyl substances (PFAS) in the River Rhine watershed

The concentration profile of 40 polyfluoroalkyl substances (PFAS) in surface water along the River Rhine watershed from the Lake Constance to the North Sea was investigated. The aim of the study was to investigate the influence of point as well as diffuse sources, to estimate fluxes of PFAS into the North Sea and to identify replacement compounds of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA). In addition, an interlaboratory comparison of the method performance was conducted. The PFAS pattern was dominated by perfluorobutane sulfonate (PFBS) and perfluorobutanoic acid (PFBA) with concentrations up to 181 ng/L and 335 ng/L, respectively, which originated from industrial point sources. Fluxes of ΣPFAS were estimated to be ∼6 tonnes/year which is much higher than previous estimations. Both, the River Rhine and the River Scheldt, seem to act as important sources of PFAS into the North Sea.     

Limited contributions of released animals from zoos to North American conservation translocations

With the loss of biodiversity accelerating, conservation translocations such as reintroductions are becoming an increasingly common conservation tool. Conservation translocations must source individuals for release from either wild or captive-bred populations. We asked what proportion of North American conservation translocations rely on captive breeding and to what extent zoos and aquaria (hereafter zoos) fulfill captive breeding needs. We searched for mention of captive breeding and zoo involvement in all 1863 articles included in the North American Conservation Translocations database, which comprises journal articles and grey literature published before 2014 on conservation translocations in Canada, the United States, Mexico, the Caribbean, and Central America before 2014 as identified by a comprehensive literature review. Conservation translocations involved captive breeding for 162 (58%) of the 279 animal species translocated. Fifty-four zoos contributed animals for release. The 40 species of animals bred for release by zoos represented only 14% of all animal species for which conservation translocations were published and only 25% of all animal species that were bred for releases occurring in North America. Zoo contributions varied by taxon, ranging from zoo-bred animals released in 42% of amphibian conservation translocations to zero contributions for marine invertebrates. Proportional involvement of zoos in captive-breeding programs for release has increased from 1974 to 2014 (r = 0.325, p = 0.0313) as has the proportion of translocation-focused scientific papers coauthored by zoo professionals (from 0% in 1974 to 42% in 2013). Although zoos also contribute to conservation translocations through education, funding, and professional expertise, increasing the contribution of animals for release in responsible conservation translocation programs presents a future conservation need and opportunity. We especially encourage increased dialogue and planning between the zoo community, academic institutions, and governments to optimize the direct contribution zoos can make to wildlife conservation through conservation translocations.     

Asymmetric mate choice,hybridization, and hybrid fitness in two sympatric grasshopper species

Hybridization between animal species has long been regarded as unusual, but is meanwhile accepted as a widespread phenomenon. Typically, sexual interactions among species are studied in secondary contact zones of closely related species (hybrid zones) or between invasive and native species, whereas hybridization between sympatric congeners has received little attention. Here, we present a study on the hybridization potential of two grasshopper species, Chorthippus parallelus and Chorthippus montanus, which occur sympatric in large parts of Eurasia. We performed a mate choice experiment with specimens from an area of local parapatry in northwestern Germany. Most copulations were conspecific, but males of both species and females of C. parallelus were indiscriminate in their mate choice, while females of C. montanus clearly preferred conspecific males. Although these results suggest asymmetric introgression, a no-choice hybridization experiment revealed that hybridization is possible in both directions. The hatching success of the hybrids was intermediate between the parental species. Female hybrids showed no clear mate preferences, indicating that back crossing in both directions is possible in principle, but the fertility of the hybrids and the fitness of the F2 generation remain unknown. Our study suggests that hybridization between sympatric species might occur more often than assumed. It might affect the ecology and local distribution of animals in a similar way as competition does.     

Adjustment of brood care behaviour in the absence of a mate in two species of Nicaraguan crater lake cichlids

In many taxa, parental strategies can vary among individuals. This is especially true in species with biparental care, with males, more often than females, deserting their mates. While there is an abundance of theoretical predictions and empirical data on factors inducing mate abandonment by males, much less is known about what consequences this may have on female behaviour, particularly in the field and in non-avian systems. Here, we compared brood defence rate, behavioural defence types, and brood success of solitary and paired females in two species of Neotropical cichlid fish in their natural habitat. In terms of the rate of territorial aggression towards potential brood predators, solitary females were able to fully compensate in the absence of a male but, in so doing, ended up maintaining smaller territories, which appeared to compromise offspring fitness in at least one of the two species. Hence, our results suggest that even extensive quantitative compensation in parental effort by solitary females may not be enough to ensure adequate qualitative compensation for the lack of male participation, highlighting the importance of distinguishing between these two aspects of compensatory parental care.     

Hidden Markov models for circular and linear-circular time series

We introduce a new class of circular time series based on hidden Markov models. These are compared with existing models, their properties are outlined and issues relating to parameter estimation are discussed. The new models conveniently describe multi-modal circular time series as dependent mixtures of circular distributions. Two examples from biology and meteorology are used to illustrate the theory. Finally, we introduce a hidden Markov model for bivariate linear-circular time series and use it to describe larval movement of the fly Drosophila. Received: September 2003 / Revised: March 2004