Nitrogen fuelling of the pelagic food web of the Tropical Atlantic

We estimated the relative contribution of atmospheric Nitrogen (N) input (wet and dry deposition and N fixation) to the epipelagic food web by measuring N isotopes of different functional groups of epipelagic zooplankton along 23°W (17°N-4°S) and 18°N (20-24°W) in the Eastern Tropical Atlantic. Results were related to water column observations of nutrient distribution and vertical diffusive flux as well as colony abundance of Trichodesmium obtained with an Underwater Vision Profiler (UVP5). The thickness and depth of the nitracline and phosphocline proved to be significant predictors of zooplankton stable N isotope values. Atmospheric N input was highest (61% of total N) in the strongly stratified and oligotrophic region between 3 and 7°N, which featured very high depth-integrated Trichodesmium abundance (up to 9.4×104 colonies m-2), strong thermohaline stratification and low zooplankton delta15N (~2 per mil). Relative atmospheric N input was lowest south of the equatorial upwelling between 3 and 5°S (27%). Values in the Guinea Dome region and north of Cape Verde ranged between 45 and 50%, respectively. The microstructure-derived estimate of the vertical diffusive N flux in the equatorial region was about one order of magnitude higher than in any other area (approximately 8 mmol m-2 d 1). At the same time, this region received considerable atmospheric N input (35% of total). In general, zooplankton delta15N and Trichodesmium abundance were closely correlated, indicating that N fixation is the major source of atmospheric N input. Although Trichodesmium is not the only N fixing organism, its abundance can be used with high confidence to estimate the relative atmospheric N input in the tropical Atlantic (r2 = 0.95). Estimates of absolute N fixation rates are two- to tenfold higher than incubation-derived rates reported for the same regions. Our approach integrates over large spatial and temporal scales and also quantifies fixed N released as dissolved inorganic and organic N. In a global analysis, it may thus help to close the gap in oceanic N budgets.

Estimation des longueurs de branche et artefact sur la datation moléculaire

La phylogénie moléculaire fournit un outil complémentaire aux études paléontologiques et géologiques en permettant la construction des relations phylogénétiques entre espèces ainsi que l’estimation du temps de leur divergence. Cependant lorsqu’un arbre phylogénétique est inféré, les chercheurs se focalisent surtout sur la topologie, c'est-à-dire l’ordre de branchement relatif des différents nœuds. Les longueurs des branches de cette phylogénie sont souvent considérées comme des sous-produits, des paramètres de nuisances apportant peu d’information. Elles constituent cependant l’information primaire pour réaliser des datations moléculaires. Or la saturation, la présence de substitutions multiples à une même position, est un artefact qui conduit à une sous-estimation systématique des longueurs de branche. Nous avons décidé d’estimer l‘influence de la saturation et son impact sur l’estimation de l’âge de divergence. Nous avons choisi d’étudier le génome mitochondrial des mammifères qui est supposé avoir un niveau élevé de saturation et qui est disponible pour de nombreuses espèces. De plus, les relations phylogénétiques des mammifères sont connues, ce qui nous a permis de fixer la topologie, contrôlant ainsi un des paramètres influant la longueur des branches. Nous avons utilisé principalement deux méthodes pour améliorer la détection des substitutions multiples : (i) l’augmentation du nombre d’espèces afin de briser les plus longues branches de l’arbre et (ii) des modèles d’évolution des séquences plus ou moins réalistes. Les résultats montrèrent que la sous-estimation des longueurs de branche était très importante (jusqu'à un facteur de 3) et que l’utilisation d'un grand nombre d’espèces est un facteur qui influence beaucoup plus la détection de substitutions multiples que l’amélioration des modèles d’évolutions de séquences. Cela suggère que même les modèles d’évolution les plus complexes disponibles actuellement, (exemple: modèle CAT+Covarion, qui prend en compte l’hétérogénéité des processus de substitution entre positions et des vitesses d’évolution au cours du temps) sont encore loin de capter toute la complexité des processus biologiques. Malgré l’importance de la sous-estimation des longueurs de branche, l’impact sur les datations est apparu être relativement faible, car la sous-estimation est plus ou moins homothétique. Cela est particulièrement vrai pour les modèles d’évolution. Cependant, comme les substitutions multiples sont le plus efficacement détectées en brisant les branches en fragments les plus courts possibles via l’ajout d’espèces, se pose le problème du biais dans l’échantillonnage taxonomique, biais dû à l‘extinction pendant l’histoire de la vie sur terre. Comme ce biais entraine une sous-estimation non-homothétique, nous considérons qu’il est indispensable d’améliorer les modèles d’évolution des séquences et proposons que le protocole élaboré dans ce travail permettra d’évaluer leur efficacité vis-à-vis de la saturation.

Sermons In Stones. Argument And Artefact For Sustainability

The focus of the study is on the values, priorities and arguments needed to advance ‘design for sustainability’. The discussion critiques conventions related to innovation and technology and offers a product design approach that emphasises minimal intervention, integrated thinking-and-doing, reinstating the familiar, localization and the particularities of place. These interdependent themes are discussed in terms of their relationship to design for sustainability and are clarified through the conceptualization, design, production and use of a simple functional object that is, essentially, a ‘symbolic sustainable artefact’. Although it is fully functional, its practical usefulness in contemporary society would probably be seen as marginal. Its potential contribution is as a symbol of an alternative direction. It asks us to consider aspects of our humanity that are beyond instrumental approaches. It challenges sustainable initiatives that become so caught up in practical and environmental concerns that they fail to question the underlying values, priorities and social drivers which affect how we act in the world; those behaviours and norms that have created the very problems we are so urgently trying to tackle. The discussion is accompanied by a parallel series of photographs that document the relationship between argument, locale and the creation of the conceptual artefact. These photographs convey some of the qualitative differences between the place of much contemporary artefact acquisition, i.e. the shopping mall, and the particular locale that yielded the artefact created during this study; they are also useful in conveying the potential relationship that exist between place and the aesthetics of functional objects.

The Brain as a Cultural Artefact

Where does biology end and culture begin? While the human body is now widely accepted as being both biological and cultural, the brain is still considered by archaeologists as being a biological entity that provides the capacity for culture and is subject to no further change after the evolution of Homo sapiens. This article reviews recent research that suggests that the brain has continued to evolve at an increasing rate in recent times under the influence Of culturally created environments and that both the anatomy and function of individual brains can be manipulated by cultural behaviour. It describes an experiment in which one of us successfully changed his own brain in response to his cultural activity.

Robustness of mutual information to inter-subject variability for automatic artefact removal from EEG

The externally recorded electroencephalogram (EEG) is contaminated with signals that do not originate from the brain, collectively known as artefacts. Thus, EEG signals must be cleaned prior to any further analysis. In particular, if the EEG is to be used in online applications such as Brain-Computer Interfaces (BCIs) the removal of artefacts must be performed in an automatic manner. This paper investigates the robustness of Mutual Information based features to inter-subject variability for use in an automatic artefact removal system. The system is based on the separation of EEG recordings into independent components using a temporal ICA method, RADICAL, and the utilisation of a Support Vector Machine for classification of the components into EEG and artefact signals. High accuracy and robustness to inter-subject variability is achieved.

Automatic artefact removal from event-related potentials via clustering

This paper outlines a method for automatic artefact removal from multichannel recordings of event-related potentials (ERPs). The proposed method is based on, firstly, separation of the ERP recordings into independent components using the method of temporal decorrelation source separation (TDSEP). Secondly, the novel lagged auto-mutual information clustering (LAMIC) algorithm is used to cluster the estimated components, together with ocular reference signals, into clusters corresponding to cerebral and non-cerebral activity. Thirdly, the components in the cluster which contains the ocular reference signals are discarded. The remaining components are then recombined to reconstruct the clean ERPs.

Design of a biomimetic skin for an octopus-inspired robot - Part II: Development of the skin artefact

In order to develop skin artefact for an octopus-inspired robot arm, which is designed to be able to elongate 60% of its original length, silicone rubber and knitted nylon sheet were selected to manufacture an artificial skin, due to their higher elastic strain and high flexibility. Tensile and scissors cutting tests were conducted to characterise the matrix and reinforcing materials and the skin artefact. Material properties of the individual and the composite materials were compared with the measured properties of real octopus skin presented in Part I. The Young’s modulus of the skin should be below 20 MPa and the elastic strain range should be over 60%. The fracture toughness should be at least 0.9 kJ·m−2. Tubes made of the skin artefact filled with liquid were tested to study volume change under deformation. Finite element analysis model was developed to simulate the material and arm structure under tensile loading. Results show that the skin artefact developed has similar mechanical properties as the real octopus skin and satisfies all the design specifications of the OCTOPUS robot.