Coherent c-axis transport in the underdoped cuprate superconductor YBCO

International audienc

Phenotypic determinants of individual fitness in female fur seals: larger is better

Inter-individual differences in fitness in female vertebrates have often been related to phenotypic discrepancies, suggesting that bigger individuals exhibit greater fitness. However, the use of the temporally variable indices of quality, such as body mass/condition, may not represent the most reliable index over longer time intervals. Few studies have assessed the direct influence of body size (BS) on individual fitness. We addressed this knowledge gap using data from long-term monitoring of individually marked female subantarctic fur seals. The females of higher quality (i.e. higher lifetime reproductive success) were larger in BS than their counterparts, which correlated with their ability to provision their pup with greater and more regular energy supply, possibly through the maximization of foraging performance and body fat storage. We accordingly found that our study population could be divided into three contrasted categories of maternal quality, with 33% of the females producing over 71% of the viable offspring constituting the next generation. We suggest that a larger BS represents a crucial selective advantage for a central place forager, especially when exploiting remotely available resources

Energetic versus sthenic optimality criteria for gymnastic movement synthesis

Dynamic synthesis of human movements raises the question of the selection of a suitable performance criterion able to generate proper dynamic behaviors. Two quite different criteria are likely to be appropriate candidates: the minimum effort cost (or sthenic criterion) and the minimum energy cost. The paper is aimed at clarifying the dynamic effects of these two fundamental criteria when considering movements executed with liveliness as they are in gymnastic. It is well known that the former cost generates movements with smooth dynamics. A special attention is devoted to the latter. The optimal control theory shows that minimizing the energy consumption results in actuating inputs of bang-off-bang type producing momentum impulses. When achieving dynamic synthesis, this criterion makes necessary to account for bounds set on driving torques. Moreover, when dealing with onesided contacts, as in floor handstands, the unilaterality of contact forces must be explicitly accounted for since it tends to be infringed by impulsive efforts. Numerical simulations of these formal properties are carried out using a parametric optimization technique, and considering the raising phase of floor handstands. It is shown that the energetic criterion tends to generate movements which exhibit similarities with their real counterpart performed by an expert gymnast. Conversely, the sthenic criterion produces movements quite different. But, a salient fact is that these ones proved to be easier to perform by young beginners. As a result, they could help to coach novice gymnasts

Potential causes and life-history consequences of sexual size dimorphism in mammals

1. Male-biased sexual size dimorphism (SSD) in mammals has been explained by sexual selection favouring large, competitive males. However, new research has identified other potential factors leading to SSD. The aim of this review is to evaluate current research on the causes of SSD in mammals and to investigate some consequences of SSD, including costs to the larger sex and sexual segregation. 2. While larger males appear to gain reproductive benefits from their size, studies have also identified alternative mating strategies, unexpected variance in mating success and found no clear relationship between degree of polygyny and dimorphism. This implies that sexual selection is unlikely to be the single selective force directing SSD. 3. Latitude seems to influence SSD primarily through variation in overall body size and seasonal food availability, which affect potential for polygyny. Likewise, population density influences resource availability and evidence suggests that food scarcity differentially constrains the growth of the sexes. Diverging growth patterns between the sexes appear to be the primary physiological mechanism leading to SSD. 4. Female-biased dimorphism is most adequately explained by reduced male–male competition resulting in a decrease in male size. Female–female competition for dominance and resources, including mates, may also select for increased female size. 5. Most studies found that sexual segregation arises through asynchrony of activity budgets between the sexes. The larger sex can suffer sex-biased mortality through increased parasite load, selective predation and the difficulty associated with sustaining a larger body size under conditions of resource scarcity. 6. None of the variables considered here appears to contribute a disproportionate amount to SSD in mammals. Several promising avenues of research are currently overlooked and long-term studies, which have previously been biased toward ungulates, should be carried out on a variety of taxa