Subcritical convection of liquid metals in a rotating sphere using a quasi-geostrophic model

We study nonlinear convection in a rapidly rotating sphere with internal heating for values of the Prandtl number relevant for liquid metals ($Pr\in[10^{-2},10^{-1}]$). We use a numerical model based on the quasi-geostrophic approximation, in which variations of the axial vorticity along the rotation axis are neglected, whereas the temperature field is fully three-dimensional. We identify two separate branches of convection close to onset: (i) a well-known weak branch for Ekman numbers greater than $10^{-6}$, which is continuous at the onset (supercritical bifurcation) and consists of thermal Rossby waves, and (ii) a novel strong branch at lower Ekman numbers, which is discontinuous at the onset. The strong branch becomes subcritical for Ekman numbers of the order of $10^{-8}$. On the strong branch, the Reynolds number of the flow is greater than $10^3$, and a strong zonal flow with multiple jets develops, even close to the nonlinear onset of convection. We find that the subcriticality is amplified by decreasing the Prandtl number. The two branches can co-exist for intermediate Ekman numbers, leading to hysteresis ($Ek=10^{-6}$, $Pr=10^{-2}$). Nonlinear oscillations are observed near the onset of convection for $Ek=10^{-7}$ and $Pr=10^{-1}$.Comment: 30 pages, 16 figures, published in JF

Do branch lengths help to locate a tree in a phylogenetic network?

Phylogenetic networks are increasingly used in evolutionary biology to represent the history of species that have undergone reticulate events such as horizontal gene transfer, hybrid speciation and recombination. One of the most fundamental questions that arise in this context is whether the evolution of a gene with one copy in all species can be explained by a given network. In mathematical terms, this is often translated in the following way: is a given phylogenetic tree contained in a given phylogenetic network? Recently this tree containment problem has been widely investigated from a computational perspective, but most studies have only focused on the topology of the phylo- genies, ignoring a piece of information that, in the case of phylogenetic trees, is routinely inferred by evolutionary analyses: branch lengths. These measure the amount of change (e.g., nucleotide substitutions) that has occurred along each branch of the phylogeny. Here, we study a number of versions of the tree containment problem that explicitly account for branch lengths. We show that, although length information has the potential to locate more precisely a tree within a network, the problem is computationally hard in its most general form. On a positive note, for a number of special cases of biological relevance, we provide algorithms that solve this problem efficiently. This includes the case of networks of limited complexity, for which it is possible to recover, among the trees contained by the network with the same topology as the input tree, the closest one in terms of branch lengths

Research Brief No. 5 - The changing impact of motherhood on employment across generations of Canadian women

Women’s work histories are closely interwoven with motherhood, as shown by previous studies that have examined Canadian women’s family histories in relation to their movements of entry into—and exit from—the labour market. These studies have either supported or reinforced, at least implicitly, the existence of an incompatibility between motherhood and paid work. The results of these studies are interesting in that they provided a broad picture of how Canadian women adapted their work lives according to family events. However, the image they reveal is static and incomplete, failing to highlight the changes experienced among recent generations of women. We examined the relationships between motherhood and women’s entry and exit from the workplace and how it has evolved across the generations, by studying women born between 1937 and 1976. Studying the various generations of women allows us to consider a range of possible strategies open to women, given the constraints and opportunities of institutional and social settings across generations. These changes are studied on the basis of retrospective data from Statistics Canada’s 2001 General Social Survey on family history

Novel Kac-Moody-type affine extensions of non-crystallographic Coxeter groups

Motivated by recent results in mathematical virology, we present novel asymmetric -integer-valued affine extensions of the non-crystallographic Coxeter groups H2, H3 and H4 derived in a Kac–Moody-type formalism. In particular, we show that the affine reflection planes which extend the Coxeter group H3 generate (twist) translations along two-, three- and five-fold axes of icosahedral symmetry, and we classify these translations in terms of the Fibonacci recursion relation applied to different start values. We thus provide an explanation of previous results concerning affine extensions of icosahedral symmetry in a Coxeter group context, and extend this analysis to the case of the non-crystallographic Coxeter groups H2 and H4. These results will enable new applications of group theory in physics (quasicrystals), biology (viruses) and chemistry (fullerenes)

Investigating the Links Between Performers' Self-Compassion, Mental Toughness and Their Social Environment: A Semi-Systematic Review

Being mentally tough while evaluating oneself in a compassionate way is still a difficult path for performers. Self-compassion, characterized by the ability to be kind to oneself, to see one’s experiences as part of the larger human experience and have a balanced awareness to one’s emotions and thoughts, was recently studied as a stepping stone to performance optimization and personal development. Despite a mistrust of this concept in the sports world, various studies show its benefits within athletes. A major question remains the environment that fosters or hinders the development of self-compassion: when role models extend compassionate attitudes, does it allow performers to respond in more self-compassionate ways? The relationship between self-compassion, mental toughness, and social environment is still unclear and is an important direction for future research within performers. This semi-systematic literature review aims at proposing an overview of the state of the art regarding self-compassion, mental toughness, and the influence of performer’s, and social environments. Sixteen studies were retrieved. We conclude that the number of multi-day intervention programs and longitudinal studies should be increased. The studies should also consider assessing the specific aspects of performance culture and settings. In addition, overall performance-specific measures could be developed to assess general levels of self-compassion. The development of a theoretical framework explaining how self-compassion affects a performer, the role of their entourage and its link to other psychological resources, such as mental toughness, could help to better understand this concept

A labour-based approach to the analysis of structural transformation: application to French agricultural holdings 2000

The question of farm size has long been a concern in the agricultural economics literature. The observation of a long-lasting persistence of so-called small farms drew the attention of numerous researchers. The size of farms is often approximated by the farm area in hectares or the added value and gross margin. We propose to investigate the opportunity to use labour (family labour and hired, permanent and seasonal, wage labour) as an entry point for a typology of agricultural holdings, with an application on French data from the Census collected in 2000. Then, we characterize the holdings belonging to the groups defined by the typology based on the type of labour.La question de la taille des exploitations agricoles, en relation avec leurs performances, a été largement abordée par la littérature dédiée à l’économie agricole. En particulier, la persistance de l’existence de petites exploitations a attiré l’attention. La taille des exploitations est le plus souvent estimée en hectares, en valeur ajoutée ou en chiffre d’affaires. Cet article propose une entrée par le travail (familial ou salarié, saisonnier ou permanent) pour construire une typologie des exploitations françaises sur la base du Recensement Agricole 2000. Il caractérise ensuite les différents types d’exploitations identifiées

Inferring gene duplications, transfers and losses can be done in a discrete framework

UMR AGAP : équipe GE2popInternational audienceIn the field of phylogenetics, the evolutionary history of a set of organisms is commonly depicted by a species tree – whose internal nodes represent speciation events – while the evolutionary history of a gene family is depicted by a gene tree – whose internal nodes can also represent macro-evolutionary events such as gene duplications and transfers. As speciation events are only part of the events shaping a gene history, the topology of a gene tree can show incongruences with that of the corresponding species tree. These incongruences can be used to infer the macro-evolutionary events undergone by the gene family. This is done by embedding the gene tree inside the species tree and hence providing a reconciliation of those trees. In the past decade, several parsimony-based methods have been developed to infer such reconciliations, accounting for gene duplications (D), transfers (T) and losses (L). The main contribution of this paper is to formally prove an important assumption implicitly made by previous works on these reconciliations, namely that solving the (maximum) parsimony DTL reconciliation problem in the discrete framework is equivalent to finding a most parsimonious DTL scenario in the continuous framework. In the process, we also prove several intermediate results that are useful on their own and constitute a theoretical toolbox that will likely facilitate future theoretical contributions in the field