Dual mixed finite element methods for the elasticity problem with Lagrange multipliers

AbstractWe study a dual mixed formulation of the elasticity system in a polygonal domain of the plane with mixed boundary conditions and its numerical approximation. The (essential) Neumann boundary conditions (or traction boundary condition) are imposed using a discontinuous Lagrange multiplier corresponding to the trace of the displacement field. Moreover, a strain tensor is introduced as a new unknown and its symmetry is relaxed, also by the use of a Lagrange multiplier (the rotation). The singular behaviour of the solution requires us to use refined meshes to restore optimal rates of convergence. Uniform error estimates in the Lamé coefficient λ are obtained for large λ. The hybridization of the problem is performed and numerical tests are presented confirming our theoretical results

A complex speciation-richness relationship in a simple neutral model

Speciation is the "elephant in the room" of community ecology. As the ultimate source of biodiversity, its integration in ecology's theoretical corpus is necessary to understand community assembly. Yet, speciation is often completely ignored or stripped of its spatial dimension. Recent approaches based on network theory have allowed ecologists to effectively model complex landscapes. In this study, we use this framework to model allopatric and parapatric speciation in networks of communities and focus on the relationship between speciation, richness, and the spatial structure of communities. We find a strong opposition between speciation and local richness, with speciation being more common in isolated communities and local richness being higher in more connected communities. Unlike previous models, we also find a transition to a positive relationship between speciation and local richness when dispersal is low and the number of communities is small. Also, we use several measures of centrality to characterize the effect of network structure on diversity. The degree, the simplest measure of centrality, is found to be the best predictor of local richness and speciation, although it loses some of its predictive power as connectivity grows. Our framework shows how a simple neutral model can be combined with network theory to reveal complex relationships between speciation, richness, and the spatial organization of populations.Comment: 9 pages, 5 figures, 1 table, 50 reference

Writer identification and verification in handwritten documents

In this communication we apply an Information Retrieval model for the writer identification task. Queries are handwreitten document images projected on a suitable feature set. The handwritten document database is indexed according to the vector space model originaly used for textual information. The approach uses both the image and textual description of handwritten documents. Identified documents are then processed by the verification stage. We use a mutual information criterion so as to verify that each identified document can have been written by the writer of the query. Decision operates using an hypothesis test. The approcah is evaluated on two different database and proves to be robust to the variability of handwriting. Perspectives are oriented towards the use of large handwritten document databaseDans cette communication, nous appliquons un modèle de recherche d’information pour la tâche d’identification du scripteur. Les requêtes sont des images de documents qui sont tout d’abord projetées dans un espace de caractéristiques. La base de documents manuscrits est indexée selon le principe du modèle vectoriel de recherche d’information textuelle. L’approche exploite donc à la fois la représentation mixte image et textuelle spécifique d’un document manuscrit. Les documents identifiés à l’issue de cette étape font ensuite l’objet d’une analyse complémentaire pour vérifier les hypothèses émises. Nous proposons d’utiliser un critère d’information mutuelle pour vérifier que chacun des documents identifiés peut avoir été produit par le scripteur de la requête. Nous utilisons un test d’hypothèse à cet effet. L’approche est testée sur deux bases d’écritures différentes et montre une grande robustesse aux différentes écritures. L’approche semble donc très intéressante pour des applications à plus grande échelle nécessitant d’interroger des bases de documents manuscrits

Correlates of Discordance between Perceived and Objective Distances to Local Fruit and Vegetable Retailers

Background: Perceptions of neighbourhood attributes such as proximity of food retailers that are discordant with objective measures of the same are associated with poor health behaviours and weight gain. Factors associated with discordant perceptions are likely relevant to planning more effective interventions to improve health. Purpose: Analysis of cross-sectional relationships between individual and neighbourhood factors and overestimations of walking distances to local fruit/vegetable retailers (FVR). Methods: Perceived walking times, converted to distances, between participant residences and FVR were compared with objectively-assessed road network distances calculated with a Geographic Information System for n = 1305 adults residing in Adelaide, South Australia. Differences between perceived and objective distances were expressed as ‘overestimated’ distances and were analysed relative to perceptions consistent with objective distances. Cross-sectional associations were evaluated between individual socio-demographic, health, and area-level characteristics and overestimated distances to FVR using multilevel logistic regression. Results: Agreement between objective and perceived distances between participants’ residence and the nearest FVR was only fair (weighted kappa = 0.22). Overestimated distances to FVR were positively associated with mental well-being, and were negatively associated with household income, physical functioning, sense of community, and objective distances to greengrocers. Conclusions: Individual characteristics and features of neighbourhoods were related to overestimated distances to FVR. Sense of connectivity and shared identity may shape more accurate understandings of local resource access, and offer a focal point for tailored public health initiatives that bring people together to achieve improved health behaviour

High expression of TROP2 characterizes different cell subpopulations in androgen-sensitive and androgenindependent prostate cancer cells

Progression of castration-resistant tumors is frequent in prostate cancer. Current systemic treatments for castration-resistant prostate cancer only produce modest increases in survival time and self-renewing Tumor-Initiating Cells (TICs) are suspected to play an important role in resistance to these treatments. However it remains unclear whether the same TICs display both chemo-resistance and self-renewing abilities throughout progression from early stage lesions to late, castration resistant tumors. Here, we found that treatment of mice bearing LNCaP-derived xenograft tumors with cytotoxic (docetaxel) and anti-androgen (flutamide) compounds enriched for cells that express TROP2, a putative TIC marker. Consistent with a tumor-initiating role, TROP2high cells from androgen-sensitive prostate cancer cell lines displayed an enhanced ability to re-grow in culture following treatment with taxane-based chemotherapy with or without androgen blockade. TROP2 down-regulation in these cells reduced their ability to recur after treatment with docetaxel, in the presence or absence of flutamide. Accordingly, in silico analysis of published clinical data revealed that prostate cancer patients with poor prognosis exhibit significantly elevated TROP2 expression level compared to low-risk patients, particularly in the case of patients diagnosed with early stage tumors. In contrast, in androgen-independent prostate cancer cell lines, TROP2high cells did not exhibit a differential treatment response but were characterized by their high self-renewal ability. Based on these findings we propose that high TROP2 expression identifies distinct cell sub-populations in androgen-sensitive and androgenindependent prostate tumors and that it may be a predictive biomarker for prostate cancer treatment response in androgen-sensitive tumors.Jinhan Xie, Christina Mølck, Sophie Paquet-Fifield, Lisa Butler, Erica Sloan, Sabatino Ventura, Frédéric Holland

Population Genetic Structure of Gray Wolves (Canis lupus) in a Marine Archipelago Suggests Island-Mainland Differentiation Consistent with Dietary Niche

Background: Emerging evidence suggests that ecological heterogeneity across space can influence the genetic structure of populations, including that of long-distance dispersers such as large carnivores. On the central coast of British Columbia, Canada, wolf (Canis lupus L., 1758) dietary niche and parasite prevalence data indicate strong ecological divergence between marine-oriented wolves inhabiting islands and individuals on the coastal mainland that interact primarily with terrestrial prey. Local holders of traditional ecological knowledge, who distinguish between mainland and island wolf forms, also informed our hypothesis that genetic differentiation might occur between wolves from these adjacent environments. Results: We used microsatellite genetic markers to examine data obtained from wolf faecal samples. Our results from 116 individuals suggest the presence of a genetic cline between mainland and island wolves. This pattern occurs despite field observations that individuals easily traverse the 30 km wide study area and swim up to 13 km among landmasses in the region. Conclusions: Natal habitat-biased dispersal (i.e., the preference for dispersal into familiar ecological environments) might contribute to genetic differentiation. Accordingly, this working hypothesis presents an exciting avenue for future research where marine resources or other components of ecological heterogeneity are present