Phase Transition in Ferromagnetic Ising Models with Non-Uniform External Magnetic Fields

In this article we study the phase transition phenomenon for the Ising model under the action of a non-uniform external magnetic field. We show that the Ising model on the hypercubic lattice with a summable magnetic field has a first-order phase transition and, for any positive (resp. negative) and bounded magnetic field, the model does not present the phase transition phenomenon whenever $\liminf h_i> 0$, where ${\bf h} = (h_i)_{i \in \Z^d}$ is the external magnetic field.Comment: 11 pages. Published in Journal of Statistical Physics - 201

Suivi de l’efficacité des passages à petite et moyenne faune sur la route 175. Bulletin d’information No. 3.

Entrepris en 2006, l’élargissement de la route 175 entre Québec et Saguenay (entre les kilomètres 53 et 227) s’est terminé en 2012. Il s’agissait à l’époque d’un des plus importants projets d’expansion routière au Canada. La route sillonne un vaste territoire naturel riche en habitats importants pour diverses espèces fauniques. La portion élargie traverse la Réserve faunique des Laurentides, et un autre tronçon important borde le Parc national de la Jacques-Cartier. La largeur de la nouvelle route est environ le triple de celle de l’ancienne, soit 90 ou 100 m au lieu de 30 ou 35 m, et les trouées dans le couvert forestier sont souvent même beaucoup plus larges. De nombreuses études réalisées en Europe, en Amérique du Nord et en Australie ont montré qu’un certain nombre d’espèces réussissent à emprunter les passages fauniques. Cependant, on observe des lacunes en matière d’information sur les petits et moyens mammifères, la recherche ayant surtout porté jusqu’à maintenant sur la grande faune. Or, malgré leur taille réduite, les petits animaux peuvent tout de même représenter un danger pour les conducteurs, notamment lorsque ces derniers essaient d’éviter de les frapper en changeant de voie et qu’ils perdent le contrôle de leur véhicule. Ce projet de recherche contribuera donc à déterminer si les passages fauniques sont efficaces dans le cas de petits et moyens mammifères et s’il convient ou non d’appliquer des mesures d’atténuation supplémentaires. L’étude de l’efficacité de telles mesures pour la grande faune a fait l’objet de travaux distincts. D’une durée de quatre ans, le présent projet permettra de recueillir de précieuses données en vue de l’élaboration d’un plan de surveillance et de gestion adaptative à long terme

Monitoring the effectiveness of wildlife passages for medium-sized and small mammals along HW 175. News Bulletin No 3.

The widening of HW 175 between Quebec City and Saguenay (between km 53 and km 227) in 2006-2012 was one of the largest road expansion projects in Canada. The surrounding area is made up mostly of natural territory that provides important habitat for various wildlife species. The expansion corridor runs through the Reserve Faunique des Laurentides with a large section adjacent to the Parc National de la Jacques-Cartier. The new road is approximately 3 times larger than before, growing from 30-35 m to 90-100 m wide and the gap in forest cover is often even significantly wider. Many studies from Europe, North America and Australia have shown that a number of species use wildlife passages successfully. However, most research has been focused on large mammals, leaving a gap of information about small to medium-sized mammals. Although smaller, these animals can also pose a risk to drivers when they cross the road, causing drivers to swerve or lose control of their vehicle. Thus, this research project will determine whether the passageways are effective for medium-sized and small mammals and whether further road management is needed. The effectiveness of the mitigation measures for large mammals along HW 175 has been studied in separate projects. This four-year project will provide important information for adaptive management and long-term monitoring of road mitigation

N-cadherin crosstalk with integrin weakens the molecular clutch in response to surface viscosity

Mesenchymal stem cells (MSCs) interact with their surroundings via integrins, which link to the actin cytoskeleton and translate physical cues into biochemical signals through mechanotransduction. N-cadherins enable cell-cell communication and are also linked to the cytoskeleton. This crosstalk between integrins and cadherins modulates MSC mechanotransduction and fate. Here we show the role of this crosstalk in the mechanosensing of viscosity using supported lipid bilayers as substrates of varying viscosity. We functionalize these lipid bilayers with adhesion peptides for integrins (RGD) and N-cadherins (HAVDI), to demonstrate that integrins and cadherins compete for the actin cytoskeleton, leading to an altered MSC mechanosensing response. This response is characterised by a weaker integrin adhesion to the environment when cadherin ligation occurs. We model this competition via a modified molecular clutch model, which drives the integrin/cadherin crosstalk in response to surface viscosity, ultimately controlling MSC lineage commitment

A hydrogel platform that incorporates laminin isoforms for efficient presentation of growth factors – neural growth and osteogenesis

Laminins (LMs) are important structural proteins of the extracellular matrix (ECM). The abundance of every LM isoform is tissue‐dependent, suggesting that LM has tissue‐specific roles. LM binds growth factors (GFs), which are powerful cytokines widely used in tissue engineering due to their ability to control stem cell differentiation. Currently, the most commonly used ECM mimetic material in vitro is Matrigel, a matrix of undefined composition containing LM and various GFs, but subjected to batch variability and lacking control of physicochemical properties. Inspired by Matrigel, a new and completely defined hydrogel platform based on hybrid LM‐poly(ethylene glycol) (PEG) hydrogels with controllable stiffness (1–25 kPa) and degradability is proposed. Different LM isoforms are used to bind and efficiently display GFs (here, bone morphogenetic protein (BMP‐2) and beta‐nerve growth factor (β‐NGF)), enabling their solid‐phase presentation at ultralow doses to specifically target a range of tissues. The potential of this platform to trigger stem cell differentiation toward osteogenic lineages and stimulate neural cells growth in 3D, is demonstrated. These hydrogels enable 3D, synthetic, defined composition, and reproducible cell culture microenvironments reflecting the complexity of the native ECM, where GFs in combination with LM isoforms yield the full diversity of cellular processes