Modeling growth in biological materials

The biomechanical modeling of growing tissues has recently become an area of intense interest. In particular, the interplay between growth patterns and mechanical stress is of great importance, with possible applications to arterial mechanics, embryo morphogenesis, tumor development, and bone remodeling. This review aims to give an overview of the theories that have been used to model these phenomena, categorized according to whether the tissue is considered as a continuum object or a collection of cells. Among the continuum models discussed is the deformation gradient decomposition method, which allows a residual stress field to develop from an incompatible growth field. The cell-based models are further subdivided into cellular automata, center-dynamics, and vertex-dynamics models. Of these the second two are considered in more detail, especially with regard to their treatment of cell-cell interactions and cell division. The review concludes by assessing the prospects for reconciliation between these two fundamentally different approaches to tissue growth, and by identifying possible avenues for further research. © 2012 Society for Industrial and Applied Mathematics

Quantized transport, strain-induced perfectly conducting modes and valley filtering on shape-optimized graphene Corbino devices

The extreme mechanical resilience of graphene and the peculiar coupling it hosts between lattice and electronic degrees of freedom have spawned a strong impetus towards strain-engineered graphene where, on the one hand, strain augments the richness of its phenomenology and makes possible new concepts for electronic devices and, on the other hand, new and extreme physics might take place. Here, we demonstrate that the shape of substrates supporting graphene sheets can be optimized for approachable experiments where strain-induced pseudomagnetic fields (PMF) can be tailored by pressure for directionally selective electronic transmission and pinching-off of current flow down to the quantum channel limit. The Corbino-type layout explored here furthermore allows filtering of charge carriers according to valley and current direction, which can be used to inject or collect valley-polarized currents, thus realizing one of the basic elements required for valleytronics. Our results are based on a framework developed to realistically determine the combination of strain, external parameters, and geometry optimally compatible with the target spatial profile of a desired physical property --- the PMF in this case. Characteristic conductance profiles are analyzed through quantum transport calculations on large graphene devices having the optimal shape.Comment: 5+7 figures. Supporting information include

Adiantum capillus-veneris (Maidenhair Fern) along the Vale of Glamorgan Coastline, South Wales, UK: a comparison of surveys over 30 years

Adiantum capillus-veneris (Maidenhair Fern), occurs on all continents except the Antarctic, and is considered stable worldwide (Lansdown & Bilz, 2013). In the UK the vascular plants red data list reports the status of A. capillusveneris as of ‘least concern’ (Cheffings et al., 2005). Native populations occur mainly in crevices or on tufa deposits, limited to a few scattered coastal localities (Stewart et al., 1994). Wales is home to about 25% of the UK’s native population (Dines, 2008) mainly concentrated along the Vale of Glamorgan Coastline and to a lesser extent in Pembrokeshire and Carmarthenshire. The earliest record (Llwyd, 1698), at Jacksons Bay, Barry Island suggest populations have been persistent for at least 300 years. Historical records for A. capillus- veneris can also be found for Porthkerry; 1838, Dunraven Bay; 1849, Aberthaw; 1862 and Font-y-Gary, 1927 and A. capillus-veneris is still present at all of the aforementioned sites. A. capillus-veneris’s natural habitat in South Wales is primarily restricted to active post glacial tufaceous cliff face seepages which are frequently, but not entirely, associated with the Jurassic Lias bedrock that defines the Vale of Glamorgan ‘Heritage Coast’. The interbedded nature of the Jurassic Lias rocks, with relatively impermeable, thinly interbedded limestones and calcareous mudstones (Wilson et al., 1990), favours the slow diffuse seepage of groundwater across large areas of cliff face supporting the formation of tufa. Tufa forms when groundwater, supersaturated with calcium carbonate dissolved from the bedrock aquifer, re-deposits the material on contact with the atmosphere. Three surveys across the Vale of Glamorgan coastline have been undertaken, the first by Peter S. Jones (1983-4) then Kate Pryor 1996 (reported in Pryor, 2001) and again in 2015 by the authors. Molecular studies of several populations along the coast (Pryor, 2001 & Pryor et al., 2001) provide insight into the genetics of satellite populations, however further discussion of this is outside of the scope of this note. The aim of this survey was to collate and compare the locations of populations recorded over the last 30 years. It is hoped that this will serve as a useful baseline for repeat surveys in the future

Persons with chronic widespread pain experience excess mortality : longitudinal results from UK Biobank and meta-analysis

This manuscript uses the UK Biobank resource (Application 1144). We acknowledge the authors of a previous meta-analysis on this topic (Diane Smith, Ross Wilkie, Olalekan Uthman, Joanne L. Jordan, John McBeth) whose published search strategy we used as the basis for our meta-analysis, albeit that our meta-analysis had a more restricted focus and the criteria for determining eligibility and the data we extracted from eligible studies was not identical and resulted in selection of a different group of studies. We thank John McBeth (University of Manchester) for providing additional data relating to one of the studies, to allow it be included in the meta-analysis. GJM had the idea for the study and together with GTJ designed the analysis plan for UK Biobank. GTJ undertook the UK Biobank analysis. MSB conducted the updated systematic review and all authors participated in undertaking the meta-analysis. GJM drafted the manuscript but all authors made an important intellectual contribution to the text. None of the authors report conflict of interest.Peer reviewedPostprin

Transition to organic farming negatively affects bat activity

1. The effectiveness of organic farming on biodiversity has been widely documented especially for plants, arthropods and birds; however, the effects of the transition period required to become an organic farm on wildlife remain poorly understood.2. We assessed the effects of organic farming on insectivorous bats in citrus orchards in the Republic of Cyprus employing two matched designs (conventional vs. 3-year organic-transitional and conventional vs. organic-certified) and a third unmatched design (3-year organic-transitional vs. organic-certified). We specifically investigated whether the transition period prior to full organic certification influenced bat activity with a special focus on any moderation effects from surrounding semi-natural areas.3. The activity of three (Pipistrellus kuhlii, Hypsugo savii and Miniopterus schreibersii) of four bat species was significantly lower in farms undergoing the transitional period than in conventional farms, and P. kuhlii and H. savii were significantly less active in organic transitional farming systems that in organic-certified ones. Furthermore, the activity of the most dominant species (P. kuhlii) was significantly higher on organic than transitional and conventional citrus orchards, thus suggesting a time-lag effect. Landscape complexity measured as the amount of semi-natural areas did not moderate the effects of farming system for any study species.4. Synthesis and application. The transition to organic farming had persistent detrimental effects on bats and potentially on the pest suppression services they provide. Future agri-environmental policy should consider the transition period and implement measures to mitigate any negative effects on biodiversity, alongside promoting asynchronous transition of nearby farms. Our findings further highlight the crucial need to consider the time since transition to organic farming when assessing potential benefits of organic management on biodiversity