7,102 research outputs found
Validity of the Cauchy-Born rule applied to discrete cellular-scale models of biological tissues
The development of new models of biological tissues that consider cells in a discrete manner is becoming increasingly popular as an alternative to PDE-based continuum methods, although formal relationships between the discrete and continuum frameworks remain to be established. For crystal mechanics, the discrete-to-continuum bridge is often made by assuming that local atom displacements can be mapped homogeneously from the mesoscale deformation gradient, an assumption known as the Cauchy-Born rule (CBR). Although the CBR does not hold exactly for non-crystalline materials, it may still be used as a first order approximation for analytic calculations of effective stresses or strain energies. In this work, our goal is to investigate numerically the applicability of the CBR to 2-D cellular-scale models by assessing the mechanical behaviour of model biological tissues, including crystalline (honeycomb) and non-crystalline reference states. The numerical procedure consists in precribing an affine deformation on the boundary cells and computing the position of internal cells. The position of internal cells is then compared with the prediction of the CBR and an average deviation is calculated in the strain domain. For centre-based models, we show that the CBR holds exactly when the deformation gradient is relatively small and the reference stress-free configuration is defined by a honeycomb lattice. We show further that the CBR may be used approximately when the reference state is perturbed from the honeycomb configuration. By contrast, for vertex-based models, a similar analysis reveals that the CBR does not provide a good representation of the tissue mechanics, even when the reference configuration is defined by a honeycomb lattice. The paper concludes with a discussion of the implications of these results for concurrent discrete/continuous modelling, adaptation of atom-to-continuum (AtC) techniques to biological tissues and model classification
Solute transport within porous biofilms: diffusion or dispersion?
Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behaviour by controllling nutrient supply, evacuation of waste products and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilmscale. We show that solute transport may be described via two coupled partial differential equations for the averaged concentrations, or telegrapherâs equations. These models are particularly relevant for chemical species, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterised by a second-order tensor whose components depend on: (1) the topology of the channelsâ network; (2) the soluteâs diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion-dominated, this analysis shows that dispersion effects may significantly contribute to transport
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Inter-sectoral Transfer of the Food for Life Settings Framework in England
Organisational settings such as schools, workplaces and hospitals are well recognised as key environments for health promotion. Whilst there is extensive literature on specific types of settings, little empirical research has investigated the transfer of frameworks between sectors. This study analyses Food for Life, an England-wide healthy and sustainable food programme that evolved in schools and is being adapted for children's centres, universities, care homes, and hospital settings. Following a case study design, we interviewed 85 stakeholders in nine settings. Food for Life's systemic framework of 'food education, skills and experience' 'food and catering quality', 'community and partnerships' and 'leadership' carried salience in all types of settings. These were perceived to act both as principles and operational priorities for driving systemic change. However, each setting type differed in terms of the mix of facilitating factors and appropriate indicators for change. Barriers in common included the level of culture-shift required, cost perceptions and organisational complexity. For settings based health promotion practice, this study points to the importance of 'frame-working' (the systematic activity of scoping and categorising the field of change) alongside the development and application of benchmarks to stimulate change. These processes are critical in the transfer of learning from between sectors in a form that balances commonality with sufficient flexibility to adapt to specific settings. Synergy between types of settings is an under-recognised, but critical, part of action to address complex issues such as those emerging from the intersection between food, health and sustainability
The roles of endolithic fungi in bioerosion and disease in marine ecosystems. I. General concepts
Endolithic true fungi and fungus-like microorganisms penetrate calcareous substrates formed by living organisms, cause significant bioerosion and are involved in diseases of many host animals in marine ecosystems. A theoretical interactive model for the ecology of reef-building corals is proposed in this review. This model includes five principle partners that exist in a dynamic equilibrium: polyps of a colonial coelenterate, endosymbiotic zooxanthellae, endolithic algae (that penetrate coral skeletons), endolithic fungi (that attack the endolithic algae, the zooxanthellae and the polyps) and prokaryotic and eukaryotic microorganisms (which live in the coral mucus). Endolithic fungi and fungus-like boring microorganisms are important components of the marine calcium carbonate cycle because they actively contribute to the biodegradation of shells of animals composed of calcium carbonate and calcareous geological substrates
First in-beam studies of a Resistive-Plate WELL gaseous multiplier
We present the results of the first in-beam studies of a medium size
(1010 cm) Resistive-Plate WELL (RPWELL): a single-sided THGEM
coupled to a pad anode through a resistive layer of high bulk resistivity
(10cm). The 6.2~mm thick (excluding readout electronics)
single-stage detector was studied with 150~GeV muons and pions. Signals were
recorded from 11 cm square copper pads with APV25-SRS readout
electronics. The single-element detector was operated in Ne\(5%
) at a gas gain of a few times 10, reaching 99
detection efficiency at average pad multiplicity of 1.2. Operation at
particle fluxes up to 10 Hz/cm resulted in 23 gain drop
leading to 5 efficiency loss. The striking feature was the
discharge-free operation, also in intense pion beams. These results pave the
way towards robust, efficient large-scale detectors for applications requiring
economic solutions at moderate spatial and energy resolutions.Comment: Accepted by JINS
56 The impact of statin therapy on the efficacy of eplerenone
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106735/1/ehfs80021-9.pd
353 Eplerenone benefit at 30 days in highârisk subgroups in the EPHESUS trial
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106771/1/ehfs80218-8.pd
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