60 research outputs found
Compression Behavior of Single-layer Graphene
Central to most applications involving monolayer graphene is its mechanical
response under various stress states. To date most of the work reported is of
theoretical nature and refers to tension and compression loading of model
graphene. Most of the experimental work is indeed limited to bending of single
flakes in air and the stretching of flakes up to typically ~1% using plastic
substrates. Recently we have shown that by employing a cantilever beam we can
subject single graphene into various degrees of axial compression. Here we
extend this work much further by measuring in detail both stress uptake and
compression buckling strain in single flakes of different geometries. In all
cases the mechanical response is monitored by simultaneous Raman measurements
through the shift of either the G or 2D phonons of graphene. In spite of the
infinitely small thickness of the monolayers, the results show that graphene
embedded in plastic beams exhibit remarkable compression buckling strains. For
large length (l)-to-width (w) ratios (> 0.2) the buckling strain is of the
order of -0.5% to -0.6%. However, for l/w <0.2 no failure is observed for
strains even higher than -1%. Calculations based on classical Euler analysis
show that the buckling strain enhancement provided by the polymer lateral
support is more than six orders of magnitude compared to suspended graphene in
air
A theoretical model of inflammation- and mechanotransduction- driven asthmatic airway remodelling
Inflammation, airway hyper-responsiveness and airway remodelling are well-established hallmarks of asthma, but their inter-relationships remain elusive. In order to obtain a better understanding of their inter-dependence, we develop a mechanochemical morphoelastic model of the airway wall accounting for local volume changes in airway smooth muscle (ASM) and extracellular matrix in response to transient inflammatory or contractile agonist challenges. We use constrained mixture theory, together with a multiplicative decomposition of growth from the elastic deformation, to model the airway wall as a nonlinear fibre-reinforced elastic cylinder. Local contractile agonist drives ASM cell contraction, generating mechanical stresses in the tissue that drive further release of mitogenic mediators and contractile agonists via underlying mechanotransductive signalling pathways. Our model predictions are consistent with previously described inflammation-induced remodelling within an axisymmetric airway geometry. Additionally, our simulations reveal novel mechanotransductive feedback by which hyper-responsive airways exhibit increased remodelling, for example, via stress-induced release of pro-mitogenic and procontractile cytokines. Simulation results also reveal emergence of a persistent contractile tone observed in asthmatics, via either a pathological mechanotransductive feedback loop, a failure to clear agonists from the tissue, or a combination of both. Furthermore, we identify various parameter combinations that may contribute to the existence of different asthma phenotypes, and we illustrate a combination of factors which may predispose severe asthmatics to fatal bronchospasms
Autosomal recessive nephrogenic diabetes insipidus caused by an aquaporin-2 mutation
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Rethinking Resilience Analytics
The article of record as published may be found at https://doi.org/10.1111/risa.13328The concept of “resilience analytics” has recently been proposed as a means to leverage the
promise of big data to improve the resilience of interdependent critical infrastructure systems
and the communities supported by them. Given recent advances in machine learning
and other data-driven analytic techniques, as well as the prevalence of high-profile natural
and man-made disasters, the temptation to pursue resilience analytics without question
is almost overwhelming. Indeed, we find big data analytics capable to support resilience to
rare, situational surprises captured in analytic models. Nonetheless, this article examines the
efficacy of resilience analytics by answering a single motivating question: Can big data analytics
help cyber–physical–social (CPS) systems adapt to surprise? This article explains the
limitations of resilience analytics when critical infrastructure systems are challenged by fundamental
surprises never conceived during model development. In these cases, adoption of
resilience analytics may prove either useless for decision support or harmful by increasing
dangers during unprecedented events. We demonstrate that these dangers are not limited
to a single CPS context by highlighting the limits of analytic models during hurricanes, dam
failures, blackouts, and stock market crashes. We conclude that resilience analytics alone are
not able to adapt to the very events that motivate their use and may, ironically, make CPS
systems more vulnerable. We present avenues for future research to address this deficiency,
with emphasis on improvisation to adapt CPS systems to fundamental surprise
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