83 research outputs found
Elastocapillary network model of inhalation
The seemingly simple process of inhalation relies on a complex interplay
between muscular contraction in the thorax, elasto-capillary interactions in
individual lung branches, propagation of air between different connected
branches, and overall air flow into the lungs. These processes occur over
considerably different length and time scales; consequently, linking them to
the biomechanical properties of the lungs, and quantifying how they together
control the spatiotemporal features of inhalation, remains a challenge. We
address this challenge by developing a computational model of the lungs as a
hierarchical, branched network of connected liquid-lined flexible cylinders
coupled to a viscoelastic thoracic cavity. Each branch opens at a rate and a
pressure that is determined by input biomechanical parameters, enabling us to
test the influence of changes in the mechanical properties of lung tissues and
secretions on inhalation dynamics. By summing the dynamics of all the branches,
we quantify the evolution of overall lung pressure and volume during
inhalation, reproducing the shape of measured breathing curves. Using this
model, we demonstrate how changes in lung muscle contraction, mucus viscosity
and surface tension, and airway wall stiffness---characteristic of many
respiratory diseases, including those arising from COVID-19, cystic fibrosis,
chronic obstructive pulmonary disease, asthma, and emphysema---drastically
alter inhaled lung capacity and breathing duration. Our work therefore helps to
identify the key factors that control breathing dynamics, and provides a way to
quantify how disease-induced changes in these factors lead to respiratory
distress.Comment: In pres
Obstructed swelling and fracture of hydrogels
Obstructions influence the growth and expansion of bodies in a wide range of
settings -- but isolating and understanding their impact can be difficult in
complex environments. Here, we study obstructed growth/expansion in a model
system accessible to experiments, simulations, and theory: hydrogels swelling
around fixed cylindrical obstacles with varying geometries. When the obstacles
are large and widely-spaced, hydrogels swell around them and remain intact. In
contrast, our experiments reveal that when the obstacles are narrow and
closely-spaced, hydrogels unexpectedly fracture as they swell. We use finite
element simulations to map the magnitude and spatial distribution of stresses
that build up during swelling at equilibrium, providing a route toward
predicting when this phenomenon of self-fracturing is likely to arise. Applying
lessons from indentation theory, poroelasticity, and nonlinear continuum
mechanics, we also develop a theoretical framework for understanding how the
maximum principal tensile and compressive stresses that develop during swelling
are controlled by obstacle geometry and material parameters. These results thus
help to shed light on the mechanical principles underlying growth/expansion in
environments with obstructions.Comment: 12 pages, 5 figures; SI: 16 pages, 14 figure
Effect of confinement on the mechanics of a swelling hydrogel bead
We recast the problem of hydrogel swelling under physical constraints as an
energy optimization problem. We apply this approach to compute equilibrium
shapes of hydrogel spheres confined within a jammed matrix of rigid beads, and
interpret the results to determine how confinement modifies the mechanics of
swollen hydrogels. In contrast to the unconfined case, we find a spatial
separation of strains within the bulk of the hydrogel as strain becomes
localized to an outer region. We also explore the contact mechanics of the gel,
finding a transition from Hertzian behavior to non-Hertzian behavior as a
function of swelling. Our model, implemented in the Morpho shape optimization
environment, can be applied in any dimension, readily adapted to diverse
swelling scenarios and extended to use other energies in conjunction
A 17 year climatology of the macrophysical properties of convection in Darwin
The validation of convective processes in global climate models (GCMs) could
benefit from the use of large datasets that provide long-term climatologies
of the spatial statistics of convection. To that regard, echo top heights
(ETHs), convective areas, and frequencies of mesoscale convective systems
(MCSs) from 17 years of data from a C-band polarization (CPOL) radar are
analyzed in varying phases of the Madden–Julian Oscillation (MJO) and
northern Australian monsoon in order to provide ample validation statistics
for GCM validation. The ETHs calculated using velocity texture and
reflectivity provide similar results, showing that the ETHs are insensitive
to various techniques that can be used. Retrieved ETHs are correlated with
those from cloud top heights retrieved by Multifunctional Transport
Satellites (MTSATs), showing that the ETHs capture the relative variability
in cloud top heights over seasonal scales.
Bimodal distributions of ETH, likely attributable to the cumulus congestus clouds and mature stages of
convection, are more commonly observed when the active phase of the MJO is
over Australia due to greater mid-level moisture during the active phase of
the MJO. The presence of a convectively stable layer at around 5 km altitude
over Darwin inhibiting convection past this level can explain the position of
the modes at around 2–4 km and 7–9 km. Larger cells were observed during
break conditions compared to monsoon conditions, but only during the inactive
phase of the MJO. The spatial distributions show that Hector, a deep
convective system that occurs almost daily during the wet season over the
Tiwi Islands, and sea-breeze convergence lines are likely more common in
break conditions. Oceanic MCSs are more common during
the night over Darwin. Convective areas were generally smaller and MCSs more
frequent during active monsoon conditions. In general, the MJO is a greater
control on the ETHs in the deep convective mode observed over Darwin, with
higher distributions of ETH when the MJO is active over Darwin.</p
Under Pressure: Hydrogel Swelling in a Granular Medium
Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). Hydrogels hold promise in agriculture as reservoirs of water in dry soil, potentially alleviating the burden of irrigation. However, confinement in soil can markedly reduce the ability of hydrogels to absorb water and swell, limiting their widespread adoption. Unfortunately, the underlying reason remains unknown. By directly visualizing the swelling of hydrogels confined in three-dimensional granular media, we demonstrate that the extent of hydrogel swelling is determined by the competition between the force exerted by the hydrogel due to osmotic swelling and the confining force transmitted by the surrounding grains. Furthermore, the medium can itself be restructured by hydrogel swelling, as set by the balance between the osmotic swelling force, the confining force, and intergrain friction. Together, our results provide quantitative principles to predict how hydrogels behave in confinement, potentially improving their use in agriculture as well as informing other applications such as oil recovery, construction, mechanobiology, and filtration
Antibody Responses against Xenotropic Murine Leukemia Virus-Related Virus Envelope in a Murine Model
Xenotropic murine leukemia virus-related virus (XMRV) was recently discovered to be the first human gammaretrovirus that is associated with chronic fatigue syndrome and prostate cancer (PC). Although a mechanism for XMRV carcinogenesis is yet to be established, this virus belongs to the family of gammaretroviruses well known for their ability to induce cancer in the infected hosts. Since its original identification XMRV has been detected in several independent investigations; however, at this time significant controversy remains regarding reports of XMRV detection/prevalence in other cohorts and cell type/tissue distribution. The potential risk of human infection, coupled with the lack of knowledge about the basic biology of XMRV, warrants further research, including investigation of adaptive immune responses. To study immunogenicity in vivo, we vaccinated mice with a combination of recombinant vectors expressing codon-optimized sequences of XMRV gag and env genes and virus-like particles (VLP) that had the size and morphology of live infectious XMRV.Immunization elicited Env-specific binding and neutralizing antibodies (NAb) against XMRV in mice. The peak titers for ELISA-binding antibodies and NAb were 1:1024 and 1:464, respectively; however, high ELISA-binding and NAb titers were not sustained and persisted for less than three weeks after immunizations.Vaccine-induced XMRV Env antibody titers were transiently high, but their duration was short. The relatively rapid diminution in antibody levels may in part explain the differing prevalences reported for XMRV in various prostate cancer and chronic fatigue syndrome cohorts. The low level of immunogenicity observed in the present study may be characteristic of a natural XMRV infection in humans
Unveiling relationships between crime and property in England and Wales via density scale-adjusted metrics and network tools
Scale-adjusted metrics (SAMs) are a significant achievement of the urban scaling hypothesis. SAMs remove the inherent biases of per capita measures computed in the absence of isometric allometries. However, this approach is limited to urban areas, while a large portion of the world’s population still lives outside cities and rural areas dominate land use worldwide. Here, we extend the concept of SAMs to population density scale-adjusted metrics (DSAMs) to reveal relationships among different types of crime and property metrics. Our approach allows all human environments to be considered, avoids problems in the definition of urban areas, and accounts for the heterogeneity of population distributions within urban regions. By combining DSAMs, cross-correlation, and complex network analysis, we find that crime and property types have intricate and hierarchically organized relationships leading to some striking conclusions. Drugs and burglary had uncorrelated DSAMs and, to the extent property transaction values are indicators of affluence, twelve out of fourteen crime metrics showed no evidence of specifically targeting affluence. Burglary and robbery were the most connected in our network analysis and the modular structures suggest an alternative to "zero-tolerance" policies by unveiling the crime and/or property types most likely to affect each other
A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)
Meeting abstrac
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