720 research outputs found
Lubricated wrinkles: imposed constraints affect the dynamics of wrinkle coarsening
We study the dynamic coarsening of wrinkles in an elastic sheet that is
compressed while lying on a thin layer of viscous liquid. When the ends of the
sheet are instantaneously brought together by a small distance, viscous
resistance initially prevents the sheet from adopting a globally buckled shape.
Instead, the sheet accommodates the compression by wrinkling. Previous scaling
arguments suggested that a balance between the sheet's bending stiffness and
viscous effects lead to a wrinkle wavelength that increases with time
according to . We show that taking proper account
of the compression constraint leads to a logarithmic correction of this result,
. This correction is significant over
experimentally observable time spans, and leads us to reassess previously
published experimental data.Comment: 12 pages. Version accepted in Phys. Rev. Fluids (with small
correction to bibliography
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Structure variation and evolution in microphase-separated grafted diblock copolymer films
The phase behavior of grafted d-polystyrene-block-poly(methyl methacrylate) diblock copolymer films is examined, with particular focus on the effect of solvent and annealing time. It was observed that the films undergo a two-step transformation from an initially disordered state, through an ordered metastable state, to the final equilibrium configuration. It was also found that altering the solvent used to wash the films, or complete removal of the solvent prior to thermal annealing using supercritical CO2, could influence the structure of the films in the metastable state, though the final equilibrium state was unaffected. To aid in the understanding to these experimental results, a series of self-consistent field theory calculations were done on a model diblock copolymer brush containing solvent. Of the different models examined, those which contained a solvent selective for the grafted polymer block most accurately matched the observed experimental behavior. We hypothesize that the structure of the films in the metastable state results from solvent enrichment of the film near the film/substrate interface in the case of films washed with solvent or faster relaxation of the nongrafted block for supercritical CO2 treated (solvent free) films. The persistence of the metastable structures was attributed to the slow reorganization of the polymer chains in the absence of solvent
Stability of a bi-layer free film: simultaneous or individual rupture events?
We consider the stability of a long free film of liquid composed of two immiscible layers
of differing viscosities, where each layer experiences a van der Waals force between its
interfaces. We analyse the different ways the system can exhibit interfacial instability
when the liquid layers are sufficiently thin. For an excess of surfactant on one gasâliquid
interface the coupling between the layers is relatively weak and the instability manifests as
temporally separated rupture events in each layer. Conversely, in the absence of surfactant
the coupling between the layers is much stronger and the instability manifests as rupture
of both layers simultaneously. These features are consistent with recent experimental
observations
The influence of porous media microstructure on filtration
We investigate how a filter media microstructure influences filtration
performance. We derive a theory that generalizes classical multiscale models
for regular structures to account for filter media with more realistic
microstructures, comprising random microstructures with polydisperse
unidirectional fibres. Our multiscale model accounts for the fluid flow and
contaminant transport at the microscale (over which the media structure is
fully resolved) and allows us to obtain macroscopic properties such as the
effective permeability, diffusivity, and fibre surface area. As the fibres grow
due to contaminant adsorption this leads to contact of neighbouring fibres. We
propose an agglomeration algorithm that describes the resulting behaviour of
the fibres upon contact, allowing us to explore the subsequent time evolution
of the filter media in a simple and robust way. We perform a comprehensive
investigation of the influence of the filter-media microstructure on filter
performance in a spectrum of possible filtration scenarios
Understanding how porosity gradients can make a better filter using homogenization theory
Filters whose porosity decreases with depth are often more efficient at removing solute from a fluid than filters with a uniform porosity. We investigate this phenomenon via an extension of homogenization theory that accounts for a macroscale variation in microstructure. In the first stage of the paper, we homogenize the problems of flow through a filter with a near-periodic microstructure and of solute transport owing to advection, diffusion and filter adsorption. In the second stage, we use the computationally efficient homogenized equations to investigate and quantify why porosity gradients can improve filter efficiency. We find that a porosity gradient has a much larger effect on the uniformity of adsorption than it does on the total adsorption. This allows us to understand how a decreasing porosity can lead to a greater filter efficiency, by lowering the risk of localized blocking while maintaining the rate of total contaminant removal
The Marangoni flow of soluble amphiphiles
Surfactant distribution heterogeneities at a fluid/fluid interface trigger
the Marangoni effect, i.e. a bulk flow due to a surface tension gradient. The
influence of surfactant solubility in the bulk on these flows remains
incompletely characterized. Here we study Marangoni flows sustained by
injection of hydrosoluble surfactants at the air/water interface. We show that
the flow extent increases with a decrease of the critical micelle
concentration, i.e. the concentration at which these surfactants self-assemble
in water. We document the universality of the surface velocity field and
predict scaling laws based on hydrodynamics and surfactant physicochemistry
that capture the flow features.Comment: 5 pages, 4 figures, submitte
The effect of local ventilation on airborne viral transmission in indoor spaces
We incorporate local ventilation effects into a spatially dependent
generalisation of the Wells--Riley model of airborne viral transmission.
Aerosol production and removal through ventilation (global and local),
biological deactivation, and gravitational settling as well as transport around
a recirculating air-conditioning flow and turbulent mixing are modelled using
an advection--diffusion--reaction equation. The local ventilation effects are
compared with the equivalent global ventilation and we find that the
streamlines of the airflow provide insight into when the global ventilation
model is a good approximation. When the agreement between ventilation models is
poor, we find that the global ventilation model generally overestimates the
infection risk.Comment: 10 pages, 4 figures, submitted to the Journal of Fluid Mechanics as a
Rapids articl
The Sleep Or Mood Novel Adjunctive therapy (SOMNA) trial: a study protocol for a randomised controlled trial evaluating an internet-delivered cognitive behavioural therapy program for insomnia on outcomes of standard treatment for depression in men
BACKGROUND: Insomnia is a significant risk factor for depression onset, can result in more disabling depressive illness, and is a common residual symptom following treatment cessation that can increase the risk of relapse. Internet-based cognitive behavioural therapy for insomnia has demonstrated efficacy and acceptability to men who are less likely than women to seek help in standard care. We aim to evaluate whether internet delivered cognitive behavioural therapy for insomnia as an adjunct to a standard depression therapeutic plan can lead to improved mood outcomes.METHODS/DESIGN: Male participants aged 50Â years or more, meeting Diagnostic and Statistical Manual of Mental Disorders criteria for current Major Depressive Episode and/or Dysthymia and self-reported insomnia symptoms, will be screened to participate in a single-centre double-blind randomised controlled trial with two parallel groups involving adjunctive internet-delivered cognitive behavioural therapy for insomnia and an internet-based control program. The trial will consist of a nine-week insomnia intervention period with a six-month follow-up period. During the insomnia intervention period participants will have their depression management coordinated by a psychiatrist using standard guideline-based depression treatments. The study will be conducted in urban New South Wales, Australia, where 80 participants from primary and secondary care and direct from the local community will be recruited. The primary outcome is change in the severity of depressive symptoms from baseline to week 12. DISCUSSION: This study will provide evidence on whether a widely accessible, evidence-based, internet-delivered cognitive behavioural therapy for insomnia intervention can lead to greater improvements than standard treatment for depression alone, in a group who traditionally do not readily access psychotherapy. The study is designed to establish effect size, feasibility and processes associated with implementing e-health solutions alongside standard clinical care, to warrant undertaking a larger more definitive clinical trial.Trial registration: Australian and New Zealand Clinical Trials Registry ACTRN12612000985886.The study is supported by beyondblue: the national depression and anxiety
initiative National Priority Driven Research Program and funded through a
donation from the Movember Foundation
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