Capillary Hysteresis in Neutrally Wettable Fibrous Media: A Pore Network Study of a Fuel Cell Electrode

Hysteresis in the saturation versus capillary pressure curves of neutrally wettable fibrous media was simulated with a random pore network model using a Voronoi diagram approach. The network was calibrated to fit experimental air-water capillary pressure data collected for carbon fibre paper commonly used as a gas diffusion layer in fuel cells. These materials exhibit unusually strong capillary hysteresis, to the extent that water injection and withdrawal occur at positive and negative capillary pressures, respectively. Without the need to invoke contact angle hysteresis, this capillary behaviour is re-produced when using a pore-scale model based on the curvature of a meniscus passing through the centre of a toroid. The classic Washburn relation was shown to produce erroneous results, and its use is not recommended when modelling fibrous media. The important effect of saturation distribution on the effective diffusivity of the medium was also investigated for both water injection and withdrawal cases. The findings have bearing on the understanding of both capillarity in fibrous media and fuel cell design

The Structure and Entrainment Characteristics of Partially Confined Gravity Currents

Seafloor channels are the main conduit for turbidity currents transporting sediment to the deep ocean, and they can extend for thousands of kilometers along the ocean floor. Although it is common for channel‐traversing turbidity currents to spill onto levees and other out‐of‐channel areas, the associated flow development and channel‐current interaction remain poorly understood; much of our knowledge of turbidity current dynamics comes from studies of fully confined scenarios. Here we investigate the role that partial lateral confinement may play in affecting turbidity current dynamics. We report on laboratory experiments of partially confined, dilute saline flows of variable flux rate traversing fixed, straight channels with cross‐sectional profiles representative of morphologies found in the field. Complementary numerical experiments, validated against high‐resolution laboratory velocity data, extend the scope of the analysis. The experiments show that partial confinement exerts a first‐order control on flow structure. Overbank and downstream discharges rapidly adjust over short length scales, providing a mechanism via which currents of varying sizes can be tuned by a channel and conform to a given channel geometry. Across a wide range of flow magnitudes and states of flow equilibration to the channel, a high‐velocity core remains confined within the channel with a constant ratio of velocity maximum height to channel depth. Ongoing overbank flow prevents any flow thickening due to ambient entrainment, allowing stable downstream flow evolution. Despite dynamical differences, the entrainment rates of partially confined and fully confined flows remain comparable for a given Richardson number

A method for measuring relative in-plane diffusivity of thin and partially saturated porous media: an application to fuel cell gas diffusion layers

A new experimental technique, extended from similar work on dry materials, is presented for measuring the in-plane components of the relative diffusivity tensor for partially saturated porous media. The method utilizes a custom-built holder and measures the transient response to oxygen concentration changes at the boundaries of a porous sample placed between two plates surrounded by a cooling block. The apparatus is kept close to the freezing temperature of water to ensure stable saturation throughout the experiment. Fick's second law is used to fit the transient change in concentration to a numerical solution to obtain the diffusion coefficient for samples of differing saturation. As expected the effective gas diffusivity is found to decrease with increasing water saturation of the media as the porosity is reduced and the tortuosity of the diffusion pathways increased. After extensive validation, this new technique is used to determine the relative in-plane diffusivity of some common fuel cell gas diffusion layer materials. The results are found to follow a power-law function dependent on the saturation consistent with previous modelling work. Samples without hydrophobic treatment are found to have lower relative gas diffusivity, compared with treated samples for the same average saturation

Scaling Analysis of Multipulsed Turbidity Current Evolution With Application to Turbidite Interpretation

Deposits of submarine turbidity currents, turbidites, commonly exhibit upward‐fining grain size profiles reflecting deposition under waning flow conditions. However, more complex grading patterns such as multiple cycles of inverse‐to‐normal grading are also seen and interpreted as recording deposition under cycles of waxing and waning flow. Such flows are termed multipulsed turbidity currents, and their deposits pulsed or multipulsed turbidites. Pulsing may arise at flow initiation, or following downstream flow combination. Prior work has shown that individual pulses within multipulsed flows are advected forward and merge, such that complex longitudinal velocity profiles eventually become monotonically varying, although transition length scales in natural settings could not be predicted. Here we detail the first high frequency spatial (vertical, streamwise) and temporal measurements of flow velocity and density distribution in multipulsed gravity current experiments. The data support both a process explanation of pulse merging and a phase‐space analysis of transition length scales; in prototype systems, the point of merging corresponds to the transition in any deposit from multipulsed to normally graded turbidites. The scaling analysis is limited to quasi‐horizontal natural settings in which multipulsed flows are generated by sequences of relatively short sediment failures (10 km) sequences of breaches or where pulsing arises from combination at confluences of single‐pulsed flows, such flows may be responsible for the pulsing signatures seen in some distal turbidites, >100 km from source

Effect of spirometry on intra-thoracic pressures

Due to the high intra-thoracic pressures associated with forced vital capacity manoeuvres, spirometry is contraindicated for vulnerable patients. However, the typical pressure response to spirometry has not been reported. Eight healthy, recreationally-active men performed spirometry while oesophageal pressure was recorded using a latex balloon-tipped catheter. Peak oesophageal pressure during inspiration was - 47 ± 9 cmH O (37 ± 10% of maximal inspiratory pressure), while peak oesophageal pressure during forced expiration was 102 ± 34 cmH O (75 ± 17% of maximal expiratory pressure). The deleterious consequences of spirometry might be associated with intra-thoracic pressures that approach maximal values during forced expiration

Optimisation of flow resistance and turbulent mixing over bed forms

Previous work on the interplay between turbulent mixing and flow resistance for flows over periodic rib roughness elements is extended to consider the flow over idealized shapes representative of naturally occurring sedimentary bed forms. The primary motivation is to understand how bed form roughness affects the carrying capacity of sediment-bearing flows in environmental fluid dynamics applications, and in engineering applications involving the transport of particulate matter in pipelines. For all bed form shapes considered, it is found that flow resistance and turbulent mixing are strongly correlated, with maximum resistance coinciding with maximum mixing, as was previously found for the special case of rectangular roughness elements. Furthermore, it is found that the relation between flow resistance to eddy viscosity collapses to a single monotonically increasing linear function for all bed form shapes considered, indicating that the mixing characteristics of the flows are independent of the detailed morphology of individual roughness elements

Reading the Complex Skipper Butterfly Fauna of One Tropical Place

BACKGROUND: An intense, 30-year, ongoing biodiversity inventory of Lepidoptera, together with their food plants and parasitoids, is centered on the rearing of wild-caught caterpillars in the 120,000 terrestrial hectares of dry, rain, and cloud forest of Area de Conservacion Guanacaste (ACG) in northwestern Costa Rica. Since 2003, DNA barcoding of all species has aided their identification and discovery. We summarize the process and results for a large set of the species of two speciose subfamilies of ACG skipper butterflies (Hesperiidae) and emphasize the effectiveness of barcoding these species (which are often difficult and time-consuming to identify). METHODOLOGY/PRINCIPAL FINDINGS: Adults are DNA barcoded by the Biodiversity Institute of Ontario, Guelph, Canada; and they are identified by correlating the resulting COI barcode information with more traditional information such as food plant, facies, genitalia, microlocation within ACG, caterpillar traits, etc. This process has found about 303 morphologically defined species of eudamine and pyrgine Hesperiidae breeding in ACG (about 25% of the ACG butterfly fauna) and another 44 units indicated by distinct barcodes (n = 9,094), which may be additional species and therefore may represent as much as a 13% increase. All but the members of one complex can be identified by their DNA barcodes. CONCLUSIONS/SIGNIFICANCE: Addition of DNA barcoding to the methodology greatly improved the inventory, both through faster (hence cheaper) accurate identification of the species that are distinguishable without barcoding, as well as those that require it, and through the revelation of species "hidden" within what have long been viewed as single species. Barcoding increased the recognition of species-level specialization. It would be no more appropriate to ignore barcode data in a species inventory than it would be to ignore adult genitalia variation or caterpillar ecology

Strategic Response by providers to specialty hospitals, ambulatory surgery centers, and retail clinics.

Radical innovation and disruptive technologies are frequently heralded as a solution to delivering higher quality, lower cost health care. According to the literature on disruption, local hospitals and physicians (incumbent providers) may be unable to competitively respond to such creative destruction and alter their business models for a host of reasons, thus threatening their future survival. However, strategic management theory and research suggest that, under certain conditions, incumbent providers may be able to weather the discontinuities posed by the disrupters. This article analyzes 3 disruptive innovations in service delivery: single-specialty hospitals, ambulatory surgical centers, and retail clinics. We first discuss the features of these innovations to assess how disruptive they are. We then draw on the literature on strategic adaptation to suggest how incumbents develop competitive responses to these disruptive innovations that assure their continued survival. These arguments are then evaluated in a field study of several urban markets based on interviews with both incumbents and entrants. The interviews indicate that entrants have failed to disrupt incumbent providers primarily as a result of strategies pursued by the incumbents. The findings cast doubt on the prospects for these disruptive innovations to transform health care

Quantification of the performance of chaotic micromixers on the basis of finite time Lyapunov exponents

Chaotic micromixers such as the staggered herringbone mixer developed by Stroock et al. allow efficient mixing of fluids even at low Reynolds number by repeated stretching and folding of the fluid interfaces. The ability of the fluid to mix well depends on the rate at which "chaotic advection" occurs in the mixer. An optimization of mixer geometries is a non trivial task which is often performed by time consuming and expensive trial and error experiments. In this paper an algorithm is presented that applies the concept of finite-time Lyapunov exponents to obtain a quantitative measure of the chaotic advection of the flow and hence the performance of micromixers. By performing lattice Boltzmann simulations of the flow inside a mixer geometry, introducing massless and non-interacting tracer particles and following their trajectories the finite time Lyapunov exponents can be calculated. The applicability of the method is demonstrated by a comparison of the improved geometrical structure of the staggered herringbone mixer with available literature data.Comment: 9 pages, 8 figure

Assertive community treatment for elderly people with severe mental illness

Background: Adults aged 65 and older with severe mental illnesses are a growing segment of the Dutch population. Some of them have a range of serious problems and are also difficult to engage. While assertive community treatment is a common model for treating difficult to engage severe mental illnesses patients, no special form of it is available for the elderly. A special assertive community treatment team for the elderly is developed in Rotterdam, the Netherlands and tested for its effectiveness.Methods: We will use a randomized controlled trial design to compare the effects of assertive community treatment for the elderly with those of care as usual. Primary outcome measures will be the number of dropouts, the number of patients engaged in care and patient's psychiatric symptoms, somatic symptoms, and social functioning. Secondary outcome measures are the number of unmet needs, the subjective quality of life and patients' satisfaction. Other secondary outcomes include the number of crisis contacts, rates of voluntary and involuntary admission, and length of stay. Inclusion criteria are aged 65 plus, the presence of a mental disorder, a lack of motivation for treatment and at least four suspected problems with functioning (addiction, somatic problems, daily living activities, housing etc.). If patients meet the inclusion criteria, they will be randomly allocated to either assertive community treatment for the elderly or care as usual. Trained assessors will use mainly observational instruments at the following time points: at baseline, after 9 and 18 months.Discussion: This study will help establish whether assertive community treatment for the elderly produces better results than care as usual in elderly people with severe mental illnesses who are difficult to engage. When assertive community treatment for the elderly proves valuable in these respects, it can be tested and implemented more widely, and mechanisms for its effects investigated