Numerical investigation of controlling interfacial instabilities in non-standard Hele-Shaw configurations

Viscous fingering experiments in Hele-Shaw cells lead to striking pattern formations which have been the subject of intense focus among the physics and applied mathematics community for many years. In recent times, much attention has been devoted to devising strategies for controlling such patterns and reducing the growth of the interfacial fingers. We continue this research by reporting on numerical simulations, based on the level set method, of a generalised Hele-Shaw model for which the geometry of the Hele-Shaw cell is altered. First, we investigate how imposing constant and time-dependent injection rates in a Hele-Shaw cell that is either standard, tapered or rotating can be used to reduce the development of viscous fingering when an inviscid fluid is injected into a viscous fluid over a finite time period. We perform a series of numerical experiments comparing the effectiveness of each strategy to determine how these non-standard Hele-Shaw configurations influence the morphological features of the inviscid-viscous fluid interface. Tapering plates in either converging or diverging directions leads to reduced metrics of viscous fingering at the final time when compared to the standard parallel configuration, especially with carefully chosen injection rates; for the rotating plate case, the effect is even more dramatic, with sufficiently large rotation rates completely stabilising the interface. Next, we illustrate how the number of non-splitting fingers can be controlled by injecting the inviscid fluid at a time-dependent rate while increasing the gap between the plates. Simulations compare well with previous experimental results for various injection rates and geometric configurations. Further, we demonstrate how the fully nonlinear dynamics of the problem affect the number of fingers that emerge and how well this number agrees with predictions from linear stability analysis

Interfacial dynamics and pinch-off singularities for axially symmetric Darcy flow

We study a model for the evolution of an axially symmetric bubble of inviscid fluid in a homogeneous porous medium otherwise saturated with a viscous fluid. The model is a moving boundary problem that is a higher-dimensional analogue of Hele-Shaw flow. Here we are concerned with the development of pinch-off singularities characterised by a blow-up of the interface curvature and the bubble subsequently breaking up into two; these singularities do not occur in the corresponding two-dimensional Hele-Shaw problem. By applying a novel numerical scheme based on the level set method, we show that solutions to our problem can undergo pinch-off in various geometries. A similarity analysis suggests that the minimum radius behaves as a power law in time with exponent $\alpha = 1/3$ just before and after pinch-off has occurred, regardless of the initial conditions; our numerical results support this prediction. Further, we apply our numerical scheme to simulate the time-dependent development and translation of axially symmetric Saffman-Taylor fingers and Taylor-Saffman bubbles in a cylindrical tube, highlighting key similarities and differences with the well-studied two-dimensional cases.Comment: 16 pages, 16 figure

Sensory textile-bacterial hybrids: textile-bacteria fusion to impart forest-associated scents

This research paper presents a study on the development of living textile-bacterial hybrids, focusing on the scent produced by Streptomyces violaceruber, a bacterial species, throughout its growth phase. The objective of this study was to observe scent profiles of S. violaceruber on two different fibres, cotton, and linen, and analyse the potential impact of fibre properties on scent profile, intensity, and duration. In doing so the research suggests potential opportunities to curate living scent through textiles and the generation of sensory textile-bacterial hybrids. Interdisciplinary methods were applied to compare changes in the volatile compounds present and identify fibres and fabrication processes most suitable to create a living textile. The paper reports on the development of textile samples that are infused with S. violaceruber and observed for their subjective scent as well as the volatile compounds, which were analysed via gas chromatography. The findings of this study confirmed the presence and development of bacterial scents on textiles during bacterial growth. The scents identified included earthy, soil-like, floral, jasmine, and fruity notes, offering potential for further exploration in fibre and yarn selection, as well as the structural design of the textile. This research contributes to the field of biotextiles by examining the influence of textile fibres and knitted textiles on bacterial volatile compounds. It establishes a platform for investigating how different fibres and structural factors influence the bacterial scent profile and provides valuable insights for the future development of living sensory textiles and their integration into various applications

Meeting USDHHS Physical Activity Guidelines and Health Outcomes

International Journal of Exercise Science 10(1): 121-127, 2017 Current public health physical activity (PA) guidelines suggest ≥500 METmin/week of PA, with additional benefits beyond 1000 METmin/week (i.e., a dose response). Revised U.S. PA guidelines are scheduled for 2018. The purpose was to relate health markers (blood pressure, percent fat, BMI, blood glucose, cholesterol, and cardiorespiratory fitness) to verify the dose response for PA guidelines revision. 505 non-smoking participants self-reported PA behaviors and completed medical screening. MANCOVA controlling for age and gender determined the relation between health markers and PA. MANCOVA indicated significantly (P\u3c.001) different health markers of percent fat, BMI, glucose, and treadmill time as a function of PA. Post-hoc Helmert contrasts (1] \u3c500 METmin/week vs. ≥500 METmin/week and 2] 500 to \u3c1000 METmin/week vs. ≥1000 METmin/week) indicated that meeting the PA guidelines was associated with better health markers and higher cardiorespiratory fitness. Effect sizes were greater for contrast 1 than for contrast 2, suggesting a plateauing effect. Revised public health guidelines should consider achievement of ≥500 METmin/week to be most important, with additional modest gain thereafter. Revised PA guidelines should stress the importance of achieving 500-1000 METmin/week

Two-interface and thin filament approximation in Hele--Shaw channel flow

For a viscous fluid trapped in a Hele--Shaw channel, and pushed by a pressure difference, the fluid interface is unstable due to the Saffman--Taylor instability. We consider the evolution of a fluid region of finite extent, bounded between two interfaces, in the limit the interfaces are close, that is, when the fluid region is a thin liquid filament separating two gases of different pressure. In this limit, we derive a geometric flow rule that describes the normal velocity of the filament centreline, and evolution of the filament thickness, as functions of the thickness and centreline curvature. We show that transverse flow along the filament is necessary to regularise the instability. Numerical simulation of the thin filament flow rule is shown to closely match level-set computations of the complete two-interface model, and solutions ultimately evolve to form a bubble of increasing radius and decreasing thickness

Moving boundary problems for quasi-steady conduction limited melting

The problem of melting a crystal dendrite is modelled as a quasi-steady Stefan 5 problem. By employing the Baiocchi transform, asymptotic results are derived in the limit that 6 the crystal melts completely, extending previous results that hold for a special class of initial and 7 boundary conditions. These new results, together with predictions for whether the crystal pinches off 8 and breaks into two, are supported by numerical calculations using the level set method. The effects of 9 surface tension are subsequently considered, leading to a canonical problem for near-complete-melting 10 which is studied in linear stability terms and then solved numerically. Our study is motivated in 11 part by experiments undertaken as part of the Isothermal Dendritic Growth Experiment, in which 12 dendritic crystals of pivalic acid were melted in a microgravity environment: these crystals were 13 found to be prolate spheroidal in shape, with an aspect ratio initially increasing with time then 14 rather abruptly decreasing to unity. By including a kinetic undercooling-type boundary condition in 15 addition to surface tension, our model suggests the aspect ratio of a melting crystal can reproduce 16 the same non-monotonic behaviour as that which was observed experimentally. 1

Ethical and methodological issues in engaging young people living in poverty with participatory research methods

This paper discusses the methodological and ethical issues arising from a project that focused on conducting a qualitative study using participatory techniques with children and young people living in disadvantage. The main aim of the study was to explore the impact of poverty on children and young people's access to public and private services. The paper is based on the author's perspective of the first stage of the fieldwork from the project. It discusses the ethical implications of involving children and young people in the research process, in particular issues relating to access and recruitment, the role of young people's advisory groups, use of visual data and collection of data in young people's homes. The paper also identifies some strategies for addressing the difficulties encountered in relation to each of these aspects and it considers the benefits of adopting participatory methods when conducting research with children and young people

Mobility, Mood and Place—Co-Designing Age-Friendly Cities: A Report on Collaborations between Older People and Students of Architecture

Mobility, Mood and Place explores how places can be designed collaboratively to make pedestrian mobility easy, enjoyable and meaningful for older people. The built environment often excludes marginalised groups such as older people, single mothers and others with special needs. ‘Co-design’ is emerging as an important approach in architectural and urban design, which diversifies stakeholder participation and representation. Participatory co-design approaches can include such stakeholders so as to address their priorities and ensure that other stakeholders empathise with their perspective. This can enhance students’ methodological flexibility and empathy. This paper critically reflects on architecture students’ experiences, together with older adults (including stroke-survivors and those with dementia), in producing co-design research on age-friendly environments and offers some methodological insights. It also discusses competing objectives between a co-design research project that involved students of architecture and landscape design on post-graduate academic programmes. Finally, the paper will offer contributions to architects interested in designing places that take into account the needs of older people

Neurosteroid modulation of GABAergic neurotransmission in the central amygdala: A role for NMDA receptors

The neurosteroid 3α-hydroxy-5α-pregnan-20-one (allopregnanolone or ALLO) positively modulates GABAA receptors, an action that may contribute to the anxiolytic effects of ALLO. Recent evidence suggests that ALLO’s anxiolytic effects appear to be mediated by the amygdala, a key neural structure for emotional and cognitive behaviors. However, little is known regarding ALLO effects on amygdala physiology. We therefore explored ALLO effects on GABA neurotransmission in the central nucleus (Ce) of the amygdala, a major output nucleus involved in fear and anxiety. We recorded evoked GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) in Ce neurons using whole-cell patch clamp techniques. We observed that ALLO significantly reduced the amplitude of evoked GABAA receptor-mediated IPSCs. However, the effect of ALLO was occluded by the NMDA receptor antagonist D-APV. D-APV alone also reduced evoked IPSCs in Ce neurons. These results suggest that ALLO-induced reduction of GABAergic transmission in Ce appears to depend on neural network activity, possibly involving an NMDA receptor-mediated mechanism. These ALLO effects on GABAergic transmission in the central amygdala may play a role in mediating its anxiolytic actions