Permeable Boundaries Research Articles

Stability of a Buoyant Oldroyd-B Flow Saturating a Vertical Porous Layer with Open Boundaries

The performance of several engineering applications are strictly connected to the rheology of the working fluids and the Oldroyd-B model is widely employed to describe a linear viscoelastic behaviour. In the present paper, a buoyant Oldroyd-B flow in a vertical porous layer with permeable and isothermal boundaries is investigated. Seepage flow is modelled through an extended version of Darcy’s law which accounts for the Oldroyd-B rheology. The basic stationary flow is parallel to the vertical axis and describes a single-cell pattern where the cell has an infinite height. A linear stability analysis of such a basic flow is carried out to determine the onset conditions for a multicellular pattern. This analysis is performed numerically by employing the shooting method. The neutral stability curves and the values of the critical Rayleigh number are evaluated for different retardation time and relaxation time characteristics of the fluid. The study highlights the extent to which the viscoelasticity has a destabilising effect on the buoyant flow. For the limiting case of a Newtonian fluid, the known results available in the literature are recovered, namely a critical value of the Darcy–Rayleigh number equal to 197.081 and a corresponding critical wavenumber of 1.05950.

A ‘prodigious latitude’ of words: vocabularies of illness in 18th-century medical treatises and women’s writing

In its examination of a selection of 18th-century medical treatises and women’s writing, this essay considers a range of context-specific and historically specific medical vocabularies and tries to illuminate the...

Exploring exposure to intertwined community violence among Uruguayan adolescents using a mixed-method approach.

Building on the case of adolescents (aged 12-16 years) from underprivileged neighborhoods in Montevideo, two studies explore patterns of exposure to community violence among understudied South American youth. Applying a mixed-methods approach, the first study (n = 117) used principal component analysis to examine response patterns on a self-reported exposure to community violence scale. The second study examined subjective experience, drawing from focus group discussions with adolescents (n = 27) and their teachers (n = 22). Events were clustered into three components: indirect violence, traumatic violence, physical/verbal abuse, and robbery. Participants described the severity of violence in relation to chronic exposure, processes of naturalization, and permeable boundaries among the neighborhood, school, family, and social media networks. Violence chronicity and potential threats to life appear to be central dimensions in community violence reporting. Delimitating the study of community violence based on the setting or perceptual closeness has limited socioecological relevance.

Religious pursuits? Chinese international students encountering Christianity in Britain

ABSTRACT The increased presence of Chinese international students has contributed to the diversity of culture and religion on British campuses. While overseas Chinese students who convert to evangelical Christianity have been well researched in the United States since the 1980s, the role of religion in secular British universities remains under-researched. This study aims to understand Chinese international students’ religious seekership and their interactions with evangelical Christians in Britain. It makes an original contribution by including evidence from non-converts. Data from a mixed methodological approach illustrate the attitudes and perceptions of newly arrived Chinese international students and the subjective reasons underlying their initial seekership in multi-ethnic English-speaking religious environments. The findings challenge the assumed lack of interest of Chinese international students in local integration. Crucially, by examining the ongoing formation and cultivation of Chinese Christian identifications on British campuses, this research demonstrates the permeable boundaries between language, culture, and religion.

Lost in the matrix: Dialectical tensions in facilitating virtual video groups during COVID-19 pandemic

The research phenomenologically explored the experience of facilitating virtual video groups during the COVID-19 pandemic. Research questions addressed relational processes in virtual video groups, including emotional presence, interpersonal communication, and intimacy. Specifically, we asked how facilitators can intervene effectively to promote these processes in the virtual space, within the context of social distancing.Semi-structured group interviews were held with 26 female group facilitators from various professional backgrounds during the first wave of COVID-19 in Israel in May 2020. Phenomenological analysis yielded five main themes addressing dialectical tensions that operate simultaneously in the virtual space, both enabling and hindering relational processes in virtual video groups: intimacy and intrusion in the domestic space; sharp transitions from presence to absence; fragmented processing despite abundant information; sterility and clarity in group communication; and the hyper-aware self – being a participant and an observer at the same time. Moving groups into a virtual sphere challenged the traditional role of facilitators, who struggled to create a safe space in an unstable virtual setting where the boundaries between personal and professional lives were reduced. Findings also point to the potential of the domestic space to promote closeness and intimacy and suggest the virtual space requires facilitators to embrace multiplicity as a state of mind when intervening. Facilitators must work with permeable boundaries between inner and outer group spaces, accept discontinuity as a basic property of the virtual, and acknowledge the limitations caused by multiple stimuli.

An approach for permeable boundary conditions in SPH

Smoothed Particle Hydrodynamics (SPH) has intrinsic advantages over the Finite Volume (FV) method for predicting multiphase flows, since the need for fluid phase interface reconstructions is avoided due to the natural advection of those interfaces based on the Lagrangian description of the control volumes. However, permeable boundary conditions are less straightforward to handle with SPH, even though domain inlets and outlets are needed in most engineering problems. In this work we propose a new framework for permeable boundary conditions for the Weakly Compressible SPH based on ghost particles. The major characteristics of our approach are the application of Navier Stokes Characteristic Boundary Conditions (NSCBC) and a particle mass generation and removal procedure at the boundary. This approach enables the application of non-reflective boundary conditions and redundantizes the need for advecting ghost particles from an external buffer zone to the internal domain. Additionally, the particle mass variation can exactly be balanced with the mass flux defined at the boundary. Furthermore, we are proposing a novel approach to set the ghost particle state based on an extrapolation of the state of particles located in the internal domain and on the domain boundary. We validate the proposed framework for permeable boundaries with one- and two-dimensional test cases. The major findings are as follows. Due to the particle mass generation and removal at the domain boundary, spurious oscillations are introduced due to a non-optimal particle distribution. Those oscillations are reduced in our work to an acceptable level (1×10−5 to 1×10−4 relative to the values of the fluid dynamics variables) using existing stabilization schemes as well as the aforementioned novel methods for setting ghost particle states and particle masses at the permeable boundaries. We observe a very good agreement between the solutions obtained with the presented approach and analytical as well as numerical solutions obtained with the FV method. The proposed approach for setting the ghost particle states is indispensable for achieving a perfect balance between particle mass variation and mass flux across the permeable interface as well as the steady state and the temporal accuracy of the solution. Additionally, the pressure reflectivity at the permeable boundary is found to be in a very good agreement with the theory of the NSCBC method. Furthermore, for a SPH-FV coupled simulation we could demonstrate an excellent agreement compared to the FV method as well as the capability of our approach to handle significant flow unsteadiness and gradients at the permeable coupling interfaces without the introduction of spurious flow behavior.

Note from the Editors

Note from the Editors

Relative rates of fluid advection, elemental diffusion and replacement govern reaction front patterns

Replacement reactions during fluid infiltration into porous media, rocks and buildings are known to have important implications for reservoir development, ore formation as well as weathering. Natural observations and experiments have shown that in such systems the shape of reaction fronts can vary significantly ranging from smooth, rough to highly irregular. It remains unclear what process-related knowledge can be derived from these reaction front patterns. In this contribution we show a numerical approach to test the effect of relative rates of advection, diffusion, and reaction on the development of reaction fronts patterns in granular aggregates with permeable grain boundaries. The numerical model takes (i) fluid infiltration along permeable grain boundaries, (ii) reactions and (iii) elemental diffusion into account. We monitor the change in element concentration within the fluid, while reactions occur at a pre-defined rate as a function of the local fluid concentration. In non-dimensional phase space using Péclet and Damköhler numbers, results show that there are no rough fronts without advection (Péclet<70) nor if the reaction is too fast (Damköhler>10−3). As advection becomes more dominant and reaction slower, roughness develops across several grains with a full microstructure mimicking replacement in the most extreme cases. The reaction front patterns show an increase in roughness with increasing Péclet number from Péclet 10 to 100 but then a decrease in roughness towards higher Péclet numbers controlled by the Damköhler number. Our results indicate that reaction rates are crucial for pattern formation and that the shape of reaction fronts is only partly due to the underlying transport mechanism.

MPM simulation of solitary wave run-up on permeable boundaries

Waves attenuate rapidly as they propagate through porous media due to significant energy dissipation. The ability of permeable armour layers to absorb wave energy is therefore of great interest to the researchers and engineers tasked with the construction of structures that defend vulnerable coastlines from the wave attack. The goal of this research is to determine the effectiveness of vertical and sloped permeable barriers in minimising the wave run-up. Traditional methods for ascertaining the efficacy of protective barriers have used small-scale physical models. However, these are expensive and have been shown to suffer from the scaling problems, therefore numerical methods are gaining popularity. This paper investigates the effect of modifying the mean grain size of a permeable barrier on the run-up response to a solitary wave, using the Material Point Method (MPM), which is capable of handling large deformation problems within a Lagrangian framework, with a background mesh facilitating the solution of the governing equations and allowing for simple imposition of the boundary conditions. A double-point MPM is adopted, with two sets of material points representing the solid and liquid phases respectively, to accurately model situations where the fluid moves through the solid skeleton, such as in the case of wave run-up on porous structures. The multi-phase version of the MPM package Anura3D (www.anura3d.com) is used in the study, with a focus on the influence of changing the mean grain size of composition particles of a porous structure on solitary wave run-ups, on both vertical and sloped permeable boundaries. It has been shown that with an increase in the mean grain size, and therefore the permeability, the overall wave run-up height can be significantly reduced. The proposed study could contribute to a better understanding on the wave run-up reduction on porous structures, and provide useful design guidelines to the coastal defences.

From Theory-Centered to Patient-Centered Treatment: How Kohut’s Attitudes Impact Contemporary Therapeutic Work

ABSTRACT Kohut struggled courageously to proffer many ideas that were opposed to the psychoanalytic theories, philosophy, and clinical ideologies of his day. Not only did he question the way psychoanalysis was practiced, more importantly, Kohut challenged the prevailing Freudian view of human nature; no one since Freud had offered such a radical Weltanschauung, a world view that discerned man and woman in such a disparate light that it precluded self-psychology’s easy integration with other theories. In this article, dedicated to my mentor Paul Ornstein, I will take you on a journey, from the time that self-psychology came unbidden into my life – a time when I was trammeled in the musty corridors of a glum and occluded psychoanalytic world both in my training and my analysis – through its dramatic impact on my clinical attitude toward therapeutic work, to my attempt to preserve and update some of Kohut’s more important attitudes and concepts. I will emphasize the frequently unrecognized clinical consequences of Kohut’s world view – his belief in protecting the patient, his faith in letting the patient teach us how to analyze him or her, his receptivity to permeable boundaries, his capacity to be vulnerable, his transformation of the atmosphere in the consulting room, and his belief in building on health rather than curing pathology. Traveling along this journey we will discover how Kohut altered the therapeutic relationship from one of shadow companions to intimate connections.

Direct effects of boundary permeability on turbulent flows: observations from an experimental study using zero-mean-shear turbulence

Abstract

Numerical simulation for electrical conducting rotating flow of Au (Gold)-Zn (Zinc)/EG (Ethylene glycol) hybrid nanofluid

Presently the engineers and scientists have received much attention about the mechanism of heat transport in various industrial processes. Base liquids like water, vegetable oils, transformer oil and ethylene glycol are essential for many industrial processes. These cover the major areas of thermal transport of great interest. An important issue occurs about low thermal conductivity of fluids in some industrial processes. This leads to development of important aspect of nanotechnology. Remarkable importance of nanotechnology is to upgrade the heat transport mechanism in various heat transferring devices (to make them efficient). Therefore, such effectiveness in mind, magnetohydrodynamic (MHD) rotating flow of ethylene glycol based hybrid nanofluid between two permeable boundaries is addressed. Gold (Au) and Zinc (Zn) are taken as the nanoparticles. Ethylene glycol (EG) is taken as the base material. The two boundaries have different stretching rates. Fluid in presence of constant applied magnetic field is conducted. Numerical solution to the non-linear problems is developed. The velocity components and temperature are graphically analyzed. Tabulated values lead to important observations for skin friction coefficient and Nusselt number.

Analysis about impact of morphological and nanoparticle volume fraction aspects of TiO2–Cu in enhancement of thermo-physical features of newtonian fluid flowing in a rotating porous channel

Current communication is addressed to elaborate features of laminar fluid flowing through a channel with permeable boundaries which is an important flow problem in real-world applications. In this work, Newtonian fluid (base fluid) in a rotating porous contracting/expanding channel with induction of TiO2-Cu nanoparticles (Suspensions) of different shapes and sizes is obliged. Formulation is executed under implementing boundary layer approach. Empirical relation representing features of nanoparticles are added in equations. Afterwards, partial differential expressions are changed into ODE’s by incorporating transformations. Solution is heeded by collaboration of R–K and shooting procedure. The impact of flow-controlling parameters is interpreted via graphs and tables. The important quantities of engineering interest like heat flux coefficient, skin friction against different parameters are explained in tabulated manner. To make results more credible different range of nanoparticles volumetric fractions (1–4)%, and different shapes of particles like, i.e., triangle, oval, prism, hexagonal, spherical, brick, cylinders, and platelets are considered. It is inferred from investigation that magnitude of heat transfer coefficient has gained optimization against concerning parameters for the platelet shape of nanoparticles. It is revealed that magnitude of wall drag force and heat flux at lower boundary of channel is more inthe case of contraction than to the expansion of channel.

Boundary-Work and the Distribution of Care for Survivors of Domestic Violence and Abuse in Primary Care Settings: Perspectives From U.K. Clinicians.

Health care encounters are opportunities for primary care practitioners to identify women experiencing domestic violence and abuse (DVA). Increasing DVA support in primary care is a global policy priority but discussion about DVA during consultations remains rare. This article explores how primary care teams in the United Kingdom negotiate the boundaries of their responsibilities for providing DVA support. In-depth interviews were undertaken with 13 general practitioners (GPs) in two urban areas of the United Kingdom. Interviews were analyzed thematically. Analysis focused on the boundary practices participants undertook to establish their professional remit regarding abuse. GPs maintained permeable boundaries with specialist DVA support services. This enabled ongoing negotiation of the role played by clinicians in identifying DVA. This permeability was achieved by limiting the boundaries of the GP role in the care of patients with DVA to identification, with the work of providing support distributed to local specialist DVA agencies.

How the Mainstream Media Help to Spread Disinformation about Covid-19

How the Mainstream Media Help to Spread Disinformation about Covid-19

Confined batch foaming of semi‐crystalline rubbery elastomers with carbon dioxide using a mold

AbstractConfined foaming of poly(ethylene‐co‐vinyl acetate‐co‐carbon monoxide) using carbon dioxide as a physical blowing agent in a mold with either permeable or impermeable boundaries has been explored as a strategy to control final foam dimensions and morphology. The results are discussed in terms of comparisons to free‐foaming experiments conducted at the same pressure and temperature conditions following the same pressurization and depressurization paths. Foaming experiments were carried out at 30 and 40°C and 100, 200, and 300 bar followed by rapid depressurization of the foaming cell. Confined foaming led to smaller pores with more uniform distributions across the polymer cross‐section. However, bulk foam densities of the foams generated under confinement were higher than those generated under the free‐foaming mode. Surface characteristics and skin layer formation were altered by expansion against both the permeable and impermeable boundaries. Confined foaming promotes uniform pore distribution and overall dimensional uniformity and may impart surface texture but the trade‐off is in the degree to which the bulk foam density can be lowered.

Aeroacoustic noise calculations of non-compact bodies with permeable boundaries

A hybrid computational aeroacoustic method with permeable boundary is developed to evaluate non-compact noise induced by low Mach number flow over arbitrarily shaped bodies. Based on Lighthill’s equation and the boundary element method, the unified integral equations are established in which the integral boundary surrounding the objects can be selected arbitrarily. Validation studies are developed for noise induced by two-dimensional NACA0012 airfoil and three-dimensional circular cylinder. For NACA0012 airfoil, the directivity patterns of calculated noise with different permeable boundaries agree well with Howe’s analytical solution for trailing edge model. The acoustic noise generated by circular cylinder has a good agreement with Revell’s experimental data and FW-H equation. It demonstrates that the noise predicted by different permeable boundary is as accurate as that calculated by the body surface.

COVID‐19 and the Future of Management Studies. Insights from Leading Scholars

Abstract The COVID-19 pandemic and its medical, social and economic impacts presented profound challenges to business, government, and society It also presents management scholars with an opportunity to rethink some of our core assumptions and directions of our research In response, in the Summer of 2020, in our capacity as co- General Editors of the Journal of Management Studies, one of the foremost academic journals of management and organization studies, we commissioned short commentaries from leading management scholars

Critical geographies of love and loss: Relational responses to the death of a spouse in Senegal

Marriage practices in the Majority world may differ considerably from dominant cultural ideals in the Minority world of ‘romantic love’ and ‘companionate marriage’ based on monogamous relationships. Similarly, mourning in the ‘Rest’ of the world often diverges from assumptions within Anglophone bereavement studies of a ‘grieving journey’. This paper provides a gendered, spatial, relational analysis of responses to the death of a spouse in Senegal, based on in-depth interviews with Serer women and men in rural and urban communities. A heightened sense of relationality with the deceased surrounded widows' bodies, with permeable boundaries that needed to be contained and “purified” through widowhood-mourning practices in order to restore social cohesion. For men, the space of the home was transformed, sometimes unbearably, by the loss of a wife and mother due to their central role in home-making practices, transforming men's relational being. ‘Embodied relationality’, alongside material constraints, also shaped perspectives on remarriage. The paper reveals the diverse material, embodied, spatial, and often explicitly gendered, ways that the effects of the death of a spouse may be manifested in the experience of the living person and draws attention to the permeable embodied boundaries of ‘relational being’ that encompass the living and the dead.

Viscous backflow from a model fracture network: influence of a permeable boundary

The leakage from a fracture network to a surrounding medium during drainage, or backflow, driven by elastic relaxation, is considered. A network model is extended to include the effects of permeable boundaries, with the permeation through the wall assumed to be proportional to the local pressure. The regimes in which leakage is dominant relative to the parallel flow along the channel are evaluated at different times. Results show that, when the aperture of the channel is large enough, the parallel flow is greater than the permeation through the wall, and the channel thickness decreases in time, $t$ , with a $t^{-1/3}$ behaviour, as reported previously. However, when the aperture is small, the channel thickness decreases exponentially in time. An asymptotic investigation of the solution for a single fracture is performed and extended to network systems. The study provides insight into the influence leakage may have on squeezing-induced flows, which is relevant to natural and engineering systems.