Velocity-sensitised Magnetic Resonance Imaging of foams

Although flowing foams are used in a variety of technologies, foam rheology is still incompletely understood. In this paper we demonstrate the use of a velocity-sensitised magnetic resonance imaging (MRI) sequence for the study of flowing foam. We employ a constant-time (pure phase encode) imaging technique, SPRITE, which is immune to geometrical distortions caused by the foam-induced magnetic field inhomogeneity. The sample magnetisation is prepared before the SPRITE imaging with the Cotts 13-interval motion-sensitisation sequence, which is also insensitive to the effects of the foam heterogeneity. We measure the development of a power-law velocity profile in the foam downstream of a Venturi constriction (in which the cross-section of the tube decreases by 89% in area) in a vertical, cylindrical pipe

Using phase interference to characterize dynamic properties—a review of constant gradient, portable magnetic resonance methods

Spatially resolved motion-sensitized magnetic resonance (MR) is a powerful tool for studying the dynamic properties of materials. Traditional methods involve using large, expensive equipment to create images of sample displacement by measuring the spatially resolved MR signal response to time-varying magnetic field gradients. In these systems, both the sample and the stress applicator are typically positioned inside a magnet bore. Portable MR instruments with constant gradients are more accessible, with fewer limitations on sample size, and they can be used in industrial settings to study samples under deformation or flow. We propose a view in which the well-controlled sensitive region of a magnet array acts as an integrator, with the velocity distribution leading to phase interference in the detected signal, which encodes information on the sample’s dynamic properties. For example, in laminar flows of Newtonian and non-Newtonian fluids, the velocity distribution can be determined analytically and used to extract the fluid’s dynamic properties from the MR signal magnitude and/or phase. This review covers general procedures, practical considerations, and examples of applications in dynamic mechanical analysis and fluid rheology (viscoelastic deformation, laminar pipe flows, and Couette flows). Given that these techniques are relatively uncommon in the broader magnetic resonance community, this review is intended for both advanced NMR users and a more general physics/engineering audience interested in rheological applications of NMR

Gas and Liquid Phase Imaging of Foam Flow Using Pure Phase Encode Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a non-invasive and non-optical measurement technique, which makes it a promising method for studying delicate and opaque samples, such as foam. Another key benefit of MRI is its sensitivity to different nuclei in a sample. The research presented in this article focuses on the use of MRI to measure density and velocity of foam as it passes through a pipe constriction. The foam was created by bubbling fluorinated gas through an aqueous solution. This allowed for the liquid and gas phases to be measured separately by probing the 1H and 19F behavior of the same foam. Density images and velocity maps of the gas and liquid phases of foam flowing through a pipe constriction are presented. In addition, results of computational fluid dynamics simulations of foam flow in the pipe constriction are compared with experimental results

The Presence of Gender Disparity on the Force Concept Inventory in a Sample of Canadian Undergraduate Students

Concept inventories (CI) are validated, research-based, multiple-choice tests, which are widely used to assess the effectiveness of pedagogical practices in bringing about conceptual change. In order to be a useful diagnostic tool, a CI must reflect only the student understanding of the conceptual material. The Force Concept Inventory (FCI) is arguably the standard for testing conceptual understanding of Newtonian mechanics. Studies in the United States and United Kingdom have shown the existence of a gender gap in FCI scores and gains between male and female students. This study aimed to examine whether such a gap exists for Canadian students at a mid-sized university. Four-hundred and thirty-four men and 379 women taking first-term introductory physics courses from the past nine years were assessed with the FCI prior to and after receiving instruction. A gender gap in the pre-instruction and post instruction scores was revealed in favour of male students (p \u3c 0.01). There also existed a gender disparity in the learning gains between the two tests, where males had significantly higher gains (p \u3c 0.01), although the effect size was small. Further analysis found that both male and female students who studied in classes that included interactive engagement methods had somewhat higher gains than students in traditional lecture courses, but that the interactive engagement methods did not eliminate the gender gap between male and female students (p \u3c 0.01). Our results sound a cross-disciplinary note of caution for anyone using concept inventories as research or self-assessment tools. Les inventaires de concepts sont des questionnaires à choix multiples validés basés sur la recherche qui sont largement utilisés pour évaluer l’efficacité de pratiques pédagogiques en instaurant un changement conceptuel. Afin d’être des outils diagnostiques utiles, les inventaires de concepts doivent refléter uniquement la compréhension qu’a l’étudiant de la matière conceptuelle. Le « Force Concept Inventory (FCI) » est sans aucun doute la norme pour tester la compréhension conceptuelle de la mécanique newtonienne. Des études menées aux États-Unis et au Royaume-Uni ont montré l’existence d’un écart hommes-femmes dans les résultats du FCI et ainsi que dans les acquis. Cette étude vise à déterminer si un tel écart existe parmi les étudiants canadiens dans une université de taille moyenne. Un total de 434 hommes et 379 femmes inscrits à un premier cours d’introduction à la physique au fil des neuf dernières années ont été évalués avec le FCI au tout début et à la toute fin de la session. Les résultats ont révélé un écart hommes-femmes dans les résultats des tests, aussi bien ceux effectués avant le cours que ceux après le cours, en faveur des étudiants masculins (p \u3c 0.01). Ils ont également révélé une disparité entre hommes et femmes dans les acquis d’apprentissage entre les deux tests : les hommes avaient atteint des acquis plus élevés (p \u3c 0.01), bien que l’ampleur de l’effet ait été faible. Des analyses complémentaires ont montré que tant les hommes que les femmes qui avaient étudié dans des classes qui comprenaient des méthodes d’engagement interactif avaient obtenu davantage d’acquis que les étudiants qui avaient suivi des cours magistraux traditionnels, mais que les méthodes d’engagement interactif n’avaient pas éliminé l’écart hommes-femmes parmi les étudiants (p \u3c 0.01). Nos résultats présentent une mise en garde à l’intention de ceux qui utilisent les inventaires de concepts en tant qu’outils de recherche ou d’auto-évaluation, quelle que soit leur discipline

Velocity-sensitised Magnetic Resonance Imaging of foams

Although flowing foams are used in a variety of technologies, foam rheology is still incompletely understood. In this paper we demonstrate the use of a velocity-sensitised magnetic resonance imaging (MRI) sequence for the study of flowing foam. We employ a constant-time (pure phase encode) imaging technique, SPRITE, which is immune to geometrical distortions caused by the foam-induced magnetic field inhomogeneity. The sample magnetisation is prepared before the SPRITE imaging with the Cotts 13-interval motion-sensitisation sequence, which is also insensitive to the effects of the foam heterogeneity. We measure the development of a power-law velocity profile in the foam downstream of a Venturi constriction (in which the cross-section of the tube decreases by 89% in area) in a vertical, cylindrical pipe

Velocity-sensitised Magnetic Resonance Imaging of foams

Although flowing foams are used in a variety of technologies, foam rheology is still incompletely understood. In this paper we demonstrate the use of a velocity-sensitised magnetic resonance imaging (MRI) sequence for the study of flowing foam. We employ a constant-time (pure phase encode) imaging technique, SPRITE, which is immune to geometrical distortions caused by the foam-induced magnetic field inhomogeneity. The sample magnetisation is prepared before the SPRITE imaging with the Cotts 13-interval motion-sensitisation sequence, which is also insensitive to the effects of the foam heterogeneity. We measure the development of a power-law velocity profile in the foam downstream of a Venturi constriction (in which the cross-section of the tube decreases by 89% in area) in a vertical, cylindrical pipe