Entrainment and scattering in microswimmer--colloid interactions

We use boundary element simulations to study the interaction of model microswimmers with a neutrally buoyant spherical particle. The ratio of the size of the particle to that of the swimmer is varied from $R^\mathrm{P} / R^\mathrm{S} \ll 1$, corresponding to swimmer--tracer scattering, to $R^\mathrm{P} / R^\mathrm{S} \gg 1$, approximately equivalent to the swimmer interacting with a fixed, flat surface. We find that details of the swimmer and particle trajectories vary for different swimmers. However, the overall characteristics of the scattering event fall into two regimes, depending on the relative magnitudes of the impact parameter, $\rho$, and the collision radius, $R^\mathrm{coll}=R^\mathrm{P} + R^\mathrm{S}$. The range of particle motion, defined as the maximum distance between two points on the trajectory, has only a weak dependence on the impact parameter when $\rho < R^\mathrm{coll}$ and decreases with the radius of the particle. In contrast, when $\rho>R^\mathrm{coll}$ the range decreases as a power law in $\rho$ and is insensitive to the size of the particle. We also demonstrate that large particles can cause swimmers to be deflected through large angles. In some instances, this swimmer deflection can lead to larger net displacements of the particle. Based on these results, we estimate the effective diffusivity of a particle in a dilute bath of swimmers and show that there is a non-monotonic dependence on particle radius. Similarly, we show that the effective diffusivity of a swimmer scattering in a suspension of particles varies non-monotonically with particle radius.Comment: 19 pages, 11 figures. Accepted in Physical Review Fluid

Coherence, engagement, and usefulness as sensemaking criteria in participatory media practice

When skilled practitioners create media artifacts such as web pages, newspaper articles, videos, or business presentations, they are engaging in a pursuit which has consequences for the people who will interact with those artifacts. The juncture of practice, artifact, and consequences involves diverse normative considerations. We have summarized these into three criteria: coherence, engagement, and usefulness. In this paper we report on initial progress to develop a method for assessing these criteria in a particular form of skilled real-time media practice

Transient radiation and conduction in a slotted slab and a hollow cylinder

Transient radiation and conduction in slotted slab and hollow cylinde

Abstract Tensor Systems as Monoidal Categories

The primary contribution of this paper is to give a formal, categorical treatment to Penrose's abstract tensor notation, in the context of traced symmetric monoidal categories. To do so, we introduce a typed, sum-free version of an abstract tensor system and demonstrate the construction of its associated category. We then show that the associated category of the free abstract tensor system is in fact the free traced symmetric monoidal category on a monoidal signature. A notable consequence of this result is a simple proof for the soundness and completeness of the diagrammatic language for traced symmetric monoidal categories.Comment: Dedicated to Joachim Lambek on the occasion of his 90th birthda

Hypotheses, evidence and relationships: The HypER approach for representing scientific knowledge claims

Biological knowledge is increasingly represented as a collection of (entity-relationship-entity) triplets. These are queried, mined, appended to papers, and published. However, this representation ignores the argumentation contained within a paper and the relationships between hypotheses, claims and evidence put forth in the article. In this paper, we propose an alternate view of the research article as a network of 'hypotheses and evidence'. Our knowledge representation focuses on scientific discourse as a rhetorical activity, which leads to a different direction in the development of tools and processes for modeling this discourse. We propose to extract knowledge from the article to allow the construction of a system where a specific scientific claim is connected, through trails of meaningful relationships, to experimental evidence. We discuss some current efforts and future plans in this area

From Open Content Repositories to Open Sensemaking Communities

The Open Content movement is concerned with enabling students and educators to access material, in order to then learn from it, and reuse it either in one’s studies or one’s own courses. The core efforts to date has focused on enabling access, e.g. building the organizational/political will to release and license content, and in developing open infrastructures for educators to then publish and reassemble it. The key challenge in the next phase of the open content movement is to improve the support for prospective students to engage with and learn from the material, and with each other though peer learning support, in the absence of formally imposed study timetables and assessment deadlines. This paper reports on tools for e-learning and collaborative sensemaking developed at the UK Open University which are now being considered as candidates for open content learning support