Modelling bacterial behaviour close to a no-slip plane boundary: the influence of bacterial geometry

We describe a boundary-element method used to model the hydrodynamics of a bacterium propelled by a single helical flagellum. Using this model, we optimize the power efficiency of swimming with respect to cell body and flagellum geometrical parameters, and find that optima for swimming in unbounded fluid and near a no-slip plane boundary are nearly indistinguishable. We also consider the novel optimization objective of torque efficiency and find a very different optimal shape. Excluding effects such as Brownian motion and electrostatic interactions, it is demonstrated that hydrodynamic forces may trap the bacterium in a stable, circular orbit near the boundary, leading to the empirically observable surface accumulation of bacteria. Furthermore, the details and even the existence of this stable orbit depend on geometrical parameters of the bacterium, as described in this article. These results shed some light on the phenomenon of surface accumulation of micro-organisms and offer hydrodynamic explanations as to why some bacteria may accumulate more readily than others based on morphology

Leveraging Naval Diplomacy to Reinforce Economic Programs and Compete with China

NPS NRP Executive SummaryAs competition between the U.S. and China intensifies, the U.S. Navy must plan and implement its overseas operations and diplomatic activities to advance U.S. influence. The main purpose of this study is to assess how the USN can leverage its operations and activities to reinforce U.S. economic programs and enhance U.S. influence. Building on an innovative influence framework developed by two of the investigators, it will systematically assess how USN activities and operations such as joint exercises, port calls, humanitarian assistance and disaster response, and training programs, generate influence in three important U.S. partner nations with significant Chinese investment and/or security presence: Chile, Senegal, and the United Arab Emirates. The project will also identify specific ways that USN activities can reinforce USG economic programs and build effective partnerships, specifying the most productive activity groupings, effective sequencing arrangements, and potential obstacles to interagency coordination. The project will produce a final report, as well as briefings to the sponsor and other interested audiences in the Navy. The report will consist of three country case studies and a comparative analysis of their findings. The precise organization and format of the deliverables will be designed to suit the needs of the topic sponsor. Interim reports will be provided to keep the sponsor apprised of our progress and to solicit feedback during the course of study.N3/N5 - Plans & StrategyThis research is supported by funding from the Naval Postgraduate School, Naval Research Program (PE 0605853N/2098). https://nps.edu/nrpChief of Naval Operations (CNO)Approved for public release. Distribution is unlimited.

Hydrodynamic flow patterns and synchronization of beating cilia

We calculate the hydrodynamic flow field generated far from a cilium which is attached to a surface and beats periodically. In the case of two beating cilia, hydrodynamic interactions can lead to synchronization of the cilia, which are nonlinear oscillators. We present a state diagram where synchronized states occur as a function of distance of cilia and the relative orientation of their beat. Synchronized states occur with different relative phases. In addition, asynchronous solutions exist. Our work could be relevant for the synchronized motion of cilia generating hydrodynamic flows on the surface of cells.Comment: 5 pages, 4 figures, v2: minor correction

Hydrodynamic attraction of swimming microorganisms by surfaces

Cells swimming in confined environments are attracted by surfaces. We measure the steady-state distribution of smooth-swimming bacteria (Escherichia coli) between two glass plates. In agreement with earlier studies, we find a strong increase of the cell concentration at the boundaries. We demonstrate theoretically that hydrodynamic interactions of the swimming cells with solid surfaces lead to their re-orientation in the direction parallel to the surfaces, as well as their attraction by the closest wall. A model is derived for the steady-state distribution of swimming cells, which compares favorably with our measurements. We exploit our data to estimate the flagellar propulsive force in swimming E. coli

Human oesophageal adenocarcinoma cell lines JROECL 47 and JROECL 50 are admixtures of the human colon carcinoma cell line HCT 116

In two recently described human oesophageal adenocarcinoma cell lines JROECL 47 and JROECL 50, derived from one tumour, we detected identical E-cadherin and β-catenin gene mutations as in colon carcinoma cell line HCT 116. We demonstrate by HLA-typing, mutation analysis and microsatellite analysis that cell lines JROECL 47 and JROECL 50 are admixtures of the human colon adenocarcinoma cell line HCT 116. © 2000 Cancer Research Campaig

Generic flow profiles induced by a beating cilium

We describe a multipole expansion for the low Reynolds number fluid flows generated by a localized source embedded in a plane with a no-slip boundary condition. It contains 3 independent terms that fall quadratically with the distance and 6 terms that fall with the third power. Within this framework we discuss the flows induced by a beating cilium described in different ways: a small particle circling on an elliptical trajectory, a thin rod and a general ciliary beating pattern. We identify the flow modes present based on the symmetry properties of the ciliary beat.Comment: 12 pages, 6 figures, to appear in EPJ

Motor-Driven Bacterial Flagella and Buckling Instabilities

Many types of bacteria swim by rotating a bundle of helical filaments also called flagella. Each filament is driven by a rotary motor and a very flexible hook transmits the motor torque to the filament. We model it by discretizing Kirchhoff's elastic-rod theory and develop a coarse-grained approach for driving the helical filament by a motor torque. A rotating flagellum generates a thrust force, which pushes the cell body forward and which increases with the motor torque. We fix the rotating flagellum in space and show that it buckles under the thrust force at a critical motor torque. Buckling becomes visible as a supercritical Hopf bifurcation in the thrust force. A second buckling transition occurs at an even higher motor torque. We attach the flagellum to a spherical cell body and also observe the first buckling transition during locomotion. By changing the size of the cell body, we vary the necessary thrust force and thereby obtain a characteristic relation between the critical thrust force and motor torque. We present a sophisticated analytical model for the buckling transition based on a helical rod which quantitatively reproduces the critical force-torque relation. Real values for motor torque, cell body size, and the geometry of the helical filament suggest that buckling should occur in single bacterial flagella. We also find that the orientation of pulling flagella along the driving torque is not stable and comment on the biological relevance for marine bacteria.Comment: 15 pages, 11 figure

Dealing with the mess (we made): Unraveling hybridity, normativity, and complexity in journalism studies

In this article, we discuss the rise and use of the concept of hybridity in journalism studies. Hybridity afforded a meaningful intervention in a discipline that had the tendency to focus on a stabilized and homogeneous understanding of the field. Nonetheless, we now need to reconsider its deployment, as it only partially allows us to address and understand the developments in journalism. We argue that if scholarship is to move forward in a productive manner, we need, rather than denote everything that is complex as hybrid, to develop new approaches to our object of study. Ultimately, this is an open invitation to the field to adopt experientialist, practice-based approaches that help us overcome the ultimately limited binary dualities that have long governed our theoretical and empirical work in the field

Superhero comics and the digital communications circuit: a case study of <i>Strong Female Protagonist</i>

This article examines the ongoing superhero webcomic Strong Female Protagonist (2012-present), by Brannon Lee Mulligan and Molly Ostertag and employs it as a case study to analyse the new communications circuit created by the digital production and delivery of comics. It adopts a perspective drawn from Book History to frame the communication model of print comics and to evaluate how webcomics such as Strong Female Protagonist redefine the role of readers, authors and publishers