A flagellated, bottom-heavy micro-organism's swimming direction in a shear flow is determined from a balance between the gravitational and viscous torques (gyrotaxis). Hitherto, the cell has been assumed to be a spheroid and the flagella have been neglected. Here we use resistive-force theory to calculate both the magnitude and the direction of a biflagellate cell's swimming velocity and angular velocity relative to the fluid when there is an arbitrary linear flow far from the cell. We present an idealized model for the flagellar beat but, in calculating the velocity of the fluid relative to an element of a flagellum, the presence of the cell body is not neglected. Results are given for the case of a spherical cell body whose flagella beat in a vertical plane, when the ambient linear flow is in the same vertical plane. Results show that resistive-force theory can be used for organisms where the cell body has significant effect on the flow past the flagella and that the viscous torque on the flagella is a significant term in the torque balance equations. A model is presented for the calculation of a cell's velocity and angular velocity in a shear flow which is valid up to high magnitudes of rate of strain or vorticity. The main application of the results will be to modify a recent continuum model for suspensions of gyrotactic micro-organisms (Pedley & Kessler 1990).
Over many decades System Safety has evolved from a more re-active nature - learning from failures and improving – not really suitable for high consequence enterprises - to today’s more pro-active form. This is now based on better fundamental understanding, better assessment processes, better standards, more comprehensive analysis tools with better audit and regulation procedures. However, unlike ‘set educational subjects’ such as engineering, science, technology and mathematics, there are less opportunities for formal System Safety education and training in academia and elsewhere, even though system safety impacts on all aspects of life. One hopes that this will continue to be rectified. This leads us directly to the importance and value of this book, which gives a complete insight into the nature of what System Safety is all about, including its approaches, methodologies and tools, and which provides guidance on the successful application of a comprehensive, pro-active approach for ensuring safe system design.
The term “Black Swan” is a familiar concept in the context of high-consequence operations. There is the continual concern that there may be an “as yet” undiscovered flaw or lack of understanding in the design of a product, process or facility that could lead to a catastrophic event. The potential incompleteness in understanding any design concept, implementation and associated assessment is of concern. Given that “absolute confidence” may never be possible, the question becomes how best to continue to search for such possible flaws with a view to subsequent removal or mitigation. At first sight, this appears to be a process without end, but the level of commitment must be balanced against any detrimental consequence that could ensue should a Black Swan exist. But when is “enough is enough?” In this paper, this subject is covered in the context of nuclear warheads, where the Black Swan could indeed be catastrophic should it exist. The paper is framed around what can be learned from the general literature associated with “Black Swan” thinking.
No abstract
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.