A spherical squirming swimmer in unsteady Stokes flow

2013 ◽  
Vol 723 ◽  
pp. 163-189 ◽  
Author(s):  
Kenta Ishimoto
Keyword(s):  
Stokes Flow ◽  
Small Amplitude ◽  
Wave Pattern ◽  
Swimming Velocity ◽  
Inertial Effects ◽  
Long Period ◽  
Long Time ◽  
Unsteady Stokes Flow ◽  
Micro Organisms ◽  
Time Periodic

AbstractThe motion of a spherical squirmer in unsteady Stokes flow is investigated for a deeper understanding of unsteady inertial effects on swimming micro-organisms and differences of swimming strokes between a wave pattern and a flapping motion. An asymptotic analysis with respect to the small amplitude and the small inertia is performed, and the average swimming velocity after a long period of time under an assumption of a time-periodic stroke is obtained. This analysis shows that the scallop theorem still holds in a long-time asymptotic sense for tangential deformation, but that the time variation of the shape generates a net velocity even for a reciprocal swimmer. It is also found that the inertial effects on the swimming velocity are significant for a flapping swimmer, as contrasted with little influence on that of a swimmer with a wave pattern. The inertial effect is also illustrated with a simple squirmer, so that a reciprocal motion can be almost an optimal stroke under a constraint on energy consumption.

Motion of slender bodies in unsteady Stokes flow

2011 ◽  
Vol 688 ◽  
pp. 66-87 ◽  
Author(s):  
Efrath Barta
Keyword(s):  
Stokes Flow ◽  
Slenderness Ratio ◽  
Creeping Flow ◽  
Slender Body Theory ◽  
Wide Range ◽  
Unsteady Stokes Flow ◽  
Slender Bodies ◽  
Set Up ◽  
Micro Organisms ◽  
Parameter Values

AbstractThe flow regime in the vicinity of oscillatory slender bodies, either an isolated one or a row of many bodies, immersed in viscous fluid (i.e. under creeping flow conditions) is studied. Applying the slender-body theory by distributing proper singularities on the bodies’ major axes yields reasonably accurate and easily computed solutions. The effect of the oscillations is revealed by comparisons with known Stokes flow solutions and is found to be most significant for motion along the normal direction. Streamline patterns associated with motion of a single body are characterized by formation and evolution of eddies. The motion of adjacent bodies results, with a reduction or an increase of the drag force exerted by each body depending on the direction of motion and the specific geometrical set-up. This dependence is demonstrated by parametric results for frequency of oscillations, number of bodies, their slenderness ratio and the spacing between them. Our method, being valid for a wide range of parameter values and for densely packed arrays of rods, enables simulation of realistic flapping of bristled wings of some tiny insects and of locomotion of flagella and ciliated micro-organisms, and might serve as an efficient tool in the design of minuscule vehicles. Its potency is demonstrated by a solution for the flapping of thrips.

Particle Transport in Quasistatic Stokes Flow

1999 ◽  
Author(s):  
Russell Keanini
Keyword(s):  
Traveling Waves ◽  
Stokes Flow ◽  
Particle Transport ◽  
Small Amplitude ◽  
Large Scale ◽  
Second Order ◽  
Particle Agglomeration ◽  
Long Time ◽  
Short Time ◽  
Streaming Flow

Abstract Particle transport associated with quasistatic second-order streaming flow in wavy-walled channels is theoretically investigated. Small amplitude tangential oscillations of both walls drive steady second-order streaming, while superposed, large-amplitude oscillations of one wall produce the time-dependent, quasisteady flows of interest. Short-time transport is characterized by collective particle motion in the direction of large-scale boundary displacement and by filamentary motion in the opposite direction, both consistent with transport in traveling waves [E. Moses and V. Steinburg, Phys. Rev. Lett. 60, 2030 (1988)]. Long time or asymptotic transport is characterized by particle agglomeration toward, or repulsion from, moving elliptic points. Under certain conditions, collective, periodic motion on the periphery of central cells also occurs. These characteristics correspond respectively to attraction or repulsion to or from period-1 elliptic points and attraction toward limit cycles on the Poincare map.

On nearly-commensurable periods in the restricted problem of three bodies, with calculations of the long-period variations in the interior 2:1 case

1966 ◽  
Vol 25 ◽  
pp. 197-222 ◽  
Author(s):  
P. J. Message
Keyword(s):  
Periodic Solution ◽  
Periodic Solutions ◽  
Large Amplitude ◽  
Restricted Problem ◽  
Small Amplitude ◽  
Minor Planets ◽  
Long Period ◽  
Numerical Integrations ◽  
Period Variations ◽  
The Mean

An analytical discussion of that case of motion in the restricted problem, in which the mean motions of the infinitesimal, and smaller-massed, bodies about the larger one are nearly in the ratio of two small integers displays the existence of a series of periodic solutions which, for commensurabilities of the typep+ 1:p, includes solutions of Poincaré'sdeuxième sortewhen the commensurability is very close, and of thepremière sortewhen it is less close. A linear treatment of the long-period variations of the elements, valid for motions in which the elements remain close to a particular periodic solution of this type, shows the continuity of near-commensurable motion with other motion, and some of the properties of long-period librations of small amplitude.To extend the investigation to other types of motion near commensurability, numerical integrations of the equations for the long-period variations of the elements were carried out for the 2:1 interior case (of which the planet 108 “Hecuba” is an example) to survey those motions in which the eccentricity takes values less than 0·1. An investigation of the effect of the large amplitude perturbations near commensurability on a distribution of minor planets, which is originally uniform over mean motion, shows a “draining off” effect from the vicinity of exact commensurability of a magnitude large enough to account for the observed gap in the distribution at the 2:1 commensurability.

scholarly journals Music for Monkeys: Building Methods to Design with White-Faced Sakis for Animal-Driven Audio Enrichment Devices

Animals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1768
Author(s):  
Roosa Piitulainen ◽  
Ilyena Hirskyj-Douglas
Keyword(s):  
Longitudinal Study ◽  
Electronic Music ◽  
Computer Systems ◽  
Interactive System ◽  
Novelty Effect ◽  
Non Invasive ◽  
Long Period ◽  
Long Time ◽  
Audio System ◽  
Computer Interaction

Computer systems for primates to listen to audio have been researched for a long time. However, there is a lack of investigations into what kind of sounds primates would prefer to listen to, how to quantify their preference, and how audio systems and methods can be designed in an animal-focused manner. One pressing question is, if given the choice to control an audio system, would or could primates use such a system. In this study, we design an audio enrichment prototype and method for white-faced sakis that allows them to listen to different sounds in their regular zoo habitat while automatically logging their interactions. Focusing on animal-centred design, this prototype was built from low fidelity testing of different forms within the sakis’ enclosure and gathering requirements from those who care for and view the animal. This process of designing in a participatory manner with the sakis resulted in an interactive system that was shown to be viable, non-invasive, highly interactive, and easy to use in a zoo habitat. Recordings of the sakis’ interactions demonstrated that the sakis triggered traffic audio more than silence, rain sounds, zen, and electronic music. The data and method also highlight the benefit of a longitudinal study within the animals’ own environment to mitigate against the novelty effect and the day-to-day varying rhythm of the animals and the zoo environment. This study builds on animal-centred methods and design paradigms to allow the monitoring of the animals’ behaviours in zoo environments, demonstrating that useful data can be yielded from primate-controlled devices. For the Animal-Computer Interaction community, this is the first audio enrichment system used in zoo contexts within the animals own environment over a long period of time that gives the primate control over their interactions and records this automatically.

scholarly journals The appearance of boundary layers and drift flows due to high-frequency surface waves

2012 ◽  
Vol 707 ◽  
pp. 482-495 ◽  
Author(s):  
Ofer Manor ◽  
Leslie Y. Yeo ◽  
James R. Friend
Keyword(s):  
Boundary Layer ◽  
Surface Waves ◽  
High Frequency ◽  
Slip Boundary Condition ◽  
Inertial Effects ◽  
Velocity Amplitude ◽  
Slip Boundary ◽  
Long Period ◽  
Bulk Waves ◽  
Schlichting Streaming

AbstractThe classical Schlichting boundary layer theory is extended to account for the excitation of generalized surface waves in the frequency and velocity amplitude range commonly used in microfluidic applications, including Rayleigh and Sezawa surface waves and Lamb, flexural and surface-skimming bulk waves. These waves possess longitudinal and transverse displacements of similar magnitude along the boundary, often spatiotemporally out of phase, giving rise to a periodic flow shown to consist of a superposition of classical Schlichting streaming and uniaxial flow that have no net influence on the flow over a long period of time. Correcting the velocity field for weak but significant inertial effects results in a non-vanishing steady component, a drift flow, itself sensitive to both the amplitude and phase (prograde or retrograde) of the surface acoustic wave propagating along the boundary. We validate the proposed theory with experimental observations of colloidal pattern assembly in microchannels filled with dilute particle suspensions to show the complexity of the boundary layer, and suggest an asymptotic slip boundary condition for bulk flow in microfluidic applications that are actuated by surface waves.

1787–1887–1987: reflections on a Sierra Leone bicentenary

Africa ◽  
1987 ◽  
Vol 57 (4) ◽  
pp. 411-421 ◽  
Author(s):  
Christopher Fyfe
Keyword(s):  
West Africa ◽  
Fifteenth Century ◽  
Sierra Leone ◽  
Forest Belt ◽  
Long Period ◽  
Language Pattern ◽  
Long Time ◽  
Opening Paragraph

Opening ParagraphSeen in the widest perspective, 1787 is only one date among the uncounted tens, perhaps hundreds, of thousands of years during which the present Sierra Leone has been inhabited. Archaeologists have done disappointingly little work there. But it is clear from their findings (and by implication from findings in the rest of forest-belt West Africa) that people have lived there a very long time. Though traditional historiography always tends to present the peoples of Sierra Leone as immigrants from somewhere else, the language pattern suggests continuous occupation over a very long period. As Paul Hair (1967) has shown, there has been a striking linguistic continuity in coastal West Africa since the fifteenth century. Nor is there evidence to suggest that before that period stability and continuity were not the norm.

scholarly journals Barns upplevelser när föräldrars missbruk upphört

2017 ◽  
Vol 34 (5) ◽  
pp. 400-414 ◽  
Author(s):  
Karin Alexanderson ◽  
Elisabet Näsman
Keyword(s):  
Symbolic Interactionism ◽  
Theoretical Framework ◽  
Interview Study ◽  
Organizational Boundaries ◽  
Long Period ◽  
Family Perspective ◽  
Parents And Children ◽  
Long Time ◽  
The Impact ◽  
The Relationship

This article is based on interviews with fifteen children, whose parents have addiction problems. Purpose: To contribute to in-depth understanding of children's situation when parents have ceased abusing drugs or alcohol. Method: An explorative interview study with childhood sociology and symbolic interactionism as theoretical framework. Outcome: The end of the abuse gives children space to feel how they feel, to reflect on the impact of the addiction on their health and personality, and to try changing themselves and their lives. Their need for processing may last for a long time. It can take time and be difficult to build up the relationship with the parent. Children can still feel care responsibility but also distrust and worry about relapses. However, teenagers can see opportunities to move on with their own life. If the abuse ends only for one of two parents with addiction problems, children are still affected by addiction. Conclusion: Children's need for processing in relation to the parents can both be time consuming and last for a long period of time, regardless of if the child lives with the parent or not. Children may need help for their own part but also in relation to the parent. Professionals should be encouraged to work with a family perspective, regardless of organizational divisions and if parents and children live together or not. This requires structures, procedures and resources for collaboration across organizational boundaries.

Infinite models for ciliary propulsion

1971 ◽  
Vol 49 (2) ◽  
pp. 209-222 ◽  
Author(s):  
J. R. Blake
Keyword(s):  
Wave Velocity ◽  
Small Amplitude ◽  
Maximum Velocity ◽  
Spherical Model ◽  
Infinite Length ◽  
Amplitude Analysis ◽  
Micro Organisms ◽  
Surface Covering

This paper discusses two infinite length models (planar and cylindrical) for ciliary propulsion of microscopic organisms. Through the concept of an extensible envelope (instantaneous surface covering the numerous cilia) over the organism, we consider a small amplitude analysis for the velocity of propulsion. A comparison of the velocities of propulsion for the infinite models reveals that they are just over twice that obtained for the finite spherical model (Blake 1971). This indicates that planeness is more important than finiteness, as the solution for typical micro-organisms (e.g. disk-shaped) should occur somewhere between these two models. The maximum velocity of propulsion obtained is one quarter of the wave velocity; that inferred for Opalina, the organism modelled, is nearly one fifth of the wave velocity. Associated shapes of the surface and paths of movement of the tips of the cilia are illustrated.

scholarly journals Structural Breaks and Explosive Behavior in the Long-Run: The Case of Australian Real House Prices, 1870–2020

2021 ◽  
Vol 15 (1) ◽  
pp. 72-84
Author(s):  
Vicente Esteve ◽  
Maria A. Prats
Keyword(s):  
Time Series ◽  
Unit Root ◽  
Structural Breaks ◽  
House Prices ◽  
Unit Root Tests ◽  
Annual Data ◽  
Bubble Behavior ◽  
Long Period ◽  
Long Run ◽  
Long Time

Abstract In this article, we use tests of explosive behavior in real house prices with annual data for the case of Australia for the period 1870–2020. The main contribution of this paper is the use of very long time series. It is important to use longer span data because it offers more powerful econometric results. To detect episodes of potential explosive behavior in house prices over this long period, we use the recursive unit root tests for explosiveness proposed by Phillips et al. (2011), (2015a,b). According to the results, there is a clear speculative bubble behavior in real house prices between 1997 and 2020, speculative process that has not yet been adjusted.

On the time periodic thermistor problem

2004 ◽  
Vol 15 (1) ◽  
pp. 55-77 ◽  
Author(s):  
WALTER ALLEGRETTO ◽  
YANPING LIN ◽  
SHUQING MA
Keyword(s):  
Periodic Solutions ◽  
Degree Theory ◽  
Time Behaviour ◽  
Uniform Attractor ◽  
Long Time Behaviour ◽  
Galerkin Approximations ◽  
Long Time ◽  
Finite Dimensionality ◽  
Time Periodic Solutions ◽  
Time Periodic

In this paper we study a nonlocal parabolic/elliptic system which models thermistor behaviour in cases where heat losses to the surrounding gas play a significant role. The existence of time periodic solutions for the system is established through Faedo-Galerkin approximations and the Leray–Schauder degree theory. We show that for the small gas pressure case, the temperature of the time periodic solutions is positive. Moreover we consider the long time behaviour of the system and prove the existence of a uniform attractor. Finally, the finite dimensionality of the attractor is discussed.

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