scholarly journals Hydrodynamic model of fish orientation in a channel flow

2021 ◽  
Author(s):  
Maurizio Porfiri ◽  
Peng Zhang ◽  
Sean D. Peterson
Keyword(s):  
Flow Speed ◽  
Hydrodynamic Interactions ◽  
Critical Flow ◽  
Incoming Flow ◽  
Background Flow ◽  
Essential Step ◽  
Vortex Dipole ◽  
Model Predictions ◽  
Surrounding Fluid

For over a century, scientists have sought to understand how fish orient against an incoming flow, even without visual and flow cues. Here, we make an essential step to elucidate the hydrodynamic underpinnings of rheotaxis through the study of the bidirectional coupling between fish and the surrounding fluid. By modeling a fish as a vortex dipole in an infinite channel with an imposed background flow, we establish a planar dynamical system for the cross-stream coordinate and orientation. The system dynamics captures the existence of a critical flow speed for fish to successfully orient while performing cross-stream, periodic sweeping movements. Model predictions are validated against experimental observations in the literature on the rheotactic behavior of fish deprived of visual and lateral line cues. The crucial role of bidirectional hydrodynamic interactions unveiled by this model points at an overlooked limitation of existing experimental paradigms to study rheotaxis in the laboratory.

scholarly journals Hydrodynamics can determine the optimal route for microswimmer navigation

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Abdallah Daddi-Moussa-Ider ◽  
Hartmut Löwen ◽  
Benno Liebchen
Keyword(s):  
Flow Field ◽  
Hydrodynamic Interactions ◽  
Optimal Trajectories ◽  
Optimal Route ◽  
Active Particles ◽  
Navigation Strategy ◽  
Navigation Strategies

AbstractAs compared to the well explored problem of how to steer a macroscopic agent, like an airplane or a moon lander, to optimally reach a target, optimal navigation strategies for microswimmers experiencing hydrodynamic interactions with walls and obstacles are far-less understood. Here, we systematically explore this problem and show that the characteristic microswimmer-flow-field crucially influences the navigation strategy required to reach a target in the fastest way. The resulting optimal trajectories can have remarkable and non-intuitive shapes, which qualitatively differ from those of dry active particles or motile macroagents. Our results provide insights into the role of hydrodynamics and fluctuations on optimal navigation at the microscale, and suggest that microorganisms might have survival advantages when strategically controlling their distance to remote walls.

scholarly journals Including the animal standpoint in critical public relations research

2021 ◽  
Vol 10 (2) ◽  
pp. 139-161
Author(s):  
Núria Almiron ◽  
Laura Fernández
Keyword(s):  
Political Economy ◽  
Public Relations ◽  
Animal Studies ◽  
Critical Animal Studies ◽  
Essential Step ◽  
Challenges And Opportunities ◽  
Discourse Studies ◽  
Theoretical Paper ◽  
Short Explanation

In this paper we argue that adopting critical animal studies perspectives in critical public relations can not only be very fruitful, but that it is also a necessity if the aims of the latter are to be achieved. To this end, this text introduces the challenges and opportunities that the field of critical animal studies brings to critical public relations studies. First, a short explanation of what critical animal studies is and why it can contribute to critical public relations studies is provided. Then the main fields of research where this contribution can be most relevant are discussed, including ethics, discourse studies and political economy. The final aim of this theoretical paper is to expand research within the field of critical public relations by including a critical animal studies approach. Eventually, the authors suggest that embracing the animal standpoint in critical public relations is an essential step to furthering the study of power, hegemony, ideology, propaganda or social change and to accomplishing the emancipatory role of research.

scholarly journals Role of Shearing Dispersion and Stripping in Wax Deposition in Crude Oil Pipelines

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4325
Author(s):  
Zhihua Wang ◽  
Yunfei Xu ◽  
Yi Zhao ◽  
Zhimin Li ◽  
Yang Liu ◽  
...  
Keyword(s):  
Crude Oil ◽  
Flow Rate ◽  
Critical Flow ◽  
Wax Deposition ◽  
Dominant Effect ◽  
Critical Flow Rate ◽  
Oil Pipelines ◽  
Oil Flow ◽  
Shearing Mechanism

Wax deposition during crude oil transmission can cause a series of negative effects and lead to problems associated with pipeline safety. A considerable number of previous works have investigated the wax deposition mechanism, inhibition technology, and remediation methods. However, studies on the shearing mechanism of wax deposition have focused largely on the characterization of this phenomena. The role of the shearing mechanism on wax deposition has not been completely clarified. This mechanism can be divided into the shearing dispersion effect caused by radial migration of wax particles and the shearing stripping effect caused by hydrodynamic scouring. From the perspective of energy analysis, a novel wax deposition model was proposed that considered the flow parameters of waxy crude oil in pipelines instead of its rheological parameters. Considering the two effects of shearing dispersion and shearing stripping coexist, with either one of them being the dominant mechanism, a shearing dispersion flux model and a shearing stripping model were established. Furthermore, a quantitative method to distinguish between the roles of shearing dispersion and shearing stripping in wax deposition was developed. The results indicated that the shearing mechanism can contribute an average of approximately 10% and a maximum of nearly 30% to the wax deposition process. With an increase in the oil flow rate, the effect of the shearing mechanism on wax deposition is enhanced, and its contribution was demonstrated to be negative; shear stripping was observed to be the dominant mechanism. A critical flow rate was observed when the dominant effect changes. When the oil flow rate is lower than the critical flow rate, the shearing dispersion effect is the dominant effect; its contribution rate increases with an increase in the oil flow temperature. When the oil flow rate is higher than the critical flow rate, the shearing stripping effect is the dominant effect; its contribution rate increases with an increase in the oil flow temperature. This understanding can be used to design operational parameters of the actual crude oil pipelines and address the potential flow assurance problems. The results of this study are of great significance for understanding the wax deposition theory of crude oil and accelerating the development of petroleum industry pipelines.

Near-Wall Microlayer Evaporation Analysis and Experimental Study of Nucleate Pool Boiling on Inclined Surfaces

1998 ◽  
Vol 120 (3) ◽  
pp. 641-653 ◽  
Author(s):  
G. F. Naterer ◽  
W. Hendradjit ◽  
K. J. Ahn ◽  
J. E. S. Venart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Inclined Surfaces ◽  
Wide Range ◽  
Model Predictions ◽  
Microlayer Evaporation ◽  
Near Wall

Boiling heat transfer from inclined surfaces is examined and an analytical model of bubble growth and nucleate boiling is presented. The model predicts the average heat flux during nucleate boiling by considering alternating near-wall liquid and vapor periods. It expresses the heat flux in terms of the bubble departure diameter, frequency and duration of contact with the heating surface. Experiments were conducted over a wide range of upward and downward-facing surface orientations and the results were compared to model predictions. More active microlayer agitation and mixing along the surface as well as more frequent bubble sweeps along the heating surface provide the key reasons for more effective heat transfer with downward facing surfaces as compared to upward facing cases. Additional aspects of the role of surface inclination on boiling dynamics are quantified and discussed.

Ypsilon Schachtel, aDrosophilaY-box protein, acts antagonistically to Orb in theoskarmRNA localization and translation pathway

Development ◽  
2002 ◽  
Vol 129 (1) ◽  
pp. 197-209 ◽  
Author(s):  
Jennifer H. Mansfield ◽  
James E. Wilhelm ◽  
Tulle Hazelrigg
Keyword(s):  
Subcellular Localization ◽  
Essential Role ◽  
Genetic Interaction ◽  
Mrna Localization ◽  
Rna Localization ◽  
Essential Step ◽  
Positive Regulator ◽  
Body Patterning ◽  
Translational Regulators

Subcellular localization of mRNAs within the Drosophila oocyte is an essential step in body patterning. Yps, a Drosophila Y-box protein, is a component of an ovarian ribonucleoprotein complex that also contains Exu, a protein that plays an essential role in mRNA localization. Y-box proteins are known translational regulators, suggesting that this complex might regulate translation as well as mRNA localization. Here we examine the role of the yps gene in these events. We show that yps interacts genetically with orb, a positive regulator of oskar mRNA localization and translation. The nature of the genetic interaction indicates that yps acts antagonistically to orb. We demonstrate that Orb protein is physically associated with both the Yps and Exu proteins, and that this interaction is mediated by RNA. We propose a model wherein Yps and Orb bind competitively to oskar mRNA with opposite effects on translation and RNA localization.

Dynamics of polymers in solution: the role of time-dependent hydrodynamic interactions

1991 ◽  
Vol 24 (22) ◽  
pp. 5997-6005 ◽  
Author(s):  
J. Bonet Avalos ◽  
J. M. Rubi ◽  
D. Bedeaux
Keyword(s):  
Time Dependent ◽  
Hydrodynamic Interactions

The Propagation Mechanism of a Vortex on the β Plane

2007 ◽  
Vol 37 (9) ◽  
pp. 2316-2330 ◽  
Author(s):  
Peter Jan van Leeuwen
Keyword(s):  
Coriolis Force ◽  
Opposite Sign ◽  
Propagation Mechanism ◽  
Reduced Gravity ◽  
Background Current ◽  
Background Flow ◽  
Coriolis Parameter ◽  
First Order ◽  
Flow Changes

Abstract The propagation velocity and propagation mechanism for vortices on a β plane are determined for a reduced-gravity model by integrating the momentum equations over the β plane. Isolated vortices, vortices in a background current, and initial vortex propagation from rest are studied. The propagation mechanism for isolated anticyclones as well as cyclones, which has been lacking up to now, is presented. It is shown that, to first order, the vortex moves to generate a Coriolis force on the mass anomaly of the vortex to compensate for the force on the vortex due to the variation of the Coriolis parameter. Only the mass anomaly of the vortex is of importance, because the Coriolis force due to the motion of the bulk of the layer moving with the vortex is almost fully compensated by the Coriolis force on the motion of the exterior flow. Because the mass anomaly of a cyclone is negative the force and acceleration have opposite sign. The role of dipolar structures in steadily moving vortices is discussed, and it is shown that their overall structure is fixed by the steady westward motion of the mass anomaly. Furthermore, it is shown that reduced-gravity vortices are not advected with a background flow. The reason for this behavior is that the background flow changes the ambient vorticity gradient such that the vortex obtains an extra self-propagation term that exactly cancels the advection by the background flow. Last, it is shown that a vortex initially at rest will accelerate equatorward first, after which a westward motion is generated. This result is independent of the sign of the vortex.

scholarly journals Hotspots of boundary accumulation: dynamics and statistics of micro-swimmers in flowing films

2016 ◽  
Vol 13 (115) ◽  
pp. 20150936 ◽  
Author(s):  
Arnold J. T. M. Mathijssen ◽  
Amin Doostmohammadi ◽  
Julia M. Yeomans ◽  
Tyler N. Shendruk
Keyword(s):  
Solid Wall ◽  
Critical Value ◽  
Hydrodynamic Interactions ◽  
Critical Flow ◽  
Natural Environments ◽  
Flow Strength ◽  
Surfaces And Interfaces ◽  
Biological Flows ◽  
The Impact ◽  
Systematic Framework

Biological flows over surfaces and interfaces can result in accumulation hotspots or depleted voids of microorganisms in natural environments. Apprehending the mechanisms that lead to such distributions is essential for understanding biofilm initiation. Using a systematic framework, we resolve the dynamics and statistics of swimming microbes within flowing films, considering the impact of confinement through steric and hydrodynamic interactions, flow and motility, along with Brownian and run–tumble fluctuations. Micro-swimmers can be peeled off the solid wall above a critical flow strength. However, the interplay of flow and fluctuations causes organisms to migrate back towards the wall above a secondary critical value. Hence, faster flows may not always be the most efficacious strategy to discourage biofilm initiation. Moreover, we find run–tumble dynamics commonly used by flagellated microbes to be an intrinsically more successful strategy to escape from boundaries than equivalent levels of enhanced Brownian noise in ciliated organisms.

Study on the Bubble Dynamics and the Exciting Force in a Bended Pipe Based on BEM

2016 ◽  
Author(s):  
Y. L. Liu ◽  
Z. L. Tian
Keyword(s):  
Numerical Model ◽  
Potential Theory ◽  
Bubble Dynamics ◽  
Flow Speed ◽  
Exciting Force ◽  
Incoming Flow ◽  
Bubble Motion ◽  
Dynamics Model ◽  
Pipe Surface ◽  
Direction Change

Nonlinear bubble dynamics in a pipeline and its exciting force are investigated by a numerical model based on BEM. The bubble motion is one of the main causes that the pipeline vibrates and generates noise in modern ships. The numerical bubble dynamics model is established under the incompressible potential theory. Bubble motion with different incoming flow in a bended pipe is simulated. We found that the bubble develops jet when it passes by the bend, and adjoin to the pipe surface in the side of the fillet center. The pulsation and the direction change of the bubble apply an exciting force on the pipe which has a positive correlation with the incoming flow speed and may lead vibration and noise.

scholarly journals Nonlinear Convective Pulsation Models of Second Overtone SMC Cepheids

2002 ◽  
Vol 185 ◽  
pp. 420-423
Author(s):  
M. Marconi ◽  
G. Bono ◽  
F. Caputo
Keyword(s):  
Short Distance ◽  
Selection Criteria ◽  
Distance Scale ◽  
Model Predictions ◽  
Distance Indicators

AbstractNonlinear convective pulsation models representative of SMC Cepheids pulsating in the second overtone mode are presented. Model predictions are compared with observations and implications are derived for second overtone selection criteria. The role of overtone Cepheids as distance indicators is finally investigated and the derived distance scale is at odds with the so called short distance scale.

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