scholarly journals Formation of Kinneyia via shear-induced instabilities in microbial mats

2013 ◽  
Vol 371 (2004) ◽  
pp. 20120362 ◽  
Author(s):  
Katherine Thomas ◽  
Stephan Herminghaus ◽  
Hubertus Porada ◽  
Lucas Goehring
Keyword(s):  
Microbial Mats ◽  
Flow Speed ◽  
Glass Beads ◽  
Flowing Water ◽  
Flow Conditions ◽  
Theoretical Predictions ◽  
Laboratory Analogue ◽  
Littoral Habitats ◽  
Over Time ◽  
Ripple Pattern

Kinneyia are a class of microbially mediated sedimentary fossils. Characterized by clearly defined ripple structures, Kinneyia are generally found in areas that were formally littoral habitats and covered by microbial mats. To date, there has been no conclusive explanation of the processes involved in the formation of these fossils. Microbial mats behave like viscoelastic fluids. We propose that the key mechanism involved in the formation of Kinneyia is a Kelvin–Helmholtz-type instability induced in a viscoelastic film under flowing water. A ripple corrugation is spontaneously induced in the film and grows in amplitude over time. Theoretical predictions show that the ripple instability has a wavelength proportional to the thickness of the film. Experiments carried out using viscoelastic films confirm this prediction. The ripple pattern that forms has a wavelength roughly three times the thickness of the film. This behaviour is independent of the viscosity of the film and the flow conditions. Laboratory-analogue Kinneyia were formed via the sedimentation of glass beads, which preferentially deposit in the troughs of the ripples. Well-ordered patterns form, with both honeycomb-like and parallel ridges being observed, depending on the flow speed. These patterns correspond well with those found in Kinneyia, with similar morphologies, wavelengths and amplitudes being observed.

Differences in kinematic plasticity between freshwater turtle species underlie differences in swimming performance in response to varying flow conditions

2019 ◽  
Vol 127 (4) ◽  
pp. 762-770
Author(s):  
Christopher J Mayerl ◽  
Kirsten E Hicks ◽  
Richard W Blob
Keyword(s):  
Swimming Performance ◽  
Flow Speed ◽  
The Body ◽  
Freshwater Turtle ◽  
Behavioural Plasticity ◽  
Flowing Water ◽  
Freshwater Turtles ◽  
Flow Conditions ◽  
Turtle Species ◽  
And Performance

Abstract The distribution and performance of aquatic vertebrates can be linked strongly to their ability to perform in variable conditions of flowing water. Performance in these variable conditions can be affected by both morphology and behaviour, and animals that experience more variable environments often show greater behavioural plasticity that improves performance in those environments. One common metric of performance is swimming stability, which can constitute a majority of the daily energy budget of swimming animals. We compared the body oscillations arising from recoil forces of the limbs of two species of freshwater turtles as they swam in different flow conditions: the lentic specialist Emydura subglobosa and the habitat generalist Chrysemys picta. We found that E. subglobosa experienced more limited oscillations in still water than C. picta, but that C. picta had a greater kinematic response to increased flow speed that might contribute to their improved performance in flowing water. These results provide insight into how secondarily aquatic tetrapods respond to the functional demands of variation in flow, helping to build understanding of the relationship between energetics, kinematics and performance of such lineages in different environments.

Electrochemical Kinetic of a Low Carbon Steel in Seawater at Different Flow Speed

2015 ◽  
Vol 1766 ◽  
pp. 73-80
Author(s):  
A. Carmona ◽  
R. Orozco-Cruz ◽  
E. Mejía-Sánchez ◽  
A. Contreras ◽  
R. Galván-Martínez
Keyword(s):  
Turbulent Flow ◽  
Rotation Speed ◽  
Electrochemical Impedance ◽  
Static Condition ◽  
Flow Speed ◽  
Localized Corrosion ◽  
Low Carbon ◽  
Flow Conditions ◽  
Static Conditions ◽  
Turbulent Flow Conditions

ABSTRACTAn electrochemical impedance spectroscopy (EIS) corrosion study of API X70 steel was carried out in synthetic seawater with different rotation speeds using a rotating cylinder electrode (RCE) to control the hydrodynamic conditions at room temperature, atmospheric pressure and 24 h of exposure time. A superficial analysis through a scanning electron microscope (SEM) was used to analyze the corrosion type. The rotation speed used was 0 rpm (static condition), 1000, 3000 and 5000 rpm (turbulent flow). The results show that the turbulent flow conditions affect directly the corrosion rate (CR) of the steel, because all values of the CR under turbulent flow conditions are higher than the CR values at static conditions. In addition, it is important to point out that at turbulent flow conditions, the CR increased as the rotation speed also increased. The morphology of the corrosion in all experiments was localized corrosion.

scholarly journals An Experimental Study of Self-Enforcing Coalitions

Games ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 31 ◽  
Author(s):  
Karl Jandoc ◽  
Ruben Juarez
Keyword(s):  
Experimental Study ◽  
Coalition Formation ◽  
Rational Behavior ◽  
Behavioral Factors ◽  
Formation Model ◽  
Economic Experiment ◽  
Theoretical Predictions ◽  
Over Time

We study a model in which agents endowed with power compete for a divisible resource by forming coalitions with other agents. The coalition with the greatest power wins the resource and divides it among its members via proportional sharing. We conduct an economic experiment using this model to investigate possible behavioral factors that may explain deviations from theoretical predictions. The main findings show that agents display rational behavior when forming coalitions, especially when they know that a large proportion of their opponents play myopic strategies from the outset. Over time, however, agents learn to behave more strategically and even more rationally, thus enabling agents to display more of the behavior predicted by the coalition formation model with farsighted agents.

scholarly journals Quantifying epileptogenesis in rats with spontaneous and responsive brain state dynamics

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Dakota N Crisp ◽  
Warwick Cheung ◽  
Stephen V Gliske ◽  
Alan Lai ◽  
Dean R Freestone ◽  
...  
Keyword(s):  
Electrical Stimulation ◽  
Rat Model ◽  
Tetanus Toxin ◽  
Brain State ◽  
Induced Responses ◽  
Spontaneous Seizure ◽  
Seizure Onset ◽  
Theoretical Predictions ◽  
Over Time

Abstract There is a crucial need to identify biomarkers of epileptogenesis that will help predict later development of seizures. This work identifies two novel electrophysiological biomarkers that quantify epilepsy progression in a rat model of epileptogenesis. The long-term tetanus toxin rat model was used to show the development and remission of epilepsy over several weeks. We measured the response to periodic electrical stimulation and features of spontaneous seizure dynamics over several weeks. Both biomarkers showed dramatic changes during epileptogenesis. Electrically induced responses began to change several days before seizures began and continued to change until seizures resolved. These changes were consistent across animals and allowed development of an algorithm that could differentiate which animals would later develop epilepsy. Once seizures began, there was a progression of seizure dynamics that closely follows recent theoretical predictions, suggesting that the underlying brain state was changing over time. This research demonstrates that induced electrical responses and seizure onset dynamics are useful biomarkers to quantify dynamical changes in epileptogenesis. These tools hold promise for robust quantification of the underlying epileptogenicity and prediction of later development of seizures.

Appointments and attrition: time and executive disadvantage in the appointments process

2019 ◽  
Vol 40 (3) ◽  
pp. 473-491
Author(s):  
Gary E. Hollibaugh ◽  
Lawrence S. Rothenberg
Keyword(s):  
Empirical Analysis ◽  
Theoretical Predictions ◽  
Political Appointments ◽  
The Relationship ◽  
Over Time

AbstractWhile the importance of political appointments is a matter of consensus, theorists and empiricists generally focus on different considerations, such as ideology and confirmation duration, respectively. More recently, there have been efforts to integrate empirical and theoretical scholarship but, to date, no empirical analysis assesses theoretical expectations about the relationship between temporal concerns and nominee ideologies. We fill this gap by examining theoretical predictions and related expectations about how the passage of time affects the President’s choices of nominees. We find that executives are disadvantaged as days pass and Presidents propose nominees with whom they are less ideologically compatible over time.

scholarly journals Structures, Compositions, and Activities of Live Shewanella Biofilms Formed on Graphite Electrodes in Electrochemical Flow Cells

2017 ◽  
Vol 83 (17) ◽  
Author(s):  
Miho Kitayama ◽  
Ryota Koga ◽  
Takuya Kasai ◽  
Atsushi Kouzuma ◽  
Kazuya Watanabe
Keyword(s):  
Wastewater Treatment ◽  
Water Flow ◽  
Biofilm Formation ◽  
Shewanella Oneidensis ◽  
Flow Conditions ◽  
Current Generation ◽  
Content Type ◽  
Flow Cells ◽  
Electrode Potentials ◽  
Over Time

ABSTRACT An electrochemical flow cell equipped with a graphite working electrode (WE) at the bottom was inoculated with Shewanella oneidensis MR-1 expressing an anaerobic fluorescent protein, and biofilm formation on the WE was observed over time during current generation at WE potentials of +0.4 and 0 V (versus standard hydrogen electrodes), under electrolyte-flow conditions. Electrochemical analyses suggested the presence of unique electron-transfer mechanisms in the +0.4-V biofilm. Microscopic analyses revealed that, in contrast to aerobic biofilms, current-generating biofilm (at +0.4 V) was thin and flat (∼10 μm in thickness), and cells were evenly and densely distributed in the biofilm. In contrast, cells were unevenly distributed in biofilm formed at 0 V. In situ fluorescence staining and biofilm recovery experiments showed that the amounts of extracellular polysaccharides (EPSs) in the +0.4-V biofilm were much smaller than those in the aerobic and 0-V biofilms, suggesting that Shewanella cells suppress the production of EPSs at +0.4 V under flow conditions. We suggest that Shewanella cells perceive electrode potentials and modulate the structure and composition of biofilms to efficiently transfer electrons to electrodes. IMPORTANCE A promising application of microbial fuel cells (MFCs) is to save energy in wastewater treatment. Since current is generated in these MFCs by biofilm microbes under horizontal flows of wastewater, it is important to understand the mechanisms for biofilm formation and current generation under water-flow conditions. Although massive work has been done to analyze the molecular mechanisms for current generation by model exoelectrogenic bacteria, such as Shewanella oneidensis, limited information is available regarding the formation of current-generating biofilms over time under water-flow conditions. The present study developed electrochemical flow cells and used them to examine the electrochemical and structural features of current-generating biofilms under water-flow conditions. We show unique features of mature biofilms actively generating current, creating opportunities to search for as-yet-undiscovered current-generating mechanisms in Shewanella biofilms. Furthermore, information provided in the present study is useful for researchers attempting to develop anode architectures suitable for wastewater treatment MFCs.

scholarly journals Microbial mats as shelter microhabitat for amphipods in an intermittent karstic spring

2018 ◽  
pp. 7 ◽  
Author(s):  
Petar Žutinić ◽  
Ines Petrić ◽  
Sanja Gottstein ◽  
Marija Gligora Udovič ◽  
Koraljka Kralj Borojević ◽  
...  
Keyword(s):  
Microbial Mats ◽  
High Water ◽  
Microbial Mat ◽  
Flow Conditions ◽  
Temporary Stream ◽  
Strong Current ◽  
Cyanobacterial Species ◽  
Animal Activity ◽  
Winter Sample ◽  
Representative Samples

Microbial mats represent complex communities where cyanobacteria and diatoms as key organisms provide shelter for diverse assemblages of aquatic invertebrates, like the small stygophilous amphipod Synurella ambulans. Studies addressing such communities in the karst springs have rarely examined springheads, and have ignored intermittent springs. During high flow conditions the stygophilic crustaceans are flushed to the surface of a temporary stream Krčić where microbial mats prevent their drift and enables their successful retreat into underground in the periods of drought. The objective of this study was to characterize the microbial mat community of the Krčić Spring as a shelter for S. ambulans during strong current and high water level. Representative samples for diatom and cyanobacterial species identification and composition, as well as the fresh mat material for potential animal activity and cyanobacterial phylogenetic analysis were collected. The most dominant diatom was Achnanthidium minutissimum, whilst Fragilaria capucina, Meridion circulare, Navicula cryptocephala and Nitzschia palea had abundance greater than 0.5%. Morphological observations of cyanobacteria revealed that Phormidium favosum was the most dominant, with Hydrocoleum muscicola as a subdominant. Cyanobacterial phylogenetic relationship revealed two distinct clusters: (i) "Phormidium cluster", confirming morphological observations in both winter and spring samples, and (ii) "Wilmottia cluster", a first report for Croatia and found exclusively in the winter sample. Laboratory observations revealed a small stygophilic amphipod S. ambulans, hiding and feeding inside the pockets of fresh microbial mat. The intermittent Krčić Spring as a predator-free and competitor-free ecosystem provides a spatiotemporal conformity between microbial mat and stygophilous amphipod.

Flutter and long-wave instabilities in compliant channels conveying developing flows

1997 ◽  
Vol 331 ◽  
pp. 37-58 ◽  
Author(s):  
P. G. LAROSE ◽  
J. B. GROTBERG
Keyword(s):  
Flow Speed ◽  
Infinite Length ◽  
Wave Instability ◽  
Flutter Instability ◽  
Long Wave ◽  
Developing Flow ◽  
Theoretical Predictions ◽  
Parameter Values ◽  
Correction Terms ◽  
Special Parameter

A partially collapsed lung airway or other flexible tube is modelled as a two-dimensional channel of infinite length. We consider the linear stability of this system conveying a developing flow, analysing the full Orr–Sommerfeld system analytically for long waves and numerically for arbitrary wavelengths. We find a long-wave instability which has not been observed in previous channel studies. This long-wave instability is stabilized by increasing the elastance of the wall, but other wall properties do not affect it except in correction terms. In addition to the long-wave instability, there is the finite wavelength (flutter) instability, which, depending on the parameter values chosen, may be critical at a higher or lower flow speed than the long-wave instability. For special parameter values the long-wave and flutter instabilities are critical at the same flow speed. Comparisons with experiments show that theoretical predictions are in agreement with experimental observations.

Larval Settlement of Corals in Flowing Water using a Racetrack Flume

2002 ◽  
Vol 36 (1) ◽  
pp. 76-79 ◽  
Author(s):  
S. Harii ◽  
H. Kayanne
Keyword(s):  
Reef Flat ◽  
Marine Invertebrates ◽  
Larval Settlement ◽  
Flow Speed ◽  
Flowing Water ◽  
Pocillopora Damicornis ◽  
Settlement Rate ◽  
Ishigaki Island ◽  
Digitally Controlled ◽  
Flow Speeds

Although the larvae of marine invertebrates settle in currents, few studies have examined settlement under flow. We studied the settlement of two brooding coral larvae with different behavior in a flow using a small racetrack flume made of polycarbonate and acrylic (58 cm long). Flow was generated using a digitally controlled gear-motor-driven paddle wheel. The settlement rates of the larvae, Heliopora coerulea and Pocillopora damicornis, were observed at three flow speeds: 1.6, 4.4, and 9.8 cm/sec, which correspond to the currents at low, mean, and ebb or flood tides, respectively, at Shiraho Reef flat, Ishigaki Island, Japan. The settlement rate of H. coerulea larvae decreased with increasing flow speed (20% at 1.6 cm/sec, 2% at 9.8 cm/sec). In contrast, the settlement rate of P. damicornis larvae was high at all flow speeds (> 50% at all flow speeds). This difference in the larval settlement rates of the two species is in accordance with the current conditions in which the adult corals are distributed.

Flow Conditions at the Inlet of Aspirating Pipes: Part 1—Theory

2010 ◽  
Author(s):  
Franc¸ois Axisa
Keyword(s):  
Degrees Of Freedom ◽  
Dynamical Behavior ◽  
Companion Paper ◽  
Low Flow ◽  
Flow Conditions ◽  
Test Loop ◽  
Theoretical Predictions ◽  
System 2 ◽  
System 1 ◽  
Flow Case

Drastic changes occur in the dynamics of pipes conveying fluid when passing from the discharging flow case to the aspirating flow case. This can be attributed to modifications in the flow conditions which prevail at the aspirating tube inlet versus those prevailing at a discharging tube outlet. In the present paper the point is investigated in relation with the behavior of two elementary systems, namely a single degree of freedom system (1-DOF oscillator) made of a rigid pipe supported at one end by a rotational spring and a two degrees of freedom system (2-DOF coupled oscillators) made of a pair of articulated tubes. In the first system, flow-structure coupling reduces essentially to a Coriolis force while in the second, it arises via both centrifugal and Coriolis forces. The present paper is devoted to theoretical modeling and prediction of the dynamical behavior of these systems according to a few basic assumptions concerning the flow conditions at the aspirating inlet. It serves as an introduction to the companion paper by Debut et al. [1] where theoretical predictions are confronted to experiment. As a major result it is found that even “small changes” in the flow conditions at the aspirating inlet can lead to important changes in the tube dynamics which are amenable to measurement, even if the experiments are restricted to relatively low flow velocities because of limited capacity of the test loop.

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