scholarly journals Viscous propulsion in active transversely isotropic media

2017 ◽  
Vol 812 ◽  
pp. 501-524 ◽  
Author(s):  
G. Cupples ◽  
R. J. Dyson ◽  
D. J. Smith
Keyword(s):  
Biological Fluids ◽  
Classical Model ◽  
Transversely Isotropic ◽  
Rheological Parameters ◽  
Energetic Cost ◽  
Swimming Velocity ◽  
Preferred Direction ◽  
The Mean ◽  
Initial Fibre ◽  
Isotropic Fluid

Taylor’s swimming sheet is a classical model of microscale propulsion and pumping. Many biological fluids and substances are fibrous, having a preferred direction in their microstructure; for example, cervical mucus is formed of polymer molecules which create an oriented fibrous network. Moreover, suspensions of elongated motile cells produce a form of active oriented matter. To understand how these effects modify viscous propulsion, we extend Taylor’s classical model of small-amplitude zero-Reynolds-number propulsion of a ‘swimming sheet’ via the transversely isotropic fluid model of Ericksen, which is linear in strain rate and possesses a distinguished direction. The energetic costs of swimming are significantly altered by all rheological parameters and the initial fibre angle. Propulsion in a passive transversely isotropic fluid produces an enhanced mean rate of working, independent of the initial fibre orientation, with an approximately linear dependence of the energetic cost on the extensional and shear enhancements to the viscosity caused by fibres. In this regime, the mean swimming velocity is unchanged from the Newtonian case. The effect of the constant term in Ericksen’s model for the stress, which can be identified as a fibre tension or alternatively a stresslet characterising an active fluid, is also considered. This stress introduces an angular dependence and dramatically changes the streamlines and flow field; fibres aligned with the swimming direction increase the energetic demands of the sheet. The constant fibre stress may result in a reversal of the mean swimming velocity and a negative mean rate of working if it is sufficiently large relative to the other rheological parameters.

scholarly journals Linear Taylor–Couette stability of a transversely isotropic fluid

2015 ◽  
Vol 471 (2178) ◽  
pp. 20150141 ◽  
Author(s):  
C. R. Holloway ◽  
R. J. Dyson ◽  
D. J. Smith
Keyword(s):  
Viscous Fluid ◽  
Shear Viscosity ◽  
Outer Cylinder ◽  
Transversely Isotropic ◽  
Biological Molecules ◽  
Preferred Direction ◽  
Stable Operating ◽  
Gap Width ◽  
Operating Regimes ◽  
Isotropic Fluid

Fibre-laden fluids are found in a variety of situations, while Couette devices are used for flow spectroscopy of long biological molecules, such as DNA and proteins in suspension. The presence of these fibres can significantly alter the rheology of the fluid, and hence must be incorporated in any modelling undertaken. A transversely isotropic fluid treats these suspensions as a continuum with an evolving preferred direction, through a modified stress tensor incorporating four viscosity-like parameters. We consider the axisymmetric linear stability of a transversely isotropic viscous fluid, contained between two rotating co-axial cylinders, and determine the critical wave and Taylor numbers for varying gap width and inner cylinder velocity (assuming the outer cylinder is fixed). Through the inclusion of transversely isotropic effects, the onset of instability is delayed, increasing the range of stable operating regimes. This effect is felt most strongly through incorporation of the anisotropic shear viscosity, although the anisotropic extensional viscosity also contributes. The changes to the rheology induced by the presence of the fibres therefore significantly alter the dynamics of the system, and hence should not be neglected.

scholarly journals Linear Rayleigh–Bénard stability of a transversely isotropic fluid

2018 ◽  
Vol 30 (04) ◽  
pp. 659-681 ◽  
Author(s):  
C. R. HOLLOWAY ◽  
D. J. SMITH ◽  
R. J. DYSON
Keyword(s):  
Lower Boundary ◽  
Transversely Isotropic ◽  
Marginal Stability ◽  
Preferred Direction ◽  
Higher Temperature ◽  
Fluid Rheology ◽  
Rayleigh Benard Convection ◽  
Rayleigh Numbers ◽  
Rayleigh Benard ◽  
Isotropic Fluid

Suspended fibres significantly alter fluid rheology, as exhibited in for example solutions of DNA, RNA and synthetic biological nanofibres. It is of interest to determine how this altered rheology affects flow stability. Motivated by the fact thermal gradients may occur in biomolecular analytic devices, and recent stability results, we examine the problem of Rayleigh–Bénard convection of the transversely isotropic fluid of Ericksen. A transversely isotropic fluid treats these suspensions as a continuum with an evolving preferred direction, through a modified stress tensor incorporating four viscosity-like parameters. We consider the linear stability of a stationary, passive, transversely isotropic fluid contained between two parallel boundaries, with the lower boundary at a higher temperature than the upper. To determine the marginal stability curves the Chebyshev collocation method is applied, and we consider a range of initially uniform preferred directions, from horizontal to vertical, and three orders of magnitude in the viscosity-like anisotropic parameters. Determining the critical wave and Rayleigh numbers, we find that transversely isotropic effects delay the onset of instability; this effect is felt most strongly through the incorporation of the anisotropic shear viscosity, although the anisotropic extensional viscosity also contributes. Our analysis confirms the importance of anisotropic rheology in the setting of convection.

The effects of metabolic inhibitors on the contraction of creatine-depleted muscle

1982 ◽  
Vol 60 (2) ◽  
pp. 114-119 ◽  
Author(s):  
G. W. Mainwood ◽  
M. Alward ◽  
B. Eiselt
Keyword(s):  
Creatine Phosphate ◽  
Diaphragm Muscle ◽  
Metabolic Inhibitors ◽  
Energetic Cost ◽  
Energy Reserves ◽  
Similar Extent ◽  
Additional Energy ◽  
Energy Stores ◽  
Wet Weight ◽  
The Mean

Rats were fed on a diet containing 1% β-guanidinopropionate (Gp) to deplete their muscles of creatine. The apparent energy reserves (creatine phosphate (CrP) + ATP) of rested state diaphragm muscle strips were found to be 79% depleted by this treatment. To determine if the effective energy reserves for contraction were depleted to a similar extent, the response to direct electrical stimulation (0.2-s tetani) was measured in the presence of inhibitors of respiration (NaCN) and glycolysis (iodoacetate). Only 4 ± 1 contractions could be elicited from strips from Gp-fed animals. Normal strips gave 15 ± 2 contractions under the same conditions. For both sets of diaphragms the energetic cost of contraction in terms of ~P was approximately 1 μmol/g wet weight. The mean level of Pi generated following stimulation to exhaustion was 10.1 μmol/g more in normal than in depleted strips. It is concluded that no significant additional energy stores such as phosphorylated Gp are readily available for contraction in muscles depleted of creatine by Gp treatment.

scholarly journals Impact of systemic cryotherapy on the rheological properties of the blood in women with rheumatoid arthritis

2017 ◽  
Vol 21 (2) ◽  
pp. 4-9
Author(s):  
Bartłomiej Ptaszek ◽  
Aneta Teległów ◽  
Jakub Marchewka
Keyword(s):  
Rheumatoid Arthritis ◽  
Rheological Properties ◽  
Treatment Time ◽  
Venous Blood ◽  
Body Height ◽  
Rheological Parameters ◽  
Study Group ◽  
Mean Values ◽  
Chamber Temperature ◽  
The Mean

Study aim: The aim of this study was to assess the effects of systemic cryotherapy on the rheological properties of the blood in women with rheumatoid arthritis. Study group: The study group consisted of 10 women with rheumatoid arthritis, aged 57.2 ± 9.4, who underwent systemic cryotherapy treatments (3 min treatment time, -120 °C chamber temperature, 10 treatment sessions - 5 times a week). Their average body height was 165.5 ± 4.6 cm, weight 68.5 ± 4.9 kg and BMI 24.8 ± 2.2 kg/m2. In order to analyze morphological and rheological parameters of the blood, venous blood samples were drawn from the participants of the study twice. The first study was held on the day of beginning treatments and the second test was conducted after a series of 10 treatments. Methodology: The morphological blood test - measurements were taken using the ABX MICROS 60 (USA) hematology analyser. Erythrocyte deformability and aggregation were tested using the LORCA analyser (Laser-assisted Optical Rotational Cell Analyser RR Mechatronics, The Netherlands). The results were obtained as the index of elongation and aggregation according to the Hardeman method (2001). Results: Analysing the average values of morphological and rheological parameters of the blood in women with rheumatoid arthritis in the study group, the mean values of RBC, Hct and AI following the series of 10 treatments were significantly higher after cryotherapy in comparison to the measurements taken before treatments. Analysing the mean concentrations of T½, there was statistically significant reduction after the series of 10 treatments. Conclusions: Regular usage of cryotherapy treatments may affect the levels of morphological and rheological parameters of the blood in women with rheumatoid arthritis - RBC, Hct and AI (increase) and T½ (reduction) in the blood. null

Mean Lifetime of an Embryo in the Homogeneous Nucleation from Solution of the Tetracyanoplatinates(II) of Barium, Calcium, and Magnesium

1973 ◽  
Vol 51 (20) ◽  
pp. 3435-3442 ◽  
Author(s):  
O. A. Bempah ◽  
O. E. Hileman Jr.
Keyword(s):  
Homogeneous Nucleation ◽  
Silicone Oil ◽  
Classical Model ◽  
Selective Extraction ◽  
Supersaturation Ratio ◽  
Mean Lifetime ◽  
High Supersaturation ◽  
The Mean ◽  
Calcium And Magnesium ◽  
Oil Crystallization

The mean lifetime of an embryo in the homogeneous nucleation from aqueous solution of the tetracyanoplatinates(II) of barium, calcium, and magnesium has been studied using the droplet technique. Supersaturation in the droplets was generated by selective extraction of the solvent into the surrounding silicone oil. Crystallization in the droplets was followed by photomicrography using plane polarized light.The data were analyzed using both the classical model and the mean lifetime model of Carlier and Frisch. The experimental results are consistent with the predicted relationship between the logarithm of the nucleation rate or the logarithm of the mean lifetime of an embryo and the inverse of the square of the logarithm of the supersaturation ratio at high supersaturation ratios. The calculated values of the inter-facial energy, using both models, are in close enough agreement to justify the assumptions made in the analysis.

Activity-related constraints on overwintering young-of-the-year striped bass (Morone saxatilis)

2001 ◽  
Vol 79 (1) ◽  
pp. 129-136 ◽  
Author(s):  
Thomas P Hurst ◽  
David O Conover
Keyword(s):  
Food Consumption ◽  
Striped Bass ◽  
Morone Saxatilis ◽  
Metabolic Cost ◽  
Hudson River ◽  
Energetic Cost ◽  
Energy Budgets ◽  
Swimming Velocity ◽  
Thermal Dependence ◽  
Young Of The Year

The importance of activity to overwintering fishes has received little attention. Activity imposes two constraints: maximum swimming speed limits habitats that can be occupied for short periods of time, while the metabolic cost of swimming limits the habitats that are suitable for long-term residence. We measured the energetic consequences of activity and maximum swimming speeds of young-of-the-year striped bass (Morone saxatilis), a species that overwinters in tidal estuaries. The energetic cost of swimming was determined from energy changes in unfed fish forced to swim at various speeds, while energy changes in fed fish provided a measure of their ability to offset swimming costs through feeding. In high-velocity treatments, mortality was size-dependent and appeared to be related to fatigue rather than to depletion of energy reserves. The energetic cost of swimming increased with swimming velocity, but fish increased food consumption and thereby met their metabolic needs. In a second experiment the thermal dependence of swimming capacity in winter-acclimated striped bass was measured. Swimming speeds increased with temperature, from 2.7 body lengths (BL)/s at 2°C to 4.8 BL/s at 8 and 11°C, but were considerably below observed flow velocities in the Hudson River, suggesting a need for behavioral or physical refuge from tidal currents. These results indicate the flexibility of energy budgets of overwintering fishes, allowing energetic stress to be minimized by reducing activity or elevating food-consumption rates when sufficient prey are available.

Dynamical Organization of Directional Tuning in the Primate Premotor and Primary Motor Cortex

2003 ◽  
Vol 89 (2) ◽  
pp. 1136-1142 ◽  
Author(s):  
Yoram Ben-Shaul ◽  
Eran Stark ◽  
Itay Asher ◽  
Rotem Drori ◽  
Zoltan Nadasdy ◽  
...  
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Hand Movement ◽  
Movement Direction ◽  
Cortical Surface ◽  
Preferred Direction ◽  
Preparation Period ◽  
Direction Of Movement ◽  
The Mean ◽  
Movement Parameters

Although previous studies have shown that activity of neurons in the motor cortex is related to various movement parameters, including the direction of movement, the spatial pattern by which these parameters are represented is still unresolved. The current work was designed to study the pattern of representation of the preferred direction (PD) of hand movement over the cortical surface. By studying pairwise PD differences, and by applying a novel implementation of the circular variance during preparation and movement periods in the context of a center-out task, we demonstrate a nonrandom distribution of PDs over the premotor and motor cortical surface of two monkeys. Our analysis shows that, whereas PDs of units recorded by nonadjacent electrodes are not more similar than expected by chance, PDs of units recorded by adjacent electrodes are. PDs of units recorded by a single electrode display the greatest similarity. Comparison of PD distributions during preparation and movement reveals that PDs of nearby units tend to be more similar during the preparation period. However, even for pairs of units recorded by a single electrode, the mean PD difference is typically large (45° and 75° during preparation and movement, respectively), so that a strictly modular representation of hand movement direction over the cortical surface is not supported by our data.

scholarly journals The Geneva–Copenhagen Survey of the Solar Neighbourhood

2004 ◽  
Vol 21 (2) ◽  
pp. 129-133 ◽  
Author(s):  
B. Nordström ◽  
J. Andersen ◽  
J. Holmberg ◽  
B. R. Jørgensen ◽  
M. Mayor ◽  
...  
Keyword(s):  
Binary Stars ◽  
Galactic Disk ◽  
Classical Model ◽  
Thin Disk ◽  
Solar Neighbourhood ◽  
Proper Motions ◽  
Kinematic Data ◽  
Model Predictions ◽  
The Mean ◽  
Metallicity Distribution

AbstractWe report on a new survey of metallicities, ages, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased all-sky sample of 16 682 nearby F- and G-dwarfs. Our ∼ 63 000 new, accurate radial velocities for nearly 13 500 of the stars, combined with Hipparcos parallaxes and Tycho-2 proper motions, complete the kinematic data for 14 139 stars and allow us to identify most of the binary stars in the sample. Isochrone ages have been determined whenever reliable results are possible, with particular attention to realistic error estimates.Among the basic properties of the Galactic disk that can be reinvestigated from our data are the metallicity distribution of G-dwarfs and the age–metallicity and age–velocity relations of the solar neighbourhood. We confirm the lack of metal-poor G-dwarfs relative to classical model predictions (the 'G-dwarf problem'), the near-constancy of the mean metallicity since the formation of the thin disk, and the appearance of the kinematic signature of the thick disk ∼ 10 Gyr ago.

Existence of a sharp transition in the peak propulsive efficiency of a low- pitching foil

2016 ◽  
Vol 800 ◽  
pp. 307-326 ◽  
Author(s):  
Anil Das ◽  
Ratnesh K. Shukla ◽  
Raghuraman N. Govardhan
Keyword(s):  
Power Coefficient ◽  
Energetic Cost ◽  
Mean Power ◽  
Thrust Coefficient ◽  
Propulsive Efficiency ◽  
Von Karman ◽  
Wide Range ◽  
The Mean ◽  
The One ◽  
Von Kármán

We perform a comprehensive characterization of the propulsive performance of a thrust generating pitching foil over a wide range of Reynolds ($10\leqslant Re\leqslant 2000$) and Strouhal ($St$) numbers using a high-resolution viscous vortex particle method. For a given $Re$, we show that the mean thrust coefficient $\overline{C_{T}}$ increases monotonically with $St$, exhibiting a sharp rise as the location of the inception of the wake asymmetry shifts towards the trailing edge. As a result, the propulsive efficiency too rises steeply before attaining a maximum and eventually declining at an asymptotic rate that is consistent with the inertial scalings of $St^{2}$ for $\overline{C_{T}}$ and $St^{3}$ for the mean power coefficient, with the latter scaling holding, quite remarkably, over the entire range of $Re$. We find the existence of a sharp increase in the peak propulsive efficiency ${\it\eta}_{max}$ (at a given $Re$) in the $Re$ range of 50 to approximately 1000, with ${\it\eta}_{max}$ increasing rapidly from about 1.7 % to the saturated asymptotic value of approximately $16\,\%$. The $St$ at which ${\it\eta}_{max}$ is attained decreases progressively with $Re$ towards an asymptotic limit of $0.45$ and always exceeds the one for transition from a reverse von Kármán to a deflected wake. Moreover, the drag-to-thrust transition occurs at a Strouhal number $St_{tr}$ that exceeds the one for von Kármán to reverse von Kármán transition. The $St_{tr}$ and the corresponding power coefficient $\overline{C_{p,}}_{tr}$ are found to be remarkably consistent with the simple scaling relationships $St_{tr}\sim Re^{-0.37}$ and $\overline{C_{p,}}_{tr}\sim Re^{-1.12}$ that are derived from a balance of the thrust generated from the pitching motion and the drag force arising out of viscous resistance to the foil motion. The fact that the peak propulsive efficiency degrades appreciably only below $Re\approx 10^{3}$ establishes a sharp lower threshold for energetically efficient thrust generation from a pitching foil. Our findings should be generalizable to other thrust-producing flapping foil configurations and should aid in establishing the link between wake patterns and energetic cost of thrust production in similar systems.

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