Convective instability by active stress

1969 ◽  
Vol 310 (1501) ◽  
pp. 183-219 ◽  
Keyword(s):  
Convective Instability ◽  
Pure Shear ◽  
Fluid Motion ◽  
Transformation Process ◽  
The Body ◽  
Equivalent Transformation ◽  
Quiescent State ◽  
Concentration Gradients ◽  
Active Stress ◽  
The Galerkin Method

Composition-dependent stress fields in continuous and mechanically isolated material can, it is shown, initiate and maintain conversion of chemical to kinetic energy. Though the process is analogous to natural convection, neither the body force of the well-known buoyancy mechanism nor the singular inhomogeneity and anisotropy of the interfacial tension mechanism is required. In the cases examined, the material is represented by the constitutive relation for incompressible Newtonian fluid augmented by an active stress which must be anisotropic or nonlinear in concentration gradients (or other, equivalent gradients) in accordance with the oft-misquoted Curie principle. The concentration gradients are supposed to be sustained by steady chemical reaction (or an equivalent transformation process) throughout the material and by exchange with surroundings. Conventional linear analysis of asymptotic stability is used to identify types of stress/concentration-gradient coupling that can render a quiescent state of reaction and diffusion unstable when concentration gradients exceed critical values. It is found that both deviatoric (pure shear) and antisymmetric active stress can support two-dimensional convective instability in a cylinder of material in which the quiescent state is circularly symmetric. Certain cases of stationary instability are solved exactly. Others involving both stationary and oscillatory instability are treated by a new version of the Galerkin method. The results establish the possibility of generating fluid motion by mechanochemical means in continuous material having appropriate subcontinuum structure. Whatever their relevance to protoplasmic movement in biological systems they do contain challenges for experimental and theoretical fluid mechanics and related areas of rheology and chemistry.

Chloride Regulation at Low Salinities by Nereis Diversicolor (Annelida, Polychaeta)

1970 ◽  
Vol 53 (1) ◽  
pp. 75-92
Author(s):  
RALPH I. SMITH
Keyword(s):  
Electrical Potential ◽  
Urine Volume ◽  
Chloride Concentration ◽  
Pond Water ◽  
The Body ◽  
Salinity Range ◽  
Concentration Gradients ◽  
North Eastern ◽  
Net Uptake ◽  
Chloride Regulation

1. N. diversicolor from estuarine conditions in north-eastern England can be adapted to a chloride concentration in a pond water (PW) medium at least as low as 0.9 mM/l, and shows a net uptake of chloride when returned to a medium 3-10 mM/l more concentrated. But in comparable transfers after adaptation at a chloride concentration of 10 mM/l, net uptake is not measurable. 2. Net uptake of chloride is demonstrable in the lowest salinities, where coelomic chloride concentration drops below the regulatory plateau. Net uptake reaches 3.5 µM/g wet weight/h. 3. Chloride loss is well correlated with weight loss after adaptation in 10 mM/l, but poorly so after adaptation in PW, suggesting that the urine is very hypotonic to body fluid in PW, and isotonic (or less hypotonic) at environmental chloride concentrations of 10 mM/l or higher. 4. Uptake of chloride occurs against both electrical and chemical-concentration gradients over the lower third of the environmental salinity range, which is the range in which hyperosmotic and hyperionic regulation are most pronounced. 5. The electrical potential across the body wall is maximal in PW (17 mV, inside-negative), and decreases to zero in 50 % SW. 6. Chloride influx (as measured with 36Cl) is highest in SW, and decreases in proportion to chloride concentration down to 50-25% SW, rises to a secondary maximum in 10% SW or less, and decreases as fresh water is approached. 7. Urinary chloride loss is low, and proportional to external chloride concentration in higher salinities, maximal in the c. 10% SW range of salinities, and apparently decreases to a minimum in FW. This may be in part the consequence of recovery of chloride from an hypotonic urine, in part the consequence of a reduction in urine volume. Evidence for these last two possibilities will be given in the papers which follow.

Finite Element Study of Oxygen Diffusion in the Intervertebral Disc

2000 ◽  
Author(s):  
E. Sélard ◽  
A. Shirazi-Adl ◽  
J. P. G. Urban
Keyword(s):  
Intervertebral Disc ◽  
Blood Supply ◽  
Oxygen Diffusion ◽  
Consumption Rate ◽  
The Body ◽  
Cellular Viability ◽  
Two Dimensional ◽  
Concentration Gradients ◽  
Exchange Area ◽  
The Matrix

Abstract The intervertebral disc consists of a water-rich extra-cellular matrix which is synthesized and maintained by its cells. The disc is the largest avascular tissue in the body with its cells lying as much as 8mm away from the blood supply. Nutrients, essential for maintaining cellular viability, diffuse through the matrix from blood supply under a concentration gradient arising from cellular demand. The oxygen concentration gradients in the intervertebral disc are investigated to examine the effects of exchange area and disc thickness on oxygen flux in the disc. The concentration gradients are computed using the two-dimensional Poisson’s equation and measured values for oxygen consumption rate and oxygen diffusion.

scholarly journals CONTRIBUTION TO THE STUDY OF SEDIMENT TRANSPORT ON A HORIZONTAL BED DUE TO WAVE ACTION

2011 ◽  
Vol 1 (6) ◽  
pp. 20 ◽  
Author(s):  
G. E. Vincent
Keyword(s):  
Boundary Layer ◽  
Wave Propagation ◽  
Sediment Transport ◽  
Liquid Velocity ◽  
Fluid Motion ◽  
Wave Action ◽  
The Body ◽  
Density Currents ◽  
Open Sea ◽  
Land Surfaces

With a view to explaining the phenomena of sediment transport in the open sea, outside the wave breaking area, the author carried out a laboratory investigation of wave action on a horizontal bed. He puts forward a number of new results regarding : 1 - The state of turbulence near the bed and the stability of the oscillatory laminar boundary layer. 2 - The setting in notion of materials under the influence of wave alone. 3 - The entrapment current caused by wave action close to the bed. 4 - The transport of material under wave action only. 5 - The indirect action of wave on the bed. The main conclusions reached are as follows : 1/ - The results given by Kuon Li regarding the onset of turbulence within the oscillatory boundary layer overestimate the range of laminar conditions. Vo (maximum orbital velocity) and e (roughness) are the principle factors governing the transition. Test waves are either generally laminar, or are only slightly turbulent within the body of liquid, but they are, however, more often turbulent in the immediate neighbourhood of the bed. 2/ - The Investigation of conditions for the onset of grain movement of the bed material shows that the action of wave can be appreciable, even at depths of several tens of metres. A wave of 6 metres amplitude, with a total length of 120 metres, would be capable of putting a 0.3 mm sand grain into motion at a depth of 60 metres. 3/ - The experimental investigation, as well as the viscous fluid theory, shows the existence, close to the bed, of an entrainment current of liquid particles which always works In the direction of wave propagation. 4/ - In test flumes, this entrainment current forms part of a mass transport within the liquid, the vertical distribution of which varies with the characteristics of the fluid motion. On a horizontal bed, It generally gives rise to an effective sediment transport, in the direction of wave propagation, as the preponderant part of the liquid velocity component, near the bed. is in this direction. 5/ - Owing to the existence of the pass transport current and the onset of suspension of material above the bed, some sediment transport can exist out to sea. These results give an explanation of why, under the action of long and regular wave . material tends to be carried in the direction of the waves and build up on the beach whereas, under storm conditions, a strong resultant turbulence produces suspension and favours erosion of the beach. 6/ - On a sloping bed, transport towards the shore is counterbalanced by the effect of gravity, currents caused by winds from seaward and density currents set up in the wave break area so that finally material eroded from land surfaces are, In part, gradually carried away towards the open sea.

The Sensory Physiology of the Harvest Mite Trombicula Autumnalis Shaw

1950 ◽  
Vol 27 (3) ◽  
pp. 461-494
Author(s):  
B. M. JONES
Keyword(s):  
Light Intensity ◽  
Natural Environment ◽  
Free Water ◽  
The Body ◽  
Quiescent State ◽  
Sensory Physiology ◽  
Linear Gradient ◽  
Dry Air ◽  
Sudden Decrease ◽  
Heated Object

Responses to stimuli Light. In a strong beam of light the harvest mite will move directly towards the source, whereas in a weak light the tracks are at first inclined to be wavy, but as they approach the source the tracks straighten. The mite moves along the bisector of two intersecting lights of equal intensity, and when blinded on one side makes circus movements. When offered a linear gradient of light intensity the mite avoids the darkened portion and moves towards the lightest part of the field. Its movement towards sunlight is a true response to light and not to heat. A sudden decrease of light intensity produces a questing response. Temperature. The sensory perception of heat is poorly developed. The mite is incapable of locating a warm tube or the body of a young live mouse. On touching a heated object it displays a well-defined response to a temperature difference of about 15° C. In a linear or concentric temperature gradient it displays avoiding reactions to low and high temperatures and appears to prefer a range extending from 15 to 26° C. Chemical stimulation. The mite is repelled at a distance of 0.5 cm. from phenol, methyl phthalate, dilute ammonia, xylene and a 3 % solution of glacial acetic acid. Toluene was repugnant at 1.5 cm., whilst a mixture of amyl acetate and water repelled the mite at 5 cm. Complete indifference was shown to the odour of skin, liver, sebum and cerumen, but perspiration induced an avoiding reaction. Humidity. Depletion of the water content influences the response of the mite to humidity. A desiccated mite is active in dry air and inactive in moist air, but a normal individual will settle in either moist or dry air, while avoiding saturated air. The mite requires high humidities for prolonged survival, but avoids free water. Touch. Unfed mites are very sensitive to touch. The extent of stimulation by contact with each other's bodies, which is regarded as high, immobilizes them, and it is primarily responsible for the quiescent state of a cluster of mites. When the stimulation is low, for example, when only the tarsi are in contact with a surface, the mite responds by displaying a high state of activity. A mite lightly touched will immediately quest, a response induced equally by vibrations of the substratum. Clustering The gregarious habit of the mites is primarily a response to the touch of each other's bodies. When the humidity is within the range 95-100% R.H. light will induce the mites to climb up a rod and form a cluster at the tip. Whether or not negative geotaxis also plays a part, it is difficult to say, because the evidence suggested that the mite is independent of gravity. Sense organs There are three types of sensilla: (1) tactile sensilla, both plumose and plain; (2) peg organs; (3) minute sensory rods, principally confined to the first leg. An elliptical lens, a discoid mass of red-pigmented oily substance, and a pronounced dark pigmented cup are conspicuous features of the better developed anterior eye of each ocular area. Identification of the responses Where possible the responses of the mite to various kinds of stimuli have been identified according to a recognized scheme of classification. Behaviour in the natural environment The responses to stimuli which the mite will encounter in the natural environment, and their value with respect to acquiring a host, are discussed.

An integral-equation method for determining the fluid motion due to a cylinder heaving on water of finite depth

1980 ◽  
Vol 372 (1748) ◽  
pp. 93-110 ◽  
Keyword(s):  
Integral Equation ◽  
Fundamental Solution ◽  
Integral Equations ◽  
Fluid Motion ◽  
Integral Equation Method ◽  
Finite Depth ◽  
The Body ◽  
Wave Source ◽  
Method Of Integral Equations ◽  
Infinite Set

The method of integral equations is used here to calculate the virtual mass of a half-immersed cylinder heaving periodically on water of finite constant depth. For general sections this method is more appropriate than the method of multipoles; particular sections that are considered are the circle and the ellipse. Green’s theorem is applied to the potential and to a fundamental solution (wave source) satisfying the conditions at the free surface, at the bottom and at infinity, but not necessarily on the body. An integral equation for the potential on the body only is thus obtained. For the simplest choice of fundamental solution the method breaks down at a discrete infinite set of frequencies, as is well known. When the fundamental solution was modified, however, a different integral equation could be obtained for the same unknown function and this was found not to break down for the circle and ellipse. The present numerical results are in good agreement with those obtained by the method of multipoles which for the circle is more efficient than the method of integral equations but which is not readily applicable to other sections. Much effort now goes into such calculations.

scholarly journals Unsteady low Reynolds number flow in a heated tube of slowly varying section

1988 ◽  
Vol 30 (2) ◽  
pp. 179-202 ◽  
Author(s):  
A. R. Bestman
Keyword(s):  
Fluid Motion ◽  
The Body ◽  
Axial Component ◽  
Axial Distance ◽  
Mean Flow ◽  
Steady Streaming ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
The Mean ◽  
Oscillatory Pressure

AbstractFluid motion established by an oscillatory pressure gradient superimposed on a mean, in a tube of slowly varying section, is studied when the temperature of the tube wall varies with axial distance. Particular attention is focussed on the mean flow and steady streaming components of the oscillatory flow of higher approximation. For the velocity components, the axial component takes the pride of place, since this component is responsible for convection of nutrients to various parts of the body of a mammal in systematic circulation. A salient point in the paper concerns consequences of free convection currents at a constriction (stenosis).

Computation of Turbulent Flows in Complex and Moving Geometries Using Immersed Boundary Method

2003 ◽  
Author(s):  
Mayank Tyagi ◽  
Sumanta Acharya
Keyword(s):  
Turbulent Flows ◽  
Immersed Boundary Method ◽  
Complex Geometry ◽  
Fluid Motion ◽  
The Body ◽  
Immersed Boundary ◽  
Full Potential ◽  
Heated Cylinder ◽  
Boundary Method ◽  
Trapped Vortex

A solution methodology for complex turbulent flows of industrial interests is developed using Immersed Boundary Method (IBM). IBM combines the efficiency inherent in using a fixed Cartesian grid to compute the fluid motion, along with the ease of tracking the immersed boundary at a set of moving Lagrangian points. IBM relies upon the body force terms added in the momentum equations to represents the complex geometry on a fixed Cartesian mesh. Resolution issues for turbulent flows can be addressed by Large Eddy Simulation (LES) technique provided an accurate and robust Subgrid Stress (SGS) model is available. Higher order of numerical accuracy schemes for turbulent flows can be maintained as well as the geometrical complexities can be rendered physically by combining LES with IBM. The proposed methodology is simple and ideally suited for the moving geometries involving no-slip walls with prescribed trajectories and locations. IBM is validated for the laminar flow past a heated cylinder in a channel and LES is validated for the turbulent lid-driven cavity flow. LES-IBM is then is used to render complex geometry of trapped vortex combustor to study fluid mixing inside trapped vortex cavity. To demonstrate the full potential of LES-IBM, a complex moving geometry problem of stator-rotor interaction is solved.

scholarly journals The Role of Breast Cancer Stem Cells as a Prognostic Marker and a Target to Improve the Efficacy of Breast Cancer Therapy

Cancers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1021 ◽  
Author(s):  
Maria Giovanna Scioli ◽  
Gabriele Storti ◽  
Federico D’Amico ◽  
Pietro Gentile ◽  
Giulia Fabbri ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Stem Cells ◽  
Cancer Stem Cells ◽  
Tumor Cells ◽  
The Body ◽  
Cell Subpopulation ◽  
Phenotypic Characterization ◽  
Quiescent State ◽  
Breast Cancer Stem Cells ◽  
Mesenchymal Transition

Breast cancer is the most common form of tumor in women and the leading cause of cancer-related mortality. Even though the major cellular burden in breast cancer is constituted by the so-called bulk tumor cells, another cell subpopulation named cancer stem cells (CSCs) has been identified. The latter have stem features, a self-renewal capacity, and the ability to regenerate the bulk tumor cells. CSCs have been described in several cancer types but breast cancer stem cells (BCSCs) were among the first to be identified and characterized. Therefore, many efforts have been put into the phenotypic characterization of BCSCs and the study of their potential as prognostic indicators and therapeutic targets. Many dysregulated pathways in BCSCs are involved in the epithelial–mesenchymal transition (EMT) and are found up-regulated in circulating tumor cells (CTCs), another important cancer cell subpopulation, that shed into the vasculature and disseminate along the body to give metastases. Conventional therapies fail at eliminating BCSCs because of their quiescent state that gives them therapy resistance. Based on this evidence, preclinical studies and clinical trials have tried to establish novel therapeutic regimens aiming to eradicate BCSCs. Markers useful for BCSC identification could also be possible therapeutic methods against BCSCs. New approaches in drug delivery combined with gene targeting, immunomodulatory, and cell-based therapies could be promising tools for developing effective CSC-targeted drugs against breast cancer.

scholarly journals Hematopoietic Stem Cell Development, Niches, and Signaling Pathways

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
Kamonnaree Chotinantakul ◽  
Wilairat Leeanansaksiri
Keyword(s):  
Stem Cell ◽  
Signaling Pathways ◽  
Cell Biology ◽  
The Body ◽  
Basic Knowledge ◽  
Stem Cell Biology ◽  
Quiescent State ◽  
Hematopoietic Stem ◽  
Medicine Development ◽  
Biology Research

Hematopoietic stem cells (HSCs) play a key role in hematopoietic system that functions mainly in homeostasis and immune response. HSCs transplantation has been applied for the treatment of several diseases. However, HSCs persist in the small quantity within the body, mostly in the quiescent state. Understanding the basic knowledge of HSCs is useful for stem cell biology research and therapeutic medicine development. Thus, this paper emphasizes on HSC origin, source, development, the niche, and signaling pathways which support HSC maintenance and balance between self-renewal and proliferation which will be useful for the advancement of HSC expansion and transplantation in the future.

Localized heat flow and Tertiary mineralization in southern New Mexico

Geophysics ◽  
1983 ◽  
Vol 48 (9) ◽  
pp. 1212-1218
Author(s):  
Gary W. Zielinski ◽  
Gail Moritz DeCoursey
Keyword(s):  
New Mexico ◽  
Heat Flow ◽  
Heat Source ◽  
Heat Production ◽  
Convective Instability ◽  
Local Scale ◽  
Surface Heat ◽  
The Body ◽  
Hydrothermal Mineralization ◽  
Granitic Intrusion

Eight shallow (<100 m deep) relative heat flow determinations from southern New Mexico reveal a systematic 3 HFU [Formula: see text] increase occurring within a distance of 2 km. The maximum surface heat flow appears roughly to overlie a Tertiary granitic body at a depth of about 600 m within an area of known hydrothermal mineralization. The presence of the anomaly, believed to be of subsurface origin, implies an active heat source centered at a depth of 1140 m, perhaps associated with hydrothermal circulation. Higher radioactive heat production in granites may contribute to convective instability and explain the apparent lateral coincidence between the anomaly and the body. This situation appears, on a local scale, analogous to coinciding zones of high present‐day heat flow and mineralization in England and Wales (Brown et al, 1980). In both cases, mineralization is associated with granitic intrusion that has occurred at a previous time which is much greater than the thermal time constant for cooling bodies. Shallow heat flow determinations may be useful in locating other similar areas and investigating possible associations of mineralization and thermal history.

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