Academic literature on the topic 'Concentration gradient force'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the lists of relevant articles, books, theses, conference reports, and other scholarly sources on the topic 'Concentration gradient force.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Journal articles on the topic "Concentration gradient force"
1
Leventis, Nicholas, and Amala Dass. "Demonstration of the Elusive Concentration-Gradient Paramagnetic Force." Journal of the American Chemical Society 127, no. 14 (April 2005): 4988–89. http://dx.doi.org/10.1021/ja043169b.
Full text
2
Coey, J. M. D., F. M. F. Rhen, P. Dunne, and S. McMurry. "The magnetic concentration gradient force—Is it real?" Journal of Solid State Electrochemistry 11, no. 6 (February 9, 2007): 711–17. http://dx.doi.org/10.1007/s10008-006-0254-4.
Full text
3
Hirano, Tetsuo, Toshiaki Yoneyama, Hiroko Matsuzaki, and Takainitsu Sekine. "Simple method for preparing a concentration gradient of serum components by freezing and thawing." Clinical Chemistry 37, no. 7 (July 1, 1991): 1225–29. http://dx.doi.org/10.1093/clinchem/37.7.1225.
Full textAbstract:
Abstract We created a simple method for obtaining a series of successively more-concentrated samples from a serum without changing the ratio of its components. We froze a pooled serum and then allowed it to thaw undisturbed. The serum components formed a gradient of increasing concentration from the top of the sample to the bottom. We found that (a) in test results, each fraction of serum in the gradient showed almost the same relative concentrations of components (i.e., inorganic and organic compounds, proteins, metals, and hormones), irrespective of atomic or molecular mass; (b) the concentration gradient depended on the thawing temperature but not on the freezing temperature; (c) when we thawed the frozen sample with centrifugation, the slope of the concentration gradient increased with increasing centrifugal force; (d) when the thawed sample was fractionated into 10 fractions from the top to the bottom, the original serum concentration was always maintained between the sixth and seventh fractions from the top; and (e) the concentration gradient became steeper with repeated freezing and thawing. By using this method, one can easily prepare serum samples at gradients of concentration useful in the clinical laboratory, although the mechanism of gradient formation is still unclear.
4
Waskaas, Magne. "On the Origin of the Magnetic Concentration Gradient Force and Its Interaction Mechanisms with Mass Transfer in Paramagnetic Electrolytes." Fluids 6, no. 3 (March 11, 2021): 114. http://dx.doi.org/10.3390/fluids6030114.
Full textAbstract:
The objective of this work is to analyze the origin of the magnetic concentration gradient force. The force will be studied in a diffusion system where a paramagnetic electrolyte diffuses through a thin, inert membrane under the influence of a homogeneous magnetic field. The force will be analyzed using the theory of magnetic circuits, i.e., by the concept of minimum reluctance principles. In addition, based on some previous studies, it will be discussed whether the minimum reluctance principle can be applied to mass transfer into and out of the diffusion layer at electrode/electrolyte interfaces. The results show that the magnetic concentration gradient force arises as a consequence of the minimum reluctance principle. Applied to the diffusion system, the magnetic concentration gradient force arises in the membrane as a consequence of the concentration gradient and hence, the reluctance gradient. The force acts on the flow in such a way that the reluctance in the membrane is minimized. The force implies two interaction mechanisms: attraction of the paramagnetic electrolyte flowing into the membrane in order to decrease the reluctance, and hindrance of the paramagnetic electrolyte flowing out of the membrane in order to hinder an increase in the reluctance. Based on previous studies, it is shown that the minimum reluctance principle can be applied to mass transfer into or out of the diffusion layer at electrode/electrolyte interfaces as well.
5
BRADY, JOHN F. "Particle motion driven by solute gradients with application to autonomous motion: continuum and colloidal perspectives." Journal of Fluid Mechanics 667 (December 3, 2010): 216–59. http://dx.doi.org/10.1017/s0022112010004404.
Full textAbstract:
Diffusiophoresis, the motion of a particle in response to an externally imposed concentration gradient of a solute species, is analysed from both the traditional coarse-grained macroscopic (i.e. continuum) perspective and from a fine-grained micromechanical level in which the particle and the solute are treated on the same footing as Brownian particles dispersed in a solvent. It is shown that although the two approaches agree when the solute is much smaller in size than the phoretic particle and is present at very dilute concentrations, the micromechanical colloidal perspective relaxes these restrictions and applies to any size ratio and any concentration of solute. The different descriptions also provide different mechanical analyses of phoretic motion. At the continuum level the macroscopic hydrodynamic stress and interactive force with the solute sum to give zero total force, a condition for phoretic motion. At the colloidal level, the particle's motion is shown to have two contributions: (i) a ‘back-flow’ contribution composed of the motion of the particle due to the solute chemical potential gradient force acting on it and a compensating fluid motion driven by the long-range hydrodynamic velocity disturbance caused by the chemical potential gradient force acting on all the solute particles and (ii) an indirect contribution arising from the mutual interparticle and Brownian forces on the solute and phoretic particle, that contribution being non-zero because the distribution of solute about the phoretic particle is driven out of equilibrium by the chemical potential gradient of the solute. At the colloidal level the forces acting on the phoretic particle – both the statistical or ‘thermodynamic’ chemical potential gradient and Brownian forces and the interparticle force – are balanced by the Stokes drag of the solvent to give the net phoretic velocity.For a particle undergoing self-phoresis or autonomous motion, as can result from chemical reactions occurring asymmetrically on a particle surface, e.g. catalytic nanomotors, there is no imposed chemical potential gradient and the back-flow contribution is absent. Only the indirect Brownian and interparticle forces contribution is responsible for the motion. The velocity of the particle resulting from this contribution can be written in terms of a mobility times the integral of the local ‘solute pressure’ – the solute concentration times the thermal energy – over the surface of contact between the particle and the solute. This was the approach taken by Córdova-Figueroa & Brady (Phys. Rev. Lett., vol. 100, 2008, 158303) in their analysis of self-propulsion. It is shown that full hydrodynamic interactions can be incorporated into their analysis by a simple scale factor.
6
Zeinali Torbati, Reza, Ian D. Turnbull, Rocky S. Taylor, and Derek Mueller. "Evaluation of the relative contribution of meteorological and oceanic forces to the drift of ice islands offshore Newfoundland." Journal of Glaciology 66, no. 256 (January 10, 2020): 203–18. http://dx.doi.org/10.1017/jog.2019.96.
Full textAbstract:
AbstractOn 29 April 2015, four beacons were deployed onto an ice island in the Strait of Belle Isle to record positional data. The ice island later broke up into many fragments, four of which were tracked by the beacons. The relative influences of wind drag, current drag, Coriolis force, sea surface height gradient and sea-ice force on the drift of the tracked ice island fragments were analyzed. Using atmospheric and oceanic model outputs, the sea-ice force was calculated as the residual of the fragments' net forces and the sum of all other forces. This was compared against the force obtained through ice concentration-dependent relationships when sea ice was present. The sea-ice forces calculated from the residual approach and concentration-dependent relationships were significant only when sea ice was present at medium-high concentrations in the vicinity of the ice island fragments. The forces from ocean currents and sea surface tilt contributed the most to the drift of the ice island fragments. Wind, however, played a minimal role in the total force governing the drift of the four ice island fragments, and Coriolis force was significant when the fragments were drifting at higher speeds.
7
Strévey, J., S. Giroux, and R. Béliveau. "pH gradient as an additional driving force in the renal re-absorption of phosphate." Biochemical Journal 271, no. 3 (November 1, 1990): 687–92. http://dx.doi.org/10.1042/bj2710687.
Full textAbstract:
The effects of the Na+ gradient and pH on phosphate uptake were studied in brush-border membrane vesicles isolated from rat kidney cortex. The initial rates of Na(+)-dependent phosphate uptake were measured at pH 6.5, 7.5 and 8.5 in the presence of sodium gluconate. At a constant total phosphate concentration, the transport values at pH 7.5 and 8.5 were similar, but at pH 6.5 the influx was 31% of that at pH 7.5. However, when the concentration of bivalent phosphate was kept constant at all three pH values, the effect of pH was less pronounced; at pH 6.5, phosphate influx was 73% of that measured at pH 7.5. The Na(+)-dependent phosphate uptake was also influenced by a transmembrane pH difference; an outwardly directed H+ gradient stimulated the uptake by 48%, whereas an inwardly directed H+ gradient inhibited the uptake by 15%. Phosphate on the trans (intravesicular) side stimulated the Na(+)-gradient-dependent phosphate transport by 59%, 93% and 49%, and the Na(+)-gradient-independent phosphate transport by 240%, 280% and 244%, at pH 6.5, 7.5 and 8.5 respectively. However, in both cases, at pH 6.5 the maximal stimulation was seen only when the concentration of bivalent trans phosphate was the same as at pH 7.5. In the absence of a Na+ gradient, but in the presence of Na+, an outwardly directed H+ gradient provided the driving force for the transient hyperaccumulation of phosphate. The rate of uptake was dependent on the magnitude of the H+ gradient. These results indicate that: (1) the bivalent form of phosphate is the form of phosphate recognized by the carrier on both sides of the membrane; (2) protons are both activators and allosteric modulators of the phosphate carrier; (3) the combined action of both the Na+ (out/in) and H+ (in/out) gradients on the phosphate carrier contribute to regulate efficiently the re-absorption of phosphate.
8
Asako, Yutaka, and Yohei Suzuki. "Oxygen Separation/Enrichment From Atmospheric Air Using Magnetizing Force." Journal of Fluids Engineering 129, no. 4 (October 3, 2006): 438–45. http://dx.doi.org/10.1115/1.2436584.
Full textAbstract:
Oxygen is a paramagnetic gas and it has relatively high magnetic susceptibility. On the contrary, nitrogen is a diamagnetic gas and it has relatively low and negative magnetic susceptibility. This results in countermagnetizing forces acting on these gases. The characteristics of oxygen separation/enrichment from atmospheric air in a capsule and air flow in a parallel-plate duct using a magnetizing force were investigated numerically. The direct simulation Monte Carlo (DSMC) method was utilized to obtain distribution of oxygen concentration of air under a strong magnetic field gradient. The molecular movement was calculated by taking into account the magnetizing forces on the molecules. The computations were performed for a wide range of pressure and magnetic flux density gradient. Quantitative characteristics of oxygen separation/enrichment from atmospheric air under a strong magnetic field gradient and a parameter which governs this phenomenon are obtained from the simulation results.
9
Renaud, J. M. "Modulation of Force Development by Na+, K+, Na+ K+ Pump and KATP Channel During Muscular Activity." Canadian Journal of Applied Physiology 27, no. 3 (June 1, 2002): 296–315. http://dx.doi.org/10.1139/h02-017.
Full textAbstract:
Extracellular K+ concentration increases during exercise and especially during fatigue development. It has been proposed that K+ is an important factor in the etiology of skeletal muscle fatigue because it suppresses membrane excitability and eventually force development. Based on the effect of K+, it has then been proposed the Na+ K+ pump reduces increases in extracellular K+ concentration while the ATP-sensitive K+ channel (KATP channel) allows for rapid increases in extracellular K+ to suppress force development when ATP levels start to fall or when the levels of metabolic end-products become high. However, recent studies have now demonstrated that an increase in extracellular K+ concentration can be advantageous to muscle during exercise because it not only stimulates vasodilatation and the exercise pressor reflex, but it also potentiates force development when the Na+ concentration gradient is maintained. A new hypothesis is therefore proposed in which the Na+ K+ pump is important in maintaining the Na+ concentration gradient (and not the K+ concentration gradient as previously suggested), while the activation of KATP channels is important to increase the K+ efflux and extracellular concentration. This situation then optimizes the development of force during exercise. Another hypothesis is proposed in which more KATP channels are activated while the activity of the Na+ K+ pump is reduced when ATP levels start to decrease to allow for an accumulation of intracellular Na+ and further increases in extracellular K+ concentration, These concentration changes then reduce membrane excitability and force development (i.e., fatigue) to protect muscle against large ATP depletion and function impairment. Key words: fatigue, exercise, energy metabolism, ATP, lactic acid, adenosine, hydrogen ion
10
Khakdaman, Hamidreza, Yves Bourgault, and Marten Ternan. "A Mathematical Model of a Direct Propane Fuel Cell." Journal of Chemistry 2015 (2015): 1–13. http://dx.doi.org/10.1155/2015/102313.
Full textAbstract:
A rigorous mathematical model for direct propane fuel cells (DPFCs) was developed. Compared to previous models, it provides better values for the current density and the propane concentration at the exit from the anode. This is the first DPFC model to correctly account for proton transport based on the combination of the chemical potential gradient and the electrical potential gradient. The force per unit charge from the chemical potential gradient (concentration gradient) that pushes protons from the anode to the cathode is greater than that from the electrical potential gradient that pushes them in the opposite direction. By including the chemical potential gradient, we learn that the proton concentration gradient is really much different than that predicted using the previous models that neglected the chemical potential gradient. Also inclusion of the chemical potential gradient made this model the first one having an overpotential gradient (calculated from the electrical potential gradient) with the correct slope. That is important because the overpotential is exponentially related to the reaction rate (current density). The model described here provides a relationship between the conditions inside the fuel cell (proton concentration, overpotential) and its performance as measured externally by current density and propane concentration.
Dissertations / Theses on the topic "Concentration gradient force"
1
Cierpka, Christian. "Zeitaufgelöste PIV-Untersuchungen zur Strömungskontrolle mittels elektromagnetischer Kräfte in schwach leitfähigen Fluiden." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1240481487194-92722.
Full textAbstract:
Die vorwiegend experimentelle Arbeit befasst sich mit der systematischen Untersuchung von Parametervariationen bei der aktiven Strömungskontrolle mit elektromagnetischen Kräften. An einer angestellten Platte und einem NACA0015-Profil wurde die saugseitige abgelöste Strömung durch das Einbringen einer periodischen wandparallelen Lorentzkraft an der Vorderkante beeinflusst und experimentell mittels zeitaufgelöster Particle Image Velocimetry (PIV) untersucht. Dabei wurde für verschiedene Anstellwinkel und Reynoldszahlen die Frequenz der Anregung, deren Impulseintrag und der zeitliche Kraftverlauf variiert. Strömungsmechanische Untersuchungen experimenteller und numerischer Natur wurden für eine elektrochemische Zelle und den Fall der Elektrolyse an Millieelektroden unter dem Einfluss externer Magnetfelder durchgeführt. Die Übereinstimmung der gemessenen und berechneten Geschwindigkeitsfelder war dabei sehr gut. Entgegen der Annahme, dass im Falle homogener Magnetfelder keine Strömungen induziert werden, konnte nachgewiesen werden, dass durch die lokale Krümmung der elektrischen Feldlinien in Elektrodennähe starke Lorentzkräfte generiert werden. Dies führt zu sehr komplexen Primär-und Sekundärströmungen. Die gleichen Effekte bewirken ebenfalls in der Nähe von Millieelektroden starke Lorentzkräfte in homogenen magnetischen Feldern. Die experimentellen Beobachtungen an Millieelektroden von Leventis et. al (2005), welche zum Beweis der Konzentrationsgradientenkraft herangezogen wurden, konnten alle auf das Wirken lokaler Lorentzkräfte zurückgeführt werden. Der experimentelle Nachweis der Konzentrationsgradientenkraft steht damit weiterhin aus. Zur Messung der Konzentrationen in elektrochemischen Systemen wurde erstmals das Hintergrundschlierenverfahren angewendet. Dieses Verfahren erlaubt die Bestimmung der räumlichen Konzentrationsgradienten mit erheblich weniger messtechnischen Aufwand gegenüber spektroskopischen Methoden und der Schlierentechnik.
2
Cierpka, Christian. "Zeitaufgelöste PIV-Untersuchungen zur Strömungskontrolle mittels elektromagnetischer Kräfte in schwach leitfähigen Fluiden." Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A23653.
Full textAbstract:
Die vorwiegend experimentelle Arbeit befasst sich mit der systematischen Untersuchung von Parametervariationen bei der aktiven Strömungskontrolle mit elektromagnetischen Kräften. An einer angestellten Platte und einem NACA0015-Profil wurde die saugseitige abgelöste Strömung durch das Einbringen einer periodischen wandparallelen Lorentzkraft an der Vorderkante beeinflusst und experimentell mittels zeitaufgelöster Particle Image Velocimetry (PIV) untersucht. Dabei wurde für verschiedene Anstellwinkel und Reynoldszahlen die Frequenz der Anregung, deren Impulseintrag und der zeitliche Kraftverlauf variiert. Strömungsmechanische Untersuchungen experimenteller und numerischer Natur wurden für eine elektrochemische Zelle und den Fall der Elektrolyse an Millieelektroden unter dem Einfluss externer Magnetfelder durchgeführt. Die Übereinstimmung der gemessenen und berechneten Geschwindigkeitsfelder war dabei sehr gut. Entgegen der Annahme, dass im Falle homogener Magnetfelder keine Strömungen induziert werden, konnte nachgewiesen werden, dass durch die lokale Krümmung der elektrischen Feldlinien in Elektrodennähe starke Lorentzkräfte generiert werden. Dies führt zu sehr komplexen Primär-und Sekundärströmungen. Die gleichen Effekte bewirken ebenfalls in der Nähe von Millieelektroden starke Lorentzkräfte in homogenen magnetischen Feldern. Die experimentellen Beobachtungen an Millieelektroden von Leventis et. al (2005), welche zum Beweis der Konzentrationsgradientenkraft herangezogen wurden, konnten alle auf das Wirken lokaler Lorentzkräfte zurückgeführt werden. Der experimentelle Nachweis der Konzentrationsgradientenkraft steht damit weiterhin aus. Zur Messung der Konzentrationen in elektrochemischen Systemen wurde erstmals das Hintergrundschlierenverfahren angewendet. Dieses Verfahren erlaubt die Bestimmung der räumlichen Konzentrationsgradienten mit erheblich weniger messtechnischen Aufwand gegenüber spektroskopischen Methoden und der Schlierentechnik.
3
Omari, Abdelaziz. "Hydrodynamique des polymères à l'interface solide-liquide : influence de la déplétion." Brest, 1987. http://www.theses.fr/1987BRES2026.
Full textAbstract:
Etude du phenomene de depletion pres de la paroi pour des solutions de polymeres (polyacrylamide, xanthane) ebn ecoulement dans des milieux poreux de taille comparable a celle des macromolecules. L'etude montre que l'epaisseur de la couche de depletion est une caracteristique intraseque du polymere
4
Boulesteix, Rémy. "Densification du grenat d'yttrium et d'aluminium pur ou dopé sous forme de céramiques transparentes : relation entre microstructure et propriétés optiques : élaboration de matériaux à gradient de concentration en néodyme." Limoges, 2009. http://www.theses.fr/2009LIMO4040.
Full text
5
Pajot, Ségolène. "Synthèse et caractérisation d’oxydes lamellaires riches en lithium et en manganèse obtenus sous la forme de gradients de concentration pour les batteries Li-ion." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0277/document.
Full textAbstract:
Ce travail présente la mise en oeuvre d’un protocole de synthèse de gradients deconcentration dans les oxydes lamellaires riches en Li et en Mn. Le but a été dedévelopper la formation d’oxydes lamellaires riches en Li et Mn au coeur des agrégatssphériques du matériau actif et, en se rapprochant de la surface, d’enrichir lacomposition de l’oxyde lamellaire en Co et en Ni, afin de combiner une forte densitéd’énergie (apportée par le coeur du gradient) et une excellente stabilité thermique etstructurale (apportée par la surface du gradient). La synthèse a été réalisée en deuxétapes, une co-précipitation pour former un carbonate de métaux de transition suivied’une calcination à haute température pour obtenir le matériau actif lithié. L’influencede différents paramètres (pH, débit d’injection, taille du réacteur, composition, …) surla nature du carbonate à gradient de concentration ainsi formé a été étudiée. De lamême façon, le contrôle du ratio Li/M (ici M = Ni, Co, Mn), de la température et de ladurée de calcination s’est révélé important pour parvenir à maintenir le gradient deconcentration dans le matériau lithié. Le ratio Li/M est également déterminant pourcontrôler la nature des matériaux obtenus (lamellaire - spinelle ou lamellaire –lamellaire). Des caractérisations extrêmement pointues, et complexes à mettre enoeuvre, ont été menées afin d’obtenir des informations pertinentes sur la distributiondes phases au sein des agrégats (composition et structure), de la surface au coeur dugradient : différentes techniques de microscopie (EPMA, MEB-EDX et FIB-STEM) ontainsi été largement utilisées. Les matériaux les plus intéressants ont été étudiés enbatteries Lithium-ion avec une électrode de graphite à la négative, les performancesélectrochimiques et la stabilité thermique à l’état chargé de la batterie sont largementdiscutées par rapport à l’état de l’art et notamment au matériau de coeur riche en Li eten MnThis work describes in details the implementation of the synthesis protocol for theformation of Li- and Mn-rich layered oxides with concentration-gradients. The purposewas to develop the synthesis of Li- and Mn-rich layered oxides in the bulk of sphericalaggregates of active material and, moving to the surface, to enrich the layered oxides’composition with Co and Ni, in order to combine a high energy density (provided bythe bulk) and an excellent thermal and structural stability (provided by the surface).The synthesis was performed in two steps, a coprecipitation to form a transition metalcarbonate followed by a calcination at high temperature to obtain the lithiated activematerial. The influence of several parameters (pH, feeding rate, size of the reactor,composition …) on the nature of the carbonates formed with concentration-gradientswas studied. Similarly, the control of the Li/M ratio (with M = Ni, Co, Mn) and of thetemperature and duration of calcination was revealed to be important to maintain theconcentration-gradient in the lithiated materials. The Li/M ratio is also the keyparameter to control the nature of the materials obtained (layered - spinel or layered -layered). Advanced characterizations, complex to be implemented, were performed inorder to obtain in-depth information on the distribution of phases within the aggregates(composition and structure), from the bulk to the surface: complementary microscopytechniques (EPMA, SEM-EDS and FIB-STEM) were widely used. The most interestingmaterials were studied in Lithium-ion batteries with graphite at the negative electrode,their electrochemical performance and the thermal stability in the charged state of thebattery were compared to the state of art, and particularly to the bulk Li and Mn-richlayered oxide
Books on the topic "Concentration gradient force"
1
Mast, Christof, Friederike Möller, Moritz Kreysing, Severin Schink, Benedikt Obermayer, Ulrich Gerland, and Dieter Braun. Toward living nanomachines. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199674923.003.0039.
Full textAbstract:
How does inanimate matter become transformed into animate matter? Living systems evolve by replication and selection at the molecular level and this chapter considers how to establish a synthetic, minimal system that can support molecular evolution and thus life. Molecular evolution cannot be explained by starting with high concentrations of activated chemicals that react toward their chemical equilibrium; persistent non-equilibria are required to maintain continuous reactivity and we especially consider thermal gradients as an early driving force for Darwinian molecular evolution. The temperature difference across water-filled compartments implements a laminar fluid convection with periodic temperature oscillations that allow for the melting and replication of DNA. Simultaneously, dissolved molecules are moved along the thermal gradient by an effect called thermophoresis. The combined result is an efficient molecule trap that exponentially favors long over short DNA and thus maintains complexity. Future experiments will reveal how thermal gradients could actively drive the Darwinian process of replication and selection.
Book chapters on the topic "Concentration gradient force"
1
Tamagawa, M., and K. Matsumura. "Driving Force of a Neutrophile in Liquid By Concentration Gradient For Developing DDS Particles and Capsules with Propulsion." In IFMBE Proceedings, 130–31. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-29305-4_36.
Full text
2
Tinker, Peter B., and Peter Nye. "Local Movement of Solutes in Soil." In Solute Movement in the Rhizosphere. Oxford University Press, 2000. http://dx.doi.org/10.1093/oso/9780195124927.003.0008.
Full textAbstract:
In the previous chapter, we dealt with the distribution of solutes between gas, liquid and solid phases in the soil at equilibrium; and with the rates of redistribution between these phases within soil pores. In this chapter, we consider movement of the order of 1 –1000 mm from one volume of soil to another. Such movements occur largely by diffusion and mass flow of the soil solution or soil air, and by mass movement of the body of the soil. Major movements that involve the balance and amount of solutes in the whole soil profile, including plant uptake and drainage losses, are treated in chapter 11. The process of diffusion results from the random thermal motion of ions, atoms or molecules. Consider a long column of unit cross-section orientated along the x axis, and containing a mixture of components in a single phase at constant temperature and external pressure. If the concentration of an uncharged component is greater at section A than at section B, then on average more of its molecules will move from A to B than from B to A. The net amount crossing a unit section in unit time, which is the flux, is given by the empirical relation known as Pick’s first law: . . . F = − D dC/dx (4.1) . . . where F is the flux, and dC/dx is the concentration gradient across the section. The minus sign arises because movement is from high to low concentration in the direction of increasing x. The diffusion coefficient, D, is thus defined by the equation as a coefficient between two quantities, F and dC/dx, which can be measured experimentally. It is not necessarily a constant. The diffusion coefficient of the molecules in a phase is directly proportional to their absolute mobility, u, which is the limiting velocity they attain under unit force. Terms D and u are related by the Nernst-Einstein equation: . . . D = ukT (4.2) . . . where k is the Boltzmann constant and T is the temperature on the Kelvin scale. The Nernst-Einstein equation is derived as follows (Atkins 1986, p. 675).
3
Bokstein, Boris S., Mikhail I. Mendelev, and David J. Srolovitz. "Thermodynamics of irreversible processes." In Thermodynamics and Kinetics in Materials Science. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780198528036.003.0011.
Full textAbstract:
The thermodynamics of irreversible processes, formulated by Onsager and Prigogine, considers small deviations from equilibrium in open systems. Despite the fact that the name contains ‘‘thermodynamics,’’ this is a type of kinetic theory that describes the rates of irreversible processes. Since there are no currents of any type in thermodynamic equilibrium, the concept of a current is never used in classical thermodynamics. On the other hand, the thermodynamics of irreversible processes introduces currents as the rates at which processes proceed: the heat or energy current (measured in J/s), matter current (measured in mole/s or kg/s), charge or electrical current (measured in C/s or Amps). Since these currents have a direction and magnitude, they are vectors. The thermodynamics of irreversible processes also considers scalar currents (e.g. rates of chemical reactions) and tensor currents (e.g. momentum currents). In this text, we will focus on current densities or fluxes (that is the current per unit area) rather than currents themselves. The dimensions of the currents described above can be converted to the dimensions of fluxes by dividing through by area or m2. Associated with each flux is a driving force. These forces are known as thermodynamic forces. How can we determine these driving forces? What is the relation between fluxes and driving forces? The answers to these questions can be found in the thermodynamics of irreversible processes briefly described in this chapter. Onsager’s first postulate states that the flux of property i ( ji) is a linear function of all thermodynamic forces, Xk, acting in the system where Lik are called Onsager (or kinetic) coefficients. This postulate was formulated as a generalization of a wide body of experimental observations. In fact, long before Onsager’s work it was known that the heat fluxes are proportional to temperature gradients (Fourier’s law, 1824), charge fluxes are proportional to electric potential gradients (Ohm’s law, 1826), and matter fluxes are proportional to concentration gradients (Fick’s law, 1855). However, Onsager’s contribution was the inclusion of the word ‘‘all’’ in his first postulate.
4
"Mass Transfer Phenomenon and Transport Resistances in Membrane Separation." In Membrane Technology for Water and Wastewater Treatment in Rural Regions, 25–71. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-7998-2645-3.ch002.
Full textAbstract:
The inevitable decline of membrane performance in membrane separation processes can be optimized through a good understanding of the mass transfer phenomenon and the transport resistances involved in the operation. Thus, this chapter focused on the discussions of mass transfer mechanisms and models in membrane separation based on several types of driving forces. This includes the pressure from a mechanical operation, partial pressure, osmotic pressure, concentration, and also thermal gradients. The chapter elaborates on the transport resistances in membrane resulting from membrane fouling and concentration polarization. The author hopes that readers, especially engineers and technical operators, gain a deep understanding and comprehensive knowledge regarding the theories and are able to utilize the knowledge to optimize the membrane operation.
5
Aveyard, Bob. "Thin liquid films." In Surfactants, 314–36. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198828600.003.0012.
Full textAbstract:
The study of soap films, which are symmetrical, has a distinguished history. More recently, other asymmetric liquid films (e.g. pseudo-emulsion films and wetting films on solids) have been widely investigated. The (meta)stability of thin liquid films can be understood in terms of disjoining pressure isotherms, the shapes of which reflect the nature of the films. Film stability in systems with only fluids present can also be considered in terms of both classical and generalized entry coefficients, defined in terms of the various interfacial tensions in the system. Film rupture obviously occurs as a result of dynamic processes. Film drainage (thinning) rate is influenced by surface concentration gradients in the surfactant layers at film surfaces and by the effects of Marangoni flow within the films. To be stable, films need to have elastic properties in order to withstand mechanical perturbations. If the repulsive forces between surfaces become insufficient, hole formation will lead to film rupture.
6
Bokstein, Boris S., Mikhail I. Mendelev, and David J. Srolovitz. "Diffusion." In Thermodynamics and Kinetics in Materials Science. Oxford University Press, 2005. http://dx.doi.org/10.1093/oso/9780198528036.003.0012.
Full textAbstract:
Diffusion is associated with the random, thermal motion of atoms that produces a change in the macroscopic concentration profile. This process occurs in gases, liquids, amorphous and crystalline solids of metals, ceramics, polymers, semiconductors, etc. The investigation of diffusion provides valuable information about the atomic structure of materials and the defects within them. Perhaps, most importantly, diffusion controls the rates of a wide range of kinetic processes associated with the synthesis of materials, processes by which we modify materials, and processes by which materials fail. The most common driving force for diffusion in a single-phase systems is associated with the entropy of mixing of its constituents (recall that we showed that the entropy of mixing of gases and the components of an ideal solution are always positive—see Sections 1.2.6 and 3.3). Since diffusional processes occur through the thermal motion of atoms (see below), it will not be surprising to learn that the rate of diffusion increases with increasing temperature. However, note that while the mechanisms of thermal motion in gases (random collision of atoms with each other) and liquids (e.g. Brownian motion) necessarily lead to mixing, the mechanisms of mixing within a solid are not as obvious. In solids, thermal motion corresponds to the vibrations of atoms near their equilibrium positions. Since the amplitude of such vibrations is much smaller than the nearest-neighbor separation, it would seem that such thermal motions cannot lead to mixing. Thus, the question ‘‘how do atoms migrate in solids’’ is not so simple. The equations describing diffusion were suggested by the physiologist Fick in 1855 as a generalization of the equations for heat transfer suggested by Fourier in 1824. Fick’s equations for diffusion can be obtained by analogy with Fourier’s equations for heat transfer by replacing heat with the number of atoms, temperature with concentration, and thermal conductivity with diffusivity. Fick’s first law provides a relationship between atomic currents and concentration gradients. As discussed above, this relationship can be understood by analogy with thermal conductivity or electrical conductivity.
7
"Benthic Habitats and the Effects of Fishing." In Benthic Habitats and the Effects of Fishing, edited by Vladimir E. Kostylev, Brian J. Todd, Oddvar Longva, and Page C. Valentine. American Fisheries Society, 2005. http://dx.doi.org/10.47886/9781888569605.ch12.
Full textAbstract:
<strong><em>Abstract. </em></strong>Seafloor habitats of the Canadian part of Georges Bank were assessed and mapped following the habitat template theory (Southwood 1988). The approach considers the primary selective forces (habitat disturbance and adversity of the environment) that have shaped the existing communities of benthic species and that have defined the life history traits of species found in different habitats. The disturbance axis of the template is modeled based on the information on sediment, currents, and bathymetry. The adversity axis is modeled based on chlorophyll concentration, bottom water temperature, salinity, and seasonal variability in temperature. A preliminary sediment map needed for assessment of the natural disturbance rate was developed from high-resolution multibeam backscatter groundtruthed with archive and current sediment sample data. The distribution of megabenthos assemblages identified from underwater photography was found to follow gradients in disturbance and adversity on the bank. We suggest that application of the habitat template theory is useful for ocean managers in defining areas that are more or less likely to suffer from adverse human impacts. If natural rates of habitat disturbance are high, then risk of harmful habitat alteration and degradation is lower than in naturally stable areas. Similarly, if the natural adversity of the environment is high, then adding additional stressors will further reduce the scope for growth of organisms, which makes natural populations in adverse environments less likely to recover than populations in benign environments.
8
Bunker, Bruce C., and William H. Casey. "The Colloidal Chemistry of Oxides." In The Aqueous Chemistry of Oxides. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780199384259.003.0014.
Full textAbstract:
Colloids are defined as suspensions of finely divided particles in a continuous medium that do not settle rapidly and are not readily filtered. To be more specific, the International Union of Pure and Applied Chemistry defines a colloid as any material for which one or more of its three dimensions lies within the size range of 1 to 1000 nm. As the nucleation and growth of oxides from aqueous solutions almost always produces suspensions containing submicron particles (see Chapter 7), typical oxide suspensions fall squarely within the colloidal domain. In this book, we consider colloidal particles to represent oxides or hydroxides that are small enough to stay in aqueous suspensions for more than a few hours, yet are larger and lacking in the specific molecular structures of typical hydrolysis products (see Chapter 5). Given the density range of most oxides (from around 2−10 g/cm3), the sizes of most colloidal oxides fall within the limits of the International Union of Pure and Applied Chemistry (see Section 8.4.5). Colloidal oxide particles suspended in water represent a complex chemical environment. At the molecular level, protons, ions, small molecules, and polymeric species interact with particle surfaces to create charged surface sites and promote adsorption and desorption phenomena (see Chapter 6). These modified surfaces perturb the adjacent liquid, creating ordered solvent layers and strong concentration gradients in ions and other dissolved species. These interfacial phenomena generate a range of forces called interaction potentials. Such forces determine whether particles repel each other (leading to stable suspensions) or are attracted to one another, resulting in agglomeration and sedimentation phenomena. The length scales of those components of the oxide–water interface that influence the interaction potentials to be discussed in this chapter are introduced in Figure 8.1. At the subatomic level, the correlated polarization of electron clouds gives rise to dispersion forces described by quantum mechanics that contribute to van der Waals interactions. At the atomic level, the inherent charge on each exposed oxygen anion that terminates the oxide surface is controlled by local chemical bonds to adjacent cations (see Chapter 6).
Conference papers on the topic "Concentration gradient force"
1
Asako, Yutaka. "Oxygen Separation/Enrichment From Atmospheric Air Using Magnetizing Force." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61073.
Full textAbstract:
The possibility of oxygen separation/enrichment from atmospheric air using a magnetizing force was investigated numerically. Direct Simulation Monte Carlo (DSMC) method was utilized to obtain distribution of oxygen concentration in a capsule under a strong magnetic field gradient. The molecular movement was calculated by taking into account the magnetizing force on the molecules. The computations were performed for a wide range of pressure and magnetic flux density gradient. The simulation results showed that there is a possibility of oxygen separation/enrichment from atmospheric air under a strong magnetic field gradient.
2
Tamagawa, Masaaki. "Fundamental Investigations of Driving Force of a Neutrophile in Liquid Using Concentration Marangoni Effect for Developing Microcapsules in Drug Delivery Systems." In ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/fedsm2008-55319.
Full textAbstract:
This paper describes the effects of gradient of cytokine concentration on chemotaxis of neutrophile by observing the motion in liquid with adding cytokine concentration. The aim of this investigation is to control of neutrophile motion in liquid by concentration gradient for drug delivery systems.
3
Tamagawa, Masaaki. "Fundamental Investigations of Driving Force of Microcapsule for Drug Delivery Systems Using the Principle of Neutrophile’s Chemotaxis." In ASME 2007 2nd Frontiers in Biomedical Devices Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/biomed2007-38091.
Full textAbstract:
This paper describes the effects of gradient of cytokine concentration on chemotaxis of neutrophile by observing the motion in liquid with adding cytokine concentration. The aim of this investigation is to distinguish the driving force by Marangoni effects from amebic motion.
4
Asako, Yutaka, and Yohei Suzuki. "Oxygen Separation/Enrichment From Atmospheric Air Using Magnetizing Force: Air Flow in a Duct Under Magnetic Field Gradient." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-79812.
Full textAbstract:
Oxygen is paramagnetic gas and it has relatively high magnetic susceptibility. On the contrary, nitrogen is diamagnetic gas and it has relatively low and negative magnetic susceptibility. This results in counter magnetizing forces acting on these gases. The possibility of oxygen separation/enrichment from atmospheric air flow using a magnetizing force was investigated numerically. Direct Simulation Monte Carlo (DSMC) method was utilized to obtain distribution of oxygen concentration of air flow in a parallel-plate duct under a strong magnetic field gradient. The molecular movement was calculated by taking into account the magnetizing forces on the molecules. The computations were performed for a wide range of pressure and magnetic flux density gradient. The simulation results showed that there is a possibility of oxygen separation/enrichment from decompressed air under a strong magnetic field gradient.
5
Tasaka, Eiji, and Yutaka Asako. "Enhancement of Oxygen Diffusion in a Gas Diffusion Layer of a Fuel Cell Electrode by Magnetizing Force." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-38428.
Full textAbstract:
Possibility of enhancement of oxygen diffusion in a gas diffusion layer of a fuel cell electrode is numerically investigated. Since oxygen is paramagnetic gas, it is attracted to a field of high magnetic flux density by the magnetizing force. If there exists gradient of the oxygen concentration and the gradient of magnetic flux density in the gas diffusion layer, air flow occurs in the layer. Numerical computations were conducted for air flow in the gas diffusion layer of the electrode under the magnetic field which is generated by parallel electric currents. Darcy model is used to represent the air flow in the layer and the oxygen concentration was solved. The effects of the permiability of the electrode, intensity of the electric current, the location of the electric wire and the thickness of the electrode on the enhancement of oxygen transfer were investigated. As a result, 5 to 20% of enhancement of oxygen transfer by using magnetizing force was observed.
6
Saputra, P. F. Geelhoed, J. F. L. Goosen, R. Lindken, J. Westerweel, and F. van Keulen. "Microfabricated Thermal Gradient Separator Device." In ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer. ASMEDC, 2009. http://dx.doi.org/10.1115/mnhmt2009-18543.
Full textAbstract:
The design and fabrication of a microfabricated fluidic device for particle thermophoresis is presented. The ability of the device to concentrate particles by generating a huge thermal gradient is demonstrated. In contrast to other microfluidics devices which use electrokinetics or pressure driven flow, in this device no external force acts on the particles. The separator device has been fabricated in a standard silicon substrate, consisting of a 20 μm deep channel and a 600 nm thick aluminum heater integrated into the device. The device is able to create a thermal gradient of approximately 104 Km−1. To maintain a thermal gradient over a long period, special attention had to be given to the design of the integrated heater and thermal insulation of the channel. In order to deposit the aluminum heater on the side wall of a micro channel, a silicon substrate was wet etched in KOH solution, forming sloping sidewalls. The temperature difference was measured using a thermocouple mounted on the two sides of the channel walls, showing about 2 K temperature difference. Experimental studies have been conducted in order to study the motion of particles in response to the thermal gradient. Particle motions are recorded before and after turning on the heater. Using polystyrene latex particles suspended in de-ionized water, it is shown that 90% of particles are concentrated on the cold side of the channel after 300 seconds using only 1W of electrical power. Apart from its applicability to particle suspensions, this device also has a great potential for DNA molecule concentration and separation in bio-chemical analysis.
7
Emdadi, Arash, Simin Emdadi, Mansour Zenouzi, and Gregory Kowalski. "Activity Coefficient of Different Salt Solutions for Reverse Electrodialysis Application." In ASME 2019 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/imece2019-10739.
Full textAbstract:
Abstract Renewable energy sources and related conversion technologies are considered as the main solution for resolving the current issues related to global warming and environmental protection. Salinity gradient energy (SGE) is a source of renewable energy which can be defined as the Gibbs Energy of mixing when two solutions with different salinities mix together. The difference in the salinity of salt solutions is the main driving force of energy production by the SGE conversion technologies. One of the main conversion technologies of SGE is reverse electrodialysis (RED). In this technology the gradient between the concentrated and diluted salt solutions, the ions with a negative charge (anion) and positive charge (cation) pass through selective ion exchange membranes known as anion exchange membrane and cation exchange membrane. The driving force for diffusion of the ions is a function of the concentration gradient. The chemical potential of the salt solution is a function of the concentration of the salt solution and plays an important role in the Gibbs energy of mixing. The chemical potential of the salt solution is a thermodynamic property which is a function of the concentration and activity coefficient of the salt solution. The activity coefficient of the salt solution is a unique parameter which depends on the ionic strength of the solution and the type of ions in the salt solution. The salts with higher activity coefficient have a higher potential to be used in the SGE conversion process due to higher released Gibbs Energy during the mixing process. In this paper the thermodynamic model presented by Bromley [1], is used to calculate activity coefficient of 20 salts at different concentrations (0.01–6 molal). Two dimensionless parameters, Φ and Ψ, are defined as the ratio of activity coefficient and concentration between the concentrated and diluted solutions in 6 and 0.5 molal respectively. Using the dimensionless parameters, the theoretical open circuit voltage (OCV) of salt solutions in a RED cell is calculated. The salts are screened and ranked based on the activity coefficients and the theoretical open circuit voltage (OCV). The best salts are selected for use in a RED cell based on the activity coefficients and theoretical OCV. These alts could have potential for developing SGE storage systems in combination with renewable energy devices.
8
Anandan, Nishita, and Mamidala Ramulu. "Experimental Investigation of Peripheral Milling of Functionally Gradient Al-SiC Metal Matrix Composite." In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71648.
Full textAbstract:
Metal matrix composites (MMCs) offer superior mechanical and thermal properties, but the poor machinability of these composites hinders their wide application [1,2]. The machinability of the MMCs are found to be largely dependent on the particle size and volume fraction of the reinforcements used. Experimental investigation on process modeling of MMCs by milling is undertaken. In this study, peripheral milling of functionally gradient concentration of SiC in aluminum matrix using carbide tools is discussed. The process conditions were varied namely, the feed was varied from 0.1 mm/rev to 0.3 mm/rev and the speed from 1000 to 5000 rpm with a constant depth of cut of 1.27mm. The variation of cutting force, surface roughness and cut surface morphology with varying SiC particle distribution, feed and speed are reported. The interaction of the cutting edge with hard SiC particles in Al matrix was also studied using the scanning electron microscopy (SEM). The cutting force and surface roughness were found to increase with increasing volume fraction of SiC particles. Preliminary observation showed that the SiC particles were either removed from the matrix by debonding due to mismatch of thermal coefficients or were fractured by the action of the cutting edge or were pushed into the aluminum matrix.
9
Dubey, Kaushlendra, Amit Gupta, and Supreet Singh Bahga. "Electrokinetic Dispersion in Field Amplified Sample Stacking." In ASME 2018 16th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/icnmm2018-7703.
Full textAbstract:
In this work, we performed an experimental study of electrohydrodynamic effects on the dispersion of sample ions in field amplified sample stacking (FASS). A typical FASS experiment involves a streamwise electrical conductivity gradient collinear to the applied electric field to enhance the sample stacking. Earlier studies on FASS have focused on how the conductivity gradient sets a non-uniform electro-osmotic flow which causes the dispersion. However, the coupling of the electric field with conductivity gradient leads to a destabilizing electric body force and generates unstable flow. This work demonstrates that generated body force influences the dynamics of FASS. We present a scaling analysis to show that at high fields, electrohydrodynamic effects play a vital role in sample dispersion. To justify our scaling arguments, we performed experiments at varied electric fields which shows that at high electric fields maximum concentration enhancement is lowered significantly. To ensure the EHD effects on the dynamics of FASS, we have also performed experiments with suppressed EOF conditions.
10
Takagi, Youhei, Atsuko Ishida, Yasunori Okano, and Sadik Dost. "A Numerical Simulation Study on the Effects of Crucible Rotation and Magnetic Fields in Growth of SiGe by the Travelling Heater Method." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-23025.
Full textAbstract:
A numerical simulation study was carried out to shed light on the effects of applied crucible rotation and static magnetic field during the THM (travelling heater method) growth of bulk SiGe single crystals. The simulation results show that the application of crucible rotation weakens the radial silicon concentration gradient due to the effect of centrifugal force. The effects of applied static magnetic field direction and strength on the concentration field in the melt were also studied. It was found that the simultaneous application of crucible rotation and static magnetic field is best to grow large crystals with uniform composition. An optimum combination of crucible rotation rates and applied magnetic field strengths is determined.