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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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Kale, G. B. "Thermodynamic Diffusion Coefficients." Defect and Diffusion Forum 279 (August 2008): 39–52. http://dx.doi.org/10.4028/www.scientific.net/ddf.279.39.
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A new form of diffusion coefficient termed as thermodynamic diffusion coefficient is introduced in this paper. Conventionally, diffusion coefficients are evaluated using concentration gradient as driving force. But truly, chemical potential gradient is the actual driving force that determines the material flow in any part of the system. Thermodynamic diffusion coefficients are based on chemical potential gradient as driving force. The relation between thermodynamic diffusion coefficients and phenomenological coefficients has been established. The advantages of thermodynamic diffusion coefficients have been underlined, especially, in the cases of line compounds where concentration difference across the phase is zero or in case of intermetallic compounds with narrow homogeneity range. The intrinsic thermodynamic diffusion coefficients are equal to tracer diffusion coefficients. This helps in estimating tracer diffusivities in cases where tracers are not easily available. The advantages of thermodynamic diffusion coefficients are shown in binary and ternary systems by illustrating them in Ni-Al and Fe-Ni-Cr systems.
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Soboll, S., C. Horst, H. Hummerich, J. P. Schumacher, and H. J. Seitz. "Mitochondrial metabolism in different thyroid states." Biochemical Journal 281, no. 1 (January 1, 1992): 171–73. http://dx.doi.org/10.1042/bj2810171.
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The protonmotive force, as well as the mitochondrial and cytosolic concentrations of malate, 2-oxoglutarate, glutamate and aspartate, were determined in livers from hypo-, eu- and hyper-thyroid rats, by density-gradient centrifugation of freeze-clamped livers in non-aqueous solvents [Soboll, Akerboom, Schwenke, Haase & Sies (1980) Biochem. J. 192, 951-954]. The mitochondrial/cytosolic pH difference and the membrane potential were significantly enhanced in hyperthyroid livers compared with the hypothyroid state, resulting in an increased protonmotive force in the presence of thyroid hormones [Soboll & Sies (1989) Methods Enzymol. 174, 118-130]. The mitochondrial concentrations of 2-oxoglutarate, glutamate and aspartate were significantly higher in the euthyroid than in the hypothyroid state, but only slightly higher in the hyperthyroid state. Mitochondrial malate, on the other hand, increased significantly from the hypothyroid to the hyperthyroid state. The mitochondrial/cytosolic concentration gradients were significantly increased in the presence of thyroid hormones only for malate. The changes in steady-state metabolite concentrations reflect a higher substrate supply and a stimulation of mitochondrial metabolism. However, a clear relationship between the increased protonmotive force, as the driving force for mitochondrial metabolite transport, and the subcellular metabolite concentrations is not observable in different thyroid states.
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BUCK, KRISTAN K. S., STEPHANIE R. DUNGAN, and RONALD J. PHILLIPS. "The effect of solute concentration on hindered gradient diffusion in polymeric gels." Journal of Fluid Mechanics 396 (October 10, 1999): 287–317. http://dx.doi.org/10.1017/s0022112099006035.
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The effect of solute concentration on hindered diffusion of sphere-like colloidal solutes in stiff polymer hydrogels is examined theoretically and experimentally. In the theoretical development, it is shown that the presence of the gel fibres enhances the effect of concentration on the thermodynamic driving force for gradient diffusion, while simultaneously reducing the effect of concentration on the hydrodynamic drag. The result is that gradient diffusion depends more strongly on solute concentration in gels than it does in pure solution, by an amount that depends on the partition coefficient and hydraulic permeability of the gel–solute system. Quantitative calculations are made to determine the concentration-dependent diffusivity correct to first order in solute concentration. In order to compare the theoretical predictions with experimental data, rates of diffusion have been measured for nonionic micelles and globular proteins in solution and agarose hydrogels at two gel concentrations. The measurements were performed by using holographic interferometry, through which one monitors changes in refractive index as gradient diffusion takes place within a transparent gel. If the solutes are modelled as spheres with short-range repulsive interactions, then the experimentally measured concentration dependence of the diffusivities of both the protein and micelles is in good agreement with the theoretical predictions.
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Hisajima, T., L. Mao, K. Shinzato, M. Nakano, and J. Suehiro. "Three Dimensional Bacteria Concentration by Negative Dielectrophoresis." Advanced Materials Research 699 (May 2013): 251–56. http://dx.doi.org/10.4028/www.scientific.net/amr.699.251.
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Thispaper reports a novel method to concentrate bacteria in three-dimension by negative dielectrophoretic (n-DEP) force in a microchannel. This was achieved by placing a thin dielectric layer on one of a pair of parallel plate electrodes. The dielectric layer having a home-plate like pentagonal shape, forms a gradient of electric field causing n-DEP. A three-dimensional numerical simulation of bacteria trajectory predicts that bacteria flowing a microchannel were three-dimensionally concentrated beneath the tip of the pentagonal dielectric thin layer. The trajectory and concentration of bacteria under n-DEP force were also experimentally confirmed using Escherichia coli cells. Bacteria moved along edges of the dielectric layer and were pushed to the opposite electrode, resulting in their concentration in three-dimension. The proposed device might be applicable to selective concentration of bacteria depending on their dielectric properties.
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Tsuda, Masahiro, Tomohiro Terada, Jun-ichi Asaka, Miki Ueba, Toshiya Katsura, and Ken-ichi Inui. "Oppositely directed H+ gradient functions as a driving force of rat H+/organic cation antiporter MATE1." American Journal of Physiology-Renal Physiology 292, no. 2 (February 2007): F593—F598. http://dx.doi.org/10.1152/ajprenal.00312.2006.
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Recently, we have isolated the rat (r) H+/organic cation antiporter multidrug and toxin extrusion 1 (MATE1) and reported its tissue distribution and transport characteristics. Functional characterization suggested that an oppositely directed H+ gradient serves as a driving force for the transport of a prototypical organic cation, tetraethylammonium, by MATE1, but there is no direct evidence to prove this. In the present study, therefore, we elucidated the driving force of tetraethylammonium transport via rMATE1 using plasma membrane vesicles isolated from HEK293 cells stably expressing rMATE1 (HEK-rMATE1 cells). A 70-kDa rMATE1 protein was confirmed to exist in HEK-rMATE1 cells, and the transport of various organic cations including [14C]tetraethylammonium was stimulated in intracellular acidified HEK-rMATE1 cells but not mock cells. The transport of [14C]tetraethylammonium in membrane vesicles from HEK-rMATE1 cells exhibited the overshoot phenomenon only when there was an outwardly directed H+ gradient, as observed in rat renal brush-border membrane vesicles. The overshoot phenomenon was not observed in the vesicles from mock cells. The stimulated [14C]tetraethylammonium uptake by an H+ gradient [intravesicular H+ concentration ([H+]in) > extravesicular H+ concentration ([H+]out)] was significantly reduced in the presence of a protonophore, carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). [14C]tetraethylammonium uptake was not changed in the presence of valinomycin-induced membrane potential. These findings definitively indicate that an oppositely directed H+ gradient serves as a driving force of tetraethylammonium transport via rMATE1, and this is the first demonstration to identify the driving force of the MATE family. The present experimental strategy is very useful in identifying the driving force of cloned transporters whose driving force has not been evaluated.
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MATSUMURA, Kosuke, and Masaaki TAMAGAWA. "G304 Propulsion mechanism of white blood cell with driving force by concentration gradient in liquid." Proceedings of the Fluids engineering conference 2009 (2009): 559–60. http://dx.doi.org/10.1299/jsmefed.2009.559.
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Weier, Tom, Kerstin Eckert, Sascha Mühlenhoff, Christian Cierpka, Andreas Bund, and Margitta Uhlemann. "Confinement of paramagnetic ions under magnetic field influence: Lorentz versus concentration gradient force based explanations." Electrochemistry Communications 9, no. 10 (October 2007): 2479–83. http://dx.doi.org/10.1016/j.elecom.2007.07.026.
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Tabushi, Kenichi, Hisashi Sato, and Yoshimi Watanabe. "Effect of Casting Condition on Density and Hardness Gradients of Al-Al2Cu Alloy FGM Fabricated by Centrifugal In Situ Method." Materials Science Forum 631-632 (October 2009): 449–54. http://dx.doi.org/10.4028/www.scientific.net/msf.631-632.449.
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Functionally graded material (FGM) is a combined material that has a component gradient from one material at one surface to another material at the opposite surface. As one of the fabrication processes of FGM, centrifugal in-situ method has been proposed. Centrifugal in-situ method is a casting that centrifugal force is applied during solidification to both the primary crystal and the matrix. In a previous study, the density and hardness gradients of Al-3mass%Cu FGM ring fabricated by centrifugal in-situ method have been investigated. According to the study, Cu concentration within the FGM ring monolithically increases towards the ring's inner position, and its density also increases toward inner region. This is because the density of the primary -Al crystal is larger than that of the molten Al-Cu alloy in the early stage of solidification. Based on this solidification process, it is considered that the casting condition and the initial Cu concentration of Al-Cu master alloy affect on the density and hardness gradients in the Al-Cu FGM ring. In this study, effects of the casting condition on the density and hardness gradients of Al-Al2Cu FGM rings fabricated by the centrifugal in-situ method were investigated. It was found that density gradient of the Al-Al2Cu FGM rings increases with increasing Cu concentration of Al-Cu master alloys. Also, processing temperature for Al-Cu master alloy can control density gradient of Al-Al2Cu FGM rings. These phenomena were explained by variation of the densities of primary -Al and the molten Al matrix during the solidification.
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Oymaci, Pelin, Pauline E. Offeringa, Zandrie Borneman, and Kitty Nijmeijer. "Effect of Osmotic Pressure on Whey Protein Concentration in Forward Osmosis." Membranes 11, no. 8 (July 29, 2021): 573. http://dx.doi.org/10.3390/membranes11080573.
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Forward osmosis (FO) is an emerging process to dewater whey streams energy efficiently. The driving force for the process is the concentration gradient between the feed (FS) and the concentrated draw (DS) solution. Here we investigate not only the effect of the DS concentration on the performance, but also that of the FS is varied to maintain equal driving force at different absolute concentrations. Experiments with clean water as feed reveal a flux increase at higher osmotic pressure. When high product purities and thus low reverse salt fluxes are required, operation at lower DS concentrations is preferred. Whey as FS induces severe initial flux decline due to instantaneous protein fouling of the membrane. This is mostly due to reversible fouling, and to a smaller extent to irreversible fouling. Concentration factors in the range of 1.2–1.3 are obtained. When 0.5 M NaCl is added to whey as FS, clearly lower fluxes are obtained due to more severe concentration polarization. Multiple runs over longer times show though that irreversible fouling is fully suppressed due to salting in/out effects and flux decline is the result of reversible fouling only.
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Lukyanov, Alexander V., Stanislav M. Orlov, and Boris R. Romanenko. "Study of the characteristics of the ascending vortex of the cyclone and the concentration of dust along its section." Vestnik MGSU, no. 8 (August 2021): 1034–44. http://dx.doi.org/10.22227/1997-0935.2021.8.1034-1044.
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Introduction. Protection of the atmosphere is a social and economic problem inextricably linked with the task of creating comfortable conditions for human life and work. Cyclones are the most typical representatives of dry inertial dust collectors. This work is aimed at reducing energy consumption when cleaning gas with cyclones.
Materials and methods. In the course of the work, analytical and experimental research methods were applied.
Results. Analytical dependences of the aerodynamics of the ascending cyclone vortex have been obtained, which showed that the ascending vortex has a complex structure and the cyclone is an artificially created spiral structure, akin to such a natural phenomenon as a tornado. The obtained mathematical model was fully confirmed by experimental studies.
Conclusions. The studies carried out show that the ascending vortex in the cyclone has a structure consisting of two zones. In the first zone (core), the force of the radial pressure gradient exceeds the centrifugal force, and the dust rushes towards the cyclone axis. In the second, the centrifugal force exceeds the force of the pressure gradient, and the dust is thrown to the periphery. The obtained theoretical model will make it possible to reasonably choose methods for more rational use of the expended energy and increasing the efficiency of cyclones.
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Huyghe, Jacques M. "Biaxial testing of canine annulus fibrosus tissue under changing salt concentrations." Anais da Academia Brasileira de Ciências 82, no. 1 (March 2010): 145–51. http://dx.doi.org/10.1590/s0001-37652010000100012.
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The in vivo mechanics of the annulus fibrosus of the intervertebral disc is one of biaxial rather than uniaxial loading. The material properties of the annulus are intimately linked to the osmolarity in the tissue. This paper presents biaxial relaxation experiments of canine annulus fibrosus tissue under stepwise changes of external salt concentration. The force tracings show that stresses are strongly dependent on time, salt concentration and orientation. The force tracing signature of are sponse to a change instrain, is one of a jumpin stress that relaxes partly as the new strain is maintained. The force tracing signature of a stepwise change in salt concentration is a progressive monotonous change in stress towards a new equilibrium value. Although the number of samples does not allow any definitive quantitative conclusions, the trends may shed light on the complex interaction among the directionality of forces, strains and fiber orientation on one hand, and on the other hand, the osmolarity of the tissue. The dual response to a change in strain is understood as an immediate response before fluid flows in or out of the tissue, followed by a progressive readjustment of the fluid content in time because of the gradient in fluid chemical potential between the tissue and the surrounding solution.
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Tiruppathi, C., D. F. Balkovetz, V. Ganapathy, Y. Miyamoto, and F. H. Leibach. "A proton gradient, not a sodium gradient, is the driving force for active transport of lactate in rabbit intestinal brush-border membrane vesicles." Biochemical Journal 256, no. 1 (November 15, 1988): 219–23. http://dx.doi.org/10.1042/bj2560219.
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An inward-directed H+ gradient markedly stimulated lactate uptake in rabbit intestinal brush-border membrane vesicles, and uphill transport against a concentration gradient could be demonstrated under these conditions. Uptake of lactate was many-fold greater in the presence of a H+ gradient than in the presence of a Na+ gradient. Moreover, there was no evidence for uphill transport of lactate in the presence of a Na+ gradient. The H+-gradient-dependent stimulation of lactate uptake was not due to the effect of a H+-diffusion potential. The uptake process in the presence of a H+ gradient was saturable [Kt (concn. giving half-maximal transport) for lactate 12.7 +/- 4.5 mM] and was inhibited by many monocarboxylates. It is concluded that a H+ gradient, not a Na+ gradient, is the driving force for active transport of lactate in rabbit intestinal brush-border membrane vesicles.
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Mukai, Kusuhiro, Masafumi Zeze, and Takashi Morohoshi. "Motion of Fine Particles under Interfacial Tension Gradient in Relation to Solidification of Steel." Materials Science Forum 508 (March 2006): 211–20. http://dx.doi.org/10.4028/www.scientific.net/msf.508.211.
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It is important to understand the behavior of argon gas bubbles and non-metallic inclusions in front of the solidifying shell in order to improve the surface quality of steel products, in the steelmaking industry. Based on a series of fundamental researches on the motion of fine particles under the interfacial tension gradient, Mukai and Lin [1] proposed a new mechanism wherein the solute concentration gradient in front of the solidifying shell, which is the interfacial tension gradient between liquid steel and particles, plays an important role in the entrapment of argon gas bubbles and non-metallic inclusions by the solidifying shell in continuous casting of steel. Developing this idea, this paper proposes Mukai-value M for use in estimating the dependence of the interfacial gradient force required to entrap the particles on solute concentrations of steel. Use of this index enables rapid quantitative prediction of the behavior of argon gas bubbles and non-metallic inclusions in the continuous casting of steel.
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Kang, Kwan Hyoung, and Dongqing Li. "Force acting on a dielectric particle in a concentration gradient by ionic concentration polarization under an externally applied DC electric field." Journal of Colloid and Interface Science 286, no. 2 (June 2005): 792–806. http://dx.doi.org/10.1016/j.jcis.2005.01.049.
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He, Xiaoyi, and Micah Dembo. "Numerical Simulation of Oil-Droplet Cleavage by Surfactant." Journal of Biomechanical Engineering 118, no. 2 (May 1, 1996): 201–9. http://dx.doi.org/10.1115/1.2795960.
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We present numerical computations of the deformation of an oil-droplet under the influence of a surface tension gradient generated by the surfactant released at the poles (the Greenspan experiment). We find this deformation to be very small under the pure surface tension gradient. To explain the large deformation of oil droplets observed in Greenspan’s experiments, we propose the existence of a phoretic force generated by the concentration gradient of the surfactant. We show that this hypothesis successfully explains the available experimental data and we propose some further tests.
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Huang, Sheng, Jianhua Wang, Heng Sun, Yuna Fu, and Yan Wang. "Probing Changes in Ca2+-Induced Interaction Forces between Calmodulin and Melittin by Atomic Force Microscopy." Micromachines 11, no. 10 (September 30, 2020): 906. http://dx.doi.org/10.3390/mi11100906.
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Mechanobiology studies the means by which physical forces and mechanical properties change intra- or inter- biological macromolecules. Calmodulin (CaM) is involved in physiological activities and various metabolic processes in eukaryotic cells. Although the configuration changes in the interaction between calmodulin and melittin have been studied, the biomechanical relationship of their interaction has rarely been explored. Here, we measured the adhesion forces between calmodulin and melittin in solutions of gradient concentration of calcium ions using atomic force microscopy (AFM). We found that the specific (Fi) and nonspecific (F0) adhesion forces between single melittin and calmodulin in a PBS solution were 69.4 ± 5.0 and 29.3 ± 8.9 pN, respectively. In the presence of 10−7 to 10−3 M Ca2+ PBS solution, the Fi increased significantly to 93.8 ± 5.0, 139.9 ± 9.0, 140.4 ± 9.7, 171.5 ± 9.0, and 213.3 ± 17.8 pN, indicating that the unbinding force between melittin and calmodulin increased in the presence of Ca2+ in a concentration-dependent manner. These findings demonstrated that biomechanical studies based on AFM could help us better understand the melittin/calmodulin-binding processes in the presence of calcium and help us design and screen peptide drugs based on calmodulin.
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Othman, Karam Mazin Zeki, and Abdulkreem M. Salih. "Scaled conjugate gradient ANN for industrial sensors calibration." Bulletin of Electrical Engineering and Informatics 10, no. 2 (April 1, 2021): 680–88. http://dx.doi.org/10.11591/eei.v10i2.2738.
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In this paper, artificial neural network is used to calibrate sensors that are commonly used in industry. Usually, such sensors have nonlinear input output characteristic that makes their calibration process rather inaccurate and unsatisfied. Artificial neural network is utilized in an inverse model learning mode to precisely calibrate such sensors. The scaled conjugate gradient (SCG) algorithm is used in the learning process. Three types of industrial sensors which are gas concentration sensor, force sensors and humidity sensors are considered in this work. It is found that the proposed calibration technique gives fast, robust and satisfactory results.
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Hasler, Udo. "Controlled aquaporin-2 expression in the hypertonic environment." American Journal of Physiology-Cell Physiology 296, no. 4 (April 2009): C641—C653. http://dx.doi.org/10.1152/ajpcell.00655.2008.
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The corticomedullary osmolality gradient is the driving force for water reabsorption occurring in the kidney. In the collecting duct, this gradient allows luminal water to move across aquaporin (AQP) water channels, thereby increasing urine concentration. However, this same gradient exposes renal cells to great osmotic challenges. These cells must constantly adapt to fluctuations of environmental osmolality that challenge cell volume and incite functional change. This implies profound alterations of cell phenotype regarding water permeability. AQP2 is an essential component of the urine concentration mechanism whose controlled expression dictates apical water permeability of collecting duct principal cells. This review focuses on changes of AQP2 abundance and trafficking in hypertonicity-challenged cells. Intracellular mechanisms governing these events are discussed and the biological relevance of altered AQP2 expression by hypertonicity is outlined.
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Jia, Puqi, Hongwei Tan, Kuiren Liu, and Wei Gao. "Adsorption behavior of methylene blue by bone char." International Journal of Modern Physics B 31, no. 16-19 (July 26, 2017): 1744099. http://dx.doi.org/10.1142/s0217979217440994.
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This work studies the adsorption behavior of methylene blue (MB) from water by bone char (BC). The effects of pH, initial dye concentration and dosage of adsorbent on the adsorption were investigated. It was found that the adsorption capacity of MB was affected by the mount of OH[Formula: see text], initial concentration gradient driving force of MB, the surface charge and adsorption site of BC.
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Khair, Abul, Nilay Kumar Dey, Mohammad Harun-Ur-Rashid, Mohammad Abdul Alim, Newas Mohammad Bahadur, Sultan Mahamud, and Syekat Ahmed. "Diffusimetry Renounces Graham’s Law, Achieves Diffusive Convection, Concentration Gradient Induced Diffusion, Heat and Mass Transfer." Defect and Diffusion Forum 407 (March 2021): 173–84. http://dx.doi.org/10.4028/www.scientific.net/ddf.407.173.
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Absolute diffusion rates of KMnO4 in vertical and flattened diffusimeters show the concentration gradient force as being stronger than the gravitational force. Hot water molecules move downward on self-diffusion against buoyancy. Diffusive convection (DC) in warm water and double-diffusive convection (DDC) in warm, saline water take place inside the diffusimeter with DDC transferring more heat than DC. In the diffusing medium the original reagents change or retain their compositions to give the diffusate molecules to diffuse. In water, the change is mostly hydration. The syngener BaCl2.2H2O separately with congeners 3CdSO4.8H2O, ZnSO4.7H2O, and ZnSO4.H2O presents two distinct pairs of overlapping concentration versus rate curves, first for having very close MWs of BaCl2 and CdSO4 and second for having ZnSO4.H2O as the common congener for both the zinc sulfates. Chlorides of Li, Na, and K diffusing at hindered rates in glucose solution show the least rate for LiCl inevitably on grounds of low mass and high Li+ hydration radius. Diffusion blocking occurs at higher glucose concentration. Diffusion of 0.6M AgNO3-0.6M NH4Cl standardizes this diffusimeter. Mass transfer of HCl, H2SO4, and H2C2O4 show oxalic acid diffusing as hydrate and 88 percentage transfer of sulfuric acid in 5 minutes. The Superdiffusive Anti Graham’s Law, Vd , is further consolidated by Ca (NO3)2-M2CO3(M = Na, K, NH4+) and Ca (NO3)2-Na2HPO4 diffusions. Odd and even diffusions are illustrated by AgNO3-NH4Cl and AgNO3-BaCl2 diffusions.
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Chen, Mengdi, Helmut Cölfen, and Sebastian Polarz. "The Effect of Centrifugal Force on the Assembly and Crystallization of Binary Colloidal Systems: Towards Structural Gradients." Zeitschrift für Naturforschung B 68, no. 2 (February 1, 2013): 103–10. http://dx.doi.org/10.5560/znb.2013-3001.
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In this study, the effect of centrifugal force on the assembly and crystallization of binary colloidal mixtures is demonstrated. Monolithic pieces have been prepared which are characterized by a structural gradient along the direction of the centrifugal force. For a given number ratio of monodisperse 154 and 300 nm latex spheres, the absolute latex concentration was varied and with it the sedimentation velocity of the individual particle species. For three different concentrations it has been demonstrated that the structure of the binary colloidal assembly obtained after centrifugation is affected significantly. For the largest initial latex absolute concentrations, the structural variation along the packed latex column in the ultracentrifuge tube is minimal, while a decrease in the absolute concentrations leads to crystalline packing in defined regions of the column. The observation of the thermodynamically favored structure resembling NaCl, but also of the aluminum boride AlB2 analog as well as unordered, glass-like packing depending on the mutual latex concentration under unchanged particle number and size ratio, shows that by centrifugation kinetically favored states can be realized. This result implies that centrifugation of binary latex mixtures is a promising route for investigating the self-organization of binary colloidal systems since the sedimentation velocities of the two particle species are different, and thus the local concentrations and mixing ratios vary continuously also enabling rare packing motifs.
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WANG, YANPING, DEMETRIOS T. PAPAGEORGIOU, and CHARLES MALDARELLI. "Increased mobility of a surfactant-retarded bubble at high bulk concentrations." Journal of Fluid Mechanics 390 (July 10, 1999): 251–70. http://dx.doi.org/10.1017/s0022112099005157.
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We study theoretically the adsorption of surfactant onto the interface of gas bubbles in creeping flow rising steadily in an infinite liquid phase containing surface-active agents. When a bubble rises in the fluid, surfactant adsorbs onto the surface at the leading edge, is convected by the surface flow to the trailing edge and accumulates and desorbs off the back end. This transport creates a surfactant concentration gradient on the surface that causes the surface tension at the back end to be lower than that at the front end, thus retarding the bubble velocity by the creation of a Marangoni force. In this paper, we demonstrate numerically that the mobility of the surfactant-retarded bubble interface can be increased by raising the bulk concentration of surfactant. At high bulk concentrations, the interface saturates with surfactant, and this saturation acts against the convective partitioning to decrease the surface surfactant gradient. We show that as the Péclet number (which scales the convective effect) increases, larger concentrations are necessary to remobilize the surface completely. These results lead to a technologically useful paradigm where the drag and interfacial mobility of a bubble can be controlled by the level of the bulk concentration of surfactant.
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Schrader, Alex M., Stephen H. Donaldson, Jinsuk Song, Chi-Yuan Cheng, Dong Woog Lee, Songi Han, and Jacob N. Israelachvili. "Correlating steric hydration forces with water dynamics through surface force and diffusion NMR measurements in a lipid–DMSO–H2O system." Proceedings of the National Academy of Sciences 112, no. 34 (August 10, 2015): 10708–13. http://dx.doi.org/10.1073/pnas.1512325112.
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Dimethyl sulfoxide (DMSO) is a common solvent and biological additive possessing well-known utility in cellular cryoprotection and lipid membrane permeabilization, but the governing mechanisms at membrane interfaces remain poorly understood. Many studies have focused on DMSO–lipid interactions and the subsequent effects on membrane-phase behavior, but explanations often rely on qualitative notions of DMSO-induced dehydration of lipid head groups. In this work, surface forces measurements between gel-phase dipalmitoylphosphatidylcholine membranes in DMSO–water mixtures quantify the hydration- and solvation-length scales with angstrom resolution as a function of DMSO concentration from 0 mol% to 20 mol%. DMSO causes a drastic decrease in the range of the steric hydration repulsion, leading to an increase in adhesion at a much-reduced intermembrane distance. Pulsed field gradient NMR of the phosphatidylcholine (PC) head group analogs, dimethyl phosphate and tetramethylammonium ions, shows that the ion hydrodynamic radius decreases with increasing DMSO concentration up to 10 mol% DMSO. The complementary measurements indicate that, at concentrations below 10 mol%, the primary effect of DMSO is to decrease the solvated volume of the PC head group and that, from 10 mol% to 20 mol%, DMSO acts to gradually collapse head groups down onto the surface and suppress their thermal motion. This work shows a connection between surface forces, head group conformation and dynamics, and surface water diffusion, with important implications for soft matter and colloidal systems.
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Mergui, S., and D. Gobin. "Transient Double Diffusive Convection in a Vertical Enclosure With Asymmetrical Boundary Conditions." Journal of Heat Transfer 122, no. 3 (April 11, 2000): 598–601. http://dx.doi.org/10.1115/1.1286673.
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This study deals with the numerical analysis of transient heat and species transfer by natural convection in a binary fluid vertical layer. The cavity is differentially heated and a solutal buoyancy force is created by imposing a concentration step at one vertical wall: This refers to the experimental situation where the composition gradient inducing the solutal buoyancy force is created by melting of pure ice in a salty solution. The constitution of the flow structure and the time evolution of the heat and mass transfer characteristics are studied for opposing body forces over a range of thermal and solutal Rayleigh numbers. The numerical results allow to provide a better insight into the mechanisms driving the heat and species transfer at high Lewis number thermohaline convection. [S0022-1481(00)00303-0]
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Marinaro, Giovanni, Mengyuan Huang, Gerd Mutschke, Xuegeng Yang, and Kerstin Eckert. "Oscillatory Copper Deposition on Conical Iron Electrodes in a Nonuniform Magnetic Field." Magnetochemistry 7, no. 4 (March 28, 2021): 46. http://dx.doi.org/10.3390/magnetochemistry7040046.
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We report the effect of a magnetic field on the deposition of copper ions on a conically shaped iron probe. In our setup, the magnetic forces and buoyancy are the key factors influencing the electrolyte flow and the mass transfer. Without external current, a spontaneous reduction of copper on the iron cone occurs, known as electroless deposition. Mach–Zehnder and differential interferometry indicate a variation in the concentration of copper ions near the cone. After an initial transient of about 60 s, temporal oscillations in the copper concentration are found under the effect of a magnetic field. In galvanostatic conditions, a similar oscillatory behavior of the concentration of the electrolyte is observed. Numerical simulations show that the oscillations are caused by the magnetic gradient, Lorentz force, and buoyancy force counteracting one another, and the oscillation frequency is estimated analytically based on this mechanism. Furthermore, we present a study on the oscillation frequency for both electroless and galvanostatic conditions with different current densities. The results of this study may stimulate future research aimed at the local control of the deposition rate and the realization of miniaturized, regularly structured deposits using magnetic fields.
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Wang, Y., G. J. Heigenhauser, and C. M. Wood. "Lactate and metabolic H+ transport and distribution after exercise in rainbow trout white muscle." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 271, no. 5 (November 1, 1996): R1239—R1250. http://dx.doi.org/10.1152/ajpregu.1996.271.5.r1239.
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An isolated-perfused tail-trunk preparation was employed to study the influence of transmembrane pH gradient and membrane potential on the transport and distribution of L(+)-lactate (Lac), metabolic H+ (delta Hm+), and related parameters in rainbow trout white muscle after exhaustive exercise. One resting [arterial pH (pHa) approximately 7.9] and four postexercise treatments (pHa approximately 7.4, 7.9, 8.4, and, high K+, pHa approximately 7.9, partially depolarized by 15 mM K+) were examined. Variations in HCO3- concentration (2-18 mM) at a constant PCO2 approximately 2 Torr were used to alter pHa. The elevated intracellular Lac (approximately 50 mM) remained unchanged after 60 min of perfusion because of very low rates of lactate efflux and oxidation. H+, HCO3-, and Lac- distributions were all well out of electrochemical equilibrium. Total CO2 efflux was reduced at high extracellular pH (pHe); alterations in the net driving force on HCO3- may have overshadowed the influence of PCO2 gradients in driving total CO2 efflux. Lac efflux and delta Hm+ flux were completely uncoupled. delta Hm+ flux reacted to both acid-base and electrochemical gradients as delta Hm+ efflux dropped and even reversed when pHe decreased, whereas partial depolarization in conjunction with depressed intracellular pH resulted in elevated delta Hm+ efflux. Lac efflux did not respond to changes in pHe. Changes in Lac efflux corresponded more closely to changes in the Lac- concentration gradient than in the lactic acid gradient. This study provides circumstantial evidence for the involvement of electroneutral mechanisms (i.e., Lac(-)-H+ cotransport and/or Lac-/anion exchange) in lactate efflux, but does not eliminate the possibility of an active transport mechanism contributing to the retention of Lac.
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Yao, X., A. K. Dahle, C. J. Davidson, and D. H. StJohn. "Effect of solute on the growth rate and the constitutional undercooling ahead of the advancing interface during solidification of an alloy and the implications for nucleation." Journal of Materials Research 21, no. 10 (October 2006): 2470–79. http://dx.doi.org/10.1557/jmr.2006.0302.
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A framework is presented for modeling the nucleation in the constitutionally supercooled liquid ahead of the advancing solid/liquid interface. The effects of temperature gradient, imposed velocity, slope of liquidus, and initial concentration have been taken into account in this model by considering the effect of interface retardation, which is caused by solute buildup at the interface. Furthermore, the effect of solute concentration on the chemical driving force for nucleation has been considered in this model. The model is used for describing the nucleation of Al–Si and Al–Cu alloys. It was found that the solute of Si has a significant impact on the chemical driving force for nucleation in Al–Si alloys whereas Cu has almost no effect in Al–Cu alloys.
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Sueyoshi, Yuuki, Takeshi Hashimoto, Masakazu Yoshikawa, and Shinsuke Ifuku. "Chitin Nanofiber Membranes for Chiral Separation." Sustainable Agriculture Research 1, no. 1 (January 29, 2012): 42. http://dx.doi.org/10.5539/sar.v1n1p42.
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Nanofiber membranes for chiral separation were prepared from chitin, which is the most abundant natural amino polysaccharide. The membrane showed chiral separation ability by adopting concentration gradient as a driving force for membrane transport. In other words, the chitin nanofiber membrane selectively transported the D-isomer of glutamic acid (Glu), phenylalanine (Phe), and lysine (Lys) from the corresponding racemic amino acid mixtures.
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TADA, SHIGERU, YAN SHEN, DAVID JACQMIN, BINGMEI FU, and ZHIYONG QIU. "UNDERSTANDING ELECTRIC INTERACTIONS IN SUSPENSIONS IN GRADIENT AC ELECTRIC FIELDS II: SIMULATIONS AND APPLICATION EXPLORATION." International Journal of Modern Physics B 25, no. 07 (March 20, 2011): 927–33. http://dx.doi.org/10.1142/s0217979211058493.
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We used numerical simulations of a continuous model and the molecular dynamics model to understand the particle instability, formation of island-like structures and existence of one critical particle concentration of 1% (v/v) for formation of island-like structures in the suspension in a gradient AC electric field reported in Paper I. The simulations of the continuous model show that the critical concentration of 1% (v/v) is the concentration of which the particles of a suspension are just fully filling the lower field region finally. According to the MD simulations, the particles instability does exist in the corn oil in a gradient AC electric field, anisotropic polarization interactions among the particles are responsible for the particle instability and have memory, and the memory is still kept even when the particles are transported by a dielectrophoresis force. The island-like structures can be regarded as signature of the memory. We explored possibilities to apply our findings in biomedical fields.
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KLIMCHITSKAYA, G. L., U. MOHIDEEN, and V. M. MOSTEPANENKO. "CONTROL OF THE CASIMIR FORCE USING SEMICONDUCTOR TEST BODIES." International Journal of Modern Physics B 25, no. 02 (January 20, 2011): 171–230. http://dx.doi.org/10.1142/s0217979211057736.
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We describe experimental and related theoretical work on the measurement of the Casimir force using semiconductor test bodies. This field of research started in 2005 and several important and interesting results have already been obtained. Specifically, the Casimir force or its gradient was measured in the configuration of an Au -coated sphere and different semiconductor surfaces. It was found that the force magnitude depends significantly on the replacement of the metal with a semiconductor and on the concentration of charge carriers in the semiconductor material. Special attention is paid to the experiment on the optical modulation of the Casimir force. In this experiment the difference in Casimir force between an Au -coated sphere and a Si plate in the presence and in the absence of laser light was measured. Possible applications of this experiment are discussed, specifically, for the realization of the pulsating Casimir force in three-layer systems. Theoretical problems arising from the comparison of the experimental data for the difference in Casimir force with the Lifshitz theory are analyzed. We consider the possibility to control the magnitude of the Casimir force in phase transitions of semiconductor materials. Experiments on measuring the Casimir force gradient between an Au -coated sphere and a Si plate covered with rectangular corrugations of different characters are also described. Here, we discuss the interplay between the material properties and nontrivial geometry and the applicability of the proximity force approximation. The review contains comparison between different experiments and analysis of their advantages and disadvantages.
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Dar, Ajaz Ahmad, and K. Elangovan. "Influence of an inclined magnetic field on heat and mass transfer of the peristaltic flow of a couple stress fluid in an inclined channel." World Journal of Engineering 14, no. 1 (February 13, 2017): 7–18. http://dx.doi.org/10.1108/wje-11-2016-0124.
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Purpose This paper aims to intend for investigating the influence of an inclined magnetic field on the peristaltic flow of a couple stress fluid through an inclined channel with heat and mass transfer. Design/methodology/approach Long wavelength and low Reynolds number methodology is actualized for simplifying the highly nonlinear equations. Mathematical expressions of axial velocity, pressure gradient and volume flow rate are obtained. Pressure rise, frictional force and pumping phenomenon are portrayed and symbolized graphically. Exact and numerical solutions have been carried out. The computed results are presented graphically for various embedded parameters. Temperature and concentration profile are also scrutinized and sketched. Findings Results from the current study concluded that the fluid motion can be enhanced by increasing the inclination of both the magnetic field and the channel. Originality/value The elemental characteristics of this analysis is a complete interpretation of the influence of couple stress parameter and inclination of magnetic field on the velocity, pressure gradient, pressure rise and frictional forces.
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Kim, Young Suk, Kyung Soo Im, and Yong Moo Cheong. "Critical Temperatures for Initiating and Arresting Delayed Hydride Cracking in a Zr-2.5Nb Pressure Tube." Key Engineering Materials 297-300 (November 2005): 1685–90. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.1685.
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The hydrogen concentration limit and critical temperatures for a delayed hydride cracking (DHC) in zirconium alloys have been reanalyzed using Kim’s DHC model that a driving force for DHC is not the stress gradient but the supersaturated hydrogen concentration or ∆C arising from a hysteresis of the terminal solid solubility on a heating and on a cooling. The DHC initiation occurs generally at the temperatures corresponding to the terminal solid solubility for precipititation (TSSP), demonstrating that the supercooling from the terminal solid solubility for dissolution (TSSD) is required to initiate the DHC. The DHC arrest temperatures correspond to the temperatures where the ∆C is reduced to zero. Therefore, we conclude that the ∆C is the driving force for the DHC and that the Kim’s DHC model is feasible.
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Svendsen, John A., and Magne Waskaas. "Mathematical modelling of mass transfer of paramagnetic ions through an inert membrane by the transient magnetic concentration gradient force." Physics of Fluids 32, no. 1 (January 1, 2020): 013606. http://dx.doi.org/10.1063/1.5130946.
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Abramson, R. G., and M. S. Lipkowitz. "Carrier-mediated concentrative urate transport in rat renal membrane vesicles." American Journal of Physiology-Renal Physiology 248, no. 4 (April 1, 1985): F574—F584. http://dx.doi.org/10.1152/ajprenal.1985.248.4.f574.
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[2-14C]Urate uptake and efflux were studied in brush border and basolateral membrane vesicles of rat renal cortex that were exposed to 20 microM copper chloride. In the presence of inwardly directed NaCl gradients urate uptake was maintained at levels in excess of chemical equilibrium. Comparison of glucose and chloride uptakes revealed that equilibrium glucose uptake was not affected by copper, but chloride failed to reach equilibrium in copper-exposed vesicles. It is suggested that the persistence of an electrolyte gradient could provide a driving force to raise the concentration of free intravesicular urate above that in the media. Preincubation of vesicles with unlabeled urate failed to diminish uptake of added urate; rather, urate uptake was trans stimulated. Uptake of labeled urate was also significantly accelerated when an outward gradient for unlabeled urate was created. Pyrazinoic and oxonic acids also trans stimulated urate uptake. The demonstration of accelerated homeo- and heteroexchange diffusion indicates that transport is carrier mediated in both brush border and basolateral vesicles. Outwardly directed hydroxyl gradients failed to influence urate uptake in either the presence or absence of copper or NaCl. Thus, this carrier, which is active only in the presence of trace amounts of copper, is distinct from a urate/anion exchanger.
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Eischen, J. W., and J. S. Everett. "Thermal Stress Analysis of a Bimaterial Strip Subject to an Axial Temperature Gradient." Journal of Electronic Packaging 111, no. 4 (December 1, 1989): 282–88. http://dx.doi.org/10.1115/1.3226548.
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Formulas are derived for the stresses and displacements in a bimaterial strip which is subjected to a temperature gradient that varies linearly in the longitudinal direction. The solution is obtained by superposing certain fundamental linear elastic stress states which are compatible with bar and beam theory. The analytical results are approximate in the sense that stress-free boundary conditions are not satisfied exactly, since only zero resultant force and moment conditions are enforced. Finite element calculations have been performed to verify the results and to ascertain the level of stress concentration near the ends of the strip.
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Xie, Yao Zhong, De Jun Fei, and Ya Gu Dang. "Kinetic Study on the Transport of Chromium(III) by Emulsion Liquid Membrane." Advanced Materials Research 781-784 (September 2013): 2750–57. http://dx.doi.org/10.4028/www.scientific.net/amr.781-784.2750.
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The interfacial reactions and thermodynamic properties of the emulsion liquid membrane on separation and concentration of chromium (III) were discussed. Interfacial chemical reaction equations of membrane phase with P204 and mass transfer mechanism of ELM system were determined. The extraction reaction enthalpy is 11.41 kJmol1, while stripping reaction enthalpy is-143.65 kJmol1, were obtained by investigating reaction temperature on the distribution ratio under two different conditions. So extraction is an endothermic process and stripping is an exothermic process. And the main driving force of the separation system is the concentration gradient of hydrogen ion between external and internal phase interface.
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Shi, J., and M. Le Maguer. "Mass Transfer Flux at Solid-Liquid Contacting Interface." Food Science and Technology International 9, no. 3 (June 2003): 193–99. http://dx.doi.org/10.1177/1082013203035261.
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When cellular materials are immersed in a solution of high concentration, the mass transfer is considered a multi-component transport process in which simultaneous and countercurrent flows occur in the biological tissue. The mass transfer process of each component in the solid-liquid system is affected not only by operational parameters, but also by the presence of other components. The main driving force for the mass transfer phenomena is attributed to the concentration gradient between external and internal solid material, and the interaction among fluxes and tissue matrix. Matrix deformation and tissue shrinkage are important characteristics influencing mass transfer. The coupled mass transfer fluxes across the interface in an isothermal solid-liquid system were analysed by means of a film model as a function of the concentration gradients, based on the generalised multi-component mass transfer theories. Several possible situations of cell structure changes are discussed, and the effect of structural shrinkage on mass transfer is modelled in this study. The mass transfer model and parameters proposed in the present study is applicable to the unit operation such as osmotic treatment of cellular porous biomaterial.
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Kibble, J. D., M. Wareing, R. W. Wilson, and R. Green. "Effect of barium on potassium diffusion across the proximal convoluted tubule of the anesthetized rat." American Journal of Physiology-Renal Physiology 268, no. 4 (April 1, 1995): F778—F783. http://dx.doi.org/10.1152/ajprenal.1995.268.4.f778.
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The role of diffusion in transepithelial potassium flux and the importance of potassium channels in the luminal cell membrane to this process were examined by applying a luminal microperfusion technique to surface tubules in kidneys of anesthetized rats. Potassium concentration gradients were applied by altering the concentration of KCl in perfusates. To some perfusates, 2 mmol/l BaCl2 was added to block potassium channels in the luminal cell membrane. The mean applied potassium concentration gradient was highly predictive of net potassium transport in the absence of any change in fluid reabsorption, with an apparent potassium permeability of 22 x 10(-5) cm/s. Thus potassium transport in the proximal tubule may have an important diffusive component. Luminal barium significantly reduced the concentration of potassium in collected fluid under conditions of net potassium secretion, although a substantial barium-insensitive potassium permeability was also observed. However, the site of action of luminally applied barium is uncertain in proximal tubule, since barium was reabsorbed by the tubule at a rate of 13.6 pmol.mm-1.min-1. We conclude that diffusion is a significant driving force for potassium reabsorption in proximal tubule and that most diffusive potassium transport occurs via a barium-insensitive route, possibly the paracellular pathway.
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Dimroth, P., G. Kaim, and U. Matthey. "Crucial role of the membrane potential for ATP synthesis by F(1)F(o) ATP synthases." Journal of Experimental Biology 203, no. 1 (January 1, 2000): 51–59. http://dx.doi.org/10.1242/jeb.203.1.51.
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ATP, the universal carrier of cell energy, is manufactured from ADP and phosphate by the enzyme ATP synthase using the free energy of an electrochemical gradient of protons (or Na(+)). The proton-motive force consists of two components, the transmembrane proton concentration gradient (delta pH) and the membrane potential. The two components were considered to be not only thermodynamically but also kinetically equivalent, since the chloroplast ATP synthase appeared to operate on delta pH only. Recent experiments demonstrate, however, that the chloroplast ATP synthase, like those of mitochondria and bacteria, requires a membrane potential for ATP synthesis. Hence, the membrane potential and proton gradient are not equivalent under normal operating conditions far from equilibrium. These conclusions are corroborated by the finding that only the membrane potential induces a rotary torque that drives the counter-rotation of the a and c subunits in the F(o) motor of Propionigenium modestum ATP synthase.
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Chuong, C. M., S. A. Ting, R. B. Widelitz, and Y. S. Lee. "Mechanism of skin morphogenesis. II. Retinoic acid modulates axis orientation and phenotypes of skin appendages." Development 115, no. 3 (July 1, 1992): 839–52. http://dx.doi.org/10.1242/dev.115.3.839.
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The factors that determine the axial orientation and phenotypes of skin appendages were analyzed by studying the effect of retinoic acid (RA) on embryonic chicken skin explant cultures. With RA uniformly distributed in the culture media, the feather buds became smaller, were disoriented or were transformed into scale-like structures in a concentration-dependent manner (from 0.05-2.5 microM). With RA distributed as a gradient created by a RA-soaked anion exchange bead, a radial zone of inhibition with a rim of disoriented buds was observed. The new axis of the disoriented buds appeared to be determined by a combination of the original feather axis determining force and a new axial force pointing centrifugally away from the RA source. This observed result can be simulated with a computer model using a vectorial sum of different feather axial determination forces. The size of the inhibited zone is linearly correlated to the RA concentration and may be used to quantify the morphogenetic activity of retinoids. These effects are specific to developmental stages (Hamburg and Hamilton stage 31–34). Both all-trans and 13-cis RA have morphogenetic activity. Retinol has no effect and retinal has a small inhibitory effect but neither phenotypic transformation nor axial disorientation were observed. The antero-posterior gradient of homeoprotein XlHbox 1 in feather buds became diffusive after RA treatment. RA dissolves dermal condensations and the distribution of N-CAM is altered from an anterior localized pattern to a diffusive presence in the bud cores. Endogenous retinoids in developing skins show developmental stage-dependent changes both quantitatively and qualitatively. The results suggest that RA either is or can modulate the endogenous morphogen(s) that determine the orientation and phenotype of skin appendages, and that this morphogenetic pathway involves Hox genes and adhesion molecules.