scholarly journals Ion-Induced Volume Transition in Gels and Its Role in Biology

Gels ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 20
Author(s):  
Matan Mussel ◽  
Peter J. Basser ◽  
Ferenc Horkay
Keyword(s):  
Nonlinear Response ◽  
Structural Changes ◽  
Ionic Composition ◽  
Biological Systems ◽  
Experimental Results ◽  
Resting Potential ◽  
Cell Secretion ◽  
Solvent Quality ◽  
Volume Transition ◽  
Biological Milieu

Incremental changes in ionic composition, solvent quality, and temperature can lead to reversible and abrupt structural changes in many synthetic and biopolymer systems. In the biological milieu, this nonlinear response is believed to play an important functional role in various biological systems, including DNA condensation, cell secretion, water flow in xylem of plants, cell resting potential, and formation of membraneless organelles. While these systems are markedly different from one another, a physicochemical framework that treats them as polyelectrolytes, provides a means to interpret experimental results and make in silico predictions. This article summarizes experimental results made on ion-induced volume phase transition in a polyelectrolyte model gel (sodium polyacrylate) and observations on the above-mentioned biological systems indicating the existence of a steep response.

Nonlinear Passive Cam-Based Springs for Powered Ankle Prostheses

2015 ◽  
Vol 9 (1) ◽  
Author(s):  
Jonathan Realmuto ◽  
Glenn Klute ◽  
Santosh Devasia
Keyword(s):  
Lower Limb ◽  
Nonlinear Response ◽  
Experimental Results ◽  
Passive Element ◽  
Ankle Torque ◽  
Lower Limb Prosthesis ◽  
Limb Prosthesis ◽  
Elastic Elements

This article studies the design of passive elastic elements to reduce the actuator requirements for powered ankle prostheses. The challenge is to achieve most of the typically nonlinear ankle response with the passive element so that the active ankle-torque from the actuator can be small. The main contribution of this article is the design of a cam-based lower-limb prosthesis to achieve such a nonlinear ankle response. Results are presented to show that the addition of the cam-based passive element can reduce the peak actuator torque requirement substantially, by ∼74%. Moreover, experimental results are presented to demonstrate that the cam-based design can achieve a desired nonlinear response to within 10%.

scholarly journals Matrix Discriminant Analysis Evidenced Surface-Lithium as an Important Factor to Increase the Hydrolytic Saccharification of Sugarcane Bagasse

Molecules ◽  
2019 ◽  
Vol 24 (19) ◽  
pp. 3614
Author(s):  
Ana Sílvia de Almeida Scarcella ◽  
Alexandre Favarin Somera ◽  
Christiane da Costa Carreira Nunes ◽  
Eleni Gomes ◽  
Ana Claudia Vici ◽  
...  
Keyword(s):  
Steam Explosion ◽  
Structural Changes ◽  
Reducing Sugars ◽  
Periodic Structures ◽  
Relative Concentration ◽  
Ionic Composition ◽  
Distribution Patterns ◽  
Sugar Cane Bagasse ◽  
Ionic Distribution ◽  
Saccharification Yield

Statistical evidence pointing to the very soft change in the ionic composition on the surface of the sugar cane bagasse is crucial to improve yields of sugars by hydrolytic saccharification. Removal of Li+ by pretreatments exposing -OH sites was the most important factor related to the increase of saccharification yields using enzyme cocktails. Steam Explosion and Microwave:H2SO4 pretreatments produced unrelated structural changes, but similar ionic distribution patterns. Both increased the saccharification yield 1.74-fold. NaOH produced structural changes related to Steam Explosion, but released surface-bounded Li+ obtaining 2.04-fold more reducing sugars than the control. In turn, the higher amounts in relative concentration and periodic structures of Li+ on the surface observed in the control or after the pretreatment with Ethanol:DMSO:Ammonium Oxalate, blocked -OH and O− available for ionic sputtering. These changes correlated to 1.90-fold decrease in saccharification yields. Li+ was an activator in solution, but its presence and distribution pattern on the substrate was prejudicial to the saccharification. Apparently, it acts as a phase-dependent modulator of enzyme activity. Therefore, no correlations were found between structural changes and the efficiency of the enzymatic cocktail used. However, there were correlations between the Li+ distribution patterns and the enzymatic activities that should to be shown.

scholarly journals Effect of acetylcholine on postjunctional membrane permeability in eel electroplaque.

1977 ◽  
Vol 70 (1) ◽  
pp. 23-36 ◽  
Author(s):  
N L Lassignal ◽  
A R Martin
Keyword(s):  
Field Equation ◽  
Membrane Potential ◽  
Membrane Permeability ◽  
Ionic Composition ◽  
Reversal Potential ◽  
Resting Potential ◽  
Constant Field ◽  
Free Solution ◽  
Positive Direction ◽  
External K

Acetylcholine (ACh) was applied iontophoretically to the innervated face of isolated eel electroplaques while the membrane potential was being recorded intracellularly. At the resting potential (about -85 mV) application of the drug produced depolarizations (ACh potentials) of 20 mV or more which became smaller when the membrane was depolarized and reversed in polarity at about zero membrane potential. The reversal potential shifted in the negative direction when external Na+ was partially replaced by glucosamine. Increasing external K+ caused a shift of reversal potential in the positive direction. It was concluded that ACh increased the permeability of the postjunctional membrane to both ions. Replacement of Cl- by propionate had no effect on the reversal potential. In Na+-free solution containing glucosamine the reversal potential was positive to the resting potential, suggesting that ACh increased the permeability to glucosamine. Addition of Ca++ resulted in a still more positive reversal potential, indicating an increased permeability to Ca++ as well. Analysis of the results indicated that the increases in permeability of the postjunctional membrane to K+, Na+, Ca++, and glucosamine were in the ratios of approximately 1.0:0.9:0.7:0.2, respectively. With these permeability ratios, all of the observed shifts in reversal potential with changes in external ionic composition were predicted accurately by the constant field equation.

Effects of shape of the neck of classical acoustical resonators on the sound absorption quality for large amplitudes: Experimental results

2020 ◽  
Vol 27 (2) ◽  
pp. 169-181
Author(s):  
Emmanuel Gourdon ◽  
Alireza Ture Savadkoohi ◽  
Bertrand Cauvin
Keyword(s):  
Sound Absorption ◽  
Nonlinear Response ◽  
Experimental Results ◽  
Resonant Frequencies ◽  
Helmholtz Resonators ◽  
Forcing Function ◽  
Amplitude Dependency ◽  
Broadband Frequency

This article presents some experimental results on Helmholtz resonators for large sound amplitudes with two general geometries of their necks: the resonators with classical (cylindrical) and quadratic nonlinear necks. Obtained results for large amplitudes show accelerated amplitude dependency of resonant frequencies of the resonators with modified shape of the neck compared to classical ones. This nonlinear response can be used as a passive controller system with nonlinear restoring forcing function for having broadband frequency absorption.

Torque Transient of Magnetically Driven Flow for Viscosity Measurement

Volume 1 ◽  
2004 ◽  
Author(s):  
Heng Ban ◽  
Bochuan Lin ◽  
Chao Li ◽  
Rosalia N. Scripa ◽  
Ching-Hua Su ◽  
...  
Keyword(s):  
Structural Changes ◽  
Viscosity Measurement ◽  
Experimental Results ◽  
Fluid Viscosity ◽  
Oscillation System ◽  
Complex Liquids ◽  
Ring Structures ◽  
Damped Oscillation ◽  
Semi Empirical ◽  
Oscillating Cup

Viscosity is a good indicator of structural changes for complex liquids, such as semiconductor melts with chain or ring structures. This paper discusses the theoretical and experimental results of the transient torque technique for non-intrusive viscosity measurement. Such a technique is essential for the high temperature viscosity measurement of high pressure and toxic semiconductor melts. In this paper, our previous work on oscillating cup technique was expanded to the transient process of a magnetically driven melt flow in a damped oscillation system. Based on the analytical solution for the fluid flow and cup oscillation, a semi-empirical model was established to extract the fluid viscosity. The analytical and experimental results indicated that such a technique has the advantage of short measurement time and straight forward data analysis procedures.

Conduction Processes in the Nerve Cord of the Moth Manduca Sexta In Relation to its Ultrastructure and Haemolymph Ionic Composition

1972 ◽  
Vol 56 (3) ◽  
pp. 717-734
Author(s):  
Y. PICHON ◽  
D. B. SATTELLE ◽  
N. J. LANE
Keyword(s):  
Tight Junctions ◽  
Manduca Sexta ◽  
Nerve Cord ◽  
Action Potentials ◽  
Fat Body ◽  
Potassium Concentration ◽  
Ionic Composition ◽  
Resting Potential ◽  
Axonal Membrane ◽  
Perineurial Cells

1. Connectives of the ventral nerve cord of Manduca sexta consist of glia-ensheathed axons surrounded by a perineuriurn and an acellular neural lamella, which is greatly expanded on the dorsal surface. The glial cells are linked to one another by desmosomea and tight junctions; the latter also occur between adjacent perineurial cells. There no continuous circum-neural fat-body sheath. 2. A ten-fold change in the external potassium concentration results in a 43 mV change in the resting potential of de-sheathed connectives. Action potentials of such exposed axons are rapidly blocked in low-sodium or sodium-free saline and under these conditions neither calcium nor magnesium is able to maintain conduction. Spikes from de-sheathed preparations are rapidly abolished on exposure to 10-6M tetrodotoxin. These iindmgs indicate a conventional ionic basis of excitation for the axonal membrane of this insect. 3. Analyses of the haemolymph reveal a mean sodium concentration of 25.4 (s.E. ± 0.98) mM/1 and a mean potassium concentration of 25.1 (s.E. ± 1.74) mM/.1 4. Action potentials recorded from sheathed connectives are maintained for extended periods in sodium-free saline. 5. Exposure of most sheathed connectives to elevated potassium concentrations results in a two-stage depolarization. A rapid, single-stage, apparently extraneuronal potential change is, however, observed in some preparations. 6. These results on sheathed connectives indicate the presence of some peripheral barrier to the movements of sodium and potassium; the tight junctions between adjacent perineurial cells are considered to be possible sites of this restriction.

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