Frequency dispersion in the fractional Langmuir approximation for the adsorption–desorption phenomena

2020 ◽  
Vol 476 (2238) ◽  
pp. 20190570 ◽  
Author(s):  
Giovanni Barbero ◽  
Luiz Roberto Evangelista ◽  
Ervin K. Lenzi
Keyword(s):  
Relaxation Times ◽  
Complex Impedance ◽  
Frequency Dispersion ◽  
Homogeneous Distribution ◽  
Spectroscopy Data ◽  
Effective Parameters ◽  
Electrolytic Cells ◽  
Interfacial Behaviour ◽  
Adsorption Desorption

We propose that a kinetic equation of fractional order may be used to account for the frequency dispersion of the effective parameters in the framework of the Langmuir approximation for the adsorption–desorption phenomena. A frequency dependence of these parameters naturally arises in this formalism, indicating that it may play a similar role of a generalization of the Langmuir isotherm obtained from a homogeneous distribution of relaxation times. The fractional approach formalism opens the possibility to consider different relaxation regimes characterizing the interfacial behaviour of electrolytic cells, and may be a powerful tool to interpret complex impedance spectroscopy data.

scholarly journals The distribution of myosin II in Dictyostelium discoideum slug cells.

1991 ◽  
Vol 115 (5) ◽  
pp. 1267-1274 ◽  
Author(s):  
S Eliott ◽  
P H Vardy ◽  
K L Williams
Keyword(s):  
Cell Motility ◽  
Dictyostelium Discoideum ◽  
Immunofluorescence Microscopy ◽  
Molecular Genetic ◽  
Myosin Ii ◽  
Three Dimensional ◽  
Homogeneous Distribution ◽  
Multicellular Development ◽  
Insight Into

While the role of myosin II in muscle contraction has been well characterized, less is known about the role of myosin II in non-muscle cells. Recent molecular genetic experiments on Dictyostelium discoideum show that myosin II is necessary for cytokinesis and multicellular development. Here we use immunofluorescence microscopy with monoclonal and polyclonal antimyosin antibodies to visualize myosin II in cells of the multicellular D. discoideum slug. A subpopulation of peripheral and anterior cells label brightly with antimyosin II antibodies, and many of these cells display a polarized intracellular distribution of myosin II. Other cells in the slug label less brightly and their cytoplasm displays a more homogeneous distribution of myosin II. These results provide insight into cell motility within a three-dimensional tissue and they are discussed in relation to the possible roles of myosin II in multicellular development.

scholarly journals Frequency dispersion reveals chromophore diversity and colour-tuning mechanism in parrot feathers

2018 ◽  
Vol 5 (7) ◽  
pp. 172010 ◽  
Author(s):  
Jonathan E. Barnsley ◽  
Elliot J. Tay ◽  
Keith C. Gordon ◽  
Daniel B. Thomas
Keyword(s):  
Frequency Dispersion ◽  
Animal Coloration ◽  
Molecular Conformations ◽  
Tuning Mechanism ◽  
Resonance Raman Spectra ◽  
Molecule Interactions ◽  
Yellow Region ◽  
Colour Tuning

Variation in animal coloration is often viewed as the result of chemically distinct pigments conferring different hues. The role of molecular environment on hue tends to be overlooked as analyses are mostly performed on free pigments extracted from the integument. Here we analysed psittacofulvin pigments within parrot feathers to explore whether the in situ organization of pigments may have an effect on hue. Resonance Raman spectra from a red region of a yellow-naped amazon Amazona auropalliata tail feather show frequency dispersion, a phenomenon that is related to the presence of a range of molecular conformations (and multiple chromophores) in the pigment, whereas spectra from a yellow region on the same feather do not show the same evidence for multiple chromophores. Our findings are consistent with non-isomeric psittacofulvin pigments behaving as a single chromophore in yellow feather barbs, which implies that psittacofulvins are dispersed into a structurally disordered mixture in yellow feathers compared with red feathers. Frequency dispersion in red barbs may instead indicate that pigments are structurally organized through molecule–molecule interactions. Major differences in the hues of parrot feathers are thus associated with differences in the organization of pigments within feathers.

scholarly journals Electrical Behaviour of Finely Divided Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 173-191 ◽  
Author(s):  
J. G. Paren ◽  
J. W. Glen
Keyword(s):  
Relaxation Times ◽  
Surface Adsorption ◽  
Frequency Dispersion ◽  
Polar Regions ◽  
Electrical Behaviour ◽  
Heterogeneous Nature ◽  
Glacier Ice ◽  
Bulk Relaxation ◽  
Adsorption Of Co ◽  
The Mean

Abstract The electrical behaviour of ice which has been finely ground and compressed was investigated during ageing in air and over a range of temperatures. The dielectric behaviour may be accurately represented as the sum of two elliptical relaxation spectra. The behaviour eventually stabilizes with similar activation energies for the mean relaxation time of each spectrum c. 0.25 eV, and the ratio of the relaxation times is ten in samples of density c. 0.42 Mg m-3. Arguments are presented on whether the higher-frequency dispersion is a consequence of the heterogeneous nature of the samples or is a bulk relaxation process. The similarities between the behaviour of such finely ground ice and of deposited snow and polar glacier ice are discussed. The extent to which the results may be attributed to surface adsorption of CO2 are examined by reference to measurements of the CO2 content of finely divided ice and ice from polar regions.

Some Considerations on Confined Water: The Thermal Behavior of Transport Properties in Water-Glycerol and Water-Methanol Mixtures

MRS Advances ◽  
2016 ◽  
Vol 1 (26) ◽  
pp. 1891-1902 ◽  
Author(s):  
Francesco Mallamace ◽  
Carmelo Corsaro ◽  
Domenico Mallamace ◽  
Cirino Vasi ◽  
Sebastiano Vasi ◽  
...  
Keyword(s):  
Hydrophobic Interactions ◽  
Molar Fraction ◽  
Relaxation Times ◽  
Confined Water ◽  
Self Diffusion ◽  
Excess Value ◽  
Water Glycerol ◽  
System Properties ◽  
Dynamical Crossover

ABSTRACTWe discuss recent literature data on the relaxation times (the primary tα), viscosity, and self-diffusion in water-glycerol and water-methanol mixtures across a wide temperature range from the stable water phase to the deep supercooled regime (373–147K). In particular, to clarify the role of hydrophilicity interactions (the hydrogen bonds) and hydrophobic interactions we study the mixture in terms of the water molar fraction (XW) with fixed temperatures at 5K steps across the entire composition range, and we find a marked deviation from the ideal thermodynamic behavior of the transport functions. This deviation is strongly T and XW dependent and spans values that range from two orders of magnitude at the highest temperature to more than five in the deeply supercooled regime (more precisely, at ≃200K). We analyze these deviations in terms of how the measured values differ from ideal values and find that the hydrogen-bonding water network dominates system properties up to XW = 0.3. We also examine an Arrhenius plot of the maximum excess value (Δtα(T) vs. 1/T) and find two significant changes due to water: one at the dynamical crossover temperature (TL ≃ 225K, i.e., the locus of the Widom line), and one at T ≃ 315K (the water isothermal compressibility χT minimum).

Role of the Adsorption Phenomenon on the Ionic Equilibrium Distribution and on the Transient Effects in Electrolytic Cells

2006 ◽  
Vol 110 (36) ◽  
pp. 17889-17897 ◽  
Author(s):  
Giovanni Barbero ◽  
Fernando C. M. Freire ◽  
Marco Scalerandi ◽  
Anca L. Alexe-Ionescu
Keyword(s):  
Equilibrium Distribution ◽  
Transient Effects ◽  
Ionic Equilibrium ◽  
Adsorption Phenomenon ◽  
Electrolytic Cells

scholarly journals Piezoelectric characterization of lead-free ferroelectric ceramics

2010 ◽  
Vol 4 (3) ◽  
pp. 199-207 ◽  
Author(s):  
Lorena Pardo ◽  
Alvaro García ◽  
Klaus Brebøl ◽  
Lavinia Curecheriu ◽  
Liliana Mitoseriu ◽  
...  
Keyword(s):  
Sol Gel ◽  
Complex Impedance ◽  
Experimental Spectrum ◽  
Lead Free ◽  
Ferroelectric Ceramics ◽  
Coarse Grained ◽  
Shear Mode ◽  
Fine Grained ◽  
Accuracy Test

The challenge to develop high piezoelectric sensitivity and lead-free composition ferro-piezoelectric ceramics has recently dragged new attention to some classic ferroelectrics. Here, Ba(CexTi1-x)O3 (Ce-BT) and 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO3 (BNBT6) ceramics were piezoelectrically characterized from measurements of complex impedance at electromechanical resonances and their analysis by Alemany et al. software. The reconstruction of the spectra for each resonance is used as an accuracy test of the set of calculated coefficients, quantitatively characterized by the regression factor (R2) of such reconstruction to the experimental spectrum. Piezoelectric activity at room temperature (RT) was observed for Ce-BT with x=0.06 and 0.1, ferroelectrics with T(?'max)>RT, but also for x=0.2 with T(?'max)<RT, which confirms its relaxor character (Ps?0 for T?T(?'max)). BNBT6 fine grained ceramics (~1 ?m) were prepared from nanopowder obtained by sol-gel autocombustion. Results obtained for the fine grained ceramic hot-pressed at 800?C for 2 h and recrystallized at 1050?C for 1 h are d33=148 pCN-1 and kp=26.8%. Despite of its lower grain size, the properties of this material are comparable with those reported for coarse grained ceramics obtained by sintering at T>1100?C. Some measurement issues, as the role of the mode coupling on the characterization results, illustrated for the shear mode of a thickness poled plate, are discussed.

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