Quiescent Solution Research Articles

Quiescent optical solitons with Kudryashov’s generalized quintuple-power law and nonlocal nonlinearity having nonlinear chromatic dispersion with generalized temporal evolution by enhanced direct algebraic method and sub-ODE approach

Revisiting the study of quiescent optical solitons with quintuple-power-law self-phase modulation and nonlinear chromatic dispersion is the focus of the current paper. The soliton solutions to the model are revealed through the intermediary Jacobi’s elliptic functions using the enhanced direct algebraic method. The intermediary Weierstrass’ elliptic functions are used by the sub-ODE approach to reveal such quiescent soliton solutions.

Method—Time-Variance In EIS Measurements: The Simple Case of Dilution

Classical analysis of Electrochemical Impedance Spectroscopy (EIS) measurements requires them to be performed on a linear, time-invariant system. Many electrochemical systems are time-variant (battery under charge/discharge, corroding sample). The effect of time-variance on these systems is not easy to study because there is no reference to which the time-variant results could be compared to. In this paper, we perform a simple dilution experiment to illustrate the time-variance on EIS measurements performed in a quiescent solution and at a Rotating Disk Electrode (RDE), in an electrolyte containing the classical K3Fe(CN)6/K4Fe(CN)6 redox couple. Using simulations based on analytical expressions of the Faradaic impedance, experimental parameters are defined. Fitting EIS data using Equivalent Circuit Models (ECM allows us to qualify the errors made when trying to fit time-variant data with time-invariant impedance expressions. Repeated impedance measurements and reconstruction of instantaneous impedance graphs via interpolation allows to reduce the effect of time-variance and improve the fitting quality. Finally, another approach is presented, which consists in fitting the time-variant data by an analytical time-dependent expression of the Faradaic impedance where the concentration evolution and its effect are accounted for.

Dissolution–precipitation kinetics during C[formula omitted]S hydration: A holographic interferometry study

Tricalcium silicate C3S has been widely employed in model systems to interpret the complex mechanisms of cement hydration. The present study aims at providing an accurate description of the dissolution rate of C3S by implementing a new approach based on holographic interferometry. We propose a protocol that allows the measurement of the pure dissolution rate constant of the C3S phase by experiments performed in supersaturated conditions with respect to C–S–H. In these experiments, a flat polycrystalline surface of C3S was monitored in a quiescent solution. The amount of calcium released within the holographic cell was measured and the aqueous solution composition was constrained to the C–S–H stoichiometry at the interface. An equilibrium approach was applied to assess interfacial pH, saturation indexes, and C–S–H precipitation at the experimental conditions. The rate law of the pure dissolution of C3S was assessed in conditions ranging from far to close-to-equilibrium.

Comparative study between natural and artificial weathering of acrylic‐coated steel, aluminum, and galvanized steel

AbstractSince testing organic coatings under natural conditions is a time‐consuming process, accelerated methods are needed to produce results in less time. A simulated environment cannot fully reproduce actual operating conditions, so it is important to investigate the correlation between accelerated and natural aging test results. In this article, the natural aging of painted steel, aluminum, and hot‐dip galvanized steel is studied for 1 year under continental climate conditions. The environmental parameters responsible for the change of the protective system in a continental urban environment were monitored: time of wetness, ultraviolet radiation, and temperature. The extent of deterioration is compared with similar samples weathered by accelerated testing using electrochemical impedance spectroscopy, differential scanning calorimetry, and gloss measurements. Neutral salt spray chamber, prohesion test, immersion in a quiescent salt solution, and ultraviolet B‐rays (UVB) exposure test are considered. The results of the accelerated cabinet tests are discussed, and the effect is evaluated for the various coated metals. This study highlights the major problems encountered in building a model to predict durability in such a critical area as the durability of organic coatings for metal structures.

Marangoni convection in a dielectric fluid layer with an AC electric field and nonuniform volumetric heat source due to incident radiation

AbstractThe role of a uniform AC electric field and a nonuniform volumetric heat source arising due to an external incident radiation on the onset of Marangoni convection in a horizontal layer of an incompressible dielectric fluid is investigated. The bottom rigid surface is fixed at a constant temperature while the top free surface at which the surface tension acts is considered to be nondeformable and a Robin boundary condition on the perturbation temperature is invoked. The nonuniform internal heating within the fluid layer alters the conduction temperature profile from linear to nonlinear in the vertical coordinate. The linear stability of the quiescent basic solution is studied with respect to normal mode disturbances. The resulting stability eigenvalue problem with variable coefficient is solved numerically using the Galerkin method. The impact of governing parameters on the instability of the system is discussed thoroughly. The forces causing instability reinforce together and are found to be tightly coupled. It is observed that the strength of nonuniform heat source and the electric Rayleigh number is to hasten, while an increase in the Biot number is to delay the onset of Marangoni electroconvection. Finally, the results obtained under the limiting cases are shown to be in good agreement with those published earlier.

Crystal growth according to the law of proportionate effect

Abstract This paper summarizes an approach to crystal growth that was published in parts in various articles over the course of 25 years by the present author and his colleagues. Evidence for this approach, which is confirmed in detail by data in the cited publications and in the figures and equations in the supplementary material that accompanies this paper (see the Online Materials1), comes mainly from the shapes of crystal size distributions (CSDs). Such distributions reveal the growth histories of natural minerals and synthetic compounds, histories that can be used to make geological interpretations and to guide industrial syntheses. CSDs have three fundamental shapes: log-normal, asymptotic, and Ostwald. These shapes result from different degrees of supersaturation near the time of nucleation. The first two distribution shapes form according to the Law of Proportionate Effect (LPE) at moderate supersaturation, and the latter rare distribution forms by Ostwald ripening at large supersaturation. Initially, the first two distributions have mean diameters of up to tens of nanometers and grow by surface-limited growth kinetics. The slow step in this reaction is the incorporation of nanoparticles (bits of crystal or adparticles) onto the crystal surface. As the crystals become larger, their demand for nutrients, as calculated by the LPE, increases exponentially. Then the slow step in the reaction changes to the rate of transfer of nutrients to the crystal (supply- or transport-limited growth). Crystal diameters often grow the most during this latter stage, and the initial CSD shapes that originally formed during surface-limited growth are retained and scaled up proportionately. Proportionate growth during the supply-limited stage can be simulated approximately by multiplying the diameter of each crystal in a distribution by a constant. Crystals can also grow by a constant rate law in which a constant length is added to each crystal diameter in the distribution. This rare process causes the original CSD to narrow so that its initial shape is not preserved. The growth law that prevails, either proportionate or constant, is determined by the manner in which nutrients are supplied to the crystal. Supply is by advective flow during proportionate growth, with the nutrient solution moving with respect to the crystals. Constant growth relies on the random diffusion of nutrients through a quiescent solution. Proportionate growth is by far the most common growth law, and therefore, nutrient supply by diffusion alone during crystal growth is uncommon. Distributions formed by Oswald ripening and those formed by other rare processes are also discussed. During Ostwald ripening, nucleation caused by mixing reactants at large supersaturation forms crystals that are extremely fine and numerous. The larger crystals grow at the expense of the finer, less stable crystals, thereby forming, on completion, the universal steady-state CSD shape predicted by the Lifshitz-Slyozov-Wagner (LSW) theory. This unique CSD shape, as well as other rare shapes, then are scaled up to larger sizes by supply limited proportionate growth.

Quantifying Brownian motion in the presence of simple shear flow with particle diffusometry.

Particle diffusometry, a technology derived from particle image velocimetry, quantifies the Brownian motion of particles suspended in a quiescent solution by computing the diffusion coefficient. Particle diffusometry has been used for pathogen detection by measuring the change in solution viscosity due to amplified DNA from a specific gene target. However, particle diffusometry fails to calculate accurate measurements at elevated temperatures and fluid flow. Therefore, these two current limitations hinder the potential application where particle diffusometry can further be used. In this work, we expanded the usability of particle diffusometry to be applied to fluid samples with simple shear flow and at various temperatures. A range of diffusion coefficient videos is created to simulate the Brownian motion of particles under flow and temperature conditions. Our updated particle diffusometry analysis forms a correction equation under three different polynomial degrees of shear flow with varying flow rates and temperatures between 25 and 65°C. An experiment in a channel with a rectangular cross section using a syringe pump to generate a constant flow is done to analyze the modified algorithm. In simulation analysis, the modified algorithm successfully computes the diffusion coefficients with 10% error for an average flow rate of up to 8 on all three flow types. Complementary experiments confirm the simulation results.

Correlation between crystallographic texture and electrochemical behavior of nano/ultrafine-grained AA2024 alloy processed by accumulative roll bonding process

This study provides an insight into the correlation between crystallographic texture and electrochemical behavior of nano/ultrafine-grained AA2024 alloy. To achieve this objective, the following AA2024 alloys were processed by accumulative roll bonding (ARB): (i) Nano/ultrafine-grained AA2024 alloy with virtually the same grain size and the texture components of S {123}⟨634⟩, Cube {001}⟨100⟩, Copper {112}⟨111⟩, and Brass {011}⟨211⟩, and (ii) Bimodal-grained structure AA2024 alloy consisting of coarse and ultrafine elongated grains and the texture components of S {123}⟨634⟩ and Brass {011}⟨211⟩. The results indicated that the grain refinement increases the corrosion current density and decreases the passive film resistance of AA2024 alloy in quiescent phosphate buffer solution (pH = 9). Overall, electrochemical studies revealed that the uniform distribution of grain size and development of Cube {001}⟨100⟩ and Copper {112}⟨111⟩ texture components provide the most advantageous electrochemical properties. Hence, it was suggested that nano/ultrafine-grained structure was preferred compared to bimodal grain structure.

Self-Powered Water Flow-Triggered Piezocatalytic Generation of Reactive Oxygen Species for Water Purification in Simulated Water Drainage

Ambient water motions presented in urban drainage systems is a rich source of renewable mechanical energy. Harvesting this energy to trigger the generation of reactive oxygen species (ROS) for water purification is a desirable yet underexplored solution. Herein, the water flow from a spiral reactor to simulate pipeline drainage was utilized to provide mechanical energy to power itself to initiate the piezo-response of molybdenum disulfide (MoS2) that was added into water flowing in the reactor. The piezocatalytic degradation efficiency of benzothiazole by MoS2 reached 94.8% after 24 cycles (ca. 144 s), which was 8.8 and 4.9 times higher than that of quiescent solution of MoS2 and non-piezoelectric commercial MoS2, respectively. Furthermore, the water flow-driven system can be extended to degrade different kinds of organic contaminants, including benzotriazole and various antibiotics (enrofloxacin, ciprofloxacin, metronidazole, etc.). All target pollutants were degraded with electric energy per order EEO in the range of 0.0161 to 0.0616 kW h/m3. In this process, the running water from the spiral reactor drove MoS2 to generate piezoelectric charges, which in turn reacted with dissolved oxygen and water to generate ROS including the hydroxyl radical, superoxide anion, and singlet oxygen to decompose the target pollutants. The system retained piezo-degradation efficiencies (>80%) in different aqueous matrices including rainwater, saline water, and pharmaceutical sewage and could be reused four times maintaining a good performance (>90%). This investigation provides a facile self-powered piezocatalytic process by harnessing ambient energy from the water flow of simulated water drainage to purify wastewater.

Role of dissolved CO in the solution on the origin of CO pre-oxidation on Pt(1 1 1)-Type electrodes

• CO pre-oxidation occurs on (1 1 1) terrace sites of catalyst surfaces defect-rich. • CO in solution determines the magnitude (and the shape of the curve) of CO pre-oxidation. • CO pre-oxidation involves the diffusion-limited bulk CO electro-oxidation at most active sites. • Main CO electro-oxidation peak is a typical behavior of a surface-confined process. In voltammetric CO stripping experiments in acid media, CO pre-oxidation usually takes place on catalysts with a high density of surface defects, obeyed the conditions of full CO ads layer formation at suitable low potentials into the “hydrogen region” and, importantly, CO traces in the bulk of the solution is required. This study aims to interrogate that. The electro-oxidation of CO was voltammetrically conducted applying different scan rates, employing Pt(1 1 1) terraced surfaces and full CO coverage equilibrated with different content of dissolved CO in the bulk of an acid quiescent solution; also experiments were performed in which CO ads was present only on the (1 1 0)-type steps in a CO-free solution. It was found that: (1) slopes of peak potentials of CO pre-oxidation versus the logarithm of scan rates were smaller for higher CO contents in the solution; (2) charge density of CO pre-oxidation was higher for slower scan rate; (3) CO pre-oxidation takes place at low potentials where the (1 1 0)-type step sites were inactive in the catalysis of CO electro-oxidation. We conclude that, in such a quiescent solution, the content of dissolved CO in the bulk of the solution determines the magnitude and the shape of the curve of the CO pre-oxidation. This can be understandable in terms of prompt provision of CO molecules from the solution (diffusion layer) to surface active sites, that is, the most active sites, released during the CO pre-oxidation. In the CO pre-oxidation on Pt(1 1 1) terraced surfaces, the most active sites lie at the bottom of (1 1 1) terraces adjacent to the steps. The results provide evidence that, in presence of CO traces in the bulk of the solution, on one hand, the pre-oxidation of CO involves the diffusion-limited electro-oxidation of bulk CO at most active sites released during the CO pre-oxidation . On the other hand, the main CO electro-oxidation peak is a typical behavior of a surface-confined process. Our proposition applies to Pt electrodes in acidic medium.

Microstructural characterization and electrochemical behavior of nano/ ultrafine grained pure copper through constrained groove pressing (CGP)

This study presents microstructural, electrochemical, and mechanical characterizations on pure copper fabricated using constrained groove pressing (CGP) in quiescent phosphate buffer solution (pH = 11.73). We tested the effect of surface modifications on electrochemical features using electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. A three-dimensional simulation via finite element modeling evaluates the CGP effects on the maximum principal stress and the plastic strain distribution. The transmission electron microscopy (TEM) micrographs confirm that the increasing CGP cycles result in a nano/ultrafine grain microstructure. Our electrochemical study showed that the CGP process can positively impact the passive behavior of pure copper. Mott–Schottky analyses illustrated that the point defect densities decline in the p-type semiconducting passive layer upon receiving CGP. Besides, increasing the CGP cycles lowers the corrosion current density and produces less defective passive films.

Sparged but not stirred: Rapid, ADH-NADH oxidase catalyzed deracemization of alcohols in a bubble column

We investigate in detail both the deracemization reaction rate and maximum conversion of (R,S)-1-phenylethanol in a bubble column and the deactivation rates of both enzymes involved, alcohol dehydrogenase (ADH) and NADH oxidase (nox2). Instead of the predicted ellipsoidal shape of the bubbles, we observe a spherical shape in all our experiments. Calculated values for the area-specific mass transfer coefficient kLa in sparged, but not stirred, solution ranged from 17 to 87 h−1. We find that minimizing the air–liquid interface over time results in the lowest rate of nox2 deactivation. The onset of nox2 dissociation beyond the initial 50 h correlates with a tenfold increase in the observed deactivation rate constant. The highest conversion (99%) for deracemizing 50 mM (R,S)-1-phenylethanol was reached in the shortest reaction time (6 h) if large air bubbles (diameter 2.6 mm) at slow flowrates (5 bubbles/s) were employed. A faster flowrate, which delivers more oxygen per unit time, increased the initial reaction rate but resulted in a slower rate at higher conversions and ultimately incomplete maximum conversion (94%). Reaction rates under sparging were 4–8 times faster than in quiescent solution. Lastly, stirring did not significantly aid conversion (41% vs 37% in quiescent solution after 12 h) but caused increased enzyme deactivation (44 h vs 136 h half-life quiescent solution).

Rust layer growth and modification by a tannin-based mixture for lowering steel corrosion rates in neutral saline solution

ABSTRACT Concomitant rust growth on a rust-free surface and conversion by a solution of tannin, propolis and benzoate has been investigated in the present study with the aim of producing a modified rust layer, more resilient and protective than a pure rust layer. Under such circumstances, balancing simultaneous but contradictory processes of corrosion acceleration by iron chelation and corrosion inhibition by ferric tannate precipitation is crucial for layer formation. Benzoate served as an iron corrosion inhibitor in the layer formation stage while the propolis added to the tannin solution improved the modified rust layer protective efficiency. Corrosion rates lower than 5 mpy that are acceptable from the practical viewpoint are attained with the inhibitor-modified rust layer, both, in quiescent solution and up to a linear velocity of the solution approximately equal to 1.5 m s−1.

Enhanced resolution of generator-collector studies of enzymatic structures by means of hydrodynamic scanning electrochemical microscopy

In this report, the effects of forced convection on scanning electrochemical microscopy (SECM) studies of enzymes in the context of the generator-collector mode (G/C mode) were investigated. Forced convection was generated via an electrical high precision stirrer integrated into the electrochemical cell. Circular spots of glucose oxidase were immobilized on a gold support serving as model substrate. The diffusion layer of enzymatically generated H2O2 was characterized recording probe scan curves (PSCs) in z-direction. Furthermore, the enzyme-modified surfaces were investigated via constant-height SECM imaging in feedback mode and in G/C mode. For methodical comparison all sets of experiments were performed in quiescent solution (conventional approach) and with forced convection, respectively. In contrast to a growing diffusion layer without forced convection by applying forced convection, a constant diffusion layer of produced H2O2 was observed. Hence, via hydrodynamic SECM time-independent images within a reasonable time scale of SECM measurements in G/C mode were enabled and their resolution was enhanced.

Modes of Thermogravitational Convection and Thermoelectrokinetic Instability Under Joule Heating in Electrolyte Between Electric Membranes

Joule heating near ion-selective cation-exchange membranes in an external electric field can cause two modes of instability, namely, the thermogravitational convection, which reminds a well-known Rayleigh–Benard convection, and a novel type of instability, the thermoelectrokinetic instability. Stability of a quiescent one-dimensional steady-state solution to infinite small sinusoidal perturbations has been investigated in a wide range of the Rayleigh numbers. It has been found that, for the both modes, instability occurs for the limiting as well as for the underlimiting currents. Hence, a transition to the overlimiting regimes can happen bypassing the limiting regime, from some point of the underlimiting regime. Note that the Rubinstein–Zaltzman instability takes place only for the limiting currents. The Rayleigh numbers, recalculated to the classical ones, vary in a range from 500 to 1300, which is consistent with the classical thermogravitational convection results. It has been also shown, that the critical Rayleigh numbers are too large and, hence, critical distances between the membranes are too small to make the thermogravitational convection possible to manifest in the microchannels. This refutes the opinion that the thermogravitational instability produces one of the key mechanisms of transition to overlimiting currents in the problems of microfluidics.

Steady, Symmetric, and Reversible Growth and Dissolution of Individual Amyloid-β Fibrils.

Oligomers and fibrils of the amyloid-β (Aβ) peptide are implicated in the pathology of Alzheimer's disease. Here, we monitor the growth of individual Aβ40 fibrils by time-resolved in situ atomic force microscopy and thereby directly measure fibril growth rates. The measured growth rates in a population of fibrils that includes both single protofilaments and bundles of filaments are independent of the fibril thickness, indicating that cooperation between adjacent protofilaments does not affect incorporation of monomers. The opposite ends of individual fibrils grow at similar rates. In contrast to the "stop-and-go" kinetics that has previously been observed for amyloid-forming peptides, growth and dissolution of the Aβ40 fibrils are relatively steady for peptide concentration of 0-10 μM. The fibrils readily dissolve in quiescent peptide-free solutions at a rate that is consistent with the microscopic reversibility of growth and dissolution. Importantly, the bimolecular rate coefficient for the association of a monomer to the fibril end is significantly smaller than the diffusion limit, implying that the transition state for incorporation of a monomer into a fibril is associated with a relatively high free energy.

Tonks-Frenkel instability in electrolyte under high-frequency AC electric fields.

The instability of an electrolyte surface to a high-frequency, 10 to 200kHz, electric field, normal to the interface is investigated theoretically. From a practical viewpoint, such a high frequency leads to the absence of undesired electrochemical reactions and provides an additional control parameter. The theory of unsteady electric double layer by Barrero and Ramos is exploited. At such a high frequency, which is much larger than the eigenfrequency of the mechanical system, the nonlinear mechanical term does not "feel" the fast part of the Coulomb force, but it feels its slower component. In fact, the system behaves as if the electric field were a DC field. The observed instability is qualitatively close to the Tonks-Frenkel instability. The problem of the linear stability of the 1D quiescent stationary solution is solved analytically. For the important limiting cases, simple analytical formulas are derived. The linear stability analysis is complemented by the DNS of the full nonlinear system of equations with broadband low-amplitude white-noise initial conditions. After a transition period, the linear instability mechanism filters out the broad spectrum except for a narrow band near the maximum growth rate in rather good agreement with the linear stability analysis. If the external field is large enough, the nonlinear evolution results in coherent structures with sharp tips resembling to a Taylor cone. An evaluation of the cone angle for different conditions gives its value of about 30° to 60° , which is smaller than the angle of 98.6° for DC field and qualitatively corresponds to the experiments (L.Y. Yeo et al., Phys. Rev. Lett. 92, 133902 (2004)) for the high-frequency AC field and to the theoretical evaluation of the AC Taylor cones in E.A. Demekhin et al., Phys. Rev. E 84, 035301(R) (2011).

Effects of Winter Flounder Antifreeze Protein on the Growth of Ice Particles in an Ice Slurry Flow in 
 Mini-Channels

The control of ice growth in ice slurry is important for many fields, including (a) the cooling of the brain during cardiac arrest, (b) the storage and transportation of fresh fish and fruits, and (c) the development of distributed air-conditioning systems. One of the promising methods for the control is to use a substance such as antifreeze protein. We have observed and report here growth states of ice particles in both quiescent and flowing aqueous solutions of winter flounder antifreeze proteins in mini-channels with a microscope. We also measured ice growth rates. Our aim was to improve the levels of ice growth inhibition by subjecting the antifreeze protein solution both to preheating and to concentrating by ultrafiltration. We have found that the ice growth inhibition by the antifreeze protein decreased in flowing solutions compared with that in quiescent solutions. In addition, unlike unidirectional freezing experiments, the preheating of the antifreeze protein solution reduced the ice growth inhibition properties. This is because the direction of flow, containing HPLC6 and its aggregates, to the ice particle surfaces can change as the ice particle grows, and thus the probability of interaction between HPLC6 and ice surfaces does not increase. In contrast to this, ultrafiltration after preheating the solution improved the ice growth inhibition. This may be due to the interaction between ice surfaces and many aggregates in the concentrates.

Acoustic characterisation of pH dependant reversible micellar casein aggregation

Ultrasound and light-based measurements were used to monitor changes in agitated and quiescent solution characteristics such as particle size distribution during casein aggregation and redistribution in a model colloidal system. The precipitation of casein micelles was controlled by adjusting the pH of the solution to alter the stability of the micelles. The studied dispersions were prepared at high pH, taken through the isoelectric point to precipitate and then re-dispersed by further lowering the pH at specific intervals. The isoelectric point was determined by zeta potential measurement at each specific pH interval. The isoelectric point of the casein dispersions was in the region of pH 4.3–4.7. Changes in the particle size of this reversible casein system were successfully measured acoustically. The dissolution rate and solution kinetics were subsequently monitored in a wide pH range using a combination of acoustic and light-based methods.

Determination of progesterone in saliva using an electrochemical immunosensor and a COTS-based portable potentiostat

This paper describes the reliable determination of progesterone (P4) in undiluted saliva making use of a disposable amperometric immunosensors implemented on low-cost and portable device/potentiostat constructed with commercial-off-the-shelf (COTS) components. The immunosensor allows the fast (45 min), selective and sensitive determination (5 pg mL−1 LOD) of P4 using amperometry in stirred solutions. The immunosensor was coupled to the COTS-based potentiostat and amperometry was made into drops of quiescent solutions. No significant differences were apparent between the analytical performance achieved with the immunosensor for P4 using both a conventional and the COST-based potentiostats. The practical applicability of the immunosensor coupled with the COTS-based potentiostat was demonstrated by determining the endogenous P4 content in different undiluted saliva samples with highly variable endogenous contents of the target hormone. The obtained results were in good agreement with those provided by the conventional ELISA methodology and with the contents reported in the literature for samples with similar characteristics. This validated the combined device for the reliable and minimally invasive determination of the target hormone involving a very simple protocol and taking only 45 min.