Dispersion Phenomena Research Articles

Congo Red Dye Removal from Aqueous Solutions by Photocatalytic Redox Reactions Using Anatase Nano-TiO2 as a Heterogeneous Catalyst: Degradation Kinetics and Simulation Using Dispersion Model

Water pollution caused by Congo red as a textile dye is a significant concern for the aquatic environment. The photocatalytic redox reactions were carried out in a closed batch photoreactor using 0.2 g/L Anatase nano-TiO2 as a catalyst to remove different initial concentrations (32, 71, and 178 ppm COD) of the dye from its neutral aqueous solutions at 40℃. The air was supplied to the reactor as an oxygen source at a rate of 0.2 L/min. The COD removal values decreased with the increasing initial dye concentration, and the best removal value was recorded (89.47 %) for the lowest initial COD (32 ppm) after 255 minutes of radiation. The kinetics study showed that the Congo red dye removal followed a first-order reaction model. A mathematical model was developed based on the axial dispersion phenomenon to simulate the product distribution of the dye through several types of reactors (ideal and nonideal plug flow and mixed flow reactors). Effects of initial concentration, dispersion number, and space-time on the organic distribution through the reactors were studied and discussed. The simulated results show that the ideal plug flow reactor (zero dispersion) performance was better than that of the nonideal plug flow reactor, and the performance decreased with the increasing dispersion number and gave the worst performance in the mixed flow reactor (infinity dispersion).

Study on the phase transition characteristics of nano-hydrated salts based on molecular dynamics simulations

Hydrated salts possess great competitiveness in terms of enhancing utilization efficiency of heat due to large densities of heat storage and low costs. However, the existence of supercooling degree is the common phenomenon for hydrated salts, which might restrict the application prospects in partial fields. This work focuses on hydrated salts with relatively larger latent heats, namely Na2CO3·10H2O and Na2HPO4·14H2O in the absence and presence of SiO2 as well as eutectic hydrated salt prepared with 40 wt% Na2CO3·10H2O and 60 wt% Na2HPO4·12H2O. Their melting/solidification temperatures were determined and the supercooling behavior was analyzed based on molecular dynamics simulations. The simulation results of melting/solidification temperatures present small deviations of 0.17–3.24 ℃ in comparison with experimental data. Additionally, the aggregation phenomenon among salt ions and dispersion phenomena among water molecules and between water molecules and salt ions for supercooled liquid hydrated salts are revealed, which are attributed to stronger electrostatic interactions and weaker van der Waals interactions as well as lower binding energies. Moreover, SiO2 not only lowers melting temperatures due to its higher thermal conductivity than hydrated salts and the existence of micro-convection, but affects solidification behavior of hydrated salts. The different influences of SiO2 on solidification temperatures of Na2HPO4·14H2O and Na2CO3·10H2O were associated with dispersion degree between water molecules and salt ions around SiO2, which would be attributed to different strengths of interaction forces between SiO2 and salt ions. On these bases, this work provides new perspectives for clarifying phase change characteristics of nano-hydrated salts.

Dynamic Phase Behavior of Amorphous Solid Dispersions Revealed with In Situ Stimulated Raman Scattering Microscopy.

This study reports the application of in situ stimulated Raman scattering (SRS) microscopy for real-time chemically specific imaging of dynamic phase phenomena in amorphous solid dispersions (ASDs). Using binary ritonavir and poly(vinylpyrrolidone-vinyl acetate) films with different drug loadings (0-100% w/w) as model systems, we employed SRS microscopy with fast spectral focusing to analyze ASD behavior upon contact with a dissolution medium. Multivariate unmixing of the SRS spectra allowed changes in the distributions of the drug, polymer, and water to be (semi)quantitatively imaged in real time, both in the film and the adjacent dissolution medium. The SRS analyses were further augmented with complementary correlative sum frequency generation and confocal reflection for additional crystallinity and phase sensitivity. In the ASDs with drug loadings of 20, 40, and 60% w/w, the water penetration front within the film, followed by both surface-directed and bulk phase separation in the film, was apparent but differed quantitatively. Additionally, drug-loading and phase-dependent polymer and drug release behavior was imaged, and liquid-liquid phase separation was observed for the 20% drug loading ASD. Overall, SRS microscopy with fast spectral focusing provides quantitative insights into water-induced ASD phase phenomena, with chemical, solid-state, temporal, and spatial resolution. These insights are important for optimal ASD formulation development.

Dispersion phenomena in EIS and DIS spectra of porous materials and their representation as transmission line bases ‘diffusion’ elements– part II - a case study of proton conductors

Porosity of materials, understood as an overall averaged parameter or as the pore-size distribution related data is an important quality of numerous functional materials including proton conductive glasses. While most of the existing techniques applied for its assessment cannot be used to monitor the behaviour of ‘live’ systems in operando conditions, it is possible to use Electrochemical Immittance Spectroscopy (EIS) for this purpose. Nevertheless, analysis of these systems still requires an approximation made using transmission lines based models, which can be equated to specific diffusion elements parameters, which can in turn be related to qualities of the porous material investigated. The changes of these parameters can be correlated with various processes– such as dehydration and phase transitions or to the material’s processing history. In this part of the material we present a case study of highly grinded, mechanochemically processed powder-pressed proton conductors: phosphate-silicate glass and two uranyl based compounds– hydroxy phosphate (HUP) and hydroxy arsenate, delivering proof that the dispersive properties of proton transporting materials can be correlated with their dehydration processes, which were followed by means of FT-IR and terahertz time domain spectroscopies.

An application of the DEM-FFT method to predict the thermal conductivity of high burnup fragmented fuel

Understanding Fuel Fragmentation, Relocation and Dispersal (FFRD) phenomena is a major item to predict the behavior of fuel rods in the event of a Pressurized Water Reactor loss-of-coolant hypothetical scenario. In order to introduce an effective medium for fragmented fuel that could be used in fuel performance codes, the heat transfer properties of UO2 granular beds in He-Kr-Xe mixes was studied numerically. The Discrete Element Method was first used to compute the spatial arrangement of powder only submitted to gravity with a representative granulometric distribution. These generated geometries were then transformed into a 3D grid (voxelized) to perform numerical homogenization and compute their effective properties using a Fast Fourier Transform solver for heat transfer. Different hypotheses were made in the voxelation process about how the treatment of gas-solid and solid-solid interfaces, which in turn provided different estimates of the effective properties. Due to limits on the discretization and extended particle size distributions, a two-scale scheme was introduced and numerically tested against direct computations. For several beds, computed thermal conductivities were compared to analytical models for granular materials. Some heat transfer properties of fragmented fuel at several burnups were then computed, taking into account approximations for Knudsen and radiation size effects.

Modeling Rayleigh wave in viscoelastic media with constant Q model using fractional time derivatives

The propagation of seismic waves within the near-surface weathering layers, characterized by their low-quality factors (Q), is often accompanied by strong attenuation and dispersion phenomena. Among these, the Rayleigh wave, with its sensitivity to dispersion, has proven to be a powerful tool for near-surface exploration. We propose a novel approach for simulating Rayleigh wave propagation in such low-Q media. Our method uses the time-domain fractional wave equation with memory effect, based on Kjartansson's constant-Q (CQ) model, for accurate characterization of the propagation process. To solve numerically the wave equation with the fractional derivatives, we employ a finite-difference method combined with the auxiliary differential equation-perfectly matched layer (ADE-PML) and the acoustic-elastic boundary approach (AEA). The algorithm's high computational accuracy is verified through comparison with the conventional integer-order wave equation based on the nearly constant-Q (NCQ) models in strong attenuation media. The research in this paper deepens our understanding of the propagation characteristics of Rayleigh waves in strongly weathering layers. This new method strongly supports those seismic imaging and inversion methods depending on seismic modeling, including the reverse time migration and the full waveform inversion of the internal structure of low-Q media.

Dispersion phenomena in EIS and DIS spectra of porous materials and their representation as transmission line bases ‘diffusion’ elements—part I: a case study of lead-acid systems

A number techniques exist to assess the porosity of materials, however a large number of them cannot be used to monitor the behaviour of such in ‘live’ systems. This problem can be overcome by the usage of Electrochemical Impedance Spectroscopy (EIS). However, porous systems and their qualities, can not be easily described using regular equivalent circuit and basic elements. An approximation of such has to be made using transmission lines, which can, in turn, be equated to specific diffusion elements. The parameters of these elements can be related to porous material qualities. And in turn, the changes of these parameters can then be related to various processes—such as ageing or degeneration. In this part of the material a case study was performed on a number of lead-acid systems—a VRLA battery, a maintenance-free one and system consisting of a lead electrode and a platinum mesh counter electrode. This was done in order to test the validity of using the Warburg impedance element in equivalent circuits. During the course of the tests it was found that not only a Gerischer element is a better choice, but the changes in its parameters can be related to different ageing-related processes.

Chaos analysis and traveling wave solutions for fractional (3+1)-dimensional Wazwaz Kaur Boussinesq equation with beta derivative

Wazwaz Kaur Boussinesq (WKB) equation can effectively simulate the behavior of water waves in shallow water, including the nonlinear effect and dispersion phenomenon of waves, which is of great significance for understanding the dynamic process of ocean, river and other water bodies. To enrich the wave equation theory, the (3+1)-dimensional integer order derivative of WKB equation is changed to the fractional one with beta derivative. The current work deals with the fractional (3+1)-dimensional WKB equation for discussing its chaotic behavior and establishing some new analytic solutions. The chaotic properties of the equation are verified by the trend of evolution along with time, Lyapunov exponents and initial sensitivity analysis. And then complete discrimination system for polynomial method is applied to derive some trigonometric, hyperbolic, Jacobi elliptic and other solutions. The graphical demonstrations are provided for part of these solutions. From these visualized graphs, the solitary, periodic and quasi-periodic wave are shown and the effect of fractional derivatives on the equation can be seen intuitively.

Study of multiferroic properties of Mn substituted Bi0.8Sm0.1Dy0.1Fe1-xMnxO3 ceramics

Abstract Transition metal Mn substituted various multiferroic Bi0.8Sm0.1Dy0.1Fe1-xMnxO3 (x = 0.00, 0.01, 0.03 and 0.05) ceramics samples were fabricated by the solid-state reaction technique. The distorted rhombohedral perovskite structure with some phase impurity of all samples is confirmed by X-ray diffraction analysis. Field Emission Scanning Electron Microscope and Energy Dispersive X-ray spectroscopy are used for microstructural and quantitative analysis, respectively. Densities are decreased and the average grain size is increased with Mn contents. The initial permeability and relative quality factor (RQF) have found to be increased with Mn contents in the samples. The peaks in RQF shifts toward the lower frequency region with increasing Mn contents can be attributed by Snoek’s relation. All the samples show paramagnetic behavior at room temperature and magnetization slightly increases with Mn contents. The frequency dependent dielectric constant is investigated and found to consequence of space charge polarization. The dispersion behavior in dielectric constants can be explained by the Maxwell-Wagner model. The dielectric constants and dielectric loss decrease with increasing of Mn contents for all the samples. The value of electric modulus is observed to increases with the increasing of frequency and this dispersion phenomena is due to short range mobility of charge carriers in conduction. The effect of grain and grain boundaries on electric properties of samples are investigated by complex impedance analysis. The ac conductivity increases with frequency due to small polaron hopping and it can be attributed according to Jonscher’s power law.

Exchanging “Mementos of Death”: Holocaust Remains in Poland and Japan

Abstract In 1962, a Japanese delegation of peace activists visited Auschwitz-Birkenau where they participated in the annual ceremony commemorating the liberation of the camp. As part of the ceremony, the delegation engaged in an exchange of Hiroshima and Auschwitz “memontos,” receiving from the Polish side, amongst others, an urn containing ashes of the victims of the camp. The exchange was the first of several that included Holocaust urns, most of which are now in Japan, and a part of a much broader phenomenon of material dispersal of human remains instituted by Polish museums established at the former Nazi camps. In this paper, we take a critical look at this practice, its development, directionalities and meanings. Tracing the journey of the urns and their various uses, we argue, reveals the complex politics and cultural landscape of the transnational commemoration of World War II in its very local meanings in Poland, Japan and beyond.

Lax integrability and nonlinear dispersive wave phenomenon for the (3 + 1) dimensional Kudryashov–Sinelshchikov equation

A (3 + 1) dimensional Kudryashov–Sinelshchikov equation is investigated in this paper, which describes bubbles in the liquid fluctuations. By virtue of the binary Bell polynomials, the bilinear representation, bilinear Bäcklund transformation with associated Lax pair are obtained, respectively. Moreover, utilizing Hirota’s bilinear representation, four new lump solutions are constructed and the interaction phenomenon between lump and periodic solution is thoroughly examined. The work also illustrates the intriguing dynamical behavior with the aid of Maple software, which plots the three-dimensional surface, two-dimensional density, and contour profiles of the solutions constructed in this work in various planes.

Elastic reverse time migration using an efficient and accurate adaptive variable grid discretization method

Abstract The conventional reverse time migration utilizes regularly sampled computational grids to simulate wave propagation. Selecting the appropriate grid sampling is important for computational accuracy and efficiency. In general, the uniform-size grid cannot represent the complexity of the geology well. The grid may appear sparse in the low-velocity zone, especially in shallow depths where dispersion may occur. Conversely, it may appear excessively dense in the high-velocity zone, such as at greater depths or within a salt body, which results in higher computational memory and time consumption. To overcome these issues, we developed an efficient and accurate adaptive variable grid discretization method that automatically selects the vertical grid size based on the velocity, depth, and dominant frequency of the wavelet in elastic medium. Then we reformulated the elastic equations based on the adaptive variable grid by introducing a mapping relationship. To test the effectiveness, accuracy, and efficiency of the equation, we implemented it to both the forward propagation and migration of elastic wavefield. Synthetic numerical examples demonstrate that our proposed method can achieve elastic wavefield separation and no significant dispersion phenomenon. The multi-component imaging accuracy of reverse time migration is nearly equivalent to the traditional method, while significantly improving computational efficiency and saving storage space.

Validation and parametric study of FFRD model in DRACCAR code

The recent revision of Emergency Core Cooling System (ECCS) regulations in Korea has necessitated the consideration of Fuel Fragmentation, Relocation, and Dispersal (FFRD) phenomena in nuclear reactor safety analyses. Consequently, the Korea Atomic Energy Research Institute (KAERI) has developed and integrated the FFRD model into the domestically licensed safety analysis code, SPACE. Globally, US NRC’s FRAPTRAN and IRSN’s DRACCAR are available for evaluating FFRD phenomena. The FRAPTRAN code incorporates the FFR model, developed by Quantum Technology, while the fuel dispersal model is currently not included. In contrast, the DRACCAR code functions as an integrated analysis platform capable of modeling multi-dimensional thermal, hydraulic, mechanical, and chemical phenomena during a Loss of Coolant Accident (LOCA). This study conducts a thorough examination of the FFRD model in the DRACCAR code and validates its applicability through analysis using the Halden IFA-650 tests. The results demonstrate satisfactory predictive capabilities. Furthermore, a parametric study of key FFRD model parameters enhances the understanding of the FFRD model in the DRACCAR code. The development of detailed physical models in the FFRD model could significantly enhance the performance of the DRACCAR code, warranting the establishment of a comprehensive framework for these advancements. In the future, code-to-code comparisons between the DRACCAR code and other domestically developed integrated analysis platforms will be conducted to investigate various phenomena in depth.

NUMERICAL COMPUTATION OF ONE- AND TWO-LAYER SHALLOW FLOW MODEL

In this research, we study a proficient computational model designed to simulate shallow flows involving one- and two-layer shallow flow. This numerical model is built upon the Saint Venant equations, which are widely used in hydraulics to depict the behavior of shallow water flow. The numerical scheme used here is constructed based on the conventional leapfrog technique implemented on a staggered grid framework, referred to as MCS. The primary objective of this research is to re-examine and implement the MCS in accurately modelling the free surface and interface waves produced by different flows passing through irregular geometries. Unlike the conventional MCS, we modify the momentum conservation principle to be more general, accommodating a non-negative wet cross-sectional area due to irregular geometry. We successfully conduct numerous numerical simulations by examining various scenarios involving one-layer and two-layer flow through irregularly shaped channels or structures. Our results show that the correct surface wave profile generated by a one-dimensional dam break through the triangular obstacle in the open channel can be simulated very well. Comparison with the existing experimental data seems promising although some disparities are being found due to dispersive phenomena with RMSE less than 5%. Furthermore, our scheme is successfully extended to simulate the steady sub-maximal exchange in two-layer flows using specific boundary conditions. The alignment between the submaximal numerical results with exchange flow theory is noticeable in the interface profile, characteristics of flow conditions and the flux values achieved when the steady situation occurs. These satisfying results indicate that our proposed numerical model can be used for practical needs involving various flow situations both one and two-layer cases

Study of inclusions-removal and slag-metal dispersion phenomenon in gas-stirred ladle

Abstract The slag-metal interface serves as a crucial locus for both chemical reactions and the adsorption of inclusions during secondary refining. This study first comprehensively reviews the methods of inclusions removal and then establishes a cold-state experiment using a water-oil system to reappear the phenomenon of slag-metal dispersion and inclusion adsorption. The distribution of slag droplets under varying slag volumes is analyzed in terms of the effect of bottom blow rates. Simultaneously, the volumetric fraction of oxygen on the slag-eye surface is analyzed. The result proved that the increase in oil layer thickness or the gas flow rate increase the volume of entrained oil. The dimensionless depth of entrained droplets was positively associated with gas flow rate or oil thickness. The dimensionless depth of “large droplets” and “small droplets” was in the range of 0–25 % and 0–60 %, respectively. Moreover, analysis of the gas composition above the slag-eye in a water-oil system is used to determine the degree of secondary oxidation. The oxygen volume fraction over the surface of the slag-eye decreases with the increase of gas flow rate. The oxygen volume fraction over the surface of the slag-eye is 1.51 % when the gas flow rate is 9 L/min.

First model of industrial noise propagation in the vicinity of the Yasuní National Park

Abstract This work addresses aspects of industrial noise produced by the facilities of oil extraction near Yasuní National Park, located in the Ecuadorian Amazon region. The acoustic sources within this kind of facilities could influence in the wildlife behavior, which could impact negatively on the species. The acoustic wave radial propagation model in an open field is proposed through a geometric divergence attenuation, atmospheric absorption effect, dispersion effects due to obstacles, and soil effects. The initial model without obstacles makes predictions based on an algorithm considering that the data are associated to a GPS position, the first propagation model without obstacles determines the level of sound pressure for each quasi-horizontal measurement (x, y). Then, dispersion factors are incorporated through the NORD2000 model to consider the local flora that introduces reflection and dispersion phenomena which are in the environment considering geometric measurements estimated in situ. The pressure level of the model without obstacles decreases as the frequency increases, but with less intensity compared to the pressure level of the model with obstacles. As the frequency increases, there are important fluctuations since the attenuating factors influence more than the correction factors.

Dispersion aware matching pursuit decomposition of Lamb wave signals for structural health monitoring of thin plates structures

Structural Health Monitoring (SHM) techniques are key to monitor in real time the health state of engineering structures, where damage type, location and severity are to be estimated by applying signal processing and deep learning techniques to temporal signals measured by sensors coming from the structure under study. Among the most widely used signal processing techniques in the SHM community is the Matching Pursuit Method (MPM), which allows to extract key features from a measured signal. MPM simply consists in approximating temporal data as a sum of different terms composed of a delayed and scaled signal called atom. This signal decomposition approach is however limited to non-dispersive signals which is not the case when dealing with Lamb waves signals widely used in the SHM of thin structures. In this case, in addition of delays and attenuations, wave packed also endure dispersion caused by the fact that all the frequencies do not propagate at the same speed within the structures under study. In this context, an improved version of Matching Pursuit is proposed in the present work, which address the dispersion phenomena by decomposing a measured signal as delayed and dispersed impulse response of an atom, obtaining better features for Lamb wave measurements. The performance of the developed technique is tested for the approximation of real measured signals, showing its better performance compared to classical MPM, especially when dealing with dispersive signals. This improved signal decomposition can be very useful for SHM purposes.

The effect of the noise on the dynamics of soliton generation in microresonator

The study demonstrated that noise changes the number of modes that can oscillate within the small cavity, and the spectral power is concentrated around the fundamental frequency. We also observed a reduction in the distortion that arises from the dispersive solitaire. This behaviour can be attributed to the magnitude of the pulse strength or the loss of its frequency due to the arbitrary interaction between the pulse train and the linear and nonlinear refractive index of the microcavity. The relationship between the dispersion and nonlinearity phenomena inside the microresonators is major in determining the inside field dynamics. The study showed that as the noise in microresonators cannot be cancelled, it is recommended to use a proper pulse width, intensity distribution, and power.

Frequency- and polarization-dependent lensing of gravitational waves in strong gravitational fields

The propagation of gravitational waves can be described in terms of null geodesics by using the geometrical optics approximation. However, at large but finite frequencies the propagation is affected by the spin-orbit coupling corrections to geometrical optics, known as the gravitational spin Hall effect. Consequently, gravitational waves follow slightly different frequency- and polarization-dependent trajectories, leading to dispersive and birefringent phenomena. We study the potential for detecting the gravitational spin Hall effect in hierarchical triple black hole systems, consisting of an emitting binary orbiting a more massive body acting as a gravitational lens. We calculate the difference in time of arrival with respect to the geodesic propagation and find that it follows a simple power-law dependence on frequency with a fixed exponent. We calculate the gravitational spin Hall-corrected waveform and its mismatch with respect to the original waveform. The waveform carries a measurable imprint of the strong gravitational field if the source, lens, and observer are sufficiently aligned, or for generic observers if the source is close enough to the lens. We present constraints on dispersive time delays from GWTC-3, translated from limits on Lorentz invariance violation. Finally, we address the sensitivity of current and future ground detectors to dispersive lensing. Our results demonstrate that the gravitational spin Hall effect can be detected, providing a novel probe of general relativity and the environments of compact binary systems. Published by the American Physical Society 2024

An analytical model for Love wave in a coated piezoelectric bar via nonlocal theory due to an impulsive source

The non-locality behavior of new advanced functionally graded (FG) and piezoelectric (PE) nanobar is presented in this study with an impulsive point source using green function derivatives. The primary aim of this study is to explore the impact of different physical parameters on the phase dispersion phenomena against wave number and depth of point source of Love wave propagation. The stress tensor is considered the linear variation of the shear stress distribution in the thickness direction, and the shear stress at the free surface of the piezoelectric bar is zero. Using the Fourier transform and Green’s function technique, the equations of motion and the dispersion relation is derived by applying admissible boundary conditions involving piezoelectricity, dielectricity, functional gradient, and nonlocal elastic parameters of the media. The obtained results are validated with existing results by considering special cases. The variation in the dispersion curves due to the impulsive point source and piezoelectricity, dielectricity, functional gradient, and non-locality parameters have been analyzed and illustrated using graphs along with a comparative study by considering four piezoelectric materials, PZT-4, PZT-5A, PZT-5H, and PZT-2. Furthermore, the relationship between nonlocal parameters in the layer and half-space is investigated to explore the influence of wave number, phase velocity, and depth of point source.