Diffuse Part Research Articles

Preparation of Silver Nanoparticles in a Water-in-Oil Microemulsion Stabilized by Ecosurf EH3 and Determination of Their Electrophoretic Mobility.

This work describes a study on the electrophoresis of silver nanoparticles in reverse microemulsions with varying water content. The microemulsion was stabilized using a nonionic ethoxylated surfactant, 2-ethylhexanol triethoxylate (Ecosurf EH3). This study represents the second example of electrophoresis research conducted in media with a low dielectric constant for etoxylated surfactants. The study also determined the boundaries of thermodynamic stability and the conditions required to obtain nanoparticles with a high yield. The hydrodynamic diameter and electrophoretic mobility of nanoparticles were measured using dynamic light scattering and laser Doppler electrophoresis. The study determined the boundary conditions for applying these methods to laser-absorbing samples. The electrophoretic mobility of nanoparticles was found to be dependent on the fraction of water in the range of 2-5%vol. (equivalent to a metal content of 10-25mM), as determined by electrophoresis in a free medium. The increase in volume fraction of water leads to agglomeration of micelles, which causes a decrease in the electrokinetic potential of nanoparticles, likely due to the blurring of the diffuse part of the electrical double layer.

Intramolecular benzene excimer formation in 13,14-diphenyldibenzo[b,j][4,7]phenanthroline.

13,14-diphenyldibenzo[b,j][4,7]phenanthroline (DBP3) in various solvents was studied by time-resolved fluorescence and fs transient absorption (fs-TA) spectroscopy. An intramolecular benzene excimer is demonstrated to form within DBP3; it exhibits strong redshifted emission with maximum at 540-640nm. "Intrinsic" fluorescence from DBP3 is dramatically quenched down to τ = 50-400fs in all the solvents studied. Fs-TA and time-resolved fluorescence spectra have proved that relaxed intramolecular benzene excimer is formed from S1 state via hot excimer state with three lifetime components: 50fs, ∼3.5ps, and ∼25ps, which are of the inertial (electronic) and diffusive parts of the relaxation due to solute-solvent interaction. Formation of triplet states via intersystem crossing was observed directly from the upper excited electronic states of DBP3.

On the study of three-dimensional compressible Navier–Stokes equations

This work is devoted to the study of three-dimensional compressible Navier–Stokes equations on unstructured meshes. The approach used is based on separating the convection and diffusion parts. The convective flux is computed using the Godunov method. For the diffusive part, we present a new finite volume scheme. Numerical results are provided to demonstrate the efficiency of the developed technique.

The Dynamics of the Hubbard Model Through Stochastic Calculus and Girsanov Transformation

As a typical quantum many body problem, we consider the time evolution of density matrix elements in the Bose-Hubbard model. For an arbitrary initial state, these quantities can be obtained from an SDE or stochastic differential equation system. To this SDE system, a Girsanov transformation can be applied. This has the effect that all the information from the initial state moves into the drift part, into the mean field part, of the transformed system. In the large N limit with g=UN\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g=UN$$\\end{document} fixed, the diffusive part of the transformed system vanishes and as a result, the exact quantum dynamics is given by an ODE system which turns out to be the time dependent discrete Gross Pitaevskii equation. For the two site Bose-Hubbard model, the GP equation reduces to the mathematical pendulum and the difference of expected number of particles at the two lattice sites is equal to the velocity of that pendulum which is either oscillatory or it can have rollovers which then corresponds to the self trapping or insulating phase. As a by-product, we also find an equivalence of the mathematical pendulum with a quartic double well potential. Collapse and revivals are a more subtle phenomenom, in order to see these the diffusive part of the SDE system or quantum corrections have to be taken into account. This can be done with an approximation and collapse and revivals can be reproduced, numerically and also through an analytic calculation. Since expectation values of Fresnel or Wiener diffusion processes, we write the density matrix elements exactly in this way, can be obtained from parabolic second order PDEs, we also obtain various exact PDE representations. The paper has been written with the goal to come up with an efficient calculation scheme for quantum many body systems and as such the formalism is generic and applies to arbitrary dimension, arbitrary hopping matrices and, with suitable adjustments, to fermionic models.

Variable-Angle Surface Spectroscopy Reveals the Water Structure in the Stern Layer at Charged Aqueous Interfaces.

At charged aqueous interfaces, the second-order nonlinear optical response originates from water molecules within the diffuse part of the electrical double layer, which are ordered by the surface field and from water that additionally experiences chemical and physical interactions with the surface in the Stern layer. These two environments can either reinforce or diminish the overall signal and can be disentangled by varying the coherence length of their interaction with external laser fields. Here, we demonstrate a method in which the angle of incidence is varied to afford a significant change in the coherence length. When this technique was applied to the silica-water interface, it was observed that water molecules in the Stern and diffuse layers direct their hydrogen atoms toward the mineral surface at a low ionic strength and neutral pH. A decrease in the signal with increasing ionic strength is attributed to hydrated cation adsorption that competes with free water for deprotonated silanol sites.

Variation in Phosphorus Concentration and Flux at Zhutuo Section in the Yangtze River and Source Apportionment

Phosphorus (P) is a pollutant of great concern in the Yangtze River Basin. The Xiangjiaba Reservoir and Xiluodu Reservoir on the lower reach of the Jinsha River began to operate in 2012 and 2013, respectively, which greatly changed the concentrations of suspended sediment and characteristics of P form and transport in the reservoirs and the downstream reach from Yibin to Jiangjin of the Yangtze River. The Zhutuo section is representative in the water quality of the Yibin-Jiangjin reach, which can not only reflect the comprehensive effects of the formation of the two reservoirs and changes in the aquatic environment in the Min-Tuo Rivers but also reflect the quality of water flowing into the Three Gorges Reservoir. The runoff, concentrations and fluxes of suspended sediments (SS), and P concentrations and fluxes at Zhutuo section were studied during 2002-2019, and the source of P was apportioned based on the principle of river base flow. The results showed that in the past 18 years, the concentrations and fluxes of total phosphorus (TP) and particulate phosphorus (PP) at Zhutuo section in the wet season were higher than those in the level and dry seasons; the rule of positive correlation between PP and SS concentrations remained unchanged. From 2002 to 2019, the concentrations and fluxes of TP, PP, and dissolved P (DP) generally increased first and then decreased, and the operation of the Xiangjiaba Reservoir was a time node for the trend turning. Compared with that in the period from 2002-2012, the SS concentration and flux decreased by 94% and 77%, TP and PP concentrations decreased by 46% and 70%, and TP and PP fluxes decreased by 58% and 74%, respectively, during 2014-2019. The decline mainly occurred in the wet season, followed by that in the level season. After the formation of the two reservoirs, the relationship between water and sediment and the form of P greatly changed, and the proportion of DP in TP increased significantly, whereas the proportion of PP was the opposite. The TP pool in overlying water in the dry and level seasons shifted from mainly particulate to mainly dissolved. The change in water and sediment conditions was the main driving force for the significant change in P concentration, flux, and form. Before the operation of the Xiangjiaba Reservoir, the Jinsha River was the maximum contributor to the whole and diffuse source part of the TP load at Zhutuo section among the contributing catchment sub-basins; however, the Minjiang River became the largest contributor after the operation. The average TP load at Zhutuo section from 2017-2019 was 3.575×104 t·a-1 (after deducting the natural background value), of which the contribution of diffuse sources and point sources accounted for 68% and 32%, respectively. The Minjiang River represented 49%, 43%, and 62% of the total TP load, diffuse source TP load, and point source TP load at Zhutuo section, respectively. Considering the load contribution and pollution intensity, the key area for P pollution control in the area upstream of the Three Gorges Reservoir was the Min-Tuo River Basin.

NeRC: Rendering Planar Caustics by Learning Implicit Neural Representations.

Caustics are challenging light transport effects for photo-realistic rendering. Photon mapping techniques play a fundamental role in rendering caustics. However, photon mapping methods render single caustics under the stationary light source in a fixed scene view. They require significant storage and computing resources to produce high-quality results. In this paper, we propose efficiently rendering more diverse caustics of a scene with the camera and the light source moving. We present a novel learning-based volume rendering approach with implicit representations for our proposed task. Considering the variety of materials and textures of planar caustic receivers, we decompose the output appearance into two components: the diffuse and specular parts with a probabilistic module. Unlike NeRF, we construct weights for rendering each component from the implicit signed distance function (SDF). Moreover, we introduce the centering calibration and the sine activation function to improve the performance of the color prediction network. Extensive experiments on the synthetic and real-world datasets illustrate that our method achieves much better performance than baselines in the quantitative and qualitative comparison, for rendering caustics in novel views with the dynamic light source. Especially, our method outperforms the baseline on the temporal consistency across frames.

Electrode microstructure design based on a CA-FD hybrid computation framework to alleviate the concentration polarization

The fast charging capability of lithium-ion batteries is considered as a critical requirement for the widespread replacement of fuel vehicles by electric ones. The high current applied in the fast charging process always causes concentration polarization due to the velocity difference between ionic diffusion and electron transport, which could lead to a low charging efficiency. The ionic diffusion velocities in both solid phase and liquid phase are strongly related to the microstructure of electrode particles. Based on the understanding of the reaction-diffusion mechanism, numerical simulation method is feasible to investigate the effect of microstructure on charging performance more economically. However, a two-dimensional model with the consideration of electrode microstructure consists of a set of highly coupled partial differential equations (PDEs), which is hard to be solved and inefficient with the irregular solid-liquid boundaries. Compared with PDEs, cellular automata (CA) is focused on the interaction between the adjacent discrete elements rather than solving the continuous variables across the whole region. According to this characteristic, mass transfer with complex solid-liquid boundaries can be simulated more conveniently by CA, but on the other hand, the restriction of applied current on the total reaction flux is hard to be considered in the CA model. Therefore, the diffusion part and the reaction part are processed by CA and finite difference (FD) method respectively. A CA-FD hybrid computation framework is proposed to consider the effect of microstructure on charging performances and visualize the concentration evolution inside the electrode particles. Based on this framework, the electrodes with uniform structure, porosity-layered structure and particle size-layered structure are constructed and applied in the charging simulations. According to the simulation results, the layered structures are beneficial for alleviating the concentration polarization in batteries, so that the charging efficiency of the electrodes can be improved without energy density loss by adopting these non-uniform structures in certain scenarios.

Models for Stabilization of Charged Particles with Surfactants in Nonpolar Media

Stabilization of charged particles in nonpolar media is one of the most complicated problems in modern colloid chemistry. The attribution to colloid chemistry is absolutely justified in this case: in nonpolar media, charged particles have, as a rule, a supramolecular nature. Low dielectric permittivity of a medium makes the existence of ions in the classical interpretation energetically disadvantageous. The key condition for the presence of charged particles in nonpolar media is their steric stabilization, which requires some revision of the classical concepts of the structure of the electrical double layer, primarily, its diffuse part. Detailed analyzing the structure of the electrical double layer in nonpolar media is of importance because of the high practical significance of electrokinetic phenomena in such systems. This review considers the main models for steric stabilization of charged particles with surfactants in dispersion media having dielectric permittivities lower than 5. The main attention is focused on not only the concentrations corresponding to the formation of reverse micelles, but also on the concentrations below the critical micelle concentration. In addition, nontypical examples of electrokinetic phenomena in organosols are considered.

A mechanical derivation of the evolution equation for scintillating crystals: Recombination–diffusion–drift equations, gradient flows and Wasserstein measures

In a series of previous papers we obtained, by the means of the mechanics of continua with microstructure, the Reaction–Diffusion–Drift equation which describes the evolution of charge carriers in scintillators. Here we deal, first of all, with the consequences of constitutive assumptions for the entropic and dissipative terms. In the case of Boltzmann–Gibbs entropy, we show that the equation admits a gradient flows structure: moreover, we show that the drift–diffusion part is a Wasserstein gradient flow and we show how the energy dissipation is correlated with an appropriate Wasserstein distance.

Models for Stabilization of Charged Particles with Surfactants in Nonpolar Media

Stabilization of charged particles in nonpolar media is one of the most complicated problems in modern colloid chemistry. The attribution to colloid chemistry is absolutely justified in this case: in nonpolar media, charged particles have, as a rule, a supramolecular nature. Low dielectric permittivity of a medium makes the existence of ions in the classical interpretation energetically disadvantageous. The key condition for the presence of charged particles in nonpolar media is their steric stabilization, which requires some revision of the classical concepts of the structure of the electrical double layer, primarily, its diffuse part. Detailed analyzing the structure of the electrical double layer in nonpolar media is of importance because of the high practical significance of electrokinetic phenomena in such systems. This review considers the main models for steric stabilization of charged particles with surfactants in dispersion media having dielectric permittivities lower than 5. The main attention is focused on not only the concentrations corresponding to the formation of reverse micelles, but also on the concentrations below the critical micelle concentration. In addition, nontypical examples of electrokinetic phenomena in organosols are considered.

Nonlinear stochastic wave equations in 1D with fractional Laplacian, power-law nonlinearity and additive [formula omitted]-regular noise

A qualitative study of nonlinear, 1D stochastic fractional wave equations with dissipative nonlinearities of power-law form is conducted on (t,x)∈[0,+∞)×Dutt+σ2(−uxx)α−a1u+a2‖u‖L2(D)ρu−κut=b0∂W0∂t on (t,x)∈[0,+∞)×D with D=[0,L], where positive fractional α-powers of Laplace operator are allowed, perturbed by additive space–time random noise W0 with fairly general covariance operator Q with finite trace(Q)<+∞ (i.e. Q-regularity). The Q-regular space–time noise W0, which is white in time and generally spatially correlated, is supposed to have a Fourier expansion along the eigenfunctions of the Laplace operator under nonrandom, Dirichlet- and Neumann-type homogeneous boundary conditions. We focus on studying the generalized energy functional V incorporating the fractional diffusive energy part and the energy part which is due to the viscous damping force both in continuous and discrete time. In continuous time, the technique of Fourier expansions and appropriate truncation by finite-dimensional systems leads to the control on the generalized energy functional, and hence we may verify existence, uniqueness and boundedness of moments of Fourier series solutions u. The total mean energy E[E(t)] cannot grow more than linearly in time t (with or without damping). Moreover, under the absence of damping (i.e. κ=0), E[E(t)] is governed by a kind of trace formula in case of additive (state-independent), Q-regular space–time noise W0. For numerical computations and more adequate discretization, we suggest to take nonstandard, partial-implicit midpoint-type methods for the Fourier coefficients. These semi-analytical numerical methods (approximate Fourier series) possess the property of conserving the expected, total energy with random initial data under the absence of nonlinearities. Eventually, we estimate probabilities of large fluctuations of some interesting functionals.

A case study on the failure analysis of 1 hp house hold electrical submersible pump in Prayagraj India

This paper deals with the failure analysis of a 1 HP household electrical submersible pump in Prayagraj city. The city is surrounded by two rivers i.e. the Ganga and the Yamuna. Therefore, domestic submersible pumps are widely used in the region. Hard water and sand particles cause various problems with the pump. The submersible pump consists of a pump section and a motor section. The failure analysis of the motor section consists of failure of the rotor, stator, cable and other parts. Similarly, the pump section consists of failure of the impeller, diffuser and other parts. Prevention methods for all failed components have also been discussed in this paper. The failure of a submersible pump can be summarized into three major categories i.e. mechanical failure (breakage, corrosion, dislocation and leakage), electrical failure (cable failure, motor failure, and connection severances) and operational failure (high temperature, high pressure and multiphase flow).

A positivity-preserving implicit-explicit scheme with high order polynomial basis for compressible Navier–Stokes equations

In this paper, we are interested in constructing a scheme solving compressible Navier–Stokes equations, with desired properties including high order spatial accuracy, conservation, and positivity-preserving of density and internal energy under a standard hyperbolic type CFL constraint on the time step size, e.g., Δt=O(Δx). Strang splitting is used to approximate convection and diffusion operators separately. For the convection part, i.e., the compressible Euler equation, the high order accurate postivity-preserving Runge–Kutta discontinuous Galerkin method can be used. For the diffusion part, the equation of internal energy instead of the total energy is considered, and a first order semi-implicit time discretization is used for the ease of achieving positivity. A suitable interior penalty discontinuous Galerkin method for the stress tensor can ensure the conservation of momentum and total energy for any high order polynomial basis. In particular, positivity can be proven with Δt=O(Δx) if the Laplacian operator of internal energy is approximated by the Qk spectral element method with k=1,2,3. So the full scheme with Qk (k=1,2,3) basis is conservative and positivity-preserving with Δt=O(Δx), which is robust for demanding problems such as solutions with low density and low pressure induced by high-speed shock diffraction. Even though the full scheme is only first order accurate in time, numerical tests indicate that higher order polynomial basis produces much better numerical solutions, e.g., better resolution for capturing the roll-ups during shock reflection.

Symmetric Fuzzy Stochastic Differential Equations Driven by Fractional Brownian Motion

We consider symmetric fuzzy stochastic differential equations where diffusion and drift terms arise in a symmetric way at both sides of the equations and diffusion parts are driven by fractional Brownian motions. Such equations can be used in real-life hybrid systems, which include properties of being both random and fuzzy and reflecting long-range dependence. By imposing on the mappings occurring in the equation the conditions of Lipschitzian continuity and additional constraints by an integrable stochastic process, we construct an approximation sequence of fuzzy stochastic processes and apply this to prove the existence of a unique solution to the studied equation. Finally, a model from population dynamics is considered to illustrate the potential application of our equations.

Learning black- and gray-box chemotactic PDEs/closures from agent based Monte Carlo simulation data.

We propose a machine learning framework for the data-driven discovery of macroscopic chemotactic Partial Differential Equations (PDEs)-and the closures that lead to them- from high-fidelity, individual-based stochastic simulations of Escherichia coli bacterial motility. The fine scale, chemomechanical, hybrid (continuum-Monte Carlo) simulation model embodies the underlying biophysics, and its parameters are informed from experimental observations of individual cells. Using a parsimonious set of collective observables, we learn effective, coarse-grained "Keller-Segel class" chemotactic PDEs using machine learning regressors: (a) (shallow) feedforward neural networks and (b) Gaussian Processes. The learned laws can be black-box (when no prior knowledge about the PDE law structure is assumed) or gray-box when parts of the equation (e.g. the pure diffusion part) is known and "hardwired" in the regression process. More importantly, we discuss data-driven corrections (both additive and functional), to analytically known, approximate closures.

Numerical studies for effect of geometrical parameters on water jet pump performance via entropy generation analysis

This paper presented an implementation of entropy generation analysis in the main flow field of a water jet pump via the CFD method. This study aimed to identify the inefficient location of energy conversion and to analyse entropy generation sources in each region of the water jet pump. The 2D-axisymmetric model and realisable k-ε (RKE) turbulence model at steady-state conditions were performed to validate jet pump performance and to assess the entropy generation. Likewise, the effects of the projection ratio and throat-aspect ratio as independent parameters were investigated. As a result, the throat is the most inefficient part due to the high total entropy generation rate, following by diffuser part. Also, the entropy generation rate was assessed dominant than viscous dissipation due to the turbulent dissipation, which was caused by a turbulent shear stress layer of mixing the streams. In conclusion, the projection ratio influenced the growth of the shear stress layer as well as the entropy generation. Further, the throat-aspect ratio affected the distribution of entropy generation in the throat section. An appropriate combination of both parameters has an impact on the jet pump performance improvements reducing the entropy generation rate in the future.

Facile Solvothermal Synthesis of NiO/g-C3N4 Nanocomposite for Enhanced Supercapacitor Application

There is a desperate demand for efficient energy storage systems to fulfill future energy demands. Herein, we exemplify a facile solvothermal approach followed by heat treatment to synthesize NiO/g-C3N4 nanocomposites for enhanced supercapacitor applications. The molar ratio of g-C3N4 is varied to achieve numerous nanostructures like nanoparticles and nanorods with optimum specific capacitance. Further, all as-prepared electrode materials are examined for supercapacitor application. The electrochemical behavior of prepared NiO/g-C3N4 nanocomposites is carried out under cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in a three-electrode cell under different electrolytes such as aqueous sodium sulphate electrolyte (1.0 M Na2SO4) and potassium hydroxide electrolyte (3.0 M KOH). Among all the electrode materials, NO-4 (1 : 2) shows the highest specific capacitance of 338.68 F/g at a scan rate of 2 mV/s and 161.3 F/g at a current density of 1 A/g in 1.0 M Na2SO4 electrolyte. Also, this electrode material shows 95.22 F/g at a scan rate of 2 mV/s in 3.0 M KOH electrolyte. The excessive specific capacitance of this electrode material is due to retarded charge transfer resistance in the interface at the electrode and electrolyte and a increased number of active sites. The investigation of the electrokinetics of all the prepared electrodes was also carried out, and it revealed the charge storage contribution of capacitive and diffusive parts which levitates the higher specific capacitance. The two-electrode study for evaluating supercapacitor performance is studied. The NO-4//NO-4 SSD in 1.0 M Na2SO4 electrolyte shows 18.23 F/g at a specific capacitance of 1 A/g with a corresponding energy density of 10.13 Wh/kg and a power density of 1.01 kW/kg, respectively.

Computational Modeling of Diffusion-Based Delamination for Active Implantable Medical Devices.

Delamination at heterogeneous material interfaces is one of the most prominent failure modes in active implantable medical devices (AIMDs). A well-known example of an AIMD is the cochlear implant (CI). In mechanical engineering, a multitude of testing procedures are known whose data can be used for detailed modeling with respect to digital twins. Detailed, complex models for digital twins are still lacking in bioengineering since body fluid infiltration occurs both into the polymer substrate and along the metal-polymer interfaces. For a newly developed test for an AIMD or CI composed of silicone rubber and metal wiring or electrodes, a mathematical model of these mechanisms is presented. It provides a better understanding of the failure mechanisms in such devices and their validation against real-life data. The implementation utilizes COMSOL Multiphysics®, consisting of a volume diffusion part and models for interface diffusion (and delamination). For a set of experimental data, the necessary diffusion coefficient could be derived. A subsequent comparison of experimental and modeling results showed a good qualitative and functional match. The delamination model follows a mechanical approach. The results of the interface diffusion model, which follows a substance transport-based approach, show a very good approximation to the results of previous experiments.

A Hypothesis on the Progression of Insulin-Induced Lipohypertrophy: An Integrated Result of High-Frequency Ultrasound Imaging and Blood Glucose Control of Patients.

To put forward a scientific hypothesis about the progression of insulin-injection-induced lipohypertrophy (LH) according to the high-frequency ultrasonic imaging of insulin injection sites and the blood glucose control of patients. A total of 344 patients were screened for LH by means of high-frequency ultrasound scanning. The results of their ultrasound examination were described in detail and categorized into several subtypes. Seventeen patients with different subtypes of LH were followed up to predict the progression of LH. To further verify our hypothesis, the effects of different types of LH on glycemic control of patients were observed by comparing glycated hemoglobin A1c (HbA1C) and other glycemic-related indicators. LH was found in 255 (74.1%) patients. According to the high-frequency ultrasonic imaging characteristics, LH can be categorized into three subtypes in general. Among all the LHs, the most common type observed was nodular hyperechoic LH (n = 167, 65.5%), followed by diffuse hyperechoic LH (n = 70, 27.5%), then hypoechoic LH (n = 18, 7.0%). At the follow-up after six months, all 10 patients with nodular hyperechoic LH had LH faded away. Of the five patients with diffuse hyperechoic LH, two had inapparent LH, and three had diffuse hyperechoic parts which had shrunk under ultrasound. No obvious changes were observed in the two cases of hypoechoic LH. Compared with the LH-free group, the mean HbA1C of the nodular hyperechoic LH group increased by 0.8% (9 mmol/mol) (95% CI:-1.394~-0.168, p = 0.005), that of the diffuse hyperechoic LH group increased by 2.0% (21 mmol/mol) (95% CI: -2.696~-1.20, p < 0.001), and that of the hypoechoic LH group increased by 1.5% (16 mmol/mol) (95% CI: -2.689~-0.275, p = 0.007). It was hypothesized that the earlier stage of LH is nodular hyperechoic LH. If nodular LH is not found in time and the patient continues to inject insulin at the LH site and/or reuse needles, LH will develop into a diffuse type or, even worse, a hypoechoic one. Different subtypes of LH may represent differences in severity when blood glucose control is considered as an important resolution indicator. Further studies are needed to confirm our hypothesis on the progression and reversion of insulin-induced lipohypertrophy.