Dispersion Phenomena Research Articles

DIELECTRIC PROPERTIES OF CONTAMINATED SOIL BY SALT CRYSTALS

Dielectric permittivity is a physical property that reflects the electric polarizability of a medium. This property is highly sensitive to the components of the studied material. It can be affected by varying the water content and the salinity of the sample. In this work, an impedance analyzer and a capacitive cell have been used to measure the complex permittivity of different samples composed of a mixture of salt crystals and soil for a frequency range between 100-10<sup>7</sup> Hz and for various proportions of salt crystals in each sample. Experimental results for permittivity spectra exhibit frequency dispersion and dielectric relaxation phenomena for all samples. The relaxation occurs in the range of frequency from 1 kHz to 100 kHz. The real and imaginary parts of the permittivity are strongly correlated with the salt crystal volume fraction at 1 kHz. However, the sensitivity at 100 kHz decreases, especially for the imaginary part. Three composite dielectric mixing models (alpha models) fitting the relationship between the permittivity and the salt crystal content are evaluated with the experimental dataset. The results indicate a good estimation of the real and imaginary parts of the complex permittivity using the complex refractive index model (CRIM). However, the experimental results are misestimated by the "parallel" and "series" models. Experimental results are better fitted at 1 kHz.

Stress and stretching regulate dispersion in viscoelastic porous media flows.

In this work, we study the role of viscoelastic instability in the mechanical dispersion of fluid flow through porous media at high Péclet numbers. Using microfluidic experiments and numerical simulations, we show that viscoelastic instability in flow through a hexagonally ordered (staggered) medium strongly enhances dispersion transverse to the mean flow direction with increasing Weissenberg number (Wi). In contrast, preferential flow paths can quench the elastic instability in disordered media, which has two important consequences for transport: first, the lack of chaotic velocity fluctuations reduces transverse dispersion relative to unstable flows. Second, the amplification of flow along preferential paths with increasing Wi causes strongly-correlated stream-wise flow that enhances longitudinal dispersion. Finally, we illustrate how the observed dispersion phenomena can be understood through the lens of Lagrangian stretching manifolds, which act as advective transport barriers and coincide with high stress regions in these viscoelastic porous media flows.

A study of radar reflection signal characteristics in multi-domain using a closed plasma generator

This paper theoretically and experimentally studies the radar reflection signal characteristics in a multi-domain using a closed plasma generator, especially for a correlation domain. A multi-domain computation method is proposed for a radar signal reflected by a metal covered with plasma. The reflected signal characteristics are studied in the time, frequency, and correlation domain. A closed plasma generator device is designed to verify the computation method for the radar signal reflected from metal plate covered with plasma experimentally. The plasma in the device is terminated by a transmission window at one end and a metal plate at another end, which is able to provide the environment for a radar signal reflection experiment. Based on the theoretical and the experimental results, the time and frequency domain of radar reflection signal not only show the amplitude attenuation characteristics but also frequency dispersion phenomenon. For the correlation domain characteristics of the radar reflection signal, the peak value in correlation domain significantly decreases, which demonstrates the stealth effect of the plasma. The effect of plasma and radar parameters on the peak value decrease phenomenon, as well as the stealth effect in the correlation domain, is further analyzed.

Method of Line Solution of Optical Soliton in Optical Communication System

The performance of fiber-optic communication is constrained by the dispersive phenomenon of group velocity dispersion (GVD) and fiber non-linearity of self-phase modulation, but when these effects are balanced, a single wave or soliton is produced. A soliton can travel a great distance with constant speed. It is suitable for use in ultra-long-distance communication because of these unique features. The non-linear Schrodinger (NLS) equation describes the optical soliton propagation in optical fibers. By using the method of line (MOL) to solve the NLS equation, this study mimics the optical soliton propagation. It demonstrates that during simulations at 400 km, the optical soliton maintains its shape and amplitude.

STUDY ON THE DISPERSION CHARACTERISTICS OF WOOD ACOUSTIC EMISSION SIGNAL BASED ON WAVELET DECOMPOSITION

Artificial AE sources were generated on the surfaces of Ulmus pumila, Zelkova schneideriana, Cunninghamia lanceolata, and Pinus sylvestris var.mongolicaLitv. specimens. The AE transverse wave signal was decomposed into 3-layers detail signalsby wavelet decomposition and reconstructed, and it was calculated based on correlation analysis. Then thelongitudinal wave speed was calculated according to the time-difference-of-arrival (TDOA) method, and the wood dispersion phenomenon was studied. The results showed that thedispersion phenomenon of Ulmus pumilawas obvious. The propagation speed of high-frequency signal was 2.38 times that of low-frequency signal. The ratio of high and low frequency propagation speed of soft wood was 1.72 and 1.73. The dispersion degree of Zelkova schneideriana was the weakest, and the propagation speed of the high frequency was 1.25 times of the low one. The ratios of longitudinal and transverse wave speedsof the four specimens were 4.59, 4.07, 4.24 and 4.2, respectively.

Interactions of fractional [formula omitted]-solitons with anomalous dispersions for the integrable combined fractional higher-order mKdV hierarchy

In this paper, we investigate the anomalous dispersive relations, inverse scattering transform with a Riemann–Hilbert (RH) problem, and fractional multi-solitons of the integrable combined fractional higher-order mKdV (fhmKdV) hierarchy, including the fractional mKdV (fmKdV), fractional fifth-order mKdV (f5mKdV), fractional combined third–fifth-order mKdV (f35mKdV) equations, etc., which can be featured via completeness of squared scalar eigenfunctions of the ZS spectral problem. We construct a matrix RH problem to present three types of fractional N-solitons illustrating anomalous dispersions of the combined fhmKdV hierarchy for the reflectionless case. As some examples, we analyse the wave velocity of the fractional one-soliton such that we find that the fhmKdV equation predicts a power law relationship between the wave velocity and amplitude, and demonstrates the anomalous dispersion. Furthermore, we illustrate other interesting anomalous dispersive wave phenomena containing the elastic interactions of fractional bright and dark solitons, W-shaped soliton and dark soliton, as well as breather and dark soliton. These obtained fractional multi-solitons will be useful to understand the related nonlinear super-dispersive wave propagations in fractional nonlinear media.

The study of twin phase solitons interaction and switching

Cavity solitons as part of dissipative localized structures have been of great interest. In cavity, there must be the double balance between dispersion phenomenon and nonlinear phenomena and at the same time the cavity losses are made up for by pumping continuous-wave coherent driving which leads to the formation of Spatio-temporal soliton. In previous studies z direction has neglected in the cavity. By taking into account of this direction the new type of solitons named “phase soliton” is introduced. In this paper, we studied the ring cavity in more detail and the intraction of duble phase soliton. We find out, switching ON and OFF process of phase soliton. Also the optimal conditions for switching ON/OFF was determined.

Temperature- and Degradation-Dependent Maximum Electric Field Stress in Wire-Bonding Power Modules Under PWM Waves

Electric field stress concentration is one of the causes of partial discharge (PD) in power modules, which threatens the power modules’ safe operation. Herein, this article investigates the influences of temperature (from 150 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$250~^{\circ }\text{C}$ </tex-math></inline-formula> ) and operation duration on the maximum electric field stress at the triple point (silicone elastomers, ceramic, and copper). It reveals that the maximum electric field stress rises with the increase in temperature, while the maximum electric field first increases but then decreases along the operation duration, especially under low temperature. Both the influences of temperature and the operation duration are related to the permittivity (dominated by the relaxation of Si–O bonds), low-frequency dispersion (LFD) phenomenon, and dc conductivities of silicone elastomers, which can be manipulated to suppress electric field stress concentration. This article provides a method to accurately calculate the electric field. The results are also critical to evaluation and improvement of power modules’ insulation.

Growth of Sobolev norms in linear Schrödinger equations as a dispersive phenomenon

In this paper we consider linear, time dependent Schrödinger equations of the form i∂tψ=K0ψ+V(t)ψ, where K0 is a strictly positive selfadjoint operator with discrete spectrum and constant spectral gaps, and V(t) a smooth in time periodic potential. We give sufficient conditions on V(t) ensuring that K0+V(t) generates unbounded orbits. The main condition is that the resonant average of V(t), namely the average with respect to the flow of K0, has a nonempty absolutely continuous spectrum and fulfills a Mourre estimate. These conditions are stable under perturbations. The proof combines pseudodifferential normal form with dispersive estimates in the form of local energy decay.We apply our abstract construction to the Harmonic oscillator on R and to the half-wave equation on T; in each case, we provide large classes of potentials which are transporters.

Perfectly matched layer and infinite element coupled with finite elements for SH waves in an imperfect piezoelectric viscoelastic structure

Discontinuities of dielectric/mechanical properties at the interfaces in piezoelectric actuators or sensors reduce the efficiency of the system. This may arise due to the uneven transfer of stress or potential across the surface. The present study encapsulates the dispersion phenomenon of SH waves in an imperfectly bonded piezoelectric viscoelastic layered structure. Besides the basic analytical study, two different numerical methodologies have been adopted to obtain the frequency curves; first, semi-analytical finite element and perfectly matched layer and second, semi analytical infinite element with reciprocal of distance decay. The solution treatment utilizes the electro-visco-mechanical field equations and the Rayleigh–Ritz method to derive the mass and stiffness matrices of the perfectly matched layer or infinite element. The assembly process of discretized elements at the mechanical/dielectric imperfect interface is a major theme of this study. Frequency curves obtained by all three aforementioned methodologies have been portrayed graphically with special emphasis on interface imperfection on them. Comparing with the analytical results, it is reported that the method of perfectly matched layer or infinite element coupled with finite element fairly emulates SH wave propagation in piezoelectric viscoelastic (layer and half-space) structure.

The way from stakeholders’ needs research to the public health policy and practice

Abstract The implementation of the project “ProfiBaza” was the unique opportunity to effectuate a data set with the possibility to showcase for the first time in Poland which public health (PH) interventions are taken and whether they cover population health needs. In order to be forethoughtful to this challenge, the needs of stakeholders within the health system were investigated. Particularly, considering the widely recognised knowledge-practice gap in the PH field. We would like to demonstrate the results of a needs analysis related to: the accessibility assessment of the information about PH interventions; the need of establishing a good practices database regarding health promotion and disease prevention; the possibility to use research findings in PH practice. All those would be presented from the perspective of researchers, politicians, decision makers and PH institutions. This research was conducted as a questionnaire-based survey and focus group interviews. Researchers were asked to assess the compatibility between the PH research and the population health needs. The group of health sector decision makers were questioned about the usage of the information available in the ProfiBaza for the process of evidence-based decision making; local government politicians - to assess their readiness to implement health programmes, use the good practices database and build partnerships for health while representatives of various sectors - to assess the need of initiating a knowledge translation platform via the launched ProfiBaza system. The results of the research demonstrate that there is a need for: solidified collaboration between different types of PH stakeholders, mobilization, coordination, sharing experiences, creating networks of cooperating institutions, which will enable the effective response to emerging challenges and opportunities and to counteract the phenomenon of dispersion of efforts in improving health and reducing social inequalities in health.

Study on the mass transfer characteristics of gas and liquid phases in a three-layer combined paddle fermenter

A three-layer combination paddle fermenter was proposed for improving the phenomenon of uneven gas dispersion and dead zones at the bottom of small and medium-sized gas-liquid fermenters. The population balance model (PBM) was used to numerically calculate the internal flow field of the fermenter, and the effects of the baffle and rotational speed on the turbulence intensity and mass transfer characteristics were systematically investigated. The results show that the addition of baffles in the three-layer combined paddle fermenter can increase the turbulence intensity and effectively improve the uneven gas dispersion. Increasing the rotational speed provides a better shear environment for bubble crushing and is conducive to enhancing the gas-liquid mass transfer capacity. The local KLa distribution in the fermenter with baffle is more uniform.

Cnoidal waves and dark solitons with linear third-order dispersion and self-steepening effect

The present paper investigates the conditions needed for the generation and propagation of cnoidal waves in the form of dark solitons under the influence of self-steepening effect and linear third-order dispersion. This kind of optical pulses could be obtained in single-mode waveguides due to the precise balance between higher orders of nonlinear and dispersive phenomena. As a basic equation, it is used the nonlinear amplitude equation (NAE). It is found a new analytical solution of this equation in the form of a cnoidal wave (Jacobi elliptic sine function). In the article it is presented that the solution can be reduced to dark soliton at specific values of the modulus of ellipticity κ.

Assessment of vehicle emissions at roundabouts: a comparative study of PEMS data and microscale emission model

Energy efficiency has a central role to play in achieving decarbonisation targets in the transport system by changing the demand for mobility (eg. by influencing on peoples behaviors) and improving the performance of the fleet. In recent years there has been an increase of use of private transport, partly due to the recent pandemic and the reduced choice of public transport. People's travel habits have changed in frequency and motivation due to the reduced number of seats on public transport, due to social distancing but also due to online education and teleworking. This increase of use private cars has led to an increase in environmental emissions as a result of the high proportion of vehicles with combustion engines in urban areas. The highest concentrations have been recorded at road intersections and in par-ticular at roundabout configurations where there is a higher number of stop-and-go's overall. The increasing im-portance of air pollution from vehicle traffic has suggested that environmental considerations should be added to these aspects as a criterion for intersection design. Several studies in the literature analyze the environmental emissions generated by vehicle traffic using different methods such as on-site recording, mathematical modeling of dispersion phenomena, micro-simulation of vehicle traffic, use of appropriately equipped vehicles with sensors. This paper pre-sents a comparison between the results obtained from the Portable Emission Measurement System (PEMS) and the results obtained from the VERSIT+ emission model. Specifically, using a Portable Emission Measurement Systems (PEMS) installed on a series of test cars, instantaneous CO2 and NOX emissions were measured on repeated trips along two-lane roundabout intersections. The study was carried out by examining a selected two-lane roundabout in the city of Rzeszow (Poland) using 9 different vehicles fueled by petrol, diesel, and LPG. The results show that the investigated VERSIT+ emission model used led to an inaccuracies in the calculation of CO2 and NOx emissions. Furthermore, cur-rent micro-scale emission models may not estimate emissions of harmful exhaust components with sufficient accuracy due to the specificities of roundabout driving. Therefore, there is a strong demand for the development of new emission models, adapted to the driving behavior of drivers appropriate for different infrastructure objects such as roundabouts.

Climate change and dispersion dynamics of the invasive plant species Chromolaena odorata and Lantana camara in parts of the central and eastern India

Lantana camara and Chromolaena odorata are categorized as the most obnoxious invasive flora globally. Their ability to combat the regeneration and proliferation of neighbouring flora, expansive nature, and robust adaptability to diverse habitats, drew global attention. Investigating the potential mutual dispersion phenomenon of these two invasive species under the climate change scenario was the primary objective of this study. The present and future (2050) prospective distribution scenarios for these two species were determined using MaxEnt in the eastern and central Indian regions encompassing the states of Jharkhand, Chhattisgarh, and West Bengal. Future projections for 2050 were derived using IPSL-CM5A-LR & MIROC5 and IPSL-CM6A-LR & MIROC6 models for different representative concentration pathways (RCPs 2.6, 4.5, 6.0, and 8.5), and Shared Socioeconomic Pathways (SSPs 126, 245, 370 and 585), respectively. The investigation revealed that currently ∼31% and ∼ 24% of the study area are susceptible to infestation of L. camara and C. odorata, respectively. Compared to the current scenario, the results showed a probable future increase of ∼1.53% in C. odorata infestation and a decrease of ∼4.95% for L. camara. The True Skill Statistics (TSS) and Kappa coefficient (in %) values of 0.71 & 76.50 for L. camara and 0.52 & 63.38 for C. odorata indicated a good model fit. Collectively, both the species exhibited robust resilience to climate change, with C. odorata outcompeting L. camara. Using both RCP and SSP pathways under the multiple climate scenarios offered a comprehensive and novel approach to acquiring greater insights into likely interactions, dominance, and distribution scenarios of these species. The results provide prior information on sensitive sites prone to future invasion, allowing management to formulate preventative measures to control infestation.

Acoustoelastic equations and Lamb waves dispersion characteristics of finitely deformed biological soft tissues with the growth-mechanical coupling

Acoustoelastic equations, especially the incremental constitutive law and the constitutive parameters associated with the growth increment, were presented for biological soft tissues coupling the growth and the mechanical effects. Both the initial growth deformation and the growth increment make biological tissues different from the general soft materials in acoustoelastic equations. Lamb waves dispersion in two finitely deformed biological soft layers was then investigated to explore the wave dispersion in biological tissues. The frequency dispersion equations were derived from which characteristics of wave dispersion of the first two modes were discussed. The influence of the predeformation and the external load on Lamb waves dispersion was quantitatively examined. It is found that some special dispersion phenomena such as the mode vanishment, frequency cut-off, frequency block, frequency pass and frequency gap may come up in Lamb waves dispersion. These dispersion features are dependent on the existence of phase velocity limits, the two-layer structure and the type of predeformation. Moreover, phase velocity limits were analytically deduced from the dispersion equations for the pre-stretched biological soft tissues. The elastic predeformation and the mechanical properties of biological tissues can then be determined from phase velocity limits, which provides a potential method to distinguish the growth deformation.

On solute dispersion in an oscillatory magneto-hydrodynamics porous medium flow under the effect of heterogeneous and bulk chemical reaction

It is well known to all of us that there is a shortage of pure drinking water across the globe. Different types of pollutants (metallic and nonmetallic) mix with the water, and they cause several diseases such as cholera, typhoid, and various kinds of skin diseases, and even it is found that these kinds of particles may cause skin cancer. In the current study, an analytical solution of a two-dimensional convection–diffusion equation is obtained using Mei's multi-scale homogenization technique to investigate the influences of homogeneous and heterogeneous reactions on dispersion phenomena of the solute in an oscillatory magneto-hydrodynamics porous medium flow. In the appearance of the applied transverse magnetic field and oscillatory pressure gradient, a mathematical model of magneto-hydrodynamics dispersion between two parallel plates is presented. The analytical expressions of Taylor dispersivity, longitudinal mean and real concentration distributions, transverse concentration distribution, and transverse uniformity rate of the concentration are obtained. Also, the effect of various flow parameters such as Péclet number, Hartmann number, Schmidt number, Darcy number, oscillatory Reynolds number, porous parameter, dispersion time, downstream and upstream locations, chemical heterogeneous boundary reaction, and bulk reaction is discussed. How the transport phenomena of the solute display different natures with the various ranges of Darcy and Hartmann numbers with the aid of homogeneous and heterogeneous boundary reactions are highlighted. To show the effect of the absorption parameters on the transport coefficient, the third-order approximation of concentration is performed. It is seen that the dispersion coefficient (DT1) corresponding to the purely time-dependent flow increases with the enhancement of the Darcy number (Da). Moreover, it is found that as the Hartmann number (M) enhances, the total dispersivity (DT) decreases. Also, the transverse concentration distribution becomes flat for larger values of the Hartmann number. It is noticed that when Da≥1, the transverse variation curve turns into a trimodal distribution from a bimodal. This model may be helpful for separating various metallic and nonmetallic particles from the water to reduce the water pollution.

Primary cementing of vertical wells: displacement and dispersion effects in narrow eccentric annuli

Laminar miscible displacement flows in narrow, vertical, eccentric annuli show a wide range of interesting physical phenomena, e.g. static layers and channels, dispersive spikes/fronts and various instabilities. These are of relevance to the primary cementing of wells, where gas leakage and greenhouse gas emissions can result from ineffective cementing. The current popular way to model this process is via a Hele-Shaw approach, reducing the Navier–Stokes equations via scaling arguments and then averaging across the annular gap: the two-dimensional (2-D) gap averaged (2DGA) model. This leads to a reduced model that is computationally efficient and represents some important features of cementing flows, but is also deficient in capturing the effects of dispersion. While three-dimensional (3-D) simulations are able to capture dispersion and most other physical phenomena, they suffer from excessive computational times due to the extreme aspect ratios of cementing geometries and non-Newtonian properties of the fluids. Here we extend the 2DGA approach by modelling the high Péclet number limit of miscible duct displacement flows, to take into account the leading-order effects of dispersion. Our modified dispersive 2DGA model is well able to approximate dispersive effects that are observed by gap-averaging the results of 3-D computations, including geometric effects of eccentricity and instabilities. This represents a marked improvement over the 2DGA approach, while keeping the computational advantages of a 2-D model.

Image Denoising Based on GAN with Optimization Algorithm

Image denoising has been a knotty issue in the computer vision field, although the developing deep learning technology has brought remarkable improvements in image denoising. Denoising networks based on deep learning technology still face some problems, such as in their accuracy and robustness. This paper constructs a robust denoising network based on a generative adversarial network (GAN). Since the neural network has the phenomena of gradient dispersion and feature disappearance, the global residual is added to the autoencoder in the generator network, to extract and learn the features of the input image, so as to ensure the stability of the network. On this basis, we proposed an optimization algorithm (OA), to train and optimize the mean and variance of noise on each node of the generator. Then the robustness of the denoising network was improved through back propagation. Experimental results showed that the model’s denoising effect is remarkable. The accuracy of the proposed model was over 99% in the MNIST data set and over 90% in the CIFAR10 data set. The peak signal to noise ratio (PSNR) and structural similarity (SSIM) values of the proposed model were better than the state-of-the-art models in the BDS500 data set. Moreover, an anti-interference test of the model showed that the defense capacities of both the fast gradient sign method (FGSM) and project gradient descent (PGD) attacks were significantly improved, with PSNR and SSIM values decreased by less than 2%.

High‐Resolution Time‐Correlated Single‐Photon Counting Using Electro‐Optic Sampling

AbstractA simple, practical method based on electro‐optic gating is experimentally shown to improve the temporal resolution of single‐photon detection by more than 16 times. Delay times between ultrafast single photons and a reference clock are stretched by a desired programmable sampling gate factor, allowing reconstruction of delay histograms with ≈0.001 photons per pulse to within 60 ps. By transferring the bandwidth of RF electronics to single‐photon counting, complex single‐photon signals with large time‐bandwidth products &gt; 2000 are temporally stretched up so that they can be resolved by slow detectors, irrespective of the quality of the detector instrument response function. This method is also applied to biphotons, in order to reconstruct the 2D histogram of joint detection delays with 15 times better resolution. The phenomenon of nonlocal dispersion, which is not resolvable directly with the slow detectors, is then observable to within the 98 ps level. The proof‐of‐concept demonstration uses off‐the‐shelf commercial fiber‐integrated LiNbO3 modulators and RF electronics, and the method is readily integrable on‐chip and to speeds &gt;100 GHz, offering a practical solution to ultrafast time‐correlated single‐photon counting beyond the research laboratory.