Different Types Of Dispersion Research Articles

Influencing effects of different types of dispersants on the permeability levels of Coal-Bearing propped fractures in coalbed methane reservoirs

This study investigated how to effectively discharge deposited pulverized coal particles in coal-bearing propped fractures and improve the permeability levels of the propped fractures in order to enhance coalbed methane production. Four types of dispersants were selected to carry out wettability and permeability tests, including sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), dodecyl dimethyl betaine (BS-12), and alkyl poly glycoside dodecyl glucoside (APG). The results showed reductions in surface tension of 63.71 to 69.75 %, and reductions in contact angles of 40.08 to 60.46 %, when compared with water injections alone. In addition, under the same closure pressure conditions, the dispersant solutions had increased the permeability of the propped fractures by 76.67 to 123.34 % when compared with that of the water injections, and the pulverized coal discharge rates were increased by 1.44 to 2.41 times. The decreases in closure stress also contributed to the enhancement of the permeability of the propped fractures, with increases of between 11.24 and 29.18 % observed. This study found that for the four tested dispersants, the order of the effective wetting of the pulverized coal particles and enhancement of the permeability of the propped fractures were (from strong to weak) as follows: SDS > BS-12 > APG > SDBS. Among the tested dispersants, the 6 mmol/L SDS dispersant solution was found to be the most effective for improving the wettability of the pulverized coal particle surfaces and achieved the highest permeability improvement of the propped fractures.

Multiple‐Group Joint Modeling of Item Responses, Response Times, and Action Counts with the Conway‐Maxwell‐Poisson Distribution

AbstractMultiple group modeling is one of the methods to address the measurement noninvariance issue. Traditional studies on multiple group modeling have mainly focused on item responses. In computer‐based assessments, joint modeling of response times and action counts with item responses helps estimate the latent speed and action levels in addition to latent ability. These two new data sources can also be used to further address the measurement noninvariance issue. One challenge, however, is to correctly model action counts which can be underdispersed, overdispersed, or equidispersed in real data sets. To address this, we adopted the Conway‐Maxwell‐Poisson distribution that accounts for different types of dispersion in action counts and incorporated it in the multiple group joint modeling of item responses, response times, and action counts. Bayesian Markov Chain Monte Carlo method was used for model parameter estimation. To illustrate an application of the proposed model, an empirical data analysis was conducted using the Programme for International Student Assessment (PISA) 2015 collaborative problem‐solving items where potential measurement noninvariance issue existed between gender groups. Results indicated that Conway‐Maxwell‐Poisson model yielded better model fit than alternative count data models such as negative binomial and Poisson models. In addition, response times and action counts provided further information on performance differences between groups.

Topological nodal line phonons: Recent advances in materials realization

The topological phenomenon has been extensively studied in condensed matter physics and has attracted much attention in many different fields. Like electrons, phonons can also be studied using critical theorems and topology concepts, giving impetus to the birth of topological phonons. Among the topological phonons, the topological nodal line phonons in crystalline materials have emerged as a new area of rapid development in both experiment and theory. Researchers have been hunting for realistic materials with nodal line phonons for the last four years. To date, however, a timely review of recent advances in topological nodal line phonons, and especially their material realization, is still lacking. Considering the classification of the nodal line states, in this review, we will first review the identification of the materials hosting the nodal line phonons with different degeneracies, different types of dispersion, and different geometric shapes in theory. Moreover, we will review and discuss the reasons for the appearance of the nodal line phonons from the viewpoint of symmetry. Second, we will review the case where the nodal line appears in the projected surface phonon states instead of the bulk phonon states. Third, we will review the experimental material realization of nodal line phonons. Finally, we will present a summary, outlook, and additional notes. We believe that this review will contribute to a more advanced understanding of topological nodal line phonons in solid materials and will offer new perspectives on this rapidly expanding field.

On periodic integer-valued moving average (INMA (q)) models

This paper deals with the study of some probabilistic and statistical properties of a Periodic Integer-Valued Moving Average Model () with Generalized Poisson and Negative Binomial innovation process, for modelling different types of dispersion in count time series. Some probabilistic properties of the process are obtained. Furthermore, the time reversibility of the model is discussed in detail. The estimation of the underlying parameters is obtained by the Conditional Least Squares method (CLS). A simulation study is carried out to evaluate the performance of the estimation method. Finally, an application on real data set is provided to show the ability of the model for fitting data.

Classification and characterization of multimodal nanoparticle size distributions by size-exclusion chromatography.

Size-exclusion chromatography (SEC) is a well-known, versatile and scalable technique for the separation of molecules according to their hydrodynamic size in solution as well as for the determination of molecular weight distributions of polymers. In this paper we demonstrate and generalize the applicability of SEC to the classification and characterization of multimodal distributions of nanoparticles over a broad size range. After calibration with gold standards from 5 nm to 80 nm, the calibration curve is used to determine the particle size distributions (PSDs) of the standards which are in agreement with comprehensive nanoparticle size analysis by analytical ultracentrifugation. Universal calibration curves independent of the core material and surface functionality can be constructed if the pore diameter of the stationary phase exceeds the particle diameter by a factor of 2-3. Mixtures of gold standards are separated by SEC and evaluated in terms of peak resolution and size-dependent separation curves depending on how well the individual peaks are resolved. Baseline separation of a multimodal mixture is observed and its PSD is determined. Mixtures can be fractionated into coarse and fine fractions with nm precision at different switching times of the fraction collector. Our study demonstrates the strength of SEC to classify multimodal PSDs as well as to accurately determine size distributions of complex nanoparticle dispersions over a broad size range.

Biocompatible Dispersants for Carbon Nanomaterials

Carbon nanomaterials (CNMs) are a fascinating class of materials that have gained considerable interest in recent years. Their favourable biocompatibility, combined with unique chemical and mechanical properties, has attracted scientists from various disciplines. A significant hurdle in their deployment in biomedical applications is their hydrophobicity in their pristine form. This review surveys and discusses existing non-covalent methods of functionalising CNMs with biocompatible dispersants to facilitate their incorporation into aqueous solutions. Different types of dispersants will be examined and compared as well as the factors affecting their efficiency. This work seeks to provide a compilation of the various methods employed in producing biocompatible CNM dispersions.

Distributed Feedback Laser Based on Tunable Photonic Hypercrystal.

In this work, we investigate the generation of light in a distributed feedback (DFB) laser composed of periodically arranged layers of hyperbolic medium and active material forming a 1D photonic hypercrystal (PHC). The scope of our study covers the analysis of laser action in the presence of different types of dispersion that are achievable in a hyperbolic medium. Using the example of a PHC structure consisting of graphene-based hyperbolic medium, we demonstrate the possibility of controlling laser action by tuning effective dispersion. Our analysis reveals the possibility of obtaining a single-frequency generation with high side-mode suppression and controllable wavelength of operation. Moreover, we present a new mechanism for the modulation of laser amplitude arising from voltage-controllable dispersion of hyperbolic medium.

Chemosensitive Thin Films Active to Ammonia Vapours.

The paper presents various dispersive systems developed for sensing toxic substance—ammonia. Polycarbonate dissolved in methylene chloride was used as a polymer matrix, which was enriched with: multi-walled carbon nanotubes (MWCNs), reduced graphene oxide (rGO) and conductive polymer (polyaniline—PANi). Dispersive systems were applied to the prefabricated substrates with comb electrodes by two methods: spraying and drop-casting, forming an active chemosensitive to ammonia vapours films. The spraying method involved applying the dispersion to the substrate by an aerograph for a specific time, whereas drop-casting involves depositing of the produced dispersive systems using a precision automatic pipette. The electrical responses of the obtained films were examined for nominal concentrations of ammonia vapours. Different types of dispersions with various composition were tested, the relationships between individual compounds and ammonia were analysed and the most promising dispersions were selected. Sensor containing rGO deposited by drop-casting revealed the highest change in the resistance (14.21%).

Interfacial phenomena of magnesium hydroxide micro phases

The magnesium hydroxide aqueous suspensions were prepared over a wide range of different types of dispersants with different dosages percentage. The effect of dispersant types and dispersant dosages on the rheological behavior and stability of magnesium hydroxide aqueous suspensions have been investigated by means of viscosity, sedimentation measurements, flowability, Total organic carbon (TOC) and zeta potential. The results showed that considering the four types of dispersants, Calcium lignosulfonate (Ca-lig) enhance the viscosity and flowability of the slurry the most. Also it decreases the pH of slurry. The study gives insights on important application process optimization.

XRAY MEDICAL IMAGE CHARACTERIZATION WITH SPARSE RADIATION BASED ON WAVELETS

In medical radiology there are large amounts of digital images in hospitals and health centers. Equipment that enables the acquisition of medical radiographs uses X-radiation sensor plates for image acquisition in medical diagnosis. Medical radiology equipment uses anti-scatter grids, which are physical devices, to avoid unwanted effects on imaging. In the present work, we analyse from a qualitative point of view the radiation scattering effect that is caused in images without the presence of the anti-scattering grid. In this research, the acquisition of radiological images was made by means of X-ray equipment with an anti-scattering grid, capturing images without scattering and others that only present radiation scattering as a point of comparison. The methodology uses the Wavelet transformation to image characterization in segment process that define the regions that affect the different types of dispersion presented in X radiation. The tool used for the analysis of the images is the multi-resolution Wavelet transform, specifically the Discrete Wavelet Transform (DWT). The methodology was applied to different 2D radiological images in shades of gray. In the images used, it showed a robustness in the differentiation of X radiation incidence zones. This work is the beginning of a distortion analysis for the reconstruction of this type of images.

Fabrication of SiCf/Ti3SiC2 by the electrophoresis of highly dispersed Ti3SiC2 powder

This paper reports the processing details and important phenomena occurred during the fabrication of a SiC fiber-reinforced Ti3SiC2 matrix composite (SiCf/Ti3SiC2). Because both SiC and Ti3SiC2 are microwave absorbing materials, the fabrication of SiCf/Ti3SiC2 deserves extensive study, where an improved mechanical property is expected due to the SiC fibers incorporated in the Ti3SiC2 matrix. To fabricate the composite, a highly dispersed Ti3SiC2 slurry was prepared by considering both steric and electrostatic dispersion mechanisms after adding different types of dispersants and polymeric processing additives. Electrophoresis was performed under a DC electric field to infiltrate the Ti3SiC2 particles into the voids of Tyranno™-SA grade 3 woven fabric, followed by hot pressing at 1350 °C under 20 MPa. High energy milling of the starting material accelerated the decomposition of Ti3SiC2 during sintering due to mechano-chemical activation. By adopting mild ball milling, however, SiCf/Ti3SiC2 with a density ≥90% and a flexural strength ≥100 MPa could be fabricated, retaining the most of Ti3SiC2 matrix phase.

The Influence of Sago Starch Dispersion on Mechanical Properties of Biodegradable Natural Rubber Latex Films

Abstract The biodegradability of natural rubber (NR) latex films can be improved by the addition of starch dispersion, which commonly prepared using anchoid as a dispersing agent. The purpose of this study was to investigate the influence of different types of dispersing agent; sodium alginate and carboxymethyl cellulose (CMC) in preparation of sago starch dispersions. The effect of different types of sago starch dispersions on mechanical properties (tensile and tear strength), swelling index and crosslink density of NR latex films were investigated. The results revealed that a good dispersion stability of sago starch sodium alginate gave better swelling index and mechanical properties, and higher crosslink density compared to NR latex with sago starch CMC. Based on the results obtained, the utilization of sodium alginate can be used as a replacement of anchoid in preparing the sago starch dispersions which gives comparable mechanical properties of biodegradable NR latex films.

Pulsed laser-based optical frequency comb generator for high capacity wavelength division multiplexed passive optical network supporting 1.2 Tbps

An architecture for flattened and broad spectrum multicarriers is presented by generating 60 comb lines from pulsed laser driven by user-defined bit stream in cascade with three modulators. The proposed scheme is a cost-effective architecture for optical line terminal (OLT) in wavelength division multiplexed passive optical network (WDM-PON) system. The optical frequency comb generator consists of a pulsed laser in cascade with a phase modulator and two Mach–Zehnder modulators driven by an RF source incorporating no phase shifter, filter, or electrical amplifier. Optical frequency comb generation is deployed in the simulation environment at OLT in WDM-PON system supports 1.2-Tbps data rate. With 10-GHz frequency spacing, each frequency tone carries data signal of 20 Gbps-based differential quadrature phase shift keying (DQPSK) in downlink transmission. We adopt DQPSK-based modulation technique in the downlink transmission because it supports 2 bits per symbol, which increases the data rate in WDM-PON system. Furthermore, DQPSK format is tolerant to different types of dispersions and has a high spectral efficiency with less complex configurations. Part of the downlink power is utilized in the uplink transmission; the uplink transmission is based on intensity modulated on-off keying. Minimum power penalties have been observed with excellent eye diagrams and other transmission performances at specified bit error rates.

A robust algorithm for estimating regression and dispersion parameters in non-stationary longitudinally correlated Com–Poisson data

In recent years, Com–Poisson has emerged as one of the most popular discrete models in the analysis of count data owing to its flexibility in handling different types of dispersion. However, in a stationary longitudinal Com–Poisson count data set-up where the covariates are time independent, estimation of regression and dispersion parameters based on a generalized quasi-likelihood (GQL) approach involves some major computational difficulties particularly in the inversion of the joint covariance matrix. On the other hand, in practical real-life longitudinal studies, time-dependent covariates leading to non-stationary responses are more frequently encountered. This implies that further computational problems will now arise when estimating parameters under non-stationary set-ups. This paper overcomes this problem by approximating the inverse of the ill-conditioned covariance matrix in the GQL approach through a multidimensional conjugate gradient method. The performance of this novel version of the GQL approach is then assessed on simulations of AR(1) stationary and AR(1) non-stationary longitudinal Com–Poisson counts and on real-life epileptic seizure counts. However, there is not yet an algorithm to generate non-stationary longitudinal Com–Poisson counts nor a GQL algorithm to estimate the parameters under non-stationary set-ups. Thus, the paper also provides a framework to generate non-stationary AR(1) Com–Poisson counts along with the construction of a GQL equation under non-stationary set-ups.

Ultrasonic backscattering method for in-situ characterisation of concentrated dispersions

An acoustic reflection measurement technique is presented, which detects and evaluates the ultrasonic waves backscattered at the particles within a liquid dispersion. The technique is based on an iterative pulse-echo method, which gathers a sufficiently high number of single reflection signals and eventually conducts a statistical analysis yielding two principal parameters of the backscattering signal: its maximum amplitude and its time-dependent decay. Theoretical considerations and experimental investigations show that maximum amplitude of the backscattering signal correlates with the averaged backscattering coefficient of the particles and that the decay rate of the backscattering signal can be attributed to sound attenuation, even though the impact of multiple scattering (i.e. non-linear concentration effects) is much more pronounced as for a transmission setup. Since the developed measurement technique is specifically designed for the in-situ characterisation of concentrated dispersion, it is necessary to adequately account for multiple scattering effects when evaluating the backscattering data. For this purpose a semi-empirical model is developed, which combines an established single particle scattering model with predictions of wave interference for defined microstructure of the dispersion. Experiments on two different types of dispersion confirm the applicability of this approach for concentrations up to 30vol.%. The experimental results additionally show that the maximum backscattering amplitude is highly sensitive to particle size, whereas the decay rate particularly reflects the impact of particle concentration. Finally a scheme is proposed, which allows for calculating the mean particle size and the volume fraction of the dispersed phase.

Manufacture of microporous ceramic layer by suspension–sedimentation for filtration applications

Microporous layers of 0.3 µm α-alumina powder were deposited on the surface of porous zirconia substrates (average pore size of about 1 µm) using suspension–sedimentation method. The characteristics of the deposited alumina microporous layer was evaluated using different types of dispersants, namely, citric acid, sodium dodecyl sulfate and Triton X-100. The effect of these dispersants on the stability and settling characteristics of alumina suspension was evaluated by sedimentation tests. Scanning electron microscopy analysis of the microporous layers (prior to sintering) revealed that sodium dodecyl sulfate dispersant produced uniform layers with least agglomeration of alumina particles, whereas citric acid showed more agglomeration of alumina particles and the use of Triton X-100 developed holes on the surface of alumina layer. The layers deposited using sodium dodecyl sulfate dispersant were then sintered at 1400 °C in air. Scanning electron microscopy observations revealed that a uniform porous alumina layer with average pore size in the range of 0.5–1.0 µm was produced with this method. The results of sedimentation tests indicated that alumina powder suspension prepared with sodium dodecyl sulfate dispersant yielded very good stability with lowest particle settling rate, whereas citric acid exhibited the highest particle settling rate.

Broadband Frequency Dispersion Small-Signal Modeling of the Output Conductance and Transconductance in AlInN/GaN HEMTs

Frequency dispersion of transconductance and output conductance in AlInN/GaN high electron mobility transistors is investigated in this paper. Broadband dispersion effects in the microwave frequency range are reported for the first time. A small-signal model is developed. Trapping effects are taken into account with parasitic electrical networks including distributed time constants. The model is compared with experimental data for several bias conditions and different types of dispersion.

Purification and Dispersion of Single-walled Carbon Nanotubes for Transparent Conducting Films

In our study, air oxidation together with three different procedures for purifying single-walled carbon nanotubes (SWCNTs) was investigated. High purity SWCNTs were obtained. The purified SWCNTs were dispersed into four different types of dispersants and different ratio of SWCNTs to dispersant was evaluated in order to find the optimal condition. Transparent conducting films were fabricated by the purified and well dispersed SWCNT solution. Nitric acid concentration was optimized to enhance the film conductivity. SWCNT films with low sheet resistance and high transmittance were obtained by nitric acid treatment.

Research on the Ultra-Fine Titanium Dioxide Suspension Stability and Fractal

Using scanning electron microscope, the microscopic pictures of the surface on sediment have been obtained from the sub-micron titanium dioxide suspensions without dispersant or adding different types of dispersants. Deposits of titanium dioxide suspension have been observed and the mechanism of the dispersant has been analyzed. Meanwhile, deposits of titanium dioxide gray distribution figure have been gained by self-compiled Matlab program, which proved that the surface sediments is fractal, and the fractal dimension has been calculated under different conditions. The rules between suspension stability and fractal dimension have been achieved.

A General ADE-FDTD Algorithm for the Simulation of Dispersive Structures

A finite-difference time-domain general algorithm, based on the auxiliary differential equation (ADE) technique, for the analysis of dispersive structures is presented. The algorithm is suited for cases where materials having different types of dispersion are modeled together. While having the same level of accuracy, the proposed algorithm finds its strength in unifying the formulation of different dispersion models into one form. Consequently, savings in both memory and computational requirements, compared to other ADE-based methods that model each dispersion type separately, are possible. The algorithm is applied in the simulation of surface plasmon polaritons using the multipole Lorentz-Drude dispersion model of silver.