Stress, voidage and velocity coupling in an avalanching granular heap

Slowly poured granular heaps evolve by a process of discrete avalanching. We separately investigate stress and voidage evolution in the dynamic boundary layer in which avalanching is initiated and takes place and patterns of stress distribution in the static regions of the heap which are not involved in avalanche activity. The defining events in the evolution of the heap are limited in number and localised in time and space. We investigate stress, voidage and avalanche velocity coupling, particularly in terms of these localised defining events.We analyse the time series that result from periodic sampling of a granular dynamics simulation and demonstrate the potential of the discrete wavelet transform that has been added to our simulation post-processing toolset as an aid to coupling of time series variables in the context of localised defining events. In particular, we show that correlation between time-lagged wavelet transform coefficients can be much more revealing than correlation functions derived from the original time series themselves and has the potential to identify time constants in the absence of clearly defined periodicity.     

Monitoring the Moisture Content of Solids in Fluidized Bed Dryers by Analysis of Pressure Fluctuations

Perusing the hydrodynamic changes of fluidized bed dryer is important for online monitoring of the drying process. The present study investigates the drying process of wetted rice particles. Air at ambient conditions with superficial velocity of 1 ms^?1 was used for drying. Absolute pressure fluctuations were measured to monitor the fluidization status of the dryer. Fast Fourier transform, discrete wavelet transform, and statistical analyses of detailed signals were employed to evaluate the fluidization quality in the bubbling regime. Pressure fluctuations were decomposed by the wavelet transform to 10 subsignals. It was shown that the energy of subsignals is more sensitive to moisture changes than other studied parameters. Specifically, the energy of the subsignals corresponding to the macrostructure (large bubbles) can be used for determining the moisture content of the solids during the drying process. This method can be used for online monitoring of drying processes in a wide range of processing conditions in fluidized beds.     

Fourier Analysis of Serial Dependence Measures

Classical spectral analysis is based on the discrete Fourier transform of the autocovariances. In this article we investigate the asymptotic properties of new frequency‐domain methods where the autocovariances in the spectral density are replaced by alternative dependence measures that can be estimated by U‐statistics. An interesting example is given by Kendall's τ, for which the limiting variance exhibits a surprising behavior.     

基于EMMS范式的离散模拟及其化工应用

化工过程通常涉及化学、化工、过程系统工程3个层次,而每个层次又包含微尺度、介尺度和宏尺度,如化工层次的颗粒、颗粒团和反应器尺度。每个层次中的微尺度单元都自然适用离散模型,即通过跟踪每个单元的运动获得整个体系演化的宏观规律。但由于单元数量巨大,工程模拟往往依赖经过统计平均的连续介质模型。由此带来的精度问题,特别是忽略了介尺度结构的问题,随着对化工过程效率和绿色度等要求的提高而日渐突出。介绍了通过问题、模型、软件和硬件结构的一致性提升离散模拟的精度、能力和效率的方法、进展及其在复杂分子体系、颗粒流、气固流态化等方面的应用,展示了通过离散模拟实现虚拟过程工程的可能性。     

Two phase natural convection: CFD simulations and PIV measurement

Buoyancy induced flow and heat transfer are important phenomena in a wide range of engineering systems e.g. electronics and photovoltaics cooling, thermosiphon heat exchangers, solar-thermal heat absorbers, passive decay heat removal systems, etc. Such systems are subject to thermal stratification. The objective of the present work is to study the single phase and two phase (boiling) natural convection accompanied by thermal stratification. We carried out velocity and temperature measurements in a rectangular tank (0.8×0.6×0.6 m³) fitted with (a) a central tube, and (b) a 10 tube assembly; which form the heat transfer surface. Flows were measured using Particle Image Velocimetry (PIV). Additionally, computational fluid dynamic (CFD) simulations of these systems were performed: first with an assumption of no-boiling (i.e. no phase change) near the heat transfer surfaces; for which we used the open source CFD code OpenFOAM-1.6. For two phase simulations, we used the boiling model of Ganguli et al. (2010) and carried out simulations using the commercial software FLUENT 6.3. The extent of stratification and mixing has been investigated for a range of Rayleigh numbers from 4.34×10¹¹ to 2.59×10¹⁴. The flow information obtained from PIV was analyzed for insights into the dynamics of turbulent flow structures. We used the signal processing technique of discrete wavelet transform (DWT) for this purpose. From the analysis, we were able to estimate the size, velocity and energy distribution of turbulent structures in our flows. This information was used to estimate wall heat transfer coefficients. A good agreement was observed between the predicted and the experimental values of heat transfer coefficients.     

Electrical behavior of dual‐morphology polyaniline

An attempt was taken to synthesize two types of polyaniline (PANI) with and without solvent followed by drying in air and vacuum oven conditions resulting different morphologies. The PANIs were prepared by chemical oxidative polymerization and studied with respect to their morphological features. Scanning electron microscopy, thermogravimetric analysis, X‐ray diffractometry, Fourier transform infrared spectroscopy, and ultraviolet–visible spectroscopy techniques were used for the characterization studies. The PANI synthesized with a solvent had a mixed morphology (fibrillar and granular), whereas PANI synthesized without a solvent had only a granular morphology. The direct‐current electrical conductivities of the samples were evaluated with an electrometer. We observed that the PANIs with mixed morphology (with solvent) were more electrically conducting than those with a single morphology (without solvent). On drying in vacuo, the conductivity of PANI decreased from 3.3 × 10^?2 to 0.3 × 10^?2 S/cm with solvent treatment, whereas it decreased from 0.1 × 10^?2 to 0.3 × 10^?3 S/cm without solvent treatment. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44091.     

Thickening of Melt During Processing of PES: A Structural Investigation

Treatment under normal processing temperature has been carried out by kneading for different times and at different roller rotating speeds, and also by successive extrusion cycles. There is an increase in melt viscosity of PES samples after processing. A phenomenon of thickening of melt during processing of PES may occur due to prolonged shear, heat, and oxidation under normal processing temperature (315°–335°C). A systematic study was conducted to investigate the structure changes during processing of PES by a variety of techniques including: Fourier–transform infrared spectroscopy, ¹³C nuclear magnetic resonance, and x-ray photoelectron spectroscopy. The results indicate that chain scission reactions occur and that long-chain branches are formed due to shear and heating. A branching mechanism provoking increase in molecular weight and thickening of melt during processing of PES is presented based on experimental data.     

In-Situ Internal Reflection Spectroscopy for the Study of Surfactant Adsorption Reactions Using Reactive Internal Reflection Elements

Abstract

Infrared spectroscopy has been one of the most useful experimental techniques for the analysis of surface reactions. In particular, Fourier transform infrared (FTIR)/internal reflection spectroscopy (IRS) is most often used for in-situ studies. To date, three FTIR/IRS methods have been used for in-situ measurements. These techniques are evaluated for use in the characterization of surface reactions common to flotation systems. The method which uses mineral crystals as reactive internal reflection elements (IREs) is of particular interest because it allows surfactant adsorption densities to be calculated directly from in-situ spectral data in real time, and is the focus of this paper.

Application of in-situ FTIR/IRS with reactive IREs is demonstrated for collector adsorption reactions in each of the four major flotation systems. Also, the use of reactive IREs in the near-IR spectral region and in spectroelec-trochemical research is discussed.     

Effect of Prolonged Duration of Gelatinization in Starch and Incorporation with Potassium Iodide on the Enhancement of Ionic Conductivity

Three systems of starch-based crust electrolytes were prepared using various gelatinization times, various weight percentages (wt%) of starch, and various wt% of starch incorporated into potassium iodide. All the samples were subjected to electrochemical impedance spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and transference number measurements. Electrochemical impedance spectroscopy shows that 1.7?wt% of starch has maximized the room temperature conductivity of the electrolyte to 1.4587?×?10^?4?S?cm^?1. The conductivity was enhanced to 4.5278?×?10^?4?S?cm^?1 on the increment of starch’s wt% from 1.7 to 3.2. This conductivity was further enhanced to 3.4609?×?10^?3?S?cm^?1 on the addition of 0.3?wt% of potassium iodide. The conductivity enhancement was found due to the formation of glucosyl carboxonium ions. The effect of longer heating time in gelatinization is attributed to the formation of glucosyl carboxonium ions. X-ray diffraction spectroscopy affirms the reduction in crystallinity of starch. Scanning electron microscopy analysis shows the porous morphology of starch electrolyte, and addition of potassium iodide shows the morphology of bean nuts like particles seated on the pores. Fourier transform infrared confirms the degradation of starch. Transference number measurements of the crust electrolyte shows that ions are the dominant conducting species. All the results are authenticating that the conductivity enhancement in starch-based crust electrolyte is due to starch and the addition of inorganic salts.     

Determination of polymer chain length distributions by numerical inversion of z-transforms

A numerical technique is presented for evaluation of the polymer chain length distribution in polymerization reaction engineering models whose governing equations can be represented in the z-transform domain. The method is based upon an appropriate z-transform inversion relationship that has the form of an inverse discrete Fourier transform which can be efficiently evaluated by the fast Fourier transform algorithm using various existing computer software. The approach is illustrated through several example problems involving polymerization systems and comparisons are made to other alternate solution methods. One of the example problems includes a complex reaction network for polycarbonate polymerization as a novel application. It is shown that the proposed technique requires an order-of-magnitude less computer time to evaluate the polymer MWD when compared to direct numerical integration.     

Development of whey protein isolate/polyaniline smart packaging: Morphological,structural, thermal,and electrical properties

Development of smart packaging from biodegradable polymers that allow monitoring food exposure conditions is important to reduce food and material packaging waste. The objective of this article is to evaluate the conductivity of polyaniline (PANI) in its doped form with dodecylbenzene sulfonic acid on morphological, structure, thermal, and electrical (Hall effect) properties of whey protein isolate (films. Films show immiscible with 10⁻³ S cm⁻¹ conductivity and semiconductor behavior due to a phase separation that is observed (scanning electron microscopy and thermogravimetric analysis). Fourier transform infrared and Raman spectra do not present changes in relation to control samples, suggesting no chemical interaction with polymers. This result is probably due to deprotonation of PANI. No significant differences are observed for conductivity of film made above 60 mg mL⁻¹ of PANI. Films showed semiconducting properties that allow a new application on smart packaging to help monitor electrical properties of foods in processes of degradable. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47316.     

Unusual functionalization of reduced graphene oxide for excellent chemical surface-enhanced Raman scattering by coupling with ZnO

A low-cost noble metal-free substrate comprised of annealed graphene oxide (GO)/ZnO composites is prepared to demonstrate an efficient chemical surface-enhanced Raman scattering effect. A high enhancement factor of about 10⁴, better than those reported for reduced GO (rGO)/Au and GO/Ag composites, is mainly attributed to the unusually abundant oxygen-containing groups generated on surface of rGO by coupling with ZnO nanoparticles at moderate temperature. High-resolution transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy are employed to examine the evolution of ZnO as well as reduction and functionalization of GO after different heat treatments.     

Structural characterisation and electrical conductivity studies of BaMoO4 nanorods prepared by modified acrylamide assisted sol–gel process

Abstract

Scheelite type BaMoO₄ nanorods have been synthesised by modified acrylamide assisted sol–gel process. The prepared samples were characterised by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Fourier transform Raman (FT-Raman), scanning electron microscope–energy dispersive X-ray (SEM–EDX) and transmission electron microscope (TEM) techniques. The crystalline phase and structure of the prepared samples were confirmed from the analysis of the obtained results of XRD, FTIR and FT-Raman respectively. The average crystallite size calculated using Scheeer’s formula and XRD data is found to be 98 nm. SEM images showed the formation one dimensional nanorods of diameter <300 nm. EDX spectra showed the existence of Ba, Mo and O elements of the prepared samples. From the TEM images, diameter and length of the rod are found to be 80 and 2070 nm respectively. The ac conductivities by impedance spectroscopy of the prepared BaMoO₄ samples were evaluated as a function of temperature ranging from 500 to 800°C in the air. The newly prepared BaMoO₄ nanorods showed electrical conductivity of 3·14×10^?3 S cm^?1.     

Effect of Au thickness on the evolution of self-assembled Au droplets on GaAs (111)A and (100)

In this paper, we report the effect of Au thickness on the self-assembled Au droplets on GaAs (111)A and (100). The evolution of Au droplets on GaAs (111)A and (100) with the increased Au thickness progress in the Volmer-Weber growth mode results in distinctive 3-D islands. Under an identical growth condition, depending on the thickness of Au deposition, the self-assembled Au droplets show different size and density distributions, while the average height is increased by approximately 420% and the diameter is increased by approximately 830%, indicating a preferential lateral expansion. Au droplets show an opposite evolution trend: the increased size along with the decreased density as a function of the Au thickness. Also, the density shifts on the orders of over two magnitude between 4.23 × 10¹⁰ and 1.16 × 10⁸ cm⁻² over the thickness range tested. At relatively thinner thicknesses below 4 nm, the self-assembled Au droplets sensitively respond to the thickness variation, evidenced by the sharper slopes of dimensions and density plots. The results are systematically analyzed and discussed in terms of atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), cross-sectional surface line profiles, and Fourier filter transform (FFT) power spectra.     

A New Covariance Function and Spatio‐Temporal Prediction (Kriging) for A Stationary Spatio‐Temporal Random Process

Consider a stationary spatio‐temporal random process and let be a sample from the process. Our object here is to predict, given the sample, for all t at the location s _o. To obtain the predictors, we define a sequence of discrete Fourier transforms using the observed time series. We consider these discrete Fourier transforms as a sample from the complex valued random variable . Assuming that the discrete Fourier transforms satisfy a complex stochastic partial differential equation of the Laplacian type with a scaling function that is a polynomial in the temporal spectral frequency ω, we obtain, in a closed form, expressions for the second‐order spatio‐temporal spectrum and the covariance function. The spectral density function obtained corresponds to a non‐separable random process. The optimal predictor of the discrete Fourier transform is in terms of the covariance functions. The estimation of the parameters of the spatio‐temporal covariance function is considered and is based on the recently introduced frequency variogram method. The methods given here can be extended to situations where the observations are corrupted by independent white noise. The methods are illustrated with a real data set.     

Xenon ion implantation induced defects and amorphization in 4H–SiC: Insights from MD simulation and Raman spectroscopy characterization

Xenon Focused Ion Beam (Xe-FIB) processing of 4H–SiC is an emerging technique with great potential for various applications. In this study, we investigate the evolution mechanism of damage caused by xenon ion implantation in 4H–SiC using a combination of molecular dynamics (MD) simulation and Raman spectroscopy. The study explores the microscopic mechanisms of damage processing and repairs using the proper potential function and the optimized simulation model. The MD simulation reveals that the vacancy and interstitial sites of silicon and carbon atoms, as identified by the Wigner-Seitz defect method, increase linearly with implanted dose until the dose reaches 2 × 10¹⁴ ions/cm². Subsequently, the growth rate of each defect site in the damaged area slows down and eventually comes to a saturation state with a continuous increase in dose. The growth rate of the amorphous region also slows down with the constant increase in dose, similar to the results obtained through variable temperature Raman spectroscopy characterization experiments on 4H–SiC (0001) nitrogen-doped substrates implanted with different doses of xenon ions. Furthermore, unlike light ions such as hydrogen and helium, Xe ions cause significant damage to the inside of 4H–SiC, resulting in the inability to produce structurally complete silicon vacancy defects. Our findings provide insights into the fundamental mechanism of Xe-FIB processing and have implications for future applications in semiconductor technology.     

Synthesis of L-Lactide-Based Segmented Polyurethanes

A series of segmented polyurethanes with polylactidediols soft segments and methylene-diphenyl-diisocyanate/1,4-butanediol hard segments with molecular weights in the range of 6.18 × 10³ to 9.36 × 10³ Da were synthesized. Stannous octoate was the catalyst for the reactions. These polymers were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, gel permeation chromatography, and thermogravimetric analyzer. Fourier transform infrared analyses revealed the formation of urethane groups and complete curing of polyurethane. The thermal degradation temperatures were in the range of 248.55–257.09°C. X-ray diffraction studies confirmed the segmented structure of polyurethanes.     

Primary and secondary crystallization of fast‐cooled poly(vinylidene fluoride) studied by Flash DSC,wide‐angle X‐ray diffraction and Fourier transform infrared spectroscopy

Industrial processing of polymeric materials normally involves fast cooling. We employed a commercial chip calorimeter (Flash DSC) to investigate the crystallization and annealing behaviors of poly(vinylidene fluoride) (PVDF) under fast cooling towards low temperatures. The corresponding polymorphic crystalline phases were identified by wide‐angle X‐ray diffraction and Fourier transform infrared spectroscopy. The results demonstrated that a cooling process faster than ?500 K s^?1 results in major thick α‐phase crystallites at high temperatures; in addition, subsequent isothermal annealing at low temperatures slowly generates minor thin β‐phase crystallites rich with trans conformation. Our observations facilitate a better understanding of structural optimization during PVDF processing for its ferroelectric and piezoresponse performance in versatile applications. © 2016 Society of Chemical Industry     

Improving dielectric properties of poly(vinylidene fluoride) composites: effects of surface functionalization of exfoliated graphene

To investigate the effects of surface functionalization of exfoliated graphene (EG) on the crystalline form of β-phase and dielectric properties of poly(vinylidene fluoride) (PVDF), we prepared PVDF-based composites reinforced by different functionalized EG. The X-ray photoelectron spectroscopy results indicated that a wide variety of chemical functional groups such as C–OH, C–O–C, C=O, COOH and C–F could be introduced on the surface of modified EG. As confirmed by results of Fourier transform infrared spectrum and X-ray diffraction, the β-phase PVDF can be produced in the composites with the incorporation of functionalized EG. In the frequency ranging from 10² to 10⁷ Hz, the dielectric permittivity of PVDF composites shows an obvious increase owing to a variation of the carbonyl group (C=O) content. Among all the composites, the EG grafted with polymethyl methacrylate/PVDF composite has the highest dielectric permittivity and dielectric loss.     

Surface tailoring of an ethylene propylene diene elastomeric terpolymer via plasma‐polymerized coating of tetramethyldisiloxane

In the research presented here, we explore the use of a low‐energy plasma to deposit thin silicone polymer films using tetramethyldisiloxane (TMDSO) (H(CH₃)₂? Si? O? Si? (CH₃)₂H) on the surface of an ethylene propylene diene elastomeric terpolymer (EPDM) in order to enhance the surface hydrophobicity, lower the surface energy and improve the degradation/wear characteristics. The processing conditions were varied over a wide range of treatment times and discharge powers to control the physical characteristics, thickness, morphology and chemical structure of the plasma polymer films. Scanning electron microscopy (SEM) shows that pore‐free homogeneous plasma polymer thin films of granular microstructure composed of small grains are formed and that the morphology of the granular structure depends on the plasma processing conditions, such as plasma power and time of deposition. The thicknesses of the coatings were determined using SEM, which confirmed that the thicknesses of the deposited plasma‐polymer films could be precisely controlled by the plasma parameters. The kinetics of plasma‐polymer film deposition were also evaluated. Contact angle measurements of different solvent droplets on the coatings were used to calculate the surface energies of the coatings. These coatings appeared to be hydrophobic and had low surface energies. X‐ray photoelectron spectroscopy (XPS) and photoacoustic Fourier‐transform infrared (PA‐FT‐IR) spectroscopy were used to investigate the detailed chemical structures of the deposited films. The optimum plasma processing conditions to achieve the desired thin plasma polymer coatings are discussed in the light of the chemistry that takes place at the interfaces. Copyright © 2004 Society of Chemical Industry