The atomic scale structure of nanographene platelets studied by X-ray diffraction,high-resolution transmission electron microscopy and molecular dynamics

The atomic structure of commercially available nanographene platelets has been studied by high energy X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and molecular dynamics simulations using the reactive empirical bond order potential. Atomic models of the structure have been constructed and then relaxed using the molecular dynamics method and the model based simulations are compared with the experimental data both in reciprocal and real space. All model relaxations and the X-ray diffraction experiments have been carried out at 300 K. The proposed models consisting of about 2500 carbon atoms arranged within four graphitic layers with a diameter of 46 Å, reproduced correctly all features of the experimental data. The atomic arrangement within an individual layer can be described in terms of the paracrystalline ordering, in which lattice distortions propagate proportionally to the square root of interatomic distances. The paracrystalline structure was simulated by introducing the topological point defects such as the Stone–Thrower–Wales defects, single- and double-vacancies, randomly distributed in the network. Such defects lead to curvature of individual layers and this effect was also analyzed. The generated models are related to the observations by high-resolution transmission electron microscopy.     

Turbulent mass transfer from a rotating disk

A new model based on the surface renewal concept was proposed to discuss the turbulent mass transfer from a rotating disk. The proposed model, in which the proportionality constants are determined by using hydrodynamic data rather than mass transfer data and no adjustable parameters are included, was in excellent agreement with the available experimental data for Newtonian fluids. The mass transfer from a disk rotating in dilute polymer solutions and power-law fluids was also investigated using the proposed model. Good agreement was found between the model and the experimental data for dilute polymer solutions and power-law fluids.     

Thermal CVD synthesis of carbon nanotubes filled with single-crystalline Cu nanoneedles at tips

Carbon nanotubes (CNTs) filled with Cu nanoneedles at tips have been synthesized using alkali-element doped Cu catalyst by a simple thermal chemical vapor deposition method. X-ray diffraction analysis reveals that Cu nanoneedles have perfect face-centered cubic structure. The carbon shells provide an effective barrier against oxidation and consequently ensure a long-term stability of the Cu core. Selected area electron diffraction indicates that these Cu nanoneedles are single crystalline with fine quality. Transmission electron microscopy and high-resolution transmission electron microscopy were employed to analyze the microstructure of Cu filled CNTs. On the basis of experimental results, a simple growth model is proposed in this paper.     

A Modified Peng-Robinson Equation State for Prediction of Gas Adsorption Isotherm

This research proposes a modified two-dimensional Peng-Robinson equation model to predict adsorp-tion isotherm in adsorbate-adsorbent systems. The parameters of the proposed model are calculated by using the op-timization of experimental data for the different single gas adsorption systems at various temperatures. The experi-mental adsorption equilibrium data of adsorbate-adsorbent systems was compared with the calculated results in our proposed model and the two-dimensional Hill-deBoer equation model. The proposed model as indicated in the re-sults shows a better prediction of the experimental results compared with two others.     

Enhanced Separation of Polyethylene Glycol from Bovine Serum Albumin Using Electro-Ultrafiltration

Electric field-enhanced separation of polyethylene glycol (PEG) from an aqueous electrolyte solution of bovine serum albumin has been carried out. Experimental results show significant improvements in both the permeate flux and the PEG transmission with the application of a suitable d.c. electric field. A mass transfer model based on film theory is proposed for prediction of permeate flux and observed retention of PEG. The model uses a single parameter, namely real retention (R_r2) of the PEG which is evaluated by optimizing the experimental values of steady state permeate flux and the permeate concentration. Model predictions are in good agreement with the experimental data.     

A one-dimensional model of plug flow pneumatic conveying

A one-dimensional model of pulse or plug flow is proposed. This type of flow is observed at high mass ratios of solids to gas and requires gas velocities orders of magnitude less than dilute phase systems. Plug stability criteria are examined by considering the axial interparticle stresses within single plugs and the effect of the radial transmission of these stresses on wall friction. Establishment of the fluid pressure gradient within the plug and the existence of a settled layer of solids in the interplug space are shown to be important requirements. These concepts are used in the formulation of an empirical pressure drop equation which is used in the correlation of experimental data. Comparison of predicted and experimental values is reasonable for the air-sand system considered. The model should be of value in the planning and interpretation of future experimental studies.     

MODEL FOR THE PREDICTION OF DEHYDRATION AND CALCINATION RATES OF BAYER PLANT GIBBSITE

A model for the prediction of rates of dehydration of Chemically Bound Moisture of Gibbsite is proposed. The theoretical dehydration rates evaluated from the model are compared with experimental values. The correlation between the experimental data and theoretically predicted values is found to be satisfactory. The curves obtained for differential thermal analysis of Gibbsite are found to resemble the DTA curves predicted theoretically using the proposed rate equations.     

MODEL FOR THE PREDICTION OF DEHYDRATION AND CALCINATION RATES OF BAYER PLANT GIBBSITE

A model for the prediction of rates of dehydration of Chemically Bound Moisture of Gibbsite is proposed. The theoretical dehydration rates evaluated from the model are compared with experimental values. The correlation between the experimental data and theoretically predicted values is found to be satisfactory. The curves obtained for differential thermal analysis of Gibbsite are found to resemble the DTA curves predicted theoretically using the proposed rate equations.     

A New Turbulent-Burst-Based Model for Particle Resuspension from Rough Surfaces in Turbulent Flow

Particle resuspension could affect human exposure to particulate matter (PM) and serves as a potential route for infection transmission in indoor environments. A new resuspension model incorporating the effects of turbulent bursts, depletion of resuspendable particles, adhesion force distribution, and environmental relative humidity (RH) is proposed. In the proposed model, Monte Carlo simulation is used to model the occurrence of turbulent bursts and the depletion of resuspendable particles on surfaces. The adhesion force distribution and RH effects were included by employing the recently proposed adhesion force distribution model. Model validation is conducted by comparing model predictions against reported experimental data found in the literature. The effects of RH and particle size on resuspension are investigated using the proposed model. The threshold free stream velocity increases by two and three times when the RH increases from 36% to 61% and 67%, respectively. The threshold friction velocity decreases by five times when the particle size increases from 30.1 μm to 111 μm. The proposed model provides a physically reasonable framework for describing particle resuspension under turbulent flow. The capability of predicting the effect of RH greatly enhances the practical application of current resuspension models.

Copyright 2014 American Association for Aerosol Research     

Acetaldehyde dimethylacetal synthesis with Smopex 101 fibres as catalyst/adsorbent

The synthesis of dimethylacetal using acetaldehyde and methanol as raw material in the presence of Smopex 101 fibres as catalyst and adsorbent in batch reactor and in a fixed bed adsorptive reactor, respectively, was studied. In the batch reactor the determination of thermodynamic and reaction kinetics data for acetalization reaction was presented. A kinetic model based on a pseudo-homogeneous rate expression using activities was proposed to describe the experimental kinetic results. The dynamic binary adsorption experiments were carried out in the absence of reaction at 293.15 K in a laboratory scale column. The experimental results of the adsorption of binary non-reactive mixtures are reported and used to obtain multi-component adsorption equilibrium isotherms of Langmuir type. The mathematical model was proposed to describe the adsorptive reactor dynamic behaviour. The experimental results obtained for the reaction and regeneration experiments were compared with the model proposed. Model equations were solved by orthogonal collocation on finite elements (OCFE) implemented by the PDECOL package, using the measured model parameters and was validated for both reaction and regeneration steps.     

Montages coaxiaux pour l'etude des phenomenes rapides de relaxation aux interfaces metal-electrolyte aqueux

For the study of the relaxation phenomena at the metal-aqueous electrolyte interfaces in the 10^?9 s or 10⁸ Hz range, the experimental set-ups must be entirely coaxial with properly selected electrode diameters. Set-ups using a coaxial line (transmission and reflexion) are proposed after having been tested in the time domain.     

喹诺酮类药物的溶解度模型

采用Glew-Hildebrand饱和技术,应用高效液相色谱法和人工神经网络技术,实验测得氧氟沙星、诺氟沙星和吡哌酸在不同温度水溶液中的溶解度,应用化工热力学理论,提出溶解度模型,用实验和文献数据作了检验．通过扩展增广距离矩阵,提出能表征杂原子、多重键和复杂环的化合物分子结构的新的分子拓扑指数,由实测3种喹诺酮类药物的溶解度数据,得到分子结构-溶解度定量相关模型．据此模型预报氟罗沙星（Fleroxacin)等9种喹诺酮类新药在25℃和37℃时的溶解度,与实验值符合良好．     

Modelling of batch ultrafiltration

A model has been developed which predicts the performance of a batch ultrafiltration. By using the relationship for flux decline proposed by Merin and Cheryan in 1990, an analytical solution is presented. The proposed model includes the initial volume, feed solution concentrations, processing time, retention, membrane area and flux across the membrane. The model predictions are compared with experimental data, and satisfactory agreement is obtained.     

Reactive oxygen species may cause amyloid beta aggregation by free radical polymerization

Alzheimer's disease (AD), the most common form of dementia, is closely related to the overproduction of reactive oxygen species (ROS). A kinetic model based on free radical polymerization of amyloid beta (Aβ) utilizing ROS as an initiator is proposed. Kinetic parameters involved in the model are tuned with the reported experimental data on fibril molecular weight. The tuned model is used to simulate time evolution of fibril length and polydispersity of Aβ aggregates. The simulated values are compared with the reported experimental values for these fibril properties. A good agreement is observed between the model simulated fibril properties and the reported experimental data. This supports the hypothesis of ROS as the cause of Aβ aggregation using the free radical polymerization. The proposed model is also able to predict the sigmoidal growth of fibrils at different set of parameter values. Sensitivity analysis has been performed to check the reliability of the proposed model. It is envisaged that the proposed model will be helpful to elucidate ROS-based therapeutic strategies for AD treatment in near future.     

A model for simultaneous measurement of gas and solid holdups in a bubble column using ultrasonic method

The ultrasonic method developed to measure the dispersed phase holdups in dispersion systems is based on the fact that the velocity of ultrasound in the dispersion is different from that in the liquid. The relationships between velocity differences in the term of transmission time differences of ultrasound and gas holdup in a gas-liquid system and solid holdup in a liquid-solid system were derived. The holdups became linearly dependent on the time differences, which is in agreement with the experimental data. Based on those relations, a model for simultaneous measurement of gas and solid holdups in three-phase systems is proposed. The model permits measurement of the dispersed phase holdups by measuring the transmission time of ultrasound transmitted through the dispersions in two frequencies. It allows investigation of local holdups distributions in a bubble column and in a suspended bubble column.     

Electrochemical Impedance Modeling of a Solid Oxide Fuel Cell Anode

A simulation package for the impedance response of SOFC anodes is presented here. The model couples the gas transport in gas channels and within a porous electrode with the electrochemical kinetics. The gas phase mass transport is modeled using mass conservation equations. A transmission line model (TLM), which is suitably modified to account for the electrode microstructural details, is used for modeling the impedance arising from the electrochemical reactions. In order to solve the system of nonlinear equations, an in‐house code based on the finite difference method was developed. Some of the model constants have been calibrated against experimental data. It is demonstrated that the simulation tool is capable of predicting the impedance response of an experimental data set obtained on symmetrical cells with Ni/ScYSZ SOFC anodes. A parametric study is also carried out using the developed simulation tool and the results are further discussed.     

A Bayesian approach to robust process identification with ARX models

In the context of process industries, outlying observations mostly represent a large random error resulting from irregular process disturbances, instrument failures, or transmission problems. Statistical analysis of process data contaminated with outliers may lead to biased parameter estimation and plant‐model mismatch. The problem of process identification in the presence of outliers has received great attention and a wide variety of outlier identification approaches have been proposed. However, there is a great need to seek for more general solutions and a robust framework to deal with different types of outliers. The main objective of this work is to formulate and solve the robust process identification problem under a Bayesian framework. The proposed solution strategy not only yields maximum a posteriori estimates of model parameters but also provides hyperparameters that determine data quality as well as prior distribution of model parameters. Identification of a simulated continuous fermentation reactor is considered to show the effectiveness and robustness of the proposed Bayesian framework. The advantages of the method are further illustrated through an experimental case study of a pilot‐scale continuous stirred tank heater. © 2012 American Institute of Chemical Engineers AIChE J, 59: 845–859, 2013     

Large-Scale Fabrication of Boron Nitride Nanotubes via a Facile Chemical Vapor Reaction Route and Their Cathodoluminescence Properties

Cylinder- and bamboo-shaped boron nitride nanotubes (BNNTs) have been synthesized in large scale via a facile chemical vapor reaction route using ammonia borane as a precursor. The structure and chemical composition of the as-synthesized BNNTs are extensively characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and selected-area electron diffraction. The cylinder-shaped BNNTs have an average diameter of about 100 nm and length of hundreds of microns, while the bamboo-shaped BNNTs are 100–500 nm in diameter with length up to tens of microns. The formation mechanism of the BNNTs has been explored on the basis of our experimental observations and a growth model has been proposed accordingly. Ultraviolet–visible and cathodoluminescence spectroscopic analyses are performed on the BNNTs. Strong ultraviolet emissions are detected on both morphologies of BNNTs. The band gap of the BNNTs are around 5.82 eV and nearly unaffected by tube morphology. There exist two intermediate bands in the band gap of BNNTs, which could be distinguishably assigned to structural defects and chemical impurities.     

Large-Scale Fabrication of Boron Nitride Nanotubes via a Facile Chemical Vapor Reaction Route and Their Cathodoluminescence Properties

Cylinder- and bamboo-shaped boron nitride nanotubes (BNNTs) have been synthesized in large scale via a facile chemical vapor reaction route using ammonia borane as a precursor. The structure and chemical composition of the as-synthesized BNNTs are extensively characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and selected-area electron diffraction. The cylinder-shaped BNNTs have an average diameter of about 100 nm and length of hundreds of microns, while the bamboo-shaped BNNTs are 100-500 nm in diameter with length up to tens of microns. The formation mechanism of the BNNTs has been explored on the basis of our experimental observations and a growth model has been proposed accordingly. Ultraviolet-visible and cathodoluminescence spectroscopic analyses are performed on the BNNTs. Strong ultraviolet emissions are detected on both morphologies of BNNTs. The band gap of the BNNTs are around 5.82 eV and nearly unaffected by tube morphology. There exist two intermediate bands in the band gap of BNNTs, which could be distinguishably assigned to structural defects and chemical impurities.