CFD simulation of particle segregation in a rotating drum. Part II: Effects of specularity coefficient

Segregation of binary particle mixture in a rotating drum is numerically studied using the Eulerian multiphase computational fluid dynamics (CFD) simulations coupling the solid phase kinetic theory of granular flow model. The corresponding solid kinetic viscosities of the two particulate phases are determined by the previous granular bed surface fitting (BSF) method. The effects of the specularity coefficients used in the simulations on the segregation patterns in the rotating drums are systematically studied by using the specularity coefficient values ranging from 0.15 to 1.0. When using a smaller specularity coefficient value in the simulation, the momentum transferring from the drum wall to the particulate phase is poorer, lowering the kinetic energy of the particulate phase. The lower particulate phase kinetic energy causes slower particle motion in the bed and hence delays the segregation core/band formation. At the same simulation time, the concentration of the smaller particles in the segregation core increases with the increasing of the specularity coefficient value used in the simulation. When the specularity coefficient values larger than 0.4 are used in our simulations, the realistic three-dimensional segregation structures are well predicted. A proper specularity coefficient value should be adopted in Eulerian multiphase CFD simulations of granular flows.     

Regularised multi-stage parallel interference cancellation for downlink CDMA systems

A hybrid receiver scheme for downlink code division multiple access (CDMA) systems over frequency selective channels is proposed. The proposed receiver combines a linear regularised zero forcing (RZF) equaliser and a parallel interference cancellation scheme with a tanh decision function (TPIC). It is called the RZF-TPIC receiver. The RAKE receiver is used to reduce the channel effects and obtain an initial estimate of the data. Multi-stages of TPIC are then employed to mitigate the multiple access interference (MAI). At the final stage, the RZF equaliser is used to provide a better estimate of the desired user?s data. The effect of the decision function used for symbol estimation in the PIC stage is investigated. The performance of the proposed scheme is evaluated and compared with the traditional RAKE receiver by computer simulations. It is found that the proposed scheme offers significant gains, even with a large number of interfering users.     

声纳输出的弱目标信息提取方法仿真分析

针对存在艇外平台强干扰的情况,对波束域MVDR（b-MVDR）和后置波束形成干扰抵消器（PIC）的弱目标提取能力进行了仿真分析。考虑到艇外平台与目标往往处于同一波束的实际情况,提出首先采用密集波束形成,再进行弱目标提取的方法。仿真结果表明：对艇外平台与目标处于同一波束的情况,PIC的目标分辨能力更强;在干扰较强时,PIC方法表现出更强的弱目标提取能力,但随信干比的增加其能力不断降低;而b-MVDR方法则在各种信干比下均具有良好的性能。     

Multiscale modeling reveals poisoning mechanisms of MgO-supported Au clusters in CO oxidation

Catalyst deactivation mechanisms on MgO-supported Au(6) clusters are studied for the CO oxidation reaction via first-principle kinetic Monte Carlo simulations and shown to depend on support vacancies. In defect-poor MgO or in the presence of a Mg vacancy, O(2) does not bind to the clusters and the catalyst is poisoned by CO. On Au clusters interacting with O vacancies of the support, O(2) can be chemisorbed and transient activity is observed. In this case, an unexpected catalyst "breathing" mechanism (restructuring) leads to carbonate formation and catalyst deactivation, rationalizing several experimental observations. Our study underscores the importance of the cluster's charge state and dynamics on catalytic activity.     

Energy and length scales in scintillator nonproportionality

The causes of energy nonlinearity (nonproportionality) in gamma-ray spectroscopy of scintillators have not been fully explained quantitatively, but are believed to involve the spatial density of thermalized electrons and holes, their transport and interactions, and competition between radiative and nonradiative recombination. Here, we relate electron–hole density to the initial ray's energy through expressions for the stopping power and distance, and then attempt to fit some “plateau-type” (e.g. BaF₂, Lu₂SiO₅, etc.) light curves via competing radiative and nonradiative processes obeying different energy power laws. We find that reasonable power laws and the assumption of a uniform energy density in the excited region lead to a fairly good agreement with many experimental curves. We then show that a simple approximation for averaging over regions of different excitation density leads to improved agreement with experiment, at the expense of making it more difficult to uncover the underlying kinetics from the experimental data. These considerations should carry over to more sophisticated models or simulations of scintillation processes.     

Blind adaptive and iterative interference cancellation receiver structures based on the constant modulus criterion in multipath channels

Blind adaptive and iterative interference cancellation (IC) receiver structures for direct sequence code division multiple access systems in multipath channels are proposed. A code-constrained constant modulus design criterion based on constrained optimisation techniques and adaptive algorithms for receiver and channel parameter estimation are described for successive IC (SIC) and parallel IC (PIC) detectors and a new hybrid IC (HIC) scheme in scenarios subject to multipath fading. The proposed HIC structure combines the strengths of linear, SIC and PIC receivers and is shown to outperform the conventional linear, SIC and PIC structures. A novel iterative detection approach that generates different cancellation orders and selects the most likely symbol estimate on the basis of the instantaneous minimum constant modulus criterion is also proposed and combined with the new HIC structure to further enhance performance. Simulation results for an uplink scenario assess the algorithms, the proposed blind adaptive IC detectors against existing receivers and evaluate the effects of error propagation of the new cancellation techniques.     

Channel estimation and interference cancellation in CP?CDMA systems

A novel iterative channel estimation approach is proposed for cyclic prefix-code division multiple access systems. Code-multiplexed pilots are used for channel estimation while maintaining bandwidth efficiency. The proposed method achieves a significant improvement when compared to the conventional correlation approach by reconstructing data signals for channel estimation. Simulation results demonstrate good estimation capability with an allocation of only 10% of the whole power to the pilot channel. In addition, an integrated channel estimator and parallel interference cancellation (PIC) detector are proposed. Data signals are reconstructed for channel estimation while the interference contributed by different data channels as well as the pilot channel are regenerated and subtracted from the received signal at the final stage. The channel estimation error reduces at each iteration and the PIC at the last stage enables further bit error rate performance improvement to be achieved for the system. The performance of the proposed scheme is studied through simulations and results verify its effectiveness     

The impact of social capital on mass customisation and product innovation capabilities

Social capital with customers has three dimensions: structural, relational and cognitive capital. We propose a research model on the joint effects of the three dimensions of social capital on mass customisation capability (MCC) and product innovation capability (PIC). The hypotheses are empirically tested using structural equation modelling and data collected from 276 manufacturing firms in China. The results show that the three dimensions of social capital contribute to MCC and PIC development through different mechanisms. In particular, cognitive capital has a significant impact on MCC; relational capital significantly influences PIC; and structural capital indirectly associates with both MCC and PIC. We also find that structural capital enhances both relational and cognitive capital. MCC improves PIC and fully mediates cognitive capital’s effect on PIC. The findings extend current understanding about the complex interrelationships among structural, relational and cognitive capital and how to develop MCC and PIC by investing in social capital.     

Numerical simulation of flow behavior of particles in a liquid-solid stirred vessel with baffles

Flow behavior of particles is simulated by means of two-fluid model combining with kinetic theory of granular flow in a liquid-solid stirred vessel with baffles. The Huilin-Gidaspow drag model is used to obtain interphase interaction of liquid and solids phases. The virtual mass force is considered in simulations. The moving reference frame is applied to the rotation of numerical domain. Predictions are compared with experimental data measured by Pianko-Oprych et al. (2009) in a liquid-solid stirred vessel. This comparison shows that the present model can capture the liquid-solid flow in a liquid-solid stirred vessel. The distributions of velocity and solids volume fraction are predicted at the different heights. The effects of particle density on flow behavior of particles are generally scarce using CFD. Simulations indicate the stirred vessel consists of three regions based on distributions of velocity and turbulent kinetic energy, they are blade circulation region, conical induced region and near-wall region. As an increasing of the impeller speed, the turbulence kinetic and solids phase velocity rise, and the particles fluctuation is intensified.     

等离子体浸没式离子注入圆形薄片均匀性研究

采用PIC（Partical in call)方法考察了等离子体浸没式离子注入工艺中，样品和靶台的几何尺寸、形状及防止溅射沾污的绝缘材料对于注入离子径向分布的影响。并对模拟结果进行了讨论分析。结果表明，影响剂量分布的主要因素是基片和靶台的横向尺寸，为改善等离子体浸没式离子注入均匀性的研究提供参考数据。     

Size-dependent damping model for DEM: improved equilibrium compared with mass-damping at no extra computational cost

In the framework of discrete element method, a new damping model is introduced. Unlike the global mass-damping, the new model applies an approximately equal damping ratio to all particles in a granular assembly. This model does not require exact stiffness calculations, hence not involved in the unnecessary cost. The new and global damping models were compared based on overall equilibrium of samples during quasi-static simulations. The equilibrium status was quantified by the unbalanced force ratio (UFR) and moment index. Moment index, proposed herein, was designed to indicate the relative magnitude of unbalanced moments. Larger unbalanced forces and moments, measured by UFR and moment index respectively, indicate larger inertial effects, and being further away from quasi-static conditions. Two samples with different particle size distributions (PSD) were tested in triaxial compression simulations under drained conditions using both damping models and various damping ratios at different strain rates. The damping ratios that resulted in the best equilibrium, so-called optimum damping ratios, were determined and typical values were suggested for each model. Applying damping ratios greater than the optimum values reduced the kinetic energy however worsened the equilibrium of particles by adding to unbalanced forces and moments. With the optimum damping ratios and at an equal loading rate, the new damping model proved superiority over global mass-damping by establishing better force and moment equilibriums while providing the same mechanical response. The new damping model allows application of higher strain rates for quasi-static simulations, consequently leads to shorter runtimes, especially for samples with wide PSDs.     

Adsorption of reactive dyes on calcined alunite from aqueous solutions

An attempt to alleviate the problem caused by the presence of reactive dyes in textile effluents was undertaken. Since alunite is a very abundant and inexpensive, we decided to experiment with it as a potential adsorbent for a certain type of the supracited pollutants used in cellulose fibers dyeing. The adsorption of Reactive Blue 114 (RB114), Reactive Yellow 64 (RY64) and Reactive Red 124 (RR124) by calcined alunite was studied by varying parameters such as the calcination temperature and time, particle size, pH, agitation time and dye concentration. Acidic pH was favorable for the adsorption of RB114 and alkaline pH was favorable to both RY64 and RR124. The equilibrium data fit the Langmuir isotherm. The adsorption capacities were found to be 170.7, 236 and 153 mg dye per gram of calcined alunite for RB114, RY64 and RR124, respectively. The pseudo first- and second-order kinetic models were used to describe the kinetic data, and the rate constants were evaluated. The experimental data were fitted by the second-order kinetic model, which indicates that chemicalsorption is the rate limiting step, inside of mass transfer.     

Molecular dynamics simulation of polarizable carbon nanotubes

This paper is aimed to develop a modified force field for molecular dynamics (MD) simulations of polarizable carbon nanotubes (CNTs). The effects of electrical polarization and the associated electronic degrees of freedom are represented by a network of negative charged shell particles which move relative to the surrounding positively charged carbon atoms in response to an applied electric field. In this setting, the negative and positive charges are exactly balanced so that the total system remains electrically neutral, and the motion of the shell particles relative to their equilibrium positions leads to polarization within the nanotube. Potential applications of the proposed model include simulations of controlled translocation of ions, water and polymers through solid-state CNT membranes.     

Effects of thoron on a radon detector of pulse-ionization chamber type

A radon detector of pulse-ionization chamber (PIC) type could have some sensitivity for thoron. Thus, the presence of thoron could interfere with precise measurement of radon. In the present study, effects of thoron on the most common type of PIC detector (commercial name AlphaGUARD) were investigated using an exposure chamber. The AlphaGUARD was exposed to a mixture of radon and thoron, together with a radon/thoron discriminative monitor that employs a silicon solid-state detector. The thoron sensitivity of the PIC detector was estimated by comparing the two detectors. As a result, the thoron sensitivity was about 10% compared with the radon sensitivity. In other words, the radon concentration (Bq m(-3)) measured with the PIC detector was approximately the sum of the actual radon concentration (Bq m(-3)) and 10% of the thoron concentration (Bq m(-3)). The sensitivity to thoron should be considered in measurements in thoron-enhanced areas.     

Multiscale simulations: application to the heat transfer simulation of sliding solids

Molecular dynamics is a powerful tool allowing the simulation of matter behaviour at the atomic scale. Due to computation time, it is clearly not possible to use molecular dynamics to simulate a forming process. However, atomistic simulations can be used to study and understand the physical phenomena that occur during matter deformation. As an example, heat transfer between the contacting solids in forming processes is one of the important physics phenomena that have to be taken into account in order to do realistic simulations. A multiscale analysis of heat transfer is presented. This analysis leads to two kinds of models: a macroscopic model which can be used for the simulation of the process itself and a microscopic model that is used to determine the parameters of the macroscopic model. In this microscopic model, the friction heat generation phenomena has to be described quite accurately. Friction heat is mainly due to plastic and elastic deformation and adhesion. Thus, to understand the underlying friction heat generation phenomena, atomistic simulations using molecular dynamics are carried out. It is shown that friction heat is the transformation of mechanical work given to the system at the macroscopic scale into potential energy during elastic deformation. This potential energy which is stored in the system is finally transformed into atomic kinetic energy (friction heat) during plastic transformation.     

Kinetics of the biodegradation of green table olive wastewaters by aerobic and anaerobic treatments

The biodegradation of the organic pollutant matter present in green table olive wastewater (GTOW) is studied in batch reactors by an aerobic biodegradation and by an anaerobic digestion. In the aerobic biodegradation, the evolution of the substrate (in terms of chemical and biochemical oxygen demand), biomass, and total polyphenolic compounds present in the wastewater are followed during the process, and a kinetic study is performed using Contois' model, which when applied to the experimental results provides the kinetic parameter of this model, resulting in a modified Contois' equation (q=3.3S/(0.31S(0)X+X), gCOD/gVSS d(-1)). Other kinetic parameters were determined: the cellular yield coefficient (YX/S=5.7x10(-2) gVSS/gCOD) and the kinetic constant of cellular death phase (kd=0.16 d(-1)). Similarly, in the anaerobic digestion, the evolution of the substrate digested and the methane produced are followed, and the kinetic study is conducted using a modified Monod model combined with the Levenspiel model, due to the presence of inhibition effects. This model leads to the determination of the kinetic parameters: kinetic constant when no inhibitory substance is present (kM0=8.4x10(-2) h(-1)), critical substrate concentration of inhibition (TP*=0.34 g/L) and inhibitory parameter (n=2.25).     

Rapid free-vibration analysis with model reduction based on coherent nodal clusters

Modal expansion is a workhorse used in many engineering analysis algorithms. One example is the coupled boundary element-finite element computation of the backscattering target strength of underwater elastic objects. To obtain the modal basis, a free-vibration (generalized eigenvalue) problem needs to be solved, which tends to be expensive when there are many basis vectors to compute. In the above-mentioned backscattering example it could be many hundreds or thousands. Excellent algorithms exist to solve the free-vibration problem, and most use some form of the Rayleigh-Ritz (RR) procedure. The key to an efficient RR application is a low-cost transformation into a reduced basis. In this work, a novel, inexpensive a priori transformation is constructed for solid-mechanics finite element models based on the notion of coherent nodal clusters. The inexpensive RR procedure then leads to significant speedups of the computation of an approximate solution to the free vibration problem.     

Low cost removal of reactive dyes using wheat bran

In this study, the adsorption of Reactive Blue 19 (RB 19), Reactive Red 195 (RR 195) and Reactive Yellow 145 (RY 145) onto wheat bran, generated as a by-product material from flour factory, was studied with respect to initial pH, temperature, initial dye concentration, adsorbent concentration and adsorbent size. The adsorption of RB 19, RR 195 and RY 145 onto wheat bran increased with increasing temperature and initial dye concentration while the adsorbed RB 19, RR 195 and RY 145 amounts decreased with increasing initial pH and adsorbent concentration. The Langmuir and Freundlich isotherm models were applied to the experimental equilibrium data depending on temperature and the isotherm constants were determined by using linear regression analysis. The monolayer covarage capacities of wheat bran for RB 19, RR 195 and RY 145 dyes were obtained as 117.6, 119.1 and 196.1 mg/g at 60 degrees C, respectively. It was observed that the reactive dye adsorption capacity of wheat bran decreased in the order of RY 145>RB 19>RR 195. The pseudo-second order kinetic and Weber-Morris models were applied to the experimental data and it was found that both the surface adsorption as well as intraparticle diffusion contributed to the actual adsorption processes of RB 19, RR 195 and RY 145. Regression coefficients (R2) for the pseudo-second order kinetic model were higher than 0.99. Thermodynamic studies showed that the adsorption of RB 19, RR 195 and RY 145 dyes onto wheat bran was endothermic in nature.     

Initial stage of gas discharge in an inhomogeneous electric field

A model of the initial stage of gas discharge has been developed within the framework of the particle in cell (PIC) method, with allowance for the space charge and particle collisions described using the Monte Carlo (MC) numerical simulation technique. The PIC/MC simulations of the initial stage of discharge under conditions of the electric field strength to gas pressure ratio E/P > 1 kV/(cm Torr) showed that a beam of runaway electrons is formed within ∼10 ps near the cathode, which consists of both emitted electrons and those generated as a result of the gas ionization. The duration of the beam pulse is determined primarily by plasma screening of the external electric field near the cathode and amounts to 10–20 ps.