Evaluation of cross-stream sample cutters using three-dimensional discrete element modelling

The quality of samples taken by cross-stream sample cutters has been investigated using three-dimensional DEM models. The sample configurations investigated here are full-size high-flow-rate configurations typical of mineral and bulk materials applications. Detailed quantitative information on overall extraction ratios, size specific extraction ratios, missed and extra sample components can be made by comparing a reference sample to the actual sample. A key advantage of using this modelling approach over physical experimentation is that the reference sample can be measured on precisely the same portion of the stream of material as the actual sample, thereby allowing the elimination of a significant fraction of the variability and allowing statistically significant results to be obtained using many fewer replicates. Quantitative analysis of results broadly supports the commonly used rule that the cutter aperture should be at least three times the nominal topsize of the material being sampled, but does not support the commonly used rule requiring increase in cutter aperture if the cutter speed exceeds 0.6 m/s. It also provides some insights into linkages between the nature of the flows through this sampling equipment and the nature of the samples obtained.     

Sampling of cohesive bulk materials by falling stream cutters

DEM has proved to be a useful method for analysing sample bias for falling stream cutters. It provides detailed information on bias and size-dependant extraction ratios based on closely matched reference and actual samples taken from the same simulations. It has allowed the identification of operational and design parameters which influence sample cutter performance and bias. To date, only cohesionless bulk materials have been considered. Wet bulk materials typically become sticky and this strongly influences their flow behaviour and particularly the mobility of fine particles and the overall flowability of the material. The inclusion of cohesion in DEM simulation of flow from a head pulley shows that the falling stream breaks up into large fragments that move as rigid bodies. The size of these fragments depends on the degree of cohesion. The effect of cohesion on sampler performance is explored. No statistically significant bias was observed with increasing cohesion level even though the extraction ratio was observed to decline. The effect of cohesion for different aperture sizes of the cutter was also investigated. As the cutter becomes narrower the extraction ratio declines sharply. However, even for a cutter of aperture twice the particle top size (which would be highly biased for a cohesionless material) no bias was detectable. For cohesive materials the extraction ratio no longer correlates with sample bias. Cohesion improves sample cutter performance by restricting the ability of different size fractions to move independently in the congested flow region that forms at the cutter opening.     

Testing the validity of the spherical DEM model in simulating real granular screening processes

We investigate the flow of a granular material over a vibrated horizontal screen. We perform a direct quantitative comparison, across a range of operating conditions, between laboratory scale experiments and simulations using the discrete element method (DEM). We test the extent to which the commonly employed DEM approximation of particles being spherical affects the ability of the model to realistically reproduce the behaviour of industrial screening systems where the particles are generally non-spherical in shape.The simulation geometry and input particle size distribution are set up to exactly match the experimental system, which consists of a horizontal screen with a wire mesh cloth onto which quarry rock is fed at a series of input flow rates. The screen is vibrated, causing the granular bed to flow over the deck and vertically stratify with finer material passing through the screen, where it is collected in a series of bins located along the length of the screen. The size distribution of the material flowing through each section of the screen is found by analyzing the contents of each collection bin.The best agreement is found for very low flow rates, where the vast majority of the below aperture size material is rapidly captured just after it enters the screen in both the simulation and experiment. At higher flow rates, significant quantitative errors are found with the over-prediction of the flow rate through the screen for near grate sized particles. This is attributed to the higher rate of percolation through the bed and the easier capture by the screen surface of the spherical shaped material. The near aperture sized spherical particles also show a very strong tendency to peg the screen, becoming trapped in the screen openings and limiting further flow through those parts the screen. The use of spherical particles in the DEM simulation of vibrating screens is therefore found to be inadequate for modelling realistic flow and separation of particles that are not actually spherical.     

Classical latent variable models for medical research

Latent variable models are commonly used in medical statistics, although often not referred to under this name. In this paper we describe classical latent variable models such as factor analysis, item response theory, latent class models and structural equation models. Their usefulness in medical research is demonstrated using real data. Examples include measurement of forced expiratory flow, measurement of physical disability, diagnosis of myocardial infarction and modelling the determinants of clients' satisfaction with counsellors' interviews.     

CaO制备及悬浮态下对CO2吸收率的影响

通过煅烧的方法得到氧化钙二氧化碳吸收剂,将碳酸化反应放入高温悬浮炉中进行颗粒特性研究,结果表明,在悬浮炉中的吸收剂微观结构对吸收剂的吸收率的变化规律与热重中相同,即吸收剂的微观结构影响着吸收剂的吸收率,具有大量小孔径,比孔容积大,累积比表面积大的吸收剂颗粒具有更好的吸收效果。     

一体化机热裁刀改造

主要探讨和研究了一体化机三角胶的裁断方式。从一体化机最容易出现问题的裁刀部分出发，对几种较为常用的三角胶裁断方式进行洋细的分析和对比，对现行的一体化机进行热裁刀改造，提高了三角胶断面的贴合精度和一体化机的生产效率。     

Attrition and abrasion models for oil shale process modelling

As oil shale is processed, fine particles, much smaller than the original shale, are created. This process is called attrition or, more accurately, abrasion. In this paper, models of abrasion are presented for oil shale processed in several unit operations. Two of these unit operations, a fluidized bed and a lift pipe, are used in the Lawrence Livermore National Laboratory hot recycle solid (HRS) process being developed for the above-ground processing of oil shale. Abrasion occurs so commonly in the handling and processing of paniculate materials that numerous studies have been conducted to characterize the phenomenon and to attempt to minimize it. In the review of the literature, materials which have been studied for attrition potential are examined, as are the specific unit operations for which either experimental or modelling studies have been conducted. Several papers are discussed in which attrition in fluidized beds or lift pipes is addressed. In this paper, empirical models are derived for the processes occurring in the HRS process from the experimental studies conducted on oil shale. The derived models are presented, as are comparisons with experimental results.     

Relationship of refractive index to mass density and self-consistency of mixing rules for multicomponent mixtures like ambient aerosols

This paper focuses on two important yet poorly addressed aspects of ambient aerosols: relationship of refractive index to mass density (index–density relationship) and consistency of the mixing rules used to calculate these two quantities of a multicomponent mixture like ambient aerosols with the index–density relationship. Combined empirical and theoretical analyses show that a denser material generally tends to have a larger refraction index because the applied electric field induces a greater number of electric dipoles, and that the index–density relationship can be described reasonably well by the Lorentz–Lorenz relation. It is shown that the commonly used volume–mean mixing rule for calculating the effective mass density, the Lorentz–Lorenz mixing rule and the molar refraction mixing rule for calculating effective refractive index form a set of mixing rules that are consistent with the Lorentz–Lorenz relation. The molar fraction mixing rule and the Lorentz–Lorenz mixing rule are shown to be equivalent for the Lorentz–Lorenz mixture while the linear volume-mixing rule is an approximation of the Lorentz–Lorenz mixing rule for quasi-homogeneous mixtures wherein the refractive indices of the constituents do not differ much. The results highlight the need for consistency of the mixing rules for calculating the effective refractive index and mass density with the index–density relationship, which not only provides a theoretical guide for judiciously choosing the mixing rules to calculate effective properties of ambient aerosols but also poses new challenges to develop an effective medium theory that applies to more than one quantity. An empirical power-law expression is obtained from the published data that relates the effective specific refractive index to the effective mass density of aerosol particles.     

盾构推进和地表沉降的变化关系探讨

根据上海某超长盾构隧道工程监测的实践,介绍了盾构隧道监测的一般内容:地表沉降和地下管线安全监测;地面房屋沉降和倾斜观测;水位测试;土体水平位移监测和局部地段隧道沉降、净空收敛监测。并从几个方面对监测数据作了详细的分析,得出了盾构推进方向和隧道纵向的沉降变化及隧道横向沉降槽的变化规律,同时分析了盾构切口距建筑物沉降点距离和沉降量的关系,最后得出了盾构推进和地表沉降的变化规律,提出了地表沉降的5个阶段,即:前期沉降阶段;开挖面前的隆沉;通过期间沉降阶段;盾尾间隙沉降阶段和后期沉降阶段。     

基于改进即时学习算法的湿法冶金浸出过程建模

针对湿法冶金浸出过程中存在的多变量、非线性和多工况等问题,采用基于即时学习算法的最小二乘支持向量机建立浸出率的预测模型。将时间有序性引入到即时学习算法学习集的选取规则中以确定系统当前工作点的建模邻域,从而提高模型精度;引入累计相似因子以提高所建模型的实时性,并利用自适应相似度阈值来判定是否需要重新建立当前工作点的局部模型。将改进的建模方法应用到湿法冶金浸出过程浸出率的预测中,仿真结果表明,所建模型具有较高的精度和实时性,可用于湿法冶金工业生产过程。     

Dimensional modelling of wood pyrolysis using a nodal approach

New gasification installations and techniques are being tested today but they all struggle with mainly the same drawbacks such as removal of various pollutants in the producer gas or clogging of material pathways.This work is oriented on developing a new model for the non-oxidative pyrolysis step of a gasification process as a part of a wider research conducted on the overall gasification of wood waste. A batch reactor is modelled by means of nodal modelling, a technique widely used for simple heat transfer processes. Additionally to the heat transport inside the batch reactor the model uses a simple and versatile generic chemistry and simplified mass transfer principles. Thermal data from modelling is compared with data obtained from an experimental batch pyrolysis reactor using wood sawdust and cutter shavings. Experimental and theoretical results regarding thermal phenomena are in good agreement.     

Influence of the nanoaerosol fraction of industrial coal dust on the combustion of methane–air mixtures

The mechanism of formation of nanosized aerosol particles during mechanical grinding of coal from Kuzbass mines is studied. The concentration and size spectrum of aerosol particles in a mine tunnel during cutter operation were measured using an aerosol spectrometer. It is found that 90% of the particles are less than 200 nm in size. In the nanometer range, there are two peaks corresponding to average diameters of 20 and 150 nm, the first of which is due to single particles, and the second to aggregates consisting of single particles. The formation of aerosol during mechanical coal grinding in a continuous flow mill was studied. The spectrum and morphology of the particles produced in the laboratory mill are in qualitative agreement with those for the nanoaerosol formed in the mine. The influence of the coal aerosol on the combustion of gas mixtures was studied. Laboratory experiments showed that the presence of the nanoaerosol in a lean methane–air mixture significantly increased its explosibility. This was manifested in an increase in the maximum pressure and a significant increase in the pressure rise rate during explosion. The study leads to the conclusion that the nanoaerosol is formed from the organic coal components released into the gas phase during local heating of coal on the cutter teeth.     

新型Ti(C,N)基金属陶瓷刀具的磨损性能

金属陶瓷由于具有优良的综合性能而广泛用作刀具材料.本文研究了纳米TiN改性TiC基金属陶瓷刀具的组织及其在加工正火态45号钢时的磨损性能.结果表明,与传统金属陶瓷相比,新型金属陶瓷的组织更细小.与传统金属陶瓷刀具、Al2O3刀具及YT15硬质合金刀具相比,新型金属陶瓷刀具具有更高的刀具寿命和切削效率,且主要以"磨损"形式失效.     

(AlCrNbSiTiV)N高熵合金氮化薄膜溅镀参数的灰关联分析优化

采用直流反应式磁控溅镀法在硅晶片和住友刀具BN2000上制备(AlCrNbSiTiV)N高熵合金氮化薄膜。通过正交试验考察了溅镀功率、沉积温度、氮氩气流量比和基材偏压对薄膜的摩擦因数、硬度和刀具磨损的影响。对信噪比进行灰关联分析,以实现多目标优化,得出最佳工艺参数为:溅镀功率200 W,沉积温度200℃,氮氩气流量比0.3,基材偏压-100 V。该条件下所得薄膜的摩擦因数为0.46,显微硬度为1 243.72 HV,刀具磨损最小。     

基于CFD⁃DEM的水下切粒装置水室内颗粒流动过程数值模拟

基于CFD?DEM耦合方法,研究了颗粒在水室内的流动状态,分析了不同刀盘转速、粒子水通入量和水室出口角度对造粒过程的影响,发现提高刀盘转速、增加粒子水通入量和水室出口倾斜一定的角度都有利于水室内颗粒的排出。进一步研究了颗粒与碎屑在水室内的流动,发现在水室出口处二者的流动基本呈现出一定的分离角度。     

Analysis of Vezin sampler performance

Vezin samplers are used to take a small fraction of a stream of material which is intended to be representative of all the material. Discrete Element Modelling (DEM) is used to investigate the effects of design, operating and material property factors on the extraction ratio and sample properties and to understand the mechanisms that can lead to sample bias when using a Vezin. This modelling suggests that this type of sampler performs very well giving a very good extraction ratio and negligible sample bias over a wide range of conditions.     

偏差加权协调预测控制算法研究

提出适用于瘦系统的偏差加权协调控制算法，并且分析其参数确定方法和稳定性。实际应用表明该算法能实现平稳过渡．控制效果良好。     

湿法脱硫旋流喷嘴雾化粒径空间分布规律

应用于湿法脱硫的旋流喷嘴孔径较大,其雾化粒径在空间上存在一定分布规律,不同于其他领域。这个规律的存在直接影响该类喷嘴本体设计和脱硫塔雾化系统设计。试验利用马尔文激光粒径分析仪,对旋流喷嘴雾化粒径空间分布规律进行了系统研究,为便于分析定义了平均粒径、粒径相对离差和单流量粒径分布平均范围。试验结果表明,大孔径旋流喷嘴的雾化粒径和雾化粒径分布随流量和流出位置的不同均呈现一定的变化规律;各流量下,在与来流夹角90°处,粒径相对离差最大,Sauter平均粒径波动较大,粒径分布范围和粒径分布平均范围均最小,这说明该处分散度小,雾化均匀性好;平均粒径与压力呈幂函数关系;单流量粒径分布平均范围与压力呈线性关系。     

Cut-and-Paste of DNA Using an Artificial Restriction DNA Cutter

DNA manipulations using a completely chemistry-based DNA cutter (ARCUT) have been reviewed. This cutter, recently developed by the authors, is composed of Ce(IV)/EDTA complex and two strands of pseudo-complementary peptide nucleic acid. The site-selective scission proceeds via hydrolysis of targeted phosphodiester linkages, so that the resultant scission fragments can be easily ligated with other fragments by using DNA ligase. Importantly, scission-site and site-specificity of the cutter are freely tuned in terms of the Watson–Crick rule. Thus, when one should like to manipulate DNA according to the need, he or she does not have to think about (1) whether appropriate “restriction enzyme sites” exist near the manipulation site and (2) whether the site-specificity of the restriction enzymes, if any, are sufficient to cut only the aimed position without chopping the DNA at non-targeted sites. Even the human genome can be manipulated, since ARCUT can cut the genome at only one predetermined site. Furthermore, the cutter is useful to promote homologous recombination in human cells, converting a site to desired sequence. The ARCUT-based DNA manipulation should be promising for versatile applications.     

BIAS CALCULATIONS FOR ADAPTIVE URN DESIGNS

A clinical trial model is considered in which two treatments with immediate binary responses are to be compared. An adaptive urn design is used to assign patients to the treatments. The bias and variance of the maximum likelihood estimators of the probabilities of success are derived by differentiating the fundamental identity of sequential analysis. By embedding the design in a continuous-time process, probability generating functions are then calculated to obtain approximations for the bias and variance. Simulation is used to assess the accuracy of the approximations. It is shown that the bias cannot be ignored, and that the adaptive rules which are subcritical in nature have the most mathematically tractable bias and are the least variable. Methods for correcting for the bias are also addressed.