The Application of Fractal to Submicron Particle Sizing

Brownian Motion is one of the important characteristics of submicron particles.On the basis of observatiorl for Brownian motion of particles,the authors present a medel to describethis physieal process by usin g fractal theory a nd this medel is proved to be valid in theory.Throughfurther an alyzing,we establish the relationship between fractal characteristics and particle sizeparameters.Combining image signal processing technique,particle size information can be obtainedby computing fractal dimension values,and then a new method for particle sking will be developedinfuture.     

The Mechanism Analysis of Anti clogging Arching Structure in Dredged Sludge

A number of lands were occupied by discarding the dredged sludge in the yard as waste materials.The Aeration Vacuum rapid Mud Water Separating (AVMWS) technique was appropriate for discarding yard with high water content and high clay particle content sludge.This technique could quickly reduce the volume of the sludge and accelerate the turnover use of the yard.In addition,the technique could overcome the clogging problem when pumping water from high water content, high clay particle content dredged sludge.Through the sampling particle size distribution tests after AVMWS and conventional vacuum pumping model tests, it was found that in the AVMWS tests the fine grained soil run off, coarse particles accumulated, and arching structure layer was formed.However, in the conventional vacuum pumping tests, fine particles did not lost and there was clogging without arching structure layer.The layer could protect the internal loss of the fine particles and ensure a high permeability of the soil at the same time.And the mechanism was explained as well.     

CFD-DEM Simulation to Study the Filtration Characteristic of the Fine Particle in the Filter Media

The gas-solid two-phase flow characteristics of fine particles in the filter media were simulated based on CFD-DEM (Discrete Element Method) in this study, and the particle group, particle size distribution, and the rebound effect between particles, particle and fiber were taken into account the calculations. Additionally, the movement characteristics of the particle group and the deposition form of the fine particles in the fibrous filtration were analyzed. The results indicate that it is convenient and feasible to simulate the filtration process of the filter media as well as the deposition process and form of the fine particle on the media surface using CFD-DEM, and the simulation results are consistent with the experimental observations in the literature. The surface filtration has larger contribution to the filtration process, and most of the particles are captured by the media surface. Meanwhile, parts of smaller particles that enter into the media are captured by the depth filtration. A larger number of particles are collected by the particle-particle capture mechanism. The filtration efficiencies of the filter media are varied with the particle systems, and for the model of the filter media in this study, the filtration efficiency of the multi-particle system is about 20% higher than that of the single-particle one.     

Investigations of the particle motion characteristics in the gas solid two phase wake of leeward side circular cylinder

This paper investigates the characteristics of the particle motion in circular cylinder wake flow of leeward side by simulating the micro particle flow around circular cylinder using Euler two fluid model combined with Reynolds stress model. It compares the particle velocity and concentration of different particle size in the leeward area. The results show that the vortex is formed after the gas flowed passing the cylinder, and the concentration and velocity of particles are affected by the turbulent intensity in the leeward side. Gas entrainment vortex and particles own inertia decide the flow form of fine particle around the cylinder. Both effects impact the particle concentration distribution of different size particles in the leeward area. With the increase of particle size, the particle concentration increases at the beginning and then decreases in the leeward area.     

填充床中细小颗粒渗流行为的DEM模拟

为进一步探索COREX过程固体物料的运动状态,对COREX过程中涉及到的细小颗粒渗流行为进行了DEM模拟。考察不同颗粒直径比、阻尼系数及滑动摩擦系数对细小颗粒渗流行为的影响,特别是计算得到不同模拟参数下细小颗粒在填充床内的运动轨迹。模拟结果显示,渗流过程中细小颗粒的平均渗流速度为一定值。随着颗粒直径比的增加,颗粒竖直方向的渗流速度逐渐减小,停留时间与径向弥散逐渐变大。随着颗粒间阻尼系数的增加,颗粒渗流速度逐渐增加,停留时间逐渐减小,径向弥散逐渐变小。滑动摩擦系数对细小颗粒的渗流行为影响较小。从细小颗粒运动轨迹分析可知,颗粒直径比变大时,细小颗粒易在空隙中缓慢移动,易趋于静止床层中,导致颗粒沉积。随着颗粒间阻尼系数变小,颗粒运动轨迹向填充床边缘发展,偏离床层中心。     

离散元法在农业工程领域的应用进展

简述了离散元法在农业工程领域方面的研究成果,根据离散元法在农业工程领域的不同应用,分别讨论了离散元法在土壤散体颗粒、农业物料颗粒、多相流中单相介质的应用研究现状,指出了存在数量级受限,颗粒模型不精准,复杂工况制约等问题。提出今后离散元法的研究趋势:开发农业工程领域的专用离散元软件,提高颗粒群的运算效率;通过准确获取物料的细观参数,从理论基础上完善接触模型,使仿真颗粒与真实颗粒更为接近;通过离散元法软件与其他软件耦合,结合API的二次开发,拓宽离散元法在复杂散体颗粒运动仿真的应用。     

Chemical amelioration of surface crusting to reduce runoff and erosion on highly weathered soils

Because of the very low soil solution ionic strengths in highly weathered soils, clay particles can be readily dispersed under the impact of raindrops. The clay fraction of many soils is dispersible under the combined effects of mechanical disturbance and low electrolyte concentration. This clay dispersion results in fine particle segregation at the soil surface, with clay particles moving into and blocking soil pores resulting in the formation of a highly impervious crust which reduces infiltration. Because the clay is dispersed, the particles usually orient themselves in a laminar fashion as they settle. As a result, runoff is substantially increased, giving rise to soil erosion. The crusts formed in this manner often have very high strengths which prevent or substantially reduce crop emergence. The formation of such crusts can be prevented by the application of relatively low rates of by-product gypsum such as phosphogypsum on the soil surface which produces sufficient electrolyte in solution during raindrop impact to maintain the clay particles in a flocculated condition. The results of a number of experiments in which different soils were treated with phosphogypsum are discussed to illustrate the effects of electrolyte concentration, level of sodium and other factors on the formation of surface crusts and the consequent runoff and erosion. As a result of the application of phosphogypsum to the soil surface, a laminar orientation of clay particles at the surface is prevented, which allows a much greater proportion of the rainfall to enter the soil. Any crusts formed are thus much weaker and do not reduce seedling emergence. This type of crust formation can also be prevented by reducing raindrop impact through the use of mulches. This phenomenon occurs on many soils not normally considered to suffer from chemically-induced physical problems, which points to the importance of considering chemical as well as physical processes in the evaluation of potential runoff and erosion.     

基于Weibull模型的细粒尾矿粒径分布

尾矿细粒化是矿业发展趋势,细粒尾矿的粒径分布对尾矿宏观力学特性及坝体稳定性具有重要影响。采用筛分法和沉降法,对82个尾矿试样进行了颗分试验,建立了细粒尾矿粒径分布的Weibull函数模型。试验结果表明:细粒尾矿粒径呈"细多粗少"的分布规律,这种规律服从Weibull分布,可以用Weibull分布对粒径分布进行描述和外推预测;传统分形模型中假设每级粒度的破碎率为常数与实际情况不符,Weibull分布可以看作对分形模型误差的一种修正;在破碎过程中,粒径的概率密度分布会出现峰值,这个峰值不断向粒径小的方向偏移,最终形成"细多粗少"的分布特点。研究结果有助于磨矿工艺的改进,并可以为土工试验做出科学的级配方案提供参考。     

筒仓中入粮自动分级的动力学分析及缓解措施研究

简述了自动分级在筒仓储粮中的危害。依据动力学原理,建立了颗粒下落的动力学方程,并推导出颗粒下落深度与飘移距离之间的关系方程。通过计算得出颗粒的水平飘移距离随着下落深度的增加而增加;在筒仓内的同一下落深度,颗粒水平飘移距离随着密度的增加而减小;在筒仓内的同一下落深度,颗粒水平飘移距离随着半径的增加而增加。针对颗粒飞行的动力学特性,提出了几种缓解自动分级的措施。     

Splash-saltation transport under wind-driven rain

Soil detachment and transport by wind- driven rain differs from that by rainless wind and from that by windless rainfall. This study deals with field measurements of particle movement during periods in which rain and wind coincide. The effect of rainfall on the movement of soil particles by wind is analyzed using a sediment sensor called SALTIPHONE. Some results are presented of field experiments at two sites in the Netherlands: a cutover peat soil and a beach sand. Results show an increase of particle movement at the sensor height during rainfall. This can be attributed to the combined action of saltation and rain-induced uplift of soil particles and subsequent transport by wind.     

In situ distribution of suspended matter during the tidal cycle in the elbe estuary

In situ size of suspended particles was measured with an underwater photographic system in the Elbe estuary. The data from the measurements at a stationary position indicate that the formation of large flocs took place at low current velocities and that the size distributions varied with the tidal cycle as a consequence of flocculation, deposition and resuspension processes.Flocculation of suspended particles in the estuary is interpreted as a dynamic process: the size of flocs changes with time and their distribution depends on the rates of aggregation and disaggregation of the particles. This is related to physical factors of which turbulence and differential particle settling play key roles in producing large flocs. Fluid shear is responsible for disaggregation of large flocs. Salinity and the organic content of particles may affect flocculation processes with respect to the particle cohesive interaction, but they have no critical effect on the variation of floc size during the tidal cycle in the estuary.     

Mechanical Response Characteristics of the Earth Pressure Cell in Sand

Sand is a typical particle structure. The effective stress and corresponding deformation are both determined by the particle characteristics of the medium skeleton, and the changeable condition of the particles will further affect the mechanical response of the earth pressure cell in the test process. To correctly measure the earth pressure value, micromechanical method was applied to analyse the force chain formed by the particles contact under loading unloading condition, and the transferring process, the force strain curve and relationship between the cell mechanical response and the ideal response curve were analyzed in detail, which verified the above mechanical response model based on Particle Flow Code (PFC) method. According to the structural characteristics of the sand and above numerical model, the loading condition, porosity, friction coefficient between the particles and stiffness of the earth pressure cell affecting mechanical response of the earth pressure cell were deeply investigated, the numerical results indicated that there were obvious hysteresis and strain irreversibility for the response curve, and the measured value was sensitive to the above factors. Therefore, research on the force chain structure and corresponding evolution law brings forward a scientific base and new research means for understanding its micromechanical characteristics, and different factors influencing the earth pressure cell are also important for cell calibration and practical monitoring to get more correct earth pressure value.     

弹性波作用下渗流多孔介质微粒运移分析

弹性波作用下渗流多孔介质微粒运移分析是对目前静态流体或稳态多相渗流中微粒运移/捕集的补充,通过分析弹性波对微粒剥离运移捕集过程的影响,建立弹性波作用下微粒运移模型,得到对微粒运移效果和储层物性变化的影响规律。由推导得到的弹性波作用下微粒剥离临界速度可知,当微粒与孔喉半径的比值越小时弹性波导致的振荡附加力影响越大,临界速度与流体粘度、微粒/孔喉半径比成负相关,与基质胶结程度、结构力、微粒半径、微粒密度成正相关。弹性波作用下微粒运移模型需同时考虑多孔介质渗流速度的变化,此时微粒剥离释放速率增加,但随着波衰减和时间延长而降低,微粒在孔隙表面沉积滞留速率先上升后下降,喉道堵塞的速率有所上升,说明弹性波作用下微粒的剥离和悬浮能力增加,但亦增加了微粒在微细孔喉"架桥"堵塞的可能性。研究结论对岩石物理学和工业化波动处理涉及的储层物性研究具有一定指导意义。     

转基因油菜研究进展

随着分子生物技术研究的快速发展,油菜的遗传转化研究日趋成熟。2003年,转基因油菜在全球种植面积为352万公顷。油菜基因工程研究的重点主要放在转化的目的基因、筛选标记、再生体系的建立和遗传转化方法方面。目前油菜已建立了子叶、下胚轴、茎段、原生质体培养、小孢子培养的再生体系;用于油菜基因转化的方法有根癌农杆菌介导法、基因枪法、PEG法、激光微束穿刺法、显微注射法和花粉介导法等。在油菜转基因中所转化的目的基因趋于多样化,如:品质改良、抗病、抗逆、不育基因等;较常用的筛选标记基因是新霉素磷酸转移酶基因(NPTII);本文主要从油菜转基因的再生体系建立、筛选标记及转化方法方面进行综述,并对油菜转基因上存在的问题及前景进行了探讨和展望。     

Numerical simulation of gas solid characteristics in double inlet square cyclone separator

This paper uses RSM turbulence model to conduct the numerical simulation on the gas flow field in double inlet square separator and calculate the velocity field and pressure distribution in the seperator. At the same time, it simulates the solid particle trajectories in the separators using Lagrangian model. The results show that the velocity field and pressure distribution in double inlet square separator have good symmetry, but the flow swirl intensity is insufficient and easy to decay; different sizes and different injection locations bring significant differences for the particle trajectories; injecting small particles can be easy to form flow short-circuit phenomenon inside the separator, injecting particles near the top of separator can be easy to form top ash ring phenomenon inside the separator; these phenomena have adverse factors to the separation efficiency. When the separation cylinder corners of square separator are changed into cutting-shaped chamfers, the flow field in the separator can be improved, and the separation efficiency of separator can be effectively improved.     

许昌市街道灰尘粒度特征及其来源分析

为获得许昌市街道灰尘的粒度特征和判断其主要来源,利用Mastersizer 2000激光粒度分析仪对2012年3月采集的许昌市街道灰尘样品进行粒度分析。结果表明,许昌市街道灰尘以粉砂为主,其次是砂粒,粘粒含量最少。粒度呈三峰型尖锐曲线,第1众数为30~145μm,第2众数为4~15μm,第3众数为0.5~1μm,平均粒径在25.42~236.15μm,分选性差,负偏。许昌市街道灰尘粒度分布与现代尘暴降尘的粒度分布模式相似,说明许昌市街道灰尘沉积是风积作用的继续,即街道灰尘主要是由低空季风环流产生的粗粒粉尘和由西风环流控制细粒粉尘混合搬运的结果,同时建筑工地就地起源的粗颗粒物质导致部分样品粒径偏大,反映出建筑行为对街道灰尘的贡献。     

METAL MATRIX PARTICULATE COMPOSITES BY SPRAYING CODEPOSITION

The spraying codeposition process is used to produce metal matrix paniculate composites, whose technical procedure and main processing parameters are analyzed. The microstructure of the composites is examined and the properties are tested. The solidification characteristics in the spraying deposition and solidification process are discussed. The results indicate that several problems involved in conventional methods can be overcome with this technique to preduce metal matrix paniculate composites. The reinforce particles are dispersed in the matrix homogeneously without solidification segregation. Compared with the matrix alloy,the composite proves to be harder and has excellent wear resistance.     

Evolutionary topology optimization of the lower stable of a hydraulic press

It is difficult to obtain the globe optimum solution by applying conventional sizing and geometrical optimization methods. Evolutionary topology optimization is conducted for the lower stable of a hydraulic press using a bi directional evolutionary structure optimization (BESO) method based on ratio of stress changes, and the evolutionary history and index are analyzed. The presented algorithm obtains the simultaneous optimization on both geometry and topology, and a new topology of the lower stable of the press is evolved which possesses a reasonable topological structure. The results of finite element analysis show that the new structure has decreased maximum stress, uniform stress distribution and good material usage.     

普洱茶多糖的提取及降血糖的研究

本试验从云南大叶种晒青毛茶经潮水渥堆做成的普洱茶中,提取茶叶多糖,通过分离、纯化得到纯品茶多糖（TPS）,配制成不同浓度的茶多糖溶液,以研究测定其对小鼠降血糖效果的差异;在动物活体试验中共设四组：正常对照组、糖尿病（DM）模型对照组、糖尿病80mg/kg/d剂量注射组、糖尿病160mg/kg/d剂量注射组,正常对照组和模型对照组注入同等体积的蒸馏水。采用腹腔注射。糖尿病试验小鼠选择经四氧嘧啶诱发造模后合格的小鼠,观 测其体重与血糖的变化情况,为期一周。其试验结果表明： 1.普洱茶多糖具有促进糖尿病小鼠体重恢复的作用,但无显著性差异。 2.普洱茶多糖能有效的降低糖尿病小鼠的血糖值,高剂量的普洱茶多糖（160mg/kg）比低剂量的普洱茶多糖（80mg/kg）降血糖效果要好,在统计上降血糖幅度差异性显著（P<0.05）,并且呈现一定剂量－反应关系。     

The Motion Characteristics and Deposition Efficiency of Particles in the Gas -Particle Rotary Flow

Based on the motion equations of particles in the gas-particle rotary flow,the relationship among the equivalence particle diameter, characteristic time of the nonequivalence particle and their deposition efficiency is analyzed , and then the results of this study agree very well with the experimental data .