风蚀作用下农田土壤细颗粒的粒度损失特征及其对土壤性质影响

以河北坝上地区作为典型研究区,采用野外观测和室内试验分析方法,通过比较农田与邻近天然草地土壤性质之间的差异,研究了农田土壤细颗粒物的损失特征及其对土壤理化性质的影响。结果表明:与风蚀较轻的天然草地相比,农田土壤中黏粒含量下降30%,粉砂含量下降14%;土壤细粒物质的损失粒径集中在0~40μm,其中1.8~24.0μm的细颗粒损失最为严重。由于土壤细颗粒物的损失,土壤砂粒含量相对增加7%,砾石含量相对增加75%,土壤平均粒径增大16%,农田土壤出现明显的粗化、沙化趋势。同时,农田土壤随着养分含量较高的细颗粒损失而变得贫瘠,表现为有机质含量减少29%,全氮含量减少24%,土壤C/N比明显下降,土壤肥力显著降低。土壤细颗粒物的损失对土壤的可风蚀性颗粒含量无明显影响,土壤风蚀可蚀性的变化趋势不明显。

埋地管线破损漏土诱发地面塌陷过程的流固耦合离散元模拟

为了探究埋地管线破损-漏土诱发地面塌陷的规律,采用DEM-CFD方法,综合考虑管线埋深、水压和破损口半径等因素,对单一砂土层和上覆黏土层两种工况的地面塌陷过程进行了数值模拟分析。结果表明:颗粒损失率和地面沉降值呈正相关关系;根据颗粒损失速率,塌陷过程可划分为颗粒运移、快速损失和沉降槽缓慢扩展3个阶段;水压是影响颗粒损失速率的主要因素;对于单一砂土层,随着水压、破损口半径的增大和管线埋深的减小,颗粒损失率逐渐增大;对于上覆黏土层,由于颗粒的黏结作用,颗粒运移阶段持续时间与上覆黏土层厚度呈正相关关系,与水压、破损口半径呈负相关关系。

基于CFD-DEM方法的深基坑降水对地面沉降的影响研究

在砂卵石地层中进行深基坑开挖时,降水引起的细砂颗粒流失一般会导致地面沉降。通过降水试验,分析了富水砂卵石地层降水引起地面沉降的规律;利用CFD-DEM耦合数值模型,分析了滤料粒度、降水速率与细颗粒损失、表面沉降量的关系;并探讨了深基坑降水与开挖耦合作用下的地面沉降规律。研究结论是:即使在地下水位恢复后,地面沉降基本没有回弹,说明地面沉降是细颗粒损失引起的固结沉降;砂卵石地层中的基坑降水开挖是地面沉降控制的关键阶段,随着滤料粒径的增大,降水对地面沉降的影响也越来越大。

海藻酸钙微胶囊对密级配沥青混合料力学性能和自愈合性能的影响

文章将不同比例的微胶囊(0、0.25%、0.50%、0.75%和1.00%)掺入沥青混合料中,研究了不同掺量下沥青混合料的间接抗拉强度、颗粒损失、疲劳寿命和自愈合等性能,评价了海藻酸钙微胶囊对密级配沥青混合料力学性能和自愈合性能的影响。结果表明:海藻酸钙微胶囊的加入对密级配沥青混合料的力学性能有影响,随着微胶囊掺量的增加,沥青混合料的平均ITS值先增大后降低,掺量为0.5%时达到最大值0.64 MPa;微胶囊的加入对混合料的颗粒损失特性与疲劳特性有影响,当掺量<0.5%时,混合料的疲劳寿命增加,颗粒损失率出现小幅度增长;当掺量>0.5%时,疲劳性能低于普通混合料,且颗粒损失率急速增加;微胶囊的掺加显著增加了密级配沥青混合料的自愈合能力,且掺量越高,愈合水平越大;混合料愈合水平随着愈合时间的增大而增大,在96h后达到最大值且稳定。

Experimental investigation of particle-induced pressure loss in solid–liquid lifting pipe

In order to investigate the characteristics of particle-induced pressure loss in the solid–liquid lifting pipe,a series of experiments were conducted in 200 mm diameter lifting pipe.Simulation manganese nodules with five different mean diameters of10 mm,20 mm,30 mm,40 mm and 50 mm were used,both in isolation and a combination in equal fraction by mass.The flow velocities in the lifting pipe ranged from 0.12 m/s to 1.61 m/s,and the mass of particles employed was 10 kg for each particle diameter.Three regimes,wavy bed,partly fluidization,and fully fluidization,were observed over the flow velocity.The solid–liquid pressure drop data were measured by differential pressure transmitter,and pressure drop caused by the solid particles was calculated and analyzed.The results show that the evolutions of the pressure loss due to solid particles are relevant to the solid–liquid flow regimes,and they are distinctly influenced by fluid velocity and particle size.

Developments of Subunit and VLP Vaccines Against Influenza A Virus

Influenza virus is a continuous and severe global threat to mankind. The continuously re-emerging disease gives rise to thousands of deaths and enormous economic losses each year, which emphasizes the urgency and necessity to develop high-quality influenza vaccines in a safer, more efficient and economic way. The influenza subunit and VLP vaccines, taking the advantage of recombinant DNA technologies and expression system platforms, can be produced in such an ideal way. This review summarized the recent advancements in the research and development of influenza subunit and VLP vaccines based on the recombinant expression of hemagglutinin antigen (HA), neuraminidase antigen (NA), Matrix 2 protein (M2) and nucleocapsid protein (NP). It would help to get insight into the current stage of influenza vaccines, and suggest the future design and development of novel influenza vaccines.

Analytical Model for Predicting the Heat Loss Effect on the Pyrolysis of Biomass Particles

This paper presents the combined influence of heat-loss and radiation on the pyrolysis of biomass particles by considering the structure of one-dimensional, laminar and steady state flame propagation in uniformly premixed wood particles. The assumed flame structure consists of a broad preheat-vaporization zone where the rate of gas-phase chemical reaction is small, a thin reaction zone composed of three regions: gas, tar and char combustion where convection and the vaporization rate of the fuel particles are small, and a broad convection zone. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity(i.e.u≥1). The principal attention is made on the determination of a non-linear burning velocity correlation. Consequently, the impacts of radiation, heat loss and particle size as the determining factors on the flame temperature and burning velocity of biomass particles are declared in this research.

Simulation Study of Electron Beam Induced Surface Plasmon Excitation at Nanoparticles

Phenomenon of localized surface plasmon excitation at nanostructured materials has attracted much attention in recent decades for their wide applications in single molecule detection,surface-enhanced Raman spectroscopy and nano-plasmonics.In addition to the excitation by external light field,an electron beam can also induce the local surface plasmon excitation.Nowadays,electron energy loss spectroscopy(EELS)technique has been increasingly employed in experiment to investigate the surface excitation characteristics of metallic nanoparticles.However,a present theoretical analysis tool for electromagnetic analysis based on the discrete dipole approximation(DDA)method can only treat the case of excitation by light field.In this work we extend the DDA method for the calculation of EELS spectrum for arbitary nanostructured materials.We have simulated EELS spectra for different incident locations of an electron beam on a single silver nanoparticle,the simulated results agree with an experimental measurement very well.The present method then provides a computation tool for study of the local surface plasmon excitation of metallic nanoparticles induced by an electron beam.

Influence of Grinding Ball⁃Motion Behavior on Particle Crushing Performance and a Way of Micro⁃particle Preparation in a Flutter Ball Mill

Motion behavior of grinding balls plays a vital role in improving efficiency of particle crushing.A method of preparing micro-particles by changing ball-motion behavior in a flutter mill is proposed and multiple grinding experiments are conducted.Crushing performance parameters,such as breakage rate Si,production rates of fine particles Fi and Fi*,are studied in different motion conditions.From the results,a better crushing performance is attained in the coupled motion modes of rotating speed ratio of 85%,with a vibrating amplitude of 8 mm and a frequency of 12 Hz.In addition,the influence of ball-motion behavior on particle crushing performance is discussed.The ball-motion behaviors,such as the collision energy loss E,among grinding balls have some relationship with the particle crushing performance of Si.Therefore,this study not just provides an efficiency way of accumulating micro-particles,but also reveals how the ball-motion behavior influence particle crushing performance in the flutter mill.

Irradiation Damage of Nano-C2S Particles Studied by In-Situ Transmission Electron Microscopy

Development of a reactive nanocement is a new approach to improve the physical and chemical properties of construction materials. However, due to the decreased size of cement particles, beam damage during transmission electron microscope （TEM） observation becomes more severe than in conventional cement. In this work, irradiation damage to nano-C2S （dicalcium silicate） is observed and studied by in-situ evolution of diffraction patterns （DP）, high resolution TEM （HRTEM）, and electron energy-loss spectroscopy （EELS）. The results show that the damage to nano-C2S occurs through a decomposition reaction. Nano-C2S is first amorphized, and then re-crystallized into CaO nano-crystals with average size of 7 nm surrounded by an amorphous matrix of Si and SiO2. During this process, C2S particles exhibit volume shrinkage. The damage energy causing the reaction was analyzed and electron-electron inelastic scattering produced radiolysis and heat, leading to the observed phenomena.

单侧受限浮力羽流对室内空气颗粒物沉积的影响

为探讨单侧受限浮力羽流作用下的颗粒物沉积特性,采用粉尘监测仪对单侧受限浮力羽流存在处和远离浮力羽流的室内空间中的不同粒径颗粒物浓度进行24 h连续监测,分析15种工况下的颗粒物衰减率损失系数随监测点高度变化情况。结果显示,单侧受限浮力羽流作用处的颗粒物浓度波动较明显;在近壁热源温度≤60℃时,近壁热源上方的颗粒物衰减率损失系数随着高度的增加而减小。提示单侧受限浮力羽流对室内空气颗粒物沉积有一定影响。

燃煤电厂烟气湿度控制对PM_(2.5)采样结果的影响

为研究脱硫后高湿烟气相对湿度的改变对颗粒物采样结果的影响,使用扩散干燥管对烟气进行除湿,并分析不同相对湿度下PM_(2.5)的粒径分布、传输损失和质量浓度变化。结果显示,模拟烟气湿度越高,PM_(2.5)粒数浓度和质量浓度也随之升高。40%相对湿度下,模拟烟气中ρ(PM_(2.5))为22.77 mg/m^(3),粒数浓度约为1.16×10^(6)个/cm^(3),模拟烟气湿度提升至50%、60%和80%时,ρ(PM_(2.5))分别升高1.06,4.35,4.69倍,粒数浓度分别升高1.31,1.70,1.76倍;使用扩散干燥管对模拟高湿烟气除湿,采集到的颗粒物质量浓度有不同程度的下降,最高相对湿度(94.9%)下,ρ(PM_(2.5))为27.17 mg/Nm^(3),湿度81.4%、68.5%、48.7%和30.4%时,质量浓度相比最高湿度时分别降低了14.5%、28.8%、43.0%和45.7%;烟气除湿可降低PM_(2.5)在管路内和切割头内的损失,在94.9%、81.4%和68.5%相对湿度下采集到的ρ(PM_(2.5))分别是对照组的3.02,2.73,2.57倍。高湿烟气除湿降低了颗粒物的含水率,使得PM_(2.5)的质量浓度测量结果随着除湿强度增加而降低,但因除湿降低了颗粒物损失,相比对照组最终采集到的PM_(2.5)质量浓度随着除湿强度增加而显著提升。