The behaviour of water-immersed glass-bronze particulate systems under vertical vibration

We report a detailed investigation of the behaviour of water-immersed binary mixtures of glass and bronze spheres under sinusoidal vertical vibration. Excellent separation with a bronze layer above a glass layer is observed for a range of particle sizes and size ratios, with very sharp boundaries between the bronze and glass regions. Convection cells exist within each separated region but convection does not cause global mixing. Separation is maintained in the presence of convection due to gaps which appear between the bronze and glass beds for part of the vibration cycle. We vary the size of the spheres and the size ratio, investigating the separation behaviour as a function of frequency and amplitude of vibration. We also discuss a number of meta-stable granular configurations. The Faraday tilting observed at low frequencies enhances the speed of separation. For very fine particles, the amplitude of vibration necessary for separation becomes very large and the time scale for separation becomes very long. For large particle diameters, the fluid damping of the particle motion weakens and separation may fail through global convective mixing.     

PEPT Investigation of Particle Separation in a Novel Vertically Vibrated Particle Separator

Separation of particle mixtures in micron size range is of concern to many industrial processes. The experimental work presented in this article has looked into the operational assessment of a novel vertical vibration driven particle separator by using a positron emission particle tracking (PEPT) technique. In addition to PEPT, a smoke blanket visualization technique was used to track the intestinal air movements during the course of vibration induced particle separation. Three different finely sized glass and bronze particle mixtures that formed an average particle bed heights of 20, 40, 60, 80, and 100 mm in separation cells of thickness 20 and 40 mm were used to investigate the particle separation behavior. For a range of operating conditions, the results showed in favor of low particle bed heights (below 40 mm), lower vibration frequency (30 ± 10% Hz) and a small partition separation gap size of 5 mm for optimum separation of bronze particles in the presence of air.     

Discrete Element Modeling (DEM) of the Vertically Vibrated Particle Bed

Discreet element modeling (DEM) is a computational tool used for detailed exploration of dynamic particle bed behaviors. One such application is the analysis of finely sized particle mixtures under the influence of external forces such as vertical vibration, which is difficult, if barely at all accessible for detailed experimental analysis. Here, we examined the differential density dynamic particle bed behaviors, by the application of a modified two dimensional DEM-fluid model that incorporates the gravity and fluid effects, to replicate some of the important experimental based observations of segregation, heaping, tilting, high density particles on top and bottom, and partition cell separation. The simulation results compared favorably with the reported literature on the density segregation attributes such as high density particles on top at vertical vibration frequency of 6.3 and 7 Hz with corresponding dimensionless acceleration magnitude of 1.6 and 2, convection currents at vertical vibration frequency of 30, 40, and 30 with corresponding dimensionless acceleration magnitude of 3.5, 4, and 3, layer separation at vertical vibration frequency of 7 Hz with corresponding dimensionless acceleration magnitude 2 and partition cell separation at vertical vibration frequency of 45 Hz and corresponding dimensionless acceleration magnitude of 2.25 for simulated glass and bronze particle mixture properties.     

Effects of wall vibration on particle deposition and reentrainment in aerosol flow

The simultaneous phenomenon of particle deposition and reentrainment on a vibrating wall has been studied experimentally. Aerosols that were generated by dispersing alumina powder, of size 3.8-12.5 Mm mass median diameter, were transported into a vertical glass tube equipped with a vibration motor. The formation process of the particle deposition layer in the tube was observed through a digital video camera with a zoom lens. The experimental results showed that wall vibration was effective to enhance particle reentrainment. Critical flow velocity for the case of no particle layer formation decreased with increasing vibration acceleration and/or particle diameter. In contrast, at a velocity below the critical value, the wall vibration increased the amount of particles deposited on the wall. The critical condition for no particle layer formation under wall vibration was explained using a moment balance model.     

九连墩楚墓出土青铜箭镞的锈蚀特征

利用光学显微镜和扫描电镜等仪器对湖北枣阳九连墩楚墓出土的两支青铜箭镞的锈蚀情况进行了分析。结果表明:两支箭镞横截面的组织结构都是由锈蚀矿化层、中间过渡层和基体三部分组成,与长江中下游其他地区出土箭镞的锈蚀形态相似;两支箭镞的表层锈蚀层并没有形成严重的粉状锈,说明其埋藏保存状况比较良好;铅含量高的箭镞比铅含量低的箭镞的锈蚀程度更严重,说明青铜器中的铅含量对其腐蚀程度有至关重要的影响。     

Conversion air velocity at which reverse density segregation converts to normal density segregation in a vibrated fluidized bed of binary particulate mixtures

It is well known, when binary mixtures of different-density particles of the same size are vertically vibrated or fluidized by airflow through the bottom, the particles segregate by density. Reverse density segregation occurs in the vibrated bed; heavier particles move upward and lighter ones move downward, and normal density segregation occurs in the fluidized bed; lighter particles move upward and the heavier ones move downward. In this study, we investigated the particles’ behavior in a vertically vibrated fluidized bed at various air velocity using two types of particulate mixtures of glass beads (GB) and stainless steel powder (SP) or iron powder (IP) of same size. We found that reverse segregation converts to normal segregation at a certain air velocity; here we call it “conversion air velocity”. Then, we investigated the likely origin of the conversion air velocity considering the minimum fluidization air velocity u_mf determined for the three monocomponent particles (GB, SP and IP) with and without vibration. We found that the conversion air velocity is close to the u_mf of the lower density particles (GB) with vibration, indicating that the conversion from reverse segregation to normal segregation occurs around u_mf of lighter particles with vibration.     

Simultaneous on-chip DC dielectrophoretic cell separation and quantitative separation performance characterization

Through integration of a MOSFET-based microfluidic Coulter counter with a dc-dielectrophoretic cell sorter, we demonstrate simultaneous on-chip cell separation and sizing with three different samples including 1) binary mixtures of polystyrene beads, 2) yeast cells of continuous size distribution, and 3) mixtures of 4T1 tumor cells and murine bone marrow cells. For cells with continuous size distribution, it is found that the receiver operator characteristic analysis is an ideal method to characterize the separation performance. The characterization results indicate that dc-DEP separation performance degrades as the sorting throughput (cell sorting rate) increases, which provides insights into the design and operation of size-based microfluidic cell separation.     

Experimental study of granular stratification

The flow of binary granular mixtures made of sand (rough) and glass spheres (smooth) into a vertical Hele Shaw cell give rises to heaps exhibiting different internal structures. We first give the phase diagram of heap morphologies classified as a function of the size ratio of rough to smooth particles. Granular stratification is one type of observable structure, which consists in the formation of alternating layers through the pile, and is found to occur only for a size ratio greater than 1.5. We present an experimental study of stratification and report that the wall separation and the mass flux can modify the layering process.     

The influence of air on the magneto-vibratory separation of binary granular mixtures

The application of an inhomogeneous magnetic field to a binary granular mixture composed of diamagnetic or paramagnetic particles exposes the two species to different effective forces of gravity. Vertical vibration may then cause the mixture to separate through the action of this differential gravity. Here we consider the influence of a background fluid, such as air, on this magneto-vibratory separation. We show that air-driven tilting and granular convection greatly influence the separation dynamics. We identify the magnetic and vibratory conditions for mixed, partially separated and very well separated states. Each corresponds to a distinct pattern of granular convection, the transition from one state to another being abrupt as the experimental conditions are altered. Magneto-vibratory separation may enhance air-driven separation, may cause inverted separation, or may be adjusted to counteract the air-driven separation and maintain the mixed state. We use computer simulations to give insight into these separation processes. We show that many of the phenomena are associated with the gaps which open up between separated regions over those fractions of the vibration cycle in which the convective motion takes place. It is these gaps which enable the abrupt transition between separated states and which prevent the convection within the separated regions from causing mixing.     

Influence of third elements on growth of Nb3Sn compounds and on global pinning force

The crystal growth of Nb₃Sn by the bronze method has been investigated by using diffusion couples consisting of niobium and bronze with the addition of third elements. When the specimens were annealed at temperatures between 973 and 1073 K, the time-dependence of layer thickness was represented approximately by the function ofd=kt ^m . The time exponent changed from 1/3 to unity depending on the annealing condition as well as on the nature of the third element. By the addition of titanium, hafnium, zirconium, indium and galium to the bronze, the growth rate of the compound layer increases. Faster layer growth corresponds to a larger time exponent. The following three processes are suggested to be important for controlling layer growth: diffusivity of tin atoms through grain boundaries in the compound layer, diffusivity of tin atoms through the matrix of the compound, and the rate of the chemical reaction to form the compound. Essentially these combined processes control the overall rate of layer growth. The grain size is found to be the most effective structural parameter to affect directly the maximum global pinning force. The critical current at a magnetic field of 5T can be scaled by both the layer thickness and the inverse grain size.     

Radial segregation of multi-component granular media in a rotating tumbler

Segregation and mixing of granular mixtures are important to the minerals, food processing and pharmaceuticals industry to name just a few. It has recently been demonstrated that a rotating tumbler is a suitable device for separating out binary granular mixtures, i.e. mixtures composed of only two different particle types. However, most practical granular mixtures are composed of multi-component particle types. We therefore study the capability of this rotating tumbler to segregate mixtures composed of more than two components where the particles differ either in size or density. The general pattern of segregation involves the formation of an inner core of smallest or densest particles followed, at larger radii, by the next largest or densest particle type and so-on in an onion-like pattern. In the mixtures where particles differ in size we always get relatively pure inner cores of the smallest particles, while the other regions are less segregated. On the other hand for mixtures whose particles differ in density we get a relatively pure outer region (adjacent to cylinder wall) consisting of the least dense particles while the other regions are less segregated. We attempt to relate the simulation results to phenomenological theory and find that size segregation in a specific multi-component mixture can be suitably described by a recent theoretical model.     

多交联体系聚氨酯材料的制备与表征

以聚酯多元醇(PEA)、2,4-甲苯二异氰酸酯(TDI-100)为原料,采用预聚法制备预聚体,将预聚体分成两部分分别以不同比例与扩链剂(MOCA)混合反应,再将两种配料不同的混合物体系混合后浇铸成型,即为多交联体系聚氨酯材料.对其力学性能、耐溶剂性能与均一体系聚氨酯材料的性能进行了比较.结果表明,多交联体系聚氨酯材料的拉伸性能稍有下降,耐撕裂性能明显提高;多交联体系聚氨酯材料的耐溶剂性能也明显提高;DMA测定结果表明,多交联体系聚氨酯材料的玻璃化转变温度降低,微相分离更好,阻尼性能下降.     

青铜文物的光电子能谱分析

采用光电子能谱(XPS)法分析了成都金沙遗址出土铜条和方孔型器两种青铜表面锈层膜的元素及其化学状态.结果表明,两种青铜的锈层膜中都存在纯铜晶粒和PbCO3/PbO,但未发现导致"青铜病"的有害元素Cl,而在方孔型器锈层膜中发现有S2-/SO42-.铜条和方孔型器夹层锈层膜中的Sn完全以SnO2形式存在,从而使青铜合金免遭进一步腐蚀.此外,还讨论了青铜的腐蚀过程与环境的关系.     

The preferential adsorption of 4He from 3He-4He mixtures onto Vycor glass

The preferential adsorption of ⁴He from liquid ³He-⁴He mixtures onto Vycor glass has been measured over a wide concentration range between 1 and 3 K. Over most of this temperature range the preferential adsorption extends beyond the second atomic layer, with a preferential binding energy of about 3.5 K/mole. Near 1 K and below, the thickness of the ⁴He layer increases rapidly as a precursor to the bulk liquid phase separation.     

Microstructural study of laser-clad Fe-Al bronze on Al-Si alloy

Microstructure studies of laser-clad Fe-Al bronze on an Al-Si alloy were carried out by OM(optical microscope), SEM(scanning electron microscope), TEM(transmission electron microscope) and XRD(X ray diffraction) analyses. The cross-section of the laser-cladding was divided into clad region and transitional region. The clad region composes a matrix with a twin structure of needle-like and feathery appearance and a second phase of Cu₉Al₄. The transitional region consists of two layers. The layer close to the clad region shows polygonal crystalline while the layer close to the substrate region displays a needle-like structure. XRD analyses show that the main phases in the polygonal crystalline layer and the needle-like structure layer are Cu₃Al + Cu₉Al₄ and CuAl₂ + -Al, respectively. Finally, the formation mechanism of two regions was analysed.     

A new cost effective method of planarisation for multiple metal layers in the sub-100 nm-region

The availability of multiple metal layers has become essential for high-density layouts and economic chip size. The presented paper describes an efficient and low-cost alternative to Chemical-Mechanical-Polishing (CMP). The method uses an auxiliary wafer as a sort of plunger. Starting with a preprocessed wafer, for example from a Complementary-Metal-Oxide-Semiconductor (CMOS) technology, a spin-on glass is applied before the deposition of the first metal layer. Afterwards a second silicon wafer will be covered homogeneously with photo resist and subsequentially coated with aluminum or titanium. This wafer serves as a plunger, while the metal layer protects the photo resist against impression. Whilst the plunger is pressed down on the spin-on glass, the first wafer is cooled down bonding the two wafers together. Separation of the wafers is accomplished by removing the photo resist layer. After the separation step any remaining photo resist as well as the aluminum layer are removed by etching. This process results in a planar surface which is optimally suited for the deposition and structuring of further metal layers which lead to more freedom concerning the complex interconnects in modern analog and digital circuits.     

Behaviors of Oxide Layer at Interface between Semi-solid Filler Metal and Aluminum Matrix Composites during Vibration

The joint interface between semi-solid Zn-Al filler metal and SiCp/Al composites with applying vibration for different time was examined. With increasing vibrating time, the oxide layer was disrupted prior at the centre to the periphery of the interface. And the solid grains near the centre of interface in semi-solid filler metal aggregated into two solid regions and compressed the composites during vibration; the solid grains near the periphery of interface moved toward the edge and scraped the composites during vibration. The models of disrupting oxide layer under the vibration condition were developed. At the centre of interface, the oxide layer was tore and stripped during the solid grains in the semi-solid filler metal depressing the composites with a very high compressive stress. At the periphery of interface, the oxide layer was cut and stripped into the filler metal during the solid grains scraping the interface.     

Ultrafast gas chromatography on single-wall carbon nanotube stationary phases in microfabricated channels

The key to rapid temperature programmed separations with gas chromatography are a fast, low-volume injection and a short microbore separation column with fast resistive heating. One of the major problems with the reduction of column dimensions for micro gas chromatography is the availability of a stationary phase that provides good separation performance. In this report, we present the first integration of single-wall carbon nanotubes (SWNTs) as a stationary phase into 100 mum x 100 mum square and 50-cm-long microfabricated channels. The small size of this column with integrated resistive heater and the robustness of the SWNT phase allow for fast temperature programming of up to 60 degrees C/s. A combination of the fast temperature programming and the narrow peak width of small-volume injections that can be obtained from a high-speed, dual-valve injection system allows for rapid separations of gas mixtures. We demonstrate highly reproducible separations of four-compound test mixtures on these columns in less than 1 s using fast temperature programming.     

Experimental study on the packing densification of mixtures of spherical and cylindrical particles subjected to 3D vibrations

To identify the dense packing of cylinder–sphere binary mixtures (spheres as filling objects), the densification process of such binary mixtures subjected to three-dimensional (3D) mechanical vibrations was experimentally studied. Various influential factors including vibration parameters (such as vibration time t, vibration amplitude A, frequency ω, vibration acceleration Γ) as well as particle size ratio r (small sphere vs. large cylinder), composition of the binary mixtures X_L (volume fraction of cylinders), and container size D (container diameter) on the packing density ρ were systematically investigated. The results show that the optimal vibration parameters for different binary cylinder–sphere mixtures are different. The smaller the size ratio, the less vibration acceleration is needed to form a stable dense packing. For each binary mixture, high packing density can be obtained when the volume fraction of large cylindrical particles is dominant. Meanwhile, increasing the container size can decrease the container wall effect and get higher packing density. The proposed analytical model has been proved to be valid in predicting the packing densification of current cylinder–sphere binary mixtures.     

新型GeS2-Ga2S3-KBr系统玻璃的形成及性能

本文研究了GeS2－Ga₂S₃－KBr系统玻璃的形成范围．根据玻璃的红外光谱、可见光谱、特征温度、热膨胀、电导、析晶和耐水性测试结果,该系统玻璃具有较宽的透过波段（0．45～11．5μm）,透过率大于60％;较高的转变温度、热膨胀软化温度（355℃）和析晶温度（593℃）;23℃时玻璃的电导率为10^-9～10^-12S／cm,270℃时电导率为10^-4～10^-6s／cm;玻璃耐水性较好．