Ultrasonic collection of small particles by a tapered metal strip

A pi-shaped ultrasonic actuator can collect small particles by its two sharp edges. However, the collection of particles is weak in air and not very stable in water. In this paper, a refinement to the pi-shaped ultrasonic actuator is made for a more efficient collection of small particles in air and water. In the refined structure, an ultrasonic actuator with a metal strip is used to collect small particles. The metal strip is mechanically driven by one corner of a rectangular, sandwich-shaped ultrasonic transducer operating in the thickness mode vibration. The metal strip is tapered along its length and has a strong vibration at its tip. Small particles in air and water can be attracted to the radiation surface near the end of the metal strip. The dependence of the number of collected particles on driving frequency and voltage is investigated for shrimp eggs, mint seeds, and grass seeds. For a given driving voltage and particle type, the number of collected particles reaches a maximum value at some driving frequency. Increasing driving voltage increases this maximum number to some extent; but too large a driving voltage decreases it. The maximum number also depends on the weight per particle. It increases as the weight per particle decreases for the particles with close densities. Furthermore, the relationship between the number of collected particles and vibration amplitude at the end of the metal strip is investigated for shrimp eggs, mint seeds, and grass seeds. The number is approximately linearly proportional to the vibration amplitude when the vibration amplitude is not too large. In addition to the application in which the length of the metal strip is parallel to gravitation, the actuator also can be used with its length perpendicular to gravitation. However, the latter has a weaker capability of collecting small particles. It is also found that the actuator has a stronger capability to collect particles in water than in air.     

Deposition of aerosol particles in vertical channels from an isotropic turbulent flow

Equations for the rate of turbulent deposition of aerosol particles in vertical tubes are suggested. It is noted that the rate of deposition of particles is determined by the gravitation component and turbulent diffusion. The thickness of the layer of depositions and its influence on the basic characteristics of a turbulent flow are determined. The results obtained are compared with available experimental values of the rate of deposition of particles in vertical tubes.     

Gravity and Neuronal Adaptation

Introduction: For interplanetary and orbital missions in human space flight, knowledge about the gravity-sensitivity of the central nervous system (CNS) is required. The objective of this study was to assess neurophysiological correlates in variable hetero gravity conditions in regard to their timing and shaping. Methods: In ten subjects, peripheral nerve stimulation was used to elicit H-reflexes and M-waves in the M. soleus in Lunar, Martian, Earth and hypergravity. Gravity-dependencies were described by means of reflex latency, inter-peak-interval, duration, stimulation threshold and maximal amplitudes. Experiments were executed during the CNES/ESA/DLR JEPPFs. Results: H-reflex latency, inter-peak-interval and duration decreased with increasing gravitation (P<0.05); likewise, M-wave inter-peak-interval was diminished and latency prolonged with increasing gravity (P<0.05). Stimulation threshold of H-reflexes and M-waves decreased (P<0.05) while maximal amplitudes increased with an increase in gravitation (P<0.05). Conclusion: Adaptations in neurophysiological correlates in hetero gravity are associated with a shift in timing and shaping. For the first time, our results indicate that synaptic and axonal nerve conduction velocity as well as axonal and spinal excitability are diminished with reduced gravitational forces on the Moon and Mars and gradually increased when gravitation is progressively augmented up to hypergravity. Interrelated with the adaptation in threshold we conclude that neuronal circuitries are significantly affected by gravitation. As a consequence, movement control and countermeasures may be biased in extended space missions involving transitions between different force environments.     

基于离散元法的果粒灌装输送过程仿真

目的 针对甜橙果粒灌装效率低的问题,提出一种高效精确的果粒灌装输送设备.方法 建立灌装设备的三维模型,研究螺旋叶片几何参数以及果粒特性对果粒罐装过程的影响.结果 果粒灌装设备能够较好地完成果粒灌装,颗粒质量流率比初始值提高了6倍以上;粘性物料颗粒在螺旋输送的过程中能保持较稳定的聚团性,这一特性只与颗粒的表面能有关;在螺旋输送过程中可通过工艺优化增大颗粒的表面能,以达到颗粒在螺旋输送过程中保持明显的稳定性和提高输送效率的目的,当颗粒表面能为0.1 J/m2时,颗粒之间表现出稳定性,在表面能为1.3 J/m2时螺旋输送效率达到最大.结论 经过分析优化,文中提出的灌装设备能够有效实现果粒的高效灌装.     

Treasure of the Past: III: Gravitational Anisotropy in Crystals

Einstein’s theory of gravitation is based upon a fundamental postulate which asserts that gravitation and inertia are identical in nature and hence indistinguishable. This if true, is of the greatest theoretical importance, for gravitation has heretofore refused to show any relationship to other physical phenomena.A most delicate test of this postulate is possible in a crystal of one of the nonisometric systems; for in such a crystal every known physical property (except inertia and, possibly, weight) varies with the axial direction in the crystal; and it is an interesting question whether, in such a crystal, gravitation will be found to align itself with inertia or will show some variability which will classify it with the great majority of physical phenomena.To test this point, large crystals were weighed in different axial positions with respect to the earth. The specimens examined represented all five nonisometric systems, and were weighed to a precision, in most cases, of 1 part in 10⁹. The results were uniformly negative, and to this degree of precision are in Einstein’s favor.Incidentally, this work has shown the practical possibility of using the gravity balance to a precision of I part in 10⁹, even when the swing of the beam must.be stopped and the object turned through a considerable angle. A precision of about the same order was attained by Majorana in 1920. In this work it was not necessary to arrest the beam or to touch the load. The next best record (in work of a somewhat different kind) at the International Bureau of Weights and Measures is 7 parts in 10⁹.     

Solid electrolyte/graphite composite particle for an all-solid-state lithium-ion battery

A great issue in the development of an all-solid-state lithium-ion battery (ASSLIB) is the fabrication of a composite electrode with good contact between active materials (AMs) and solid electrolytes (SEs). To overcome this challenge, it is important to develop a powder processing technology that produces composite particles of AMs and SEs. In this study, we investigated a dry impact blending process for producing graphite composite particles (typical anode AM) and sulfide SEs. First, by controlling the rotating speed of the rotor in the dry impact blending process, two types of composite particles, namely surface-coated (SC) composite particles with no graphite breakage and matrix-type (MT) composite particles with graphite breakage, were produced. The SC composite particles showed higher electrochemical performance than the MT composite particles due to less change in the graphite crystallinity. Second, the longer the processing times for the preparation of SC composite particles, the higher the SE coating on graphite, resulting in higher electrochemical performance. Third, we demonstrated that the SC composite particles exhibited higher electrochemical performance than those prepared using a conventional lab-scale mixing technique. We demonstrated the effectiveness of the dry impact blending process for the preparation of an anode composite electrode for ASSLIBs.     

Conditioning following powder micronization: influence on particle growth of salbutamol sulfate

Micronization is a high-energy process that induces changes in the crystallinity of materials. As a result, the crystalline structures on the particles' surface are being destroyed and amorphous areas are formed. After micronization of salbutamol sulfate to be used in dry powder inhalers, only small amounts of amorphous material are produced. Nevertheless, even these small amounts can have important effects on the physical stability of the powder. The amorphous state is thermodynamically unstable and tends to convert to the stable, crystalline state. The recrystallization process of disordered regions on the particles' surface leads to particle growth of milled particles. In this case, bridges of solid material are being formed between the individual particles, which leads to particle growth. This is an undesirable process, because particles for pulmonary administration are designed to range between 1 and 10 µm in diameter to exert respirative effect. In the present investigation, salbutamol sulfate is micronized by an air jet mill, and the generated products are exposed to different conditions. Thereafter, the best possible conditioning parameters and storage conditions for the micronized salbutamol sulfate are worked out and rated. The aim of this treatise is to demonstrate the importance of conditioning following micronization.     

Production of composite particles using an innovative continuous dry coating process derived from extrusion

Dry particle coating is used to modify surface properties and monitor the end use properties of powders. These processes are mainly running in batch mode. In certain cases, continuous processes may present interest for specific applications (limitation of investments, stability, versatility…). In this study, the feasibility of dry coating particles by an innovative way derived from the well-known extrusion process was investigated. Adhesion between host and guest particles is induced by mechanical shear stress during processing. A preliminary parametric study on microcrystalline cellulose particles as host particles was carried out in order to determine the operating condition range. Then, coating was successfully performed using talc and a microcrystalline cellulose system, which demonstrates the feasibility of this novel process and led to different morphologies according to the operating conditions.     

用Mises屈服条件求内边界固支环板的极限荷载

在锂离子电池的充放电过程中,随着电极颗粒中锂的嵌入和脱出,颗粒会发生膨胀和收缩而导致应力的产生,应力过大时会发生电极材料的脱落、破裂,致使电池内阻增加、循环性能下降、容量衰减,最终导致电池失效。该文对正负极椭球颗粒建立三维电化学-力耦合模型,计算了充电过程中电极颗粒的锂浓度分布以及负极石墨颗粒的应力分布。结果表明：两个颗粒接触的部位应力较大,且过大的应力会削弱锂离子的脱嵌能力,导致两个负极颗粒接触的部位锂浓度较低而两个正极颗粒接触的部位锂浓度较高。此外,颗粒表面径向应力为零,径向应力最大值出现在颗粒中心,最大切向应力出现在两个颗粒接触的表面。     

DEM analysis of powder deaggregation and discharge from the capsule of a carrier-based Dry Powder Inhaler

In carrier-based Dry Powder Inhalers (DPI), fine API powder covers the surface of bigger carrier particles giving rise to dry coated particles, such that their flow properties are improved. In the hard-shell capsule of Cyclohaler DPI, powder deaggregation and discharge occurs as a result of the centrifugal motion and the subsequent aerodispersion to the mouthpiece induced by the patient’s inhalation. In this work, the crucial initial transient of this dispersion process was analysed through DEM (Discrete Element Method) simulations, by considering the solid phase only. The accelerated rotational motion of the capsule was simulated in the frame of reference of an observer rotating with the capsule, appropriately considering fictitious forces. The effect of the vibrations due to collisions between the capsule and the inhaler on powder discharge was evaluated as well for carrier particle systems. The results provide a punctual mapping of the particle-wall collisions within the capsule, allowing the path of the solids to be tracked until discharge. Simulations were carried out on drug-carrier blends with extreme size difference, considering adhesive interactions, elucidating the early-stage dynamics of the detachment process that occurs inside the capsule due to the interactions between particles and between particles and walls.     

Theoretical Study of the Reorganization of Fractal Aggregates by Diffusion

Precipitation processes are commonly used in industry to efficiently produce large amounts of solids. During these processes a fast formation of colloidal structures is often followed by an aggregation process if the systems are unstable. In many cases these aggregates are highly porous networks that may subsequently reorganize to form a more compact particulate material. In this article, the reorganization process is theoretically examined for fractal aggregates. Two different mechanisms are proposed. For the first mechanism, particles are selected for diffusion moves inside the cluster based on their distance to the center of mass. In a second mechanism, the detachment of primary particles is described by an Arrhenius type expression. The detachment probability is assumed to be linearly dependent on the number of nearest neighbors of the primary particle. This last mechanism is demonstrated to be valid for the restructuring of silica aggregates. The obtained activation energy of 4.87 × 10^?21 J for breaking a bond between neighboring particles is similar to values found in secondary minimum coagulation.     

A model for simulating the grinding and classification cyclic system of waste PCBs recycling production line

Crushing and separating technology is widely used in waste printed circuit boards (PCBs) recycling process. A set of automatic line without negative impact to environment for recycling waste PCBs was applied in industry scale. Crushed waste PCBs particles grinding and classification cyclic system is the most important part of the automatic production line, and it decides the efficiency of the whole production line. In this paper, a model for computing the process of the system was established, and matrix analysis method was adopted. The result showed that good agreement can be achieved between the simulation model and the actual production line, and the system is anti-jamming. This model possibly provides a basis for the automatic process control of waste PCBs production line. With this model, many engineering problems can be reduced, such as metals and nonmetals insufficient dissociation, particles over-pulverizing, incomplete comminuting, material plugging and equipment fever.     

Stabilisation in and rejection of ceramic particles from molten aluminium alloy: modelling and experimental testing

A model has been developed to explain the stabilisation of ceramic particles dispersed in a molten metal by equilibrium interfacial coupling between the ceramic particles and the molten metal. Such equilibrium interfacial coupling is proposed to be an energy-activated process determined by the equilibrium conversion and the overall kinetics of the applied interfacial chemical interaction. In addition, the model was experimentally verified by observing the rejection of BN-coated SiC particles from the molten aluminum alloy. The moment of rejection was experimentally determined by measuring changes in electrical resistance of the slurry and the variations in electrical power required for its constant stirring. Experiments also showed that BN surface-coated SiC powder used in this study can be successfully immersed in an aluminum melt. Furthermore, this cost-effective processing technique can be applied in order to prepare a stable and highly concentrated (>30 vol%) metallic suspension of ceramic particles different in their particle size and specific surface area, which is of great practical interest in production of discontinuously reinforced metal-matrix composites.     

Densification of pure magnesium by spark plasma sintering-discussion of sintering mechanism

In this study, high-quantity pure magnesium was prepared by SPS, and the sintering densification mechanism was discussed by using numerical simulation and simultaneous experiment. Results show that a layer of dense magnesium oxide was formed at the surface of Mg particles, and the oxide reduction can be observed owing to the effect of oxide film removal in SPS. The high energy pulsed current flows preferentially through particle contact surfaces, which provides the conditions for the generation of micro-arc between particles and the temperature at the particles contact point can be up to 1979 °C. With the low pressure at the initial sintering stage, local high temperature induced by micro-arc makes the melting (even evaporation) appearance. At the same sintering temperature of 570 °C, the obvious difference in bending strength also demonstrates the significance of spark discharge in SPS. The formation process of sintering neck demonstrates that sintering process is the reflection of melting (even evaporation), diffusion and plastic deformation. In order to realize tiny area and high-quality connection between powder particles, an innovative powder sintering technology using high-frequency pulse electric current (High frequency pulse current assisted sintering) is proposed based on the enlightenment of the skin, proximity and arc discharge effect of high-frequency pulse current. This technology is also instructive for other alloys and engineering materials.     

Geometrically nonlinear gravito-elasticity: Hyperelastostatics coupled to Newtonian gravitation

A theory of nonlinear elasticity is presented that incorporates a spatially non-constant Newtonian gravitational field as is appropriate if deformable heavy masses of finite volume are considered. For Newtonian gravitation the mass density is a sink for the (scaled) gravitational field. This Gauss-type law for gravitation is incorporated into the mechanical balance equations of linear and angular momentum as well as into the thermomechanical balance equations of energy and entropy. To this end, a total energy density as well as total Piola and Cauchy stresses are introduced that directly capture the contribution of Newtonian gravitation. For the nonlinear elastic case the pertinent relations for the gravito-elastically coupled problem are recovered from a variational setting in terms of the nonlinear deformation map and a gravitational potential.     

Steering coefficient in ordered lattice pile of two-dimensional granular systems

Interparticle forces in granular system form an inhomogeneous distribution of filamentary force chains. For the granular system with an established packed structure, the normal pressure is steered through the force chains among the particles and the value of horizontal pressure is various at the different positions. In this paper, the steering coefficient in two-dimensional horizontal and vertical granular system is studied experimentally. The results show that, in the process of slowly increasing compression, the normal force increases slowly at first and gradually transforms into a nonlinear form, and changes into the linear growth finally. This phenomenon corresponds to the dynamic processes of friction-slip-extrusion. Through theoretical analysis, we revealed that how friction among particles, friction between particles and glass plate and stacking angle affect the steering coefficient. The saturated value of steering coefficient decreases with the stacking angle in experiment, which is agreed well with theoretical result. In addition, our experiment shows that the steering coefficient is independent of the width of container.     

Construction and characterization of a sputter deposition system for coating granular materials

In many modern ceramic or metal matrix composites the interface between the matrix and the reinforcements (particles or fibres) plays an important role. Either no or only weak mechanical bonding is observed or severe reactions between the matrix and the filler during the manufacturing process take place. A method to promote adhesion or to avoid severe reactions is to use coated reinforcements. A uniform film can act as an adhesion promoter, a compliant layer, a reaction inhibitor or a promoter of thermal transport across the interface.The aim of this work was to construct a particle coating system based on magnetron sputter deposition which allows to keep the particles or the granular material in motion during the deposition process to guarantee a homogenous coating on every single particle. As particles to be coated diamond granulates and carbon fibres were investigated. For transparent diamond particles the uniformity of a metallic coating could be evaluated by transmission optical methods and was found to be quite high. Carbon fibres, on the other hand, could only partially be coated due to agglomeration and shadowing effects. The system presented here can be considered as suitable for coating spherical or close to spherical granular matter.     

Influence of interparticle forces on selective wet agglomeration

The influence of interparticle forces between primary particles, which include interaction force between dispersed particles in liquid calculated by DLVO theory and two kinds of forces caused by a liquid bridge of bridging liquid between particles, on selective wet agglomeration was investigated on the basis of the relationships between the results of separation efficiency obtained in author’s previous study and these interparticle forces. The first step of selective wet agglomeration is the collision between bridging liquid droplets and objective particles to be agglomerated. This collision is mainly influenced by the interparticle force calculated by DLVO theory. Incorporation of two objective particles, the second step in the agglomeration process, is influenced by liquid bridge force between objective particles. Growth to pellet-type agglomerates, the third step in the agglomeration process, is thought to be influenced mainly by aggregation force in the agglomerates by entry suction potential. The results of this study showed that selective wet agglomeration under the experimental conditions used in this study is influenced greatly by liquid bridge force and entry suction potential, which play major roles in the second step and third step, respectively, of the selective wet agglomeration process.     

Effect of SiC content on the processing, compaction behavior, and properties of Al6061/SiC/Gr hybrid composites

Aluminum matrix composites reinforced with SiC and graphite (Gr) particles are a unique class of advanced engineered materials that have been developed to use in tribological applications. The conventional techniques for producing these composites have some drawbacks. In this study, a new method, namely In situ Powder Metallurgy (IPM), is applied for the preparation of Al6061/SiC/Gr hybrid composites. In this method, the stir casting and the powder metallurgy synthesizing processes are combined into an integrated net shape forming process. 0?C40 vol.% of SiC particles with an average size of 19 ??m, along with 9 vol.% of uncoated Gr particles, were introduced to the molten 6061 aluminum alloy. Then, the slurries were stirred in a specified time?Ctemperature regime resulting in mixtures of the SiC, Gr, and aluminum powder particles. The powder mixtures were cold pressed in six different pressures (between 250 and 750 MPa) and sintered. Finally, the produced composites were heat treated and their hardness and wear properties were investigated. Homogenous distribution of the SiC and Gr particles within the powder mixtures and the hybrid composites is clear from the SEM images. The results also show that the SiC particles decrease the compressibility of the hybrid powders and improve the hardness of composites. The best wear resistance is achieved in the hybrid composite containing 20 vol.% SiC particles.     

Coagulation and Collection of PM2.5 Based on a Stack Coagulator

China recently put forward stronger requirements for PM2.5 emission in 2012. Electrostatic precipitators have relatively low efficiency for the collection of submicron particle, especially for PM2.5. An alternate way to increase its efficiency is to enforce the coagulation and, thereby, form larger particles. In this work, we propose an efficient way to enhance the coagulation between oppositely charged particles by using a stack coagulator. Firstly, in order to explore the impact of the bipolar charging and coagulation to the separation efficient of PM2.5, we use system modeling and simulation to explore the whole charge-coagulation-collection process of PM2.5. The results show that the coagulation rate of bipolarly charged particles can be increased by a factor of 10² ～ 10⁴ compared to the neutral particles and the collection efficiency of dust particles increases as the particle size grows. Subsequently, via the dust particles coagulation experiments, the emission rate chart and emission reduction charts of PM2.5 are plotted, which indicate that the average emission reduction of PM2.5 is almost 85%.