Influence of interparticle interactions on the kinetics of self-assembly and mechanical strength of nanoparticulate aggregates

Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude.     

JT-60U装置温度分布剖面不变性的实验研究

在一系列H模放电条件下，建立了一个旨在研究等离子体温度分布剖面不变性的数据库。介绍了数据库建立过程中要解决的关键问题和所用软件，对等离子体温度分布剖面不变性及芯部约束与边缘参数的关系进行了研究。     

Performance of slotted pores in particle manufacture using rotating membrane emulsification

This paper addresses the use of different slotted pores in rotating membrane emulsification technology.Pores of square and rectangular shapes were studied to understand the effect of aspect ratio (1-3.5) and their orientation on oil droplet formation.Increasing the membrane rotation speed decreased the droplet size,and the oil droplets produced were more uniform using slotted pores as compared to circular geometry.At a given rotation speed,the droplet size was mainly determined by the pore size and the fluid velocity of oil through the pore (pore fluid velocity).The ratio of droplet diameter to the equivalent diameter of the slotted pore increased with the pore fluid velocity.At a given pore fluid velocity and rotation speed,pore orientation significantly influences the droplet formation rate: horizontally disposed pores (with their longer side perpendicular to the membrane axis) generate droplets at double the rate of vertically disposed pores.This work indicates practical benefits in the use of slotted membranes over conventional methods.     

Predicting thermal conductivity of liquid suspensions of nanoparticles (nanofluids) based on rheology

A methodology is proposed for predicting the effective thermal conductivity of dilute suspensions of nanoparticles (nanofluids) based on rheology.The methodology uses the rheological data to infer microstructures of nanoparticles quantitatively,which is then incorporated into the conventional Hamilton-Crosser equation to predict the effective thermal conductivity of nanofluids.The methodology is experimentally validated using four types of nanofluids made of titania nanoparticles and titanate nanotubes dispersed in water and ethylene glycol.And the modified Hamilton-Crosser equation successfully predicted the effective thermal conductivity of the nanofluids.     

The edge-defined film-fed growth of controlled shape crystals

The growth of shaped crystals is examined in the various meniscus-controlled growth processes such as Czochralski, floating zone, Stepanov, and edge-defined film-fed growth (EFG). The basic physical processes which shape the crystal are the same in these techniques; they involve the interaction of the three interfaces at the crystal–liquid–vapor junction. Specifically, for a crystal of constant dimensions, the angle ø between the meniscus and the growth axis must be ø_o (a constant; for silicon, ø_o 11°). The degree of crystal shape control and the range of cross-sectional shapes which can be grown in a stable manner by the different techniques are shown to depend on the details of the meniscus shape and of the heat flow in the systems. The use of a die shaper which constrains the meniscus distinguishes the EFG and Stepnov processes from the other methods. The use of a wetted die in EFG versus a non-wetted die in Stepnov growth is shown to have an additional effect on the ability to control the crystal shape and dimensions. The role of the die shaper is examined in detail from the points of view of die material selection (e.g., wettability and chemical compatibility) and die design. The advantages and disadvantages of using wetted and non-wetted dies in the shaping process are discussed from both the theoretical and practical points of view. Specific numerical examples in the paper deal with the growth of silicon ribbons.     

Nanoporous metal organic framework materials for hydrogen storage

Hydrogen is expected to play an important role in future transportation as a promising alternative clean energy source to carbon-based fuels.One of the key challenges to commercialize hydrogen energy is to develop appropriate onboard hydrogen storage systems,capable of charging and discharging large quantities of hydrogen with fast enough kinetics to meet commercial requirements.Metal organic framework (MOF) is a new type of inorganic and organic hybrid nanoporous particulate materials.Its diverse networks can enhance hydrogen storage through tuning the structure and property of MOFs.The MOF materials so far developed adsorb hydrogen through weak disperston interactions,which allow significant quantity of hydrogen to be stored at cryogenic temperatures with fast kinetics.Novel MOFs are being developed to strengthen the interactions between hydrogen and MOFs in order to store hydrogen under ambient conditions.This review surveys the development of such candidate materials,their performance and future research needs.     

Enhanced EPR sensitivity from a ferroelectric cavity insert.

We report the development of a simple ferroelectric cavity insert that increases the electron paramagnetic resonance (EPR) sensitivity by an order of magnitude when a sample is placed within it. The insert is a hollow cylinder (length 4.8 mm, outside diameter 1.7 mm, inside diameter 0.6 mm) made from a single crystal of KTaO(3), which has a dielectric constant of 230 at X-band (9.5 GHz). Its outside dimensions were chosen to produce a resonant frequency in the X-band range, based on electromagnetic field modeling calculations. The insert increases the microwave magnetic field (H(1)) at the center of the insert by a factor of 7.4 when placed in an X-band TM(110) cavity. This increases the EPR signal for a small (volume 0.13 microL) unsaturated nitroxide spin label sample by a factor of 64 at constant microwave power, and by a factor of 9.8 at constant H(1). The insert does not significantly affect the cavity quality factor Q, indicating that this device simply redistributes the microwave fields within the cavity, focusing H(1) onto the sample inside the insert, thus increasing the filling factor. A similar signal enhancement is obtained in the TM(110) and TE(102) cavities, and when the insert is oriented either vertically (parallel to the microwave field) or horizontally (parallel to the DC magnetic field) in the TM(110) cavity. This order-of-magnitude sensitivity enhancement allows EPR spectroscopy to be performed in conventional high-Q cavities on small EPR samples previously only measurable in loop-gap or dielectric resonators. This is of particular importance for small samples of spin-labeled biomolecules.