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.     

A phenomenological approach to pion condensation

The threshold of π-condensation in isospin symmetric nuclear matter is studied with a field theoretic model which reproduces the low energy πN data. We find a critical density around normal nuclear matter density. Besides the role of the nucleon-nucleon correlations we investigate the effect of the s-wave πN interaction on- and off-mass-shell. The chiral symmetry breaking Σ-term may impede pion condensation.     

Quark-Quark Correlations in the Nucleon in a Generalized Nambu-Jona-Lasinio Model

We present a relativistic model of the nucleon based upon a quark-diquark structure that emerges from a study of the Nambu-Jona-Lasinio model. Similar calculations, made by other authors, have been carried out after a Wick rotation is performed. These previous calculations have neglected confinement; therefore, the masses of the quarks and diquarks had to be adjusted so that the diquarks and the nucleon were stable, in which case the Wick rotation may be made. In our work, we include a momentum-space model of confinement developed earlier and we are therefore able to carry out the calculation in Minkowski space, after making a number of approximations. We determine the relative admixture of a scalar-isoscalar diquark and an axialvector-isovector diquark dynamically and find that an approximately equal admixture provides a reasonable fit to the nucleon magnetic moments. While the original problem (without approximation) requires the specification of eight scalar functions of two variables, our various approximations allow us to calculate several functions of a single variable. We find that only two of these functions are important. Therefore, we can exhibit a relatively simple relativistic wave function of the nucleon expressed in terms of two wave functions describing the relative motion of the quarks and diquarks. Received December 5, 1995; accepted for publication February 13, 1996     

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.     

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.     

Measurement of pion-nucleus total cross sections as a test for the existence of a pion condensate

We suggest an experimental verification of the existence of a pion condensate in finite nuclei by measuring pion-nucleus total cross sections in the vicinity of T_π ≈ 1.2 GeV. Scattering of the pion beam from the condensate pions leads to a measurable modification both in the energy dependence and magnitude of the pion-nucleus total cross section if the condensate is present with a sufficient strength.