Search

Abstract: The present paper examines the instability of a double-walled carbon nanotube embedded in an elastic medium under pure bending. Effect of surrounding elastic medium and van der Waals forces between the inner and outer nanotubes is taken into consideration. From the point of view of continuum modeling, an elastic double-shell model is presented for the pure bending buckling of a double-walled carbon nanotube. Based on this model, a condition is derived in terms of the buckling modes of the shell, from which the critical bending moment can be predicted. The paper emphasizes bifurcation instability. It is shown that buckling may occur. Finally, a simplified analysis is carried out to estimate the moment causing bifurcation instability of the double-walled carbon nanotube. [Copyright &y& Elsevier]

Abstract: The influence of van der Waals (vdW) force on the stability of electrostatic torsional nano-electro-mechanical systems (NEMS) actuators is analyzed in the paper. The dependence of the critical tilting angle and voltage is investigated on the sizes of structure with the consideration of vdW effects. The pull-in phenomenon without the electrostatic torque is studied, and a critical pull-in gap is derived. A dimensionless equation of motion is presented, and the qualitative analysis of it shows that the equilibrium points of the corresponding autonomous system include center points, stable focus points, and unstable saddle points. The Hopf bifurcation points and fork bifurcation points also exist in the system. The phase portraits connecting these equilibrium points exhibit periodic orbits, heteroclinic orbits, as well as homoclinic orbits. [Copyright &y& Elsevier]

Abstract: The interaction between electrically neutral surfaces at sub-micron separation is dominated by the force arising from quantum fluctuations of the electromagnetic field, known as the Casimir force. This effect has been witnessing a renewed interest because of its potential impact in micro- and nanotechnology. Most recent literature has focused on the study of the attraction between bulk-like metallic surfaces in vacuum. Because electromagnetic fluctuations depend on the dielectric function of the surfaces, the use of different materials might reveal new aspects of the Casimir force and suggest novel solutions for the design of micro- and nanofabricated devices. Following this approach, we have measured the Casimir force using Hydrogen Switchable Mirrors—a metallic mirror that switches from highly reflective to transparent when exposed to hydrogen. The comparison of the results obtained in air and in hydrogen sheds light on the relative contribution of visible and infrared wavelengths to the Casimir interaction. We have also studied the dependence of the Casimir force on the metallic film thickness and have shown the effect of the skin-depth. The final section of the paper discusses the torque induced by quantum fluctuations on two birefringent plates and describes an experiment that should allow us to observe this phenomenon. [Copyright &y& Elsevier]

Particle flowability and compactibility are the two critical process parameters tested when a pharmaceutical material is formulated for a tabletting process. These behavioral descriptions are strongly affected by geometrical, physical, chemical and mechanical particle properties, as well as operational conditions. The property influences are broadly known in a qualitative sense, but have largely escaped fundamental quantitative description. Various measurement methods have been separately developed for each of these properties which provide comparative indices to assist in process and formulation design. This paper seeks to establish the connections between interparticle van der Waals force and both flowability and compactibility, and therefore also the inter-relations between the two apparently distinct properties. Paracetamol and the excipients often associated with it for tabletting are used as test materials to provide an initial validation of the theoretical development. These powders are well-characterized and known to be particularly difficult with respect to flowability and compactibility. [Copyright &y& Elsevier]