A Note on Thermocapillary Instability in the Presence of a Magnetic Field

We formulate the asymptotic theory of thermocapillary instability in a planar fluid layer heated from below in the presence of a strong magnetic field corresponding to high Hartmann number. Explicit asymptotic expressions are derived for the velocity perturbation, temperature perturbation and electric current density. Their spatial structure is characterized in terms of Hartmann boundary layers - a concept which permits a physical understanding of more complicated situations involving surface deformation, buoyancy and thermoelectric effects. The physical nature of large scale instabilities in the case of a deformable surface is clarified

Evidence of 1D behaviour of He4^4 confined within carbon-nanotube bundles

We present the first low-temperature thermodynamic investigation of the controlled physisorption of He$^{4}$ gas in carbon single-wall nanotube (SWNT) samples. The vibrational specific heat measured between 100 mK and 6 K demonstrates an extreme sensitivity to outgassing conditions. For bundles with a few number of NTs the extra contribution to the specific heat, C$_{ads}$, originating from adsorbed He$^{4}$ at very low density displays 1D behavior, typical for He atoms localized within linear channels as grooves and interstitials, for the first time evidenced. For larger bundles, C$_{ads}$ recovers the 2D behaviour akin to the case of He$^{4}$ films on planar substrates (grafoil).Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

Interplay between structure and magnetism in Mo12S9I9Mo_{12} S_9 I_9 nanowires

We investigate the equilibrium geometry and electronic structure of Mo$_{12}$S$_{9}$I$_{9}$ nanowires using ab initio Density Functional calculations. The skeleton of these unusually stable nanowires consists of rigid, functionalized Mo octahedra, connected by flexible, bi-stable sulphur bridges. This structural flexibility translates into a capability to stretch up to approximate 20% at almost no energy cost. The nanowires change from conductors to narrow-gap magnetic semiconductors in one of their structural isomers.Comment: 4 pages with PRL standards and 3 figure

Ferromagnetic semiconductor single wall carbon nanotube

Possibility of a ferromagnetic semiconductor single wall carbon nanotube (SWCNT), where ferromagnetism is due to coupling between doped magnetic impurity on a zigzag SWCNT and electrons spin, is investigate. We found, in the weak impurity-spin couplings, at low impurity concentrations the spin up electrons density of states remain semiconductor while the spin down electrons density of states shows a metallic behavior. By increasing impurity concentrations the semiconducting gap of spin up electrons in the density of states is closed, hence a semiconductor to metallic phase transition is take place. In contrast, for the case of strong coupling, spin up electrons density of states remain semiconductor and spin down electron has metallic behavior. Also by increasing impurity spin magnitude, the semiconducting gap of spin up electrons is increased.Comment: 10 pages and 9 figure