Condensation of helium in nanotube bundles

Helium atoms are strongly attracted to the interstitial channels within a bundle of carbon nanotubes. The strong corrugation of the axial potential within a channel can produce a lattice gas system wherein the weak mutual attraction between atoms in neighboring channels induces a transition to an anisotropic condensed phase. At low temperatures, the specific heat of the adsorbate phase (with fewer than 2% of the atoms) greatly exceeds that of the host.     

Attainment of lead titanate

Crystalline PbTiO₃ was obtained through the thermal decomposition of 8-hydroxyquinolinate of lead(II) and that of titanium(IV), which was monitored by TG/DTG/DTA under different atmospheric conditions and with varying heating rates. The compound was prepared from adding 8-hydroxyquinoline solution in the solution of metallic ions Pb(II):Ti(IV) (1:1) under constant stirring at 3°C, having the pH adjusted to 10. The results of these investigations show that different thermal behavior related to the precursor occurred and also the consequent formation of residues which have different crystallinities. No carbonate residues from the thermal decomposition could be determined by XRD and IR. Only PbTiO₃ was observed and confirmed by DSC at 470°C, temperature lower than the tetragonal-cubic transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of charge-transfer enhancement on the efficiency and rotary mechanism of an oxindole-based molecular motor

Harvesting energy and converting it into mechanical motion forms the basis for both natural and artificial molecular motors. Overcrowded alkene-based light-driven rotary motors are powered through sequential photochemical and thermal steps. The thermal helix inversion steps are well characterised and can be manipulated through adjustment of the chemical structure, however, the insights into the photochemical isomerisation steps still remain elusive. Here we report a novel oxindole-based molecular motor featuring pronounced electronic push–pull character and a four-fold increase of the photoisomerization quantum yield in comparison to previous motors of its class. A multidisciplinary approach including synthesis, steady-state and transient absorption spectroscopies, and electronic structure modelling was implemented to elucidate the excited state dynamics and rotary mechanism. We conclude that the charge-transfer character of the excited state diminishes the degree of pyramidalisation at the alkene bond during isomerisation, such that the rotational properties of this oxindole-based motor stand in between the precessional motion of fluorene-based molecular motors and the axial motion of biomimetic photoswitches.

A novel oxindole-based light-driven molecular motor with pronounced push–pull character was investigated. The rotary mechanism stands in between the precessional motion of fluorene-based motors and the axial motion of biomimetic photoswitches.     

Catalytic nanomotors: autonomous movement of striped nanorods

Rod-shaped particles, 370 nm in diameter and consisting of 1 microm long Pt and Au segments, move autonomously in aqueous hydrogen peroxide solutions by catalyzing the formation of oxygen at the Pt end. In 2-3% hydrogen peroxide solution, these rods move predominantly along their axis in the direction of the Pt end at speeds of up to 10 body lengths per second. The dimensions of the rods and their speeds are similar to those of multiflagellar bacteria. The force along the rod axis, which is on the order of 10(-14) N, is generated by the oxygen concentration gradient, which in turn produces an interfacial tension force that balances the drag force at steady state. By solving the convection-diffusion equation in the frame of the moving rod, it was found that the interfacial tension force scales approximately as SR(2)gamma/muDL, where S is the area-normalized oxygen evolution rate, gamma is the liquid-vapor interfacial tension, R is the rod radius, mu is the viscosity, D is the diffusion coefficient of oxygen, and L is the length of the rod. Experiments in ethanol-water solutions confirmed that the velocity depends linearly with the product Sgamma, and scaling experiments showed a strong dependence of the velocity on R and L. The direction of motion implies that the gold surface is hydrophobic under the conditions of the experiment. Tapping-mode AFM images of rods in air-saturated water show soft features that are not apparent in images acquired in air. These features are postulated to be nanobubbles, which if present in hydrogen peroxide solutions, would account for the observed direction of motion.     

Determination of 226Ra in biological samples by adsorption on specific adsorbers

The determination of 226Ra in biological samples, such as milk and grass, was studied. 226Ra analysis of cow's milk was studied starting from de-fatted milk. The proteins were eliminated by coagulation of the colloidal phase with trichloroacetic acid. Phosphorus was then removed by precipitating it as molybdophosphate and finally adsorption was carried out by using two different adsorbers in order to concentrate and purify radium. Lead rhodizonate (LEHRO) adsorbed on charcoal and partially reduced tin dioxide (PRTD) were utilised. A method for the determination of 226Ra in grass ashes was also investigated. The main interference, due to magnesium, hinders the use of LERHO, so the proposed procedure is based on adsorption of radium on PRTD at pH 9.5. The magnesium concentration was depleted by precipitating barium (carrier) and radium with calcium carbonate at pH 8 before the adsorption step. The high phosphorus concentration in grass also interferes in the determination of 226Ra; phosphorus was eliminated as above via molybdophosphate precipitation. The radium was carried by barium and spiked with 133Ba. The yield of the chemical procedure was evaluated on the basis of 133Ba activity. Radium samples were alpha-counted and the activity was evaluated with a suitable calibration curve. Both exchangers in the milk analysis and PRTD in grass analysis were shown to be helpful in order to set up an easily performed procedure, which allows many samples to be processed simultaneously. All the methods adopted were shown to be very sensitive. Under the experimental conditions used, with 1 L of milk or 5 g of grass ashes, the limit was about 3 mBq 226Ra L-1 milk and < 1 mBq 226Ra g-1 grass ashes.     

Application of non-isothermal cure kinetics on the interaction of poly(ethylene terephthalate) — Alkyd resin paints

Samples of paint (P), reused PET (PET-R) and paint/PET-R mixtures (PPET-R) were evaluated using DSC to verify their physical-chemical properties and thermal behavior. Films from paints and PPET-R are visually similar. It was possible to establish that the maximum amount of PET-R that can be added to paint without significantly altering its filming properties is 2%. The cure process (80–203°C) was identified through DSC curves. The kinetic parameters, activation energy (E _a) and Arrhenius parameters (A) for the samples containing 0.5 to 1% of PET-R, were calculated using the Flynn-Wall-Ozawa isoconversional method. It was observed that for greater amounts of PET-R added, there is a decrease in the E _a values for the cure process. A Kinetic compensation effect (KCE), represented by the equation InA=−2.70+0.31E _a was observed for all the samples. The most suitable kinetic model to describe this cure process is the autocatalytic Šesták-Berggreen, model applied to heterogeneous systems.     

Observation of isomeric decays in the r-process waiting-point nucleus 130Cd82

The gamma decay of excited states in the waiting-point nucleus (130)Cd(82) has been observed for the first time. An 8(+) two-quasiparticle isomer has been populated both in the fragmentation of a (136)Xe beam as well as in projectile fission of 238U, making (130)Cd the most neutron-rich N = 82 isotone for which information about excited states is available. The results, interpreted using state-of-the-art nuclear shell-model calculations, show no evidence of an N = 82 shell quenching at Z = 48. They allow us to follow nuclear isomerism throughout a full major neutron shell from (98)Cd(50) to (130)Cd(82) and reveal, in comparison with (76)Ni(48) one major proton shell below, an apparently abnormal scaling of nuclear two-body interactions.     

Carbon nanostructures as an electromechanical bicontinuum

A two-field model provides a unifying framework for elasticity, lattice dynamics and electromechanical coupling in graphene and carbon nanotubes, describes optical phonons, nontrivial acoustic branches, strain-induced gap opening, gap-induced phonon softening, doping-induced deformations, and even the hexagonal graphenic Brillouin zone, and thus explains and extends a previously disparate accumulation of analytical and computational results.     

Electronic bisection of a single-wall carbon nanotube by controlled chemisorption

Conversion of two diametrically opposed atomic rows on a carbon nanotube to sp(3) hybridization produces two identical weakly coupled one-dimensional electronic systems within a single robust covalently bonded package: a biribbon. Arm-chair tubes, when so divided, acquire a pair of narrow spin-polarized bands at the Fermi energy; interaction across the sp(3) dividers produces a tunable band splitting in the THz range. For semiconducting tubes, the eigenvalues of the low-energy electronic states are surprisingly unaffected by the bifurcation; however, the tubes' response functions to external electric fields are dramatically altered. These modified tubes could be produced by uniaxial compression transverse to the tube axis followed by site-selective chemisorption.     

Ground state lost but degeneracy found: the effective thermodynamics of artificial spin ice

We analyze the rotational demagnetization of artificial spin ice, a recently realized array of nanoscale single-domain ferromagnetic islands. Demagnetization does not anneal this model system into its antiferromagnetic ground state: the moments have a static disordered configuration similar to the frozen state of the spin ice materials. We demonstrate that this athermal system has an effective extensive degeneracy and we introduce a formalism that can predict the populations of local states in this icelike system with no adjustable parameters.