Growth of multiwalled carbon nanotubes from acetylene over in situ formed Co nanoparticles on MgO support

The performance of Co catalysts supported on MgO at different Co loading (10%-75%) for the formation of carbon nanotubes through acetylene decomposition at 600 ^°C with H₂/C₂H₂ mixture for 1 h is investigated. The yield of MWNTs increases with an increase in Co loading (up to 50%). Starting from 1 g of catalyst precursor, about 8 g of MWNTs was obtained. The XRD patterns of catalyst precursor indicate the presence of cobalt in oxidic phase that eventually transformed into the catalytically active Co nanoparticles (12-18 nm) under the influence of acetylene and was responsible for the growth of coiled-like multi-walled CNTs as revealed by SEM and HRTEM images. It is suggested that bending in coil shaped MWNTs has the potential for functionalization for its biomedical applications.     

The intensity-dependent dielectric function of an exciton system

The nonlinear dielectric function of a direct band gap semiconductor is calculated using non-equilibrium Green's function technique. The interaction between the semiconductor and the intense radiation field is assumed to occur via excitons. As an example we calculate the polariton dispersion relation and the intensity-dependent changes of refraction index for GaAs.The author would like to thank Prof. Nguyen Van Hieu for projecting the problem and helpful discussions.     

Graphs with Prescribed Mean Curvature on Poincare Disk

We establish the existence and uniqueness of a solution of aquasilinear elliptic equation in the unit disk of R². Usingthis result, we obtain the existence of graphs with prescribedcurvature on the Poincaré disk.     

Decomposition of nondegenerate singularities of integrable Hamiltonian systems

The main perpose of this letter is to give a topological classification of stable nondegenerate singularities of smooth integrable Hamiltonian systems. Namely, we show that all such singularities can be decomposed diffeomorphically, after a finite covering, to the direct product of simplest (codimension 1 and codimension 2 focus-focus) singularities.     

Doubly ordered superconducting state in a doped antiferromagnet

In a weakly doped quasi-two-dimensional antiferromagnet with a Fermi contour in the form of small pockets, the Coulomb repulsion gives rise to a doubly ordered superconducting state of coexisting condensates with a large pair momentum and a zero one. The pairing with the large momentum determines the superconducting transition temperature, below which the order with zero momentum coexists as an induced order until the temperature corresponding to the initiation of the phonon pairing mechanism is reached. The superconductivity-induced orbital current density wave eliminates the pairing-repulsion-caused zero points from the two-gap quasiparticle spectrum and leads to a deviation of the relative phase of the superconducting order parameter components from π.     

Synthesis of 2-substituted 4-quinazolone-5-carboxylic acids as inhibitors of DNA-gyrase

A series of 4-quinazolone-5-carboxylic acids were designed as bacterial DNA gyrase inhibitors. The syntheses of the target compounds were accomplished by reacting 3-aminophthalimide with aroyl chlorides followed by rearrangement of the resulting 3-acylaminophthalimides under basic conditions. The designed compounds showed moderate DNA gyrase inhibitory activity.     

Transport and structural properties of polymerized AC60 (A = K, Rb) under zero and high pressure conditions

60 display transport properties vastly different from their unpolymerized counterparts. We here describe structural (X-ray diffraction and transmission electron microscopy) and dc resistivity measurements of polymerized AC₆₀ (A = K, Rb) at zero and high pressures. The structural and electronic properties are rich, and evidence is found for unusual phase transitions in both materials. Received: 28 October 1996/Accepted: 13 December 1996