Subharmonic gap structures in asymmetric superconducting tunnel junctions

Tunneling in the asymmetric superconducting junctions of PbIn and PbTl shows sharp current steps at voltages eV = Δ₁ + Δ₂,$\text{2Δ}{}_2\text{2n}\text{and}\text{2Δ}{}_1\text{2n}$ (structures for n > 1 not readily observed); 2Δ₁ and 2Δ₂ are the energy gaps and n is an integer. We obtain new results for the relative magnitude of the structures, where the larger of the two structures is observed at the larger of the two voltages $\text{Δ}{}_1\text{ρ}\text{and}\text{Δ}{}_2\text{ρ}$. These results, in contrast to other available experimental results on different superconductors, seem to exclude self-coupling theory as the mechanism.     

Polarization dynamics for spin 12-spin I systems with Breit-Rabi interaction

We study the full polarization dynamics of two interacting systems of spin $\text{1}\text{2}$ and spin I for the Breit-Rabi hamiltonian, the sum of contact hyperfine and Zeeman terms. We obtain the time dependence of the polarizations by solving the eigenvalue problems for the interaction hamiltonian and discuss some applications.     

Almost sure convergence of sums of maxima and minima of positive random variables

For a sequence of independent and identically distributed positive random variables, the almost sure convergence of sums of maxima (when suitably normalized) to appropriate constants is proved for both bounded and unbounded random variables. A similar result is also proved for sums of minima of such variables.     

Confirmation of far infrared laser assignments from CH3-deformation and CH3-rocking states of optically pumped methanol

High-resolution Fourier transform spectroscopy has been applied to confirm previously proposed assignments for nine far infrared (FIR) laser lines from the CH₃-deformation state of CH₃OH and one line from the CH₃-rocking state. Accurate frequencies are deduced for the observed and other predicted FIR laser transitions. FIR torsional branch frequencies in the ground state which were used in the confirmation are presented. Comments are also made on the OH-bending mode of CH₃OH.     

Synthesis of single- and multi-wall carbon nanotubes over supported catalysts

The quantities of deposited carbon were measured and the quality of the nanotubes was characterized by means of transmission electron microscopy and scanning tunneling microscopy. The inner and outer diameters of the nanotubes were also measured and the diameter distribution histograms were established. The multi-wall straight and coiled nanotubes were found to be quite regular with an average inner (outer) diameter of 4–7 nm (15–25 nm) and with lengths up to 50 μm. The walls contain concentric cylindrical graphene sheets separated by the graphitic interlayer distance. The single-wall nanotubes were found as bundles of hundreds of aligned straight 1-nm-diameter nanotubes with lengths up to 1-μm. The influence of various parameters such as the method of catalyst preparation, the nature and the pore size of the support, the nature of the metal, the quantity of catalyst active particles, and the reaction conditions on the nanotubes formation were studied. The numbers and dimensions of the catalyst active particles dispersed on the support were found to be of importance in regulating the shape of the produced nanotubes. Following these results, a model of growth mechanism was suggested for the nanotubes obtained by this method. Received: 5 January 1998     

A consistency relation for the electron liquid

The Pauli-relation for the ground state energy of an interacting electron liquid gives an exact relation between the kinetic and potential energy. The purpose of this note is to emphasize that this also provides a direct relation between the momentum distribution of the electrons and the static structure factor. It is also demonstrated how this can be used to test the consistency of the existing theories or experiments.     

SOLVENT-INDUCED ENHANCEMENT OF WEAKLY ALLOWED VIBRONIC TRANSITIONS OF AROMATIC HYDROCARBONS

Abstract— The enhancement of weakly allowed vibronic bands in the fluorescence and absorption spectra of 1,12-benzoperylene, 1,2,3,4-dibenzanthracene, naphthalene and 1-methylnaphthalene has been observed in polar solvents at room temperature. No satisfactory correlation has been found between the extent of solvent effect and the solvent dielectric constant, dipole moment or the Kosower's Z -value. It is proposed that, as we previously found for pyrene, the enhancement is the result of complex formation between the hydrocarbons and the polar solvents which reduces the molecular symmetry and gives, in turn, rise to the intensification of weakly allowed vibronic transitions. The finding that the 2-methyl, 1,3-dimethyl and 1,6-dimethyl derivatives of naphthalene, which have in inert solvents more strongly allowed transitions than naphthalene, do not show the solvent effect to any appreciable extent is consistent with this interpretation.     

The dipolar plasmon modes of a small metallic sphere

We consider here a treatment of the dipolar plasmon of a small metallic sphere, for which the radial extension of the surface profile is small compared with the radius of the sphere. We obtain the eigenvalues and damping by solving the classical equations for a non-uniform system. The theory is applicable also to the driven response. We compare our results with those recently reported by Apell and Ljungbert.     

Carbon-13 resonance assignments of some friedelanes and taraxasteranes

Carbon-13 signal assignments of taraxasteryl acetate, taraxasteryl palmitate, taraxasterol and epi-friedelinyl acetate are reported. Some signal assignments of the friedelanones, reported recently by others, are inconsistent and require revision.