Modelling the initial motion of large cylindrical and spherical bubbles

A two-dimensional, transient, finite difference technique based on a volume fraction specification of the free surface position and accounting for the effects of surface tension is shown to accurately predict the initial motion of large cylindrical and spherical bubbles. The predictions compare very favourably with the experimental data of Walters and Davidson. The initial acceleration of cylindrical and spherical bubbles is properly predicted as g and 2g respectively. The penetration of a tongue of liquid from below is the dominant process by which large deformations from the original shape take place and is well predicted by the model in both cases. For the spherical case the eventual transition into a toroidal bubble is demonstrated and the circulation associated with a rising toroidal bubble as a function of its volume upon release is shown to agree very well with experiments. Iterative linear equation-solving techniques applicable to the special nature of the linear system resulting from such a free surface specification are surveyed and a simple Jacobi iteration based on red-black ordering is found to perform well. The impact of the free surface on the relaxation of the linear system and the convergence criteria is also explored.     

Synthesis of 5-benzyl and 5-benzyloxybenzyl-3′-azido-2′,3′-dideoxyuridine and their analogues as potential anti-AIDS agents

5-Benzyl and 5-benzyloxybenzyl-substituted 3′-azido-2′,3′-dideoxyuridine, ( 8a and 8b ), 3′-halogeno-2′,3′-dideoxyuridine, 9a, 9b, 10a, 10b, 11a and 11b , and 2′,3′-dideoxyuridine, 12a and 12b , of Scheme I were synthesized as potential anti AIDS agents. Synthesis of epimers of 8a and 8b , 5-benzyl- and 5-benzyloxybenzyl-1-(3′-azido-2′,3′-dideoxy-β-D-threo-pentafuranosyl)uracil, 15a and 15b , and 5-benzyl- and 5-benzyloxy-5′-azido-2′,5′-dideoxyuridine, 16a and 16b , shown in Scheme II, were also reported.     

Benzooxirene. Ab initio calculations

Ab initio calculations have been performed on benzooxirene, the corresponding oxo carbene (“ketocarbene”), and the transition state linking the two. At the highest level used, QCISD(T)/6-31G^*//MP2(FULL)/6-1G^* with MP2(FULL)/ 6-31G^* zero point energy corrections, the relative energies of the oxirene, the transition state and the carbene are 0, 24.6, and −17.8 kJ mol⁻¹. Correlation energy effects are very important in this system: at the QCISD(T) level the oxirene lies above the carbene, as at the MP4 and HF levels, but at the MP2 level the ordering is reversed. Benzooxirene is probably slightly nonplanar: the HF/6-31G^* geometry is C_2v but the MP2(Fermi contact)/6-31G^* geometry is C_s with a 6-/3-ring coplanarity deviation of about 6.9 °, although in the MP2(FULL)/6-31G^* geometry this is reduced to about 3.1 °.     

Photoemission and energy loss spectroscopy on semiconductor surfaces

The application of multiple experimental techniques to silicon surface studies is discussed. Two specific cases are considered: the chemisorption of oxygen on silicon at coverages up to one monolayer and the intrinsic surface states on cleaved and on annealed Si (111) surfaces. It is shown that by combining electron energy loss spectroscopy and ultraviolet photoemission spectroscopy, one can obtain an approximate energy level model for both occupied and unoccupied states     

Calculations of the giant dipole resonance for sd-shell nuclei in the open-shell random phase approximation

The systematics of the giant dipole resonance have been calculated in the open-shell RPA for all the self-conjugate sd-shell nuclei, using (i) a phenomenological Rosenfeld interaction, (ii) Barret, Hewitt and McCarthy G-matrix elements and (iii) Kuo G-matrix elements. The excitations are based on shell model ground states for all nuclei except ²⁸Si for which a projected Hartree-Fock ground state was used.     

Waves with random coupling and random propagation constants

We study the mathematical treatment of transmission statistics of coupled wave devices with random imperfections. Such devices include multi-mode waveguides or optical fibers, directional couplers at waveguide or optical frequencies, dominant-wave transmission lines (with the reflected wave the spurious mode), lumped filters composed of circuit or of waveguide elements, multi-layer optical coatings to achieve high or low reflectivity.If the random parameters have very rapid spatial variations, we assume they have white spectra. Exact results for transmission statistics are obtained in such cases. These exact results can be extended to random parameters with almost-white spectra, and narrow-band spectra that are far from white.These calculations are carried out in a simple way by using Kronecker matrix products.