Modelling large-bubble formation at submerged orifices

The formation of large gas bubbles at submerged orifices is investigated numerically with a two-dimensional, transient, finite difference model using a volume fraction specification to track the movement of the gas-liquid interface. Experimentally observed features of large-bubble formation such as the initial toroidal shape of the bubbles and the penetration of liquid down the pipe centreline are well predicted by the model. The expected oscillatory nature of growth is also observed. The bubble departure volume corresponds to experiments and to the model of Davidson and Schuler. At present the simulations do not extend far enough to investigate multiple-bubble ejection and important bubble-to-bubble interactions during growth and after departure.     

The splitting of giant multipole states of deformed nuclei

A vibrating potential model is applied to deformed nuclei with a deformed harmonic oscillator potential in order to discuss the splitting of isoscalar giant quadrupole states. Eigenfrequencies of the collective states are estimated to be $\text{√2ω(1 ?}\text{1}\text{3}\text{δ)}$, $\text{√2ω(1 ?}\text{1}\text{6}\text{δ)}\text{and}\text{√2ω(1 +}\text{1}\text{3}\text{δ)}\text{fo and 2}{}^{\mathrm{+}}$ modes, respectively. The splitting of isovector dipole and isovector quadrupole states is also studied according to a schematic model as proposed by Bohr and Mottelson. It is shown that. isovector dipole states are split, as in a hydrodynamic model, while isovector quadrupole states with the same scaling factors as those of isoscalar quadrupole modes.     

Anisotropic photoemission and chemisorption-bond geometry on Ge(111) and Si(111) surfaces

In order to study the effects of photon-polarization selection rules on chemisorptionbond geometry, we have measured photoelectron spectra as a function of angle of incidence, θ_i, in the range 28° ? θ ? 80°. A noble-gas UV resonance lamp and cylindrical mirror analyzer were used to measure both bonding and non-bonding surface Orbitals. A large enhancement (200–400%) of the photocmission is found when photon electric field intensity is near the maximum normal to the surface. This indicates a spatial variation of microscopic fields which is approximately independent of adsorbate bonding since it is determined by the optical properties of the substrate. In addition, we observe some effects on adsorbate photoelectron peaks due to different orbital symmetry. The case of atomic hydrogen chemisorption is discussed as an example of this latter effect.     

Competitive self-assembly and electrochemistry of some ferrocenyl-n-alkanethiol derivatives on gold

Three ferrocenyl-alkanethiol derivatives with different functional groups linking ferrocene to an alkanethiol chain have been synthesized and characterized electrochemically in bulk solution and in self-assembled monolayer films on gold electrodes. Relative affinities of the ferrocenyl-alkanethiols and of the corresponding n-alkanethiols for the electrode surface were evaluated by the competitive self-assembly method. The affinity of the ferrocenyl-alkanethiols for the surface, relative to that of the corresponding alkanethiols, is a function of the polarity of the functional group linking ferrocene to the alkanethiol chain. In general, nonpolar linking groups (methylene) show a stronger affinity for the surface than do polar groups (carboxamides) and especially charged groups (quaternary ammonium salts). It is postulated that electrostatic effects are critically important during self-assembly. Redox potentials for the three ferrocenyl-alkanethiol derivatives scale approximately with the electron donating/withdrawing effects of the functional groups on the cyclopentadiene rings. However, redox potentials for the surface-confined molecules are consistently more positive than for the identical molecules in bulk solution.     

Investigations in the field of fluidization,carried out at London University College

The main trend in investigations carried out at London University College is an elucidation of the mechanism of the operation of chemical reactors with a fluidized bed. The work involved in these investigations consisted of a detailed study of the corresponding physical processes to permit the development of an adequate model of a reactor. Verification of the model by a study of the chemical reactions taking place in a reactor with a fluidized bed is one of the most important stages of the work. The investigations were limited to the case of fluidization by gases. The nature of isolated unperturbed bubbles has been rather thoroughly studied, which makes it possible to construct a simple model [1, 2] which with subsequent refinenment, can become considerably more complicated. The necesary information with respect to two essential elements of this model is lacking. In the first place, heat transfer between the gas in a cloud, surrounded by bubbles, and the gas in the adjacent parts of the fluidized bed has been little studied. In the second place, for actual cases there is no acceptable method for calculating the mean size of the bubbles, their particle-size distribution, the change in their dimensions with height, as a function of the determining parameters such as the velocity of the gas, the particle size, and the construction of the gas-distributing device. Over the course of the last five years, a group of associates^* carried out investigations aimed at obtaining this information, as well as at testing models, and at analyzing of the process of stratification of the solid phase. A review of the latest results is given below.London. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 50–60, November–December, 1972.     

Direct measurement of the phase-coherence length in a GaAs/GaAlAs square network

The low temperature magnetoconductance of a large array of quantum coherent loops exhibits Altshuler-Aronov-Spivak oscillations with a periodicity corresponding to 1/2 flux quantum per loop. We show that the measurement of the harmonics content provides an accurate way to determine the electron phase-coherence length L(phi) in units of the lattice length with no adjustable parameters. We use this method to determine L(phi) in a square network realized from a 2D electron gas in a GaAs/GaAlAs heterojunction, with only a few conducting channels. The temperature dependence follows a power law T(-1/3) from 1.3 K to 25 mK with no saturation, as expected for 1D diffusive electronic motion and electron-electron scattering as the main decoherence mechanism.