Structure and thermal properties of supported catalyst clusters for single-walled carbon nanotube growth

Structure and thermal properties of supported iron clusters were studied using molecular dynamics simulations. When supported clusters are in the liquid state, their surfaces have spherical curvature, whereas solid clusters form a layered crystalline structure. The cluster freezing (melting) point increases dramatically with increasing cluster-substrate interaction strength, and rapid diffusion of cluster surface atoms is observed below the freezing point.     

Retarded dielectric theory of electron energy loss in multilayers and superlattices

This work uses computer algebra to develop the dielectric theory of energy loss for fast electrons travelling in multilayer systems and superlattices. The interaction of a relativistic electron beam is analysed in detail for beams travelling normal or parallel to the interfaces.     

Fundamental photochemical approach to the concepts of fluence (UV dose) and electrical energy efficiency in photochemical degradation reactions

For photochemical reactions in a quasi collimated beam, derivations are presented that introduce 'rate constants' based on the fluence (UV dose) received within the irradiated solution. These fluence-based 'rate constants' are shown to be fundamental and depend only on the quantum yield and the molar absorption coefficient at the irradiation wavelength. An experimental example is given, where the quantum yield for the photolysis of atrazine is determined to be 0.033. The new concepts are developed further to analyze the Figure-of-Merit Electrical Energy per Order (E _EO), and it is shown that the E _EO depends on the same fundamental photochemical parameters. An example of the photolysis of N-nitrosodimethylamine (NDMA) is presented, and it is shown that the E _EO should decrease (increased electrical energy efficiency) as the radius of the UV reactor increases (increased path length), and should increase as the percent transmittance of the water decreases.     

Nucleophilic displacement in polyhalogenoaromatic compounds. Part X. Transmission of substituent effects in polyfluorobiphenyl derivatives

The rate of methoxydefluorination (NaOMe-MeOH, 323.2 K) and the ¹⁹F-NMR chemical shifts of some substituted penta- and nona-fluorobiphenyls have been measured. The observed substituent effects parallel those found in the corresponding pentafluorobenzenes and demonstrate proportionate transmission of the total substituent electronic effect across the aromatic system.     

Charge stripping reactions of ions formed from methane,ammonia, water and hydrogen sulphide by protonation and by electron impact

The minimum energy, Q_min, necessary to convert an ion m₁⁺ to a doubly charged ion m₁²⁺ is obtained for 19 different ions from methane, ammonia, water and hydrogen sulphide by charge stripping using nitrogen collision gas. The ions studied include the [MH]⁺ ions formed by chemical ionization in a high pressure source. Stable m₁²⁺ ions could not be formed in the case of [NH₄]⁺, [NH]^+˙, [H₂O]^+˙ and [OH]⁺. Even in these cases the value of Q_min could be estimated by studying the fragments formed from the unstable m₂₊ ions. In several cases, the energy required to form m₁²⁺ ions is less than the literature value for the ionization energy of m₁⁺. This is discussed in terms of the possibility of the presence of excited states of m₁⁺ in the present experiments.     

Nucleophilic displacement in polyhalogenoaromatic compounds. Part V. Fluorodechlorination of 1,2,3,4- and 1,2,3,5-tetrachlorobenzenes and 2,3,4,5,6-pentachlorotoluene in sulpholan

Potassium fluoride in sulpholan (tetramethylene sulphone) reacted readily with 1,2,3,4- and 1,2,3,5-tetrachlorobenzenes at 250°, but needed temperatures of 270° before fluorodechlorination of pentachlorotoluene proceeded readily. Individual rate constants for the formation and decomposition of some of the fluorochloroarenes have been isolated; their values are discussed in terms of the electronic effects of the substituents.     

Formation of rodlike structures of water between oppositely charged ions in decane and polyethylene

The Gibbs ensemble Monte Carlo method has been combined with the connectivity altering osmotic Gibbs ensemble to study water solubility and clustering in decane and polyethylene. We show that the presence of oppositely charged ion pairs that have fixed positions in the hydrocarbon matrices leads to an order of magnitude increase in the water solubility. This is important to a wide range of technical applications, since the uptake of the water leads to an increase in volume--or expansion--of the hydrocarbon phase which, in the case of polyethylene, may change the polymer properties and lead to water treeing. The increase in solubility is largest when the ions are sufficiently close so that rod-shaped clusters of water molecules form between the ions.     

Source characterization of a subsonic jet by using near-field acoustical holography

In the present study, patch near-field acoustical holography was used in conjunction with a multireference, cross-spectral sound pressure measurement to visualize the sound field emitted by a subsonic jet and to predict its farfield radiation pattern. A strategy for microphone array design is described that accounts for the low spatial coherence of aeroacoustic sources and for microphone self-noise resulting from entrained flow near the jet. In the experiments, a 0.8-cm-diameter burner was used to produce a subsonic, turbulent jet with a Mach number of 0.26. Six fixed, linear arrays holding eight reference microphones apiece were disposed circumferentially around the jet, and a circular array holding sixteen, equally spaced field microphones was traversed along the jet axis to measure the sound field on a 30-cm-diameter cylindrical surface enclosing the jet. The results revealed that the jet could be modeled as a combination of eleven uncorrelated dipole-, quadrupole-, and octupole-like sources, and the contribution of each source type to the total radiated sound power could be identified. Both the total sound field reconstructed in a three-dimensional space and the farfield radiation directivity obtained by using the latter model were successfully validated by comparisons to directly measured results.     

Reconstruction of source distributions from sound pressures measured over discontinuous regions: multipatch holography and interpolation

In the present work, a method of alternating orthogonal projections is described in the context of near-field acoustical holography; it allows missing (or "not measured") data to be recovered, thus relieving the strictness of measurement requirements related to the use of the discrete Fourier transform. The method described here provides the detailed foundation for the patch holography procedure that has previously been introduced to mitigate finite measurement aperture effects by allowing the sound field to be iteratively extended beyond the measurement aperture. It is also shown that the latter iterative algorithm can be used regardless of the spatial distribution of measured data: i.e., patches can be discontinuous. Numerical simulations performed by using a synthetic sound field created by a point-driven, simply supported plate were used to demonstrate the latter point. In particular, a multipatch holography procedure is described that allows a source distribution to be reconstructed from the hologram pressure measured over multiple, unconnected patches. It is finally shown that a related approach allows spatial resolution enhancement by interpolation between measured points.