A Mössbauer study of the substituted hexagonal ferrites BaSrxCa1−xFe4O8 (0 ⩽ x ⩽ 1)

Ferrites of the formula BaCa_1?xSr_xFe₄O₈ (0 ? x ? 1) gave rise to magnetically split Mössbauer spectra indicative of antiferromagnetic ordering at room temperature. These spectra were analysed to yield the isomer-shift, quadrupole splitting, internal magnetic field and its orientation. The unit cell dimensions were obtained from X-ray powder patterns and were used in obtaining estimates of the electric field gradient (e.f.g.). The calculated and observed e.f.g. values indicate increasing symmetry as x → 1. A temperature dependence study of BaCaFe₄O₈ gave a Neel temperature T_N = 670 K and H_eff(O) = 485 kOe.     

Non-linear free surface flows and an application of the Orlanski boundary condition

The focus of this paper is the analysis of spatially two-dimensional non-linear free surface problems. The critical aspects of the problem concern the treatment of the non-linear free surface, the body boundary condition for large motions and the imposition of suitable radiation conditions. To address such complexities, time domain simulation was chosen as the method of analysis. With the use of a finite domain for simulation, a major concern is with the radiation condition to be applied at the open or truncation boundary. For the two-dimensional problem at hand, no theoretical radiation conditions are known to exist. An extension of the Orlanski open boundary condition, based on phase velocity determination at the free surface, is proposed. Three categories of problems were analysed using numerical simulation-namely, freely moving steep waves, waves over a submerged body and forced body motion. Simulation results have been compared with linear theory and experiments.     

THE EFFECT OF COORDINATING LIGANDS ON THE TRIPLET STATE OF CHLOROPHYLL

Under laser excitation at 457.9 and 514.5 nm, a frozen solution of chlorophyll a in n -octane displays fluorescence peak maxima at 2K that may be assigned to two distinct monomeric chlorophyll species. Using zero-field fluorescence-detected magnetic resonance the triplet state properties of the two chlorophyll species have been assigned to the monoligated and biligated chlorophyll monomer in which water serves as the ligand coordinated to the magnesium metal center. These triplet state properties for chlorophyll in solution are then utilized in interpreting triplet state results for in vivo chlorophylls associated with the light harvesting chlorophyll protein complex. It is shown that the triplet state data are consistent with attachment of the chlorophyll molecule to the protein site with a single ligand coordinated to the chlorophyll metal center.     

The elucidation of the 1H- and 13C-NMR spectra of bis[N,N-di(2,3-epoxypropyl)-4-aminophenyl]methane (TGMDA) and composite with bis(4-animophenyl)sulfone (DDS) using two-dimensional fourier transform techniques

The application of Fourier transform (FT) two-dimensional nuclear magnetic resonance spectroscopy to the study of the composite of bis[N,N-di(2,3-epoxypropyl)-4-aminophenyl] methane (TGMDA) and the curing agent bis(4-aminophenyl)sulfone (DDS) is discussed. The combination of 2D-J resolved and homonuclear (proton) shift correlated experiments permits the complex proton spectrum due to the glycidylamine moiety to be completely elucidated. The potential utility of this in the study of the aging of prepreg is briefly discussed.     

Preparation and mössbauer studies of tetraaquabis[maleato(1-)]-iron(II)

Summary Tetraaquabis[maleato(1-)]iron(II), Fe(C₄H₃O₄)₂ · 4H₂O has been synthesised. The compound is monomeric and is isomorphous with the manganese(II) analogue. The temperature dependence of quadrupole splitting and optical spectral data giveca. 10000 cm^–1,ca. 650 cm^–1,ca. 190 cm^–1 andca. 1400 cm^–1 for the 10 Dq, tetragonal field, rhombic field and the splitting of the E_g level, respectively. The quadrupole splitting data indicate that distortion from cubic symmetry increases in the order oxalate < malonate < maleate. DTA, TGA and Mössbauer studies indicate elimination of one molecule of maleic acid at 235 °C. The resulting product shows a less distorted structure and this is attributed to the formation of maleato(2-)iron(II).     

Water removal from porous media by gas injection: experiments and simulation

The flow of a saturated gas through a porous medium, partially occupied by a liquid phase, causes evaporation due to gas expansion. This process, referred to as flow-through drying, is important in a wide variety of natural and industrial applications, such as natural gas production, convective drying of paper, catalysts, fuel cells and membranes. X-ray imaging experiments were performed to study the flow-through drying of water-saturated porous media during gas injection. The results show that the liquid saturation profile and the rate of drying are dependent on the viscous pressure drop, the state of saturation of the gas and the capillary characteristics of the porous medium. During the injection of a completely saturated gas, drying occurs only due to gas expansion. Capillary-driven flow from regions of high saturation to regions of low saturation lead to more uniform saturation profiles. During the injection of a dry gas, a drying front develops at the inlet and propagates through the porous medium. The experimental results are compared with numerical results from a continuum model. A good agreement is found for the case of sandstone. The comparison is less satisfactory for the experiments with limestone.     

Linear programming with stochastic processes as parameters as applied to production planning

In formulating stochastic programming with recourse models, the parameters of the linear programs are usually assumed to be random variables with known distributions. In this paper, the requirement vector parameter is assumed to be a stochastic process { _i (t),tT,i=1,...,m}. The properties of the deterministic equivalents for the cases of the discrete and continuous index setT are derived. The results of the paper are applied to a multi-item production planning model with continuous (periodic) review of the stock on hand of various items.