Showing papers by "University of Salford published in 1976"

Flow of inelastic and viscoelastic fluids past a sphere

Abstract: This is essentially an engineering study undertaken with a view to providing drag coefficient correlations for the motion of a solid sphere in inelastic and viscoelastic fluids over a wide range of Reynolds numbers. An approximate closed form analytical solution has been obtained for the motion of a solid sphere in powerlaw fluids and this solution has been verified experimentally. The high Reynolds number flow was analysed theoretically using boundary layer theory; the results were used to separate form and skin friction. Viscoelastic fluids showed “drag reduction” at high Reynolds number. About 300 experimental data points were used to obtain drag coefficient correlations over a wide range of material and flow parameters.

A theoretical study of body drag in subcritical axisymmetric flow.

Abstract: A method of predicting body drag in subcritical axisymmetric flow is outlined which requires only detailed body shape, free-stream conditions and transition point to be prescribed. Results of calculations for a range of body shapes are shown essentially to confirm information in Royal Aeronautical Society Data Sheets but clearly demonstrate that fineness ratio alone is not sufficient to characterise body shape. For example, at a fixed fineness ratio of 0.18, detailed changes in body contour are shown to produce 10 per cent changes in drag coefficient.

Low-frequency Raman spectra of lysozyme.

Abstract: Synopsis New techniques in laser Raman spectroscopy are used to obtain spectra of aqueous solutions of lysozyme for frequency shifts as small as 5 ern-'. In addition, Raman measurements are made on two crystalline forms of hen egg white lysozyme. The spectra obtained from the solution and from the crystal are found to be similar for frequencies above 100 cm-'. However, a low-frequency band at 25 cm-' observed in crystalline lysozyme is not found in the solution, indicating that this band cannot be attributed to an internal molecular vibration.

Theory and design of axially ordered filters for high intensity magnetic separation

Abstract: A single-wire theory of an axially ordered filter has been developed and its consequencies discussed. A typical example of the design of ordered filters has been investigated and attention given to filter elements capable of holding magnetic fibres in a desired position in space.

The influence of surface diffusion on topography development of an amorphous solid during sputtering

Abstract: The erosion and development of topography on an initially contoured amorphous solid due to the simultaneous action of ion beam sputtering and surface diffusion, is analysed. It is shown that derivation of formal expressions for the local rate of co-ordinate motion and radius of curvature is straight forward. Application of detailed prediction of the time varying behaviour of the surface profile is analytically difficult, however, and computational methods are suggested. The case of radiation enhanced surface diffusion is also considered briefly.

Surface density of states and field emission

Abstract: The relation between the total energy distribution of electrons field emitted from metals and the surface density of states is analyzed in general terms. Numerical reslts on the total energy distribution of field-emitted electrons from the (100) and (110) planes of tungsten obtained previously by the authors and extended here to a wider energy region are interpreted in terms of surface density-of-states effects. It is shown in particular that the peak in the total energy distribution from the (100) plane at 0.29 eV below the Fermi level is due to virtual surface states which give rise to enhanced tunneling at that energy. For the (100) plane of tungsten virtual surface states are shown to exist in an energy region extending from 0.20 to 0.95 eV below the Fermi level, but only the states at 0.29 eV below ${E}_{F}$ give rise to peaks in the total energy distribution of the emitted electrons. Another broad peak in the total energy distribution from the (100) plane observed at about 1.3 eV below the Fermi level is also reproduced by our calculation. This peak is the cumulative effect of a number of factors which cannot be disentangled in a simple way, but is not a result of surface states.

Surface Plasmon-Polaritons in a Spatially Dispersive Inhomogeneous Medium

Abstract: The dispersion of surface plasmon-polaritons and their associated fluctuation densities and electric fields are calculated for a spatially dispersive semi-infinite electron plasma, with, parameters appropriate to the metallic state. The model is hydrodynamic and the electron density is assumed to be uniform and equal to the bulk value, except for a small region near the surface. In this surface neighbourhood the electron density is assumed to fall in a step-function manner as in previously reported successful models of surface profile properties. The momentum range covers that which is experimentally available and includes both the retardation and electrostatic regimes. It is emphasised that the inclusion of spatial dispersion, by the introduction of a pressure gradient, is an essential feature. This is because the distance over which the surface density changes is such that the transit time of the carriers is the same order of magnitude as the inverse plasma frequency. Resonances are possible, therefore, which are entirely absent in pure retardation models which ignore spatial dispersion. Fluctuation densities, electric fields, and polarisation plots are presented. The previously reported assertion that the charge distributions can be rigorously classified into multipoles is investigated numerically. Fur ein raumlich dispersives, semi-infinites Elektronenplasma werden die Dispersion von Oberflachenplasmonen-Polaritonen und deren assoziierte Fluktuationsdichten und elektri-sche Felder berechnet, wobei Parameter benutzt werden, die dem metallischen Zustand angepast sind. Das Modell ist hydrodynamisch, wobei angenommen wird, das die Elek-tronendichte einheitlich und mit Ausnahme eines kleinen Bereiches in der Nahe der Ober-flache gleich dem Volumenwert ist. In der Nachbarschaft dieser Oberflache wird angenommen, das die Elektronendichte in Form einer Stufenfunktion abnimmt, wie in fruher ver-offentlichten erfolgreichen Modellen von Oberflachenprofileigenschaften. Der Impuls-bereich uberstreicht das experimentell zugangliche Gebiet und sohliest sowohl Retardie-rungs- als auch elektrostatische Regimes ein. Es wird hervorgehoben, das die Einbeziehung von raumlicher Dispersion, durch die Einfuhrung eines Druckgradienten, ein wesentliches Merkmal ist. Dies ruhrt da von her, das die Entfernung, uber welche die Oberflachendichte sich andert, so ist, das die Transitzeit der Ladungstrager von der gleichen Grosenordnung wie die inverse Plasmafrequenz ist. Es sind deshalb Resonanzen moglich, die sonst in reinen Retardierungsmodellen, die die raumliche Dispersion ignorieren, vollstandig fehlen. Fluktuationsdichten, elektrische Felder und Polarisierungskurven werden angegeben. Die fruher veroffentlichte Behauptung, das die Ladungsverteilungen sich vollstandig nach Multipolen klassifizieren lassen, wird numerisch untersucht.

Non-crystallinity of ion-irradiated metals

Abstract: THE preparation of various metals and metallic alloys in a non-crystalline state using splat cooling, vapour quenching or electrochemical deposition techniques has been reported by many authors. A distinguishing characteristic of such amorphous films is a severe modification of the structure factor from that of the crystalline state. Although usually formed only at low temperatures the non-crystalline state may in some cases be metastable to above room temperature, this being particularly true for alloys near the eutectic. We examine here evidence for metastable non-crystalline alloys resulting from ion irradiation.

Calculation of Steel Diaphragm Behavior

Abstract: The available approaches to diaphragm design are reviewed and it is concluded that for panels that fall within its scope, the best available approach is the one proposed by Bryan in \IConstrado Monographs\N, but there are certain deficiencies in this method as presently formulated. A modified approach is presented for a wide range of diaphragm types which satisfy the following conditions: (1)The diaphragm is rectangular in plan; and (2)it is regular in construction, in particular there are no opening of significant size. It is proposed that diaphragms satisfying the preceding criteria be termed “simple diaphragms” and such diaphragms need not be investigated by the more expensive methods of testing or finite element analysis because the theory described in this paper is quite adequate. Diaphragms which fall outside the scope of the preceding definition should be termed “complex diaphragms” and require a more comprehensive investigation. The basic design expressions are summarized and these expressions form a basis for diaphragm design.

Torque suppression in mechanically stirred liquids and multiphase liquid systems

Abstract: Both polymeric and fibrous drag-reducing additives can be used to suppress the torque of agitators operating in a turbulent regime. Unlike the tubular flow, the influence of the fibrous additive is stronger than that of the polymer but their combined action seems to be additive. The action of the drag-reducing additives is further enhanced by the presence of a second phase (gaseous or liquid) in the stirred tank. In aerated tanks, the torque on the shaft of the agitator is not only reduced by more than 70% but also the flooding point is shifted to higher gas rates. An application of this phenomenon to fermentation tanks and similar technologies has been suggested.

Photochemical reactions in an MDI‐based elastomeric polyurethane

Abstract: Polyurethanes based on diphenylmethane 4,4′-diisocyanate (MDI) were examined by electronic spectroscopy and by continuous and laser flash photolysis. Fluorescence and phosphorescence emissions were observed, and although the source of the fluorescence could not be identified, the phosphorescence appears to originate from a benzophenone-type oxidation impurity. On laser flash photolysis, transient absorptions were observed at 375 nm and 580 nm. The latter is assigned to a ketyl radical center formed by hydrogen abstraction from the polymer matrix. Participation of these species in the photochemical reactions leading to deterioration of the MDI-based polyurethane is discussed.