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Showing papers in "Philosophical Transactions of the Royal Society A in 1980"


Journal ArticleDOI
TL;DR: In this article, the locus of the critical line in pressure-temperature-composition space is determined exactly by solving a set of equations with the aid of a computer and nine characteristic types of critical lines are distinguished and these correspond to nine separate regions on a van der Waals equation-based phase diagram.
Abstract: The van der Waals equation of state is used to determine phase diagrams for a wide variety of binary fluid mixtures. The locus of the critical line in pressure-temperature-composition space is determined exactly by solving a set of equations with the aid of a computer. The van der Waals constants a$\_{\text{m}}$ and b$\_{\text{m}}$ for the mixture depend quadratically and linearly upon the mole fractions x$\_{\text{i}}$: a$\_{\text{m}}$ = $\sum\_{\text{i}}\sum\_{\text{j}}$ x$\_{\text{i}}$ x$\_{\text{j}}$a$\_{\text{ij}}$ and b$\_{\text{m}}$ = $\sum\_{\text{i}}$x$\_{\text{i}}$b$\_{\text{ii}}$. Mixtures are characterized by three non-dimensional parameters: $\xi $ = (b$\_{22}$-b$\_{11}$)/(b$\_{11}$+b$\_{22}$), $\zeta $ = (a$\_{22}$b$\_{22}^{-2}$-a$\_{11}$b$\_{11}^{-2}$)/(a$\_{11}$b$\_{11}^{-2}$+a$\_{22}$b$\_{22}^{-2}$) and $\Lambda $ = (a$\_{11}$b$\_{11}^{-2}$-2a$\_{12}$/b$\_{11}$b$\_{22}$+a$\_{22}$b$\_{22}^{-2}$)/(a$\_{11}$b$\_{11}^{-2}$+a$\_{22}$b$\_{22}^{-2}$). The parameter $\Lambda $ can be related to the low-temperature enthalpy of mixing and the parameter $\zeta $ to the difference between the gas-liquid critical pressures of the pure fluids. Most of the calculations are for molecules of equal size ($\xi $ = 0), but calculations for a size ratio of two ($\xi $ = $\frac{1}{3}$) are also reported. Nine characteristic types of critical lines are distinguished and these correspond to nine separate regions on a $\Lambda $, $\zeta $-diagram. Isobaric temperature-composition diagrams and pressure-temperature projections are given for one example from each region to illustrate the possible types of phase equilibrium. Special attention is given to the details of lower critical solution temperature behaviour (type IV) such as is found in the system methane + n-hexane, to tricritical points (symmetrical and unsymmetrical), to azeotropy, and to the possibility of double azeotropy. The phase diagrams calculated from the van der Waals equation seem to account, at least qualitatively, for all but one of the varieties of phase equilibria found in binary fluid mixtures: the low-temperature lower critical solution points in some highly structured aqueous solutions of alcohols and amines.

1,248 citations


Journal ArticleDOI
TL;DR: Lead isotopic compositions of young volcanic rocks from different tectonic environments have distinctive characteristics their differences are evaluated within the framework of global tectonics and mantle differentiation Ocean island leads are in general more radiogenic than mid-ocean ridge basalt (morb) leads as discussed by the authors.
Abstract: Lead isotopic compositions of young volcanic rocks from different tectonic environments have distinctive characteristics Their differences are evaluated within the framework of global tectonics and mantle differentiation Ocean island leads are in general more radiogenic than mid-ocean ridge basalt (morb) leads They form linear trends on lead isotopic ratio plots Many of the trends extend toward the field of morb On plots of 207 P b / 204 Pb against 206 Pb / 204 Pb, their slopes are generally close to 01 Island arc leads in general are confined between sediment and morb type leads with slopes of ca 030 on a plot of 207 P b / 204 Pb against 206 Pb / 204 Pb Pb, Sr and Nd isotopic data of Hawaiian volcanics are closely examined Data from each island support a two-component mixing model However, there is a lack of full range correlation between islands, indicating heterogeneity in the end members This mixing model could also be extended to explain data from the Iceland-Reykjanes ridge, and from 45° N on the Atlantic Ridge The observed chemical and isotopic heterogeneity in young volcanic rocks is considered to be a result of long-term as well as short-term mantle differentiation and mixing Lead isotopic data from ocean islands are interpreted in terms of mantle evolution models that involve long-term (more than 2 Ga) mantle chemical and isotopic heterogeneity Incompatible element enriched ‘plume’-type morb have Th/U ratios ca 30 too low and Rb/Sr ratios ca 004 too high to generate the observed 208 Pb and 87 Sr respectively for long periods of time Elemental fractionation in the mantle must have occurred very recently This conclusion also applies to mantle sources for ocean island alkali basalts and nephelinites Depletion of incompatible elements in morb sources is most probably due to continuous extraction of silicate melt and/or fluid phase from the low-velocity zone throughout geological time Data on Pb isotopes, Sr isotopes and trace elements on volcanic rocks from island arcs are evaluated in terms of mixing models involving three components derived from (1) sub-arc mantle wedge, (2) dehydration or partial melting of subducted ocean crust, and (3) continental crust contamination In contrast to the relation between 87 Sr/ 86 Sr and 143 Nd / 144 Nd ratios of ocean volcanics, there is a general lack of correlation between Pb and Sr isotopic ratios except that samples with very radiogenic Pb ( 206 Pb / 204 Pb > 195) have low 87 Sr/ 87 Sr ratios (07028- 07035) These samples also have inferred source Th/U ratios (30-35) not high enough to support long-term growth of 208 Pb Data suggest that their mantle sources have long-term integrated depletion in Rb, Th, U and light ree High 238 U / 204 Pb (y a)values required by the Pb isotopic data are most probably due to depletion of Pb by separation of a sulphide phase Relations between Pb, Sr and Nd isotopic ratios of young volcanic rocks could be explained by simultaneous upward migration of silicate and/or fluid phase and downward migration of a sulphide phase in a differentiating mantleration of a sulphide phase in a differentiating mantle

1,167 citations


Journal ArticleDOI
TL;DR: In this article, various models have been proposed to explain the oxidation resistance of high temperature alloys as a result of additions of rare earth elements, other reactive metals, or dispersions of stable oxides.
Abstract: The improvement in oxidation resistance of high temperature alloys as a result of additions of rare earth elements, other reactive metals, or dispersions of stable oxides, has been known for many years. Two effects seem the most important: first, the adhesion between scale and alloy is markedly improved and this increases the alloy’s resistance to thermal cycling exposure; secondly, in some but not all cases the actual growth rate of the oxide is also reduced. The various models proposed to explain these phenomena are discussed in the light of currently available experimental evidence. The most significant of these involve modification to the early, transient stages of oxidation, doping of the oxide which changes its transport properties, mechanical keying of the surface scale to the substrate by the formation of intrusions of oxide penetrating into the alloy and the elimination of void formation at the alloy-scale interface. The efficacies of the various beneficial additions are compared.

677 citations


Journal ArticleDOI
TL;DR: In this paper, a rigorous theory of dispersion in both granular and sintered spatially-periodic porous media is presented, utilizing concepts originating from Brownian motion theory.
Abstract: A rigorous theory of dispersion in both granular and sintered spatially-periodic porous media is presented, utilizing concepts originating from Brownian motion theory. A precise prescription is derived for calculating both the Darcy-scale interstitial velocity vector $\overline{v}^{\ast}$ and dispersivity dyadic $\overline{D}^{\ast}$ of a tracer particle. These are expressed in terms of the local fluid velocity vector field v at each point within the interstices of a unit cell of the spatially periodic array and, for the dispersivity, the molecular diffusivity D of the tracer particle through the fluid. Though the theory is complete, numerical results are not yet available owing to the complex structure of the local interstitial velocity field v. However, as an illustrative exercise, the theory is shown to correctly reduce in an appropriate limiting case to the well-known Taylor-Aris results for dispersion in circular capillaries.

430 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the role of low-pressure fractional crystallization or partial melting conditions in halogen variations and suggested that mantle-derived heterogeneities in halogens, with major enrichments in the mantle beneath the Azores, are suggested.
Abstract: F, Cl and Br contents of tholeiitic volcanic glasses dredged along the Mid-Atlantic Ridge from 53 degrees to 28 degrees N, including the transect over the Azores Plateau, are reported. The halogen variations parallel those of $^{87}$Sr/$^{86}$Sr, La/Sm or other incompatible elements of varying volatility. The latitudinal halogen variation pattern is not obliterated if only Mg-rich lavas are considered. Variations in extent of low-pressure fractional crystallization or partial melting conditions do not appear to be the primary cause of the halogen variations. Instead, mantle-derived heterogeneities in halogens, with major enrichments in the mantle beneath the Azores, are suggested. The Azores platform is not only a 'hotspot' but also a 'wetspot', which may explain the unusually intense Azores volcanic activity. The magnitude of the halogen and incompatible element enrichments beneath the Azores appear strongly dependent on the size of these anions and cations, but independent of relative volatility at low pressure. The large anions Cl and Br behave similarly to large cations Rb, Cs and Ba, and the smaller anion F similarly to Sr and P. Processes involving crystal and liquid (fluid and/or melt), CO$\_{2}$ rahter than H$\_{2}$O dominated, seem to have produced these largescale mantle heterogeneities. Geochemical 'anomalies' beneath the Azores are no longer apparent for coherent element pair ratios of similar ionic size. Values of such 'unfractionated' coherent trace element ratios provide an indication of the mantle composition and its nature before fractionation event(s) which produced the inferred isotopic and trace element heterogeneities apparently present beneath the North Atlantic. The relative trace element composition of this precursor mantle does not resemble that of carbonaceous chondrites except for refractory trace element pairs of similar ionic size. It is strongly depleted in halogens, and to a lesser extent in large alkali ions Rb and Cs relative to refractory Ba. These relative depletions are comparable within a factor of 5 to Ganapathy & Anders's estimates for the bulk Earth, with the exception of Cs. There is also evidence for removal of phosphorus into the iron core during its formation. With the exception of San Miguel, alkali basalts from the Azores Islands appear to have been derived from the same mantle source as tholeiitic basalts from the ridge transect over the Azores Platform but by half as much degree of partial melting. The Azores subaerial basalts seem to have been partly degassed in Cl, Br and F, in decreasing order of intensity. A working model involving metasomatism from release of fluids at phase transformation during convective mantle overturns is proposed to explain the formation of mantle plumes or diapirs enriched in larger relative to smaller halogen and other incompatible trace elements. The model is ad hoc and needs testing. However, any other dynamical model accounting for the 400-1000 km long gradients in incompatible trace elements, halogens and radiogenic isotopes along the Mid-Atlantic Ridge should, at some stage, require either (1) some variable extent of mixing or (2) differential migration of liquid relative to crystals followed by re-equilibration (or both), as a diffusion controlled mechanism over such large distances is clearly ruled out, given the age of the Earth.

304 citations


Journal ArticleDOI
TL;DR: In this paper, a model for the chemical evolution of the Earth's mantle is proposed, which describes the evolution of a continuously differentiating convecting mantle at the mineral scale.
Abstract: Trace element variations have established the present concept of chemical heterogeneity of the Earth’s mantle. A continuous range of variations is observed for the mantle source of basalts, from mantle depleted in incompatible trace elements to mantle enriched in such elements, in particular light rare earth elements. This heterogeneity is supported by the study of orogenic lherzolites and ultramafic nodules from volcanoes and kimberlite pipes. Radiogenic isotopes of Sr, Pb and Nd confirm this heterogeneity and show that it results from ancient chemical fractionations. This trace element and radiogenic isotope heterogeneity is identifiable in the Precambrian mantle. Pb isotopes are the clearest tracers of this past heterogeneity. Correlations are observed between variations in incompatible element ratios, radiogenic isotope ratios and radiogenic isotope and trace element ratios. These correlations define large domains (source of alkali basalts, source of mid-oceanic ridge basalts) and more restricted domains (e.g. the Canary Islands). Thus, they show that the mantle is heterogeneous on very large scales (ocean scales) as well as in more limited areas. Radiogenic data on ultramafic nodules also show that these mantle materials have isotopic heterogeneities at the mineral scale. These data also allow an estimation of the time scale of creation of these heterogeneities: they are of the order of some 10 9 years (= 1 Ga). The mechanisms involved in the chemical evolution of the mantle are discussed. Heterogeneity is created by chemical fractionation during petrogenetic processes; essentially oceanic lithosphere formation, storage into the continental crust and also recycling of sediments during lithospheric plate subduction. This heterogeneity tends to be erased in the mantle by convection and diffusion. The former efficiently mixes the mantle at large scales. The latter is very inefficient in solid mantle conditions, but can homogenize the radiogenic isotopes during partial melting. All these processes have been continuously active through geological time. A mathematical model is proposed which describes the chemical evolution of a continuously differentiating convecting mantle. The correlations, and in particular mantle isochrons, appear as artefacts without time significance. Evolution of both trace element ratios and isotopic compositions can be described simultaneously if isotopic homogenization is easier than chemical mixing. Variations of lead isotopes tend to indicate an ancient (initial) heterogeneity of the mantle which can be possibly attributed to loss of lead from mantle to core. The rate of chemical fractionation of the mantle cannot have been constant with time but was faster during the Archaean than at present.

185 citations


Journal ArticleDOI
TL;DR: In this paper, a comparison of FeO contents with trace element and isotope contents of basaltic rocks was conducted to understand the evolution of the mantle and its major elements, trace elements and isotopes.
Abstract: Understanding the evolution of the mantle requires a knowledge of the relative variations of the major elements, trace elements and isotopes in the mantle Most of the evidence for mantle heterogeneity is based on variations in the trace element and isotopic ratios of basaltic rocks These ratios are presumed to reflect variations in the mantle sources To compare major element heterogeneities with trace element and isotopic heterogeneities, it is necessary that the major element abundances in basalts also reflect variations in the mantle sources Probably the only major element for which this is so is iron If a basalt has only undergone fractional crystallization of olivine, then the abundance of FeO in the basalt reflects the FeO/MgO ratio of the mantle source, the degree of melting, and the pressure at which melting occurs Relative pressures and degrees of melting can often be constrained, so that variations in the abundances of FeO can be used to obtain information about variations in the FeO/MgO ratio of the mantle sources of basalts Comparison of FeO contents with trace element and isotopic contents of basalts shows some striking correlations and leads to the following conclusions 1 Parental magmas for Kilauean basalts from Hawaii may be related by different degrees of melting of a homogeneous, garnet-bearing source 2 Mid-ocean ridge basalts from the North Atlantic show a negative correlation of La/Sm with FeO, suggesting that the sources that are most enriched in incompatible trace elements are most depleted in FeO relative to MgO, and are probably also depleted in the other components of basalt This correlation does not apply to the entire suboceanic mantle 3 A comparison of tholeiites from near the Azores and from Hawaii shows that sources with similar Nd and Sr isotope ratios may have undergone distinctly different histories in the development of their major and trace element abundances 4 Ocean island tholeiites tend to be more enriched in FeO than ocean floor tholeiites Either the ocean island sources have greater FeO/MgO ratios, or melting begins at significantly greater pressures beneath ocean islands than beneath ocean ridges 5 Major element variations in the mantle are controlled mainly by tectonics and the addition or removal of silicate melts Trace element variations, however, may be controlled by the addition or removal of fluids as well Thus major elements, trace elements and isotopes may each give a different perspective important to the understanding of the evolution of the mantle

173 citations


Journal ArticleDOI
TL;DR: A summary of the rock and mineral nodules erupted with kimberlites is presented in this article, where the nodule types are separated into various categories according to their relatively depleted and fertile chemical character; their deformed and undeformed nature; and the Ca/(Ca + Mg) ratio of their clinopyroxenes (with associated temperature characteristics).
Abstract: A summary of the rock and mineral nodules erupted with kimberlites is presented. Garnet-peridotites are separated into various categories according to: their relatively depleted and fertile chemical character; their deformed and undeformed nature; and the Ca/(Ca + Mg) ratio of their clinopyroxenes (with associated temperature characteristics). Some bulk chemical similarities are noted between high-temperature, deformed and less depleted peridotites and the wall rocks to minor intrusions. There is clear evidence of the occurrence of infiltration metasomatism (involving K, Ti and other incompatible elements) in some mantle xenoliths before their incorporation in the kimberlite. These metasomatic effects may be linked with earlier magmatic events. Extreme chemical heterogeneities may be produced by metasomatism, as with restricted partial melting. Attempts to find homogeneous rocks with average or pristine upper mantle compositions are considered unrealistic. Within the Kaapvaal craton there is no overall pattern of lateral variations in the nodule types from kimberlite, though there is evidence of local heterogeneity and regional changes at craton margins. Boyd & Nixon’s models of vertical layering of rocks and minerals in the upper mantle are contrasted with a model in which horizontal variations in temperatures occur after magma intrusion. It is suggested that the high-temperature deformed peridotites and the megacrysts result from the intrusion of high-temperature magmas into overlying cooler mantle, and that xenoliths from kimberlite provide little direct evidence of mantle stratification with depth.

168 citations


Journal ArticleDOI
TL;DR: In this paper, a catalogue of simple periodic nets is given, in most cases, the plane group short symbol, and the unit cell parameters and the coordinates of the nodes in terms of unit spacing between nearest nodes.
Abstract: In the present paper we consider not only the simplest periodic nets (such as arise from the equivalent circle packings of Niggli, Fejes Toth and others) but also less regular ones, ignored by mathematicians but nevertheless of widespread occurrence and usefulness in crystal chemistry. After a general introduction including some mathematical theorems a catalogue of about 30 nets gives, in most cases, the plane group short symbol, and the unit cell parameters and the coordinates of the nodes in terms of unit spacing between nearest nodes. Examples of their occurrence in compounds of established structure are given in each case. The related concepts of the dual of a simple net and primary and secondary nets in less simple cases are then treated briefly. Transformations between nets are discussed, also with crystal structure examples: first in the case that there is no change in the shape of the unit cell, and using a proposed ‘compatibility’ principle. It transpires that compatible nets are simply derivable from one another, and that in most classes the simplest member is a regular net (4 4 , 3 6 , or 6 3 ). A few of the transformations are relatively well known, but most are new. Together they emphasise the fact that crystal structures do not constitute a massive collection of unrelated types, but rather a group of patterns largely derivable one from another by a few simple, geometrical-crystallographic operations. Here, as elsewhere in the paper, it frequently occurs that transformations are equivalent to the regular incorporation of ‘point defects’ (missing atoms = ‘vacancies’ or additional atoms = ‘interstitials’). Hence ‘point defects’ may be readily generated (even in very small concentrations) by cooperative operations, without any need for longrange diffusion of single atoms. This possibility is not generally considered in theories of diffusion in solids. Another type of transformation involves slip, and does result in a change in the shape of the unit cell, sometimes by a homogeneous deformation. It allows transformation between different (compatibility) classes of nets. §9 deals with the (hexagon-pentagon-triangle) net description of ‘tetrahedrally closed packed’ alloy structures - Frank-Kasper and Friauf-Laves phases - and transformations relating them. The p-U 3 O 8 and related nets discussed in § 10 are somewhat similar, but also contain quadrangles. In § 11 a different type of operation is used to relate structures: adjacent planes are combined by collapse to form a composite net on a single plane. This produces further crystal structure relations that were not previously available, e.g. between ReO 3 , HTB and the pyrochlore framework. Finally, in § 12, some conclusions are drawn, and some of the more novel points developed in the paper are summarized and emphasized.

131 citations


Journal ArticleDOI
TL;DR: In this article, a linear stability analysis of the Laminar flow of air over water confined between two infinite parallel plates was made and the conditions at which small amplitude surface waves first begin to grow were determined.
Abstract: The fully developed laminar flow of air over water confined between two infinite parallel plates was used to study nonlinear effects in the generation of surface waves. A linear stability analysis of the basic flow was made and the conditions at which small amplitude surface waves first begin to grow were determined. Then, following Stewartson & Stuart (1971), the nonlinear stability of the flow was examined and the usual parabolic equation with cubic nonlinearity obtained for the amplitude of the disturbances. The calculation of the linear stability characteristics and the coefficients appearing in the amplitude equation was a lengthy computational task, with most interest centred on the coefficient of the nonlinear terms in the amplitude equation. In two profiles, used as crude models of a boundary layer flow of air over water, the calculations indicated that, over a range of parameters, the non-linear effects would reduce the growth rate of the surface waves and hence lead to equilibrium amplitude waves.

126 citations


Journal ArticleDOI
TL;DR: The stratospheric and mesospheric sounder (s.a.m.s.) instrument was launched on the Nimbus G satellite on 24 October 1978 as mentioned in this paper, and was designed to measure temperature and concentration profiles of various gases in the height range 20-100 km by detecting either their thermal emission or, in some cases, resonant scattering of sunlight.
Abstract: The stratospheric and mesospheric sounder (s.a.m.s.) instrument was launched on the Nimbus G satellite on 24 October 1978. It is designed to measure temperature and concentration profiles of various gases in the height range 20-100 km by detecting either their thermal emission or, in some cases, resonant scattering of sunlight. The gases selected, CO 2 , CO, CH 4 , NO, N 2 O and H 2 O, significantly affect the upper atmosphere energy budget by their influence on the concentration of the primary sunlight absorber, ozone. This influence is disproportionate to their own concentration because of the existence of 9catalytic cycles’ which destroy ozone while regenerating the catalyst. A description of the instrument, its principles of operation and some of the methods of retrieval used is presented, together with some preliminary results from the first 3 months of operations.

Journal ArticleDOI
TL;DR: In this paper, the dependence of the work of fracture on various parameters was discussed together with some suggestions for compensating for the loss of stiffness without reducing the energy absorbing capacity of the system.
Abstract: [Plates I and 2] Results obtained when investigating the fracture behaviour of wood have suggested the possibility of making composite materials with high work of fracture and low density, at the expense of moderate loss of stiffness. The reinforcing elements of the composite are made in the form of cylindrical tubes with helically wound walls of glass or carbon fibres, simulating, to a certain extent, the structure of wood cells. The hollow tubes, under tensile stress and in certain circumstances, are capable of deforming pseudo-plastically absorbing large amounts of energy in a manner which is effectively similar to that of ductile fibres Work of fracture in excess of 4 x 105 J/m2 has been obtained, comparable to that of ductile metals. The dependence of the work of fracture on various parameters will be discussed together with some suggestions for compensating for the loss of stiffness without reducing the energy absorbing capacity of the system.

Journal ArticleDOI
TL;DR: In this article, the theory of Lagrangian means and Stokes drifts is reviewed, with particular attention to recent developments and to possibilities for applying the ideas to the stratosphere.
Abstract: The theory of Lagrangian means and Stokes drifts is reviewed, with particular attention to recent developments and to possibilities for applying the ideas to the stratosphere. The properties of Lagrangian means for finite-amplitude disturbances in spherical geometry pose certain conceptual and technical problems, which appear unavoidable if the notion of Lagrangian mean is to be defined in an exact, coordinate- independent manner compatible with Stokes’s classical theory.

Journal ArticleDOI
TL;DR: A model involving recent metasomatism of the subcontinental mantle beneath Kenya, which could account for the correlated silica undersaturation and incompatible element content of the lavas, is proposed.
Abstract: Nd, Sr and Pb isotope data, together with new major and trace element data are presented for lavas from northern Kenya. A general trend towards silica saturation and decreasing incompatible element contents is observed from the Miocene to the present day. Significantly, the abundances of different incompatible elements decrease at different rates. The Nd, Sr and Pb isotope compositions of the basic lavas are similar to those observed on the Atlantic ocean islands. Comparison of the Sm/Nd ratios required to produce the Nd isotope ratios with those observed in the rocks indicates that light rare earth elements (r.e.e.) have probably been added to the source region of the lavas comparatively recently. A model involving recent metasomatism of the subcontinental mantle beneath Kenya, which could account for the correlated silica undersaturation and incompatible element content of the lavas, is proposed.

Journal ArticleDOI
TL;DR: In situ observations are defined as those made at the point where the instrument is located as discussed by the authors, which is a subset of observations made at a point where a sensor is located. Since a large variety of techniques have been used for in situ measurements, the general features, capabilities and problems of these techniques are reviewed.
Abstract: In situ observations are defined as those made at the point where the instrument is located. Since a large variety of techniques have been used for in situ measurements, the general features, capabilities and problems of these techniques are reviewed. To illustrate capabilities and problems more specifically, examples of recent measurements are presented which have a bearing on the chlorofluoromethane—ozone problem . These include: (1) resonance fluorescence for the measurement of Cl and CIO, (2) grab and cryogenic collection of whole air samples for the m easurem ent of CFCl 3 and CF 2 Cl 2 (as well as CH 4 , H 2 , CO and N 2 O ) , (3) im pregnated filters for acid chloride, and (4) matrix isolation for HO 2 and NO 2 .

Journal ArticleDOI
TL;DR: In this article, the authors used seismic data from the eastern Atlantic off Africa and the western Atlantic off the Blake Escarpment to illustrate the recognition and dating of deep sea unconformities.
Abstract: Lowstands of sea level produce significant unconformities, both on the continental shelves as subaerial unconformities and on the ocean basin slopes and floors by submarine erosion and shifts in depositions patterns. This report utilizes seismic data from the eastern Atlantic off Africa and the western Atlantic off the Blake Escarpment to illustrate the recognition and dating of deep sea unconformities. Twenty-eight major and minor deep sea unconformities are identified on these seismic data and tentatively dated by means of well control and a chart showing global relative changes of sea level. The major unconformities identified are basal Sinemurian, basal Callovian, basal Valanginian, basal middle Aptian, basal middle Cenomanian, basal Thanetian, basal upper Ypresian, basal middle Chattian, basal Burdigalian, basal middle Tortonian, and basal Messinian. Unconformity identification and correlation on seismic data from the deep sea is useful for building a stratigraphic framework for palaeoenvironmental studies and correlating deep-sea stratigraphy with the stratigraphy of continental shelves and interior basins.

Journal ArticleDOI
TL;DR: In this paper, the major factors that influence the interactions between high-performance fibres and organic resins are established and discussed, as illustrated in a few selected examples, and various possible treatments may be classified under three headings: chemical surface modification of the fibre, sizing and polymer fixation.
Abstract: The mechanical characteristics of a fibre-resin composite depend primarily on the mechanical properties of the combined materials, the surface of the fibre, the nature of the fibre-resin bonding as well as the mode of stress transfer at the interface. These two last points are related to the surface properties of the fibres. The various types of bonding that may occur between fibrous materials (carbon, glass and organic fibres) and organic polymers, including the relevant theories, are briefly reviewed. In order to optimize the fibre-resin interactions, it is often essential that the interface should be chemically modified. The various possible treatments may be classified under three headings: chemical surface modification of the fibre, sizing and polymer fixation (grafting). The major factors that influence the interactions between high-performance fibres and organic resins will be established and discussed, as illustrated in a few selected examples.

Journal ArticleDOI
TL;DR: In this article, a salt gradient is imposed on a black-bottomed pond about 1 m deep; this creates a density gradient (positive measured downwards) which suppresses convection when the pond is heated from the bottom by absorbed solar radiation.
Abstract: A salt gradient is imposed on a black-bottomed pond about 1 m deep; this creates a density gradient (positive measured downwards) which suppresses convection when the pond is heated from the bottom by absorbed solar radiation. Between 15 and 25 % of the incident radiation, depending upon pond cleanliness, reaches the bottom and can be decanted by stratified hydrodynamic flow of the bottom layer. Temperatures approaching the boiling point have been recorded. At 32° latitude and under Israel sunshine conditions, estimated annual thermal output from a pond of 1 km 2 is equivalent to 43000 t of fuel oil. A method of avoiding salt diffusion, which would slowly destroy the gradient, is described. Practical problems include suppression of surface mixing by wind and the possible effects of heating large areas of ground.

Journal ArticleDOI
TL;DR: In this paper, a theory of multiple cracking and constrained failure is reviewed and applied to simple laminates and laminated hybrids and demonstrated that it can be applied to preventing cracking due to thermal strain.
Abstract: A hybrid like a multidirectional laminate contains at least two major load-bearing components whose failure strains are different. The failure strain of the higher elongation component is invariably reduced by the presence of the other, but the ultimate strain of the lower elongation component may remain the same or can be increased by decreasing its dimensions. The relevant dimension may be the diameter of a bundle or of separate fibres or the thickness of the transverse ply in a 0 degrees /90 degrees laminate. Our previous theory of multiple cracking and constrained failure is reviewed and applied to simple laminates and laminated hybrids. We also demonstrate that it can be applied to preventing cracking due to thermal strain. It is pointed out that, in 0 degrees /90 degrees /0 degrees laminates, longitudinal splitting of the 0 degrees plies may occur owing to the constraint imposed by the 90 degrees plies, whether these have cracked or not. Simple rules are given to account for the longitudinal ultimate strength and ultimate fracture strain of intermingled glass and carbon hybrids in epoxy resin. In this system, stress concentrations due to failure of the low elongation component do not appear to be very important.

Journal ArticleDOI
TL;DR: Aatite-rich inclusions in some basaltic rocks from eastern Australia are interpreted as mantle crystallization products of a carbonatitic/kimberlitic fluid enriched in low atomic number rare earth elements.
Abstract: [Plate 1] Apatite-rich inclusions in some basaltic rocks from eastern Australia are interpreted as mantle crystallization products of a carbonatitic/kimberlitic fluid enriched in low atomic number rare earth elements (l.r.e.e.), and are a priori evidence for mantle heterogeneity. The chondrite-normalized rare earth abundances of separated apatite, clinopyroxene, amphiboles and micas are high, with La in apatite being up to 4600 times chondrite. Apatites show a significant variation in rare earth content and in La: Lu ratios, indicating the occurrence of some crystal fractionation. The absence of europium anomalies from all mineral phases is indicative of a relatively high oxygen fugacity for the parent magma. The nature of the rare earth element distribution between mineral pairs suggests that some xenoliths represent equilibrium assemblages while some of the amphibole-bearing ones do not. The fluid from which these xenoliths crystallized would be an ideal agent for the metasomatism of upper mantle material and may account for l.r.e.e. enriched patterns of primary magmas in some alkaline provinces.

Journal ArticleDOI
A. K. Dhingra1
TL;DR: Fibre FP as mentioned in this paper is a continuous filament, polycrystalline a-alumina yarn that is suitable for reinforcing a variety of materials, especially non-ferrous metal castings because of a combination of properties such as high strength and modulus.
Abstract: A new experimental inorganic fibre currently under development at the Du Pont Company is a continuous filament, polycrystalline a-alumina yarn designated Fibre FP. This fibre is suitable for reinforcing a variety of materials, especially non-ferrous metal castings because of a combination of properties such as high strength and modulus, stability at elevated temperatures, composite castability and potentially low cost. Fibre FP, essentially > 99 % a-Al 2 O 3 , is made by a novel continuous ceramic fibre process utilizing low cost textile fibre spinning technology and is produced as a yarn containing 210 filaments. The modulus of Fibre FP is 379 GPa (55 x 10 6 lbf in -2 ) with a tensile strength of 1380 MPa (200000 lbf in -2 ). The room temperature strength and modulus of the fibre are retained to about 1000 °C. Recently, higher strength FP fibres with a tensile strength of 2070 MPa (300000 lbf in -2 ) have been demonstrated on a laboratory scale.

Journal ArticleDOI
TL;DR: In this article, large-scale heterogeneities in the primordial mantle are investigated through trace elements measured in oceanic basalts from different locations in the Atlantic and Pacific oceans, based upon the physico-chemical properties of the elements and their classification according to their partition coefficients.
Abstract: Large-scale heterogeneities in the mantle are investigated through trace elements measured in oceanic basalts from different locations in the Atlantic and Pacific oceans. The study relies upon the physico-chemical properties of the elements and their classification according to their partition coefficients. High partition coefficient elements (Co, Ni, Cr) have concentrations in peridotite that are not sensitive to solid-liquid equilibrium (partial melting); the mantle should therefore be homogeneous with respect to these elements. The ratios of elements that have equal or very similar low partition coefficients (Y/Tb, Zr/Hf and Nb/Ta) are constant in all samples studied, despite their large concentration range. These ratios are equal to chondritic ratios and favour a chondritic nature for the primordial mantle. The La/Ta ratio shows two values, either 9 or 18, which are closely related to topography (9 for topographic highs). When the difference between partition coefficients of two hygromagmaphilic elements increases, the local variations observed for their ratio can be interpreted either as local heterogeneities of mantle sources or as the effect of magmatic processes (e.g. partial melting).

Journal ArticleDOI
TL;DR: A survey of the present state of knowledge in this field can be found in this paper, where the authors place particular emphasis on the need for an understanding of the interactions between trace elements.
Abstract: The problems of hot shortness and overheating have beset the metallurgist, forgemaster and smith for a surprisingly long time. In recent years the increase in electric steelmaking has emphasized the difficulties arising from the steady build up of residual elements which is the inexorable consequence of scrap recirculation. Although many of the early investigations considered the influence of individual trace elements on hot ductility, in practice such relatively simple situations seldom arise. More often than not it is the interaction between a combination of trace elements which has to be understood if their net influence on high temperature mechanical properties is to be evaluated. This survey of the present state of knowledge in this field therefore places particular emphasis on the need for an understanding of the interactions between trace elements

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TL;DR: In this paper, a brief review of the general metallurgical properties of temper brittleness in low alloy steels emphasizes that this intergranular embrittlement is sensitive to essentially two categories of independent variables: the chemical composition of the grain boundaries (segregation of the solutes on an atomic scale), as well as the "mechanical-microstructural" parameters of the alloy (microstructure and strength of the matrix, morphology of the carbides and grain boundaries, etc.).
Abstract: A brief review of the general metallurgical properties of temper brittleness in low alloy steels emphasizes that this intergranular embrittlement is sensitive to essentially two categories of independent variables: the chemical composition of the grain boundaries (segregation of the solutes on an atomic scale), as well as the ‘mechanical-microstructural’ parameters of the alloy (microstructure and strength of the matrix, morphology of the carbides and grain boundaries, etc.). This paper, essentially devoted to the former, reviews and discusses the available segregation data in the light of recently proposed models. The segregation potencies and embrittling powers of the various impurities are compared, and their dependence on the alloy’s metallic components through chemical interaction between both types of solutes is particularly emphasized. The link between segregation and solubility in multicomponent systems and its use as a predictive means for impurity segregations is outlined. The discussion aims at showing that temper embrittlement is in no way a unique phenomenon, specific to low alloy steels, as was formerly considered, but rather a strikingly illustrative case of multicomponent segregation induced embrittlement, where some metallic alloying elements, although not embrittling per se , can drastically enhance the segregation of residual impurities, while some others can be used as scavengers to alleviate it.

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TL;DR: In this paper, the accuracy of the geoid maps and sets of harmonic coefficients of order 14, 15 and 30 in the Goddard Earth Model 10B were compared with values obtained independently by analysis of resonant orbits: the results suggest that the values in GEM 10B are realistic for these orders.
Abstract: In recent years the Earth’s gravitational field has been determined with continually improving accuracy, by using hundreds of thousands of observations of Earth satellites, chiefly optical, laser and Doppler, together with surface gravimetry and, most recently, altimeter measurements from the Geos 3 satellite. The geopotential is usually expressed as a double series of tesseral harmonics, and several hundred of the harmonic coefficients are evaluated. Progress in this work during the 1970s is briefly outlined, and some attempt is made to assess the accuracy of current geoid maps and sets of harmonic coefficients, as exemplified in the latest models derived at the Goddard Space Flight Center. The harmonic coefficients of order 14, 15 and 30 in the Goddard Earth Model 10B are compared with values obtained independently by analysis of resonant orbits: the results suggest that the values in GEM 10B are realistic for these orders, and presumably others. It appears that the accuracy of the geoid maps is now approaching 1 m.

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TL;DR: In this article, a general imaging theory is developed from which the performance of scanning and conventional microscopes may be investigated, including the effects of defocus, Zernike phase contrast, and interference and resonant microscopy.
Abstract: The imaging performance of scanning microscopes may be improved by introducing a pinhole in the detector plane, thus forming a confocal (or type 2) scanning microscope. A general imaging theory is developed from which the performance of scanning and conventional microscopes may be investigated. Various methods of obtaining phase imaging are considered, including the effects of defocus, Zernike phase contrast, and interference and resonant microscopy.

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TL;DR: In this paper, a finite element algorithm employing Newton iteration and, for the stability and bifurcation eigenproblem, a block-Lanczos method is applied to gyrostatic liquid drops of fixed volume held captive between two co-rotating, parallel, concentric faces or contact circles and acted on by surface tension and centrifugal force.
Abstract: Computer-aided means are presented for constructing entire families of solutions to Young and Laplace’s nonlinear partial differential equation of capillarity, with the enclosed volume prescribed, and of determining the stability of the solutions and bifurcations between families having different three-dimensional symmetry properties; equivalently, these are means for surveying the topography of corresponding energy surfaces in especially convenient finite-dimensional function spaces spanned by socalled finite element bases in which both the solutions and variations of them are represented. The means are a finite element algorithm employing Newton iteration and, for the stability and bifurcation eigenproblem, a block-Lanczos method. The algorithm is applied to gyrostatic liquid drops of fixed volume held captive between two co-rotating, parallel, concentric faces or contact circles and acted on by surface tension and centrifugal force. The results for the special case of captive cylindrical drops compare well with published and new results of conventional stability and bifurcation analysis. Axisymmetric drop shapes that evolve from rest shapes of constant mean curvature are found to form a one-parameter family in rotational Bond number £ = Q 2 R 3 Ap/8cr. Bifurcating axisymmetric and three-dimensional families are calculated. The limit of stability is found to lie in the family of simplest axisymmetric drops, except in the case of very fat ones, which exchange stability with G-shaped drops, a remarkable fact. Implications for the experiments of Plateau, Carruthers & Grasso, and others are discussed.

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S. Yajima1
TL;DR: In the process of converting organometallic polymers into SiC ceramics by heat treatment, an apparently amorphous state appears which has a parallel in the preparation of glassy carbon made by the pyrolysis of cross linked resins such as phenolformaldehyde as mentioned in this paper.
Abstract: From various new organosilicon polymers many useful ceramics are obtained by heat treatments. The new polymers that have been made in my Laboratory are called Mark I, II and III. High strength SiC fibre, SiC sintered bodies, refractory alloys, and refractory polymers have been obtained from those polymers. In the process of converting organometallic polymers into SiC ceramics by heat treatment, an apparently amorphous state appears which has a parallel in the preparation of glassy carbon made by the pyrolysis of cross linked resins such as phenolformaldehyde. This glassy state of SiC has many interesting features in the fields of physics and chemistry.

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TL;DR: In this article, a depth, gravity and total intensity magnetic profiles have been obtained in the westernmost Gulf of Aden along the direction N 32/212°, estimated to be the direction of sea floor spreading from the computer fit of Arabia and Somalia and a continuous seismic reflexion profile was obtained over the northern part of one of the profiles from the axial rift zone to the Arabian continental margin.
Abstract: The Gulf of Aden has the features of a miniature Atlantic Ocean, namely a central rough zone, main trough and continental margins. It has probably evolved within the last 45 Ma, i.e. it is approximately one third the age of the Atlantic. Being youthful, it is a good place for studying the early stages of continental drift, sea floor spreading and evolution of continental margins. Sixteen precision depth, gravity and total intensity magnetic profiles have been obtained in the westernmost Gulf of Aden along the direction N 32/212°, estimated to be the direction of sea floor spreading from the computer fit of Arabia and Somalia. In addition, a continuous seismic reflexion profile was obtained over the northern part of one of the profiles from the axial rift zone to the Arabian continental margin. The reflexion profile reveals that the basement (surface of oceanic layer 2) has at least three distinct slopes. Changes in the characters of the gravity and magnetic anomalies are noticed corresponding to the changes in slopes of the basement. In accord with recent ideas on the formation and cooling of oceanic lithosphere, it seems unlikely that the Gulf of Aden has evolved by continuous sea floor spreading and more likely it has evolved in at least three distinct phases. The earliest of these is difficult to date from the magnetic anomalies and three possible models are presented. The most likely indicates sea floor spreading from 0 to 4.5 Ma (Plio-Pleistocene), 16 to 23.5 Ma (latest Oligocene to lower Miocene) and 35.5 to 43 Ma (upper Eocene to lower Oligocene). The most surprising result is that the seismic reflexion and gravity data require the ocean-continent boundary to be between the 100 fathom contour and the coast. This implies that the continental margins are underlain by early oceanic crust and should more accurately be called oceanic margins rather than continental margins. Other discoveries include three previously unmapped transform faults and a jump in the spreading axis in the eastern part of the survey area. These, together with the locations of the recent spreading axes and a possible triple junction, are shown on a new tectonic map of the area.

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TL;DR: In this article, the skin regions of type I fibres are seen to contain misorientated crystallites interlinked in a complex manner; these are flaws that will limit the intrinsic tensile strength of the material.
Abstract: Carbon fibre structure is usually characterized by means of X-ray diffraction measurement and electron microscope observation. The meaning of the most important parameters is discussed in terms of the structures revealed by high resolution transmission electron microscopy. Recently, dark-field electron microscopy and electron diffraction of selected areas has been used to reveal and characterize skin-core and sheath-core heterogeneity in type I (2500 degrees C) polyacrylonitrile (PAN)-based carbon fibres. Lattice-fringe electron microscopy has given some insight into the nature of the surface layers in type I, type II (1500 degrees C) and type A (1000 degrees C) fibres. The skin regions of type I fibres are seen to contain misorientated crystallites interlinked in a complex manner; these are flaws that will limit the intrinsic tensile strength of the material.