The Royal Society
0080-4614
2054-0272
Cơ quản chủ quản: N/A
Lĩnh vực:
Phân tích ảnh hưởng
Thông tin về tạp chí
Các bài báo tiêu biểu
Polymeric nonlinear optical materials This paper briefly reviews the design requirements for polymeric nonlinear optical materials. Progress in synthesis that leads towards meeting some of these objectives is described with respect to the preparation, characterization and properties of conjugated hydrocarbon polymers.
Tập 330 Số 1610 - Trang 117-125 - 1990
Development of continuum damage in the creep rupture of notched bars
The creep rupture of circumferentially notched, circular tension bars which are subjected to constant load for long periods at constant temperature is studied both experimentally and by using a time-iterative numerical procedure which describes the formation and growth of creep damage as a field quantity. The procedure models the development of failed or cracked regions of material due to the growth and linkage of grain boundary defects. Close agreement is shown between experimental and theoretical values of the representative rupture stress, of the zones of creep damage and of the development of cracks for circular (Bridgman,
Studies in large plastic flow and fracture
, New York: McGraw-Hill (1952)) and British Standard notched specimens (B.S. no. 3500 (1969)). The minimum section of the circular notch is shown to be subjected to relatively uniform states of multi-axial stress and damage while the B.S. notch is shown to be subjected to non-uniform stress and damage fields in which single cracks grow through relatively undamaged material. The latter situation is shown to be analogous to the growth of a discrete crack in a lightly damaged continuum. The continuum damage mechanics theory presented here is shown to be capable of accurately predicting these extreme types of behaviour.
Tập 311 Số 1516 - Trang 103-129 - 1984
New developments in understanding the chemistry of cement hydration
Portland cement is based on calcium silicates with lesser amounts.of calcium aluminates. Its reaction with water, which is responsible for strength development, is a complex process involving the precipitation of hydration products in colloidal gel and crystalline forms. This paper describes the microstructural development of the hydrates the structure of colloidal C—S—H gel, which is the main hydration product, the kinetics of hydration and the aqueous solution chemistry of cement pastes and pastes made with pure C
3
S. Theories relating to the mechanism of cement hydration are examined and these are discussed in terms of studies of the effect of accelerating and retarding admixtures for cement.
Tập 310 Số 1511 - Trang 53-66 - 1983
Turbulence and mixing in a Scottish Loch It is nearly three-quarters of a century since E. R. Watson (1904) and E. M. Wedderburn (1907) made the observations in Loch Ness which showed conclusively, and for the first time, that large bodies of water contain beneath their surface the wave motions which have now come to be known as internal waves. The observations and theory of these waves have developed much since those days, but the Loch is still very useful as a site in which to observe and examine phenomena which are also found in other bodies of water, particularly the ocean. In particular the Loch provides a large-scale natural ‘laboratory’ in which a variety of small-scale phenomena associated with turbulence in a stratified fluid may be studied. Observations have been made with a novel profiling instrument which measures the horizontal velocity of the water and its temperature, from which the density may be inferred. These observations serve to illustrate a variety of local conditions which occur in calm weather, as the Loch responds to the wind and during the passage of an internal surge. Analysis of the records is conducted in terms of an intermittency index (the fraction of fluid in which the density decreases with depth), the Richardson number and a length scale which characterizes the vertical scale of the regions which are found to be unstably stratified. Semi-empirical formulae for the eddy diffusion coefficient and the rate of dissipation of kinetic energy in the turbulent motion are examined to see whether they are consistent with observations. No universal value of the Richardson number is found, but this may be a consequence of the rather low values of Reynolds number found in the Loch thermocline.
Tập 286 Số 1334 - Trang 125-181 - 1977
The shelf-sea fronts: implications of their existence and behaviour
This paper reviews the results of recent observations of the shelf-sea fronts and discusses the relation of these features to w hat is known of the mean circulation. Evidence from satellite infrared imagery and ship data are presented to illustrate the movements and structure of the fronts. Many of the data can be rationalized in terms of models of tidal mixing based on vertical exchange only, with a feedback element, which is needed to account for the small observed adjustment to the springs-neaps stirring cycle. The density gradients within the front imply strong geostrophic currents along the isobars but the available evidence does not support the idea of a frontal jet. The complicated velocity field observed may be the result of large-scale (20—40 km) eddies that develop from instability of the flow. The relative success of local energy models implies that horizontal advection normal to the fronts is weak. A simple model of depth-uniform advection indicates that frontal positions and gradients should be sensitive to flows as small as 1 cm s
-1
, and two examples of such influence are tentatively identified.
Tập 302 Số 1472 - Trang 531-546 - 1981
Slope turbulence, internal waves and phytoplankton growth at the Celtic Sea shelf-break
The edge of the Celtic Sea shelf is characterized during the summer by a band of cold water (
ca
. 100 km broad), which is generally conspicuous in high resolution infrared images from satellites, particularly under high pressure atmospheric conditions with clear skies. Preliminary studies of mixing in this region were made in 1972, 1973 and 1974 and were followed by more detailed interdisciplinary studies in 1976, 1979 and 1980 relating phytoplankton growth to the ways in which turbulence in the environment controls the availability of nutrients and light energy. The results have shown the cooler water to be about 1-2 °C colder than the adjacent surface waters of the Celtic Sea and Atlantic Ocean. This cold band also exhibits higher than background surface values of inorganic nitrate and chlorophyll
a
. Although these values are generally low compared with the values that have been observed near the neighbouring shelf tidal fronts, the increased surface values along the shelf break in summer appear to be significant. The observed increases of chlorophyll
a
are thought to be related to physical processes associated with the slopes, ridges and canyons where enhanced mixing, particularly due to internal waves or upwelling, results in nutrient renewal and subsequent phytoplankton growth along the shelf-break region of the Celtic Sea.
Tập 302 Số 1472 - Trang 663-682 - 1981
The tides of the northeast Atlantic Ocean
The results of a ten-year programme of measurement and analysis of the tides in the open sea west of Europe are described. Instrumental techniques were developed during the period from capacitance-plane sensors used in shelf seas to strain-gauges and quartz crystal sensors used in oceanic depths up to about 4 km. The measuring stations form two chains, one on the edge of the shelf surrounding the British Isles, and the other surrounding an oceanic area bounded by Scotland, Iceland, the Azores and South Portugal, which is subdivided by a line of stations along the 53
1/2
° parallel from Inishbofin to the mid-Atlantic Ridge. Records from tide gauges at strategic oceanic sites were collected and analysed over long periods to provide a basis for accurate analysis of the relatively short-term pelagic pressure records. Tidal admittances to the generating potential vary smoothly over the region except for a change in the age (phase slope) of the diurnal tides towards Reykjavik. The shelf-edge chain included current meters, enabling a direct estimation of the M
2
power transmission on to the shelf, namely 60 GW between Malin Head (Eire) and Floro (Norway) and 190 GW between Valentia (Eire) and the Brittany coast near Ouessant. When combined with known power fluxes into the Irish Sea and through the Dover Strait, these give figures for tidal dissipation in the North and Scottish seas that considerably exceed direct estimates based on bottom friction, confirming similar results by Robinson (1979) for the Irish Sea. Dissipation in the English Channel and western Celtic Sea is also much greater than was assumed by Miller (1966). Further, when the eastward flux of energy out of the ocean is computed solely on the basis of the cotidal map drawn for M
2
it is found that about 360 GW is fed into the shelf region between Lisbon and Valentia Island, indicating a substantial loss along the Biscay shelf south of Ouessant. Thus, all estimates of energy loss in the region studied greatly exceed previously assumed values. Dissipation within the main oceanic area itself is, however, about as small as expected. The diurnal tides in the shelf zones are considerably unlike Kelvin-waves, having short wavelength variations and a tendency for larger amplitudes on the open shelf than at the coast. This probably results from the presence of shelf-wave modes previously identified only in the region of St Kilda. The semi-diurnal tides however have much more regular behaviour along the shelf, with a Kelvin-wave profile west of Inishbofin. The tidal constants at two representative oceanic sites are compared with estimates from recent computational models, with wide ranges from fair agreement to disagreement, showing that tidal computations for the North Atlantic are not so uncontroversial as is often supposed. Avoiding reliance on computational modelling, the authors present cotidal maps of plausible accuracy for the constituents O
1
, K
1
, M
2
, S
2
and M
3
. Currents and power fluxes calculated from the M
2
map are presented and discussed. The principal oceanic amphidromes for the diurnal and semi-diurnal tides are west of the area studied, but their positions are estimated reliably. A major semi-diurnal amphidrome east of Iceland is confirmed, but there is no evidence for a supposed amphidrome centred on the Faeroe Islands. The cotidal map for M
3
is the first ever produced for an oceanic area. It contains two amphidromes near the mid-Atlantic Ridge.
Tập 298 Số 1436 - Trang 87-139 - 1980
Biological implications of fronts on the northwest European continental shelf The results of recent biological investigations of three types of frontal system — tidal, coastal, and shelf-break - are summarized. Each is characterized by high standing crops of phytoplankton and is important as a biogeographic boundary between water masses with distinct plankton communities. Evidence for relatively high rates of primary production along tidal fronts is discussed in relation to secondary production.
Tập 302 Số 1472 - Trang 547-562 - 1981
Analytical treatment of two-dimensional supersonic flow. I. Shock-free flow A solution is presented for the general, wave-interaction problem of steady, irrotational, homentropic flow of a perfect gas. It can be interpreted as a convergent process of successive approximations, based on the solution of linearized theory, for shock-free flow. It constitutes an approximate solution for flow with weak shocks. In part I, the equations of motion are transformed into linear equations in characteristic variables. Their solution is of different type according to whether the flow is near-sonic, hypersonic, or in between these extremes. Special attention is given to the types of boundary condition which occur in physical problems, and solution methods are devised to cope with these types in the medium Mach number range. The method of Riemann functions is used to calculate accurately the pressure distribution in the first interaction region of a jet expanding from a perfect nozzle. It is shown by the help of double power series that shock waves will always occur in the first period of such a jet, even for pressure ratios arbitrarily near unity. The Riemann function approach is also shown to be suitable for the approximate calculation of the flow past aerofoils of prescribed shape; when the requirements of accuracy are exacting, the method of double power series expansion presents the problem in a form suited to high-speed digital computers.
Tập 248 Số 952 - Trang 467-498 - 1956
Brunhes-Matuyama polarity transition in three deep-sea sediment cores
The Brunhes-Matuyama polarity transition was studied in three deep-sea sediment cores obtained from the mid-northern and equatorial Pacific Ocean. Rates of sedimentation vary from 0.7 to 1.1 cm k a
-1
. The cores were sampled across the transition in 4 mm slices, and each level was further subdivided into three specimens. Inclinations above and below the transition interval are in close agreement with that of an axial dipole field. Estimates of transition duration based on directional change range from 4900 to 8500 years. The transition can be described by a longitudinally confined portion in each of the v.g.p. paths, but is complicated by broad loops in all three records. While fine-scale sampling reveals considerable detail, the notable increase in within-level dispersion observed in the transition and the apparent differences in v.g.p. paths in nearby cores from the same region indicate that factors other than the geomagnetic field may contribute to these transition records.
Tập 306 Số 1492 - Trang 113-119 - 1982