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  • Articles  (32)
  • Cambridge University Press  (32)
  • 1990-1994  (10)
  • 1955-1959  (16)
  • 1945-1949  (6)
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  • Articles  (32)
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  • 1
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    On the evolution of a turbulent boundary layer induced by a three-dimensional roughness element (1992)
    Cambridge University Press
    Details
    Publication Date: 1992-04-01
    Description: An experimental investigation is described which has as its objectives the extension of the technical data base pertaining to roughness-induced transition and the advancement of the understanding of the physical processes by which three-dimensional roughness elements induce transition from laminar to turbulent flow in boundary layers. The investigation was carried out primarily with single hemispherical roughness elements surface mounted in a well-characterized zero-pressure-gradient laminar boundary layer on a flat plate. The critical roughness Reynolds number at which turbulence is regarded as originating at the roughness was determined for the roughness elements herein considered and evaluated in the context of data existing in the literature. The effect of a steady and oscillatory free-stream velocity on eddy shedding was also investigated. The Strouhal behaviour of the ‘hairpin’ eddies shed by the roughness and role they play in the evolution of a fully developed turbulent boundary layer, as well as whether their generation is governed by an inflexional instability, are examined. Distributions of mean velocity and intensity of the u-fluctuation demonstrating the evolution toward such distributions for a fully developed turbulent boundary layer were measured on the centreline at Reynolds numbers below and above the critical Reynolds number of transition. A two-region model is postulated for the evolutionary change toward a fully developed turbulent boundary layer: an inner region where the turbulence is generated by the complex interaction of the hairpin eddies with the pre-existing stationary vortices that lie near the surface and are inherent to a flow about a three-dimensional obstacle in a laminar boundary layer; and an outer region where the hairpin eddies deform and generate turbulent vortex rings. The structure of the resulting fully developed turbulent boundary layer is discussed in the light of the proposed model for the evolutionary process.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 2
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    The characterization of the humic complexes of soil organic matter (1947)
    Cambridge University Press
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    Publication Date: 1947-04-01
    Description: 1. During the course of the alkali fractionation and the preparation of the humic precipitates, the qualitative characters of the fractions were followed by employing a standard hydrolysis with dilute acid. Humic acid itself was shown to be unhydrolysed by this reagent, and, therefore, the extent of hydrolysis of a humic fraction can be used as a criterion of purity.2. Studies on the fractionation of the humic precipitate with aqueous, anhydrous, and alcoholic bases, led to the following conclusions:(a) The humic precipitate as normally prepared i s always a mixture of true humic acid with varying amounts of co-precipitated material of a non-humic nature.(b) This non-humic material is not an integral part of the humic molecules, it is merely co-precipitated and adsorbed contaminants.(c) The non-humic material is differentiated from the humic acids by the following properties: (i) it is hydrolysable with acid; (ii) it does not give the characteristic nitro-humic compound on nitration.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 3
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    Turbulent structure in a channel flow with polymer injection at the wall (1990)
    Cambridge University Press
    Details
    Publication Date: 1990-09-01
    Description: Two-component laser velocimeter measurements in a fully developed turbulent water channel flow with polymer injection were used to examine the effect of polymer injection on the Reynolds stresses and the production terms in the Reynolds stress transport equations. These measurements show that while the root-mean-square (r.m.s.) fluctuation level of the streamwise velocity was increased, the r.m.s. of the wall-normal velocity and the Reynolds shear stress were reduced. The decrease in the Reynolds shear stress resulted from altered contributions from the quadrants of the (u,p)-plane. Although the Reynolds shear stress decreased, the magnitude of the velocity fluctuation products which most contributed to that stress increased. Production of the streamwise Reynolds normal stress was decreased but production of the Reynolds shear stress was unchanged. This shows that the processes represented by pressure-strain correlation terms in the Reynolds stress transport eauations mav be directly affected bv the nolvmer. © 1990, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 4
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    Mitochondrial DNA variation of Champsocephalus gunnari Lönnberg (Pisces: Channichthyidae) stocks on the Kerguelen Plateau, southern Indian Ocean (1994)
    Cambridge University Press
    Details
    Publication Date: 1994-09-01
    Description: The distribution of the icefish Champsocephalus gunnari on the Kerguelen Plateau is confined to the inner shelves of Heard and Kerguelen islands and outlying banks where the water depth is less than 350 m. For fisheries management purposes, it is necessary to know whether fish from the various shelves and banks belong to one single or several separate populations. Analysis of the mitochondrial DNA of fish from various localities using restriction endonclease enzymes revealed no significant genetic heterogeneity between any of the localities. This does not preclude the existence of isolated stocks at the present time but indicates that the populations have been separated too recently for genetic isolation to be manifested, or that low-level interchange of fish between the populations may be maintaining genetic homogeneity.
    Print ISSN: 0954-1020
    Electronic ISSN: 1365-2079
    Topics: Biology , Geography , Geosciences
    Published by Cambridge University Press
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  • 5
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    The storage of ware potatoes in permanent buildings II. The temperature of unventilated stacks of potatoes (1955)
    Cambridge University Press
    Details
    Publication Date: 1955-08-01
    Description: 1. Under normal English storage conditions, the heat production of mature potatoes drops rapidly from a value of probably about 150 b.th.u./ton/hr. immediately after harvest to about 30–50 b.th.u./ton/hr. Sprouting is accompanied by an increase in the rate of heat production. The initial heat production of immature potatoes may be of the order of 250 b.th.u./ton/hr.2. As a result of the production of heat, the temperatures in stacks of potatoes will tend to rise to levels above that of the outside air which are just sufficient to cause the convection and conduction necessary to remove the metabolic heat as fast as it is produced.3. The difference in temperature between the potatoes and the ambient air is a function of the heat production of the potatoes and of the height of the stack, and is practically independent of its other dimensions if these exceed twice the height. Under average conditions during the middle of the storage season, and for heights of storage of from about 6 to 12 ft. it may be taken as a rough practical guide that the average and maximum temperatures of the potatoes will tend to exceed the average temperature of the store air by about 2/3 and 1° F. respectively for every foot of height.4. Overheating is possible at both the beginning and end of the storage season, when heat production is high and the outside temperatures also possibly high. In general it is safe to store unventilated potatoes to a height of about 6 ft. if they are mature, though if they are harvested with a great deal of earth late storage should not be attempted. If there is no intention of storing late, and the potatoes are fairly clean, storage to aheight of 12 ft. may be permissible. Immature potatoes should not be stored to a height of more than 3 ft.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 6
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    Improvement of carrot crop establishment by combining seed treatments with increased seed-bed moisture availability (1990)
    Cambridge University Press
    Details
    Publication Date: 1990-08-01
    Description: SUMMARYIn studies of carrots sown on three dates at Wellesbourne in 1986, mean time to seedling emergence and spread of times to seedling emergence of untreated and fluid-drilled seeds increased as seed-bed moisture at sowing decreased. These differences were not observed with irrigation before sowing.Osmotic priming increased the percentage of seeds with emerged radicles at the time of fluid drilling from 17% in the untreated control to 56%. Irrespective of seed-bed moisture, time to emergence was shorter from primed germinating seeds than from germinating seeds, both treatments giving earlier seedling emergence than untreated seeds. Seedling shoot weight was greater from treated than from untreated seeds.Seed-bed characteristics on unirrigated plots had no effect on seedling emergence when soil moisture was adequate but, where soil moisture was limiting, rolling the seed bed to increase capillarity resulted in 79% emergence compared with the 67% average from seed beds that were not rolled. Application of a soil conditioner to stabilize the seed-bed surface structure generally improved emergence when rain fell soon after sowing. The results suggested that a combination of seed-bed and seed treatments can significantly improve the predictability of crop establishment of carrots on different dates.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 7
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    Refraction correction for radio-echo sounding of large ice masses (1992)
    Cambridge University Press
    Details
    Publication Date: 1992-01-01
    Description: This paper presents a simple mathematical formula for correcting radio-echo-sounding data from an ice sheet or glacier for the effects of varying refractive index. The method requires some knowledge of the variation of refractive index with depth. In rare cases this may be known from direct measurement, but it can be estimated from the density profile. If even this is unknown, we show that the corrections can be estimated to an accuracy of about 3% of the depth to bubble close-off (i.e. to about ±12 m for dry-snow conditions), and that the size of the refraction correction for a glacier or ice sheet with a flat bed is typically 6–10 m under these conditions.
    Print ISSN: 0022-1430
    Electronic ISSN: 1727-5652
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 8
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    Refraction correction for radio-echo sounding of large ice masses (1992)
    Cambridge University Press
    Details
    Publication Date: 1992-01-01
    Description: This paper presents a simple mathematical formula for correcting radio-echo-sounding data from an ice sheet or glacier for the effects of varying refractive index. The method requires some knowledge of the variation of refractive index with depth. In rare cases this may be known from direct measurement, but it can be estimated from the density profile. If even this is unknown, we show that the corrections can be estimated to an accuracy of about 3% of the depth to bubble close-off (i.e. to about ±12 m for dry-snow conditions), and that the size of the refraction correction for a glacier or ice sheet with a flat bed is typically 6–10 m under these conditions.
    Print ISSN: 0022-1430
    Electronic ISSN: 1727-5652
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 9
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    Cambridge University Press
    Details
    Publication Date: 1955-12-01
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
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  • 10
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    Rhynchonellids of the Boueti Bed of the Great Oolite Series of Langton Herring, Dorset: A Study in Variation (1948)
    Cambridge University Press
    Details
    Publication Date: 1948-02-01
    Description: (1) The range of variation in the external characters of the rhynchonellids examined is illustrated by means of graphs and scatter-diagrams.(2) The three-variable scatter compares directly the proportions of thickness, breadth, and length, and defines the assemblage as adequately as several scatters which relate only pairs of variables. A close relationship is shown to exist between the three-variable scatter in which the positions of specimens are mathematically determined and the scatter in which the specimens are placed according to general appearance.(3) The three-variable scatter, when considered with size-groups, indicates that with growth, breadth and thickness increase more rapidly than does length. All the scatters indicate that proportionate thickness Varies to a greater degree than does proportionate breadth or proportionate length.(4) The sample, being random, is probably nearly representative of the goniorhynch rhynchonellid fauna of the Boueti Bed at Langton Herring. The stratigraphical value of the work, however, can only be proved by examination of assemblages from other localities and horizons.(5) Since the scatters show that all gradations occur between the extreme variants, the forms behave as though belonging to a single homogenetic community. It is recognized that internal characters may in due course be found to show discontinuity in their variation, but on present evidence it appears that only one species is present.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
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