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  • Cambridge University Press  (13,204)
  • 1995-1999  (11,417)
  • 1950-1954  (1,787)
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  • 1
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    Oscillatory enhancement of the squeezing flow of yield stress fluids: a novel experimental result (1997)
    Cambridge University Press
    Details
    Publication Date: 1997-05-25
    Description: The extrusion of a yield stress fluid from the space between two parallel plates is investigated experimentally. Oscillating the magnitude of the squeezing force about a mean value (F = f[1+αcos(ωt)]) was observed to significantly enhance the flow rate of yield stress fluids, while having no effect on the flow rate of Newtonian fluids. This is a novel result. The enhancement depends on the magnitude of the force, the oscillatory frequency and amplitude, the fluid being squeezed, and the thickness of the fluid layer. Non-dimensional results for the various flow quantities have been presented by using the flow predicted for the constant-force squeezing of a Herschel-Bulkley yield stress fluid as the reference. In the limit of constant-force squeezing, the present experimental results compare very well with those of our earlier theoretical model for this situation (Zwick, Ayyaswamy & Cohen 1996). The results presented in this paper have significance, among many applications, for injection moulding, in the adhesive bonding of microelectronic chips, and in surgical procedures employed in health care.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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  • 2
    Electronic Resource
    Electronic Resource
    Yang, Dali L.: Calamity and Reform in China: State, Rural Society, and Institutional Change Since the Great Leap Famine : Stanford, Cambridge University Press, 1996 (1998)
    Cambridge : Cambridge University Press
    The @China quarterly 155 (1998), S. 669-670 
    Details
    ISSN: 0305-7410
    Source: Cambridge Journals Digital Archives
    Topics: Linguistics and Literary Studies , History , Political Science , Sociology , Economics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1017/S0305741000050050
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    Paper (German National Licenses)
    Fulltext
  • 3
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    Glaciol isostasy and the crustal structure of Antarctica (1998)
    Cambridge University Press
    Details
    Publication Date: 1998-01-01
    Description: Traditional models of Glaciol isostasy, derived predominantly for studying the response of the earth to the retreat of Northern Hemisphere ice sheets since the last ICC age, use earth models which assume constant lithospheric thickness. For Antarctica, where the continent below the ice sheet is two separate land masses differing in geological form, the assumption thai a uniform lithosphere can explain isostatic bchavioitr is questionable. Here, a method to calculate the glacio-isostatic adjustment of the continent with a laterally varying lithospheric thickness IS presented. The method is then used in a time-dependent ice-sheet model to model the isostatic response of the continent when the ice sheet passes through a Glaciol/interglacial transition. Various relations bet ween the “crustal thickness” beneath Antarctica, derived from seismic data, and the “lithospheric thickness” estimate used in glacio-isostatic calculations are assumed in a sensitivity study. Using the simplest relationships between crustal and lithospheric thickness, the greatest sensitivity of the ice sheet to the crustal structure of Antarctica is not in the interior but at coastal locations, particularly near the major ice shelves. During periods of ice-sheet advance the grounding-line migration of the shelves varies according to the depression of the earth peripheral to the ice sheet. The peripheral depression depends on the regional elasticity of the lithosphere which is controlled by the lithospheric thickness. Therefore the capacity for the ice sheet to advance varies with the regional thickness of the crust.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 4
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    Areal distribution of the oxygen-isotope ratio in Antarctica: comparison of results based on field and remotely sensed data (1998)
    Cambridge University Press
    Details
    Publication Date: 1998-01-01
    Description: An updated compilation of oxygen-isotope ratio data for 562 sites in Antarctica shows a significant increase in the number of sites and an improvement in the representation of the coastal zone oyer previous versions. The data hase consists of ratio values (δ18O; multi-year mean 18O/16O relative to Standard Mean Ocean Water, in ‰) compiled as the dependent variable, together with data for the so-called independent variables: latitude, surface elevation, mean annual surface temperature and mean annual shortest distance to open ocean denoted by the 20% sea-ice concentration boundary. The problem of covariation between so-called independent variables is minimized using stepwise regression analyses. A general model is described using all the field data, and the regional variation at drainage-system scale is assessed by contrasting models for two physiographically distinct regions. in addition, entity-specific models are determined using data subsets for the conterminous grounded-ice and ice-shelf areas. Inversions of the specific models are applied to a 100 km grid data base to produce two contoured distributions of the ratio, one based on field data, and the other on remotely sensed data. The difference between these produces residuals that, relative to the summation of standard errors of the models, are small in most of the interior area of the ice sheet, and large in several areas of mountain and coastal regions, where interpolation and extrapolation of field data are particularly unreliable. Remotely sensed data generally produce ratio values which are isotopically cooler.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 5
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    Accumulation in Antarctica and Greenland derived from passive-microwave data: a comparison with contoured compilations (1995)
    Cambridge University Press
    Details
    Publication Date: 1995-01-01
    Description: The annual rate of net mass accumulation at the surface in the Antarctic and Greenland ice sheets is determined from firn emissivity based on Nimbus-5 ESMR and Nimbus-7 THIR data. In this study the determinations are limited to the areas of dry-snow facies and are based on a hyperbolic function of emissivity. Two coefficients of the function are selected for particular regions of each ice sheet after a comparison with field data selected for their reliability (82 stations in East Antarctica, 69 stations in West Antarctica and 89 stations in Greenland). Derived accumulation values are produced for grid-point locations 100 km apart which cover 56–94% of the dry-snow areas and 32–58% of the accumulation areas of each ice sheet. These values are compared with interpolated values obtained from the latest contoured compilations of field data. The means of derived values for East and West Antarctica are 12% and 39% larger, respectively, than the mean obtained from interpolated values, suggesting that the isopleth patterns as drawn in the compilation of field data lead to underestimates. The mean of derived values for Greenland is 5% smaller than the mean obtained from interpolated values, suggesting that the compilation of field data may lead to small overestimates that are within the error of determination and the variability of accumulation. Improving facies zonation and the determination of coefficients for the areas of upper percolation facies should improve these preliminary assessments.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 6
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    Areal distribution of the oxygen-isotope ratio in Greenland (1997)
    Cambridge University Press
    Details
    Publication Date: 1997-01-01
    Description: Mean values of the oxygen-isotope ratio relative to standard mean ocean water (δ18O, in ‰) reported for 46 sites on the Greenland ice sheet are compiled together with data on mean annual surface temperature, latitude, δ18O elevation, and mean annual shortest distance to the open ocean denoted by the 10% sea-ice concentration boundary. Stepwise regression analyses, with δ18O as the dependent variable, define two robust models. In the forward mode at the 99.9% confidence level, only temperature enters the model. In the backward mode at the 95% confidence level, only temperature, latitude and distance to the open ocean remain in the model. Inversions of the models on the basis of 160 gridpoint locations 100 km apart in the area delimited by the surface equilibrium line produce four contoured distributions of δ18O. Two distributions are based on the bivarrate model and two on the multivariate model. The second distribution for each model is obtained substituting mean annual surface-temperature values obtained from the Nimbus-7 Temperature Humidity Infrared Radiometer (THIR) database. All four distributions are considered valid, and differences between them are evaluated using contoured anomaly maps. It is suggested that the inversion of the multivariate model using THIR data provides the more reliable pattern for studies of atmospheric advection or for the derivation of ice-flow adjustments for δ18O series obtained from deep-core or ablation-zone sites.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 7
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    Accumulation in Antarctica and Greenland derived from passive-microwave data: a comparison with contoured compilations (1995)
    Cambridge University Press
    Details
    Publication Date: 1995-01-01
    Description: The annual rate of net mass accumulation at the surface in the Antarctic and Greenland ice sheets is determined from firn emissivity based on Nimbus-5 ESMR and Nimbus-7 THIR data. In this study the determinations are limited to the areas of dry-snow facies and are based on a hyperbolic function of emissivity. Two coefficients of the function are selected for particular regions of each ice sheet after a comparison with field data selected for their reliability (82 stations in East Antarctica, 69 stations in West Antarctica and 89 stations in Greenland). Derived accumulation values are produced for grid-point locations 100 km apart which cover 56–94% of the dry-snow areas and 32–58% of the accumulation areas of each ice sheet. These values are compared with interpolated values obtained from the latest contoured compilations of field data. The means of derived values for East and West Antarctica are 12% and 39% larger, respectively, than the mean obtained from interpolated values, suggesting that the isopleth patterns as drawn in the compilation of field data lead to underestimates. The mean of derived values for Greenland is 5% smaller than the mean obtained from interpolated values, suggesting that the compilation of field data may lead to small overestimates that are within the error of determination and the variability of accumulation. Improving facies zonation and the determination of coefficients for the areas of upper percolation facies should improve these preliminary assessments.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 8
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    Areal distribution of the oxygen-isotope ratio in greenland (1997)
    Cambridge University Press
    Details
    Publication Date: 1997-01-01
    Description: Mean values of the oxygen-isotope ratio relative to standard mean ocean water (δ 18O, in ‰) reported for 46 sites on the Greenland ice sheet are compiled together with data on mean annual surface temperature, latitude, δ 18O elevation, and mean annual shortest distance to the open ocean denoted by the 10% sea-ice concentration boundary. Stepwise regression analyses, with δ 18O as the dependent variable, define two robust models. In the forward mode at the 99.9% confidence level, only temperature enters the model. In the backward mode at the 95% confidence level, only temperature, latitude and distance to the open ocean remain in the model. Inversions of the models on the basis of 160 gridpoint locations 100 km apart in the area delimited by the surface equilibrium line produce four contoured distributions of δ 18O. Two distributions are based on the bivarrate model and two on the multivariate model. The second distribution for each model is obtained substituting mean annual surface-temperature values obtained from the Nimbus-7 Temperature Humidity Infrared Radiometer (THIR) database. All four distributions are considered valid, and differences between them are evaluated using contoured anomaly maps. It is suggested that the inversion of the multivariate model using THIR data provides the more reliable pattern for studies of atmospheric advection or for the derivation of ice-flow adjustments for δ 18O series obtained from deep-core or ablation-zone sites.
    Print ISSN: 0260-3055
    Electronic ISSN: 1727-5644
    Topics: Geography , Geosciences
    Published by Cambridge University Press on behalf of International Glaciological Society.
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  • 9
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    Modelling albedo and specific balance of the Greenland ice sheet: calculations for the Søndre Strømfjord transect (1996)
    Cambridge University Press
    Details
    Publication Date: 1996-01-01
    Description: Glacio-meteorological data obtained during the Greenland Ice Margin Experiment (GIMEX) investigations in West Greenland (the Søndre Strømfjord transect) have been used to test and calibrate energy-balance/mass-balance models for the ice/snow surface. The region is characterised by the development of a wide zone of low surface albedo in the course of the melting season. This zone was simulated in one of the energy-balance models by including the effect of surficial meltwater on albedo. Observed mass-balance and albedo data were used to constrain the models. Although all the models are capable of predicting the transect balance reasonably well, only the model with the meltwater albedo coupling, is able to reproduce the observed albedo pattern and mass-balance profile along the transect. By including the feedback between surficial meltwater and albedo in the model, the sensitivity of the specific balance to changes in air temperature is found to be greatest just below the equilibrium line (in contrast to what is generally found for valley glaciers). A 1 K warming of the air temperature would increase the mean ablation along the transect by 0.5 m w.e.year −1.
    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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  • 10
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    Modelling albedo and specific balance of the Greenland ice sheet: calculations for the Søndre Strømfjord transect (1996)
    Cambridge University Press
    Details
    Publication Date: 1996-01-01
    Description: Glacio-meteorological data obtained during the Greenland Ice Margin Experiment (GIMEX) investigations in West Greenland (the Søndre Strømfjord transect) have been used to test and calibrate energy-balance/mass-balance models for the ice/snow surface. The region is characterised by the development of a wide zone of low surface albedo in the course of the melting season. This zone was simulated in one of the energy-balance models by including the effect of surficial meltwater on albedo. Observed mass-balance and albedo data were used to constrain the models. Although all the models are capable of predicting the transect balance reasonably well, only the model with the meltwater albedo coupling, is able to reproduce the observed albedo pattern and mass-balance profile along the transect. By including the feedback between surficial meltwater and albedo in the model, the sensitivity of the specific balance to changes in air temperature is found to be greatest just below the equilibrium line (in contrast to what is generally found for valley glaciers). A 1 K warming of the air temperature would increase the mean ablation along the transect by 0.5 m w.e.year−1.
    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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