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  • 1
    Electronic Resource
    Electronic Resource
    Cambridge : Cambridge University Press
    Science in context 2 (1988), S. 163-175 
    ISSN: 0269-8897
    Source: Cambridge Journals Digital Archives
    Topics: History , Natural Sciences in General
    Notes: The ArgumentIdealizations and approximations are an indispensable tool for the scientist. This paper argues that idealizations and approximations are equally indispensable for the philosopher of science. In particular, it is shown that the deductive model of scientific theories is an idealization in precisely the same sense that frictionless motion is an idealization in mechanics. By its very nature, an idealization cannot be criticized as not being absolutely true to the facts, for it need not be. Thus, the usual type of criticism levelled against the deductive model is shown to be irrelevant. The main step in the argument consists in using a logic of approximation to clarify the notions of approximate implication and approximate entailment, which are usually rejected as hopelessly vague. More generally, the conception underlying the paper is that the desiderata of science should be formulated in such a way that complying with them could be a matter of degree, and that pragmatic considerations could be taken into account. This conception is motivated by the wish to introduce some quantitative concepts in the philosophy of science, thereby bringing the philosopher's perspective closer to that of the scientist.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Cambridge : Cambridge University Press
    The @journal of modern African studies 27 (1989), S. 23-46 
    ISSN: 0022-278X
    Source: Cambridge Journals Digital Archives
    Topics: Ethnic Sciences , History , Political Science , Economics
    Notes: The Approach of the Reagan Administration towards the Third World was criticised as too simply anti-communist: a growing ‘predisposition toward globalism’,1 so it was claimed, led to a ‘Sovietcentric orientation’,2 an ‘obsession with the Soviet Union’,3 which obscured regional complexities.4 But American decisions about what actions to take in Southern Africa during the 1980s were part of a surprisingly effective strategy that often ignored Reagan's doctrine of aid to anti-communist resistance. That strategy was shaped by several hands, and the President's were not even the most important.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 1985-09-01
    Description: Two formulas, based on analytical considerations, which are capable of predicting the wedge angle of transition from Mach to regular reflection over cylindrical concave wedges, are developed. They are derived using Hornung, Oertel & Sandeman’s (1979) conclusion that a Mach reflection can exist only if the corner-generated signals can catch up with the incident shock wave. The good agreement between the present models and the experimental results confirm Hornung et al.’s (1979) concept. The predictions of these models are in better agreement with experimental results than the predictions of Itoh, Okazaki & Itaya’s (1981) model. The present models are very simple to use and apply but, like Itoh et al.’s (1981) model, they also lack the ability to account for the dependence of the transition angle on the radius of curvature of the cylindrical wedge. © 1985, 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
    Publication Date: 1987-09-01
    Description: The analytical solution of a pseudo-steady Mach reflection was considered. It was found that the solution of the well-known perfect-gas conservation equations of a pseudo-steady Mach reflection-the three-shock theory-failed to accurately predict the angles between the incident, reflected and Mach stem shock waves. The disagreement between theory and experiments was not settled even when real-gas effects were accounted for. However, the inclusion of real-gas effects did improve the analytical predictions. In order to improve the analytical model, the boundary layers developing on both sides of the slipstream were integrated into the analysis. Using these boundary layers, the displacement thickness as a function of distance along the slipstream from the triple point was calculated. The displacement thickness was then related to the angular displacement of the slipstream, as a function of that distance. Finally it was shown that the displacement, taken at a distance equivalent to the incident-shockwave thickness, could be used to obtain computed results which agree with experimentally measured data. © 1987, 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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  • 5
    Publication Date: 1987-03-01
    Description: An analysis is presented of the shock wave configurations which will occur when a plane shock is incident on a double wedge for which the second wedge may have a greater (concave case) or a smaller (convex case) inclination than the first wedge. It is shown that seven different reflection processes may be expected depending on the Mach number of the incident shock Mi and the two wedge angles 0^ and 0%,. These processes may be defined by seven regions in the (θ1W θ2W)-plane, for a given value of Mi. Each of the seven processes has been verified by sequences of shadowgraph and schlieren photographs. A shock polar analysis of each of the seven processes has provided information about the pressure changes and the wave structures which develop immediately behind the main reflections along the wedge surfaces. These wave structures have been verified experimentally, and two types have been observed: one normal to the reflecting surface, and the other in the form of a regular reflection. The criteria to determine which of these configurations will occur have not yet been established. It is believed that the present study will be of value in predicting the loading of shock waves on structures, and may lead to a better understanding of shock reflections from concave and convex cylindrical surfaces. © 1987, 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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  • 6
    Publication Date: 1987-03-01
    Description: The effect of surface roughness on the transition from regular (RR) to Mach reflection (MR) over straight wedges in pseudo steady flows was investigated both experimentally and analytically. A model for predicting the RR ⇄ MR transition in the (Miθw)-plane was developed (Miis the incident shock wave Mach number and θwis the reflecting wedge angle). Its validity was checked against experimental results. Since the experimental results are limited to the ranges 1 〈 Mi 〈 2 and surface roughness heights of 0 〈 e ≤ 0.2 cm, the proposed model is applicable to these ranges only. In the proposed model (the boundary layer displacement thickness model), the RR ⇄ MR transition is related to the boundary layer thickness which in turn depends on the surface roughness. © 1987, 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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  • 7
    Publication Date: 1986-11-01
    Description: Conodont colour alteration index (CAI) values from Upper Paleozoic rocks in the Cantabrian zone of northern Spain show that temperatures during Hercynian metamorphism locally exceeded 300 °C. Various temperature domains have been defined, which are generally separated by fundamental structures. These domains do not correspond with the tripartite subdivision based on stratigraphic analysis.The observed CAI values of conodonts are in general agreement with the mineral paragenesis. Areas with high CAI values display extensive alteration and mineralization, and where CAI values exceed 4–4.5 (〉200 °C) slaty cleavage has developed.The Cantabrian zone is an area of very low grade metamorphism, where peak conditions were reached in Upper Carboniferous to Lower Permian times. The characteristics of the metamorphism and its spatial relationship with major faults suggest that fluids were the main source for regional heating and that fluid transport was focussed along crustal-scale structural features.The overall deformation regime in this part of the Variscan orogen of western Europe is interpreted to be large-scale transtension. This is in agreement with earlier proposed models for the formation of Upper Palaeozoic basins in this area.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
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