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  • 1995-1999  (1)
  • 1970-1974  (7)
  • 1
    ISSN: 1573-7160
    Keywords: captive breeding ; in situ conservation ; ex situ conservation ; zoos ; protected areas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract Growing deterministic and stochastic threats to many wild populations of large vertebrates have focused attention on the conservation significance of captive breeding and subsequent reintroduction. However, work on both gorillas and black rhinos questions this shift in emphasis. In these species, field-based conservation can be effective if properly supported and, although this is not cheap, per capita costs may still be considerably lower than for ex situ propagation in captivity. Here we attempt to broaden the scope of this debate by contrasting the breeding success and costs of in situ and captive programmes for a range of threatened mammals. Data are scarce, but we find that across nine large-bodied genera, in situ conservation achieves comparable rates of population growth to those seen in established captive breeding programmes. Moreover, comparing budgets of well-protected reserves with zoos' own estimates of maintenance costs and the costs of zoo adoption schemes, we find that per capita costs for effective in situ conservation are consistently lower than those of maintenance in captivity. Captive breeding may be more cost-effective for smaller-bodied taxa, and will often remain desirable for large mammals restricted to one or two vulnerable wild populations. However, our results, coupled with the fact that effective in situ conservation protects intact ecosystems rather than single species, lead us to suggest that zoos might maximize their contribution to large mammal conservation by investing where possible in well-managed field-based initiatives, rather than establishing additional ex situ breeding programmes.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2019-06-27
    Description: An analytical study was conducted to develop a sensor for measuring the temperature of a planetary atmosphere from an entry vehicle traveling at supersonic speeds and having a detached shock. Such a sensor has been used in the Planetary Atmosphere Experiments Test Probe (PAET) mission and is planned for the Viking-Mars mission. The study specifically considered butt-welded thermocouple sensors stretched between two support posts; however, the factors considered are sufficiently general to apply to other sensors as well. This study included: (1) an investigation of the relation between sensor-measured temperature and free-stream conditions; (2) an evaluation of the effects of extraneous sources of heat; (3) the development of a computer program for evaluating sensor response during entry; and (4) a parametric study of sensor design characteristics.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TN-D-6947 , A-4412
    Format: application/pdf
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  • 3
    Publication Date: 2011-08-16
    Description: Analytical solutions were obtained for the thermal response of a transpiration- or sublimation-cooled spherical mirror coating exposed to convective and radiative heating. The solutions allow unlimited spectral detail to be accounted for. Results indicate that transpiration-cooled thick coatings (1 cm) may withstand up to 10 kW/sq cm on a steady basis without excessive temperature rise for quartzlike materials with an internal absorption coefficient of 0.01 per cm. On a transient basis, fluxes up to 20 kW/sq cm can be accommodated for a second (cW laser exposure time), 4 kW/sq cm for 5 sec (planetary entry heating time), and of the order of MW/sq cm for millisecond times (short-duration laser bursts) without transpiration cooling for a material with an absorption coefficient of 0.1 per cm. Proportionately higher fluxes can be accommodated with lower absorption coefficients. Thermal stresses produced by the heat pulse are found to be high but within the strength of the materials. The regime in which meaningful solutions may be obtained is mapped in detail.
    Keywords: THERMODYNAMICS AND COMBUSTION
    Type: AIAA Journal; 11; Jan. 197
    Format: text
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  • 4
    Publication Date: 2011-08-16
    Description: Boundary layer flow with large mass injection rate, presenting numerical method with rapid convergence for increasing blowing parameter
    Keywords: FLUID MECHANICS
    Type: ; YAL SOCIETY (
    Format: text
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  • 5
    Publication Date: 2019-06-27
    Description: The application of a 'two-flux' technique is considered for determining the reflective characteristics and approximate temperature distribution in highly backscattering materials characterized by a very small absorption coefficient. With respect to the transmitted internal radiation fields, the internal radiative emission is assumed to be negligible. A comparison of theory and experiment is presented.
    Keywords: THERMODYNAMICS AND COMBUSTION
    Type: AIAA Journal; 10; Sept
    Format: text
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  • 6
    Publication Date: 2019-06-27
    Description: A numerical method for the solution of large systems of nonlinear differential equations of the boundary-layer type is described. The method is a modification of the technique for satisfying asymptotic boundary conditions. The present method employs inverse interpolation instead of the Newton method to adjust the initial conditions of the related initial-value problem. This eliminates the so-called perturbation equations. The elimination of the perturbation equations not only reduces the user's preliminary work in the application of the method, but also reduces the number of time-consuming initial-value problems to be numerically solved at each iteration. For further ease of application, the solution of the overdetermined system for the unknown initial conditions is obtained automatically by applying Golub's linear least-squares algorithm. The relative ease of application of the proposed numerical method increases directly as the order of the differential-equation system increases. Hence, the method is especially attractive for the solution of large-order systems. After the method is described, it is applied to a fifth-order problem from boundary-layer theory.
    Keywords: FLUID MECHANICS
    Type: NASA-TN-D-7068 , A-4544
    Format: application/pdf
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  • 7
    Publication Date: 2011-08-16
    Description: The behavior of dielectric materials having densely packed internal scattering centers subject to extreme convective and radiative environments is analyzed. Experiments have shown that these materials act as volume reflectors of incident radiation even when the exposed surface is being eroded by thermochemical ablation. The analysis was applied to interpret experiments of subliming Teflon models exposed to combined radiative and convective fluxes up to 1.7 kW/sq cm for several seconds. Results show that, although the exposed surface receded at an apparently steady rate, the internal temperature climbed continually, due to internal absorption of radiation and would have caused failure internally if the test duration were extended a few seconds. Thus, performance is time-limited by the internal absorption coefficient. Results were obtained for larger configurations and other materials. Typically, Teflon shells may withstand radiant fluxes up to 20 kW/sq cm for about 5 sec and fritted quartz up to 50 kW/sq cm for about 8 sec (corresponding to the Jupiter entry).
    Keywords: THERMODYNAMICS AND COMBUSTION
    Type: AIAA Journal; 11; July 197
    Format: text
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  • 8
    Publication Date: 1971-02-01
    Description: SUMMARYSeveral criteria which have been used hitherto in the hope of selecting large-yielding clones of tea have been examined. The heights, girths, root weights and branching a gles of young seedlings in the nursery are correlated with the sizes and yields of the same plants when mature, but not with the rates of growth in the nursery, or the yields at maturity, of the plants derived from these seedlings by vegetative propagation. The pruning weight, size and yield of a mature plant grown from seed are not related to the rate of growth in the nursery or the yield at maturity of the clone derived from that plant. The proportion of cuttings which form roots and the growth rate of the cuttings of a clone are not related to the yield of the clone. It is concluded that these criteria are, at best, of limited value in the selection of large-yielding clones.Phloem Index, which is the number of calcium oxalate crystals counted in the phloem parenchyma in a cross-section of the petiole, varies with the age and rate of development of the shoot from which the petiole is taken and with the concentration of nutrients in the soil. It is therefore not useful as an alternative selection criterion under normal field conditions.
    Print ISSN: 0021-8596
    Electronic ISSN: 1469-5146
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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