Showing papers by "Peter Davies published in 1999"

Ecosystem measures of river health and their response to riparian and catchment degradation

Abstract: SUMMARY 1. Measurements of ecological patterns are often used as primary biological indicators of river health. However, these patterns provide little information about important stream ecosystem processes (e.g. the sources and fate of energy and nutrients). The direct measurement of these processes is considered fundamental to the determination of the health of stream and river ecosystems. 2. In this paper we used two basic approaches to assess stream ecosystem response to catchment disturbance and, particularly, to the loss of riparian vegetation in different forested biomes across Australia. Benthic gross primary production (GPP) and respiration (R24) provided measures of the amounts of organic carbon produced and consumed within the system, respectively. Stable isotope analysis was used to trace the fate of terrestrial and instream sources of organic matter in the aquatic food web. In a focal catchment in SE Queensland, additional measurements were taken of riparian attributes, catchment features and water quality. 3. Baseline measurements of GPP and R24 from undisturbed forest streams provided reference values for healthy streams for comparison with sites where the catchment or riparian vegetation had been disturbed. These values of metabolism were low by world standards in all biomes examined. Preliminary data from the Mary River catchment in SE Queensland indicated that these parameters were sensitive to variations in riparian canopy cover and, to a lesser extent, catchment clearing, and predictive models were developed. The ratio P : R (GPP : R24) was used to determine whether sites were net consumers (P R) of carbon but this was not considered a reliable indicator of stream health on its own. 4. Although forest streams were typically net consumers of carbon (P << R), stable isotope analysis of metazoan food webs indicated a high dependence on inconspicuous epilithic algae in some biomes. 5. A dramatic decline in the health of forest streams was observed when GPP substantially exceeded R24, especially when instream primary producers shifted from palatable unicellular algae to prolific filamentous green algae and macrophytes. These sources of instream production do not appear to enter aquatic food webs, either directly through grazing or indirectly through a detrital loop. Accumulation of these plants has led to changes in channel morphology, loss of aquatic habitat and often a major decline in water quality in some of the streams studied.

Comparison of test configurations for determination of mode II interlaminar fracture toughness results from international collaborative test programme

Abstract: This paper presents a summary of the tests performed within a Versailles Project on Advanced Materials and Standards collaborative test programme to examine the measurement of mode II interlaminar fracture toughness using four different test methods based on end notched flexure, stabilised end notched flexure, end loaded split, and four point end notched flexure carbon fibre reinforced epoxy specimens. Tests were performed by members of the European Structural Integrity Society, the Japan Industrial Standards group, and the American Society for Testing and Materials.

Schooling Quasi‐Markets: Reconciling Economic and Sociological Analyses

Abstract: We provide an economic assessment of the operation of schooling quasi-markets, re-interpreting the findings of the mainly sociologically-based empirical research. We find that economic analysis is complementary to that of sociology, providing further explanations for the failure of greater competition to increase the diversity of provision and challenge traditional school hierarchies.

An experimental study of scale effects in marine composites

Abstract: This paper addresses the characterization of marine composites, i.e. polyester resins reinforced with glass fibres in the form of woven and mat layers produced by hand lay-up. Design with these materials requires verification that the mechanical properties determined by tests on small specimens are representative of the behaviour of larger structures. A study of scale effects is presented. Results from tensile and flexural specimens over a range from 1 to 10 show no effect of specimen scale on elastic constants. However, measured shear strength determined in tension at 45° to the fibres increases with specimen width and scale, rather than decreasing as would be predicted. The scatter in measured properties is shown to be low.

Comparison of test configurations for the determination of giic : results from an international round robin

Abstract: This paper presents a summary of the tests performed within a VAMAS (Versailles Project on Advanced Materials and Standards) round robin to examine the measurement of mode II interlaminar fracture toughness using four different test methods based on: End Notched Flexure (ENF), Stabilised End Notched Flexure (SENF), End Loaded Split (ELS), and four point End Notched Flexure (4ENF) carbon fibre reinforced epoxy specimens. Tests were performed by members of ESIS (European Structural Integrity Society), JIS (Japan Industrial Standards group) and ASTM (American Society for Testing and Materials).

Testing of large cables for mooring line applications

Abstract: This paper describes recent tests performed to determine stiffness and long term behaviour of polyester cables for mooring lines. Particular emphasis is placed on the potential sources of error associated with extensometry and verification of the uniformity of the strain field in the rope sample. Results from a series of tests on large cables (500 Tons minimum break load), sub-ropes and yarns are presented. Use of video systems with image analysis to check strain fields during tests will be described. Test details will be discussed in terms of OCIMF and Bureau Veritas guidelines for rope testing.