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11.
Leonie E. A. Jones 《Physics and Chemistry of Minerals》1979,4(1):23-42
The elastic moduli (c) of single crystal KMgF3 have been determined by the ultrasonic pulse superposition technique as a function of temperature from T=298?550 K, and as a function of pressure from P=1 bar?2.5 kbar. Room temperature values of the elastic moduli and their temperature derivatives are consistent with Reshchikova's (1969) values. Comparison with the data for SrTiO3 indicates that, for most of the moduli, 1/c(?c/?T) P and (?c/?P) T are very similar for the fluoride-oxide analogue pair, KMgF3-SrTiO3. Values of (?c/?P) T for KMgF3 are calculated from a simple central force model using parameters determined for KF and are in good agreement with the measured values. The bulk sound velocity-mean atomic weight relationship, v ф M 1/2=constant, is well obeyed by the fluoroperovskites; comparison with the perovskite oxide data on a log-log plot of v ф versus M leads to a value of 70% for the relative effective charge of the oxides with respect to the fluorides. 相似文献
12.
Leonie E.A. Jones Robert C. Liebermann 《Physics of the Earth and Planetary Interiors》1974,9(2):101-107
Fluorides are considered as models for the physical properties of oxides on the basis of Goldschmidt's crystal chemical arguments. The well-established bulk modulus (K)-volume (V) relationship KV = constant is sddddhown to hold for fluorides and oxides belonging to the four isostructural series. The bulk moduli of equivolume oxides and fluorides are scaled as 4S2, where S = ZO/2ZF is the ratio of the effective unit charges and is approximately 77% for all of the crystal structures. The fluorides have distinctly lower melting and Debye temperatures which offers the possibility of using these compounds as models for the high-temperature elastic behaviour of their oxide analogues. 相似文献
13.
Unsuitability of TAC management within an ecosystem approach to fisheries: An ecological perspective
Henning Reiss Simon P.R. Greenstreet Leonie Robinson Siegfried Ehrich Lis L. Jørgensen Gerjan J. Piet Wim J. Wolff 《Journal of Sea Research》2010,63(2):85-92
Fisheries management in European waters is gradually moving from a single-species perspective towards a more holistic ecosystem approach to management (EAM), acknowledging the need to take all ecosystem components into account. Prerequisite within an EAM is the need for management processes that directly influence the ecological effects of fishing, such as the mortality of target and non-target species. Up until recently, placing limits on the quantities of fish that can be landed, through the imposition of annual total allowable catches (TACs) for the target species, has been the principal management mechanism employed. However, pressure on non-target components of marine ecosystems is more closely linked to prevailing levels of fishing activity, so only if TACs are closely related to subsequent fishing effort will TAC management serve to control the broader ecosystem impacts of fishing. We show that in the mixed fisheries that characterise the North Sea, the linkage between variation in TAC and the resulting fishing effort is in fact generally weak. Reliance solely on TACs to regulate fishing activity is therefore unlikely to mitigate the impacts of fishing on non-target species. Consequently, we conclude that the relationship between TACs and effort is insufficient for TACs to be used as the principal management tool within an EAM. The implications, and some alternatives, for fisheries management are discussed. 相似文献
14.
Itrax micro X-ray fluorescence (μ-XRF) core scanning is a non-destructive, rapid approach to measuring elemental concentrations and their variability in sediment cores. As such, it records elemental signatures of tephra layers, which serve as correlation tie points and chronological markers for these sedimentary archives of past climatic changes. The traditional tephra identification approach using electron microprobe-based geochemical fingerprinting of glass shards is a slow and invasive process, whilst μ-XRF scanning of rhyolite tephra in sediment cores from Auckland (New Zealand) could provide a faster, non-invasive approach to aid the recognition of tephra layers. This study highlights the potential and pitfalls in this novel approach: changes in most scanning parameters, and the use of two different Itrax core scanners, still led to similar chemical characterizations of the tephra layers. Changes in other scanning parameters have a biasing influence on the chemical characterization of the tephra, which would lead to misidentification of unknown layers. We demonstrate that μ-XRF core scanning provides a faster and non-invasive approach to correlation of sediment sequences using chemically distinct, visually pure tephra layers if a strict scanning protocol is followed. Nevertheless, an extensive database of μ-XRF-scanned rhyolite tephra is required for recognition of unknown tephra units using this approach. 相似文献
15.
The continuing use of petrochemicals in mineral nitrogen(N) production may be affected by supply or cost issues and climate agreements.Without mineral N,a larger area of cropland is required to produce the same amount of food,impacting biodiversity.Alternative N sources include solar and wind to power the Haber-Bosch process,and the organic options such as green manures,marine algae and aquatic azolla.Solar power was the most land-efficient renewable source of N,with using a tenth as much land as wind energy,and at least 100 th as much land as organic sources of N.In this paper,we developed a decision tree to locate these different sources of N at a global scale,or the first time taking into account their spatial footprint and the impact on terrestrial biodiversity while avoiding impact on albedo and cropland,based on global resource and impact datasets.This produced relatively few areas suitable for solar power in the western Americas,central southern Africa,eastern Asia and southern Australia,with areas most suited to wind at more extreme latitudes.Only about 2% of existing solar power stations are in very suitable locations.In regions such as coastal north Africa and central Asia where solar power is less accessible due to lack of farm income,green manures could be used,however,due to their very large spatial footprint only a small area of low productivity and low biodiversity was suitable for this option.Europe in particular faces challenges because it has access to a relatively small area which is suitable for solar or wind power.If we are to make informed decisions about the sourcing of alternative N supplies in the future,and our energy supply more generally,a decision-making mechanism is needed to take global considerations into account in regional land-use planning. 相似文献
16.
Collaborative management, or co-management, is recognized as best practice for protected area management. A vast literature explores the benefits and challenges of implementing co-management, but more literature is not always better. We propose that the term co-management has been uncritically “stretched”, losing its original framing of actors working together collaboratively. Co-management has become a facade under which traditional hierarchical and market-based management regimes can occur. Conceptual stretching inhibits the capacity to critically articulate variations within models of collaborative governance. We investigate this stretching through a nuanced framework of co-management models with varying intensities. By considering participating actors, institutions and delivery objectives, the theoretically informed and empirically tested framework highlights the stretched implementation of co-management, enabling protected area managers an opportunity to align their practice with the promise of co-management. 相似文献
17.
Leonie E.A. Jones 《Physics of the Earth and Planetary Interiors》1977,15(1):77-89
The elastic moduli of single-crystal CaF2, SrF2 and BaF2 have been determined by the ultrasonic pulse superposition technique as a function of temperature from T = 298 to T = 650°K. These new data are consistent with other data obtained by ultrasonic pulse techniques in the region of room temperature and are superior to previous high-temperature data from resonance experiments. The elastic moduli (c) are represented by quadratic functions in T over the experimental temperature range with the curvature in the same sense for all the moduli. Evaluation of the temperature derivatives of the elastic moduli at constant volume indicates that the dominant temperature effect is extrinsic for (?KS/?T)P and intrinsic for (?μ/?T)P, where KS and μ are the isotropic bulk and shear moduli, respectively. For the series CaF2SrF2BaF2, |(?c/?T)p| decreases with increasing molar volume for all moduli; however there are no theoretical or empirical grounds on which to derive a simple relationship between (?c/?T)P and crystallographic parameters. 相似文献
18.
Leonie E.A. Jones 《Physics of the Earth and Planetary Interiors》1976,13(2):105-118
The elastic moduli of single-crystal LiF and NaF have been determined by the ultrasonic pulse superposition technique as a function of temperature from T = 298–650° K. These new data are consistent with low-temperature (T < 298° K) data obtained by other ultrasonic pulse techniques and are superior to previous high-temperature data from resonance experiments. The elastic moduli (c) are represented by quadratic functions in T over the experimental temperature range although the curvature is not in the same sense for all modes. For LiF, NaF, MgO and CaO, evaluation of the temperature derivatives of the elastic moduli at constant volume (V) indicates that the elastic moduli are only weakly dependent on T at constant volume. The fluoride—oxide analogue pair LiFMgO both exhibit high-temperature elastic behaviour at approximately the same absolute temperature. Mitskevich's theory and observed KS-V systematics imply that (?c/?T)P should be a function of the nearest neighbour distance for rocksalt fluorides and oxides; this result lends further support to a fluorideoxide modelling scheme based on similar ionic radii. 相似文献
19.
In January 2006, 25 tonnes of heavy fuel oil spilled into the Port of Gladstone in Queensland, Australia, from the breached hull of a bulk carrier ship. While approximately 18 tonnes of the oil was recovered, a certain amount of oil was deposited in the intertidal areas of Port Curtis leaving a highly visible, viscous residue. The objectives of this research were to assess the short-term (one month post-spill) and medium-term (six months post-spill) impacts on the intertidal habitat.Sediment polycyclic aromatic hydrocarbons (PAHs) and metal concentrations, mangrove communities and intertidal macroinvertebrates were assessed at oil impacted sites, adjacent sites which were not visibly impacted and reference sites which were located outside the recorded distribution of the oil spill.At one month post-spill, highest PAH concentrations were found at the impacted sites, with concentrations of some PAHs exceeding Australian and New Zealand sediment quality guidelines (SQG) [ANZECC/ARMCANZ, 2000. Sediment Quality Guidelines. Australia and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand]. However, by six months post-spill PAH concentrations had significantly decreased. PAH concentrations tended to be higher in the back (upper) intertidal zone than at the front of the mangrove stand, and sediment cores indicated that PAH contaminants had remained in the top 4 cm of the sediment. These results indicate that the overall decreased PAH concentrations are likely to be due to evaporation, photoxidation and tidal flushing of the residual oil in these impacted sites.During the initial survey, the impact site contained very few or no crabholes in the high intertidal area, indicating a low crab density in comparison to reference sites. However, at six months post-spill mangrove crab communities appeared to be fully recovered with crabhole densities in impact sites similar to reference sites.While little immediate impact was evident on mangrove parameters, significantly higher seedling mortality and defoliation was apparent at six months post-spill, particularly in the upper intertidal zone. Intertidal macrobenthic communities did not appear to be impacted, either immediately or at six months post-spill. Monitoring of these oil impacted intertidal areas will continue to examine the long-term impacts/recovery from the oil spill. 相似文献