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221.
O'Leary BC Smart JC Neale FC Hawkins JP Newman S Milman AC Roberts CM 《Marine pollution bulletin》2011,62(12):2642-2648
We analysed the extent to which European politicians have adhered to scientific recommendations on annual total allowable catches (TACs) from 1987 to 2011, covering most of the period of the Common Fisheries Policy (CFP). For the 11 stocks examined, TACs were set higher than scientific recommendations in 68% of decisions. Politically-adjusted TACs averaged 33% above scientifically recommended levels. There was no evidence that the 2002 reform of the CFP improved decision-making, as was claimed at the time. We modelled the effects of such politically-driven decision-making on stock sustainability. Our results suggest that political adjustment of scientific recommendations dramatically increases the probability of a stock collapsing within 40 years.In 2012 European fisheries policy will undergo a once-a-decade reform. Ten years ago radical reforms were promised but the changes failed to improve sustainability. It is likely that the 2012 reform will be similarly ineffective unless decision-making is changed so that catch allocations are based on science rather than politics. 相似文献
222.
William K. Dewar 《地球物理与天体物理流体动力学》2013,107(1-4):53-85
Abstract The term ‘‘solitary wave'’ is usually used to denote a steadily propagating permanent form solution of a nonlinear wave equation, with the permanency arising from a balance between steepening and dispersive tendencies. It is known that large-scale thermal anomalies in the ocean are subject to a steepening mechanism driven by the beta effect, while at the smaller deformation scale, such phenomena are highly dispersive. It is shown here that the evolution of a physical system subject to both effects is governed by the ‘‘frontal semi-geostrophic equation'’ (FSGE), which is valid for large amplitude thermocline disturbances. Solitary wave solutions of the FSGE (here named planetons) are calculated and their properties are described with a view towards examining the behavior of finite amplitude solitary waves. In contrast, most known solitary wave solutions belong to weakly nonlinear wave equations (e.g., the Korteweg—deVries (KdV) equation). The FSGE is shown to reduce to the KdV equation at small amplitudes. Classical sech2 solitons thus represent a limiting class of solutions to the FSGE. The primary new effect on planetons at finite amplitudes is nonlinear dispersion. It is argued that due to this effect the propagation rates of finite amplitude planetons differ significantly from the ‘‘weak planeton'', or KdV, dispersion relation. Planeton structure is found to be simple and reminiscent of KdV solitons. Numerical evidence is presented which suggests that collisions between finite amplitude solitary waves are weakly inelastic, indicating the loss of true soliton behavior of the FSGE at moderate amplitudes. Lastly, the sensitivity of solitary waves to the existence of a nontrivial far field is demonstrated and the role of this analysis in the interpretation of lab experiments and the evolution of the thermocline is discussed. 相似文献
223.
Structural controls of lode-gold mineralization by mafic dykes in late-Paleozoic granitoids of the Kochkar district, southern Urals, Russia 总被引:2,自引:0,他引:2
A. F. M. Kisters F. M. Meyer S. E. Znamensky I. B. Seravkin R. G. W. Ertl A. M. Kosarev 《Mineralium Deposita》2000,35(2-3):157-168
The Kochkar gold district in the East Uralian Zone of the southern Urals is located in late-Paleozoic granite gneisses of
the Plast massif. Gold mineralization is associated with tabular quartz lodes that are preferentially developed along the
margins of easterly trending mafic dykes. Fabric development indicates that dykes had a profound influence on the development
of shear zones in granitoids. ENE- and SE-trending dykes have been reactivated as dextral and sinistral oblique strike-slip
shear zones, respectively, forming a set of approximately conjugate shear zones related to the Permian, regional-scale E-W
directed shortening. Dyke-shear zone relationships in the Plast massif are the result of strain refraction due to the presence
of biotite-rich, incompetent dykes in more competent granite-gneisses. Deformation and the formation of associated gold-quartz
lodes occurred close to peak-metamorphic, upper-greenschist to lower-amphibolite facies conditions. Strain refraction has
resulted in partitioning of the bulk strain into a component of non-coaxial mainly ductile shear in mafic dykes, and a component
of layer-normal pure shear in surrounding granitoids where deformation was brittle-ductile. Brittle fracturing in granitoids
has resulted in the formation of fracture permeabilities adjacent to sheared dykes, that together with the layer-normal dilational
component, promoted the access of mineralizing fluids. Both ore-controlling dykes and gold-quartz lodes were subsequently
overprinted by lower greenschist-facies, mainly brittle fault zones and associated hydrothermal alteration that post-date
gold mineralization.
Received: 15 October 1998 / Accepted: 18 August 1999 相似文献
224.
Analysis of reservoir water quality using fuzzy synthetic evaluation 总被引:12,自引:0,他引:12
R.-S. Lu S.-L. Lo J.-Y. Hu 《Stochastic Environmental Research and Risk Assessment (SERRA)》1999,13(5):327-336
A general methodology for fuzzy synthetic evaluation is developed and illustrated with a case study of trophic status assessment
for Fei-Tsui Reservoir in Taiwan. The historical data base was collected from the management agency of Fei-Tsui Reservoir
from 1987 to 1996. In fuzzy synthetic evaluation, the classification is determined by a matrix operation of the weighted vector
with the fuzzy evaluation matrix. After all individual membership functions of evaluated factors have been determined, the
fuzzy evaluation matrix can be established. The weighted vector is determined by the analytic hierarchy process method (AHP).
The results of this investigation show that the long-term change of water quality and the overturn phenomena cannot be observed
with the Carlson index from 1987 to 1992 but is expressed by fuzzy synthetic evaluation. Fuzzy synthetic evaluation is better
suited than the Carlson index to rating the trophic status of self-sustaining lakes. Interpretation of the results can provide
valuable information to decision makers and aid reservoir management. 相似文献
225.
Polycyclic aromatic hydrocarbons (PAHs) and the trophic structure of polychaete assemblages were studied in sediments at 28 stations in Todos os Santos Bay. Total PAH concentrations varied from 8 to 4163 ng g(-1) dry weight. The indexes used for the determination of PAH origin suggested both pyrolytic and petrogenic sources. A total of 397 individuals of polychaetes was recorded which were classified in three trophic groups. The PCA ordination resulted in the formation of three groups of stations, Group I characterised by sandy sediments, low organic content, low total PAH concentration and percentage of potentially harmful PAH was dominated by subsurface deposit-feeders. The other two groups (IIa and IIb), showed similar percentages of silt and clay, however, Group IIb formed by those stations with high total organic carbon, total nitrogen, sulphur contents, high total PAH concentration and percentage of potentially harmful PAH was dominated by carnivores. Trophic changes could be explained by the level of exposure to PAH effects relative to differences in the life style and feeding strategies between deposit-feeders and carnivores. 相似文献
226.
227.
228.
We have applied the method of Wiener-Hopf technique to obtain the Green's functions of one-group transport equations (with anisotropic unit plane source and with isotroic unit plane source) for a finite slab of passive and multiplying media. 相似文献
229.
A method has been proposed for detecting hidden periodicities in nonstationary finite time series with strong noise. The successive
application of the spectral singular expansion and wavelet transform makes it possible to calculate the energy of short signals
with an arbitrary form against a suppressing noise back-ground, the amplitude of which is several times as large as that of
a useful signal. This method has been used to identify variations in the galactic cosmic ray (GCR) flux related to IMF disturbances
due to the earthward propagation of solar magnetic clouds in the heliosphere. 相似文献
230.
M. Lester M. Lockwood T. K. Yeoman S. W. H. Cowley H. Lühr R. Bunting C. J. Farrugia 《Annales Geophysicae》1995,13(2):147-158
We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°-78°. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71° by the time of the expansion phase onset. A westward electrojet, centred at 65.4°, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1° at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the “distant” neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary. 相似文献