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31.
IJ Van der Merve 《GeoJournal》1995,37(4):513-523
In the changing multi-ethnic South African society of the nineties, language planning has become a top priority on the national agenda of reform. Comprehension of the territorial dimensions of language is crucial if we are to penetrate its true cultural, economic and political effect. South Africa's language policy, as defined in the interim constitution, focuses mainly on the fact that in future the country will accommodate eleven official languages with equal status. Obviously, the nine provinces do not each have eleven official languages. A provincial legislative may, by a two-thirds majority vote, declare any of the national languages a provincial official language for the whole province or a part thereof. In the light of this it is of vital importance that the country's regional language patterns be analysed on a geographical basis. A visual and statistical representation of the geolinguistic realities in South Africa could support the planning and transformation process currently taking place at all levels of government in this multilingual country. The aim of this paper is to address the following geolinguistic issues on a national scale:
- The spatial identification of the official language distribution on a macro level;
- The time-space pattern of language change between 1980 and 1991;
- The demographic and socio-economic profile of language speakers;
- The consequences of the findings for ethno-linguistic restructuring in a post-apartheid South Africa.
32.
Long-term fluctuations in fish recruit abundance in the western Wadden Sea in relation to variation in the marine environment 总被引：1，自引：0，他引：1
33.
Andreas M. Waser Rob Dekker Johannes IJ. Witte Niamh McSweeney Bruno J. Ens Jaap van der Meer 《Estuaries and Coasts》2018,41(2):507-520
Many subtidal predators undertake regular tidal migrations into intertidal areas in order to access abundant prey. One of the most productive habitats in soft bottom intertidal systems is formed by beds of epibenthic bivalves such as blue mussels (Mytilus edulis) and Pacific oysters (Crassostrea gigas). In the Dutch Wadden Sea, these bivalves might face substantial predation pressure by the shore crab (Carcinus maenas), which increased considerably in numbers during the last 20 years. However, the quantification of this species on bivalve beds is challenging, since most methods common for quantifying animal abundance in marine habitats cannot be used. This study investigated the potential of two methods to quantify the abundance of C. maenas on 14 epibenthic bivalve beds across the Dutch Wadden Sea. The use of the number of crabs migrating from subtidal towards intertidal areas as a proxy of abundance on bivalve beds yielded unreliable results. In contrast, crabs caught with traps on the beds were correlated with the abundance assessed on the surrounding bare flats by beam trawl and therefore provided usable results. The estimates, however, were only reliable for crabs exceeding 35 mm in carapace width (CW). The application of these estimates indicated that crab abundances on bivalve beds were influenced by the biogenic structure. Beds dominated by oysters attracted many large crabs (> 50-mm CW), whereas abundances of medium-sized crabs (35–50-mm CW) showed no relationship to the oyster occurrence. The combination of traps and trawls is capable of quantifying crab abundance on bivalve beds, which offers the possibility to study biotic processes such as predator-prey interactions in these complex structures in more detail. 相似文献
34.
35.
Waves impinging on rubble mound breakwaters and seawalls induce a mean flow within the breakwater, analogous to the so-called undertow within the surf zone. Here, using a plane wave approximation (kh<1.5), a second-order problem is solved for an idealized breakwater with a rectangular cross-section to show the origin and the nature of the mean flow within the porous structure. The mean flow is expressed in terms of a mean stream function analytically derived, obtained based on the mass flux balance between the incident, reflected and transmitted waves. Furthermore, the evolution of other second-order magnitudes such as mean water level and mass flux is analyzed under different incident wave conditions, structure geometry and porous material characteristics. Results show that the evolution of the different mean quantities is controlled mainly by reflection and consequently depends highly on structure geometry and porous material characteristics. Furthermore, it is shown that the return flow is stronger with increasing mass flux decay. Some qualitative experiments to show the described mechanism are also presented. 相似文献
36.
Melisa Menéndez Fernando J. Méndez Cristina Izaguirre Alberto Luceño Inigo J. Losada 《Coastal Engineering》2009
A time-dependent generalized extreme value (GEV) model for monthly significant wave heights maxima is developed. The model is applied to several 3-hour time series from the Spanish buoy network. Monthly maxima show a clear non-stationary behavior within a year, suggesting that the location, scale and shape parameters of the GEV distribution can be parameterized using harmonic functions. To avoid a possible over-parameterization, an automatic selection model, based on the Akaike Information Criterion, is carried out. Results show that the non-stationary behavior of monthly maxima significant wave height is adequately modeled, drastically increasing the significance of the parameters involved and reducing the uncertainty in the return level estimation. The model provides new information to analyze the seasonal behavior of wave height extremes affecting different natural coastal processes. 相似文献
37.
Vnia Freitas Joana F.M.F. Cardoso Sílvia Santos Joana Campos Jan Drent Sofia Saraiva Johannes IJ. Witte Sebastiaan A.L.M. Kooijman Henk W. Van der Veer 《Journal of Sea Research》2009,62(2-3):75
Required assimilated energy to support observed growth was reconstructed for four common bivalve species (Mya arenaria, Cerastoderma edule, Mytilus edulis and Macoma balthica) from various Northeast Atlantic coastal areas, along the species distributional range. The approach applied was based on the Dynamic Energy Budget (DEB) theory whereby observed growth patterns in the field, in combination with prevailing temperatures, were used to reconstruct the average food intake experienced in the field scaled to the maximum possible. For all species, results suggest food limitation over the range of locations. In general, reconstructed food intake indicated better conditions for C. edule compared to the other species, while M. edulis presented the lowest food conditions in all the areas. Despite the indications for a latitudinal trend in primary production, no clear pattern or relationship between reconstructed food conditions and latitude was observed suggesting that any trend may be overruled by local conditions. 相似文献
38.
Numerical modeling of nonlinear resonance of semi-enclosed water bodies: Description and experimental validation 总被引：1，自引：0，他引：1
Inigo J. Losada Jose M. Gonzalez-Ondina Gabriel Diaz-HernandezErnesto M. Gonzalez 《Coastal Engineering》2008
The purpose of this work is to a present a numerical model to solve a set of modified Boussinesq equations to analyse nonlinear resonance of semi-enclosed water bodies. The equations are solved on a finite element unstructured grid in order to achieve an optimal mesh resolution with the local geometry. The model is able to simulate long time lapses and realistic forcing in real bathymetries with a reasonable computational cost. To validate the numerical results, a set of experiments was carried out in a physical model of two adjacent elongated basins. Comparisons between numerical and experimental results for different geometries and nonlinear conditions show that the model is able to simulate with an excellent agreement the transient nonlinear resonant process. 相似文献
39.
A regional climate model simulation over West Africa: parameterization tests and analysis of land-surface fields 总被引：2，自引：2，他引：0
The West African Monsoon has been simulated with the regional climate model PROMES, coupled to the land-surface model ORCHIDEE
and nested in ECMWF analysis, within AMMA-EU project. Three different runs are presented to address the influence of changes
in two parameterizations (moist convection and radiation) on the simulated West African Monsoon. Another aim of the study
is to get an insight into the relationship of simulated precipitation and 2-m temperature with land-surface fluxes. To this
effect, data from the AMMA land-surface model intercomparison project (ALMIP) have been used. In ALMIP, offline simulations
have been made using the same land-surface model than in the coupled simulation presented here, which makes ALMIP data particularly
relevant for the present study, as it enables us to analyse the simulated soil and land-surface fields. The simulation of
the monsoon depends clearly on the two analysed parameterizations. The inclusion of shallow convection parametrization affects
the intensity of the simulated monsoon precipitation and modifies some dynamical aspects of the monsoon. The use of a fractional
cloud-cover parameterization and a more complex radiation scheme is important for better reproducing the amplitude of the
latitudinal displacement of the precipitation band. This is associated to an improved simulation of the surface temperature
field and the easterly jets. However, the parameterization changes do not affect the timing of the main rainy and break periods
of the monsoon. A better representation of downward solar radiation is associated with a smaller bias in the surface heat
fluxes. The comparison with ALMIP land-surface and soil fields shows that precipitation and temperature biases in the regional
climate model simulation are associated to certain biases in land-surface fluxes. The biases in soil moisture seem to be driven
by atmospheric biases as they are strongly affected by the parameterization changes in atmospheric processes. 相似文献
40.
A multi-model approach to the Atlantic Equatorial mode: impact on the West African monsoon 总被引：2，自引：0，他引：2
T. Losada B. Rodríguez-Fonseca S. Janicot S. Gervois F. Chauvin P. Ruti 《Climate Dynamics》2010,35(1):29-43
This paper is focused on the West African anomalous precipitation response to an Atlantic Equatorial mode whose origin, development and damping resembles the observed one during the last decades of the XXth century. In the framework of the AMMA-EU project, this paper analyses the atmospheric response to the Equatorial mode using a multimodel approach with an ensemble of integrations from 4 AGCMs under a time varying Equatorial SST mode. The Guinean Gulf precipitation, which together with the Sahelian mode accounts for most of the summer West African rainfall variability, is highly coupled to this Equatorial Atlantic SST mode or Atlantic Niño. In a previous study, done with the same models under 1958–1997 observed prescribed SSTs, most of the models identify the Equatorial Atlantic SST mode as the one most related to the Guinean Gulf precipitation. The models response to the positive phase of equatorial Atlantic mode (warm SSTs) depicts a direct impact in the equatorial Atlantic, leading to a decrease of the local surface temperature gradient, weakening the West African Monsoon flow and the surface convergence over the Sahel. 相似文献