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381.
Mathematical models applied to urban and regional planning have been widely developed during the sixties. Since that time
the scientific and technologic developments have deeply transformed the field of spatial modelling. There has been a reaction
against the idea that reality could be reduced to deterministic models. The paradigms of complexity, chaos, self-organisation,
fractal geometry have made obvious the unpredictability of complex socio-economic systems. At the same time the progress of
computation has led to the substitution of simulation methods to analytic solutions of mathematical models. In such a context,
models are loosing in generality and reproducibility what they earn in adaptation to empirical situations. An important challenge
is also to confirm the pertinence and specificity of the geographical approach. In that respect the spatial analysis programs
must prove the evidence of a common methodology dealing either with physical or human and economic domain. We are working,
for instance, on cellular automata programs applied to the historical evolution of an urban space and also to the run-off
process in an elementary basin. The spatial structure of the models may be slightly different: rectangular or hexagonal tessellations
in the “Human Geography” program, TIN structure, closer to the physical reality, in the other. The relations between the cells
may also differ: they are often defined by a distance matrix for the socio-economic models, but a contiguity matrix is of
course needed for the streaming process. But, beyond these technical differences, it appears that the geographical programs
are developed on a macro-level, that is on aggregate statistical units. The elementary particle is always (or should be for
a geographer...) a material, spatial unit, unlike the drop of water of the hydrologists, or the individual “agents” of the
sociologists' multi-agents systems. The difference between the micro and macro level is not a question of scale, but a difference
of logic. The simulation approach has a requisite, which is a need of systematic validation by a permanent comparison with
the actual situation, but the objective is not prediction. The scientific concern is, before all, a precise understanding
of the past and recent evolutions, more than a forecasting, which escapes to the specific field of scientific research. What
is scientific is what can be measured. The possible prediction may rely on the scientific research, but belongs strictly to
the domain of intellectual and personal thinking.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
382.
Antonella Cattaneo Yves Couillard Sybille Wunsam Michel Courcelles 《Journal of Paleolimnology》2004,32(2):163-175
We studied diatom taxonomic composition and the presence of morphological alterations (size and deformations) along a sediment core collected in Lac Dufault, Abitibi, whose watershed has a long history of mining pollution presently undergoing mitigation. According to sediment dating with 210Pb and metal profiles along the core, we could identify four periods in the contamination history of the lake, which were characterized by different diatoms. Tabellaria flocculosa was dominant in the pre-mining period but was drastically reduced at the onset of pollution when Fragilaria cf. tenera became important. This diatom, together with other Fragilaria species and cysts of Chaetoceros muelleri, typified the transition period in which Cu reached its maximum value and other metals started to increase. During the period of maximum contamination with Zn, Cd, and Fe accompanied by acid mine drainage, Achnanthes minutissima and Brachysira vitrea were dominant. These taxa started to wane in the most recent sediments representing a partial chemical recovery. Asterionella formosa, which almost vanished at mining onset, reappeared with high abundance in these superficial sections. Beside these taxonomical shifts, we observed during the contamination period significant reduction in valve length together with increased percentages of valve deformations. Because available data on water chemistry and a diatom-based pH reconstruction suggest that Lac Dufault escaped severe acidification, diatom patterns observed in the core can be mostly ascribed to metal contamination. Individual diatom abundance and valve length had strong statistical relationships with the different metals identified in the core. Diatom changes both taxonomic and morphological can be excellent specific indicator of metal contamination and early recovery. 相似文献
383.
Two parameters GO2– and HO2– are defined as the differences between respectively the Gibbs free energies and the enthalpies of formation of an oxide and its corresponding aqueous cation. The Gibbs free energies and enthalpies of formation of phosphates from their consituent oxides are shown to be linear functions of respectively GO2– and HO2– of their constituent cations. 相似文献
384.
A parameter GO2– is defined as the difference between the Gibbs free energy of formation from the elements of a given oxide and its corresponding aqueous cation. The Gibbs free energies of formation of compounds such as sulfates, nitrates or carbonates, from their constituent oxides, are shown to be linear functions of GO2– values of their constituent cations. 相似文献
385.
According to Koopmans' theorem, only the electrons associated with molecular levels of negative energy are stable. Many ions which cannot exist in the isolated state because certain occupied levels are positive, become stable in crystals under the stabilization effect arising from the crystal field. As examples, we have studied CO 3 2? in calcite, NO 3 ? in NaNO3, and several natural limpurities: O 3 ? in fluorite, [(OH)4]4?, [(OH)3F]4? and [(OH)2F2]4? in zircon and thorite, by means of the molecular self-consistent field, the crystal field being simulated by point charges. As expected, all the energies corresponding to the occupied levels are negative within the crystal field, contrary to what occurs in the isolated state. Informations concerning the structure and the size of the critical germ are obtained for CaCO3 and NaNO3. 相似文献
386.
Yves J. Balkanski Daniel J. Jacob Richard Arimoto Mark A. Kritz 《Journal of Atmospheric Chemistry》1992,14(1-4):353-374
The atmospheric distribution of222Rn over the north Pacific is simulated with a three-dimensional chemical tracer model using meteorological input from the NASA-GISS general circulation model (4°×5° resolution). Radon-222 (half-life 3.8 days) is a tracer of continental air. Model results are in good agreement with measurements from ships and aircraft. Strong Asian influence is found throughout the tropospheric column over the north Pacific in spring, reflecting a combination of frequent convection over the continent, strong westerly winds at altitude, and subsidence over the ocean. In summer, the upper troposphere over the north Pacific is heavily affected by deep convection over China; however, Asian influences at the surface are then at their yearly minimum. In winter, strong Asian influence is found near the surface but not at high altitudes. Transport of American air over the Pacific is important only at low latitudes. American sources account for 11% of total222Rn in the model at Midway, 30% at Mauna Loa and 59% at Oahu. Results for Hawaii indicate two seasonal peaks of American influence, one in summer and one in winter. The tropical western Pacific is particularly remote from continental influences year round. 相似文献
387.
388.
The Jason-1 Mission 总被引:1,自引:2,他引:1
Yves M nard Lee-Lueng Fu P. Escudier F. Parisot J. Perbos P. Vincent S. Desai B. Haines G. Kunstmann 《Marine Geodesy》2003,26(3):131-146
On December 7, 2001, the Jason-1 satellite was successfully launched by a Boeing Delta II rocket from the Vandenberg site in California, USA. Its main mission was to maintain the high accuracy altimeter measurements, provided since 1992 by TOPEX/Poseidon (T/P), ensuring continuity in observing and monitoring the ocean for intraseasonal to interannual changes, mean sea level, tides, and so forth. Despite four times less mass and power, the Jason-1 system has been designed to have the same performances as T/P, measuring sea surface topography at the centimeter level. This new Centre National d'Etudes Spatiales/National Aeronautics and Space Administration (CNES/NASA) mission also provides near real-time data for sea state and ocean forecast. The first 10 months of the Jason mission were dedicated to the verification of the system performance and cross-calibration with T/P measurements. A complete CALVAL plan was conducted by the Science and Project Teams of the mission based on in situ and regional experiments, global statistical approaches, and multisatellite comparisons, taking advantage of the T/P-Jason overlap during the first months of the mission. CALVAL and first science results showed that the Jason-1 performances were compliant with prelaunch specifications. This was a needed preamble before starting the routine phase of the mission in July 2003 with generation and distribution of validated geophysical data records to the whole user community. 相似文献
389.
Jessica Saïag Pierre‐Yves Collin Jean‐Pierre Sizun Frdric Herbst Ophlie Faÿ‐Gomord Carmela Chateau Smith Bruno Caline ric Lasseur 《Sedimentology》2019,66(7):2976-3007
Microtexture describes the type of particles and their arrangement in matrix samples at scanning electron microscopy scale. Although a microtexture classification exists for micritic limestone, it cannot be directly applied to chalk. This study therefore proposes a classification of chalk microtextures and discusses the origin of microtexture variability. Chalk was sampled at thirteen spatio‐temporal locations along the coastline of northern France (Cenomanian–Santonian). Four criteria are defined to describe, characterize and determine chalk matrix microtexture: (i) mineralogical content; (ii) biogenic fraction; (iii) micritic fraction; and (iv) cement fraction. From these criteria, two major groups are defined: Pure Chalk Microtexture Group, with seven classes, and Impure Chalk Microtexture Group, divided into two subgroups: Argillaceous Microtexture with four classes and Siliceous Microtexture with two classes. Microtexture variability is related both to initial sedimentation and to diagenesis. Sedimentological conditions (for example, climate and distance from shore) affect chalk composition (carbonate content and type of insoluble particles), thus influencing microtexture. Changes in Pure Chalk Microtexture are the result of increasing diagenetic intensity. This classification can also be used to characterize the microtexture of subsurface chalk reservoirs. Reservoir quality depends on the petrophysical and mechanical properties of reservoir rocks, which can be better understood by exploring their sedimentary and diagenetic history, revealed by the study of chalk microtexture variability. 相似文献
390.