Showing papers by "École Normale Supérieure published in 1986"
TL;DR: In this paper, two general algorithms for solving constrained minimization problems are presented and discussed in the context of analysis and assimilation of meteorological observations, in particular in terms of their computational cost.
Abstract: Two general algorithms for solving constrained minimization problems are presented and discussed in the context of analysis and assimilation of meteorological observations. In both algorithms, the original constrained problem is transformed by appropriate modifications into one unconstrained problem, or into a sequence of unconstrained problems. The main advantage of proceeding in this way is that the new unconstrained problems can be solved by classical descent algorithms, thus avoiding the need of directly solving the Euler-Lagrange equations of the original constrained problem. The first algorithm presented in the augmented lagrangian algorithm. It generalizes the more classical penalty and duality algorithms. The second algorithm, inspired from optimal control techniques, is based on an appropriate use of an adjoint dynamical equation, and seems to be particularly well adapted to the assimilation of observations distributed in time. Simple numerical examples show the ability of these algorithms to solve non-linear minimization problems of the type encountered in meteorology. Their possible use in more complex situations is discussed, in particular in terms of their computational cost. DOI: 10.1111/j.1600-0870.1986.tb00459.x
1,572 citations
TL;DR: In this article, Toulouse et al. examined the relationships of chief executive need for achievement and the traditional contingencies of size, technology, and environmental uncertainty with organizational structure.
Abstract: The authors would like to thank Jean-Marie Toulouse and Jeannine Robichaud for their help with the data gathering and sample design, Richard Germain for his advice and analytical contributions to the LISREL analysis, Morty Yalovsky, Peter H. Friesen, Donald C. Hambrick, Alex Whitmore, and Richard P. Bagozzi for their suggestions, and the Social Sciences and Humanities Research Council of Canada and the Government of Quebec FCAC program, respectively, for grants #494-84-0012 and #EQ1 867. A study was undertaken to examine the relationships of chief executive need for achievement and the traditional contingencies of size, technology, and environmental uncertaintywith organizational structure. A number of models relating the structural constructs of formalization, centralization, and integration with their hypothesized determinants were examined using LISREL and multipleregression analyses. CEO need for achievement and size were found to have the strongest relationships to most structural constructs; technology and uncertainty had very little impact on structure. The relationships between need for achievement and structure were usually highest in samples of small and young firms, suggesting that CEO personality might be influencing structure, rather than the reverse.
835 citations
TL;DR: In this paper, the main fields of development (spin glasses, optimization theory, and physics) of ultrametricity have been surveyed, and some tentative conclusions on the common causes for the occurrence of such structures in nature are drawn from present knowledge.
Abstract: Ultrametricity is a simple topological concept, but its appearance in the language of physicists is recent. This review provides all the elementary background (from mathematics, taxonomy, and statistical physics) and surveys the main fields of development (spin glasses, optimization theory). Static and dynamic aspects are covered. From present knowledge, one can already draw some tentative conclusions on the common causes for the occurrence of ultrametric structures in nature. Some perspectives on unresolved problems in physics and biology are also presented.
729 citations
TL;DR: In this article, the Arnold-Beltrami-childress (ABC) flows are investigated both analytically and numerically, and a systematic search for integrable cases is done using Painleve tests, i.e. studying complex-time singularities of fluidparticle trajectories.
Abstract: The particle paths of the Arnold-Beltrami-Childress (ABC) flows
\[
u = (A \sin z+ C \cos y, B \sin x + A \cos z, C \sin y + B \cos x).
\]
are investigated both analytically and numerically. This three-parameter family of spatially periodic flows provides a simple steady-state solution of Euler's equations. Nevertheless, the streamlines have a complicated Lagrangian structure which is studied here with dynamical systems tools. In general, there is a set of closed (on the torus, T3) helical streamlines, each of which is surrounded by a finite region of KAM invariant surfaces. For certain values of the parameters strong resonances occur which disrupt the surfaces. The remaining space is occupied by chaotic particle paths: here stagnation points may occur and, when they do, they are connected by a web of heteroclinic streamlines.When one of the parameters A, B or C vanishes the flow is integrable. In the neighbourhood, perturbation techniques can be used to predict strong resonances. A systematic search for integrable cases is done using Painleve tests, i.e. studying complex-time singularities of fluid-particle trajectories. When ABC ≠ 0 recursive clustering of complex time singularities occurs that seems characteristic of non-integrable behaviour.
674 citations
TL;DR: In this paper, a statistical method is presented for the determination of the global solar radiation at ground level, which makes use of data from the meteorological satellites, which provide extensive coverage as well as adequante ground resolution.
549 citations
TL;DR: This paper shows that, if ordered lists can be put in a one-to-one correspondence with the nodes of a graph of degreed so that the iterative search always proceeds along edges of that graph, then this structure can be built, called afractional cascading structure, in which all original searches after the first can be carried out at only logd extra cost per search.
Abstract: In computational geometry many search problems and range queries can be solved by performing an iterative search for the same key in separate ordered lists. In this paper we show that, if these ordered lists can be put in a one-to-one correspondence with the nodes of a graph of degreed so that the iterative search always proceeds along edges of that graph, then we can do much better than the obvious sequence of binary searches. Without expanding the storage by more than a constant factor, we can build a data-structure, called afractional cascading structure, in which all original searches after the first can be carried out at only logd extra cost per search. Several results related to the dynamization of this structure are also presented. A companion paper gives numerous applications of this technique to geometric problems.
464 citations
TL;DR: In this article, the authors determined that, in hydrothermal systems, REE are immobile at temperatures below 350°C and for water/rock ratios of <105.
447 citations
TL;DR: In this paper, from 1984 data on the chemistry of precipitation collected in South Corsica, they show that due to its CaCO3 content, Saharan dust significantly increases the pH of rain water, which may counteract the effects of acidic rain.
Abstract: It has long been recognized that Saharan dust may be transported a long way from its sources, particularly over the ocean1, and especially over the tropical North Atlantic, as far as the Caribbean2–7, and over various areas of the Mediterranean8–10. The eolian transport of desertic aerosols is a major contribution to oceanic sedimentation11–13 and may have important climatic implications14. This phenomenon is responsible for episodes of so-called ‘red rain’ or ‘red snow’ which have been identified in various areas of the European continent15–17. Numerous red rains and red dust falls have been observed in Corsica. From 1984 data on the chemistry of precipitation collected in South Corsica, we show here that due to its CaCO3 content, Saharan dust significantly increases the pH of rain water. This may counteract the effects of acidic rain. An assessment of African dust deposition indicates that, compared with the sediments discharged by the Rhone river, atmospheric input to the northwestern Mediterranean contributes significantly to sedimentation in that region.
436 citations
TL;DR: In this paper, the electronic energy levels of semiconductor heterostructures within the envelope function scheme were described and the Coulombic bound states in heterostructure (impurities, excitons) were discussed, and the effect of a static electric field on the carrier and exciton energy levels in semiconductor quantum wells.
Abstract: This paper describes the electronic energy levels of semiconductor heterostructures within the envelope function scheme. Quantum well and superlattice electronic states are calculated and discussed, especially the in-plane dispersion relations. The Coulombic bound states in heterostructures (impurities, excitons) are then discussed. Finally, we present a brief overview of the effect of a static electric field on the carrier and exciton energy levels in semiconductor quantum wells.
397 citations
TL;DR: In this paper, the authors review the geological and geophysical structural framework of the deep Black Sea and Caspian Sea basins and conclude that the deep basins have an oceanic crust formed in a marginal sea environment.
395 citations
TL;DR: In this paper, the authors focus on the refting-derived structures, more especially to the major tilted crustal blocks, a few tens of kilometres wide, which can be either reconstructed or directly observed.
TL;DR: The main theorem allows an elegant algorithm to be refined into an efficient one based on ‘marking of’ regular expressions based on derivatives of regular expressions, which constructs an automaton for the marked expression.
TL;DR: The 3D Navier-Stokes equations were obtained from two different lattice gas models as mentioned in this paper, one having its sites on a cubic lattice and particle speeds zero, one and √ 2.
Abstract: The 3D Navier-Stokes equations are obtained from two different lattice gas models The first one has its sites on a cubic lattice and has particle speeds zero, one and √2 The second one is a 3D projection of a lattice gas implementation of the 4D Navier-Stokes equations, residing on a face-centred hypercubic lattice
TL;DR: In this paper, the authors investigated the kinetics of hydrodechlorination of chlorobenzene over Pd Al 2 O 3 and Rh Al 2O 3 catalysts of varying dispersion and proposed a reaction scheme which is formally analogous to the Mars-van Krevelen mechanism for the oxidation of hydrocarbons.
TL;DR: In this article, the spontaneous formation of couples of opposite-sign vortices in von Karman wakes is investigated experimentally in thin liquid films, and the structure of these couples, their behaviour and their role in turbulent flows are studied using both a numerical simulation and laboratory results.
Abstract: Two-dimensional turbulence is investigated experimentally in thin liquid films. This study shows the spontaneous formation of couples of opposite-sign vortices in von Karman wakes. The structure of these couples, their behaviour and their role in turbulent flows is then studied using both a numerical simulation and laboratory results.
TL;DR: The single-vehicle dial-a-ride problem with time window constraints for both pick-up and delivery locations, and precedence and capacity constraints, is solved using a forward dynamic programming algorithm.
Abstract: SYNOPTIC ABSTRACTThe single-vehicle dial-a-ride problem with time window constraints for both pick-up and delivery locations, and precedence and capacity constraints, is solved using a forward dynamic programming algorithm. The total distance is minimized. The development of criteria for the elimination of infeasible states results in solution times which increase linearly with problem size.
TL;DR: In this article, high resolution 29 si-, 27 Al- and 11 B magic angle spinning NMR evidences Si substitution by Al and B in the zeolite framework, showing that the presence of fluoride in the as-synthesized samples leads to organic fluro compounds formation on calcination.
Abstract: Silica-rich, Al-, B- and (Al + B) MFI zeolites called Zeosilites, Aluzeosilites, Borozeosilites and Aluborozeosilites respectively were obtained by hydrothermal crystallization at 60–200°C from mixtures containing F anions and tetra-, tri- and di-propylamraonium cations as templates; pH values were 3–10. Crystal size is a function of the Si substitution degree, it may reach 800 um in some cases. DSC, DTA and TG curves corresponding to the decomposition of the templates occluded as fluoride salts are different from those observed for samples obtained in alkaline medium. Mass spectrometer analysis shows that the presence of fluoride in the as-synthesized samples leads to organic fluro compounds formation on calcination. High resolution 29 si-, 27 Al- and 11 B magic angle spinning NMR evidences Si substitution by Al and B in the zeolite framework.
TL;DR: In this article, the existence, uniqueness, and long time behavior of spin processing in the magnetic field created by their closest neighbours were investigated, and the results concerning existence and uniqueness were presented.
Abstract: The continuum limit of a cubic latice of classical spins processing in the magnetic field created by their closest neighbours is considered. Results concerning existence, uniqueness and (for initially small spin deviation) long time behaviour, are presented.
TL;DR: The microbial activity is first strongly stimulated by more favourable physical conditions and it increases as intestinal mucus is expended, and the microflora appears to become more able to digest the more complex organic matter of the soil for the benefit of the earthworm.
Abstract: Soil ingested by Pontoscolex corethrurus Muller, a geophagous tropical earthworm, was transformed considerably during passage through the digestive tract. Readily-assimilable water-soluble compounds (mucus) with a high energy content represented 16 and 12.7% of the dry mass of soil in the anterior and posterior intestine respectively but comprised only 0.12% of the control soil and 0.43% of the fresh casts. Water content increased from 35% in the soil to 149% in the anterior part of the gut; it was 122% in the terminal part and 99% in the fresh casts. Ingested soil of pH 4.6 was neutralized in the anterior part of the gut (pH 6.8); the pH decreased to 6.0 in the posterior part and declined to 4.8 in the casts.
These physicochemical modifications and the intense mixing within the gizzard and gut stimulated an increase in the respiratory activity of the microflora ranging from 1.37 fold in the anterior part of the gut to 7.30-fold in the posterior part and declining to 1.69-fold in the casts. Thus, the microbial activity is first strongly stimulated by more favourable physical conditions and it increases as intestinal mucus is expended. The microflora appears to become more able to digest the more complex organic matter of the soil for the benefit of the earthworm. A mutualistic relationship is proposed between microflora and earthworms for the exploitation of the complex organic matter of tropical soils.
TL;DR: A formal description of the network design problem with continuous decision variables representing link capacities can be cast into a framework of multilevel programming and various suboptimal procedures to solve it are developed.
Abstract: Recently much attention has been focused on multilevel programming, a branch of mathematical programming that can be viewed either as a generalization of min-max problems or as a particular class of Stackelberg games with continuous variables The network design problem with continuous decision variables representing link capacities can be cast into such a framework We first give a formal description of the problem and then develop various suboptimal procedures to solve it Worst-case behaviour results concerning the heuristics, as well as numerical results on a small network, are presented
TL;DR: In this article, a new model of the opening of the Japan Sea is proposed based on the synthesis of both on-land and offshore structural data, which gives new constraints about the structural evolution of the system.
TL;DR: In the presence of TMSCl, the conjugate addition of organocuprates to various α, β-unsaturated esters, amides, ketones and nitriles is greatly improved.
TL;DR: A general formulation allows for an exploration of some basic issues in learning theory and two learning schemes are constructed, which avoid the overloading deterioration and keep learning and forgetting, with a stationary capacity.
Abstract: One characteristic behaviour of the Hopfield model of neural networks, namely the catastrophic deterioration of the memory due to overloading, is interpreted in simple physical terms. A general formulation allows for an exploration of some basic issues in learning theory. Two learning schemes are constructed, which avoid the overloading deterioration and keep learning and forgetting, with a stationary capacity.
TL;DR: In this paper, spectral methods (Fourier Galerkin, Fourier pseudospectral, Chebyshev Tau, Chebyhev collocation, spectral element) and standard finite differences are applied to solve the Burgers equation with small viscosity (v = 1 100 π ).
TL;DR: In this paper, the authors report radiocarbon dates from a Brazilian site which establish that early man was living in South America at least 32,000 years ago, based on the large painted rockshelter of Boqueirao do Sitio da Pedra Furada.
Abstract: The view that man did not arrive on the American continent before the last glaciation has been supported by the fact that until now the known and dated archaeological sites have not been of very great antiquity. But now we report radiocarbon dates from a Brazilian site which establish that early man was living in South America at least 32,000 years ago. These new findings come from the large painted rockshelter of Boqueirao do Sitio da Pedra Furada, the walls and the ceiling of which are decorated with a rich set of prehistoric paintings. We have excavated a sequence containing abundant lithic industry and well-structured hearths at all levels. Carbon-14 dates from charcoal establish a continuous chronology indicating human occupation from 6,160±130 to 32,160±100 years BP. A date of 17,000±400 BP, obtained from charcoal found in a level with fragments of a pictograph fallen from the walls, testifies to the antiquity of rupestral art in this region of Brazil.
TL;DR: In this article, a large number of new geometric, ergodic and statistical properties of the Kuramoto-Sivashinsky equation were presented for modeling interfacial turbulence in various physical contexts.
TL;DR: In this paper, the existence, uniqueness and properties of asymptotic behavior for solutions of the Milne and Kramers problems for the linearized Boltzmann equation for a gas of hard spheres are proved.
Abstract: Existence, uniqueness and properties of asymptotic behavior are proved for solutions of the Milne and Kramers problems for the linearized Boltzmann equation for a gas of hard spheres. The proof uses energy-like estimates and follows the analysis of Bardos, Santos and Sentis for the equations of neutron transport.