Criterion of stability and implementation issues of hybrid frequency-time-domain procedure for non-linear dynamic analysis     

Georges R. Darbre  John P. Wolf 《地震工程与结构动力学》1988,16(4):569-581

A criterion of stability pertaining to the hybrid frequency-time-domain procedure is derived. It stems from the initial-value theorem on one side and from the condition of convergence which applies to the harmonic counterpart of the procedure on the other side. The criterion depends on the dynamic stiffnesses of both the original non-linear system and the pseudo-linear system evaluated at the Nyquist frequency. Since at this frequency both stiffnesses are usually controlle by the mass, the criterion of stability is satisfied for most structural systems. The procedure must, however, be applie sequentially to individual time segments. The validity of this criterion is confirmed by a numerical investigation performe for a SDOF system. The solution of non-linear dynamic problems requires consideration of implementation issues which are also discusse in the paper. The analysis of a non-linear soil-structure-interaction system in which the soil's stiffness coefficients an directly defined in the frequency domain also demonstrates the accuracy of the hybrid frequency-time-domain procedure.  相似文献   

Carboxylic monoacids in the air of mayombe forest (Congo): Role of the forest as a source or sink     

Jean Servant  Georges Kouadio  Bernard Cros  Robert Delmas 《Journal of Atmospheric Chemistry》1991,12(4):367-380

In the tropical rain forests of the Congo during the dry season, from June to September 1987, carboxylic acid partial pressures (P _gas) in the air above the canopy, at ground level, and at the boundary layer, were estimated from water samples such as fog and rainwater. The concentrations of these acids were also measured in the sap of tree leaves. Tree leaves act as a sink or as a source if the acid P _gas is greater of lower than the acid concentrations in molecular form in sap. For each of these soluble gases, there is a value of P _gas where the exchange is nul. This is called the compensation point. Values of the compensation point for some tree leaves were evaluated according to Henry's law. Henry's law coefficients at ppm levels were redetermined for formic (HCOOH), acetic (CH₃COOH), propionic (CH₃CH₂COOH), and isobutyric (CH₃CH(CH₃)COOH) acids.By comparison of P _gas and compensation points, it is concluded that the forest was a potential source for these acids. The soil-or the litter-acts as a significant source of a carboxylic acid of C₃ or C₄ atoms in the aliphatic chain. This carboxylic acid, not yet fully characterized, could play an important role in the rain acidity in forested zones of the equatorial areas.The direct emission of these carboxylic acids by vegetation was the main source in the boundary layer above the forest. The average emissions were 3.1×10⁹, 7.8×10⁹, and 8.4×10⁹ molecules cm^-2 s^-1 for HCOOH, CH₃COOH, and CH₃CH₂COOH, respectively. The savanna is an exogenous source of HCOOH and CH₃CH₂COOH during moderately rainy days for 30% of the time. The ozonolysis of isoprene seems to be a small source of HCOOH.  相似文献   

Chromite crystallization in a multicellular magma flow: Evidence from a chromitite dike in the Oman ophiolite     

Marc Leblanc  Georges Ceuleneer 《Lithos》1991,27(4):231-257

The investigated chromitite dike is located at the top of an upwelling mantle structure of the Oman ophiolite (Maqsad diapir), in undeformed dunites displaying evidence for magma impregnation and circulation, just below the paleo-ridge axis. The chromitite dike is undeformed, its shape is that of an upward widening tube. It exhibits an internal layering which is roughly perpendicular to the cavity axis and comprises a vertical succession of four main layers showing a graded-bedding. Chromitite magmatic structures are beautifully preserved and result from a progressive crystallization from small euhedral crystals to wide octahedron-shaped nodules; dissolution textures provide evidence for late magmatic desequilibrium; sedimentation structures include flattening of the largest nodules. The silicate matrix comprises poikilitic forsterite and a locally abundant association of primary pargasite and plagioclase and alteration minerals (vesuvianite-chlorite-dolomite); pargasite inclusions are very abundant in the chromite. Chromite composition changes from one layer to the other and from core to rim in the chromite nodules (chromium decreases and titanium increases); Ti contents are generally high (0.4 to 0.8 wt.% TiO₂) with respect to podiform chromites. Platinum-group elements are not abundant but they show a strong fractionation at the scale of the orebody and of the main graded-bedded layers (Pd/Ir ratio varies from 0.5 to 11.5). REE patterns of chromitite parallel to those of gabbros and furthermore display a sea water related hydrothermal alteration (Ce negative anomaly).

The chromitite dike of Maqsad provides evidence for the crystallization of chromitite bodies in subvertical magma conduits below oceanic ridges; it corroborates the model of Cassard et al. (1981) and Lago et al. (1982) concerning the formation of chromitite pods in ophiolites which were later deformed and transposed into the horizontal plane due to the plastic flow prevailing away from the paleo-axial zone. Layering and chromite compositional variations are ascribed to a multicellular convective system segregating various stocks of chromite particles either in the upwelling flow of fresh magma or in the convective cells of fractionated residual magma in the confined part of the cavity. The estimated life-time for the magma influx is very short (<2 months). The parent-magma was probably of MORB-type and already fractionated (Ti-rich and PGE-poor), which is consistent with the strong evidence of magma-peridotite interactions in the core of the Maqsad diapir. Hydrous fluids were present during chromite crystallization (pargasite inclusions) suggesting that fluid-rich melts occur in the upper mantle.  相似文献   

Nonlinear least-squares method via an isomorphic geometrical setup     

Georges Blaha  Robert P. Bessette 《Journal of Geodesy》1989,63(2):115-137

The resolution of a nonlinear parametric adjustment model is addressed through an isomorphic geometrical setup with tensor structure and notation, represented by a u-dimensional “model surface” embedded in a flat n-dimensional “observational space”. Then observations correspond to the observational-space coordinates of the pointQ, theu initial parameters correspond to the model-surface coordinates of the “initial” pointP, and theu adjusted parameters correspond to the model-surface coordinates of the “least-squares” point . The least-squares criterion results in a minimum-distance property implying that the vector Q must be orthogonal to the model surface. The geometrical setup leads to the solution of modified normal equations, characterized by a positive-definite matrix. The latter contains second-order and, optionally, thirdorder partial derivatives of the observables with respect to the parameters. This approach significantly shortens the convergence process as compared to the standard (linearized) method.  相似文献   

Determination of Fluorine in Eighty International Geochemical Reference Samples by Proton Induced Gamma Ray Emission Spectrometry (PIGE)     

Iwan ROELANDTS  Guy ROBAYE  Georges WEBER  Jeanne-Marie DELBROUCK 《Geostandards and Geoanalytical Research》1985,9(2):191-192

Fluorine content has been determined non destructively in eighty international geochemical reference samples (GRS) including rocks, soils, sediments, minerals and ores, by proton induced gamma ray emission spectrometry (PIGE) using the nuclear reaction ¹⁹F(p,αγ) ¹⁶O. Under our operating conditions, the detection limit is around 25 ppm. Our analytical results are compared with the presently preferred values when available or with other published data. The general agreement between this work and reported values is reasonably good. The present paper includes results on several GRS for which existing data are rather scarce or even inexistant.  相似文献   

Sites occupancy of Fe3+ in Garfield Nontronite: A spectroscopic study     

Dominique Bonnin  Georges Calas  Hélène Suquet  Henri Pezerat 《Physics and Chemistry of Minerals》1985,12(1):55-64

New data on the structure of Garfield nontronite have been produced by the use of different spectroscopic techniques: Mössbauer spectroscopy, optical spectroscopy, X-ray absorption edges and EXAFS and NMR. The tetrahedral iron content is found to be no higher than 1 percent. All iron atoms belong to the octahedral sheet excluding the possibility of the presence of non crystallized phases. Some ambiguities remain about the coherence of the octahedral sheet because of the presence of two doublets in the Mössbauer spectrum and at least two lineshapes in NMR spectra of OH which correspond to different environments.  相似文献   

Archosaurier-Fährtenfaunen der Trias: Die Bedeutung ihrer Ähnlichkeiten und ihrer Verschiedenheiten; ihre mögliche Verwendung im Rahmen der Stratigraphie der Trias     

Dr. Georges Demathieu 《International Journal of Earth Sciences》1982,71(3):741-746

Zusammenfassung Die wichtigsten Merkmale der Ichnofaunen des mittleren und oberen Buntsandsteins, der Mittleren Trias (wesentlich der Fährtensandstein du Lyonnais), des Oberen Trias werden hier betrachtet. Die Verschiedenheiten beziehen sich auf ihre Zusammensetzung, die Morphologie der Eindrücke und die Häufigkeiten der Arten oder Gattungen. Für die Vergleiche wurden nicht nur charakteristische Artenverbindungen sondern auch spezielle lokale Arten benutzt. Unter der Bedingung, die Ichnofaunen sind repräsentativ, erlauben die vorhergehenden Punkte und die Kenntnis der Archosaurierextremitäten Entwicklung während der Trias, die bezügliche stratigraphische Lagen der verschiedenen Fundschichten zu präzisieren.

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The main characters of the Ichnofaunas of 1) the middle and upper Buntsandstein, 2) the Middle Triassic (essentially the Fährtensandstein du Lyonnais) and 3) the upper Triassic are here considered. The difference between these Ichnofaunas relate to their composition, the morphology of the footprints and the frequencies of the ichnogenera or the ichnospecies. For the comparisons are utilized not only ichnospecies associations but also the local or peculiar ichnospecies.On condition that these Ichnofaunas are representative, the results of the studies described above and the knowledge of the evolution of the Archosaur appendicular skeletons during the Triassic, allow to settle the relative stratigraphical positions of the different layers.

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Résumé Les caractères principaux des Ichnofaunes du Buntsandstein moyen et supérieur, du Trias moyen (essentiellement le Fährtensandstein du Lyonnais) et du Trias supérieur sont mis en évidence. Les différences entre ces Ichnofaunes portent sur leur composition, la morphologie des empreintes et les fréquences des ichnogenres ou des ichnoespèces. Pour les comparaisons sont utilisées non seulement les associations d'ichnoespèces mais également les ichnoespèces locales ou particulières.Sous la condition que ces ichnofaunes soient représentatives, les points évoqués cidessus et la connaissance de l'évolution des autopodes des Archosauriens pendant le Trias permettent d'établir les positions stratigraphiques relatives des différents gisements.

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Preface     

Prof. Georges Prevelakis 《GeoJournal》2001,52(4):281-283

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Book review     

John C. Davis  David B. Kitts  Georges Verly 《Mathematical Geosciences》1992,24(5):577-586

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Théorie du pendule de Zöllner et du pendule de Lettau     

Georges Jobert 《Pure and Applied Geophysics》1959,44(1):25-73

Summary The theory of a Zöllner's horizontal pendulum with perfect wires of suspension is made. We use the Euler's angles of the axes of a system fixed in the moving body relatively to fixed axes and a fourth angle caracterising the amplitude of a motion of translation. We give the conditions for the decoupling of the four types of motion (pure rotation, pitching, rolling, translation) and the equations of forced motions.A rigorous theory of Lettau's double pendulum is initiated. We suppose that the primary pendulum has only one degree of freedom. First the case of a secondary pendulum not disturbing the primary one is examined, and then the case of an indifferent primary pendulum, wich enables us to understand what happens in the normal case. The potential energy of the secondary pendulum is not always a minimum in the central position when the plane of symmetry is vertical and it is possible that parasitesolutions appear, stabler than the central one. This study is extended to the case of a non-vertical plane of symmetry and indications are given for the study of the free motions of the system.In conclusion we could say that this system is simple only at first sight. Its use would be necessary in the case of a real great drift of the underground of the station. But in the contrary case ordinary simple pendulums are sufficient and more easy to understand.

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Resumo La movoj de horizontala Zöllnera pendolo estas difinataj pere de la Euleraj anguloj de triaksa sistemo ligita al la pendolo, rilate al fiksa sistemo, kaj de kvara angulo rilata al translacia movado. Ni donas la kondiojn necesajn por la senkuplado de tiuj kvar movoj (pura rotacio, tangado, ruligado, translacio) kaj la ekvaciojn de la devigataj movoj.La teorio de Lettaùa duobla pendolo estas multe pli kompleksa. Supozente ke la primara pendolo havas nur unu gradon de libereco, ni studas unue la movojn de la sistemo kiam la sekundara pendolo ne perturbas la primaran aù kiam tiu-i estas en indiferenta ekvilibro. Tio permesas kompreni tion kio okazas en la normala kazo. ar la potenciala energio de la sekundara pendolo ne estas iam minimuma en la centra pozicio kiam la simetria ebeno estas vertikala, parazitaj pozicioj povas ekzisti kiuj estas pli stabilaj ol la centra. Ni ekzamenas ankaù la kazon de nevertikala ebeno de simetrio kaj indikas kiel studi la liberajn movojn de la sistemo.

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