From networks to uses patterns: the digital divide as seen from Africa

This paper gives an account of the work carried out in the AFRICA’NTI research network, which gathered together a hundred, mostly African, researchers. The results were presented at the conference on “the North–South Digital Divide” in 2003 and 2004 (see www.africanti.org). From network to uses patterns, it first questions the way in which the subject is defined. This is a controversial question; should we speak of a “ditch” rather than of “fracture”? This depends on the point of view, but also on the geopolitical situation, and is difficult to measure. The digital divide may be less important than it is usually believed. This paper presents several types of approaches dealing with the opportunities of new technologies for Africa, geographical aspects stressing the diversity of the situations considered, and the importance of a multilevel systemic analysis based on case studies. It is shown that a slow down in the dynamics of equipment has been observed in Africa for both mobile telephony and the Internet. This then raises the question of a risk of regression for the continent, based on the idea that inequalities in access and uses of ICTs matter less than whether these uses improve the living conditions of the poor people concerned.     

Enregistrements sismologiques de l'explosion sur le site de l'usine AZF (Toulouse,France)Seismological records of an explosion at the AZF chemical complex in Toulouse,France

This study presents a detailed analysis of the seismic records of a strong explosion that occurred on 21 September 2001 at a chemical complex located south of Toulouse, France, and provoked important damages. The explosion, which is equivalent to a 3.4 magnitude earthquake, has been recorded at most of the stations of the National Seismological Network, as well as at a station under test at the ‘Observatoire Midi-Pyrénées’, 4.2 km away from the epicentre. The main seismic phases are interpreted using the known crustal structures, and a modelling with synthetic seismograms is performed. To cite this article: A. Souriau et al., C. R. Geoscience 334 (2002) 155–161.     

Age and significance of the North Pyrenean metamorphism

³⁹Ar-⁴⁰Ar and ⁸⁷Rb-⁸⁷Sr studies of some metamorphic minerals from the North Pyrenean zone indicate that they crystallized about 92–104 m.y. ago on the east, 85 m.y. or older on the west. An amphibole from a lherzolite in the eastern area gives a plateau age at 103 m.y. The North Pyrenean metamorphism is shown to be a thermal effect of forcible lherzolite emplacement along the North Pyrenean zone. This latter process is related to the early breakup of the Europe-Iberia plate during the middle Cretaceous time.     

North American Precambrian history recorded in a single sample: high-resolution UPb systematics of the Potsdam sandstone detrital zircons,New York State

Zircons separated from the Cambrian Potsdam sandstone of New York yield four distinct populations which can be defined by a number of analytical techniques. U-Pb isotopic analyses of small samples and monozircons of each population reveal a fine chronology not apparent in milligram-sized sample analysis, and define source area ages of 1180, 1320, 2100 and 2700 m.y. for the Cambrian detrital suite. These ages correspond to well-defined sources in the Superior and Grenville Provinces of the Canadian Shield (2700 and 2100 m.y.) and the well established Grenville age rocks of the Adirondack Mountains (1180 m.y.). The 1320-m.y. age appears to be derived from the Adirondacks, and suggests the existence of pre-Grenville basement in that massif. Our techniques allow the interpretation of the Precambrian history of a large portion of eastern North America from a single sample, and thus should be valuable in the definition of source areas in paleogeographic reconstruction, and in studies of continental crustal evolution.     

Attenuation of Rayleigh waves across the volcanic area of the Massif Central,France

Rayleigh wave attenuation is investigated for periods ranging from 20 to 90 s, along a 450 km-long profile following the Oligocene tensile zone of the French Massif Central. A model is deduced by inversion, assuming that the S-wave intrinsic quality factor Q_β is frequency-independent, and yields a mean value Q_β = 43 ± 10 for the first 100 km in the upper mantle. This value, far lower than the mean value obtained in Eurasia, is close to those obtained in other recent tensile areas, e.g., the western United States or mid-oceanic ridges.A velocity-depth model for S-waves, deduced in a previous study from surface-wave propagation, has been corrected for the attenuation effect. We find a discrepancy between the corrected S-model and P-wave residuals in the same area, implying that Q_β must be frequency-dependent. This can be a clue for partial melting in the upper mantle beneath this region.     

Geoid anomalies over Gorringe Ridge,North Atlantic Ocean

Gorringe Ridge is a strong uplifted block of oceanic crust and upper mantle lying at the eastern end of the Azores-Gibraltar plate boundary. The geoid over this structure derived from Seasat altimeter data exhibits a 9-m height anomaly with a north-south lateral extension smaller than 200 km. An attempt is made to interpret this geoid together with the gravity anomalies and with the seismicity, which has been compiled as a function of depth.It is first shown that the flexure of the oceanic lithosphere due to the ridge loading does not provide a good fit of the geoid anomalies and probably should be discarded, as it assumes a continuous unfractured elastic plate.Models involving local heterogeneities are then tested. The comparison of the observed geoid anomalies with the anomalies due to the uncompensated relief indicates that the topographic high has no shallow compensation.Uncompensated models, previously proposed to explain the gravity anomalies, are tested using the geoid. One model (Purdy and Bonnin, in Bonnin [11]), which involves an uplift of upper mantle material at depth, generates too strong geoid anomalies and must be discarded. Another model, which represents a nascent subduction zone (Le Pichon et al. [25]), fits both the gravity and geoid anomalies, but leads to difficulties in explaining the deep seismicity north of Gorringe Ridge.A model in isostatic equilibrium is also able to fit both gravity and geoid anomalies. This model involves a deep root of density 3.0 g cm^?3, as has been previously proposed for many oceanic ridges and plateaus. This model is compatible with the deep seismicity, but the origin of this low-density material at great depth is up to now an unresolved question.More likely, dynamical models taking into account the forces induced by the convection related to the slow plate convergence in this area will have to be considered.     

De l'emploi des methodes chimiques et spectrographiques pour l'etude des poteries antiques

Résumé Le but de mon travail est de vérifier dans quelle mesure l'analyse chimique et spectrographique des poteries antiques peut permettre de différencier entre elles ces poteries, et apporter des élémentes susceptibles de résoudre certains problèmes archéologiques de localisation.J'ai analysé un certain nombre échantillons de poteries antiques — 300 échantillons environ — qui ont été mis à ma disposition par MonsieurVallet, professeur à la Faculté des Lettres de Clermont-Ferrand. Ces échantillons sont de provenance diverse: France, Italie, Sicile, Grèce propre et îles grecques, Asie Mineure, Afrique du Nord.L'analyse chimique a porté sur les éléments suivants: Fer, Titane et Manganèse. L'analyse spectrographique porte sur les oligoéléments métalliques suivants: Plomb, Etain, Argent, Cuivre, Chrome, Nickel et Cobalt.Les teneurs en Titane, Plomb, Etain et Argent ne montrent pas de différences significatives. Par contre, les teneurs en Fer, Manganèse d'une part, Cuivre, Chrome, Nickel et Cobalt d'autre part, apportent des éléments de différenciation.

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The aim of this study is to verify to what extent chemical and spectrochemical analysis can distinguish among sherds from various localities and to give new data to solve some of the archaeological problems about location.About 300 sherds have been analysed; I got them from D.Vallet, Professor at the Faculté des Lettres in Clermont-Ferrand, Auvergne — These samples come from various countries, namely from: France, Italy, Greece, Greek Islands, Asia Minor, North Africa.The chemical analysis was for: Iron, Titanium and Manganese. The determination of trace elements such as: Lead, Tin, Silver, Copper, Chronium, Nickel, Cobalt, is now being carried out by means of spectrochemical analysis.The amount of Titanium, Lead, Tin and Silver shows no significant differences — On the contrary the amount of Iron, Manganese, Copper, Chronium, Nickel and Cobalt, give a good criterion for comparing and contrasting sherds of different provenance.

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Zusammenfassung Das Ziel meiner Arbeit ist, zu untersuchen, in welchem Maße es die chemische und spektrographische Analyse von antiken Tonwaren erlaubt, zwischen diesen Tonwaren zu unterscheiden und Lösungen für archäologische Ortsprobleme zu finden.Ich habe eine bestimmte Anzahl von antiken Tonwaren — ungefähr 300 Proben — analysiert die mir M.Vallet, Professor an der Geisteswissenschaftlichen Fakultät von Clermont-Ferrand, zur Verfügung gestellt hat. Diese Proben sind verschiedener Herkunft: Frankreich, Italien, Sizilien, Griechisches Festland, Griechische Inseln, Kleinasien und Nordafrika.Die chemische Analyse betraf die folgenden Elemente: Eisen, Titan, Mangan. Durch die spektrographische Analyse wurden die folgenden Elemente untersucht: Blei, Zink, Silber, Kupfer, Chrom, Nickel und Kobalt.Der Gehalt an Titan, Blei, Zink und Silber der einzelnen Proben zeigte keine wesentlichen Differenzen. Im Gegensatz dazu schwankte der Gehalt an Eisen und Mangan einerseits und Kupfer, Chrom, Nickel und Kobalt anderseits.

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Galactic evolution and star counts in the milky way

A model of population synthesis for our Galaxy is used to estimate the constraints imposed by photometric and astrometric star counts. We construct a statistical method to compute the degree of compatibility of the model with the data in the form of a multidimensional functionf(V, B-V, U-B, ). We apply the method to the determination of the star formation history in the Galaxy from Schmidt plates towards the anticentre. Although the presently available data do not allow us to draw firm conclusions, we show that the same kind of data with a slightly better photometric accuracy and with proper motions would give new constraints on the past star formation rate of the Galaxy.