129 research outputs found

    The construction of a reliable potential for GeO2 from first-principles

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    The construction of a reliable potential for GeO2, from first-principles, is described. The obtained potential, which includes dipole polarization effects, is able to reproduce all the studied properties (structural, dynamical and vibrational) to a high degree of precision with a single set of parameters. In particular, the infrared spectrum was obtained with the expression proposed for the dielectric function of polarizable ionic solutions by Weis et al. [J.M. Caillol, D. Levesque and J.J. Weis, J. Chem. Phys. 91, 5544 (1989)]. The agreement with the experimental spectrum is very good, with three main bands that are associated to tetrahedral modes of the GeO2 network. Finally, we give a comparison with a simpler pair-additive potential.Comment: 9 pages, 8 figure

    Intermediate range chemical ordering of cations in simple molten alkali halides

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    The presence of first sharp diffraction peaks in the partial structure factors is investigated in computer simulations of molten mixtures of alkali halides. An intermediate range ordering appears for the Li+ ions only, which is associated with clustering of this species and is not reflected in the arrangement of other ions. This ordering is surprising in view of the simplicity of the interionic interactions in alkali halides. The clustering reflects an incomplete mixing of the various species on a local length scale, which can be demonstrated by studying the complementary sub-space of cations in the corresponding pure alkali halides by means of a void analysis.Comment: 5 pages, 5 figure

    Microhardness and friction coefficient of multi-walled carbon nanotube-yttria-stabilized ZrO2 composites prepared by spark plasma sintering

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    Multi-walled carbon nanotubes (eight walls) are mixed with an yttria-stabilized ZrO2 powder. The specimens are densified by spark plasma sintering. Compared to ZrO2, there is a 3.8-fold decrease of the friction coefficient against alumina upon the increase in carbon content. Examinations of the friction tracks show that wear is very low when the carbon content is sufficient. Exfoliation of the nanotubes due to shearing stresses and incorporation of the debris into a lubricating film over the contact area is probable

    The new 14C chronology for the Palaeolithic site of La Ferrassie, France: the disappearance of Neanderthals and the arrival of Homo sapiens in France

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    The grand abri at La Ferrassie (France) has been a key site for Palaeolithic research since the early part of the 20th century. It became the eponymous site for one variant of Middle Palaeolithic stone tools, and its sequence was used to define stages of the Aurignacian, an early phase of the Upper Palaeolithic. Several Neanderthal remains, including two relatively intact skeletons, make it one of the most important sites for the study of Neanderthal morphology and one of the more important data sets when discussing the Neanderthal treatment of the dead. However, the site has remained essentially undated. Our goal here is to provide a robust chronological framework of the La Ferrassie sequence to be used for broad regional models about human behaviour during the late Middle to Upper Palaeolithic periods. To achieve this goal, we used a combination of modern excavation methods, extensive geoarchaeological analyses, and radiocarbon dating. If we accept that Neanderthals were responsible for the Ch√Ętelperronian, then our results suggest an overlap of ca. 1600 years with the newly arrived Homo sapiens found elsewhere in France.info:eu-repo/semantics/publishedVersio

    The new 14C chronology for the Palaeolithic site of La Ferrassie, France: the disappearance of Neanderthals and the arrival of Homo sapiens in France

    Get PDF
    The grand abri at La Ferrassie (France) has been a key site for Palaeolithic research since the early part of the 20th century. It became the eponymous site for one variant of Middle Palaeolithic stone tools, and its sequence was used to define stages of the Aurignacian, an early phase of the Upper Palaeolithic. Several Neanderthal remains, including two relatively intact skeletons, make it one of the most important sites for the study of Neanderthal morphology and one of the more important data sets when discussing the Neanderthal treatment of the dead. However, the site has remained essentially undated. Our goal here is to provide a robust chronological framework of the La Ferrassie sequence to be used for broad regional models about human behaviour during the late Middle to Upper Palaeolithic periods. To achieve this goal, we used a combination of modern excavation methods, extensive geoarchaeological analyses, and radiocarbon dating. If we accept that Neanderthals were responsible for the Ch√Ętelperronian, then our results suggest an overlap of ca. 1600 years with the newly arrived Homo sapiens found elsewhere in France

    Assessing the integrity of older archeological collections: An example from La Ferrassie

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    Initially excavated in the early twentieth century, La Ferrassie is one of the most important sites for the Middle Paleolithic of Western Europe. Aside from the numerous Neanderthal remains found there, the stone artifacts recovered from the site are featured prominently in discussion and debates of Mousterian variability. Recent renewed excavation of the site, however, suggests a considerable preference in the kinds of stone artifacts saved during the initial excavation. Here, we assess the nature and extent of this selection and its effects on the final collection. Results indicate that large, complete, retouched pieces were preferentially retained by the original excavators, and that the artifact collection available for study represents only 2--3% of the original lithic assemblage present in the deposits. This has significant implications for early interpretations of Mousterian industries that were based on such collections and their potential analytical value
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