Shape Variation in Aterian Tanged Tools and the Origins of Projectile Technology: A Morphometric Perspective on Stone Tool Function

BACKGROUND: Recent findings suggest that the North African Middle Stone Age technocomplex known as the Aterian is both much older than previously assumed, and certainly associated with fossils exhibiting anatomically modern human morphology and behavior. The Aterian is defined by the presence of 'tanged' or 'stemmed' tools, which have been widely assumed to be among the earliest projectile weapon tips. The present study systematically investigates morphological variation in a large sample of Aterian tools to test the hypothesis that these tools were hafted and/or used as projectile weapons. METHODOLOGY/PRINCIPAL FINDINGS: Both classical morphometrics and Elliptical Fourier Analysis of tool outlines are used to show that the shape variation in the sample exhibits size-dependent patterns consistent with a reduction of the tools from the tip down, with the tang remaining intact. Additionally, the process of reduction led to increasing side-to-side asymmetries as the tools got smaller. Finally, a comparison of shape-change trajectories between Aterian tools and Late Paleolithic arrowheads from the North German site of Stellmoor reveal significant differences in terms of the amount and location of the variation. CONCLUSIONS/SIGNIFICANCE: The patterns of size-dependent shape variation strongly support the functional hypothesis of Aterian tools as hafted knives or scrapers with alternating active edges, rather than as weapon tips. Nevertheless, the same morphological patterns are interpreted as one of the earliest evidences for a hafting modification, and for the successful combination of different raw materials (haft and stone tip) into one implement, in itself an important achievement in the evolution of hominin technologies

Inserting Tin or Antimony Atoms into Mg2Si: Effect on the Electronic and Thermoelectric Properties

International audienceDensity functional and Boltzmann transport theories have been used to investigate the effect of constraints generated by substituting tin for silicon atoms or by inserting antimony atoms into Mg2Si on the electronic and thermoelectric properties of this compound. The investigated hypothetical structures are Mg2Si1-x Sn (x) with x equal to 0.125, 0.25, 0.375, 0.625, 0.75, and 0.875, and Mg8Si4Sb, Mg8Si4Sb3, and Mg2SiSb. The transport properties are presented with respect to the energy at three predefined temperatures and with respect to temperature for low and high electron and hole dopings. The effects of Sn-for-Si substitution are very similar to those observed for Mg2Si subjected to uniaxial and biaxial tensile strains. Overall, the power factor decreases as the doping level or tensile strain increases. In contrast, the maximum of the power factor increases with temperature. Irrespective of the temperature and electron or hole doping levels, the electrical conductivity of the Sb-inserted Mg2Si structures is far higher than that of Mg2Si. In the Fermi level energy region, the Seebeck coefficient S of the Sb-inserted Mg2Si structures is lower than that of Mg2Si. For Mg8Si4Sb3 and Mg2SiSb, the opposite is observed in the region where the electron density is very small (about 2 eV below the Fermi level). As a consequence, the power factor follows the same trends as the Seebeck coefficient

Strain-induced electronic band convergence: effect on the Seebeck coefficient of Mg2Si for thermoelectric applications

International audienceThe present theoretical study, performed using density-functional theory and Boltzmann transport theory formalisms, shows that under 2.246 % isotropic tensile strain, the two energy-lowest conduction bands of Mg2Si overlap. The two, threefold-degenerated orbitals become a unique, sixfold-degenerated orbital. It is demonstrated that such degeneracy implies an increase of the Seebeck coefficient, of the electrical conductivity, of the power factor, and in fine of the figure of merit

Polycrystalline Mg2Si thin films: A theoretical investigation of their electronic transport properties

International audienceThe electronic structures and thermoelectric properties of a polycrystalline Mg2Si thin film have been investigated by first-principle density-functional theory (DFT) and Boltzmann transport theory calculations within the constant-relaxation time approximation. The polycrystalline thin film has been simulated by assembling three types of slabs each having the orientation (001), (110) or (111) with a thickness of about 18 angstrom. The effect of applying the relaxation procedure to the thin film induces disorder in the structure that has been ascertained by calculating radial distribution functions. For the calculations of the thermoelectric properties, the energy gap has been fixed at the experimental value of 0.74 eV. The thermoelectric properties, namely the Seebeck coefficient, the electrical conductivity and the power factor, have been determined at three temperatures of 350 K. 600 K and 900 K with respect to both the energy levels and the p-type and n-type doping levels. The best Seebeck coefficient is obtained at 350 K: the S-yy), component of the tensor amounts to about +/- 1000 mu V K-1, depending on the type of charge carriers. However, the electrical conductivity is much too small which results in low values of the figure of merit ZT. Structure-property relationship correlations based on directional radial distribution functions allow us to tentatively draw some explanations regarding the anisotropy of the electrical conductivity. Finally, the low Zr values obtained for the polycrystalline Mg2Si thin film are paralleled with those recently reported in the literature for bulk chalcogenide glasses. 0 2015 Elsevier Inc. All rights reserved

Electronic and transport properties of Mg2Si under isotropic strains

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Computational investigation of interstitial neon diffusion in pure hematite

International audienceMulti-scale simulations were used to investigate the neon diffusivity in hematite for thermochronometry applications. Analyses of the magnetic, electronic, and structural properties of antiferromagnetic α-Fe2O3 are reported. At the microscopic scale, Ne insertion and atomic jumps in hematite are studied by means of the spin polarized Density Functional Theory + U, and the Transition State Theory. The minimum path energy of Ne migration between interstitial sites, and its position at the transition state, are determined by the climbing image-Nudged Elastic Band method (CI-NEB). Finally, these microscopic output data are used as inputs to a homemade code, based on Kinetic Monte Carlo (KMC) algorithms, in order to calculate the effective activation enthalpy and the diffusivity at infinite temperature for Ne in hematite. The Ne diffusion coefficient in pure hematite is calculated according to: D=9.78×10−3(cm2/s)exp(−2.42eVkBT) This formula shows very high retentivity of hematite relative to Ne at surface temperatures, and opens new geological dating fields

Helium diffusion in pure hematite (-Fe2O3) for thermochronometric applications : a theoritical multi-scale study

International audienceHe diffusion coefficient in iron oxide α-hematite crystal has been determined using computational multi-scale approach in the purpose of geological dating as He is produced during U-Th-Sm decay in this mineral. Natural hematite samples are generally made of nanometric to micrometric scale crystals leading to the difficulty to determine the total He diffusion behavior. A multi-scale theoretical approach will so bring new information on the He diffusion coefficient in 3D. Investigations, at microscopic scale, of helium insertion and atomic jumps into hematite crystal have been performed by DFT and transition state theory. The minimum path energy of helium migration between interstitial sites and its position at transition state are determined by the climbing image-Nudged Elastic Band method