9,531 research outputs found

    Raíces en movimiento : prácticas religiosas

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    Technological behaviour in the early Acheulean of EF-HR (Olduvai Gorge, Tanzania)

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    Technological strategies of early humans are discussed in the light of a recently excavated stone tool assemblage from EF-HR, an archaeological site older than 1.33 Ma at Olduvai Gorge, Tanzania. Renewed fieldwork at EF-HR has unearthed a lithic collection containing over 2300 artefacts (including a hundred handaxes in stratigraphic position), which represents one of the largest assemblages for the early Acheulean in East Africa. Our technological study shows co-occurrence of two distinctive reduction sequences in the same assemblage, one aimed at obtaining small flakes and the other focused on the production of large, thick, heavy flakes that were then used as blanks for handaxe shaping. Flaking of small cores is expedient and low intensity, and knapping methods are similar to those observed in earlier Oldowan assemblages. Large Cutting Tools (LCTs) show no evidence of planform and biconvex symmetry, and shaping sequences are brief and discontinuous, indicating short use-lives for handaxes. Bifaces are rare and atypical. Recurrent morphotypes are knives, which are poorly-shaped, scraper-like, large-sized handaxes. Despite the apparent expediency of EF-HR handaxe production, a closer inspection of the interplay between debitage and façonnage stages reveals remarkably standardized procedural patterns. Large Cutting Tool blanks were produced following fixed knapping rules resulting in flakes with a specific morphology and mass distribution. Adapted to the idiosyncrasies of each blank, shaping was almost invariably imposed over the same areas in all LCTs and sought to produce morphotypes that, technologically, are remarkably identical to each other. This strongly supports the existence of mental templates and technical rules that were systematically practiced in LCT production at EF-HR, and underscore the structured nature of technological behaviour at the onset of the Acheulean in East Africa

    Oldowan technological behaviour at HWK EE (Olduvai Gorge, Tanzania)

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    HWK EE (Olduvai Gorge, Tanzania) is a late Oldowan site dated to ∼1.7 Ma that contains a large fossil and lithic assemblage. This paper reports on the technology of the recently excavated stone tool collection, over 18,000 pieces. Our results indicate that reduction sequences were generally short, flaking productivity was low, and knapping methods were largely simple and expedient, lacking the technical skills observed in other Oldowan assemblages. Conspicuous differences are observed in the chaînes opératoires of the three main raw materials used at HWK EE: the quartzite reduction sequence can be reconstructed in full at the site, most of the lava detached pieces are missing, and there is a preferential use of chert for retouched tools. This portrays a composite picture, where knapping expediency and low productivity are accompanied by raw material selectivity and consistent presence of retouched artefacts. Coexistence of these features in the same assemblage leads us to question the monolithic structure of the Oldowan techno-complex, and highlights the kaleidoscopic nature of technological strategies at Olduvai immediately before the earliest Acheulean handaxes appear in the sequence

    Theory of Weak Hypernuclear Decay

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    The weak nonmesonic decay of Lambda-hypernuclei is studied in the context of a one-meson-exchange model. Predictions are made for the decay rate, p/n stimulation ratio and the asymmetry in polarized hypernuclear decay.Comment: Standard 41 page Latex fil

    Intrinsic switching field distribution of arrays of Ni80Fe20 nanowires probed by in situ\mathit{in\, situ} magnetic force microscopy

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    The progress of magnetization reversal of weakly packed ferromagnetic Ni80Fe20 nanowire arrays of different diameters (40, 50, 70 and 100 nm) electrodeposited in polycarbonate membranes was studied by magnetic force microscopy (MFM). For such a low packing density of nanomagnets, the dipolar interactions between neighbouring wires can be neglected. The intrinsic switching field distribution has been extracted from in situ MFM images and its width was found to be considerably smaller than for densely packed nanowire arrays.Comment: 4 pages, 5 figures. To appear in Journal of Superconductivity and Novel Magnetis

    Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes

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    The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements.Comment: 7 pages, 5 figure

    Toxic effect of antibiotics in grapevine (Vitis vinifera 'Albariño') for embryo emergence and transgenic plant regeneration from embryogenic cell suspension

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    Regeneration of grapevine (Vitis vinifera L.) from embryogenic cultures after gene transfer is traditionally linked to a selection procedure using antibiotic containing media. The neomycin phosphotransferase II (npt-II) and hygromycin phosphotransferase (hpt) genes that confer resistance to the antibiotics kanamycin and hygromycin, respectively, have been the selectable marker genes most frequently used for selection of transgenic grapevines. In this work, the phytotoxic effects on embryo development and plant growth of these two antibiotics were examined in 'Albariño'. Embryogenic cell suspensions were evaluated based on a twostep strategy using untransformed and transformed tissues. The phytotoxic effect was significantly different at 20 mg∙L-1 (and higher) for kanamycin and at 5 mg∙L-1 (and higher) for hygromycin. Minimal killing concentrations of kanamycin and hygromycin for 'Albariño' cell suspensions were 50 and 12.5 mg∙L-1, respectively. Embryogenic cell suspensions were bombarded using the biolistic system with the construct pBI426, harboring the selectable npt-II gene, and incubated on kanamycin containing media to determine the best inhibitory concentration allowing embryo and shoot development of only transgenic events. Only 20 % of PCR-positive transgenic embryos and 20 % of plant regeneration resulted from embryos emerged on 30 mg∙L-1. However, 80 % of PCR-positive transgenic embryos but only 10 % of plant regeneration were obtained from embryos emerged on 40 mg∙L-1. The method described, based in untransformed and transformed plant material, could be used to determine the optimal antibiotic concentration for other V. vinifera cultivars for efficient selection and regeneration of transgenic events.
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