Numerical simulation of the force generated by a superelastic NiTi orthodontic archwire during tooth alignment phase: comparison between different constitutive models

International audienceNickel Titanium (NiTi) Superelastic (SE) Shape Memory Alloys (SMAs) are widely considered for applications that need high reversible strain or high recovery forces. In particular, the SE SMAs present a high interest for biomedical applications such as endodontic and orthodontic apparatus. They are available in a large variety of archwires exerting continuum forces to ensure the dental displacement. The purpose of this study is to report the clinical implications of NiTi SE wires for dental treatment in a given configuration. Three main constitutive models of the literature (Lagoudas and Boyd 1996 Int. J. Plast. 12 805–842, Auricchio and Petrini 2004 Int. J. Numer. Meth. Engng . 61 807–836 and Chemisky et al 2011 Mech. Mater . 68 361–376) are considered for the finite element (FE) numerical simulations of the SMA archwires response. Tensile tests had been carried out in order to identify the material parameters of these constitutive models. The FE numerical study allowed to predict the dental displacement and its corresponding orthodontic force level exerted by the wire in similar conditions to those in the oral environment. This work allows to predict the orthodontic generated load by a NiTi SE archwire with a 0.64 × 0.46 mm 2 rectangular cross section under prescribed thermomechanical conditions. The effect of the temperature and the alveolar bone stiffness on the orthodontic load level and the tooth displacement degree has been investigated. The performed numerical simulations demonstrate that the orthodontic load is sensitive to the displacement magnitude, to the tooth stiffness and to the temperature variations. The obtained forces applied continuously and at a constant level are within the acceptable orthodontic force level range. Some directives are therefore provided to help orthodontists to select the optimal archwire

Synthetic smectite colloids: Characterization of nanoparticles after co-precipitation in the presence of lanthanides and tetravalent elements (Zr, Th)

The magnesian smectite hectorite is a corrosion product frequently detected in nuclear waste glass alteration experiments. The structural incorporation of a single trivalent lanthanide was previously demonstrated. Hectorite was presently synthesized, for the first time, in the presence of several lanthanides (La, Eu, Yb) following a multi-step synthesis protocol. The smallest-sized particles (nanoparticles, NPs) were isolated by centrifugation and analyzed by asymmetrical flow field-flow fractionation (AsFlFFF) coupled to ICP-MS, in order to obtain information on the elemental composition and distribution as a function of the size. Nanoparticles can be separated from the bulk smectite phase. The particles are able to accommodate even the larger-sized lanthanides such as La, however, with lower efficiency. We, therefore, assume that the incorporation proceeds by substitution for octahedral Mg accompanied by a concomitant lattice strain that increases with the size of the lanthanides. The presence of a mixture does not seem to affect the incorporation extent of any specific element. Furthermore, syntheses were performed where in addition the tetravalent zirconium or thorium elements were admixed, as this oxidation state may prevail for many actinide ions in a nuclear waste repository. The results show that they can be incorporated as well

One sea but many routes to Sail. The early maritime dispersal of Neolithic crops from the Aegean to the western Mediterranean.

This paper explores the first maritime westward expansion of crops across the Adriatic and the northern coast of the western Mediterranean. Starting in Greece at c.6500 cal BC and following the coastline to the Andalusian region of Spain to c.4500 cal BC, the presence of the main cereal, pulse, oil and fibre crops are recorded from 122 sites. Patterns in the distribution of crops are explored through ubiquity scores, correspondence analysis and Simpson's diversity index. Our findings reveal changes in the frequencies of crops as farming regimes developed in Europe, and show how different crops followed unique trajectories. Fluctuations in the diversity of the crop spectrum between defined areas are also evident, and may serve to illustrate how founder effects can explain some of the patterns evident in large-scale spatio-temporal evaluations. Within the broader westward expansion of farming, regionalism and multi-directional maritime networks described through archaeological materials are also visible in the botanical records

Quantitative description and local structures of trivalent metal ions Eu(III) and Cm(III) complexed with polyacrylic acid

The trivalent metal ion (M(III) = Cm, Eu)/polyacrylic acid (PAA) system was studied in the pH range between 3 and 5.5 for a molar PAA-to-metal ratio above 1. The interaction was studied for a wide range of PAA (0.05 mg L−1–50 g L−1) and metal ion concentrations (2×10−9–10−3 M). This work aimed at 3 goals (i) to determine the stoichiometry of M(III)–PAA complexes, (ii) to determine the number of complexed species and the local environment of the metal ion, and (iii) to quantify the reaction processes. Asymmetric flow-field-flow fractionation (AsFlFFF) coupled to ICP-MS evidenced that size distributions of Eu–PAA complexes and PAA were identical, suggesting that Eu bound to only one PAA chain. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements performed with Eu and Cm showed a continuous shift of the spectra with increasing pH. The environment of complexed metal ions obviously changes with pH. Most probably, spectral variations arose from conformational changes within the M(III)–PAA complex due to pH variation. Complexation data describing the distribution of complexed and free metal ion were measured with Cm by TRLFS. They could be quantitatively described in the whole pH-range studied by considering the existence of only a single complexed species. This indicates that the slight changes in M(III) speciation with pH observed at the molecular level do not significantly affect the intrinsic binding constant. The interaction constant obtained from the modelling must be considered as a mean interaction constant

An 11th century a.d. burnt granary at La Gravette, south-western France : preliminary archaeobotanical results

International audienceA thick layer of carbonised seeds was encountered in an 11th century a.d. room situated in the seigneurial part of the village of La Gravette. This paper presents the first results of charcoal and seed analyses which give information on the food products stored in the granary and on their arrangement there. Triticum aestivum/durum/turgidum was by far the most important stored crop, while Avena sp., then Hordeum vulgare, Secale cereale, Triticum monococcum and Vitis vinifera were secondary. Weeds were poorly represented. Charcoals were dominated by deciduous Quercus sp., and 11 additional wood taxa were recorded, including especially Fagus sylvatica, Fraxinus sp., Rosaceae, Corylus avellana, Acer campestre and Ulmus sp. According to the charcoal distribution, Quercus and Fagus were probably building materials while most of other taxa would have been used for basketry, wattling or joinery work. In the western part of the granary, naked wheat was stored in bulk. In the eastern part, various crops (at least naked wheat, barley, rye, oat and grape) were stored in small amounts, most of which were probably separated by light wooden structures. The cereal crops had largely been processed and cleaned. The stored products probably represent taxes paid to the lord who owned the granary

Middle Neolithic farming of open-air sites in SE France: new insights from archaeobotanical investigations of three wells found at Les Bagnoles (L'Isle-sur-la-Sorgue, Dépt. Vaucluse, France)

Previous reviews of Middle Neolithic agricultural practice (4400–3500 cal bc) in southern France have highlighted a change in crop assemblages after 4000 cal bc, with a reduction of naked wheat and an increase of emmer and partly of einkorn. The recent investigation of three wells from the site of Les Bagnoles (4250–3800 cal bc) in the periphery of the southern Rhône valley yielded an unprecedented amount of waterlogged uncharred and charred plant macro remains that offer new insights into crop diversity and its changes over time. The results from the wells at Les Bagnoles were compared with other dated sunken features from open-air sites (in contrast to caves and rock shelters), with the aim of identifying patterns sug-gesting changes in the crop spectra between the early (MN1) and late (MN2) Middle Neolithic phases from taphonomically comparable contexts. The results from Les Bagnoles demonstrate that oil crops and pulses are underrepresented in dry sites and that they were a significant part of Middle Neolithic agriculture. They also indicate an increase in the representation of einkorn (instead of emmer) during MN2 that is also visible in other open-air sites. The comparison of the archaeobotani-cal results with silo storage capacity values as a proxy for average production capacity per household leads us to propose a possible drop in naked wheat productivity and opens new questions in factors affecting crop choice at the beginning of the 4th millennium cal bc

Palaeogenomic insights into the origins of French grapevine diversity

Ramos-Madrigal, Jazmín, Runge, Anne Kathrine Wiborg, Bouby, Laurent, Lacombe, Thierry, Castruita, José Alfredo Samaniego, Adam-Blondon, Anne-Françoise, Figueiral, Isabel, Hallavant, Charlotte, Martínez-Zapater, José M., Schaal, Caroline, Töpfer, Reinhard, Petersen, Bent, Sicheritz-Pontén, Thomas, This, Patrice, Bacilieri, Roberto, Gilbert, M. Thomas P., Wales, Nathan (2019): Palaeogenomic insights into the origins of French grapevine diversity. Nature Plants 5: 595-603, DOI: 10.1038/s41477-019-0437-