Viscoelastic liquid curtains: Experimental results on the flow of a falling sheet of polymer solution

International audienceWe experimentally investigate the extensional flow of a sheet-or curtain-of viscoelastic liquid falling freely from a slot at constant flow rate under gravity. Extruded liquids are aqueous solutions of flexible polyethylene oxide (PEO) and of semi-rigid partially hydrolysed polyacrylamide (HPAM) with low shear viscosities. Velocimetry measurements reveal that the mean velocity field U(z), z being the distance from the slot exit, does not reduce to a free-fall. More precisely, we show that the liquid falls initially with sub-gravitational accelerations up to a distance from the slot which scales as gτ 2 f il , where g is gravity and τ f il is the extensional relaxation time of the liquid, beyond which the local acceleration reaches the asymptotic free-fall value g. The length of the sub-gravitational part of the curtain is shown to be much larger than the equivalent viscous length ((4η/ρ) 2 /g) 1/3 for Newtonian liquids of density ρ and dynamic viscosity η, which is usually small compared to the length of the curtain. The elastic length gτ 2 f il can indeed be surprisingly large when adding high molecular weight polymer molecules to a low-viscosity Newtonian solvent. By analogy with Newtonian curtains, we show that the velocity field U(z) rescales on a master curve. Besides, we show that the flow is only weakly affected by the history of polymer deformations in the die upstream of the curtain. Furthermore, investigations of the curtain stability reveal that polymer addition reduces the minimum flow rate required to maintain a continuous sheet of liquid

Application des micro-spectrométries infrarouge et Raman à l’étude des processus diagénétiques altérant les ossements paléolithiques

Différents processus post-mortem peuvent altérer les ossements et limiter l’utilisation de leur composition élémentaire et isotopique comme marqueurs paléo-environnementaux/climatiques, paléo-alimentaires ou encore géochronologiques. De part leur structure complexe et hiérarchisée, les ossements in vivo sont des tissus hétérogènes. La prise en compte de cette hétérogénéité, renforcée au cours de la fossilisation, nécessite l’utilisation de techniques d’analyses adaptées permettant l’étude des variations de structure et de compositions à micro-échelle. De précédents travaux ont montré que des techniques de micro-spectrométrie vibrationnelle telle que la micro-spectrométrie infrarouge pouvait permettre de caractériser les modifications induites par les processus diagénétiques et de déterminer les états de préservation des échantillons fossiles. Dans cette étude, des indices permettant de déterminer la composition d’ossements fossiles ont été acquis en spectrométrie infrarouge et Raman, ceci dans le but de comparer les informations fournies par ces deux techniques. Les micro-spectrométries IR et Raman ont ensuite été appliquées à des échantillons fossiles préparés sous forme de coupes minces ou de lames épaisses. Ces premiers résultats de cartographie obtenus par micro-spectrométrie Raman permettent de mettre en évidence l’apport de cette technique à la compréhension des processus diagénétiques en permettant de déterminer la répartition des principaux composés des ossements fossiles (teneur en collagène, en carbonates, cristallinité de la phase minérale, etc.).Various post-mortem processes can alter bone materials and then limit the use of their elemental or isotopic composition as markers for palaeo-environmental/climatic, paleodiet, or geochronological studies. Due to their complex and hierarchical structure, in vivo bones correspond to a highly heterogeneous tissue. The study of this heterogeneity, reinforced during fossilization processes, requires the use of adapted analytical techniques to investigate the variation of composition at microscale. Previous works have demonstrated that vibrational spectroscopic techniques like infrared micro-spectroscopy can be used to characterize the modification of composition induced by diagenetic processes and to determine the preservation state of the fossil samples. In this study, some spectral parameters, used to determine the composition of fossil bones, were measured by both infrared and Raman spectroscopy in order to compare the information supplied by these two techniques. Infrared and Raman micro-spectroscopy were then applied to fossil samples prepared as thin sections or polished thick sections. These first results of chemical mapping obtained on fossil bones by Raman micro-spectroscopy are in good agreement with the data obtained by FTIR micro-spectroscopy. These results demonstrated the capacity of this method for the understanding of diagenetic processes by monitoring the main components of fossil bone tissues (carbonates and collagen content, mineral crystallinity, etc.)

Analyse in situ des dessins préhistoriques de la grotte de Rouffignac par fluorescence X et diffraction X portable

La Grotte de Rouffignac (Dordogne, France) est un site d'art paléolithique qui renferme de nombreux dessins réalisés au trait noir (mammouths, bisons, rhinocéros laineux, chevaux, bouquetins...). Bien qu'aucune datation directe n'ait été réalisée à ce jour, les œuvres graphiques de cette caverne sont en général rattachées au Magdalénien.The Cave of Rouffignac (Dordogne, France) is a Palaeolithic rock art site which contains numerous black drawings (mammoths, bisons, rhinoceros, horses, ibexes…). Although no direct dating was carried out until now, the artworks of this cave are generally connected with the Magdalenian Culture

Magnetically controlled growing rod in early onset scoliosis: a 30-case multicenter study

PURPOSE: Preliminary results of magnetically controlled growing rods (MCGR) are encouraging. However, only short case series of MCGR for the treatment of early onset scoliosis (EOS) have been reported. Our aim was to evaluate its effectiveness and complications. METHODS: We report a 30-case retrospective, consecutive, multicenter series of MCGR. Effectiveness was judged upon: deformity correction and difficulties to achieve desired distraction. Secondary endpoints included complications and revision surgeries. RESULTS: Median age at surgery was 9.1 years (5-13). Mean follow-up was 18.4 months (12-33.9). Mean Cobb angle was 66° preoperatively and 44° at latest follow-up. MCGR has avoided an average of 2.03 scheduled surgical procedures per patient compared to traditional growing rod (GR). The intended total length gain was 40.1 mm per patient (5-140) and the total measured length gain was 21.9 mm (45.5% discrepancy). There were 24 complications: 7 proximal pull-outs of the hooks, 3 rod breakages, 6 failures of the lengthening of which 4 complete blockages and 2 complete blockages followed by backtracking, 1 proximal junctional kyphosis, 1 wound dehiscence, 1 superficial infection, 1 deep infection requiring implant removal, 1 pulmonary embolism, 1 pulmonary insufficiency, 1 secondary lumbar scoliosis, and 1 painful outpatient distraction. Eight patients had a gradual loss of effectiveness of distractions. There were 13 revision surgeries in 9 patients. CONCLUSIONS: MCGR provides satisfactory deformity correction and avoids repeated surgical procedures for lengthening. However, it has substantial complication rate. Although less frequent than in GR, the law of diminishing returns also applies to MCGR

Strontium isotope evidence for Pre-Islamic cotton cultivation in Arabia

With a view to understanding the dynamics of ancient trade and agrobiodiversity, archaeobotanical remains provide a means of tracing the trajectories of certain agricultural commodities. A prime example is cotton in Arabia, a plant that is non-native but has been found in raw seed and processed textile form at Hegra and Dadan, in the region of al-ʿUlā, north-western Saudi Arabia—sites of critical importance given their role in the trans-Arabian trading routes during Antiquity. Here, we demonstrate that the measurement of strontium isotopes from pre-cleaned archaeological cotton is methodologically sound and is an informative addition to the study of ancient plant/textile provenance, in this case, putting forward evidence for local production of cotton in oasis agrosystems and possible external supply. The presence of locally-grown cotton at these sites from the late 1st c. BCE–mid 6th c. CE is significant as it demonstrates that cotton cultivation in Arabia was a Pre-Islamic socio-technical feat, while imported cotton highlights the dynamism of trade at that time

COLONISATION A L'ADMISSION ET DIFFUSION DES BACTERIES MULTIRESISTANTES (BMR) EN SERVICE DE GERIATRIE SOINS AIGUS (A PROPOS D'UNE ETUDE PROSPECTIVE DE DEPISTAGE DES PATIENTS PORTEURS DE BMR CHEZ 239 PATIENTS ADMIS DANS LES SERVICES DE MEDECINE INTERNE GERIATRIQUE DU CENTRE HOSPITALIER UNIVERSITAIRE D'AMIENS)

AMIENS-BU Santé (800212102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

When phylogeny meets geology and chemistry: doubts on the dating of Ethiopian amber

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Approche expérimentales appliquées à l’étude des processus de combustion des matériaux osseux

International audienceApproche expérimentales appliquées à l’étude des  processus de combustion des matériaux osseu

Caractérisation par spectrométrie infrarouge à transformée de Fourier des ossements chauffés en contexte archéologique (comparaison entre référentiel moderne et matériel fossile, implications diagénétiques)

Différents processus taphonomiques peuvent modifier la coloration et la texture des ossements fossiles chauffés rendant difficile leur identification en contexte archéologique. Au cours de cette étude, la spectroscopie infrarouge à transformée de Fourier (IR-TF) a été utilisée pour caractériser les modifications de la composition des os durant la chauffe. L étude d un domaine particulier du spectre infrarouge (massif 1 3PO4) d échantillons modernes chauffés expérimentalement, a servi à définir des marqueurs minéralogiques permettant d évaluer la cristallinité et la perfection de la structure cristalline des os chauffés. Le protocole analytique ainsi mis en place a ensuite été appliqué à du matériel archéologique et a permis d identifier les ossements chauffés dès 250C pour du matériel fossile provenant de niveaux magdaléniens (vieux de 15 000 ans), et l établissement d indicateurs de l état d altération de la phase minérale des ossements fossiles non chauffés.Several taphonomic processes can modify the color and the texture of burnt bones making their identification difficult in archaeological contextes. In the present study, Fourier Transform Infrared Spectrometry (FTIR) was applied to characterize the modifications induced on bones by heating. Particularly, the analysis of a specific domain of the infrared spectrum ( 1 3PO4 domain) of modern bones experimentally heated was used to define mineralogical proxies that ensure the evaluation of both crystallinity and crystal lattice perfection. The developed analytical protocol was then applied on archaeological material and has allowed the identification of bones heated from 250C for archaeological samples carried out from Magdalenian layers (15 000 years old) and the establishment of new parameters for the evaluation of the alteration state of fossil bone mineral.PARIS-Museum Hist.Naturelle (751052304) / SudocSudocFranceF

ATR-FTIR pre-screening analyses for determining radiocarbon datable bone samples from the Kings' Valley, Egypt

International audienceThe tomb KV 40 in the Kings' Valley (Luxor, Egypt) has revealed mummified and highly fragmented remains of 83 adults, children, new-borns and infants, some of whom were, according to inscriptions, 18th dynasty king's sons or daughters (∼1370 BCE). This tomb was then secondarily reused by priestly families during the 22nd to early 25th dynasty (∼900-700 BCE). Radiocarbon dating of such bone remains would allow the evaluation of the ratio of burials by period and the identification of those from the 18th dynasty. As the bones were buried within a shaft tomb under hot and dry climatic conditions and have been partially burnt by fires, the applicability of radiocarbon dating on collagen extracted from them was uncertain and highly challenging. Prior to collecting samples, the state of collagen preservation in the bones had to be evaluated to ensure the feasibility of radiocarbon dating.Following the method of Lebon et al. (2016), three ATR-FTIR systems (benchtop and portables) were used to determine the effective and appropriate calibration of each instrument thanks to a set of reference bones. From this, we provide methodological recommendations to ensure the reliability of the quantifications obtained whatever the instrument used. As a demonstration of the efficiency of the proposed methodology, portable ATR-FTIR spectroscopy has been tested in situ in KV 40, and the N %wt contents thus evaluated have been compared to ATR-FTIR analyses in a laboratory (using a different spectrometer) and to elemental analyses. The results obtained on thirteen KV 40 individuals clearly show quite good consistency on ATR-FTIR analyses between both spectrometers, validating the relevance of this on-site analytical approach with each spectrometer properly calibrated and measurements performed according to a strict protocol. Regarding the estimation of the nitrogen content, all the KV 40 samples are radiocarbon datable despite challenging preservation conditions. Discrepancies have been highlighted between some of the ATR-FTIR results and elemental analyses, the latter systematically providing higher N %wt than the former. For these samples, the C %wt contents are also very high, showing that these bones are contaminated by organic materials. This underlines the efficacy of the ATR-FTIR analysis specifically for the quantification of bone collagen.The developed analytical approach based on the ATR-FTIR method and its mobile instrumentation clearly operates effectively on site and under challenging conditions, which opens up new perspectives for the collection of bone remains prior to radiocarbon dating