Utilisation des minéraux lourds comme indicateurs de paléoplacers alluvionnaires diamantifères en République centrafricaine (RCA). Use of heavy minerals as indicators of diamantiferous (alluvial) paleo-placers in Central African Republic (CAR).

International audienceLe diamant est la première ressource minérale de la République Centrafricaine (RCA). Exclusivement exploité par plusieurs sociétés minières avant 1960, il l'est maintenant de façon artisanale. Avec une production annuelle d'envi-ron 500 000 carats (1 carat = 0,2 g), la RCA est le dixième producteur de diamant (en valeur) dans le monde. Les diamants gemmes (pierres de joaillerie, taillables) représentent 70 à 75 % de la production. Deux principales zones diamantifères présentant une relation spatiale évidente existent en RCA : la Formation de Mouka-Ouadda à l'Est et celle de Carnot à l'Ouest. Ces formations, représentant les 'roches magasins' du diamant, constituent ainsi des 'gisements secondaires', en ce sens que le diamant a subi des remaniements depuis son émission à partir des kim-berlites constituant les 'gisements primaires' ou 'roches mères' ; ces dernières sont inconnues à ce jour en RCA. L'érosion des gisements secondaires et le transport limité, avec re-concentration par le réseau hydrographique actuel ou subactuel, conditionnent l'existence de gîtes alluvionnaires. La mise en place du diamant dans la partie orientale de la République Centrafricaine remonterait au Kibarien (1100 Ma), ce qui coïncide avec un événement distensif en Afrique Centrale. Compte tenu de ce contexte particulier, retracer l'histoire géologique du diamant de la RCA consiste d'une part à se focaliser sur la dynamique sédimentaire et les milieux de dépôt des formations fluviatiles crétacées de Mouka-Ouadda et de Carnot, d'autre part à établir et à préciser, éventuellement, les filiations de ces dernières avec les gîtes quaternaires, notamment grâce à l'étude des minéraux lourds. Des échantillons de sables prélevés dans les alluvions sableuses sur graviers ont été traités en vue d'analyser les minéraux lourds de la fraction FII (63-125 μm). Cette étude constitue une indication préliminaire des accompagnateurs du diamant dans les concentrés et peut re-présenter une méthode de prospection diamantifère efficace, applicable pour l'exploitation des gisements alluvion-naires. Diamonds are the first mineral resource of Central African Republic (CAR). Exclusively mined by several companies before 1960, it is now prospected in a craftsman's way. With an annual production of about 500,000 carats (1 carat = 0.2 g), CAR is the 10th diamond producer (in value) in the world, and diamond gems (talliable, jewellery stones) account for 70%-75% of this production. Two principal diamantiferous zones presenting an obvious spatial relation-ship exist in CAR: the Mouka-Ouadda Formation in the East and the Carnot Formation in the West. These forma-tions, representing the store-rocks ("roches magasins"), constitute the "secondary deposits" in the sense that the diamond has been subjected to some modifications since it was eroded from the kimberlites which are the primary occurrences or "parent rocks". At the moment, the latter are unknown in the CAR. The weathering of the secondary occurrences and the limited transport, with re-concentration by the actual or sub-actual hydrographic network, con-dition the existence of alluvial deposits. The diamond formation in the eastern part of the Central African Repuublic is as old as the Kibarian (1100 Myr), which corresponds to an extensive event in Central Africa. Considering the particular context that prevails today in the CAR, i.e. no evidence is given of primary occurrences of kimberlitic nature, retracing the diamond geological history in CAR consists, on the one hand, in focussing on the sedimentary dynamics and depositional environments of the Cretaceous fluviatile formations of Mouka-Ouadda and Carnot, and on the other hand, in more precisely stating the affiliations of the latter with Quaternary alluvial deposits, in particular by means of the heavy mineral study. In order to analyse the heavy minerals in the FII (63-125 m) fraction, sand samples from the sandy alluvial deposits over gravel have been processed. This paper presents a preliminary study of diamond-accompanying minerals in concentrates and can represent an efficient method for diamond prospecting, applicable to the exploitation of diamantiferous alluvial deposits

Tectonique salifère et déformation gravitaire de la marge passive sud-gabonaise de l'Albien au Turonien (secteur de Mayumba) Salt tectonic and thin-skinned deformation in south Gabon passive margin during the Albian-Turonian (Mayumba area).

International audienceL'observation de données sismiques de bonne qualité relatives à la marge passive sud-gabonaise montre : 1) les structures extensives, compressives et inversives albo-turoniennes, associées à la tectonique gravitaire au-dessus du niveau salifère Ezanga (Aptien supérieur). D'est en ouest, ces structures synsédimentaires, d'échelle kilo-métrique, sont en blocs basculés, en anticlinaux, en roll over, en " carapace de tortue ", de nouveau en plis et failles inverses, et enfin en langues de sel déversées vers l'ouest. 2) l'influence du niveau salifère sur la structuration gravitaire ; 3) l'héritage passif syn-rift au niveau des zones hautes anté-salifères qui favorisent la terminaison du sel en biseau et la caractérisation de deux domaines structuraux : l'un interne, peu subsident, où se développent des structures de faible espacement et l'autre externe, très subsident, marqué par des structures de grand espacement. Observation of excellent quality seismic data from the passive margin of the South Gabon basin margin shows: i) Structures associated with thin-skinned deformation of the albo-turonian platform over the Ezanga salt formation (Upper Aptian). The study domain shows a series of Albian-Turonian kilometric extensional, compressional and inver-sional syn-sedimentary structures. From east to west, the domain features tilted blocs, fold and anticline structures, roll-over and turtleback extensive structures, and again fold and inverse faults compressional structures and west-wards salt overhangs. ii) The role of the salt layer in the structural thin-skinned distribution. iii) The high topographic syn-rift control by exhibiting the bevelled salt ending and the characterisation of two structural domains: an internal domain characterised by low subsidence and short extensional structures, and an external domain characterised by high subsidence and long extensional structures

Self-replicating Reverse Micelles

Conditions are described, under which the hydrolysis of octyl octanoate (O-OA) takes place at the interface of reverse micelles fanned by sodium octanoate (OA) in isooctane. Since the micelle-mediated hydrolysis affords fresh OA, which spontaneously assemble into new micelles, the reaction can be seen as a self-replicating process. The kinetics and the spectroscopy of this self-replication process are presented

Effect of alloying elements in melt spun Mg-alloys for hydrogen storage

In this paper we report the effect of alloying elements on hydrogen storage properties of melt-spun Mg-based alloys. The base alloys Mg90Si10, Mg90Cu10, Mg65Cu35 (at%) were studied. We also investigated the effect of rare earths (using MM: mischmetal) and Al in Mg65Cu25Al10, Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys. All the melt-spun alloys without MM show a crystalline structure, and the Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys showed an amorphous and partially amorphous structure respectively. At 350˚C all the alloys had a crystalline structure during the hydrogen absorption-desorption tests. It was observed that Si and Cu in the binaries alloys hindered completely the activation of thehydrogen absorption. The partial substitution of Cu by MM or Al allowed activation. The combined substitution of Cu by MM and Al showed the best results with the fastest absorption and desorption kinetics, which suggests that this combination can be used for new Mg-alloys to improve hydrogen storage properties.Fil: Rozenberg, Silvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería ; ArgentinaFil: Saporiti, María Fabiana Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería ; ArgentinaFil: Lang, Julien. Université du Québec a Montreal; CanadáFil: Audebert, Fernando Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Botta, Pablo Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Stoica, Mihai. Leibniz Institute for Solid State and Materials Research Dresden; AlemaniaFil: Huot, Jacques. Université du Québec a Montreal; CanadáFil: Eckert, Jürgen. The Erich Schmid Institute of Materials Science; Austri

Poor blood pressure control in general practice: In search of explanations

SummaryBackgroundArterial hypertension is managed mainly by general practitioners. The blood pressure level of most patients treated in a general practice setting is greater than or equal to 140/90mmHg.AimsTo understand why a blood pressure level greater than or equal to 140/90mmHg does not lead to a change of treatment.MethodsOver a 2-week period, 479 hypertensive patients were included in a cross-sectional study by 27 general practitioners. Consultation data were collected, as were reasons why patients with a blood pressure level greater than or equal to 140/90mmHg did not have their treatment changed.ResultsBlood pressure level was greater than or equal to 140/90mmHg in 58% of patients; treatment was changed in 15% of these individuals. The lack of change in treatment was justified by the physicians as follows: the blood pressure measurements were not considered to be representative (about 30% of cases); the therapeutic result was considered to be satisfactory in the circumstances (about 30% of cases); change was not appropriate given the patient's specific context (the remaining third of cases). The proportion of uncontrolled hypertensive patients whose treatment remained the same was significantly higher among patients with a disease that affected their lifestyle or threatened their life expectancy.ConclusionThe disappointing therapeutic results observed in the management of arterial hypertension do not arise only from poor application of guidelines by general practitioners. Reluctance to rely on blood pressure measurements, a perception that guidelines are revised frequently and are not always clear, and consideration of the general practitioner's activity in the patient's specific context are the main factors involved

Microfluidic flow direction and rate vector sensor based on a partially gold-coated TFBG

In microfluidic chips applications, the monitoring of the rate and the direction of a microfluidic flow is very important. Here, we demonstrate a liquid flow rate and a direction sensor using a partially gold-coated tilted fiber Bragg grating (TFBG) as the sensing element. Wavelength shifts and amplitude changes of the TFBG transmission resonances in the near infrared reveal the direction of the liquid flowing along the fiber axis in the vicinity of the TFBG due to a nanoscale gold layer over part of the TFBG. For a device length of 10 mm (and a diameter of 125 µm for easy insertion into microfluidic channels), the flow rates and the direction can be detectable unequivocally. The TFBG waveguiding properties allow such devices to function in liquids with refractive indices ranging from 1.33 to about 1.40. In addition, the proposed sensor can be made inherently temperature-insensitive by referencing all wavelengths to the wavelength of the core mode resonance of the grating, which is isolated from the fiber surroundings

Effect of Alloying Elements in Melt Spun Mg-alloys for Hydrogen Storage

In this paper we report the effect of alloying elements on hydrogen storage properties of melt-spun Mg-based alloys. The base alloys Mg90Si10, Mg90Cu10, Mg65Cu35 (at%) were studied. We also investigated the effect of rare earths (using MM: mischmetal) and Al in Mg65Cu25Al10, Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys. All the melt-spun alloys without MM show a crystalline structure, and the Mg65Cu25MM10 and Mg65Cu10Al15MM10 alloys showed an amorphous and partially amorphous structure respectively. At 350˚C all the alloys had a crystalline structure during the hydrogen absorption-desorption tests. It was observed that Si and Cu in the binaries alloys hindered completely the activation of the hydrogen absorption. The partial substitution of Cu by MM or Al allowed activation. The combined substitution of Cu by MM and Al showed the best results with the fastest absorption and desorption kinetics, which suggests that this combination can be used for new Mg-alloys to improve hydrogen storage properties

The sonic hedgehog signaling pathway is reactivated in human renal cell carcinoma and plays orchestral role in tumor growth

<p>Abstract</p> <p>Background</p> <p>Human clear cell renal cell carcinoma (CRCC) remains resistant to therapies. Recent advances in Hypoxia Inducible Factors (HIF) molecular network led to targeted therapies, but unfortunately with only limited clinical significance. Elucidating the molecular processes involved in kidney tumorigenesis and resistance is central to the development of improved therapies, not only for kidney cancer but for many, if not all, cancer types. The oncogenic PI3K/Akt, NF-kB and MAPK pathways are critical for tumorigenesis. The sonic hedgehog (SHH) signaling pathway is crucial to normal development.</p> <p>Results</p> <p>By quantitative RT-PCR and immunoblot, we report that the SHH signaling pathway is constitutively reactivated in tumors independently of the von Hippel-Lindau (VHL) tumor suppressor gene expression which is inactivated in the majority of CRCC. The inhibition of the SHH signaling pathway by the specific inhibitor cyclopamine abolished CRCC cell growth as assessed by cell counting, BrdU incorporation studies, fluorescence-activated cell sorting and β-galactosidase staining. Importantly, inhibition of the SHH pathway induced tumor regression in nude mice through inhibition of cell proliferation and neo-vascularization, and induction of apoptosis but not senescence assessed by in vivo studies, immunoblot and immunohistochemistry. Gli1, cyclin D1, Pax2, Lim1, VEGF, and TGF-β were exclusively expressed in tumors and were shown to be regulated by SHH, as evidenced by immunoblot after SHH inhibition. Using specific inhibitors and immunoblot, the activation of the oncogenic PI3K/Akt, NF-kB and MAPK pathways was decreased by SHH inhibition.</p> <p>Conclusions</p> <p>These findings support targeting SHH for the treatment of CRCC and pave the way for innovative and additional investigations in a broad range of cancers.</p

Herschel observations of interstellar chloronium

Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared (HIFI), we have observed para-chloronium (H2Cl+) toward six sources in the Galaxy. We detected interstellar chloronium absorption in foreground molecular clouds along the sight-lines to the bright submillimeter continuum sources Sgr A (+50 km/s cloud) and W31C. Both the para-H2-35Cl+ and para-H2-37Cl+ isotopologues were detected, through observations of their 1(11)-0(00) transitions at rest frequencies of 485.42 and 484.23 GHz, respectively. For an assumed ortho-to-para ratio of 3, the observed optical depths imply that chloronium accounts for ~ 4 - 12% of chlorine nuclei in the gas phase. We detected interstellar chloronium emission from two sources in the Orion Molecular Cloud 1: the Orion Bar photodissociation region and the Orion South condensation. For an assumed ortho-to-para ratio of 3 for chloronium, the observed emission line fluxes imply total beam-averaged column densities of ~ 2.0E+13 cm-2 and ~ 1.2E+13 cm-2, respectively, for chloronium in these two sources. We obtained upper limits on the para-H2-35Cl+ line strengths toward H2 Peak 1 in the Orion Molecular cloud and toward the massive young star AFGL 2591. The chloronium abundances inferred in this study are typically at least a factor ~10 larger than the predictions of steady-state theoretical models for the chemistry of interstellar molecules containing chlorine. Several explanations for this discrepancy were investigated, but none has proven satisfactory, and thus the large observed abundances of chloronium remain puzzling.Comment: Accepted for publication in the Astrophysical Journa