A Re-examination of the Portevin-Le Chatelier Effect in Alloy 718 in Connection with Oxidation-Assisted Intergranular Cracking

In Alloy 718, a sharp transition exists in the fracture path changing from an intergranular brittle mode to a transgranular ductile mode which is associated with a transition of flow behavior from smooth in the dynamic strain aging regime to a serrated one in the Portevin-Le Chatelier (PLC) regime. In order to better understand both deformation and rupture behavior, PLC phenomenon in a precipitation-hardened nickel-base superalloy was carefully investigated in a wide range of temperatures [573 K to 973 K (300°C to 700°C)] and strain rates (109^-5 to 3.2910^-2 s^-1 ). Distinction was made between two PLC domains characterized by different evolutions of the critical strain to the onset of the first serration namely normal and inverse behavior. The apparent activation energies associated with both domains were determined using different methods. Results showed that normal and inverse behavior domains are related to dynamic interaction of dislocations with, respectively, interstitial and substitutional solutes atoms. This analysis confirms that normal PLC regime may be associated to the diffusion of carbon atoms, whereas the substitutional species involves in the inverse regime is discussed with an emphasis on the role of Nb and Mo

Effects of 5-day hypoxia on cardiac adrenergic neurotransmission in rats

Chronic hypoxia induces an overall sympathetic hyperactivation associated with a myocardial beta-receptor desensitization. The mechanisms involved in this desensitization were evaluated in 32 male Wistar rats kept in a hypobaric pressure chamber (Po-2 = 40 Torr, atmospheric pressure = 450 Torr) for 5 days. In hypoxic compared with normoxic conditions, plasma norepinephrine (NE) levels were higher(2.1 +/- 0.7 vs. 0.6 +/- 0.2 ng/ml) with no difference in the plasma epinephrine levels (2.2 +/- 0.7 vs. 1.8 +/- 0.3 ng/ml). In hypoxia neuronal NE uptake measured by [H-3]NE was decreased by 32% in the right ventricle (RV) and by 35% in the left ventricle (LV), and [H-3]mazindol in vitro binding showed a decrease in uptake-1 carrier protein density by 38% in the RV and by 41% in the LV. In vitro binding assays with [H-3]CGP-12177 indicate beta-adrenoceptor density reduced by 40% in the RV and by 32% in the LV, and this was due to reduced beta(1)-subtype fraction (competition binding experiments with practolol). Hypoxia reduced the production of cAMP induced by isoproterenol (36% decrease in the RV and 41% decrease in the LV), 5'-guanylylimododiphosphate (40% decrease in the RV and 42% decrease in the LV), and forskolin (39% decrease in the RV and 41% decrease in the LV) but did not alter the effect of MnCl2 and NaF. Quantitation of inhibitory G-protein alpha-subunit by immunochemical analysis showed a 46% increase in the cardiac-specific isoform Gi(alpha 2) in hypoxic hearts. The present data demonstrate that in rats 5-day hypoxia leads to changes in pre- and postsynaptic myocardial adrenergic function. The myocardial desensitization associated with both a reduction in externalized beta(1)-adrenoceptor and an increase in inhibitory G-protein subunit may be caused by increased synaptic NE levels due to impaired uptake-1 system

Architecture funéraire du sud du Massif central au littoral languedocien, du Bronze final IIIb à la fin du premier âge du Fer

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Kinetics of the norepinephrine analog [76Br]-metabromobenzylguanidine in isolated working rat heart

A related set of kinetic studies of the norepinephrine analog [Br-76]-meta-bromobenzylguanidine (MBBG) were performed with an isolated working rat heart preparation. A series of constant infusion studies over a wide range of MBBG concentrations allowed estimation of the Michaelis-Menten constants for transport by the neuronal norepinephrine transporter (uptake(1)) and the extraneuronal uptake system (uptake(2)). Pharmacological blocking studies with inhibitors of uptake(1), uptake(2) and vesicular uptake were performed to delineate the relative importance of these norepinephrine handling mechanisms on the kinetics of MBBG in the rat heart. Bolus injection studies were done to assess the ability of compartmental modeling techniques to characterize the kinetics of MBBG. These studies demonstrate that MBBG shares many of the same uptake mechanisms as norepinephrine in the rat heart. PET imaging studies with MBBG would be useful for assessing sympathetic nerve status in the living human heart. (C) 1998 Elsevier Science Inc

Architecture funéraire du sud du Massif central au littoral languedocien, du Bronze final IIIb à la fin du premier âge du Fer

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First retrievals of methyl chloride from ground-based high-resolution FTIR solar observations

Methyl chloride (CH3Cl) is one of the most abundant chlorine-bearing gas in the Earth’s troposphere and a significant contributor to the organic chlorine budget. Measurements by in situ networks indicate a mean volume mixing ratio of 550 pptv, with a significant seasonal cycle of about 80 pptv, peak to peak. This species also exhibits inter-annual variability, but no long-term trend. Major sources are from tropical and sub-tropical plants and dead leaves, the oceans and biomass burning. Some industrial processes and waste incineration further add to the emissions. Oxidation by the hydroxyl radical is by far the largest CH3Cl sink, followed by soil uptake. Although balanced, its atmospheric budget is still affected by large uncertainties and contributions from unidentified sources and sinks cannot be ruled out. Methyl chloride has an atmospheric lifetime of 1 year, a global warming potential of 13 (100-yr horizon) and an ozone depleting potential of 0.02. The retrieval of methyl chloride from ground-based infrared (IR) spectra is very challenging. Indeed, numerous interferences by strong water vapor and methane lines complicate the detection of small CH3Cl absorptions, close to 1%, near 3 microns. In addition, and although weak, ethane features contribute to the difficulty, in particular since a significant number of ethane branches were absent until very recently from official HITRAN compilations. Therefore, the scientific literature does not report thus far about any investigations of CH3Cl from ground-based remote sensing observations. In this contribution, we will present first CH3Cl total column retrievals, using the SFIT-2 algorithm (v3.94) and high-resolution Fourier Transform Infrared (FTIR) solar absorption observations recorded with a Bruker 120HR instrument, at the high altitude station of the Jungfraujoch (46.5°N, 8°E, 3580 m asl), within the framework of the Network for the Detection of Atmospheric Composition Change (NDACC, visit http://www.ndacc.org). In our retrievals, we use new ethane absorption cross sections recorded at the Molecular Spectroscopy Facility of the Rutherford Appleton Laboratory (Harrison et al., 2010). They were calibrated in intensity by using reference low-resolution spectra from the Pacific Northwest National Laboratory (PNNL) IR database. These new cross sections were recently released as a HITRAN update (see http://www.hitran.com). Pseudoline parameters fitted to these ethane spectra have been combined with HITRAN 2004 line parameters (including all the 2006 updates) for all other species encompassed in the selected microwindows, including our target CH3Cl. We will evaluate the improvement brought by the new ethane line parameters on the fitting residuals, and characterize the quality, the precision and the reliability of the retrieved product. If successful, a long-term CH3Cl total column time series will be produced using the Jungfraujoch observational database, and we will perform preliminary investigations of the seasonal and inter-annual variations of methyl chloride total columns at northern mid-latitudes

Bromine-76-Metabromobenzylguanidine: A PET Radiotracer for Mapping Sympathetic Nerves of the Heart

Iodine-123-metaiodobenzylguanidine (MIBG) is used to qualitatively assess heart innervation with single-photon emission computed tomography (SPECT). This approach is clinically useful in the prognostic evaluation of congestive heart failure. To improve quantification of uptake of the tracer using positron emission tomography (PET), we studied the characteristics of the bromoanalog of MIBG. Bromine-76-metabromobenzylguanidine (76Br-MBBG) was prepared from a heteroisotopic exchange between radioactive bromine atoms (noncarrier-added (76Br) BrNH4) and the cold iodine atoms of the precursor metaiodobenzylguanidine. Biodistribution was studied in rats and PET cardiac imaging performed in dogs. Myocardial uptake was high and prolonged in both species (mean half-life in dogs: 580 min). In rats, myocardial uptake was inhibited by desipramine by 64%, whereas after pretreatment with 6- hydroxydopamine uptake was reduced by 84%. In dogs pretreated with 6- hydroxydopamine or with desipramine, a steep washout of the tracer occurred (mean half-life: 136 min and 118 min, respectively). The non-specific uptake plus the passive neuronal diffusion of the tracer could be estimated at about 25%-30% of the total fixation. In dogs, analysis of unchanged 76Br-MBBG in plasma showed that radiotracer metabolism was slow: 60 min after injection, 80% of the radioactivity was related to unchanged 76Br-MBBG. These preliminary findings suggest that 76Br-MBBG could be used to quantitatively assess adrenergic innervation in heart disease using PET. When combined with use of 11C-CGP 12177, cardiac adrenergic neurotransmission can be assessed

Du Bronze moyen au début du Bronze final dans le Sud-Est de la France (Provence-Alpes-Côte d’Azur, Languedoc-Roussillon, Sud de Rhône-Alpes et de l’Auvergne)

International audienceThis work constitutes an overview of data from the Middle and the beginning of the Late Bronze Age in south-eastern France, area that encompasses the administrative regions of Languedoc-Roussillon and Provence-Alpes-Côte d’Azur,as well as the south of Rhône-Alpes and Auvergne. At the beginning of the Middle Bronze Age, the pottery styles show clear analogies to the Italian peninsula, the precise origin of which can differ from one area to another. There seems however to be consistency in funerary practices and the deposition metal objects. At the end of this period, italic influenced pottery styles become standardised in a large area covering the Mediterranean coast. In Auvergne these Mediterranean influences disappear in favour of the Duffaits style from the Centre-West of France. At the beginning of the Late Bronze Age, cultural areas are redefined even though their boundaries remain permeable. The stylistic links with the north of Italy and the presence of cremation burials are mainly limited to the footholds of the Southern Alps. In contrast, pottery groups of the Rhône Valley incorporate characteristics from the North that are reminiscent of the «southern cannelated» group of the “Tumulus Culture”. The composition of the hoards and their objects can also be compared to the Saone area and the Paris Basin. These observations lead towards an increasing cultural distinction between the area around the Rhône and the Alps during the first phase of the Late Bronze Age. They prefigure the ascension of the North-Alpine material culture that penetrates the middle and lower Rhône Valley during the middle phase of the Late Bronze Age.Ce travail constitue une synthèse des données concernant le Bronze moyen et le début du Bronze final dans le quart Sud-Est de la France, restreint aux entités administratives du Languedoc-Roussillon et de Provence-Alpes-Côte d’Azur ainsi qu’au sud de la région Rhône-Alpes et de l’Auvergne. Au début du Bronze moyen, les styles céramiques montrent des affinités avec la péninsule italienne, dont l’origine précise semble néanmoins varier en fonction des secteurs. Une grande cohérence peut également être décelée dans les pratiques funéraires et de dépôts d’objets métalliques. A la fin de cette période, une homogénéisation des styles céramiques, d’affinité toujours italique, concerne une grande partie du littoral méditerranéen. En parallèle, en Auvergne, les caractères méditerranéens disparaissent au profit du style des Duffaitsdu Centre ouest. Au début du Bronze final, une recomposition des espaces culturels est manifeste bien que leurs limites soient largement perméables. Les connexions stylistiques avec le nord de l’Italie restent principalement limitées aux contreforts des Alpes méridionales, de même que l’apparition de sépultures à incinérations. En revanche, la vallée du Rhône voit l’apparition de faciès céramiques intégrant des caractères septentrionaux, évoquant le groupe cannelé méridional de la “culture des Tumulus”, ainsi que de dépôts d’objets métalliques dont la composition et la typologie des objets trouvent également des comparaisons dans la région de la Saône et le Bassin parisien. Ces observations vont donc dans le sens d’une distinction culturelle croissante entre les régions rhodaniennes et alpines lors de l’étape initiale du Bronze final. Elles préfigurent l’ascendance des cultures matérielles nord-alpines qui intéresseront la moyenne et basse vallée du Rhône lors de l’étape moyenne de cette période