6,187 research outputs found

    Les Grands Musées d’Histoire Naturelle de Province : le Muséum de Nantes

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    Variations in water use by a mature mangrove of Avicennia germinans, French Guiana

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    In the tropical intertidal zones, little is known on water uptake by mangroves. Transpiration rates are generally measured at leaf level, but few studies exist on water use at tree or stand levels. The objective of this study was to measure sap flow in trees of different sizes to appreciate the range of variation in water use that may exist in a site dominated by 80% mature Avicennia germinans. The results showed that from the dry to the wet season the mean water use increased from 3.2 to 5.3 dm3 d−1 in small trees (DBH ∼ 13 cm), from 11.5 to 30.8 dm3 d−1 in medium trees (∼24 cm) and from 40.8 to 64.1 dm3 d−1 in large ones (∼45 cm). Sapwood remained active up to a depth of 8 cm with radial variations within the stem. Weak correlations were obtained with VPD and net radiation. This study confirmed that transpiration was larger under low levels of salinity. Water use at stand level (∼1900 living stems ha−1) was estimated to be in the range of 5.8 to 11.8 m3 ha−1 d−1 according to the season

    Maxillary Sinus Lift with Beta-Tricalcium Phosphate (β-TCP) in Edentulous Patients: A Nanotomographic and Raman Study

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    Sinus lift elevation restores bone mass at the maxilla in edentulate patients before the placement of dental implants. It consists of opening the lateral side of the sinus and grafting beta-tricalcium phosphate granules (β-TCP) under the olfactory membrane. Bone biopsies were obtained in five patients after 60 weeks. They were embedded undecalcified in poly(methyl methacrylate) (pMMA); blocks were analyzed by nanocomputed tomography (nanoCT); specific areas were studied by Raman microspectroscopy. Remnants of β-TCP were osseointegrated and covered with mineralized bone; osteoid tissue was also filling the inner porosity. Macrophages having engulfed numerous β-TCP grains were observed in marrow spaces. β-TCP was identified by nanoCT as osseointegrated particles and as granules in the cytoplasm of macrophages. Raman microspectroscopy permitted to compare the spectra of β-TCP and bone in different areas. The ratio of the ~820 cm(-1) band of pMMA (-CH2 groups) on the ν1 phosphate band at 960 cm(-1) reflected tissue hydration because water was substituted by MMA during histological processing. In bone, the ratio of the ~960 cm(-1) phosphate to the amide 1 band and the ratio ν2 phosphate band by the 1240-1250 amide III band reflect the mineralization degree. Specific bands of β-TCP were found in osseointegrated β-TCP granules and in the grains phagocytized by the macrophages. The hydration degree was maximal for β-TCP phagocytized by macrophages. Raman microspectroscopy associated with nanoCT is a powerful tool in the analysis of the biomaterial degradation and osseointegration

    Blunted cardiovascular responses to acute psychological stress predict low behavioral but not self-reported perseverance

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    Emerging evidence relates attenuated physiological stress reactions to poor behavioral regulation. However, only a small number of behaviors such as impulsivity and risk taking have been explored. Nevertheless, one opportunistic study suggested that blunted reactivity might relate to poor perseverance. The present study examined the relationship between cardiovascular reactivity to acute active psychological stress and self‐reported and behavioral perseverance. Participants (N = 64) completed a self‐report perseverance questionnaire before heart rate (HR) and blood pressure (BP) were measured at rest and in response to 4‐min active (paced auditory serial addition; PASAT) and passive (cold pressor) stress tests. This was followed by an unsolvable Euler puzzle tracing task, with the time spent and number of attempts endeavoring to solve the puzzle recorded as behavioral perseverance measures. Blunted systolic and diastolic BP reactivity to the PASAT was associated with fewer attempts at the impossible puzzle, and lower diastolic BP PASAT reactivity related to less time persevering at the puzzle. Moreover, attenuated diastolic BP and HR PASAT reactivity predicted poorer perseverance at keeping one's hand in the iced water of the cold pressor task. There was no association between reactivity and self‐reported perseverance. These preliminary findings add to the evidence that implicates blunted reactivity as a physiological marker of poor behavioral regulation, and this may indicate why individuals with blunted reactivity are at increased risk of developing negative health outcomes (e.g., obesity and addictions)

    Augmentation des cinétiques de diffusion des composés de la pellicule des raisins rouge et blanc par des champs électriques pulsés

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    In recent years, Pulsed Electric Field (PEF) technology has been developing in laboratories and is starting to be established in the industry, mainly in the agri-food sector. So far all experimentations on the use of PEF in the wine industry was carried out at the laboratory scale on some kilograms of grapes, or liters of wines. Since 2015, we are studying the interest of the use of PEF on grape polyphenols extraction on a semi-industrial scale of 2 tons per hour. The first tests were carried out by comparing the PEF technology to a control, and a conventional thermovinification with liquid phase vinification and traditional vinification with different fermentation times. The first results obtained are encouraging. Vinified in the liquid phase, the grapes treated with PEF give wines with a color intensity of 20 to 30% higher than the control and a higher TPI of 7 to 17%. In the liquid phase, the treatment of the harvest by PEF does not make it possible to obtain the extraction level of the thermovinification. After a short maceration of 3 days, the polyphenols extraction level is similar to the thermovinification, and greater after 14 days, and so is the color (respectively +12 and +16%). No change in IBMP content was observed. The wines resulting from treatment of the harvest by PEF do not have the aromatic profile of thermovinification wines. The PEF has a fruity character comparable to the control and accentuates the aromatic characteristics of the grape variety. The wine are often judged less aggressive and astringent by reinforcing the perception of sweetness and full bodied. A few tests in white grape harvest by PEF, shows a significant gain of the thiols and terpenols

    Pressure-induced amorphization and polyamorphism in one-dimensional single crystal TiO2 nanomaterials

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    The structural phase transitions of single crystal TiO2-B nanoribbons were investigated in-situ at high-pressure using the synchrotron X-ray diffraction and the Raman scattering. Our results have shown a pressure-induced amorphization (PIA) occurred in TiO2-B nanoribbons upon compression, resulting in a high density amorphous (HDA) form related to the baddeleyite structure. Upon decompression, the HDA form transforms to a low density amorphous (LDA) form while the samples still maintain their pristine nanoribbon shape. HRTEM imaging reveals that the LDA phase has an {\alpha}-PbO2 structure with short range order. We propose a homogeneous nucleation mechanism to explain the pressure-induced amorphous phase transitions in the TiO2-B nanoribbons. Our study demonstrates for the first time that PIA and polyamorphism occurred in the one-dimensional (1D) TiO2 nanomaterials and provides a new method for preparing 1D amorphous nanomaterials from crystalline nanomaterials.Comment: 4 figure

    A Study of the Formation of Single- and Double-Walled Carbon Nanotubes by a CVD Method

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    The reduction in H2/CH4 atmosphere of aluminum-iron oxides produces metal particles small enough to catalyze the formation of single-walled carbon nanotubes. Several experiments have been made using the same temperature profile and changing only the maximum temperature (800-1070 °C). Characterizations of the catalyst materials are performed using notably 57Fe Mo¨ssbauer spectroscopy. Electron microscopy and a macroscopical method are used to characterize the nanotubes. The nature of the iron species (Fe3+, R-Fe, ç-Fe-C, Fe3C) is correlated to their location in the material. The nature of the particles responsible for the high-temperature formation of the nanotubes is probably an Fe-C alloy which is, however, found as Fe3C by postreaction analysis. Increasing the reduction temperature increases the reduction yield and thus favors the formation of surface-metal particles, thus producing more nanotubes. The obtained carbon nanotubes are mostly single-walled and double-walled with an average diameter close to 2.5 nm. Several formation mechanisms are thought to be active. In particular, it is shown that the second wall can grow inside the first one but that subsequent ones are formed outside. It is also possible that under given experimental conditions, the smallest (<2 nm) catalyst particles preferentially produce double-walled rather than single-walled carbon nanotubes

    Measurement of Strange Quark Contributions to the Nucleon's Form Factors at Q^2=0.230 (GeV/c)^2

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    We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2Q^2 of 0.230 (GeV/c)^2 and a scattering angle of \theta_e = 30^o - 40^o. Using a large acceptance fast PbF_2 calorimeter with a solid angle of \Delta\Omega = 0.62 sr the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A_{phys} =(-5.44 +- 0.54_{stat} +- 0.27_{\rm sys}) 10^{-6}. The Standard Model expectation assuming no strangeness contributions to the vector form factors is A0=(6.30+0.43)106A_0=(-6.30 +- 0.43) 10^{-6}. The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G^s_E + 0.225 G^s_M = 0.039 +- 0.034 or F^s_1 + 0.130 F^s_2 = 0.032 +- 0.028.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Letters on Dec 11, 200

    Polarity in GaN and ZnO: Theory, measurement, growth, and devices

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    This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Rev. 3, 041303 (2016) and may be found at https://doi.org/10.1063/1.4963919.The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade
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