Intergranular and transgranular fracture surfaces obtained in a face centered cubic alloy are studied using 3D maps reconstructed by scanning electron microscopy stereo imaging. The roughness exponents measured in the intergranular and transgranular surfaces, respectively, zeta = 0.83 +/- 0.05 and zeta = 0.75 +/- 0.05, are in agreement with the universal roughness value of 3D fractures. However, the slightly smaller value related to the transgranular surface could be a consequence of crystallographic transgranular zones disseminated on the surface whose roughness exponent zeta = 0.65 +/- 0.07 is close to the one usually measured on 2D fractures. 相似文献
Direct supercritical fluid extraction (SFE) of wines with carbon dioxide was compared to SFE of the sorbent used for solid-phase extraction of the same wine samples (SPE-SFE). Compared to SPE-SFE, the direct SFE results in amore specific and representative gas chromatographic fingerprint of the wine sample. The multivariate statistical processing of the direct SFE-GC data provides a clear-cut and sharp discrimination among the individual wine varieties while the discrimination based on the SPE-SFE-GC data is relatively poor. This finding reflects the adverse effects of additional analyte-sorbent interactions and sorption/desorption steps involved in SPE-SFE. 相似文献
Magnetic anisotropy has been measured in multiply twinned, icosahedral cobalt clusters. It is found that the low-temperature magnetization of deposited cluster layers is well defined with the Stoner–Wohlfarth model by averaging over clusters with a range of anisotropy energy. Anisotropy energy calculation based on Néel's pair model shows that the icosahedral structure and the layer-by-layer growth of the clusters induce oscillations of the magnetic anisotropy as a function of the filling of the outer surface of the particle. The magnetization measurement at room temperature indicates a weakly correlated cluster glass, as deduced from the approach to saturation that is well described with 2D random anisotropy model. 相似文献
4-13C-isoprene was prepared by the Wittig reaction. All reaction steps were optimised using unlabelled compounds. By reaction with triphenyl phosphine, 13C labelled methyl iodide afforded labelled methyl-triphenyl phosphine iodide in 84% yield. This reacted with meth acrolein with production of 4-13C-isoprene in 64% yield. Labelled polyisoprene was prepared by anionic polymerisation initiated by t-butyl lithium. Based on 13CH3I the overall yield is ca 30%. The polymer was characterized by 1H and 13C NMR spectroscopy. The contribution of each microstructure was [cis 1-4, 72%]; [trans 1-4, 10%]; [3-4, 18%]. 相似文献
New antimicrobial microfibrous electrospun mats from styrene/maleic anhydride copolymers were prepared. Two approaches were applied: (i) grafting of poly(propylene glycol) monoamine (Jeffamine® M‐600) on the mats followed by formation of complex with iodine; (ii) modification of the mats with amines of 8‐hydroxyquinoline or biguanide type with antimicrobial activity. Microbiological screening against S. aureus, E. coli and C. albicans revealed that both the formation of complex with iodine and the covalent attachment of 5‐amino‐8‐hydroxyquinoline or of chlorhexidine impart high antimicrobial activity to the mats. In addition, S. aureus bacteria did not adhere to modified mats.
The objective of the presented study was to develop and optimize a simple, high-throughput method for the control of 32 mycotoxins (Fusarium and Alternaria toxins, aflatoxins, ergot alkaloids, ochratoxins, and sterigmatocystin) in beer. Due to the broad range of their physicochemical properties, the sample preparation step was simplified as much as possible to avoid analyte losses. The addition of acetonitrile to beer samples enabled precipitation of abundant matrix components. The clean-up efficiency was controlled by ambient mass spectrometry employing a direct analysis in real time (DART) ion source. For determination of analytes, ultra-high-performance liquid chromatography hyphenated with high-resolution mass spectrometry utilizing an orbitrap (U-HPLC-orbitrapMS) or time-of-flight (TOFMS) technology was used. Because of significantly better detection capabilities of the orbitrap technology, the U-HPLC-orbitrapMS method was chosen as a determinative step and fully validated. To compensate matrix effects, matrix-matched calibration was employed. The lowest calibration levels for most of the target mycotoxins ranged from 1 to 8 μg L(-1) beer and the recoveries of analytes were in range from 86 to 124%. 相似文献
This paper deals with the modelling and numerical simulation of isothermal bubbly flows with multi-size bubbles. The study of isothermal bubbly flows without phase change is a first step towards the more general study of boiling bubbly flows. Here, we are interested in taking into account the features of such isothermal flow associated to the multiple sizes of the different bubbles simultaneously present inside the flow. With this aim, several approaches have been developed. In this paper, two of these approaches are described and their results are compared to experimental data, as well as to those of an older approach assuming a single average size of bubbles. These two approaches are (i) the moment density approach for which two different expressions for the bubble diameter distribution function are proposed and (ii) the multi-field approach. All the models are implemented into the NEPTUNE_CFD code and are compared to a test performed on the MTLOOP facility. These comparisons show their respective merits and shortcomings in their available state of development. 相似文献
Three new tetracyclic polyisoprenylated xanthones, named oxy-guttiferones M, K2, and I, along with oxy-guttiferone K and guttiferone M, have been isolated from the fruits of Garcinia cambogia. Their structures were elucidated by MS and NMR spectroscopic experiments. The absolute configurations of oxy-guttiferone K, taken as a model of tetracyclic xanthones, and guttiferone M, as a model of polyisoprenylated benzophenones, have been determined by comparison of their experimentally measured circular dichroism (CD) curves with the TDDFT-predicted curves. 相似文献