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141.
I. Favero G. Cassabois D. Darson C. Voisin J. Tignon C. Delalande Ph. Roussignol R. Ferreira J. M. Grard 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):336
We report the first direct observation of Huang–Rhys side-bands in the photoluminescence spectrum of a single InAs/GaAs quantum dot (QD). At low temperature (10 K) the single QD spectrum has a quasi-Lorentzian profile. At higher temperatures, we observe a strong deviation from a Lorentzian profile with the appearance of asymmetric side-bands which become symmetric above 70 K. We obtain an excellent agreement with theoretical calculations done in the framework of the Huang–Rhys formalism. We conclude that the zero-phonon linewidth is the relevant parameter for the observation of the low-energy acoustic phonon side-bands. 相似文献
142.
Let G be a strongly connected, aperiodic, two-out digraph with adjacency matrix A. Suppose A = R + B are coloring matrices: that is, matrices that represent the functions induced by an edge-coloring of G. We introduce a matrix Δ = 1/2 (R − B) and investigate its properties. A number of useful conditions involving Δ which either are equivalent to or imply a solution
to the road coloring problem are derived. 相似文献
143.
Ph. Boullay G. TrolliardD. Mercurio J.M. Perez-MatoL. Elcoro 《Journal of solid state chemistry》2002,164(2):252-260
A generalized structural model of Aurivillius-type compounds is presented using a 4D superspace group analysis where Aurivillius structures are considered as cation-deficient perovskites with the general formula AB1−xO3. Being essentially composition independent, the model is valid for any Aurivillius-type compounds where x is the only composition-dependent parameter. The atomic domains representing the atoms in superspace are described by means of crenel functions. For any composition, the conventional space groups can be easily derived from a unique superspace group. This work is supported by a TEM investigation where the continuously variable character of the diffraction diagram indicates that the various stacking sequences can be interpreted in terms of a structural modulation over a common average structure. 相似文献
144.
145.
Kinetics of oil saponification by lead salts in ancient preparations of pharmaceutical lead plasters and painting lead mediums 总被引:1,自引:0,他引:1
M. Cotte E. Checroun J. Susini P. Dumas P. Tchoreloff M. Besnard Ph. Walter 《Talanta》2006,70(5):1136
Lead soaps can be found in archaeological cosmetics as well as in oil paintings, as product of interactions of lead salts with oil. In this context, a better understanding of the formation of lead soaps allows a follow-up of the historical evolution of preparation recipes and provides new insights into conservation conditions. First, ancient recipes of both pharmaceutical lead plasters and painting lead mediums, mixtures of oil and lead salts, were reconstructed. The ester saponification by lead salts is determined by the preparation parameters which were quantified by FT-IR spectrometry. In particular, ATR/FT-IR spectrometer was calibrated by the standard addition method to quantitatively follow the kinetics of this reaction. The influence of different parameters such as temperature, presence of water and choice of lead salts was assessed: the saponification is clearly accelerated by water and heating. This analysis provides chemical explanations to the historical evolution of cosmetic and painting preparation recipes. 相似文献
146.
Ph. Vermeulen J. A. Fernández Pierna H. P. van Egmond J. Zegers P. Dardenne V. Baeten 《Analytical and bioanalytical chemistry》2013,405(24):7765-7772
In recent years, near-infrared (NIR) hyperspectral imaging has proved its suitability for quality and safety control in the cereal sector by allowing spectroscopic images to be collected at single-kernel level, which is of great interest to cereal control laboratories. Contaminants in cereals include, inter alia, impurities such as straw, grains from other crops, and insects, as well as undesirable substances such as ergot (sclerotium of Claviceps purpurea). For the cereal sector, the presence of ergot creates a high toxicity risk for animals and humans because of its alkaloid content. A study was undertaken, in which a complete procedure for detecting ergot bodies in cereals was developed, based on their NIR spectral characteristics. These were used to build relevant decision rules based on chemometric tools and on the morphological information obtained from the NIR images. The study sought to transfer this procedure from a pilot online NIR hyperspectral imaging system at laboratory level to a NIR hyperspectral imaging system at industrial level and to validate the latter. All the analyses performed showed that the results obtained using both NIR hyperspectral imaging cameras were quite stable and repeatable. In addition, a correlation higher than 0.94 was obtained between the predicted values obtained by NIR hyperspectral imaging and those supplied by the stereo-microscopic method which is the reference method. The validation of the transferred protocol on blind samples showed that the method could identify and quantify ergot contamination, demonstrating the transferability of the method. These results were obtained on samples with an ergot concentration of 0.02 % which is less than the EC limit for cereals (intervention grains) destined for humans fixed at 0.05 %. Online Abstract Figure
Pictures showing a the manual removal of ergot bodies and b the observation by the stereo-microscopic method (official method); c the metallic holder with the reference material, and d the NIR hyperspectral SisuCHEMA instrument 相似文献
147.
R.J. Van De Nesse G.Ph. Hoornweg C. Gooijer U.A.Th. Brinkman N.H. Velthorst 《Analytica chimica acta》1989
Laser-induced fluorescence (LIF) detection in conventional-size column liquid chromatography is achieved at 257 nm with a frequency-doubled argon-ion laser. Short-wavelength excitation offers two important advantages: firstly, a wide variety of analytes can be excited, and secondly, the Raman scatter of the eluent does not interfere with the fluorescence of the analytes. A standard mixture of polynuclear aromatic hydrocarbons was studied, both with LIF detection and with a commercially available sensitive conventional fluorescence detector. The improvement in the detection limits ranges from about a factory of 4 to 30; the LIF detection limits are typically at the 50 ng l?1 level, which corresponds to an injected amount of 0.5 pg. 相似文献
148.
B. Vezin Ph. Dugourd D. Rayane P. Labastie J. Chevaleyre M. Broyer 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(Z1):128-130
Ionization Potentials of LinHm clusters have been measured by photoionization. As in Lin, odd-even alternations and shell closing effects are observed. In a first approximation, we find that LinH clusters behave like Lin–1 and LinH2 like Lin–2. The results may be interpreted by assuming that the bonding of one hydrogen localizes one electron and that the other electrons remain delocalized. 相似文献
149.
P. Kavouras Th. Kehagias K. Chrissafis Ph. Komninou Th. Karakostas 《Journal of Thermal Analysis and Calorimetry》2006,86(3):715-719
Three batch compositions of pure oxides (SiO2,
Fe2O3, PbO, Na2O)
with equivalent SiO2, Fe2O3
and PbO contents and a gradually increased Na2O content
were vitrified through heating in a high temperature electric furnace and
subsequent quenching. The resulting vitreous products were thermally treated
in order to study the devitrification behaviour, under conditions designated
from differential thermal analysis experiments. Depending on the Na2O
content, crystal phase separation gave rise to the growth of acmite and hematite
or maghemite. A uniformly phase separated glass-ceramic material, with crystallites
of similar size and population density, was produced from devitrification
of the vitreous product with the higher Na2O content. 相似文献
150.
T. de Beer G. Ph. Hoornweg G. J. Grootendorst N. H. Velthorst C. Gooijer 《Analytica chimica acta》1996,330(2-3):189-197
An explorative study on the compatibility of liquid separation systems, such as (micro) liquid chromatography (LC) and capillary electrophoresis (CE), and forward-scattering degenerate four-wave mixing (F-D4WM) as a detection method is presented. F-D4WM is a laser-based technique showing some analogy with holographic spectroscopy: a signal on a theoretical dark background is observed as a result of light absorption by an analyte. Parameters considered are solvent composition focussing on acetonitrile, methanol and water; mobile phases in LC and CE), detector cell construction, and influences of laser beam powers. A specially designed detector cell has been developed to meet the Brewster condition, both at the air-quartz and the quartz-liquid boundaries. For practical reasons, the tested cell has an optical pathlength of 1 mm; reduction to 100 μm is required to apply the cell in microseparations. The F-D4WM technique has been involved for detection in a conventional-size, reversed-phase LC separation of 1- and 2-aminoanthraquinones. The detection limit obtained (for the 1 mm cell) is 2 × 10−5 absorbance units. The experiments indicate that further reduction of background deserves explicit attention. 相似文献