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61.
Wael M. Badawy Octavian G. Duliu Marina V. Frontasyeva Hussein El Samman Arnaud Faanhof 《Isotopes in environmental and health studies》2018,54(5):535-547
The activity concentrations of natural 40K, 232Th, and 238U in 89 soil and 84 sediment samples collected over the entire Egyptian Nile River basin including the Nile delta are reported based on the results of epithermal neutron activation analysis. The average activity concentrations of 40K, 232Th, and 238U equal to 15.3?±?6.6, 15.6?±?11.1 and 220?±?31 Bq/kg, respectively, are significantly lower than those reported for the Upper Continental Crust, World Average Sediments as well as World Average Soils, suggesting the presence of a considerable portion of mafic material, most probably originating from the Ethiopian High Plateau. Their average activity concentrations are statistically the same in soil and sediments, indicating that the Nile sediments and soil material are of the same origin. The main goal of this study was not only to estimate the radiological hazards but also to show the influence of sedimentary material transportable by the Blue Nile from the Ethiopian High Plateau. The different hazard indices like the radium equivalent, gamma index, external hazard as well as the internal hazard show a low radiological exposure either on direct contact or if local mud bricks are used in the construction of dwellings. 相似文献
62.
Julie Febvay Dr. Charles S. Demmer Dr. Pascal Retailleau Dr. Jeanne Crassous Dr. Laura Abella Prof. Jochen Autschbach Dr. Arnaud Voituriez Dr. Angela Marinetti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(68):15609-15614
Phosphahelicenes with thiophosphinic acid and ester functions have been obtained by the oxidative photocyclisation of olefins bearing both a benzophenanthrene and a benzophosphole unit. When the method has been extended to olefins bearing a partially saturated benzophospholene unit, a divergent regioselectivity of the photocyclisation step has been observed, leading to new helicenes in which the phosphorus function is located on the external rim of the helical backbone. The observed regioselectivity correlates well with the free-valence numbers of the atoms involved in the photocyclisation reaction (DFT calculations). 相似文献
63.
Paul Podsiadlo Galyna V. Krylova Arnaud Demortière Elena V. Shevchenko 《Journal of nanoparticle research》2011,13(1):15-32
In this article, we review the state-of-the-art in the preparation and characterization of multicomponent self-assembled superlattices
of colloidal nanoparticles with core sizes in the range of 2–20 nm and interparticle spacing less than 2 nm down to intimate
contact stemming from sintering. Several aspects of the field are discussed, including: structural organization, the role
of particle size distribution, key interparticle forces at play, and methods of investigation of the structures. Contrary
to the extensively studied colloidal crystals composed of microscale particles, the nanoparticles possess unique size-dependent
properties, such as electronic, optical, or magnetic, which when combined into periodic structures can potentially lead to
new collective states stemming from precise positioning of the nanocolloids. As such, we examine a number of emerging applications
of this new class of metamaterials. Finally, we speculate on the potential impact of these materials, the new directions,
and the challenges for the researchers. 相似文献
64.
The tetxaacetylation of isobutene has been perfomed in AlCl3/AcCl. Treatment of the crude reaction medium with liquid ammonia yields the title compound. 相似文献
65.
Magrez A Seo JW Mikó C Hernadi K Forró L 《The journal of physical chemistry. B》2005,109(20):10087-10091
Multiwalled carbon nanotubes (MWCNTs) were grown by chemical vapor deposition by applying C(2)H(2) fluxed over Fe(1)(-x)Co(x) catalyst supported by alkaline earth carbonate. Detailed investigations of the chemical process occurring prior and during the growth allowed us a significant improvement of the nanotube production rate and quality. We observed a strong influence of the catalyst stoichiometry on the carbon deposition rate and the nanotube characteristics. We also found evidence for the active role of the support in the growth process, which is explained by the decomposition of the carbonate at the growth temperature. Using the optimized parameters obtained from our study performed in a fixed bed furnace, we could improve the production rate to about 500 g/day of purified MWCNTs in our large-scale rotary tube furnace. 相似文献
66.
Arbouet A Christofilos D Del Fatti N Vallée F Huntzinger JR Arnaud L Billaud P Broyer M 《Physical review letters》2004,93(12):127401
The absorption of a single isolated metal cluster is directly measured using a novel far-field optical technique based on modulation of its position. Single gold nanoparticles with average diameters down to 5 nm, dispersed on a transparent substrate, are optically detected and their absolute absorption cross section determined. 相似文献
67.
68.
Henry-dit-Quesnel A Toupet L Pommelet JC Lequeux T 《Organic & biomolecular chemistry》2003,1(14):2486-2491
The synthesis of difluoromethylphosphonates is becoming difficult due to environmental protective laws restricting the use of HCFCs and CFCs as starting chemicals. To circumvent this limitation, we report the preparation of a thioether as a new source of the lithiodifluoromethylphosphonate. This methodology avoiding the use of HCFCs involves a selective fluorination of sulfide followed by a thiaphilic addition of an organometallic reagent, which offers an alternative route to obtain phosphonodifluoromethyl carbanion. A contrasted reactivity, due to a medium effect, was also noted which allows addition of a wide range of electrophiles including nitroalkenes and DMF to thioethers. 相似文献
69.
The cyclization reactions of the 4-pentenyl, 5-hexenyl, 6-heptenyl, and 7-octenyl fluorinated and ether radicals have been studied by a hybrid Hartree-Fock density functional method. The reliability of this approach has been confirmed in agreement with experimental data and post-Hartree-Fock projected M?ller-Plesset second-order method. The analysis of the theoretical results shows that two factors are crucial for the determination of the regiochemistry and the reactivity of these reactions. The first factor is the ability of the starting radical to have a stable conformation in position to form the transition state, and the second one is the enthalpic effect of the reaction through the stability of the resulting cyclized radical. It should be pointed out that these factors are not linked to the polarity of the radicals due to the presence of CF2 groups. 相似文献
70.
P. Billaud J.-R. Huntzinger E. Cottancin J. Lermé M. Pellarin L. Arnaud M. Broyer N. Del Fatti F. Vallée 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):271-274
The extinction spectrum of single silver nanoparticles
with size ranging from 20 to 80 nm is investigated with the spatial
modulation spectroscopy technique using either a tunable laser or a white
lamp as the broadband source. Results are in good agreement with the
prediction of the Mie theory, permitting to extract the nanoparticle size
from the measured absolute value of the optical extinction cross-section. In
contrast, the deduced refractive index of the nanoparticle environment and
the reduction of the electron mean free path show a large dependence on the
precise value of the bulk silver dielectric function. 相似文献