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991.
Peter Thissen Vera Thissen Stefan Wippermann Yves J. Chabal Guido Grundmeier Wolf Gero Schmidt 《Surface science》2012,606(11-12):902-907
The structure and energetics of water on MgO(100) surfaces are studied by atomic force microscopy (AFM) and density-functional theory (DFT). Computationally, the adsorption of water monomers, small water clusters and water monolayers on MgO(100) surfaces is considered. The calculations predict the non-dissociative adsorption for water monomers. The potential energy surface for single monomers is characterized by very low diffusion barriers. Increasing water coverage leads to the formation of structures containing alternatively dissociated and molecularly adsorbed water molecules. The magnitude of the calculated adsorption energy per water molecule increases from 0.57 eV for the water monomer to 0.79 eV for the water monolayer. The present experimental and theoretical results show furthermore that the stability of MgO(100) surfaces in the presence of water depends on its pH value. The etching of MgO(100) surfaces in aqueous medium is studied with the AFM in situ with pH value changing from basic to acidic. While the atomically flat MgO(100) surface remains stable in basic and neutral pH ranges, it is easily etched when the pH turns below a value of 6. This agrees qualitatively with the present DFT calculations showing that square pits resulting from the etching reduce the MgO(100) surface energy in acidic environments. 相似文献
992.
Although uncertainty is rife in many project management contexts, little is known about adaptively optimizing project schedules. We formulate the problem of adaptively optimizing the expected present value of a project’s cash flow, and we show that it is practical to perform the optimization. The formulation includes randomness in activity durations, costs, and revenues, so the optimization leads to a recursion with a large state space even if the durations are exponentially distributed. We present an algorithm that partially exercises the “curse of dimensionality” as computational results demonstrate. Most of the paper is restricted to exponentially distributed task durations, but we sketch the adaptation of the algorithm to approximate any probability distribution of task duration. 相似文献
993.
Edvard E. Nifantiev Vera I. Maslennikova Elena N. Rasadkina 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6-7):1545-1548
Electronic effects in the design of new types of phosphocontaining cavity systems were considered. The matter of this phenomenon consists in supramolecular interaction of the organic radicals of substrates with the cyclophosphorylating reagents. 相似文献
994.
995.
Alexey Bobrovsky Valery Shibaev Vera Hamplova Miroslav Kaspar Milada Glogarova 《Colloid and polymer science》2010,288(14-15):1375-1384
For the first time, a photochromic azobenzene-containing liquid crystalline (LC) acrylic polymer was used for gelation of low-molar-mass nematic mixture (LMNM). Dissolution of LC polymer in amount of only 2.5 wt.% in LMNM at 120°C (isotropic state) followed by cooling down results in formation of the solid-like photochromic LC gel. Gelation is associated with a phase separation and formation of microsized LC polymer domains, which form a physical “network” containing encapsulated nematic host. Textural changes of mixture during gel formation were analyzed, and absorbance spectra were measured. A special attention was paid to the kinetic study of photoinduced E-Z and Z-E isomerization of azobenzene side groups of polymer in gel. It was shown that ultraviolet (UV)-irradiation and E-Z isomerization processes are accompanied by disruption of H-aggregates of azobenzene moieties and partial dissolution of polymer. 相似文献
996.
Continuity of the dynamics in a localized large diffusion problem with nonlinear boundary conditions
Vera Lúcia Carbone Karina Schiabel-Silva 《Journal of Mathematical Analysis and Applications》2009,356(1):69-85
This paper is concerned with singular perturbations in parabolic problems subjected to nonlinear Neumann boundary conditions. We consider the case for which the diffusion coefficient blows up in a subregion Ω0 which is interior to the physical domain Ω⊂Rn. We prove, under natural assumptions, that the associated attractors behave continuously as the diffusion coefficient blows up locally uniformly in Ω0 and converges uniformly to a continuous and positive function in . 相似文献
997.
Vera Koponen 《Archive for Mathematical Logic》2009,48(6):515-522
A probability distribution can be given to the set of isomorphism classes of models with universe {1, ..., n} of a sentence in first-order logic. We study the entropy of this distribution and derive a result from the 0–1 law for first-order
sentences.
相似文献
998.
999.
Slaveykova VI Guignard C Eybe T Migeon HN Hoffmann L 《Analytical and bioanalytical chemistry》2009,393(2):583-589
This work demonstrates the capabilities of nanoscale secondary-ion mass spectrometry, using the Cameca NanoSIMS50 ion microprobe,
to detect and image the copper-ion distribution in microalgal cells exposed to nanomolar and micromolar copper concentrations.
In parallel to 63Cu− secondary-ion maps, images of 12C−, 12C14N−, and 31P− secondary ions were collected and analysed. A correlation of 63Cu− secondary-ion maps with those found for 12C14N− and 31P− demonstrated the possible association of Cu with cell components rich in proteins and phosphorus. The results highlighted
the potential of NanoSIMS for intracellular tracking of essential trace elements such as Cu in single cells of the microalga
Chlorella kesslerii.
Figure
12C14N-, 63Cu- secondary-ion distributions in algal cell 相似文献
1000.
The oxygen radical absorbance capacity (ORAC) method has been adapted to the instrumental laboratory and optimized for the
determination of the antioxidant capacity of a novel active packaging. As the ORAC assay requires the monitorization of a
reaction at controlled temperature by means of the fluorescence signal decrease over time, specific instrumental is usually
necessary. In this work, a common liquid chromatographic device has been adapted to perform the ORAC assay, leaving it accessible
to any laboratory. Using this adaptation, five different essential oils have been determined resulting in the following antioxidant
order: clove (2.66 g Trolox per gram of essential oil), oregano (2.25), cinnamon (1.93), rosemary (1.66), and ginger (1.47).
After incorporating the essential oils to the film, its antioxidant capacity has also been checked and related to the concentration
of essential oil as well as the thickness of the active film. The results point out that for the same amount of essential
oil incorporated measured as grams per square meter, thicker films have more antioxidant capacity than the thinner and more
concentrated ones. Furthermore, the antioxidant capacity found in the films was always higher than expected taking into account
the amount of essential oil incorporated. Some likely explanations have been proposed, leading to the improvement of the antioxidant
film under development. 相似文献