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61.
Petr Praus Ladislav Svoboda Richard Dvorský Martin Reli 《Ceramics International》2018,44(4):3837-3846
Tin dioxide nanoparticles were prepared in the presence of graphitized carbon nitride (g-C3N4) forming nanocomposites with different contents of SnO2 up to 40 %. G-C3N4 was synthetized by heating of melamine at 550 °C in the open air and Sn2+ ions were precipitated by sodium hydroxide in g-C3N4 aqueous dispersions. Resulting mixtures were dried by freezing at ?20 °C and calcined at 450 °C to obtain SnO2/g-C3N4 nanocomposites.The nanocomposites were characterized by common characterization methods in solid state and in their aqueous dispersions using dynamic light scattering (DLS) analysis and photocatalysis. SnO2 nanoparticles in the nanocomposites were found to have an average size of 4 nm, however, those precipitated without g-C3N4 had an average size of 14 nm. Separation of photoinduced electron and holes via heterojunction between SnO2 and g-C3N4 was demonstrated by photocatalytic decomposition of Rhodamine B (RhB) under LED visible irradiation (416 nm) and photocurrent measurements. The most photocatalytically active nanocomposite contained 10 % of SnO2. Graphitized carbon nitride was assumed to serve as a template structure for the preparation of SnO2 nanoparticles with a narrow size distribution without using any stabilizing additives. 相似文献
62.
Miroslav Mrlik Michal Sedlacik Vladimir Pavlinek Pavel Bazant Petr Saha Petra Peer Petr Filip 《应用聚合物科学杂志》2013,128(5):2977-2982
One of the crucial problems of classical magnetorheological (MR) fluids is their high rate of sedimentation. This disadvantage may be substantially eliminated using core‐shell particles. The aim of this study is to prepare spherical carbonyl iron (CI) particles coated with conducing polymer polypyrrole (PPy) with ribbon‐like morphology. Scanning electron microscopy proved the formation of the ribbon‐like layer onto CI particles while Fourier transform infrared spectroscopy confirmed the chemical structure of PPy. The magnetic properties observed via vibrating sample magnetometer showed decreased magnetization saturation of core‐shell‐structured particles due to the existence of non‐magnetic surface layer. MR measurements performed under oscillatory shear flow as a function of the applied magnetic flux density, temperature, and particle concentration showed that core‐shell particle‐based MR suspension exhibits sufficient MR performance for practical applications. Moreover, the suspension stability is promoted significantly when core‐shell particles are used as a dispersed phase. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
63.
Petr Petkevich Konstantin Mikityuk Paul Coddington Rakesh Chawla 《Annals of Nuclear Energy》2009,36(8):1262-1269
The reference fuel design currently being considered within the Generation-IV Gas-cooled Fast Reactor (GFR) project is a ceramic plate matrix with a honeycomb inner structure containing small fuel cylinders. The fuel is mixed plutonium–uranium carbide, while the matrix material is silicon carbide. The present paper describes the mechanical part of a thermal–mechanical model being developed for studying the transient behavior of this highly heterogeneous fuel type. Benchmarking has been carried out against detailed finite-elements modeling (FEM).The resultant thermal–mechanical model can provide reliable fuel and cladding (matrix) stress/strain conditions to evaluate temperatures and neutronic feedbacks. As such, it has been integrated into PSI’s coupled code system “FAST”, which aims at the comprehensive safety analysis of advanced fast reactor systems.The detailed FEM analysis of the GFR fuel has been useful not only for benchmarking the new model, but also for obtaining an in-depth understanding of fuel stress/strain characteristics, which cannot be reproduced with simplified models. Thereby, the range of applicability of the new model has clearly been defined. In particular, the 3D FEM analysis has revealed a concentration of stresses at the pellet corners during pellet/matrix contact, which could lead to fuel element failure. This effect is found to be mitigated considerably, if the fuel pellets are shaped in a manner which enhances the contact area. 相似文献
64.
This review discusses recent emerging techniques that have been used to couple flow‐injection analysis (FIA) and electrospray ionization‐mass spectrometry (ESI‐MS) for the quantitation of noncovalent binding interactions. Focus is placed predominantly on two such methods. Diffusion‐based measurements, developed by Konermann and co‐workers, uses controlled‐band dispersion prior to ESI‐MS to determine diffusion constants and binding constants based on the temporal variation of ligand signal measured in the mass spectrum (an indirect technique). Dynamic titration, developed by Schug and co‐workers, is a direct method, where a temporal compositional gradient of a guest molecule is induced in the presence of host in solution to monitor the concentration dependence of complex formation as a function of observed complex ion abundance after ESI‐MS. Further discussion places these techniques in the context of a variety of other direct and indirect ESI‐MS‐based binding determination methods, and highlights advantages, disadvantages, and practical considerations for their proper use to investigate a broad range of macromolecular and small‐molecule interaction systems. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:806–829, 2010 相似文献
65.
Khoruzhaya Vera G. Martsenyuk Petr S. Meleshevich Konstantin A. Velikanova Tamara Ya. 《Powder Metallurgy and Metal Ceramics》2002,41(5-6):278-283
The reaction of components of the Si — Al — O — N — Ti system in its elements Si 3N4 — AlN, TiN — AlN, and Al 2O 3 — AlN was investigated by differential thermal and x-ray diffraction analysis. It was established that upon hot pressing mixtures of Si3N 4 and AlN (up to 1950°C) free silicon is formed by the decomposition of Si 3N4, which reacts with oxygen present as an impurity to form SiO. When TiN reacts with AlN a phase with the spinel structure (Al23O 27N 5), which can form only in the presence of excess oxygen, appears in addition to the initial components. Spinel is also produced by the reaction of Al 2O3 with AlN. In this case a eutectic between Al 23O27N5 and Al2O3 is observed. 相似文献
66.
Elena?Muriel Teresa?Antequera Maria?Jesus?Petrón Diana?Martín Jorge?RuizEmail author 《European Food Research and Technology》2004,219(5):445-451
The profile of volatile compounds from external and internal areas of Iberian dry-cured loin was studied by headspace solid-phase microextraction. Higher levels of 16 volatile compounds (hexane, decane, 3-methylbutanal, several sulphur compounds and some aromatic hydrocarbons) were detected in the outer part of the loins. These differences could be owing to several factors, such as greater exposure to oxygen and dehydration conditions in the surface of the product, which favour oxidation reactions and Strecker degradation of amino acids. Moreover, the addition of spices on the surface and the proximity of a mould layer growing on the surface of the product could also contribute to the higher levels of these compounds on the external layer. However, other sulphur compounds coming from spices showed similar levels on the surface and within the loins. This different behaviour could be a consequence of different diffusion rates depending on the features of the compound and the matrix. 相似文献
67.
Somol P Pudil P Kittler J 《IEEE transactions on pattern analysis and machine intelligence》2004,26(7):900-912
A novel search principle for optimal feature subset selection using the Branch & Bound method is introduced. Thanks to a simple mechanism for predicting criterion values, a considerable amount of time can be saved by avoiding many slow criterion evaluations. We propose two implementations of the proposed prediction mechanism that are suitable for use with nonrecursive and recursive criterion forms, respectively. Both algorithms find the optimum usually several times faster than any other known Branch & Bound algorithm. As the algorithm computational efficiency is crucial, due to the exponential nature of the search problem, we also investigate other factors that affect the search performance of all Branch & Bound algorithms. Using a set of synthetic criteria, we show that the speed of the Branch & Bound algorithms strongly depends on the diversity among features, feature stability with respect to different subsets, and criterion function dependence on feature set size. We identify the scenarios where the search is accelerated the most dramatically (finish in linear time), as well as the worst conditions. We verify our conclusions experimentally on three real data sets using traditional probabilistic distance criteria. 相似文献
68.
In this paper we study the classical problem of finding disjoint paths in
graphs. This problem has been studied by a number of authors both for specific
graphs and general classes of graphs. Whereas for specific graphs many
(almost) matching upper and lower bounds are known for the competitiveness of
on-line algorithms, not much is known about how well on-line algorithms can
perform in the general setting. The best results obtained so far use the
expansion of a network to measure the algorithms performance. We use a
different parameter called the routing number that, as we will show, allows
more precise results than the expansion. It enables us to prove tight upper and
lower bounds for deterministic on-line algorithms. The upper bound is obtained
by surprisingly simple greedy-like algorithms. Interestingly, our upper bound
on the competitive ratio is even better than the best previous approximation
ratio for off-line algorithms. Furthermore, we introduce a refined variant of
the routing number and show that this variant allows us, for some classes of
graphs, to construct on-line algorithms with a competitive ratio significantly
below the best possible upper bound that could be obtained using the routing
number or the expansion of a network only. We also show that our on-line
algorithms can be transformed into efficient algorithms for the more general
unsplittable flow problem. 相似文献
69.
Toxicity increases in ice containing monochlorophenols upon photolysis: environmental consequences 总被引:4,自引:0,他引:4
Bláha L Klánová J Klán P Janosek J Skarek M Růzicka R 《Environmental science & technology》2004,38(10):2873-2878
The toxic effects of photoproducts formed upon the photolysis of 2- and 4-chlorophenol (CP) frozen solutions in polycrystalline ice phase were determined with a bacterial luminescence test (Vibrio fisheri), and in vitro biomarker assay for dioxin-like effects (inductions of AhR-dependent luciferase in H4IIE-luc cells) and compared to the toxic effects of products of the same photoreaction in aquatic phase. Coupling photoproducts formed in ice samples (3'-chlorobiphenyl-2,4'-diol and 3-chlorobiphenyl-2,2'-diol from 2-CP photolysis and 5-chlorobiphenyl-2,4'-diol from 4-CP photolysis) were found to be more toxic to V. fisheri than parent CPs and elicited significant inductions of dioxin-like effects (the effective concentrations EC50 approximately 3 x 10(-5) mol L(-1) corresponded to known weaker ligands of AhR, such as nonplanar polychlorinated biphenyls or polycyclic aromatic hydrocarbons). To complete the picture, a photoproduct formed from 4-CP (5-chlorobiphenyl-2,4'-diol) was synthesized, and a detailed toxicity assessment with purified compound confirmed the results obtained with irradiated samples. Our findings support a recently proposed model according to which solar radiation can trigger the formation of new types of organic pollutants in polar ice or tropospheric ice cloud particles, presenting possibly greater risk to the environment than the parent compounds. 相似文献
70.
Hoops and Fuzzy Logic 总被引:4,自引:0,他引:4
Esteva Francesc; Godo Lluis; Hajek Petr; Montagna Franco 《Journal of Logic and Computation》2003,13(4):532-555