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排序方式: 共有303条查询结果,搜索用时 15 毫秒
101.
Ioana Fechete Philippe Caullet Emil Dumitriu Vasile Hulea Henri Kessler 《Applied Catalysis A: General》2005,280(2):245-254
(Al,Ga)EMT-type zeolites (Al:Ga = 1:0, 0.75:0.25 and 0.5:0.5) were prepared and tested as catalysts in the gas-phase toluene–methanol alkylation and toluene–trimethylbenzene transalkylation. Various techniques including XRD, N2 sorption, MAS NMR and SEM were used to monitor the physico-chemical properties of these solids. The results revealed a high purity and crystallinity of the materials, and that the Ga atoms are entirely incorporated into the framework. The ammonia TPD measurements indicated that the isomorphous substitution of aluminium by gallium leads to a decrease of both acidic strength and acid sites concentration. The catalytic performances of the EMT-type solids in the conversion of methylaromatic hydrocarbons were correlated with their acid properties. Thus, the less acidic (Al,Ga)EMT samples exhibited a lower activity, but a higher selectivity towards the xylenes formation by comparison with (Al)EMT. 相似文献
102.
Agnieszka Mech Wendel Wohlleben Antoine Ghanem Vasile‐Dan Hodoroaba Stefan Weigel Frank Babick Raphael Brüngel Christoph M. Friedrich Kirsten Rasmussen Hubert Rauscher 《Small (Weinheim an der Bergstrasse, Germany)》2020,16(36)
Identifying nanomaterials (NMs) according to European Union legislation is challenging, as there is an enormous variety of materials, with different physico‐chemical properties. The NanoDefiner Framework and its Decision Support Flow Scheme (DSFS) allow choosing the optimal method to measure the particle size distribution by matching the material properties and the performance of the particular measurement techniques. The DSFS leads to a reliable and economic decision whether a material is an NM or not based on scientific criteria and respecting regulatory requirements. The DSFS starts beyond regulatory requirements by identifying non‐NMs by a proxy approach based on their volume‐specific surface area. In a second step, it identifies NMs. The DSFS is tested on real‐world materials and is implemented in an e‐tool. The DSFS is compared with a decision flowchart of the European Commission’s (EC) Joint Research Centre (JRC), which rigorously follows the explicit criteria of the EC NM definition with the focus on identifying NMs, and non‐NMs are identified by exclusion. The two approaches build on the same scientific basis and measurement methods, but start from opposite ends: the JRC Flowchart starts by identifying NMs, whereas the NanoDefiner Framework first identifies non‐NMs. 相似文献
103.
In this work, an originally bio-inspired cryptosystem is developed. It is based on the use of cellular automata (CAs) as pseudorandom bit generators and programmable cellular automata (PCA) to construct the block ciphering functions of the proposed enciphering scheme. The cryptosystem is featured by resistance on different types of attacks and high speed due to the cellular automata's parallel information processing property. The proposed architecture could be efficiently implemented in reconfigurable hardware like field programmable gate arrays (FPGAs) and could be applied in high-speed data communication. The project was implemented in two experimental hardware platforms based on Spartan 3 XC3S400fg456-4 and XILINX Spartan 3E XC3S500E. 相似文献
104.
In this article, the problem of H 2-control of a discrete-time linear system subject to Markovian jumping and independent random perturbations is considered. Different H 2 performance criteria (often called H 2-norms) are introduced and characterised via solutions of some suitable linear equations on certain spaces of symmetric matrices. Some aspects specific to the discrete-time framework are revealed. The problem of optimisation of H 2-norms is solved under the assumption that full state vector is available for measurements. One shows that among all stabilising controllers of higher dimension, the best performance is achieved by a zero-order controller. The corresponding feedback gain of the optimal controller is constructed based on the stabilising solution of a system of discrete-time generalised Riccati equations. 相似文献
105.
Mihaela Chiriac Bogdan Silvestru Munteanu Gina‐Gabriela Bumbu Maria Burlacel Aurelia Ioanid Cornelia Vasile 《大分子材料与工程》2000,283(1):26-35
Polystyrene (PS)/polyolefin (PO) blends in various mixing ratios compatibilized by a triblock copolymer polystyrene‐block‐poly(ethene‐co‐butylene)‐block‐polystyrene (SEBS) and a diblock copolymer polystyrene‐block‐poly(ethene‐co‐propene) (SEP) and subsequently γ‐irradiated were prepared. The blends have been subjected to extraction in different solvents (chloroform or toluene) for various periods of time to obtain porous films. The efficiency of the extraction and the morphology of the films have been assessed by infrared spectrometry (IR), optical and electronic microscopy, differential scanning calorimetry (DSC) and thermogravimetry (TG); glass transition, melting heat, thermal stability, overall kinetic parameters and weight losses have been evaluated. The extraction behavior is close related to compatibility of the components, so on the base of the obtained results optima compatibility ratios have been established. 相似文献
106.
Alina-Livia Maciuca Cristina-Elena Ciocan Emil Dumitriu Franois Fajula Vasile Hulea 《Catalysis Today》2008,138(1-2):33
Catalytic oxidation of thioethers and thiophene derivatives with H2O2 was performed at 40 °C and atmospheric pressure, in presence of W-, V- and Mo-containing layered double hydroxides (LDH). The catalysts were prepared by direct ion exchange with metal-oxoanions, i.e. WO42−, W7O246−, V2O74−, V10O286−, MoO42− and Mo7O246−, of the LDH containing aluminum and magnesium atoms in the brucite layer. All the catalysts showed good activity and selectivity in the sulfoxidation reaction, but the catalyst performances strongly depended on the nature of the anion species intercalated in the interlayer gallery. Thus, the W-based LDH was more active and more stable than the V-LDH and Mo-LDH catalysts. The conversion of sulfur-containing compounds is also dependent on the nucleophilicity of substrates and the following order of reactivity was observed benzothiophene < dibenzothiophene < diphenyl-sulfide < benzyl-phenyl-sulfide < methyl-phenyl-sulfide. 相似文献
107.
Vasile Lupulescu 《Information Sciences》2008,178(23):4523-4533
A new concept of inner product on the fuzzy space (En,D) is introduced, studied and used to prove several theorems stating the existence, uniqueness and boundedness of solutions of fuzzy differential equations. A stability result is also proved in the same context. 相似文献
108.
Florentina Neau Alexander Kraynov Lawrence D'Souza Vasile I. Prvulescu Kritof Kranjc Marijan Ko
evar Victor Kuncser Ryan Richards 《Applied Catalysis A: General》2008,346(1-2):28-35
Fe3O4 colloids modified by the chiral ligand cinchonidine were prepared with the goal of obtaining a magnetic and catalytic nano-material and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by TEM and XRD measurements, while the Mössbauer technique was applied for measuring the magnetic properties of the Fe3O4 colloids. The hyperfine magnetic field distribution was consistent with one type of Fe oxide, namely, the magnetite (Fe3O4). These colloids, both as ‘quasi-homogenous catalysts’ (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of complex bicyclo[2.2.2]oct-7-enes (bicyclo[2.2.2]oct-2-enes when unsubstituted). 相似文献
109.
Carmen Racle Anton Airinei Vasile Cozan Maria Cazacu Istvan E. Sajo 《应用聚合物科学杂志》2003,90(11):3093-3099
By polycondensation reactions, starting from α, ω‐bis(chloromethyl)polydimethylsiloxanes with different molecular weights and 2,6‐bis(4‐hydroxybenzylidene)cyclohexanone, new polyethers were obtained. The structure of resulting polymers was confirmed by IR and 1H‐NMR spectroscopy and their thermal properties and mesophase behavior were studied by TGA, DSC, and polarizing light microscopy. Depending on the length of the siloxane spacer, some of the obtained compounds exhibited thermotropic liquid‐crystalline properties. A possible smectic texture was investigated by X‐ray diffraction measurements at room temperature. A decrease of the transition temperatures values was observed as the spacer length increased. The photochemical behavior of the siloxane polyethers was studied by ultraviolet absorption spectroscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3093–3099, 2003 相似文献
110.
Summary Influence of the temperature on the compatibility of the polystyrene / AB-g-S graft copolymer / cyclohexanone have been studied by light scattering and viscosity measurement. It was established that the compatibility of components is changed in the temperature range where the conformational transitions take place. 相似文献