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排序方式: 共有293条查询结果,搜索用时 109 毫秒
1.
Manal Benyoussef Moneim Zannen Jamal Belhadi Bouchaib Manoun Jean-Luc Dellis Mimoun El Marssi Abdelilah Lahmar 《Ceramics International》2018,44(16):19451-19460
In this work, Na0.5(Bi1-xDyx)0.5TiO3 (0?≤?x?≤?15%) ceramics were prepared via solid state reaction method and were characterized. A stable and pure perovskite phase was revealed by X-ray diffraction analysis for all compositions and a symmetry change from rhombohedral to orthorhombic phase was detected beyond 10% of Dy substitution. The incorporation of Dy3+ into Sodium Bismuth Titanate (Na0.5Bi0.5TiO3) matrix allows a substantial decrease of the coercive field, an increase in the resistivity, and leads to a high stability of the dielectric permittivity (??/?(150?°C) ≤?±?15%) over a wide temperature range. Furthermore, this system was found to exhibit improved energy storage properties at high temperatures with a maximum energy density of 1.2?J/cm3 obtained for 2%Dy composition at 200?°C. The obtained results are very promising for energy storage capacitors operating at high temperatures. 相似文献
2.
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Nina Georgieva Kostova Elka Kraleva Alla A. Spojakina Erika Godocikova Peter Balaz 《Journal of Materials Science》2007,42(10):3321-3325
The Al-MCM-41 has been used as support to prepare Mo-containing catalysts. The 12- molybdophosphoric heteropoly acid (HPMo)
is used as initial compound. The catalysts are synthesized by two different methods: incipient impregnation with aqueous solution
of the acid and mechanochemical synthesis. The samples were tested in the reaction of the thiophene hydrodesulfurization after
activation with mixture H2 + H2S. The effect of the preparation method of the catalysts on their physicochemical and catalytic properties has been studied.
A partial destruction of the loaded compound is observed in mechanochemically treated sample whereas the aggregates are formed
from the particles of different size in the impregnated sample. The specific surface area of the sample prepared by mechanical–chemical
treatment decreases 2–3 times, while the total pore volume is about four times lower. The HDS activity is higher on the impregnated
sample than on the mechanochemically treated one. 相似文献
4.
The main phase transformations during synthesis of β‐sialon from kaolin of the Prosyanovskii deposit (Ukraine) under test-industrial production conditions have been studied. Sialon was prepared by carbothermal reduction in graphite-tube furnaces in nitrogen. It is shown that the process is characterized by the simultaneous occurrence of several chemical reactions with formation of intermediate phases (Si2ON2, X1‐phase), silicon carbide, and (apart from β‐sialon) sialons based on AlN polytypes. The phase composition of the final product is determined not only by the charge composition but also by the set of production parameters. Results of the work may provide a basis for commercial preparation of sialon powder. 相似文献
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Use has been made of potentiodynamic polarization curves, XRD, and scanning electron microscopy (SEM) in the electrolytic oxidation in 3% NaCl solution for specimens of nitrogen-deficient zirconium nitride (ZrN0.67, ZrN0.77, ZrN0.87, and ZrN0.97), as well as pure zirconium. In all cases, the anodic polarization curves have several stages which characterize during oxidation both active dissolution of ZrN x and Zr in the electrolyte as well as the formation of surface layers of ZrOCl2, ZrN x O y , and α‐ZrO2 of monoclinic form. The corrosion resistance of single-phase ZrN x specimens in 3% NaCl solution decreases in the sequence ZrN0.97 → ZrN0.87 → ZrN0.77, and the initial stages of interaction between the specimen surface and the electrolyte largely determine the subsequent behavior of specimens. It is found that ZrN x containing a large number of nitrogen atom vacancies, in particular ZrN0.77, is closer in corrosion behavior to metallic zirconium than it is to stoichiometric ZrN (the reduction in the corrosion resistance is undoubtedly due to the reduction in the ionic-covalent components of the bonds in ZrN x ). 相似文献
7.
Anna A. Pendina Mikhail I. Krapivin Olga A. Efimova Andrei V. Tikhonov Irina D. Mekina Evgeniia M. Komarova Alla S. Koltsova Alexander M. Gzgzyan Igor Yu. Kogan Olga G. Chiryaeva Vladislav S. Baranov 《International journal of molecular sciences》2021,22(11)
The human lifespan is strongly influenced by telomere length (TL) which is defined in a zygote—when two highly specialised haploid cells form a new diploid organism. Although TL is a variable parameter, it fluctuates in a limited range. We aimed to establish the determining factors of TL in chromosomes of maternal and paternal origin in human triploid zygotes. Using Q-FISH, we examined TL in the metaphase chromosomes of 28 human triploid zygotes obtained from 22 couples. The chromosomes’ parental origin was identified immunocytochemically through weak DNA methylation and strong hydroxymethylation in the sperm-derived (paternal) chromosomes versus strong DNA methylation and weak hydroxymethylation in the oocyte-derived (maternal) ones. In 24 zygotes, one maternal and two paternal chromosome sets were identified, while the four remaining zygotes contained one paternal and two maternal sets. For each zygote, we compared mean relative TLs between parental chromosomes, identifying a significant difference in favour of the paternal chromosomes, which attests to a certain “imprinting” of these regions. Mean relative TLs in paternal or maternal chromosomes did not correlate with the respective parent’s age. Similarly, no correlation was observed between the mean relative TL and sperm quality parameters: concentration, progressive motility and normal morphology. Based on the comparison of TLs in chromosomes inherited from a single individual’s gametes with those in chromosomes inherited from different individuals’ gametes, we compared intraindividual (intercellular) and interindividual variability, obtaining significance in favour of the latter and thus validating the role of heredity in determining TL in zygotes. A comparison of the interchromatid TL differences across the chromosomes from sets of different parental origin with those from PHA-stimulated lymphocytes showed an absence of a significant difference between the maternal and paternal sets but a significant excess over the lymphocytes. Therefore, interchromatid TL differences are more pronounced in zygotes than in lymphocytes. To summarise, TL in human zygotes is determined both by heredity and parental origin; the input of other factors is possible within the individual’s reaction norm. 相似文献
8.
Achraf Benba Abdelilah Jilbab Ahmed Hammouch 《International Journal of Speech Technology》2016,19(4):743-754
In this study, we wanted to discriminate between two groups of people. The database used in this study contains 20 patients with Parkinson’s disease and 20 healthy people. Three types of sustained vowels (/a/, /o/ and /u/) were recorded from each participant and then the analyses were done on these voice samples. Firstly, an initial feature vector extracted from time, frequency and cepstral domains. Then we used linear and nonlinear feature extraction techniques, principal component analysis (PCA), and nonlinear PCA. These techniques reduce the number of parameters and choose the most effective acoustic features used for classification. Support vector machine with its different kernel was used for classification. We obtained an accuracy up to 87.50 % for discrimination between PD patients and healthy people. 相似文献
9.
This paper deals with the problem of forbidden states in safe Petri nets to obtain a maximally permissive controller. To prevent the system from entering the forbidden states, assigning some constraints to them is possible. The constraints can be enforced on the system using control places. When the number of forbidden states is large, a large number of constraints should be assigned to them. This results in a large number of control places being added to the model of the system, which causes a complicated model. Some methods have been proposed to reduce the number of constraints. Nevertheless, they do not always give the best results. In this paper, two ideas are offered to reduce the number of constraints, giving a more simplified controller. 相似文献
10.
A framework is introduced for monitoring the interrupting faults in the timed discrete events systems. We introduce the notion of acceptable behavior of the system subjected to these faults: permanent or intermittent. The acceptable behavior of a system is modeled by a stopwatch automaton. The timed sub-spaces in the locations of the automaton delimit exactly the range of the acceptable behavior. They are synthesized using the techniques of reachability analysis of stopwatch automata in a way to detect the system faults as early as possible. 相似文献