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241.
β-sialon ceramics sintered with yttria additives have been studied with the use of an electron probe X-ray analysis (EPMA).
Sialon ceramics were prepared from a carbothermally derived β-sialon powder and then sintered in a nitrogen atmosphere with
yttria admixture. The above process was followed by annealing in flowing nitrogen. Scanning electron microscope (SEM) observations
have shown that the sintered material contains a glassy phase (Y-Si-Al-O-N) on the grain boundaries. X-ray diffraction (XRD)
after annealing in nitrogen revealed the presence of a considerable amount of yttrium aluminium garnet (YAG). The higher voltage
of 30 kV was used in order to excite the yttrium Kα radiation (14.96 keV) at an appropriate overvoltage ratio because in some phases of the material, the disappearance of the
yttrium Lα line has been observed during EPMA examination at an accelerating voltage of 15 kV in energy dispersive spectra (EDS). The
intensity of the yttrium Kα line was sufficiently high, while the Y Lα line was not seen in the ED spectrum. Because the position of the yttrium Lα line (1.922 keV) is very close to the Si (K) absorption edge (1.84 keV), the strong absorption at this edge is probably responsible
for the effect. This result should be considered as a serious warning in the case of EPMA (EDS) studies on compounds or mixtures
suspected to contain both silicon and yttrium, because at electrons energies lower than 15 keV, the presence of yttrium in
materials can go unnoticed. In wavelength dispersive spectra (WDS) obtained at 15 keV the intensity of the yttrium Lα line was also very low but measurable. 相似文献
242.
Studies on diisopropylnaphthalene substitutional isomerism 总被引:2,自引:0,他引:2
Robert Brzozowski Jan Cz. Dobrowolski Micha
H. Jamrz Wincenty Skupi
ski 《Journal of molecular catalysis. A, Chemical》2001,170(1-2):95-99
The concentrations of diisopropylnaphtalene (DIPN) isomers in experimental equilibrium mixtures obtained on amorphous aluminosilicate and HY zeolite have been measured by GC method. The total energy and Gibbs free energy of the isomers were calculated by DFT method at the B3PW91/3-21G level. Comparison of the populations based on the DFT energies with the experimental concentrations of DIPN isomers are in good agreement. This fact can suggest that isomerization is mainly determined by thermodynamic equilibrium. 相似文献
243.
Alexandre Jean Jacques Rouden Jacques Maddaluno Michaël De Paolis Jérôme Blanchet 《Tetrahedron letters》2019,60(7):534-537
Benzyltrimethylammonium hydroxide act as an efficient metal-free catalyst for the intramolecular hydroalkoxylation of alkynes. Notably, the use of microwave irradiation allowed reaction to operate in only two minutes. Under optimized reaction conditions, linear alkynes bearing aryl and heteroaryl substituents were successfully cyclized with good level of stereoselectivity. 相似文献
244.
Dr. Hanna Jędrzejewska Dr. Ewelina Wielgus Dr. Sławomir Kaźmierski Halina Rogala Dr. Michał Wierzbicki Dr. Aneta Wróblewska Dr. Tomasz Pawlak Prof. Marek J. Potrzebowski Prof. Agnieszka Szumna 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(7):1558-1566
Mechanical grinding/milling can be regarded as historically the first technology for changing the properties of matter. Mechanically activated molecular units (mechanophores) can be present in various structures: polymers, macromolecules, or small molecules. However, only polymers have been reported to effectively transduce energy to mechanophores, which induces breakage of covalent bonds. In this paper, a second possibility is presented—molecular capsules as stress-sensitive units. Mechanochemical encapsulation of fullerenes in cystine-based covalent capsules indicates that complexation takes place in the solid state, despite the fact that the capsules do not possess large enough entrance portals. By using a set of solvent-free MALDI (sf-MALDI) and solid-state NMR (ss-NMR) experiments, it has been proven that encapsulation proceeds during milling and in this process hydrazones and disulfides get activated for breakage, exchange, and re-forming. The capsules are porous and therefore prone to collapse under solvent-free conditions and their conformational rigidity promotes the collapse by the breaking of covalent bonds. 相似文献
245.
JPC – Journal of Planar Chromatography – Modern TLC - An HPTLC method has been developed to give qualitative and quantitative information on red wine pigments. The samples are prepared... 相似文献
246.
I. V. Ajinenko H. Białkowska H. Böttcher F. Botterweck F. Crijns A. De Roeck E. A. De Wolf K. Dziunikovska A. M. F. Endler P. F. Ermolov Z. C. Garutchava Y. A. Golubkov N. G. Grigoryan G. R. Gulkanyan P. van Hal T. Haupt J. K. Karamyan Z. A. Kirakosyan D. Kisielewska W. Kittel S. S. Megrabyan F. Meijers A. B. Michałowska K. Olkiewicz L. P. Petrovikh A. M. Rybin H. Saarikko L. Scholten E. K. Shabalina F. Verbeure R. Wischnewski S. A. Zotkin 《Zeitschrift fur Physik C Particles and Fields》1991,49(3):367-374
Collective characteristics are studied of hadrons produced in beam fragmentation of non-single-diffractive π+ p-interactions at 250 GeV/c. An attempt is made to obtain experimental information on the properties of leading cluster production and fragmentation. On average, the leading cluster carries 0.8±0.1 of the incident momentum, so that the mean value of the inelasticity coefficient of 〈k〉=0.2±0.1 is significantly smaller than that deduced from leading single hadron spectra. The momentum transfer distribution shows that nonsingle-diffractive processes are less peripheral than diffraction dissociation. The analysis of thrust and sphericity shows jet-like structure of pion fragmentation, that of the charge flow an average forward charge of 〈Q f 〉=0.45±0.04, in agreement with the average charge of the beam valence quarks. Our data are compared to diffraction dissociation and to the Fritiof model. 相似文献
247.
248.
MichaŁ Rozwadowski Roman Wojsz 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(5):561-567
Fundamental thermodynamic functions have been derived for equations of adsorption isotherms including structural heterogeneity connected with micropore dimensions. Good agreement has been achieved between values of the differential molar enthalpy of adsorption and values of the isosteric adsorption heats obtained experimentally. 相似文献
249.
In this paper we consider a problem of preemptive scheduling of multiprocessor tasks on dedicated processors in order to minimize the sum of completion times. Using a standard notation, our problem can be denoted as P ∣ fixj, pmtn ∣ ∑Cj. We give a polynomial-time algorithm to solve P ∣ fixj, G = {P4, dart}-free, pmtn ∣ ∑Cj problem. This result generalizes the following problems: P2 ∣ fixj, pmtn ∣ ∑Cj, P ∣ ∣fixj∣ ∈ {1, m}, pmtn ∣ ∑Cj and P4 ∣ fixj = 2, pmtn ∣ ∑Cj. 相似文献
250.
We extend the notion ofk-sets and (≤k)-sets (see [3], [12], and [19]) to arrangements of curves and surfaces. In the case of curves in the plane, we assume that
each curve is simple and separates the plane. Ak-point is an intersection point of a pair of the curves which is covered by exactlyk interiors of (or half-planes bounded by) other curves; thek-set is the set of allk-points in such an arrangement, and the (≤k)-set is the union of allj-sets, forj≤k. Adapting the probabilistic analysis technique of Clarkson and Shor [13], we obtain bounds that relate the maximum size of
the (≤k)-set to the maximum size of a 0-set of a sample of the curves. Using known bounds on the size of such 0-sets we obtain asympotically
tight bounds for the maximum size of the (≤k)-set in the following special cases: (i) If each pair of curves intersect at most twice, the maximum size is Θ(nkα(nk)). (ii) If the curves are unbounded arcs and each pair of them intersect at most three times, then the maximum size is Θ(nkα(n/k)). (iii) If the curves arex-monotone arcs and each pair of them intersect in at most some fixed numbers of points, then the maximum size of the (≤k)-set is Θ(k
2λ
s
(nk)), where λ
s
(m) is the maximum length of (m,s)-Davenport-Schinzel sequences. We also obtain generalizations of these results to certain classes of surfaces in three and
higher dimensions. Finally, we present various applications of these results to arrangements of segments and curves, high-order
Voronoi diagrams, partial stabbing of disjoint convex sets in the plane, and more. An interesting application yields andO(n logn) bound on the expected number of vertically visible features in an arrangement ofn horizontal discs when they are stacked on top of each other in random order. This in turn leads to an efficient randomized
preprocessing ofn discs in the plane so as to allow fast stabbing queries, in which we want to report all discs containing a query point.
Work on this paper has been supported by Office of Naval Research Grant N00014-87-K-0129, by National Science Foundation Grants
DCR-83-20085 and CCR-89-01484, and by grants from the U.S.-Israeli Binational Science Foundation, the NCRD—the Israeli National
Council for Research and Development-and the Fund for Basic Research in Electronics, Computers and Communication, administered
by the Israeli Academy of Sciences. 相似文献