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81.
Shmuel Yariv Isaak Lapides Mikhail Borisover 《Journal of Thermal Analysis and Calorimetry》2012,110(1):385-394
Na-montmorillonite was loaded with tetraethylammonium cations (TEA) or with benzyltrimethylammonium cations (BTMA) by replacing 77 and 81% of the exchangeable Na with TEA or BTMA, labeled TEA-MONT and BTMA-MONT, respectively. TEA- and BTMA-MONT were heated in air up to 900?°C. Thermally treated organoclays are used in our laboratory as sorbents of organic compounds from water. The two organoclays were studied by TG and DTG in air and under nitrogen. Carbon content in each of the heated sample was determined. They were diffracted by X-ray, and fitting calculations of d(001) peaks were performed on each diffractogram. TG and thermo-C analysis showed that at 150 and 250?°C both organoclays lost water but not intercalated ammonium cations. DTG peak of the first oxidation step of the organic cation with the formation of low-temperature stable charcoal (LTSC) appeared at 364 and 313?°C for TEA- and BTMA-MONT, respectively. The charcoal was gradually oxidized by air with further rise in temperature. DTG peak of the second oxidation step with the formation of high-temperature stable charcoal (HTSC) appeared at 397 and 380?°C for TEA- and BTMA-MONT, respectively. DTG peak of the final oxidation step of the organic matter appeared at 694 and 705?°C for TEA- and BTMA-MONT, respectively, after the dehydroxylation of the clay. Thermo-XRD analysis detected TEA-MONT tactoids with spacing 1.40 and 1.46?nm up to 300?°C. At 300 and 360?°C, LTSC-MONT tactoids were detected with spacing of 1.29?nm. At higher temperatures, HTSC-MONT-?? and -?? tactoids were detected with spacings of 1.28 and 1.13?nm, respectively. BTMA-MONT tactoids with spacings 1.46 and 1.53?nm were detected up to 250?°C. At 300 and 360?°C, LTSC-MONT tactoids were detected with a spacing of 1.38?nm. At higher temperatures, HTSC-MONT-?? and -?? tactoids were detected with spacings of 1.28 and 1.17?nm, respectively. At 650?°C, both clays were collapsed. HTSC-??-MONT differs from HTSC-??-MONT by having carbon atoms keying into the ditrigonal holes of the clay-O-planes. At 900?°C, the clay fraction is amorphous. Trace amounts of spinel and cristobalite are obtained from thermal recrystallization of amorphous meta-MONT. 相似文献
82.
Three related cyclic peptides, aeruginazole DA1497 (1), aeruginazole DA1304 (2), and aeruginazole DA1274 (3), were isolated from the freshwater cyanobacteria, Microcystis aeruginosa, bloom material collected on October 2007 from the Dalton water-reservoir in Northern Israel. Aeruginazoles DA1304 (2), DA1338 (4), and DA1372 (5) were isolated as an inseparable mixture from a bloom material of M. aeruginosa collected from the same water-reservoir on August 2000. Their structures were elucidated using a combination of various spectroscopic techniques, mainly NMR and MS, while the absolute stereochemistry of the chiral centers were determined by Marfey’s method. Aeruginazoles 1–3 were tested in various bioassays (antibacterial, cytotoxicity, and protease inhibition). Aeruginazole DA1497 (1) showed a mild antimicrobial activity against Staphylococcus aureus, but was inactive like the rest of the compounds in all other bioassays. 相似文献
83.
We consider an infinitely repeated two-person zero-sum game with incomplete information on one side, in which the maximizer
is the (more) informed player. Such games have value v
∞ (p) for all 0≤p≤1. The informed player can guarantee that all along the game the average payoff per stage will be greater than or equal to
v
∞ (p) (and will converge from above to v
∞ (p) if the minimizer plays optimally). Thus there is a conflict of interest between the two players as to the speed of convergence
of the average payoffs-to the value v
∞ (p). In the context of such repeated games, we define a game for the speed of convergence, denoted SG
∞ (p), and a value for this game. We prove that the value exists for games with the highest error term, i.e., games in which v
n (p)− v
∞ (p) is of the order of magnitude of . In that case the value of SG
∞ (p) is of the order of magnitude of . We then show a class of games for which the value does not exist. Given any infinite martingale 𝔛∞={X
k }∞
k=1, one defines for each n : V
n (𝔛∞) ≔E∑n
k=1 |X
k+1 − X
k|. For our first result we prove that for a uniformly bounded, infinite martingale 𝔛∞, V
n (𝔛∞) can be of the order of magnitude of n
1/2−ε, for arbitrarily small ε>0.
Received January 1999/Final version April 2002 相似文献
84.
We prove the direct sum conjecture for various sets of systems of bilinear forms. Our results depend on a priori knowledge of the complexity of at least one of the direct summands and its underlying algebraic structure. We also briefly survey some previous results concerning the complexity and structure of minimal algorithms for various direct sum systems. 相似文献
85.
We determine the maximum spectral radius for 0–1 matrices with m2 + l ones for l=2m, 2m ? 3 for all m and for a fixed l and m> M(l). Similar results are obtained for symmetric 0–1 matrix with zero diagonal. In all cases, equality is characterized. 相似文献
86.
We discuss the perturbation of continuum eigenvalues without analyticity assumptions. Among our results, we show that generally a small perturbation removes these eigenvalues in accordance with Fermi's Golden Rule. Thus, generically (in a Baire category sense), the Schrödinger operator has no embedded non-threshold eigenvalues.Supported in part by NSF Grant DMS 8602826 相似文献
87.
Hugo Pattyn Peter Hendrickx Karen Milants Jo de Wachter Shmuel Bukshpan 《Hyperfine Interactions》1993,79(1-4):807-813
The formation and properties of Cs inclusions in Mo and W are observed through a preimplanted133Xe(Cs) local probe, which is found to reside in three sites: a substitutional site, an interfacial one and a further site which is not detectable directly, but the presence of which can be inferred from the Mössbauer measurements. The location of the probe at the interface of small Cs inclusions is characterized by large Debye temperatures of around 200 K, a quadrupole interaction of +1.86(15) mms–1, which is close to known surface site values, and an isomer shift of –0.33(12) mms–1. From the latter value an approximate local pressure of 5 GPa is deduced. In W the site populations are followed as a function of Cs dose. The observed interchange of populations in the low dose range is thought to represent the initial formation of the second phase inclusions. 相似文献
88.
Pnina Ashkenazi Jürgen Kettenring Shmuel Migdal Arie L. Gutman David Ginsburg 《Helvetica chimica acta》1985,68(7):2033-2036
The title diketone has been prepared by a synthetic sequence beginning with decane-1,10-dicarboxylic acid. 相似文献
89.
Shmuel Cohen Georgia Wollmann Lina Ben-Dor Yizhak Marcus 《Journal of Crystal Growth》2004,270(3-4):589-592
Single crystals of the congruently melting equimolar mixture of magnesium nitrate hexahydrate and nickel nitrate hexahydrate have been grown. The compound crystallizes in a structure foreign to both components, namely in the monoclinic cobalt nitrate hexahydrate structure. The cations are located at random on the cation sub-lattice of the latter crystalline structure. 相似文献
90.