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101.
Summary Purine derivative drugs, aminophylline, theophylline, xantinolnicotinate, 6-mercaptopurine, 6-thyoguanine, azathioprine, 1-methylxantine, 3-methylxantine, 1-methyluric acid, 1,3-dimethyluric acid, 6-thioxantine, 2-amino-6-methylmercaptopurine, were separated by thin-layer chromatography on rice starch and cellulose by three different solvent systems. Conditions for quantitative fluorodensitometric determination of purine derivatives drugs were investigated. 相似文献
102.
We show that for every n > 0 there is a planar topological disk A0 and n translates A1, A2, ..., An of A0 such that the interiors of A0, ..., An are pairwise disjoint, but with each Ai touching A0 for 1 ≤ i ≤ n. 相似文献
103.
A criterion used for the determination of first- and second-order magnetic phase transitions from purely magnetic methods is applied to manganese perovskites of formula La2/3(Ca1−xSrx)1/3MnO3. A crossover from first- to second-order character at a tolerance factor t=0.92 is found, which also brings about several variations in other physical properties. At t=0.92 a change from orthorhombic to rhombohedral symmetry also takes place. The impossibility of establishing static cooperative Jahn–Teller distortions in the rhombohedral symmetry is suggested as being responsible for the observed behaviour. 相似文献
104.
To gain an initial understanding of the copper-based catalysts in commercially important chemical reactions such as the oxygen-assisted water-gas shift reaction, we performed density-functional theory calculations, investigating the interaction of oxygen and copper, focusing on the relative stability of surface oxides and oxide surfaces of the O/Cu system. By employing the technique of “ab initio atomistic thermodynamics”, we show that surface oxides are only metastable at relevant pressures and temperatures of technical catalysis, with no stable chemisorption phase observed even at very low coverage. Although exhibiting only metastability, these surface oxides resemble the bulk oxide material both geometrically and electronically, and may serve as a precursor phase before onset of the bulk oxide phase. Having identified the bulk oxide as the most stable phase under realistic catalytic conditions, we show that a Cu2O(1 1 1) surface with Cu vacancies has a lower free energy than the stoichiometric surface for the considered range of oxygen chemical potential and could be catalytically relevant. 相似文献
105.
[reaction: see text] HOF.CH(3)CN, a very efficient oxygen-transfer agent, made readily from F(2), H(2)O, and CH(3)CN, was reacted with various 1,10-phenanthroline derivatives to form the corresponding N,N'-dioxides in good yields and short reaction times. 相似文献
106.
Mira J Rivadulla F Rivas J Fondado A Guidi T Caciuffo R Carsughi F Radaelli PG Goodenough JB 《Physical review letters》2003,90(9):097203
MnAs exhibits a first-order phase transition from a ferromagnetic, high-spin metal hexagonal phase to a paramagnetic, lower-spin insulator orthorhombic phase at T(C)=313 K. Here, we report the results of neutron diffraction experiments showing that an external magnetic field, B, stabilizes the hexagonal phase above T(C). The phase transformation is reversible and constitutes the first demonstration of a bond-breaking transition induced by a magnetic field. The field-induced phase transition is accompanied by an enhanced magnetoresistance of about 17% at 310 K. The phenomenon appears to be similar to that of the colossal magnetoresistance response observed in the Mn [corrected] perovskite family. 相似文献
107.
108.
Mira Sarkar 《Journal of Mathematical Analysis and Applications》1981,79(2):384-394
In this paper, a few separation properties and some aspects of subspace fuzzy topology have been studied, where both the crisp and the fuzzy elements have been taken into consideration. Since the conventional definition of compactness is not quite meaningful in Hausdorff fuzzy spaces (as introduced by us), a new more natural definition of proper compactness is given and a few properties resulting from this are established. 相似文献
109.
José Antonio Cuenca Mira 《Israel Journal of Mathematics》2013,193(1):343-358
In this paper we first characterize the pre-Hilbert algebras with a norm-one central idempotent e such that ‖ex‖ = ‖x‖ for any x ∈ A. This generalizes a well-known theorem by Ingelstam asserting that every alternative pre-Hilbert algebra with a unit 1 such that ‖1‖ = 1 is isomorphic to ?, ?, ? or $\mathbb{O}$ . We also show that every power-associative pre-Hilbert algebra satisfying ‖x 2‖ = ‖x‖2 for every element has a unique nonzero idempotent, which is a unit element. In fact, the same conclusion will be proved in a more general setting. As application we give some conditions characterizing when a real algebra A, which is a prehilbert space, is isomorphic to one of the Hilbert algebras ?, ?, ? or $\mathbb{O}$ . 相似文献
110.
Miraç Ocak Tuğba Ak Ayşe Aktaş Nurhayat Özbek Osman Can Çağılcı Abidin Gümrükçüoğlu Halit Kantekin Ümmühan Ocak Hakan Alp 《Journal of fluorescence》2017,27(1):59-68
Four new Schiff base ligands carrying naphthalene groups were prepared from the reaction of 2,4-diamino-6-methyl-1,3,5-triazine and 2,4-diamino-6-undecyl-1,3,5-triazine with 2-hydroxy-1-naphthaldehyde. The influence of a series of metal ions including Cu2+, Co2+, Hg2+, Al3+, Cr3+, Fe3+, Pb2+, Ni2+, Cd2+, Zn2+, Mn2+, Ag+, Ba2+, Ca2+ and Mg2+ on the spectroscopic properties of the ligands was investigated by means of absorption and emission spectrometry. The results of spectrophotometric and spectrofluorimetric titrations disclosed the complexation stoichiometry and complex stability constant of the ligands with metal ions. A simple spectrofluorimetric method was developed using the Schiff base derived from 2,4-diamino-6-undecyl-1,3,5-triazine to determine Hg2+ ion. No cleanup or enrichment of the tap water sample was required. A modified standard addition method was used to eliminate matrix effect. The standard addition graph was linear between 0.2 and 2.6 mg/L in determination of Hg2+. Detection and quantification limits were 0.08 and 0.23 mg/L, respectively. The simple and cost-effective method can be applied to water samples. 相似文献