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51.
Oleg V. Belegradek 《Proceedings of the American Mathematical Society》1996,124(2):623-625
We show that for any arithmetical -degree there is a first order decision problem such that has -degree for the free 2-step nilpotent group of rank 2. This implies a conjecture of Sacerdote.
52.
53.
Structurally novel cyclitols, 1-aryl-1-deoxyconduritols F, were efficiently prepared from d-xylose, utilizing RCM as a key step. Various aromatic residues were incorporated in the cyclitol skeleton with total stereochemical control, utilizing a diastereoselective aryl cuprate addition to a gamma-alkoxy enoate. The synthetic route establishes a firm foundation for a practical synthesis of the antitumor alkaloid pancratistatin and its aryl analogues. [structure: see text] 相似文献
54.
55.
I. E. Baranov S. A. Demkin V. K. Zhivotov I. I. Nikolaev V. D. Rusanov N. G. Fedotov 《High Energy Chemistry》2004,38(3):191-195
A method for enhancing the hydrocarbon pyrolysis process by introducing atomic hydrogen into the reaction medium from an arcjet plasma source was considered. It was shown that hydrogen atoms could effectively be introduced by mixing under low pressure. The atomic hydrogen–stimulated methane pyrolysis process was experimentally studied in a continuous stirred reactor with a plasma plume. When hydrogen atoms were present in the plasma jet, the amount of the valuable product increased by a factor of two. 相似文献
56.
Novel approximate methods for calculating the vibrational structure of the electronic spectra of polyatomic molecules—a method
for the direct calculation of the overlap integrals of vibrational wave functions for the electronic states involved in a
transition and a variational method for the solution of the vibrational problem for the excited states—are discussed. The
methods are based on the consideration of the displacement and entanglement of normal coordinates, the quasiorthogonality
of the Dushinsky transformation, and the classification of the states by total vibrational quantum numbers. Matrix perturbation
theory is employed. It is shown that the accuracy of these methods compares well with the accuracy of the available “exact”
techniques (the errors are ∼1 cm−1 for frequency and 10% for relative intensity). At the same time, calculations by the new methods are performed more than
two orders of magnitude faster than by the previously known methods.
K. A. Timiryazev Agricultural Academy, Moscow. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 217–230, March–April, 1995.
Translated by I. Izvekova 相似文献
57.
58.
It has been shown that 1,3-thiazolidine-2,4-dione and 1,3-oxazolidine-2,4-dione react with hydrazine with a rearrangement of the ring to form a triazolinone ring. In each case, the reaction begins with the formation of an ionic adduct of hydrazine with the azolidinedione. On heating, the adduct undergoes decyclization (water catalyzes the process). The further course of the reaction is governed by the temperature and pH of the medium, which determine whether dehydration of the intermediate product with the formation of a triazolinone ring (in acid media) or rearrangement into a 1-acylsemicarbazide (at elevated temperatures) predominates. The influence of substituents in the thiazolidinone ring on the course of the reaction has been studied.For Communication I, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 7, pp. 991–996, July, 1970. 相似文献
59.
The adsorption of triethylenediamine (TEDA) at 300 K is observed to occur via hydrogen bonding to isolated Al-OH groups on the surface of partially dehydroxylated high area gamma-Al(2)O(3) powder. This form of bonding results in +0.3 to +0.4% blue shifts in the CH(2) scissor modes at 1455 cm(-1) and a -0.4% red shift in the CN skeletal mode at 1060 cm(-1), compared to the gas-phase frequencies. Other modes are red shifted less than 0.1%. The isolated OH modes are red shifted by -200 to -1000 cm(-1) due to the strong hydrogen bonding association of Al-OH groups with an N atom in TEDA. Thermal desorption of adsorbed TEDA from the surface occurs in the range 300-700 K. Mass spectral and infrared studies indicate that the decomposition of TEDA occurs on Al(2)O(3) above 725 K, and that C-H bonds are broken, forming adsorbed species with N-H bonds which are stable to 1000 K or above. In contrast to adsorption at 300 K, adsorption of TEDA at 85 K results in the formation of a condensed ice of TEDA, which covers the outer surface of the porous Al(2)O(3) and which does not interact with Al-OH groups inside the porous powder due to immobility. 相似文献
60.
Kolen'ko YV Kovnir KA Gavrilov AI Garshev AV Meskin PE Churagulov BR Bouchard M Colbeau-Justin C Lebedev OI Van Tendeloo G Yoshimura M 《The journal of physical chemistry. B》2005,109(43):20303-20309
Mesoporous nanosized TiO2 and Zn(x)Ti(1-x)O(2-x) solid solution having a Zn content below 10 mol % with a particles size between 13 and 17 nm are prepared by a template-free sol-gel method followed by high-temperature supercritical drying in 2-propanol. The structural, textural, and electronic properties of the obtained nanomaterials are methodically investigated by using XRD, SEM, TEM, ED, HREM, EDX, ICP-OES, N(2) adsorption-desorption, Raman spectroscopy, and diffuse reflectance UV-vis spectroscopy. It is shown that the proposed synthesis technique leads to the formation of a Zn(x)Ti(1-x)O(2-x) solid solution based on the anatase crystal structure rather than a two-phase sample. High-resolution electron microscopy and electron diffraction indicate that the distribution of zinc atoms over the anatase structure does not lead to a considerable deformation of the crystal structure. 相似文献