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941.
We have used SOM and grid 3D and 4D QSAR schemes for modeling the activity of a series of dihydrofolate reductase inhibitors. Careful analysis of the performance and external predictivities proves that this method can provide an efficient inhibition model. 相似文献
942.
Synthesis and magnetic studies of a new class of organic spin clusters, possessing alternating connectivity of unequal spins, are described. Polyarylmethyl polyether precursors to the spin clusters, with linear and branched connectivity between calix[4]arene-based macrocycles, are prepared via modular, multistep syntheses. Their molecular connectivity and stereoisomerism are analyzed using NMR spectroscopy. The absolute masses (4-10 kDa) are determined by FABMS and GPC/MALS. Small angle neutron scattering (SANS) provides the radii of gyration of 1.2-1.8 nm. The corresponding polyradicals with 15, 22, and 36 triarylmethyls, which are prepared and studied as solutions in tetrahydrofuran-d(8), may be described as S' = 7/2, 1/2, 7/2 spin trimer (average S = 5-6), S' = 7/2, 1/2, 6/2, 1/2, 7/2 spin pentamer (average S = 7-9), and spin nonamer (average S = 11-13), respectively, as determined by SQUID magnetometry and numerical fits to linear combinations of the Brillouin functions. For spin trimer and pentamer, the quantitative magnetization data are fit to new percolation models, based upon random distributions of chemical defects and ferromagnetic vs antiferromagnetic couplings. The value of S = 13 is the highest for an organic molecule. 相似文献
943.
944.
We present a new method to show concentration of the upper tail of random variables that can be written as sums of variables with plenty of independence. We compare our method with the martingale method by Kim and Vu, which often leads to similar results.Some applications are given to the number X
G
of copies of a graph G in the random graph
(n,p). In particular, for G = K
4 and G = C
4 we improve the earlier known upper bounds on —ln (X
G
2
X
G
) in some range of p = p(n).* Research of the second author supported by KBN grants 2 P03A 032 16 and 2 P03A 015 23. 相似文献
945.
Tadeusz Borowiecki Andrzej Denis Wiesaw Grzegorczyk Andrzej Gobiowski 《Reaction Kinetics and Catalysis Letters》2002,77(1):163-172
For a long time the microbalance reactor has played an important role in catalyst deactivation studies, but it has a number of limitations. The initial temperatures of coking of Ni and Ni-Mo catalysts in the temperature-programmed reaction (TPReaction) of n-butane with steam are compared with the results of coking rates obtained by the traditional thermogravimetric method. The investigations show good agreement of the results. 相似文献
946.
Zimniak A 《Journal of mass spectrometry : JMS》2002,37(11):1145-1151
Two binuclear bis(tricarbonyliron) title complexes with N(2)Fe(2) tetrahedral cores, 1 and 2, respectively, which show different molecular folding resulting from the appearance (in 1), and absence (in 2) of the N-N sigma-bond, were compared in terms of mass spectral fragmentation routes. A multipath fragmentation noted for the molecule 1 revealing internal stress contrasts with the single-route fragmentation of 2. The fragmentation paths resulting from the admixtures were defined and analyzed from the fragment ion B/E and parent ion B(2)/E linked scan spectra. 相似文献
947.
948.
Alechia Crown Ines R. Moraes Andrzej Wieckowski 《Journal of Electroanalytical Chemistry》2001,500(1-2)
Ruthenium and osmium were deposited in submonolayer amounts on Pt(111) single crystal surfaces using the previously reported ‘spontaneous deposition’ procedure [Chrzanowski et al., Langmuir, 13 (1997) 5974]. Such surfaces were first explored using ex situ scanning tunneling microscopy (STM) to image the deposition characteristics of ruthenium and osmium islands on Pt(111). It was found that, using the spontaneous deposition procedure, a maximum coverage of 0.20 ML ruthenium is formed on the surface after 120 s of exposure to a RuCl3 solution in 0.1 M HClO4. A homogeneous deposition on the Pt(111) surface was found, with no observed preferential deposition on step edges or surface defect sites. In contrast, in the spontaneous deposition of osmium, osmium clusters form preferentially at, though not limited to, surface defect sites and step edges. Osmium island deposition occurs at a greater rate than ruthenium on Pt(111), and possible explanations are presented. Methanol activity on the Pt(111)/Ru and Pt(111)/Os surfaces is also studied, using the coverage values determined to yield the highest activity for methanol electro-oxidation (0.20 ML coverage for Ru and 0.15 ML for Os). At potentials more negative than 0.40 V vs. RHE, the Pt(111)/Ru surface yields a higher surface activity than Pt(111)/Os. However, at potentials more positive than 0.04 V, Pt(111)/Os exhibits demonstrably higher surface activity. The relevance of this data is discussed and future avenues of interest are indicated. 相似文献
949.
Andrzej Krasiński 《General Relativity and Gravitation》2001,33(1):145-161
The program Ortocartan for algebraic calculations in relativity has just been implemented in the Codemist Standard Lisp and can now be used under the Windows 98 and Linux operating systems. The paper describes the new facilities and subprograms that have been implemented since the previous release in 1992. These are: the possibility to write the output as Latex input code and as Ortocartan's input code, the calculation of the Ellis evolution equations for the kinematic tensors of flow, the calculation of the curvature tensors from given (torsion-free) connection coefficients in a manifold of arbitrary dimension, the calculation of the lagrangian from a given metric by the Landau-Lifshitz method, the calculation of the Euler–Lagrange equations from a given lagrangian (only for sets of ordinary differential equations) and the calculation of first integrals of sets of ordinary differential equations of second order (the first integrals are assumed to be polynomials of second degree in the first derivatives of the functions). 相似文献
950.
Andrzej Gzella 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(4):505-507
The X‐ray crystal structure analyses of 3β‐hydroxy‐11‐oxo‐18α‐olean‐12‐en‐28‐oic acid methyl ester ethanol solvate, C31H48O4·C2H6O, (I), and 3,11‐dioxo‐18α‐olean‐12‐en‐28‐oic acid methyl ester, C31H46O4, (II), are described. These two compounds differ only in the structure of ring A. In (I), ring A has a chair conformation, while in (II), it has a twisted boat conformation. In both compounds, ring C has a slightly distorted sofa conformation, rings B, D and E are in chair conformations, and rings D and E are trans‐fused. The asymmetric unit of (I) contains one molecule of ethanol linked by hydrogen bonds with two different molecules of (I). 相似文献