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31.
Xin Liu 《Graphs and Combinatorics》1995,11(3):267-273
LetG be ak-connected (k 2) graph onn vertices. LetS be an independent set ofG. S is called essential if there exist two distinct vertices inS which have a common neighbor inG. LetV
r, be a clique which is a complete subgraph ofG. In this paper it is proven that if every essential independent setS ofk + 1 vertices satisfiesS V
r , thenG is hamiltonian, orG{u} is hamiltonian for someu V
r, orG is one of three classes of exceptional graphs. Our theorem generalizes several well-known theorems. 相似文献
32.
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34.
The addition of carboxylic acids to terminal alkynes is efficiently catalyzed by the early transition-metal complex Re(CO)5Br in toluene or n-heptane at 110 degrees C in an air atmosphere, affording the anti-Markovnikov adducts in good yields with high selectivity. In most cases, the reactions afford unusual Z-adduct predominantly. When n-heptane was used as solvent, Re(CO)5Br can be partly recovered from the reaction mixture. 相似文献
35.
A novel layered K(4)Ag(2)Sn(3)S(9) x 2KOH was synthesized solvothermally. A mixture of ethanol and HSCH(2)CH(SH)CH(2)OH was used for the synthesis. The HSCH(2)CH(SH)CH(2)OH plays an important role and appears to serve as a mineralizer for the solvothermal reaction. A layer comprises Sn(3)S(9)(6)(-) clusters linked by Ag(+) ions and possesses two types of 1D channels in which potassium ions are located. The compound crystallizes in the monoclinic P2(1)/m space group [a = 7.8071(2) A, b = 27.3508(1) A, c = 10.5008(2) A, alpha = 90 degrees, beta = 103.874(1) degrees, gamma = 90 degrees, Z = 4]. Its crystal structure, composition analysis, and IR are presented. 相似文献
36.
A facile process to prepare uniform dumbbell-shaped ZnO crystallites was presented. The evidence in this Article discovered a unique morphological effect on the UV-blocking property. The as-prepared ZnO crystallites were characterized by XRD, HRTEM, FESEM, UV-blocking, and Raman scattering spectra. Our tentative investigation created a breakthrough to both the ultrahigh "Ultraviolet protection factor" (UPF) and the overall-range of complete UV-radiation blocking. Therefore, the as-prepared structural material demonstrated a significant advance in protective functional treatment and provided a potential commercialization. 相似文献
37.
Equilibrium gas-phase acidities of the six isomeric cyclohexanediols were measured in a Fourier transform ion cyclotron resonance mass spectrometer. Although all six cyclohexanediols have the same functional groups and similar structures, the acidities vary over 11 kcal/mol. This large difference is due mostly to the balance between hydrogen bonding and geometric strain. To understand the origins of the acidity differences in more detail, the conformations and energetics of the cyclohexanediols were studied using density functional theory, which gave good agreement with the experimental acidities. Finally, methanol-methoxide and methanol-methanol interactions were used as a model for the hydrogen bonding. 相似文献
38.
An atomic-absorption spectrometric method is reported for the determination of cobalt, nickel, and copper in a variety of geological materials including iron- and manganese-rich, and calcareous samples. The sample is decomposed with HP-HNO3 and the residue is dissolved in hydrochloric acid. Ammonium fluoride is added to mask iron and 'aluminum. After adjustment to pH 6, cobalt, nickel, and copper are chelated with sodium diethyl-dithiocarbamate and extracted into methyl isobutyl ketone. The sample is set aside for 24 h before analysis to remove interferences from manganese. For a 0.200-g sample, the limits of determination are 5–1000 ppm for Co, Ni, and Cu. As much as 50% Fe, 25% Mn or Ca, 20% Al and 10% Na, K, or Mg in the sample either individually or in various combinations do not interfere. Results obtained on five U.S. Geological Survey rock standards are in general agreement with values reported in the literature. 相似文献
39.
The vanadium trapping effect of Mg and La containing additives in cracking catalyst contaminated with 2300 ppm Ni and 4700 ppm V has been analyzed by microactivity test (MAT) and imaging secondary ion mass spectrometry (SIMS). The results of SIMS imaging are consistent with cracking activity data and show that the La/spinel is a superior vanadium trap for the fluid catalytic cracking of hydrocarbons (FCC) operation. La/spinel serves as a dual function additive for both vanadium trap and SOx removal. The optimum amount of La/spinel added to the cracking catalyst is about 15% by weight. This results in an increased catalytic activity, an increase in gasoline yield, and a decrease in coke and gas factors. The MgAl2O4 phase of Mg/Al2O3 additive is found capable of trapping vanadium while its MgO of Mg/Al2O3 phase can migrate to zeolite particles (the active component of the FCC catalyst) that, in turn, causes a decline in the activity of that catalyst. 相似文献
40.
双电层相互重叠时蒙脱胶体表面阴离子的负吸附 总被引:2,自引:0,他引:2
本文用Ag-AgCl电极判断平衡,测定双电层处于不同重叠程度下肢体表面阴离子的负吸附量Γ.结果表明,胶体表面双电层相互重叠程度可由两胶体表面间的中点电位φd与外Helmhotz面处的电位φd之比表征;阴离子负吸附随双电层重叠程度和电解质浓度的增加而显著减小. 相似文献