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11.
In this paper we give a method for constructing sharply 1-transitive permutation sets inside a finite permutation group with certain properties and we apply this method to obtain a family of sharply 1-transitive permutation subsets of the sharply 3-transitive permutation group M(p
2f
) on PG(1, p
2f
) for p
f
1 (mod 4).Work supported by G.N.S.A.G.A. and M.P.I. 相似文献
12.
13.
Substrate relaxation is shown to play an important role in the 1 : 2 regular chemisorption of hydrogen atoms above alternate carbon atoms in a graphite monolayer. Binding energy, population analysis and electron density maps show that the direct HC bond is strengthened on relaxation. 相似文献
14.
Axel Vogt 《manuscripta mathematica》1987,57(2):239-247
It Is shown that Elkik's results on deformations of rational singularities hold without Cohen-Macaulay assumptions: let f:XS be flat with normal fibres Xs and desingularisations s:YsXs; then the sets
are open for all d. 相似文献
15.
Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenylacetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal-ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pKa1 values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pKa2 and pKa3 values between 9.47-9.41 and 11.55-11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group. 相似文献
16.
Haralampus-Grynaviski N Ransom C Ye T Rôzanowska M Wrona M Sarna T Simon JD 《Journal of the American Chemical Society》2002,124(13):3461-3468
Urocanic acid, UCA, is characterized by two electronic transitions in the UV-B (280-320 nm) which comprise its broad absorption spectrum and give rise to wavelength-dependent isomerization quantum yields. The absorption spectrum of UCA extends into the UV-A (320-400 nm). Given the UV-A component of sunlight is significantly greater than the UV-B component it is hypothesized even weak UV-A photochemistry of UCA could be important for in vivo responses to UV radiation. Degenerate pump-probe experiments performed on t-UCA at several wavelengths in the UV-A reveal an excited-state absorption that undergoes a rapid, approximately 1 ps decay. Photoacoustic experiments performed on both the cis and trans isomers reveal the formation of a long-lived intermediate following UV-A excitation. The efficiency and action spectra for this latter photoactive process are presented and are similar for both isomers of UCA. Cholesterol hydroperoxide assays designed to investigate the nature of the UV-A photoreactivity of t-UCA confirm the production of reactive oxygen species. The bimolecular rate constant for the quenching of singlet oxygen by t-UCA is determined to be 3.5 x 10(6) M(-1) s(-1). Taking into consideration recent theoretical calculations and jet expansion studies of the electronic structure of gas-phase t-UCA, a model is proposed to explain the isomerization and photoreactivity of t-UCA in solution over the UV-A region. 相似文献
17.
J. R. Vogt C. C. Graham M. D. Glascock R. H. Cobean 《Journal of Radioanalytical and Nuclear Chemistry》1982,69(1-2):271-289
An extensive study of Mesoamerican obsidian source samples from 37 sites has been begun to better differentiate and define
the trace element content at known Mesoamerican obsidian quarries, with particular emphasis on those in Mexico. This paper
reports on the first results in that study as well as studies of sample contamination by grinding and results for the new
National Bureau of Standards No. 278 Obsidian SRM. 相似文献
18.
The frequency-domain technique is applied to measure the photodegradation rate of fluorescein in aqueous solutions. The illuminating light is modulated, and the changes in fluorescence from the illuminated region are detected synchronously. A constant flow rate is imposed on the fluorescein solution to control the mass transport of fluorescein into the illuminated region. The fluorescence response is described by a model that assumes that photodegradation occurs from the triplet excited state. The predictions of the model are consistent with the observed variations in the fluorescence response with flow rate, modulation frequency and incident power. We discuss in this article how the dependence of the model parameters on experimental conditions can be used to infer the photodegradation rate as well as some of the details of the photodegradation mechanism. The results are consistent with the known mechanism of photodegradation of fluorescein. The frequency-domain technique gives a photodegradation rate of 53 s(-1) in an air-saturated solution and 37 s(-1) in solutions purged with argon gas. 相似文献
19.
Carla Milanesi Roberta Biolo Elena Reddi Giuuo Jori 《Photochemistry and photobiology》1987,46(5):675-681
Abstract Balb/c mice bearing a transplanted MS-2 fibrosarcoma were injected with 2.5 mg kg 1 of either tetra(4-sulfonatophenyl/porphine (TPPS) in phosphate-buffered saline or 0.5 mg kg−1 of Zn2+ -phthalocyanine (Zn-Pc) incorporated into unilamellar liposomes of dipalmitoyl-phosphatidylcholine. Chromatographic studies showed that TPPS is mainly transported in the serum by globulins and albumin, while Zn-Pc is specifically bound by lipoproteins. Exposure of the injected mice to red light (300 J cm−2 ) caused extensive tumor necrosis. The ultrastructural analysis of tumor specimens taken from mice at 15 h after PDT showed that TPPS photoinduces a preferential necrosis of the neoplastic cells, while Zn-Pc causes severe photodamage to both the vascular system and the neoplastic cells. The different modes of tumor photosensitization by TPPS and Zn-Pc are discussed on the basis of the transport mechanism of the two dyes. 相似文献
20.
Zijp EJ van der Vlugt JI Tooke DM Spek AL Vogt D 《Dalton transactions (Cambridge, England : 2003)》2005,(3):512-517
Chiral aminophosphines Ph2PN(R)(CH2)nN(R)PPh2 1-4 [n= 2, R = CH(CH3)(Ph) 1; n= 3, R = CH(CH2CH3)(Ph) 2, n= 2, R = CH(CH3)(1-naphthyl) 3; n= 2, R = CH(CH3)(C6H11) 4] were synthesized by the reaction of ClPPh2 with the appropriate easily accessible enantiopure amine building blocks. For compounds 1 and 2, the corresponding selenides 5 and 6 were prepared to determine the electronic character of the phosphine moieties. By reaction of 1 with either PdCl2(cod) or PdCl(CH3)(cod) the cis-complexes 7 and 8 were obtained. The molecular structure for complex 7, cis-[PdCl2(1)], was determined by X-ray crystallography. Reaction of PtCl2(cod) with 1 or 2 yielded the corresponding monomeric cis-isomers 9 and 10. The rhodium derivative [RhCl(CO)(1)] (11) was obtained as a mixture of cis and trans-isomers. Preliminary results in the rhodium catalyzed hydroformylation of styrene and vinyl acetate, with ee's up to 51% and high regioselectivities, showed the potential of these chiral aminophosphines for homogeneous catalysis. 相似文献