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991.
Open photoacoustic cell x-ray detection 总被引:1,自引:0,他引:1
A. C. Bento M. M. F. Aguiar H. Vargas M. D. da Silva I. N. Bandeira L. C. M. Miranda 《Applied physics. B, Lasers and optics》1989,48(3):269-272
A simple open-cell configuration photoacoustic x-ray detector is experimentally demonstrated. The front air chamber of a commercial electret microphone is used as the transducer medium of conventional photoacoustics. The observed signal is well described by the thermal diffusion model for the photoacoustic signal. 相似文献
992.
Francílio de C. Oliveira José Schneider Abner Siervo Richard Landers Ana M. G. Plepis Jean-Jacques Pireaux Ubirajara Pereira Rodrigues-Filho 《Surface and interface analysis : SIA》2002,34(1):580-582
Composites of Keggin heteropolymetalates have been prepared and characterized by SEM, XPS, 31P-magic angle spinning/nuclear magnetic resonance and differential scanning calorimetry. The phosphotungstic acid and phosphomolybdic acid form nanocomposites where the oxocluster structure is preserved and is highly dispersed over the material, probably inserted between the polymeric chains. Phosphovanadotungstic clusters suffer partial decomposition during composite formation, resulting in a biphasic microcomposite. The decomposition product, phosphotungstic acid presents surface segregation as shown by comparison of XPS and nuclear magnetic resonance results. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
993.
Luciano Canovese Fabiano Visentin Gavino Chessa Claudio Santo Paolo Uguagliati Giuliano Bandoli 《Journal of organometallic chemistry》2002,650(1-2):43-56
Neutral methyl- and acyl-palladium chloro complexes containing pyridylthioether ancillary ligands (R′N---SR) (R′=H, Me, Cl; R=Me, Et, i-Pr, t-Bu, Ph) have been synthesised and characterised by elemental analysis and spectroscopic methods. The reactivity of these complexes toward allene (allene=DMA=1,1-dimethylpropadiene; TMA=1,1,3,3-tetramethylpropadiene) insertion into the palladium–carbon bond has been studied by 1H-NMR and UV–vis techniques. The rate of reaction appears to be strongly influenced by the steric and electronic properties of the ancillary ligand. The distortion induced by the substituent R′ in position 6 of the pyridine ring on the main coordination plane of the substrate (allowed by sulphur sp3 hybridisation) renders the substrate itself more prone to nucleophilic attack by the allene. The rate of allene insertion can further be enhanced by lowering the basicity of the chelating atoms in the N---S moiety which results in an increase of electrophilicity of the palladium core, so that the rate constants measured in the case of the complexes containing the ligand 6-chloro-2-phenylthiomethylpyridine (ClN---SPh) are by far the greatest observed so far for similar reactions. Furthermore, on the basis of the indications emerging from the exhaustive study on the behaviour of all the related pyridylthioether methyl complexes, an associative asynchronous bond making mechanism for the rate determining nucleophilic attack by allene is proposed. 相似文献
994.
Olga M. S. Ritter Aloir A. Merlo Fabiano V. Pereira Nadya P. Da Silveira Erik Geissler J. Zukerman-Schpector 《Liquid crystals》2002,29(9):1187-1200
The synthesis of chiral side chain liquid crystalline polyacrylates with a two-stereogenic centre from L-alpha-aminoacid is described. The chiral tail is 2-chloroalcohol obtained from L-isoleucine and the spacer group has either four or eleven methylene units. The mesogenic moiety is derived from phenyl benzoate. The stereochemistry of the key intermediate (2 S ,3 S )-(+)-4- [1-(2-chloro-3-methyl)pentyloxy]phenyl benzoate ( 6 ) obtained by a Mitsunobu reaction was established by single crystal X-ray analysis. This result indicates that the nucleophilic displacement of chiral diazonium salts proceeds with overall retention of configuration. The liquid crystalline behaviour of polyacrylates P 13 and P 14 was investigated by DSC, optical microscopy, small angle X-ray scattering and depolarized light scattering. The polyacrylate P 13 , with eleven methylene units in the spacer, exhibits a chiral smectic A phase whereas the polyacrylate P 14 , with a spacer containing four methylene units, displays a chiral nematic phase. 相似文献
995.
A. M. D'A. Rocha Gonsalves Mariette M. Pereira 《Journal of heterocyclic chemistry》1985,22(3):931-933
meso-Tetraalkylporphyrinogens are easily formed and unexpectedely stable compounds. Only through forced oxidation can they efficiently be converted into porphyrins. meso-Tetraphenylphlorin was trapped as an intermediate in the Rothemund meso-tetraphenylporphyrin synthesis. 相似文献
996.
Paulo Henrique Trombetta Zannin Fabiano Belisário DinizWiliam Alves Barbosa 《Applied Acoustics》2002,63(4):351-358
This paper presents the results obtained in a study on environmental noise pollution in the city of Curitiba, Brazil. The equivalent sound level values—LAeq, 2hr—were measured and tabulated for 1000 locations spread over the urban zones of the city of Curitiba. It has been found out that 93.3% out of the locations display during the day equivalent sound levels over 65 dB(A), and 40.3% out of the total number of locations measured display during the day extremely high values of equivalent sound levels: over 75 dB(A). 相似文献
997.
M. L. Cardoso W. A. Ortiz A. J. A. de Oliveira E. C. Pereira 《Physica B: Condensed Matter》2002,320(1-4):192-194
The magnetic behavior as a function of magnetic field and temperature of nanostructures of Co deposited on insulator templates of Al2O3 is presented. The results show that the granular Co was formed inside the pores and the characteristics of granular ferromagnetics, such as high saturation of the magnetization and paramagnetic behavior at high magnetic fields, were observed. 相似文献
998.
Leonor Pérez-Trejo Arturo F. Méndez-Sánchez José Pérez-González Prof. Lourdes de Vargas 《Rheologica Acta》1996,35(2):194-201
An analysis of the flow of polymer solutions through capillaries by means of pressure profiles was performed in this work. The experiments were carried out with aqueous solutions of flexible and semirigid macromolecules, Polyox and Xanthan respectively. The influence of the macromolecules' conformation on the flow field development is reflected on the different magnitudes of the entry length, being of the order of 60 diameters for the solutions of rigid macromolecules, and of the order of 10 diameters for flexible ones. In addition, the calculated end effects were larger for the rigid macromolecules than for the flexible ones. From these results, it is found that an increase in the entrance length is observed when the pseudoplastic behavior of the polymer solutions is increased.Dedicated to Prof. Dr. J. Meissner on the occasion of his retirement from the chair of Polymer Physics at the Eidgenössische Technische Hochschule (ETH) Zürich, Switzerland 相似文献
999.
J. A. Facin D. Pereira E. C. C. Vasconcellos A. Scalabrin C. A. Ferrari 《Applied physics. B, Lasers and optics》1989,48(3):245-248
This work reports 83 new optically pumped far infrared laser lines, using deuterated methyl alcohol, CHD2OH, as active medium. For each line we list the measured wavelength, its polarization relative to the pump line, the optimum gas pressure and the CO2 laser pump power at the maximum absorption. 相似文献
1000.