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排序方式: 共有410条查询结果,搜索用时 15 毫秒
1.
P. Di Martino P. Conflant M. Drache J. -P. Huvenne A. -M. Guyot-Hermann 《Journal of Thermal Analysis and Calorimetry》1997,48(3):447-458
The polymorphic forms II and III of paracetamol were obtained by melting the marketed form I. Under the melting and cooling conditions used, it was possible to obtain forms I, II and III. The recrystallization conditions and the physical properties of forms II and III were investigated by means of various techniques: thermomicroscopy, DSC analysis, infrared microspectrometry and X-ray powder diffraction at room temperature and as a function of temperature. Form III was found to be very unstable. However, its formation seems to be an important intermediate step in the preparation of form II. 相似文献
2.
A. Ouardaoui D. M. Martino C. A. Steren H. van Willigen 《Applied magnetic resonance》1997,13(3-4):275-284
The mechanism of 4-chlorophenol (4CP) photolysis was investigated with the aid of Fourier Transform Electron Paramagnetic Resonance (FT-EPR) and pulsed-laser photolysis combined with High Performance Liquid Chromatography (HPLC) detection-of stable (diamagnetic) products. With FT-EPR transient free radicals produced by pulsed-laser excitation of solutions of 4CP in alcohols could be identified. Time profiles of the FT-EPR spectra provided information on reaction kinetics and Chemically Induced Dynamic, Electron Polarization (CIDEP) effects. It was found that 4CP photolysis in alcohols leads to the simultaneous formation of the phenoxyl radical and radicals produced by hydrogen abstraction from the solvent. CIDEP patterns establish that these radicals are formed in a reaction sequence involving a triplet state precursor and radical pair intermediate. Results of earlier transient optical absorption measurements indicate that the triplet precursor must be the carbene 4-oxocyclohexa-2,5-dienylidene. This assignment is supported by the finding that photolysis of quinone diazide in a hydrogen-donating solvent gives the same free radical products as those obtained from 4CP. The formation of the phenoxyl radical intermediate accounts for the finding that photolysis of deoxygenated solutions of 4CP in alcohols gives phenol as stable diamagnetic product. By contrast, photolysis of aerated and deoxygenated aqueous solutions of 4CP produces benzoquinone and hydroquinone as primary products, respectively. 相似文献
3.
FexNi100−x nanometric films were deposited on SiO2/Si substrates at room temperature using the pulsed laser deposition technique. The targets were Fe-Ni amorphous magnetic foils with composition Fe50Ni50, Fe35Ni65 and Fe22Ni78. Morphological and structural properties of the deposited films were investigated using scanning electron microscopy, Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, and X-ray reflectivity. Electrical and magnetic characteristics of the films were investigated by using the four-point probe and the magneto-optic Kerr effect techniques, respectively. The film properties are strictly dependent on the Fe-Ni compositional ratio. 相似文献
4.
5.
Jill Dietz John Martino Stewart Priddy 《Proceedings of the American Mathematical Society》1996,124(7):2261-2266
We determine the cohomology algebras for all groups with a metacyclic Sylow -subgroup. The complete -local stable decomposition of the classifying space is also determined.
6.
Characterization of Two Light-Harvesting Subunits Isolated from the Brown Alga Pelvetia canaliculata: Heterogeneity of Xanthophyll Distribution 总被引:1,自引:0,他引:1
Alessandra De Martino Dominique Douady Bernard Rousseau Jean Claude Duval Lise Caron 《Photochemistry and photobiology》1997,66(2):190-197
The main light-harvesting fraction from Pelvetia canaliculata was isolated on a sucrose density gradient from digitonin-solubilized chloroplasts. After further solubilization by dodecyl maltoside, the bulk fraction was separated into two subunits by preparative isoelectric focusing. The more acidic brown fraction was mainly composed of 22 kDa polypeptides having an apparent pI of 4.55. Its pigment composition was very simple, containing chlorophyll (Chi) a, Chi c and fucoxanthin. The in vivo spectral properties of fucoxanthin, namely a shift in light absorption to the green and efficient energy transmission to Chi a, were conserved in this subunit. No xanthophyll associated with photoprotection was found in this band, even when obtained from photoinhibited thalli. The less acidic green band contained predominantly 22 kDa polypeptides that were resolved into numerous components by denaturing isoelectric focusing. Its pigment composition was more complex, containing, in addition, pigments of the so-called xanthophyll cycle. In photoinhibited thalli, about half of the violaxanthin was converted into antheraxanthin and zeaxanthin. All the pigments of the xanthophyll cycle were specifically associated with this subunit, and it may thus have a central role in the thermal dissipation of the absorbed light energy as postulated for light-harvesting complex II isolated from green plants. 相似文献
7.
C. Ferrero M. N. Martino N. E. Zaritzky 《Journal of Thermal Analysis and Calorimetry》1996,47(5):1247-1266
Differential scanning calorimetry (DSC) was used to analyze the influence of different hydrocolloids (xanthan, guar, and locust bean gums, carboxymethylcellulose and sodium alginate) on the gelatinization of corn starch in systems with starch concentration ranging between 0.1 and 0.7 g starch/g mixture. The reduction of available water produced a shift in gelatinization temperature, especially of the conclusion temperature. The effect was more marked for ionic hydrocolloids. The influence of hydrocolloids on glass transition temperature (T
g) of gelatinized starch suspensions and on the glass transition temperature of the maximally freeze-concentrated solute/unfrozen water matrix (T
g) was also studied.T
g onset values ranged between –4.5 and –5.5C for corn starch pastes with and without hydrocolloids. Those hydrocolloids that increased the viscosity of the unfrozen matrix inhibited additional ice formation during thawing (devitrification).Starch concentration and final heating temperature were found to be relevant factors affecting the kinetics of amylopectin retrogradation during frozen storage at –4C. Xanthan gum failed to prevent amylopectin retrogradation; this observation could be attributed to the fact that gums act outside the starch granule, while amylopectin retrogradation takes place within the granule. 相似文献
8.
We performed ab initio molecular orbital (MO) calculations using Hartree—Fock SCF, and second- and fourth-order Møller—Plesset perturbation theory for hydrogen migration reactions on the singlet vinyl fluoride potential energy surface. We used different basis sets and polarization functions to obtain the stationary point geometries and activation barriers. Basis set and the polarization function extension have small effects, while the correlation energy evaluation leads to new conclusions for one of the studied reactions: the product singlet CHCH2F is not a true local minimum on the potential energy surface. 相似文献
9.
Enrico DRIOLI Enrica FONTANANOVA Marcella BONCHIO Mauro CARRARO Martino GARDAN Gianfranco SCORRANO 《催化学报》2008,29(11):1152-1158
The design of new heterogeneous photooxygenation systems able to employ visible light, oxygen, mild temperatures, and solvent with a low environmental impact has been investigated. In particular, the heterogenization of decatungstate (W10O4-32), a polyoxometalate with photocatalytic activity in oxidation reactions, has been carried out in polymeric membranes of polyvinylidenefluoride. The polymeric catalytic membranes prepared by phase inversion technique have been successfully applied in the aerobic mineralization of phenol in water, which was used as an example of organic pollutant. In order to evaluate the effect of the polymeric environment on the overall catalyst behavior, we have also heterogenized the decatungstate (opportunely functionalized) in perfluorinated membrane made of Hyflon. The photocatalytic composite membranes are characterized by different and tuneable properties depending on the nature of the polymeric micro-environment, in which the catalyst is confined. Moreover, the selective separation function of the membrane results in enhanced performance in comparison with homogeneous reactions. 相似文献
10.
Jorge L. Flores Gastón A. Ayubi Julia R. Alonso Ariel Fernández J. Matías Di Martino José A. Ferrari 《Optik》2013
We present a hybrid method for segmentation of intensity images, which combines an optical contouring technique and digital algorithms for linking edge points or image segmentation. In a first stage, the digital image to be processed is displayed in a twisted-nematic liquid-crystal display (LCD), which is placed between a polarizer–analyzer pair at 45 deg (instead of 90 deg as occurs in standard LCDs). It is not difficult to demonstrate that the proposed setup produces a resultant image with very pronounced dark contours at middle intensity. After the optical preprocessing, two different digital algorithms are applied: an edge linking algorithm (modified chain code) and a simple thresholding technique for image segmentation. The proposed procedure works well with monochromatic and color images. The method could be useful as a robust technique for segmentation of large images in real-time, which presents potential applications in medical and biological imaging. 相似文献