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71.
Marcelo Kobelnik Douglas Lopes Cassimiro Diógenes dos Santos Dias Clóvis Augusto Ribeiro Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2012,108(3):1281-1286
The ara?á is a well-known fruit, which belongs to the Myrtaceae family, Psidium cattleianum Sabine species, frequently found in the southern region of Brazil. The extraction of ara?a oil was carried out from seeds, and the fatty acid profile of this oil indicates the predominant presence of linoleic acid (81.38%). Thermogravimetry, derivative thermogravimetry, and differential scanning calorimetry (DSC) were used to characterize this oil. In addition, this oil was evaluated by DSC from 25 to ?60?°C, where the crystallization behavior was verified. Details concerning thermal decomposition as well as data of kinetic parameters of these stages have been described here. The kinetic behavior of the thermal decomposition was evaluated from several heating rates with mass samples of 5 and 20?mg in open crucibles under nitrogen and synthetic air atmospheres. 相似文献
72.
Marques R. F. C. Zorel H. E. Crespi M. S. Jafelicci M. Paiva-Santos C. O. Varanda L. C. Godoi R. H. M. 《Journal of Thermal Analysis and Calorimetry》1999,56(1):143-149
The compound obtained via state solid reaction of the La2O3 and SrO oxides and expose the room atmosphere shows the crystallographic data of the compound reported as La2SrOx. However, thermogravimetric, differential thermal analysis and XRD with controlled temperature indicated that the stoichiometry
of the compound is 2La(OH)3-SrCO3, which structural parameters were determined by using the Rietveld method. It was verified that when the compound exposed
at room atmosphere, the mixture oxide absorbs H2O and CO2 producing hydroxide and carbonate of lanthanum and strontium, respectively, which thermal decomposition occurs by the same
steps, producing the La2O3-SrO.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
73.
Marcelo Kobelnilk Gustavo Guadagnucci Fontanari Douglas Lopes Cassimiro Clóvis Augusto Ribeiro Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2045-2052
Coffee seeds are a source for obtaining oil which is used in the candy, soluble coffee, and cosmetics industries. The main purpose of this study was the investigation of the lipid profile and thermal behavior of the roasted and in nature coffee oil of Arabica and Robusta species, using thermogravimetry, differential thermal analysis, derivative thermogravimetry, differential scanning calorimetry (DSC), and modulated DSC. Details concerning the thermal decomposition as well as data of the kinetic parameters have been described here. The kinetic studies were evaluated from several heating rates with a sample mass of 10 mg in open crucible under nitrogen atmospheres. The obtained data were evaluated with the isoconversional kinetic method, where the values of activation energy (E a/kJ mol?1) were evaluated in function of the conversion degree (α). In addition, this oil was evaluated by modulated DSC from 25 to ?60 °C, where the transition phase behavior was verified. 相似文献
74.
Competing Pathways in the Photogeneration of Didehydrotoluenes from (Trimethylsilylmethyl)aryl Sulfonates and Phosphates 下载免费PDF全文
Stefano Crespi Dr. Davide Ravelli Dr. Stefano Protti Prof. Angelo Albini Prof. Maurizio Fagnoni 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(52):17572-17578
The scope of the photochemical generation of α,n‐didehydrotoluene diradicals from aryl sulfonates and phosphates and their chemistry are explored. The thermally inaccessible α,2‐ and α,4‐ intermediates are efficiently obtained by irradiation of ortho‐ and para‐(trimethylsilylmethyl)phenyl triflates through heterolytic splitting of the ester anion from the substrate in the triplet state. Triplet phenyl cations are formed and the loss of trimethylsilyl cation from them affords the desired diradicals (3Me3SiCH2C6H4‐OZ→3Me3SiCH2C6H4+→ ? CH2C6H4 ? ). Triplet sensitization is required, for which acetone is used throughout. Direct irradiation leads, on the contrary, to photo‐Fries fragmentation (1Me3SiCH2C6H4O‐Z→Me3SiCH2C6H4O ? +Z ? ). With mesylates, where ester cleavage is less convenient, a further competition from the triplet is direct desilylation. Didehydrotoluenes are also obtained from the corresponding phosphates, although with poor efficiency. 相似文献
75.
Zhang S Li J Bartell J Ke X Nisoli C Lammert PE Crespi VH Schiffer P 《Physical review letters》2011,107(11):117204
We have studied the moment correlations within triangular lattice arrays of single-domain coaligned nanoscale ferromagnetic islands. Independent variation of lattice spacing along and perpendicular to the island axis tunes the magnetostatic interactions between islands through a broad range of relative strengths. For certain lattice parameters, the sign of the correlations between near-neighbor island moments is opposite to that favored by the pairwise interaction. This finding, supported by analysis of the total correlation in terms of direct and convoluted indirect contributions across multiple pairwise interactions, indicates that indirect interactions and/or those mediated by further neighbors can be tuned to be dominant, with implications for the wide range of systems composed of interacting nanomagnets. 相似文献
76.
Ke X Li J Nisoli C Lammert PE McConville W Wang RF Crespi VH Schiffer P 《Physical review letters》2008,101(3):037205
We study ac demagnetization in frustrated arrays of single-domain ferromagnetic islands, exhaustively resolving every (Ising-like) magnetic degree of freedom in the systems. Although the net moment of the arrays is brought near zero by a protocol with sufficiently small step size, the final magnetostatic energy of the demagnetized array continues to decrease for finer-stepped protocols and does not extrapolate to the ground-state energy. The resulting complex disordered magnetic state can be described by a maximum-entropy ensemble constrained to satisfy just nearest-neighbor correlations. 相似文献
77.
Carbon nanotubes are one dimensional and very narrow. These obvious facts imply that, under doping with boron and nitrogen, microscopic doping inhomogeneity is much more important than for bulk semiconductors. We consider the possibility of exploiting such fluctuations to create interesting devices. Using the self-consistent tight-binding technique, we study heavily doped highly compensated nanotubes, revealing the spontaneous formation of structures resembling chains of random quantum dots, or nanoscale diodelike elements in series. We also consider truly isolated impurities, revealing simple scaling properties of bound state sizes and energies. 相似文献
78.
The electronic structure of graphitic cones exhibits distinctive topological features associated with the apical disclinations. Ahranov-Bohm magnetoconductance oscillations (period Phi(0)) are completely absent in rings fabricated from cones with a single pentagonal disclination. Close to the apex, the local density of states changes qualitatively, either developing a cusp which drops to zero at the Fermi energy, or forming a region of nonzero density across E(F), a local metallization of graphite. 相似文献
79.
Rinaldo Cervellati Nicoletta Crespi‐Perellino StanleyD. Furrow Anacleto Minghetti 《Helvetica chimica acta》2000,83(12):3179-3190
Inhibitory effects by addition of aqueous extracts of soy flour to an active Briggs‐Rauscher mixture are reported. The effect consists of an immediate cessation of oscillations, but, after some time, the oscillatory behavior is regenerated with amplitude and frequency different from those observed in a reference mixture. The inhibition time depends linearly on the concentration of substances contained in the extract in a wide range of concentration. The inhibitory effects are due to the high free‐radical scavenging activity of substances contained in the soy flour. Two preponderant products contained in the soy flour extract were identified and characterized as malonyldaidzin and malonylgenistin. The antioxidant activity of these isoflavones contained in the extracts was determined on the basis of the inhibition time. A qualitative mechanistic explanation of the inhibitory effects is given. Our findings are decisive indirect evidence of involvement and important role played by HOO. radicals in establishing oscillations in the Briggs‐Rauscher (BR) system. The linear relationship between the inhibition time and the whole‐mass concentration of antioxidant contained in soy extracts added to a BR mixture is an indication of the possibility to develop and implement an analytical procedure for monitoring the activity of antioxidant scavengers of free radicals based on the oscillating Briggs‐Rauscher reaction. 相似文献
80.
Hernani S. Barud Clóvis A. Ribeiro Jorge M. V. Capela Marisa S. Crespi Sidney. J. L. Ribeiro Younes Messadeq 《Journal of Thermal Analysis and Calorimetry》2011,105(2):421-426
Cellulose can be obtained from innumerable sources such as cotton, trees, sugar cane bagasse, wood, bacteria, and others.
The bacterial cellulose (BC) produced by the Gram-negative acetic-acid bacterium Acetobacter xylinum has several unique properties. This BC is produced as highly hydrated membranes free of lignin and hemicelluloses and has
a higher molecular weight and higher crystallinity. Here, the thermal behavior of BC, was compared with those of microcrystalline
(MMC) and vegetal cellulose (VC). The kinetic parameters for the thermal decomposition step of the celluloses were determined
by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and at heating
rates of 5, 10, and 20 °C/min, the E
α
and B
α
terms could be determined and consequently the pre-exponential factor A
α as well as the kinetic model g(α). The pyrolysis of celluloses followed kinetic model
g(a) = [ - ln(1 - a)]1 \mathord