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971.
Diego Oliveira Cordeiro Amanda Duarte Gondim Antonio Souza Araújo Marta Maria da Conceição Antonio Gouveia de Souza Valter José FernandesJr 《Journal of Thermal Analysis and Calorimetry》2017,127(2):1253-1260
The aim of this work was to evaluate the influence of the purification process on the stability of Jatropha curcas biodiesel. The biodiesel was obtained using a variety of purification processes: three wet methods with different drying processes (vacuum oven, conventional oven and anhydrous sodium sulfate) and one dry method (purification with adsorbent magnesium silicate). Biodiesel was characterized through the analysis of carbon residue, acidity index, infrared and gas chromatography. The composition J. curcas oil indicated 56.3 % of unsaturated fatty acids and 43.7 % of saturated fatty acids. Jatropha oil presented high quantity of saturated acids, which are less susceptible at oxidation. The biodiesel sample that was chemically purified (PUsq) presented better purity, indicating be the process more efficient in remove the residues of synthesis. Thermogravimetric curves of purified biodiesel by wet method, PUsq, with chemical drying using anhydrous sodium sulfate, and PUsv, with vacuum drying, showed the highest initial decomposition temperatures, indicating higher thermal stability. The carbon residue and infrared analyses suggested that contamination by catalyst residue is a determining factor in reduction of the oxidative stability of biodiesel. The oxidative stability was evaluated using Rancimat and pressure differential scanning calorimetry. Biodiesel samples showing better oxidative stability were purified using PUsq and PUsv, which obtained stability of 6 h using the Rancimat technique, the minimum limit set by Brazilian legislation, without the addition of antioxidant, suggesting that these methods least influenced the stability of biodiesel. 相似文献
972.
Veronika Takács-Kollár Miklós Nyitrai Dénes Lőrinczy Gábor Hild 《Journal of Thermal Analysis and Calorimetry》2017,127(2):1261-1266
Differential scanning calorimetry was applied to compare the effects of mammalian twinfilin-1 or toxofilin on the thermodynamic properties of actin monomer. Although twinfilin and toxofilin have different structure and actin-binding sites, they similarly increased the thermodynamic stability of monomeric actin. The mammalian twinfilin increased, while the toxofilin did not significantly change the T1/2 value (the width at half-height of the transition peak) during the complex formation between the actin and the monomer binding proteins. In case of toxofilin, the EA value (activation energy) significantly increased compared to twinfilin where the activation energy was nearly insensitive to the complex formation. It seems that toxofilin can achieve its main function as an actin monomer sequestering protein by more effectively and consistently modifying the basic thermodynamic properties of the monomeric actin. 相似文献
973.
Alex Virgilio Renata Stabile Amais Daniela Schiavo José Anchieta Gomes Neto Joaquim de Araújo Nóbrega 《Analytical letters》2017,50(5):842-852
A procedure for the determination of As, Cd, Cr, Ni, Pb, and V in phytotherapy medicines by inductively coupled plasma–tandem mass spectrometry is reported. The use of tandem mass spectrometry with oxygen into an octopole reaction system at various gas flow rates and the combination of on-mass and mass-shift modes was evaluated. Cadmium, Cr, Ni, and Pb were determined as free atomic ions while As and V were determined as the oxides AsO+ and VO+ in the same run. Samples were prepared by microwave-assisted digestion with dilute nitric acid and hydrogen peroxide. Two plant-certified reference materials (apple leaves and tomato leaves) were used to check the accuracy. For tandem mass spectrometry with 0.5?mL min?1 O2, recoveries in the 85–113% were typically obtained and no statistical differences were observed at the 95% confidence level (t-test) in comparison with the certified values. Using these conditions, the limits of detection for the method were 0.01, 0.0002, 0.008, 0.008, 0.003, and 0.002?µg g?1 for As, Cd, Cr, Ni, Pb, and V, respectively. The procedure was used for the analysis of four phytotherapic drugs and the determined concentrations were up to 0.168?µg g?1 As, 0.03?µg g?1 Cd, 0.82?µg g?1 Cr, 1.18?µg g?1 Ni, 0.52?µg g?1 Pb, and 2.4?µg g?1 V with average precision values of 8% as the relative standard deviation. The found concentrations were compared with limits proposed in official guidelines and, in most cases, the values were below the maximum limits allowed. 相似文献
974.
Cristian Rodrigo Muzzio Nicolás Gabriel Dini Adrián César Razzitte 《Physics and Chemistry of Liquids》2017,55(4):506-521
Highly concentrated electrolyte solutions were studied through a Monte Carlo-based simulator, developed to consider the water molecules not a homogeneous dielectric as usual, but as dipoles that can move and rotate within a 3D lattice. This approach allowed fast calculations of detailed interactions between the particles, which were described from mechanistic potentials including dipole–dipole, ion–dipole, ion–ion, and hydrogen bonding (HB) interactions. A good agreement was found between experimental data and simulated results. The study also provides new insights about the balance of the different interactions in systems with or without electrolytes, and the effects of the electrolytes addition on the original water structure. The proposed model was also compared with previous explicit models. 相似文献
975.
Crystal orbital calculations on cis- and trans-polyacethylene chains indicate two kinds of geometry changes on charge transfer. (1) increase (decrease) of the CC bond lenght and CCC bond angles in the trans conformer taking up (losing) electrons, and a tendency towards bond-length equalization on electron uptake and loss for both conformers. 相似文献
976.
E. Cortés N. Gras L. Muñoz V. Cassorla 《Journal of Radioanalytical and Nuclear Chemistry》1982,69(1-2):401-415
Seven trace elements were determined in milk formulas, powder milk and infant food. Instrumental neutron activation analysis
was used for the analysis of Fe, Zn, Co, Cr and Rb, while As and Cu content was determined using radiochemical neutron activation
analysis. Differences were found in the trace element content of foods of the same type. Milk formulas are comparable with
human milk according to the results obtained for the elements analyzed. The samples of powder cow's milk presented similar
concentrations of the elements studied. Liver with vegetables was found to have the highest Cu content. A meal prepared at
home, made of beef and fresh vegetables showed a higher trace element content than its similar commercial one. An estimation
of the daily intake of the elements analyzed was made and compared with minimum recommended daily ingestion. 相似文献
977.
J. Morales L. Hernan L. V. Flores A. Ortega 《Journal of Thermal Analysis and Calorimetry》1982,24(1):23-34
Differential thermal analysis and differential scanning calorimetry techniques have been used to study the kinetics of phase transitions. The aragonite/calcite transformation was chosen as test reaction.Marked discrepancies were observed between the DTA kinetic results and those obtained from isothermal kinetic measurements. This disagreement is associated with the difficulty of determining accurately the reaction rate of the process from a DTA curve.In contrast, in DSC measurements, where the reaction rate is given by the height of the peak from the base-line, it is possible to get a satisfactory fit of the data, and the kinetic results obtained with this technique are in good agreement with the isothermal ones.
Zusammenfassung Die Differentialthermoanalyse und DSC wurden zur Untersuchung der Kinetik von Phasenübergängen eingesetzt. Die Umwandlung Aragonit/Calcit wurde als Testreaktion gewählt.Bedeutende Diskrepanzen wurden zwischen den kinetischen Ergebnissen der DTA und den durch isotherme kinetische Messungen erhaltenen Ergebnissen beobachtet. Diese Abweichungen sind damit verbunden, daß es schwierig ist, die Reaktionsgeschwindigkeit des Vorgangs aus einer DTA-Kurve genau zu ermitteln.Bei DSC-Messungen,wo die Reaktionsgeschwindigkeit durch die Höhe des Peaks von der Grundlinie gegeben ist, kann eine befriedigende Anpassung der Daten erhalten werden, und die durch diese Technik erhaltenen kinetischen Ergebnisse sind in guter Übereinstimmung mit den isothermen Ergebnissen.
. /. , . -. , , , , , .相似文献
978.
Yu. A. Ryndin S. Gbölös V. I. Zaikovskii J. Margitfalvi Yu. I. Yermakov 《Reaction Kinetics and Catalysis Letters》1982,21(1-2):91-95
The addition of gallium is shown to increase Pt dispersity and its stability to deactivation in n-hexane dehydrocyclization, to decrease the rate of n-hexane hydrogenolysis and to increase the selectivity to benzene, apparently, due to the interaction of Pt clusters with surface Ga ions.
, -, - . .相似文献
979.
Nitrogen bridgehead compounds part 21. Preparation of new quaternary 2,3a,6a-triazaphenalenium salts
István Bitter Béla Pete István Hermecz Gábor Tóth Kálmán Simon Mátyás Czugler Zoltán Mészáros 《Tetrahedron letters》1982,23(28):2891-2894
The first representatives of a new ring system, the 2,3a,6a-triazaphenalenium quaternary salts are prepared by the cycloaddition of tetrahydro-4H-pyrido[1,2-a] pyrimidin-4-ones containing an α-chloroenamine moiety with azomethines. 相似文献
980.