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301.
A new dissolution microcalorimeter that can measure enthalpies of dissolution of slightly soluble solids was developed by Ingemar Wadsö at Lund University, and the prototype as well as the commercial vessel were tested in our laboratory. Recently we did report the testing of the prototype and we are now extending the previous investigation to measurements with an organic solvent in the commercial vessel. The instrument performance was found to be as good with formamide as with water.The vessel was calibrated chemically (dissolution of KCl in water) and electrically, by means of a permanent and an insertion heater. The results obtained from the three methods are compared and discussed.The enthalpy of dissolution of α-cyclodextrin, dry and hydrated with six water molecules, was determined in water and in formamide. The results are discussed in terms of the difference between water and formamide as regarding dissolution and binding to the cyclodextrin molecule. 相似文献
302.
M. Agostinha R. Matos Margarida S. Miranda Victor M.F. Morais 《The Journal of chemical thermodynamics》2008,40(4):625-631
The standard (p° = 0.1 MPa) molar enthalpies of combustion and sublimation of 3,4,5-trimethoxyphenol were measured, respectively, by static bomb combustion calorimetry in oxygen atmosphere and by Calvet microcalorimetry. From these measurements, the standard molar enthalpy of formation in both the crystalline and gaseous phase, at T = 298.15 K, were derived: ?(643.4 ± 1.9) kJ · mol?1 and ?(518.1 ± 3.6) kJ · mol?1, respectively. Density functional theory calculations for this compound and respective phenoxyl radical and phenoxide anion were also performed using the B3LYP functional and extended basis sets, which allowed the theoretical estimation of the gaseous phase standard molar enthalpy of formation through the use of isodesmic reactions and the calculation of the homolytic and heterolytic O–H bond dissociation energies. There is good agreement between the calculated and experimental enthalpy of formation. Substituent effects on the homolytic and heterolytic O–H bond dissociation energies have been analysed. 相似文献
303.
This note studies the structure of the divisorial fixed part of for a 1-connected curve D on a smooth surface S. It is shown that if the divisorial fixed part F of is non empty then it has arithmetic genus ≤ 0 and each component of F is a smooth rational curve. The structure of curves D, with non empty divisorial fixed part F for , is also described.
Received: 16 August 2007 相似文献
304.
Margarida L. Castelló Jo Dweck Donato A. G. Aranda 《Journal of Thermal Analysis and Calorimetry》2009,97(2):627-630
During the last years, the demand for biofuels has increased significantly. In Brazil, a production of 1 billion liters of
biodiesel was produced by the end of 2007, due to its obligatory use in the composition of the diesel for vehicle use. In
this production, a hundred thousand tons of glycerol are produced as by-product, for which alternative uses are needed. As
glycerol has already been studied by other conventional characterization methods in the past, thermal analysis has been used
mostly for characterization of sub ambient temperature properties of glycerol. In this paper, thermogravimetry (TG), derivative
thermogravimetry (DTG) and differential thermal analysis (DTA) were used for its thermal characterization above room temperature.
Thermal stability was determined from experimental data, which show that even in air, only a very small part of the volatilized
glycerol is burned out. A thermogravimetric quantitative method was developed to determinate the water content of glycerol–water
mixtures, which also was used to quantify the water impurity in pro-analysis samples of glycerol, showing compatible results
with those obtained by Karl Fischer method. 相似文献
305.
Micro/mesoporous chromium, aluminium-containing silicates of the type TUD-1 (Al-TUD-1, Cr-TUD-1, CrAl-TUD-1) and zeolite BEA, Cr-BEA, and related composites BEA/TUD-1 and Cr-BEA/TUD-1, were prepared, characterised, and tested as solid acids coupled with the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([bmim]Cl) as solvent, in the transformation of D-glucose into 5-(hydroxymethyl)-2-furaldehyde (Hmf), at 120 °C. The chromium-containing catalytic systems lead to considerably higher Hmf yields in comparison to the related systems without chromium. The IL is a favourable solvent for this target reaction (in terms of Hmf yields reached) compared to water or dimethylsulfoxide. A detailed study on the stabilities of the nanoporous solid acids in the IL medium is presented. 相似文献
306.
Guangyue Bai Vasco Castro Marieta Nichifor Margarida Bastos 《Journal of Thermal Analysis and Calorimetry》2010,100(2):413-422
Dextran modified with deoxycholic acid (Dex-DCA) was synthesized by grafting DCA along the polymer backbone, with degrees
of substitution (DS)—2% and 3%. The thermodynamics of the association processes of the mixed systems is followed by isothermal
titration calorimetry for sodium deoxycholate/sodium dodecyl sulfate (NaDCA/NaDS), Dex-DCA with different surfactants—Dex-DCA/NaDS,
Dex-DCA/NaDCA, and Dex-DCA/DTAB (dodecyltrimethylammonium bromide). Calorimetric measurements for the micellization processes
of the pure surfactants in aqueous solution were also performed for comparison with the results obtained for the mixed systems.
We have obtained and herein present the enthalpies of micelle formation and critical micelle concentrations for the referred
pure surfactants, as well as the interaction and aggregation enthalpies for the mixed systems-surfactant/polymer. The dependence
of the observed aggregation behavior on the surfactant and temperature is discussed in detail. Finally, we should stress that
calorimetry allowed us to ascertain a very important fact in polymer/surfactant interaction. From the comparison between NaDCA/NaDS
and Dex-DCA/NaDS calorimetric titration curves, we could clearly see that the interaction between Dex-DCA and NaDS is driven
by the interaction between the bile acid moiety and the surfactant. 相似文献
307.
308.
Marta Mesquita Margarida Moz Ana Paias Margarida Pato 《European Journal of Operational Research》2013
The integrated vehicle-crew-roster problem with days-off pattern aims to simultaneously determine minimum cost vehicle and daily crew schedules that cover all timetabled trips and a minimum cost roster covering all daily crew duties according to a pre-defined days-off pattern. This problem is formulated as a new integer linear programming model and is solved by a heuristic approach based on Benders decomposition that iterates between the solution of an integrated vehicle-crew scheduling problem and the solution of a rostering problem. Computational experience with data from two bus companies in Portugal and data from benchmark vehicle scheduling instances shows the ability of the approach for producing a variety of solutions within reasonable computing times as well as the advantages of integrating the three problems. 相似文献
309.
Mario F. S. Ferreira Margarida M. V. Facao Sofia C. V. Latas 《Fiber and Integrated Optics》2013,32(1):31-41
Stable soliton propagation in a system with linear and nonlinear gain and spectral filtering is investigated. Different types of exact analytical solutions of the cubic and the quintic complex Ginzburg-Landau equation (CGLE) are reviewed. The conditions to achieve stable soliton propagation are analyzed within the domain of validity of soliton perturbation theory. We derive an analytical expression defining the region in the parameter space where stable pulselike solutions exist, which agrees with the numerical results obtained by other authors. An analytical expression for the soliton amplitude corresponding to the quintic CGLE is also obtained. We show that the minimum value of this amplitude depends only on the ratio between the linear gain and the quintic gain saturating term. 相似文献
310.
Williams TL Vareiro MM Jenkins AT 《Langmuir : the ACS journal of surfaces and colloids》2006,22(15):6473-6476
This letter describes a new method for studying the interaction of the membrane-lysing enzyme phospholipase A(2) (PLA(2)) with phospholipid bilayers by simultaneous measurements of enzyme binding and vesicle lysis using surface plasmon resonance (SPR) and permeabilization using surface plasmon field-enhanced fluorescence spectroscopy (SPFS). The PLA(2) inhibitor dimethyl-eicosadienoic acid was incorporated into the surface-bound vesicles and support bilayer in order to study its role in preventing PLA(2)-mediated vesicle lysis. This methodology has a generic applicability for the study of a range of membrane-disrupting agents. 相似文献