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131.
François Clautiaux Cláudio Alves José Valério de Carvalho 《Annals of Operations Research》2010,179(1):317-342
Dual-feasible functions are valuable tools that can be used to compute both lower bounds for different combinatorial problems
and valid inequalities for integer programs. Several families of functions have been used in the literature. Some of them
were defined explicitly, and others not. One of the main objectives of this paper is to survey these functions, and to state
results concerning their quality. We clearly identify dominant subsets of functions, i.e. those which may lead to better bounds or stronger cuts. We also describe different frameworks that can be used to create
dual-feasible functions. With these frameworks, one can get a dominant function based on other ones. Two new families of dual-feasible
functions obtained by applying these methods are proposed in this paper. 相似文献
132.
133.
We study the dynamics of spatially homogeneous and isotropic spacetimes containing a fluid undergoing microscopic velocity diffusion in a cosmological scalar field. After deriving a few exact solutions of the equations, we continue by analyzing the qualitative behavior of general solutions. To this purpose we recast the equations in the form of a two dimensional dynamical system and perform a global analysis of the flow. Among the admissible behaviors, we find solutions that are asymptotically de-Sitter both in the past and future time directions and which undergo accelerated expansion at all times. 相似文献
134.
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136.
Cleoci Beninca Tiago André Denck Colman Luiz Gustavo Lacerda Marco Aurélio da Silva Carvalho Filho Ivo Mottin Demiate Gilbert Bannach Egon Schnitzler 《Journal of Thermal Analysis and Calorimetry》2013,111(3):2217-2222
The use of chemically modified starches is widely accepted in various industries, with several applications. In this research, natural cassava starch granules were treated with standard sodium hypochlorite solution at 0.8, 2.0, and 5.0 g Cl/100 g starch. The native and modified starch samples were investigated by means of the following techniques: simultaneous thermogravimetry–differential thermal analysis, which allowed us to verify the thermal decomposition associated with endothermic or exothermic phenomena; and differential scanning calorimetry that was used to determine gelatinization enthalpy as well as the rapid viscoamylographic analysis that provided the pasting temperature and viscosity. By means of non-contact-atomic force microscopy method and X-ray powder patterns diffractometry, it was possible to observe the surface morphology, topography of starch granules, and alterations in the granules’ crystallinity. 相似文献
137.
Michelle Gonçalves Mothé Cheila Gonçalves Mothé Carlos Henrique Monteiro de Carvalho Marcia Cristina Khalil de Oliveira 《Journal of Thermal Analysis and Calorimetry》2013,113(2):525-531
Present study investigates thermal behavior of two heavy crude oils with different °API values by simultaneous thermogravimetry–differential scanning calorimetry–fourier transform infrared spectroscopy (TG–DSC–FTIR), and an evaluation of the chemical element levels present in the oils’ ashes was done by energy dispersive X-ray fluorescence spectrometry. TG and DSC curves were obtained for two samples in nitrogen atmosphere. Among all inorganic components evaluated, the highest concentration in the two oils was SO3. Thus this study may contribute to a better understanding of the thermal behavior of heavy crude oils and their composition. 相似文献
138.
Georgina M. S. Alves Júlia M. C. S. Magalhães Helena M. V. M. Soares 《Electroanalysis》2013,25(5):1247-1255
A simple, fast, sensitive and greener voltammetric procedure for simultaneous analysis of nickel (Ni) and cobalt (Co) by square wave adsorptive cathodic stripping voltammetry (SW‐AdCSV) using a solid bismuth vibrating electrode is presented for the first time. The procedure enables to determine Ni together with Co, in ammonia buffer 0.1 M (pH 9.2) and in the presence of oxygen, and involves an adsorptive accumulation of metal‐dimethylglyoxime (Ni‐DMG and Co‐DMG) complexes on the electrode surface. For Ni and Co, the detection limits, obtained with 30 s of accumulation time, were 0.6 and 1.0 µg L?1, respectively. The method was free of metals (Cd2+, Cr3+, Cr6+, Cu2+, Fe3+ and Pb2+ up to 50 µg L?1, Al3+ and Mn2+ up to 500 µg L?1; Zn2+ up to 300 µg L?1) interferences up to the concentrations mentioned in brackets. The proposed method was validated for simultaneous determination of Ni and Co in a certified reference surface and river waters with good results. 相似文献
139.
Georgina M. S. Alves Júlia M. C. S. Magalhães Roma Tauler Helena M. V. M. Soares 《Electroanalysis》2013,25(8):1895-1906
Simultaneous anodic stripping voltammetric determination of Pb and Cd is restricted on gold electrodes as a result of the overlapping of these two peaks. This work describes the quantitative determination of a binary mixture system of Pb and Cd, at low concentration levels (up to 15.0 and 10.0 µg L?1 for Pb and Cd, respectively) by differential pulse anodic stripping voltammetry (DPASV; deposition time of 30 s), using a green electrode (vibrating gold microwire electrode) without purging in a chloride medium (0.5 M NaCl) under moderate acidic conditions (HCl 1.0 mM), assisted by chemometric tools. The application of multivariate curve resolution alternating least squares (MCR‐ALS) for the resolution and quantification of both metals is shown. The optimized MCR‐ALS models showed good prediction ability with concentration prediction errors of 12.4 and 11.4 % for Pb and Cd, respectively. The quantitative results obtained by MCR‐ALS were compared to those obtained with partial least squares (PLS) and classical least squares (CLS) regression methods. For both metals, PLS and MCR‐ALS results are comparable and superior to CLS. For Cd, as a result of the peak shift problem, the application of CLS was unsuitable. MCR‐ALS provides additional advantage compared to PLS since it estimates the pure response of the analytes signal. Finally, the built up multivariate calibration models, based either in MCR‐ALS or PLS regression, allowed to quantify concentrations of Pb and Cd in surface river water samples, with satisfactory results. 相似文献
140.
Marco Bellagamba Luigi Bencivenni Lorenzo Gontrani Leonardo Guidoni Claudia Sadun 《Structural chemistry》2013,24(3):933-943
In this work, we report a multitechnique (energy-dispersive X-ray diffraction, computational methods, and FTIR spectroscopy) study of the tautomeric equilibrium of 1,2,3-triazole, one of the few small nitrogen-containing eterocycles liquid at room temperature. The T-2H form (C 2v symmetry) is found to be strongly favored in gas and solid phases, whereas the neat liquid gives diffraction patterns that can be interpreted satisfactorily with the structure functions calculated from some molecular dynamics results for both T-2H and T-1H tautomers, although the T-2H form gives a slightly better agreement. 相似文献