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Computational fluid dynamics, where simulations require largecomputation times, is one of the areas of application of highperformance computing. Schemes such as the SIMPLE (semi-implicitmethod for pressure-linked equations) algorithm are often usedto solve the discrete Navier-Stokes equations. Generally theseschemes take a short time per iteration but require a largenumber of iterations. For simple geometries (or coarser grids)the overall CPU time is small. However, for finer grids or morecomplex geometries the increase in the number of iterationsmay be a drawback and the decoupling of the differential equationsinvolved implies a slow convergence of rotationally dominatedproblems that can be very time consuming for realistic applications.So we analyze here another approach, DIRECTO, that solves theequations in a coupled way. With recent advances in hardwaretechnology and software design, it became possible to solvecoupled Navier-Stokes systems, which are more robust but implyincreasing computational requirements (both in terms of memoryand CPU time). Two approaches are described here (band blockLU factorization and preconditioned GMRES) for the linear solverrequired by the DIRECTO algorithm that solves the fluid flowequations as a coupled system. Comparisons of the effectivenessof incomplete factorization preconditioners applied to the GMRES(generalized minimum residual) method are shown. Some numericalresults are presented showing that it is possible to minimizeconsiderably the CPU time of the coupled approach so that itcan be faster than the decoupled one. 相似文献
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Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi
x
La1−x
FeO3 (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of
these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz
to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz).
All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature
shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds
to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity
as well as ε′ are found to be maximum for the sample x=0.2 at room temperature. 相似文献
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Monoglycerides and Diglycerides Synthesis in a Solvent-Free System by Lipase-Catalyzed Glycerolysis 总被引:1,自引:0,他引:1
Fregolente PB Fregolente LV Pinto GM Batistella BC Wolf-Maciel MR Filho RM 《Applied biochemistry and biotechnology》2008,146(1-3):165-172
Five lipases were screened (Thermomyces lanuginosus free and immobilized forms, Candida antarctica B, Candida rugosa, Aspergillus niger, and Rhizomucor miehei) to study their ability to produce monoglycerides (MG) and diglycerides (DG) through enzymatic glycerolysis of soybean oil.
Lipase from C. antarctica was further studied to verify the enzyme load (wt% of oil mass), the molar ratio glycerol/oil, and the water content (wt%
of glycerol) on the glycerolysis reaction. The best DG and MG productions were in the range 45–48% and 28–30% (w/w, based on the total oil), respectively. Using immobilized lipases, the amount of free fatty acids (FFA) produced was about
5%. However, the amount of FFA produced when using free lipases, with 3.5% extra water in the system, is equivalent to the
MG yield, about 23%. The extra water content provides a competition between hydrolysis and glycerolysis reactions, increasing
the FFA production. 相似文献
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Several gentamicin bulk samples from different origins were investigated using an LC/MS method.LC equipped with ion trap MS with positive ionization was performed on a Capcell Pak C18(AQ) column with the mobile phase containing 50 mM trifluoroacetic(TFA) and methanol.Impurities present in batches of gentamicin bulk samples were elucidated and compared according to their fragmentation behavior.In total seventeen impurities present in samples,five impurities were not elucidated and two compounds were identifi... 相似文献
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Fregolente LV Batistella CB Filho RM Wolf Maciel MR 《Applied biochemistry and biotechnology》2006,131(1-3):680-693
Monoglycerides (MG) are emulsifiers widely used in food and pharmaceutical industries. Current industrial processes for MG production consist of the interesterification of triglycerides with glycerol (GL), in the presence of inorganic catalysts at high temperatures (>200 degrees C). This reaction is known as glycerolysis and produces a mixture of approx 50% of MG. This level of concentration is suitable for many applications, although, for some specific uses like margarine, shortening, icing, and cream filling, require distilled MGs, which are purified MG (min. 90%) obtained by the molecular distillation process. Therefore, in this work, a 2(3) factorial design was employed to evaluate the effects of reaction parameters in the MG content after the interesterification reaction of refined soybean oil with GL in the presence of sodium hydroxide as catalyst. After that, the MG content in the reaction product was enhanced through the molecular distillation process in order to obtain distilled MG. 相似文献
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Laís G. Fregolente Joo Vitor dos Santos Giovanni Vinci Alessandro Piccolo Altair B. Moreira Odair P. Ferreira Mrcia C. Bisinoti Riccardo Spaccini 《Molecules (Basel, Switzerland)》2021,26(4)
Hydrochar is a carbon-based material that can be used as soil amendment. Since the physical-chemical properties of hydrochar are mainly assigned to process parameters, we aimed at evaluating the organic fraction of different hydrochars through 13C-NMR and off-line TMAH-GC/MS. Four hydrochars produced with sugarcane bagasse, vinasse and sulfuric or phosphoric acids were analyzed to elucidate the main molecular features. Germination and initial growth of maize seedlings were assessed using hydrochar water-soluble fraction to evaluate their potential use as growth promoters. The hydrochars prepared with phosphoric acid showed larger amounts of bioavailable lignin-derived structures. Although no differences were shown about the percentage of maize seeds germination, the hydrochar produced with phosphoric acid promoted a better seedling growth. For this sample, the greatest relative percentage of benzene derivatives and phenolic compounds were associated to hormone-like effects, responsible for stimulating shoot and root elongation. The reactions parameters proved to be determinant for the organic composition of hydrochar, exerting a strict influence on molecular features and plant growth response. 相似文献
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Using the evolution history of the universe, one can make constraint on the parameter space of dynamic dark energy models. We discuss two different parameterized dark energy models. Our results further restrict the combined constraints obtained from supernova and the first-year Wilkinson-microwave-anisotropy-probe observations. From the allowed parameter space, it is found that our universe will experience an eternal acceleration. We also estimate the bound on the physically relevant regions both in the re-inflationary and inflationary phases. 相似文献
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Patricia Bogalhos Lucente Fregolente Gláucia Maria F. Pinto Maria Regina Wolf-Maciel Rubens Maciel Filho 《Applied biochemistry and biotechnology》2010,160(7):1879-1887
Distilled glycerides are obtained through distillation of the system mono-diglycerides which is produced from the esterification
reaction between a triglyceride with glycerol. In this work, monoglycerides (MG) and diglycerides (DG) are produced through
lipase-catalyzed glycerolysis of soybean oil using Candida antarctica B in a solvent-free system. To separate the products of the reaction in order to obtain essentially MG and an oil of DG,
it is necessary to use a suitable process in order to preserve the stability of the components and to keep the products free
of inappropriate solvents. So, after 24 h of enzymatic reaction, the mixture of acylglycerols and fatty acids was distilled
into a centrifugal molecular distiller, since it provides a free solvent and lower temperature environment to increase the
desired product concentration. Starting from a material with 25.06% of triglycerides (TG), 46.63% of DG, 21.72% of MG, 5.38%
of free fatty acids (FFA), and 1.21% of glycerol, the MG purity in the distillate stream was 80% at evaporator temperature
(T
E) equal to 250 °C and feed flow rate (Q) equal to 10.0 mL/min. At these conditions, the MG recovery was 35%. The material collected in the residue stream presented
DG-enriched oil with TG unhydrolyzed, residual MG, and low acidity (29.83% of TG, 53.20% of DG, 15.64% of MG, and 1.33% of
FFA), which is suitable to replace TG oil in the human diet. 相似文献
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