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排序方式: 共有281条查询结果,搜索用时 15 毫秒
131.
Juan Límaco Haroldo Rodrigues Clark Cicero Lopes Frota Luis Adauto Medeiros 《Mathematical Methods in the Applied Sciences》2011,34(16):2047-2059
In this paper, we analyze from the mathematical point of view a model for small vertical vibrations of an elastic string with weak internal damping and quadratic term, coupled with mixed boundary conditions of Dirichlet type and acoustic type. Our goal is to extend some of the results of Frota‐Goldstein work in the sense of considering a weaker internal damping and one more quadratic nonlinearity in the elastic string equation. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
132.
This paper presents results on a verification test of a Direct Numerical Simulation code of mixed high‐order of accuracy using the method of manufactured solutions (MMS). This test is based on the formulation of an analytical solution for the Navier–Stokes equations modified by the addition of a source term. The present numerical code was aimed at simulating the temporal evolution of instability waves in a plane Poiseuille flow. The governing equations were solved in a vorticity–velocity formulation for a two‐dimensional incompressible flow. The code employed two different numerical schemes. One used mixed high‐order compact and non‐compact finite‐differences from fourth‐order to sixth‐order of accuracy. The other scheme used spectral methods instead of finite‐difference methods for the streamwise direction, which was periodic. In the present test, particular attention was paid to the boundary conditions of the physical problem of interest. Indeed, the verification procedure using MMS can be more demanding than the often used comparison with Linear Stability Theory. That is particularly because in the latter test no attention is paid to the nonlinear terms. For the present verification test, it was possible to manufacture an analytical solution that reproduced some aspects of an instability wave in a nonlinear stage. Although the results of the verification by MMS for this mixed‐order numerical scheme had to be interpreted with care, the test was very useful as it gave confidence that the code was free of programming errors. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
133.
de Souza Merli LA de Medeiros VP Toma L Reginato RD Katchburian E Nader HB Faloppa F 《Photochemistry and photobiology》2012,88(5):1293-1301
The low level laser therapy (LLLT) has been used as an option to accelerate the regeneration of bone tissue. In this study, both femurs of male Wistar rats (30 animals) were injured with a drill and the effect of LLLT using a laser diode (100 mW at 660 nm) in the bone matrix on the left paw measured. LLLT effect on the healing bone tissue matrix was evaluated by a combination of immunohistochemical histomorphometry, confocal immunofluorescence microscopy and isolation and characterization of glycosaminoglycans. Histomorphometric analysis showed that LLLT increased bone matrix and showing more organized. Alcian Blue and PAS staining seems to suggest differential glycosaminoglycans and glycoproteins. The data showed increased expression of chondroitin sulfate and hyaluronic acid, after reduction as the LLLT and mature bone, resembling the expression of osteonectin and biglycan. The difference in expression of siblings (DMP‐1, OPN and BSP) is in accordance with the repair accelerated bone formation after the application of LLLT as compared with control. The expression of osteonectin and osteocalcin supports their role in bone mineralization protein, indicating that LLLT accelerates this process. The overall data show that LLLT bone changes dynamic array, shortening the time period involved in the bone repair. 相似文献
134.
Érico Marlon de Moraes Flores Adriane Medeiros Nunes Valderi Luiz Dressler Jiri Dědina 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009
A systematic study was performed to evaluate the performance of a multiple microflame (MM) quartz tube atomizer (QTA) for minimizing interferences and to improve the extent of the calibration range using a batch system for hydride generation atomic absorption spectrometry (HG AAS). A comparison of the results with conventional QTA on the determination of antimony, arsenic, bismuth and selenium was performed. The interference of As, Bi, Se, Pb, Sn and Sb was investigated using QTA and MMQTA atomizers. Better performance was found for MMQTA, and no loss of linearity was observed up to 160 ng for Se and Sb and 80 ng for As, corresponding to an enhancement of two times for both analytes when compared to QTA (analyte mass refers to a volume of 200 μl). For Bi, the linear range was the same for QTA and MMQTA (140 ng). With the exception of Bi, the tolerance limits for hydride-forming elements were improved more than 50% in comparison to the conventional QTA system, especially for the interferences of As, Sb and Se. However, for Sn as an interferent, no difference was observed in the determination of Se and Sb using the MMQTA system. The use of MMQTA-HG AAS complied with the relatively high sensitivity of conventional QTA and also provided better performance for interferences and the linear range of calibration. 相似文献
135.
Rodrigo Irani Medeiros Nelson Roberto Antoniosi Filho Maria Inês Gon?alves Leles 《Journal of Thermal Analysis and Calorimetry》2009,97(1):337-342
The objective of this work is the TG and DSC analysis of “Merla” samples as well as the separation and identification of organic
compounds by Ultra Fast GC method. The obtained results showed the grouping and the establishment of the degree of the sample’s similarity based in
the Euclidean Distance. The cluster was a useful tool to determine if the samples, confiscated from different users by police,
were manufactured in the same or different laboratories. Consequently one can conclude if in any city operates one or more
drug manufacturing laboratories. 相似文献
136.
Veras G Gomes Ade A da Silva AC de Brito AL de Almeida PB de Medeiros EP 《Talanta》2010,83(2):565-568
This article describes the classification of biodiesel samples using NIR spectroscopy and chemometric techniques. A total of 108 spectra of biodiesel samples were taken (being three samples each of four types of oil, cottonseed, sunflower, soybean and canola), from nine manufacturers. The measurements for each of the three samples were in the spectral region between 12,500 and 4000 cm−1. The data were preprocessed by selecting a spectral range of 5000-4500 cm−1, and then a Savitzky-Golay second-order polynomial was used with 21 data points to obtain second derivative spectra. Characterization of the biodiesel was done using chemometric models based on hierarchical cluster analysis (HCA), principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA) elaborated for each group of biodiesel samples (cotton, sunflower, soybean and canola). For the HCA and PCA, the formation of clusters for each group of biodiesel was observed, and SIMCA models were built using 18 spectral measurements for each type of biodiesel (training set), and nine spectral measurements to construct a classification set (except for the canola oil which used eight spectra). The SIMCA classifications obtained 100% accurate identifications. Using this strategy, it was feasible to classify biodiesel quickly and nondestructively without the need for various analytical determinations. 相似文献
137.
In the bi-dimensional parameter space of an impact-pair system, shrimp-shaped periodic windows are embedded in chaotic regions. We show that a weak periodic forcing generates new periodic windows near the unperturbed one with its shape and periodicity. Thus, the new periodic windows are parameter range extensions for which the controlled periodic oscillations substitute the chaotic oscillations. We identify periodic and chaotic attractors by their largest Lyapunov exponents. 相似文献
138.
Anna Carolina da Silva Alana Emília Soares de França Queiroz Talita Camila Evaristo dos Santos Nascimento Cristine Rodrigues José Erick Galindo Gomes Cristina Maria Souza-Motta Luciana Porto de Souza Vandenberghe Erika Valente de Medeiros Keila Aparecida Moreira Polyanna Nunes Herculano 《Applied biochemistry and biotechnology》2014,173(7):1652-1666
Of the many reported applications for xylanase, its use as a food supplement has played an important role for monogastric animals, because it can improve the utilisation of nutrients. The aim of this work was to produce xylanase by extractive fermentation in an aqueous two-phase system using Aspergillus tamarii URM 4634, increasing the scale of production in a bioreactor, partially characterising the xylanase and evaluating its influence on monogastric digestion in vitro. Through extractive fermentation in a bioreactor, xylanase was obtained with an activity of 331.4 U mL?1 and 72 % yield. The xylanase was stable under variable pH and temperature conditions, and it was optimally active at pH 3.6 and 90 °C. Xylanase activity potentiated the simulation of complete monogastric digestion by 6 %, and only Mg2+ inhibited its activity. This process provides a system for efficient xylanase production by A. tamarii URM 4634 that has great potential for industrial use. 相似文献
139.
Rancimat and PDSC accelerated techniques for evaluation of oxidative stability of soybean oil with plant extracts 总被引:1,自引:0,他引:1
A. M. T. M. Cordeiro M. L. Medeiros M. A. A. D. Silva I. A. A. Silva L. E. B. Soledade A. L. Souza N. Queiroz A. G. Souza 《Journal of Thermal Analysis and Calorimetry》2013,114(2):827-832
Taking into account the importance of natural antioxidants in the preservation of oils and fats, the present study evaluated the antioxidant action of five plant extracts in the control of soybean oil stability, by means of the accelerated techniques Rancimat and PDSC. These plants are rosemary (Rosmarinus officinalis L.), chamomile (Matricaria recutita L.), coriander (Coriandrum sativum L.), fennel (Foeniculum vulgare), and senna (Cassia angustifolia Vahl). The plant extracts and also the synthetic antioxidant BHT were added to the samples of crude soybean oil at the concentration of 1,000 mg kg?1. The values of total phenolic contents ranged from 8.7 ± 0.4 to 63.0 ± 2.3 mg GAE g?1 extract and a strong positive correlation was observed between the total phenolic contents and the overall antioxidant activity of the plant extracts. Such high values indicate a good protection of the analyzed soybean oil, moreover for the Rosemary extract that was superior to the remaining extracts. In the Rancimat technique the rosemary extract was more effective than the synthetic BHT antioxidant. The OIT values of Rosemary extract and the BHT antioxidant were equivalent, and the former, showed the highest phenolic contents among the extracts, for all the performed tests, confirming that it is a powerful natural source of antioxidants. 相似文献
140.
Nascimento Rebecca A. B. Medeiros Rodolfo L. B. A. Costa Tiago R. Oliveira Ângelo A. S. Macedo Heloísa P. Melo Marcus A. F. Melo Dulce M. A. 《Journal of Thermal Analysis and Calorimetry》2020,140(6):2673-2685
Journal of Thermal Analysis and Calorimetry - Mn-based solid oxygen carriers supported on MgAl2O4 were prepared by the microwave-assisted combustion method followed by wet impregnation of the... 相似文献