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排序方式: 共有337条查询结果,搜索用时 15 毫秒
1.
Julio Penin Santos Fernando J.G. Landgraf Geraldo Caixeta Guimarães 《Journal of magnetism and magnetic materials》2006
The paper describes effect of texture on the anisotropy of magnetic properties and shows that an Epstein strip arrangement including strips cut in a direction 45° to the rolling direction gives property values that are closer to the average values than the traditional RD+TD arrangement. 相似文献
2.
Inês Nunes Nuno Mesquita Sandra Cabo Verde Maria João Trigo Armando Ferreira Maria Manuela Carolino António Portugal Maria Luísa Botelho 《Radiation Physics and Chemistry》2012,81(12):1943-1946
Parchments are important documents that give testimony for History; therefore these materials should be respected and preserved. Considering incremental biodeterioration problems that have to be faced daily, the Archive of the University of Coimbra (AUC) is involved in different scientific projects in order to evaluate and determine new methods for document decontamination and preservation.The aim of this study was to evaluate gamma radiation effects on the colour and texture of the AUC parchment documents. The assessment of these effects was used to estimate the maximum gamma radiation dose (Dmax) that could guarantee parchment documents′ decontamination treatment, without significant alteration of their physical properties. Parchment samples were exposed to gamma radiation doses ranging from 10 to 30 kGy. The texture and colour of samples were assessed before and after the irradiation procedure, using a texture analyser and an electronic colorimeter. Hardness and springiness were determined based on texture spectra. Lightness (L?), Chroma (C), greenness vs. redness (a*) and yellowness vs. blueness (b*) values were obtained from colorimetric measures. Results indicate no significant effects of gamma radiation on the texture and colour of parchment for the studied doses. 相似文献
3.
Cristiane P. de Macedo Charles A. B. Negrão Luiz G. M. de Macedo José R. Zamian Geraldo N. da Rocha Filho Carlos E. F. da Costa 《Journal of Thermal Analysis and Calorimetry》2014,115(1):31-36
The Al-MCM-41 molecular sieve with Si/Al = 20 molar ratio was synthesized at room temperature and characterized by X-ray diffractometry, surface area, thermogravimetry, and infrared spectroscopy. The kinetic study was conducted by Vyazovkin and Ozawa method, in order to verify the activation energy during the Hofmann degradation between 130 and 370 °C, in which most of surfactant removal occurs. The results suggest that the activation energy for template removal is close to 80 kJ mol?1 lower in Al-MCM-41 synthesized at room temperature, when compared to results obtained for mesopores Al-MCM-41 and MCM-41 synthesized by hydrothermal method. This lower activation energy may be understood as consequence of textural properties, such as higher pore size. 相似文献
4.
Heloisa Beraldo Ricardo F. F. da Costa Rejane Lima Geraldo M. de Lima Ivana S. Lula Bernard Mahieu 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2455-2463
The reaction of tin(IV) tetrachloride with 3-formylpyridine semicarbazone and different 3-formylpyridine thiosemicarbazones produces [Sn(HL)CL 3 ][SnCl 5 ] where HL stands for the neutral ligand. The tin(IV) complexes were characterized using a variety of spectroscopic techniques. Coordination through the pyridine nitrogen occurs in all cases. Solvation studies in DMSO indicated that dissociation of the ligands and their complete replacement by solvent molecules occurs. 相似文献
5.
Junia O. Alves Bruno G. Botelho Marcelo M. Sena Rodinei Augusti 《Journal of mass spectrometry : JMS》2013,48(10):1109-1115
Direct infusion electrospray ionization mass spectrometry in the positive ion mode [ESI(+)‐MS] is used to obtain fingerprints of aqueous–methanolic extracts of two types of olive oils, extra virgin (EV) and ordinary (OR), as well as of samples of EV olive oil adulterated by the addition of OR olive oil and other edible oils: corn (CO), sunflower (SF), soybean (SO) and canola (CA). The MS data is treated by the partial least squares discriminant analysis (PLS‐DA) protocol aiming at discriminating the above‐mentioned classes formed by the genuine olive oils, EV (1) and OR (2), as well as the EV adulterated samples, i.e. EV/SO (3), EV/CO (4), EV/SF (5), EV/CA (6) and EV/OR (7). The PLS‐DA model employed is built with 190 and 70 samples for the training and test sets, respectively. For all classes (1–7), EV and OR olive oils as well as the adulterated samples (in a proportion varying from 0.5 to 20.0% w/w) are properly classified. The developed methodology required no ions identification and demonstrated to be fast, as each measurement lasted about 3 min including the extraction step and MS analysis, and reliable, because high sensitivities (rate of true positives) and specificities (rate of true negatives) were achieved. Finally, it can be envisaged that this approach has potential to be applied in quality control of EV olive oils. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
6.
Pedro Rocha ngela Vilas‐Boas Natacha Fontes Dulce Geraldo Ftima Bento 《Electroanalysis》2020,32(1):159-165
The electrochemical oxidation processes that occur during a voltammetric assay in wine samples lead to the formation of species that obstructs the surface and reduce their active area. This effect is critical for screen printed carbon electrodes (SPCE) and leads to abnormal low values of the total polyphenols content of wines, ca. 72 % lower than those obtained with glassy carbon electrodes. This effect was examined using 10 red and Port wine samples. Mechanical polishing and electrochemical‐based treatments for the removal of this fouling layer were tested. The best results were obtained by electrochemical activation in at a constant potential of 1.2 V during 100 s Na2CO3 saturated solution, and by polishing. The success of some of these treatments brings an added value to SPCE, as it opens the possibility of their reuse in the wine analysis. This outcome is particularly relevant for quality control where a huge number of analysis is performed and the reduction of cost may dictates the choice of the analytical method. 相似文献
7.
New applications of cotype to the theory of absolutely summing linear operators between Banach spaces are proved in this paper. Among other consequences we extend/complement some classical results of Bennett (Duke Math J 44:603?C639, 1977) on the existence of non-absolutely summing operators between ? p spaces and of Davis and Johnson (Stud Math 51:81?C85, 1974) on the existence of compact non-absolutely summing linear operators. We also point out that some of our results are sharp. 相似文献
8.
A distribution network problem arises in a lower level of an hierarchical modeling approach for telecommunication network planning. This paper describes a model and proposes a lagrangian heuristic for designing a distribution network. Our model is a complex extension of a capacitated single commodity network design problem. We are given a network containing a set of sources with maximum available supply, a set of sinks with required demands, and a set of transshipment points. We need to install adequate capacities on the arcs to route the required flow to each sink, that may be an intermediate or a terminal node of an arborescence. Capacity can only be installed in discrete levels, i.e., cables are available only in certain standard capacities. Economies of scale induce the use of a unique higher capacity cable instead of an equivalent set of lower capacity cables to cover the flow requirements of any link. A path from a source to a terminal node requires a lower flow in the measure that we are closer to the terminal node, since many nodes in the path may be intermediate sinks. On the other hand, the reduction of cable capacity levels across any path is inhibited by splicing costs. The objective is to minimize the total cost of the network, given by the sum of the arc capacity (cables) costs plus the splicing costs along the nodes. In addition to the limited supply and the node demand requirements, the model incorporates constraints on the number of cables installed on each edge and the maximum number of splices at each node. The model is a NP-hard combinatorial optimization problem because it is an extension of the Steiner problem in graphs. Moreover, the discrete levels of cable capacity and the need to consider splicing costs increase the complexity of the problem. We include some computational results of the lagrangian heuristics that works well in the practice of computer aided distribution network design. 相似文献
9.
Eliane Gonçalves Gomes João Carlos Correia Baptista Soares de Mello Geraldo da Silva e Souza Lidia Angulo Meza João Alfredo de Carvalho Mangabeira 《Annals of Operations Research》2009,169(1):167-181
The aim of this paper is to use DEA models to evaluate sustainability in agriculture. Several variables are taken into account
and the resulting efficiency is measured by comparison. The performance of family farms is analysed here (variables: farmed
area, work force, and production). As agricultural sustainability depends on the maintenance of systems of production for
long periods of time, the models were run for the years of 1986 and 2002. Tiered DEA models were used to group farmers in
sustainability categories. Non-parametric regression models were used to identify the factors affecting the efficiency measurements.
All the results indicate that the majority of the farmers increased their efficiency along the time. These improvements may
support the existence of sustainability. 相似文献
10.
S. M. Dal Bosco R. S. Jimenez C. Vignado J. Fontana B. Geraldo F. C. A. Figueiredo D. Mandelli W. A. Carvalho 《Adsorption》2006,12(2):133-146
The adsorption capacities of commercial and Brazilian natural clays were evaluated to test their applications in wastewater
control. We investigated the process of sorption of manganese(II) and cadmium(II) present in synthetic aqueous effluents,
by calculating the adsorption isotherms at 298 K using batch experiments. The influence of temperature and pH on the adsorption
process was also studied. Adsorption of metals was best described by a Langmuir isotherm, with values of Q
0 parameter, which is related to the sorption capacity, corresponding to 6.3 mg g− 1 for K-10/Cd(II), 4.8 mg g− 1 for K-10/Mn(II), 11.2 mg g− 1 for NT-25/Cd(II) and 6.0 mg g− 1 for NT-25/Mn(II). We observed two distinct adsorption mechanisms that may influence adsorption. At the first 5 min of interaction,
a cation exchange mechanism that takes place at exchange sites located on (001) basal planes is predominant. This process
is inhibited by low pH values. After this first and fast step, a second sorption mechanism can be related to formation of
inner-sphere surface complexes, which is formed at edges of the clay. The rate constants and the initial sorption rates correlate
positively with temperature in all studied systems, denoting the predominance of a physisorption process. The addition of
complexing agents that are incorporated within the K10 structure, enhance metal uptake by the adsorbent. The results have
shown that both Cd(II) and Mn(II) were totally retained from a 50 mg L− 1 solution when K10 grafted with ammonium pyrrolidinedithiocarbamate (APDC) was used as adsorbent. 相似文献