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51.
Diogo P. Rivelli Carlos A. H. Filho Rebeca L. Almeida Cristina D. Ropke Tânia C. H. Sawada Silvia B. M. Barros 《Photochemistry and photobiology》2010,86(5):1005-1007
Chlorogenic acid is a natural potent antioxidant. It can be used in cosmetics formulations, but for this purpose its photochemical stability should be determined to ensure that the compound will not be degraded after UV radiation exposure. To evaluate this possibility, the concentration of a chlorogenic acid solution was determined by HPLC before and after UVA and UVB irradiation. The results indicate that chlorogenic acid is not degraded under UVA or UVB irradiation. 相似文献
52.
Rodrigo R. O. Barros Raul A. Oliveira Leda Maria F. Gottschalk Elba P. S. Bon 《Applied biochemistry and biotechnology》2010,161(1-8):448-454
Although a number of filamentous fungi, such as Trichoderma and Aspergillus, are well known as producers of cellulases, xylanases, and accessory cellulolytic enzymes, the search for new strains and new enzymes has become a priority with the increase in diversity of biomass sources. Moreover, according to the type of pretreatment applied, biomass of the same type may require different enzyme blends to be efficiently hydrolyzed. This study evaluated cellulases, xylanases, and β-glucosidases produced by two fungi, the thermotolerant Acrophialophora nainiana and Ceratocystis paradoxa. Cells were grown in submerged culture on three carbon sources: lactose, wheat bran, or steam-pretreated sugarcane bagasse, a commonly used cattle feed in Brazil. Xylanase and endo-1-4-β-glucanase (CMCase) highest production were found in A. nainiana growing on lactose and reached levels of 2,200 and 2,016 IU/L, respectively. C. paradoxa showed highest activity for xylanase when grown on wheat bran and for β-glucosidase when grown on steam-treated bagasse, at levels of 12,728 and 1,068 IU/mL, respectively. 相似文献
53.
Silvânia Marilene de Lima Jorge Antonio Gómez Valéria P. Barros Greice de S. Vertuan Marilda das Dores Assis Carlos Frederico de Oliveira Graeff Grégoire Jean-François Demets 《Polyhedron》2010
This work presents a new oxovanadium(IV)–cucurbit[6]uril complex, which combines the catalytic properties of the metal ion with the size-excluding properties of the macrocycle cavity. In this coordination compound, the VO2+ ions are coordinated to the oxygen atoms located at the rim of the macrocycle in slightly distorted square-pyramidal configurations, which are in fact C2v symmetries. This combination results in a size-selective heterogeneous catalyst, which is able to oxidize linear alkanes like n-pentane at room temperature, but not styrene, cyclohexane or z-cyclooctene, which are too big to enter the cucurbit[6]uril cavity. The results presented here contribute to understanding the mechanism of alkane catalytic oxidation by oxovanadium(IV) complexes. 相似文献
54.
Paulo J. Magalhães Joana S. VieiraLuís M. Gonçalves João G. PachecoLuís F. Guido Aquiles A. Barros 《Journal of chromatography. A》2010,1217(19):3258-3268
The aim of the present work was the development of a suitable methodology for the separation and determination of phenolic compounds in the hop plant. The developed methodology was based on the sample purification by adsorption of phenolic compounds from the matrix to polyvinylpolypyrrolidone (PVPP) and subsequent desorption of the adsorbed polyphenols with acetone/water (70:30, v/v). At last, the extract was analyzed by HPLC–DAD and HPLC–ESI-MS/MS. The first phase of this work consisted of the study of the adsorption behavior of several classes of phenolic compounds (e.g. phenolic acids, flavonols, and flavanols) by PVPP in model solutions. It has been observed that the process of adsorption of the different phenolic compounds to PVPP (at low concentrations) is differentiated, depending on the structure of the compound (number of OH groups, aromatic rings, and stereochemistry hindrance). For example, within the phenolic acids class (benzoic, p-hydroxybenzoic, protocatechuic and gallic acids) the PVPP adsorption increases with the number of OH groups of the phenolic compound. On the other hand, the derivatization of OH groups (methylation and glycosylation) resulted in a greatly diminished binding. The use of PVPP revealed to be very efficient for adsorption of several phenolic compounds such as catechin, epicatechin, xanthohumol and quercetin, since high adsorption and recovery values were obtained. The methodology was further applied for the extraction and isolation of phenolic compounds from hops. With this methodology, it was possible to obtain high adsorption values (≥80%) and recovery yield values (≥70%) for the most important phenolic compounds from hops such as xanthohumol, catechin, epicatechin, quercetin and kaempferol glycosides, and in addition it allows the identification of about 30 phenolic compounds by HPLC–DAD and HPLC–ESI-MS/MS. 相似文献
55.
S. Di Maria S. Barros J. Bento P. Teles C. Figueira M. Pereira P. Vaz G. Paulo 《Radiation measurements》2011,46(10):1103-1108
The main purpose of this study was to validate and compare Mean Glandular Dose (MGD) values obtained using Monte Carlo simulations with experimental values obtained from Entrance Surface Dose (ESD) and depth dose measurements performed in a Hospital mammography unit. ESD and depth dose were measured using ThermoLuminescent Dosimeters (TLDs), and a tissue equivalent mammography phantom recommended by the American College of Radiology (ACR). Measurements and Monte Carlo simulations were also compared with the MGD calculated using the Automatic Exposure Control (AEC) system of the mammographic unit. In the simulations the Doppler energy broadening effect was also taken into account. The simulated ESD are about 5%–10% higher than the measured ESD values. The deviation between the measured and simulated MGD values in the phantom is of about 15%. The MGD evaluated using the AEC system is smaller both with respect to the Monte Carlo simulation and experimental result by a factor of about 15% and 25% respectively. Moreover the BackScatter Factor (BSF) estimated by Monte Carlo simulations was used for the MGD calculation according to the Wu’s method. Finally the inclusion of the energy broadening effect on MGD calculation produces negligible variations on the simulated results. 相似文献
56.
Lanah Evers Ana Isabel Barros Herman Monsuur Albert Wagelmans 《European Journal of Operational Research》2014
In this paper we simultaneously consider three extensions to the standard Orienteering Problem (OP) to model characteristics that are of practical relevance in planning reconnaissance missions of Unmanned Aerial Vehicles (UAVs). First, travel and recording times are uncertain. Secondly, the information about each target can only be obtained within a predefined time window. Due to the travel and recording time uncertainty, it is also uncertain whether a target can be reached before the end of its time window. Finally, we consider the appearance of new targets during the flight, so-called time-sensitive targets, which need to be visited immediately if possible. We tackle this online stochastic UAV mission planning problem with time windows and time-sensitive targets using a re-planning approach. To this end, we introduce the Maximum Coverage Stochastic Orienteering Problem with Time Windows (MCS-OPTW). It aims at constructing a tour with maximum expected profit of targets that were already known before the flight. Secondly, it directs the planned tour to predefined areas where time-sensitive targets are expected to appear. We have developed a fast heuristic that can be used to re-plan the tour, each time before leaving a target. In our computational experiments we illustrate the benefits of the MCS-OPTW planning approach with respect to balancing the two objectives: the expected profits of foreseen targets, and expected percentage of time-sensitive targets reached on time. We compare it to a deterministic planning approach and show how it deals with uncertainty in travel and recording times and the appearance of time-sensitive targets. 相似文献
57.
58.
Magali A. Rodrigues Sérgio Brochsztain Teresa C. Barros Mauricio S. Baptista Mario J. Politi 《Photochemistry and photobiology》1999,70(1):35-39
Abstract— The effect of the protonation state of a novel aqueous soluble N,N'-di(2-phosphonoethyl)-l,4,5,8-naphthalene-diimide (DPN) on its spectroscopic properties is studied. In aqueous solution DPN depicts linear Lambert-Beer plots up to the solubility limits at pH 1.0, 7.1 and 10.1, in accordance with its solubilization as a monomer. A small increase in the extinction coefficients with pH is observed. Conversely a strong decrease in the fluorescence emission yields are observed with the increase in pH. These results are shown to originate from the distinct efficiencies of the intersystem crossing of DPN as a function of the net charge on the phosphono moieties. Accordingly, from the decrease in fluorescence emission, titration curves were obtained resulting in two pKa of –1.5 and 6.7 in agreement with the potentiometric analysis. In parallel monitoring the amount of heat deposited in the system shows an inverse pattern, that is, increase in the thermal tensing time-resolved signal with pH. Laser flash photolysis and thermal Iensing data in the absence and presence of oxygen show the interplay of an intersystem crossing process with the protonation state of the dye. The changes in protonation from neutral to two- and four-fold charged species are accompanied by an enhancing effect on the naphthalenediimide ring toward spin inversion (triplet formation) and consequently in different fluorescence yields 相似文献
59.
The aim of this note is to clarify a minor mistake in the article: Some Applications of the Hodge-de Rham Decomposition to Ricci solitons. 相似文献
60.
M. Gaspar O. Goncalves S. de Barros J. Eichler 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,1(3):287-290
Differential cross section for scattering of 145.4 keV gamma rays by B, C, Al, Cu and Cd have been measured from 5–25°. For angles <10° it was not possible to separate Rayleigh and Compton scattering; therefore, the sum of the cross sections is given. Rayleigh cross sections have been measured for Pb at 122.1 and 136.5 keV at angles between 20° and 70°. The experimental results are compared with the form factor theory for Rayleigh scattering and the incoherent scattering factor theory for Compton scattering. 相似文献