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81.
Wenden Charles J.A. Soriano Flávio A. Falcão Nascimento J.H. Rodrigues 《Journal of Differential Equations》2013
In this paper we consider a vibrating system of Bresse type, in a one-dimensional bounded domain with nonlinear localized damping mechanisms acting in all the three wave equations. We obtain some rates of decay for its solutions with no restrictions around the coefficients as well as the condition of equal-speed wave propagation. A new result concerning an internal observability for the conservative system was also proved in order to reach the asymptotics above. 相似文献
82.
Layered stable equilibria of a reaction-diffusion equation with nonlinear Neumann boundary condition
Arnaldo Simal do Nascimento Renato José de Moura 《Journal of Mathematical Analysis and Applications》2008,347(1):123-135
In this work we investigate the existence and asymptotic profile of a family of layered stable stationary solutions to the scalar equation ut=ε2Δu+f(u) in a smooth bounded domain Ω⊂R3 under the boundary condition εν∂u=δεg(u). It is assumed that Ω has a cross-section which locally minimizes area and limε→0εlnδε=κ, with 0?κ<∞ and δε>1 when κ=0. The functions f and g are of bistable type and do not necessarily have the same zeros what makes the asymptotic geometric profile of the solutions on the boundary to be different from the one in the interior. 相似文献
83.
do Amaral M. G. Aragão de Carvalho C. Pol M. E. Shellard R. C. 《Zeitschrift fur Physik C Particles and Fields》1986,32(4):609-614
Zeitschrift für Physik C Particles and Fields - We study the finite temperature behaviour of λφ4 theory in two and three dimensions, using Monte Carlo simulations. We renormalize the... 相似文献
84.
C.V.S. Ieggli D. Bohrer S. Noremberg P.C. do Nascimento L.M. de Carvalho S.L. Vieira R.N. Reis 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009
An oil-in-water formulation has been optimized to determine trace levels of selenium in whole hen eggs by graphite furnace atomic absorption spectrometry. This method is simpler and requires fewer reagents when compared with other sample pre-treatment procedures. Graphite furnace atomic absorption spectrometric (GF AAS) measurement was carried out using standard addition calibration and Pd as a modifier. The precision, expressed as relative standard deviation, was better than 5% and the limit of detection was 1 µg L− 1. The validation of the method was performed against a standard reference material Whole Egg Powder (RM 8415), and the measured Se corresponded to 95.2% of the certified value. The method was used for the determination of the Se level in eggs from hens treated with Se dietary supplements. Inorganic and organic Se sources were added to hen feed. The Se content of eggs was higher when hens were fed with organic Se compared to the other treatments. The proposed method, including sample emulsification for subsequent Se determination by GF AAS has proved to be sensitive, reproducible, simple and economical. 相似文献
85.
A. R. Lopes M. H.F. Bettega M.T. do N. Varella M. A.P. Lima 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,37(3):385-392
We report elastic (rotationally summed) and rotationally resolved
cross-sections for scattering of low-energy electrons by the
C3H4 isomers allene, propyne, and cyclopropene, which belong
to the D2d, C3v, and C2v groups, respectively. We
employed the Schwinger multichannel method with pseudopotentials at
the static-exchange approximation, combined with the
adiabatic-nuclei-rotation (ANR) approximation to calculate the
rotational excitation cross-sections for energies ranging from 5
to 30 eV. Our rotational resolved cross-sections show the isomer effect
more strongly related to scattering potentials of different molecular
geometries and to transition selection rules than to differences in mass
distribution which account for the energy spacing in the rotational
spectra of the molecules. 相似文献
86.
Solvent effect on the tautomers' stabilities of protonated N,N‐dimethylnitrosamine: The role of hydrogen bonds network
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Railton B. de Andrade Elizete Ventura Silmar A. do Monte 《International journal of quantum chemistry》2017,117(4)
DFT calculations have been applied in order to study the free energies of the structures corresponding to the three different protonation sites of N,N‐dimethylnitrosamine (DMNA). The solvent effect has been taken into account through the study of clusters consisting of protonated DMNA and up to four explicit water molecules, either in the absence or in the presence of a continuum (CPCM) solvation model. Addition of water molecules has been done by a careful screening procedure through which all important hydrogen bonds are likely to be considered. Protonation of DMNA makes all their lone pairs no longer available for hydrogen bond formation with water molecules, such that hydrogen bonds have been observed, for almost all structures, only between water molecules and between one water molecule and the protonated DMNA, in this latter case intermediated by the proton. The stabilities of the solvated structures are governed not only by the number of hydrogen bonds but also by the positions of the water molecules involved in these bonds, as well as by which of them donate or accept H atoms. Our results indicate that oxygen protonation is the most favorable one, regardless of the presence of water molecules. In vacuum protonation at the N‐amino ( 2a ) is approximately as favorable as protonation at the N nitroso ( 2c ). However, in water the former protonation is by far the less favorable one. Our best estimates for the ΔG values in bulk solvent are: ΔG( 2a ) ≈ 17.9, ΔG( 1c ) ≈ 4.3, and ΔG( 2c ) ≈ 4.9 kcal/mol. 相似文献
87.
A novel approach of using a gold disc microelectrode to analyze sweat samples for copper ions by anodic square wave stripping voltammetry (SW stripping voltammetry) is described. Sweat was collected from the lower back of four subjects after physical exercise and the sample volume required for the determinations was 100 μL. Under the optimized conditions, the calibration plot was linear over the range 1-100 μmol L−1 Cu(II) with a limit of detection of 0.25 μmol L−1. The precision was evaluated by carrying out five replicate measurements in a 1 μmol L−1 Cu(II) solution and the standard deviation was found to be 1.5%. Measurements were performed by inserting the microelectrode into sweat drops and Cu(II) concentrations in the analyzed samples ranged from 0.9 to 28 μmol L−1. Values obtained by the proposed voltammetric method agreed well with those found using graphite furnace atomic absorption spectroscopy (GFAAS). 相似文献
88.
Maurício Hilgemann Fritz Scholz Heike Kahlert Leandro Machado de Carvalho Marcelo Barcellos da Rosa Ulrike Lindequist Martina Wurster Paulo C. do Nascimento Denise Bohrer 《Electroanalysis》2010,22(4):406-412
A new electrochemical assay has been developed which is based on quantifying the attack of OH. radicals on a self‐assembled thiol monolayer on electrodes in the presence and absence of antioxidants. The OH. radicals were produced in Fenton solutions. The radical scavengers diminish the concentration of the OH. radicals in the Fenton solution, and the extent of thiol layer destruction is monitored with the help of a redox probe in solution, the signal of which is only generated at SAM‐free electrode surface. The results of the electrochemical assay were compared with those of the standard DPPH. assay. In case of each plant extract, an excellent linear correlation was observed between the radical scavenging activity and the concentration of plant extracts; however, the scavenging properties of different plants strongly differ in the electrochemical and the DPPH. assay. Since the proposed new method probes the reactivity of radical scavengers towards OH., one of the most important reactive oxygen radicals in tissues, it is supposed to provide much more relevant information than the DPPH. or other assays. 相似文献
89.
In this work Cu and Fe bioavailability in cashew nuts was evaluated using in vitro method. Extractions with simulated gastric and intestinal fluids and dialysis procedures were applied for this purpose. The proteins separation and quantification were performed by size exclusion chromatography (SEC) coupled on-line to ultra-violet (UV) and off-line to simultaneous multielement atomic absorption spectrometry (SIMAAS). The SEC-UV and SIMAAS profiles of the protein fractions obtained by alkaline extraction (NaOH) and precipitation with HCl indicated the presence of high and low molecular weight species in the range between >75 kDa and 9.3 kDa. Almost 83% of Cu and 78% of Fe were extracted during cashew nut digestion and 90% of both elements were dialyzed. With these results it is possible to assume that 75% of Cu and 70% of Fe present in cashew nut could be bioavailable. The SEC-UV and SIMAAS chromatographic profiles obtained after in vitro gastrointestinal digestion reveal that Cu and Fe not dialyzed can be associated to a compound of 9.2 kDa. 相似文献
90.
Aline Machado de Castro Kelly Cristina Nascimento Rodrigues Pedro Juliana Cunha da Cruz Marcela Costa Ferreira Selma Gomes Ferreira Leite Nei Pereira 《Applied biochemistry and biotechnology》2010,162(7):2111-2122
Sugarcane bagasse is an agroindustrial residue generated in large amounts in Brazil. This biomass can be used for the production
of cellulases, aiming at their use in second-generation processes for bioethanol production. Therefore, this work reports
the ability of a fungal strain, Trichoderma harzianum IOC-4038, to produce cellulases on a novel material, xylan free and cellulose rich, generated from sugarcane bagasse, named
partially delignified cellulignin. The extract produced by T. harzianum under submerged conditions reached 745, 97, and 559 U L−1 of β-glucosidase, FPase, and endoglucanase activities, respectively. The partial characterization of this enzyme complex
indicated, using a dual analysis, that the optimal pH values for the biocatalysis ranged from 4.9 to 5.2 and optimal temperatures
were between 47 and 54 °C, depending on the activity studied. Thermal stability analyses revealed no significant decrease
in activity at 37 °C during 23 h of incubation. When compared to model strains, Aspergillus niger ATCC-16404 and Trichoderma reesei RutC30, T. harzianum fermentation was faster and its extract showed a better balanced enzyme complex, with adequate characteristics for its application
in simultaneous saccharification and fermentation processes. 相似文献