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91.
92.
J. C. P. Pina A. M. Dias P. F. P. de Matos P. M. G. P. Moreira P. M. S. T. de Castro 《Experimental Mechanics》2005,45(1):83-88
In this paper we present the methods of determination and the stress obtained at the periphery of a cold expanded hole in
a 2024-T3 Alclad aluminum alloy sheet. The measurements in the aluminum clad were performed by the sin2Ψ method, taking experimental precautions to deal with the texture effects. In the core aluminum a special method had to be
implemented to determine the stress values in a direction not accessible to the X-ray diffraction. The strains were measured
in sample orientations selected according to the texture characteristics and stress factorsF
ij
were used to calculate the stress tensor. TheF
ij
values were determined assuming a quasi-isotropic material behavior, after concluding that the stress results were not significantly
affected by factors calculated for textured material. The residual stress profile, both in the clad and in the sheet, shows
a nearly axisymmetric stress state. Compressive stresses were observed near the periphery of the hole, with values that are
higher on the exit than on the entrance face. Residual stresses were also higher in the hoop direction than in the radial
direction. They decreased with the radial distance to the hole and affected the previous stress state over a distance of 6
mm. The plastic deformation induced by the cold expansion is well evidenced by the FWHM values, which in the affected zone
decrease with increasing distance from the hole edge. 相似文献
93.
Signori AM Santos Kde O Eising R Albuquerque BL Giacomelli FC Domingos JB 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):17772-17779
A new and straightforward method for screening highly catalytically active silver nanoparticle-polymer composites derived from branched polyethyleneimine (PEI) is reported. The one-step systematic derivatization of the PEI scaffold with alkyl (butyl or octyl) and ethanolic groups led to a structural diversity correlated to the stabilization of silver nanoparticles and catalysis. Analysis of PEI derivative libraries identified a silver nanoparticle-polymer composite that was able to efficiently catalyze the p-nitrophenol reduction by NaBH(4) in water with a rate constant normalized to the surface area of the nanoparticles per unit volume (k(1)) of 0.57 s(-1) m(-2) L. Carried out in the presence of excess NaBH(4), the catalytic reaction was observed to follow pseudo-first-order kinetics and the apparent rate constant was linearly dependent on the total surface area of the silver nanoparticles (Ag-NPs), indicating that catalysis takes place on the surface of the nanoparticles. All reaction kinetics presented induction periods, which were dependent on the concentration of substrates, the total surface of the nanoparticles, and the polymer composition. All data indicated that this induction time is related to the resistance to substrate diffusion through the polymer support. Hydrophobic effects are also assumed to play an important role in the catalysis, through an increase in the local substrate concentration. 相似文献
94.
Paula Santos Nunes Marília Santos Bezerra L. P. Costa Juliana Cordeiro Cardoso R. L. C. AlbuquerqueJr. M. O. Rodrigues Gabriela Borin Barin Francilene Amaral da Silva A. A. S. Araújo 《Journal of Thermal Analysis and Calorimetry》2010,99(3):1011-1014
The purpose of this study was to evaluate the physical–chemical properties of collagen (CL) and usnic acid/collagen-based
(UAC) films, using differential thermal analysis (DTA), thermogravimetry (TG/DTG), infrared spectroscopy (FTIR), and scanning
electron microscopy (SEM). Both films were prepared by casting process using polyethylene glycol 1500 (PEG 1500) as plasticizer.
In the spectrum of UAC, similar bands of the usnic acid are observed, indicating that the polymerization (film formation)
did not affect the stability of the drug. Distinctly, DTA curve of UAC did not show an endothermic peak at 201 °C, indicative
that the drug was incorporated into the polymeric system. These results were corroborated by the scanning electron microscopy
(SEM). The TG/DTG curves of UAC presented a different thermal decomposition profile compared to the individual compounds and
CL. These findings suggest the occurrence of molecular dispersion or solubilization of the drug in the collagen film. 相似文献
95.
96.
E. G. Moreira M. B. A. Vasconcellos M. G. M. Catharino V. A. Maihara M. Saiki 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(3):819-822
Homogeneity study is one of the steps in reference material, RM, characterization. Due to its inherent characteristics, Instrumental
Neutron Activation Analysis, INAA, is an analytical technique of choice for homogeneity testing. An interesting possibility
is the use of complementary gamma ray photopeaks to confirm INAA homogeneity test results. In this study, the use of the complementary
gamma ray photopeaks of 110mAg, 82Br, 60Co, 134Cs, 152Eu, 59Fe, 140La, 233Pa (for Th determination), 46Sc and 75Se radionuclides was investigated in the between bottle homogeneity study of a mussel candidate RM under preparation at IPEN–CNEN/SP.
Although some photopeaks led to biased element content results, the use of complementary gamma ray photopeaks proved to be
helpful in supporting homogeneity study conclusions for the new RM under characterization. 相似文献
97.
In a paper from 1954 Marstrand proved that if K ⊂ ℝ2 is a Borel set with Hausdorff dimension greater than 1, then its one-dimensional projection has positive Lebesgue measure
for almost-all directions. In this article, we give a combinatorial proof of this theorem, extending the techniques developed
in our previous paper [9]. 相似文献
98.
Fabric dependence of quasi-waves in anisotropic porous media 总被引:1,自引:0,他引:1
Assessment of bone loss and osteoporosis by ultrasound systems is based on the speed of sound and broadband ultrasound attenuation of a single wave. However, the existence of a second wave in cancellous bone has been reported and its existence is an unequivocal signature of poroelastic media. To account for the fact that ultrasound is sensitive to microarchitecture as well as bone mineral density (BMD), a fabric-dependent anisotropic poroelastic wave propagation theory was recently developed for pure wave modes propagating along a plane of symmetry in an anisotropic medium. Key to this development was the inclusion of the fabric tensor--a quantitative stereological measure of the degree of structural anisotropy of bone--into the linear poroelasticity theory. In the present study, this framework is extended to the propagation of mixed wave modes along an arbitrary direction in anisotropic porous media called quasi-waves. It was found that differences between phase and group velocities are due to the anisotropy of the bone microarchitecture, and that the experimental wave velocities are more accurately predicted by the poroelastic model when the fabric tensor variable is taken into account. This poroelastic wave propagation theory represents an alternative for bone quality assessment beyond BMD. 相似文献
99.
A new, Eddington inspired theory of gravity was recently proposed by Ba?ados and Ferreira. It is equivalent to general relativity in vacuum, but differs from it inside matter. This viable, one-parameter theory was shown to avoid cosmological singularities and turns out to lead to many other exciting new features that we report here. First, for a positive coupling parameter, the field equations have a dramatic impact on the collapse of dust, and do not lead to singularities. We further find that the theory supports stable, compact pressureless stars made of perfect fluid, which provide interesting models of self-gravitating dark matter. Finally, we show that the mere existence of relativistic stars imposes a strong, near optimal constraint on the coupling parameter, which can even be improved by observations of the moment of inertia of the double pulsar. 相似文献
100.
We study the coupling of massive scalar fields to matter in orbit around rotating black holes. It is generally expected that orbiting bodies will lose energy in gravitational waves, slowly inspiraling into the black hole. Instead, we show that the coupling of the field to matter leads to a surprising effect: because of superradiance, matter can hover into "floating orbits" for which the net gravitational energy loss at infinity is entirely provided by the black hole's rotational energy. Orbiting bodies remain floating until they extract sufficient angular momentum from the black hole, or until perturbations or nonlinear effects disrupt the orbit. For slowly rotating and nonrotating black holes floating orbits are unlikely to exist, but resonances at orbital frequencies corresponding to quasibound states of the scalar field can speed up the inspiral, so that the orbiting body sinks. These effects could be a smoking gun of deviations from general relativity. 相似文献