Nanoindentation mechanical properties characterization of glassy polymeric carbon treated with ion beam

Phenolic resins when heat treated in inert atmosphere up to 1000 degreesC become glassy polymeric carbon (GPC), a chemically inert and biocompatible material useful for medical applications, such as in the manufacture of heart valves and prosthetic devices. In earlier work we have shown that ion bombardment can modify the surface of GPC, increasing its roughness. The enhanced roughness, which depends on the species, energy and fluence of the ion beam, can improve the biocompatibility of GPC prosthetic artifacts. In this work, ion bombardment was used to make a layer of implanted ions under the surface to avoid the propagation of microcracks in regions where cardiac valves should have pins for fixation of the leaflets. GPC samples prepared at 700 and 1500 degreesC were bombarded with ions of silicon. carbon, oxygen and gold at energies of 5, 6, 8 and 10 MeV, respectively, and fluences between 1.0 x 10(13) and 1.0 x 10(16) ions/cm(2). Nanoindentation hardness characterization was used to compare bombarded with non-bombarded samples prepared at temperatures up to 2500 degreesC. The results with samples not bombarded showed that the hardness of GPC increases strongly with the heat treatment temperature. Comparison with ion bombarded samples shows that the hardness changes according to the ion used, the energy and fluence. (C) 2002 Elsevier B.V. B.V. All rights reserved.

A BEM formulation for analysing the coupled stretching-bending problem of plates reinforced by rectangular beams with columns defined in the domain

In this work, a boundary element formulation to analyse plates reinforced by rectangular beams, with columns defined in the domain is proposed. The model is based on Kirchhoff hypothesis and the beams are not required to be displayed over the plate surface, therefore eccentricity effects are taken into account. The presented boundary element method formulation is derived by applying the reciprocity theorem to zoned plates, where beams are treated as thin sub-regions with larger rigidities. The integral representations derived for this complex structural element consider the bending and stretching effects of both structural elements working together. The standard equilibrium and compatibility conditions along interface are naturally imposed, being the bending tractions eliminated along interfaces. The in-plane tractions and the bending and in-plane displacements are approximated along the beam width, reducing the number of degrees of freedom. The columns are introduced into the formulation by considering domain points where tractions can be prescribed. Some examples are then shown to illustrate the accuracy of the formulation, comparing the obtained results with other numerical solutions.

Inclusive b-hadron production cross section with muons in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Non-linear boundary element analysis of floor slabs reinforced with rectangular beams

In this work, a numerical model to perform non-linear analysis of building floor structures is proposed. The presented model is derived from the Kirchhoff-s plate bending formulation of the boundary element method (BENI) for zoned domains, in which the plate stiffness is modified by the presence of membrane effects. In this model, no approximation of the generalized forces along the interface is required and the compatibility and equilibrium conditions along interfaces are imposed at the integral equation level. In order to reduce the number of degrees of freedom, the Navier Bernoulli hypothesis is assumed to simplify the strain field for the thin sub-regions (rectangular beams). The non-linear formulation is obtained from the linear formulation by incorporating initial internal force fields, which are approximated by using the well-known cell sub-division. Then, the non-linear solution of algebraic equations is obtained by using the concept of the consistent tangent operator. The Von Mises criterion is adopted to govern the elasto-plastic material behaviour checked at points along the plate thickness and along the rectangular beam element axes. The numerical representations are accurately obtained by either computing analytically the element integrals or performing the numerical integration accurately using an appropriate sub-elementation scheme. (C) 2007 Elsevier Ltd. All rights reserved.

A BEM formulation based on Reissner's theory to perform simple bending analysis of plates reinforced by rectangular beams

In this work, the plate bending formulation of the boundary element method (BEM), based on the Reissner's hypothesis, is extended to the analysis of plates reinforced by rectangular beams. This composed structure is modelled by a zoned plate, being the beams represented by narrow sub-regions with larger thickness. The integral equations are derived by applying the weighted residual method to each sub-region, and summing them to get the equation for the whole plate. Equilibrium and compatibility conditions are automatically imposed by the integral equations, which treat this composed structure as a single body. In order to decrease the number of degrees of freedom, some approximations are considered for both displacements and tractions along the beam width. The accuracy of the proposed model is illustrated by simple examples whose exact solution are known as well as by more complex examples whose numerical results are compared with a well-known finite element code.

Theoretical model and experimental analysis of glulam beam reinforced with FRP

This work present a study of glulam beams reinforced with FRP. It was developed a theoretical model that calculates strength and stiffness of the beams. The model allows for the calculation of the bending moment, the hypothetical distribution of linear strains along the height of the beam, and considers the wood has a linear elastic fragile behavior in tension parallel to the fibers and bilinear in compression parallel to the fibers, initially elastic and subsequently inelastic, with a negative decline in the stress-strain diagram. The stiffness was calculated by the transformed section method. Twelve non-reinforced and fiberglass reinforced glulam beams were evaluated experimentally to validate the proposed theoretical model. The results obtained indicate good congruence between the experimental and theoretical values.

Resistência ao cisalhamento de vigas “T” de concreto armado: verificação das longarinas da ponte sobre o rio Sororó

O comportamento estrutural de uma viga T permite avaliar diferentes contribuições de resistência ao cisalhamento entre partes distintas de uma mesma seção transversal, permitindo estabelecer diretrizes para a disposição de armadura nessas regiões. Para quantificar as participações de mesas colaborantes e almas desse tipo de seção na resistência característica ao cisalhamento, foram investigadas experimentalmente 10 vigas de concreto armado constituídas de seções T, visando avaliar as recomendações da norma NBR, ACI e EC2 no que se refere ao desempenho de vigas T ao cisalhamento. Uma das vigas foi confeccionada para testemunho e as demais foram idealizadas com variação nas dimensões da mesa, para aumentar assim a área de concreto colaborante da seção. A armadura de flexão foi mantida constante em todos os casos e a armadura de cisalhamento foi suprimida, para que todas as vigas tivessem rupturas por cisalhamento antecipadas em relação à ruína por flexão. O concreto utilizado teve resistência à compressão de 47 MPa. Percebe-se claramente a influência da mesa colaborante na resistência última ao cisalhamento dos elementos estruturais ensaiados. O aumento da carga última foi significativo nas vigas com abas, passando do dobro da carga da viga de referência, e mais ainda, nas vigas com altura (hf) de 80 mm, nas quais a contribuição da mesa foi capaz de modificar o modo de ruptura das peças cujas armaduras de flexão entraram em processo de escoamento e o incremento de rigidez dado aos elementos em virtude do aumento da área de concreto (abas) da seção transversal foi em torno de 25%. A partir destes e outros resultados foi possível amplificar a resistência ao cisalhamento das longarinas da ponte sobre o rio Sororó da ferrovia Carajás em 1,93 vezes a resistência teórica para viga retangular no caso.

A quantum theory for the excitation spectrum of a rectangular Andreev billiard

We consider a N - S box system consisting of a rectangular conductor coupled to a superconductor. The Green functions are constructed by solving the Bogoliubov-de Gennes equations at each side of the interface, with the pairing potential described by a step-like function. Taking into account the mismatch in the Fermi wave number and the effective masses of the normal metal - superconductor and the tunnel barrier at the interface, we use the quantum section method in order to find the exact energy Green function yielding accurate computed eigenvalues and the density of states. Furthermore, this procedure allow us to analyze in detail the nontrivial semiclassical limit and examine the range of applicability of the Bohr-Sommerfeld quantization method.

Evaluation of hollow fiberoptic tips for the conduction of Er : YAG laser

Objective: The use of Er:YAG laser operating in the 3 μm range with adjustable power and pulses has become popular for dental and medical practice due to its high photoablative capacity, surgical precision and antimicrobial action. Background data: The existing fiberoptic tips irradiate lasers parallel to the long axes of the tooth limiting its efficiency in the root canal. Methods: We evaluated hollow fiberoptic tips obtained from silicate glass as a means of Er:YAG laser conduction in dental procedures. The fiber tips were molded from capillary tubes with different profiles so that their ends would have cylindric, conical or spherical shapes. The performance of the three fibers as a means of propagation of Er:YAG (λ = 2.94 μm) laser radiation was compared to that of a solid sapphire fiber at 10 Hz and 200 mJ and of 20 Hz and 500 mJ. The profiles of frontal and lateral burning were visualized on thermal paper. Results: Analysis of these profiles demonstrated that the sapphire tip and the hollow fiber of cylindric section did not differ significantly in the profiles of frontal burning, and no lateral burning was detected. The fibers of the conical and spherical sections, although presenting attenuation in the frontal output power, showed a larger burning area in the frontal profile, in addition to producing lateral burning. Conclusions: The results indicate that commercial hollow fiberoptics have advantages such as easy manufacture of the different tip shapes, great adaptability, low cost, and a low loss of transmission. © Mary Ann Liebert, Inc.

Investigation of the optical absorption of a magnetic colloid from the thermal to the electronic time-scale regime: measurement of the free-carrier absorption cross-section

The free-carrier absorption cross-section sigma of a magnetic colloid composed of magnetite nanoparticles dispersed in oil is obtained by using the Z-scan technique in different experimental conditions of the laser beam. We show that it is possible to obtain sigma with picosecond pulsed and millisecond chopped beams with pulse frequencies smaller than about 30 Hz. For higher pulse frequencies, the heating of the colloidal system triggers the appearance of the Soret effect. This effect artificially increases the value of sigma calculated from the experimental results. The limits of the different experimental setups are discussed. (C) 2012 Optical Society of America

Vibro-Acoustography Beam Formation with Reconfigurable Arrays

In this work, we present a numerical study of the use of reconfigurable arrays (RCA) for vibro-acoustography (VA) beam formation. A parametric study of the aperture selection, number of channels, number of elements, focal distance, and steering parameters is presented to show the feasibility and evaluate the performance of VA imaging based on RCA. The transducer aperture was based on two concentric arrays driven by two continuous-wave or toneburst signals at slightly different frequencies. The mathematical model considers a homogeneous, isotropic, inviscid medium. The point-spread function of the system is calculated based on angular spectrum methods using the Fresnel approximation for rectangular sources. Simulations considering arrays with 50 x 50 to 200 x 200 elements with number of channels varying in the range of 32 to 128 are evaluated to identify the best configuration for VA. Advantages of two-dimensional and RCA arrays and aspects related to clinical importance of the RCA implementation in VA, such as spatial resolution, image frame rate, and commercial machine implementation, are discussed. It is concluded that RCA transducers can produce spatial resolution similar to confocal transducers and steering is possible in the elevational and azimuthal planes. Optimal settings for number of elements, number of channels, maximum steering, and focal distance are suggested for VA clinical applications. Furthermore, an optimization for beam steering based on the channel assignment is proposed for balancing the contribution of the two waves in the steered focus.

Searching for resonances in the unbound Be-6 nucleus by using a radioactive Be-7 beam

Knowledge of the He-3(He-3,2p)He-4 reaction is important for understanding stellar burning and solar neutrino production. Previous measurements have found a surprisingly large rise in the cross section at low energies that could be due to a low-energy resonance in the He-3 + He-3 (Be-6) system or electron screening. In the Be-6 nucleus, however, no excited states have been observed above the first 2(+) state at E (x) = 1.67 MeV up to 23 MeV, even though several are expected. The H-2(Be-7,H-3)Be-6 reaction has been studied for the first time to search for resonances in the Be-6 nucleus that may affect our understanding of the He-3(He-3,2p)He-4 reaction. A 100-MeV radioactive Be-7 beam from the Holifield Radioactive Ion Beam Facility (HRIBF) was used to bombard CD2 targets, and tritons were detected by using the silicon detector array (SIDAR). A combination of reaction mechanisms appears to be necessary to explain the observed triton energy spectrum.

Latent track radius of PTFE irradiated with high energy ion beam

PTFE foils were irradiated with different ion beams (Xe, Au and U) with energies up to 1.5 GeV and fluences between 1 x 10(8) and 1 x 10(13) ions/cm(2) at room temperature. The induced modifications in the polymer were analyzed by FTIR, UV-Vis spectroscopy, and XRD. In the FTIR spectra, the CF2 degradation accompanied by the formation of CF3 terminal and side groups were observed. In the UV-Vis spectra, the observed increase in the absorption at UV wavelengths is an indication of polymer carbonization. From XRD, the amorphization of the material was evidenced by the decrease in the intensity of the main diffraction peak. An exponential fit of the intensity of the IR absorption peaks resulted in the following values: 2.9 +/- 0.8; 4.5 +/- 0.9 and 5.6 +/- 0.8 nm for the latent track radius after irradiation with Xe, Au and U beams, respectively. (C) 2011 Elsevier B.V. All rights reserved.

Discovery and cross-section measurement of neutron-rich isotopes in the element range from neodymium to platinum with the FRS

Using the high-resolution performance of the fragment separator FRS at GSI we have discovered 60 new neutron-rich isotopes in the atomic number range of 60 <= Z <= 78. The new isotopes were unambiguously identified in reactions with a U-238 beam impinging on a Be target at 1 GeV/nucleon. The production cross-section for the new isotopes have been measured down to the pico-barn level and compared with predictions of different model calculations. For elements above hafnium fragmentation is the dominant reaction mechanism which creates the new isotopes, whereas fission plays a dominant role for the production of the new isotopes up to thulium. (C) 2012 Elsevier B.V. All rights reserved.

Performance of electronic devices submitted to X-rays and high energy proton beams

In this work we have studied the radiation effects on MOSFET electronic devices. The integrated circuits were exposed to 10 key X-ray radiation and 2.6 MeV energy proton beam. We have irradiated MOSFET devices with two different geometries: rectangular-gate transistor and circular-gate transistor. We have observed the cumulative dose provokes shifts on the threshold voltage and increases or decreases the transistor's off-state and leakage current. The position of the trapped charges in modern CMOS technology devices depends on radiation type, dose rate, total dose, applied bias and is a function of device geometry. We concluded the circular-gate transistor is more tolerant to radiation than the rectangular-gate transistor. (C) 2011 Elsevier B.V. All rights reserved.