A preform design method for sheet superplastic bulging with finite element modeling

Superplastic bulging is the most successful application of superplastic forming (SPF) in industry, but the non-uniform wall thickness distribution of parts formed by it is a common technical problem yet to be overcome. Based on a rigid-viscoplastic finite element program developed by the authors, for simulation of the sheet superplastic forming process combined with the prediction of microstructure variations (such as grain growth and cavity growth), a simple and efficient preform design method is proposed and applied to the design of preform mould for manufacturing parts with uniform wall thickness. Examples of formed parts are presented here to demonstrate that the technology can be used to improve the uniformity of wall thickness to meet practical requirements. (C) 2004 Elsevier B.V. All rights reserved.

Superplastic deformation of directionally solidified nanofibrillar Al2O3-Y3Al5O12-ZrO2 eutectics

Nanofibrillar Al2O3–Y3Al5O12–ZrO2 eutectic rods were manufactured by directional solidification from the melt at high growth rates in an inert atmosphere using the laser-heated floating zone method. Under conditions of cooperative growth, the ternary eutectic presented a homogeneous microstructure, formed by bundles of single-crystal c-oriented Al2O3 and Y3Al5O12 (YAG) whiskers of ≈100 nm in width with smaller Y2O3-doped ZrO2 (YSZ) whiskers between them. Owing to the anisotropic fibrillar microstructure, Al2O3–YAG–YSZ ternary eutectics present high strength and toughness at ambient temperature while they exhibit superplastic behavior at 1600 K and above. Careful examination of the deformed samples by transmission electron microscopy did not show any evidence of dislocation activity and superplastic deformation was attributed to mass-transport by diffusion within the nanometric domains. This combination of high strength and toughness at ambient temperature together with the ability to support large deformations without failure above 1600 K is unique and shows a large potential to develop new structural materials for very high temperature structural applications.

Superplasticity and superplastic forming ability of a Zr-Ti-Ni-Cu-Be bulk metallic glass in the supercooled liquid recgion

The superplastic deformation behavior and superplastic forming ability of the Zr41.25Ti13.75Ni10Cu12.5Be22.5 (at.%) bulk metallic glass (BMG) in the supercooled liquid region were investigated. The isothermal tensile results indicate (hat the BMG exhibits a Newtonian behavior at low strain rates but a non-Newtonian behavior at hiqh-strain rates in the initial deformation stage. The maximum elongation reaches as high as 1624% at 656 K. and nanocrystallization was found to occur during the deformation process. Based cm the analysis on tensile deformation. a gear-like micropart is successfully die-forged via a superplastic forgings process. demonstrating that the BMG has excellent workability in the supercooled liquid region. (C) 2004 Elsevier B.V. All rights reserved.

On the finite element modeling of fatigue crack growth in pressurized cylindrical shells

A methodology for the computational modeling of the fatigue crack growth in pressurized shell structures, based on the finite element method and concepts of Linear Elastic Fracture Mechanics, is presented. This methodology is based on that developed by Potyondy [Potyondy D, Wawrzynek PA, Ingraffea, AR. Discrete crack growth analysis methodology for through crack in pressurized fuselage structures. Int J Numer Methods Eng 1995;38:1633-1644], which consists of using four stress intensity factors, computed from the modified crack integral method, to predict the fatigue propagation life as well as the crack trajectory, which is computed as part of the numerical simulation. Some issues not presented in the study of Potyondy are investigated herein such as the influence of the crack increment size and the number of nodes per element (4 or 9 nodes) on the simulation results by means of a fatigue crack propagation simulation of a Boeing 737 airplane fuselage. The results of this simulation are compared with experimental results and those obtained by Potyondy [1]. (C) 2008 Elsevier Ltd. All rights reserved.

Biomechanical analysis of sutures used for mesh fixation in the donor area after removal of the rectus abdominis muscle

Background: The use of synthetic mesh for abdominal wall closure after removal of the rectus abdominis is established but not standardised. This study compares two forms of mesh fixation: a simple suture, which fixes the mesh to the edges of the defect on the anterior rectus abdominis fascia; and total fixation, which incorporates the fasciae of the internal oblique, external oblique and transverse muscles in the suture, anchoring the mesh in the position of the removed muscle. Method: A total of 16 fresh cadavers were dissected. Two sutures were compared: simple and total. Three different sites were analysed: 5 cm above, 5 cm below and at the level of the umbilicus. The two sutures compared were tested in each region using a standardised technique. All sutures were performed with nylon 0, perpendicular to the linea alba. Each suture was secured to a dynamometer, which was pulled perpendicularly towards the midline until the rupture of the aponeurosis. `Rupture resistance` was measured in kilogram force. The mean among the groups was compared using the paired Student`s t-test to a significance level of 1% (p < 0.01). Results: The mean rupture resistance of the total suture was 160% higher than that of the simple suture. Conclusion: The total suture includes the external oblique, internal oblique and transverse fasciae, which are multi-directional, and creates a much higher resistance when compared with the simple suture. Total suture may reduce the incidence of bulging and hernias of the abdominal wall after harvesting the rectus abdominis muscle, but comparative clinical studies are necessary. (C) 2010 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.

Mechanical ventilation for the treatment of severe excessive dynamic airway collapse

[Excerpt] We read with interest the case report by Ismael et al1 describing a patient with Sjo¨gren’s syndrome and cystic lung disease who could not be weaned from a ventilator due to severe central excessive dynamic airway collapse (EDAC) of the lower part of the trachea and proximal bronchi. EDAC corresponds to the expiratory bulging of the tracheobronchial wall without known airway structural abnormalities, leading to a decrease of at least 50% in internal diameter.2 It is a rare and underdiagnosed entity, commonly confused with other respiratory diseases such as asthma and COPD. Although noninvasive procedures such as cervicothoracic computed tomography scan on inspiration and expiration may suggest the disorder, the accepted standard method for diagnosis is bronchoscopy.3-7 (...).

A long, naturally presented immunodominant epitope from NY-ESO-1 tumor antigen: implications for cancer vaccine design.

The tumor antigen NY-ESO-1 is a promising cancer vaccine target. We describe here a novel HLA-B7-restricted NY-ESO-1 epitope, encompassing amino acids 60-72 (APRGPHGGAASGL), which is naturally presented by melanoma cells. The tumor epitope bound to HLA-B7 by bulging outward from the peptide-binding cleft. This bulged epitope was not an impediment to T-cell recognition, however, because four of six HLA-B7(+) melanoma patients vaccinated with NY-ESO-1 ISCOMATRIX vaccine generated a potent T-cell response to this determinant. Moreover, the response to this epitope was immunodominant in three of these patients and, unlike the T-cell responses to bulged HLA class I viral epitopes, the responding T cells possessed a remarkably broad TCR repertoire. Interestingly, HLA-B7(+) melanoma patients who did not receive the NY-ESO-1 ISCOMATRIX vaccine rarely generated a spontaneous T-cell response to this cryptic epitope, suggesting a lack of priming of such T cells in the natural anti-NY-ESO-1 response, which may be corrected by vaccination. Together, our results reveal several surprising aspects of antitumor immunity and have implications for cancer vaccine design.

Extratracheal biodegradable splint to treat life-threatening tracheomalacia.

A 9-month-old girl presented with life-threatening acute respiratory failure 1 week after the surgical correction of a double aortic arch, which was due to a severe bulging of the pars membranacea into the lumen of the trachea that produced a complete obstruction of the lower trachea. Under cardiopulmonary bypass, a Y-shaped posterior biodegradable splint was placed behind the trachea and sutured to the posterior trachea, and a simultaneous right aortic arch aortopexy was performed. Thereafter, the child recovered normal respiratory function. Follow-up bronchoscopy showed a posterior dip at the splint level and an asymptomatic persistent posterior compression of the right main bronchus.

Partial trisomy 20q in a newborn with dextrocardia.

A female newborn is reported with dextrocardia and a partial trisomy 20q, derived from a t(2;20) paternal translocation. The most discriminating findings of the condition include brachycephaly, bulging forehead, deep set eyes, short nose, large ears, dimpled chin, short neck and a heart defect. Previously reported patients with this rare chromosomal anomaly are reviewed.

Benign fibro-osseous lesions of the maxillas: analysis of 11 cases

Introduction: A study is made of the principal characteristics of the oral lesions biopsied in our Service of Oral Surgery and histologically diagnosed as corresponding to fibro-osseous lesions of the maxillas. Patients and methods: A retrospective review was made of all the biopsies made in a Service of Oral Surgery between 1996 and 2003. The reason for consultation was analyzed, along with patient age, sex, clinical and radiological characteristics, tentative diagnosis, histological diagnosis and treatment provided. Results: A total of 1238 biopsies were performed during the study period. Of these, only 11 corresponded to benign fibro-osseous lesions (7 women and 4 men). The mean patient age was 44 years (range 19-72 years). The most frequent location was the mandible (8 of the cases). In 7 patients the lesions constituted casual radiological findings; 4 presented bulging of the vestibular cortical bone, though only one of them reported pain. The histological diagnoses comprised 7 cemento-ossifying fibromas and 4 fibrous dysplasias. In 9 cases surgical resection was carried out, while in one case an incisional biopsy was performed, and in the remaining case curettage was decided. Discussion: These lesions are more frequent in women than in men, and the age at presentation is variable. In terms of lesion location, fibrous dysplasia is more common in the upper maxilla, while cemento-ossifying fibroma is more frequently found in the mandible. The diagnosis of such lesions is established upon contrasting the data obtained from the anamnesis, physical examination, the radiological characteristics, the intraoperative findings and the histological study, since both disorders have similar clinical and histological features- despite the fact that they constitute distinct disease conditions.

Estado del arte sobre la producción institucional y de la teoría crítica en torno al derecho a la ciudad.

Puede entenderse la ciudad como una manifestación de las disputas surgidas desde el plano de lo social. En ese mismo sentido surge el concepto del derecho a la ciudad, entendido en términos generales como aquel que se tiene para decidir el tipo de urbe y su organización. Así, este derecho ha estado limitado a la construcción de espacios propicios para la acumulación de capital, para una élite minoritaria capaz de configurar la ciudad, generando un caos urbano que se evidencia en la segregación socio-espacial, abultando las arcas de los poderosos a la vez que se aíslan a las mayorías trabajadoras del ejercicio el derecho a cambiar y reinventar la ciudad para satisfacer sus necesidades y garantizar sus sueños.

Wave trapping in a two-dimensional sound-soft or sound-hard acoustic waveguide of slowly-varying width

In this paper we derive novel approximations to trapped waves in a two-dimensional acoustic waveguide whose walls vary slowly along the guide, and at which either Dirichlet (sound-soft) or Neumann (sound-hard) conditions are imposed. The guide contains a single smoothly bulging region of arbitrary amplitude, but is otherwise straight, and the modes are trapped within this localised increase in width. Using a similar approach to that in Rienstra (2003), a WKBJ-type expansion yields an approximate expression for the modes which can be present, which display either propagating or evanescent behaviour; matched asymptotic expansions are then used to derive connection formulae which bridge the gap across the cut-off between propagating and evanescent solutions in a tapering waveguide. A uniform expansion is then determined, and it is shown that appropriate zeros of this expansion correspond to trapped mode wavenumbers; the trapped modes themselves are then approximated by the uniform expansion. Numerical results determined via a standard iterative method are then compared to results of the full linear problem calculated using a spectral method, and the two are shown to be in excellent agreement, even when $\epsilon$, the parameter characterising the slow variations of the guide’s walls, is relatively large.

Quartz recrystallization regimes, c-axis texture transitions and fluid inclusion reequilibration in a prograde greenschist to amphibolite facies mylonite zone (Ribeira Shear Zone, SE Brazil)

The crystal-plastic behavior of quartz mylonites from the Ribeira Shear Zone (SE Brazil), a major strike-slip structure that was active during a prograde metamorphic phase related to the Neoproterozoic Brasiliano-Pan African Orogeny, was investigated using a multi-method approach. Geothermobarometry results indicate deformational conditions ranging from similar to 300 to similar to 630 degrees C and 500-700 MPa. A strong correlation between mapped metamorphic zones and a dominance of different dynamic recrystallization mechanisms of quartz occurs within the mylonite zone. Bulging recrystallization (BLG) dominates within the chlorite zone between 300 and 410 degrees C, subgrain rotation recrystallization (SGR) operates within the biotite zone from 410 to 520 degrees C, and grain boundary migration recrystallization (GBM) dominates in the garnet zone above 520 degrees C. The development of quartz c-axis textures is mainly governed by temperature and dynamic recrystallization mechanisms. Textures from BLG zone mylonites are characterized by maxima around Z; SGR zone mylonites display single girdles or asymmetric type I crossed girdles; and GBM zone mylonites comprise maxima around Y and intermediate between X and Z. The scarcity or absence of water-bearing fluid inclusions in quartz mylonites from the SGR and GBM zones, which are dominated by carbonic inclusions, suggests water-deficient conditions, whereas BLG zone mylonites are dominated by water-bearing inclusions. This evidence indicates that water was available in the protoliths but has been eliminated with increasing deformation and deformation temperature. No effect of the water content variation on the quartz microstructural and recrystallized grain size evolution was detected, and little influence on c-axis texture development was observed. Most of the fluid inclusion densities were reequilibrated during the shear zone exhumation history, recording a decompression in the range of 300-500 MPa, while microstructural reequilibration effects related to the prograde metamorphism are largely preserved. Fluid inclusion microstructures and densities from two SGR zone samples preserved evidence for a near isothermal compression within the interior of the Ribeira Shear Zone during the prograde metamorphism. (C) 2009 Elsevier B.V. All rights reserved.

Controle de erosão em estradas rurais não pavimentadas, utilizando sistema de terraceamento com gradiente associado a bacias de captação

Pós-graduação em Agronomia (Irrigação e Drenagem) - FCA