In Saccharomyces cerevisiae, the transcriptional repressor Nrg1 (Negative Regulator of Glucose-repressed genes) and the β-Zip transcription factor Rtg3 (ReTroGrade regulation) mediate glucose repression and signalling from the mitochondria to the nucleus, respectively. Here, we show a novel function of these two proteins, in which alanine promotes the formation of a chimeric Nrg1/Rtg3 regulator that represses the ALT2 gene (encoding an alanine transaminase paralog of unknown function). An NRG1/NRG2 paralogous pair, resulting from a post-wide genome small-scale duplication event, is present in the Saccharomyces genus. Neo-functionalization of only one paralog resulted in the ability of Nrg1 to interact with Rtg3. Both nrg1Δ and rtg3Δ single mutant strains were unable to use ethanol and showed a typical petite (small) phenotype on glucose. Neither of the wild-type genes complemented the petite phenotype, suggesting irreversible mitochondrial DNA damage in these mutants. Neither nrg1Δ nor rtg3Δ mutant strains expressed genes encoded by any of the five polycistronic units transcribed from mitochondrial DNA in S. cerevisiae. This, and the direct measurement of the mitochondrial DNA gene complement, confirmed that irreversible damage of the mitochondrial DNA occurred in both mutant strains, which is consistent with the essential role of the chimeric Nrg1/Rtg3 regulator in mitochondrial DNA maintenance.

Forging is a widely used manufacturing process, and its design and modeling are important to reducing production costs, increasing die lifespan, and improving the mechanical properties of the final product. In this study, the forging process of a connecting rod was modeled using 3D coupled Eulerian Lagrangian (CEL) analysis by FEM. The methodology adopted achieved to determine a preform geometry that reduces final flash and forging load, while ensuring complete filling of the stamp. Starting from the final geometry, the final die was designed. After the first result for an approximately 27% of flash, the material distribution was adjusted decreasing it at the regions where the flash was too large. After an iterative method was applied to determine better preform, a proposal was found that reduced forging force by approximately 42% and the percentage of flash volume by 64% in comparison with the first one. A final flash of about 10% is considered a good objective to reach. Lower values may cause many iterations, not a significant difference in forging loads, the risk of an unfilled die, and complex preform geometries.

The failure of the connectors between the slip ring and rotor of a 2 MW wind turbine was investigated. Visual inspection, low magnification stereomicroscopy and scanning electron microscopy showed the presence of highly branched transgranular cracks. The cracks are in zones of increased stress, as demonstrated by finite elements. The observations show that the failure is caused by stress corrosion cracking (SCC). Fourier transform infrared spectroscopy (FTIR) was used to characterise the insulating varnish of the slip ring. Tropical climate conditions cause the wetting of the components and with a close-by livestock plant is a source of NH3 contamination. Corrections to the design and manufacturing process of the slip rings were suggested to increase the life expectancy of the generator, although the selection of an insulating varnish with higher resistance to environmental exposure is probably the most efficient manner to reduce the incidence of this phenomenon in the future.

Machining is one of the more widely used manufacturing processes in the industry, for this reason, several studies have focused on predicting the effect of variables related to it. In this work, the effect of the equivalent plastic displacement on the orthogonal cutting process, using coupled Lagrangian–Eulerian (CEL) analysis was studied. The workpiece was considered Eulerian solid material to simulate its interaction with the cutting tool and thus, predict material separation and chip morphology. In the present model, the chip morphology was evaluated in terms of the equivalent plastic displacement, segmented chip formation was achieved without the necessity to apply a method of mesh separation and undeleting elements during the calculation solution, which represents an important advantage over the purely Lagrangian method. Additionally, the cutting forces, contact length, angle of the cutting plane, as well as stress, strain, and temperature distribution were obtained.

Bone marrow plays an important role on the mechanical properties of trabecular bone. Its effect on the mechanical properties of porcine trabecular bone is studied in this paper. Uniaxial compression at a low strain rate (0.01 s(-1) to 20% strain) and stress relaxation tests (600 s at 85, 70 and 55% of the max. load) were done on 90 different femur samples. Half the samples were treated to extract the bone marrow. The average pore size of the trabecular network was 0.280 +/- 056 mm. Higher values of elastic modulus (37%), 0.2% yield stress (48%), maximum stress (39%), strain at maximum stress (54%), and toughness (300%), were found for the samples which had the bone marrow extracted and were saturated with a saline solution. A linear relation between the applied load and the relaxation stress of sigma(rel) = 0.76 sigma(o) was found, which means that the trabecular bone behaves as a linear viscoelastic material. A mathematical approximation of the relaxation response was done using a Kohlrausch Williams-Watts model for viscoelastic materials. Results show that it is essential to consider the viscoelastic behavior that the marrow has on the mechanical properties of the trabecular bone. The effect that the bone marrow has on the stress relaxation was found to be negligible at low strain rates and in the elastic stage of deformation.

In this paper, a tube extrusion process by finite element was analyzed, using coupled Eulerian-Lagrangian method (CEL) due to the severe deformation that material presents and thereby avoids distortion of the mesh and adaptive meshing used in Lagrangian models, in order to obtain stress distribution, strains, extrusion force, and flow material behavior. Four isothermal models were performed by modifying the sensitivity of ram speed using discrete rigid tools with general contact option to simulate the interaction between them; 7005 aluminum was considered as the material to be extruded. In order to reduce high computational time application, speed was increased to observe its influence on the results, in other words the variations between the models. As a consequence of this analysis, it was found that while the kinetic energy does not exceed 5 to 10 % of whole internal energy, material flow behavior and stress level are not affected.

In this paper is presented a methodology to generate two-dimensional models of cancellous bone from images, with the main objective to achieve a closer representation to reality, in terms of the geometries that can be obtained.The methodology mainly uses Python™ language programming to establish instructions for using Abaqus™ graphical tools and therefore automatically generate the trabecular structure from the original image.As a first step, each trabecula of the image is idealized as an ellipse and each one is taken as basis for generating the geometries of pores and trabeculae in the model.A simulation of a compression test is also presented for three models made with this methodology, where finite element software was used.It is concluded that the methodology allows getting a very similar trabecular structure to the real one.

This work reviews the failures in the structural components of heavy road vehicles, to present a broad spectrum of failure causes in structural parts, ranging from poor manufacturing practices over design errors to the unforeseen combination of operating conditions and materials selection. The study starts with a series of examples of poorly welded parts in the structural frame of passenger buses. Three examples of failure in forged parts are included to show increasing degrees of complexity in the failure analysis: a suspension Z-bar, a heavy transmission shaft, and a torsion bar. The analyses are backed-up with finite-element models and results were compared with the location and size of defects and correlated to fractographic observation. Conclusions about the causes for failure could be formulated with a high degree of certainty, illustrating how failure analysis can be used as a tool for continuous improvement in design and manufacturing.

Knowledge of bone mechanical properties is important for bone substitutes design and fabrication, and more efficient prostheses development. The aim of this study is to characterize the viscoelastic behavior of bone specimens, through stress relaxation and fatigue tests performed to trabecular bone samples from bovine femoral heads. Relaxation tests consisted on preloading the samples at five different magnitudes and evaluate them for 1020 seconds, adjusting the results to a KWW mathematical model. Fatigue tests consisted of 700 load cycles and analyze their status at the end of the tests. As a conclusion we have that between relaxation stress and each preload there is linear relation and for samples with initial Young ́s modulus greater than 1.5 GPa showed no effects due fatigue test loading cycles. Keywords—Bone viscoelasticity, fatigue test, stress relaxation test, trabecular bone properties.

The usage of modern suspension systems in passenger buses increases the performance of the vehicle, to include a new kind of suspension in a passenger bus requires a careful examination of the packaging needs, load transfer and structure characteristics which leads to a safe design to be manufactured. The main objective of this paper is to provide a design proposal for a passenger bus frame to incorporate a commercial tri-axle pneumatic suspension, a system level CAE evaluation is presented to validate and optimize the proposed design. The main initial inputs for the design process were a set of Finite Element Analysis Simulations of the suspension to be implemented. The space requirements were determined by the design of the global bus structure. With these inputs, a series of concepts for the frame design were proposed and evaluated to determine the basis of the design to be constructed upon; a detailed design for each one of the three axles was presented and refined to a final stage where they were evaluated as assembled into the final structure. Following the aforementioned methodology, a structure that is capable of sustaining the selected commercial suspension was obtained. The final proposal consists of detailed CAD files for each of the portions and bus frame assemblies to be constructed.

Al 19%Sn 1%Cu (SAE 783) and Al 12%Sn 2.5%Si (SAE 788) alloys are ductile triboalloys which are produced by thin-slab casting followed by cold rolling. For SAE783, rolling defects are rare and generally associated to gross defects in the cast microstructure. SAE 788 forms the metastable β-AlFeSi phase, creating a brittle network within the microstructure. Heat treatment of the as-cast slabs allows reducing the effect of this phase by a reduction in its volume fraction and a change of composition, but this is a slow process. Instead, modification of the casting procedures, according to well-established rules for the production of sound aluminium castings, together with the use of base material of higher purity were shown to be equally efficient in the prevention of rolling defects. The heat treatment could then be omitted while rolling defects were eliminated.

In this paper is established a spongy bone bidimensional models methodology for its analysis by finite element software. The models are focused to represent the bone trabecular structure by Voronoi cells, using the coordinates of the porous center, contained within the bone structure, obtained by optical microscope images. Looking for a better geometrical similarity, it was assigned a thicker transversal area in the trabecula union zone, because has been reported that this factor gives a better approximation to experimental results. To feed the finite element models, compression test has been done to trabecular specimens, taking the maximum strain and maximum stress, to obtain the elastic modulus. By means of strained specimen images analysis, it has been established the structure collapse moment. It was when the 36% of total trabeculae failed. Finally it was obtained a tissue Young modulus of 323 [MPa] and with this value, the resistance variation in function of density and trabecular architecture.

Cancellous bone possesses a complicated structure of beam and plate-like elements whose architecture depends on the specific tissue and physiology of the individual. Classical, Voxel-based modelling is computation intensive and thus sub-optimal for parametric studies. Therefore, synthetic 2D-microstructures, based on sections of cancellous bone were generated and the effect of local architecture (vertebra and femur), bone density and loss of connectivity was researched by varying the parameters of the model. It was demonstrated that the use of bone density as a sole parameter induces considerable uncertainty on the assessment of the rigidity and resistance of the tissue under consideration.

Trabecular bone, rather than being considered as a homogeneous material, must be analysed as a structure of interconnected beam and plate-like elements. The arrangement and morphology of these elements depend on the specific tissue studied as well as on the physiology of the individual. It is therefore impossible to define the mechanical properties trabecular bone in general. To estimate the properties of an individual structure, flexible numerical models must be developed, which allow the calculation of elastic constants and resistance of tissue previously characterised by non-destructive observation. Voxel-based modelling of structures observed by X-ray microtomography is computation intensive. Here, synthetic 2D-microstructures are analysed, constructed as a collection of Voronoi-cells obtained from the observation of plane sections of cancellous bone. The effect of architecture (vertebra and femur), bone density and loss of trabecular connectivity was researched. The study confirms findings of earlier experimental and numerical studies relating to the effect of these parameters; the technique is efficient in terms of experimental effort and numerical analysis. Consequently, the use of synthetic microstructures based on a Voronoi-cell approximation of the real bone architecture may be a promising approach for the prediction of the mechanical properties of trabecular bone.

Resumen es: Tratando de entender un sistema complejo, es muy util extraer lo mas esencial y usarlo para crear una representacion simplificada. Un modelo permite obse...

A fine microstructure stabilised by dispersed particles is an interesting option for increasing the resistance of Al-Sn tribo-alloys without sacrificing ductility. Particle stimulated and continuous recrystallisation allow achieving this goal, but require careful preconditioning of the microstructure to obtain the desired particle distribution. As-cast slabs of Al 12%Sn2%Pb3%Si contain large plates of b-AlFeSi and modified silicon in an aluminium matrix. Sn forms a reticular network which is liquid at conventional annealing temperatures. Experiments show that metastable b-AlFeSi initially coarsens due to Ostwald ripening, but later dissolves and the remainder transforms into FeSiAl12. Silicon partitions to the liquid, allowing the nucleation of numerous small Si-grains.