Temperature estimation and slip-line force analytical models for the estimation of the radial forming force in the RARR process of flat rings

open2noIn this study, a mathematical model for the prediction of the temperature evolution in the ring during the radial-axial ring rolling process is developed and used, together with the authors’ previous results, to determine analytically the flow stress of the material during process. These results, combined with Hill's slip-line field solution adapted to the RARR process, allow a fast and reasonably precise calculation of the radial forming force, a key parameter at the preliminary stage of the process design. The approach is validated by applying the proposed model to a case available in the literature and comparing the analytical results with those of the laboratory experiment and FEM simulation. Following the successful comparison, the models were applied to a large variety of flat rings, comparing analytical predictions with the results of FEM simulations. The accuracy of the analytical calculation and the reliability of the proposed models, for different ring configuration and process parameters, are presented and discussed.embargoed_20190501Quagliato, Luca; Berti, GuidoQuagliato, Luca; Berti, Guid

Analytic temperature evaluation and process forces estimation for the RARR process of flat rings

Two different analytical models are derived for the estimation of the temperature drop in the two deformation stages of radial-axial ring rolling process of flat rings. The temperature estimation, along with previous results regarding geometry, strain and strain rate, is used to calculate the variation of the flow stress of the material during the process and accordingly to derive the process forces, utilizing different forces estimation models already available in the literature

Periodic solutions for completely resonant nonlinear wave equations

We consider the nonlinear string equation with Dirichlet boundary conditions $u_{xx}-u_{tt}=\phi(u)$, with $\phi(u)=\Phi u^{3} + O(u^{5})$ odd and analytic, $\Phi\neq0$, and we construct small amplitude periodic solutions with frequency \o for a large Lebesgue measure set of \o close to 1. This extends previous results where only a zero-measure set of frequencies could be treated (the ones for which no small divisors appear). The proof is based on combining the Lyapunov-Schmidt decomposition, which leads to two separate sets of equations dealing with the resonant and nonresonant Fourier components, respectively the Q and the P equations, with resummation techniques of divergent powers series, allowing us to control the small divisors problem. The main difficulty with respect the nonlinear wave equations $u_{xx}-u_{tt}+ M u = \phi(u)$, $M\neq0$, is that not only the P equation but also the Q equation is infinite-dimensiona

El comercio electrónico on-line y las operaciones de comercio digital en el derecho venezolano

The contemporary historical context, requires jurisdictions, evolving and adapting to new concepts and figures, thanks to the benefits of information technologies and communication, which affect the legal scope of the regulations. In this sense, the study of digital operations within the e-commerce is a subject of interest in the Venezuelan law, because every day more recurring operations digital commerce activity mercantile country, however existing legal instruments, briefly contemplated this figure or simply not regulated. It is therefore important to consider the on-line e-commerce conducted by an act of trade magazine characters immateriality, incorporeal and intangible, in full digitization of the act forming the trade as part of operations and negotiations commercial-economic life activity.El contexto histórico contemporáneo, exige de los ordenamientos jurídicos, evolución y adaptación a figuras y conceptos novedosos, gracias a las bondades de las tecnologías de la información y comunicación, que, inciden en el ámbito jurídico de las legislaciones vigentes. En tal sentido, el estudio de operaciones digitales dentro del comercio electrónico, es un tema que reviste interés dentro del derecho venezolano, debido a que cada día son más recurrentes las operacionesde comercio digital en la actividad mercantil patria; empero los instrumentos jurídicos vigentes, contemplan someramente esta figura o, simplemente no la regulan. Por ello, es importante considerar al comercio electrónico on-line llevado a cabo por un acto de comercio que revista caracteres de inmaterialidad, intangibilidad e incorporeidad, en un todo conformando la digitalización del acto de comercio, como parte de las operaciones y negociaciones de la actividad económica-mercantil del país

radial forging of aluminum to steel preform for the production of light weighted wheel bearing outer race

Abstract In this research work an innovative procedure through which to manufacture the outer race of vehicles wheels bearing, aiming to reduce their total weight, is proposed. Utilizing the radial forging process, an aluminum workpiece is forged on a steel core, resulting in the same geometry for the wheel bearing outer race but allowing to achieve a considerable weight reduction. By considering the most burdensome load conditions the outer race has to stand, a stress analysis is implemented in ABAQUS/Standard by applying both bolts and bearing ball forces. Based on the stress distribution, the portion of the cross-section where the load is bearable by the aluminum 6061 alloy is identified and a new steel workpiece, realized by removing the above-mentioned volume, is created. The aluminum workpiece is then hot-forged on the steel part, replacing the removed steel volume and recreating the original shape of the bearing outer race, afterwards tested with the same load conditions to verify that the combined forged part is able to withstand the same loads. To optimize the interface behavior between hot-forged Al6061 and 45Cr steel, simple tension test specimens, realized by forging an aluminum workpiece on a steel plate, have been manufactured realizing different surface knurling on the steel plate and by pre-heating the aluminum part at different temperatures. With the proposed approach, the weight of the bearing outer race has been reduced of 35.8% while granting the same mechanical performances of the original component

Periodic solutions for a class of nonlinear partial differential equations in higher dimension

We prove the existence of periodic solutions in a class of nonlinear partial differential equations, including the nonlinear Schroedinger equation, the nonlinear wave equation, and the nonlinear beam equation, in higher dimension. Our result covers cases where the bifurcation equation is infinite-dimensional, such as the nonlinear Schroedinger equation with zero mass, for which solutions which at leading order are wave packets are shown to exist.Comment: 34 page

Crop rotations sustain cereal yields under a changing climate

Agriculture is facing the complex challenge of satisfying increasing food demands, despite the current and projected negative impacts of climate change on yields. Increasing crop diversity at a national scale has been suggested as an adaptive measure to better cope with negative climate impacts such as increasing temperatures and drought, but there is little evidence to support this hypothesis at the field scale. Using seven long-term experiments across a wide latitudinal gradient in Europe, we showed that growing multiple crop species in a rotation always provided higher yields for both winter and spring cereals (average +860 and +390 kg ha(-1) per year, respectively) compared with a continuous monoculture. In particular, yield gains in diverse rotations were higher in years with high temperatures and scant precipitations, i.e. conditions expected to become more frequent in the future, rendering up to c. 1000 kg ha(-1) per year compared to monocultures. Winter cereals yielded more in diverse rotations immediately after initiation of the experiment and kept this advantage constant over time. For spring cereals, the yield gain increased over time since diversification adoption, arriving to a yearly surplus of c. 500 kg ha(-1) after 50-60 years with still no sign of plateauing. Diversified rotations emerge as a promising way to adapt temperate cropping systems and contribute to food security under a changing climate. However, novel policies need to be implemented and investments made to give means and opportunities for farmers to adopt diversified crop rotations

Specific Involvement of Pilus Type 2a in Biofilm Formation in Group B Streptococcus

Streptococcus agalactiae is the primary colonizer of the anogenital mucosa of up to 30% of healthy women and can infect newborns during delivery and cause severe sepsis and meningitis. Persistent colonization usually involves the formation of biofilm and increasing evidences indicate that in pathogenic streptococci biofilm formation is mediated by pili. Recently, we have characterized pili distribution and conservation in 289 GBS clinical isolates and we have shown that GBS has three pilus types, 1, 2a and 2b encoded by three corresponding pilus islands, and that each strain carries one or two islands. Here we have investigated the capacity of these strains to form biofilms. We have found that most of the biofilm-formers carry pilus 2a, and using insertion and deletion mutants we have confirmed that pilus type 2a, but not pilus types 1 and 2b, confers biofilm-forming phenotype. We also show that deletion of the major ancillary protein of type 2a did not impair biofilm formation while the inactivation of the other ancillary protein and of the backbone protein completely abolished this phenotype. Furthermore, antibodies raised against pilus components inhibited bacterial adherence to solid surfaces, offering new strategies to prevent GBS infection by targeting bacteria during their initial attachment to host epithelial cells

Electronic structure and magnetism of strained bcc phases across the fcc to bcc transition in ultrathin Fe films

We investigated the electronic structure of the bcc metastable phases involved in the fcc to bcc transition of Fe. Ultrathin Fe films were grown on a 2-monolayer (ML) Ni/W(110) substrate, where a fcc lattice is stabilized at low Fe coverages and the transition proceeds through the formation of bcc nuclei showing a specific "Kurdjumov-Sachs" orientation with the substrate. A comprehensive description of the electronic structure evolution is achieved by combining spin-resolved UV photoemission spectroscopy and ab initio calculations. According to our results, an exchange-split band structure is observed starting from 2 ML of Fe, concomitant with the formation of ferromagnetic bcc nuclei. Continuous modifications are observed in the spin-resolved photoemission spectra for increasing Fe coverage, especially for what concerns the minority states, possibly indicative of the progressive relaxation of the strained bcc phase starting from the bcc/fcc interface