Dislocation nucleation and vacancy formation during high-speed deformation of fcc metals

Recently, a dislocation free deformation mechanism was proposed by Kiritani et al., based on a series of experiments where thin foils of fcc metals were deformed at very high strain rates. In the experimental study, they observed a large density of stacking fault tetrahedra, but very low dislocation densities in the foils after deformation. This was interpreted as evidence for a new dislocation-free deformation mechanism, resulting in a very high vacancy production rate. In this paper we investigate this proposition using large-scale computer simulations of bulk and thin films of copper. To favour such a dislocation-free deformation mechanism, we have made dislocation nucleation very difficult by not introducing any potential dislocation sources in the initial configuration. Nevertheless, we observe the nucleation of dislocation loops, and the deformation is carried by dislocations. The dislocations are nucleated as single Shockley partials. The large stresses required before dislocations are nucleated result in a very high dislocation density, and therefore in many inelastic interactions between the dislocations. These interactions create vacancies, and a very large vacancy concentration is quickly reached.Comment: LaTeX2e, 8 pages, PostScript figures included. Minor modifications only. Final version, to appear in Philos. Mag. Let

Modelling of dislocation generation and interaction during high-speed deformation of metals

Recent experiments by Kiritani et al. have revealed a surprisingly high rate of vacancy production during high-speed deformation of thin foils of fcc metals. Virtually no dislocations are seen after the deformation. This is interpreted as evidence for a dislocation-free deformation mechanism at very high strain rates. We have used molecular-dynamics simulations to investigate high-speed deformation of copper crystals. Even though no pre-existing dislocation sources are present in the initial system, dislocations are quickly nucleated and a very high dislocation density is reached during the deformation. Due to the high density of dislocations, many inelastic interactions occur between dislocations, resulting in the generation of vacancies. After the deformation, a very high density of vacancies is observed, in agreement with the experimental observations. The processes responsible for the generation of vacancies are investigated. The main process is found to be incomplete annihilation of segments of edge dislocations on adjacent slip planes. The dislocations are also seen to be participating in complicated dislocation reactions, where sessile dislocation segments are constantly formed and destroyed.Comment: 8 pages, LaTeX2e + PS figures. Presented at the Third Workshop on High-speed Plastic Deformation, Hiroshima, August 200

Growth kinetics of physical vapor transport processes: Crystal growth of the optoelectronic material mercurous chloride

Physical vapor transport processes were studied for the purpose of identifying the magnitude of convective effects on the crystal growth process. The effects of convection on crystal quality were were studied by varying the aspect ratio and those thermal conditions which ultimately affect thermal convection during physical vapor transport. An important outcome of the present study was the observation that the convection growth rate increased up to a certain value and then dropped to a constant value for high aspect ratios. This indicated that a very complex transport had occurred which could not be explained by linear stability theory. Better quality crystals grown at a low Rayleigh number confirmed that improved properties are possible in convectionless environments

Envisioning Futures of Design Education: An Exploratory Workshop with Design Educator

The demand for innovation in the creative economy has seen the adoption and adaptation of design thinking and design methods into domains outside design, such as business management, education, healthcare, and engineering. Design thinking and methodologies are now considered useful for identifying, framing and solving complex, often wicked social, technological, economic and public policy problems. As the practice of design undergoes change, design education is also expected to adjust to prepare future designers to have dramatically different demands made upon their general abilities and bases of knowledge than have design career paths from years past. Future designers will have to develop skills and be able to construct and utilize knowledge that allows them to make meaningful contributions to collaborative efforts involving experts from disciplines outside design. Exactly how future designers should be prepared to do this has sparked a good deal of conjecture and debate in the professional and academic design communities. This report proposes that the process of creating future scenarios that more broadly explore and expand the role, or roles, for design and designers in the world’s increasingly interwoven and interdependent societies can help uncover core needs and envision framework(s) for design education. This approach informed the creation of a workshop held at the Design Research Society conference in Brighton, UK in June of 2016, where six design educators shared four future scenarios that served as catalysts for conversations about the future of design education. Each scenario presented a specific future design education context. One scenario described the progression of design education as a core component of K-12 curricula; another scenario situated design at the core of a network of globally-linked local Universities; the third scenario highlighted the expanding role of designers over time; and the final scenario described a distance design education context that made learning relevant and “close” to an individual learner’s areas of interest. Forty participants in teams of up to six were asked to collaboratively visualize a possible future vision of design education based on one of these four scenarios and supported by a toolkit consisting of a set of trigger cards (with images and text), along with markers, glue and flipcharts. The collaborative visions that were jointly created as posters using the toolkit and then presented by the teams to all the workshop participants and facilitators are offered here as a case study. Although inspired by different scenarios, their collectively envisioned futures of what design education should facilitate displayed some key similarities. Some of those were: Future design education curricula will focus on developing collaborative approaches within which faculty and students are co-learners; These curricula will bring together ways of learning and knowing that stem from multiple disciplines; and Learning in and about the natural environment will be a key goal (the specifics of how that would be accomplished were not elaborated upon.) In addition, the need for transdisciplinarity was expressed across the collaborative visions created by each of the teams, but the manner that participants chose to express their ideas about this varied. Some envisioned that design would evolve by drawing on other disciplinary knowledge, and others envisioned that design would gradually integrate with other disciplines

Micropropagation of Dendrocalamus strictus nees from mature nodal explants

An effort has been made to propagate Dendrocalamus strictus Nees using nodal explants from mature plants. The explants, after surface sterilization, were inoculated on solidified MS basal medium with 2 mg/l BAP. The buds, which started growing, were transferred to solidified MS basal medium with 4 mg/l BAP and 15 mg/l AdS to achieve about three fold multiplication. Single shoots or 2-shoot clusters did not survive and therefore all the experiments were conducted with a cluster of minimum 3-shoots. The rooting was found difficult. Three hormones viz. IAA, IBA and NAA with a concentration of 1, 3 and 5 mg/l were used in various combinations for rooting. Out of the total 9 treatments, only 20% rooting was found only in one treatment, namely in the medium with 5 mg/l indole butyric acid (IBA)

Myxobacteria in soils and composts; their distribution, number and lytic action on bacteria

RESP-262