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

Developers, the State, and the Politics of Private Property Rights

This article uses a new institutionalist approach to investigate major land use conflicts and regional land use policy changes in the Toronto region that affected the property relations of land developers. Institutionalist approaches focus on the role of key actors, ideas, and strategies in influencing the trajectories of political institutions, and the confrontation of political and strategic maneuvering in the face of existing institutions and structures. Through comparison of the processes driving enactment of two major regional land use statutes—the Oak Ridge Moraine Conservation Act and the Greenbelt Act—this article pays close attention to the relationships between political actors and land developers, as well as the underlying political climate in shaping the development and outcomes of these statutes. This article shows that these two environmental land use statutes, which both had significant implications for the private property rights of land owners, differed in important ways in both their development and enactment. This article also shows that the enactment of provincial land use laws and their effects on private property rights are subject to greater political negotiation and contestation, and more unpredictable outcomes, than previously considered within new institutionalism. This article draws on case study research to illuminate the varied ways that land developers and key governmental decision makers exercise power, working within and against existing legal structures to forward particular agendas vis-à-vis urban land use

A library of ab initio Raman spectra for automated identification of 2D materials

Raman spectroscopy is frequently used to identify composition, structure and layer thickness of 2D materials. Here, we describe an efficient first-principles workflow for calculating resonant first-order Raman spectra of solids within third-order perturbation theory employing a localized atomic orbital basis set. The method is used to obtain the Raman spectra of 733 different monolayers selected from the computational 2D materials database (C2DB). We benchmark the computational scheme against available experimental data for 15 known monolayers. Furthermore, we propose an automatic procedure for identifying a material based on an input experimental Raman spectrum and illustrate it for the cases of MoS$_2$ (H-phase) and WTe$_2$ (T$^\prime$-phase). The Raman spectra of all materials at different excitation frequencies and polarization configurations are freely available from the C2DB. Our comprehensive and easily accessible library of \textit{ab initio} Raman spectra should be valuable for both theoreticians and experimentalists in the field of 2D materialsComment: 17 pages, 7 figure

Politics of Land Developers and Development in the Toronto Region

Urban land developers are influential actors in the governance, planning, and transformation of urban land. Yet developers and the development industry are not well understood, and are seldom scrutinized critically in academic scholarship. This dissertation investigates the role of land developers in the governance and transformation of land at the urban-rural fringe in the Toronto region. Critical theories of property, land use conflict, planning, and urban geography illuminate social, spatial, and policy issues associated with the rapid transformation of land. Theories of interpretive institutionalism contribute richly to these urban theories by directing attention to the historical, economic, and cultural contexts within which state and non-state actors and institutions operate, and the importance of discourse, the roles of individual actors, and the flow of ideas across spaces and scales. Drawing on these theories, I carried out extensive case study research on suburban developers and land use conflict in an urban-rural fringe area of the Toronto region. I investigated ongoing relationships between developers and policy makers in the context of Ontario provincial greenbelt and growth plan legislation. I interviewed developers, municipal and provincial planners, civil society actors, and planning and development consultants. Drawing on these interviews, archival research, and media analysis, I show that the Toronto region development industry, as well as many individual developers and development firms, are in practice powerful governance actors, deeply influential to land use decisions and outcomes. The development industry downplays its power and influence, working hard to reframe its economic interests as public good interests. Developers exercise power in new and subtle ways, by operating as privileged governance partners through consensus-based consultations, and by maintaining close, interdependent personal and financial relationships with political leaders and decision makers. But developers are also wealthy corporate elites capable of exercising raw money power, often in response to, and at times generative of, land use conflict. This dissertation draws upon, in new ways, diverse theories that contribute to a greater understanding of the power of developers and the development industry over land use change

Depression, osteoporosis, serotonin and cell membrane viscosity between biology and philosophical anthropology

Due to the relationship between biology and culture, we believe that depression, understood as a cultural and existential phenomenon, has clear markers in molecular biology. We begin from an existential analysis of depression constituting the human condition and then shift to analysis of biological data confirming, according to our judgment, its original (ontological) structure. In this way philosophy is involved at the anthropological level, in as much as it detects the underlying meanings of depression in the original biological-cultural horizon of human life. Considering the integration of knowledge it is the task of molecular biology to identify the aforementioned markers, to which the existential aspects of depression are linked to. In particular, recent works show the existence of a link between serotonin and osteoporosis as a result of a modified expression of the low-density lipoprotein receptor-related protein 5 gene. Moreover, it is believed that the hereditary or acquired involvement of tryptophan hydroxylase 2 (Tph2) or 5-hydroxytryptamine transporter (5-HTT) is responsible for the reduced concentration of serotonin in the central nervous system, causing depression and affective disorders. This work studies the depression-osteoporosis relationship, with the aim of focusing on depressive disorders that concern the quantitative dynamic of platelet membrane viscosity and interactome cytoskeleton modifications (in particular Tubulin and Gsα protein) as a possible condition of the involvement of the serotonin axis (gut, brain and platelet), not only in depression but also in connection with osteoporosis

The Columbia City Trailhead: A Collaborative Construction Engineering Technology Capstone Experience

In 2010, a collaborative effort between a nonprofit trail advocacy organization, a small rural Indiana city, trade unions, grantmaking organizations, materials suppliers, contractors, and the Construction Engineering Technology program at Indiana University – Purdue University Fort Wayne (IPFW) led to the successful construction of a trailhead building in a city park. Multidisciplinary collaboration began with a design charrette in January, bringing together architects, brickmasons, carpenters, electricians, engineers, greenbuilding experts, landscapers, professors, and students. Starting with a site plan by a local architect and a construction blueprint from another trailhead elsewhere in the state, charrette participants improved the design and site location. Students completed the design, obtained approval from the customer (the nonprofit trail group), and obtained approval from local and state governments. Because this was a capstone course, students were required to demonstrate knowledge and skills they acquired during their four-year degree program. As such, they created the blueprints of the new design, estimated costs and materials, scheduled the construction, and fulfilled the role of project manager. Construction professionals mentored the students as they built the trailhead restroom. The magic words “student project” led to substantial donations of money, labor, excavating, and materials from many sources. As a result, the project was completed at one-quarter the price bid by a private contractor. Assessment of student learning was conducted by the instructor, departmental colleagues, and working construction professionals