Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

http://oa.upm.es/35412/7/INVE_MEM_2013_192429.pdf

Recent progress in research on tungsten materials for nuclear fusion applications in Europe

Heterostructured materials are an emerging class of materials with superior performances that are unattainable by their conventional homogeneous counterparts. They consist of heterogeneous zones wi...

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Heterostructured materials: superior properties from hetero-zone interaction

Bulk nanostructured (ns)/ultrafine-grained (UFG) metallic materials possess very high strength, making them attractive for high strength, lightweight and energy efficient applications. The most effective approach to produce bulk ns/UFG metallic materials is severe plastic deformation (SPD). In the last 30 years, significant research efforts have been made to explore SPD processing of materials, SPD-induced microstructural evolutions, and the resulting mechanical properties. There have been a few comprehensive reviews focusing mainly on SPD processing and the mechanical properties of the resulting materials. Yet no such a review on SPD-induced microstructural evolutions is available. This paper aims to provide a comprehensive review on important microstructural evolutions and major microstructural features induced by SPD processing in single-phase metallic materials with face-centered cubic structures, body-centered cubic structures, and hexagonal close-packed structures, as well as in multi-phase alloys. The corresponding deformation mechanisms and structural evolutions during SPD processing are discussed, including dislocation slip, deformation twinning, phase transformation, grain refinement, grain growth, and the evolution of dislocation density. A brief review on the mechanical properties of SPD-processed materials is also provided to correlate the structure with mechanical properties of SPD-processed materials, which is important for guiding structural design for optimum mechanical properties of materials.

Structural evolutions of metallic materials processed by severe plastic deformation

VOLUME ONE: CLASSICAL AND CONTEMPORARY STUDIES Banana Time: Job Satisfaction and Informal Interaction - Donald Roy Perceptions and Methods in Men Who Manage - Melville Dalton Men and Women of the Corporation - Rosabeth Kanter Manufacturing Consent - Michael Burawoy Breakfast at Spiro's: Dramaturgy and Dominance - Michael Rosen The World of Corporate Managers - Robert Jackall Engineering Humour: Masculinity Joking and Conflict in Shop-Floor Relations - David Collinson Extract from Crafting Selves: Power Gender and Discourses of Identity in a Japanese Workplace - Dorinne Kondo Engineering Culture: Control and Commitment in a High-Tech Corporation - Gideon Kunda Theorizing Managerial Work: A Pragmatic Pluralist Approach to Interdisciplinary Research - Tony Watson Rational Choice Situated Action and the Social Control of Organizations: The Challenger Launch Decision - Diane Vaughan Strategizing as Lived Experience and Strategists - Dalvir Samra-Fredericks Power Control and Resistance in 'The Factory that Time Forgot' - Mahmoud Ezzamel et al. Extract from Talking about Machines: An Ethnography of a Modern Job - Julian Orr Extract from The Business of Talk: Organizations in Action - Diedre Boden Extract from Investigating Small Firms: Nice Work? - Ruth Holliday Narrative Interviewing and Narrative Analysis in a Study of a Cross-Border Merger - Anne-Marie Soderberg Speech Timing and Spacing: The Phenomenon of Organizational Closure - Francois Cooren and Gail T. Fairhurst, VOLUME TWO: METHODS APPROACHES TECHNIQUES: GUIDES AND EXEMPLARS The Infeasibility of Invariant Laws in Management Studies: A Reflective Dialogue in Defence of Case Studies - Tsuyoshi Numagami The Interview: From Neutral Stance to Political Involvement - Andrea Fontana and James Frey Rethinking Observation: From Method to Context - Michael Agrosino et al. Notes on (Field) notes - James Clifford The Textual Approach: Risk and Blame in Disaster Sensemaking - Robert Gephart Triangulation in Organizational Research: A Re-presentation - Julie Wolfram Cox and John Hassard The Storytelling Organization: A Study of Performance in an Office Supply Firm - David Boje Semiotics and the Study of Occupational and Organizational Cultures - Stephen Barley The Use of Grounded Theory for the Qualitative Analysis of Organizational Behaviour - Barry Turner Reflecting on the Strategic Use of CAQDAS to Manage and Report on the Qualitative Research Process - Mark Wickham and Megan Woods Longitudinal Field Research on Change - Andrew Pettigrew Historical Perspectives in Organization Studies: Factual Narrative and Archeo-Genealogical - Michael Rowlinson Action Research: Explaining the Diversity - Cathy Cassell and Phil Johnson Photography and Voice in Critical Qualitative Management Research - Samantha Warren Moments Mixed Methods and Paradigm Dialogues - Norman Denzin VOLUME THREE: PRACTICES AND PREOCCUPATIONS Extract from The Discipline and Practice of Qualitative Research - Norman Denzin and Yvonna Lincoln Learning to Be a Qualitative Management Researcher - Catherine Cassell et al. Getting In Getting On Getting Out and Getting Back - David Buchanan et al. Reflections on the Researcher-Researched Relationship: A Woman Interviewing Men - Terry Arendell Real-Time Reflexivity: Prods to Reflection - Karl Weick Towards an Integrative Reflexivity in Organizational Research - Leah Tomkins and Virginia Eatough Appealing Work: An Investigation of How Ethnographic Texts Convince - Karen Golden-Biddle and Karen Locke The Philosophy and Politics of Quality in Qualitative Organizational Research - John Amis and Michael Silk Objectivity and Reliability in Qualitative Analysis: Realist Contextualist and Radical Constructionist Epistemologies - Anna Madill et al. Whatever Happened to Organizational Ethnography: A Review of the Field of Organizational Ethnography and Anthropological Studies - S.P. Bate Working with Pluralism: Determining Quality in Qualitative Research - Mark Easterby-Smith, Karen Golden-Biddle and Karen Locke The Role of the Researcher: An Analysis of Narrative Position in Organisation Theory - Mary Jo Hatch The Professional Apprentice: Observations of Fieldwork Roles in Two Organizational Settings - John Van Maanen and Deborah Kolb In Defense of Being "Native": The Case for Insider Academic Research - Teresa Brannick and David Coghlan Ethics and Ethnography - Robert Dingwall Extract from Qualitative Methods in Management Research - Evert Gummesson Making Sense as a Personal Process - Judi Marshall My Affair with the "Other": Identity Journeys across the Research-Practice Divide - Laura Empson VOLUME FOUR: CHALLENGES AND PROSPECTS Secrecy and Disclosure in Fieldwork - Richard Mitchell Organization Science as Social Construction: Postmodern Potentials - Kenneth Gergen and Tojo Joseph Thatchenkerry Farewell to Criteriology - Thomas Schwandt Reflexive Inquiry in Organizational Research: Questions and Possibilities - Ann Cunliffe The Action Turn: Towards a Transformational Social Science - Peter Reason and William Torbert Signing My Life Away? Researching Sex and Organization - Joanna Brewis Evaluating Qualitative Management Research: Towards a Contingent Criteriology - Phil Johnson et al. Postcolonialism and the Politics of Qualitative Research in International Business - Gavin Jack and Robert Westwood Organization Studies and Epistemic Coloniality in Latin America: Thinking Otherness from the Margins - Eduardo Ibbaro-Colado Fitting Oval Pegs into Round Holes: Tensions in Evaluating and Publishing Qualitative Research in Top-Tier North American Journals - Michael Pratt Hegemonic Academic Practices: Experiences of Publishing from the Periphery - Susan Merilainen et al., Case Study as Disciplinary Convention: Evidence from International Business Journals - Rebecca Piekkari, Catherine Welsh and Eriikka Paavilainen Managerialism and Management Research: Would Melville Dalton Get a Job Today? - Emma Bell Ways of constructing research questions: gap-spotting or problematization? - Jorgen Sandberg and Mats Alvesson

Challenges and prospects

A study of heavy-ion damage in Fe and Fe–Cr alloys started in Part 1 1 was continued with an investigation of damage development in UHP Fe and Fe–8%Cr at higher doses up to 2 × 1019 ions m−2 (∼13 dpa). In thin-foil irradiations with 150 keV Fe+ ions at 300°C and room temperature (RT), more complex microstructures started to develop in thicker regions of the foils at doses greater than about 2 × 1018 ions m−2, apparently involving cooperative interaction, alignment and coalescence of smaller loops. First strings of loops all with the same ½⟨111⟩ Burgers vectors formed. In UHP Fe irradiated at 300°C the damage then developed into colonies of resolvable interstitial loops with ½⟨111⟩ Burgers vectors. By a dose of 2 × 1019 ions m−2, large (several hundred nanometre) finger-shaped loops with large shear components had developed by the growth and subsequent coalescence of smaller loops. Similar but finer-scale damage structures developed in UHP Fe irradiated at RT and in Fe–8%Cr irradiated at both RT and 300°C.

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Heavy-ion irradiations of Fe and Fe–Cr model alloys Part 2: Damage evolution in thin-foils at higher doses

Dynamic observations of heavy-ion damage in Fe and Fe-Cr alloys.

A transition is reported in the dislocation microstructure of pure Fe produced by heavy-ion irradiation of thin foils, which took place between irradiation temperatures (T irr) of 300°C and 500°C. At T irr ≤ 400°C, the microstructure was dominated by round or irregular non-edge dislocation loops of interstitial nature and with Burgers vectors b = ½ ⟨111⟩, although interstitial ⟨100⟩ loops were also present; at 500°C only rectilinear pure-edge ⟨100⟩ loops occurred. At intermediate temperatures there was a gradual transition between the two types of microstructure. At temperatures just below 500°C, mobile ½⟨111⟩ loops were seen to be subsumed by sessile ⟨100⟩ loops. A possible explanation of these observations is given.

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The temperature dependence of heavy-ion damage in iron: A microstructural transition at elevated temperatures

The strain rate dependence of the brittle-to-ductile transition (BDT) temperature was investigated in notched and un-notched miniature bars made of high-purity polycrystalline tungsten and in notched bars of less-pure sintered material. The activation energy, E BDT, for the process controlling the BDT in pure tungsten was equal to 1.0 eV both in un-notched and notched specimens, though the brittle–ductile transition temperature, T BDT, was ≈ 40 K lower at each strain rate for the un-notched samples, indicating that the activation energy, E BDT, is a materials parameter, independent of geometrical factors. The experimental data obtained from pure tungsten are described well by a two-dimensional dislocation-dynamics model of crack-tip plasticity, which is also discussed. For sintered tungsten, E BDT was found to be 1.45 eV; T BDT at a given strain rate was higher than in the pure tungsten by ≈ 90 K, suggesting that the BDT in tungsten is very sensitive to impurity levels.

Brittle-ductile transitions in polycrystalline tungsten

Irradiation induces the formation of stacking fault tetrahedra (SFTs) in a number of fcc metals, such as stainless steel and pure copper. In order to understand the role of the material's parameters on this formation, pure Cu, Ni, Pd and Al, having a respective stacking fault energy of 45, 125, 180 and 166 mJ m−2, have been irradiated with high energy protons to a dose of about 10−2 dpa at room temperature. The irradiation-induced microstructure has been investigated using transmission electron microscopy. All irradiated metals but Al present SFTs. The proportion of perfect, truncated and grouped SFTs has been determined. The SFT energy as a function of size has been calculated using elasticity of the continuum, with respect to the energy of a number of other possible defect configurations. It appears that the key parameters are the stacking fault energy and the shear modulus. Their implication on the formation and stability of the SFTs is discussed.

Zhongwen Yao

Papers

Heavy-ion irradiations of Fe and Fe–Cr model alloys Part 2: Damage evolution in thin-foils at higher doses

Dynamic observations of heavy-ion damage in Fe and Fe-Cr alloys.

The temperature dependence of heavy-ion damage in iron: A microstructural transition at elevated temperatures

Brittle-ductile transitions in polycrystalline tungsten

Irradiation-induced stacking fault tetrahedra in fcc metals