Backward correlations and dynamic heterogeneities: a computer study of ion dynamics

We analyse the correlated back and forth dynamics and dynamic heterogeneities, i.e. the presence of fast and slow ions, for a lithium metasilicate system via computer simulations. For this purpose we define, in analogy to previous work in the field of glass transition, appropriate three-time correlation functions. They contain information about the dynamics during two successive time intervals. First we apply them to simple model systems in order to clarify their information content. Afterwards we use this formalism to analyse the lithium trajectories. A strong back-dragging effect is observed, which also fulfills the time-temperature superposition principle. Furthermore, it turns out that the back-dragging effect is long-ranged and exceeds the nearest neighbor position. In contrast, the strength of the dynamic heterogeneities does not fulfill the time-temperature superposition principle. The lower the temperature, the stronger the mobility difference between fast and slow ions. The results are then compared with the simple model systems considered here as well as with some lattice models of ion dynamics.Comment: 12 pages, 10 figure

Complex lithium ion dynamics in simulated LiPO3 glass studied by means of multi-time correlation functions

Molecular dynamics simulations are performed to study the lithium jumps in LiPO3 glass. In particular, we calculate higher-order correlation functions that probe the positions of single lithium ions at several times. Three-time correlation functions show that the non-exponential relaxation of the lithium ions results from both correlated back-and-forth jumps and the existence of dynamical heterogeneities, i.e., the presence of a broad distribution of jump rates. A quantitative analysis yields that the contribution of the dynamical heterogeneities to the non-exponential depopulation of the lithium sites increases upon cooling. Further, correlated back-and-forth jumps between neighboring sites are observed for the fast ions of the distribution, but not for the slow ions and, hence, the back-jump probability depends on the dynamical state. Four-time correlation functions indicate that an exchange between fast and slow ions takes place on the timescale of the jumps themselves, i.e., the dynamical heterogeneities are short-lived. Hence, sites featuring fast and slow lithium dynamics, respectively, are intimately mixed. In addition, a backward correlation beyond the first neighbor shell for highly mobile ions and the presence of long-range dynamical heterogeneities suggest that fast ion migration occurs along preferential pathways in the glassy matrix. In the melt, we find no evidence for correlated back-and-forth motions and dynamical heterogeneities on the length scale of the next-neighbor distance.Comment: 12 pages, 13 figure

PPAR-δ is repressed in Huntington's disease, is required for normal neuronal function and can be targeted therapeutically

Huntington’s disease (HD) is a progressive neurodegenerative disorder caused by a CAG-polyglutamine repeat expansion in the huntingtin (htt) gene. We found that peroxisome proliferator-activated receptor delta (PPARδ) interacts with htt and that mutant htt represses PPARδ-mediated transactivation. Increased PPARδ transactivation ameliorated mitochondrial dysfunction and improved cell survival of HD neurons. Expression of dominant-negative PPARδ in CNS was sufficient to induce motor dysfunction, neurodegeneration, mitochondrial abnormalities, and transcriptional alterations that recapitulated HD-like phenotypes. Expression of dominant-negative PPARδ specifically in the striatum of medium spiny neurons in mice yielded HD-like motor phenotypes, accompanied by striatal neuron loss. In mouse models of HD, pharmacologic activation of PPAR δ, using the agonist KD3010, improved motor function, reduced neurodegeneration, and increased survival. PPAR δ activation also reduced htt-induced neurotoxicity in vitro and in medium spiny-like neurons generated from human HD stem cells, indicating that PPAR δ activation may be beneficial in individuals with HD and related disorders

Benefits of lean teaching

Lean Engineering has matured into a credible and useful set of tools and philosophies to satisfy customer demand. Almost all applications of lean have been in commercial settings where increased value can easily be measured by increased sales, less defects and generally a higher output. The authors of this paper report on their experiences of teaching lean engineering to engineering students. The focus is on how these students were enabled to develop problem solving skills, to think in systems and to consider sustainability of their designs or engineering interventions. Further, the authors describe the metrics used to assess student learning, and what were the lessons learned for the course conveners in communicating Lean Principles. The authors will demonstrate that teaching Lean to engineering students enhance their understanding of engineering professional practice. Copyright © 2011 by ASME

Benefits of lean teaching

Lean Engineering has matured into a credible and useful set of tools and philosophies to satisfy customer demand. Almost all applications of lean have been in commercial settings where increased value can easily be measured by increased sales, less defects and generally a higher output. The authors of this paper report on their experiences of teaching lean engineering to engineering students. The focus is on how these students were enabled to develop problem solving skills, to think in systems and to consider sustainability of their designs or engineering interventions. Further, the authors describe the metrics used to assess student learning, and what were the lessons learned for the course conveners in communicating Lean Principles. The authors will demonstrate that teaching Lean to engineering students enhance their understanding of engineering professional practice. Copyright © 2011 by ASME

Why require ethics in engineering?

This theoretical paper will provide a review of the literature regarding the need for ethics in the workplace and how taxonomical ethical development can be used in engineering education. In fact, advocacy to educate for ethics in engineering education by design is discussed as a solution to this problem. By spiraling ethical competency development into engineering education as a body of practice, rather than as a theory of knowledge, it is possible to integrate engineering hard science content with engineering soft science competency. This means that current programs\u27 scopes and sequences may remain in place, with recommended changes in pedagogy. Copyright © 2012 by ASME

The möbius strip of lean engineering and systems engineering

Lean Engineering has come a long way from its first conception in the 1940s. What started as a production philosophy to enable manufacturing in Japan under severe resource constraints has developed into a globally adopted, widely aspired, often misinterpreted, and sometimes poorly understood, way and means of doing business . Short-sighted implementations of lean engineering in industrialized countries in a first wave in the 1970s were quickly accompanied by the slogan \u27lean is mean\u27 because of the focus on short-term financial gains at the expense of a complete understanding of the entire production and value chains. In a second wave in the 1990s, the focus of lean engineering implementations shifted to the core objective of lean engineering philosophies, the establishment of flow in the value chain through standardization. In parallel, Systems Engineering has continuously developed as a discipline which has moved away from the integration of components and ubsystems, to the co-development of such units and building blocks of engineering and engineered products. This continued development of Systems Engineering as a discipline reflects the growing demand for systems thinking competency, to challenge the complexity of manufacturing and operations in an environment where product development, production and distribution is spread over large, not co-located teams on all continents. In this paper, the authors tie together the developments, tools and methodologies of Lean Engineering and Systems Engineering, and they show the growing similarity of both disciplines. In fact, these disciplines often describe the same effects, processes, and challenges in the workplace. The similarity has grown to a level where value streams in production or service delivery are analyzed and described in terms of one engineering discipline, while following methodologies and applying tools stemming from the other engineering discipline. The authors advocate that the debate should therefore not be over which engineering discipline to follow, but what tools and methodologies are most appropriate to enhance systems thinking competency, and to understand complexity in systems. Copyright © 2013 by ASME