Friction vs Texture at the Approach of a Granular Avalanche

We perform a novel analysis of the granular texture of a granular bed close to stability limit. Our analysis is based on a unique criterion of friction mobilisation in a simulated two-dimensional packing. In this way, we recover the bimodal character of granular texture, and the coexistence of weak and strong phases in the sense of distinct contacts populations. Moreover, we show the existence of a well-defined subset of contacts within the weak contact network. These contacts are characterized by their important friction, and form a highly coherent population in terms of fabric. They play an antagonistic role with respect to force chains. We are thus able to discriminate between incoherent contacts and coherent contacts in the weak phase, and to specify the role that the latter plays in the destabilisation process.Comment: 4 pages, 6 figure

Uncovering learning at work.

The Australian Research Council project, Uncovering Learning at Work explored the extent and nature of informal learning and its contribution and significance to the TAFE workplace and its employees. The research was a qualitative study carried out in partnership between the University of Technology, Sydney and the TAFE Professional Development Network unit. This collaborative arrangement was ideal for this study because TAFE, as an organisation, are interested in the relationship between work and learning. The research employed the term ‘everyday learning’ to describe the phenomenon under investigation. This understanding recognises that there are elements of both formality and informality in all learning situations. Uncovering Learning at Work was conducted in three stages. The first involved one-to-one interviews and the collection of initial qualitative data. In the second the researchers worked closely with individual workgroups around particular workplace issues. The final stage examined the implications of the project for TAFE and its employees in collaboration with key TAFE stakeholders. The questions the research focused on were about: • ideas staff had about learning • staff perceptions of learning opportunities in TAFE • how staff constructed learning through their work relationships for their own benefit and for the strategic goals for TAFE • key strategies for identifying and utilising learning opportunities without undermining existing informal learning processes • theories of adult learning that took account of the work-related learning of TAFE staff in an organisational context. This research followed four workgroups over a period of three years. The four workgroups came from two Sydney metropolitan Institutes of TAFE. The workgroups represented a range of organisational areas including a trade teaching unit, an administrative unit, a group of senior managers and a unit responsible for workplace delivery. Analysis of project data resulted in several important findings. These are presented in four themes, which are briefly discussed in this report: full details are available in the listed publications. The four themes are: 1. What we learn and who we learn from - Three significant areas of learning were evident in analysis of the interviews. Analysis of the project data yielded two interesting findings with regard to who workers learned from. Very few people that were actively sought by staff to help them learn are generally understood as people with an ‘official’ role in promoting workplace learning. 2. Naming learning and naming oneself as a learner – The research suggests there is a complex politics involved in the naming of learning and the naming of oneself as a learner in this organisation. This is further complicated given that TAFE has learning as its raison d’etre and, as a workplace, there is much more informed discourse about workplace learning and its value compared to most other organisations. 3. Spaces of learning – this report suggests ‘Space’ is a helpful concept for thinking about everyday learning in TAFE and at work in general. The research drew on broad understandings of space, identity and learning and found the analysis of everyday learning in spatial terms can open opportunities for investigating workplace learning. The focus drew attention to what was called ‘in-between’ spaces. These new understandings unsettled the binaries that are commonly accepted by most workplaces: on-the-job / off-the-job, worker / learner etc. It is these ‘in-between’ spaces that interesting things were happening in regard to everyday learning. 4. Researching learning in contemporary workplaces - Throughout the project the research team explored the complexities of collaboratively researching workplace learning. This was important because while workplaces are popular sights for contemporary research, and collaborative research is popular catchcry of contemporary researchers, both workplace and collaborative research typically gloss over the complexities and contradictions this type of research often encompasses. Arising from its analysis, this report puts forward a number of discussion points for consideration by TAFE. The areas for discussion include: - relationships between informal and formal - significance of everyday learning - imposing formality - languages of learning - learning dimensions of change - local relationships - role for structured learning - future research. These areas for discussion suggest some possible strategies that TAFE may consider in order to enhance the everyday learning of the organisation

Stress transmission in wet granular materials

We analyze stress transmission in wet granular media in the pendular state by means of three-dimensional molecular dynamics simulations. We show that the tensile action of capillary bonds induces a self-stressed particle network organized in two percolating "phases" of positive and negative particle pressures. Various statistical descriptors of the microstructure and bond force network are used to characterize this partition. Two basic properties emerge: 1) The highest particle pressure is located in the bulk of each phase; 2) The lowest pressure level occurs at the interface between the two phases, involving also the largest connectivity of the particles via tensile and compressive bonds. When a confining pressure is applied, the number of tensile bonds falls off and the negative phase breaks into aggregates and isolated sites

Chronic viral infection promotes sustained Th1-derived immunoregulatory IL-10 via BLIMP-1

During the course of many chronic viral infections, the antiviral T cell response becomes attenuated through a process that is regulated in part by the host. While elevated expression of the immunosuppressive cytokine IL-10 is involved in the suppression of viral-specific T cell responses, the relevant cellular sources of IL-10, as well as the pathways responsible for IL-10 induction, remain unclear. In this study, we traced IL-10 production over the course of chronic lymphocytic choriomeningitis virus (LCMV) infection in an IL-10 reporter mouse line. Using this model, we demonstrated that virus-specific T cells with reduced inflammatory function, particularly Th1 cells, display elevated and sustained IL-10 expression during chronic LCMV infection. Furthermore, ablation of IL-10 from the T cell compartment partially restored T cell function and reduced viral loads in LCMV-infected animals. We found that viral persistence is needed for sustained IL-10 production by Th1 cells and that the transcription factor BLIMP-1 is required for IL-10 expression by Th1 cells. Restimulation of Th1 cells from LCMV-infected mice promoted BLIMP-1 and subsequent IL-10 expression, suggesting that constant antigen exposure likely induces the BLIMP-1/IL-10 pathway during chronic viral infection. Together, these data indicate that effector T cells self-limit their responsiveness during persistent viral infection via an IL-10-dependent negative feedback loop.This work was supported by an Australian NHMRC Overseas Biomedical Postdoctoral Fellowship (to I.A. Parish); a Yale School of Medicine Brown-Coxe Postdoctoral Fellowship (to I.A. Parish); the Alexander von Humboldt Foundation (SKA2010, to P.A. Lang); a CIHR grant (to P.S. Ohashi); and by the Howard Hughes Medical Institute and NIH grant RO1AI074699 (to S.M. Kaech). P.S. Ohashi holds a Canada Research Chair in Autoimmunity and Tumor immunity

Pre-avalanche instabilities in a granular pile

We investigate numerically the transition between static equilibrium and dynamic surface flow of a 2D cohesionless granular system driven by a continuous gravity loading. This transition is characterized by intermittent local dynamic rearrangements and can be described by an order parameter defined as the density of critical contacts, e.g. contacts where the friction is fully mobilized. Analysis of the spatial correlations of critical contacts shows the occurence of ``fluidized'' clusters which exhibit a power-law divergence in size at the approach of the stability limit. The results are compatible with recent models that describe the granular system during the static/dynamic transition as a multi-phase system.Comment: 9 pages, 6 figures, submitted to Phys. Rev. Let

Memory of the Unjamming Transition during Cyclic Tiltings of a Granular Pile

Discrete numerical simulations are performed to study the evolution of the micro-structure and the response of a granular packing during successive loading-unloading cycles, consisting of quasi-static rotations in the gravity field between opposite inclination angles. We show that internal variables, e.g., stress and fabric of the pile, exhibit hysteresis during these cycles due to the exploration of different metastable configurations. Interestingly, the hysteretic behaviour of the pile strongly depends on the maximal inclination of the cycles, giving evidence of the irreversible modifications of the pile state occurring close to the unjamming transition. More specifically, we show that for cycles with maximal inclination larger than the repose angle, the weak contact network carries the memory of the unjamming transition. These results demonstrate the relevance of a two-phases description -strong and weak contact networks- for a granular system, as soon as it has approached the unjamming transition.Comment: 13 pages, 15 figures, soumis \`{a} Phys. Rev.

A zone melting device for the in situ observation of directional solidification using high-energy synchrotron x rays editors-pick

Directional solidification (DS) is an established manufacturing process to produce high-performance components from metallic materials with optimized properties. Materials for demanding high-temperature applications, for instance in the energy generation and aircraft engine technology, can only be successfully produced using methods such as directional solidification. It has been applied on an industrial scale for a considerable amount of time, but advancing this method beyond the current applications is still challenging and almost exclusively limited to post-process characterization of the developed microstructures. For a knowledge-based advancement and a contribution to material innovation, in situ studies of the DS process are crucial using realistic sample sizes to ensure scalability of the results to industrial sizes. Therefore, a specially designed Flexible Directional Solidification (FlexiDS) device was developed for use at the P07 High Energy Materials Science beamline at PETRA III (Deutsches Elektronen–Synchrotron, Hamburg, Germany). In general, the process conditions of the crucible-free, inductively heated FlexiDS device can be varied from 6 mm/h to 12 000 mm/h (vertical withdrawal rate) and from 0 rpm to 35 rpm (axial sample rotation). Moreover, different atmospheres such as Ar, N2, and vacuum can be used during operation. The device is designed for maximum operation temperatures of 2200 °C. This unique device allows in situ examination of the directional solidification process and subsequent solid-state reactions by x-ray diffraction in the transmission mode. Within this project, different structural intermetallic alloys with liquidus temperatures up to 2000 °C were studied in terms of liquid–solid regions, transformations, and decompositions, with varying process conditions

Murine but Not Human Basophil Undergoes Cell-Specific Proteolysis of a Major Endoplasmic Reticulum Chaperone

Basophil has been implicated in anti-parasite defense, allergy and in polarizing T(H)2 response. Mouse model has been commonly used to study basophil function although the difference between human and mouse basophils is underappreciated. As an essential chaperone for multiple Toll-like receptors and integrins in the endoplasmic reticulum, gp96 also participates in general protein homeostasis and in the ER unfolded protein response to ensure cell survival during stress. The roles of gp96 in basophil development are unknown.We genetically delete gp96 in mice and examined the expression of gp96 in basophils by Western blot and flow cytometry. We compared the expression pattern of gp96 between human and mouse basophils.We found that gp96 was dispensable for murine basophil development. Moreover, gp96 was cleaved by serine protease(s) in murine but not human basophils leading to accumulation of a nun-functional N-terminal ∼50 kDa fragment and striking induction of the unfolded protein response. The alteration of gp96 was unique to basophils and was not observed in any other cell types including mast cells. We also demonstrated that the ectopic expression of a mouse-specific tryptase mMCP11 does not lead to gp96 cleavage in human basophils.Our study revealed a remarkable biochemical event of gp96 silencing in murine but not human basophils, highlighting the need for caution in using mouse models to infer the function of basophils in human immune response. Our study also reveals a novel mechanism of shutting down gp96 post-translationally in regulating its function