935 research outputs found
Toy nanoindentation model and incipient plasticity
A toy model of two dimensional nanoindentation in finite crystals is
proposed. The crystal is described by periodized discrete elasticity whereas
the indenter is a rigid strain field of triangular shape representing a hard
knife-like indenter. Analysis of the model shows that there are a number of
discontinuities in the load vs penetration depth plot which correspond to the
creation of dislocation loops. The stress vs depth bifurcation diagram of the
model reveals multistable stationary solutions that appear as the
dislocation-free branch of solutions develops turning points for increasing
stress. Dynamical simulations show that an increment of the applied load leads
to nucleation of dislocation loops below the nanoindenter tip. Such
dislocations travel inside the bulk of the crystal and accommodate at a certain
depth in the sample. In agreement with experiments, hysteresis is observed if
the stress is decreased after the first dislocation loop is created. Critical
stress values for loop creation and their final location at equilibrium are
calculated.Comment: 22 pages, 5 figures, to appear in Chaos, Solitons and Fractal
The new ASDEX upgrade upper divertor for special alternative configurations: Design and FEM calculations
CXCR2 deficient mice display macrophage-dependent exaggerated acute inflammatory responses
CXCR2 is an essential regulator of neutrophil recruitment to inflamed and damaged sites and plays prominent roles in inflammatory pathologies and cancer. It has therefore been highlighted as an important therapeutic target. However the success of the therapeutic targeting of CXCR2 is threatened by our relative lack of knowledge of its precise in vivo mode of action. Here we demonstrate that CXCR2-deficient mice display a counterintuitive transient exaggerated inflammatory response to cutaneous and peritoneal inflammatory stimuli. In both situations, this is associated with reduced expression of cytokines associated with the resolution of the inflammatory response and an increase in macrophage accumulation at inflamed sites. Analysis using neutrophil depletion strategies indicates that this is a consequence of impaired recruitment of a non-neutrophilic CXCR2 positive leukocyte population. We suggest that these cells may be myeloid derived suppressor cells. Our data therefore reveal novel and previously unanticipated roles for CXCR2 in the orchestration of the inflammatory response
The chemokine RANTES is secreted by human melanoma cells and is associated with enhanced tumour formation in nude mice
Modulation of tumour cell growth by tumour-infiltrating leucocytes is of high importance for the biological behaviour of malignant neoplasms. In melanoma, tumour-associated macrophages (TAM) and tumour-infiltrating lymphocytes (TIL) are of particular interest as inhibitors or enhancers of cell growth. Recruitment of leucocytes from the peripheral blood into the tumour site is mediated predominantly by chemotaxins, particularly by the group of chemokines
Three-dimensional jamming and flows of soft glassy materials
Various disordered dense systems such as foams, gels, emulsions and colloidal
suspensions, exhibit a jamming transition from a liquid state (they flow) to a
solid state below a yield stress. Their structure, thoroughly studied with
powerful means of 3D characterization, exhibits some analogy with that of
glasses which led to call them soft glassy materials. However, despite its
importance for geophysical and industrial applications, their rheological
behavior, and its microscopic origin, is still poorly known, in particular
because of its nonlinear nature. Here we show from two original experiments
that a simple 3D continuum description of the behaviour of soft glassy
materials can be built. We first show that when a flow is imposed in some
direction there is no yield resistance to a secondary flow: these systems are
always unjammed simultaneously in all directions of space. The 3D jamming
criterion appears to be the plasticity criterion encountered in most solids. We
also find that they behave as simple liquids in the direction orthogonal to
that of the main flow; their viscosity is inversely proportional to the main
flow shear rate, as a signature of shear-induced structural relaxation, in
close similarity with the structural relaxations driven by temperature and
density in other glassy systems.Comment: http://www.nature.com/nmat/journal/v9/n2/abs/nmat2615.htm
An optimized upper divertor with divertor-coils to study enhanced divertor configurations in ASDEX Upgrade
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