Cytosolic Sequestration of Prep1 Influences Early Stages of T Cell Development

Objective: Prep1 and Pbx2 are the main homeodomain DNA-binding proteins of the TALE (three amino acid loop extension) family expressed in the thymus. We previously reported reduced Pbx2 expression and defective thymocyte maturation in Prep1 hypomorphic mice. To further investigate the role of this homeodomain DNA-binding protein in T cell development, we generated transgenic mice expressing the N-terminal fragment of Pbx1 (Pbx1NT) under the control of the Lck proximal promoter. Principal Findings: Pbx1NT causes Prep1 cytosolic sequestration, abolishes Prep1-dependent DNA-binding activity and results in reduced Pbx2 expression in developing thymocytes. Transgenic thymi reveal increased numbers of CD4 2 CD8 2 CD44 2 (DN3 and DN4) thymocytes, due to a higher frequency of DN2 and DN4 Pbx1NT thymocytes in the S phase. Transgenic thymocytes however do not accumulate at later stages, as revealed by a normal representation of CD4/CD8 double positive and single positive thymocytes, due to a higher rate of apoptotic cell death of DN4 Pbx1NT thymocytes. Conclusion: The results obtained by genetic (Prep1 hypomorphic) and functional (Pbx1NT transgenic) inactivation of Prep

Modeling dislocation-grain boundary interactions through gradient plasticity and nanoindentation

By considering an interface energy term in gradient plasticity an "interfacial" yield criterion, indicating the stress at which the interface begins to deform plastically can be developed. From an experimental point of view interfacial yielding has been observed during nanoindentation on an Fe-2.2weight% Si bi-crystal and a Nb polycrystal. In the present study after illustrating the interaction of a grain boundary with the grain interior for a plastically deforming bi-crystal the theoretically determined interfacial yield stress expression is fit to the nanoindentation data for Fe-2.2% Si and Nb. This fit allows first estimates to be obtained for the internal length, a key material parameter that comes into play in all gradient theories. Based on the predicted values the internal length is physically related to the dislocation source distance. © 2007 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Elastic modulus of nanostructured polymer surfaces

Living cell cultures exhibit improved adhesion on polymer surfaces engineered with nano-scale structures as compared to their flat counterparts. During fabrication their polymer-chain structure can be altered, thus affecting their mechanical properties. Here, we demonstrate using atomic-force-microscope nanoindentation that the modulus of nanostructured PDMS is doubled, while that of nanostructured ORMOCER increases by an order of magnitude, when compared to their flat counterparts. © 2011 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex

Modelling Thin Film Microbending: A Comparative Study of Three Different Approaches

Constitutive models which describe crystal microplasticity in a continuum framework can be envisaged as average representations of the dynamics of dislocation systems. Thus, their performance needs to be assessed not only by their ability to correctly represent stress-strain characteristics on the specimen scale but also by their ability to correctly represent the evolution of internal stress and strain patterns. In the present comparative study we consider the bending of a free-standing thin film. We compare the results of 3D DDD simulations with those obtained from a simple 1D gradient plasticity model and a more complex dislocation-based continuum model. Both models correctly reproduce the nontrivial strain patterns predicted by DDD for the microbending problem. © 2011 American Institute of Physics

Cracking in Si-based anodes for Li-ion batteries

In attempts to increase the anode capacity of rechargeable Li-ion batteries, composite materials with micro- and nano-scale domains of Li active material surrounded by Li inactive material are being investigated. Materials such as Si, Al and Sn that provide capacities between 900 and 4000 mAh g(-1) during the formation of Li-alloys can be used as the active sites, while inert ceramics or glasses can be as the inactive matrix. During Li insertion the volume of the active sites expands over 100% at maximum capacity. As a result large internal stresses are produced, which lead to a loss of mechanical integrity at the active site/matrix interface and eventually cracking of the electrode. Therefore, before these types of composite material systems are used commercially it is of great importance to model their mechanical response. The present study applies a previously developed formulation to predict stable crack growth in anodes which are comprised of spherical Si nanospheres embedded in a soda glass matrix

Observation and measurement of grain rotation and plastic strain in nanostructured metal thin films

The deformation behavior of nanostructured gold thin films, with grain diameters of 10 nm and film thicknesses of 10-20 nm, has been studied by means of in situ high resolution transmission electron microscopy. Grain rotation was observed by measuring the changes in the angular relationships between the lattice fringes of different grains during deformation at low strain rates. The strain tensor was calculated by measuring the relative displacements of three material points, and using an analysis similar to that for strain gage rosettes. Relative grain rotations of up to 15 degrees, along with effective plastic strains on the order of 30%, were measured. No evidence of dislocation activity was detected during or after straining. Identical experiments on coarser-grained silver thin films, with grain diameters around 110 nm, yielded clear evidence of dislocation activity. These results indicate that grain rotation and grain boundary sliding can make significant contributions to the deformation of nanostructured thin films at low homologous temperatures. © 1995

In situ studies of deformation and fracture in nanophase materials

Nanocrystalline gold (8-25 nm grain size) and gold/silicon nanocomposites were prepared by sputtering and then strained to fracture in a transmission electron microscope. In situ and post mortem analyses revealed that the nanophase gold films were ductile, and significant plasticity was associated with fracture. Observations of pore formation, as well as a strain-rate effect on deformation behavior and direct lattice imaging of deformation, all indicated that the deformation occurred by diffusion-based mechanisms. Fracture was intergranular, but not brittle. Gold/silicon nanocomposites containing large volume fractions of brittle, amorphous Si and nanocrystalline gold precipitates exhibited behavior indicating significant toughness. © 1993