Science melas in connection with national science campaign
The iron running in our blood, calcium in our teeth, the sand we walk on, were all made inside stars. All elements heavier than boron are formed by nuclear reactions inside stars. We owe our existence to these stellar pots. Stars live for millions to billions of years and then it is a fierce battle for their survival. Ultimately they loose the battle and the resulting supernovae disperse the synthesized elements in the universe. Nature does not know of waste products and from stellar dust many more stars are created. In this talk we would discuss the birth and demise of stars. It is for the audience to decide if it is more of stellar science or abstract art.
Semiconductor nanowires (NWs) are attracting wide interest due to their unique physical properties and potential for application in nanodevices. NWs can be obtained by a number of growth methods, and their highly anisotropic growth originates by the presence of a metal particle, the catalyst, that determines the position and the diameter of the nanostructure. The most widely used catalyst is gold. The growth mechanism of catalyst assisted nanowires involves the incorporation of material both impinging on the catalyst particle and diffusing from the free substrate surface to the sidewalls of the wire. The interplay of these two phenomena is critical especially for the growth of alloy semiconductor compound NWs and one dimensional (1-D) heterostructure. Difference in the surface mobility between the constituents could give compositional inhomogeneities in alloy NWs and degradation of the interface sharpness in 1-D heterostructure. The systematic presence of a metal particle at the NWs tip could be exploited in single NW devices. Moreover, one of the most interesting characteristic of the III-V NWs grown by catalyst assisted self assembling is the peculiarity of having an hexagonal lattice structure (wurtzite), while their bulk and epitaxial parent materials have the cubic structure (zinc blend). In our laboratory we have synthesized GaAs NWs by molecular beam epitaxy (MBE) either using a thin gold, manganese, Ga layer as the growth catalyst or without any catalyst. In this talk some of the basics of NWs, their growth and potential applications will be covered.
Cells reside and operate in a complex and dynamic extra-cellular matrix. The mechanical, structural and chemical properties of the matrix regulate a variety of cellular functions including signaling, adhesion, migration as well as invasion and metastasis in tumor systems. Unfortunately cell-matrix interactions have traditionally been studied in the context of artificial 2D environments, which are far from in vivo conditions. As a result, our understanding of the complex interactions at the cell-matrix interface has been quite limited. In particular, the mechano-chemical effects of the matrix, the proteolytic pathways and surface receptor dynamics on a 3D surface that are critical in invasion and tumor metastasis, and can not be fully studied in a 2D environment. In order to overcome the limited powers of observation in 2D, we utilize a combination of high resolution and high throughput confocal microscopy, bulk and micro-rheological measurements and multi-scale simulations rooted in statistical and continuum mechanics. Using an interdisciplinary approach allows us to understand and quantify the mechanical and chemical roles of the matrix in regulating signaling, adhesion and motility. Our results demonstrate that both cell structure and cell function are strikingly different in 3D than in 2D and that cellular response to minor mechanical changes in its extra-cellular environment is amplified in 3D than in 2D environments. Our experimental results are complemented by multi-scale simulations, that probe the physical foundations of cell-matrix interactions from the nano to the macro level. Our hybrid approach, combining high-resolution experimental and computational techniques demonstrates how a balance of cellular parameters (e.g. integrin expression and MMP activity) co-operate with matrix properties (e.g. composition, stiffness and porosity) to regulate adhesion, invasion and motility of tumor cells in native like environments.