Nano-Indentation Device for Investigating the Mechanics of Compliant Materials

Indentation testing has long been used to measure the mechanical properties of a wide range of materials from metals and ceramics to brain tissue and hydrogels. The purpose of this study was to build and validate a Nano-Tissue Indenter (NTI) capable of performing indentation testing on micro-scale structures within the liver’s extracellular matrix. Two silicone-based tissue simulant materials were selected with elastic properties similar to hydrogels used for liver cell cultures. Samples of each material formulation, EcoFlex0030 (EF30) and EcoFlex0010 (EF10), were indented with NTI and also tested in unconfined compression to provide benchmark shear moduli. The resulting force and displacement measurements from NTI with resolutions of 300 nN and 700 nm respectively were analyzed using the Pietrement-Troyon model of adhesive contact. Using this method, NTI was able to distinguish a 10 kPa difference in shear modulus between EF30 and EF10 with comparable significance as unconfined compression (p?<?0.001). General agreement between the results of the two test methods is evidenced by the overlapping of the mean ± S.D. range for the NTI-indentation and benchmark unconfined compression shear moduli measured for both formulations. NTI was used successfully to perform nano-indentation tests on samples of compliant material undergoing adhesive contact, similar to the extracellular matrix of organs such as the liver.     

Ab initio prediction of half-metallic ferromagnetism in Zn(TM)O2 (TM=Cr,Mn, Fe,Co, Ni) compounds

From the results of first principles tight-binding linear muffin-tin orbital (TB-LMTO) calculations, half-metallic ferromagnetism is proposed in Zn(TM)O₂ with a chalcopyrite structure. The calculated electronic and magnetic property shows that consistent with the integer value for the total magnetic moment, half metallicity is obtained for ZnCrO₂, ZnMnO₂, ZnFeO₂, ZnCoO₂ and ZnNiO₂. A careful analysis of the spin density reveals the ferromagnetic coupling between the p–d states and the cation dangling-bond p states, which is believed to be responsible for the stabilization of the ferromagnetic phase. The calculated heat of formation, bulk modulus and cohesive energy are reported.     

Molecular sieving platinum nanoparticle catalysts kinetically frozen in nanoporous carbon

Highly active shape selective catalysts with excellent thermal stability are synthesized by entrapping well dispersed platinum nanoparticles in a polyfurfuryl alcohol derived nanoporous carbon matrix; these nanocomposites are excellent candidates for new catalytic applications including fuel cells, pharmaceutical synthesis and biomass conversion.     

Tunneling and coupled motion in the Escherichia coli dihydrofolate reductase catalysis

H-transfer was studied in the complex kinetic cascade of dihydrofolate reductase. Intrinsic kinetic isotope effects, their temperature dependence, and other temperature-dependent parameters indicated H-tunneling, but no 1 degrees to 2 degrees coupled motion. The data also suggested environmentally coupled tunneling and commitment to catalysis on pre-steady-state isotope effects.     

Base catalysed rearrangement of a spiro oxy-cope system and related studies: A new entry into perhydrophenalene and perhydroacenaphthylene systems

The spirovinyl carbinol 5 when treated with methanolic potassium hydroxide was found to rearrange to perhydrophenalene- 1,4-dione 6 via an anionic oxy-Cope rearrangement followed by an intramolecular Michael addition. The epimeric mixture of ketol acetates 15a and 15b was also found to rearrange to 2-hydroxy-2-methyl perhydroacenaphthylene-1,3-dione 16 on treatment with base.     

Path integral analysis of harmonic oscillators with time-dependent mass

Two cases of forced harmonic oscillators with time dependent mass for which exact propagators can be evaluated are presented. From the exact propagators, normalized solutions of the corresponding Schrödinger equations are arrived at. Time-dependent invariants are also found.     

On perfect images of ordinals

In the first section of this paper, the ordinal space [1, ω] is characterized. Then its quotients are completely described in easy terms. In the second section, the ideas of a well-ordered sum of an arbitrary collection of T₂spaces and a Chandelier space are introduced. The Chandelier spaces are obtained by taking compact ordinals and forming their interweaves and well ordered sums and one-point compactification of such spaces. Finally it is proved that the Hausdorff quotients of compact ordinals are precisely the Chandelier spaces. A problem of M. Hu ek on quotients of [1, ω] is thus solved.     

A chain compact space which is not strongly scattered

A compactT ₂ spaceX which is separable, scattered and uncountable, but still so thatX ^α−X^α+1is countable for all α∈[1, ω) is constructed. This answers one of the problems presented by M. E. Rudin in a conference as an open problem and attributed by her to Telgarsky. The author acknowledges a faculty research grant from Memphis State University when this paper was written.     

Direct determination of free energies of colloidal dispersions

Helmholtz free energies of electrostatically-stabilized colloidal dispersions of monodispersed spherical particles have been obtained using computer experiments. Boltzmann sampling has been shown to be sufficient for determining free energy differences between two dispersions whose pair-potentials are close to each other. Non-Boltzmann sampling has been used when the pair-potentials differ substantially. These results have been compared with the results based on perturbation theory. The techniques used, thus, offer a direct method to test the latter.