Some recent investigations of materials under high pressures

By subjecting materials to high pressures one can significantly reduce interatomic and intermolecular distances. This causes drastic changes in the nature of electronic and vibrational states and also in bonding, bringing about several unusual structural, electronic and magnetic phase transitions. In addition, these studies provide a very useful data about the equation of state of the materials of interest. Several examples from our work are presented which elucidate the richness of physics under these conditions

Analysis of the absorption spectrum of ruby at high pressures

It is shown that at high pressures, results of absorption measurements are inconsistent with R-line fluorescence data. The observed constancy of R1-R2 splitting under hydrostatic conditions is supported by crystal field analysis. The present findings suggest the need for absorption measurements in ruby crystals under better defined stress conditions

High pressure investigations on hydrous Magnesium Silicate-Phase A using first principles calculations, H---H repulsion and O-H bond compression

We have carried out first principles structural relaxation calculations on the hydrous magnesium silicate Phase A (Mg7Si2O8(OH)6) under high pressures. Our results show that phase A does not undergo any phase transition upto ~ 45 GPa. We find that nonbonded H---H distance reaches a limiting value of 1.85 Å at about 45 GPa. The H---H repulsive strain releasing mechanism in Phase A is found to be dramatically different from the hydrogen bond bending one that was proposed by Hofmeister et al1 for Phase B. It is based on the reduction of one of the O-H bond distances with compression

Differential responsiveness of MET inhibition in non-small-cell lung cancer with altered CBL.

Casitas B-lineage lymphoma (CBL) is an E3 ubiquitin ligase and a molecule of adaptor that we have shown is important for non-small-cell lung cancer (NSCLC). We investigated if MET is a target of CBL and if enhanced in CBL-altered NSCLC. We showed that CBL wildtype cells have lower MET expression than CBL mutant cells. Ubiquitination of MET was also decreased in CBL mutant cells compared to wildtype cells. Mutant cells were also more sensitive to MET inhibitor SU11274 than wild-type cells. sh-RNA-mediated knockdown of CBL enhanced cell motility and colony formation in NSCLC cells, and these activities were inhibited by SU11274. Assessment of the phospho-kinome showed decreased phosphorylation of pathways involving MET, paxillin, EPHA2, and VEGFR. When CBL was knocked down in the mutant cell line H1975 (erlotinib-resistant), it became sensitive to MET inhibition. Our findings suggest that CBL status is a potential positive indicator for MET-targeted therapeutics in NSCLC

Low temperature and high pressure Raman and x-ray studies of pyrochlore Tb2_2Ti2_2O7_7 : phonon anomalies and possible phase transition

We have carried out temperature and pressure-dependent Raman and x-ray measurements on single crystals of Tb$_2$Ti$_2$O$_7$. We attribute the observed anomalous temperature dependence of phonons to phonon-phonon anharmonic interactions. The quasiharmonic and anharmonic contributions to the temperature-dependent changes in phonon frequencies are estimated quantitatively using mode Gr\"{u}neisen parameters derived from pressure-dependent Raman experiments and bulk modulus from high pressure x-ray measurements. Further, our Raman and x-ray data suggest a subtle structural deformation of the pyrochlore lattice at $\sim$ 9 GPa. We discuss possible implications of our results on the spin-liquid behaviour of Tb$_2$Ti$_2$O$_7$.Comment: 10 figures, 26 pages. Appeared in Physical Review B, vol-79, pp-134112 (2009

High pressure investigations on Hydrous Magnesium Silicate-Phase A using first principles calculations, H---H repulsion and O-H bond compression

We have carried out first principles structural relaxation calculations on the hydrous magnesium silicate Phase A (Mg 7 Si 2 O 8 (OH) 6 ) under high pressures. Our results show that phase A does not undergo any phase transition upto ~ 45 GPa. We find that nonbonded H---H distance reaches a limiting value of 1.85 Å at about 45 GPa. The H---H repulsive strain releasing mechanism in Phase A is found to be dramatically different from the hydrogen bond bending one that was proposed by Hofmeister et al 1 for Phase B. It is based on the reduction of one of the O-H bond distances with compression