Phase transformations of crystalline SiO2 versus dynamic disorder between room temperature and liquid state.

The sequence of phase transitions of crystalline silica has been probed by infrared emission spectroscopy. The lattice dynamics, deeply impacted by the low frequency dynamic disorder, exhibit with increasing temperature signs of inhomogeneous broadening of the symmetry allowed normal modes. High frequency supplementary components are also activated. The analysis with a causal Voigt dielectric function model within the framework of hard mode spectroscopy allowed a fine characterization of solid­solid phase transitions. We also report experimental evidence showing that the occurrence of the intermediate ill-defined region above 1300 K is concomitant with the reactivation of the low frequency dynamic disorder; a behavior change that on the way explains the appearance of the negative thermal expansion regime.

Effect of interferon-gamma on the expression of HLA-DR by human melanoma cells of varying metastatic potential.

Three human melanoma cell lines of varying invasive and metastatic potential were analyzed for their ability to express HLA-DR antigens on the cell surface as well as transcriptionally at the mRNA level in the presence and absence of IFN-gamma treatment. Cells of low and intermediate metastatic and invasive potential showed a high percentage of HLA-DR surface expression, both before (91.2-99.9%) and after (97.8-99.9%) IFN-gamma treatment, as quantitated by flow cytometry. In contrast, cells of high metastatic and invasive potential expressed barely detectable levels of HLA-DR-positive cells before IFN-gamma treatment (0.3-0.6%) and displayed elevated levels following treatment (42.3-89.4%). Allowing the highly metastatic cells to recover for 7 or 14 days following IFN-gamma treatment resulted in barely detectable levels of HLA-DR-positive cells. Northern blot analyses of HLA-DR transcription levels showed a strong expression in cells of low and intermediate metastatic and invasive potential. HLA-DR mRNA levels were not detectable in control cells of high metastatic potential nor in those cells which had undergone 7- and 14-day recovery periods following IFN-gamma treatment. There was, however, an induction of HLA-DR expression in the cells that had been treated with IFN-gamma for 72 hr and allowed no recovery period. In addition, a punctate, receptor-like pattern of immunofluorescence staining pattern for cell surface HLA-DR was seen after a 72 hr IFN-gamma treatment in the highly metastatic cells. In contrast, cells of low and intermediate metastatic potential expressed a homogeneous ring-like pattern of antigen expression.