Component Analysis of Radiation-Induced Thermoe-lasticity Using Modulation Polarimetry

A radiation field of an external or internal origin creates a non-uniform temperature gradient in a glass specimen. In this case, there appears a heat flux in the specimen, which generates mechanical stresses and induces an optical anisotropy in the form of birefringence. In this work, using the optical-polarization method, the birefringence magnitude is measured as the phase difference between the orthogonal components of the linearly polarized probing radiation. The capability of the method is enhanced by modulating the radiation polarization, which provided a reliable registration of stresses in the specimen at a temperature drop of about 0.1 K. The stress kinetics with a complicated behavior and ambiguous by sign is detected at the observation point within the temperature establishment time interval. Its modeling in terms of exponential functions made it possible to decompose the measurement results into components associated with the radiative, conductive, and convective heat transfer mechanisms, as well as determine their relaxation parameters. The measurement data can be of practical use while determining such technically important material characteristics as the thermal diffusion and heat transfer coefficients.

In vitro cytotoxicity of self-curing acrylic resins of different colors

OBJECTIVE: The aim of this study was to assess the in vitro cytotoxicity of acrylic resins of different colors over time. METHODS: Specimens were divided into 4 groups (n = 6) according to the color of the acrylic resin (Orto Class, Clássico, Campinas, São Paulo, Brazil): Group 1: clear acrylic resin; group 2: pink acrylic resin; group 3: blue acrylic resin and group 4: green acrylic resin. All specimens were fabricated according to the mass manipulation technique and submitted to mechanical polishing protocol. The control was performed with an amalgam specimen (C+), a glass specimen (C-) and cell control (CC). Specimens were immersed in Minimum Eagle's Medium (MEM) and incubated for 24 h at 37o C. The extracts from the experimental material were filtered and mixed with L929 fibroblast. Cytotoxicity was evaluated at 4 different times, 24, 48, 72 and 168 h. After contact, cells were incubated for 24 h and added to 100 µ of 0.01% neutral red dye. The cells were incubated for 3 h for pigment incorporation and fixed. Cells viability was determined by a spectroscopic (BioTek, Winooski, Vermont, USA) with a 492-nm wavelength λ=492 nm). RESULTS: There were no statistical differences between the experimental groups and the CC and C- groups. CONCLUSION: Clear, pink, blue and green self-curing acrylic resins fabricated by means of the mass manipulation technique and mechanically polished are not cytotoxic. Neither the pigment added to the self-curing acrylic resin nor the factor of time influenced the cytotoxicity of the material.

Chemo-Mechanical Grinding for K9 Optical Glass

K9 optical glass was widely used in national defense and civilian fields. In this paper, chemo-mechanical grinding (CMG) was applied to process the K9 optical glass. Selecting CeO2, MgO and Fe2O3as CMG abrasives, the corresponding CMG tools were purposely developed for the check experiment. High surface and subsurface qualities on the K9 optical glass specimen were obtained as the polished results by the CeO2-CMG tools. Surface roughness and material removal rate were used to evaluate the grinding performance. The low-abrasive ratio of CeO2-CMG tool was proved as the optimal one, by which the surface roughness Ra reached 0.586nm, and the surface morphology appeared smooth and flat. The angle polishing was applied to detect the subsurface quality and the subsurface cracks were not observed.