Radiation-induced attenuation in aluminum- and aluminum-thulium-doped optical fibers.

Gamma-ray-induced attenuation in Al-doped and Al/Tm-co-doped optical fibers is investigated in the visible and near-infrared domain up to 1 Gy. The behavior of radiation-induced attenuation (RIA) regarding dose and dose rate is discussed. Our results reveal high sensitivities for both types of fibers at low gamma ray doses and also reveal that Al/Tm fibers are very promising at original interrogation wavelengths for dosimetry applications.

Influence of temperature and dose rate on radiation-induced attenuation at 1542 nm in fluorine-doped fibers.

Radiation-induced attenuation (RIA) at 1542 nm of fluorine-doped fibers under gamma radiation source has been investigated for different dose rates and temperatures. Both the temperature and dose rate dependencies are unusual. First, the fiber presents an enhanced low dose rate sensitivity that is favored by increasing temperature. Furthermore, in certain conditions, RIA increases with irradiation temperature, which is a very rare phenomenon. We have built a phenomenological model that shows that these behaviors can be explained considering that two color centers previously identified in the literature are responsible for RIA: inherent and strain-assisted self-trapped holes.

Histological Method to Study the Effect of Shear Stress on Cell Proliferation and Tissue Morphology in a Bioreactor.

Background: Tissue engineering represents a promising approach for the production of bone substitutes. The use of perfusion bioreactors for the culture of bone-forming cells on a three-dimensional porous scaffold resolves mass transport limitations and provides mechanical stimuli. Despite the recent and important development of bioreactors for tissue engineering, the underlying mechanisms leading to the production of bone substitutes remain poorly understood. Methods: In order to study cell proliferation in a perfusion bioreactor, we propose a simplified experimental set-up using an impermeable scaffold model made of 2 mm diameter glass beads on which mechanosensitive cells, NIH-3T3 fibroblasts are cultured for up to 3 weeks under 10 mL/min culture medium flow. A methodology combining histological procedure, image analysis and analytical calculations allows the description and quantification of cell proliferation and tissue production in relation to the mean wall shear stress within the bioreactor. Results: Results show a massive expansion of the cell phase after 3 weeks in bioreactor compared to static control. A scenario of cell proliferation within the three-dimensional bioreactor porosity over the 3 weeks of culture is proposed pointing out the essential role of the contact points between adjacent beads. Calculations indicate that the mean wall shear stress experienced by the cells changes with culture time, from about 50 mPa at the beginning of the experiment to about 100 mPa after 3 weeks. Conclusion: We anticipate that our results will help the development and calibration of predictive models, which rely on estimates and morphological description of cell proliferation under shear stress.