ABSTRACT
This paper presents the numerical simulation and fabrication of a metasurface composed of silver nanorings with a split-ring gap. These nanostructures can exhibit optically-induced magnetic responses with unique possibilities to control absorption at optical frequencies. The absorption coefficient of the silver nanoring was optimized by performing a parametric study with Finite Difference Time Domain (FDTD) simulations. The absorption and scattering cross sections of the nanostructures are numerically calculated to assess the impact of the inner and outer radii, the thickness and the split-ring gap of one nanoring, as well as the periodicity factor for a group of four nanorings. This showed full control on resonance peaks and absorption enhancement in the near infrared spectral range. The experimental fabrication of this metasurface made of an array of silver nanorings is achieved by e-beam lithography and metallization. Optical characterizations are then carried out and compared to the numerical simulations. In contrast to usual microwave split-ring resonator metasurfaces reported in literature, the present study shows both the realization by a top-down process and modelling performed in the infrared frequency range.
ABSTRACT
Interferon regulatory factor-1 (IRF-1) has been recognized as an important tumor suppressor and growth regulatory transcription factor, which is also involved in cell differentiation. In this study we investigated the role of IRF-1 in phorbol 12-myristate 13-acetate (PMA)-induced monocyte/macrophage differentiation of human monoblastic U937 cells. For this purpose U937 cells were stably transfected with a vector overexpressing IRF-1 antisense mRNA (U937 IRF-1A cells) and with the SV-40 empty vector (U937-SV40 e.v. cells). We report here that U937 and U937-SV40 e.v. cells differentiated into macrophage-like cells upon PMA stimulation and showed IRF-1 up-regulation. On the contrary, U937 IRF-1A cells stimulated with PMA kept an undifferentiated phenotype and proliferated actively. A direct correlation between induction of IRF-1 and up-regulation of IRF-1 gene targets such as ornithine decarboxylase (ODC) and WAF-1/CIP-1 was also observed in U937 cells. On the other hand U937 IRF-1A cells down-regulated ODC and did not express WAF-1. Results show that IRF-1 plays a pivotal role in PMA-induced monocyte/macrophage differentiation.
