Interpretation of azimuthal angle dependence of periodic gratings in Mueller matrix spectroscopic ellipsometry.

Mueller matrix spectroscopic ellipsometry becomes increasingly important for determining structural parameters of periodic line gratings. Because of the anisotropic character of gratings, the measured Mueller matrix elements are highly azimuthal angle dependent. Measurement results are interpreted by basic principles of diffraction on gratings. The spectral and azimuthal angle dependent intensity changes are correlated to so-called Rayleigh singularities, i.e., wavelengths where the number of diffraction orders changes. The positions of the Rayleigh singularities are calculated analytically and overlapped with measured spectra of two different types of photomasks with transparent and reflecting substrates. For both types of gratings, the Rayleigh singularities reproduce the contours of the spectra. Increasing grating periods result in a shift of these contours to longer wavelengths. Characteristic differences between the two photomasks are explained by the influence of the transmission orders, which are determined by the substrate transparency.

RNA interference protects horse cells in vitro from infection with Equine Arteritis Virus.

Equine Arteritis Virus (EAV) belongs to the Arteriviridae and causes viral arteritis in horses. In an attempt to develop novel and save therapies against the infection it was tested whether EAV is susceptible to RNA interference (RNAi) in an equine in vitro system. Horse cells were transfected with chemically synthesized small interfering RNA oligonucleotides (siRNAs) and challenged with EAV. Application of these siRNAs led to a significant protection of the cells, and virus titers decreased drastically. siRNAs derived from DNA plasmids expressing small hairpin RNAs (shRNAs) were also effective. The protection was most pronounced with two siRNAs targeting the open reading frame 1 (coding for non-structural proteins), whereas siRNAs targeting sequences for several structural proteins had less or no effect. In addition, it was investigated whether RNAi could be used to treat cells with an already established viral infection. Only application of the siRNAs shortly after viral challenge led to significant survival rates of the cells, whereas transfection at later time points caused much less benefit for the cells. These findings are discussed in a perspective of using RNAi as a therapeutic approach to combat EAV.