Analysis of rectangular waveguide discontinuities by the method oflines

An efficient analysis of discontinuities in the rectangular waveguide is presented using the method of lines with one-dimensional discretization. As the line numbers in the incoming and outgoing waveguides are automatically correctly chosen in the method of lines, relative convergence is avoided. Scattering parameters for the E-plane step discontinuity are determined and an equivalent circuit for the diaphragm, the displacement, and a step with diaphragm is presented     

Analysis of velocity sedimentation techniques in cell separation. Influence of apparative and sample properties on separative power, resolution and sensitivity

In the present investigation the velocity sedimentation technique was analysed with respect to separation resolution, power and sensitivity. It was found that apparative modifications do not influence the resolution, which is a function of the contribution of apparative errors to the dispersion. A surprisingly small parameter of 0.15 was determined and it seems unlikely that this value can be improved. On the other hand an apparative modification is presented which improves the separation power and makes sample loading independent of the gradient filling. If cells (from rat bone marrow) were separated, a several times higher dispersion for a given cell volume was observed than was due to the apparative error. It was concluded that density variations were the major source of this dispersion. Since cell volume and density apparently show independent variations within a biological cell population the cell density cannot be disregarded if velocity sedimentation profiles are discussed in physical terms as is often done.     

Epitaxial Bragg mirrors for the mid-infrared and their applications

Bragg interference mirrors consisting of stacks of dielectric layers with an optical thickness of a quarter wavelength are of great importance for optoelectronic device applications. For the mid-infrared spectral range mirrors with high reflectivity stop bands are fabricated from combinations of Pb_1−xEu_xTe/EuTe materials by molecular beam epitaxy on BaF₂ substrates. These mirrors designed by the transfer matrix method exhibit reflectivities in excess of 99% by only 3 Bragg mirror layer pairs and very wide stop band regions, reaching a width of up to 60% of the target wavelength. Based on these very efficient mirrors, planar microcavities are demonstrated with an ultra-high effective finesse of up to 1700. Stimulated emission between 3 and 6 μm is obtained by optically pumping a vertical-cavity surface-emitting laser containing PbTe quantum wells with Pb_1−xEu_xTe barriers as active medium embedded between two dielectric Bragg mirrors. Depending on the design of the resonator, pulsed laser operation is observed up to 65°C. The enhancement of light absorption in the cavity is used to study the absorption of superlattices containing correlated self-organized PbSe quantum dots.