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This paper explores the sensitivity of torsional modes and maximum torsional torques to turbine-generator shaft mechanical parameters. The analysis is performed on a typical single machine infinite bus system. Small-signal stability analysis, as well as large-disturbance analysis, are performed on six rotational mass mechanical system with and without inclusion of saturation of the generator. It is shown that mechanical parameters of the shaft, namely, inertia, shaft spring constant, internal shaft damping, and external damping, can significantly influence damping and frequency of torsional modes, mode shapes, and maximum torsional torques. [ABSTRACT FROM AUTHOR]

In order to avoid losses in metamaterial unit cells at frequencies of interest, caused by metallic inclusions, an active medium design has been proposed. As candidate structures for this active medium, we have chosen quantum cascade lasers because of their high output gain. Here we analyze and compare two quantum cascade structures that emit at 4.6 THz and 3.9 THz, respectively, placed under the influence of a strong magnetic field. We first solve the full system of rate equations for all relevant Landau levels, and obtain the necessary information about carrier distribution among the levels, after which we are able to evaluate the permittivity component along the growth direction of the structure. With these data one can determine the conditions under which negative refraction occurs, and calculate the values of the refractive index of the structure, as well as the range of frequencies at which the structure exhibits negative refraction for a predefined total electron sheet density. [ABSTRACT FROM AUTHOR]