An rf pulse compressor has a single high Q cavity resonator fed by a four port hybrid coupler which is connected to the resonator at coupling ports located at the intersection of two of the resonator’s orthogonal axes with the resonator cavity walls. In one aspect of the present invention, an optical structure includes an optical medium having a number of strain-localization regions. When recording an ECG, the cardiac output can be determined in this manner under the influence of a magnetic field. The middle light source is disposed in a middle region of the light source set and the edge light source is disposed at an edge of the light source set. The throttle valve is moveable generally between a closed position and an open position. The second solution is solution which contains the first substance at a density higher than a density of the first liquid.