Mueller-matrix polarimeter using analysis of the nonlinear voltage-retardance relationship for liquid-crystal variable retarders.

A method for using liquid-crystal variable retarders (LCVRs) with continually varying voltage to measure the complete Mueller matrix of a general sample is presented. The LCVRs are usually employed with fixed retardance values due to the nonlinear voltage-retardance behavior that they show. For the measurement method presented here, the nonlinear voltage-retardance relationship is first measured, and then a linear fit of the known retardance terms to the detected signal is performed. For a gap of air, the measurement error in the Mueller-matrix polarimeter is estimated at 1%-10%, depending on the Mueller-matrix element. Also, we present experimental results for a Glan-Thompson prism polarizer as a test sample, and we use the measured Mueller parameters as functions of the orientation of the optical axes of the polarizer as an indication of the quality of the polarimeter. In addition, results are compared to a typical step-voltage method to measure the Mueller matrix. Both methods give good results.

Stokes polarimetry using analysis of the nonlinear voltage-retardance relationship for liquid-crystal variable retarders.

We present a method for using liquid-crystal variable retarders (LCVR's) with continually varying voltage to measure the Stokes vector of a light beam. The LCVR's are usually employed with fixed retardance values due to the nonlinear voltage-retardance behavior that they show. The nonlinear voltage-retardance relationship is first measured and then a linear fit of the known retardance terms to the detected signal is performed. We use known waveplates (half-wave and quarter-wave) as devices to provide controlled polarization states to the Stokes polarimeter and we use the measured Stokes parameters as functions of the orientation of the axes of the waveplates as an indication of the quality of the polarimeter. Results are compared to a Fourier analysis method that does not take into account the nonlinear voltage-retardance relationship and also to a Fourier analysis method that uses experimental voltage values to give a linear retardance function with time. Also, we present results of simulations for comparison.

[Chronic high levels of CK-MB]. / Elevação crônica da CK-MB.

We presented two cases of falsely elevated CK-MB due to the presence of a type 2 macro CK, showed by isoenzymes electrophoresis. The association of this CK-MB falsely elevated with some digestive diseases are frequent. Quantification of CK isoenzymes by electrophoresis could be indicated in those cases in which the clinical course or ECG changes do not correlate with the CK-MB values.

Backache after extradural anaesthesia in the postpartum period: dissection of thoracic aneurysm.

We describe a case of postpartum ruptured dissecting aneurysm of the thoracic aorta, unrelated to the anaesthetic management with extradural anaesthesia. This complication is discussed in detail, as the anaesthetist may be the specialist required to respond to the common presenting symptom of severe back pain.