RESUMEN
An experimental device that can accurately measure the magnetic entropy change, Δs, as a function of temperature, T, and magnetic field, H, is presented. The magnetic field source is in this case a set of counter-rotating concentric Halbach-type magnets, which produce a highly homogeneous applied field with constant orientation. The field may be varied from 0 to 1.5 T in a continuous way. The temperature stability of the system is controlled to within ±10 mK and the standard range for the current setup is from 230 K to 330 K. The device is under high vacuum and we show that thermal losses to the ambient are negligible in terms of the calorimetric determination of the magnetic entropy change, while the losses cannot be ignored when correcting for the actual sample temperature. We apply the device to two different types of samples; one is commercial grade Gd, i.e., a pure second-order phase transition material, while the other is Gd5Si2Ge2, a first order magnetic phase transition material. We demonstrate the device's ability to fully capture the thermal hysteresis of the latter sample by following appropriate thermal resetting scheme and magnetic resetting scheme.
RESUMEN
This study was performed in order to assess whether 500mg of azithromycin given orally once per week could produce tonsil tissue concentrations above minimum inhibitory concentrations for key target pathogens in patients with recurrent tonsillitis. For the measurement of tissue concentrations an automated solid phase extraction (SPE) method for cleaning the tissue extracts was developed. Concomitantly, the influence of this treatment on the microbiological flora of the tonsillar surface was monitored. The mean concentration of azithromycin in the tonsillar tissue was 1.8 microg/g (0.4 microg/g to 5.1 microg/g), i.e. therapeutic concentrations of azithromycin were found in most tonsils 1 week after medication. The validated SPE method developed provided a clean extract for high performance liquid chromatographic determination of azithromycin. The surface microbiology of the tonsils at surgery showed the usual pathogens in most patients. In conclusion, therapeutic levels of azithromycin were present in tonsil tissue during weekly medication with minimal influence on surface microbiology. A placebo-controlled, double-blind study of long-term treatment is in progress.