Complex homogeneous and heterogeneous fluorescence anisotropy decays: enhancing analysis accuracy.

In biological macromolecules, fluorophores often exhibit multiple depolarizing motions that require multiple lifetimes and rotational relaxation times to define fluorescence intensity and anisotropy decays. The related analysis of time-correlated single-photon counting data becomes uncertain due to the multitude of decay parameters and numerical sensitivity to deconvolution of the instrument response function (IRF) via discretization of integrals. By using simulations we show that improved discretizations based on quadratic and cubic local approximations of the IRF yield more accurate estimation of short rotational relaxation times and lifetimes than the commonly used Grinvald-Steinberg discretization, which in turn appears more reliable than two discretizations based on linear local approximations of the IRF. In addition, our simulation suggests that cubic approximation is the most advantageous in discriminating complex heterogeneous and homogeneous anisotropy decay. We show that among three different information criteria, the Akaike information criterion is best suited for detection of heterogeneity in rotational relaxation times. It is capable of detecting heterogeneity even when anisotropy decay appears homogeneous within statistical errors of estimation.

[The effect of atmospheric conditions on the occurrence of peptic ulcer hemorrhage]. / Utjecaj atmosferskih uvjeta na ucestalost krvarenja iz peptickog ulkusa.

The influence of atmospheric factors on the frequency of bleeding from the peptic ulcer was studied within the period from April 1, 1984, to March 31, 1989, consequently through 1826 days. The average daily atmospheric pressure, the average daily temperature and the relative humidity have been examined. There were 1102 cases of bleeding peptic ulcer, 537 bleeding gastric ulcers and 565 bleeding duodenal ulcers. During the study period there were 454 days with bleeding form ventricular ulcer and 465 days with bleeding from duodenal ulcer. There was 793 days with bleeding form either lesion. The discriminatory analysis demonstrated that the atmospheric pressure is the variable that discriminates the days with bleeding and the days prior to bleeding from the days without bleeding. The relative humidity occurs as the relevant discriminatory variable in the days prior to bleeding for the duodenal ulcer group and for the entire group. The centroids of the discriminatory function demonstrate that the days with ulcer bleeding are characterized by the fall of atmospheric pressure. The factor analysis of meterological variables clearly shows the correlation of the atmospheric pressure and the bleeding regardless to the localisation of bleeding ulcer, where the greatest number of bleedings is correlated with lower atmospheric pressure. We conclude that the incidence of bleeding form the peptic ulcer of the stomach and duodenum correlates in great measure with low atmospheric pressure in the days prior to bleeding and in the days of bleeding, as well as with fall of atmospheric pressure in the days of bleeding with respect to previous day.(ABSTRACT TRUNCATED AT 250 WORDS)