Abstract. We have performed systematic frequency analysis of the LMC Cepheids observed by OGLE project. Several new types of pulsation behaviour are identified, including triple-mode and amplitude-modulated double-mode pulsations. In ∼ 10% of the first overtone Cepheids we find low amplitude secondary periodicities corresponding to nonradial modes. This is the first evidence for excitation of nonradial oscillations in Classical Cepheid variables.

Abstract:The paper explains a method for discerning the parts of a water supply system in need of renovation. The results are based on technical data collected over the last twenty one years, concerning more than two hundred sections of both renovated and nonrenovated pipelines. In the study, an appropriately prepared data set was used for training an artificial neural network (ANN) in the form of a multilayer perceptron (MLP). Further comparison between the responses of the trained MLP and the decisions made by human experts showed satisfactory consistency, although 15% of the database records produced certain discrepancies. The presented method can help create an expert system capable of supporting failure-free operation of a water distribution system.

I have performed a detailed analysis of multiperiodic RR Lyr stars of the Galactic Bulge and the Small Magellanic Cloud. In the rich OGLE-II database on the Galactic Bulge objects I detected more than 2500 RR Lyr stars, with almost 600 of them exhibiting multiperiodic behavior of various, sometimes unique, kinds. Many of them can only be explained by excitation of nonradial modes. There are two major, striking differences between the two discussed stellar systems: the incidence rate of RRd double mode pulsators is over 30 times higher in the SMC than in the Galactic Bulge, and there are more than twice as many Blazhko stars in the Galactic Bulge as in the SMC.

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