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The paper introduces novel dual-mode crystal oscillator (DMXO) that employs a standard 10-MHz 3 rd overtone stress compensated (SC) quartz resonator. In the DMXO, the two overtones (c-modes) of the SC-cut resonator are simultaneously excited: the 3 rd overtone and the 5 th overtone. The ability of utilization of the two excited overtones to implement the resonator self-thermometry we have evaluated. The resonator self-temperature-sensing method eliminates temperature offset and lag effects, since no external temperature sensor is used [1], [2], [3]. Eventual applications of the DMXO with excitation of the two overtones include the stabilization of the SC-cut resonator's temperature as well as compensation for frequency shifts due to the variations of the ambient temperature. I. INTRODUCTIONStress compensated (SC) quartz resonator selftemperature-sensing utilizing simultaneous excitation of two slow thickness-shear modes (i.e. c-modes) has been introduced by Schodowski in 1989 [1]. Processing of both c-mode actual frequencies enables prediction of their frequency shifts due to ambient temperature variations in a wide range. Temperature offset and lag effects are eliminated, since no external temperature sensor is used. For example, in microcomputer compensated crystal oscillator (MCXO) that operates in temperature range between -55 o C and +85 o C, a dual-mode crystal oscillator (DMXO) utilizes simultaneous excitation of fundamental c-mode and 3 rd overtone c-mode of special SC-cut resonator. In the case of the optimum MCXO SC-cut resonator, the lower turnover temperature of the 3 rd overtone is close to +20 o C [2], [3]. The minimization of the differences between aging rates of the two excited c-mode's frequencies is very important for MCXO, since the different aging rates cause an offset with a tilt in the MCXO frequency output over the operating temperature range [4].

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Our research deals with a broad spectrum of problems concerning the variability of geotechnical factors and their influence on the safety of the biggest group of dam constructions in Slovakia, i.e., low earthfill dams. Its specific aim is the observation of their risk factors by using our experience and knowledge gained while working in the sector of technical and safety supervision. To achieve the aims of a research thesis, we analyzed 39 low earthfill dams. We performed observations and documented their conditions with the aim of clarifying the risk factors. After an analysis of the information materials that characterize dams and after a statistical analysis of the measurement results in situ, including measurements from technical and safety supervision databases, we performed an analysis by using mathematical modeling to evaluate the safety of the dam constructions. Out of the total number of 39 dam constructions, an analysis of the stability of the dam slopes was performed on 37 dams, and deformation problems were analyzed on 28 of the dams. Filtration problems were analyzed at 26 dams, and a complete evaluation of the intensity of filtration movements was performed on 19 of the constructions. On the basis of a detailed analysis of the 39 dam constructions, we specified their problems and the concomitant consequences of the problems. Geotechnical risk factors and specific risks that determine the safety of water constructions were characterized. The analysis confirmed the importance of an engineer-geological and geotechnical checkup in the process of preparation and building (alternatively, during reconstructions and sanitation work) of such water constructions and also the importance of monitoring in the process of dam usage. Technical and safety checkups were also shown to be important when analyzing risk factors. The conclusions of the knowledge gained and the recommendations for the practice deal with recommendations to change the flow policy, develop a central project register, and develop documents and databases that are needed for analyses of the safety of low earthfill dam constructions in the Slovak Republic.