Criticality Hidden in Acoustic Emissions and in Changing Electrical Resistance during Fracture of Rocks and Cement-Based Materials

Acoustic emissions (AE) due to microcracking in solid materials permit the monitoring of fracture processes and the study of failure dynamics. As an alternative method of integrity assessment, measurements of electrical resistance can be used as well. In the literature, however, many studies connect the notion of criticality with AE originating from the fracture, but not with the changes in the electrical properties of materials. In order to further investigate the possible critical behavior of fracture processes in rocks and cement-based materials, we apply natural time (NT) analysis to the time series of AE and resistance measurements, recorded during fracture experiments on cement mortar (CM) and Luserna stone (LS) specimens. The NT analysis indicates that criticality in terms of electrical resistance changes systematically precedes AE criticality for all investigated specimens. The observed greater unpredictability of the CM fracture behavior with respect to LS could be ascribed to the different degree of material homogeneity, since LS (heterogeneous material) expectedly offers more abundant and more easily identifiable fracture precursors than CM (homogenous material). Non-uniqueness of the critical point by varying the detection threshold of cracking events is apparently due to finite size effects which introduce deviations from the self-similarity

Design Considerations of an Interactive Robotic Agent for Public Libraries

The role of public libraries has long been recognized, rendering them a timeless offered form of public service. Users of a public library should have easy access to catalogs and full text of printed and electronic versions of books, magazines, and periodicals, as well as to multimedia databases. Every day, most public libraries are in service for several hours, thus computer-based library service applications provide a valuable service supplement. In this study, a robotic agent which guides users in libraries is proposed. The robotic agent is equipped with sound acquisition and reproduction chains and is capable of understanding some specific commands and guiding the users. The agent is currently able to understand commands and respond in English. Therefore, it may be useful for public libraries visited or remotely used by foreign, English speaking, users. Future work consists of the implementation of language packages for Turkish and the evaluation of field tests that will be held at the library and documentation center of Trakya University, Edirne, Turkey

Design Considerations of an Interactive Robotic Agent for Public Libraries

The role of public libraries has long been recognized, rendering them a timeless offered form of public service. Users of a public library should have easy access to catalogs and full text of printed and electronic versions of books, magazines, and periodicals, as well as to multimedia databases. Every day, most public libraries are in service for several hours, thus computer-based library service applications provide a valuable service supplement. In this study, a robotic agent which guides users in libraries is proposed. The robotic agent is equipped with sound acquisition and reproduction chains and is capable of understanding some specific commands and guiding the users. The agent is currently able to understand commands and respond in English. Therefore, it may be useful for public libraries visited or remotely used by foreign, English speaking, users. Future work consists of the implementation of language packages for Turkish and the evaluation of field tests that will be held at the library and documentation center of Trakya University, Edirne, Turkey

Statistical Mechanics and Information-Theoretic Perspectives on Complexity in the Earth System

Peer reviewedPublisher PD

Statistical mechanics and information-theoretic perspectives on complexity in the Earth system

This review provides a summary of methods originated in (non-equilibrium) statistical mechanics and information theory, which have recently found successful applications to quantitatively studying complexity in various components of the complex system Earth. Specifically, we discuss two classes of methods: (i) entropies of different kinds (e.g., on the one hand classical Shannon and R´enyi entropies, as well as non-extensive Tsallis entropy based on symbolic dynamics techniques and, on the other hand, approximate entropy, sample entropy and fuzzy entropy); and (ii) measures of statistical interdependence and causality (e.g., mutual information and generalizations thereof, transfer entropy, momentary information transfer). We review a number of applications and case studies utilizing the above-mentioned methodological approaches for studying contemporary problems in some exemplary fields of the Earth sciences, highlighting the potentials of different techniques