To enable wireless remote control of unmanned underwater vehicles, such as compact underwater drones, it is essential to miniaturize communication systems for underwater acoustic communication (UWA). Unlike previous studies that utilized a single transmitter with multiple receivers, this study introduces a novel approach combining time diversity—repeatedly transmitting and receiving signals with one transmitter and receiver—with Doppler-resilient orthogonal signal division multiplexing (D-OSDM), a modulation method optimized for underwater environments. Experiments explored the relationship between retransmission intervals and performance metrics such as output signal-to-noise ratio and bit error rate. The results indicate that to improve communication quality using time diversity in UWA communication with D-OSDM, it is vital to set an appropriate guard interval and maintain a proper distance between the transmitter and receiver. These findings highlight the effectiveness of time diversity in enhancing the stability of UWA communication systems.

This study explores the correspondence between original parameter space and synaptic weight space in the framework of parameter-space estimation, with the objective of achieving accurate and reliable prediction of critical transitions. Recent studies have increasingly used early warning signals as diagnostic tools for detecting critical transitions. However, although these signals have proven effective across a wide range of applications, they lack the precision necessary to accurately predict the timing of critical transitions. To address this limitation, parameter-space estimation has been used to reconstruct bifurcation diagrams from limited time-series data. The parameter space necessary for constructing these diagrams is inferred within the synaptic weight space through linear interpolation between two synaptic weight vectors, each trained on time-series datasets generated by systems with distinct parameter values. By reconstructing bifurcation diagrams, the timing of critical transitions can be identified precisely, particularly in cases exhibiting dynamics characteristic of saddle-node bifurcations. This study evaluates the validity of the linear interpolation approach by examining its consistency with underlying theoretical assumptions and assessing its practical applicability through numerical experiments. Based on the validation results, we propose an auxiliary technique that offers better predictive performance with greater accuracy and reliability.

This paper reports on a fire detection method using an ultrasonic probe that measures room temperature based on the speed of sound. We establish the relationship between the time-of-flight (ToF) of acoustic waves and air temperature in the presence of flames. An ultrasonic probe consisting of a speaker and a microphone was developed, and fire experiments were conducted to measure the ToF at multiple flame locations. Results indicate that temperature increases caused by a flame can be detected using acoustic waves. However, the correlation between the transmitted and received waveforms decreases when the acoustic wave passes through the flame, thereby interfering with the cross-correlation function used in the ToF measurement. These findings suggest that the ultrasonic probe has potential for early fire detection in indoor environments by monitoring changes in ToF.

Heaviside reformulated the Maxwell equations (P. J. Nahin: OLIVER HEAVISIDE, The Johns Hopkins University Press, 2002). The vector analysis based on the quaternions defined by Hamilton was employed as the analytical method to derive the Poynting vector in the reformulation. However, the treatment of quaternions became invalid once the Poynting vector was obtained with the reformulation. Instead, Heaviside's analytical method has been switched to vector analysis using complex numbers (based on Euler's formula). This method is considered to have contributed significant development to modern mathematics and is also considered to be a problem-posing question that is comparable to “Hilbert's 23 Problems". In this Session, we will present one solution to this problem by applying the quaternions defined by Pauli.