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Recognizing human cognitive performance is important for preserving working efficiency and preventing human error. This paper presents a method for estimating cognitive performance by leveraging multiple information available in a smartphone. The method employs the Go-NoGo task to measure cognitive performance, and fuses contextual and behavioral features to identify the level of performance. It was confirmed that the proposed method could recognize whether cognitive performance was high or low with an average accuracy of 71%, even when only referring to inertial sensor logs. Combining sensing modalities improved the accuracy up to 74%.

Recently, inferring the state of people’s mental health via passive mobile sensing has attracted significant attention. Previous studies have used the self-assessed stress levels as the ground truth; however, these are subjective measures. In this study, we use a physiologically-assessed stress metric to minimize the effect of participant subjectivity and further estimate it using behavioral features based on the smartphone usage logs. We initially requested the study participants (39 participants) to attach heart rate sensors for 8 hours per day and simultaneously collected continuous heart rate data and smartphone logs for 42 days. Further, we divided the participants into four types via clustering using the behavioral features derived from their smartphone sensor logs and trained each model via supervised learning using the heart rate data as the ground truth. Our results exhibit that the proposed method is more accurate (71%) as compared to the baseline method (54%). This demonstrates that physiologically-assessed stress levels can be estimated based on the implicit features that are gathered from the smartphone logs.

A prototype for a space-borne smart reconfigurable reflector, whose reflector surface can be changed intentionally using surface adjustment actuators, has been developed, and its performance was evaluated through experiments. The smart reconfigurable reflector was designed as a sub-reflector of a space antenna for observations in the extremely highfrequency band (frequency range: 30 -300 GHz) and is used for correcting the path length errors in the antenna system caused by surface deformations of the main reflector. It consists of a solid surface, supporting members, and surface adjustment actuators. The surface adjustment actuators are a key part of the smart reconfigurable reflector, and each consists of a piezoelectric stack actuator and a displacement magnifying mechanism. Functional tests were performed in order to investigate the performance of the actuator. The results indicate that the actuator has a stroke of more than 0.9 mm with an accuracy of 0.01 mm and a force of more than 90 N. The control accuracy was much better than the required surface accuracy for an extremely high-frequency antenna system. The effectiveness of the developed reflector system was demonstrated through numerical simulations and shape modification experiments. In order to clarify the effectiveness of the developed smart reconfigurable reflector, the performance of the antenna system, equipped with the smart reconfigurable reflector, was evaluated. The experimental results confirmed the performance expected from the numerical simulation and indicated that the antenna could be adequately controlled as expected.

Mental health has received increasing attention in recent years, and a correlation between social interaction during eating and mental health noted. The purpose of this research is to determine if wearable devices can be used to recognize whether a person is eating alone or has company. Using a watch-type device and smartphone, the data, while eating in daily life, was collected. Using this data, we were able to recognize whether a person is eating alone or has company with an accuracy of 96.3%.

資料番号: SA1160205000

This study clarifies the effect of thermal deformation in the reconfigurable space reflector system, through a series of experiments in a thermostatic chamber using a prototype of reconfigurable space reflectors. This study then discusses possible countermeasures against precision degradation of such system due to the thermal deformation, exploiting a finiteelement model that is tuned to the experimental results. Though reconfigurable reflector systems inherently have the mismatch in the coefficients of thermal expansion among their structural members, the effect of the mismatch may be minimized by a proper combination of several materials. The prototype used in this study is designed as a preliminary model of a secondary mirror for future radio astronomy satellites.

This paper examines the effects of connecting multiplexing shunt circuits composed of inductors and resistors to piezoelectric transducers so as to improve the robustness of a piezoelectric vibration absorber (PVA). PVAs are well known to be effective at suppressing the vibration of an adaptive structure; their weakness is low robustness to changes in the dynamic parameters of the system, including the main structure and the absorber. In the application to space structures, the temperature-dependency of capacitance of piezoelectric ceramics is the factor that causes performance reduction. To improve robustness to the temperature-dependency of the capacitance, this paper proposes a multiple-PVA system that is composed of distributed piezoelectric transducers and several shunt circuits. The optimization problems that determine both the frequencies and the damping ratios of the PVAs are multi-objective problems, which are solved using a real-coded genetic algorithm in this paper. A clamped aluminum beam with four groups of piezoelectric ceramics attached was considered in simulations and experiments. Numerical simulations revealed that the PVA systems designed using the proposed method had tolerance to changes in the capacitances. Furthermore, experiments using a thermostatic bath were conducted to reveal the effectiveness and robustness of the PVA systems. The maximum peaks of the transfer functions of the beam with the open circuit, the single-PVA system, the double-PVA system, and the quadruple-PVA system at 20 °C were 14.3 dB, −6.91 dB, −7.47 dB, and −8.51 dB, respectively. The experimental results also showed that the multiple-PVA system is more robust than a single PVA in a variable temperature environment from −10 °C to 50 °C. In conclusion, the use of multiple PVAs results in an effective, robust vibration control method for adaptive structures.