Aichi University

Reliable and cost-effective DC circuit breakers (DC CBs) are essential for DC power systems. In a previous study, we developed a hybrid DC CB that utilizes a current-limiting fuse as the main path. Additionally, the commutation path incorporates a single IGBT and a contactor connected in series to suppress the voltage across the IGBT. However, its practical implementation faces challenges related to operational delay and speed. In this study, the limitations of using a typical contactor, a plate-plate contactor, is first verified. To address these challenges, two novel contactor designs is proposed: a hemisphere-plate contactor and a sliding contactor. These designs are expected to reduce the duration between the commutation and interruption, thereby providing a promising solution to ensure reliable fault current interruption in hybrid DC CBs.

This paper shows (1) a positive analysis demonstrating that recent high inflation rates can be explained by the Bank of Japan (BOJ)’s monetary policy for the COVID-19 pandemic period, “Inflation-Overshooting Commitment,” and (2) a normative analysis showing that the BOJ’s inflation-overshooting commitment aligns with the optimal monetary policy in a liquidity trap within a new Keynesian model with inflation persistence. In detail, we calibrate a hybrid new Keynesian model by Japanese parameters and show optimal monetary policy under commitment. Optimal monetary policy prolongs the zero interest rate until the second quarter of 2024 even after inflation rates overshoot 2 percent. Similarly, the BOJ continues the zero interest rate policy until the second quarter of 2024. The current average inflation rates from 2023Q4 to 2024Q3 reach 2.6 percent and 2.5 percent in the data and the model, respectively. Our conclusion holds for a variety of situations with Japanese parameters, such as a low output gap response to the real interest rate, discounted IS curve, alternative inflation persistences, interest-rate smoothing for the policy rate, an alternative specification of the Phillips curve, inflation target, and low/high anchored inflation expectations and natural interest rates. • Calibrate new Keynesian model with inflation persistence by Japanese parameters. • The BOJ’s monetary policy shares several similarities with optimal monetary policy. • Recent high inflation can be explained by a prolonged zero interest rate policy.

This study updates the mid-Cretaceous (100 Ma) paleomagnetic pole for the inner arc of the southwestern Japanese islands, referred to as southwest Japan, to investigate potential stagnation in its apparent polar wander path (APWP). The updated pole interpolates the Cretaceous APWP for southwest Japan, providing insights into the geodynamic characteristics of the region during this period. For paleomagnetic analysis, red mudstone samples were collected from four sites in the 100 Ma Hayama Formation in the Hayama area. A high-temperature remanent magnetization component, carried by hematite, was isolated from the four sites, passing the fold test. The primary nature of the magnetization was confirmed by the detrital origin of the magnetic carrier. The primary directions, combined with previously reported results, were used to define a paleomagnetic pole representing the 100 Ma pole for southwest Japan, located within the group of Cretaceous poles. The APWP for southwest Japan between 110 and 70 Ma was revised to evaluate stagnation in polar motion in this region.

Over the years, research in the field of cultural heritage preservation and document analysis has exponentially grown. In this study, we propose an advanced approach for non-destructive estimation of paper fibers using macro images. Expanding on studies that implemented EfficientNet-B0, we explore the effectiveness of six other deep learning networks, including DenseNet-201, DarkNet-53, Inception-v3, Xception, Inception-ResNet-v2, and NASNet-Large, in conjunction with enlarged patch sizes. We experimentally classified three types of paper fibers, namely, kozo, mitsumata, and gampi. During the experiments, patch sizes of 500, 750, and 1000 pixels were evaluated and their impact on classification accuracy was analyzed. The experiments demonstrated that Inception-ResNet-v2 with 1000-pixel patches achieved the highest patch classification accuracy of 82.7%, whereas Xception with 750-pixel patches exhibited the best macro-image-based fiber estimation performance at 84.9%. Additionally, we assessed the efficacy of the method for images containing text, observing consistent improvements in the case of larger patch sizes. However, limitations exist in background patch availability for text-heavy images. This comprehensive evaluation of network architectures and patch sizes can significantly advance the field of non-destructive paper analysis, offering valuable insights into future developments in historical document examination and conservation science.