Open Access Collection of International and Scholarly Papers
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Bias Estimation for Low-Cost IMU Including X- and Y-Axis Accelerometers in INS/GPS/Gyrocompass
No full textInertial navigation systems (INSs) provide autonomous position estimation capabilities independent of global navigation satellite systems (GNSSs). However, the high cost of traditional sensors, such as fiber-optic gyroscopes (FOGs), limits their widespread adoption. In contrast, micro-electromechanical system (MEMS)-based inertial measurement units (IMUs) offer a low-cost alternative; however, their lower accuracy and sensor bias issues, particularly in maritime environments, remain considerable obstacles. This study proposes an improved method for bias estimation by comparing the estimated values from a trajectory generator (TG)-based acceleration and angular-velocity estimation system with actual measurements. Additionally, for X- and Y-axis accelerations, we introduce a method that leverages the correlation between altitude differences derived from an INS/GNSS/gyrocompass (IGG) and those obtained during the TG estimation process to estimate the bias. Simulation datasets from experimental voyages validate the proposed method by evaluating the mean, median, normalized cross-correlation, least squares, and fast Fourier transform (FFT). The Butterworth filter achieved the smallest angular-velocity bias estimation error. For X- and Y-axis acceleration bias, altitude-based estimation achieved differences of 1.2 × 10−2 m/s2 and 1.0 × 10−4 m/s2, respectively, by comparing the input bias using 30 min data. These methods enhance the positioning and attitude estimation accuracy of low-cost IMUs, providing a cost-effective maritime navigation solution.公開日: 2025-02-21journal articl
Ship control of unberthing manoeuvring using an online estimation model under disturbance
No full textBecause a ship’s manoeuvrability changes nonlinearly with speed variations, designing controllers for berthing and unberthing requires a motion model that reflects these variations. This study proposes a control method with an online estimation model, where parameters are estimated based on observed ship motion. Using the gradient descent method for model estimation stabilizes updates in the presence of noise. To compensate for steady disturbances such as tidal currents, the effect of external force is estimated and used to calculate corrections for control inputs. The proposed method was verified by simulations under multiple disturbance conditions. The control system using the online estimation model demonstrated stable control in unberthing manoeuvring and effective disturbance compensation under steady deviation conditions.公開日: 2025-03-11journal articl
The genetic legacy of a global marine invader
No full textThe massive geographic expansion of terrestrial plant crops, livestock, and marine aquacultured species during the 19th and 20th centuries provided local economic benefits, stabilized food demands, and altered local ecosystems. The invasion history of these translocations remains uncertain for most species, limiting our understanding of their future adaptive potential and historical roles as vectors for coinvaded species. We provide a framework for filling this gap in invasion biology using the widely transplanted Pacific oyster as a case study. A two-dimensional summary of population-level variation in single nucleotide polymorphisms in native Japan reflected the geographical map of Japan and allowed identification of the source regions for the worldwide expansion. Pacific oysters proliferate in nonnative areas with environmental temperatures similar to those areas where native lineages evolved. Using Approximate Bayesian Computation, we ranked the likelihood of historical oyster or shipping vectors to explain current-day distribution of genotypes in 14 coinvaded algal and animal species. Oyster transplants were a more likely vector than shipping for six species, shipping activity was more likely for five species, and a vector was ambiguous for three species. Applying this approach to other translocated species should reveal similar legacy effects, especially for economically important foundation species that also served as vectors for nonnative species.公開日: 2025-04-07journal articl
A preliminary study on larval culture and metamorphosis of the cone snail Conus fulmen: Effects of microalgal prey, biofilm, and reduced salinity
No full textTo elucidate larval life history traits of the cone snail Conus fulmen, we conducted three culture experiments using artificial seawater. In experiment 1, larvae were fed Tetraselmis sp. and Chaetoceros calcitrans at three different densities. Early veliger mortality was high, likely due to low initial larval quality, but two larvae exhibited typical Conus development and survived without metamorphosis for 110 days. In experiment 2, 27-day-old larvae—possibly competent to metamorphose—were exposed to tiles potentially coated with biofilm from the adult culture tank, but no metamorphosis occurred. In experiment 3, salinity was reduced from 34 ppt by 3 ppt every three days starting 21 days after hatching. Larvae began velum resorption at 19 ppt; however, mortality sharply increased at 16 ppt, and metamorphosed juveniles retained partial velum. Hawaiian Conus larvae are known to undergo rapid metamorphosis in response to biofilms present in natural seawater. Our findings suggest that reduced salinity in inshore environments may serve as a cue for metamorphosis in C. fulmen, but it is unlikely to function as the primary inducer. Further laboratory studies using seawater from natural habitats are needed to clarify the environmental factors—such as biofilms and salinity levels—that initiate metamorphosis in this species.公開日: 2025-09-25journal articl
Assessing the impact of emission control areas policy on ship emissions in the Gulf of Thailand using AIS data
No full textThe rising concern over ship emissions has prompted the exploration of Emission Control Areas (ECAs) in various regions. This study provides a comparative analysis of ship emissions in non-ECA areas and offers insights for implementing ECA policies in the Gulf of Thailand. Utilizing Automatic Identification System (AIS) data from January 1 to 31, 2023, this study models ship emissions of nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter (PM). Spatial analysis reveals critical emission hotspots associated with ship density, port locations, and major shipping lanes, identifying oil tankers as primary emitters. A comparative analysis with existing ECAs demonstrates that implementing an ECA in the Gulf of Thailand could substantially reduce emissions. The findings offer actionable insights for policymakers, including strategies like adopting low-sulfur fuels, optimizing shipping routes, and incentivizing cleaner technologies. Furthermore, this study highlights the importance of addressing economic challenges and ensuring comprehensive data collection to capture seasonal and demand-driven emission variations.公開日: 2025-01-19journal articl
Survey Report on Gender Diversity Management in Bus Companies
Full text linkバス会社における女性の活躍推進の取り組みについてのアンケート調査の結果を報告する。第1 に、バス会社の大半が、職種の拡大、運転士の採用、ワークライフバランス支援を実施している。第2に、これらの具体的な取り組みとして、免許取得のための支援、女性のための社内施設の整備、短時間労働勤務などが実施されている。第3に、管理職への登用、女性従業員の役割に対する固定的な概念・意識を払拭するための取り組みについてはやや遅れている。ただし、職務経験や業務知識にとらわれない管理職への登用などの人事制度の見直しを行っている会社も一定程度ある。第4に、会社の規模別では、管理職への登用を除き、大規模のバス会社ほど、女性活躍推進の取り組みをより積極的に実施している。This study reports the results of survey to understand the trend of recruiting and promoting women in the workforce of bus companies. First, the majority of bus companies are expanding the range of job opportunities available to women, hiring female bus drivers and implementing work-life balance practices. Second, popular specific initiatives include financial support for obtaining licenses, in-house facilities for women and flexible ways of working. Third, the appointment of women to managerial positions and organizational reform related to changing fixed ideas towards the role of female employees are somewhat delayed, although a certain number of companies are reviewing and reforming their personnel systems. Fourth, by company size, the larger company has the more diversity management initiatives, except for the appointment to managerial positions.遠藤伸明: 東京海洋大学学術研究院流通情報工学部門Endo Nobuaki: Department of Logistics and Information Engineering, Faculty of Marine Technology, Tokyo University of Marine Science and
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Relationship between escape behavior of juvenile Pacific bluefin tuna and bag net shape of set net
No full text定置網におけるクロマグロの漁獲量の調整方法の開発は課題の1つである。その調整方法の1つとして網から自然逃避しやすいと言われているクロマグロの行動特性を利用することが考えられる。そこで，クロマグロ小型魚の箱網外への逃避と，漁場の流速，箱網底面の深度，経過時間，尾叉長の関係を調査した。その結果，潮流による箱網底面の吹き上がりがクロマグロの自然逃避を促すことがわかった。箱網深度よりも定置網漁業での利用機会が多い潮流の情報は，クロマグロ小型魚の漁獲コントロールに役立つ可能性がある。Controlling the catch of Pacific bluefin tuna in set nets is an important issue in stock management of the species in order to comply with quotas under international regulations. Bluefin tuna, once inside set net gear, tend to escape naturally due to the structure of set net gear before landing. Investigating the shape of the set net depending on oceanographic conditions, which are relevant for natural escape, may yield clues for controlling the catch. We therefore studied the relationship between fishing conditions and escape behavior of Pacific bluefin tuna by a tagging experiment. The test results were analyzed by a generalized linear model and the best model was selected by Akaike’s information criterion. The explanatory variables were body length of Pacific bluefin tuna, tidal current velocity, bottom of the minimum bag net depth, and elapsed time. The results showed that escape of Pacific bluefin tuna was affected by minimum bag net depth and tidal current speed, because the tidal current raised the bag net bottom and reduced the swimming space for the tuna. These results may be useful for future resource management of Pacific bluefin tuna in set nets.公開日: 2025-07-10journal articl
Effects of cheliped autotomy on molting and growth in the porcellanid crab Petrolisthes japonicus (Decapoda: Anomura: Porcellanidae) under laboratory conditions
No full textPorcellanids avoid predation by autotomizing a cheliped, a strategy that enhances immediate survival but incurs costs. Previous research that did not consider sex differences has suggested that cheliped loss accelerates molting and reduces growth at molt. As female decapods typically allocate more energy to reproduction than males do, molting and growth patterns may vary between sexes. This study investigated the effects of cheliped autotomy on molting and growth in the porcellanid crab Petrolisthes japonicus. Male and female crabs were cultured under three autotomy conditions: both chelipeds intact, the larger cheliped autotomized, and both chelipeds autotomized. Loss of both chelipeds reduced growth at the first molt in both sexes, but this effect disappeared in subsequent molts for females, likely due to energy allocation to reproduction in all groups. Sex-specific differences emerged in crabs with intact or single-cheliped loss, with males exhibiting longer molt cycles and fewer molts than females, potentially enhancing male mating opportunities and female reproductive output. However, autotomizing both chelipeds increased the molting frequency in males, counteracting these patterns. These findings highlight the interplay between autotomy, molting, and sex-specific energy allocation, suggesting that cheliped loss affects growth and reproduction differently in males and females, with potential fitness trade-offs.公開日: 2025-10-16journal articl
機械学習と数理最適化の融合とその応用
Full text link東京海洋大学博士(工学)東京海洋大学博士学位論文 2024年度(2025年3月) 応用環境システム学 課程博士 甲第728号指導教員: 久保幹雄全文公表年月日: 2025-05-21doctoral thesi
周波数特性の違いを活用したIEEE802.11mc距離測定による移動体向け通信品質指標の研究
Full text link東京海洋大学修士(工学)東京海洋大学修士学位論文 2024年度(2025年3月) 海洋システム工学 修士 第4593号指導教員: 大島浩太全文公表年月日: 2025-06-13master thesi