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Takuya Nakashima

Publications and source records attributed to Takuya Nakashima.

5 recordsLinked to original sources
arXiv2026

"Sail Fast, Then Wait" in First-come, First-served Port Queues: Information Sharing for Sustainable Shipping

This study develops a novel class of queueing game to explain a common practice in cargo shipping "Sail Fast, Then Wait" (SFTW), and demonstrates that resolving information asymmetry among ships can deconcentrate port arrival times. We formulate a competitive navigating environment as an incomplete information game where players strategically decide their arrival time within heterogeneous feasible sets under First-Come, First-Served port policy. Our results show that in incomplete information settings, SFTW emerges as the unique symmetric equilibrium. Conversely, under complete information, the set of equilibria expands, allowing for slower and more environmentally friendly actions without compromising service order. We further quantitatively evaluate the effect of information enrichment based on empirical data. Our findings suggest that the prevalence of technologies enabling ships to infer others' private information can effectively reduce SFTW and enable more energy-efficient and environmentally sustainable operations.

econ.TH↗
arXiv2026

Introducing a Novel Systems Thinking approach inspired by STPA: Road Safety Intervention design case study

According to the latest provisional statistics released by the UK Department for Transport, Great Britain recorded 1,633 road deaths in 2024, representing a slight increase from 2023 and raising concerns about safety progress, which indicates that preventable fatalities remain a challenge. The deployment of advanced mobility systems, even certified and safety-assessed, is not sufficient to deliver improved safety outcomes, and existing road infrastructure is not sufficiently equipped to prevent severe collisions. Successful application of the ``Safe System'' approach demands systems thinking in an integrated and holistic manner, encompassing all aspects of road safety. This paper argues that road safety must be managed as a complex socio-technical system where risk evolves dynamically and must be continuously monitored. To address these safety gaps, we propose a systems thinking approach that identifies factors contributing to fatal outcomes and mitigates them. The framework consists of four steps: 1) List stakeholders who influence road safety, 2) Model the interactions between these stakeholders, 3) List assumptions that might be identified as factors for fatalities, and 4) Monitor these assumptions throughout the system lifecycle. The approach is applied to the United Kingdom (UK) road network to demonstrate feasibility. The study provides actionable guidance and new KPIs categories for stakeholders to implement road safety monitoring and eliminate any unreasonable road safety risks.

physics.soc-ph↗
arXiv2025

A Scalable Framework for the Management of STPA Requirements: a Case Study on eVTOL Operations

System-Theoretic Process Analysis (STPA) is a recommended method for analysing complex systems, capable of identifying thousands of safety requirements often missed by traditional techniques such as Failure Mode and Effects Analysis (FMEA) and Fault Tree Analysis (FTA). However, the absence of a structured framework for managing and prioritising these requirements presents challenges, particularly in fast-paced development environments. This paper introduces a scalable framework for prioritising STPA-derived requirements. The framework integrates outputs from each STPA step and incorporates expert evaluations based on four key factors: implementation time, cost, requirement type, and regulatory coverage. To reduce subjectivity, Monte-Carlo Simulation (MCS) is employed to calculate and stabilise requirement rankings. An automation toolchain supports the framework, enabling dynamic mapping of prioritised requirements in a scaling matrix. This visualisation aids decision-making and ensures traceability across development phases. The framework is applicable from early conceptualisation to more advanced stages, enhancing its utility in iterative system development. The framework was validated through a real-world case study focused on Electric Vertical Take-off and Landing (eVTOL) operations, conducted in collaboration with the UK Civil Aviation Authority. The findings contributed directly to CAP3141, a Civil Aviation Publication that identifies systemic operational risks and safety mitigations for regulators, operators, and vertiports. The prioritisation process supported decision-making by helping stakeholders identify and manage high-impact requirements efficiently. This work contributes a practical solution for managing STPA outputs, bridging gaps in requirement prioritisation and supporting safety-critical development in emerging technologies.

cs.SE↗
arXiv2015

Pronounced - Log T Divergence in Specific Heat of Nonmetallic CeOBiS$_2$: A Mother Phase of BiS$_2$-Based Superconductor

The low-temperature properties of CeOBiS$_2$ single crystals are studied by electrical resistivity, magnetization, and specific heat measurements. Ce 4f -electrons are found to be in a well-localized state split by crystalline-electric-field (CEF) effects. The CEF ground state is a pure $J_z$ = $\pm$ 1/2 doublet, and excited doublets are located far above. At low temperatures in zero field, we observe pronounced $-\log T$ divergence in the specific heat, revealing the presence of quantum critical fluctuations of 4f magnetic moments near a quantum critical point (QCP). Considering that CeOBiS$_2$ is a nonmetal, this phenomenon cannot be attributed to the competition between Kondo and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions as in numerous f-electron-based strongly correlated metals, indicating an unconventional mechanism. We suggest that CeOBiS$_2$ is the first material found to be located at a QCP among geometrically frustrated nonmetallic magnets.

cond-mat.str-el↗