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Masaki Takeuchi

Publications and source records attributed to Masaki Takeuchi.

7 recordsLinked to original sources
arXiv2026

Shadowless Projection Mapping for Tabletop Workspaces with Synthetic Aperture Projector

Projection mapping (PM) enables augmented reality (AR) experiences without requiring users to wear head-mounted displays and supports multi-user interaction. It is regarded as a promising technology for a variety of applications in which users interact with content superimposed onto augmented objects in tabletop workspaces, including remote collaboration, healthcare, industrial design, urban planning, artwork creation, and office work. However, conventional PM systems often suffer from projection shadows when users occlude the light path. Prior approaches employing multiple distributed projectors can compensate for occlusion, but suffer from latency due to computational processing, degrading the user experience. In this research, we introduce a synthetic-aperture PM system that uses a significantly larger number of projectors, arranged densely in the environment, to achieve delay-free, shadowless projection for tabletop workspaces without requiring computational compensation. To address spatial resolution degradation caused by subpixel misalignment among overlaid projections, we develop and validate an offline blur compensation method whose computation time remains independent of the number of projectors. Furthermore, we demonstrate that our shadowless PM plays a critical role in achieving a fundamental goal of PM: altering material properties without evoking projection-like impression. Specifically, we define this perceptual impression as ``sense of projection (SoP)'' and establish a PM design framework to minimize the SoP based on user studies.

cs.HC↗
arXiv2026

High-Contrast Projection Mapping under Light Field Illumination with LED Display and Aperiodic Lens Array

Projection Mapping (PM) is a technology that projects images onto the surfaces of physical objects, allowing multiple users to share an augmented reality experience without special devices. However, its practical use has been constrained by the need for dark environments to ensure high-quality projection. To overcome this ``dark-room constraint,'' we propose a novel target-excluding lighting method that selectively illuminates the surrounding environment while avoiding the PM target. Our system achieves light-field illumination by combining an LED display panel with an optimized aperiodic lens array. The key contributions include a compact form factor that provides a large effective light source area, reproducing natural soft shadows comparable to typical lighting, while maintaining the spatial controllability needed to precisely avoid the target. We also introduce a computational technique for optimizing aperiodic lens placement to suppress undesired dark spots caused by crosstalk, and efficient methods for computing LED luminance patterns that enable dynamic PM. Experiments with a prototype system demonstrate that our approach achieves high-contrast PM even in bright environments.

cs.HC↗
arXiv2025

Performance Improvement of LTS Undulators for Synchrotron Light Sources

The joint expertise of ANL and FNAL has led to the production of Nb3Sn undulator magnets in operation in the ANL Advanced Photon Source (APS). These magnets showed performance reproducibility close to the short sample limit, and a design field increase of 20% at 820A. However, the long training did not allow obtaining the expected 50% increase of the on-axis magnetic field with respect to the ~1 T produced at 450 A current in the ANL NbTi undulator. To address this, 10-pole long undulator prototypes were fabricated, and CTD-101K was replaced as impregnation material with TELENE, an organic olefin-based thermosetting dicyclopentadiene resin produced by RIMTEC Corporation, Japan. Training and magnet retraining after a thermal cycle were nearly eliminated, with only a couple of quenches needed before reaching short sample limit at over 1,100 A. TELENE will enable operation of Nb3Sn undulators much closer to their short sample limit, expanding the energy range and brightness intensity of light sources. TELENE is Co-60 gamma radiation resistant up to 7-8 MGy, and therefore already applicable to impregnate planar, helical and universal devices operating in lower radiation environments than high energy colliders.

physics.acc-ph↗
arXiv2024

Projection Mapping under Environmental Lighting by Replacing Room Lights with Heterogeneous Projectors

Projection mapping (PM) is a technique that enhances the appearance of real-world surfaces using projected images, enabling multiple people to view augmentations simultaneously, thereby facilitating communication and collaboration. However, PM typically requires a dark environment to achieve high-quality projections, limiting its practicality. In this paper, we overcome this limitation by replacing conventional room lighting with heterogeneous projectors. These projectors replicate environmental lighting by selectively illuminating the scene, excluding the projection target. Our contributions include a distributed projector optimization framework designed to effectively replicate environmental lighting and the incorporation of a large-aperture projector, in addition to standard projectors, to reduce high-luminance emitted rays and hard shadows -- undesirable factors for collaborative tasks in PM. We conducted a series of quantitative and qualitative experiments, including user studies, to validate our approach. Our findings demonstrate that our projector-based lighting system significantly enhances the contrast and realism of PM results even under environmental lighting compared to typical lights. Furthermore, our method facilitates a substantial shift in the perceived color mode from the undesirable aperture-color mode, where observers perceive the projected object as self-luminous, to the surface-color mode in PM.

cs.GR↗
arXiv2023

A New Ductile, Tougher Resin for Impregnation of Superconducting Magnets

A major remaining challenge for $Nb_3Sn$ high field magnets is their training due to random temperature variations in the coils. The main objective of our research is to reduce or eliminate it by finding novel impregnation materials with respect to the epoxies currently used. An organic olefin-based thermosetting dicyclopentadiene (DCP) resin, $C_10H_12$, commercially available in Japan as TELENE by RIMTEC, was used to impregnate a short $Nb_3Sn$ undulator coil developed by ANL and FNAL. This magnet reached short sample limit after only two quenches, compared with several dozens when $CTD-101K$ was used. Ductility, i.e. the ability to accept large strains, and toughness were identified as key properties to achieve these results. In addition, we have been investigating whether mixing TELENE with high heat capacity ceramic powders, increases the specific heat ($C_p$) of impregnated $Nb_3Sn$ superconducting magnets. The viscosity, heat capacity, thermal conductivity, and other physical properties of TELENE with $high-C_p$ powder fillers were measured in this study as a function of temperature and magnetic field. Mixing TELENE with either $Gd_2O_3$, $Gd_2O_2S$, and $HoCu_2$ increases its $C_p$ tenfold. We have also investigated the effect on the mechanical properties of pure and mixed TELENE under 10 $Gy$ of gamma-ray irradiation at the Takasaki Advanced Radiation Research Institute in Takasaki, Japan. Whereas both $TELENE-82wt\%Gd_2O_3$ and $TELENE-83wt\%HoCu_2$ performed well, the best mechanical properties after irradiation were obtained for $TELENE-87wt\%Gd2O_2S$. Testing a short undulator in the future with the latter impregnation material will verify whether it will further improve the coils thermal stability. Short magnet training will lead to better magnet reliability, lower risk and substantial saving in accelerators commissioning costs.

physics.ins-det↗
arXiv2004

Whistler wave plasma production in CHS

Rf plasma production in Whistler waves range of frequency f/fci >1 is applied on the compact helical system (CHS) in a steady state operation with low toroidal magnetic field strength, where f and fci are rf and ion cyclotron frequencies, respectively. Maximum rf power and pulse width are is170kW and 10 msec at 9MHz, respectively. The line averaged plasma density as high as 2x10^18 m-3 (He plasma) is produced in the region of toroidal magnetic field strength on magnetic axis B=100G~1.5kG and the electron temperature measured at plasma periphery is about 20eV. The wave magnetic field strength measured at the plasma periphery showed the evidence of the toroidal eigen modes of the Whistler waves. The additional long pulse microwave heating of 2.45GHz (>200msec) is applied and it sustains the plasmas while the microwave itself can not ignite plasmas when B<600G.

physics.plasm-ph↗