arXiv subjects

Yuta Kojima

Publications and source records attributed to Yuta Kojima.

3 recordsLinked to original sources

arXiv2026

Hardwired Pattern Formation by Mobile Robots with Common Unit Distance

The pattern formation (PTF) problem requires mobile robots to form a specified target pattern. Existing papers investigated the PTF problem and revealed the effect of obliviousness and synchronization on distributed coordination of mobile robots. However, the PTF problem allows translation, rotation, and scaling of the target pattern. In this paper, we introduce a novel pattern formation problem, called the hardwired pattern formation (HwPTF) problem that requires the robots to form a given target pattern in a specified size. Although two oblivious semi-synchronous robots cannot solve the HwPTF problem of multiplicity two (i.e., the rendezvous problem), we show that they can solve the HwPTF problem without multiplicity. We also show that two oblivious asynchronous robots equipped with lights can solve the HwPTF problem, while oblivious asynchronous robots cannot. We finally present a size-adjusting algorithm for more than four oblivious semi-synchronous robots, that yields a HwPTF algorithm when combined with some existing pattern formation algorithms.

cs.DC↗

arXiv2026

Fast variability and circular polarization of the 6.7 GHz methanol maser in G33.641$-$0.228

The 6.7 GHz methanol maser in a high-mass star-forming region G33.641$-$0.228 is known to exhibit burst-like flux variability due to an unknown mechanism. To investigate the burst mechanism, we conducted high-cadence flux and circular polarization monitoring observations, simultaneously using left- and right-hand circular polarizations. We found that the flux density increased and decreased on a short timescale of 0.3 d during a burst. We also found strong circular polarization, reaching up to 20\% in the component exhibiting the bursts. Circular polarization of 0--20\% was continuously observed from 2009 to 2016, even in the quiescent period. The polarization also varied on timescales of less than one day. When a burst occurred and the flux density increased, the circular polarization decreased to zero. To explain the observational properties of the flux variability and circular polarization, we propose a model in which an explosive event similar to a solar radio burst occurs on the line of sight behind the maser cloud, producing circularly polarized continuum emission due to gyro-synchrotron or gyro-resonance radiation, which is then amplified by the maser.

astro-ph.SR↗

arXiv2024

Conditional diffusion model for inverse prediction of process parameters and dendritic microstructures from mechanical properties

In this study, we develop a conditional diffusion model that proposes the optimal process parameters and predicts the microstructure for the desired mechanical properties. In materials development, it is costly to try many samples with different parameters in experiments and numerical simulations. The use of data-driven inverse design method can reduce the cost of materials development. This study develops an inverse analysis model that predicts process parameters and microstructures. This method can be used for any material, but in this study it is applied to polymeric material, which is the matrix resin of carbon fiber reinforced thermoplastics as an example. Matrix resins contain a mixture of dendrites, which are crystalline phases, and amorphous phases even after crystal growth is complete, and it is important to consider the microstructures consisting of the crystalline structure and the remaining amorphous phase to achieve the desired mechanical properties. Typically, the temperature during forming affects the microstructures, which in turn affect the macroscopic mechanical properties. The trained diffusion model can propose not only the processing temperature but also the microstructure when Young's modulus and Poisson's ratio are given. The capability of our conditional diffusion model to represent complex dendrites is also noteworthy.

cs.CE↗