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Yoshiaki Uchida

Publications and source records attributed to Yoshiaki Uchida.

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Stochastic Collision Theory of Magnetism in Radical Fluids

How stochastic, microscopic events generate deterministic, macroscopic properties is a fundamental question in physics. We address this question by developing a quantum master equation model for concentrated radical solutions, where random molecular collisions govern the magnetic properties of the system. Our theory reveals a simple mechanism: the first-order exchange contribution averages to zero over collisions, while the second-order term survives as an effective ferromagnetic coupling that enhances magnetization. The model captures the experimentally observed trends in magnetic behavior that deviate from conventional theories. Because the mechanism arises from statistical averaging, it may apply to a broader class of soft matter phenomena, including liquid crystals.

physics.chem-ph

In situ estimation of local acoustic pressure amplitude by force balancing with a ferrofluid droplet probe

Acoustic tweezers enable non-contact manipulation of microscale objects, but quantitative in situ evaluation of the peak local pressure amplitude remains difficult in confined devices. Conventional hydrophone-based measurements are often limited at the microscale by probe size and installation constraints. Here, we present a force-balance method in which a trapped ferrofluid droplet serves as a local probe in a standing-wave acoustic field and an externally applied magnetic-field gradient is tuned so that the magnetic force balances the maximum primary acoustic radiation force on the droplet. From the magnetic force on the ferrofluid droplet, determined at the balance point, we estimate a peak local pressure amplitude of $2.2\times10^{5}$~Pa for 7.2~MHz operation at 10~V$_{\mathrm{pp}}$. This approach provides a practical route for quantitative in situ characterization of microscale acoustic fields and for setting operating conditions in compact acoustofluidic devices.

cond-mat.mtrl-sci

Reflection of Phase Anisotropy on Molecule

This study explores how molecular shape changes influence the phase behavior of liquid crystals, particularly the nematic (N) phase of 5CB, through all-atom molecular dynamics (MD) simulations. The results demonstrate that molecular shape anisotropy increases in the N phase, with molecules adopting more elongated conformations as aggregation occurs. We find that the shape distribution is temperature- and aggregation-dependent, and the molecular shape relaxation time is longer in the N phase compared to isolated molecules. Additionally, the study proposes a revision to Onsager and Maier-Saupe theories, considering molecular shape distribution changes, which could improve the explanation of the N-I phase transition in liquid crystals. These findings contribute to a better understanding of the molecular behavior in liquid crystalline phases.

cond-mat.soft

Sergeants and Soldiers in Chiral Nematic Liquid Crystal

This study explores the mechanisms behind the helical structures in cholesteric liquid crystalline (CLC) phases using molecular dynamics simulations. By adding chiral agents to the nematic liquid crystalline (NLC) compound, 5CB, the research examines how the shape and motion chirality of the agents influence the overall twisting behavior. The results show that chiral agents induce shape chirality in the 5CB molecules, but dynamic chirality is not detectable at this stage. The study suggests that equilibrium is required for motion chirality to become evident, highlighting the need for further investigation.

cond-mat.soft

ProcBench: Benchmark for Multi-Step Reasoning and Following Procedure

Reasoning is central to a wide range of intellectual activities, and while the capabilities of large language models (LLMs) continue to advance, their performance in reasoning tasks remains limited. The processes and mechanisms underlying reasoning are not yet fully understood, but key elements include path exploration, selection of relevant knowledge, and multi-step inference. Problems are solved through the synthesis of these components. In this paper, we propose a benchmark that focuses on a specific aspect of reasoning ability: the direct evaluation of multi-step inference. To this end, we design a special reasoning task where multi-step inference is specifically focused by largely eliminating path exploration and implicit knowledge utilization. Our dataset comprises pairs of explicit instructions and corresponding questions, where the procedures necessary for solving the questions are entirely detailed within the instructions. This setup allows models to solve problems solely by following the provided directives. By constructing problems that require varying numbers of steps to solve and evaluating responses at each step, we enable a thorough assessment of state-of-the-art LLMs' ability to follow instructions. To ensure the robustness of our evaluation, we include multiple distinct tasks. Furthermore, by comparing accuracy across tasks, utilizing step-aware metrics, and applying separately defined measures of complexity, we conduct experiments that offer insights into the capabilities and limitations of LLMs in reasoning tasks. Our findings have significant implications for the development of LLMs and highlight areas for future research in advancing their reasoning abilities. Our dataset is available at \url{https://huggingface.co/datasets/ifujisawa/procbench} and code at \url{https://github.com/ifujisawa/proc-bench}.

cs.AI