Searcharxiv⌕ Search

arXiv subjects

Takahiro Saito

Publications and source records attributed to Takahiro Saito.

10 recordsLinked to original sources
arXiv2026

Development of Electroformed X-ray Optics Bridging Synchrotron Technology and Space Astronomy

We have developed X-ray telescope mirrors using an original electroforming replication technique established through the fabrication of millimeter-aperture, ultra-short-focal-length nanofocusing mirrors for synchrotron X-ray microscopy. This paper presents detailed results of X-ray illumination tests of a 60-mm-diameter, full-circumference, double-reflection monolithic electroformed nickel mirror and its Mirror Module Assembly (MMA). The experiments were conducted at the 1-km beamline BL29XUL at SPring-8. To simulate a parallel X-ray beam from celestial sources, we constructed a dedicated evaluation system, the High-Brilliance X-ray Kilometer-long Large-Area Expanded-beam Evaluation System (HBX-KLAEES). Owing to the high photon flux and the quasi-point-like source with a small divergence provided by HBX-KLAEES, the imaging performance was evaluated with high fidelity, resolving both the sharp core and large-angle components of the Point Spread Function (PSF). The results show an extremely sharp core with a Full Width at Half Maximum (FWHM) of 0.7 arcsec and a Half Power Diameter (HPD) of 14 arcsec, even after integration into the MMA. In addition, a positive correlation was found between angular resolution and axial figure error in both the primary and secondary mirror sections, indicating that axial figure errors contribute to image degradation. Based on these results, the MMA was selected as one of the hard X-ray optics for the FOXSI-4 sounding rocket experiment, which performs high-resolution soft and hard X-ray imaging spectroscopy of solar flares and was successfully launched. These results demonstrate the potential for further improvements in angular resolution and the development of high-resolution, ultra-short focal length X-ray optics for small satellites, including CubeSats.

astro-ph.IM↗
arXiv2025

Hodge microsheaves on cotangent bundles and plumbings

We introduce and study the category of Hodge microsheaves which is a Hodge-version of the category of microsheaves for a certain class of holomorphic exact symplectic manifolds. We then study Hodge-theoretic version of wrapped sheaves and discuss applications in topology and representation theory. Namely, we study (1) Hain's Hodge structures on the cohomology of based loop spaces of algebraic varieties, and (2) the Koszul duality of Ginzburg algebras by Etgü-Lekili from a mixed geometric perspective.

math.AG↗
arXiv2023

The Hodge filtration of a monodromic mixed Hodge module and the irregular Hodge filtration

For an algebraic vector bundle $E$ over a smooth algebraic variety $X$, a monodromic $D$-module on $E$ is decomposed into a direct sum of some $O$-modules on $X$. We show that the Hodge filtration of a monodromic mixed Hodge module is decomposed with respect to the decomposition of the underlying $D$-module. By using this result, we endow the Fourier-Laplace transform $M^{\wedge}$ of the underlying $D$-module $M$ of a monodromic mixed Hodge module with a mixed Hodge module structure. Moreover, we describe the irregular Hodge filtration on $M^{\wedge}$ concretely and show that it coincides with the Hodge filtration at all integer indices.

math.AG↗
arXiv2022

A description of monodromic mixed Hodge modules

For a smooth algebraic variety $X$, a monodromic $D$-module on $X\times \mathbb{C}$ is decomposed into a direct sum of some $D$-modules on $X$. We show that the Hodge filtration of a mixed Hodge module on $X\times \mathbb{C}$ whose underlying $D$-module is monodromic is also decomposed. Moreover, we show that there is an equivalence of categories between the category of monodromic mixed Hodge modules on $X\times \mathbb{C}$ and the category of ``gluing data''. As an application, we endow the Fourier-Laplace transformation of the underlying $D$-module of a monodromic mixed Hodge module with a mixed Hodge module structure.

math.AG↗
arXiv2021

On the monodromies and the limit mixed Hodge structures of families of algebraic varieties

We study the monodromies and the limit mixed Hodge structures of families of complete intersection varieties over a punctured disk in the complex plane. For this purpose, we express their motivic nearby fibers in terms of the geometric data of some Newton polyhedra. In particular, the limit mixed Hodge numbers and some part of the Jordan normal forms of the monodromies of such a family will be described very explicitly.

math.AG↗
arXiv2020

The bifurcation set of a rational function via Newton polytopes

The bifurcation sets of polynomial functions have been studied by many mathematicians from various points of view. In particular, Némethi and Zaharia described them in terms of Newton polytopes. In this paper, we will show analogous results for rational functions.

math.AG↗
arXiv2019

Semi-supervised Approach to Soft Sensor Modeling for Fault Detection in Industrial Systems with Multiple Operation Modes

In industrial systems, certain process variables that need to be monitored for detecting faults are often difficult or impossible to measure. Soft sensor techniques are widely used to estimate such difficult-to-measure process variables from easy-to-measure ones. Soft sensor modeling requires training datasets including the information of various states such as operation modes, but the fault dataset with the target variable is insufficient as the training dataset. This paper describes a semi-supervised approach to soft sensor modeling to incorporate an incomplete dataset without the target variable in the training dataset. To incorporate the incomplete dataset, we consider the properties of processes at transition points between operation modes in the system. The regression coefficients of the operation modes are estimated under constraint conditions obtained from the information on the mode transitions. In a case study, this constrained soft sensor modeling was used to predict refrigerant leaks in air-conditioning systems with heating and cooling operation modes. The results show that this modeling method is promising for soft sensors in a system with multiple operation modes.

eess.SP↗
arXiv2019

Fault Diagnosis Method Based on Scaling Law for On-line Refrigerant Leak Detection

Early fault detection using instrumented sensor data is one of the promising application areas of machine learning in industrial facilities. However, it is difficult to improve the generalization performance of the trained fault-detection model because of the complex system configuration in the target diagnostic system and insufficient fault data. It is not trivial to apply the trained model to other systems. Here we propose a fault diagnosis method for refrigerant leak detection considering the physical modeling and control mechanism of an air-conditioning system. We derive a useful scaling law related to refrigerant leak. If the control mechanism is the same, the model can be applied to other air-conditioning systems irrespective of the system configuration. Small-scale off-line fault test data obtained in a laboratory are applied to estimate the scaling exponent. We evaluate the proposed scaling law by using real-world data. Based on a statistical hypothesis test of the interaction between two groups, we show that the scaling exponents of different air-conditioning systems are equivalent. In addition, we estimated the time series of the degree of leakage of real process data based on the scaling law and confirmed that the proposed method is promising for early leak detection through comparison with assessment by experts.

eess.SP↗
arXiv2017

On the mixed Hodge structures of the intersection cohomology stalks of complex hypersurfaces

We consider a hypersurface in $\mathbb{C}^n$ with an isolated singular point at the origin, and study the mixed Hodge structure of the stalk of its intersection cohomology complex at the origin. In particular we express the dimension of each graded piece of the weight filtration of this mixed Hodge structure in terms of the numbers of the Jordan blocks in the Milnor monodromy.

math.AG↗