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Ryo Yamamoto

Publications and source records attributed to Ryo Yamamoto.

11 recordsLinked to original sources
arXiv2024

Commissioning of a compact multibend achromat lattice: A new 3 GeV synchrotron radiation facility

NanoTerasu, a new 3 GeV synchrotron light source in Japan, began user operation in April 2024. It provides high-brilliance soft to tender X-rays and covers a wide spectral range from ultraviolet to tender X-rays. Its compact storage ring with a circumference of 349 m is based on a four-bend achromat lattice to provide two straight sections in each cell for insertion devices with a natural horizontal emittance of 1.14 nm rad, which is small enough for soft X-rays users. The NanoTerasu accelerator incorporates several innovative technologies, including a full-energy injector C-band linear accelerator with a length of 110 m, an in-vacuum off-axis injection system, a four-bend achromat with B-Q combined bending magnets, and a TM020 mode accelerating cavity with built-in higher-order-mode dampers in the storage ring. This paper presents the accelerator machine commissioning over a half-year period and our model-consistent ring optics correction. The first user operation with a stored beam current of 160 mA is also reported. We summarize the storage ring parameters obtained from the commissioning. This is helpful for estimating the effective optical properties of synchrotron radiation at NanoTerasu.

physics.acc-ph↗
arXiv2024

Self-adaptive Traffic Anomaly Detection System for IoT Smart Home Environments

With the growth of internet of things (IoT) devices, cyberattacks, such as distributed denial of service, that exploit vulnerable devices infected with malware have increased. Therefore, vendors and users must keep their device firmware updated to eliminate vulnerabilities and quickly handle unknown cyberattacks. However, it is difficult for both vendors and users to continually keep the devices safe because vendors must provide updates quickly and the users must continuously manage the conditions of all deployed devices. Therefore, to ensure security, it is necessary for a system to adapt autonomously to changes in cyberattacks. In addition, it is important to consider network-side security that detects and filters anomalous traffic at the gateway to comprehensively protect those devices. This paper proposes a self-adaptive anomaly detection system for IoT traffic, including unknown attacks. The proposed system comprises a honeypot server and a gateway. The honeypot server continuously captures traffic and adaptively generates an anomaly detection model using real-time captured traffic. Thereafter, the gateway uses the generated model to detect anomalous traffic. Thus, the proposed system can adapt to unknown attacks to reflect pattern changes in anomalous traffic based on real-time captured traffic. Three experiments were conducted to evaluate the proposed system: a virtual experiment using pre-captured traffic from various regions across the world, a demonstration experiment using real-time captured traffic, and a virtual experiment using a public dataset containing the traffic generated by malware. The experimental results indicate that a system adaptable in real time to evolving cyberattacks is a novel approach for ensuring the comprehensive security of IoT devices against both known and unknown attacks.

cs.CR↗
arXiv2020

Detector Algorithms of Bounding Box and Segmentation Mask of a Mask R-CNN Model

Detection performances on bounding box and segmentation mask outputs of Mask R-CNN models are evaluated. There are significant differences in detection performances of bounding boxes and segmentation masks, where the former is constantly superior to the latter. Harmonic values of precisions and recalls of linear cracks, joints, fillings, and shadows are significantly lower in segmentation masks than bounding boxes. Other classes showed similar harmonic values. Discussions are made on different performances of detection metrics of bounding boxes and segmentation masks focusing on detection algorithms of both detectors.

cs.CV↗
arXiv2020

Fine-tuned Pre-trained Mask R-CNN Models for Surface Object Detection

This study evaluates road surface object detection tasks using four Mask R-CNN models as a pre-study of surface deterioration detection of stone-made archaeological objects. The models were pre-trained and fine-tuned by COCO datasets and 15,188 segmented road surface annotation tags. The quality of the models were measured using Average Precisions and Average Recalls. Result indicates substantial number of counts of false negatives, i.e. left detection and unclassified detections. A modified confusion matrix model to avoid prioritizing IoU is tested and there are notable true positive increases in bounding box detection, but almost no changes in segmentation masks.

cs.CV↗
arXiv2019

A Search for a Contribution from Axion-Like Particles to the X-Ray Diffuse Background Utilizing the Earth's Magnetic Field

The Axion Like Particle (ALP) is a hypothetical pseudo-scalar particle beyond the Standard Model, with a compelling possible connection to dark matter and early universe physics. ALPs can be converted into photons via interactions with magnetic fields in the universe, i.e., the so-called inverse Primakoff effect. In this paper, we propose a novel method to explore ALP-induced photons from X-ray data obtained from the {\it Suzaku} satellite, arising from a possible interaction of ALPs with the direction-dependent Earth's magnetic field viewed from the satellite. {\it Suzaku} data is suitable for this purpose because its low-altitude Earth orbit result in intrinsically low cosmic-ray background radiation. We study whether the X-ray diffuse background (XDB) spectra estimated from the four deep fields collected over eight years, vary with the integrated Earth's magnetic strength in the direction of each target field at each observation epoch, which amounts to $10^2$ Tm-a value greater than that achieved by terrestrial experiments due to the large coherent length. From the detailed analysis, we did not find evidence of the XDB confidence level spectra having dependence on the Earth's magnetic strength. We obtained 99 % confidence level upper limit on a possible residual contribution to the cosmic X-ray background (CXB) surface brightness to be $1.6\times 10^{-9}~{\rm ergs~s}^{-1}{\rm cm}^{-2}{\rm sr}^{-1}$ normalized at $10^4$ T${}^2$ m${}^2$ in the 2-6 keV range, which corresponds to 6-15 % of the observed CXB brightness, depending on which model of unresolved point sources are used in the interpretation. It is consistent with 80-90 % of the CXB now being resolved into point sources.

astro-ph.HE↗
arXiv2016

Near infrared diffuse interstellar bands toward the Cygnus OB2 association

We obtained the near-infrared (NIR) high-resolution ($R\equivλ/Δλ\sim20,000$) spectra of the seven brightest early-type stars in the Cygnus OB2 association for investigating the environmental dependence of diffuse interstellar bands (DIBs). The WINERED spectrograph mounted on the Araki 1.3m telescope in Japan was used to collect data. All 20 of the known DIBs within the wavelength coverage of WINERED ($0.91<λ<1.36μ$m) were clearly detected along all lines of sight because of their high flux density in the NIR wavelength range and the large extinction. The equivalent widths (EWs) of DIBs were not correlated with the column densities of C$_2$ molecules, which trace the patchy dense component, suggesting that the NIR DIB carriers are distributed mainly in the diffuse component. On the basis of the correlations among the NIR DIBs both for stars in Cyg OB2 and stars observed previously, $λλ$10780, 10792, 11797, 12623, and 13175 are found to constitute a "family", in which the DIBs are correlated well over the wide EW range. In contrast, the EW of $λ$10504 is found to remain almost constant over the stars in Cyg OB2. The extinction estimated from the average EW of $λ$10504 ($A_V\sim3.6$mag) roughly corresponds to the lower limit of the extinction distribution of OB stars in Cyg OB2. This suggests that $λ$10504 is absorbed only by the foreground clouds, implying that the carrier of $λ$10504 is completely destroyed in Cyg OB2, probably by the strong UV radiation field. The different behaviors of the DIBs may be caused by different properties of the DIB carriers.

astro-ph.GA↗
arXiv2015

Near-infrared diffuse interstellar bands in 0.91-1.32 micron

We present a comprehensive survey of diffuse interstellar bands (DIBs) in $0.91-1.32μ$m with a newly-developed near-infrared (NIR) spectrograph, WINERED, mounted on the Araki 1.3 m Telescope in Japan. We obtained high-resolution ($R=28,300$) spectra of 25 early-type stars with color excesses of $0.07<E(B-V)<3.4$. In addition to the five DIBs previously detected in this wavelength range, we identified 15 new DIBs, 7 of which were reported as DIB "candidates" by Cox. We analyze the correlations among NIR DIBs, strong optical DIBs, and the reddening of the stars. Consequently, we found that all NIR DIBs show weaker correlations with the reddening rather than the optical DIBs, suggesting that the equivalent widths of NIR DIBs depend on some physical conditions of the interstellar clouds, such as UV flux. Three NIR DIBs, $λλ$10780, 10792, and 11797, are found to be classifiable as a "family," in which the DIBs are well correlated with each other, suggesting that the carriers of these DIBs are connected with some chemical reactions and/or have similar physical properties such as ionization potential. We also found that three strongest NIR DIBs $λ\lambda10780, 11797, 13175$ are well correlated with the optical DIB $λ5780.5$, whose carrier is proposed to be a cation molecule with high ionization potential, indicating that the carriers of the NIR DIBs could be cation molecules.

astro-ph.GA↗
arXiv2015

A Warm Near-Infrared High-Resolution Spectrograph with Very High Throughput (WINERED)

WINERED is a newly built high-efficiency (throughput$ > 25-30\%$) and high-resolution spectrograph customized for short NIR bands at 0.9-1.35 ${\rm μ}$m. WINERED is equipped with ambient temperature optics and a cryogenic camera using a 1.7 ${\rm μ}$m cut-off HgCdTe HAWAII-2RG array detector. WINERED has two grating modes: one with a conventional reflective echelle grating (R$\sim$28,300), which covers 0.9-1.35 $μ$m simultaneously, the other with ZnSe or ZnS immersion grating (R$\sim$100,000). We have completed the development of WINERED except for the immersion grating, and started engineering and science observations at the Nasmyth platform of the 1.3 m Araki Telescope at Koyama Astronomical Observatory of Kyoto-Sangyo University in Japan. We confirmed that the spectral resolution ($R\sim$ 28,300) and the throughput ($>$ 40\% w/o telescope/atmosphere/array QE) meet our specifications. We measured ambient thermal backgrounds (e.g., 0.06 ${\rm [e^{-}/sec/pixel]}$ at 287 K), which are roughly consistent with that we expected. WINERED is a portable instrument that can be installed at any telescope with Nasmyth focus as a PI-type instrument. If WINERED is installed on a 10 meter telescope, the limiting magnitude is expected to be J=18-19, which can provide high-resolution spectra with high quality even for faint distant objects.

astro-ph.IM↗
arXiv2013

Long Term Variability of O VII Line Intensity toward the Lockman Hole Observed with Suzaku from 2006 to 2011

Long-term time variabilities of the OVII (0.57 keV) emission in the soft X-ray diffuse background were studied using six Suzaku annual observations of blank sky towards the Lockman Hole made from 2006 to 2011. After time intervals in which the emission was enhanced on time scales of a few tens of ks were removed, the O VII intensity was found to be constant from 2006 to 2009 within the 90% statistical errors. The intensity in 2010 and 2011 was higher by 2-3 LU (photons/s/cm/sr) than the earlier values. The most plausible origin of the fast variable component is Solar wind charge exchange (SWCX). The intensity increase is not positively correlated with the proton flux at the L1 point. Since all the observations were made in the same season of a year, the variation cannot be explained by parallax of the SWCX induced X-ray emission from the Heliosphere. We consider that it is related to the geometrical change of slow and fast solar wind structures associated with the 11 year solar activity. The observed variation was compared with that expected from the SWCX induced X-ray emission model.

astro-ph.HE↗
arXiv2006

Lattice Model of Sweeping Interface for Drying Process in Water-Granule Mixture

Based on the invasion percolation model, a lattice model for the sweeping interface dynamics is constructed to describe the pattern forming process by a sweeping interface upon drying the water-granule mixture. The model is shown to produce labyrinthine patterns similar to those found in the experiment[Yamazaki and Mizuguchi, J. Phys. Soc. Jpn. \textbf{69} (2000) 2387]. Upon changing the initial granular density, resulting patterns undergo the percolation transition, but estimated critical exponents are different from those of the conventional percolation. Loopless structure of clusters in the patterns produced by the sweeping dynamics seems to influence the nature of the transition.

cond-mat.stat-mech↗