arXiv subjects

Hiroshi Ito

Publications and source records attributed to Hiroshi Ito.

At least 37 records · Page 2Linked to original sources

arXiv2023

Generalized equilibria for color-gradient lattice Boltzmann model based on higher-order Hermite polynomials: A simplified implementation with central moments

We propose generalized equilibria of a three-dimensional color-gradient lattice Boltzmann model for two-component two-phase flows using higher-order Hermite polynomials. Although the resulting equilibrium distribution function, which includes a sixth-order term on the velocity, is computationally cumbersome, its equilibrium central moments (CMs) are velocity-independent and have a simplified form. Numerical experiments show that our approach, as in Wen et al. [Phys. Rev. E 100, 023301 (2019)] who consider terms up to third order, improves the Galilean invariance compared to that of the conventional approach. Dynamic problems can be solved with high accuracy at a density ratio of 10; however, the accuracy is still limited to a density ratio of $1\,000$. For lower density ratios, the generalized equilibria benefit from the CM-based multiple-relaxation-time model, especially at very high Reynolds numbers, significantly improving the numerical stability.

physics.comp-ph↗

arXiv2023

Real-time Motion Generation and Data Augmentation for Grasping Moving Objects with Dynamic Speed and Position Changes

While deep learning enables real robots to perform complex tasks had been difficult to implement in the past, the challenge is the enormous amount of trial-and-error and motion teaching in a real environment. The manipulation of moving objects, due to their dynamic properties, requires learning a wide range of factors such as the object's position, movement speed, and grasping timing. We propose a data augmentation method for enabling a robot to grasp moving objects with different speeds and grasping timings at low cost. Specifically, the robot is taught to grasp an object moving at low speed using teleoperation, and multiple data with different speeds and grasping timings are generated by down-sampling and padding the robot sensor data in the time-series direction. By learning multiple sensor data in a time series, the robot can generate motions while adjusting the grasping timing for unlearned movement speeds and sudden speed changes. We have shown using a real robot that this data augmentation method facilitates learning the relationship between object position and velocity and enables the robot to perform robust grasping motions for unlearned positions and objects with dynamically changing positions and velocities.

cs.RO↗

arXiv2023

Direction-sensitive dark matter search with three-dimensional vector-type tracking in NEWAGE

NEWAGE is a direction-sensitive dark matter search experiment with a three-dimensional tracking detector based on a gaseous micro time projection chamber. A direction-sensitive dark matter search was carried out at Kamioka Observatory with a total live time of 318.0 days resulting in an exposure of 3.18 kg$\cdot$days. A new gamma-ray rejection and a head-tail determination analysis were implemented for this work. No significant non-isotropic signal from the directional analysis was found and a 90% confidence level upper limit on spin-dependent WIMP-proton cross section of 25.7 pb for WIMP mass of 150 GeV/c2 was derived. This upper limit is the most stringent in the direction-sensitive dark matter searches.

hep-ex↗

arXiv2023

Analyzing the neutron and $γ$-ray emission properties of an americium-beryllium tagged neutron source

Americium-beryllium (AmBe), a well-known tagged neutron source, is commonly used for evaluating the neutron detection efficiency of detectors used in ultralow background particle physics experiments, such as reactor neutrino and diffuse supernova neutrino background experiments. In particular, AmBe sources are used to calibrate neutron tagging by selecting the 4438-keV $γ$-ray signal, which is simultaneously emitted with a neutron signal. Therefore, analyzing the neutron and $γ$-ray emission properties of AmBe sources is crucial. In this study, we used the theoretical shape of a neutron energy spectrum, which was divided into three parts, to develop models of the energy spectrum and verify the results using experimental data. We used an AmBe source to measure the energy spectra of simultaneously emitted neutrons and $γ$-rays and determine the emission ratio of the neutrons with and without $γ$-ray emission. The measured spectrum was consistent with that obtained from the simulated result, whereas the measured emission ratio was significantly different from the corresponding simulated result. Here, we also discuss the feasibility of determining the neutron emission rates from the spectra divided into three parts.

physics.ins-det↗

arXiv2023

A method to measure the quenching factor for recoil energy of oxygen in bismuth germanium oxide scintillators

Bismuth germanium oxide ($\rm Bi_{4} Ge_{3} O_{12}$, BGO) scintillation crystals are widely used as detectors in the fields of particle physics and astrophysics due to their high density, and thus higher efficiency for gamma-ray detection. Owing to their good chemical stability, they can be used in any environment. For rare-event searches, such as dark matter and coherent elastic neutrino-nucleus scattering, BGO crystals are essential to comprehend the response of nuclear recoil. In this study, we have analyzed the events of neutron elastic scattering with oxygen in BGO crystals. Then, we have measured the quenching factor for oxygen recoil energy in the BGO crystal as a function of recoil energy by using a monoenergetic neutron source.

physics.ins-det↗

arXiv2022

Guided Visual Attention Model Based on Interactions Between Top-down and Bottom-up Information for Robot Pose Prediction

Deep robot vision models are widely used for recognizing objects from camera images, but shows poor performance when detecting objects at untrained positions. Although such problem can be alleviated by training with large datasets, the dataset collection cost cannot be ignored. Existing visual attention models tackled the problem by employing a data efficient structure which learns to extract task relevant image areas. However, since the models cannot modify attention targets after training, it is difficult to apply to dynamically changing tasks. This paper proposed a novel Key-Query-Value formulated visual attention model. This model is capable of switching attention targets by externally modifying the Query representations, namely top-down attention. The proposed model is experimented on a simulator and a real-world environment. The model was compared to existing end-to-end robot vision models in the simulator experiments, showing higher performance and data efficiency. In the real-world robot experiments, the model showed high precision along with its scalability and extendibility.

cs.RO↗

arXiv2022

Enhanced precision of circadian rhythm by output system

Circadian rhythms are biological rhythms of approximately 24 h that persist even under constant conditions without environmental daily cues. The molecular circadian clock machinery generates the physiological rhythms, which can be transmitted into the downstream output system. Owing to the stochastic nature of the biochemical reactions, the oscillation period of circadian rhythms exhibited by individual organisms or cells is not constant on a daily basis with variations as high as 10 % in terms of the coefficient of variation. Although the fluctuations in circadian rhythm is measured through a reporter such as bioluminescence or fluorescence, experimentally confirming whether the fluctuations found in the reporter system are the same as those in the clock itself is challenging. This study numerically and analytically investigated a coupled system of a circadian clock and its output system, and then compared the fluctuations in the oscillation period of the two systems. We found that the amount of fluctuation in the output system is smaller than that in the circadian clock when the degradation rate of the molecules responsible for the output system was at typical values. The results obtained imply that the output system improves the accuracy of the circadian rhythm without the need for any special denoising processes.

q-bio.MN↗

arXiv2022

Deep Active Visual Attention for Real-time Robot Motion Generation: Emergence of Tool-body Assimilation and Adaptive Tool-use

Sufficiently perceiving the environment is a critical factor in robot motion generation. Although the introduction of deep visual processing models have contributed in extending this ability, existing methods lack in the ability to actively modify what to perceive; humans perform internally during visual cognitive processes. This paper addresses the issue by proposing a novel robot motion generation model, inspired by a human cognitive structure. The model incorporates a state-driven active top-down visual attention module, which acquires attentions that can actively change targets based on task states. We term such attentions as role-based attentions, since the acquired attention directed to targets that shared a coherent role throughout the motion. The model was trained on a robot tool-use task, in which the role-based attentions perceived the robot grippers and tool as identical end-effectors, during object picking and object dragging motions respectively. This is analogous to a biological phenomenon called tool-body assimilation, in which one regards a handled tool as an extension of one's body. The results suggested an improvement of flexibility in model's visual perception, which sustained stable attention and motion even if it was provided with untrained tools or exposed to experimenter's distractions.

cs.RO↗

arXiv2022

Contact-Rich Manipulation of a Flexible Object based on Deep Predictive Learning using Vision and Tactility

We achieved contact-rich flexible object manipulation, which was difficult to control with vision alone. In the unzipping task we chose as a validation task, the gripper grasps the puller, which hides the bag state such as the direction and amount of deformation behind it, making it difficult to obtain information to perform the task by vision alone. Additionally, the flexible fabric bag state constantly changes during operation, so the robot needs to dynamically respond to the change. However, the appropriate robot behavior for all bag states is difficult to prepare in advance. To solve this problem, we developed a model that can perform contact-rich flexible object manipulation by real-time prediction of vision with tactility. We introduced a point-based attention mechanism for extracting image features, softmax transformation for predicting motions, and convolutional neural network for extracting tactile features. The results of experiments using a real robot arm revealed that our method can realize motions responding to the deformation of the bag while reducing the load on the zipper. Furthermore, using tactility improved the success rate from 56.7% to 93.3% compared with vision alone, demonstrating the effectiveness and high performance of our method.

cs.RO↗

arXiv2022

Optical transmittance measurements of sheet resistors for the $\rm {CF}_4$ scintillating light in a gaseous time-projection chamber

A gaseous time-projection chamber (TPC) with a reconstructable $z$ coordinate for nuclear recoil tracks has been developed for dark-matter searches and $α$ particle imagings in a low radioactivity background. A TPC with a sheet-resistor field cage shows a potential to detect charge and photons produced by tracks if the sheet resistor has optical transmittance for visible light, and determine a drift length from a time difference between these signals. In this study, an optical transmittance of sheet resistors was measured to be $24.5\pm0.1_{\rm stat}\pm0.6_{\rm syst}\%$ for the $\rm {CF}_4$ gas scintillating light using an $α$-particle source. The number of photoelectrons is observed to be $\rm\sim20~p.e.$ for 5.3~MeV$α$ with the existence of a sheet resistor in the $\rm CF_4$ gas. Then, it is discussed how many photoelectrons to be observable by using multi-alkali-cathode phototubes and SiPMs for near-infrared light in order to detect lower energy tracks.

physics.ins-det↗

arXiv2021

Direction-sensitive dark matter search with a low-background gaseous detector NEWAGE-0.3b''

NEWAGE is a direction-sensitive dark matter search using a low-pressure gaseous time projection chamber. A low alpha-ray emission rate micro pixel chamber had been developed in order to reduce background for dark matter search. We conducted the dark matter search at the Kamioka Observatory in 2018. The total live time was 107.6 days corresponding to an exposure of 1.1 kg${\cdot}$days. Two events remained in the energy region of 50-60 keV which was consistent with 2.5 events of the expected background. A directional analysis was carried out and no significant forward-backward asymmetry derived from the WIMP-nucleus elastic scatterings was found. Thus a 90% confidence level upper limit on Spin-Dependent WIMP-proton cross section of 50 pb for a WIMP mass of 100 GeV/c2 was derived. This limit is the most stringent yet obtained from direction-sensitive dark matter search experiments.

hep-ex↗

arXiv2021

Spatial Attention Point Network for Deep-learning-based Robust Autonomous Robot Motion Generation

Deep learning provides a powerful framework for automated acquisition of complex robotic motions. However, despite a certain degree of generalization, the need for vast amounts of training data depending on the work-object position is an obstacle to industrial applications. Therefore, a robot motion-generation model that can respond to a variety of work-object positions with a small amount of training data is necessary. In this paper, we propose a method robust to changes in object position by automatically extracting spatial attention points in the image for the robot task and generating motions on the basis of their positions. We demonstrate our method with an LBR iiwa 7R1400 robot arm on a picking task and a pick-and-place task at various positions in various situations. In each task, the spatial attention points are obtained for the work objects that are important to the task. Our method is robust to changes in object position. Further, it is robust to changes in background, lighting, and obstacles that are not important to the task because it only focuses on positions that are important to the task.

cs.RO↗

arXiv2021

Injection Locking and Noise Reduction of Resonant Tunneling Diode Terahertz Oscillator

We studied the injection-locking properties of a resonant-tunneling-diode terahertz oscillator in the small-signal injection regime with a frequency-stabilized continuous THz wave. The linewidth of the emission spectrum dramatically decreased to less than 120 mHz (HWHM) from 4.4 MHz in the free running state as a result of the injection locking. We experimentally determined the amplitude of injection voltage at the antenna caused by the injected THz wave. The locking range was proportional to the injection amplitude and consistent with Adler's model. As increasing the injection amplitude, we observed decrease of the noise component in the power spectrum, which manifests the free-running state, and alternative increase of the injection-locked component. The noise component and the injection-locked component had the same power at the threshold injection amplitude as small as $5\times10^{-4}$ of the oscillation amplitude. This threshold behavior can be qualitatively explained by Maffezzoni's model of noise reduction in general limit-cycle oscillators.

physics.app-ph↗

arXiv2020

First limits from a 3d-vector directional dark matter search with the NEWAGE-0.3b' detector

The first directional dark matter search with three-dimensional tracking with head-tail sensitivity (3d-vector tracking analysis) was performed with a gaseous three-dimensional tarcking detector, or the NEWAGE-0.3b' detector. The search was carried out from July 2013 to August 2017 (Run14 to Run18) at the Kamioka underground laboratory. The total livetime is 434.85 days corresponding to an exposure of 4.51 kg$\cdot$days. A 90 % confidence level upper limit on spin-dependent WIMP-proton cross section of $4.3 \times10^{2}$ pb for WIMPs with the mass of 150 GeV/$c^2$ is obtained.

hep-ex↗

arXiv2020

Development of a low-$α$-emitting $μ$-PIC as a readout device for direction-sensitive dark matter detectors

Direction sensitivity could provide robust evidence for the direct detection of weakly interacting massive particles constituting dark matter. However, the sensitivity of this method remains low due to the radioactive backgrounds. The purpose of this study is to develop a low-background detector as a two-dimensional imaging device for a gaseous time projection chamber. In direction-sensitive dark matter experiments~(e.g. NEWAGE), $α$-rays emitted from the detector components often create substantial radioactive backgrounds. Based on the study of the background of NEWAGE, a new detector "low-$α$ $μ$-PIC" is developed. The produced $μ$-PIC performs well as a gas detector and the $α$-ray emission rate from the $μ$-PIC reduced by a factor of 100.

physics.ins-det↗

arXiv2020

Input-to-state stability and Lyapunov functions with explicit domains for SIR model of infectious diseases

This paper demonstrates input-to-state stability (ISS) of the SIR model of infectious diseases with respect to the disease-free equilibrium and the endemic equilibrium. Lyapunov functions are constructed to verify that both equilibria are individually robust with respect to perturbation of newborn/immigration rate which determines the eventual state of populations in epidemics. The construction and analysis are geometric and global in the space of the populations. In addition to the establishment of ISS, this paper shows how explicitly the constructed level sets reflect the flow of trajectories. Essential obstacles and keys for the construction of Lyapunov functions are elucidated. The proposed Lyapunov functions which have strictly negative derivative allow us to not only establish ISS, but also get rid of the use of LaSalle's invariance principle and popular simplifying assumptions.

math.OC↗

arXiv2020

Interpreting models of infectious diseases in terms of integral input-to-state stability

The notions of integral input-to-state stability (iISS) and input-to-state stability (ISS) have been effective in addressing nonlinearities globally without domain restrictions in analysis and design of control systems. In particular, they provide useful tools of module-based methods integrating characteristics of components. This paper applies the framework of module-based analysis to ordinary differential equations which deterministically describe dynamics of prevalence and the duration of epidemics. The objective is to express fundamental properties of models of infectious diseases and vaccination through the language of iISS and ISS. The systematic treatment is expected to facilitate development of effective schemes of controlling the spread of diseases via non-conventional Lyapunov functions.

math.OC↗

arXiv2019

Interval Observer of Minimal Error Dynamics

This paper proposes a simple interval observer which can generate tighter interval estimates of variables in transient states than the standard interval observer. The simple nonlinear dynamics shrinks the estimated intervals to true state variables at the maximum velocity in the absence of disturbances. In the presence of bounded disturbances, ultimate bounded of the interval estimates are given under the standard assumption for interval observer design.

math.OC↗