arXiv subjects

Makoto Kobayashi

Publications and source records attributed to Makoto Kobayashi.

16 recordsLinked to original sources

arXiv2026

Numerical speckle reduction for optical coherence tomography based on an analytical image formation model

Speckle is an intrinsic granular pattern that limits the effective resolution of optical coherence tomography (OCT). We propose a numerical speckle reduction method using the "real part of a shifted complex conjugate product" (real-SCCP), which is a new image representation designed based on an analytical imaging model of OCT. In the real-SCCP image representation, the speckle can be fully numerically modulated after OCT signal acquisition. By averaging multiple SCCP images with different speckle realizations, the speckle is effectively reduced. Furthermore, this method enables clear visualization of structures in tumor spheroids and zebrafish eyes, and significantly outperforms conventional frame-averaging-based speckle reduction techniques.

physics.optics↗

arXiv2026

Image-based investigation of the zebrafish developmental process using in vivo dynamic and multi-contrast optical coherence tomography

We demonstrate in vivo dynamic optical coherence tomography (DOCT) imaging of zebrafish development from 2 weeks to 12 months post-fertilization, integrated with polarization-sensitive OCT (PS-OCT), OCT angiography (OCTA), and histological validation. Two DOCT algorithms were utilized: logarithmic intensity variance and late OCT correlation decay speed, which characterize the occupancy of dynamic scatterers and their motion speeds, respectively. Our results show that skin stripes exhibit high DOCT signals and it varies among the pigment-cell types. Furthermore, the combination of DOCT and PS-OCT captures the maturation of these stripes. In addition, DOCT and OCTA successfully visualized the developmental progression of blood and lymphatic vessels, as well as spinal tissues.

physics.optics↗

arXiv2025

An Estimation of the Effective Number of Electrons Contributing to the Coordinate Measurement with a TPC

For time projection chambers (TPCs) the accuracy in measurement of track coordinates along the pad row direction deteriorates with the drift distance ($z$): $σ_{\rm X}^2 \sim D_{\rm X}^2 \cdot z / N_{\rm eff}$, where $D_{\rm X}$ is the diffusion constant and $N_{\rm eff}$ is the effective number of electrons. Experimentally it has been shown that $N_{\rm eff}$ is smaller than the average number of drift electrons per pad row ($\overline{N}$). We estimated $N_{\rm eff}$ by means of a simple numerical simulation. The simulation shows that $N_{\rm eff}$ can be as small as $\sim$ 30\% of $\overline{N}$ due to the combined effect of statistical fluctuations in the number of drift electrons ($N$) and in their multiplication in avalanches.

physics.ins-det↗

arXiv2024

Polarization-artifact reduction and accuracy improvement of Jones-matrix polarization-sensitive optical coherence tomography by multi-focus averaging

Polarization-sensitive optical coherence tomography (PS-OCT) is a promising biomedical imaging tool for differentiation of various tissue properties. However, the presence of multiple-scattering (MS) signals can degrade the quantitative polarization measurement accuracy. We demonstrate a method to reduce MS signals and increase the measurement accuracy of Jones matrix PS-OCT. This method suppresses MS signals by averaging of multiple Jones matrix volumes measured using different focal positions. The MS signals are decorrelated among the volumes by focus position modulation and are thus reduced by averaging. However, the single scattering signals are kept consistent among the focus-modulated volumes by computational refocusing. We validated the proposed method using a scattering phantom and a postmortem medaka fish. The results showed reduced artifacts in birefringence and degree-of-polarization uniformity measurements, particularly in deeper regions in the samples. This method offers a practical solution to mitigate MS-induced artifacts in PS-OCT imaging and improves quantitative polarization measurement accuracy.

physics.optics↗

arXiv2023

Theoretical model for en face optical coherence tomography imaging and its application to volumetric differential contrast imaging

A new formulation of lateral imaging process of point-scanning optical coherence tomography (OCT) and a new differential contrast method designed by using this formulation are presented. The formulation is based on a mathematical sample model called the dispersed scatterer model (DSM), in which the sample is represented as a material with a spatially slowly varying refractive index and randomly distributed scatterers embedded in the material. It is shown that the formulation represents a meaningful OCT image and speckle as two independent mathematical quantities. The new differential contrast method is based on complex signal processing of OCT images, and the physical and numerical imaging processes of this method are jointly formulated using the same theoretical strategy as in the case of OCT. The formula shows that the method provides a spatially differential image of the sample structure. This differential imaging method is validated by measuring in vivo and in vitro samples.

physics.optics↗

arXiv2023

A novel technique for the measurement of the avalanche fluctuation of gaseous detectors

We have developed a novel technique for the measurement of the avalanche fluctuation of gaseous detectors using a UV laser. The technique is simple and requires a short data-taking time of about ten minutes. Furthermore, it is applicable for relatively low gas gains. Our experimental setup as well as the measurement principle, and the results obtained with a stack of Gas Electron Multipliers (GEMs) operated in several gas mixtures are presented.

physics.ins-det↗

arXiv2022

Double-hit separation and dE/dx resolution of a time projection chamber with GEM readout

A time projection chamber (TPC) with micropattern gaseous detector (MPGD) readout is investigated as main tracking device of the International Large Detector (ILD) concept at the planned International Linear Collider (ILC). A prototype TPC equipped with a triple gas electron multiplier (GEM) readout has been built and operated in an electron test beam. The TPC was placed in a 1 T solenoidal field at the DESY II Test Beam Facility, which provides an electron beam up to 6 GeV/c. The performance of the readout modules, in particular the spatial point resolution, is determined and compared to earlier tests. New studies are presented with first results on the separation of close-by tracks and the capability of the system to measure the specific energy loss dE/dx. This is complemented by a simulation study on the optimization of the readout granularity to improve particle identification by dE/dx.

physics.ins-det↗

arXiv2019

A Beam Test of Prototype TPCs using Micro-Pattern Gas Detectors at KEK

We conducted a series of beam tests of prototype TPCs for the International Linear Collider (ILC) experiment, equipped with an MWPC, a MicroMEGAS, or GEMs as a readout device. The prototype operated successfully in a test beam at KEK under an axial magnetic field of up to 1 T. The analysis of data is now in progress and some of the preliminary results obtained with GEMs and MicroMEGAS are presented along with our interpretation. Also given is the extrapolation of the obtained spatial resolution to that of a large TPC expected for the central tracker of the ILC experiment.

physics.ins-det↗

arXiv2018

Buffering Time Strategies for Wireless Full-duplex Systems under Poisson Traffic

Full-duplex wireless communication has the potential to double the capacity of wireless networks by reducing the band occupancy of transmissions. However, a full-duplex capability cannot always reduce the band occupancy because the real traffic is not fully buffered. Buffering time while waiting for a packet to arrive at an opposite node is expected to reduce the band occupancy. In this study, we provide the first theoretical analysis of band occupancy and the mean waiting time for full-duplex communication with and without buffering time under traffic that is not fully buffered based on queueing theory, as well as the closed-form results. We also present the results of simulations of band occupancy and the mean waiting time. The basic analysis provided in this study shows how the mean waiting time and band occupancy are affected by the buffering time. When the buffering time is half the packet length, the band occupancy is reduced by approximately 15 %. In addition, under asymmetrical traffic, the results suggest that the buffering time should not be set at the node who has a higher traffic intensity compared with another node. These results support the design of a full-duplex medium access control protocol and devices.

cs.NI↗

arXiv2017

Wireless Full-duplex Medium Access Control for Enhancing Energy Efficiency

Recent years have witnessed a proliferation of battery-powered mobile devices, e.g., smartphones, tablets, sensors, and laptops, which leads a significant demand for high capacity wireless communication with high energy efficiency. Among technologies to provide the efficiency is full-duplex wireless communication. Full-duplex wireless enhances capacity by simultaneously transmitting uplink and downlink data with limited frequency resources. Previous studies on full-duplex wireless mostly focuses on doubling the network capacity, whereas in this paper we discuss that full-duplex wireless can also provide higher energy efficiency. We propose low power communication by wireless full-duplexing (LPFD), focusing on the fact that the full-duplex communication duration becomes half of the halfduplex communication duration. In the LPFD, by using the sleep state in which the transceiver provided in the wireless communication terminal is turned off, power consumption of the wireless communication terminal is reduced and energy efficiency in wireless full duplex is improved. Simulation results show that the energy efficiency achieved by LPFD is up to approximately 17.3 times higher than the energy efficiency achieved by existing full-duplex medium access protocol. Further, it is up to approximately 27.5 times higher than the energy efficiency using power saving mode of half-duplex communication.

cs.NI↗

arXiv2016

A Time Projection Chamber with GEM-Based Readout

For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1 T solenoidal field and read out with three independent GEM-based readout modules, are reported. The TPC was exposed to a 6 GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.

physics.ins-det↗

arXiv2016

An estimation of the effective number of electrons contributing to the coordinate measurement with a TPC II

For time projection chambers (TPCs) the accuracy in measurement of the track coordinates along the pad-row direction deteriorates with the drift distance (z): Resolution**2 = D**2 * z / N_eff, where D is the diffusion constant and N_eff is the effective number of electrons. Experimentally it has been shown that N_eff is smaller than the average number of drift electrons per pad row ( ). In the previous work we estimated N_eff by means of a simple numerical simulation for argon-based gas mixtures, taking into account the diffusion of electrons only in the pad-row direction [1]. The simulation showed that N_eff could be as small as 30% of because of the combined effect of statistical fluctuations in the number of drift electrons (N) and in their multiplication in avalanches. In this paper, we evaluate the influence of the diffusion normal to the pad-row direction on the effective number of electrons. The de-clustering of the drift electrons due to the diffusion makes N_eff drift-distance dependent. However, its effect was found to be too small to explain the discrepancy between the values of N_eff measured with two TPC prototypes different in size.

physics.ins-det↗

arXiv2008

Electric Dipole Moments of Dyon and `Electron'

The electric and magnetic dipole moments of dyon fermions are calculated within N=2 supersymmetric Yang-Mills theory including the theta-term. It is found, in particular, that the gyroelectric ratio deviates from the canonical value of 2 for the monopole fermion (n_m=1,n_e=0) in the case theta\not=0. Then, applying the S-duality transformation to the result for the dyon fermions, we obtain an explicit prediction for the electric dipole moment (EDM) of the charged fermion (`electron'). It is thus seen that the approach presented here provides a novel method for computing the EDM induced by the theta-term.

hep-th↗

arXiv2007

Electric Dipole Moment of Magnetic Monopole

The electric dipole moment of magnetic monopoles with spin is studied in the N=2 supersymmetric gauge theory. The dipole moments of the electric charge distributions, as well as the dipole moments due to the magnetic currents, are calculated. The contribution of charge distribution of the fermion to the gyroelectric ratio is expressed by using zeta(3).

hep-th↗

arXiv2006

The universe out of a monopole in the laboratory?

To explore the possibility that an inflationary universe can be created out of a stable particle in the laboratory, we consider the classical and quantum dynamics of a magnetic monopole in the thin-shell approximation. Classically there are three types of solutions: stable, collapsing and inflating monopoles. We argue that the transition from a stable monopole to an inflating one could occur either by collision with a domain wall or by quantum tunneling.

gr-qc↗

arXiv2000

Pseudo-Dirac Scenario for Neutrino Oscillations

We argue how pseudo-Dirac scenario for neutrinos leads to rich neutrino oscillation phenomena, including oscillation inside each generation. The pseudo-Dirac scenario is generalized by incorporating generation mixings and formulae for the various neutrino oscillations are derived. As the application we compare the formulae with the corresponding data. We find that observed pattern of mixings, such as almost maximal mixing in the atmospheric neutrino oscillation, is naturally explained in the generalized Pseudo-Dirac scenario with small generation mixings. We, however, also point out that there remain some problems to be settled for this scenario to be viable. The possible theoretical framework to realize the pseudo-Dirac scenario is also briefly commented on.

hep-ph↗