arXiv subjects

N. Takahashi

Publications and source records attributed to N. Takahashi.

At least 19 recordsLinked to original sources

arXiv2024

Earthquake detection capacity of the Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET)

We studied the earthquake detection capacity of DONET (Dense Oceanfloor Network system for Earthquakes and Tsunamis) operating in the Nankai Trough, a target region monitored for future megathrust earthquakes. The focus of this paper was to evaluate the impact on this capacity from the malfunction of parts of the network. For this purpose, the completeness magnitude, above which all earthquakes are considered to be detected by a seismic network, was used. Then, a catalog that includes events observed by DONET was used. We found spatiotemporal variability of completeness magnitude, ranging from values below 1 in one of the areas where stations are densely deployed to values above 2 at the periphery and outside of the DONET area. We conducted a simulation computation for cases of malfunction of densely distributed stations. The results showed that completeness estimates in the area near the malfunctioning stations were about 1 magnitude larger. This implies that malfunction repair and/or replacement with new stations would be desirable because they pronouncedly affect earthquake monitoring. We then demonstrated an example of how to use the information of completeness magnitude as prior knowledge to compute the b value of the Gutenberg-Richter distribution. The result indicates the b value as a proxy that can help to image stress heterogeneity when there is a magnitude-6 class slow slip event on the Nankai Trough plate boundary.

physics.geo-ph↗

arXiv2016

Measurement of Wave Electric Fields in Plasmas by Electro-Optic Probe

Electric field measurement in plasmas permits quantitative comparison between the experiment and the simulation in this study. An electro-optic (EO) sensor based on Pockels effect is demonstrated to measure wave electric fields in the laboratory magnetosphere of the RT-1 device with high frequency heating sources. This system gives the merits that electric field measurements can detect electrostatic waves separated clearly from wave magnetic fields, and that the sensor head is separated electrically from strong stray fields in circumference. The electromagnetic waves are excited at the double loop antenna for ion heating in electron cyclotron heated plasmas. In the air, the measured wave electric fields are in good absolute agreement with those predicted by the TASK/WF2 code. In inhomogeneous plasmas, the wave electric fields in the peripheral region are enhanced compared with the simulated electric fields. The potential oscillation of the antenna is one of the possible reason to explain the experimental results qualitatively.

physics.plasm-ph↗

arXiv2015

Atomic layer deposition of Y2O3 on h-BN for a gate stack in graphene FETs

The combination of h-BN and high-k dielectrics is required for a top gate insulator in miniaturized graphene field-effect transistors because of the low dielectric constant of h-BN. We investigated the deposition of Y2O3 on h-BN using atomic layer deposition. The deposition of Y2O3 on h-BN was confirmed without any buffer layer. An increase in the deposition temperature reduced the surface coverage. The deposition mechanism could be explained by the competition between the desorption and adsorption of the Y precursor on h-BN due to the polarization. Although a full surface coverage was difficult to achieve, the use of an oxidized metal seeding layer on h-BN resulted in a full surface coverage.

cond-mat.mtrl-sci↗

arXiv2015

The astrometric Gaia-FUN-SSO observation campaign of 99 942 Apophis

Astrometric observations performed by the Gaia Follow-Up Network for Solar System Objects (Gaia-FUN-SSO) play a key role in ensuring that moving objects first detected by ESA's Gaia mission remain recoverable after their discovery. An observation campaign on the potentially hazardous asteroid (99 942) Apophis was conducted during the asteroid's latest period of visibility, from 12/21/2012 to 5/2/2013, to test the coordination and evaluate the overall performance of the Gaia-FUN-SSO . The 2732 high quality astrometric observations acquired during the Gaia-FUN-SSO campaign were reduced with the Platform for Reduction of Astronomical Images Automatically (PRAIA), using the USNO CCD Astrograph Catalogue 4 (UCAC4) as a reference. The astrometric reduction process and the precision of the newly obtained measurements are discussed. We compare the residuals of astrometric observations that we obtained using this reduction process to data sets that were individually reduced by observers and accepted by the Minor Planet Center. We obtained 2103 previously unpublished astrometric positions and provide these to the scientific community. Using these data we show that our reduction of this astrometric campaign with a reliable stellar catalog substantially improves the quality of the astrometric results. We present evidence that the new data will help to reduce the orbit uncertainty of Apophis during its close approach in 2029. We show that uncertainties due to geolocations of observing stations, as well as rounding of astrometric data can introduce an unnecessary degradation in the quality of the resulting astrometric positions. Finally, we discuss the impact of our campaign reduction on the recovery process of newly discovered asteroids.

astro-ph.EP↗

arXiv2013

A Critical Examination on L/E Analysis in the Underground Detectors with a Computer Numerical Experiment Part 1

In the present paper we consider neutrino events due to quasi-elastic scattering (QEL) as the most reliable events among various candidate events to be analyzed, and have carried out the first step of an L/E analysis which aims to confirm the survival probability with a Numerical Computer Experiment. The most important factor in the survival probability is Lnu and Enu, but this cannot be measured for such neutral particles. Instead, Lmu and Emu is utilized in the L/E analysis, where Lnu, Lmu, Enu and Emu denote the flight path lengths of the incident neutrinos, those of the emitted leptons, the energies of the incident neutrinos and those of the emitted leptons, respectively. According to our Computer Numerical Experiment, the relation of Lnu/Enu is nearly equal to Lmu/Emu doesn't hold. In subsequent papers, we show the results on an L/E analysis with the Computer Numerical Experiment based on our results obtained in the present paper.

astro-ph.HE↗

arXiv2013

Beta-delayed neutron and gamma-ray spectroscopy of 17C utilizing spin-polarized 17B

Excited states in 17C were investigated through the measurement of beta?-delayed neutrons and gamma rays emitted in the ? decay of 17B. In the measurement, three negative-parity states and two inconclusive states, were identified in 17C above the neutron threshold energy, and seven gamma-lines were identified in a beta?-delayed multiple neutron emission of the 17B ? decay. From these transitions, the beta?-decay scheme of 17B was determined. In the present work, the fibeta-NMR technique is combined with the ?-delayed particle measurements using a fragmentation-induced spin-polarized 17B beam. This new scheme allows us to determine the spin parity of beta?-decay feeding excited states based on the difference in the discrete fibeta-decay asymmetry parameters, provided the states are connected through the Gamow-Teller transition. In this work, 1/2-, 3/2-, and (5/2-) are assigned to the observed states at Ex = 2.71(2), 3.93(2), and 4.05(2) MeV in 17C, respectively.

nucl-ex↗

arXiv2011

Measurement of the 8B Solar Neutrino Flux with the KamLAND Liquid Scintillator Detector

We report a measurement of the neutrino-electron elastic scattering rate from 8B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5 MeV analysis threshold is 1.49+/-0.14(stat)+/-0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a 8B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77+/-0.26(stat)+/-0.32(syst) x 10^6 cm^-2s^-1. The analysis threshold is driven by 208Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic 11Be. The measured rate is consistent with existing measurements and with Standard Solar Model predictions which include matter enhanced neutrino oscillation.

hep-ex↗

arXiv2011

On the Relation between the True Directions of Neutrinos and the Reconstructed Directions of Neutrinos in L/E Analysis Performed by Super-Kamiokande Collaboration Part1

It should be regarded that the confirmation of the maximum oscillation in neutrino oscillation through L/E analysis by Super-Kamiokande is a logical consequence of their establishment on the existence of neutrino oscillation through the analysis of the zenith angle distribution for atmospheric neutrino events. In the present paper (Part1) with the computer numerical experiment, we examine the assumption made by Super-Kamiokande Collaboration that the direction of the incident neutrino is approximately the same as that of the produced lepton, which is the cornerstone in their L/E analysis, and we find this approximation does not hold even approximately. In a subsequent paper (Part2), we apply the results from Figures 16, 17, 18 and 19 to L/E analysis and conclude that one cannot obtain the maximum oscillation in L/E analysis in the single ring muon events due to quasi-elastic scattering reported by Super-Kamiokande which shows strongly the oscillation pattern from the neutrino oscillation.

hep-ex↗

arXiv2011

On the Relation between the True Directions of Neutrinos and the Reconstructed Directions of Neutrinos in L/E Analysis Performed by Super-Kamiokande Collaboration Part2

In the previous paper (Part1), we have verified that the SK assumption on the direction does not hold in the analysis of neutrino events occurred inside the SK detector, which is the cornerstone for their analysis of zenith angle distributions of neutrino events. Based on the correlation between L_nu and L_mu (Figures~16 to 18 in Part1) and the correlation between E_nu and E_mu (Figure19 in Part1), we have made four possible L/E analyses, namely L_nu/E_nu, L_nu/E_mu, L_mu/E_mu and L_mu/E_nu. Among four kinds of L/E analyses, we have shown that only L_nu/E_nu analysis can give the signature of maximum oscillations clearly, not only the first maximum oscillation but also the second and third maximum oscillation and etc., as they should be, while the L_mu/E_mu analysis which are really done by Super-Kamiokande Collaboration cannot give any maximum oscillation at all. It is thus concluded from those results that the experiments with the use of the cosmic-ray beam for neutrino oscillation, such as Super-Kamiokande type experiment, are unable to lead the maximum oscillation from their L/E analysis, because the incident neutrino cannot be observed due to its neutrality. Therefore, we would suggest Super-Kamiokande Collaboration to re-analyze the zenith angle distribution of the neutrino events which occur inside the detector carefully, since L_nu and L_mu are alternative expressions of the cosine of the zenith angle for the incident neutrino and that for the emitted muon, respectively.

hep-ex↗

arXiv2010

A Detailed Study on the Range Fluctuations of $10^{11}$eV to $10^{18}$eV Muons in Water and the Fluctuations of the Cherenkov Lights due to the Accompanied Cascade Showers initiated by Muons

The validity of our Monte Carlo simulation procedure ({\it the integral method}) had been verified by the corresponding analytical procedure of which is quite independent of our method methodologically. Also, the results obtained by our procedure are compared with those obtained by the different Monte Carlo simulation procedure ({\it the differential method}) which have been exclusively utilized by the different authors and the agreement between them are found to be well. By utilizing our Monte Carlo procedures, the validity of which is guaranteed in two different procedures, we investigate not only the fluctuation of high energy muons themselves but also fluctuation of the various quantities related to the energy losses by the muons, which are difficult to obtain by {\it the differential method}. Namely, we obtain fluctuation on energy losses of the muons, fluctuation on Cherenkov lights due to the accompanied cascade showers initiated by the muon and the correlations between them . Finally, we obtain the transition curves for Cherenkov lights in KM3 detector, taking into account of all possible fluctuations in the stochastic processes and point out the difficulty of the reliable estimation of the energy of the muons which are resultants of muon neutrino events in the KM3 detectors.

astro-ph.HE↗

arXiv2010

(Ultra-)High Energy Muon Neutrino Propagation through the Earth and Induced Muon Energy Distribution near the One Cubic Kilometer Detector

We calculate high and (ultra-)high energy upward-going muon neutrino propagation through the Earth and the induced muon energy distribution near the one cubic kilometer detector using the Monte Carlo simulation, due to both charged current interaction and neutral one. The initiated neutrino energies on the surface of the Earth are 1PeV, 1EeV and 1ZeV. The mean free paths of (ultra-)high energy neutrino events generated by the deep inelastic scattering may be comparable with the diameter of the Earth or less than it. Therefore, the induced muon production distribution is influenced by the change of the densities interior to the Earth. Furthermore, in such situation, the contribution from the neutral current neutrino interaction to the induced muon production distribution cannot be neglected. We report several examples of the deep inelastic scattered depth of muon neutrino in the Earth and the induced muon energy distribution near the detector.

astro-ph.HE↗

arXiv2010

Fluctuation of TeV to EeV Energy Muons and Induced Muon Showers in Water

By using the integral method in the muon propagation through water, we calculate the range fluctuation of high and ultra high energy muons. Many authors divide all radiative processes into two parts, namely, the continuous part and radiative part in their Monte Carlo simulation in order to consider the fluctuation in the both ranges and energies of the muons, while we treat all stochastic processes as exactly as possible, without the introduction of the continuous parts in all stochastic processes. The validity of our Monte Carlo method is checked by the corresponding analytical method which is methodologically independent on the Monte Carlo procedure. Accompanied cascade showers are generated by the direct electron pair production, bremsstrahlung and photo-nuclear interaction. These showers are calculated by the exact Monte Carlo Method in one dimensional way. We report survival probabilities, range distributions and examples of individual muon behavior.

astro-ph.HE↗

arXiv2010

Atmospheric muon flux at PeV energies

In the near future the energy region above few hundreds of TeV may really be accessible for measurements of the atmospheric muon spectrum by the IceCube array. Therefore one expects that muon flux uncertainties above 50 TeV, related to a poor knowledge of charm production cross sections and insufficiently examined primary spectra and composition, will be diminished. We give predictions for the very high-energy muon spectrum at sea level, obtained with the three hadronic interaction models, taking into account also the muon contribution due to decays of the charmed hadrons.

astro-ph.HE↗

arXiv2010

On the Sensitivity of L/E Analysis of Super-Kamiokande Atmospheric Neutrino Data to Neutrino Oscillation Part~2 --- Four Possible L/E Analyses for the Maximum Oscillation by the Numerical Computer Experiment ---

In the previous paper (Part~1), we have verified that the SK assumption on the direction does not hold in the analysis of neutrino events occurred inside the SK detector. We have made four possible L/E analyses, L_nu/E_nu, L_nu/E_mu, L_mu/E_nu and L_mu/E_mu. Among four kinds of L/E analyses, we have shown that only L_nu/E_nu analysis can give the signature of maximum oscillations clearly, while the L_mu/E_mu analysis which are really done by Super-Kamiokande Collaboration cannot give the maximum oscillation at all. It is thus concluded that Super-Kamiokande type experiment cannot find the maximum oscillation from L/E analysis. Therefore, we would suggest Super-Kamiokande Collaboration to re-analyze the zenith angle distribution of the neutrino events which occur inside the detector carefully.

hep-ex↗

arXiv2010

On the Sensitivity of L/E Analysis of Super-Kamiokande Atmospheric Neutrino Data to Neutrino Oscillation Part~1

It is said that the finding of the maximum oscillation in neutrino oscillation by Super-Kamiokande is one of the major achievements of the SK. In present paper, we examine the assumption made by Super-Kamiokande Collaboration that the direction of the incident neutrino is approximately the same as that of the produced lepton, which is the cornerstone in their L/E analysis and we find this approximation does not hold even approximately. In the Part 2 of the subsequent paper, we apply the results from Figures 12, 13 and 14 to L/E analysis and conclude that one cannot obtain the maximum oscillation in L/E analysis which shows strongly the oscillation pattern from the neutrino oscillation.

hep-ex↗

arXiv2009

Hard thermal loops in static external fields

We study, in the imaginary-time formalism, the high temperature behavior of n-point thermal loops in static Yang-Mills and gravitational fields. We show that in this regime, any hard thermal loop gives the same leading contribution as the one obtained by evaluating the loop at zero external energies and momenta.

hep-th↗

arXiv2008

Comprehensive Analysis of Neutrinos in SK part II -- L/E Analysis for Single Ring Muon Events I --

By referring to the procedures developed in the preceeding paper, we re-analyze the L/E distribution for Fully Contained Events resulting from quasi-elatic scattering (QEL) obtained from the Super-Kamiokande Experiment in relation to their assumption that the direction of the incident neutrino coincide with that of the produced leptons. As the result of it, we clarify that they do not measure L_nu/E_nu distribution itself, but L_mu/E_nu distribution, which cannot show the maximum oscillation existed in the original L_nu/E_nu distribution, because L_nu could not be approximated by L_mu due to the backscattering effect and the azimuthal angle effect in QEL.

hep-ex↗

arXiv2008

Comprehensive Analysis of Neutrinos in SK part 3 -- L/E Analysis for Single Ring Muon Events II --

Following the L_nu/E_nu analysis in the preceding paper of the Fully Contained Muon Events resulting from the quasi-elastic scattering obtained from our numerical computer experiment. In the present paper, we carry out the analyses of L_nu/E_mu, L_mu/E_nu and L_mu/E_mu among four possible combinations of L and E. As the result of it, we show that we can not find the characteristis of maximum oscillation for neutrino oscillation among two of three, L_mu/E_mu and L_mu/E_nu. Only the L_nu/E_mu distribution can show something like maximum oscillation, however it cannot be detected owing to the neutral character of L_nu. It is concluded that the Super-Kamiokande Experiment could not have found the existence of the maximum oscillation for neutrino oscillation.

hep-ex↗