arXiv subjects

M. Nakano

Publications and source records attributed to M. Nakano.

17 recordsLinked to original sources

arXiv2024

Advanced LIGO detector performance in the fourth observing run

On May 24th, 2023, the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), joined by the Advanced Virgo and KAGRA detectors, began the fourth observing run for a two-year-long dedicated search for gravitational waves. The LIGO Hanford and Livingston detectors have achieved an unprecedented sensitivity to gravitational waves, with an angle-averaged median range to binary neutron star mergers of 152 Mpc and 160 Mpc, and duty cycles of 65.0% and 71.2%, respectively, with a coincident duty cycle of 52.6%. The maximum range achieved by the LIGO Hanford detector is 165 Mpc and the LIGO Livingston detector 177 Mpc, both achieved during the second part of the fourth observing run. For the fourth run, the quantum-limited sensitivity of the detectors was increased significantly due to the higher intracavity power from laser system upgrades and replacement of core optics, and from the addition of a 300 m filter cavity to provide the squeezed light with a frequency-dependent squeezing angle, part of the A+ upgrade program. Altogether, the A+ upgrades led to reduced detector-wide losses for the squeezed vacuum states of light which, alongside the filter cavity, enabled broadband quantum noise reduction of up to 5.2 dB at the Hanford observatory and 6.1 dB at the Livingston observatory. Improvements to sensors and actuators as well as significant controls commissioning increased low frequency sensitivity. This paper details these instrumental upgrades, analyzes the noise sources that limit detector sensitivity, and describes the commissioning challenges of the fourth observing run.

gr-qc↗

arXiv2021

Effects of lightning strokes on underground gravitational waves observatories

For ground-based gravitational wave (GW) detectors, lightning strokes in the atmosphere are sources of environmental noise. Some GW detectors are built or planned in underground facilities, and knowledge of how lightning strokes affect them is of interest. In this paper, the lightning detection system in KAGRA is introduced, and the properties of the magnetic field measured inside and outside the KAGRA tunnel are shown. One lightning-induced event in the GW channel of the KAGRA main interferometer is also shown. Finally, possible applications of lightning events for the GW experiments are discussed.

gr-qc↗

arXiv2019

Vibration isolation system with a compact damping system for power recycling mirrors of KAGRA

A vibration isolation system called Type-Bp system used for power recycling mirrors has been developed for KAGRA, the interferometric gravitational-wave observatory in Japan. A suspension of the Type-Bp system passively isolates an optic from seismic vibration using three main pendulum stages equipped with two vertical vibration isolation systems. A compact reaction mass around each of the main stages allows for achieving sufficient damping performance with a simple feedback as well as vibration isolation ratio. Three Type-Bp systems were installed in KAGRA, and were proved to satisfy the requirements on the damping performance, and also on estimated residual displacement of the optics.

physics.ins-det↗

arXiv2017

The status of KAGRA underground cryogenic gravitational wave telescope

KAGRA is a 3-km interferometric gravitational wave telescope located in the Kamioka mine in Japan. It is the first km-class gravitational wave telescope constructed underground to reduce seismic noise, and the first km-class telescope to use cryogenic cooling of test masses to reduce thermal noise. The construction of the infrastructure to house the interferometer in the tunnel, and the initial phase operation of the interferometer with a simple 3-km Michelson configuration have been completed. The first cryogenic operation is expected in 2018, and the observing runs with a full interferometer are expected in 2020s. The basic interferometer configuration and the current status of KAGRA are described.

gr-qc↗

arXiv2016

Direct observation of the lattice dynamics of transition metals using ultrafast electron diffraction

We report the lattice dynamics of transition metal thin films by using the ultrafast electron diffraction. We observe a suppression of the diffraction intensity in a few picosecond after the photoexcitation, which is directly interpreted as the lattice heating via the electron-phonon interaction. The electron-phonon coupling constants for Au, Cu and Mo are quantitatively evaluated by employing the two-temperature model, which are consistent with those obtained by optical pump-probe methods. The variation in the lattice dynamics of the transition metals are systematically explained by the strength of the electron-phonon coupling, arising from the elemental dependence of the electronic structure and atomic mass.

cond-mat.mtrl-sci↗

arXiv2012

Wide-Field Survey of Emission-line Stars in IC 1396

We have made an extensive survey of emission-line stars in the IC 1396 HII region to investigate the low-mass population of pre-main sequence (PMS) stars. A total of 639 H-alpha emission-line stars were detected in an area of 4.2 deg^2 and their i'-photometry was measured. Their spatial distribution exhibits several aggregates near the elephant trunk globule (Rim A) and bright-rimmed clouds at the edge of the HII region (Rim B and SFO 37, 38, 39, 41), and near HD 206267, which is the main exciting star of the HII region. Based on the extinction estimated from the near-infrared (NIR) color-color diagram, we have selected pre-main sequence star candidates associated with IC 1396. The age and mass were derived from the extinction corrected color-magnitude diagram and theoretical pre-main sequence tracks. Most of our PMS candidates have ages of < 3 Myr and masses of 0.2-0.6 Mo. Although it appears that only a few stars were formed in the last 1 Myr in the east region of the exciting star, the age difference among subregions in our surveyed area is not clear from the statistical test. Our results may suggest that massive stars were born after the continuous formation of low-mass stars for 10 Myr. The birth of the exciting star could be the late stage of slow but contiguous star formation in the natal molecular cloud. It may have triggered to form many low-mass stars at the dense inhomogeneity in and around the HII region by a radiation-driven implosion.

astro-ph.SR↗

arXiv2010

Small gap semiconducting organic charge-transfer interfaces

We investigated transport properties of organic heterointerfaces formed by single-crystals of two organic donor-acceptor molecules, tetramethyltetraselenafulvalene (TMTSF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Whereas the individual crystals have un-measurably high resistance, the interface exhibits a resistivity of few tens of MegaOhm with a temperature dependence characteristic of a small gap semiconductor. We analyze the transport properties based on a simple band-diagram that naturally accounts for our observations in terms of charge transfer between two crystals. Together with the recently discovered tetrathiafulvalene (TTF)-TCNQ interfaces, these results indicate that single-crystal organic heterostructures create new electronic systems with properties relevant to both fundamental and applied fields.

cond-mat.mtrl-sci↗

arXiv2006

Limitations of the Giant Spin Hamiltonian in Explaining Magnetization Tunneling in a Single-Molecule Magnet

EPR studies of a Ni4 single-molecule magnet yield the zero-field-splitting (zfs) parameters, D, B40 and B44, based on a giant spin approximation (GSA) with S = 4. Experiments on an isostructural Ni-doped Zn4 crystal establish the Ni(II) ion zfs parameters. The 4th-order zfs parameters in the GSA arise from the interplay between the Heisenberg interaction, Js1.s2, and the 2nd-order single-ion anisotropy, giving rise to mixing of higher lying states into the S = 4 state. Consequently, J directly influences the zfs in the ground state, enabling its direct determination by EPR.

cond-mat.mes-hall↗

arXiv2005

A ferromagnetic oxide semiconductor as spin injection electrode in magnetic tunnel junction

A magnetic tunnel junctions composed of room temperature ferromagnetic semiconductor rutile Ti1-xCoxO2-d and ferromagnetic metal Fe0.1Co0.9 separated by AlOx barrier showed positive tunneling magnetoresistance (TMR) with a ratio of ~11 % at 15 K, indicating that Ti1-xCoxO2-d can be used as a spin injection electrode. The TMR decreased with increasing temperature and vanished above 180 K. TMR action at high temperature is likely prohibited by the inelastic tunneling conduction due to the low quality of the amorphous barrier layer and/or the junction interface.

cond-mat.mtrl-sci↗

arXiv2003

Sliding Mechanism for Actin Myosin System

Based on the Stochastic Inclined Rods Model (SIRM) proposed by H. Matsuura and M. Nakano, we study the microscopic motion of actin myosin system including the motion of the G-actin. Our model is composed of an inclined spring (rod), a myosin head, a myosin filament and G-actins. We discuss the stochastic resonance between the myosin head and random noise. The results of calculation show that the model can convert the random motion to one directional motion, and the myosin head works as a resonator of random noise which absorbs the energy through the stochastic resonance. The intermolecular potential between the myosin head and G-actin and the inclined rod play a key role for the muscle's motion. The energy consumed by the motor is directly supplied from the surroundings (i.e., the thermal motions of water molecules).

physics.bio-ph↗

arXiv1999

Effective Vector Meson Masses in a Cutoff Field Theory

Based on quantum hadrodynamics with a finite cutoff, the effective masses of vector mesons(ω, ρ) in nuclear medium are calculated. We use a low-energy effective Lagrangian which is obtained by integrating high-energy quantum fluctuations. Although we use an artificial cutoff, the cutoff-dependence can be removed order by order. It is shown that there is a strong correlation between the effective ω-meson mass and the effective nucleon mass at the normal density. It is also found that the effective ρ-meson mass m_ρ^* decreases as density increases. The rate of the decrease becomes smaller at high density. As a result, at the normal density, the m^*_ρ/m_ρis 0.85 \sim 0.95.

nucl-th↗

arXiv1999

Dispersion relations in quantum hadrodynamics with a finite cutoff

The dispersion relations in the real and imaginary parts of the meson self-energies are studied to check the consistency of the "renormalization" in cutoff field theory. It is shown that the dispersion relations are preserved by the "renormalization"even if the finite cutoff and regulator are introduced in the calculation by hand.

nucl-th↗

arXiv1998

Antiproton Production in p+d Reaction at Subthreshold Energies

An enhancement of antiprotons produced in p+d reaction in comparison with ones in p+p elementary reaction is investigated. In the neighborhood of subthreshold energy the enhancement is caused by the difference of available energies for antiproton production. The cross section in p+d reaction, on the other hand, becomes just twice of the one in elementary p+p reaction at the incident energy far from the threshold energy when non-nucleonic components in deuteron target are not considered.

nucl-th↗

arXiv1996

Properties of nuclear matter in cut-off field theory and renormalization group methods

The properties of nuclear matter are studied in the cut-off field theory. It is found that, under the Hartree approximation, the small cut-off makes the equations of state hard, especially at higher densities. The theory is modified in the framework of the renormalization group methods with arbitrary cut-off $Λ^\prime$. It is found that the expansion in terms of the $σ$ meson field is more favorable than the naive expansion of the inverse of $Λ^\prime$, when we do not use very large $Λ^\prime$.

nucl-th↗

arXiv1995

Volume, Coulomb, and volume-symmetry coefficients of nucleus incompressibility in the relativistic mean field theory with the excluded volume effects

The relation among the volume coefficient $K$(=incompressibility of the nuclear matter), the Coulomb coefficient $K_c$, and the volume-symmetry coefficient $K_{vs}$ of the nucleus incompressibility are studied in the framework of the relativistic mean field theory with the excluded volume effects of the nucleons, under the assumption of the scaling model. It is found that $K= 300\pm 50$MeV is necessary to account for the empirical values of $K$, $K_c$, and $K_{vs}$, simultaneously, as is in the case of the point-like nucleons. The result is independent on the detail descriptions of the potential of the $σ$-meson self-interaction and is almost independent on the excluded volume of the nucleons.

nucl-th↗

arXiv1995

Compressional properties of nuclear matter in the relativistic mean field theory with the excluded volume effects

Compressional properties of nuclear matter are studied by using the mean field theory with the excluded volume effects of the nucleons. It is found that the excluded volume effects make it possible to fit the empirical data of the Coulomb coefficient $K_{c}$ of nucleus incompressibility, even if the volume coefficient $K$ is small($\sim 150$MeV). However, the symmetry properties favor $K=300\pm 50$MeV as in the cases of the mean field theory of point-like nucleons.

nucl-th↗

arXiv1995

Incompressibility of nuclear matter, and Coulomb and volume-symmetry coefficients of nucleus incompressibility in the relativistic mean field theory

The volume coefficient $K$(=incompressibility of the nuclear matter), the Coulomb coefficient $K_c$, and the volume-symmetry coefficient $K_{vs}$ of the nucleus incompressibility are studied in the framework of the relativistic mean field theory, with aid of the scaling model. It is found that $K= 300\pm 50$MeV is necessary to account for the empirical values of $K_v$, $K_c$, and $K_{vs}$, simultaneously. The result is independent on the detail descriptions of the potential of the $σ$-meson self-interaction and is almost independent of the strength of the $ω$-meson self-interaction.

nucl-th↗