arXiv subjects

Akira Sato

Publications and source records attributed to Akira Sato.

11 recordsLinked to original sources

arXiv2026

Observing the Relationship between QoS Unpredictability, Prediction Error, and User Activity in a Remote Desktop Service

With the increasing need for remote work, especially since the COVID-19 era, Remote Desktop Services (RDS) have become widely used. Because interactive RDS usage depends heavily on communication quality, some studies have investigated the relationship between QoS metrics and user activity in RDS. However, these works have een conducted in experimental environments, where the number of samples is limited and may not reflect real-world usage. Consequently, the relationship between temporal fluctuations in QoS and user activity remains underexplored. This paper investigates the relationship between QoS statistics and user activity using real-world usage logs of an RDS, Thin-Telework System. We analyze time-series data of round-trip time (RTT), the number of sent packets, and the number of received bytes per user. Notably, we find that not only the average RTT but also its temporal fluctuation (e.g., standard deviation over time) and its instantaneous deviation from the mean are significantly associated with user activity. From the users' perspective, these features correspond to QoS unpredictability and the prediction error, respectively, and may provide insights into psychological mechanisms underlying user behavior.

cs.NI↗

arXiv2025

Lepton flavor violating decay of true muonium: $\boldsymbol{(μ^+ μ^-) \to μ^\pm e^\mp}$

We propose a new channel for probing charged lepton flavor violation (CLFV): the decay of true muonium into a lepton pair of different flavor, $(μ^+ μ^-) \to μ^\pm e^\mp$. This purely leptonic two-body decay provides a clean experimental signature in the form of energetic, oppositely charged leptons. It is sensitive not only to photonic dipole interactions but also to four-fermion contact interactions, and is free from hadronic uncertainties in theoretical predictions. We evaluate the branching ratios induced by scalar-, vector-, and dipole-type CLFV operators. Our results show that the branching ratio can reach up to $\mathcal{O}(10^{-20})$ within current experimental bounds. This decay mode may be discovered as an early-stage physics opportunity of the muon collider program by utilizing the large number of muons produced at its front end.

hep-ph↗

arXiv2025

A 55-nm SRAM Chip Scanning Errors Every 125 ns for Event-Wise Soft Error Measurement

We developed a 55 nm CMOS SRAM chip that scans all data every 125 ns and outputs timestamped soft error data via an SPI interface through a FIFO. The proposed system, consisting of the developed chip and particle detectors, enables event-wise soft error measurement and precise identification of SBUs and MCUs, thus resolving misclassifications such as Pseudo- and Distant MCUs that conventional methods cannot distinguish. An 80-MeV proton irradiation experiment at RARiS, Tohoku University verified the system operation. Timestamps between the SRAM chip and the particle detectors were successfully synchronized, accounting for PLL disturbances caused by radiation. Event building was achieved by determining a reset offset with sub-ns resolution, and spatial synchronization was maintained within several tens of micrometers.

physics.ins-det↗

arXiv2022

A Measurement of Proton, Deuteron, Triton and Alpha Particle Emission after Nuclear Muon Capture on Al, Si and Ti with the AlCap Experiment

Heavy charged particles after nuclear muon capture are an important nuclear physics background to the muon-to-electron conversion experiments Mu2e and COMET, which will search for charged lepton flavor violation at an unprecedented level of sensitivity. The AlCap experiment measured the yield and energy spectra of protons, deuterons, tritons, and alpha particles emitted after the nuclear capture of muons stopped in Al, Si, and Ti in the low energy range relevant for the muon-to-electron conversion experiments. Individual charged particle types were identified in layered silicon detector packages and their initial energy distributions were unfolded from the observed energy spectra. Detailed information on yields and energy spectra for all observed nuclei are presented in the paper.

physics.ins-det↗

arXiv2019

Radiation hardness study for the COMET Phase-I electronics

Radiation damage on front-end readout and trigger electronics is an important issue in the COMET Phase-I experiment at J-PARC, which plans to search for the neutrinoless transition of a muon to an electron. To produce an intense muon beam, a high-power proton beam impinges on a graphite target, resulting in a high-radiation environment. We require radiation tolerance to a total dose of $1.0\,\mathrm{kGy}$ and $1\,\mathrm{MeV}$ equivalent neutron fluence of $1.0\times10^{12}\,\mathrm{n_{eq}\,cm^{-2}}$ including a safety factor of 5 over the duration of the physics measurement. The use of commercially-available electronics components which have high radiation tolerance, if such components can be secured, is desirable in such an environment. The radiation hardness of commercial electronic components has been evaluated in gamma-ray and neutron irradiation tests. As results of these tests, voltage regulators, ADCs, DACs, and several other components were found to have enough tolerance to both gamma-ray and neutron irradiation at the level we require.

physics.ins-det↗

arXiv2015

A ferroelectric-like structural transition in a metal

Metals cannot exhibit ferroelectricity because static internal electric fields are screened by conduction electrons, but in 1965, Anderson and Blount predicted the possibility of a ferroelectric metal, in which a ferroelectric-like structural transition occurs in the metallic state. Up to now, no clear example of such a material has been identified. Here we report on a centrosymmetric (R-3c) to non-centrosymmetric (R3c) transition in metallic LiOsO3 that is structurally equivalent to the ferroelectric transition of LiNbO3. The transition involves a continuous shift in the mean position of Li+ ions on cooling below 140K. Its discovery realizes the scenario described by Anderson and Blount, and establishes a new class of materials whose properties may differ from those of normal metals.

cond-mat.mtrl-sci↗

arXiv2013

Fermi surface in KFe2As2 determined via de Haas-van Alphen oscillation measurements

We have completely determined the Fermi surface in KFe$_2$As$_2$ via de Haas-van Alphen (dHvA) measurements. Fundamental frequencies $ε$, $α$, $ζ$, and $β$ are observed in KFe$_2$As$_2$. The first one is attributed to a hole cylinder near the X point of the Brillouin zone, while the others to hole cylinders at the $Γ$ point. We also observe magnetic breakdown frequencies between $α$ and $ζ$ and suggest a plausible explanation for them. The experimental frequencies show deviations from frequencies predicted by band structure calculations. Large effective masses up to 19 $m_e$ for $B \parallel c$ have been found, $m_e$ being the free electron mass. The carrier number and Sommerfeld coefficient of the specific heat are estimated to be 1.01 -- 1.03 holes per formula unit and 82 -- 94 mJmol$^{-1}$K$^{-2}$, respectively, which are consistent with the chemical stoichiometry and a direct measure of 93 mJmol$^{-1}$K$^{-2}$ [H. Fukazawa \textit{et al}., J. Phys. Soc. Jpn. \textbf{80SA}, SA118 (2011)]. The Sommerfeld coefficient is about 9 times enhanced over a band value, suggesting the importance of low-energy spin and/or orbital fluctuations, and places KFe$_2$As$_2$ among strongly correlated metals. We have also performed dHvA measurements on Ba$_{0.07}$K$_{0.93}$Fe$_2$As$_2$ and have observed the $α$ and $β$ frequencies.

cond-mat.supr-con↗

arXiv2010

Comment on "Quantum Criticality and Nodal Superconductivity in the FeAs-Based Superconductor KFe$_2$As$_2$"

In a recent Letter [J. K. Dong et al., Phys. Rev. Lett. 104, 087005 (2010)], Dong \textit{et al}. have observed a $T^{1.5}$ dependence of resistivity $ρ$ in KFe$_2$As$_2$ at the upper critical field $B_{c2}$ = 5 T parallel to the c axis and have suggested the existence of a field-induced quantum critical point (QCP) at $B_{c2}$. In this comment, we argue that observation of a $T^{1.5}$ dependence of $ρ$ in a sample showing broad resistive transitions does not constitute evidence for a QCP and that recent dHvA results do not support the proposed QCP.

cond-mat.supr-con↗

arXiv2010

Fermi surface and mass enhancement in KFe$_2$As$_2$ from de Haas-van Alphen effect measurements

We report on a band structure calculation and de Haas-van Alphen measurements of KFe$_2$As$_2$. Three cylindrical Fermi surfaces are found. Effective masses of electrons range from 6 to 18$m_e$, $m_e$ being the free electron mass. Remarkable discrepancies between the calculated and observed Fermi surface areas and the large mass enhancement ($\gtrsim 3$) highlight the importance of electronic correlations in determining the electronic structures of iron pnicitide superconductors.

cond-mat.supr-con↗

arXiv2005

Intense Muon Physics Working Group Summary

The intense muon beams which will be available at a neutrino factory provide a unique opportunity for searching for physics beyond the standard model, both in lepton flavor violation and in the search for a permanent electric dipole moment for the muon. Other experiments which can use intense muon beams will also be possible.

hep-ex↗

arXiv2005

ZZ brane amplitudes from matrix models

We study instanton contribution to the partition function of the one matrix model in the k-th multicritical region, which corresponds to the (2,2k-1) minimal model coupled to Liouville theory. The instantons in the one matrix model are given by local extrema of the effective potential for a matrix eigenvalue and identified with the ZZ branes in Liouville theory. We show that the 2-instanton contribution in the partition function is universal as well as the 1-instanton contribution and that the connected part of the 2-instanton contribution reproduces the annulus amplitudes between the ZZ branes in Liouville theory. Our result serves as another nontrivial check on the correspondence between the instantons in the one matrix model and the ZZ branes in Liouville theory, and also suggests that the expansion of the partition function in terms of the instanton numbers are universal and gives systematically ZZ brane amplitudes in Liouville theory.

hep-th↗