arXiv subjects

J. Yi

Publications and source records attributed to J. Yi.

9 recordsLinked to original sources

arXiv2026

Narrow spectral artifact investigation and mitigation in LIGO data from the fourth LIGO-Virgo-KAGRA observing run

We present efforts to identify, characterize, and mitigate narrow spectral artifacts in LIGO detector data during the fourth LIGO-Virgo-KAGRA observing run. Narrow spectral artifacts in gravitational-wave detectors are non-astrophysical noise sources that can degrade searches for narrowband persistent gravitational waves. Identifying and, where possible, mitigating these noise sources is one of the core efforts of the LIGO Detector Characterization group. Key software tools have been updated and new tools deployed for the fourth LIGO-Virgo-KAGRA observing run to facilitate investigations and data monitoring. We discuss these tool upgrades, and present several identified narrowband artifacts that have been successfully investigated and mitigated in LIGO data. Regardless of whether artifacts are mitigated or not, narrowband persistent gravitational-wave searches require information on which frequency bands contain non-astrophysical artifacts. Minimizing the number of bands containing non-astrophysical artifacts is essential to maximize the potential for discovery of a new class of gravitational-wave signals.

astro-ph.IM↗

arXiv2025

Real-Time AI-Driven Milling Digital Twin Towards Extreme Low-Latency

Digital twin (DT) enables smart manufacturing by leveraging real-time data, AI models, and intelligent control systems. This paper presents a state-of-the-art analysis on the emerging field of DTs in the context of milling. The critical aspects of DT are explored through the lens of virtual models of physical milling, data flow from physical milling to virtual model, and feedback from virtual model to physical milling. Live data streaming protocols and virtual modeling methods are highlighted. A case study showcases the transformative capability of a real-time machine learning-driven live DT of tool-work contact in a milling process. Future research directions are outlined to achieve the goals of Industry 4.0 and beyond.

eess.SY↗

arXiv2024

Investigation of low band gap silicon alloy thin film solar cell for improving short and long wavelength response

Numerical simulation of a solar cell can provide various information that can be useful to maximize its power conversion efficiency (PCE). In that respect we carried out a set of numerical simulation using AFORS-HET simulation program. Separately, in order to get a better understanding, the optical absorption in individual layers devices were analyzed. Current-voltage characteristic curve of a reference cell (Cell-A) was used as the starting device. The PCE of the reference device was $8.85\%$ with short circuit current density $J_{sc}$ of 15.43 mA/cm$^{2}$ and fill factor (FF) of $68.3\%$. However, it was noticed that the reference cell had high parasitic optical absorption at the window layer and the device structure was also not optimized. After suitable optimization the PCE of this device (Cell-B2) improves to $11.59\%$ ($J_{sc}$ and FF of 13.0 mA/cm$^{2}$ and $87\%$ respectively). The results show that the effective optical absorption in the active layer can be improved significantly by optimizing the device structure. The short wavelength response can be improved by reducing the parasitic optical absorption by the doped window layer, while its long wavelength response improves by raising effective absorption length of the active layer. Furthermore, its optimum thickness, for the highest possible PCE, is found to be dependent upon the material properties, more importantly on its defect density.

physics.optics↗

arXiv2023

Performance of the electromagnetic and hadronic prototype segments of the ALICE Forward Calorimeter

We present the performance of a full-length prototype of the ALICE Forward Calorimeter (FoCal). The detector is composed of a silicon-tungsten electromagnetic sampling calorimeter with longitudinal and transverse segmentation (FoCal-E) of about 20$X_0$ and a hadronic copper-scintillating-fiber calorimeter (FoCal-H) of about 5$\lambda_{\rm int}$. The data were taken between 2021 and 2023 at the CERN PS and SPS beam lines with hadron (electron) beams up to energies of 350 (300) GeV. Regarding FoCal-E, we report a comprehensive analysis of its response to minimum ionizing particles across all pad layers. The longitudinal shower profile of electromagnetic showers is measured with a layer-wise segmentation of 1$X_0$. As a projection to the performance of the final detector in electromagnetic showers, we demonstrate linearity in the full energy range, and show that the energy resolution fulfills the requirements for the physics needs. Additionally, the performance to separate two-showers events was studied by quantifying the transverse shower width. Regarding FoCal-H, we report a detailed analysis of the response to hadron beams between 60 and 350 GeV. The results are compared to simulations obtained with a Geant4 model of the test beam setup, which in particular for FoCal-E are in good agreement with the data. The energy resolution of FoCal-E was found to be lower than 3% at energies larger than 100 GeV. The response of FoCal-H to hadron beams was found to be linear, albeit with a significant intercept that is about factor 2 larger than in simulations. Its resolution, which is non-Gaussian and generally larger than in simulations, was quantified using the FWHM, and decreases from about 16% at 100 GeV to about 11% at 350 GeV. The discrepancy to simulations, which is particularly evident at low hadron energies, needs to be further investigated.

physics.ins-det↗

arXiv2013

A Very High Momentum Particle Identification Detector

The construction of a new detector is proposed to extend the capabilities of ALICE in the high transverse momentum (pT) region. This Very High Momentum Particle Identification Detector (VHMPID) performs charged hadron identification on a track-by-track basis in the 5 GeV/c < p < 25 GeV/c momentum range and provides ALICE with new opportunities to study parton-medium interactions at LHC energies. The VHMPID covers up to 30% of the ALICE central barrel and presents sufficient acceptance for triggered- and tagged-jet studies, allowing for the first time identified charged hadron measurements in jets. This Letter of Intent summarizes the physics motivations for such a detector as well as its layout and integration into ALICE.

nucl-ex↗

arXiv2011

VHMPID: a new detector for the ALICE experiment at LHC

This article presents the basic idea of VHMPID, an upgrade detector for the ALICE experiment at LHC, CERN. The main goal of this detector is to extend the particle identification capabilities of ALICE to give more insight into the evolution of the hot and dense matter created in Pb-Pb collisions. Starting from the physics motivations and working principles the challenges and current status of development is detailed.

hep-ex↗

arXiv2002

A pure-carbon ring transistor: The role of topology and structure

We report results on the rectification properties of a carbon nanotube (CNT) ring transistor, contacted by CNT leads, whose novel features have been recently communicated by Watanabe et al. [Appl. Phys. Lett. 78, 2928 (2001)]. This paper contains results which are validated by the experimental observations. Moreover, we report on additional features of the transmission of this ring device which are associated with the possibility of breaking the lead inversion symmetry. The linear conductance displays a "chessboard"-like behavior alternated with anomalous zero-lines which should be directly observable in experiments. We are also able to discriminate in our results structural properties (quasi-onedimensional confinement) from pure topological effects (ring configuration), thus helping to gain physical intuition on the rich ring phenomenology.

cond-mat.mes-hall↗

arXiv1997

Quantum Phase Transitions in Josephson Junction Chains

We investigate the quantum phase transition in a one-dimensional chain of ultra-small superconducting grains, considering both the self- and junction capacitances. At zero temperature, the system is transformed into a two-dimensional system of classical vortices, where the junction capacitance introduces anisotropy in the interaction between vortices. This leads to the superconductor-insulator transition of the Berezinskii-Kosterlitz-Thouless type, as the ratios of the Josephson coupling energy to the charging energies are varied. It is found that the junction capacitance plays a role similar to that of dissipation and tends to suppress quantum fluctuations; nevertheless the insulator region survives even for arbitrarily large values of the junction capacitance.

cond-mat.mes-hall↗

arXiv1997

Experimental Study of Bifurcations in A Parametrically Forced Pendulum

An experimental study of bifurcations associated with stability of stationary points (SP's) in a parametrically forced magnetic pendulum and a comparison of its results with numerical results are presented. The critical values for which the SP's lose or gain their stability are experimentally measured by varying the two parameters $Ω$ (the normalized natural frequency) and $A$ (the normalized driving amplitude). It is observed that, when the amplitude $A$ exceeds a critical value, the normal SP with $θ=0$ ($θ$ is the angle between the permanent magnet and the magnetic field) becomes unstable either by a period-doubling bifurcation or by a symmetry-breaking pitchfork bifurcation, depending on the values of $Ω$. However, in contrast with the normal SP the inverted SP with $θ=π$ is observed to become stable as $A$ is increased above a critical value by a pitchfork bifurcation, but it also destabilizes for a higher critical value of $A$ by a period-doubling bifurcation. All of these experimental results agree well with numerical results obtained using the Floquet theory.

chao-dyn↗