arXiv subjects

Juyoung Kim

Publications and source records attributed to Juyoung Kim.

6 recordsLinked to original sources

arXiv2026

Patchy Reionization Delays Quenching in Isolated Ultra-faint Dwarf Galaxies

The spatially inhomogeneous nature of cosmic reionization is directly encoded in the quenching timescales of ultra-faint dwarf galaxies (UFDs). While most cosmological simulations employ a spatially uniform UV background (UVB) for computational efficiency, such homogeneous treatment may oversimplify the physical impact of reionization on UFDs, whose star formation histories (SFHs) are highly sensitive to local environments. Under these idealized, instantaneous UVB frameworks, star formation in UFDs is typically truncated abruptly at the onset of reionization, creating a tension with the extended and diverse SFHs observed in Local Group UFDs. To address this discrepancy, we perform high-resolution cosmological zoom-in simulations to contrast two distinct reionization models: a conventional uniform UVB and an on-the-fly radiative transfer (RT)-based patchy reionization model. We find that RT-based reionization delays star-formation quenching by ~440 Myr on average, a result consistent with recent observational constraints. However, this extended star formation does not necessarily leave a discernible imprint on the stellar metallicity distribution, indicating that the delay--while physically significant for gas dynamics--is still insufficient to drive substantial chemical enrichment. Our results emphasize the necessity of more realistic, patchy reionization modeling to explain the observed diversity of the Local Group population.

astro-ph.GA↗

arXiv2026

BPBO: Blindness-Preserving Brickwork Optimization by Certified Region Resynthesis

Universal blind quantum computation (UBQC) hides a client's computation by using a computation-independent BFK09 brickwork graph and encoding the computation in measurement angles, which limits the use of graph-changing optimizations. We study blindness-preserving brickwork optimization (BPBO): certified local resynthesis of BFK09-compatible brickwork patterns below the blinding layer. BPBO detects one-, two-, and three-wire regions; for each candidate region it either proves a semantic floor or supplies an executable witness, and it accepts a replacement only after its branch-frame, output-frame, and blinding behavior have been checked. The optimized outputs remain standard brickwork patterns and are evaluated with a logical qubit-recycled UBQC execution stack that runs arbitrary-length patterns using n x 2 active logical qubits. The layer evidence includes a one-wire H-count floor, a two-wire CNOT-cost floor, a three-wire parity-ledger floor, a clean three-cell CCZ witness whose optimality claim is scoped to the CNOT+T phase-gadget family, and an endpoint-target three-cell CCX/Toffoli application witness; the fixed middle-target CCX case is retained as a four-cell fallback. The security statement is a compatibility result: BPBO preserves UBQC blindness at the declared optimized dimensions and remains compatible with inherited verification guarantees under explicit test-round conditions, without introducing a new trap-soundness theorem. On Bell/CX, Grover-2, endpoint-Toffoli, and Grover-3 evaluation cases, BPBO demonstrates certified local reductions; in the largest case, Grover-3, the materialized pattern is reduced from 3 x 725 to 3 x 98 while preserving the expected marked-state statistics up to sampling noise.

quant-ph↗

arXiv2022

Crime and social environments: Differences between misdemeanors and felonies

Owing to the growing population density of urban areas, many people are being increasingly exposed to criminal activity. Increasing crime rates raise the risk of both physical and psychological injury to law-abiding citizens, creating anxiety. From the viewpoint of complex systems, crime prevention through data science can be a solution to such issues. However, previous studies have focused only on a single aspect of crime, ignoring the complex interplay between the various characteristics, which must be considered in an analysis to understand the dynamics underlying criminal activities. In this study, we examined 12 features that have been identified as correlates of crime rates using state-level statistics from the USA. We found that the correlates of misdemeanors and felonies differ. The number of misdemeanors is strongly associated with the police precinct, whereas felony rates are strongly correlated with gun possession and happiness. Our findings suggest that the countermeasures for misdemeanors should be treated differently from those for felonies.

cs.SI↗

arXiv2015

Design of Optical Metamaterial Mirror with Metallic Nanoparticles for Broadband Light Absorption in Graphene Optoelectronic Devices

A general metallic mirror (i.e., a flat metallic surface) has been a popular optical component that can contribute broadband light absorption to thin-film optoelectronic devices; nonetheless, such electric mirror with a reversal of reflection phase inevitably causes the problem of minimized electric field near at the mirror surface (maximized electric field at one quarter of wavelength from mirror). This problem becomes more elucidated, when the deep-subwavelength-scaled two-dimensional (2D) material (e.g., graphene and molybdenum disulfide) is implemented into optoelectronic device as an active channel layer. The purpose of this work was to conceive the idea for using a charge storage layer (spherical Au nanoparticles (AuNPs), embedded into dielectric matrix) of the floating-gate graphene photodetector as a magnetic mirror, which allows the device to harness the increase in broadband light absorption. In particular, we systematically examined whether the versatile assembly of spherical AuNP monolayer within a dielectric matrix (i.e., optical metamaterial mirror), which should be designed to be placed right below the graphene channel layer for floating-gate device, can be indeed treated as the effective magnetic mirror. In addition to being capable of the enhancement of broadband light absorption, versatile access to various structural motifs of AuNPs benefitting from recent advances in chemical synthesis promises compelling opportunities for sophisticated engineering of optical metamaterial mirror. High amenability of the AuNP assembly with the semiconductor-related procedures may make this strategy widely applicable to various thin film optoelectronic devices. Our study thereby illustrates advantages in advancing the design of mirror for rational engineering of light-matter interaction within deep-subwavelength-scaled optoelectronic devices.

physics.optics↗

arXiv2014

Efficient Confinement of Ultraviolet Light into the Self-Assembled, Dielectric Colloidal Monolayer on a Flat Aluminum Film

Here we propose the efficient confinement of ultraviolet (UV) light into the plasmonic-photonic crystal hybrid, which can be practically developed by the self-assembly of dielectric colloidal nanosphere monolayer onto a flat aluminum (Al) film. Using a numerical approach, we analyzed modal characteristics of each different resonant mode at the UV wavelengths including surface plasmon polariton (SPP) mode and waveguided (WG) mode and tuned these resonant modes from deep to far UV simply by adjusting the size of dielectric colloidal nanosphere. The calculated quality-factor (Q-factor) of such plasmonic-photonic crystal hybrid is at least one order of magnitude higher than that of the existing Al nanostructures (Al nanoparticles, nanodisks, nanovoids, or nanogratings) standing on the dielectric substrate. Also, we systematically studied how the amount of native oxide, which can be generated during the general process for the deposition of Al, can influence on both the SPP and WG modes of such plasmonic-photonic crystal hybrid in order to guide strategies for a realistic experimental fabrication and exploitation of relevant optical responses. We anticipate that the theoretical results in this paper enable a promising step in the enhancement of UV light interaction with the nanophotonic structure in a versatile, but highly efficient way.

physics.optics↗

arXiv2011

Observation of warping effects in the band and angular momentum structures of topological insulator Bi2Te3

We performed angle resolved photoemission (ARPES) experiments on Bi2Te3 with circularly polarized light. ARPES data show very strong circular dichroism, indicating existence of orbital angular momentum (OAM). Moreover, the alignment of OAM is found to have a strong binding energy dependence. Such energy dependence comes from a relatively strong band warping effect in Bi2Te3 compared to Bi2Se3. OAM close to Dirac point has an ideal chiral structure (sin ?) without out-of-plane component. Warping effect comes in as the binding energy decreases and circular dichroism along a constant energy contour can no longer be explained by a simple sin? function but requires a sin3? term. When the warping effect becomes even stronger near the Fermi energy, circular dichroism gains an additional sin6? term. Such behavior is found to be compatible with the theoretically predicted OAM structure.

cond-mat.mtrl-sci↗