arXiv subjects

Seonghyun Kim

Publications and source records attributed to Seonghyun Kim.

10 recordsLinked to original sources

arXiv2026

Phenomenological Criteria of Halo Nuclei in Ne Isotopes via Diffuseness and Helm-Model Approaches with Reaction Cross Sections

We present a systematic study of halo characteristics in the neutron-rich isotopes 28-32Ne within the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc). Microscopic density distributions are analyzed in coordinate space, momentum space, and reaction observables to establish a quantitative and locally defined criterion for halo identification in medium-mass nuclei. The DRHBc densities reveal a pronounced neutron extension in 31Ne. A phenomenological analysis based on deformed Woods-Saxon fits shows a clear isotopic anomaly in the surface diffuseness parameter, with a value of about 1.1 fm for 31Ne, significantly larger than those of neighboring isotopes. The anomalously large diffuseness is therefore treated as the primary phenomenological halo signature, whereas the reduced fitted radius parameter is used only as a supporting consequence of the chosen normalization and tail-sensitive fit. Helm-model form-factor analysis demonstrates that deformation contributes to geometric smearing but does not fully account for the extended spatial structure, as reflected in the enhanced difference between microscopic and folded rms radii. Glauber reaction cross section calculations further confirm a robust relative enhancement of the interaction cross section for 31Ne that persists across reasonable nucleon-nucleon interaction prescriptions. These complementary analyses consistently identify 31Ne as the most prominent halo candidate within the 28-32Ne isotopic chain, while 32Ne exhibits intermediate features and 29Ne shows no clear halo signature. The present framework provides a practical and quantitative approach for identifying halo phenomena in deformed, neutron-rich nuclei beyond the light-mass region.

nucl-th↗

arXiv2024

Unveiling dynamic bifurcation of Resch-patterned origami for self-adaptive impact mitigation structure

A long-standing challenge in impact mitigation is the development of versatile and omnifarious protective structures capable of encompassing a wide spectrum of scenarios, for example, ranging from low-speed pedestrian impacts to high-speed vehicle collisions. However, most existing impact mitigation strategies rely on fixed geometries or pre-tuned material properties targeting specific impact speed, lacking the ability to adapt in real time. Here, we draw inspiration from origami to design impact mitigation structures that exhibit multi-modal and self-adaptive behavior. We introduce a Resch-patterned origami structure that hosts two distinctive deformation modes: a monostable folding mode and a bistable unfolding mode featuring snap-through. Impact experiments reveal a speed-dependent dynamic bifurcation, wherein the structure autonomously switches between folding and unfolding in response to the applied impact velocity. This dynamic bifurcation, intrinsically distinct from kinematic or static origami bifurcations, enables real-time selection of deformation pathways that enhance energy dissipation across a broad range of impact conditions. We further demonstrate the scalability and practical relevance of this mechanism by fabricating tessellations in a bumper-like configuration and evaluating their performance using a pendulum-based mannequin impact test. Together, these results establish dynamic bifurcation in origami-based structures as an adaptive impact mitigation strategy. This approach enables scalable and programmable protective systems that autonomously select deformation modes in real time, with broad relevance to adaptive robotics, smart protective armor, and aerospace damping technologies.

cond-mat.mtrl-sci↗

arXiv2024

Nuclear mass table in deformed relativistic Hartree-Bogoliubov theory in continuum, II: Even-$Z$ nuclei

The mass table in the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the PC-PK1 density functional has been established for even-$Z$ nuclei with $8\le Z\le120$, extended from the previous work for even-even nuclei [Zhang $\it{et.~al.}$ (DRHBc Mass Table Collaboration), At. Data Nucl. Data Tables 144, 101488 (2022)]. The calculated binding energies, two-nucleon and one-neutron separation energies, root-mean-square (rms) radii of neutron, proton, matter, and charge distributions, quadrupole deformations, and neutron and proton Fermi surfaces are tabulated and compared with available experimental data. A total of 4829 even-$Z$ nuclei are predicted to be bound, with an rms deviation of 1.477 MeV from the 1244 mass data. Good agreement with the available experimental odd-even mass differences, $\alpha$ decay energies, and charge radii is also achieved. The description accuracy for nuclear masses and nucleon separation energies as well as the prediction for drip lines is compared with the results obtained from other relativistic and nonrelativistic density functional. The comparison shows that the DRHBc theory with PC-PK1 provides an excellent microscopic description for the masses of even-$Z$ nuclei. The systematics of the nucleon separation energies, odd-even mass differences, pairing energies, two-nucleon gaps, $\alpha$ decay energies, rms radii, quadrupole deformations, potential energy curves, neutron density distributions, and neutron mean-field potentials are discussed.

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arXiv2023

Deformed relativistic Hartree-Bogoliubov theory in continuum with a point-coupling functional. II. Examples of odd Nd isotopes

The aim of this work is to extend the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) based on the point-coupling density functionals to odd-$A$ and odd-odd nuclei and examine its applicability by taking odd-$A$ Nd isotopes as examples. In the DRHBc theory, the densities and potentials with axial deformation are expanded in terms of Legendre polynomials, and the relativistic Hartree-Bogoliubov equations are solved in a Dirac Woods-Saxon basis to include the continuum effects. For an odd-$A$ or odd-odd nucleus, the blocking effect of unpaired nucleon(s) is taken into account with the equal filling approximation. To determine its ground state, an automatic blocking procedure is adopted, in which the orbital with the lowest quasiparticle energy is blocked during the iteration. This procedure is justified by comparing with the results from the orbital-fixed blocking calculations, in which the blocked orbital near the Fermi surface is fixed during the iteration. The ground states for both light and heavy nuclei can be provided by the automatic blocking procedure as the orbital-fixed blocking procedure, but with considerably reduced computational cost. The numerical details for even-even nuclei are found to be valid for odd-$A$ and odd-odd nuclei as well. Taking Nd isotopes including both even-even and odd-$A$ ones as examples, the calculated ground-state properties with PC-PK1 are in good agreement with the available experimental data. This work paves the way to construct the DRHBc mass table including all even-even, odd-$A$ and odd-odd nuclei in the nuclear chart.

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arXiv2023

Effects of neutron-rich nuclei masses on symmetry energy

We explore the impact of neutron-rich nuclei masses on the symmetry energy properties using the mass table evaluated by the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) model. First, using the semi-empirical mass formula with the DRHBc mass table, we investigate the symmetry energy at saturation density $ρ_0$, denoted as $S_0$, and the ratio of surface to volume contributions to the symmetry energy, $κ$. As a result, we obtain $S_0=27.85\,{\rm MeV}$ ($κ=1.38$) for $a_{\rm sym}(A) =S_0 (1 - κA^{-1/3})$ (Type I) and $S_0=32.66\,{\rm MeV}$ ($κ=3.15$) for $a_{\rm sym}(A) = S_0 (1 + κA^{-1/3} )^{-1}$ (Type II), which are lower than those obtained using the AME2020 mass table, $S_0=28.54\,{\rm MeV}$ ($κ=1.29$) for Type I and $S_0=33.81\,{\rm MeV}$ ($κ=3.04$) for Type II. Second, we further investigate the effect of these changes in $a_{\rm sym}(A)$ on the density-dependent symmetry energy by employing the empirical model of $S(ρ) = C_k(ρ/ρ_0)^{2/3} + C_1(ρ/ρ_0) + C_2(ρ/ρ_0)^γ$ and universal relation of $a_{\rm sym}(A=208) = S(ρ=0.1\,{\rm fm}^{-3})$. Compared to the experimental constraints, we find that $S_0$ and slope parameter $L$, determined by the DRHBc mass table with Type II, are more suitable to explain the constraints by heavy ion collisions and isobaric analog states than AME2020. We also discuss the neutron skin thickness derived from the $L$, comparing it with experimental measurements.

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arXiv2023

Odd-even shape staggering and kink structure of charge radii of Hg isotopes by the deformed relativistic Hartree-Bogoliubov theory in continuum

We examined the shape staggering of relative charge radii in $^{180 - 186}$Hg isotopes, which was first measured in 1977 and recently confirmed using advanced spectroscopy techniques. To understand the nuclear structure underlying this phenomenon, we employed the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc). Our analysis revealed that the shape staggering can be attributed to nuclear shape transition in the Hg isotopes. Specifically, we demonstrated that prolate shapes of $^{181,183,185}$Hg lead to an increase in the charge radii compared to oblate shapes of $^{180,182,184,186}$Hg isotopes. We explained the nuclear shape staggering in terms of the evolution of occupation probability (OP) of $\nu 1 i_{13/2}$, $\nu 1 h_{9/2}$, $\pi 1 h_{9/2}$, and $\pi 3 s_{1/2}$ states. Additionally, we clarified the kink structure of the charge radii in the Hg isotopes near $N = 126$ magic shell does not come from the change of the OP of $\pi 1 h_{9/2}$ state, but mainly by the increase of the OPs of $\nu 1 i_{11/2}$ and $\nu 2 g_{9/2}$ states.

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arXiv2022

Nuclear mass table in deformed relativistic Hartree-Bogoliubov theory in continuum: I. even-even nuclei

Ground-state properties of even-even nuclei with $8\le Z\le120$ from the proton drip line to the neutron drip line have been investigated using the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the density functional PC-PK1. With the effects of deformation and continuum included simultaneously, 2583 even-even nuclei are predicted to be bound. The calculated binding energies, two-nucleon separation energies, root-mean-square (rms) radii of neutron, proton, matter, and charge distributions, quadrupole deformations, and neutron and proton Fermi surfaces are tabulated and compared with available experimental data. The rms deviation from the 637 mass data is 1.518 MeV, providing one of the best microscopic descriptions for nuclear masses. The drip lines obtained from DRHBc calculations are compared with other calculations, including the spherical relativistic continuum Hartree-Bogoliubov (RCHB) and triaxial relativistic Hartree-Bogoliubov (TRHB) calculations with PC-PK1. The deformation and continuum effects on the limits of the nuclear landscape are discussed. Possible peninsulas consisting of bound nuclei beyond the two-neutron drip line are predicted. The systematics of the two-nucleon separation energies, two-nucleon gaps, rms radii, quadrupole deformations, potential energy curves, neutron densities, neutron mean-field potentials, and pairing energies in the DRHBc calculations are also discussed. In addition, the $α$ decay energies extracted are in good agreement with available data.

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arXiv2021

Shape coexistence and neutron skin thickness of Pb isotopes by the deformed relativistic Hartree-Bogoliubov theory in continuum

We investigate ground states properties of Pb isotopes located between neutron and proton drip-lines estimated by two-neutron (two-proton) separation energies and Fermi energies within the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc). First, we report some candidates of nuclear shape coexistence in the isotope chain. They are accessed by calculating total energy as a function of the deformation parameter $β_2$, and for the coexistence candidates we take a couple of the deformation region bringing about minima of the energy within energy difference $ΔE < $ 1 MeV. Second, the Pb isotopes near neutron drip-lines are also investigated and compared to the results by other nuclear mass models. We find out eleven neutron emitters, $^{278 - 296, 300}$Pb, giving rise to the Pb peninsular near the neutron drip-line. Finally, by exploiting the neutron and proton density we deduce the neutron skin thickness (NST) of the Pb isotopes and compare to the available experimental data. The recent data regarding the shape coexistence of $^{184,186,188}$Pb and the NST of $^{208}$Pb are shown to be well matched with the present results.

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arXiv2021

KLUE: Korean Language Understanding Evaluation

We introduce Korean Language Understanding Evaluation (KLUE) benchmark. KLUE is a collection of 8 Korean natural language understanding (NLU) tasks, including Topic Classification, SemanticTextual Similarity, Natural Language Inference, Named Entity Recognition, Relation Extraction, Dependency Parsing, Machine Reading Comprehension, and Dialogue State Tracking. We build all of the tasks from scratch from diverse source corpora while respecting copyrights, to ensure accessibility for anyone without any restrictions. With ethical considerations in mind, we carefully design annotation protocols. Along with the benchmark tasks and data, we provide suitable evaluation metrics and fine-tuning recipes for pretrained language models for each task. We furthermore release the pretrained language models (PLM), KLUE-BERT and KLUE-RoBERTa, to help reproducing baseline models on KLUE and thereby facilitate future research. We make a few interesting observations from the preliminary experiments using the proposed KLUE benchmark suite, already demonstrating the usefulness of this new benchmark suite. First, we find KLUE-RoBERTa-large outperforms other baselines, including multilingual PLMs and existing open-source Korean PLMs. Second, we see minimal degradation in performance even when we replace personally identifiable information from the pretraining corpus, suggesting that privacy and NLU capability are not at odds with each other. Lastly, we find that using BPE tokenization in combination with morpheme-level pre-tokenization is effective in tasks involving morpheme-level tagging, detection and generation. In addition to accelerating Korean NLP research, our comprehensive documentation on creating KLUE will facilitate creating similar resources for other languages in the future. KLUE is available at https://klue-benchmark.com.

cs.CL↗

arXiv2020

Deformed relativistic Hartree-Bogoliubov theory in continuum with point coupling functional: examples of even-even Nd isotopes

The aim of this work is to develop the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) theory based on the point-coupling density functionals and extend it to provide a unified description for all even-even nuclei in the nuclear chart by overcoming all possible challenges. The nuclear superfluidity is considered via Bogoliubov transformation. Densities and potentials are expanded in terms of Legendre polynomials to include the axial deformation degrees of freedom. Sophisticated relativistic Hartree-Bogoliubov equations in coordinate space are solved in the DiracWoods-Saxon basis to consider the continuum effects. Numerical checks are performed from light nuclei to heavy nuclei. The techniques to construct the DRHBc mass table for even-even nuclei are explored. The DRHBc theory is extended to study heavier nuclei beyond magnesium isotopes. Taking Nd isotopes as examples, the experimental binding energies, two-neutron separation energies, quadrupole deformations, and charge radii are reproduced rather well. The deformation and continuum play essential roles in the description of nuclear masses and prediction of drip-line nuclei. By examining the single-particle levels in the canonical basis and their contributions to the total density, the thickness of the neutron skin, the particles number in continuum, and the Coulomb barrier, the exotic structures including the neutron skin and the proton radioactivity are predicted.

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