arXiv subjects

Hosik Lee

Publications and source records attributed to Hosik Lee.

6 recordsLinked to original sources

arXiv2026

A linear residual structure across galaxy rotation curves

Galaxy rotation curves exhibit systematic discrepancies between the observed dynamics and the gravitational contribution expected from baryonic matter. Identifying empirical regularities in these discrepancies may provide insight into the organization of galaxy dynamics. We investigate whether the residual component of galaxy rotation curves contains a common structure across galaxies spanning a broad range of masses and morphologies. Using rotation-curve data from the SPARC and LITTLE THINGS surveys, we analyze residual velocity-squared profiles after accounting for the baryonic contribution and allowing for uncertainties in the baryonic normalization. We find that the residuals are not randomly distributed but instead follow a common linear pattern across a diverse galaxy population. Population-level analysis shows that the data preferentially select this linear residual structure over alternative radial dependences. The residual component separates into a mass-coupled contribution and a second contribution that remains nearly independent of galaxy mass. These empirical trends are observed across both spiral and dwarf galaxy samples. The existence of a common residual structure across galaxies spanning a broad range of masses and morphologies provides a new empirical constraint on theories of galaxy dynamics.

astro-ph.GA↗

arXiv2026

Rotation-curve residuals reveal a suppressed acceleration branch in dwarf galaxies

Galaxy rotation curves exhibit systematic deviations from the Newtonian expectation inferred from visible matter alone. Existing phenomenological descriptions capture many aspects of these deviations, but a common residual structure across massive disks and dwarf irregular galaxies remains unclear. We investigate whether rotation-curve residuals organize into a simple empirical form across the SPARC and LITTLE THINGS samples. We analyze 175 SPARC galaxies and 22 LITTLE THINGS dwarf irregular galaxies in velocity-squared space after subtracting a leading Newtonian-like term. We fit a generalized residual family, v^2-A/r=B+Cr^{q+1}, and examine which radial scaling is selected by the data. The galaxy population systematically favors the limit $q\simeq0$, corresponding to an approximately linear residual relation, $v^2-A/r=B+Cr$. SPARC galaxies generally occupy a high-$B$ branch, whereas LITTLE THINGS dwarf galaxies show suppressed residual intercepts, including several systems consistent with $B=0$. For the SPARC sample, the high-$B$ branch approximately follows $B\propto M_{\rm bar}^{0.72}$. {Rotation-curve residuals are not featureless scatter beyond the leading Newtonian-like contribution, but instead show a simple population-dependent empirical organization across massive and dwarf galaxy systems.}

astro-ph.GA↗

arXiv2021

Adaptable Multi-Domain Language Model for Transformer ASR

We propose an adapter based multi-domain Transformer based language model (LM) for Transformer ASR. The model consists of a big size common LM and small size adapters. The model can perform multi-domain adaptation with only the small size adapters and its related layers. The proposed model can reuse the full fine-tuned LM which is fine-tuned using all layers of an original model. The proposed LM can be expanded to new domains by adding about 2% of parameters for a first domain and 13% parameters for after second domain. The proposed model is also effective in reducing the model maintenance cost because it is possible to omit the costly and time-consuming common LM pre-training process. Using proposed adapter based approach, we observed that a general LM with adapter can outperform a dedicated music domain LM in terms of word error rate (WER).

eess.AS↗

arXiv2019

Mechanism of CO-oxidation on Pd/CeO2(100): The unique surface-structure of CeO2(100) and the role of peroxide

Understanding the atomic mechanism of low-temperature CO oxidation on a heterogeneous catalyst is challenging. We performed density functional theory (DFT) calculations to identify the surface structure and reaction mechanism responsible for low-temperature CO oxidation on Pd/CeO2 (100) surfaces. DFT calculations reveal the formation of a unique zigzag chain structure by the oxygen and Ce atoms of the topmost surface of CeO2(100) with Pd atoms located between the zigzag chains. O2 adsorbed on such Pd atoms is stable in the presence of CO but plays a very important role in lowering the activation barrier for low-temperature CO oxidation by forming a square-planar PdO4 structure and facilitating further O2 adsorption. In-situ Raman spectroscopy studies confirm the adsorbed oxygen species to be peroxides. The calculated activation barrier for CO oxidation, based on the mechanism suggested by these unique structures and peroxides, is 31.2 kJ/mol, in excellent agreement with our experimental results.

physics.chem-ph↗

arXiv2018

Harnessing the giant out-of-plane Rashba effect and the nanoscale persistent spin helix via ferroelectricity in SnTe thin films

A non-vanishing electric field inside a non-centrosymmetric bulk crystal transforms into a momentum- dependent magnetic field, namely, a spin-orbit field (SOF). SOFs are of great use in spintronics because they enable spin manipulation via the electric field. At the same time, however, spintronic applications are severely limited by the SOF, as electrons traversing the SOF easily lose their spin information. Here, we propose that in-plane ferroelectricity in (001)-oriented SnTe thin films harness the Janus-faced SOF in a reconcilable way to enable electrical spin controllability and suppress spin dephasing. The in-plane ferroelectricity produces a unidirectional out-of-plane Rashba SOF that can host a long-lived helical spin mode known as a persistent spin helix (PSH). Through direct coupling between the inversion asymmetry and the SOF, the ferroelectric switching reverses the out-of-plane Rashba SOF, giving rise to a maximally field-tunable PSH. Furthermore, the giant out- of-plane Rashba SOF seen in the SnTe thin films is linked to the nano-sized PSH, potentially reducing spintronic device sizes to the nanoscale. We combine the two ferroelectric-coupled degrees of freedom, longitudinal charge and transverse PSH, to design intersectional electro-spintronic transistors governed by non-volatile ferroelectric switching within nanoscale lateral and atomic-thick vertical dimensions.

cond-mat.mes-hall↗

arXiv2016

High-throughput screening of metal-porphyrin-like graphenes for selective capture of carbon dioxide

Nano-materials, such as metal-organic frameworks, have been considered to capture CO$_2$. However, their application has been limited largely because they exhibit poor selectivity for flue gases and low capture capacity under low pressures. We perform a high-throughput screening for selective CO$_2$ capture from flue gases by using first principles thermodynamics. We find that elements with empty d orbitals selectively attract CO$_2$ from gaseous mixtures under low CO$_2$ pressures at 300 K and release it at ~450 K. CO$_2$ binding to elements involves hybridization of the metal d orbitals with the CO$_2$ $π$ orbitals and CO$_2$-transition metal complexes were observed in experiments. This result allows us to perform high-throughput screening to discover novel promising CO$_2$ capture materials with empty d orbitals and predict their capture performance under various conditions. Moreover, these findings provide physical insights into selective CO$_2$ capture and open a new path to explore CO$_2$ capture materials.

cond-mat.mtrl-sci↗