애초에 하늘을 날던 물고기_강혜성/한국문연

강혜성 시와세계 2023 시와세계 Vol.- No.82

DIFFUSIVE SHOCK ACCELERATION BY MULTIPLE WEAK SHOCKS

강혜성 한국천문학회 2021 Journal of The Korean Astronomical Society Vol.54 No.3

The intracluster medium (ICM) is expected to experience on average about three passages of weak shocks with low sonic Mach numbers, M≤3, during the formation of galaxy clusters. Both protons and electrons could be accelerated to become high energy cosmic rays (CRs) at such ICM shocks via diffusive shock acceleration (DSA). We examine the effects of DSA by multiple shocks on the spectrum of accelerated CRs by including in situ injection/acceleration at each shock, followed by repeated re-acceleration at successive shocks in the test-particle regime. For simplicity, the accelerated particles are assumed to undergo adiabatic decompression without energy loss and escape from the system, before they encounter subsequent shocks. We show that in general the CR spectrum is flattened by multiple shock passages, compared to a single episode of DSA, and that the acceleration efficiency increases with successive shock passages. However, the decompression due to the expansion of shocks into the cluster outskirts may reduce the amplification and flattening of the CR spectrum by multiple shock passages. The final CR spectrum behind the last shock is determined by the accumulated effects of repeated re-acceleration by all previous shocks, but it is relatively insensitive to the ordering of the shock Mach numbers. Thus multiple passages of shocks may cause the slope of the CR spectrum to deviate from the canonical DSA power-law slope of the current shock.

의왕시내손도서관 글마루 리모델링

강혜성 한국실내디자인학회 2020 한국실내디자인학회 학술대회논문집 Vol.22 No.1

아동기 역경 경험과 아동의 미디어기기 중독과의 연관성

강혜성,기쁘다 한국건강심리학회 2023 한국심리학회지 건강 Vol.28 No.5

본 연구는 아동기 역경 경험(Adverse Childhood Experiences [ACEs])이 아동의 미디어기기 중독에 미치는 영향력을 검증하고자 하였다. 이를 위해 한국육아정책연구소의 한국아동패널 2008년(1차)부터 2020년(13차) 종단 자료를 활용하여 아동이 생애 초기부터 경험한 다양한 역경 경험(가정폭력 노출, 신체적 학대, 정서적 학대, 또래폭력 피해, 부모의 사망·이혼·별거)이 초등학교 6학년(13차) 때의 미디어기기 중독에 미치는 영향력을 로지스틱 분석을 통해 분석하였으며, 그 연관성이 성별에 따라 어떻게 달라지는지 검토하였다. 분석 결과 아동기 역경 경험이 많을수록 미디어기기 중독을 보일 승산이 높았으며, 정서적 학대, 신체적 학대, 또래폭력 피해가 미디어기기 중독에 영향을 미치는 것으로 나타났다. 성별에 따라 나누었을 때 연구결과는 상이하게 나타났는데, 남아의 경우 신체적 학대와 정서적 학대가 미디어기기 중독에 유의한 영향을 미친 반면, 여아의 경우 정서적 학대만 미디어기기 중독에 유의미한 영향을 미쳤다. 아동기 역경 경험의 누적효과의 경우 남아와 여아 모두 누적 역경 경험이 많을수록 미디어기기 중독을 보일 확률이 높았으며, 여아의 경우 승산비가 더 큰 것으로 나타났다. 이를 토대로 미디어기기 중독 이해 및 예방을 위한 실천적, 정책적 방안들을 논의하였고, 향후 연구 과제를 제안하였다. This study investigated the influence of adverse childhood experiences (ACEs) on media device addiction using longitudinal data from the Panel Study of Korean Children (PSKC), from waves 1 to 13. The ACEs predictor variables included family violence, physical abuse, emotional abuse, experiences of being bullied, parents’ death, divorce, and separation. Frequency and logistic regression analyses were conducted. The results showed that the cumulative ACEs indicated a higher odds ratio on media device addiction. Physical abuse, emotional abuse, and experiences of being bullied were statistically significant predictors of media device addiction. The factors influencing media device addiction were different by gender. Men had a higher risk of media device addiction when they experienced physical abuse or emotional abuse. For women, only emotional abuse increased the likelihood of media device addiction. The influence of ACEs on media device addiction was discussed with an emphasis on prevention and intervention strategies.

Re-Acceleration of Fossil Electrons by Shocks Encountering Hot Bubbles in the Outskirts of Galaxy Clusters

강혜성 한국천문학회 2018 Journal of The Korean Astronomical Society Vol.51 No.6

Galaxy clusters are known to host many active galaxies (AGNs) with radio jets, which could expand to form radio bubbles with relativistic electrons in the intracluster medium (ICM). It has been suggested that fossil relativistic electrons contained in remnant bubbles from extinct radio galaxies can be re-accelerated to radio-emitting energies by merger-driven shocks via diffusive shock acceleration (DSA), leading to the birth of radio relics detected in clusters. In this study we assume that such bubble consist primarily of thermal gas entrained from the surrounding medium and dynamically-insignificant amounts of relativistic electrons. We also consider several realistic models for magnetic fields in the cluster outskirts, including the ICM field that scales with the gas density as $B_{\rm ICM}\propto n_{\rm ICM}^{0.5}$. Then we perform time-dependent DSA simulations of a spherical shock that runs into a lower-density but higher-temperature bubble with the ratio $n_{\rm b}/n_{\rm ICM} \approx T_{\rm ICM}/T_{\rm b}\approx 0.5$. We find that inside the bubble the shock speed increases by about 20 \%, but the Mach number decreases by about 15\% in the case under consideration. In this re-acceleration model, the observed properties of a radio relic such as radio flux, spectral index, and integrated spectrum would be governed mainly by the presence of seed relativistic electrons and the magnetic field profile as well as shock dynamics. Thus it is crucial to understand how fossil electrons are deposited by AGNs in the ICM and how the downstream magnetic field evolves behind the shock in detailed modeling of radio relics.

10mm 이하의 대장 폴립에서 올가미 크기에 따른 저온올가미 절제술의 예후 분석

강혜성,윤홍진,천재영,이유진,권태근,정윤호 대한내과학회 2022 대한내과학회 추계학술대회 Vol.2022 No.2

Impact of Postshock Turbulence on the Radio Spectrum of Radio Relic Shocks in Merging Clusters

강혜성 한국천문학회 2024 Journal of The Korean Astronomical Society Vol.57 No.1

This study investigates the impact of magnetic turbulence on cosmic ray (CR) electrons through Fermi-II acceleration behind merger-driven shocks in the intracluster medium and examines how the ensuing synchrotron radio emission is influenced by the decay of magnetic energy through dissipation in the postshock region. We adopt simplified models for the momentum diffusion coefficient, specifically considering transit-time-damping resonance with fast-mode waves and gyroresonance with Alfvén waves. Utilizing analytic solutions derived from diffusive shock acceleration theory, at the shock location, we introduce a CR spectrum that is either shock-injected or shock-reaccelerated. We then track its temporal evolution along the Lagrangian fluid element in the time domain. The resulting CR spectra are mapped onto a spherical shell configuration to estimate the surface brightness profile of the model radio relics. Turbulent acceleration proves to be a significant factor in delaying the aging of postshock CR electrons, while decaying magnetic fields have marginal impacts due to the dominance of inverse Compton cooling over synchrotron cooling. However, the decay of magnetic fields substantially reduces synchrotron radiation. Consequently, the spatial distribution of the postshock magnetic fields affects the volume-integrated radio spectrum and its spectral index. We demonstrate that the Mach numbers estimated from the integrated spectral index tend to be higher than the actual shock Mach numbers, highlighting the necessity for accurate modeling of postshock magnetic turbulence in interpreting observations of radio relics.

RADIO EMISSION FROM WEAK SPHERICAL SHOCKS IN THE OUTSKIRTS OF GALAXY CLUSTERS

강혜성 한국천문학회 2015 Journal of The Korean Astronomical Society Vol.48 No.2

In Kang (2015) we calculated the acceleration of cosmic-ray electrons at weak spherical shocks that are expected to form in the cluster outskirts, and estimated the diffuse synchrotron radiation emitted by those electrons. There we demonstrated that, at decelerating spherical shocks, the volume integrated spectra of both electrons and radiation deviate significantly from the test-particle power-laws predicted for constant planar shocks, because the shock compression ratio and the flux of inject electrons decrease in time. In this study, we consider spherical blast waves propagating through a constant density core surrounded by an isothermal halo with $\rho\propto r^{-n}$ in order to explore how the deceleration of the shock affects the radio emission from accelerated electrons. The surface brightness profile and the volume-integrated radio spectrum of the model shocks are calculated by assuming a ribbon-like shock surface on a spherical shell and the associated downstream region of relativistic electrons. If the postshock magnetic field strength is about $0.7$ or $7\muG$, at the shock age of $\sim 50$~Myr, the volume-integrated radio spectrum steepens gradually with the spectral index from $\alpha_{\rm inj}$ to $\alpha_{\rm inj}+0.5$ over 0.1--10~GHz, where $\alpha_{\rm inj}$ is the injection index at the shock position expected from the diffusive shock acceleration theory. Such gradual steepening could explain the curved radio spectrum of the radio relic in cluster A2266, which was interpreted as a broken power-law by Trasatti et al. (2015), if the relic shock is young enough so that the break frequency is around $1$~GHz.

RE-ACCELERATION MODEL FOR THE “TOOTHBRUSH” RADIO RELIC

강혜성 한국천문학회 2016 Journal of The Korean Astronomical Society Vol.49 No.3

The Toothbrush radio relic associated with the merging cluster 1RXS J060303.3 is presumed to be produced by relativistic electrons accelerated at merger-driven shocks. Since the shock Mach number inferred from the observed radio spectral index, $M_{\rm radio}\approx 2.8$, is larger than that estimated from X-ray observations, $M_{\rm X}\lesssim 1.5$, we consider the re-acceleration model in which a weak shock of $M_s\approx 1.2-1.5$ sweeps through the intracluster plasma with a preshock population of relativistic electrons. We find the models with a power-law momentum spectrum with the slope, $s\approx 4.6$, and the cutoff Lorentz factor, $\gamma_{e,c}\approx 7-8\times 10^4$ can reproduce reasonably well the observed profiles of radio fluxes and integrated radio spectrum of the head portion of the Toothbrush relic. This study confirms the strong connection between the ubiquitous presence of fossil relativistic plasma originated from AGNs and the shock-acceleration model of radio relics in the intracluster medium.

RE-ACCELERATION MODEL FOR THE ‘SAUSAGE’ RADIO RELIC

강혜성 한국천문학회 2016 Journal of The Korean Astronomical Society Vol.49 No.4

The Sausage radio relic is the arc-like radio structure in the cluster CIZA J2242.8+5301, whose observed properties can be best understood by synchrotron emission from relativistic electrons accelerated at a merger-driven shock.However, there remain a few puzzles that cannot be explained by the shock acceleration model with only in-situ injection. In particular, the Mach number inferred from the observed radio spectral index, $M_{\rm radio}\approx 4.6$, while the Mach number estimated from X-ray observations, $M_{\rm X-ray}\approx 2.7$. In an attempt to resolve such a discrepancy, here we consider the re-acceleration model in which a shock of $M_s\approx 3$ sweeps through the intracluster gas with a pre-existing population of relativistic electrons. We find that observed brightness profiles at multi frequencies provide strong constraints on the spectral shape of pre-existing electrons. The models with a power-law momentum spectrum with the slope, $s\approx 4.1$, and the cutoff Lorentz factor, $\gamma_{e,c}\approx 3-5\times 10^4$, can reproduce reasonably well the observed spatial profiles of radio fluxes and integrated radio spectrum of the Sausage relic.The possible origins of such relativistic electrons in the intracluster medium remain to be investigated further.