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Formation of three-dimensional black strings from gravitational collapse of dust cloud
Hyun, Seungjoon,Jeong, Jaehoon,Kim, Wontae,Oh, John J. Institute of Physics Pub 2007 The journal of high energy physics Vol.2007 No.4
We study the formation of black strings from a gravitational collapse of cylindrical dust clouds in the three-dimensional low-energy string theory. New junction conditions for the dilaton as well as two junction conditions for metrics and extrinsic curvatures between both regions of the clouds are presented. As a result, it is found that the collapsing dust cloud always collapses to a black string within a finite collapse time, and then a curvature singularity formed at origin is cloaked by an event horizon. Moreover, it is also shown that the collapse process can form a naked singularity within finite time, regardless of the choice of initial data.
Chung, Seungjoon,Kim, Seungjin,Kim, Jong-Oh,Chung, Jinwook American Chemical Society 2014 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.53 No.39
<P>The feasibility of reverse osmosis (RO) separation combined with ferrite reaction was investigated for the reclamation and recovery of heavy metals from metal plating wastewater. Disc tube-type RO modules were used for simultaneous purification and concentration of wastewaters containing zinc and chromium ions. A subsequent ferrite reaction was performed to recover zinc ions from RO concentrates. The operating conditions of the RO and ferrite reaction were determined in several lab-scale experiments with several types of model wastewater. Pilot-scale RO test results revealed that the zinc plating wastewater treated by one-pass RO and the chrome plating wastewater treated by two-pass RO were acceptable for preplating rinsewater. After ferrite reaction, 99.7% of zinc ions were recovered from the second-stage RO concentrate in the form of zinc ferrite, while significant amounts of chromium ions were retained in the concentrate. As a result of economic analysis, we suggested a retrofitting option, including a combined RO and ferrite process, for a wastewater treatment facility in a local metal plating company.</P>
Formation of five-dimensional string solutions from gravitational collapse
Hyun, Seungjoon,Jeong, Jaehoon,Kim, Wontae,Oh, John J Institute of Physics 2007 Classical and quantum gravity Vol.24 No.13
<P>We study the formation of five-dimensional string solutions including the Gregory–Laflamme (GL) black string, the Kaluza–Klein (KK) bubble and geometry with a naked singularity from gravitational collapse. The interior solutions of five-dimensional Einstein equations describe collapsing non-isotropic matter clouds. It is shown that the matter cloud always forms the GL black string solution while the KK bubble solution cannot be formed. The numerical study seems to suggest that the collapsing matter forms the geometries with timelike naked curvature singularities, which should be taken cautiously as general relativity is not reliable in the strong curvature regime.</P>
Outside Directors’ Insider Trading Around Board Meetings
( Seil Kim ),( Seungjoon Oh ) 한국금융연구원 2022 금융연구 working paper Vol.2022 No.15
Using a novel dataset containing U.S. companies’ regular board meeting schedules, we find evidence of informed trading by outside directors prior to board meetings. In the days prior to board meetings, when outside directors possess private information, they make purchases that yield higher abnormal returns and are larger than those made during periods distant from board meetings. We find no such pattern for inside directors who possess private information regardless of the timing of board meetings. Moreover, we find that these patterns are especially exhibited by trades made by more sophisticated directors, trades made prior to board meetings that result in news disclosures, and nonroutine trades. Our results suggest that outside directors trade based on information they obtain in preparation for board meetings.