• Investigative Magnetic Resonance Imaging
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• v.22 no.1
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• pp.26-36
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• 2018

Purpose: Children born with single ventricle physiology demonstrate poor growth rate and suffer from malnutrition, which lead to increased morbidity and mortality in this population. We assume that an anabolic steroid, oxandrolone, will promote growth in these infants by improving myocardial energy utilization. The purpose of this paper is to study the efficacy of oxandrolone on myocardial energy consumption in these infants. Materials and Methods: We modeled single ventricle physiology in a lamb by prenatally shunting the aorta to the pulmonary artery and then postnatally, we monitored cardiac energy utilization by quantitatively measuring the first order reaction rate constant, $k_f$ of the creatine-kinase reaction in the heart using magnetization transfer $^{31}P$ magnetic resonance spectroscopy, home built $^1H/^{31}P$ transmit/receive double tuned coil, and transmit/receive switch. We also performed cine MRI to study the structure and dynamic function of the myocardium and the left ventricular chamber. The spectroscopy data were processed using home-developed python software, while cine data were analyzed using Argus software. Results: We quantitatively measured both the first order reaction rate constant and ejection fraction in the control, shunted, and the oxandrolone-treated lambs. Both $k_f$ and ejection fraction were found to be more significantly reduced in the shunted lambs compared to the control lambs, and they are increased in oxandrolone-treated lambs. Conclusion: Some improvement was observed in both the first order reaction rate constant and ejection fraction for the lamb treated with oxandrolone in our preliminary study.

• Journal of The Korean Astronomical Society
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• v.35 no.3
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• pp.151-157
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• 2002

From the data of solar wind observation by ACE spacecraft orbiting the Earth-Sun Lagrangian point, we selected 48 forward interplanetary shocks(IPSs) occurred in 2000, maximum solar activity period. Examining the profiles of solar wind parameters, the IPSs are classified by their shock drivers. The significant shock drivers are the interplanetary coronal mass ejection(ICME) and the high speed stream(HSS). The IPSs driven by the ICMEs are classified into shocks driven by magnetic clouds and by ejectas based on the existence of magnetic flux rope structure and magnetic field strength. Some IPSs could be formed as the blast wave by the smaller energy and shorter duration of shock drivers such as type II radio burst. Out of selected 48 forward IPSs, $56.2\%$ of the IPSs are driven by ICME, $16.7\%$ by HSS, and $16.7\%$ of the shocks are classified into blast-wave type shocks. However, the shock drivers of remaining $10\%$ of the IPSs are unidentified. The classification of the IPSs by their driver is a first step toward investigating the critical magnitudes of the IPS drivers commencing the magnetic storms in each class.

• Publications of The Korean Astronomical Society
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• v.2 no.1
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• pp.13-20
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• 1985

Magnetic reconnect ion is studied numerically by means of a two dimensional MHD code. The initial magnetic field configuration is the two-dimensional dipole field, and the simulation model involves magnetic reconnect ion driven by the magnetized plasma flow. Strong plasma jetting, plasmoid formation and its fast ejection are observed in the downstream region. The dependence of reconnection rate on the incoming energy flux is found to be very sensitive, while the magnitude of the resistivity does not influence much on the reconnection rate. The simulation results are discussed in the context of the geomagnetic substorm.

• Journal of the Korean Magnetics Society
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• v.8 no.5
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• pp.255-260
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• 1998

Fabrication condition and magnetic properties of ultrathin Co-based amorphous alloy have been investigated. When the ejection gas pressure was lower than 0.05 kgf/$\textrm{cm}^2$ at the roll speed of 55 m/s, ultrathin ribbons with the thickness less than 10 ${\mu}{\textrm}{m}$ were successfully obtained. The ribbon thickness decreased linearly with the decrease in ejection pressure. Moreover the significant decrease in ribbon width was accompanied with the decrease of thickness in the range of ejection pressure to form an ultrathin ribbon. This behavior was attributed to the decrease of effective ejection pressure in the both end-sides of rectangular nozzle due to the larger friction between molten metal and nozzle wall. The effective permeability at low frequency (1 kHz) decreased largely with the decrease in ribbon thickness, while the coercive force increased with the thickness decrease. It was considered that these behaviors were due to the enhancement of surface effect leading to the suppression of wall motion. However effective permeability at high frequency (1 MHz) increased with the decrease in ribbon thickness, and this was ascribed to the easier magnetization rotation owing to the reduction of eddy current.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.89.1-89.1
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• 2013

We present a multiwavelength study of the X-class flare, which occurred in active region (AR) NOAA 11339 on 3 November 2011. The EUV images recorded by SDO/AIA show the activation of a remote filament (located north of the AR) with footpoint brightenings about 50 min prior to the flare occurrence. The kinked filament rises-up slowly and after reaching a projected height of ~49 Mm, it bends and falls freely near the AR, where the X-class flare was triggered. Dynamic radio spectrum from the Green Bank Solar Radio Burst Spectrometer (GBSRBS) shows simultaneous detection of both positive and negative drifting pulsating structures (DPSs) in the decimetric radio frequencies (500-1200 MHz) during the impulsive phase of the flare. The global negative DPSs in solar flares are generally interpreted as a signature of electron acceleration related to the upward moving plasmoids in the solar corona. The EUV images from AIA $94{\AA}$ reveal the ejection of multiple plasmoids, which move simultaneously upward and downward in the corona during the magnetic reconnection. The estimated speeds of the upward and downward moving plasmoids are ~152-362 and ~83-254 km/s, respectively. These observations strongly support the recent numerical simulations of the formation and interaction of multiple plasmoids due to tearing of the current-sheet structure. On the basis of our analysis, we suggest that the simultaneous detection of both the negative and positive DPSs is most likely generated by the interaction/coalescence of the multiple plasmoids moving upward and downward along the current-sheet structure during the magnetic reconnection process. Moreover, the differential emission measure (DEM) analysis of the active region reveals presence of a hot flux-rope structure (visible in AIA 131 and $94{\AA}$) prior to the flare initiation and ejection of the multi-temperature plasmoids during the flare impulsive phase.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.26.1-26.1
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• 2010

In this talk we outline the current understanding of solar flares, mainly focusing on magnetohydrodynamic (MHD) processes. A flare causes plasma heating, mass ejection, and particle acceleration which generates high-energy particles. The key physical processes producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), formation of current-concentrated areas (current sheets) in the corona, and magnetic reconnection proceeding in a current sheet to cause shock heating, mass ejection, and particle acceleration. A flare starts with the dissipation of electric currents in the corona, followed by various dynamic processes that affect lower atmosphere such as the chromosphere and photosphere. In order to understand the physical mechanism for producing a flare, theoretical modeling has been develops, where numerical simulation is a strong tool in that it can reproduce the time-dependent, nonlinear evolution of a flare. In this talk we review various models of a flare proposed so far, explaining key features of individual models. We introduce the general properties of flares by referring observational results, then discuss the processes of energy build-up, release, and transport, all of which are responsible for a flare. We will come to a concluding viewpoint that flares are the manifestation of the recovering and ejecting processes of a global magnetic flux tube in the solar atmosphere, which has been disrupted via interaction with convective plasma while rising through the convection zone.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.25.1-25.1
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• 2010

This talk outlines the current understanding of solar flares, mainly focusing on magnetohydrodynamic (MHD) processes. A flare causes plasma heating, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes related to a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), formation of current-concentrated areas (current sheets) in the corona, and magnetic reconnection proceeding in current sheets that causes shock heating, mass ejection, and particle acceleration. A flare starts with the dissipation of electric currents in the corona, followed by various dynamic processes which affect lower atmospheres such as the chromosphere and photosphere. In order to understand the physical mechanism for producing a flare, theoretical modeling has been developed, in which numerical simulation is a strong tool reproducing the time-dependent, nonlinear evolution of plasma before and after the onset of a flare. In this talk we review various models of a flare proposed so far, explaining key features of these models. We show observed properties of flares, and then discuss the processes of energy build-up, release, and transport, all of which are responsible for producing a flare. We come to a concluding view that flares are the manifestation of recovering and ejecting processes of a global magnetic flux tube in the solar atmosphere, which was disrupted via interaction with convective plasma while it was rising through the convection zone.

• The Journal of the Korea Contents Association
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• v.21 no.2
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• pp.437-444
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• 2021

The aim of this study was to compare the cardiac CT and cardiac MRI in calculating and correcting the left ventricle ejection fraction by analyzing the physical and temporal resolution for reducing the misdiagnosis rate. One hundred thirty-eight patients with aortic value regurgitation who underwent both cardiac CT and cardiac MRI were analyzed. Left ventricle ejection fractions calculated from each exam were corrected based on the physical and temporal resolution differences and the reliability test evaluated whether the misdiagnosis rate of cardiac CT was improved after the correction. As a result of the study, the misdiagnosis rate of cardiac CT ejection fraction before correcting the difference in physical and temporal resolution was 38.4%(53 persons). In addition, it can be seen that the corrected cardiac CT ejection fraction confirmed in the Bland-Altman plot was highly consistent with the ejection fraction of cardiac MRI. In conclusion, as the cardiac CT is less well suited for measuring ejection fraction, physical characteristics and the time resolution correction using cardiac MRI is needed and the misdiagnosis rate after correction decreased to 14.5%(20 persons). Therefore, this study appears more appropriate for better prediction of ejection fraction and clinical utility.

• Journal of The Korean Astronomical Society
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• v.42 no.6
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• pp.175-184
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• 2009

A method of estimating the lower bound of coronal magnetic field strength in the neighborhood of an ejecting plasmoid is presented. Based on the assumption that the plasma ejecta is within a magnetic island, an analytical expression for the force acting on the ejecta is derived. The method is applied to a limb coronal mass ejection event, and a lower bound of the magnetic field strength just below the CME core is estimated. The method is expected to provide useful information on the strength of reconnecting magnetic field if applied to X-ray plasma ejecta.

• Journal of the Korean Society of Radiology
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• v.5 no.5
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• pp.289-294
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• 2011

The aim of this study is to evaluate the differences of ejection fraction of left ventricle through the quantitative analysis of diastolic and systolic volumes according to slices selected using cardiac MR imaging. A total of 12 volunteers (7 normal, 1 myocardium bridge, and 4 arrhythmia) underwent cardiac MRI on a MR scanner(Magnetom Trio, Siemens, Germany). Ejection fractions for quantitative analysis were calculated at single slice of center of left ventricle, 3, 5, and 6-7 slices extending from the center of left ventricle. Average values were analyzed for evaluating differences of ejection fraction according to the number of slices selected. Mean value of normal person of ejection fraction were 67.14% at single slice of center of left ventricle, 66.24% at 3 slices, 65.63% at 5 slices, and 65.29% at 6-7 slices. While ejection fraction obtained from a patient with 61.74% at single slice of center of left ventricle, 60.92% at 3 slices, 60.89% at 5 slices, and 61.89% at 6-7 slices. There was no significant differences by the number of slices selected. This study demonstrates that ejection fraction obtained from single slice of center of left ventricle may represent a optimum parameter for cardiac function, instead of the value calculated on the variable slices selected.