• 천문학회보
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• 제40권1호
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• pp.66.1-66.1
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• 2015

We present the first observational detection of radial and azimuthal oscillations in full halo coronal mass ejections (HCMEs). We analyze nine HCMEs well-observed by LASCO from Feb 2011 to Jun 2011. Using the LASCO C3 running difference images, we estimated the instantaneous apparent speeds of the HCMEs in different radial directions from the solar disk center. We find that the development of all these HCMEs is accompanied with quasi-periodic variations of the instantaneous radial velocity with the periods ranging from 24 to 48 mins. The amplitudes of the instant speed variations reach about a half of the projected speeds. The amplitudes are found to anti-correlate with the periods and correlate with the HCME speed, indicating the nonlinear nature of the process. The oscillations have a clear azimuthal structure in the heliocentric polar coordinate system. The oscillations in seven events are found to be associated with distinct azimuthal wave modes with the azimuthal wave number m=1 for six events and m=2 for one event. The polarization of the oscillations in these seven HCMEs is broadly consistent with those of their position angles with the mean difference of $42.5^{\circ}$. The oscillations may be connected with natural oscillations of the plasmoids around a dynamical equilibrium, or self-oscillatory processes, e.g. the periodic shedding of Alfvenic vortices. Our results indicate the need for advanced theory of oscillatory processes in CMEs.

• 천문학회보
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• 제40권1호
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• pp.67.1-67.1
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• 2015

In the past two decades, diverse methods and computer codes for reconstruction of coronal magnetic fields have been developed. Some of them can reproduce a known analytic solution quite well when the magnetic field vector is fully specified by the known solution at the domain boundaries. In practical problems, however, we do not know the boundary conditions in the computational domain except the photospheric boundary, where vector magnetogram data are provided. We have developed a new, simple variational method employing vector potentials. We have tested the computational code based on this method for problems with known solutions and those with actual photospheric data. When solutions are fully given at all boundaries, the accuracy of our method is almost comparable to best performing methods in the market. When magnetic field vectors are only given at the photospheric boundary, our method excels other methods in "figures of merit" devised by Schrijver et al. (2006). Our method is expected to contribute to the real time monitoring of the sun required for future space weather prediction.

• 음성과학
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• 제11권1호
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• pp.87-103
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• 2004

This study investigates Korean listeners' perception of the English stop epenthesis between the sonorant and fricative segments. Specifically this study investigates 1) how often English epenthetic stops are perceived by native Korean listeners, given the fact that Korean does not allow consonant clusters in codas; and 2) whether perception of the epenthetic stops, which are optional phonetic variations, not phonemes, could be improved without any explicit training. 120 English non-words with a mono-syllable structure of CVC1C2, where C1=/m, n, $\eta$, 1/, and C2=/s, $\theta$, $\int$/, were given to two groups of native Korean listeners, and they were asked to detect the target stops such as [p], [t], and [k]. The number of their responses were computed to determine how often listeners succeed in recovering the string of segments produced by the native English speaker. The results of the present study show that English epenthetic stops are poorly identified by native Korean listeners with low English proficiency, even in the case where stimuli with strong acoustic cues are provided with, but perception of epenthetic stops is closely related with listeners' English proficiency, showing the possibility of the improvement of perception. It further shows that perception of epenthetic stops shows asymmetry between coronal and non-coronal consonants.

• 대한족부족관절학회지
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• 제11권1호
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• pp.18-22
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• 2007

Purpose: To provide basic data on anatomy of the ankle joint in adults using magnetic resonance imaging as well as to compare measurements with available data of corresponding dimension in the different sizes of the total ankle replacements design ($HINTEGRA^{(R)}$). Materials and Methods: Magnetic resonance (MR) sagittal and coronal images from one hundred-forty nine were studied. Post traumatic, arthritic, or grossly deformed ankles at any reason were excluded. Lengths, widths of the main parts of this articulation and also the radius of curvature of talar dome were measured in the MR images. Statistical analysis was performed on these measurements. Results: On MR coronal image data, average tibial width was $30.0{\pm}4.1\;mm$ and talar width was $27.0{\pm}3.4\;mm$. On sagittal image date, average anteroposterior length of the distal tibia was $39.0{\pm}4.2\;mm$, average anteroposterior length of the talus was $31.3{\pm}2.8\;mm$, and average sagittal radius of curvature of talar dome was $20.1{\pm}2.9\;mm$. All measurements in male were significantly larger than in female (p<0.01), but a significant difference according to age was not found. Conclusion: Ankle morphometric data define a basis of size, particularly useful in the design of ankle prostheses.

• 말소리와 음성과학
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• 제3권4호
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• pp.71-81
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• 2011

This paper investigated how prosodic position and word type affect the phonetic structure of Korean coronal stops. Initial segments of prosodic domains were known to be more strongly articulated and longer relative to prosodic domain-medial segments. However, there are few studies examining whether the properties of prosodic domain-initial segments are affected by the information content of words (real vs. nonsense words). In addition, since the scope of domain-initial effect was known to be local to the initial consonant and the effects on the following vowel have been found to be limited, it is thus worth examining whether the prosodic domain-initial effect extends into the vowel after the initial consonant in a systematic way across different prosodic domains. The acoustic properties of Korean coronal stops (lenis /t/, aspirated /$t^h$/, and tense /t'/) were compared across Intonational Phrase, Phonological Phrase and Word-initial positions both in real and nonsense words. The durational intervals such as VOT and CV duration were cumulatively lengthened for /t/ and /$t^h$/ in the higher prosodic domain-initial positions. However, tense stop /t'/ did not show any variation as a function of prosodic position and word type. The domain-initial lenis stop showed significantly longer duration in nonsense words than in real words. But the prosodic domain-initial effect was not found in the properties of F0 and [H1-H2] of the vowel after initial stops. The present study provided evidence that speakers tend to enhance speech clarity when there is less contextual information as in prosodic domain-initial position and in nonsense words.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2011년도 한국우주과학회보 제20권1호
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• pp.28.3-28.3
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• 2011

Halo coronal mass ejections (HCMEs) are mainly responsible for the most severe geomagnetic storms. To minimize the projection effect of the HCMEs observed by coronagraphs, several cone models have been suggested. These models allow us to determine the geometrical and kinematic parameters of HCMEs : radial speed, source location, angular width, and the angle between the central axis of the cone and the plane of the sky. In this study, we compare these parameters form two representative cone models (the ice-cream cone model and the asymmetric cone model) using well-observed HCMEs from 2001 to 2002. And we obtain the root mean square error (rms error) between observed projection speeds and calculated projection speeds for both cone models. It is found that the average rms speed error (89 km/s) of the asymmetric cone model is a little smaller than that (107 km/s) of the ice-cream cone models, implying that the radial speeds from both models are reasonably estimated. We also find that the radial speeds obtained from two models are similar to each other with the correlation coefficient of about 0.8.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제27권4호
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• pp.337-343
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• 2001

Objective. Disc displacement may affect the joint space narrowing between condyle head and glenoid fossa. This study was designed to evaluate the correlation between the joint space change and the directions of disc displacement. Study Design. Two hundreds temporomandibular joints MR images of TMD patients (170 joints) and asymptomatic volunteers (30 joints) were evaluated for this purpose. Anterior disc displacement was divided into 3 stages (normal, little to mild, and moderate to severe displacement) based on sagittal images. And sideways displacement was classified as 3 categories (center, medial and lateral displacement) based on coronal images, then joint spaces were measured at medial, central and lateral parts of condyle head on coronal MR images, respectively. The joint spaces of 7 groups divided according to the severity and the direction of disc displacement were compared. Results. The reduction of the joint space was affected by sideways disc displacement at the opposite side of the condyle head, except the cases accompanied with severe anteriorly and laterally displaced disc. Conclusion. The sideways disc displacement affected on the opposite side temporomandibular joint space width.

• Journal of Astronomy and Space Sciences
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• 제15권2호
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• pp.307-320
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• 1998

다중 위성 관측을 이용하여 지구 근처에서의 태양물질 방출현상(CME: Coronal Mass Ejection)의 전파 속도와 방향에 대하여 조사하였다. 이를 위해 1994년 11월까지 지구에 영향을 미친 CME 중에서 세 개 이상의 위성에서 관측되고 각 위성들이 충분한 거리를 두고 떨어져 있는 1997년 1월 6-11일과 1997년 11월 4-7일의 두 CME 자료를 선택하였다. 위성들의 위치를 공통 좌표 계로 전환하여 위성간의 거리와 CME에 의한 물리량의 변화 시간을 조사하여 CME의 전파 방향과 속도를 계산하였다. 선택된 자료에 대한 조사 결과 지구 자기권 내부에서 CME 전파 속도가 급격히 줄어들었으며 또한 자기권 외부에서의 CME 전파 방향이 GSE 좌표계상의 -x 방향과 일치함을 알 수 있었다.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
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• pp.24.1-24.1
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• 2008

We examine the eccentricity parameter (EP) of Coronal Mass Ejections (CMEs). For this, we select 298 front-side CMEs from SOHO LASCO CMEs whose speed is larger than 1000km/s and angular width is greater than $120^{\circ}$ during from 1997 to 2007. These are thought to be the most plausible candidate of geoeffective CMEs. We examine the relation between CMEs eccentricity parameter and the minimum value of the Dst index. We find that strong geomagnetic storms (Dst < -200nT) are well correlated with the EP from the scattered plot. We also find that CMEs have high geoeffectiveness when they occurred near the center of the solar disk with the small EP and they have the small speed with the small EP. These results indicate that the CME EP also can be an important indicator to forecast CME geoeffectiveness such as Earthward direction parameter (Moon et al. 2005, Kim et al. 2008).

• Journal of Korean Neurosurgical Society
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• 제30권12호
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• pp.1417-1421
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• 2001

Objective : The purposes of this study are to compare imaging features with operative findings and to determine significance of imaging studies for early detection of craniosynostosis(CS). Methods : Plain radiograph of skull and three-dimensional(3D) CT reconstruction were analyzed in 10 consecutive patients with CS to assess the presence and the extent of synostosis. The radiological findings were investigated and compared with operative findings. Results : The locations of lesion were coronal suture in 6, sagittal suture in 3 and multiple sutures in one patient, and the age ranged 1 to 53 months(mean age : 17.4 months). Reconstructive procedures with or without advancement of supraorbital rim were performed in coronal CS patients and ${\pi}$-procedures or synostectomy were done in sagittal CS patients. Radi-ological abnormalities such as sutural indistinctness or sclerosis, bony ridge, bossing and other bony deformities were nearly consistent with surgical findings. Conclusion : The interpretation of imaging study are very important for early detection of craniosynostosis, especially, the plain radiographs of skull. Also 3D CT imaging is helpful in diagnosis and surgical planing of craniosynostosis. There are no significant differences between imaging features and operative findings in CS patients.