• 대기
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• 제31권2호
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• pp.171-183
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• 2021

The sensitivity of the extratropical jet to the stratospheric mean state is investigated by conducting a series of idealized numerical experiments using a dynamic-core general circulation model. When the polar stratosphere is forced to be cold, the extratropical jet, defined by the 850-hPa zonal wind, tends to shift poleward without much change in its intensity. The opposite is also true when the polar stratosphere becomes warm. This jet response, however, is not exactly linear. A poleward jet shift under a cold vortex is much weaker than an equatorward jet shift under a warm vortex. The jet intensity change is also larger under a warm vortex. This result indicates that the stratosphere-troposphere downward coupling is more efficient for the warm and weak polar vortex. This finding is consistent with a stronger downward coupling during stratospheric sudden warming than vortex intensification events in the Northern Hemisphere winter, possibly providing a clue to better understand the observed stratosphere-troposphere downward coupling.

• Geomechanics and Engineering
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• 제24권6호
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• pp.531-543
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• 2021

Freezing and thawing of pore water within backfill can affect the stability of retaining wall as the phase change of pore water causes changes in the mechanical characteristics of backfill material. In this study, the effects of freezing and thawing on the mechanical performance of retaining wall with granular backfill were investigated for various temperature and groundwater level (GWL) conditions. The thermal and mechanical finite element analyses were performed by assigning the coefficient of lateral earth pressure according to phase change of soil for at-rest, active and passive stress states. For the at-rest condition, the mobilized lateral stress and overturning moment changed markedly during freezing and thawing. Active-state displacements for the thawed condition were larger than for the unfrozen condition whereas the effect of freezing and thawing was small for the passive condition. GWL affected significantly the lateral force and overturning moment (Mo) acting on the wall during freezing and thawing, indicating that the reduction of safety margin and wall collapse due to freezing and thawing can occur in sudden, unexpected patterns. The beneficial effect of an insulation layer between the retaining wall and the backfill in reducing the heat conduction from the wall face was also investigated and presented.

• 대한기계학회논문집B
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• 제24권1호
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• pp.132-142
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• 2000

The objective of this study is to experimentally investigate the noise propagating characteristics, the noise reduction mechanism and the performance of a slotted tube attached at the exit plane of a circular convergent nozzle. The experiment is performed through the systematic change of the jet pressure ratio and the slot length under the condition of two kinds of open area ratios, 25% and 51%. The open area ratio calculated by the tube length equivalent for the slot length is defined as the ratio of the total slot area to the surface area of a slotted tube. The experimental results for the near and far field sound, the visualization of jet structures and the static pressure distributions in the jet passing through a slotted tube are presented and explained in comparison with those for a simple tube. The propagating characteristics of supersonic jet noises from the slotted tube is closely connected with the slot length rather than the open area ratio, and its propagating pattern is similar to the simple tube. It is shown that the slotted tube has a good performance to suppress the shock-associated noise as well as the turbulent mixing noise in the range of a limited jet pressure and slot dimension. The considerable suppression of the shock‘associated noise is mainly due to the pressure relief caused by the high-speed jets passing through the slots on the tube. Both the strength of shock waves and the interval between them in a jet plume are decreased by the pressure relief. Moreover, the pressure relief is divided into the gradual and the sudden relief depending upon the open area ratio of the slotted tube. Consequently, the shock waves in a jet plume are also changed by the type of pressure relief. The gradual pressure relief caused by the slotted tube with the open area ratio 25% generates the weak oblique shock waves. On the contrary, the weak normal shock waves appear due to the sudden pressure relief caused by the slotted tube with the open area ratio 51%.

• 감성과학
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• 제11권2호
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• pp.245-256
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• 2008

최근 실내디자인산업은 내, 외적으로 많은 성장을 지속적으로 이루어지고 있으며 점차 국제화, 전문화되어 가는 추세에 있으나 이러한 성장세와 동시에 실내 디자인업계의 급격한 변화를 경험하고 있는 실정이다. 이러한 변화는 업계의 전반적인 문제일수도 있으나 실내디자인을 운영하는 틀과 이념에 대한 본질적인 면과 이에 따른 변화 경영 패러다임의 전환 즉 디자인경영전략이 요구가 필요한 시점이 아닌가 생각되어 진다. 따라서 지금까지 적용되었던 디자인업계의 각종 전략들이 유용한 전략이 되지 못하고 있으며 단순한 경영의 논리를 벗어나, 새로운 환경과 변화된 가치관에 걸맞은 철저한 시장조사와 분석을 통하여 가장 합리적이고, 만족스런 디자인이 탄생될 수 있는 틀로 전환하는 기업만이 생존할 수 있는 시대에 접어들었다 할 수 있다. 본 연구는 새로운 변화에 당면한 실내디자인업체의 현재 당면과제와 다양한 환경변화 요인들을 검토하고, 팽창과 다양한 변화에 따른 환경변화 요인들 중 현황 및 경향을 조사, 분석해봄으로써, 앞으로 전개될 국내시장 개방과 고도산업사회로의 전환에 따른 환경변화에 능동적인 대처를 할 수 있는 자료를 구축하여 올바른 방향을 제시하는데 그 시사점을 찾은 연구의 목적이 있다.

• 전력전자학회논문지
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• 제13권2호
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• pp.128-134
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• 2008

독립형 전원시스템에서 엔진을 이용한 발전시스템은 지금까지 에너지의 효율적인 측면보다는 설치 단가 및 신뢰성이 중요한 이슈가 되어왔으나, 최근 들어 신뢰성과 함께 에너지의 효율적 사용, 대기 환경 개선 및 발전 전력 품질 등이 점차 중요시 되어가고 있다. 가변속 엔진 발전 시스템의 경우 출력 전력에 대응하여 엔진 속도를 가변함으로써, 경부하시 획기적인 효율 개선이 가능하다. 또한 부하 전압, 주파수는 출력 인버터에 의해 제어되므로, 그 응답 속도가 빨라 고 품질의 전력을 전원에 공급할 수 있다. 특히 급격한 부하 증가 시 엔진 출력이 늘어나는 시간동안 부족한 전력을 슈퍼캐패시터로부터 공급받음으로써, 부하 급증 시에도 안정된 전력 공급이 가능하다. 본 논문에서는 소형 디젤 엔진과 슈퍼캐패시터를 이용한 가변속 엔진 발전 시스템의 개념을 설명하고, 가변속 운전의 필요성, 고정 운전속 대비 연비 절감 및 3상 4선식 인버터를 사용한 고품질의 전력 공급 등의 타당성을 모의 실험과 실험을 통하여 검증하도록 한다.

• The Korean Journal of Pain
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• 제13권2호
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• pp.191-195
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• 2000

Background: Vascular occlusive event is one of the etiologies of sudden sensorineural hearing loss (SNHL). Stellate ganglion block (SGB) induces dramatic and intense vasodilatation in head and neck. Based on this principle, SGB has used as one of the treatment modalities in SNHL. This study was performed to evaluate immediate response of SGB on pure tone audiogram (PTA) in SNHL. Methods: Forty patients were studied. Each patient received daily ipsilateral SGB in paratracheal approach using 0.2% bupivacaine for 2 weeks. On first, third, and fifth day of treatment, we checked their PTA twice 1 hour before (Pre-PTA) and after (Post-PTA) SGB. Pre- and Post-PTA were compared. Several factors were analyzed as a prognostic factor of therapeutic results. Results: Eleven of 40 patients revealed decreased PTA after SGB. Degree of decreased PTA were insignificant ($2.5{\pm}1.6$ dB). Initial and final PTA results was $76.2{\pm}22.5$ and $49.8{\pm}28.3$ dB, respectively. Thirty-one of 40 patients were improved their PTA over 10 dB. The recovery was mainly influenced by the severity of initial hearing loss (P<0.001) and slightly by age (P<0.05). However, the change of PTA after SGB, time interval to receive SGB, sex, site, and number of SGB were not correlated to therapeutic outcome. Conclusions: These results suggest that vasodilatation by SGB has no immediate improvement in SNHL. Therefore, we question whether SGB is beneficial to all patients with SNHL as a therapeutic modality.

• Journal of Korean Neurosurgical Society
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• 제39권1호
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• pp.26-31
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• 2006

Objective : The authors study on the clinical presentations and the surgical outcomes of the tumors in the ventricular system. Methods : 15 patients with ventricular tumor were studied. The clinical presentation, radiological findings, different surgical approaches, and outcome were analyzed. Tumors were classified into three groups based on their locations in MRI : lateral, third and fourth ventricle. Surgical methods were transcortical approach in eight patients, transcallosal approach in four, median suboccipital approach in two, and subfrontal approach in one. Gross total removal was achieved in 10 patients. Subtotal resections were performed in the rest. Glasgow outcome scale was used for evaluation of the surgical outcome. Results : Main clinical presentations were chronic headache in patients with the tumor in the lateral ventricular tumor and sudden onset of headache and consciousness change in patients with the tumor in the third and fourth ventricular tumor Development of hydrocephalus was more predominant in patients with the tumors in the third ventricle. Postoperatively, good outcome [Glasgow outcome scale IV, V] were in 73%, and better results was observed in patients with the tumors in the lateral ventricular tumor. The differences of outcome according to surgical approach were not recognized, even though it was not reliable statistically. Conclusion : In ventricular tumor, postoperative outcome is not good in patients with sudden development of headache, hydrocephalus, high grade tumor. Outcome is good in patients with the tumor in the lateral ventricle relatively. There is no difference in outcome according to the approach method to the tumors. And it is necessary to be aware of various approach methods to the tumors and anatomy surrounding the ventricle for avoidance of neurological complications.

• 소음진동
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• 제5권4호
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• pp.543-553
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• 1995

Modern steam turbine generators are being built as a higher power and larger system, experiencing more frequent starts and stops of operation due to a constant change of power demands. Hence, they are inevitably more vulnerable to various vibrations, and more often exposed to the danger of sudden vibration accidents than ever before. Even under the circumstances, in order to secure the system reliability of steampower plants and there by to supply safely the public electricity, it is important to prevent a sudden vibration accident in one hand and even when it happens, to raise an operating efficiency of the plants throught swift and precise treatments in the other. In this study, an interactive vibration diagnostic system has been developed to make the on-site vibration diagnosis of steam turbine generators possible and convenient, utilizing a note-book PC. For this purpose, at first the principal vibration phenomena, such as various unbalance and unstable vibrations as well as rubbing, misalignment, and shaft crack vibrations, have been systematically classified as grouped parameters of vibration frequencies, amplitudes, phases, rotating speeds at the time of accident, and operating conditions or condition changes. A new complex vibration diagnostic table has been constructed from the causal relations between the characteristic parameters and the principal vibration phenomena. Then, the diagnostic system has been developed to screen and issue the corresponding vibration phenomena by assigning to each user-selected combination of characteristic parameters a unique characteristic vector and comparing this vector with a diagnostic vector of each vibration phenomenon based on the constructed diagnostic table. Moreover, the diagnostic system has a logic whose diagnosis may be performed successfully by inputing only some of the corresponding characteristic parameters without having to input all the parameters. The developed diagnostic system has been applied to perform the diagnosis of several real cases of steam turbine vibration accidents. And the results have been quite satisfactory.

• International Journal of Air-Conditioning and Refrigeration
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• 제7권
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• pp.1-10
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• 1999

In this study, a numerical analysis is made on the ice-formation for laminar water flow inside a stenotic tube. The study takes into account the interaction between the laminar flow and the stenotic port in the circular tube. The purpose of the present numerical investigation is to assess the effect of a stenotic shape on the instantaneous shape of the flow passage during freezing upstream/downstream of the stenotic channel. In the solution strategy, the present study is substantially distinguished from the existing works in that the complete set of governing equations in both the solid and liquid regions are resolved. In a channel flow between parallel plates, the agreement between the of predictions and the available experimental data is very good. Numerical analyses are performed for parametric variations of the position and heights of stenotic shape and flow rate. The results show that the stenotic shape has the great effect on the thickness of the solidification layer inside the tube. As the height of a stenosis grows and the length of a stenosis decreases, the ice layer thickness near the stenotic port is thinner, due to backward flow caused by the sudden expansion of a water tunnel. It is found that the flow passage has a slight uniform taper up to the stenotic channel, at which a sudden expansion is observed. It is also shown that the ice layer becomes more fat in accordance with its Reynolds number.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 추계학술대회
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• pp.451-454
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• 1997

It has been reported that sudden cardiac death and ventricular tachycardia occur after treatment of tetralogy of fallot(TOF). It is regarded that ventricular arrythmia is the main source or the sudden cardiac death, but it is not verified. It is likely that TOF has effect on the heart rate variability because of the ventricular arrythmia. We study how complex and periodic heart rate dynamics change in the normal children (n=13) and TOF children (n=13) throughout 24 hours. We recorded 24-hour holter ECG, and segmented each ECG data into 1 hour length. We analyze each HR time series, and quantify the overall complexity of each HR time series by its correlation dimension. We also calculate the power spectrum of HR, and obtain low-frequency component (0.03-0.15Hz) and high-frequency component (0.15-0.4Hz). We compare the results between normal and TOF groups throughout 24 hours. TOF group have lower correlation dimension ($4.055{\pm}0.4134$ vs. $4.9310{\pm}0.2054$, p<0.05) than the normal group, even though there are no significant differences in the low($0.9864{\pm}0.5598$ vs. $1.5560{\pm}0.8325$, p<0.05) and high($1.1168{\pm}0.1.1448$ vs. $0.9271{\pm}0.6528$, p<0.05) frequency components. It can be concluded that HR time series of TOF group are more regular than that of normal group, and that correlation dimension reveals a nonlinear characteristics of HR time series which is not determined in the frequency domain.