• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.920-932
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• 1994

The combustion phenomena of a reciprocating engine is one of the most important processes affecting performance and emissions. One effective way to improve the engine combustion is to control the motion of the charge inside a cylinder by means of optimum induction system design, because the flame speed is mainly determined by the turbulence at compression(TDC) process in S.I. engine. It is believed that the tumble and swirl motion generated during intake breaks down into small-scale turbulence in the compression stroke of the cycle. However, the exact nature of their relationship is not well known. This paper describes cycle resolved LDV measurement of turbulent flow inside the cylinder of a 4-valve engine under motoring(non-firing) conditions, and studies the effect of intake port configurations on the turbulence characteristics using following parameters ; Eulerian temporal autocorrelation coefficient, turbulence energy spectral density function, Taylor micro time scale, integral time scale, and integral length scale.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1813-1820
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• 2001

The purpose of this study was to investigate the significant characteristics in atomization process of industrial etching spray fur the design or Precise pressure-swirl nozzles. The experiment was carried out with different viscosities and densities of the liquid. The macro characteristics of liquid spray, such as the spray angle and breakup process were captured by PMAS and the micro characteristics of liquid spray. such as droplet size and velocity measurements were obtained by PDA. The droplet axial and radial velocity and SMD were measured along axial and radial direction. The RMS of two velocities was measured along radial direction. It was found that the fluid with higher kinematic viscosity resulted in the larger SMD and the lower mean droplet velocity. And we could divide breakup processes into three regions that is atomization, non-dilution and dilution one in spray of pressure-swirl nozzle. The radial as well as axial velocity of droplet played an important role in the atomization process of higher kinematic viscosity fluid.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.48.3-49
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• 2016

Current high-resolution IR spectroscopy at ground-based observatories made it possible to observe $3-{\mu}m\;CH_4$ emission lines from the atmospheres of Jupiter, Saturn, and Titan through narrow atmospheric windows avoiding the counterparts of telluric $CH_4$ absorptions if proper Doppler shifts betwen Earth and these planetary objects are provided. We are also expecting low-resolution (R~300) infrared spectra of Jupiter from the upcoming observations by JUNO's infrared $2-5{\mu}m$ spectrograph during the encounter with Jupiter approximately starting from July 4, 2016. Although the spectral resolution is not enough to resolve the $3-{\mu}m$ P, Q, R branch lines of CH4, the gross envelopes of the P, Q, R branches should yield information on rotational temperatures. The rotational temperatures are useful because theycan be regarded as local temperatures, as discussed by Kim et al. (2014). Since the $3-{\mu}m\;CH_4$ emission is mostly formed at micro-bar pressure levels, the derived rotational temperatures represent the local temperatures near the hompause of Jupiter. We discuss possible sciences from the derived homopause temperatures in the auroral and non-auroral regions of Jupiter.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.4
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• pp.276-280
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• 2020

A linear piezoelectric actuator that utilizes the elliptical motion of the two tips of the actuator is proposed. This device is easy to fabricate owing to its simple structure, consisting of three piezo ceramic benders and is suitable for use in micro robotic applications. A π-shaped structure, which was composed of four piezo ceramic benders, was constructed. Two of the benders were positioned on the center of the actuator, and the joints were attached at the ends of the cantilever. The other two benders were positioned on the side of the actuator and were attached between the joint and the tips. The actuator structure was designed to obtain the first bending mode of the horizontal vibration and the vertical vibration at the same frequency, resulting in elliptical motions at the tips. When two sinusoidal wave voltages with a 90-degree phase difference were applied to the two pairs of the actuator benders, elliptical motions were obtained at the tips. The driving characteristics of the prototype actuator were then measured using a laser doppler vibrometer.

• Journal of the Korean Vacuum Society
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• v.22 no.5
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• pp.250-256
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• 2013

It is described that the proton beam induces micro-size defects and electronic deep levels in luminescence Thin Film. Coincidence Doppler Broadening Positron Annihilation Spectroscopy (CDBPAS) and Positron lifetime Spectroscopy were applied to study of characteristics of a poly crystal samples. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S-parameter value. The samples were exposed by 3.0 MeV proton beams with the intensities ranging between 0 to ${\sim}10^{14}$ particles. The S-parameter values decreased as increased the proton beam, that indicates the protons trapped in vacancies. Lifetime ${\tau}_1$ shows that positrons are trapped in mono vacancies. Lifetime ${\tau}_2$ is not changed according to proton irradiation that indicate the cluster vacancies of the grain structure.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.7
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• pp.540-549
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• 2018

Classifying the front body of the missile and debris of a high-speed missile in intercepting a high-speed missile is an important issue. The motion of the front body of the missile is characterized by precession, but the motion of the debris in the boosting part separation phase is characterized by tumbling. There are periodic patterns caused by the precession or tumbling motion on the dynamic radar cross section (RCS). In addition, there are statistical properties caused by the change pattern of the dynamic RCS. A method is proposed to classify the front body of the missile and debris using periodic and statistical properties of the dynamic RCS. Three kinds of feature vector are extracted from the periodic and statistical properties of the dynamic RCS. The front body of the missiles and debris was classified using a support vector machine.

• Journal of Korean Neurosurgical Society
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• v.42 no.4
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• pp.281-285
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• 2007

Objective : Distal anterior cerebral artery (DACA) aneurysms are fragile and known to have high risks for intraoperative premature rupture and a relatively high associated morbidity. To improve surgical outcomes of DACA aneurysms, we reviewed our surgical strategy and its results postoperatively. Methods : A total of 845 patients with ruptured cerebral aneurysms were operated in our hospital from January 1991 to December 2005. Twenty-three of 845 patients had ruptured DACA aneurysms which were operated on according to our surgical strategy. Our surgical strategy was as follows; early surgery, appropriate releasing of CSF, appropriate surgical approach, using neuronavigating system, securing the bridging veins, using temporary clipping and/or tentative clipping, meticulous manipulation of aneurysm, and using micro-Doppler flow probe. Twenty of 23 patients who had complete medical records were studied retrospectively. We observed the postoperative radiographic findings and checked Glasgow Outcome Scale score sixth months after the operation. Results : Nineteen DACA aneurysms were clipped through a unilateral interhemispheric approach and one DACA aneurysm was clipped through a pterional approach. Postoperative radiographic findings revealed complete clipping of aneurysmal neck without stenosis or occlusion of parent arteries. In two patients, a residual neck of aneurysm was visualized. Seventeen patients showed good recovery, one patient resulted in moderate disability, while 2 patients died. Conclusion : With our surgical strategy it was possible to achieve acceptable surgical morbidity and mortality rates in patients with DACA aneurysms. Appropriate use of tentative clipping, temporary clipping and neuro-navigating systems can give great help for safe approach and clipping of DACA aneurysm.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.253-256
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• 2009

In the micro turbojet engine less than 350kw power class, it is not easy to find out the good atomization fuel injector with good spray quality. However conceptually, rotating fuel injection system can give high atomization quality by only the centrifugal force of a high speed rotating shaft of the engine without high-pressure fuel pump. With this motivation, we manufactured very small rotating fuel injector of 40 mm diameter and performed under a variety of injection orifices. We measured droplet size, velocity and spray distribution by the PDPA(Phase Doppler Particle Analyzer) system. Also spray was visualized by using high speed camera. From the test results, we could understand that the length of liquid column from the injection orifice is mainly controlled by the rotational speeds. Furthermore, droplet size(SMD) is decreased with the rotational speeds and is influenced by the diameter of the injection orifice and liquid film thickness.

• Archives of Plastic Surgery
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• v.38 no.3
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• pp.315-318
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• 2011

Purpose: An aneurysm is defined as a permanent, localized dilation of an artery with a 50% increase in diameter over its expected normal diameter. Aneurysms can be classified by cause as traumatic and nontraumatic. Traumatic aneurysms can be divided into true and false aneurysms. Nontraumatic causes of peripheral artery aneurysms include mycotic, atherosclerotic, inflammatory, and idiopathic. In the hand, true aneurysms occurring at the common digital artery have been rarely reported. We present a rare case of a true aneurysm of the common digital artery that was resected and reconstructed using a reversed vein graft. Methods: A 49-year-old male patient was refered to our institution with a $0.73{\times}0.44{\times}1.37cm$ sized pulsating mass between 2nd and 3rd flexor digitorum tendons on Lt. palm area. The mass had been present for 5 years and had increased in size over the previous year. No history of trauma was reported. After a physical examination and ultrasound sonography review, a diagnosis of aneurismal dilatation of common digital artery was made. Surgical treatment by excision of the aneurysm, and a reversed vein graft was performed. Results: Histologic examination of the specimen ($3.4{\times}0.7cm$) showed aneurismal dilatation, with elastin fibers present in the arterial wall. The lesions were healed without any complications and there were no evidence of recurrence. Doppler examination of the reconstruction showed good perfusion. Conclusion: Early excision is recommended to relieve symptoms and avoid neurologic damage. Also, artery reconstruction can be performed by primary end-to-end anastomosis or the placement of a reversed interposition vein graft. Micro surgical repair was the only possible treatment in this case. The authors believe that the vascular anatomy should always be restored as natural as possible.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.883-888
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• 2007

일반적인 하천의 흐름방향으로 발생하는 주흐름(primary flow)에 중첩하여 주흐름 방향의 수직단면에 이차류(secondary flow)가 발생하게 되며 이러한 이차류의 발달은 투입된 오염물질의 횡혼합을 증대시킨다. 오염물질의 혼합은 이송(advection)과 확산(diffusion) 또는 분산(dispersion)의 과정으로 설명되며 본 연구에서는 수로전체의 혼합과정을 설명하기 위해서 이송 확산 방정식을 적용하였다. 본 연구에서는 실험수조를 $150^{\circ}$의 중심각을 갖는 S자 형태의 만곡수로를 제작하여 유량조건은 15, 30, $60\;{\ell}l/sec$의 세 가지 경우로, 수심은 15, 20, 30, 40 cm의 경우로 총 12 케이스의 실험을 수행하였다. 유속장의 측정은 Sontek사의 3차원 micro-ADV(Acoustic Doppler Velocimeter)를 이용하였다. 오염물질 확산실험은 소금물 용액에 주변수와의 밀도차를 없애기 위해서 메탄올 용액을 첨가하여 추적자로 이용하여 농도장의 분석을 일본 KENEK사의 전기전도도계(conductivity meter)와 Gartner사의 DAS(data acquisition system)를 이용하여 횡방향 유속장의 분포와 오염운의 거동을 비교하여 다음과 같은 결론을 얻게 되었다. 주 흐름은 직선구간에서는 중앙에서 최대 유속을 나타내며, 좌우대칭적인 유속분포의 모습을 보이고, 만곡부에서는 수로안쪽을 따라 최대유속이 발생하였다. 수로의 직선구간에서는 최대유속이 발생하는 즉, 중앙에서의 오염물질의 분산이 가장 활발하게 이뤄졌으며 농도의 퍼짐형상인 오염운 역시 만곡부에서는 수로만곡부의 안쪽을 따라 확산 이동함을 알 수 있었다. 만곡부 외측에서는 오염물질의 정체현상이 일시적으로 발생하며, 유속구조의 횡방향 비대칭구조로 인한 종 횡방향의 분리현상이 발생하고, 오염운의 중첩현상이 종방향으로 연속되게 나타난다. 향후 수심방향 거동을 포함한 3차원적 분석이 요구되며 이 연구결과는 2차원적 수치해석의 적용 및 분석 자료로써 이용이 가능하다.