• Korean Journal of Remote Sensing
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• v.18 no.5
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• pp.243-253
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• 2002

Time-mean and absolute geostrophic velocities of the Kuroshio current south of Japan are derived from TOPEX/Poseidon altimeter data using a Gaussian jet model. When compared with simultaneous measurements from a shipboard acoustic Doppler current profiler (ADCP) at two intersection points, the altimetric and ADCP absolute velocities correlate well with the correlation coefficient of 0.55 to 0.74. The accuracy of time-mean velocity ranges from 1 cm s$^{-1}$ to 5 cm s$^{-1}$. The errors in the absolute and the mean velocities are similar to those reported previously for other currents. The comparable performance suggests the Gaussian jet model is a promising methodology for determining absolute geostrophic velocities, noting that in this region the Kuroshio does not meander sufficiently and thus provides unfavorable environment for the performance of the Gaussian jet model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.1-5
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• 2008

An experimental study was performed to develop the rotational fuel injection system of the micro turbojet engine. In this system, fuel is sprayed by centrifugal forces of engine shaft. The test rig was designed and manufactured to get droplet information on combustion space. This experimental apparatus consist of a high speed rotational device(Air-Spindle), fuel feeder, rotational fuel injector and acrylic case. To understand spray characteristics, spray droplet size, velocity and distribution were measured by PDPA (Phase Doppler Particle Analyzer) and spray was visualized by using Nd-Yag laser-based flash photography. From the test results, the length of liquid column from injection orifice is controlled by the rotational speeds and Sauter Mean Diameter(SMD) is decreased with rotational speed. Also, Sauter Mean Diameter is increased as increasing mass flow rate at same rotational speeds.

• Clinical and Experimental Pediatrics
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• v.65 no.1
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• pp.47-52
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• 2022

Background: An adequate large-scale pediatric cohort based on nationwide administrative data is lacking in Korea. Purpose: This study aimed to differentiate patients with VVS by autonomic dysfunction severity using the composite autonomic severity score (CASS) and compare the clinical manifestations and prognosis between patient subgroups. Methods: We retrospectively reviewed the medical records of 66 VVS patients divided into 3 groups by CASS. To compare the differences between these groups, we analyzed VVS type, triggers, prodromal symptoms, management of syncope, and prognosis between patients with mild versus moderate autonomic dysfunction. Results: Of our 66 patients with VVS, 41 had mild autonomic dysfunction (62.1%) and 25 had moderate autonomic dysfunction (37.9%). We found no significant intergroup differences in age, sex, inducible factor (P=0.172), prodromal symptoms, laboratory findings, head-up tilt test, type of syncope, or prognosis (P=0.154). Conclusion: We found no evidence that autonomic dysfunction degree is affected by VVS characteristics, test findings, parameters, or prognosis; therefore, no further evaluations are needed to classify autonomic dysfunction severity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.6
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• pp.793-803
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• 1997

This experimental study was mainly investigated on the swirl flow characteristics in the cylinder generated by a helical intake port. LDA system was used for the measurement of in-cylinder velocity fields. Tangential and axial velocity profiles, with varying valve lifts, valve eccentricity ratios and axial distance, were measured. When the intake valve was set in the cylinder center, we could find that in-cylinder swirl flow fields were composed of a forced vortex motion and a free vortex motion in the vicinity of the cylinder center and the cylinder wall respectively. In case of valve eccentricity ratio, N$_{y}$ = 0.45, the vortex flow which rotates to the opposite direction of a main rotating flow in the cylinder was found. And the reverse flow toward the cylinder head surface was also found in axial velocity profile and it showed the tendency of the linear decrease in the region of 0.leq.Y/B.leq.1.2.2.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.117-124
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• 2001

This paper presents turbulent characteristics of an impinging F-O-O-F type injector in which fuel ad oxidizer impinge on each other to atomize under the different momentum ratio. Water was used as an inert simulant liquid instead of fuel and oxidizer. The droplet size and velocity in the impinging spray flow field were measured using a PDPA. The gradient of the spray half-width(b$_2$) along the long-axis direction declined throughout the entire spray flow field with increasing the momentum ratio from 1.19 to 6.48. However, the gradient of the half-width(b$_1$) along the short-axis direction decreased with increasing the momentum ratio. The turbulence intensity and turbulent kinetic energy were converged into the center of the center of the initial region with increasing the momentum ratio. As the momentum ratio increased from MR=1.19 to MR=6.48, the turbulent shear stress decreased. The results of this study can be used for the design of an impinging type injector for liquid rackets.

• Childhood Kidney Diseases
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• v.14 no.1
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• pp.84-88
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• 2010

Posterior nutcracker phenomenon (PNP) was found to be the cause of significant proteinuria in a 10-year-old female. PNP was documented by Doppler ultrasonography and abdominal 3D CT as a cause of her proteinuria. Despite treatment with ACE inhibitor for several months, her persistent and progressive proteinuria lead us to perform a left renal biopsy, which revealed no significant finding except for focal effacement of foot processes. We speculate that nutcracker phenomenon can induce not only orthostatic proteinuria but also significant proteinuria by focal effacement of foot processes.

• Archives of Reconstructive Microsurgery
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• v.25 no.2
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• pp.37-42
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• 2016

Purpose: Soft tissue coverage of the distal leg and ankle region represents a surgical challenge. Beside various local and free flaps, the perforator flap has recently been replaced as a reconstructive choice because of its functional and aesthetic superiority. Although posterior tibial artery perforator flap (PTAPF) has been reported less often than peroneal artery perforator flap, it also provides a reliable surgical option in small to moderate sized defects especially around the medial malleolar region. Materials and Methods: Seven consecutive patients with soft tissue defect in the ankle and foot region were enrolled. After Doppler tracing along the posterior tibial artery, the PTAPF was elevated from the adjacent tissue. The average size of the flap was $28.08{\pm}9.31cm^2$ (range, 14.25 to $37.84cm^2$). The elevated flap was acutely rotated or advanced. Results: Six flaps survived completely but one flap showed partial necrosis because of overprediction of the perforasome. No donor site complications were observed during the follow-up period and all seven patients were satisfied with the final results. Conclusion: For a small to medium-sized defect in the lower leg, we conducted the close-by islanded PTAPF using a single proper adjacent perforator. Considering the weak point of the conventional propeller flap, this technique yields much better aesthetic results as a simple and reliable technique especially for defects of the medial malleolar region.

• Korean Journal of Head & Neck Oncology
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• v.39 no.2
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• pp.31-34
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• 2023

Pilomatricoma is characterized by a semi-transparent epidermis, especially pigmented pilomatricoma, containing melanocytes in basaloid cells, which are dark and purple, resembling vessel-derived skin masses. If the vascularity at doppler ultrasound is high before surgery, it may be misdiagnosed. A 10-year-old female patient visited our clinic because of a mass in the right ear triangular fossa. Ultrasonography was performed, and a vascular-origin tumor was suspected because of the high vascularity. The excised mass was diagnosed as pigmented pilomatricoma by a pathologist. Pilomatricoma is mistaken for other masses owing to its various phenotypes. A misdiagnosis can lead to misdirected strategies which can cause delayed treatment and can result in an increase in the size of the pilomatricoma, making the sequalae of surgery more complicated. For proper treatment, careful examination and evaluation are required before surgery.

• Journal of Korean Neurosurgical Society
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• v.54 no.3
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• pp.159-163
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• 2013

Objective : Cerebral hyperperfusion syndrome (CHS) is a serious complication after carotid endarterectomy (CEA). However, the prevalence of CHS has decreased as techniques have improved. This study evaluates the role of strict blood pressure (BP) control for the prevention of CHS. Methods : All 18 patients who received CEA from February 2009 through November 2012 were retrospectively reviewed. All patients were routinely managed in an intensive care unit by a same protocol. The cerebral perfusion state was evaluated on the basis of the regional cerebral blood flow (rCBF) study by perfusion computed tomography (pCT) and mean velocity by transcranial doppler (TCD). BP was strictly controlled (<140/90 mm Hg) for 7 days. When either post-CEA hyperperfusion (>100% increase in the rCBF by pCT or in the mean velocity by TCD compared with preoperative values) or CHS was detected, BP was maintained below 120/80 mm Hg. Results : TCD and pCT data on the patients were analyzed. Ipsilateral rCBF was significantly increased after CEA in the pCT (p=0.049). Post-CEA hyperperfusion was observed in 3 patients (18.7%) in the pCT and 2 patients (12.5%) in the TCD study. No patients developed clinical CHS for one month after CEA. Furthermore, no patients developed additional neurological deficits related to postoperative cerebrovascular complications. Conclusion : Intensive care with strict BP control (<140/90 mm Hg) achieved a low prevalence of post-CEA hyperperfusion and prevented CHS. This study suggests that intensive care with strict BP control can prevent the prevalence of post-CEA CHS.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.211-219
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• 2014

Closed cracks are difficult to detect using conventional ultrasonic testing because most incident ultrasound passes completely through these cracks. Nonlinear ultrasound inspection using sub-harmonic frequencies a promising method for detecting closed cracks. To implement this method, a sub-harmonic phased array (PA) is proposed to visualize the length of closed cracks in solids. A sub-harmonic PA generally consists of a single transmitter and an array receiver, which detects sub-harmonic waves generated from closed cracks. The PA images are obtained using the total focusing method (TFM), which (with a transmitter and receiving array) employs a full matrix in the observation region to achieve fine image resolution. In particular, the receiving signals are measured using a laser Doppler vibrometer (LDV) to collect PA images for both fundamental and sub-harmonic frequencies. Oblique incidence, which is used to boost sub-harmonic generation, inevitably produces various surface waves that contaminate the signals measured in the receiving transducer. Surface wave interference often degrades PA images severely, and it becomes difficult to read the closed crack's position from the images. Various methods to prevent or eliminate this interference are possible. In particular, enhancing images with signal processing could be a highly cost-effective method. Because periodic patterns distributed in a PA image are the most frequent interference induced by surface waves, spatial frequency filtering is applicable for removing these waves. Experiments clearly demonstrate that the spatial frequency filter improves PA images.