• Journal of Energy Engineering
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• v.8 no.1
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• pp.189-201
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• 1999

범용 열가소성 플라스틱(polyethylene(PE), polypropylene(PP), polystyrene(PS), polyethylene-terephthalate(PET), acrylonitrile-butandiene-styrene(ABS))과 폐윤활유의 동시처리 열분해반응 실험을 수행하였다. 반응실험은 40$m\ell$ 용량의 회분식 미분반응기(microreactor)를 이용한 실험과 1리터 용량의 autoclave를 이용한 실험의 두 가지로 구분하여 행하였다. 전자의 경우는 통계적 실험적계획법(statistical experimental design)의 하나인 회전계획실험(rotatable design experiments)으로서 오각형 실험계획(pentagonal experimental design)에 의거한 반응변수 실험을 수행한 후 반응표면(response surface)을 회기분석법에 의하여 분석함으로써 최대의 오일 수율을 얻을 수 있는 최적 반응조건을 추적, 결정하였다. Autoclave 반응실험의 기본적인 목적은 실제 연속공정에 있어서 열분해 반응기 거동을 모사하기 위한 전초단계로서 충분한 시료의 확보를 통하여 이 때 생성된 연로유의 체계적인 분석(비등점분포특성, 진공증류, 기체분석, 원소분석, 발열량, 비중 등)을 행함으로써 연료유 수율 및 품질을 모사하고자 하였다. 미분반응기 실험에 있어서 주 범용열가소성수지인 PE, PP 그리고 PS는 각각의 최적반응조건하에서 거의 100%에 가깝게 오일로 전환되었지만 응축수지인 PET와 그래프트공중합수지인 ABS의 오일수율은 각기 78% 및 90%로서 상대적으로 낮게 나타났다. Autoclave를 이용한 실험의 경우 혼합플라스틱을 폐유에 대하여 40wt% 혼합하여 열분해하였을 때, 80wt% 오일, 15wt% 코우크, 그리고 나머지 5wt%는 탄화수소기체(C1-C6)로 전환되었다. 진공증류(252$^{\circ}C$,2 torr) 결과, 기/액-분리도는 3으로서 이는 생성오일의 75wt%가 경질연료유(가솔린, 등유, 경유)로 회수 가능하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04b
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• pp.72-75
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• 2000

The effect of $Al_2O_3+Y_2O_3$ additives on fracture toughness of ${\beta}-SiC-TiB_2$ composites by hot-pressed sintering were investigated, The ${\beta}-SiC-TiB_2$ ceramic composites were hot-presse sintered and annealed by adding 4, 8, 12wt% $Al_2O_3+Y_2O_3$(6 : 4wt%) powder as a liquid forming additives at low temperature($1800^{\circ}C$) for 4h. In this microstructures, the relative density is over 97% of the theoretical density and the porosity increased with increasing $Al_2O_3+Y_2O_3$ contents because of the increasing tendency of pore formation. But the fracture toughness showed the highest of $7.0MPa{\cdot}m^{1/2}$ for composites added with 12wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity showed the lowest of $1.59\times10^{-3}\Omega{\cdot}cm$ for composite added with 8wt% $Al_2O_3+Y_2O_3$ additives at room temperature and is all positive temperature coefficient resistance(PTCR} against temperature up to $700^{\circ}C$.

• Journal of Korean Neurosurgical Society
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• v.58 no.1
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• pp.43-49
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• 2015

Objective : $Dynesys^{(R)}$ is one of the pedicle-based dynamic lumbar stabilization systems and good clinical outcome has been reported. However, the cylindrical spacer between the heads of the screws undergoes deformation during assembly of the system. The pre-strain probably change the angle of instrumented spine with time and oblique-shaped spacer may reduce the pre-strain. We analyzed patients with single-level stabilization with $Dynesys^{(R)}$ and simulated oblique-shaped spacer with finite element (FE) model analysis. Methods : Consecutive 14 patients, who underwent surgery for single-level lumbar spinal stenosis and were followed-up more than 24 months (M : F=6 : 8; age, $58.7{\pm}8.0$ years), were analyzed. Lumbar lordosis and segmental angle at the index level were compared between preoperation and postoperative month 24. The von Mises stresses on the obliquely-cut spacer ($5^{\circ}$, $10^{\circ}$, $15^{\circ}$, $20^{\circ}$, $25^{\circ}$, and $30^{\circ}$) were calculated under the compressive force of 400 N and 10 Nm of moment with validated FE model of the L4-5 spinal motion segment with segmental angle of $16^{\circ}$. Results : Lumbar lordosis was not changed, while segmental angle was changed significantly from $-8.1{\pm}7.2^{\circ}$ to $-5.9{\pm}6.7^{\circ}$ (p<0.01) at postoperative month 24. The maximum von Mises stresses were markedly decreased with increased angle of the spacer up to $20^{\circ}$. The stress on the spacer was uneven with cylindrical spacer but it became even with the $15^{\circ}$ oblique spacer. Conclusion : The decreased segmental lordosis may be partially related to the pre-strain of Dynesys. Further clinical and biomechanical studies are required for relevant use of the system.

• Journal of Korean Neurosurgical Society
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• v.52 no.4
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• pp.396-403
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• 2012

Objective : The predictors of cranioplasty infection after decompressive craniectomy have not yet been fully characterized. The objective of the current study was to compare the long-term incidences of surgical site infection according to the graft material and cranioplasty timing after craniectomy, and to determine the associated factors of cranioplasty infection. Methods : A retrospective cohort study was conducted to assess graft infection in patients who underwent cranioplasty after decompressive craniectomy between 2001 and 2011 at a single-center. From a total of 197 eligible patients, 131 patients undergoing 134 cranioplasties were assessed for event-free survival according to graft material and cranioplasty timing after craniectomy. Kaplan-Meier survival analysis and Cox regression methods were employed, with cranioplasty infection identified as the primary outcome. Secondary outcomes were also evaluated, including autogenous bone resorption, epidural hematoma, subdural hematoma and brain contusion. Results : The median follow-up duration was 454 days (range 10 to 3900 days), during which 14 (10.7%) patients suffered cranioplasty infection. There was no significant difference between the two groups for event-free survival rate for cranioplasty infection with either a cryopreserved or artificial bone graft (p=0.074). Intergroup differences according to cranioplasty time after craniectomy were also not observed (p=0.083). Poor neurologic outcome at cranioplasty significantly affected the development of cranioplasty infection (hazard ratio 5.203, 95% CI 1.075 to 25.193, p=0.04). Conclusion : Neurologic status may influence cranioplasty infection after decompressive craniectomy. A further prospective study about predictors of cranioplasty infection including graft material and cranioplasty timing is necessary.

• Journal of Korean Neurosurgical Society
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• v.56 no.2
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• pp.121-129
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• 2014

Objectives : Patients with cervical ossification of posterior longitudinal ligament (OPLL) are susceptible to cord injury, which often develops into myelopathic symptoms. However, little is known regarding the prognostic factors that are involved in minor trauma. We evaluated the relationship between minor trauma and neurological outcome of OPLL and investigated the prognostic factors with a focus on compressive factors and intramedullary signal intensity (SI). Methods : A total of 74 patients with cervical myelopathy caused by OPLL at more than three-levels were treated with posterior decompression surgeries. We surveyed the space available for spinal cord (SAC), the severity of SI change on T2-weighted image, and diabetes mellitus (DM). The neurological outcome using Japanese Orthopedic Association (JOA) scale was assessed at admission and at 12-month follow-up. Results : Among the variables tested, preoperative JOA score, severity of intramedullary SI, SAC, and DM were significantly related to neurological outcome. The mean preoperative JOA were $11.3{\pm}1.9$ for the 41 patients who did not have histories of trauma and $8.0{\pm}3.1$ for the 33 patients who had suffered minor traumas (p<0.05). However, there were no significant differences in the recovery ratios between those two groups. Conclusions : Initial neurological status and high intramedullary SI in the preoperative phase were related to poorer postoperative outcomes. Moreover, the patients with no histories of DM and larger SACs exhibited better improvement than did the patients with DM and smaller SACs. Although the initial JOA scores were worse for the minor trauma patients than did those who had no trauma prior to surgery, minor trauma exerted no direct effects on the surgical outcomes.

• Journal of KIISE:Information Networking
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• v.34 no.4
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• pp.287-295
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• 2007

IETF's FMIPv6 protocol enables a mobile node to switch to the reactive mode of handover operation when the prediction of the movement is incorrect. In this case, the mobile node may experience severe service disruption due to large handover latency and packet loss. In order to solve this problem, we propose a fast mobile IP handover with multiple pre-registrations. In the proposed approach, the new temporary IP addresses are prepared in advance at multiple locations where the mobile node may probably move into. In this case, even though the prediction is wrong, the mobile node can move into the alternative locations without causing service disruption. We have designed and implemented a prototype system, and measured the performance of the proposed system. The experimental results show that the proposed approach can reduce the handover latency drastically.

• The Journal of Korean Medicine
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• v.27 no.4
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• pp.225-232
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• 2006

Objective : To test the hypotheses that individualized traditional Korean acupuncture improves pain and disability in patients with osteoarthritis of the knee and that benefits remain after stopping treatment more so than is the case for standardized minimal acupuncture. Design : Randomized single blind controlled trial with two intervention arms (individualized traditional Korean acupuncture, standardized minimal acupuncture) of six weeks' duration and three months follow-up. Setting : Acupuncture interventions were applied by two training doctors in the Department of Acupuncture and Moxibustion in a 1000-bed hospital. Assessment of the result was performed in a university-based laboratory. Participants : 50 patients with symptoms of knee osteoarthritis as diagnosed by an orthopedist. Intervention : Individualized traditional Korean acupuncture or standardized minimal acupuncture for six weeks. Main outcome measures: Primary outcome measure was pain as measured by the visual analogue scale. Secondary measures of pain and disability included the Western Ontario and McMaster Universities (WOMAC) index, Short Form-36 (SF-36), Lequesne Functional Index (LFI) score and Korean version of Health Assessment Questionnaire (KHAQ). Discussion : This paper presents detail on the rationale, design, methods and operational aspects of the trial.

• Progress in Superconductivity
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• v.9 no.1
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• pp.29-34
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• 2007

The baseline selection is the first and important step to analyze magnetocardiography (MCG) parameters. There are no difficulties to select the baseline between P- and Q-wave peak (P-Q interval) of MCG wave recorded from healthy subjects because the P-Q intervals of the healthy subjects do not much vary. However, patients with ischemic heart disease often show an unstable P-Q interval which does not seem to be appropriate for the baseline. In this case, T-P interval is alternatively recommended for the baseline. However, there has been no study on the difference made by the baseline selection. In this study, we studied the effect of the different baseline selection. MCG data were analyzed from twenty healthy subjects and twenty one patients whose baselines were alternatively selected in the T-P interval for their inappropriate P-Q interval. Paired T-test was used to compare two set of data. Fifteen parameters derived from the R-wave peak, the T-wave peak, and the period, $T_{max/3}{\sim}T_{max}$ were compared for the different baseline selection. As a result, most parameters did not show significant differences (p>0.05) except few parameters. Therefore, there will be no significant differences if anyone of two intervals were selected for the MCG baseline. However, for the consistent analysis, P-Q interval is strongly recommended for the baseline correction.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1513-1519
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• 2010

Recently, on-line process monitoring systems using sensors are being extensively used to produce highquality products. However, the difficulty in installing the sensors within the mold in the cases of micro-molds, optical molds, and molds with complex structures is a serious disadvantage of such process monitoring systems. In this study, the quantitative index of a process monitoring system was evaluated with the mold cavity pressure and the nozzle pressure for the injection molding machine. In order to evaluate the effect of the nozzle pressure, we performed correlation analysis for the weight of the molded product. We also examined the control characteristics of the injection molding machine by analyzing the effect of multistage injection speed, holding pressure, and injection pressure limit on the process monitoring data.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.182-188
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• 2017

In this work, a new type speaker which features various resonant frequencies is proposed utilizing a magneto-rheological (MR) fluid and its performance is evaluated in terms of the change of the field-dependent sound pressure level. In order to achieve this goal, a whole concept of the speaker system is firstly discussed and subsequently a controllable diaphragm is made using MR fluid whose rheological properties such as viscosity are controllable by the magnitude of magnetic field. Then, the proposed speaker system consisting of the inner structure and the squeeze mode type of MR diaphragm is established in an anechoic room The effectiveness of the proposed speaker system is experimentally evaluated at two different conditions; with and without the magnetic field. It is shown from experimental tests that the sound pressure level at different sound source can be controlled which is not able to achieve using one conventional speaker system.