• Journal of radiological science and technology
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• v.29 no.3
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• pp.157-165
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• 2006

In order to analyze clinical characteristics like sex- and age-based onset frequency and onset region from vertebral disease cases, this study investigated total 1,291 cases of vertebral disease that were diagnosed via magnetic resonance imaging(MRI) from January to December 2004 at B University Hospital in metropolitan area. For higher diagnostic accuracy in cases of spinal disorder diagnosed, this study analyzed findings from data reading conducted by veteran specialists in diagnostic radiology. But this study excluded uncertain lesion cases, the cases requiring differential diagnosis from other disorders and so on from subjects under analysis. This study employed superconductive 1.5 Tesla SIGNA MR/i for MRI test and basically received resulting images via FSE(fast spin echo). In particular, this study obtained T1 and T2 myelogram with regard to regional characteristics(such as cervical vertebrae, thoracic vertebrae and lumbar vertebra) and imaging characteristics for sagittal and transverse section. As a result, this study came to the following conclusions : 1. In terms of general characteristics of subjects under analysis, male group comprised 53.5% and female 46.5% out of total 1,291 subjects. 2. The regional onset frequency of spinal disorders was converged primarily on lumbar vertebra(65.5%), which was followed by cervical vertebrae(27.3%) and thoracic vertebrae(7.0%) respectively. 3. Top 10 cases with high onset frequency of spinal disorders can be listed as follows : 1) posterior bulging disc 65.8% 2) narrowing of neural foramen 23.8% 3) herniated intervertebral disc (HIVD) 22.4% 4) spinal stenosis 16.7% 5) osteochondrosis 6.4% 6) compression fracture 6.4% 7) facet joint arthropathy 6.2% 8) spondylolisthesis 6.0% 9) spinal cord tumor 3.5% 10) inter body fusion 2.6%

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.1
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• pp.43-50
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• 2001

In order to analyze the dynamic motions of fish cage systems made of a frame and a netting under the conditions of waves and current, the hydraulic model experiment at towing tank and the numerical computation using boundary integral element method based on linear potential theory were carried out on a square and a circular type of fish cage, The computed and measured results for the dynamic motions of model fish cage systems showed that the heave and pitch motions were almost unaffected by the inclusion of nets, while the surge motions were very reduced by drag force acting on them. In addition, irregular wave-induced motions of fish cages included non-negligible 2nd order harmonic components at high frequency nearly twice the wave frequency. The reason why these motions were considered was due to resonance or structural components of frames being overflown and out of water during a wave cycle. It was found that circular type was more desirable structure in the open sea than square one only in the respect of dynamic motions due to waves and current. Further verifications were needed considering hydrodynamic forces, fatigue life, and structure analysis based on long term stochastic waves including frequency and time domain for the purpose of analyzing and designing fish cage systems.

• Advances in aircraft and spacecraft science
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• v.5 no.2
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• pp.225-237
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• 2018

The difficulties of satellite vibration testing are due to the commonly expressed qualification requirements being incompatible with the limited performance of the entire controlled system (satellite + interface + shaker + controller). Two features cause the problem: firstly, the main satellite modes (i.e., the first structural mode and the high and low tank modes) are very weakly damped; secondly, the controller is just too basic to achieve the expected performance in such cases. The combination of these two issues results in oscillations around the notching levels and high amplitude beating immediately after the mode. The beating overshoots are a major risk source because they can result in the test being aborted if the qualification upper limit is exceeded. Although the abort is, in itself, a safety measure protecting the tested satellite, it increases the risk of structural fatigue, firstly because the abort threshold has been already reached, and secondly, because the test must restart at the same close-resonance frequency and remain there until the qualification level is reached and the sweep frequency can continue. The beat minimum relates only to small successive frequency ranges in which the qualification level is not reached. Although they are less problematic because they do not cause an inadvertent test shutdown, such situations inevitably result in waiver requests from the client. A controlled-system analysis indicates an operating principle that cannot provide sufficient stability: the drive calculation (which controls the process) simply multiplies the frequency reference (usually called cola) and a function of the following setpoint, the ratio between the amplitude already reached and the previous setpoint, and the compression factor. This function value changes at each cola interval, but it never takes into account the sensor signal phase. Because of these limitations, we firstly examined whether it was possible to empirically determine, using a series of tests with a very simple dummy, a controller setting process that significantly improves the results. As the attempt failed, we have performed simulations seeking an optimum adjustment by finding the Least Mean Square of the difference between the reference and response signal. The simulations showed a significant improvement during the notch beat and a small reduction in the beat amplitude. However, the small improvement in this process was not useful because it highlighted the need to change the reference at each cola interval, sometimes with instructions almost twice the qualification level. Another uncertainty regarding the consequences of such an approach involves the impact of differences between the estimated model (used in the simulation) and the actual system. As limitations in the current controller were identified in different approaches, we considered the feasibility of a new controller that takes into account an estimated single-input multi-output (SIMO) model. Its parameters were estimated from a very low-level throughput. Against this backdrop, we analyzed the feasibility of an LQG control in cancelling beating, and this article highlights the relevance of such an approach.

• Geotechnical Engineering
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• v.7 no.1
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• pp.41-52
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• 1991

A study of the effects of dynamic pile-soil-structure interactions on the response of super- structures, supported by group piles, are presented in this paper. The dynamic impedance functions of single pile generated by soil-pile interactions are obtained and compared among others using the methods proposed by Novak, Gazetas, and Kuhlemeyer, and using the equivalent cantilever method. Group pile effects are also considered by the following approaches : neglecting interaction effects : group efficiency ratio concept : static interaction approach . and dynamic interaction approach. The responses of a nuclear containment structure are obtained by using the elastic half-space analysis, based on the impedance functions mentioned above. Main conclusions drawn from this study are as follows : 1. The numerical results of the impedance functions calculated by each method were quite different : the Novak's was the smallest, and the Kuhlemeyer's the highest. Considering group effects, similar values in each approach were obtained for the stiffness : the difference was very big for the damping. 2. The top displacement of the structure was reduced by 20% or more by pile installations. However, the base shear force, the base moment, and the resonance frequency were increased by more than two times due to stiffening effect of the ground by pile installations. 3. Whether frequency dependant impedence functions or frequency independant functions were used, the responses of the structure were not so much affected by the choice of the impedance functions. 4. The reduction effect of the top displacement increased with the increase of the maximum ground acceleration.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.1
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• pp.42-52
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• 2008

Purpose: Resonance Frequency Analysis(RFA) technique can be used as an effective method in measuring the implant stability and documenting the clinical results. This technique also determines how stable the implant is before performing a prosthetic practice. Having become one the guidelines of the implant therapy whose final objective is the immediate loading, the $Osstell^{TM}$ mentor is giving a lot of information to the clinicians recently. In this communication, experiments were performed to investigate how reliable the measured ISQ values by $Osstell^{TM}$ mentor are, and to see if those are also stable even after sterilization. As five objectives: 1) How stable measured ISQ values after fixation $Smartpeg^{TM}s$ for 400 times. 2) How stable measured ISQ values after 'attach-detach'$Smartpeg^{TM}'s$ for 400 times. 3) How stable measured ISQ values after clinical sterilization methods. 4) How stable measured ISQ values after repeatedly sterilization in autoclave for 10 times. 5) What is the critical temperature which is lost the magnetism of $Smartpeg^{TM}$. Materials and Methods: Clinical sterilization methods(Autoclave sterilization, Dentistar sterilization, Ultra violet sterilization, Vacuum dry unit sterilization, Boiling water sterilization, combined $H_{2}O_{2}$ and Alcohol sterilization).$Smartpeg^{TM}s$. D3 Block bone($3{\times}9{\times}2cm$). Osstem implant(${\emptyset}4.1$-10mm).$Osstell^{TM}$ mentor. Individual experiment was used 8 number of $Smartpeg^{TM}s$ and they had measured to ISQ values of before experiment and after experiment. Results: 1. The measured ISQ values did not change after fixation $Smartpeg^{TM}s$ for 400 times. 2. There was no significant changes in the measured ISQ values of 'attach-detach $Smartpeg^{TM}s'$ for 400 times. 3. The measured ISQ values did not change after the usual clinical sterilization methods. 4. The measured ISQ values did not change after sterilization in autoclave for 10 times. 5. It was impossible to exactly measure the critical temperature which is lost the magnetism of $Smartpeg^{TM}s$. But, the results was resulted to lost its magnetism in higher temperature than $150^{\circ}C$/10 minute. Conclusion: The measured ISQ values showed insignificant differences in case of no changes in the magnetism of the $Smartpeg^{TM}s$. It seems that the $Smartpeg^{TM}s$ can be used repeatedly in every measurement if the original magnetisms of the $Smartpeg^{TM}s$ can be recognized. There seems to be no significant changes in the measured ISQ values of 'attach-detach $Smartpeg^{TM}s'$ only if the screw pitches were unimpaired. The clinical sterilization methods seems acceptable because the result was resulted to lost its magnetism in higher temperature than $150^{\circ}C$/10minute.

• The Journal of the Korean dental association
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• v.50 no.1
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• pp.31-37
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• 2012

Objective : This research compared stabilities between two types of dental implant ($SLA^{TM}$, Institut Straumann AG, Waldenburg, Switzerland and $SSII^{TM}$, Osstem co, Busan, Korea) using Osstell Mentor (Integration Diagnostics AB, Goteborg, Sweden) considering surgery methods, surgery area, diameter of implant, systemic disease, and smoking for obtaining prognosis information when installing fixture of dental implant. Materials & Methods : 206 implants of 131 patients taken by resonance frequency analysis (RFA) were determined as a final sample. Dental implants were installed as protocol of supplier by a excellent dentist who had 10 years experience about dental implants. Before connecting abutments (3 months after installation of fixture), RFA were measured twice for buccal and lingual direction to obtain average value. Results : Dental implants at mandible showed significantly higher stabilities significantly than at maxilla (p<0.001). Diameter 4.8 implants had also higher stabilities than diameter 4.1 in case of $SLA^{TM}$ implants (p<0.001). $SLA^{TM}$ implants showed more excellent stabilities than $SSII^{TM}$ implants, especially at posterior area of mandible (p=0.045) and premolar area of maxilla (p=0.032). Conclusions : This research revealed higher stabilities of $SLA^{TM}$ implants than $SSII^{TM}$ implant, especially at posterior area of mandible (p=0.045) and premolar area of maxilla (p=0.032).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.9 s.100
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• pp.883-892
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• 2005

We propose a T-shaped UWB printed monopole antenna and investigate the effect of the surface currents of the radiator and ground plane. The measured impedance bandwidth of the antenna covers the range of 3.1 to 11 GHz for a VSWR$\le$2, which satisfies the requirement of the UWB operation. From the analysis of the surface currents, the proposed antenna can be treated as two asymmetric dipoles with the included angle of 90 degrees which lie along z-direction symmetrically. It is observed that the effect of the surface currents on the radiation patterns is similar to that of the corresponding dipole. The length and width of the found plane correspond the radius and length of the dipole respectively. This approach is also valid to general printed monopole antennas. Finally, we included an antenna example having resonance at a lower frequency by tapering the edges of the ground plane and another example having a bandstop characteristic by inserting an inverted-U slot on the radiator, and explain those antennas using the surface currents.

• The Journal of the Korean dental association
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• v.54 no.7
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• pp.529-540
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• 2016

Objective: The objective of this study was to evaluate the osseointegration of narrow-diameter implant with trapezoid-shape and to evaluate the effect of coronal microthreads on trapezoid-shape narrow-diameter implant. Materials and Methods: The experimental narrow-diameter implants were classified into two groups according to absence or presence of coronal microthreads: trapezoid-shape narrow diameter implant (TN group) and trapezoid-shape narrow-diameter implant with microthreads (TNM group). They were installed alternately in bilateral mandible in three dogs. After 8 weeks, the animals were sacrificed. Resonance frequency analysis, removal torque test, and histometric analysis were performed. Results: Statistically higher implant stability quotient (ISQ) values were observed in TNM group than in TN group at the time of implant installation. However, significant ISQ values difference was not observed between groups at 8 weeks. Both groups showed significantly increased ISQ values at 8 weeks, compared to the time of implant installation. There was no significant difference between groups in removal torque test. Bone-implant contact ratio also showed no significant difference between groups in total and coronal part. Conclusion: Within the limitation of this study, it could be concluded that the trapezoid-shape design on narrow-diameter implant showed successful ossointegration, and the microthreads on coronal part did not result in significant bone-implant contact and biomechanical stability at 8 weeks.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.5
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• pp.549-560
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• 2006

Purpose : This experiment examined the effects of anodization on commercially pure titanium implant fixtures. Material & methods : The implant fixtures were anodized at three different voltage levels, producing three different levels of oxidation on the surface of the fixure. Implant were divided into four groups according to the level of oxidation. Group 1 consist of the control group of machined surface implants, Group 2 implants were treated by anodizing to 100 voltage, Group 3 implants were treated by anodizing oxidation to 200 voltage Group 4 implants were treated by anodizing oxidation to 350 voltage. Surface morphology was observed by Scanning Electron Microscope(SEM) and the surface roughness was measured using NanoScan $E-1000^{\circledR}$. Implantation of the fixtures were performed using New Zealand white rabbits. $Periotest^{\circledR}$ value(PTV) resonance frequency analysis(RFA), and removal torque were measured in 0, 2, 4, 8, 12 weeks after implantation. Results : The results of the study were as follows: 1. Values for the measured surface roughness indicate statistically significant differences in Ra, Rq, and Rt values among group 1, 2, 3, and 4 at the top portion of the thread,(p<0.05) while values at the base of the threads indicated no significant difference in these values. 2. A direct correlation between the firming voltage, and surface roughness and irregularities were observed using scanning electron microscope. 3. No statistically significant differences were found between test groups regarding $Periotest^{\circledR}$ values. 4. Analysis of the data produced by RFA, significant differences were found between group 1 and group 4 at 12 weeks after implantation.(p<0.05) Conclusions : In conclusion, no significant differences could be found among test groups up to a certain level of forming voltage threshold, beyond this firming voltage threshold, statistically significant differences occurred as the surface area of the oxide layer increased with the increase in surface porosity, resulting in enhanced bone response and osseointegration.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.8
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• pp.1035-1044
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• 2010

Head-related transfer function (HRTF) is an acoustic transfer function from a sound source to the ear canal entrance position. HRTFs are very important information in the construction of virtual sound fields. HRTFs also vary for different individuals. In this study, characteristics of HRTF for an average Korean are investigated numerically by comparing with the HRTF for a standard Knowles Electronics Manikin for Acoustic Research (KEMAR). A boundary element (BE) model for an adult Korean is developed using the computerized tomography (CT) data in order to investigate the variation in HRTFs for different individuals. The boundary conditions of the BE model are identified by comparing the numerical results with the experimental results. The numerical model shows that accurate HRTFs can be calculated efficiently over full audible frequency range for individuals.