• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.477-486
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• 2009

This paper deals with the strongest static arches with the solid regular polygon cross-section. Both span length and volume of arch are always held constant regardless the shape functions of cross-sectional depth of regular polygon. The normal stresses acting on such arches are calculated when both static vertical and horizontal point loads are subjected. By using the calculating results of stresses, the optimal shapes of strongest static arches are obtained, under which the maximum normal stress become to be minimum. For determining the redundant of such indeterminate arches, the least work theorem is adopted. As the numerical results, the configurations, i.e. section ratios, of the strongest static arches are reported in tables and figures. The results of this study can be utilized in the field of the minimum weight design of the arch structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2A
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• pp.155-162
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• 2009

This paper deals with the strongest beams with the solid regular polygon cross-section, whose volumes are always held constant. The differential equation of the elastic deflection curve of such beam subjected to the concentrated and trapezoidal distributed loads are derived and solved numerically. The Runge-Kutta method and shooting method are used to integrate the differential equation and to determine the unknown initial boundary condition of the given beam. In the numerical examples, the simple beams are considered as the end constraint and also, the linear, parabolic and sinusoidal tapers are considered as the shape function of cross sectional depth. As the numerical results, the configurations, i.e. section ratios, of the strongest beams are determined by reading the section ratios from the numerical data related with the static behaviors, under which static maximum behaviors become to be minimum.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3A
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• pp.251-258
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• 2009

This paper deals with the strongest beams with the solid regular polygon cross-section, whose volumes are always held constant. The differential equation of the elastic deflection curve of such beam subjected to the concentrated and trapezoidal distributed loads are derived and solved by using the double integration method. The Simpson's formula was used to numerically integrate the differential equation. In the numerical examples, the clamped-clamped and clamped-hinged ends are considered as the end constraints and the linear, parabolic and sinusoidal tapers are considered as the shape function of cross sectional depth. As the numerical results, the configurations, i.e. section ratios, of the strongest beams are determined by reading the section ratios from the numerical data obtained in this study, under which static maximum behaviors become to be minimum.

• The Journal of the Acoustical Society of Korea
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• v.27 no.6
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• pp.271-278
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• 2008

The electro-mechanical characteristics were theoretically analyzed for the wideband ultrasonic transducer made of non-uniform thickness piezoelectric vibrator. This paper proposes a combination of exponential functions which describes the thickness variation along the length of the vibrator to derive the input admittance and power transfer function of the transducer. The bandwidth and the power transfer function of the transducer were investigated while the lateral shape of the vibrator changes. The results showed there is an optimum shape for the wideband characteristics of the transducer, and the bandwidth has increased up to over 100% as the ratio of minimum value of thickness to maximum value decreases. However, the power transfer function had a downward trend as the ratio of thickness decreases. Also we confirmed that even though the value of transfer function increases as the length of the piezoelectric vibrator increases, the shape providing wideband characteristics is very limited. It means that precision processing is required to manufacturing a wideband ultrasonic transducer with high efficiency.

• Journal of radiological science and technology
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• v.27 no.4
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• pp.11-16
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• 2004

Classification of esophageal motility disorders not yet finalized and is still ongoing as the new disorders are reported, and the existing classification is changed or removed. In terms of radiology, the primary peristalsis does not exist, and the lower end of the esophagus show the smooth, tapered, beak-like appearance. The esophageal motility disorder, which mostly occurs in the smooth muscle area, show the symptoms of reduction or loss (hypomotility) or abnormal increase (hypermotility) of peristalsis of the esophagus. It is important to understand the anatomy and physiology of the esophagus for the appropriate radiological method and diagnosis. Furthermore, the symptom of the patient and the manometry finding must be closely referred for the radiological diagnosis. The lower esophageal sphincter can be normally functioning and open completely as the food moves lower. Sperandio M et al. argues that the name diffuse esophageal spasm must be changed to distal esophageal spasm (DES) as most of the spasm occurs in the distal esophagus, composed of the smooth muscle. According to Ott et al., usefulness of barium method for diagnosing the esophageal motility disorder is Achalasia 95%, DES 71% and NEMD 46%, with the overall sensitivity of 56%. However, excluding the nutcracker esophagus or nonspecific disorder which cannot be diagnosed with the radiological methods, the sensitivity increases to 89%. Using videofluoroscopy and 5 time swallows, the average sensitivity was over 90%. In conclusion, the barium method is a simple primary testing method for esophageal motility test. Using not only the image but also the videofluoroscopy with good knowledge of the anatomy and physiology, it is believed that the method will yield the accurate diagnosis.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.3
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• pp.300-305
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• 2012

In this paper, a miniaturized bow-tie monopole UWB antenna with band rejection characteristic is proposed. To miniaturize the proposed antenna, a perfect magnetic wall(PMW) condition is applied to primitive bow-tie monopole antenna. An uneven ground patch, a tapered feeding structure and a edge-chopped main patch are adapted for impedance matching. A quater-lambda slot resonator is inserted at main patch to prevent interference in UWB band from another band. The proposed antenna is fabricated on Taconic RF60-A substrate with relative permittivity of 6.15. The size of the proposed antenna is $30.0{\times}39.7mm^2$, which is only 45 % of the conventional bow-tie monopole antenna. The proposed antenna covers full UWB band with return losses less than -10 dB and has band stop characteristic in 5 GHz WLAN band. The maximum gains are within -1.0~5.0 dBi, the group delay variations are within 1.0 ns and the radiation patterns show directivity characteristics in x-y plane.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.2
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• pp.151-158
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• 2012

This paper proposes a H-plane 8-way rectangular waveguide power divider using Y-junction. A general N-way power divider can be composed of multi-stage T-junctions. However, if the distances of output ports are close, the matching characteristic is not improved by using only T-junctions because of space limitation. In this case, since other types of 3-port junctions should be used to final output stage, Y-junctions are used with T-junctions in this paper. The proposed Y-junction uses the tapered-line impedance transformer and inductive irises to improve impedance matching characteristic. The 8-way power divider using Y-junction is fabricated and measured. The measured return loss and insertion loss from input port to output port are -30.8 dB and -9.3 dB at operating frequency, respectively. The measured maximum phase difference is about $1^{\circ}$. Therefore, the proposed power divider will be useful to apply to various microwave systems, which need to divide the input power equally, such as feed networks for array antennas.

• The korean journal of orthodontics
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• v.37 no.1 s.120
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• pp.5-15
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• 2007

Objective: The purpose of this study was to evaluate the mechanical performance of mini-screws during insertion into artificial bone with use of the driving torque tester (Biomaterials Korea, Seoul, Korea), as well as testing of Pull-out Strength (POS). Methods: Experimental bone blocks with different cortical bone thickness were used as specimens. Three modules of commercially available drill-free type mini-screws (Type A; pure cylindrical type, Biomaterials Korea, Seoul, Korea, Type B; partially cylindrical type, Jeil Medical, Seoul, Korea, Type C; combination type of cylindrical and tapered portions, Ortholution, Seoul, Korea), were used. Results: Difference in the cortical bone thickness had little effect on the maximum insertion torque (MIT) in Type A mini-screws. But in Type B and C, MIT increased as the cortical bone thickness Increased. MIT of Type C was highest in all situations, then Type B and Type A in order. Type C showed lower POS than Type A or B in all situations. There were statistically significant correlations between cortical bone thickness and MIT, and POS for each type of the mini-screws. Conclusion: Since different screw designs showed different insertion torques with increases in cortical bone thickness, the best suitable screw design should be selected according to the different cortical thicknesses at the implant sites.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.285-289
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• 2015

With the miniaturization with both high functionality and high integrity of the probe cards, the highly precise laser punching on the zero-shrinkage high strength substrate has attracted more attention recently. Taper occurrence during laser-punching on green sheets appears as a problem in process. The size (diameter) difference between the entrance hole and the exit hole in tapered holes appeared to be inversely proportional to the hole size itself. To suppress taper occurrence, two-stage punching was adopted as the size of second hole was varied from $70{\mu}m$ to $79{\mu}m$ when punching $80{\mu}m$ via holes on the substrate with thickness of $380{\mu}m$. The minimal taper ratio of 11.9 % appeared with second hole size between 70 to $79{\mu}m$ before sintering. Taper ratio reduced to 7 % after zero-shrinkage sintering. The size difference between first hole and second hole appeared minimal when the size of second hole was 95~97 % to that of first hole.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.508-517
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• 2004

We described a near-field scanning microwave microscope which uses a high-quality dielectric resonator with a tunable screw. The operating frequency is f=4.5 5GHz. The probe tip is mounted in a cylindrical resonant cavity coupled to a dielectric resonator We developed a hybrid tip combining a reduced length of the tapered part with a small apex. In order to understand the function of the probe, we fabricated three different tips using a conventional chemical etching technique and observed three different NSMM images for patterened Cr films on glass substrates. We measured the reflection coefficient of different metal thin film samples with the same thickness of 300m and compared with theoretical impedance respectly. By tuning the tunable screw coming through the top cover, we could improve sensitivity, signal-to-noise ratio, and spatial resolution to better than $1{\mu}m$. To demonstrate the ability of local microwave characterization, the surface resistance of metallic thin films has been mapped.