• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1417-1425
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• 1990

In this paper, when the glass plate of fragile material is subjected to impact load, the fracture pattern and the generation phenomenon of cone crack were theoretically clarified by using the analysis method of impulsive stress in the first paper. The numerical analysis results of strain distribution at a distance of 0.1cm, from the impact loading point to 5cm, were compared with experimental results. The main conclusions obtained are as follows; (1) The generation phenomenon of cone crack at the impact fracture of the glass plate can be analytically confirmed by using the three dimensional dynamic theory of elasticity. And the numerical analysis results of strain distribution using this theory are relatively in close agreement with the crack size obtained from the impact fracture experiment. (2) After the stress wave generated at the impact point propagated to the spherical compressive wave, this stress wave reflected from the back surface and reached again at the surface of the plate to the spherical stress wave. Then the generation of cone crack can be confirmed along the stress wave surface. (3) The plate is the thicker, the more is the generation phenomenon of cone crack at the lower impact velocity range (20m/s-35m/s). Because the fracture generate before the maximum tensile stress acting to the glass plate, cone crack was rarely ever generated.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.3
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• pp.50-56
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• 2010

In this paper, compact broad-band antenna using circular spiral slot and CPW (coplanar waveguide) feed is proposed. The proposed antenna is designed on the same plane of the substrate by using CPW fed structure, archimediean spiral slot structure. So it was achieved both the size of compact antenna and the broad band. A archimediean spiral slot structure is introduced for resonance of medium band operation. The distances of a CPW feeder line and a ground plane are modified for impedance matching and lower/higher band operation. The proposed antenna has a compact size ($8mm\;{\times}\;13mm$) and it is etched on the FR-4 (relative dielectric constant 4.4, thickness 0.8mm) dielectric substrate. The simulated impedance bandwidth (VSWR $\leq$ 2) and maximum gain of the proposed antenna are 5.98GHz (4.1GHz ~ 10.08GHz) and 3.97dBi, respectively. The measured impedance bandwidth (VSWR $\leq$ 2) and maximum gain of the proposed antenna are 6.02GHz (4.48GHz ~ 10.5GHz) and 2.68dBi, respectively. The simulation and measured result shows good impedance matching and radiation pattern over the interesting frequency bands. It can be applied to antenna of broad-band wireless communication system.

• Economic and Environmental Geology
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• v.28 no.4
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• pp.395-404
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• 1995

The geologic structure of the Cheju volcanic island has been investigated by analyzing the gravity and magnetic data. Bouguer gravity map shows apparent circular low anomalies at the central volacanic edifice, and the maximum difference of the anomaly values on the island appears to be 30 mgal. The subsurface structure of the island is modeled by three-dimensional depth inversion of gravity data by assuming the model consists of a stacked grid of rectangular prisms of volcanic rocks bounded below by basement rocks. The gravity modeling reveals that the interface between upper volvanic rocks and underlying basement warps downward under Mt. Halla with the maximum depth of 5 km. Magnetic data involve aeromagnetic and surface magnetic survey data. Both magnetic anomaly maps show characteristic features which resemble the typical pattern of total magnetic anomalies caused by a magnetic body magnetized in the direction of the geomagnetic field in the middle latitude region, though details of two maps are somewhat different. The reduced-to-pole magnetic anomaly maps reveal that main magnetic sources in the island are rift zones and the Halla volcanic edifice. The apparent magnetic boundaries inferred by the method of Cordell and Grauch (1985) are relatively well matched with known geologic boundaries such as that of Pyosunri basalt and Sihungri basalt which form the latest erupted masses. Inversion of aeromagnetic data was conducted with two variables: depth and susceptibility. The inversion results show high susceptibility bodies in rift zones along the long axis of the island, and at the central volcano. Depths to the basement are 1.5~3 km under the major axis, 1~1.5 km under the lava plateau and culminates at about 5 km under Mt. Halla. The prominent anomalies showing N-S trending appear in the eastern part of both gravity and magnetic maps. It is speculated that this trend may be associated with an undefined fault developed across the rift zones.

• Journal of radiological science and technology
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• v.40 no.1
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• pp.19-25
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• 2017

The aim of this study was to evaluate Magnetic Resonance Imaging safety by measuring the translational attraction, torque and susceptibility artifact for Bone-Anchored Hearing Aid (BAHA) implant at 1.5 T and 3.0 T MRI by standard criteria. In vitro assessment tools were made of acrylic-resin by American Society for Testing and Materials (ASTM) F2052-06 and F2119-07 standard. Translational attraction of BAHA implant was measured by the maximum deflection angle at 96 cm position, where the magnetically induced deflection was the greatest. The torque was assessed by the qualitative criteria of evaluating the alignment and rotation pattern, when the BAHA implant was positioned on a line with $45^{\circ}$ intervals inside the circular container in the center of the bore. The susceptibility artifact images were obtained using the hanged test tool, which was filled with $CuSO_4$ solution. And then the artifact size was measured using Susceptibility A rtifact Measurement (SA M) software. In results, the translational attraction was 0 mm at both 1.5 T and 3.0 T and the torque was 0(no torque) at 1.5 T, and +1(mild torque) at 3.0 T. The size of susceptibility artifacts was between 13.20 mm and 38.91 mm. Therefore, The BAHA implant was safe for the patient in clinical MR environment.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.81.2-81.2
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• 2012

To fabricate a metal mold for injection molding, hot-embossing and imprinting process, mechanical machining, electro discharge machining (EDM), electrochemical machining (ECM), laser process and wet etching ($FeCl_3$ process) have been widely used. However it is hard to get precise structure with these processes. Electrochemical etching has been also employed to fabricate a micro structure in metal mold. A through mask electrochemical micro machining (TMEMM) is one of the electrochemical etching processes which can obtain finely precise structure. In this process, many parameters such as current density, process time, temperature of electrolyte and distance between electrodes should be controlled. Therefore, it is difficult to predict the result because it has low reliability and reproducibility. To improve it, we investigated this process numerically and experimentally. To search the relation between processing parameters and the results, we used finite element simulation and the commercial finite element method (FEM) software ANSYS was used to analyze the electric field. In this study, it was supposed that the anodic dissolution process is predicted depending on the current density which is one of major parameters with finite element method. In experiment, we used stainless steel (SS304) substrate with various sized square and circular array patterns as an anode and copper (Cu) plate as a cathode. A mixture of $H_2SO_4$, $H_3PO_4$ and DIW was used as an electrolyte. After electrochemical etching process, we compared the results of experiment and simulation. As a result, we got the current distribution in the electrolyte and line profile of current density of the patterns from simulation. And etching profile and surface morphologies were characterized by 3D-profiler(${\mu}$-surf, Nanofocus, Germany) and FE-SEM(S-4800, Hitachi, Japan) measurement. From comparison of these data, it was confirmed that current distribution and line profile of the patterns from simulation are similar to surface morphology and etching profile of the sample from the process, respectively. Then we concluded that current density is more concentrated at the edge of pattern and the depth of etched area is proportional to current density.

• Korean journal of applied entomology
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• v.24 no.3 s.64
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• pp.141-149
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• 1985

Embryonic developmental rates of the Oriental tobacco budworm, Heliothis assulta Guenee, were compared at various constant temperatures and 16 hours of light, and detailed embryogenesis was also studied at $25^{\circ}C$. The egg was nearly globular in form and had an average equatorial diameter of 0.53mm. A single micropyle was in the center of the circular area at the anterior pole of the egg. Durations of embryogenesis at 20, 25, 30, and $35^{\circ}C$ were 147, 81, 61, and 67hrs, respectively. Embryonic death was especially higher at $35^{\circ}C$ than any other temperatures investigated. Embryogenesis progressed with changes in color and pattern, which are quite characteristic at each developmental stage of the embryo. At $25^{\circ}C$, organogenesis began in 14hrs after oviposition, formation of gut completed in 44hrs and eclosion occurred in 80hrs. The embryo formed along the long axis at early developmental stage, moved towards the equatorial plane in 24hrs, and made a half-turn on the plane in 36hrs. In 40hrs, head was oriented to the anterior pole of the egg until eclosion.

• Korean Journal of Optics and Photonics
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• v.24 no.5
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• pp.213-216
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• 2013

This paper presents a combination of linear Fresnel lenses optimized for ${\times}25$ solar concentration. The combined lens consists of $5{\times}5$ linear Fresnel lenses. Each Fresnel lens is of $10{\times}10$ mm and optimized to tilt the incoming light onto a solar cell of the same size. All of the optimized Fresnel segments have the same pattern height of 35 ${\mu}m$, draft angle of $4^{\circ}$, and edge groove round of 1 ${\mu}m$ but with different facet angles varying from $14.1^{\circ}$ to $31.2^{\circ}$. The solar concentrating efficiency of the combination is shown to be over 80% and more robust than a conventional single ${\times}25$ circular Fresnel lens in terms of pointing misalignment and manufacturing errors. A sensitivity analysis finds that the edge groove round should be kept as small as machining allows since the concentrating efficiency drops ~5% per 1 ${\mu}m$ increase of the edge groove.

• Journal of Industrial Technology
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• v.9
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• pp.21-28
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• 1989

For the study of the fatigue behavior, high-strength bolted connections on a small scale were manufactured, and carried on fatigue tests. Its experimental values were analysed by stress-fatigue life (S-N) curve. Three types of specimens : the base metal, the cireular hole and the welded sperimens had same net section were made. Through the same tests those experimental values were compared with those of the high-strength bolted conneetions. The results of these studies are as followings. It was found that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the high-strength bolted conneetions were much more about 14% and 16% than that of the base metal specimen. It was thought that this trend was due to frictional force increasing fatigue strength. It was known that fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the welded joints were less 29% and 21% than that of base metal specimen. It was thought that that trend was due to weld flaw. It was appeared that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the high-strength bolted connections were much more about 38% and 30% than that of welded joint. It was thought that it was due to both frictional force increasing the fatigue strength in bolted connections and weld flaw decreasing the fatigue strength in welded connections. It was found that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the B3 specimens were much more 2% and -2% than that of the B4 specimen. It was thought that that trend was due to the frictional force, which concerned with shape of specimen. It was known that the fatigue strength in $F_{n=100,000}$ and $F_{n=2,000,000}$ of the specimen with circular hole was less 61% and 65% than that of base metal. It was known that the allowable stress for bolted joint was higher than that of welded Joints. If that research is continued and more data are accumulated it can be expected that a basic pattern to provided the indicator of the fatigue design of the bolted connections of steel structures and persume the safety and lifeproof of existing structures is given.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.7
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• pp.678-685
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• 2013

In this paper, we propose a design of dual-band patch antennas for Global Positioning System(GPS) applications, and the designed antenna is used as an individual element of GPS arrays. A low distortion and a high isolation of the array are achieved by adjusting rotating angles of each array element. The antenna consists of two radiating patches that operate in the GPS $L_1$ and $L_2$ bands, and the two ports feeding network with a hybrid chip coupler is adopted to achieve a broad circular polarization(CP) bandwidth. The rotating angles of each antenna element are varied with four directions(${\phi}=0^{\circ}$, ${\phi}=90^{\circ}$, ${\phi}=180^{\circ}$, ${\phi}=270^{\circ}$) in order to minimize the pattern distortion and maximize the isolation among array elements. The measurement shows bore-sight gains of 0.3 dBic($L_1$) and -1.0 dBic($L_2$) for the center element. Bore-sight gains of 1.6 dBic($L_1$) and 1.0 dBic($L_2$) are observed for the edge element. This results demonstrate that the proposed antenna is suitable for GPS array applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.156-156
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• 2000

Recently, the surface electronic states have attracted much attention since their standing wave patterns created around steps, defects, and adsorbates on noble metal surfaces such as Au(111), Ag(110), and Cu(111) were observed by scanning tunneling microscopy (STM). As a typical example, a striking circular pattern of "Quantum corral" observed by Crommie, Lutz, and Eigler, covers a number of text books of quantum mechanics, demonstrating a wavy nature of electrons. After the discoveries, similar standing waves patterns have been observed on other metal and demiconductor surfaces and even on a side polane of nano-tubes. With an expectation that the surface states could be utilized as one of ideal cases for studying two dimensionakl (sD) electronic system, various properties, such as mean free path / life time of the electronic states, have been characterized based on an analysis of standing wave patterns, . for the 2D electron system, electron density is one of the most importnat parameters which determines the properties on it. One advantage of conventional 2D electron system, such as the ones realized at AlGaAs/GaAs and SiO2/Si interfaces, is their controllability of the electrondensity. It can be changed and controlled by a factor of orders through an application of voltage on the gate electrode. On the other hand, changing the leectron density of the surface-state 2D electron system is not simple. On ewqy to change the electron density of the surface-state 2D electron system is not simple. One way to change the electron density is to deposit other elements on the system. it has been known that Pd(111) surface has unoccupied surface states whose energy level is just above Fermi level. Recently, we found that by depositing Pd on Cu(111) surface, occupied surface states of Cu(111) is lifted up, crossing at Fermi level around 2ML, and approaches to the intrinsic Pd surface states with a increase in thickness. Electron density occupied in the states is thus gradually reduced by Pd deposition. Park et al. also observed a change in Fermi wave number of the surface states of Cu(111) by deposition of Xe layer on it, which suggests another possible way of changing electron density. In this talk, after a brief review of recent progress in a study of standing weaves by STM, I will discuss about how the electron density can be changed and controlled and feasibility of using the surface states for a study of 2D electron system. One of the most important advantage of the surface-state 2D electron system is that one can directly and easily access to the system with a high spatial resolution by STM/AFM.y STM/AFM.