• Korean Journal of Optics and Photonics
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• v.17 no.1
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• pp.94-98
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• 2006

An optical microphone based on a dual-core fiber collimator and a membrane type micromirror serving as an optical head and a reflective diaphragm respectively was implemented. The micromirror diaphragm is suspended by a thin silicon bar linked with a frame, thus it is subject to a displacement induced by acoustic waves. The optical head incorporating two collimators integrated in a single housing gives light to and receives it from the diaphragm, rendering the optical microphone structure simple and compact. This dual-core collimator having a slowing varying beam profile facilitates the initial alignment of the optical head with the diaphragm, especially the distance between them. For the assembled microphone, the static characteristics were investigated tofind the operation point defined as the optimum distance between the head and the diaphragm, and a frequency response with a variation of about $\pm$5 dB for the range of up to 3kHz was achieved.

• Nuclear Engineering and Technology
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• v.47 no.4
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• pp.479-487
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• 2015

The thallium-doped sodium iodide [NaI(Tl)] scintillation detector is preferred as a gamma spectrometer in many fields because of its general advantages. A silicon photomultiplier (SiPM) has recently been developed and its application area has been expanded as an alternative to photomultiplier tubes (PMTs). It has merits such as a low operating voltage, compact size, cheap production cost, and magnetic resonance compatibility. In this study, an array of SiPMs is used to develop an NaI(Tl) gamma spectrometer. To maintain detection efficiency, a commercial NaI(Tl) $2^{\prime}{\times}2^{\prime}$ scintillator is used, and a light guide is used for the transport and collection of generated photons from the scintillator to the SiPMs without loss. The test light guides were fabricated with polymethyl methacrylate and reflective materials. The gamma spectrometer systems were set up and included light guides. Through a series of measurements, the characteristics of the light guides and the proposed gamma spectrometer were evaluated. Simulation of the light collection was accomplished using the DETECT 97 code (A. Levin, E. Hoskinson, and C. Moison, University of Michigan, USA) to analyze the measurement results. The system, which included SiPMs and the light guide, achieved 14.11% full width at half maximum energy resolution at 662 keV.

• The Journal of the Petrological Society of Korea
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• v.15 no.2 s.44
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• pp.90-105
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• 2006

The Cretaceous volcanic rocks in the study area represented by andesitic rocks occupy eastern part of the Kyeongsan Caldera. The volcanic rocks comprise andesite I, andesitic tuff, andesite II, and andesitic tuff breccia in their stratigraphic succession, and andesitic porphyry. Andesite I is distinguished from andesite II in their color, texture, phenocryst mineralogy and petrochemisty. In outcrops, andesite I is compact and dark-green, and andesite II is brick red in color and porphyritic in texture. In their phenocryst mineralogy, andesite I contains olivine phenocryst in addition to plagioclase and pyroxene which occur in both of andesites. Compared to andesite II, andesite I is higher in $SiO_2$ and $K_2O$ contents and lower in CaO, MgO, MnO, $TiO_2,\;Fe_2O_3$, and $P_2O_5$. Major elements petrochemistry shows that magma series of the volcanic rocks spread widely from calc-alkaline to alkaline series. On the other hand, immobile trace elements petrochemistry shows that the magma series is calc-alkaline without exception, suggesting that the volcanics has experienced more or less alkali enrichment after their eruption. Trace element diagrams for discrimination of tectonic setting show that the volcanics of the study area might be originated from calc-alkaline continental volcanic arc.

• Korean Journal of Optics and Photonics
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• v.18 no.4
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• pp.256-263
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• 2007

High NA objective design by using SELFOC materials was studied, and two kinds of objective for optical pick-up were designed. The SELFOC materials have radial gradient index distribution, and it gives additional degree of freedom in optical design. Therefore, we expect that optical design of high NA objective without aspheric surface will be possible. In this study, the variation of ms spot diameter was investigated as a function of quadratic constant and refractive index on axis for various combinations of axial thickness and entrance pupil diameter. For the survey, Code V was used for optimization and evaluation of the objective lenses. The result suggested that larger quadratic constant and higher refractive index on axis could give us better imaging performance for all combinations of axial thickness and pupil diameter. Based on the survey, we designed high NA objectives for DVR. There were two kinds of design solution consisting two spherical SELFOC lenses. The solution I had positive-positive lens configuration with short over-all-length, but it had poor off-axial performance compared with the solution II. The solution II had negative-positive lens configuration with good off-axial imaging performance. But the solution II had some disadvantages, long over-all-length and large diameter of the second lens.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.155-169
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• 2002

The objective of this study was to investigate the effect of crack opening and closure in the AE activities during fatigue test. Laboratory experiment using various materials and test conditions were carried out to identify AE characteristics of fatigue crack propagation. Compact tension specimens of 2024-T4 and 6061-T6 aluminum alloy were prepared for fatigue test. AE activities were analyzed based on the phase of the loading cycle. Generally, most of AE were generated when the crack begins' opening and the crack closes fully, whereas a few in the pull opening of the crack. Also AE activity in the peak loading of cycle was different with each specimen. However, in the same material, AE activity was not affected by the change of cyclic frequency (0.1, 0.2, 1.0Hz). It was found that AE activities during crack opening and closure depend on material properties such as micro-structure, tensile strength and yield strength.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.471-478
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• 2010

Thin films play an important role in many technological applications including microelectronic devices, magnetic storage media, MEMS and surface coatings. It is well known that a thin film's material properties can be very different from the corresponding bulk properties and thus there has been a strong need for the development of a reliable test method to measure the mechanical properties of a thin film. We have developed an alternative and convenient test method to overcome the limitations of previous membrane deflection experiment and uniaxial tensile test by adopting a white light interferometer having sub-nanometer out-of-plane displacement resolution. The freestanding aluminium specimens are tested to verity the effectiveness of the test method developed and get the tensile properties. The specimens are 0.5 rum wide, $1{\mu}m$ thick and fabricated through MEMS processes including sputtering. 1 to 5 specimens are fabricated on Si dies. The membrane deflection experiments are carried out by using a homemade tester consisted of a motor-driven loading tip, a load cell, and 6 DOF alignment stages. The test system is compact enough to set it up beneath a commercial white light interferometric microscope. The white light fringes are utilized to align a specimen with the tester. The Young's modulus and yield point stress of the aluminium film are 62 GPa and 247 MPa, respectively.

• Journal of the Korean Society of Radiology
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• v.5 no.6
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• pp.357-361
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• 2011

In this study, the liquid-crystal optical modulation X-ray detection system using a CdS which is a family of II-IV compound semiconductor was proposed. The system consist of the detector, the signal processing part, the liquid-crystal driving parts, microcontroller, and I/O parts, and was designed to be suitable for miniaturization and portable. In addition, the system can measure a wide range X-ray by using the detecting range selection. In order to evaluate the performance of the proposed system, the CdS sensor's output characteristics were confirmed in accordance with changes of dose, and excellent correlation was determined. And also, the optical penetration ratio was discussed in accordance with changes of the applied voltage by measuring the change of the liquid-crystal in accordance with changes of the applied voltage. Through these results, the characteristics of the liquid-crystal optical modulation system such as the excellent reproducibility and the noise immunity were confirmed. And we considered that the CdS cell-based liquid-crystal optical modulated portable X-ray detection system could be applied to compact, low-cost, portable system.

• Journal of Korea Soil Environment Society
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• v.1 no.1
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• pp.89-102
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• 1996

An integrated model is presented to describe underground flow and mass transport, using a multicomponent multiphase approach. The comprehensive governing equation is derived considering mass and force balances of chemical species over four phases(water, oil, air, and soil) in a schematic elementary volume. Compact and systemati notations of relevant variables and equations are introduced to facilitate the inclusion of complex migration and transformation processes, and variable spatial dimensions. The resulting nonlinear system is solved by a multidimensional finite element code. The developed code with dynamic array allocation, is sufficiently flexible to work across a wide spectrum of computers, including an IBM ES 9000/900 vector facility, SP2 cluster machine, Unix workstations and PCs, for one-, two and three-dimensional problems. To reduce the computation time and storage requirements, the system equations are decoupled and solved using a banded global matrix solver, with the vector and parallel processing on the IBM 9000. To avoide the numerical oscillations of the nonlinear problems in the case of convective dominant transport, the techniques of upstream weighting, mass lumping, and elementary-wise parameter evaluation are applied. The instability and convergence criteria of the nonlinear problems are studied for the one-dimensional analogue of FEM and FDM. Modeling capacity is presented in the simulation of three dimensional composite multiphase TCE migration. Comprehesive simulation feature of the code is presented in a companion paper of this issue for the specific groundwater or flow and contamination problems.

• Journal of Korean Society of Steel Construction
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• v.26 no.2
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• pp.91-103
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• 2014

High performance steel for bridges(HSB 800) with a minimum tensile stress of 800MPa was recently developed. However, the study for local buckling behavior of plate girders considering interactive effects of flanges and webs is still insufficient. In this study, the flange local buckling(FLB) strength of plate girders with HSB 800 was evaluated by nonlinear finite element analysis. The flanges and webs of plate girders having I-section were modeled as 3D shell elements in the nonlinear analysis. Initial imperfection and residual stress were imposed on the plate girder. The high performance steel was modeled as a multi-linear material. Thus, parametric study of compression flanges with a compact, noncompact and slender web was performed. The flange local buckling behavior of plate girders was analyzed, and the nonlinear analysis results were compared with the nominal flexural strength of both AASHTO LRFD(2012) and KHBDC LSD(2012) codes.

• Journal of Korean Society of Steel Construction
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• v.26 no.2
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• pp.119-132
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• 2014

In this paper, a series of numerical analyses were performed to evaluate the flexural resistance of steel plate girder with longitudinally stiffened and slender web. The SM490 steel was adopted for the study and the flexural resistances evaluated from the numerical analysis were compared with those suggested by the AASHTO LRFD and the Eurocode 3 codes, respectively. It was found that the AASHTO LRFD code could considerably underestimate the flexural resistance as the web slenderness becomes smaller. This comes from the fact that current AASHTO LRFD code does not consider a possible increase of slenderness limits for compact and noncompct web, and also an additional effect of web restraint on the rotation of compression flange in longitudinally stiffened web. Therefore, the slenderness limits of web and flange have been newly proposed for the plate girders with longitudinally stiffened web and it is analytically verified that the flexural resistance can be appropriately estimated by applying the proposed slenderness limits to the AASHTO LRFD code.