• 연구논문집
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• s.25
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• pp.105-113
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• 1995

Fresnel lenses are developed for flat optics with the optical characteristics close to aspherical lens such as sharp focusing and dispersion instead of spherical or aspherical surface. Usually, these fresnel lenses and diffraction gratings are machined by high-energy beam such as electron beam machining, but recently with the development of ultra precision machine tool and machining technology, 3-dimension micro machining becomes preferable. This study on the micro machining of fresnel lens is carried out to develop the basic technology of ultra precision micro machining. The machined lens mold will be used for the manufacturing of fresnel lens with 120mm focal distance using synthetic resin material with 1.49 refractive index(PMMA), and the shape of lens is 48mm diameter, $300\mum$ pitch and about $5-700\mum$depth of groove in brass.

• Current Optics and Photonics
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• v.8 no.5
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• pp.472-483
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• 2024

This paper presents an intuitive method for selecting an optical material for achromatic and athermal design using the material selection index (MSI). In addition, in the case of a wide wavelength range such as a short-wave infrared (SWIR) waveband, we propose a new material selection method for apochromatic and athermal design by introducing the relative error of partial dispersion (REPD) and a first-order quantity redistribution method. To obtain a suitable material for effective apochromatic design, we first evaluate the REPDs of all lenses, deviated from that of an equivalent lens. Materials with a small REPD are then selected on a glass map to correct residual chromatic aberration while maintaining the existing MSI values to realize athermalization simultaneously. Using this proposed glass selection method, we successfully obtained an apochromatic and athermal telephoto system for SWIR that realizes stable performance over the specified temperature and wide waveband ranges.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.5 no.6
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• pp.14-23
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• 2002

Daejeon is a large city in Korea and very high-speedly developing city. Recently urban area is expanding and large forest patch is fragmenting into small habitats because of urban sprawl. The fragmentation of large forest patch decreases the size of habitats and increases the loss of biodiversity in urban area. This study is to analysis the connectivity of green space of Daejeon metropolitan city, and suggest the optimum location of greening site and corridor in order to increase the connectivity of green space of Daejeon metropolitan city. The findings of this study are as follows; (1) The result of this study showed that ${\alpha}$ and ${\gamma}$ index are -0.24 and 0.20. A ${\alpha}$ index is very low and a ${\gamma}$ index is relatively low. (2) The dispersion was very high, for urban forest patches were isolated through fragmentation. Therefore, it needed ecological corridors in order to connect the patches. (3) A urban streams were very important in connectivity of urban green space. Urban riparian corridor must be preserved and restored. (4) A urban green space policy and planning must be prepared to increase the connectivity and assessment of alternatives must be accomplished from perspective of connectivity. The results of this study show the practical implications in perspective of green space planning and policy in Daejeon metropolitan city. The suggestions by findings of this study are to connect green space between large forest patch in urban fringe and island green space in inner city. Also, It is required that urban stream is restored to natural feature for use of corridor by wildlife.

• Advances in nano research
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• v.8 no.4
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• pp.283-292
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• 2020

In the present research, differential quadrature (DQ) method has been utilized for investigating free vibrations of porous functionally graded (FG) micro/nano beams in thermal environments. The exact location of neutral axis in FG material has been assumed where the material properties are described via porosity-dependent power-law functions. A scale factor related to couple stresses has been employed for describing size effect. The formulation of scale-dependent beam has been presented based upon a refined beam theory needless of shear correction factors. The governing equations and the associated boundary conditions have been established via Hamilton's rule and then they are solved implementing DQ method. Several graphs are provided which emphasis on the role of porosity dispersion type, porosity volume, temperature variation, scale factor and FG material index on free vibrational behavior of small scale beams.

• Journal of the Optical Society of Korea
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• v.8 no.4
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• pp.163-167
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• 2004

We propose and demonstrate an external optical modulation method based on TE/TM-mode absorption nulls in a Multiple Quantum Well(MQW) Fabry-Perot laser diode(FP-LD). The center wavelength of the absorption nulls is rapidly shifted to short-wavelength by the small current change(~1mA) in the FP-LD, which can modulate an optical signal with more than 10 dB of extinction ratio(ER). The shift of the center wavelength comes from the refractive index change due to anomalous dispersion and the plasma effect in MQW FP-LD waveguide. Non-inverting and inverting signals are made by TE- and TM-mode absorption nulls at 155.52 Mbps and BERs for the signals are measured.

• Journal of Magnetics
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• v.20 no.2
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• pp.110-113
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• 2015

Two kinds of magnetic fluids with different volume fractions are symmetrically filled into the W0.9 photonic crystal waveguide structure. The 2D plane-wave expansion method is used to investigate the slow light properties numerically. The constant group index criterion is employed to evaluate the slow light performance. The wavelength bandwidth ${\Delta}{\lambda}$ centering at ${\lambda}_0=1550nm$ varies from 32.4 to 44.2 nm when the magnetic field factor ${\alpha}_{\parallel}$ changes from 0 to 1. And the corresponding normalized delay bandwidth product can be tuned from 0.221 to 0.258. For comparison and optimization, two infiltration cases are investigated and the more advantageous infiltration scheme is found.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.3
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• pp.393-402
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• 2014

ICT environment to the survey released by the Bureau of Statistics 2012 Household Finance. Korean Welfare survey 24.9% of all households in financial assets, real estate is about three times more than 69.9%, respectively. The problem is that the information is slow and income deciles(deciles 1-4), a relatively high proportion of households with low(78.8 to 69%) of the real estate assets of the expansion of the world economy with low growth and low uncertainty, work from home due to the information changes in the structure of the economy, such as increases in real estate prices remain exposed to the risk of a phenomenon such as Pour House Pour Talent and low-income people is bound to be more serious symptoms. This low correlation is by constructing a composite asset portfolio, the weighted average risk of the individual assets while increasing overall revenue decrease that risk is based on the principle of portfolio by type and different areas in the ICT environment in a portfolio of real estate price index low correlation to financial assets by including the effect of dispersion stable complex asset portfolio and empirical Growth was divided.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.3
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• pp.149-159
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• 2008

We present new methods which transfer the color style of a source image into an arbitrary given reference image. Misidentification problem of color cause wrong indexing in low saturation. Therefore, the proposed method do indexing after Image separating chromatic and achromatic color from saturation. The proposed method is composed of the following four steps : In the first step, Image separate chromatic and achromatic color from saturation using threshold. In the second step, image of separation do indexing using cylindrical metric. In the third step, the number and positional dispersion of pixel decide the order of priority for each index color. And average and standard deviation of each index color be calculated. In the final step, color be transferred in Lab color space, and post processing to removal noise and pseudo-contour. Experimental results show that the proposed method is effective on indexing and color transfer.

• Advances in concrete construction
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• v.14 no.3
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• pp.169-183
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• 2022

In this article, vibrational behavior and wave propagation characteristics in (FG) functionally graded plates resting on Kerr foundation with three parameters is studied using a 2D dimensional (HSDT) higher shear deformation theory. The new 2D higher shear deformation theory has only four variables in field's displacement, which means has few numbers of unknowns compared with others theories. The shape function used in this theory satisfies the nullity conditions of the shear stresses on the two surfaces of the FG plate without using shear correction factors. The FG plates are considered to rest on the Kerr layer, which is interconnected with a Pasternak-Kerr shear layer. The FG plate is materially inhomogeneous. The material properties are supposed to vary smoothly according to the thickness of the plate by a Voigt's power mixing law of the volume fraction. The equations of motion due to the dynamics of the plate resting on a three-parameter foundation are derived using the principle of minimization of energies; which are then solved analytically by the Navier technique to find the vibratory characteristics of a simply supported plate, and the wave propagation results are derived by using the dispersion relations. Perceivable numerical results are fulfilled to evaluate the vibratory and the wave propagation characteristics in functionally graded plates and some parameters such wave number, thickness ratio, power index and foundation parameters are discussed in detail.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.587-601
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• 1997

This study had three purposes: (1) to investigate the enrichment levels and dispersion patterns of potentially toxic elements in the rock-soil-plant system; (2) to evaluate the uptake ratios of heavy metals from soils into plants and (3) to assess the chemical speciation of heavy metals in soils. Rock, surface soil and plant samples were collected in the Boeun area underlain by black shales of the Okchon Zone. These samples were analyzed for multi-elements using INAA, ICP-AES and AAS. The maximum abundance of U in black shales is 16 mg/kg and radioactivity counts up to 300 cpm. In particular, Mo, V, Ba, Cd, Pb and U are enriched in black shales. Most of soils derived from black shales show high concentrations of U, As, Mo, Ba, Cu, Cd, Pb, Zn and mean concentrations of As and Mo in soils (20 mg/kg of As and 6.6 mg/kg of Mo) are higher than the permissible level suggested by Kloke (1979). Enrichment index values of soils are calculated and higher than 1.0 in the black shale area with the highest value of 6.4. Mean concentration of Cd in plants is higher than those of Cu, Pb and Zn. The concentration of Cd in plant species decreases in the order of Chinese cabbage > red pepper > soybean=sesame > rice stalk > com > rice grain. The biological absorption coefficients (BAC) in plants are in the order of Cd > Zn=Cu > Pb, which suggests that Cd is more bioavailable to plants than Cu, Pb and Zn. From the results of sequential extraction analysis of soils, relatively high proportion of Cu, Pb and Zn are present as residual fractions whereas that of Cd as non-residual fractions. Cadmuim occurs predominantly as exchangeable/water-acid soluble phase in soils, and Cd is more mobile and bioavailable than Cu, Pb and Zn.