• Korean Journal of Optics and Photonics
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• v.11 no.6
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• pp.390-394
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• 2000

An optical system for iris pattern recognition of the human eye is designed. The lens system is triplet type, and characterized to minimize longitudinal chromatic aberration and Petzval sum. The distance from object to image is 200 mm-300 mm and the effective focal length is 50 mm. Performance of the imaging system is assessed by calculating the ray-fan and spot diagram for Fraunhofer C, d and F line for object height 0 mm, 4 mm and 6 mm. Furthermore, MTFs are calculated. All of the spot sizes are less than 0.05 mm in diameter. The MTF values are higher than 0.5 in the spatial frequency range up to 20 lines/mm for all of the object heights. ights.

• Journal of Magnetics
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• v.21 no.3
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• pp.450-459
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• 2016

Experimental results and data of numerical simulations are presented, concerning generation of wideband radio frequency (RF) oscillations in a nonlinear transmission line (NLTL) which contains a pre-magnetized core of ferrite material. Emphasis is made on the means for extracting the RF signal from the line, in order to radiate it into free space. Antennas of two types that can be used for the purpose are considered, both featuring a coaxial design. This permits availing of the principal advantages of coaxial systems, such as operation in the mode of a traveling TEM wave; wide range of the transmitted frequencies, and a reasonably simple design. The antennas studied, specifically a disc-cone dipole (DCD) and an impulse reflector antenna ('Half-IRA', or HIRA type) differ significantly in effective width of the radiated spectrum and in spatial characteristics of the radiated field in far region.

• Journal of the Korean Institute of Landscape Architecture
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• v.35 no.2 s.121
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• pp.55-63
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• 2007

The purpose of this study is to create a planting design for progressive realization. For this, visual preferences as measured via questionnaire were evaluated by the Scenic Beauty Estimation(SBE) and paired comparison methods. The results can be summarized as follows. Through photo observation, the average visual blockage ratio was 38% and the range of degree of the visual blockage ratio was $30{\sim}50%$. The sketch simulation and filtered pattern received the highest preference score and fumed out to be the most practical pattern out of all the patterns evaluated. Also, in the sketch simulation, the high preference values were observed for a distance of 9 to 12m from the view point to the blockage tree with a D/H ratio of 2. The preference score significantly decreased with the increase of the visual blockage ratio having a turning point at $30{\sim}35%$ of the visual blockage ratio, even though the distance parameters were more important than the visual blockage ratio in the scores. An outstanding view must be handled properly to be preserved or accentuated. Framed, open, enclosed, screened or filtered pattern views should be completely revealed only from their best vantage point, not given away at first glimpse. It this sense, parallax spatial beauty with trees could be improved through the visual aspects of plan arrangements and seems to be an effective design technique for landscape planning and planting design.

• Journal of Korean Society for Geospatial Information Science
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• v.10 no.2 s.20
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• pp.29-37
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• 2002

Many of the traffic accidents on roads are a result of alignment defect of the roads. This alignment of the road needs to lie analyzed with accuracy for improving design of road, and it needs the design drawing of road, and coordinates of the main point. Accordingly, in this study the precision of location based on existing design drawing was compared with the data acquired by the combination of RTK GPS/GLONASS. The result of study is included within range 5cm, we would like to propose an effective and useful approach method to utilize the satellite for road alignment information system by evaluating the represented road alignment.

• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.216-221
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• 2011

A diffraction grating is a highly symmetric optical element with a physical structure that is invariant under translational spatial movements. The translational symmetry is reflected in the fields that are diffracted from the grating. Here, we introduce a plane-parallel mirror pair onto the grating, which translates the fields through double reflections, and we describe a method of exploiting the symmetry to enhance the spectral resolution of a diffraction grating beyond the limit that is set by the number of grooves. The mirror pair creates another virtual grating beside the original one, effectively doubling the number of grooves. Addition of more mirror pairs can further increase the effective number of grooves despite the increased complexity and difficulty of experimental implementation. We experimentally demonstrate the spectral linewidth reduction by a factor of four in a neon fluorescence spectrum. Even though the geometrical restriction on the mirror deployment limits our method to a certain range of the whole spectrum, as a practical application example, a bulky spectrometer that is nearly empty inside can be made compact without sacrificing the resolution.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.12
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• pp.131-137
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• 2009

Recent technological advances made a vehicle more intelligent to increase safety and comfort. An intelligent vehicle provides drivers with safety warning information through audible sounds, visual displays, and tactile devices. However, elderly drivers have been known to decrease the physical and cognitive abilities such as muscular strength, hearing, eyesight, short term memory, and spatial perception. Therefore, possible age-related deficits should be considered to design an effective warning system. This paper aims to evaluate the impact of advancing age on response performance on audible safety warnings which are widely used for alerting driving hazards. In order to understand the effect of age-related hearing loss and movement slowing, three sound characteristics (frequency, intensity, and period) and three age groups (younger, middle, and older) are considered. Data was drawn from 38 drivers who drove a simulated rural road in a driving simulator. Experimental results show that age influences driver's response performance. In conclusion, the appropriate range of a warning sound is suggested.

• Journal of Korean Society for Geospatial Information Science
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• v.14 no.1 s.35
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• pp.37-47
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• 2006

In the last years a low-altitude image acquisition technology has been developed in application of frequent change monitoring in urban area md speedy surveillance in disaster area. A low-altitude photogrammetric system have advantages of accurate observation and free data-acquisition time. Especially, an unmaned RC-helicopter, improving safety, durability and portability, comes into the spotlight as a built-in vehicle in close range photogrammetric application due to their capability of safe near-by observation and effective flight performance. This paper gives a methodology for generating image map by development of low cost and timesaving low-altitude photogrammetric UAV(unmaned aerial vehicles) for collecting high-resolution image data, and implement of geo-rectification and image mosaicking.

• Journal of Forest and Environmental Science
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• v.29 no.2
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• pp.131-137
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• 2013

This study attempts to classify forest species using hyperspectral data for supporting resources management. The primary dataset used was AISA sensor. The sensor was mounted onboard the NOMAD GAF-27 aircraft at 2,000 m altitude creating a 2 m spatial resolution on the ground. Pre-processing was carried out with CALIGEO software, which automatically corrects for both geometric and radiometric distortions of the raw image data. The radiance data set was then converted to at-sensor reflectance derived from the FODIS sensor. Spectral Angle Mapper (SAM) technique was used for image classification. The spectra libraries for tree species were established after confirming the appropriate match between field spectra and pixel spectra. Results showed that the highest spectral signature in NIR range were Kembang Semangkok (Scaphium macropodum), followed by Meranti Sarang Punai (Shorea parvifolia) and Chengal (Neobalanocarpus hemii). Meanwhile, the lowest spectral response were Kasai (Pometia pinnata), Kelat (Eugenia spp.) and Merawan (Hopea beccariana), respectively. The overall accuracy obtained was 79%. Although the accuracy of SAM techniques is below the expectation level, SAM classifier was able to classify tropical tree species. In future it is believe that the most effective way of ground data collection is to use the ground object that has the strongest response to sensor for more significant tree signatures.

• Current Optics and Photonics
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• v.5 no.4
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• pp.458-465
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• 2021

Borate nonlinear optical crystals have been used as frequency conversion devices in many fields due to their unique transparency and nonlinearity from ultraviolet to visible spectral range. In this study, we theoretically and numerically investigate the properties of broadband second harmonic generation (SHG) in the recently reported Pna2₁-Ba₃Mg₃(BO₃)₃F₃ (BMBF) crystal. The technique is based on the simultaneous achievement of birefringence phase matching and group velocity matching between interacting waves. We discussed all factors required for broadband SHG in the BMBF in terms of two types of phase matching and group velocity matching conditions, the beam propagation direction and the corresponding effective nonlinearity and spatial walk-off, and the spectral responses. The results show that bandwidths calculated in the broadband SHG scheme are 220.90 nm (for Type I) and 165.85 nm (for Type II) in full-width-half-maximum (FWHM). The central wavelength in each case is 2047.76 nm for Type I and 1828.66 nm for Type II at room temperature. The results were compared with the non-broadband scheme at the telecom C-band.

• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.573-587
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• 2023

A conventional tuned mass damper (TMD) provides a passive control option to suppress the structures' wind- or earthquake-induced vibrations. However, excessive displacements of the TMD raise concerns in the practical implementation. Therefore, this study proposes a novel TMD designed for and deployed on a high-rise sightseeing tower. The device consists of an integrated two-way slide rail mount and an eddy current damper (ECD) with a stroke control mechanism. This stroke control mechanism allows the damping coefficient to automatically increase when the stroke reaches a predetermined value, preventing excessive damper displacements during large earthquakes. The corresponding two-stage damping parameters are designed with a variable-thickness copper plate to enable the TMD stroke within a specified range. Thus, this study discusses the detailed design schemes of the device components in TMD. The designed two-stage damping parameters are also numerically verified, and the structural responses with/without the TMD are compared. As seen in the results, the proposed TMD yields effective control authority to limit the acceleration response within a comfort level. In addition, this TMD resolves the spatial availability for the damper movement in high-rise buildings by the controllable damping mechanism.