• Journal of the Korean Wood Science and Technology
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• v.43 no.6
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• pp.777-783
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• 2015

Wood is an anisotropic material that shows the changes in hardness, quality and dimensions depending on the types of cells on three cross sections, size, array and so on. It can also be used in different ways according to its use, which requires a meticulous research, in order to maximize the utilization by understanding the nature and use; and by clarifying the theory and technologies. The research on relationship among wood's physical properties, density, and elasticity of modulus have been studied in Korea and abroad, but those studies were based on correlation gained through standardized specimen. Rather, the study on complete product is rare. Moreover, the previous reports are mostly concentrating on vibration mode and batting, though the wood's physical properties as a material have not been in the main focus. Therefore, this study will carried out for analyzing MOE through figuring material property out and comparing frequency adapting to the Canadian HardMaple bat. For comparison of material properties, we studied the annual ring and density of the bat; calculated the MOE with resonance frequency and formula (ASTM C1259); and verified the repulsive force of this material. As a result, the relevance of the resonance frequency and annual ring is weak, and in comparison in the grain direction in wood, the MOE value is higher when the grain direction in wood is excited horizontally than when is excited vertically, because the material is repulsive when grain direction is horizontal.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.3
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• pp.181-189
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• 2016

An analytical model was developed by Sim to estimate the two-phase damping ratio for upward two-phase flow perpendicular to horizontal tube bundles. The parameters of two-phase flow, such as void fraction and pressure loss evaluated in the model, were calculated based on existing experimental formulations. However, it is necessary to implement a few improvements in the formulations for the case of tube bundles. For the purpose of the improved formulation, we need more information about the two-phase parameters, which can be found through experimental test. An experiment is performed with a typical normal square array of cylinders subjected to the two-phase flow of air-water in the tube bundles, to calculate the two-phase Euler number and the two-phase friction multiplier. The pitch-to-diameter ratio is 1.35 and the diameter of cylinder is 18mm. Pressure loss along the flow direction in the tube bundles is measured with a pressure transducer and data acquisition system to calculate the two-phase Euler number and the two-phase friction multiplier. The void fraction model by Feenstra et al. is used to estimate the void fraction of the two-phase flow in tube bundles. The experimental results of the two phase friction multiplier and two-phase Euler number for homogeneous and non-homogeneous two-phase flows are compared and evaluated against the analytical results given by Sim's model.

• The Journal of the Petrological Society of Korea
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• v.17 no.4
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• pp.206-221
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• 2008

We have studied general orientational characteristics of microcracks distributed in Bulgugsa Granites of southwestern Gyeongsang Basin. Microcracks of 131 sets, which were developed on horizontal surfaces of II rock samples collected from Sacheon-Gosung, Geoje-si and Namhae-gun areas, were distinguished by image processing. Then, 45 sets with a distinct linear array on image were sorted out. These microcracks can be comparable with vertical grain planes. Orientations of these microcracks were compared with those of vertical rift and grain planes developed in Cretaceous and Jurassic granites of Korea. In the distribution chart, the agreement of the distribution pattern between microcracks of 45 sets and above vertical planes suggests that microcrack systems developed all over the study area also occur regionally in Cretaceous and Jurassic granites of Korea. Whole domain of the directional angle-frequency chart can be divided into 20 domains in terms of the phases of the distribution of microcracks. Meanwhile, 18 domains from 45 sets of microcracks were compared with the maximum principal stress orientations suggested from previous studies. The majority of maximum principal stress orientations pertain to domain $1{\sim}2$, $5{\sim}6$, $11{\sim}15$, $17{\sim}18$ and $19{\sim}20$, and these domains are coincident with the orientation of the 1st and 2nd-frequency orders represented in a rose diagram for 45 sets of microcracks. Representative orientations of open microcrack reflect the maximum principal stress orientations suggested in previous studies.

• Geophysics and Geophysical Exploration
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• v.1 no.1
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• pp.57-63
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• 1998

The electrical resistivity method, one of old and widely used geophysical prospecting methods, has extended its scope to civil & environmental engineering areas. The electrical resistivity imaging technique was performed at the waste disposal site located in Junju to verify the applicability to the environmental engineering area. The dipole-dipole array, with the dipole spacing of 10 m, was applied along eight survey lines. The field data were obtained under the control of automatic acquisition softwares and topographic effects were corrected during processing stage. The processed resistivity images show that very low resistivity develops inside the disposal site and the distribution of low resistivity is exactly in accord with the boundary of the site except the river side. The depth of low resistivity zones is deeper toward the river side, which is interpreted that there is a high possibility for contaminants to be scattered to the river. From resistivity images, it was feasible to deduce the depth of waste disposal as well as the horizontal/vertical distribution of the contaminated zone, which proved the applicability of the electrical resistivity imaging technique to the environmental engineering area.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.2
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• pp.21-34
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• 2002

In this paper we propos a new hardware architecture of modular exponentiation using a division chain method which has been proposed in (2). Modular exponentiation using the division chain is performed by receding an exponent E as a mixed form of multiplication and addition with divisors d=2 or $d=2^I +1$ and respective remainders r. This calculates the modular exponentiation in about $1.4log_2$E multiplications on average which is much less iterations than $2log_2$E of conventional Binary Method. We designed a linear systolic array multiplier with pipelining and used a horizontal projection on its data dependence graph. So, for k-bit key, two k-bit data frames can be inputted simultaneously and two modular multipliers, each consisting of k/2+3 PE(Processing Element)s, can operate in parallel to accomplish 100% throughput. We propose a new encoding scheme to represent divisors and remainders of the division chain to keep regularity of the data path. When it is synthesized to ASIC using Samsung 0.5 um CMOS standard cell library, the critical path delay is 4.24ns, and resulting performance is estimated to be abort 140 Kbps for a 1024-bit data frame at 200Mhz clock In decryption process, the speed can be enhanced to 560kbps by using CRT(Chinese Remainder Theorem). Futhermore, to satisfy real time requirements we can choose small public exponent E, such as 3,17 or $2^{16} +1$, in encryption and verification process. in which case the performance can reach 7.3Mbps.

• The Journal of the Acoustical Society of Korea
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• v.41 no.4
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• pp.435-445
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• 2022

In this study, the reverberation of a bistatic sonar operated in southeastern coast in the East Sea in July 2020 was analyzed. The reverberation sensor data were collected through an LFM sound source towed by a research vessel and a horizontal line array receiver 1 km to 5 km away from it. The reverberation sensor data was analyzed by various methods including geo-plot after signal processing. Through this, it was confirmed that the angle reflected from the sound source through the scatterer to the receiver has a dominant influence on the distribution of the reverberation sound, and the probability distribution characteristics of bistatic sonar reverberation varies for each beam. In addition, parametric factors of K distribution and Rayleigh distribution were estimated from the sample through moment method estimation. Using the Kolmogorov-Smirnov test at the confidence level of 0.05, the distribution probability of the data was analyzed. As a result, it could be observed that the reverberation follows a Rayleigh probability distribution, and it could be estimated that this was the effect of a low reverberation to noise ratio.

• Journal of Internet of Things and Convergence
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• v.9 no.6
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• pp.29-35
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• 2023

Braille can be said to be an essential means used for the visually impaired to communicate or acquire information on visual materials in their lives. However, the rate of interpretation of braille among the visually impaired is insignificant at 5%. As a result, libraries for the visually impaired produce various types of materials that can obtain various information for the visually impaired and also have assistive technology equipment to interpret them. However, the publication rate of Braille books is too low to purchase and interpret Braille books. In addition, the Braille interpretation rate is too low, and the purchase of assistive technology devices is too expensive and slow. Therefore, in this paper, we implemented a system that displays Braille using Arduino to help visually impaired people in addition to the existing methods they use to obtain information. For Braille display, Korean data is transmitted from Python through serial communication between Python and Arduino, and Arduino, which receives the data, compares the Korean data with the data in the array in the program and retrieves the Braille values of the Korean data. Here, the Braille value was expressed by controlling the servo motor perpendicular or horizontal to the body using white and black circles based on the Braille list.

• Journal of Soil and Groundwater Environment
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• v.7 no.3
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• pp.3-17
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• 2002

Data analysis of groundwater monitoring wells and geostatistical methods are used to identify the local characteristics of sea water intrusion and the range of sea water intrusion at the southeastern coastal area of Busan, Korea. Rainfall and groundwater level of two monitoring wells show a linear correlation because of the direct groundwater recharge by the precipitation. However, rainfall and electric conductivity have the inverse relationship because of the increase of groundwater. Electric conductivity rapidly increased at 24m depth and exceeded 20,000$\mu\textrm{s}$/cm near 26m depth in the monitoring wells. The variations of groundwater level and electric conductivity show that the interface between sea water and fresh water tends to move upward when groundwater level goes down. In the cross correlation analysis, groundwater level versus rainfall represents the largest cross correlation coefficient in 0 time lag but the cross correlation coefficient of electric conductivity versus rainfall is the largest when the time lag is 9 days. This suggests that the fluctuations of groundwater level respond to rainfall in a short time, but the interface between sea water and fresh water respond very slow to rainfall. Horizontal extents of sea water intrusion are estimated to 14 m from the east of Line 1, and 25 m from the southeast end of Line 2 in the inversion of dipole-dipole profiling data of two survey lines. The data of VES by the Schulumberger array in May and July show lognormal distributions. In the kriged apparent resistivity and earth resistivity distributions, the resistivities of July are increased comparing to those of May. This reflects that the concentration of sea water in aquifer is reduced due to the increased groundwater recharge from the rainfall in June and July. In analyzing the vertical and horizontal apparent resistivities and earth resistivity distributions, the geostatistical methods are very useful to identify the variations of earth resistivity distributions at the coastal area.

• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.132-142
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• 2009

The Tamar rift valley runs through the City of Launceston, Tasmania. Damage has occurred to city buildings due to earthquake activity in Bass Strait. The presence of the ancient valley, the Tamar valley, in-filled with soft sediments that vary rapidly in thickness from 0 to 250mover a few hundreds metres, is thought to induce a 2D resonance pattern, amplifying the surface motions over the valley and in Launceston. Spatially averaged coherency (SPAC), frequency-wavenumber (FK) and horizontal to vertical spectrum ratio (HVSR) microtremor survey methods are combined to identify and characterise site effects over the Tamar valley. Passive seismic array measurements acquired at seven selected sites were analysed with SPAC to estimate shear wave velocity (slowness) depth profiles. SPAC was then combined with HVSR to improve the resolution of these profiles in the sediments to an approximate depth of 125 m. Results show that sediments thicknesses vary significantly throughout Launceston. The top layer is composed of as much as 20m of very soft Quaternary alluvial sediments with a velocity from 50 m/s to 125 m/s. Shear-wave velocities in the deeper Tertiary sediment fill of the Tamar valley, with thicknesses from 0 to 250m vary from 400 m/s to 750 m/s. Results obtained using SPAC are presented at two selected sites (GUN and KPK) that agree well with dispersion curves interpreted with FK analysis. FK interpretation is, however, limited to a narrower range of frequencies than SPAC and seems to overestimate the shear wave velocity at lower frequencies. Observed HVSR are also compared with the results obtained by SPAC, assuming a layered earth model, and provide additional constraints on the shear wave slowness profiles at these sites. The combined SPAC and HVSR analysis confirms the hypothesis of a layered geology at the GUN site and indicates the presence of a 2D resonance pattern across the Tamar valley at the KPK site.

• The Journal of the Acoustical Society of Korea
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• v.20 no.2E
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• pp.30-45
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• 2001

This study considers the environmental factors affecting propagation loss and sonar performance in the continental regions of the East Coast Sea of Korea. Water mass distributions appear to change dramatically in a few weeks. Simple calculation with the case when the NKCW (North Korean Cold Water) develops shows that the difference in propagation loss may reach in the worst up to 10dB over range 5km. Another factor, an eddy, has typical dimensions of 100-200km in diameter and 150-200m in thickness. Employing a typical eddy and assuming frequency to be 100Hz, its effects on propagation loss appear to make lower the normal formation of convergence zones with which sonars are possible to detect long-range targets. The change of convergence zones may result in 10dB difference in received signals in a given depth. Thermal fronts also appear to be critical restrictions to operating sonars in shallow waters. Assuming frequency to be 200Hz, thermal fronts can make 10dB difference in propagation loss between with and without them over range 20km. An observation made in one site in the East Coast Sea of Korea reveals that internal waves may appear in near-inertial period and their spectra may exist in periods 2-17min. A simulation employing simple internal wave packets gives that they break convergence zones on the bottom, causing the performance degradation of FOM as much as 4dB in frequency 1kHz. An acoustic experiment, using fixed source and receiver at the same site, shows that the received signals fluctuate tremendously with time reaching up to 6.5dB in frequencies 1kHz or less. Ambient noises give negative effects directly on sonar performance. Measurements at some sites in the East Coast Sea of Korea suggest that the noise levels greatly fluctuate with time, for example noon and early morning, mainly due to ship traffics. The average difference in a day may reach 10dB in frequency 200Hz. Another experiment using an array of hydrophones gives that the spectrum levels of ambient noises are highly directional, their difference being as large as 10dB with vertical or horizontal angles. This fact strongly implies that we should obtain in-situ information of noise levels to estimate reasonable sonar performance. As one of non-stationary noise sources, an eel may give serious problems to sonar operation on or under the sea bottoms. Observed eel noises in a pier of water depth 14m appear to have duration time of about 0.4 seconds and frequency ranges of 0.2-2.8kHz. The 'song'of an eel increases ambient noise levels to average 2.16dB in the frequencies concerned, being large enough to degrade detection performance of the sonars on or below sediments. An experiment using hydrophones in water and sediment gives that sensitivity drops of 3-4dB are expected for the hydrophones laid in sediment at frequencies of 0.5-1.5kHz. The SNR difference between in water and in sediment, however, shows large fluctuations rather than stable patterns with the source-receiver ranges.