• Korean Journal of Metals and Materials
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• v.49 no.12
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• pp.924-929
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• 2011

It is well known that grain boundary cavitation is the main failure mechanism in austenitic stainless steel under tensile hold creep-fatigue interaction conditions. The cavities are nucleated at the grain boundary during cyclic loading and grow to become grain boundary cracks. The attenuation of ultrasound depends on scattering and absorption in polycrystalline materials. Scattering occurs when a propagation wave encounters microstructural discontinuities, such as internal voids or cavities. Since the density of the creep-fatigue cavities increases with the fatigue cycles, the attenuation of ultrasound will also be increased with the fatigue cycles and this attenuation can be detected nondestructively. In this study, it is found that individual grain boundary cavities are formed and grow up to about 100 cycles and then, these cavities coalesce to become cracks. The measured ultrasonic attenuation increased with the cycles up to cycle 100, where it reached a maximum value and then decreased with further cycles. These experimental measurements strongly indicate that the open pores of cavities contribute to the attenuation of ultrasonic waves. However, when the cavities develop, at the grain boundary cracks whose crack surfaces are in contact with each other, there is no longer any open space and the ultrasonic wave may propagate across the cracks. Therefore, the attenuation of ultrasonic waves will be decreased. This phenomenon of maximum attenuation is very important to judge the stage of grain boundary crack development, which is the indication of the dangerous stage of the structures.

• Journal of Digital Convergence
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• v.20 no.4
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• pp.389-396
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• 2022

Deep Learning is based on a perceptron, and is currently being used in various fields such as image recognition, voice recognition, object detection, and drug development. Accordingly, a variety of learning algorithms have been proposed, and the number of neurons constituting a neural network varies greatly among researchers. This study analyzed the learning characteristics according to the number of neurons of the currently used SGD, momentum methods, AdaGrad, RMSProp, and Adam methods. To this end, a neural network was constructed with one input layer, three hidden layers, and one output layer. ReLU was applied to the activation function, cross entropy error (CEE) was applied to the loss function, and MNIST was used for the experimental dataset. As a result, it was concluded that the number of neurons 100-300, the algorithm Adam, and the number of learning (iteraction) 200 would be the most efficient in deep learning learning. This study will provide implications for the algorithm to be developed and the reference value of the number of neurons given new learning data in the future.

• Journal of Fisheries and Marine Sciences Education
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• v.25 no.2
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• pp.341-348
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• 2013

The auditory thresholds for 7 specimens of the sharp toothed eel Muraensox cinerus were measured at 5 frequencies by heartbeat conditioning method using pure tones coupled with a delayed electric shock. The audible range of the sharp toothed eel extended from 80Hz to 300Hz with the best sensitivity around 80Hz and 100Hz. In addition, the auditory thresholds over 200Hz increased rapidly. The mean auditory thresholds of the sharp toothed eel at the test frequencies of 80Hz, 100Hz, 200Hz and 300Hz were 87dB, 86dB, 105dB and 126dB, respectively. Auditory masking was determined for the sharp toothed eel by using masking stimuli with the spectrum level range of about 70~80dB (0dB re $1{\mu}Pa/\sqrt{Hz}$). According to white noise level, the auditory thresholds increased as compared with thresholds in a quiet background noise. The noise spectrum level at the start of masking was distributed at the range of about 64dB within 80~100Hz. Critical ratio ranged from minimum 24dB to maximum 40dB at test frequencies of 80Hz~200Hz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.46-49
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• 2002

The aim of this paper is to investigate the influence of various deformation ratio on texture of Ag tapes that can be used as a RE-$Ba_2Cu_3O_{7-{\delta}}$ coated conductor tapes without any buffer layer. We fabricated as-rolled Ag substrate with various deformation ratio per step. Thickness and total deformation ratio of Ag tapes were $100{\mu}m$ and >98%, respectively. And as-rolled Ag substrate was annealed at $750^{\circ}C$ for 30min. The as-rolled and recrystallization textures were measured using x-ray pole figures and orientation distribution function (ODF) analysis. With the increase of rolling ratio from 5 to 20%, deformation texture are changed from {1l0}<311> to {1l0}<112>, {032}<100>, {051}<211>. After recrystallization by annealing, main texture was observed to {013}<100> under present condition.

• Korean Journal of Medicinal Crop Science
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• v.20 no.1
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• pp.63-71
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• 2012

The objectives of this study were to investigate the antioxidant activity of Schizandra chinensis seed oil and its active ingredients. Schizandra chinensis seed oil content extracted with hexane was 36.06%. Schizandra chinensis seed oil extracted with hexane was purified during 20 min at $85^{\circ}C$ with phosphoric acid 0.15% for degumming and 20 min at $80^{\circ}C$ with 3 M NaOH 1% for deaciding. The purified oil consisted of unsaturated fatty acid (88.7%), fatty acid (9.97%), and so on. The major unsaturated fatty acids of purified oil were linoleic acid (71.1%) followed by oleic acid (15.7%), while the main saturated fatty acid was palmitic acid (6.56%). The purified oil was found that contents of phenolic compounds, vitamin A, and E were 1.45 g/100 g, 1494.86 RE/100 g, and 0.58 mg ${\alpha}$-TE/100 g, respectively. Schizandra chinensis seed oil exhibited strong antioxidant activity (91.7%) as compared to grape seed oil and canola seed oil with 87.4% and 85.1% in the DPPH assays. Present results suggest that Schizandra chinensis seed oil could be potentially used as bioactive source for health and preventing numerous diseases.

• Tribology and Lubricants
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• v.35 no.2
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• pp.106-113
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• 2019

We investigated the application of tetrahedral amorphous carbon (ta-C) coatings to fabricate a glass lens manufactured using a glass molding process (GMP). In this work, ta-C coatings with different thickness (50, 100, 150 and 200 nm) were deposited on a tungsten carbide (WC-Co) mold using the X-bend filter of a filtered cathode vacuum arc. The effects of thickness on mechanical and tribological properties of the coating were studied. These ta-C coatings were characterized by atomic force microscopy, scanning electron microscopy, nano-indentation measurements, Raman spectrometry, Rockwell-C tests, scratch tests and ball on disc tribometer tests. The nano-indentation measurements showed that hardness increased with an increase in coating thickness. In addition, the G-peak position in the Raman spectra analysis was right shifted from 1520 to $1586cm^{-1}$, indicating that the $sp^3$ content increased with increasing thickness of ta-C coatings. The scratch test showed that, compared to other coatings, the 100-nm-thick ta-C coating displayed excellent adhesion strength without delamination. The friction test was carried out in a nitrogen environment using a ball-on-disk tribometer. The 100-nm-thick ta-C coating showed a low friction coefficient of 0.078. When this coating was applied to a GMP, the life time, i.e., shot counts, dramatically increased up to 2,500 counts, in comparison with Ir-Re coating.

• Journal of the Korean Solar Energy Society
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• v.26 no.4
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• pp.93-100
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• 2006

An experimental study of a counterflow heat exchanger was performed. The heat exchanger had an effective heat transfer length of 1000mm and was operated in a counterflow arrangement with hot water($30{\pm}0.5^{\circ}C$, $Re_i=3500{\sim}20000$) in the inner tube(copper tube, $d_0=9.52mm$) and cold water($15{\pm}0.5^{\circ}C$, $Re_{DH}=10700{\sim}39000$) in the annulus(copper tube, $D_0=19.05mm$). Overall heat transfer coefficients were calculated and heat transfer coefficients in the inner tube and the annulus were determined using Wilson plots. The inner Nusselt number was compared with that of Gnielinski's correlation and they agreed within ${\pm}10%$ error. The trends were typical for a fluid-to-fluid heat exchanger with the overall heat transfer coefficient increasing with both inner and annulus flow rates. In the range of this experiment, Nusselt numbers for the inner tube flow were almost identical with those of the annulus flow at the same Reynolds number.

• Communications for Statistical Applications and Methods
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• v.22 no.6
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• pp.575-587
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• 2015

The development in data collection techniques results in high dimensional data sets, where discrimination is an important and commonly encountered problem that are crucial to resolve when high dimensional data is heterogeneous (non-common variance covariance structure for classes). An example of this is to classify microbial habitat preferences based on codon/bi-codon usage. Habitat preference is important to study for evolutionary genetic relationships and may help industry produce specific enzymes. Most classification procedures assume homogeneity (common variance covariance structure for all classes), which is not guaranteed in most high dimensional data sets. We have introduced regularized elimination in partial least square coupled with QDA (rePLS-QDA) for the parsimonious variable selection and classification of high dimensional heterogeneous data sets based on recently introduced regularized elimination for variable selection in partial least square (rePLS) and heterogeneous classification procedure quadratic discriminant analysis (QDA). A comparison of proposed and existing methods is conducted over the simulated data set; in addition, the proposed procedure is implemented to classify microbial habitat preferences by their codon/bi-codon usage. Five bacterial habitats (Aquatic, Host Associated, Multiple, Specialized and Terrestrial) are modeled. The classification accuracy of each habitat is satisfactory and ranges from 89.1% to 100% on test data. Interesting codon/bi-codons usage, their mutual interactions influential for respective habitat preference are identified. The proposed method also produced results that concurred with known biological characteristics that will help researchers better understand divergence of species.

• Journal of computational fluids engineering
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• v.6 no.2
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• pp.22-31
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• 2001

The two-dimensional unsteady incompressible viscous flow behind rectangular bluff bodies between two parallel plates was analyzed numerically. The steady state flow and the vortex flow behind rectangular bluff bodies in the channel were investigated for two regimes i.e., the laminar(Re = 100, 300, 500) and the turbulent flows(Re = 10⁴∼10/sup 6/). The vortex shedding was generated by a physical disturbance(6%) numerically imposed at the rear of the bluff bodies for a short time. It was observed that the perturbed flow became periodic after a transient period. And in the case of unsteady inflow, the sinusoidal pulsatile flow was applied as the inlet condition in the turbulent flow of Reynolds number of 1.0×10/sup 5/. FLUENT code was employed to solve the problems. The power-law scheme was used to get stable linearized equations and the PISO algorithm was applied to finding the solution of them.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.1
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• pp.21-30
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• 1999

The present study were investigated changes of precipitation behaviour of laves phase in ferrite single phase and ferrite-martensite dual phase and precipitation of laves phase under stress. Hardness changes in ferrite phase appeared two hardness peaks by precipitation of initial fine precipitator and laves phase in 3Mo-0.3Si and 3Mo-0.3Si-C specimens, respectively. Hardness changes in martensite phase of 3Mo-0.3Si-C specimen was lower in the initial stage of aging by carbide precipitation and after this, increased by re-hardening due to precipitation of laves phase. In the ferrite phase, laves phase was mainly precipitated, whereas in the martensite phase, carbide was preferentially formed during the initial stage of aging and with increasing aging time, laves phase and carbide were simultaneously precipitated by precipitation of laves phase at around carbide. In the ferrite-martensite interface, laves phase was mainly precipitated and carbide was mainly formed at boundary of lath martensite than grain boundary. Adding the stress in aging, fine precipitator of inital precipitation of laves phase precipitated in (100) of perpendicular to tensile direction and has grown to only followed<010>direction and also, volume fraction of laves phase increased. Consequently, the stress added was accelerated initial precipitation of laves phase.