• 한국자기학회지
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• 제13권2호
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• pp.70-75
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• 2003

비선형 자기이방성 물질을 이용하여 3차원 유한요소법으로 강자성 배관 벽에 형성된 결함 근처에서 누설되는 자속에 미치는 부피인장응력(bulk tensile stress) 및 수직 응력의 영향을 계산할 수 있다. 배관의 외$.$내부 벽의 racetrack형 결함(racetrack pit) 깊이와 계산된 부피응력 (bulk stress)이 축(x) 방향, 원주(y) 방향 및 방사상(z) 방향의 누설자속에 미치는 영향을 계산하였다. 그 결과 배관의 축 및 방사상 방향의 MFL 신호는 배관 외$.$내부 면의 racetrack 결함깊이와 부피인장응력에 의해 영향을 받으며, 결함의 깊이가 깊어질수록 부피인장응력이 커질수록 MFL 신호는 증가하였다. 그러나 원주 방향의 MFL 신호는 결함깊이와 부피인장응력에 거의 영향을 받지 않았다.

• 비파괴검사학회지
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• 제23권5호
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• pp.480-487
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• 2003

식물의 환경제어 향상을 위하여, 비파괴적인 방법을 사용하여 식물의 신호 특성이 연구되고 있다. 본 연구에서는 속씨식물과 겉씨식물에서 검출되는 음향방출 신호에 미치는 물 스트레스의 영향에 대하여 검토하였다. 낮 시간의 음향방출 신호는 밤 시간 보다 훨씬 많았으며, 낮 시간의 신호는 식물의 물 스트레스에 의해서 발생한 것으로 판단된다. 속씨식물과 겉씨식물은 음향 신호의 강한 주파수 대역이 다르게 나타났으며, 실외에서 검출한 식물의 음향 신호 주파수는 동일한 식물을 사용하여 실내에서 검출한 신호의 주파수 범위와 일치하였다.

• 지질공학
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• 제28권3호
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• pp.349-365
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• 2018

The strain and acoustic emission (AE) signals of Pocheon granite were measured during uniaxial compression tests to investigate microcrack formation and damage. Crack closure, initiation, and damage stresses of each sample were determined through an analysis of the crack volumetric strain and stiffness. The samples experienced four damage stages according to stress levels: stage 1 = crack closure stage; stage 2 = elastic stage; stage 3 = crack initiation stage; stage 4 = crack damage stage. At least 75% of all AE signals occurred in stages 3 and 4, and different AE parameters were detected in the four stress stages. Rise time, count, energy, and duration clearly showed a tendency to gradually increase with the damage stress stage. In particular, the rise time, energy, and duration increased by at least 95% in stage 4 as compared with stage 1. However, the maximum amplitude showed a smaller increase, and the average frequency decreased slightly at higher stages. These results indicate that as the degree of rock damage increases, the crack size grows larger. The crack types corresponding to the AE signals were determined using the relationship between RA (Rise time / Amplitude) values and average frequencies. Tension cracking was dominant in all stress stages. Shear cracking was rare in stages 1 and 2, but increased in stages 3 and 4. These results are consistent with previous studies that reported cracking begins after samples have already been damaged. Our study shows that the state of rock damage can be investigated solely through an analysis of AE parameters when rocks are under compressive stress. As such, this methodology is suitable for understanding and monitoring the stress state of bedrock.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 춘계학술대회 논문집
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• pp.130-133
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• 2002

Polyethylene pressure pipe has been used with a gas pipe material because of workability and stability etc.. Researches on characteristics of polyethylene pressure pipe are carried out, but there are rare. In this study, the tensile test was performed on polyethylene pipe. From the tensile test, AE signals were detected and estimated in real time. Also, the time-frequency analysis of AE signals was analyzed. From test results, PE pipes were displayed typical stress-strain curves oj semi-crystalline polymer. As result analyzed AE signals, could divide stress-strain curves could be divided into four stages. In the elastic region, signals were not detected. Low amplitude distributions of 30-35dB appeared after yielding, and high amplitude distributions of 30-60dB appeared with increased extension. From the time-frequency analysis of AE signals, the frequency band of 100kHz appeared mainly. Also, the frequency band of 300kHz appeared before the necking phenomenon spreads into the whole region, and the frequency band of 500kHz appeared on extension earlier.

• 한국환경농학회지
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• 제27권4호
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• pp.362-367
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• 2008

The legume-rhizobia symbiosis is an important source of plant growth and nitrogen fixation for many agricultural systems. This study was conducted to investigate the effects of salinity stress on nitrogen fixation and growth of pea (Pisum sativum L.), which has antimutagenic activities against chemical mutagen, inoculated with R. leguminosarum bv. viciae cultured with additional plant-to-rhizobia signal compounds, naringenin (NA,15 uM), methyl-jasmonate (MJ, 50 uM) or both, under greenhouse conditions. Three salinity levels (0.6, 3.0 and $6.0\;dS\;m^{-1}$) were imposed at 3 days after transplanting and maintained through daily irrigations. Addition of signal compounds under non-stress and stress conditions increased dry weight, nodule numbers, leaf area and leaf greenness. The inducers increased photosynthetic rate under non-stress and stress conditions, by approximately 5-20% when compared to that of the non-induced control treatment. Under stress conditions, proline content was less in plants treated with plant-to-bacteria signals than the control, but phenol content was significantly increased, compared to that of the control. The study suggested that pre-incubation of bacterial cells with plant-to-bacteria signals could enhance pea growth, photosynthesis, nitrogen fixation and biomass under salinity stress conditions.

• 한국지반공학회논문집
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• 제18권4호
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• pp.95-104
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• 2002

최근, SPT 롯드에서 측정되는 동적신호(힘 및 가속도신호)에 대한 이론적. 해석적 연구가 활발히 진행되고 있다. 본 연구에서는 SPT시험에서 롯드(rod)를 통해 전파되는 탄성파에 대한 동적신호(힘 신호)의 특성을 모형 롯드-지반 시스템에 대하여 실험적으로 검토하였다. 시험결과, 단부조건에 따른 입사파와 반사파의 크기는 이론적으로 알려진 것과 매우 잘 일치하고 있음을 확인하였다. 따라서, 만일 SPT 시험에서 측정된 하중신호에서 입사파와 반사파의 특성이 정량적으로 평가된다면, 지반의 임피던스를 결정할 수 있을 것으로 예상된다. 한편, 주면저항에 의한 반사파의 영향은 대단히 작은 것으로 나타나, SPT 동적하중의 해석에서는 샘플러 주면의 마찰저항은 무시하고, 샘플러 선단의 단부저항만을 고려하는 해석모델의 적용이 가능할 것으로 판단된다.

• ETRI Journal
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• 제45권1호
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• pp.105-118
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• 2023

We tested the feasibility of automated discrimination of patients with panic disorder (PD) from healthy controls (HCs) based on multimodal physiological responses using machine learning. Electrocardiogram (ECG), electrodermal activity (EDA), respiration (RESP), and peripheral temperature (PT) of the participants were measured during three experimental phases: rest, stress, and recovery. Eleven physiological features were extracted from each phase and used as input data. Logistic regression (LoR), k-nearest neighbor (KNN), support vector machine (SVM), random forest (RF), and multilayer perceptron (MLP) algorithms were implemented with nested cross-validation. Linear regression analysis showed that ECG and PT features obtained in the stress and recovery phases were significant predictors of PD. We achieved the highest accuracy (75.61%) with MLP using all 33 features. With the exception of MLP, applying the significant predictors led to a higher accuracy than using 24 ECG features. These results suggest that combining multimodal physiological signals measured during various states of autonomic arousal has the potential to differentiate patients with PD from HCs.

• Molecules and Cells
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• 제25권1호
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• pp.1-6
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• 2008

Osteoarthritis (OA), one of the most common skeletal disorders characterized by cartilage degradation and osteophyte formation in joints, is induced by accumulated mechanical stress; however, little is known about the underlying molecular mechanism. Several experimental OA models in mice by producing instability in the knee joints have been developed to apply approaches from mouse genetics. Although proteinases like matrix metalloproteinases and aggrecanases have now been proven to be the principal initiators of OA progression, clinical trials of proteinase inhibitors have not been successful for the treatment, turning the interest of researchers to the upstream signals of proteinase induction. These signals include undegraded and fragmented matrix proteins like type II collagen or fibronection that affects chondrocytes through distinct receptors. Another signal is proinflammatory factors that are produced by chondrocytes and synovial cells; however, recent studies that used mouse OA models in knockout mice did not support that these factors have a role in the central contribution to OA development. Our mouse genetic approaches found that the induction of a transcriptional activator Runx2 in chondrocytes under mechanical stress contributes to the pathogenesis of OA through chondrocyte hypertrophy. In addition, chondrocyte apoptosis has recently been identified as being involved in OA progression. We hereby propose that these endochondral ossification signals may be important for the OA progression, suggesting that the related molecules can clinically be therapeutic targets of this disease.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 봄 학술발표회 논문집
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• pp.537-543
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• 1997

A new procedure for the advanced one-side measurement of longitudinal wave and surface wave velocities in concrete is presented in this paper. Stress waves are generated in a consistent fashion with a DC solenoid. Two piezoelectric accelerometers are mounted on the surface of a specimen as receivers. Stress waves propagate along the surface of the specimen and are detected by the receivers. In order to reduce the large incoherent noise levels of the signals, signals are collected and manipulated by a computer program for each velocity measurement. For a known distance between the two receivers and using the measured flight times, the velocities of the longitudinal wave and the surface wave are measured. The velocities of the longitudinal wave determined by this method are compared with those measured by conventional methods on concrete, PMMA and steel.

• Nuclear Engineering and Technology
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• 제49권7호
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• pp.1524-1536
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• 2017

During the fabrication process of reactor vessel head penetration (RVHP), the grain size of the tube material can be changed by hot or cold work and the inner side of the tube can also be shrunk due to welding outside of the tube. Several nonregular time-of-flight diffraction (TOFD) signals were found because of deformed grains. In this paper, an investigation of nonregular TOFD indications acquired from RVHP tubes using experiments and computer simulation was performed in order to identify and distinguish TOFD signals by coarse grains from those by Primary Water Stress Corrosion Crack (PWSCC). For proper understanding of the nonregular TOFD indications, microstructural analysis of the RVHP tubes and prediction of signals scattered from the grains using Finite Element Method (FEM) simulation were performed. Prediction of ultrasonic signals from the various sizes of side drilled holes to find equivalent flaws, determination of the size of the nonregular TOFD indications from the coarse grains, and experimental investigation of TOFD signals from coarse grain and shrinkage geometry to identify PWSCC signals were performed. From the computer simulation and experimental investigation results, it was possible to obtain the nonregular TOFD indications from the coarse grains in the alloy 690 penetration tube of RVHP; these nonregular indications may be classified as PWSCC. By comparing the computer simulation and experimental results, we were able to confirm a clear difference between the coarse grain signal and the PWSCC signal.