• Geomechanics and Engineering
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• 제22권2호
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• pp.187-196
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• 2020

The changeable stress environment directly affect the propagation law of a stress wave. Stress wave propagation tests in sandstone with different axial stresses were carried using a modified split Hopkinson Pressure bar (SHPB) assuming the sandstone has a uniform pore distribution. Then the waveform and stress wave energy dissipation were analyzed. The results show that the stress wave exhibits the double peak phenomenon. With increasing axial stress, the intensity difference decreases exponentially and experiences first a dramatic decrease and then gentle development. The demarcation stress is σ/σ_c=30%, indicating that the closer to the incident end, the faster the intensity difference attenuates. Under the same axial stress, the intensity difference decreases linearly with propagation distance and its attenuation intensity factor displays a quadratic function with axial stress. With increasing propagation distance, the time difference decays linearly and its delay coefficient reflects the damage degree. The stress wave energy attenuates exponentially with propagation distance, and the relations between attenuation rate, attenuation coefficient and axial stress can be represented by the quadratic function.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.454-460
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• 2015

Acoustic emission (AE) is one of the promising methods for detecting the formation of stress corrosion cracks (SCCs) in laboratory tests. This method has the advantage of online inspection. Some studies have been conducted to investigate the characteristics of AE parameters during SCC propagation. However, it is difficult to classify the distinct features of SCC behavior. Because the previous studies were performed on slow strain rate test or compact tension specimens, it is difficult to make certain correlations between AE signals and actual SCC behavior in real tube-type specimens. In this study, the specimen was a AISI 304 stainless steel tube widely applied in the nuclear industry, and an accelerated test was conducted at high temperature and pressure with a corrosive environmental condition. The study result indicated that intense AE signals were mainly detected in the elastic deformation region, and a good correlation was observed between AE activity and crack growth. By contrast, the behavior of accumulated counts was divided into four regions. According to the waveform analysis, a specific waveform pattern was observed during SCC development. It is suggested that AE can be used to detect and monitor SCC initiation and propagation in actual tubes.

• 대한임상검사과학회지
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• 제50권3호
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• pp.370-374
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• 2018

빗장밑혈류빼앗김증후군은 왼쪽 근위부 빗장밑동맥이나 오른쪽 팔머리동맥에 심한 협착 혹은 폐색으로 인해 반대쪽 척추동맥으로부터 관류압이 감소된 병변쪽 빗장밑동맥으로 혈류가 역으로 유입되는 현상이 나타나게 되고, 그 결과로 척추-뇌바닥혈류부전이나 허혈성 말초동맥질환 증상이 동반되는 경우를 말한다. 빗장밑동맥을 포함한 뇌혈관 협착증에서 신경중재술을 이용한 혈류의 회복 및 방향 교정은 환자의 증상과 예후를 좋게 한다고 알려져 있다. 저자는 오른팔에 비해 왼팔 혈압이 12 mmHg 낮은 환자에서 이중초음파검사를 시행하였고, 왼쪽 척추동맥에서 빗장밑혈류빼앗김증후군의 특징적인 혈류파형이 관찰되어 혈관성형술 및 스텐트 설치술을 통해 성공적으로 치료된 증례를 보고하고자 한다. 6개월 후 추적검사에서 왼쪽 척추동맥의 혈류파형은 정상으로 회복되었고, 양팔의 혈압 차는 5 mmHg로 감소하였다.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1533-1542
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• 2003

In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40. vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90$^{\circ}$ the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권4호
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• pp.1209-1223
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• 2022

Blood pressure is one of the key physiological parameters for determining human health, and can prove whether human cardiovascular function is healthy or not. In general, what we call blood pressure refers to arterial blood pressure. Blood pressure fluctuates greatly and, due to the influence of various factors, even varies with each heartbeat. Therefore, achievement of continuous blood pressure measurement is particularly important for more accurate diagnosis. It is difficult to achieve long-term continuous blood pressure monitoring with traditional measurement methods due to the continuous wear of measuring instruments. On the other hand, radar technology is not easily affected by environmental factors and is capable of strong penetration. In this study, by using machine learning, tried to develop a linear blood pressure prediction model using data from a public database. The radar sensor evaluates the measured object, obtains the pulse waveform data, calculates the pulse transmission time, and obtains the blood pressure data through linear model regression analysis. Confirm its availability to facilitate follow-up research, such as integrating other sensors, collecting temperature, heartbeat, respiratory pulse and other data, and seeking medical treatment in time in case of abnormalities.

• 전자공학회논문지SC
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• 제49권2호
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• pp.46-54
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• 2012

본 논문에서는 연속 가압방식으로 측정된 맥파 신호의 분석에 적합한 시작점 검출 알고리즘을 제안한다. 연속 가압방식은 가압의 크기를 조금씩 증가시키면서 맥파 신호를 측정하는 방식인데 이를 이용하면 가압크기에 대응하는 맥파 신호의 분해능이 크게 향상되기 때문에 현재 상용맥진기의 맥파 측정방식인 단계별 가압방식의 정확성과 신뢰성 문제를 해결할 수 있다. 시작점 검출을 위해서 고속 푸리에 변환을 이용한 주기계산, Center-to-edges 방법의 피크 검출, 기저선 보정, 접선 교점 방법에 의한 시작점 검출, 분석 구간 설정을 순차적으로 적용한 알고리즘을 개발하였다. 30명의 피험자를 대상으로 실험한 결과 제안된 알고리즘의 정확도는 99.46%, 민감도는 99.51%로 나타났는데 이는 기존 알고리즘보다 정확도 4.82%, 민감도 2.46%가 향상된 결과이다. 본 연구에서 제안한 연속 가압방식의 맥파 측정방법과 맥파 시작점 검출 알고리즘을 사용한다면 맥파 특징점의 정확한 검출은 물론 허실맥이나 부침맥 등의 맥상 판별 정확성을 높일 수 있을 것으로 기대된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1844-1847
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• 1996

In the paper, we have obtained electron energy distribution function (EEDF) in plasma by using two differentiators. In addition, we have investigated the comparision of the EEDFs by sawtooth and triangle waveform voltages. It is found that as pressure is decreased, electron density is decreased, and plasma potential is increased. And as the position of probe moves the outer of plasma, plasma potential is decreased, and electron temperature is decreased.

• Journal of Multimedia Information System
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• 제9권2호
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• pp.161-170
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• 2022

Under General anesthesia with isoflurane, we insert a chicken's esophageal catheter into the near the left atrium. 1MHz radio wave was added to electrocardiogram electrodes of the esophagus, and the change of impedance (phase) was obtained by amplitude synchronous detection technique. At the same time, a thin tube is surgically inserted into the axillary artery to continuously measure blood pressure. The correlation between impedance (phase) and blood pressure was obtained. Both showed a very high correlation (R²=0.9665). It was also observed the waveform flowing from the left atrium into the left ventricle. When an individual infected with the avian influenza virus develops, the cytokine storms lead to hypotension earlier than the test for antigen-antibody reaction. In order to detect this, in the future, this impedance technique will be useful for screening individuals infected with avian influenza virus by measuring the blood pressure of chickens in cages in a non-contact manner using microwaves.

• 전기전자학회논문지
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• 제23권3호
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• pp.865-872
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• 2019

대기압에서의 Ar 직류 글로우방전 현상을 1차원 유체모델을 통하여 시뮬레이션을 수행하였다. Ar 기체방전의 여기입자들로부터 방출되는 광원으로서 4가지(${\lambda}_{128nm}$, ${\lambda}_{727nm}$, ${\lambda}_{912nm}$ 그리고 ${\lambda}_{966nm}$) 파장의 빛을 검토하였다. 그 결과, 사인형태의 전원 전압을 인가하였을 경우, ${\lambda}_{128nm}$와 ${\lambda}_{727nm}$의 광원이 직류 전압파형을 인가하였을 때보다 거의 2배에 가까운 빛을 방출하는 것을 확인하였다. 또한, 전원전압의 스위칭 시간이 짧을수록, ${\lambda}_{128nm}$와 ${\lambda}_{727nm}$의 방출이 더 많아지는 것을 알 수 있었다. 본 연구에서는 하전입자에 의한 줄 열과 소모 전력에 관해서도 논의하였다.

• 대한의용생체공학회:의공학회지
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• 제29권5호
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• pp.371-375
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• 2008

In blood pressure measurement, the oscillometric method detects and analyzes the pulse pressure oscillation while deflating the cuff around the arm. For its principle, one has to inflate cuff pressure above the subject's systolic pressure and deflate below the diastolic pressure. Most of the commercialized devices inflate until the fixed target pressure and deflate until the fixed completion pressure because there is no way to know the systolic and diastolic pressure before measurement. Too high target pressure makes stress to the subject and too low target pressure makes big error or long measurement time because of re-inflation. There are similar problems for inadequate completion pressure. In this study, we suggest new algorithm to set proper target and completion pressure for each subject by analyzing pressure waveform while inflating period. We compared our proposed method and auscultation method to see the errors of estimation. The differences between the two measurements were -4.02$\pm$4.80mmHg, -10.50$\pm$10.57mmHg and -0.78$\pm$5.l7mmHg for mean arterial pressure, systolic pressure and diastolic pressure respectively. Consequently, we could set the target pressure by 30 mmHg higher than our estimation and we could stop at 20mmHg lower than our estimated diastolic pressure. Using this method, we could reduce the measurement time.