• Journal of Biomedical Engineering Research
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• v.8 no.1
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• pp.41-48
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• 1987

In estimating the freguency-dependent attenuation coefficient, we analyzed the range-dependent ultrasonic beam and proposed the method of calculating the experimental equation of beam pattern in order to reduce the error on the influence of beam pattern. These experimental equations are divided into the spectral centroid and the spec ural standard deviation slope according to axial propagation length. These are repnesented by the first-order equation in the near field of the beam and the second- order eqLlatlon In the far field. In order to prove the validity of this method, the attenuation coefficients of the non-corrected ease and the corrected case are compared. Using the reflected signal from acryle plate, the attenuation coefficients were estimated by the spectral shift method ann the spectral difference method. The result shows attenuation coeffi talents after correction are better than attenuation coefficients before correction. And this method can be applied In vivo measurement.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.390-390
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• 2013

유기물을 이용하여 제작한 비휘발성 메모리 소자는 저전압 구동, 간단한 공정과 플렉서블 모바일에 응용 가능성 때문에 많은 연구가 진행되고 있다. 나노복합체를 사용하여 제작한 비휘발성 메모리 소자의 전기적 특성에 대한 연구가 많이 진행되었으나 고분자를 저장매체로 사용한 메모리 소자의 전기적 특성에 대한 연구는 미흡하다. 본 연구에서 poly (methylmethacrylate) (PMMA)와 poly (3-hexylthiophene) (P3HT) 혼합한 용액을 이용하여 제작한 메모리 소자의 전기적 특성을 연구하였다. P3HT와 PMMA를 같이 클로로벤젠에 용해한 후 초음파 교반기를 사용하여 두 물질을 고르게 섞었다. Indium-tin-oxide가 코팅된 유리 기판 위에 제작한 고분자 용액을 스핀 코팅하고, 열을 가해 용매를 제거하였다. P3HT박막 위에Al을 상부전극으로 열증착하여 소자를 제작하였다. 제작된 소자의 전류-전압(I-V) 측정결과는 같은 전압에서 전도도가 큰 ON 상태와 전도도가 작은 OFF 상태의 큰 ON/OFF 전류비율을 가진 전류의 히스테리시스를 보여주었다. P3HT를 포함하지 않은 소자의 I-V 측정결과는 전류의 히스테리시스 특성이 보이지 않았고 이것은 P3HT 박막이 메모리 특성을 나타내는 저장매체가 됨을 알 수 있었다. 소자의 전류-시간 특성 측정 결과는 전류의 ON/OFF 비율이 시간에 따라 큰 감쇠 현상 없이 오랫동안 지속적으로 유지됨을 보여줌으로 소자의 동작 안정성을 알 수 있었다.

• Journal of dental hygiene science
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• v.15 no.5
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• pp.603-611
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• 2015

This research is aimed at cutting off hearing loss and other harmful factors due to noise and providing basic material for noise reduction plan. As the research method, this research assessed noise by measuring acoustic pressure level and frequency in various situation of non-treatment and treatment. As the measurement result, average noise degree of high speed handpiece of non-treatment, ultrasonic waves scaler, and low speed handpiece showed 58~66 dB(A). Average noise degree of scaling of treatment, tooth elimination, and denture adjust showed 73~81 dB(A). The result is inferior to recognized standards of noise induced hearing loss. But the result of assessing this with (noise rating) NR curve was NR-73~78, which exceeded general workplace noise standard. This level can cause hearing loss when exposed to a long time. Therefore, treatment office noise during dental treatment can cause psychological and physical damage in dental clinic employees, and it is urgently required to establish systematic and active noise reduction plan.

• 한국해양학회지
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• v.26 no.1
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• pp.59-66
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• 1991

Laboratory studies were carried out to measure the sound velocity (V/SUB p/) and quality factor (Q/SUB p/, inverse attenuation) in the horizontal (H) and vertical (V) direction on the core sampled sediment of deep-sea basin (1,850 meter water depth), East Sea of Korea (Sea of Japan). Sampled core was about 250 cm long and 500 kHz ultrasonic p-wave transducer was used for a sound soured. V/SUB p/ varies from 1,480 m/sec to 1,500 m/sec, it is not clear which direction is faster, V/SUB PH/ or V/SUB pv/, within${\pm}$ 1.0% anisotropy (A/SUB p/). It is thought because the core sediment facies is highly (or slightly) bioturbated homogeneous mud with very high porosity (more than 80%). The general trend of Q/SUB p/ is decreasing 10 to 5 with the buried depth, it is strongly affected by the variation of sediment texture (increasing silt, decreasing clay) with increasing of CaCO$_3$ and organic matter content, But Q/SUB PH/ is jumping up to 14.9 near the bottom of core sediment as including volcanic ash richly. The relationship between V/SUB PH/ and Q/SUB PH/ shows the mirror image nearly, it is interpreted that not only the geotechnical properties and texture but also sea-water characteristics (high Q/SUB p/, low V/SUB p/) according to rich water content affect strongly in the upper part of the unconsolidated deep-sea basin sediment.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.75-82
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• 2007

As one of the main support systems, rock bolts play a crucial role in the reinforcement of tunnels. Numerical and experimental studies using a transmission method of ultrasonic guided waves are performed to evaluate the integrity of rock bolts encapsulated by grouting paste. Numerical simulations using "DISPERSE" are carried out for the selection of the optimal experimental setup, i.e. non-destructive testing (NDT) system of the rock bolt. Based on results of the numerical simulation, the calculated frequency range for NDT testing is between 20kHz and 70kHz with the first longitudinal L(1) mode. Laboratory transmission tests are performed by attaching the piezo electric sensor at the tip of the rock bolt before embedding. Both of analytical and experimental results show that the amplitude of signals as well as the wave velocity increases with increase in the defect ratio of grouting paste. The defect in grouting paste means that the space around the rock bolt is not fully filled with the grouting paste. Experimental results also show that the increase of the wave velocity is more sensitive to the defect ratio increase than that of the amplitude. This study demonstrates that the transmission technique of ultrasonic guided waves may be a valuable tool in the evaluation of the rock bolt integrity.

• The Journal of the Acoustical Society of Korea
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• v.8 no.4
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• pp.29-38
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• 1989

Detection of an underwater target by acoustic wave raises various difficulties due to unpredictable noise interference which originates from clutter, reverberation, and variations of medium characteristics with time and location. The SNR and the range resolution of conventional SONAR systems using a matched filter are generally poor, since the latter is optimum only in the additive white noise case. Furthermore, it cannot compensate for variations of the detection level which are responsible for the resultant detection errors. In this paper, the unpredictable interferences are compensated for by using an adaptive filter. It recursively estimates the channel impulse response based on the received echo signal. In the low noise environments, the estimated impulse response is close to the true one, providing a good range resolution, and a matched filter is used subsequently for the purpose of detection. It is shown through computer simulation that good performance can be achieved via the two steps of filtering. Also, the detection level remains unchanged without any additional provisions. Finally, we present the characteristics of the employed adaptive filter parameters.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.381-381
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• 2012

유기물/무기물 나노 복합체를 이용하여 제작한 메모리 소자는 저전력 구동, 간단한 공정, 플렉서블한 성격과 같은 장점 때문에 많은 연구가 진행되고 있다. 다양한 유기물/무기물 나노 복합체를 이용한 비휘발성 메모리 소자에 대한 연구는 많이 진행되었으나, fullerene 계열의 [6,6]-phenyl-C85 butyric acid methyl ester (PCBM) 나노 입자와 poly (methylmethacrylate) (PMMA)의 나노 복합체를 사용하여 제작한 유기 쌍안정성 메모리 소자의 전기적 특성과 메커니즘에 대한 연구는 미흡하다. 본 연구에서는 기억층으로 PMMA 박막 안에 분산되어 있는 PCBM 나노 입자를 트랩층으로 사용하는 메모리 소자를 제작하여 전기적 특성 및 안정성에 대하여 관찰하였다. 소자제작을 위하여 PCBM 나노 입자를 PMMA와 함께 용매인 클로로벤젠에 용해한 후에 초음파 교반기를 사용하여 두 물질을 고르게 섞었다. Indium-tin-oxide 가 코팅된 glass위에 PCBM 나노 입자와 PMMA가 섞인 나노 복합체를 스핀 방법으로 적층한 후, 열을 가해 클로로벤젠을 제거하여 PCBM 나노 입자가 PMMA 안에 분산되어 있는 전하 수송 층을 형성하였다. 형성된 전하수송 층 위에 열 증착 방식으로 상부 Al 전극을 형성하여 유기 쌍안정성 메모리 소자를 제작하였다. 제작된 소자의 전류-전압 (I-V) 측정 결과 특정 전하 수송 층의 두께에서는 큰 ON/OFF 전류 비율을 보여준다. PMMA만을 사용한 소자에서는 I-V 메모리 특성이 나타나지 않는 결과로부터 PCBM 나노 입자가 전하 수송 층 내에서 메모리 특성의 역할을 한다는 것을 보여준다. 전류-시간 (I-t) 측정 결과로 소자의 ON/OFF 전류 비율이 시간이 지남에 따라 큰 감쇠 없이 104 s까지 103값을 지속적으로 유지되어 메모리 소자의 안정성을 보여주었다. 실험의 결과로 PCBM이 포함된 메모리 소자의 메커니즘과 전하 수송 층의 두께에 따른 메모리 특성을 설명하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.274-274
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• 2011

유기물/무기물 나노복합체를 이용하여 제작한 비휘발성 메모리 소자는 저전력 구동과 간단한 공정과 같은 장점 때문에 많은 연구가 진행되고 있다. 무기물 나노 입자를 포함한 고분자 박막을 사용한 비휘발성 메모리 소자에 대한 연구는 많이 진행되었으나, [6,6]- phenyl-C85 butyric acid methyl ester (PCBM) 나노 입자가 고분자 박막에 분산되어 있는 나노복합체를 사용하여 제작한 메모리 소자의 전기적 특성과 안정성에 대한 연구는 미흡하다. 본 연구에서는 PCBM 나노 입자가 poly (methylmethacrylate) (PMMA) 박막 안에 분산되어 있는 나노복합체를 사용한 메모리 소자를 제작하여 전기적 특성 및 안정성에 대하여 관찰하였다. PCBM 나노 입자를 PMMA와 함께 용매인 클로로벤젠에 용해한 후에 초음파 교반기를 사용하여 두 물질을 고르게 섞었다. 전극이 되는 indium-tin-oxide 가 성장된 유리 기판 위에 PCBM과 PMMA가 섞인 용액을 스핀 코팅한 후, 열을 가해 용매를 제거하여 PCBM입자가 PMMA에 분산되어 있는 나노복합체 박막을 형성하였다. 형성된 나노복합체 박막 위에 상부 전극으로 Al을 열증착하여 비휘발성 메모리 소자를 완성하였다. 제작된 소자의 전류-전압 측정 결과는 큰 ON/OFF 전류비율을 보여주었다. PCBM 나노입자를 포함하지 않은 소자에서는 메모리 특성이 나타나지 않았기 때문에 PCBM 나노 입자가 비휘발성 메모리 소자의 기억 특성을 나타내는 저장매체가 됨을 알 수 있었다. 전류-시간 측정 결과는 소자의 ON/OFF 전류 비율이 시간이 지남에 따라 큰 감쇠 현상 없이 104 sec 까지 지속적으로 유지됨을 알 수 있었다. 제작된 각각의 메모리 소자의 ON/OFF 전류 비율 결과는 103 이상의 일정한 값이 측정되어 제작된 소자의 안정성을 보여주었다.

• Journal of Veterinary Clinics
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• v.30 no.3
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• pp.189-192
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• 2013

An 8-year-old, neutered female Korean short hair cat was referred with severe vomiting and anorexia. Abdominal mass effect was seen in the cranial abdomen on radiographs, and a mass with a heterogeneous echogenic pattern was observed medial to the right kidney on ultrasonography. On computed tomography, a large mass with soft tissue attenuation and a contrast-enhanced capsule was seen. In histopathological findings, the acinar structures were lined with irregular cuboidal cells that have pale eosinophilic cytoplasm and round to oval nuclei. Based on these diagnostic imaging and histopathological findings, the mass was diagnosed as pancreatic exocrine adenocarcinoma.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.60-66
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• 2006

Three differing sandstones, two synthetic and one field sample, have been tested ultrasonically under a range of confining pressures and pore pressures representative of in-situ reservoir pressures. These sandstones include: a synthetic sandstone with calcite intergranular cement produced using the CSIRO Calcite In-situ Precipitation Process (CIPS); a synthetic sandstone with silica intergranular cement; and a core sample from the Otway Basin Waarre Formation, Boggy Creek 1 well, from the target lithology for a trial $CO_2$ pilot project. Initial testing was carried on the cores at "room-dried" conditions, with confining pressures up to 65 MPa in steps of 5 MPa. All cores were then flooded with $CO_2$, initially in the gas phase at 6 MPa, $22^{\circ}C$, then with liquid-phase $CO_2$ at a temperature of $22^{\circ}C$ and pressures from 7 MPa to 17 MPa in steps of 5 MPa. Confining pressures varied from 10 MPa to 65 MPa. Ultrasonic waveforms for both P- and S-waves were recorded at each effective pressure increment. Velocity versus effective pressure responses were calculated from the experimental data for both P- and S-waves. Attenuations $(1/Q_p)$ were calculated from the waveform data using spectral ratio methods. Theoretical calculations of velocity as a function of effective pressure for each sandstone were made using the $CO_2$ pressure-density and $CO_2$ bulk modulus-pressure phase diagrams and Gassmann effective medium theory. Flooding the cores with gaseous phase $CO_2$ produced negligible change in velocity-effective stress relationships compared to the dry state (air saturated). Flooding with liquid-phase $CO_2$ at various pore pressures lowered velocities by approximately 8% on average compared to the air-saturated state. Attenuations increased with liquid-phase $CO_2$ flooding compared to the air-saturated case. Experimental data agreed with the Gassmann calculations at high effective pressures. The "critical" effective pressure, at which agreement with theory occurred, varied with sandstone type. Discrepancies are thought to be due to differing micro-crack populations in the microstructure of each sandstone type. The agreement with theory at high effective pressures is significant and gives some confidence in predicting seismic behaviour under field conditions when $CO_2$ is injected.