나노 스케일 MOS device의 1/f 노이즈 특성 : 1/f Noise Characteristics of Nano-Scale MOS devices

이정현 경북대학교 대학원 2007 국내석사

유효 채널 길이가 100 nm 이하인 MOS 소자와 고압 중수소 열처리 한 소자, 3차원 구조의 채널을 가진 소자들에 대해서 DC 특성, HCS (Hot Carrier Stress)및 NBTI (Negative Bias Temperature Instability) Stress 등에 대한 소자의 신뢰성 평가를 하였으며, 이러한 Stress 및 여러 가지 bias 조건에서의 1/f noise를 측정하여 gate oxide의 quality 및 interface trap density를 상대적으로 비교 하였다. 유효 채널 길이가 100 nm 이하인 소자의 경우 Lorentzian형태의 1/f noise 모양이 많이 관찰 되며 이러한 소자의 경우 RTN (Random Telegraph Noise)이 보다 확실하게 관찰이 되었으며, drain bias에 따른 1/f noise를 측정함으로서 지배적인 1/f noise source의 위치를 대략적으로 파악 할 수 있었다. 이러한 1/f noise의 source이자 소자의 reliability를 감소시키는 interface trap을 줄이기 위한 방법으로 고압 중수소 열처리 공정을 제시하였다. 고압 중수소 열처리 공정 진행 후 NMOS의 경우 Vth의 증가, interface trap density에 비례하는 charge pumping current의 감소, HCS에 대한 내성의 증가, 1/f noise level의 감소 등 여러 가지 특성이 좋아졌으나 PMOS의 경우, NBTI stress 내성만 좋아지는 결과를 얻었다. 3차원 구조의 MOS device의 경우 DC 특성은 기존의 planar MOSFET에 비해 월등히 뛰어난 결과를 보였으나, Recess Channel이나 Fin body etching시 etching damage에 의해 interface에 보다 많은 trap이 생기게 되며, 채널의 다양한 결정 방향으로 dangling 결함이 많으므로 기존의 planar MOSFET에 비해 1/f noise level이 높았으며, Bulk FinFET이 가장 큰 noise 산포를 가진다. 여러 가지 소자에 대한 1/f noise 특성 및 reliability 특성을 측정을 하였다. 소자의 크기가 계속 줄어들고 기존의 2차원 구조에서 3차원 구조의 소자들이 제시되고 있는 상황에서 1/f noise 특성의 평가 및 개선에 대한 연구는 계속 이루어질 예정이다.

Noise and vibration analysis for wheel/rail interaction

김정훈 Graduate School, Korea University 2012 국내박사

According to increase of the interest about environmental problem nowadays, social requirements about environmental friendliness rapidly increase in the railway. Along with changes, these have increased such as the civil complaint, conflict and enforcement of environmental standard. However, the noise and vibration research in the railway is significantly inadequate in Korea. Therefore, development of the railway noise and vibration core technology is needed. Moreover, in recent years, a number of researches about the dynamic characteristics of the noise and vibration in the railway have been performed. As a result, as the high frequency vibration which occurs in the irregularity of the wheel and rail running surfaces causes the track noise in railway system, the noise and vibration analytic studies with measurement for the wheel and rail is needed. Theoretical models describing the interaction between the wheel and track are used for noise and vibration analysis. The high frequency vibration analysis model is as follows. An infinite homogeneous structure consisting of double beams continuously supported by elastic layers is a common model for this kind of track. The upper beam describes the rail, the lower one models the concrete slab, while the two elastic layers reflect the properties of the rail-pad and the track sub-grade. The wheel is modeled as two masses model. The contact spring stiffness (kH), damping (c1) and stiffness (k1) of the rail-pad among these wheel and track properties are particularly very important to dynamic analysis model. This Analysis Models that have been developed for wheel/rail noise and vibration are generally linear in order to make use of a frequency-domain approach. In fact, the local elasticity between the wheel and the rail exhibits a nonlinear stiffness behavior due to geometrical effects. Also, when most of the researches for the noise and vibration analysis of the wheel/rail interaction are performed, the hysteretic damping to reflect the damping coefficient is considered. However, characteristics of the hysteretic and viscous damping are a little different. Therefore, the noise and vibration analysis for the wheel/rail interaction using the nonlinear contact spring and viscous damping are performed and analyzed in this study. Using that developed program, analytical studies on the concrete slab and ballast track were performed and evaluated in this study. This is able to provide especially the analysis tool and technique for noise/vibration guidelines on the design. To obtain the same results between the analysis and measurement, the noise and vibration studies for the railway structure should be continuously for the further study

마우스에서 aldosterone 전처치가 소음에 의한 내이손상에 미치는 영향

송형민 울산대학교 일반대학원 2007 국내석사

연구배경 및 목적: 소음성 내이손상에서 스테로이드의 보호효과에 대해서는 많은 연구가 있으나 대부분 glucocorticoid에 대한 보고이다. 하지만 와우에서 내림프의 항상성 유지에 관여하는 aldosterone이 소음성 외상에서 glucocorticoid와 동일한 보호효과를 갖는지에 대한 문헌 보고는 없다. 본 연구에서는 마우스에서 aldosterone이 소음에 의한 내이손상에 미치는 영향에 대해서 알아보고자 하였다. 대상 및 연구 방법: 청성 뇌간 유발 반응에서 25 dBHL 이하의 정상 청력을 보인 BALB/c 마우스를 실험에 사용하였다. 42마리의 마우스를 water군, prednisolone(PD)군, aldosterone(AD)군으로 구분하였고 청력의 영구역치변동과 일과성역치변동에 대한 aldosterone의 효과를 알기 위해 120 dB SPL의 광대역 백색잡음에 하루에 3시간씩 각각 3일군과 2일군으로 나누어 노출시켰다. 소음을 주기 전에 청성뇌간유발반응으로 청력역치를 먼저 측정한 후, 소음에 노출시킨 후 청력을 측정하여 청력감소를 확인하였다. 그 후 7일과 14일 뒤 다시 청력을 측정하여 소음 노출 후 청력의 변화를 확인하였다. 소음노출에 따른 혈청 aldosterone의 변화를 알아보기 위해 9마리의 마우스를 대상으로 상용 radioimmunoassay킷을 이용하여 혈청 aldosterone을 측정하였다. 결과: 소음에 노출된 마우스는 비노출군에 비해 혈청 aldosterone의 농도가 유의하게 감소하였다. 영구역치변동을 일으킨 마우스에서 PD군과 AD군은 대조군과 비교하여 청력보호 효과를 보이지 않았다. 또한 일과성역치변동을 일으킨 마우스에서 Water군, PD군, AD군은 투여약물에 따른 차이가 없이 소음노출 후 7일째 부분적인 청력의 호전을 보였고 소음노출 후 14일까지 더 이상의 청력의 호전은 없었다. 결론: BALB/c 마우스에서 소음노출 후 혈청 aldosterone의 유의한 감소가 관찰되었다. 하지만 aldosterone과 prednisolone의 전처치는 영구역치변동과 일과성역치변동을 일으킨 실험군 모두 대조군과 비교하여 소음성 내이손상에 대하여 보호효과가 없었다. Background and objectives : While the prevention of noise-induced hearing loss had been widely studied, the preventive effect of aldosterone on the noise trauma has not been documented to date. The study was designed to measure the serum aldosterone level after noise exposure and to determine the protective effects of aldosterone pretreatment on hearing in noise trauma. Materials and Method : BALB/c hybrid mice with 25 dB HL or less in ABR were used in this study. 42 mice were randomly assigned to one of several pretreatment drugs and divided into two day-exposure group (N=21) and three day-exposure group (N=12) according to the noise exposure time. All drugs were given in the drinking water, shown previously to be effective, daily from 4 days before noise exposure. The three day-exposure groups were: Water group (N=4), prednisolone (PD) group (N=4), and aldosterone (AD) group (N=4). The two day-treatment groups were: Water group (N=7), PD (N=7), AD group (N=7). Mice were exposed to 120 dB SPL broad white band noise for 3 hours per day for 2 days or 3 days. The preventive effects of PD and AD on noise trauma were determined by comparing the threshold shifts of auditory brainstem responses (ABR) before and after noise exposure and also 7 and 14 days following the exposure. The serum aldosterone level was measured in 3 mice without noise exposure and 6 mice with noise exposure. Result: The decrease of serum aldosterone level was seen in mice after noise exposure. The ABR threshold shifts were 80 dBHL or more in the three day-exposure groups. In Water, PD, AD groups of the two day-exposure groups, the threshold shifts were 70 dBHL or more noted after the noise exposure and some degree of hearing recovery was observed on the 7^(th) day after the exposure. But, ETOH, SP, PD+SP, AD+SP groups showed permanent threshold shift (PTS) on the 7^(th) day after the exposure. Conclusion: In BALB/c mice, the decrease of serum aldosterone level was seen after noise exposure. But pretreatment of aldosterone and prednisolone before noise exposure didn’t demonstrate the prevention of the elevated thresholds.

일시적 소음노출이 인체생리에 미치는 영향

현경애 부산가톨릭대학교 보건과학대학원 2005 국내석사

배경: 산업 및 과학기술의 발전에 따라 소음발생의 원인은 크게 증가되고 있다. 소음은 인체에 있어 청각기능의 손상과 고혈압 및 심혈관 질환 발생의 주요한 원인이 되고 있다. 그럼에도 불구하고, 우리나라의 경우 인체생리에 대한 소음의 다양한 효과를 이해하기 위한 충분한 연구 자료가 없는 실정이다. 목적: 이 연구는 20대 젊은 연령층에 있어 일시적 소음노출에 따른 생리학적 반응을 조사하고, 성별 혹은 흡연유무에 따라 특정한 차이가 있는지를 규명하기 위해 전향적으로 실시되었다. 방법: 평균연령이 23.45±2.40세인 80명(n=80)의 젊은이들을 연구대상으로 하여 이오폰을 통해 90 데시벨의 굴착기 소음을 15분간 청취시켰다. 심장박동수, 혈압, 심장부담지수, 혈정 cortisol 농도, 중대뇌 동맥, 전대뇌 동맥, 후대뇌 동맥의 평균 혈류속도(각각 MCA-Vm, ACA-Vm, PCA-Vm), 박동지수(pulsatility index, PI), 저항지수(resistance index, RI), 호흡정지 상태 때의 평균 뇌혈류속도(Vh) 등과 혈액학적 변수 및 생화학적 변수들을 소음 노출 전(기준치)과 노출 동안 측정하였다. 80명에 대한 각 변수의 기준치와 소음노출 동안의 변화치를 비교하였고, 각 군 간에도 비교 검정하였다(흡연남자군 vs 흡연남자군, 비흡연남자군 vs 비흡연여자군, 소음노출시 혈압상승군 vs 소음노출시 혈압하강군). 결과: 혈압, 뇌혈류역학 변수들, cortisol 농도의 경우 개인차는 있었지만, 소음 노출 동안 전체 대상자의 평균 심장박동수, 수축기 및 확장기 혈압, MCA-Vm, MCA-PI, MCA-RI, ACA-Vm, ACA-PI, ACA-RI, PCA-Vm, PCA-PI, PCA-RI, cortisol 농도, 총 백혈구 수, 적혈구 수, 혈소판 수, 단핵구 분획, 혈색소농도, 헤마토크리트치, 평균적혈구 혈색소농도(MCHC), 중성지방 농도, K? Na? 등은 기준치보다 유의하게 감소된 반면 림프구 분획만이 유의한 증가를 보였다(p<0.05 혹은 p<0.01). 흡연남자군의 경우 비흡연남자군에 비해 소음노출 동안 ACA-Vh와 호중구 분획은 유의하게 높았으나 림프구 분획, 단핵구 분획, 헤마토크리트치, K?, Cl? 농도는 유의하게 낮았다(p<0.05). 소음노출 동안 비흡연여자군이 비흡연남자군보다 ACA-Vm, ACA-Vh, PCA-Vm는 높았으나 유의성은 없었고 MCV, AST, K?, conrtisol 농도 등은 유의하게 낮았다(p<0.05). 소음노출시 혈압상승군은 혈압하강군보다 MCA-PI, MCA-RI ACA-RI는 낮았으나 단핵구 분획은 유의성 있게 높았다(p<0.05) 결론: 연구의 결과들은 휴식상태에서 굴착기 소음에 대한 일시적 노출이 여러 가지 다양한 생리학적 반응을 유발시켰으며 이러한 반응은 개인적 차이에 의함도 시사하고 있다. 향후 장시간의 소음노출과 정신적 활동 시 소음노출로 인해 미치는 인체의 영향과 생리학적 변화에 관한 더 많은 연구가 필요할 것으로 판단된다. Background: As industrial and technological developments have been evolved, the sources of noise have increased as a whole. Noise may lead to the damage of the auditory system, hypertension, and cardiovascular disease. However, we haven't the data enough to be available for understanding various effects of noise on human physiology. Purpose: The current study was prospectively designed to investigate the physiological responses following a transient exposure to noise in young people in their twenties and to clarify differences between men and women, or smoker and nonsmoker in the physiological responses. Methods: 80 subjects(mean aged 23.45±2.40 years) participated in this experiment and were exposed to excavator-noise with 90 decibels during 15 minutes using ear-phone. Heart rate(HR), blood pressure(BP), heart rate-systolic pressure product(RPP), serum cortisol level, mean blood flow velocity(Vm), pulsatility index(PI), resistance index(RI) and mean blood flow velocity at breathing-hold(Vh) in the middle(MCA), anterior(ACA) and posterior cerebral arteries(PCA), and hematological and biochemical markers were measured before(control) and during the noise-exposure. The data were compared between controls and exposure-results in all subjects(n=80), and then among groups(i,e., smoking-man group vs nonsmoking-woman group, or noise-induced BP-increase group vs BP-decrease group). Results: Although there were individual differences in BP, cerebral hemodynamics, and cortisol level, HR, systolic and diastolic BP, RPP, MCA-Vm, MCA-PI, MCA-RI, ACA-Vm, ACA-PI, ACA-RI, PCA-Vm, PCA-PI, PCA-RI, cortisol level, total leukocyte, platelet and RBC counts, mononuclear cell fraction, hemoglobin(Hgb), hematocrit(Hct), MCHC, triglyceride concentration, K?, and Na? levels during the noise-exposure decreased, whereas only lymphocyte fraction increased compared with baseline(p<0.05 or p<0.01). Smoking-man group had higher ACA-Vh and neutrophil level, and lower lymphocyte and mononuclear cell fractions, Hct, K? and Cl? levels than nonsmoking-man group during the noise-exposure(p<0.05). During the noise-exposure, ACA-Vm, ACA-Vh and PCA-Vm were higher while MCV, AST, K? and cortisol levels were lower in nonsmoking-woman group than in nonsmoking-man group(p<0.05). Noise-induced BP-increase group had lower MCA-PI, MCA-RI and ACA-RI and higher level of mononuclear cell fraction than noise-induced BP-decrease group(p<0.05). Conclusions: The findings of the present study suggest that a transient exposure to excavator-noise at rest cause various physiological responses with individual differences. Further studies need to be carried out for clarifying the influences of longer exposure and the combination of mental activity with noise exposure.

A Novel Noise Mitigation using Adjacent Pixel Values

성치혁 금오공과대학교 대학원 2017 국내석사

디지털 이미지나 비디오는 여러 가지 요인들로 인해 저장이나 전송 과정에서 잡음을 얻을 수 있다. 본 논문에서는 이러한 잡음을 완화할 수 있는 인접한 픽셀의 값들을 이용한 새로운 잡음 완화 기법을 제안한다. 잡음 환경으로는 Salt & Pepper Noise와 Additive White Gaussian Noise를 고려하였고, 각각 0이나 255의 픽셀 값 탐지와 Cyclic Redundancy Check (CRC)를 통해 잡음을 감지한다. 그리고 이미지의 가장 자리에서 보다 정확한 잡음 완화를 Extended Error Mask를 생성한 후, 이를 바탕으로 훼손된 픽셀에서 주변의 정상 픽셀의 값들의 평균값을 계산하여 잡음을 완화한다. 제안한 기법의 성능을 평가하기 위한 척도로는 Peak Signal-to-Noise Ratio (PSNR), Structural Similarity Index Method (SSIM)를 사용하였으며, 제안한 방법과 기존의 방법을 사용한 모의 실험 결과를 비교하여 성능을 평가하였다. Digital images or videos can contain noise during storage and transmission due to various reasons. In this paper, a novel noise mitigation method using adjacent pixels is proposed. This method is applicable to images with distorted pixels and uses the adjacent pixel values of damaged values of damaged pixels. Salt & pepper noise and Additive White Gaussian Noise (AWGN) are considered as noise environment. In Salt & Pepper noise environment, 0 or 255 values are searched to detect error. In AWGN environment, Cyclic Redundancy Check (CRC) is used to detect error. And extended error mask is created to accurate noise mitigation in boundary pixels. Then, based on extended error mask, APNMF mitigates noise. Furthermore, Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Method (SSIM) is used to estimate the performance. And result of proposed method is compared with results of conventional methods in simulation.

Binaural Asymmetric Directional Microphone Algorithm with Automatic Switching Mode for Better Noise Reduction

김진률 한양대학교 2015 국내박사

Noise reduction algorithm on digital hearing aid has been used to improve speech quality and intelligibility at noisy signal. Noise reduction algorithm can be classified by the number of microphone; single channel- or multichannel- noise reduction. At the previous studies about the improvement of speech quality and intelligibility in noisy situation, single channel algorithm is only improved the performance of speech quality by normal and impaired hearing person. However, multichannel algorithm is improved the both performances. The algorithm that has two or more microphones is called a beamforming or spatial filtering. In order to change a directionality of input signals, the algorithm adjusts a phase difference corresponding to a distance of both microphones by additional delay according to the direction of input signal and controls relative amplitude of the input signal at each microphone by a constrained weighting function according to the direction of input signal. As a result, the directionality changes according to the direction of input signal. When the beamforming is used hearing aid, it has several weaknesses. First, the number of microphone is limited by size of hearing aid. That is why the directionality is constrained to the front or rear. Second, manual or automatic switching between non-directionality and directionality is uncomfortable for the users. So many users often do not use the algorithm. Third, the beamforming, that distort the input signal according to the direction, disrupts the brain functions when the direction of the mismatch between the desired signal and input signal is occurred. Human can listen to the speech or desired signal in noisy situation without any other device. It is because the brain functions such as Auditory Scene Analysis and auditory attention. Its phenomenon is demonstrated by the cocktail party effect. In other word, center auditory system of human’s brain play a sound source separator role in noisy situation. Most hearing impaired persons still have the brain functions. Even if an interest signal is front, beamforming has benefit. But if that is the others direction, the algorithm distort the input signal that want to hearing. That is because the brain functions can be disrupted through the beamforming. In order to overcome the above mentioned weaknesses, bilateral asymmetric directional microphone fitting is presented. The method has different directionality at each ear in order to maintain the brain functions. Left ear has directional mode to enhance the front signal, such as beamforming, and Right ear has omnidirectional mode to receive equal signals regardless of direction. Because of the input signal of right ear do not distort according to input direction, the brain functions connected right ear are better performance than that of left. Thereby, left ear has a benefit of directional mode. And right ear has a benefit omnidirectional mode that maintains the brain functions. Also the method removes the necessity for manual or automatic switching between non-directionality and directionality. That is why the method has both directional and omnidirectional mode. As above mentioned, the asymmetric directional microphone fitting has several benefits. But, a dominant noise, when locate in the side of directional mode, may be reduced. However, if a dominant noise locates in the side of omnidirectional mode, its noise may not be reduced. In other words, the performance of the method is expected to be dependent on the according to the direction of the input noise. That is because the directionality modes are not switched according to the direction of input noise. In my study, novel binaural asymmetric directional microphone algorithm was developed and evaluated. The proposed algorithm operates automatically directionality modes switching between left directional and right omnidirectional mode according to the input signal-to-noise ratio. When a dominant noise locates in the side of omnidirectional mode, the proposed algorithm detects the direction of the dominant noise and switches the directionality from omnidirectional to directional mode. MATLAB and Simulink are used to implement the algorithms. For the evaluation, the performance of detection of the dominant noise on the proposed algorithm was measured on 3 kind of scenario (non-reverberant, reverberant, realistic reverberant) by personal computer simulation. And the comparison of performance between the proposed algorithm and conventional asymmetric directional fitting was executed on personal computer simulation and KEMAR test. Finally, the proposed algorithm was tested by normal hearing person. The output signal-to-noise ratio, Perceptual Evaluation of Speech Quality (PESQ) and Hearing Aid Speech Quality (HASQI) are used as objective measurement. As subjective measurement, 10 normal hearing persons are tested by Comparison Mean Opinion Score (CMOS). The result of detection of dominant noise is higher accurate at all scenario (non-reverberant > realistic reverberant > reverberant). As result of objective measurement on personal computer simulation and KEMAR test, when a dominant noise locates in the side of directional mode, the objective measurements of the proposed algorithm is similar to conventional algorithm. But the objective measurements are higher than that of the conventional algorithm, when a dominant noise locates in the side of omnidirectional mode. Especially, objective measurement relative to intelligibility is high at KEMAR test than at personal computer simulation. At the result of CMOS on normal hearing person, the subjective quality of normal hearing person is slightly better on the proposed algorithm. In my study, novel binaural asymmetric directional microphone algorithm that automatically switches the directionality modes between both ears and adjusts the directionality on the one side ear according to the direction of input signal was presented. Through the evaluation on person computer simulation, KEMAR test, and normal hearing person, the proposed algorithm is better performance of objective and subjective measurement than conventional algorithm. It is more influenced by the automatically switching the directionality modes between left and right ear than by the adjusting the directionality on one side ear. Speech intelligibility and quality of normal hearing person is even high on noisy situation. That may be why the result of CMOS is slightly better on normal hearing person. In my study, novel binaural asymmetric directional microphone algorithm was developed and evaluated. I expect that the algorithm is applied to the hearing aid through additional clinical trials for hearing impaired person is tested.

Noise thermometry using a broadband radio-frequency measurement at low temperatures

박정환 서울대학교 대학원 2012 국내박사

This thesis presents the development of the broadband radio-frequency noise measurement techniques at low temperatures. Especially, these techniques were used to realize noise thermometry using broadband noise measurement. The noise thermometer can be usable in the temperature range from 0.1 K to 300 K. A metallic tunnel junction which generates temperature-dependent thermal noise and voltage-dependent shot noise is used as a noise source. From thermal noise we can get information about the temperature of the electrons in the tunnel junction and the background noise level can be calculated using shot noise. Very small noise signal from the tunnel junction is amplified by a cryogenic low noise amplifier and then detected by Schottky diode detector which converts broadband noise power into the DC voltage. For a radio-frequency measurement at low temperatures we developed an experimental setup in cryogenic refrigeration systems like He4 probe, He3 cryostat, and dilution refrigerator. The system consists of two measurement chains. One of them, DC measurement chain, is used to apply currents and read the voltage across the tunnel junction. The other, RF measurement chain, is used to transmit RF signal from the tunnel junction to the diode detector. Because the thermal conductivity of most metals decreases with decreasing temperature, careful tuning of the RF and DC components is performed for sufficient cooling of the electron temperature. By developing the filtering processes for preventing the external RF noise from reaching the tunnel junction, the precision of the noise thermometer was increased. And with an imperfect tunnel junction we got the result that an inelastic tunneling process can make the electron temperature look higher. This result was analyzed by using numerical simulation. Finally, an experimental plan for the electron-phonon scattering rate using this measurement technique will be introduced. 이 논문은 저온에서의 광대역 무선주파수 잡음 측정기술 개발에 관해서 기술한다. 특히, 이 기술은 광대역 잡음측정을 이용한 잡음온도계 구현에 이용되었다. 잡음온도계는 0.1 K에서 300 K까지의 온도영역에서 사용이 가능하다. 온도 의존적인 열적잡음과 전압 의존적인 산탄잡음을 발생시키는 금속 터널접합이 잡음원으로 사용되었다. 열적잡음으로부터는 터널접합에 있는 전자들의 온도에 관한 정보를 얻을 수 있고, 배경잡음은 산탄잡음을 이용하여 계산될 수 있다. 터널접합으로부터 나오는 매우 작은 잡음신호는 저온 저잡음 증폭기에 의해 증폭된 후 쇼키 다이오드 디텍터를 통하여 DC 전압으로 변환된다. 저온에서의 무선주파수 측정을 위해서 He4 프로브와 He3 냉동기, 희석냉동기와 같은 극저온 냉장 시스템에 실험장치를 구성하였다. 이 시스템은 두 개의 측정체인으로 이루어져 있다. 터널접합으로 전류를 흘리고 전압을 읽을 수 있는 DC 측정 체인이 있고, 터널접합에서의 RF 신호를 다이오드 디텍터로 전송하는 RF 측정 체인이 있다. 대부분의 금속은 저온으로 갈수록 열전도도가 낮아지기 때문에, 전자온도의 충분한 냉각을 위해서 RF 와 DC 측정 체인에 사용되는 부품들을 신중하게 조율하였다. 외부 무선잡음이 터널접합으로 들어오는 것을 막기 위한 필터링 작업을 통해서 잡음온도계의 정밀도가 개선되었다. 그리고 불완전한 터널접합에서는 비탄성 터널링 현상이 전자의 온도를 높게 보이도록 만든다는 결과를 얻게 되었다. 이 결과는 수치 모사실험을 통하여서 분석하였다. 마지막으로, 이 측정기술을 이용한 전자-포논 산란비 실험 계획을 소개한다.

Occupational and nonoccupational noise exposure over 24hr/7day among underserved occupations

강태선 서울대학교 보건대학원 2014 국내박사

The World Health Organization (WHO) has stated that hearing loss is one of the top ten health problems worldwide, and that noise induced hearing loss (NIHL) is the leading occupational disease. The true prevalence of NIHL may be higher than expected because of the small proportion of occupations assessed and under-reporting. Coverage of risk assessment should increase to determine the true prevalence of NIHL. In the same context, the new Noise Directive 2003/10/EC went into effect in 2006. The EU emphasized that noise exposure assessments should cover all sectors and lowered the noise exposure limit. Occupational health research and services in Korea are still concentrated in the manufacturing sector. The purposes of this study were to assess the occupational noise exposure of underserved occupations, as well as their nonoccupational activities, which have been excluded from previous studies. Construction workers, firefighters, musicians, service workers, office workers, housewives, and students were selected as underserved occupations. Although construction workers, musicians, firefighters, and service workers are exposed to occupational noise, an assessment of noise exposure among them has rarely been conducted. Office workers, housewives, and students are not thought to be adversely affected by noise. However, an occupational noise exposure limit was established on the assumption that nonoccupational noise exposure could be ignored; however, that needs verification because environmental noise continues to grow in extent, frequency, and severity as a result of population growth, urbanization, and technological developments. ∙ Assessment of apartment construction worker noise exposure A noise exposure assessment was performed for 139 construction workers from 10 construction trades working at 53 apartment construction sites located in the northern part of Gyeonggi-do. The mean LMOEL for 139 dosimeter samples was 87.8 ± 4.3 dBA. The mean noise exposure level of each construction trade (trade mean) was calculated. Significant differences were observed between construction trades. The highest LMOEL values were measured for concrete chippers (93.2 ± 2.6 dBA), followed by ironworkers (88.4 ± 0.7 dBA), concrete finishers (88.3 ± 2.7 dBA), masonry workers (87.7 ± 1.9 dBA), pile driver operators (85.6 ± 1.7 dBA), concrete carpenters (84.9 ± 2.4 dBA), interior carpenters (83.5 ± 2.1 dBA), and other groups (81.4 ± 2.2 dBA). These results indicate that almost all construction workers in this study are at risk of NIHL, and that construction trades are a useful exposure metric at apartment construction sites. ∙ Assessment of noise measurements made with continuous monitoring over time (24 hours/7 days) among underserved occupations The average Leq 24hr,w among 47 individuals in the underserved occupations was 74 dBA (range, 64-96 dBA). The average Leq 24hr,w was highest for Korean traditional music apprentices, followed by heavy equipment operators, firefighters, service workers, office workers, industrial hygienists, graduate and undergraduate students, and housewives (89, 77, 76, 76, 75, 71, 71, and 71 dBA, respectively, p < 0.001). A total of 38 (80.9%) were exposed to noise levels > 70 dBA, which corresponds to the WHO exposure limit. Additionally, 60% (15 of 24) of the participants with occupations thought to have low noise exposure (office workers, housewives, and students) were over the recommended limit. Furthermore, the mean nonoccupational noise exposure level of all participants (72 ± 6 dBA) that normalized to a nominal 24h was over the recommended limit; thus, nonoccupational noise exposure may not be negligible. ∙ Task-specific noise exposure assessment of firefighters The firefighter noise-sample datasets revealed that most firefighters are exposed to higher than recommended exposures at a low-action value of Lep,d (shift-adjusted daily personal noise exposure level) = 80 dBA. The highest mean level of noise exposure was for rescuers (84.6 ± 6.2 dBA), followed by drivers (83.3 ± 2.7 dBA) and suppressors (79.5 ± 3.5 dBA). Noise measurements were combined with time-at-task information to concentrate on noise exposure, which showed that 82.3% of sound exposure occurred while checking equipment and responding to fire or emergency calls. This information can be obtained only through a task-specific noise exposure assessment, which is useful for controlling noise. ∙ Hearing among male firefighters: A comparison with hearing data from screened and unscreened male population A comparison of firefighter hearing threshold levels (HTLs) with those of an otologically normal male Korean population (KONP) and non-industrial noise-exposed male Korean population (KNINEP) by age and frequency showed that the firefighter HTLs were significantly increased (poorer hearing) across most age groups and frequencies compared with those of the KONP. The firefighter HTLs were worse in the younger age groups (< 45 years) but not different in the older age groups (> 45 years) compared with those of the KNINEP. The firefighter age-adjusted HTLs were significantly worse than those of the KONP (prevalence ratio [PR] = 5.29, p < 0.001), but not different from those of the KNINEP (PR = 0.99, p = 0.550). Rescuers (PR = 1.006, p < 0.001) had worse hearing than the unscreened general population after adjusting for age. The noise exposure assessments showed that some firefighters were at risk for NIHL, consistent with the results of the HTL comparisons. In brief, the underserved occupations assessed in this study, including construction workers, Korean traditional music apprentices, and firefighters, are almost at risk of NIHL. The hearing levels of younger firefighters and rescuers were worse than expected by normal age alone. These data indicate the need for a comprehensive assessment and noise reduction efforts in these occupational groups. The general assumption that housewives, students, and office workers are exposed to negligible noise may be incorrect. Nonoccupational noise exposure should be considered when assessing noise health hazards.

Protective Effect of Avenanthramide-C on Ototoxicity

알폰스 우무기레 전남대학교 2017 국내석사

Introduction: There are many types of hearing loss and sensorineural hearing loss ranks among them. However, no adequate treatment has so far been elucidated to rectify this problem. Noise exposure causes various physical damages and major cellular changes within the cochlea systems that result in hearing loss, with outer hair cells (OHCs) located at the basal turn of the cochlea being most vulnerable and susceptible pathological targets and lost in first instance. Reactive Oxygen Species (ROS) found in the cochlea orchestrates cascade reactions with different molecules within the cochlea and disrupt normal physiological mechanisms, and results in hair cell death and lesion with permanent hearing loss as an endpoint. Avenanthramides (AVNs) extracted from oats possess antioxidant properties to reduce free radicals, and exert adequate protection on various cell types. In this present study, I wanted to investigate whether AVN-C can protect auditory hair cell and preserve hearing from ototoxicity. Methods: B6 mouse was randomly used in 6 to 12 subjects per individual study group. Mouse tissue fluid samples were analyzed using Liquid Chromatography-mass spectrophotometry (LM/MS), to detect AVN-C into mouse tissue fluids. Animals were subjected to noise stimuli centered at 95 and 100 dB, 8 kHz for 6 hours once a day for various length of time with or without pre-treatment of 10 mg/Kg of AVN-C. Click and frequency stimuli were determined in a decreasing order from 90 to 10 dB of visual auditory brainstem response (ABR) threshold. OHCs were visualized by immunohistochemistry using confocal microscope. HEI-OC cells were cultured under normal and standard conditions, treated with AVN-C 5 hours following the culture. Gentamicin was added to the HEI-OC cell media culture 24 hours later, to generate cell ototoxicity in vitro. Flow cytometry and real-time quantitative polymerase chain reaction (RT-qPCR) were conducted and results analyzed. Statistical significance was determined using SPSS 17.0 (SPSS Inc., Chicago, IL, USA), independent student t-test was used for pairs of data with significance set at p<0.05. Results: AVN-C reached its climax into mouse serum after 1 hour post intraperitoneal administration and decreased with time, to be washed out within 6 hours. Furthermore, AVN-C crossed blood brain barrier and peaked within 2 hours. The permeability of AVN-C towards blood labyrinth barrier was outlined by its presence into perilymph and noise exposure enhanced its clearance. Both noise stimuli centered at 95 and 100 dB respectively, were responsible to cause hearing loss at 1 week post exposure; with a complete recovery observed with time. Pre-treatment of AVN-C 24 hours contributed to preserve hearing vis-à-vis to noise exposure, moreover subjects regained their threshold shifts at their baseline implying temporary threshold shift. Overstimulation with 100 dB for 7 days consecutively triggered significant impact of threshold shift in exposed subjects, however 30 minutes pre-administration of 10 mg/Kg of AVN-C to subjects at each noise time point, proved to procure prominent protection to noise exposed subjects, one month post noise exposure. Cochlea histological analysis demonstrated loss of OHCs at the basal turn in noise induced only group, and preservation of OHCs in AVN-C pre-treated subjects confirming the noteworthy protective effect provided by AVN-C over noise overexposure. AVN-C exhibited protective effect, and thwarted the toxicity caused by gentamicin when treated to HEI-OC cell culture 24 hours in advance to Gentamicin. Several apoptotic and ROS genes were down-regulated by AVN-C. Conclusion: AVN-C provided a protective effect over ototoxicity in noise overexposed subjects, and revealed to be a good candidate molecule for future preventive therapy on ototoxic sensorineural hearing loss.

The Physiological and Neurological Study of Noise-Induced Hearing Loss in Mice : 마우스 모델을 이용한 소음성 난청의 전기생리학적·신경학적 분석에 관한 연구

이병현 경북대학교 대학원 2020 국내박사

Hearing loss is mostly due to genetic causes, and acquired hearing loss has become a social problem due to the increase in life expectancy at the turn of modern society and the increase in presbycusis and minor hearing loss due to the development of various industries. In particular, in the case of small deafness, the research on the developmental mechanism is deficient, and as a result, no effective therapeutic agent has been developed so far. In this study, I established a mouse animal model of noise-induced hearing loss, and investigated the physiological and neurological mechanisms of noise-induced hearing loss. Depending on the strength of the noise stimulus, white noise 100 dB for 2 hours, 4 hours, or 110 dB for 2 hours, 4 hours to establish a mouse model of temporary hearing loss and permanent hearing loss respectively. Auditory brainstem response was measured 2 hours after noise stimulation in exposed mouse models, and continuous monitoring at 1-week intervals in mice with confirmed hearing loss. It was confirmed that when the noise of 100dB was given for 2 hours, a temporary hearing loss was shown, and when the noise of 110 dB was given for 4 hours, the permanent small hearing loss was displayed. Morphological analysis of hair cells in the inner ear to determine the exact causative mechanism of hearing loss revealed that no direct hair cell damage had occurred. I analyzed the results measured by auditory brainstem response in detail, and predicted that changes in nerve cell activity appeared in response to noise stimulation. In order to investigate changes in nerve cells associated with hair cells, I confirmed the connection of hair cell ribbon synapses by immunofluorescence, and as a result, the connection of synapses was rapidly reduced by about 50% immediately after noise stimulation. On the other hand, after 3 weeks, the number of normal synapses was restored in the case of temporary hearing loss, while only about 10% was observed in the case of permanent hearing loss. This revealed that in the case of small deafness, the damage of nerve cells appears first rather than the direct damage of hair cells and the deafness is induced. Based on the results of this study, by explaining the mechanism by which minor deafness is displayed, the target is accurately presented for future research and development of therapeutic agents for noise-induced hearing loss. 난청은 대부분 유전적 원인에 의해서 나타나지만 현대사회로 접어들면서 평균수명 증가 및 다양한 산업 발전에 따른 노인성 난청과 소음성 난청의 증가에 따라 후천성 난청이 사회적 문제로 나타나고 있다. 특히, 소음성 난청의 경우에는 발생기작에 대한 연구가 미비하며 이에 따라 아직까지 효과적인 치료제의 개발이 이루어지지 않고 있는 실정이다. 본 연구에서는 이러한 소음성 난청을 연구하기 위한 기초가 되는 소음성 난청 마우스 동물모델을 확립하고 소음성 난청에 대한 생리적, 신경학적 기전에 대해 알아보고자 하였다. 소음자극의 강도에 따라 일시적인 소음성 난청과 영구적인 소음성 난청 마우스 모델을 각각 확립하기 위하여 백색소음 100dB 을 2시간, 4시간 또는 110dB을 2시간, 4시간을 각각 노출시킨 마우스모델을 소음자극 후 2시간 뒤 청성뇌간유발반응을 측정하여 소음성 난청이 확인된 마우스를 대상으로 1주일 간격으로 지속적인 모니터링을 통해 100dB 소음을 2시간 주었을 때 일시적인 소음성 난청을 나타내고 110dB 소음을 4시간 주었을 때 영구적인 소음성 난청이 나타나는 것을 확인 할 수 있었다. 정확한 난청 원인 기작을 알아보기 위해 내이의 유모세포의 형태학적 분석을 통해 유모세포의 직접적인 손상은 일어나지 않았다는 것을 알 수 있었다. 청성뇌간유발반응에 의해 측정된 결과를 심층 분석하여 소음자극에 따라 신경세포의 활성의 변화가 나타나는 것을 예측하였다. 이에 유모세포와 이와 연결된 신경세포의 변화를 알아보기 위해 유모세포의 리본시냅스의 연결을 면역형광법을 통해 확인 한 결과 소음자극 직후 시냅스의 연결이 50%가량 급격히 줄어든 반면 3주 뒤에는 일시적 소음성난청의 경우 정상적인 시냅스 수를 회복하는 반면 영구적 소음성 난청의 경우 10% 가량의 회복만 관찰되었다. 이를 통해 소음성 난청의 경우 유모세포의 직접적인 손상보다 신경세포의 손상이 일차적으로 나타나 난청이 유발 되고 있음을 밝힐 수 있었다. 본 연구 결과를 바탕으로 소음성 난청이 나타나는 기작을 설명함으로써 앞으로 진행될 소음성 난청 치료제 개발 연구에 타깃을 정확히 제시 해줌으로써 난청 극복에 큰 기여할 것으로 전망된다.