• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2005년도 춘계 학술발표회 논문집
• /
• pp.33-40
• /
• 2005

Impact-echo test, a kind of simple and economical method to evaluate the integrity of drilled piles has some limitations to use because the stress wave can be generated only on the head of a pile and the wave propagation in the pile with surrounding soils are very complicated. Numerical analyses and model tests in the laboratory have shown that both the ratio of length to diameter of a pile and the stiffness ratio of pile to soil have influence on the resolution of testing results. Full scale testing piles which have artificial defects were used to verify the capability of impact-echo technique as a tool for the pile integrity evaluation. Behaviour of the reflected signal of stress wave was investigated according to the type of defects. Elastic modulus of the pile was calculated using the wave velocity in the pile and the unconfined strength of concrete specimen. Influences of the stiffness difference between the pile and the ground on the characteristics of a wave signal were also examined.

• 한국의류산업학회지
• /
• 제19권1호
• /
• pp.40-48
• /
• 2017

In this study, the impact of the fashion design education on the brain wave and the psychological change of the senior females and its change was intended to analyze. 16 senior females were selected as a subject and the brain wave and the psychology were analyzed before and after the educational program of 4 hours a day for total 3 weeks. Out of the brain wave, the increase of alpha wave represents the mental stability and the comfortable state and its decrease represents the tension and stress. On the contrary, the increase of beta wave represents the tension and the excitation. In the brain wave analysis results, the alpha wave was increased and the beta wave was decreased after the design education program, through which it is deemed that the design education would help to increase the psychological stability and to decrease the tension and the stress in the senior females. In the results of analyzing the psychological test, while the test results for 4 senior females were shown as anxious out of 16 senior females, the BAI score was decreased to 'minor anxiety' after the education and the BAI score was decreased except 2 subjects, through it is deemed that the fashion design education would help to reduce the anxiety in the senior females and it seems that it is coincided with the beta wave analysis results.

• Journal of the Korean Wood Science and Technology
• /
• 제31권3호
• /
• pp.35-41
• /
• 2003

The mechanical and physical properties of wood are strongly dependent upon the slope of grain. Specially, tensile strength is more severely affected by the slope of grain. Therefore, tension tests were performed on small thin wood samples made from Pinus radiata with varying the slope of grain. Determining the tensile strength for clear thin wood samples the other variabilities associated with material, size, drying, defects, etc were discarded. Slope of grain was measured by the slope of grain indicator and actual slope of grain was also determined by a protractor. Correlation coefficients between machine measured and actual slope of grain for 40 pieces of 2×20 mm, 300 mm long Pinus radiata were 0.84 for wide face measurement. Results also showed that tensile strength and MOE from stress wave tests decreased with increasing the slope of grain. This study did not establish a relationships for tensile strength and MOE from stress wave with slope of grain. However, the trends of MOEs from stress wave test with both slope of grain are agreed well with Hankinson's equation. Predicted tension strength curve by Hankinson's equation was also agreed well with the experimental data over the range from 0 to 13 degrees for slope of grain.

• 감성과학
• /
• 제18권1호
• /
• pp.95-102
• /
• 2015

본 연구의 목적은 아로마 향이 학업 스트레스와 뇌파에 어떠한 영향을 미치는 지를 연구하기 위함이다. 피험자는 뇌생리학적 실험에 참가한 경험이 없는 남자 중학생 24명을 대상으로 하였으며, 이들은 각각 아로마 흡입집단과 무향 통제집단에 무작위로 12명씩 할당되었다. 참가자의 스트레스 수준을 측정하기 위해 이보영(2007)의 학업스트레스 수준 검사지를 사용하였다. 뇌파측정은 국제 10-20 전극배치법에 따라 스트레스와 관련이 있다고 여겨지는 4개의 영역(Fp1, Fp2, F3, F4)을 측정하였다. 과제는 스트레스 검사지 작성 후 편안한 의자에 앉아 있는 3분 동안 아로마 냄새 맡고 다시 스트레스 검사지를 작성하는 것이었다. 본 연구 결과 아로마 흡입집단이 무향통제집단에 비해 학업으로 받은 스트레스가 줄어들 뿐만 아니라 알파파도 증가하였다. 본 연구의 결과는 아로마향이 스트레스를 해소시키는 잠재적인 도구로 사용될 수 있음을 입증해 주었다.

• 전기학회논문지P
• /
• 제62권2호
• /
• pp.103-109
• /
• 2013

In this study, the three sounds effects on subjects due to EEG type, and it researched to find optimal sound to increase their amenity and productivity. EEG and HRV were compared and analyzed in the environmental test room by classifying subjects into two type: A and B. The condition of the environmental test room was in temperature $31[^{\circ}C]$, relative humidity 50[RH%], air current speed 0.02[m/s] and illuminance 1000[lux] with setting up three different sounds which are U type sound, V type sound and Z type sound. The result of this study, at U type sound for A and B type, relative $M{\alpha}$ wave, relative $M{\beta}$ wave and SEF50 were revitalized. Also at Z type sound for A and B type, stress index, fatigue degree and HRT were decreased and SDNN was revitalized. Therefore U type sound is very effective to increase amenity, productivity and concentration, and Z type sound is very effective to decrease stress and fatigue degree.

• 한국가스학회지
• /
• 제4권1호
• /
• pp.55-62
• /
• 2000

Pit형 표면결함으로부터 발생하는 작은 피로균열의 거동을 초음파의 표면파를 이용하여 이를 위하여 피로시험중인 Al 2024-T3를 시험재료, 피로시험도중 초음파를 이용하여 피로균열의 거동을 조사하였다. 즉, 피로시험에서 균열이나 Pit로부터 발생하는 작은 피로균열을 여러 응력조건하에서 나타나는 표면파의 반사특성에 관하여 연구하였다. 또한 이론적 결과와 실험적 결과를 상호 비교, 분석하였고, SEM을 사용하여 이들 작은 피로균열을 관찰하였다. 초음파를 이용한 피로균열의 균열 개구 거동에 관한 연구에서 피로균열의 유효균열 특성을 초음파법으로 평가 할 수 있었다.

• 한국정밀공학회지
• /
• 제13권4호
• /
• pp.53-60
• /
• 1996

In the conventional linear elasticity, sound speed is determined by only elastic modulus and density of the medium. In actual, however, sound speed depends on the stress and this dependency becomes nonlinear as the stress increases. These phenomena can be introducing nonlinear elastic modulus. In this paper, relationships between nonlinear elastic modulus up to 4th order and the internal status of materials are discussed through computer simulations and experiments. For the measurement of sound speed, a new type of measurement system using ultrasonic wave is proposed on the basis of ultrasonic pulse echo method which has been generally used in nondestructive ultrasonic test equipment. In order to confirm the stress dependency of sound speed, several experiments are carried out for alumina specimen.

• 한국조명전기설비학회:학술대회논문집
• /
• 한국조명전기설비학회 2006년도 춘계학술대회 논문집
• /
• pp.125-130
• /
• 2006

In this study, tests of brain waves were carried out to investigate the driver's physiological characteristics by the change of the headlight. The participants were 20 men in their 20s and twenty-three different conditions in combinations of waveform of light, voltage, and alteration time were used. The measurement of the brain waves was performed by internationally standardized 10-20 method using LXE3232-RF. The results were analyzed by Power Spectrum Analysis using alpha-, and beta-wave and by the analysis of different brain domains using Brain wave Map. The results were as follows. 1. From the results of the Brain wave Map analysis, it was suggested that A waveform increases mental stress and B waveform affects mental and visual stress. The longer the stimulation time, the more stress level was detected. 2 The voltage alteration time of B waveform should be kept less than 1500msec, and the voltage should not fall below 11.5V.

• Geomechanics and Engineering
• /
• 제21권3호
• /
• pp.227-236
• /
• 2020

Non-destructive exploration using elastic waves has been widely used to characterize rock mass properties. Wave propagation in jointed rock masses is significantly governed by the characteristics and orientation of discontinuities. The relationship between spatial heterogeneity (i.e., joint spacing) and wavelength for elastic waves propagating through jointed rock masses have been investigated previously. Discontinuous rock masses can be considered as an equivalent continuum material when the wavelength of the propagating elastic wave exceeds the spatial heterogeneity. However, it is unclear how stress-dependent long-wavelength elastic waves propagate through a repetitive rock-joint system with multiple joints. A preliminary numerical simulation was performed in in this study to investigate long-wavelength elastic wave propagation in regularly jointed rock masses using the three-dimensional distinct element code program. First, experimental studies using the quasi-static resonant column (QSRC) testing device are performed on regularly jointed disc column specimens for three different materials (acetal, aluminum, and gneiss). The P- and S-wave velocities of the specimens are obtained under various normal stress levels. The normal and shear joint stiffness are calculated from the experimental results using an equivalent continuum model and used as input parameters for numerical analysis. The spatial and temporal sizes are carefully selected to guarantee a stable numerical simulation. Based on the calibrated jointed rock model, the numerical and experimental results are compared.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
• /
• pp.1261-1266
• /
• 2000

In the impact echo method, a stress pulse is introduced into an object at on accessible surface by a transmitter. The pulse propagates into the test object and is reflected by flaws or interfaces. In this paper, void and crack locations of concrete specimens were detected using impact echo method. In their modal identification procedures, the double least squares solution for Ibrahim Time Domain technique was used.