• 한국생산제조학회지
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• 제23권1호
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• pp.48-55
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• 2014

Many techniques are available for destructive and nondestructive measurement of mechanical hardness. The ultrasonic method could be widely applicable as a nondestructive technique. Many studies have examined how changes in the mechanical hardness affect the longitudinal velocity of ultrasonic waves. This approach aims to estimate the overall velocity variations in specimens. However, proper nondestructive examination techniques are needed as effective tools for analyzing the effects of heat treatment on the surface of the specimens. Therefore, in this study, the effect on the hardness of piston rods was nondestructively measured using surface ultrasonic waves. The hardness after heat treatment was investigated at various depths in the specimens, and the velocity of the surface ultrasonic waves was measured with respect to the hardness of the piston rods. In addition, finite element method simulations were performed to confirm the behavior of the waves.

• 패션비즈니스
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• 제12권6호
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• pp.1-10
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• 2008

Public interest in healthy hairs gets growing as damaged hairs are seen more frequently with the generalization of heat permanent waves. For this study, experiments have been conducted to understand the influences on the changes in physical and morphological features of wave forms and damaged hairs, by collecting virgin hairs from the women in their mid-20's, who had not experienced chemical applications, and by dividing the applications of heat perm hair treatments, PPT(for pre-treatment) and LPP(for post-treatment), into the pre-treatment, the post-treatment, the pre & post-treatment, and the non-treatment. For the wave formations, curl waves were investigated by the bare eyes using the pictures taken by a digital camera. For the comparison of physical features, the experiments of tensile strength and elongation were done and their mean values were found. For the observations of morphological features, the pictures were taken by SEM for comparison. As for the findings, regarding the curl wave shapes of hairs, the most even and elastic S curl was formed in the case of non-treatment. In the physical features, both of the tensile strength and elongation showed a decreasing tendency in line with the hair damage levels, and the case of the pre & post-treatment indicated the tendency most similar to the control group. In the morphological features of the cuticle, observed with an SEM, the pre-treatment showed the higher possibility of reducing the cuticle damages than the post-treatment did. LPP was found to play the role of protective membrane for the post-treatment, and the pre & post-treatment turned out to reduce most effectively the cuticle damages.

• 대기
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• 제17권1호
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• pp.45-53
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• 2007

In order to investigate the impacts of heat wave on human health, cluster analysis of meteorological elements (e.g., temperature, dewpoint, sea level pressure, visibility, cloud amount, and wind components) for identifying offensive synoptic air masses is employed. Meteorological data at Seoul during the past 30 years are used. The daily death data at Seoul are also employed. Occurrence frequency of heat waves which is defined by daily maximum temperature greater than the threshold temperature (i.e., $31.2^{\circ}C$) was analyzed. The result shows that the frequency and duration of heat waves at Seoul are increasing during the past 30 years. In addition, the increasing trend of the frequency and duration clearly appears in late spring and early autumn as well as summer. Factor analysis shows that 65.1% of the total variance can be explained by 4 components which are linearly independent. Eight clusters (or synoptic air masses) were classified and found to be optimal for representing the summertime air masses at Seoul, Korea. The results exhibit that cluster-mean values of meteorological variables of an offensive air mass (or cluster) are closely correlated with the observed and standardized deaths.

• 대기
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• 제16권4호
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• pp.269-278
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• 2006

Extremely hot weathers may cause major weather-related deaths in the summertime. Influences of heat waves on daily mortalities in 6 major cities of South Korea were investigated. Daily deaths at Seoul were exponentially increased with the daily maximum temperature. However, there were regional differences of the temperature dependence on the mortality because of an acclimation effect of inhabitants. The threshold temperature (with respect to daily maximum temperature) at Seoul was found to be about $31^{\circ}C$ provided that it is determined by a two-phase regression model. The meteorological causes of recordable hot summer in late July of 1994 and their impacts on human health were also investigated. Strong surface heating caused by strong insolation under conditions with clear sky and dry surface due to prolonged drought was likely to be closely associated with the extreme hot weather in 1994 in South Korea.

• 한국연소학회지
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• 제23권1호
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• pp.28-35
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• 2018

Entropy waves(or hot spots) in a gas turbine combustor are generated by irregular heat release from flames, then can be coupled with acoustic waves when they are accelerated at the exit of the combustor. This coupling mechanism between the entropy and the acoustic waves is generally known to be one of the triggers for combustion instability, which is commonly called "indirect" combustion noise. This paper reviews the fundamental theories on generation, propagation, and coupling with acoustic field of entropy waves and recent research results on the indirect combustion noise for gas turbine combustors.

• 대한토목학회논문집
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• 제42권2호
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• pp.263-272
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• 2022

폭염과 도시열섬현상은 기후변화가 진행됨에 따라 피해가 더욱 커지고 있으며, 2050년까지 폭염 발생빈도는 2~6배가 증가될 것으로 예측된다. 특히, 폭염기간동안 건설공사현장에서의 근로자가 느끼는 더위체감지수는 매우 높으며, 도시열섬현상까지 고려하게 되면 체감지수는 더욱 높아진다. 열에 취약한 건설현장 환경과 건설근로자의 상황은 나아지지 않고 있으며, 피해를 줄이기 위해서는 효과적인 대응이 필요한 시점이다. 본 연구에서는 인공위성영상 이미지와 Land Surface Temperature (LST)와 Long Short Term Memory (LSTM) 딥러닝 모델 기법을 적용하여 33℃ 이상 온도가 되는 지역을 분석하고, 폭염에 취약한 건설공사현장을 식별하여 폭염 및 도시열섬현상의 복합적인 피해를 가중시킬 수 있는 가장 취약한 지역을 예측하여 도출하였다. 예측 결과를 통해 건설근로자의 안전을 보장하고, 건설현장 경보시스템의 기반이 될 수 있기를 기대한다.

• Structural Engineering and Mechanics
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• 제85권3호
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• pp.305-314
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• 2023

The article is about the theoretical analysis of the transmission and reflection of elastic waves through the interface of perfectly connected materials. The solid continuum mediums considered are piezoelectric semiconductors and transversely isotropic in nature. The connection among the mediums is considered in such a way that it holds the continuity property of field variables at the interface. The concept of strain and stress introduced by non-local theory is also being involved to make the study more applicable It is found that, the incident wave results in the generation of four reflected and three transmitted waves including the thermal and elastic waves. The thermal waves generated in the medium are encountered by using the concept of three phase lag heat model along with fractional ordered time thermoelasticity. The results obtained are calculated graphically for a ZnO material with piezoelectric semiconductor properties for medium M₁ and CdSc material with transversely isotropic elastic properties for medium M₂. The influence of fractional order parameter, non-local parameter, and steady carrier density parameter on the amplitude ratios of reflected and refraction waves are studied graphically by MATLAB.

• 한국측량학회지
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• 제38권4호
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• pp.295-304
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• 2020

IPCC는 기상이변의 예방 대책의 중요성을 권고하였으며 폭염은 주요 예방대책수립 주제 중 하나이다. 일반적으로 예방대책수립을 위한 기존 연구는 지형적 특성과 사회적 특성을 따로 구분하여 폭염취약지역을 도출하였으나 본 연구에서는 공간, 지형적 특성뿐만 아니라 사회적 특성을 함께 고려하여 폭염취약지역을 분석하고자 하였다. 에너지 사용량, 인구밀도, 정규식생지수, 수변이격거리, 태양복사량, 도로분포를 변수로 하여 점검하고, 여러 회귀모형 중 가장 적합한 모형인 Spatial Lag Model을 선택하여 사용가능한 변수를 추출하였다. 그리고 Fuzzy 이론에 기초하여 각 변수에 대한 폭염 취약정도를 분석하고, 6개의 변수를 중첩분석하여 최종적으로 폭염취약지역을 도출하였다. 연구 대상지는 폭염의 영향이 큰 대구광역시를 선정하였으며, 취약지역의 경우 기존 도심지이며 수변 및 식생에 영향을 적게 받은 대구 서구, 남구, 달서구에 주로 분포되어있음을 확인하였다. 이를 통해 대구광역시의 폭염 저감을 위한 정책적 지원에 있어 공간적, 사회적 특성을 모두 고려해야 함을 확인하였다.

• 한국재난정보학회 논문집
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• 제16권4호
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• pp.747-757
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• 2020

연구목적: 본 연구는 폭염으로 인한 유사 환경 조건이라도 개인의 내적 특성에 따라 다른 대처를 하게 되어 피해의 정도에 개인차가 있음을 주목하였다. 이에 개인의 심리적 특성과 온열질환 증상 경험의 영향 관계를 분석하였다. 연구방법: 건설노동자를 대상으로 온열질환 증상의 경험 유무에 따라 개인특성의 설문과 폭염 피해에 연관성이 있을 강박신념, 자아 존중감, 성격에 대한 심리척도를 통해 영향관계를 분석하였다. 연구결과: 로지스틱 회귀분석 결과, 책임감은 온열질환 증상의 경험에 정(+)의 영향, 집단에서의 자아 존중감은 온열질환 증상의 경험에 음(-)의 영향을 미치는 것으로 나타났다. 결론: 본 연구는 폭염으로 인한 피해자의 심리적 특성을 파악하기 위하여 폭염에 취약한 대상인 건설노동자를 대상으로 강박신념, 자아 존중감, 성격을 분석한 첫 번째 연구로 기초자료를 제시하였다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.166-171
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• 2000

A two-dimensional/axisymmetric CSCM upwind flux difference splitting Wavier-Stokes method has been developed to study the finite rate chemically react-ing invisicd and viscous hypersonic flows over blunt-body. A upwind method was chosen due to its robustness in capturing the strong bow shock waves. For the nonequilibrium chemically reacting air, NS-I species conservation equations were strongly coupled with flowfield equations through convection and species production terms. The nonequilibrium wall pressure and heat transfer rate distributions along the vehicle were compared with those from equilibrium and perfect gas calculations. The nonequilibrium species distribution shows the reduced concentrations of O and N species when compared with equilibrium species distribution. The solutions resolved strong bow shock waves md heat transfer rate very accurately when compared with central difference schemes.