• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1286-1291
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• 2004

In order for studying pressure-coupled dynamic responses of droplet vaporization, open-loop experiment of an isolated droplet vaporization exposed to pressure perturbations in stagnant gaseous environment is numerically conducted. Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous nitrogen. Results show that wave instability in view of pressure-coupled vaporization response seems more susceptible at higher pressures and higher wave frequencies. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Augmentation of perturbation frequency also enhances amplification due to the reduction of phase differences between pressure perturbation and surface temperature fluctuation.

• 설비공학논문집
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• 제12권8호
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• pp.782-790
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• 2000

A numerical study has been conducted to characterize the transient pressure in a building water supply system with an air chamber by utilizing a commercial code that employs the method of characteristics. Some results produced for the purpose of verification in the study agree quite well with the previously reported. Several parameters are then varied. Among them are the valve closure time, the wave speed, the static pressure, the polytropic exponent, the air chamber volume, the inner diameter and the shape of orifice in the air chamber, etc, while the water temperature and velocity are kept constant at $20^P{circ}C $,/TEX> and 0.8 m/s, respectively, Results reported in this parametric study may be useful to understand the unsteady behavior of the system.

• Macromolecular Research
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• 제13권4호
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• pp.321-326
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• 2005

Photochromic diarylethene polymers (DPs) in which 1,2-bis(2-methylbenzo[b ]thiophene-3-yl)hexafluorocyclopentene (BTF6) were covalently grafted onto the polymer main chain as pendant photochromic units were newly synthesized and their photochromic properties were investigated using steady-state and picosecond timeresolved spectroscopies. Polysiloxanes substituted with BTF6 molecules were prepared by sol-gel process using a mixture of tetraethoxysilane (TEOS), a silylated BTF6, and an organically modified silane precursor in the presence of HCl. The polysiloxane film (DP1) prepared from $\omega-methoxy$ poly(ethylene glycol) 3-(triethoxysilyl) propylcarbainate (MPGSC) as the silane precursor showed a much lower glass transition temperature than that (DP2) from heptadecafluorodecyltrimethoxysilane (HDFTMS). The ring-closure quantum yields of DP1 and DP2 were determined to be 0.20 and 0.02, respectively. Such a large difference in the quantum yield was attributed to the polymer matrix environment of the free inner volume.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.155-164
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• 2004

In order for studying pressure-coupled dynamic responses of droplet vaporization, open-loop experiment of an isolated droplet vaporization exposed to pressure perturbations in stagnant gaseous environment is numerically conducted, Governing equations are solved for flow parameters at gas and liquid phases separately and thermodynamic parameters at the interfacial boundary are matched for problem closure. For high-pressure effects, vapor-liquid interfacial thermodynamics is rigorously treated. A series of parametric calculations in terms of mean pressure level and wave frequencies are carried out employing a n-pentane droplet in stagnant gaseous nitrogen. Results show that wave instability in view of pressure-coupled vaporization response seems more susceptible at higher pressures and higher wave frequencies. Mass evaporation rate responding to pressure waves is amplified with increase in pressure due to substantial reduction in latent heat of vaporization. Augmentation of perturbation frequency also enhances amplification due to the reduction of phase differences between pressure perturbation and surface temperature fluctuation.

• The Plant Pathology Journal
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• 제34권3호
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• pp.236-240
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• 2018

Crop yield is critically related to the physiological responses and disease resistance of the crop, which could be strongly affected by high temperature conditions. We observed the changes in the growth of barley under higher than ambient air-temperature conditions using a temperature gradient field chamber (TGFC) during winter and spring. Before the stem extension stage of barley growth, Cladosporium sp. spontaneously appeared in the TGFC. The severity of disease became serious under warmer temperature conditions. Further, the stomata closed as the severity of the disease increased; however, stomatal conductance at the initial stage of disease was higher than that of the normal leaves. This was likely due to the Iwanov effect, which explains that stressed plants rapidly and transiently open their stomata before longer-term closure. In this study, we tested three optical methods: soil-plant analysis development (SPAD) chlorophyll index, photochemical reflectance index (PRI), and maximum quantum yield (Fv/Fm). These rapid evaluation methods have not been used in studies focusing on disease stress, although some studies have used these methods to monitor other stresses. These three indicative parameters revealed that diseased barley exhibited lower values of these parameters than normal, and with the increase in disease severity, these values declined further. Our results will be useful in efficient monitoring and evaluation of crop diseases under future warming conditions.

• 한국해양공학회지
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• 제11권4호
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• pp.61-75
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• 1997

The social demand urges us to use some equipments and structures in high temperature environment. By this occasion, the necessity of studying the fatigue crack growth is an important aspect of new materials. However, the present situation is rarely to accumulate the fatigue data. Especially, 1Cr-1Mo-0.25V steel and 304 stainless steel have been increased to be used under the severe condition of high temperature. And so, the fatigue estimation of those materials is important and appropriate. Fatigue tests have been carried out to examine the crack initiation, growth behaviour for the small fatigue crack of 1Cr-1Mo-0.25V steel and 304 stainless steel at room temperature and 538^{\circ}C$. The remote measurement system which has many merits of checking and saving the image for detailed examination was applied to closely detect the crack length. Generally, the fatigue crack initiated in the form of multiple cracks and grew each other. And then it coalesced to become a major crack. The major crack governed the rest of the fatigue life. In the growing process, each peripheral cracks interact and grow for a certain period. After then, it coalesced and fractured. On the basis of the above experimental data for the small crack, a simulation program was developed to predict the residual life time and to estimate the integrity of machine elements and structures. At the same time, the simulation was extended to 1Cr-1Mo-0.25V steel. The simulation results have shown a good agreement to those of the experimental ones for both materials of 1Cr-1Mo-0.25V steel and 304 stainless steel with small cracks. The NASCRAC has applied to compare the fatigue life with the experimental results. And so, it can be said that the simulation program is valuable tools to the industrial fields.

• 한국조경학회지
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• 제47권6호
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• pp.67-77
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• 2019

본 연구는 미세먼지 문제가 심각한 도심에서 도시근린공원의 중심이 입구에 비해 어느 정도 저감된 공간인지 분석해 보는데 목적이 있다. 또한 공원중앙의 공간 차폐율과 미세먼지 저감율과의 상관관계를 실험을 통해 도출해 내고자 하였다. 대구시 수성구 평지형 도시근린공원 7개를 대상으로 3일동안 같은 장소에서 측정하였다. 연구결과, 첫째, 도시근린공원 중심은 입구보다 온도는 평균 1.05℃ 낮고, 습도는 평균 2.57% 높았다. 둘째, 미세먼지 감소율은 PM1 17.09%, PM2.5 17.65%, PM10 14.99%의 저감율로 초미세먼지가 더 높은 것으로 분석되었으며, 공원의 규모가 작을수록 저감효과가 더 높았다. 또한 기상청발표 미세먼지 농도가 높은날일수록 공원중앙에서의 저감율은 낮았으며, 공원입구의 농도가 높을수록 저감율은 높았다. 셋째, 공원중심에서 공간차폐율이 높을수록 미세먼지 저감효과가 높은 것으로 파악되었다. 도시근린공원의 미세먼지 저감정도와 공간차폐율과의 상관관계를 파악할 수 있었으며, 더 확대된 실험데이터들의 기초가 되기를 기대한다.

• 대한의생명과학회지
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• 제8권3호
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• pp.143-154
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• 2002

The effect of cardiopulmonary bypass (CPB) on cerebral physiology during heart surgery remains incompletely understood. This study was carried out to investigate changes of cerebral metabolism and the association between the changes and clinical factors during heart surgery. Seventy adult patients (n=70) scheduled for elective cardiac surgery were participated in the present study. Middle cerebral artery blood flow velocity (V$_{MCA}$), cerebral arteriovenous oxygen content difference (C(a-v)O$_2$), cerebral oxygen extraction (COE), and modified cerebral metabolic rate for oxygen (MCMRO$_2$) were measured during six phases of the operation; Pre-CPB, CPB-10 min, Rewarm-1 (nasopharyngeal temperature 34$^{\circ}C$), Rewarm-2 (nasopharyngeal temperature 37$^{\circ}C$), CPB-off, and Post-OP (at skin closure after CPB-off). Each relationship of age, arterial blood gas parameters, or other variables to V$_{MCA}2$, C(a-v)O$_2$, COE, or MCMRO$_2$ was evaluated. V$_{MCA}$ increased (P<0.0001) whereas C(a-v)O$_2$ decreased (P<0.01) throughout the five phases of the operation compared to Pre-CPB value (control). COE diminished at CPB-10, Rewarm-1, and CPB-off (P<0.05) while MCMRO$_2$ reduced at CPB-10 and Rewarm-1 (P<0.05) compared to Pre-CPB value. Positive correlation was found between age and cerebral metabolic parameters (V$_{MCA}$, C(a-v)O$_2$, COE, or MCMRO$_2$) during CPB (range r=0.24 to 0.38, p<0.05). Four cerebral metabolic parameters had partially negative or positive correlation with arterial blood gas parameters and other variables (arterial blood pH, $O_2$ tension, $O_2$ content, $CO_2$ tension, blood pressure, blood flow, temperature, or hematocrit) during the operation. In conclusion, CPB led to marked alterations of cerebral metabolism and age, pH, and $CO_2$ tension profoundly influenced the changes during cardiac surgery.

• 동굴
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• 제59권
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• pp.21-36
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• 1999

Most scholars calssify caves into natural resource, but caves possess values of natural and human resource, mix up the features of natural resources and human resources. Now, caves are distributed 260 in Korea. Seongryu Cave is showed in 1967 for the first time, till 1997 12 caves is opened to tourist. But since 1996 the 12 show caves of all is not launched the safety and environment-protection check-up adduced reason for IMF. Then caves must maintain environment of the normal temperature, humidity and dark. But the environment of caves are destroyed by tourism development. Thus to maintain environment of caves, it used to consider the counterplan as follows in restraint of the environmental change. Firstly, in case of development work to open caves, it must keep up with the prototype. Secondly, it must establish a freight depositary to prevent the influence of the caves's stain and damage due to tourist's objects. Thirdly, to maintain the normal temperature and humidity, it must install artificial poultice equipment of the inner parts of caves. Fourthly, in order to prevent the occurrence of $CO_2$, it must assessment of the optimum number of the greatest stayer. Fifthly, the control of closure for a given period of time is useful of the restoration to the cave's original state. Sixthly, by means of make narrow entrance, it should not influence the outer's air on the inner parts on caves. Seventhly, to keep the temperature of the inner part of caves, the lightening should be maintained moderately considering the convenience of a tour. Eightly, when water-proof cables for the lightening bulbs are connected each other, silicon tape is suitable and circuit breakers should be installed at the diverging points of the cables. Ninthly, the direction and angle of the lightening must be changed periodically to prevent green-pollution at the lightening spot. Lastly, when facilities and arrangements are equipped, corrosive materials should be excluded if circumstances allow.

• 대한기계학회논문집
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• 제12권5호
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• pp.1150-1157
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• 1988

본 연구에서는 수치계산을 통해 진행하는 방향에 수직으로 일정한 압력구배를 받는 2차원 난류 자유제트의 발달을 고려해 보고자 한다.속도장을 구한 후에는 제 트의 온도가 주위온도 보다 높을 경우와 또 제트를 사이에 둔 양쪽 유체에 온도차가 있을때의 열확산 특성도 함께 알아보려는 것이다. 수직 방향으로 압력구배가 있는 유동장은 최근 활발히 연구가 진행되는 분야인 제트축에 수직방향으로 주위유동이 있 는 경우와 흡사하며 제트를 통한 열확산현상은 air curtain등 실제 응용도가 큼에도 불구하고 문헌에 보고된 것이 별로 없는 것으로 보여진다.