• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.284-291
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• 2000

A basic pulse tube refrigerator has been constructed with extensive instrumentation to study the characteristics of the heat exchanger experimentally under the oscillating pressure and the oscillating flow. This paper describes the sequential experiments with the basic pulse tube refrigerator. The experiments were performed for various cycle frequencies under the square pressure wave forms. First, the heat flux was measured through the cycle at the both cold and warm end heat exchangers without the regenerator. In order to enhance the thermal communication capability of the heat exchanger with the gas at low operating frequencies, a unique design of the triangular shape radial fin concept was applied to the heat exchangers. For the fin heat exchanger, the measured heat flux and the calculated heat flux from the two well-known oscillating heat transfer correlations were compared and discussed. Second, the regenerator was added to the pulse tube to make a basic pulse tube refrigerator configuration. The experiment showed the great impact of the regenerator on the temperature and the heat flux profiles. At the warm-end, the cyclic averaged heat flux had its maximum value at the specific operating frequency. The paper presents the explanation of the surface heat pumping effect as well as the experimental data.

• Geomechanics and Engineering
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• v.18 no.6
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• pp.615-626
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• 2019

Lightweight concrete (LWC) provides an attractive alternative to conventional piles by improving the durability of deep foundations. In this paper, the drivability of cylindrical and tapered piles made of lightweight and common concrete (CC) under hammer impacts was investigated by performing field tests and numerical analysis. The different concrete mixtures were considered to compare the mechanical properties of light aggregate which replaced instead of the natural aggregate. Driving tests were also conducted on different piles to determine how the pile material and geometric configurations affect driving performance. The results indicated that the tapering shape has an appropriate effect on the drivability of piles and although lower driving stresses are induced in the LWC tapered pile, their final penetration rate was more than that of CC cylindrical pile under hammer impact. Also by analyzing wave propagation in the different rods, it was concluded that the LWC piles with greater velocity than others had better performance in pile driving phenomena. Furthermore, LWC piles can be driven more easily into the ground than cylindrical concrete piles sometimes up to 50% lower hammer impacts and results in important energy saving.

• Journal of Digital Convergence
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• v.17 no.10
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• pp.447-452
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• 2019

This paper analyzed the impact of nation and celebrity reputation on purchase intention in Kazakhstan. Kazakhstan people aged 10 to 30 years were surveyed. The study proved that the national reputation has positive impacts on the purchase intention of Korean products. However, the Korean celebrity reputation has not statistically affected the intention of purchasing Korean products. In other words, it confirmed that the country of origin effect of Korea is affecting purchases of products from the countries concerned. Therefore, based on the country's reputation for Korea in Kazakhstan, it is believed that the promotion activities of Korean products will encourage consumers to make purchases.

• Journal of Environmental Science International
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• v.28 no.10
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• pp.831-840
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• 2019

Recently, summer high temperature events caused by climate change and urban heat island phenomenon have become a serious social problem around the world. Urban areas have low albedo and huge heat storage, resulting in higher temperatures and longer lasting characteristics. To effectively consider the urban heat island measures, it is important to quantitatively grasp the impact of urban high temperatures on the society. Until now, the study of urban heat island phenomenon had been carried out focusing only on the effects of urban high temperature on human health (such as heat stroke and sleep disturbance). In this study, we focus on the effect of urban heat island phenomenon on air pollution. In particular, the relationship between high temperature phenomena in urban areas during summer and the concentration of photochemical oxidant is investigated. High concentrations of ozone during summer are confirmed to coincide with a day when the causative substances (NO2,VOCs) are high in urban areas during the early morning hours. Further, it is noted that the night urban heat island intensity is large.. Finally, although the concentration of other air pollutants has been decreasing in the long term, the concentration of photochemical oxidant gradually increases in Daegu.

• Korean Journal of Childcare and Education
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• v.16 no.6
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• pp.105-122
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• 2020

Objective: The study aimed to examine the impact of a supportive school environment on children's prosocial behavior by investigating the sequential mediating effects of children's self-esteem and happiness. Methods: Results of the study were obtained by analysing data collected from 633 nine-year-old children in the 10th wave of the Panel Study on Korean Children(2017). The data were analyzed by descriptive statistics, correlation analysis and significance of mediated pathways using SPSS 23.0 and PROCESS macro 3.3. Results: First, children's self-esteem did not have mediational effects with respect to a supportive school environment and children's prosocial behavior. Second, children's happiness had mediational effects with respect to a supportive school environment and children's prosocial behavior. Lastly, a supportive school environment affects children's self-esteem, which affects children's happiness, thereby promoting children's prosocial behavior. Conclusion/Implications: In order to promote children's prosocial behavior, we should put emphasis on developing a supportive school environment, and increasing children's self-esteem and happiness. It is important that teachers treat children and classmates treat each other with a warm attitude so that they can value themselves and feel happiness in their lives.

• Human Ecology Research
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• v.59 no.3
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• pp.341-351
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• 2021

The purpose of this study was to examine the longitudinal relationships between Korean adolescents'mobile phone dependency, trajectories of depression, and self-regulated learning abilities. To achieve these goals, structural equation modeling analysis was conducted, using the 3rd, 5th and 7th wave of the data on 4th graders taken from the Korean Children and Youth Panel Survey. The results can be summarized as follows. First, growth-curve longitudinal analysis indicates that depression in 6th through 10th grade has increased. Second, mobile phone dependency among adolescents at 6th grade has a significant effect on both the initial value and the rate of change in depression. Also, the initial value and the rate of change in depression have significant relationships with mobile phone dependency at 10th grade. Moreover, both increased levels of mobile phone dependency and the rate of change in depression significantly influence adolescents'self-regulated learning abilities at 10th grade. Based on a longitudinal data set, these findings demonstrate the causal relationships between Korean adolescents'trajectories of depression and their mobile phone dependency. The findings also provide a comprehensive framework with implications for adolescents'development through an understanding of the relationships between adolescents'depression and mobile phone dependency, which impact their self-regulated learning abilities.

• Safety and Health at Work
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• v.12 no.2
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• pp.261-267
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• 2021

Background: The series of serious industrial accidents in recent years at contractors to large companies has highlighted risk outsourcing as a real and urgent problem. This study aims to review the difference in the degree of risk exposure and the occurrence of industrial accidents depending on the type of company relations. Among in-house contractors, the focus will be on those handling hazardous chemicals that include companies for which outsourcing requires approval. Methods: This study uses the 9th wave of the Industrial Safety and Health Survey (2018). For determining the degree of risk exposure, the occurrence of industrial accidents, and industrial accident rate, multivariate, logistic, and fractional logit, regression analyses were used, respectively. Results: First, In-house contractors' degree of risk exposure is higher than that of the client companies. In particular, this gap is even greater for companies dealing with chemicals. Second, among only those that handle hazardous chemicals, in-house contractors do show a significantly higher rate of industrial accident occurrence. Third, In-house contractors have a significantly higher rate of industrial accidents from diseases than client companies. Conclusion: The analysis supports the intent of the legal amendment that strengthens the protection of in-house contracted workers who handle hazardous chemicals. Second, the results of this study suggest that safety and health management must go beyond legal compliance and ensure that it has substance and effectiveness. Last, there should be policy consideration is necessary to reduce attempts to hide industrial accidents.

• Acta Via Serica
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• v.7 no.1
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• pp.105-130
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• 2022

This paper argues that the war in Syria is partly the result of a global Islamist wave that contributed to fuelling conflict across large regions of Asia and Africa. Of course, the war that has consumed Syria since 2011 most certainly has multiple interrelated causes and driving forces, and any attempt to isolate one or even two or three runs the risk of advancing an overly simplistic interpretation of history. This essay, therefore, does not aim to offer an appraisal of the multiple variables that contributed to the war in Syria. Instead, it zeroes in on how political Islam came to impact Syria and its people. In doing so, it demonstrates how competing varieties of political Islam represented leading causes of conflict. Indeed, different Islamist movements contributed to the outbreak of the war in 2011, fuelled the conflict for years on end, and to this day represent major obstacles to the achievement of sustainable peace. Four broad Islamist currents are especially relevant to the case of Syria: the Muslim Brotherhood; the Shia revivalist movement at the nexus of the alliance between Iran, Hezbollah, and Syria; Salafi jihadism and its volatile and fractious underworld of competing armed groups, from Al-Qaeda to the Islamic State; and Recep Tayyip Erdoğan's market-friendly Islamism, which induced Turkey to intervene in Syria's civil war.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.17 no.4
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• pp.15-27
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• 2021

In this study, the effect of design factors in a pump station on the pressure variations which are the main cause of water hammering has been investigated by numerical simulations. As design factors, the flow rate, Young's modulus, diameter, thickness, roughness coefficient of pipeline are considered. The relationships between the pressure variations and the design factors are analyzed. The results show that the pressure variation increases sensitively with the flow rate and Young's modulus, and increases gradually with the thickness and roughness coefficient of pipe, whereas it decreases with the pipe diameter. The wavelength of the pressure wave becomes longer for a smaller Young's modulus, a smaller pipe thickness and a bigger pipe diameter. These relationships are nondimensionalized, and logarithmic curve-fitted functions are proposed by regression analysis. Most effective factors on the nondimensional pressure variation is Young's modulus. Flow rate, roughness coefficient, relative thickness and pipe diameters are the next impact factors.

• Corrosion Science and Technology
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• v.21 no.2
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• pp.138-146
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• 2022

The cavitation and potentiodynamic polarization experiments were conducted simultaneously to investigate the effect of cavitation amplitude on the super austenitic stainless steel (UNS N08367) electrochemical behavior in seawater. The results of the potentiodynamic polarization experiment under cavitation condition showed that the corrosion current density increased with cavitation amplitude increase. Above oxygen evolution potential, the current density in a static condition was the largest because the anodic dissolution reaction by intergranular corrosion was promoted. In the static condition, intergranular corrosion was mainly observed. However, damage caused by erosion was observed in the cavitation environment. The micro-jet generated by cavity collapse destroyed the corrosion product and promoted the repassivation. So, weight loss occurred the most in static conditions. After the experiment, wave patterns were formed on the surface due to the compressive residual stress caused by the impact pressure of the cavity. Surface hardness was improved by the water cavitation peening effect, and the hardness value was the highest at 30 ㎛ amplitude. UNS N08367 with excellent mechanical performance due to its high hardness showed that cavitation inhibited corrosion damage.