• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.11
• /
• pp.1369-1375
• /
• 2011

Shot ball impacts to materials cause residual compressive stress on their surfaces. Improving the fatigue strength of a material that has this residual compress stress is the purpose of the shot peening process. A numerical study was performed to evaluate the effect of the strain rate sensitivity and hardness of the shot ball on the residual compressive stress. We calculated the residual compressive stress due to multiple impact shot peening using ABAQUS 6.9-1. AISI 4340 steel was the material used in this study. We compared the effects of high strain rate sensitivities and low strain rate sensitivities and found that when the material's sensitivity to the strain rate increased, the residual compressive stress decreased. In addition, the residual compressive stress of low-hardness material is higher than that of high-hardness material.

• The Bulletin of The Korean Astronomical Society
• /
• v.46 no.1
• /
• pp.45.2-46
• /
• 2021

The Hayabusa 2 mission target asteroid (162173) Ryugu is a near-Earth, carbonaceous (C-type) asteroid. Before the arrival, this asteroid is expected to be covered with mm- to cm- sized grains through the thermal infrared observations [1]. These grains are widely understood to be formed by past impacts with other celestial bodies and fractures induced by thermal fatigue [2]. However, the close-up images by the MASCOT lander showed lumpy boulders but no abundant fine grains [3]. Morota et al. suggested that there would be submillimeter particles on the top of these boulders but not resolved by Hayabusa 2's onboard instruments [4]. Hence, we conducted polarimetry of Ryugu to investigate microscopic grain sizes on its surface. Polarimetry is a powerful tool to estimate physical properties such as albedo and grain size. Especially, it is known that the maximum polarization degree (Pmax) and the geometric albedo (pV) show an empirical relationship depending on surface grain sizes [5]. We observed Ryugu from UT 2020 November 30 to December 10 at large phase angles (ranging from 78.5 to 89.7 degrees) to derive Pmax. We modified TRIPOL (Triple Range Imager and POLarimeter, [6]) to attach to the 1.8-m telescope at the Bohyunsan Optical Astronomy Observatory (BOAO). With this instrument, we observed the asteroid and determined linear polarization degrees at the Rc-band filter. We obtained sufficient data sets from 7 nights at this observatory to determine the Pmax value, and collaborated with other observatories in Japan (i.e., Hokkaido University, Higashi-Hiroshima, and Nishi-Harima) to acquire linear polarization degrees of the asteroid from total 24 nights observations with large phase angle coverage (From 28 to 104 degrees). The observational results have been published in Kuroda et al. (2021) [7]. We thus found the dominance of submillimeter particles on the surface of Ryugu from the comparison with other meteorite samples from the campaign observation. In this presentation, we report our activity to modify the TRIPOL for the 1.8-m telescope and the polarimetric performance. We also examine the rotational variability of the polarization degree using the TRIPOL data.

• The Journal of Korean Academic Society of Nursing Education
• /
• v.30 no.1
• /
• pp.49-60
• /
• 2024

Purpose: The coronavirus disease 2019 (COVID-19) pandemic has had significant physical and psychological impacts on registered nurses (RNs). This study aimed to identify long COVID symptoms and their associated factors specifically among RNs. Methods: This descriptive correlational study's sample comprised 189 nurses (31.57±5.98 years, 93.7% female) in Korea. Self-reported long COVID symptoms were assessed using the COVID-19 Yorkshire Rehabilitation Scale. Data were collected from December 31, 2022, to January 13, 2023, using the online survey method and were analyzed using independent t-test, Wilcoxon signed-rank test, one-way ANOVA, Pearson's correlation, and a multiple linear regression analysis with the IBM SPSS Statistics 26.0 program. Results: A total of 179 participants (94.7%) experienced one or more long COVID symptoms. The most prevalent symptoms were weakness (77.8%), fatigue (68.3%), breathlessness (67.7%), cough/throat sensitivity/voice change (50.3%), and sleep problems (50.3%). The factors related to long COVID symptoms were marital status, type of institution, working time, acute COVID-19 symptoms, and vaccination status. The quarantine period (β=.26, p<.001) and the nursing workforce after COVID-19 (β=-.17, p=.018) were significantly associated with long COVID symptoms (Adjusted R² =.33). Conclusion: Providing comprehensive recognition is necessary for the understanding of long COVID symptoms and their associated factors among nurses and could promote a long COVID symptom management education program targeted at nurses. Moreover, it could facilitate effective nursing care and education plans for long COVID patients.

• Applied Chemistry for Engineering
• /
• v.16 no.5
• /
• pp.603-608
• /
• 2005

This study was conducted to investigate particle attrition characteristics in a gas desulfurization using zinc titanate sorbent in a 0.035 m i.d. by 1.34 m height gas fluidized bed reactor. Gas jetting from the distributor and bubbling in the gas fluidized bed were found to be the main causes of particle attrition. The experiment was carried out under a slow attrition rate condition to compare the performance of the batch reactor to that of a continuous reactor. The attrition index (AI) and corrected attrition index (CAI) were measured at various the gas velocity, temperature, pressure, and bed weight, in the gas fluidized bed, during the dexulfurization process. The AI (5) and CAI (5) decreased as the bed weight increased. Particle destruction occurred when the particles started to experience physical fatigue under specific impacts over several iterations. AI (5) and CAI (5) also increased as relative humidity, gas velocity and pressure increased, and as temperature decreased. Particle attrition was mainly affected by gas jetting from the distributor, and abrasion resulted in smaller particles than fragmentation did.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.22 no.3
• /
• pp.278-285
• /
• 2016

The key features of maritime accidents are the change of their attributes by new risks from time to time. To prevent maritime accidents in Korea, the impacts by new risks on domestic safety environments should be identified or predicted. The purpose of this paper is to find the hazard factors by new risks on maritime safety in Korea. The meaning of new risks is the elements of accident hazard which is compiled from new or rare or unprecedented events in the worldwide maritime transportations. The problems of new risks are the lacks of optimum countermeasures to mitigate accident risks. Using the questionnaires with 152 event scenarios classified by 20 accident causes, the hazard identification and risk analysis of new risks was performed based on the Formal Safety Assessment (FSA) by IMO. A total of 22 Influence Diagrams, which is to depict the transit flows between accident causes to consequences, is used in the construction of 152 event scenarios. A total of 20 accidents causes is the same contents as the causation factors represented in Statistical Year Book for Maritime Accidents of Korean Maritime Safety Tribunals. After defining the evaluation equations to the response results of questionnaires by 46 experts, the work for risk analysis is carried out. As results from the analysis of 152 scenarios, it is known that the root cause to affect on maritime safety in Korea is the pressure of business competition and it led to the lacks of well experienced crews, the overload of vessel operations and crew's fatigue. In addition, as results from the analysis of 20 accident causes, the three accident causes are to be candidate as main issues in Korea such as the inadequate preparedness of departure, the neglecting of watch keeping in bridge and the inadequate management of ship operations. All of the results are thought to be as basic hazard factors to safety impediments. It is thus found that the optimum Risk Control Options to remove the hazard factors and to mitigate consequences required are the following two factors: business competition and crewing problems.

• Safety and Health at Work
• /
• v.8 no.1
• /
• pp.99-104
• /
• 2017

Background: Workers laboring in steel industries in tropical settings with high ambient temperatures are subjected to thermally stressful environments that can create well-known risks of heat-related illnesses and limit workers' productivity. Methods: A cross-sectional study undertaken in a steel industry in a city nicknamed "Steel City" in Southern India assessed thermal stress by wet bulb globe temperature (WBGT) and level of dehydration from urine color and urine specific gravity. A structured questionnaire captured self-reported heat-related health symptoms of workers. Results: Some 90% WBGT measurements were higher than recommended threshold limit values ($27.2-41.7^{\circ}C$) for heavy and moderate workloads and radiational heat from processes were very high in blooming-mill/coke-oven ($67.6^{\circ}C$ globe temperature). Widespread heat-related health concerns were prevalent among workers, including excessive sweating, fatigue, and tiredness reported by 50% workers. Productivity loss was significantly reported high in workers with direct heat exposures compared to those with indirect heat exposures ($x^2=26.1258$, degrees of freedom = 1, p < 0.001). Change in urine color was 7.4 times higher among workers exposed to WBGTs above threshold limit values (TLVs). Conclusion: Preliminary evidence shows that high heat exposures and heavy workload adversely affect the workers' health and reduce their work capacities. Health and productivity risks in developing tropical country work settings can be further aggravated by the predicted temperature rise due to climate change, without appropriate interventions. Apart from industries enhancing welfare facilities and designing control interventions, further physiological studies with a seasonal approach and interventional studies are needed to strengthen evidence for developing comprehensive policies to protect workers employed in high heat industries.