• Title/Summary/Keyword: Fatigue Level

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Optimization for Underwater Welding of Marine Steel Plates (선박용 강판의 수중 용접 최적화에 관한 연구)

  • 오세규
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.20 no.1
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    • pp.49-59
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    • 1984
  • Optimizing investigation of characteristics of underwater welding by a gravity type arc welding process was experimentally carried out by using six types of domestic coated welding electrodes for welding of domestic marine structural steel plates (KR Grade A-1, SWS41A, SWS41B,) in order to develop the underwater welding techniques in practical use. Main results obtained are summarized as follows: 1. The absorption speed of the coating of domestic coated lime titania type welding-electrode became constant at about 60 minutes in water and it was about 0.18%/min during initial 8 minutes of absorption time. 2. Thus, the immediate welding electrode could be used in underwater welding for such a short time in comparison with the joint strength of in-atmosphere-and on-water-welding by dry-, wet-or immediate-welding-electrode. 3. By bead appearance and X-ray inspection, ilmenite, limetitania and high titanium oxide types of electrodes were found better for underwater-welding of 10 mm KR Grade A-1 steel plates, while proper welding angle, current and electrode diameter were 6$0^{\circ}C$, above 160A and 4mm respectively under 28cm/min of welding speed. 4. The weld metal tensile strength or proof stress of underwater-welded-joints has a quadratic relationship with the heat input, and the optimal heat input zone is about 13 to 15KJ/cm for 10mm SWS41A steel plates, resulting from consideration upon both joint efficiency of above-100% and recovery of impact strength and strain. Meanwhile, the optimal heat input zone resulting from tension-tension fatigue limit above the base metal's of SWS41A plates is 16 to 19KJ/cm. Reliability of all the empirical equations reveals 95% confidence level. 6. The microstructure of the underwater welds of SES41A welded in such a zone has no weld defects such as hydrogen brittleness with supreme high hardness, since the HAZ-bond boundary area adjacent to both surface and base metal has only Hv400 max with the microstructure of fine martensite, bainite, pearlite and small amount of ferrite.

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A Study on Job Stress and Eating Behavior and Habits of Dental Hygienists (치과위생사의 직무스트레스와 식행동 및 식습관에 관한 연구)

  • Koong, Hwa-Soo;Kim, Seong-Min
    • Journal of dental hygiene science
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    • v.12 no.5
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    • pp.525-534
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    • 2012
  • Study the effect of stress factors and increases in stress at work on the changes in eating behavior and habits and the influence of these changes on the health of dental hygienists. Use the responses of 273 dental hygienists who work in or around the Seoul area after surveying them by post or face to face. The biggest reason for skipping breakfast was having no time (60.4%) and the most desired change in eating habits was over eating (33.0%) while 51.6% responded that they over ate or binge ate due to stress. The largest stress factor was work load 39.6% and subjects responded that after stress the amount of food consumed increased very much for 12.1%, very for 49.8%, indicating increased food consumption than usual. The group with the most job stress had a high level of self stress awareness (p<0.001), nervousness (p<0.01), back pains (p<0.001), optical fatigue (p<0.01), headache (p<0.01) and indigestion (p<0.01). The higher the job stress, the poorer the eating behavior was (p<0.01) and job stress was high for dental hygienists working in dental clinics with less than three dental hygienists (p<0.05). Low eating behavior scores could be seen in groups that took 4 night shifts per week (p<0.05). Job stress scores for high for groups with no break time during work (p<0.001) and these groups showed low eating behavior scores (p<0.01). Furthermore, if high levels of self stress awareness was present, job stress was very high (p<0.001) and eating behavior scores were the lowest (p<0.05). Job stress of dental hygienists impede the eating behavior and habits therefore has a negative influence on their health. There is a need for more efforts to solve this problem and thus maintain the health of dental hygienists.

Effects of School Attendance Policy on Breakfast Eating, Sleep, and Physical Activity in Middle School Students (9시 등교정책이 중학생의 아침식사, 수면 및 신체활동에 미치는 영향)

  • Kim, Ha Na;Kim, Seong Yeong
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.46 no.11
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    • pp.1397-1407
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    • 2017
  • The aim of a school attendance policy (SAP) is to ensure breakfast time for school-aged adolescents. Therefore, this study investigated the effects of SAP on dietary behavior, particularly breakfast consumption, among adolescent middle school students (n=426) in the Ansan area of Gyeonggi-do. After implementation of the SAP, the response rates for eating breakfast every-day among boys (P>0.05) and girls (P<0.05) slightly increased by 44.6% and 35.8%, respectively, compared to before the SAP. Further, the degree of satisfaction with breakfast increased among both boys ('satisfied' and 'strongly satisfied'; 32.4% and 21.6%, respectively) (P<0.01) and girls ('satisfied' and 'strongly satisfied'; 32.8% and 14.2%, respectively) (P<0.001) compared to before the SAP. Moreover, boys (56.8%) and girls (53.9%) were aware that the SAP increased breakfast-eating frequency. Increases in deep sleep as a result of the SAP were high in both boys (39.2%) and girls (47.1%), and sleeping hours among boys (P<0.05) and girls (P<0.01) increased compared to before the SAP. The respondents were aware of the positive effects on physical function such as reduction of physical fatigue (boys 40.1%, girls 38.2%) and improvement of physical health (boys 36.5%, girls 32.8%). Thus, systematic and sustained political support at the national level is required to encourage healthy breakfast eating and physical activity in middle school students.

The Psychological Relaxation Effects of College Students in Location Targeting Seonyudo Park in Autumn (가을철 선유도공원의 주제공간이 대학생들의 심리적 안정에 미치는 영향)

  • Yoon, Yong-Han;Oh, Deuk-Kyun;Kim, Jeong-Ho
    • Journal of the Korean Institute of Landscape Architecture
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    • v.43 no.2
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    • pp.13-22
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    • 2015
  • The study discovers mood state and enhancement effect of users by scenery of location targeting Seonyudo Park; where is widely recognized as the representative recycling environmental park as well as theme experience space and scenery admiration in Korea. Also, the influence level of park and thematic space upon wellness was researched for future park design and its base data. As a result of semantic differential(SD), the most items showed low point in positive way when people admiring the scenery in Seonyudo. Also, a subject experienced differently depending on each inside scenery element of the park. As a result of profile of mood states(POMS), a tension and anxiety points were shown in order of Urban (7.78) > Water Purification Basin(3.33) > Gardens of Water Plants(2.11) > Garden of Green Pillar(2.00) > Garden of Time (0.89). The depression points were shown in order of Urban(4.94) > Water Purification Basin(3.50) > Garden of Green Pillar(2.94) > Garden of Time(1.61) > Gardens of Water Plants(1.38). The anger and hostility points were shown in order of Urban(4.22) > Water Purification Basin(3.33) > Garden of Green Pillar(2.22) > Garden of Time(1.39) > Gardens of Water Plants(1.11). The fatigue points were shown in order of Urban(6.5) > Water Purification Basin(3.39) > Garden of Green Pillar(2.78) > Garden of Time(2.28) > Gardens of Water Plants (2.06). The vigor points were shown in order of Gardens of Water Plants(11.39) > Garden of Time(11.00) > Garden of Green Pillar(8.39) > Water Purification Basin(7.77) > Urban(5.28). Also, as a result of statistics analysis, difference value of scenery type is significant. The result of total emotional disturbance(TED) was analyzed in order of Urban(24.5) > Water Purification Basin(9.5) > Garden of Green Pillar(4.67) > Garden of Time(-1.39) > Gardens of Water Plants(-1.22).

Cyclic Seismic Testing of Cruciform Concrete-Filled U-Shape Steel Beam-to-H Column Composite Connections (콘크리트채움 U형합성보-H형강기둥 십자형 합성접합부의 내진성능)

  • Park, Chang-Hee;Lee, Cheol-Ho;Park, Hong-Gun;Hwang, Hyeon-Jong;Lee, Chang-Nam;Kim, Hyoung-Seop;Kim, Sung-Bae
    • Journal of Korean Society of Steel Construction
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    • v.23 no.4
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    • pp.503-514
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    • 2011
  • In this research, the seismic connection details for two concrete-filled U-shape steel beam-to-H columns were proposed and cyclically tested under a full-scale cruciform configuration. The key connecting components included the U-shape steel section (450 and 550 mm deep for specimens A and B, respectively), a concrete floor slab with a ribbed deck (165 mm deep for both specimens), welded couplers and rebars for negative moment transfer, and shear studs for full composite action and strengthening plates. Considering the unique constructional nature of the proposed connection, the critical limit states, such as the weld fracture, anchorage failure of the welded coupler, local buckling, concrete crushing, and rebar buckling, were carefully addressed in the specimen design. The test results showed that the connection details and design methods proposed in this study can well control the critical limit states mentioned above. Especially, the proposed connection according to the strengthening strategy successfully pushed the plastic hinge to the tip of the strengthened zone, as intended in the design, and was very effective in protecting the more vulnerable beam-to-column welded joint. The maximum story drift capacities of 6.0 and 6.8% radians were achieved in specimens A and B, respectively, thus far exceeding the minimumlimit of 4% radians required of special moment frames. Low-cycle fatigue fracture across the beam bottom flange at a 6% drift level was the final failure mode of specimen A. Specimen B failed through the fracture of the top splice plate of the bolted splice at a very high drift ratio of 8.0% radian.

Corona Blue and Leisure Activities : Focusing on Korean Case (코로나 블루와 여가 활동 : 한국 사례를 중심으로)

  • Sa, Hye Ji;Lee, Won Sang;Lee, Bong Gyou
    • Journal of Internet Computing and Services
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    • v.22 no.2
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    • pp.109-121
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    • 2021
  • As the global COVID-19 pandemic is prolonged, the Corona Blue phenomenon, combined with COVID-19 and blue, is intensifying. The purpose of this study is to analyze the current trend of Corona Blue in consideration of the possibility of increasing mental illness and the need for countermeasures, especially after COVID-19. This study tried to find out the relationship between stress and leisure activities before and after COVID-19 by using Corona Blue news article analysis through the topic modeling method, and questionnaire find out the help of stress and leisure activities. This study was compared and analyzed using two research methods. First, a total of 363 news articles were analyzed through topic modeling based on newspaper articles from January 2020, when COVID- 19 was upgraded to the "border" stage, until September, where the social distancing stage was strengthened to stage 2.5 in Korea. As a result of the study, a total of 28 topics were extracted, and similar topics were grouped into 7 groups: mental-demic, generational spread, causes of depression acceleration, increased fatigue, attitude to coping with long-term wars, changes in consumption, and efforts to overcome depression. Second, the SPSS statistical program was used to analyze the level of stress change according to leisure activities before/after COVID-19 and the main help according to leisure activities. As a result of the study, it was confirmed that the average difference in stress reduction according to participation in leisure activities before COVID-19 was larger than after COVID-19. Also, leisure activities were found to be effective in stress relief even after COVID-19. In addition, if the main help from leisure activities before COVID-19 was the meaning of relaxation and recharging through physical and social activities. After COVID-19, psychological roles such as mood swings through nature, outdoor activities, or intellectual activities were found to play a large part. As such, in this study, it was confirmed that understanding the current status of Corona Blue and coping with leisure in extreme stress situations has a positive effect. It is expected that this research can serve as a basis for preparing realistic and desirable leisure policies and countermeasures to overcome Corona Blue.

Distress and Associated Factors in Patients with Breast Cancer Surgery : A Cross-Sectional Study (유방암 수술환자의 디스트레스 및 연관인자 : 단면연구)

  • Lee, Sang-Shin;Rim, Hyo-Deog;Woo, Jungmin
    • Korean Journal of Psychosomatic Medicine
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    • v.26 no.2
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    • pp.77-85
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    • 2018
  • Objectives : This study aimed to investigate the level of distress using the distress thermometer (DT) and the factors associated with distress in postoperative breast cancer (BC) patients. Methods : DT and WHOQOL-BREF (World Health Organization Quality of Life Scale Abbreviated Version) along with sociodemographic variables were assessed in patients undergoing surgery for their first treatment of BC within one week postoperatively. The distress group consisted of participants with a DT score ${\geq}4$. The prevalence and associative factors of distress were examined by descriptive, univariable, and logistic regression analysis. Results : Three hundred seven women were recruited, and 264 subjects were finally analyzed. A total of 173 (65.5%) were classified into the distress group. The distress group showed significantly younger age (p=0.045), living without a spouse (p=0.032), and worse quality of life (QOL) as measured by overall QOL (p=0.009), general health (p=0.005), physical health domain (p<0.000), and psychological health domain (p=0.002). The logistic regression analysis showed that patients aged 40-49 years were more likely to experience distress than those aged ${\geq}60years$ (Odds ratios [OR]=2.992, 95% confidence interval [CI] 1.241-7.215). Moreover, the WHOQOL-BREF physical health domain was a predictive factor of distress (OR=0.777, 95% CI 0.692-0.873). Conclusions : A substantial proportion of patients are experiencing significant distress after BC surgery. It would be expected that distress management, especially in the middle-aged patients and in the domain of physical QOL (e.g., pain, insomnia, fatigue), from the early BC treatment stage might reduce chronic distress.

The Association Between Working Overtime and Job Performance for Dental Hygienists (치과위생사의 야간진료와 직무성과의 관련성)

  • Mi-Sook Yoon;Young-Eun Kim;Han-A Cho
    • Journal of Korean Dental Hygiene Science
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    • v.7 no.1
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    • pp.39-52
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    • 2024
  • Background: Dental hygienists provide direct dental care in the closest proximity to the patient, and each practice requires a high level of focus and concentration. These skills are an important human resource that can impact the quality of dental care services. Since more than half of dental clinics provide as overtime work in addition to regular hours, this study aims to determine the association between working overtime and job performance for dental hygienists. Methods: The study was conducted using a combination of online and in-person surveys via Google Forms among 131 employed dental hygienists. The survey consisted of 7 questions on demographic and work characteristics, 16 questions on characteristics related to overtime and the effect of overtime on job security, health, and life, and 10 questions on job performance, for a total of 33 questions. Chi-square analysis and independent samples t-test were used to identify the characteristics of demographic and work characteristics, and descriptive statistics analysis was used for the characteristics of overtime. Independent samples t-test was used to test the difference in the mean of job performance according to whether or not they worked overtime, and linear regression analysis was used to show the association of working overtime and job performance. Results: The study found that 71% of dental clinics worked overtime. The average number of overtime per week was once (78.5%), and the most common problems with overtime were fatigue (52.7%) and lack of personal and leisure time (41.9%). The appropriate number of overtime per week considered by dental hygienists was once a week, which was confirmed to be 94.6%. When comparing job performance by overtime status, those who worked overtime were 3.38 points higher than those who did not (35.45 vs. 32.07). Multiple linear regression analysis of the association of working overtime night and job performance showed that a one-unit increase in worked overtime was associated with a statistically significant increase in job performance of about 3.1 (p<0.01). Conclusion: Working overtime was found to have a positive effect on job performance among dental hygienists. Therefore, as a way to improve the working environment, providing appropriate compensation or welfare for overtime can reduce the negative aspects of overtime and turn it into a positive influence on job performance. This could ultimately raise awareness of the dental hygienist as a professional and effect the efficiency of dental care services.

Self-optimizing feature selection algorithm for enhancing campaign effectiveness (캠페인 효과 제고를 위한 자기 최적화 변수 선택 알고리즘)

  • Seo, Jeoung-soo;Ahn, Hyunchul
    • Journal of Intelligence and Information Systems
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    • v.26 no.4
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    • pp.173-198
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    • 2020
  • For a long time, many studies have been conducted on predicting the success of campaigns for customers in academia, and prediction models applying various techniques are still being studied. Recently, as campaign channels have been expanded in various ways due to the rapid revitalization of online, various types of campaigns are being carried out by companies at a level that cannot be compared to the past. However, customers tend to perceive it as spam as the fatigue of campaigns due to duplicate exposure increases. Also, from a corporate standpoint, there is a problem that the effectiveness of the campaign itself is decreasing, such as increasing the cost of investing in the campaign, which leads to the low actual campaign success rate. Accordingly, various studies are ongoing to improve the effectiveness of the campaign in practice. This campaign system has the ultimate purpose to increase the success rate of various campaigns by collecting and analyzing various data related to customers and using them for campaigns. In particular, recent attempts to make various predictions related to the response of campaigns using machine learning have been made. It is very important to select appropriate features due to the various features of campaign data. If all of the input data are used in the process of classifying a large amount of data, it takes a lot of learning time as the classification class expands, so the minimum input data set must be extracted and used from the entire data. In addition, when a trained model is generated by using too many features, prediction accuracy may be degraded due to overfitting or correlation between features. Therefore, in order to improve accuracy, a feature selection technique that removes features close to noise should be applied, and feature selection is a necessary process in order to analyze a high-dimensional data set. Among the greedy algorithms, SFS (Sequential Forward Selection), SBS (Sequential Backward Selection), SFFS (Sequential Floating Forward Selection), etc. are widely used as traditional feature selection techniques. It is also true that if there are many risks and many features, there is a limitation in that the performance for classification prediction is poor and it takes a lot of learning time. Therefore, in this study, we propose an improved feature selection algorithm to enhance the effectiveness of the existing campaign. The purpose of this study is to improve the existing SFFS sequential method in the process of searching for feature subsets that are the basis for improving machine learning model performance using statistical characteristics of the data to be processed in the campaign system. Through this, features that have a lot of influence on performance are first derived, features that have a negative effect are removed, and then the sequential method is applied to increase the efficiency for search performance and to apply an improved algorithm to enable generalized prediction. Through this, it was confirmed that the proposed model showed better search and prediction performance than the traditional greed algorithm. Compared with the original data set, greed algorithm, genetic algorithm (GA), and recursive feature elimination (RFE), the campaign success prediction was higher. In addition, when performing campaign success prediction, the improved feature selection algorithm was found to be helpful in analyzing and interpreting the prediction results by providing the importance of the derived features. This is important features such as age, customer rating, and sales, which were previously known statistically. Unlike the previous campaign planners, features such as the combined product name, average 3-month data consumption rate, and the last 3-month wireless data usage were unexpectedly selected as important features for the campaign response, which they rarely used to select campaign targets. It was confirmed that base attributes can also be very important features depending on the type of campaign. Through this, it is possible to analyze and understand the important characteristics of each campaign type.