• Journal for History of Mathematics
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• v.30 no.2
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• pp.87-100
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• 2017

The ontological status of Newtonian space-time has been debated under the name of substantivalism-relationism controversy. The debates between the two parties are concerned with the nature of existence of space-time. Substantivalism maintains that the points of space-time have existence analogous to material substance. Relationism claims that space-time should be understood as the framework of possible spatio-temporal relations between bodies. Newtonian space is considered as a three dimensional entity in accordance with our geometric common sense. Yet given that the concept of motion is defined as the change of position throughout time, it is possible to interpret space-time as a 4 dimensional entity. In this essay, substantivalist-relationist debate is considered within the context of non-relativistic 4 dimensional space-time theory. This essay attempts to clarify the dispute over the ontology of space-time by elucidating the relationship between the ontology of space-time, motion, and space-time symmetry.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.387-393
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• 2021

This paper proposes a system to synchronize the time of computers over an unmanned aerial vehicle (UAV) network. With the proposed system, the UAVs can perform missions that require precise relative time. Also, data collected by UAVs can be fused precisely with synchronized time. In the system, to synchronize the time of all computers over the UAV network, two-step synchronization is performed. In the first step, the mission computers of the UAVs are synchronized through the server of the system. After the first step, the mission computers measure time offset between the time of the mission computers and the flight computers. The offset values are delivered to the server. In the second step, virtual time is determined by the server from the collected time offset. The measured offset is compensated by moving the synchronized time of mission computers to the reasonable virtual time. Since only the time of mission computers are controlled, any flight computers that use micro air vehicle link (MAVLink) protocol can be synchronized in the proposed system.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.4
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• pp.405-409
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• 2020

This paper proposes time management system for unmanned aerial vehicle (UAV) network. The computers of the UAVs need time synchronization that time offset does not exceed the minimum interval of data samples for errorless data blending between the computers. The proposed time management system is composed of time synchronization and general management systems for UAV control. The systems communicate each other for time information and control signals. The synchronization system uses improved version of existing time offset estimation that network time protocol (NTP) uses. The time synchronization is operated when the time offset of any UAV exceeds threshold that preconfigured by the general management system. The demonstration of prototype shows stable time synchronization satisfying preconfigured threshold.

• Journal of Family Resource Management and Policy Review
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• v.15 no.3
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• pp.131-151
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• 2011

This study attempted to estimate the level of perceived lack of time in Korean society, to link it to time management and to identify the possible association that accounts for time shortage. I employed the gender perspective in order to reveal the dynamics and complexity of the perception of a lack of time in the population. The sample for the study was drawn from the 1999 and 2009 Korean time diary data collected by the Korean National Statistical Office. From the original data, I selected a sample of second shift families(men and women who are presently working and raising children) living in metropolitan areas(including Seoul and six major urban areas in Korea). The dependent variable was time pressure measured by a single-item question on a four-point likert scale. The results of the study showed that working mothers perceived a greater time shortage as compared to working fathers. The time use pattern showed change during the periods, indicating that people worked fewer hours in paid labor and enjoyed more leisure hours and personal care hours. However, on average, people seemed to have experienced a greater time lack in 2009 as compared to 1999. The results from the ordered logistic regression model revealed that even though there were similarities in the impact of relevant factors, men's perception of a lack of time was more closely linked with their work role and social status, while for women, this perception was influenced by work and family duties. This indicates that Korean working mothers and fathers are facing a double jeopardy of time shortage in terms of combining their work and family roles. As a result, the level of time pressure by gender is converging toward a "never enough" phase. These findings generated policy implications and detailed suggestions.

• Journal of Korean Society of Transportation
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• v.12 no.1
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• pp.55-73
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• 1994

The objective of this research is to evaluate the pedestrian signal time involving green and flashing green times. The minimum pedestrian green indication should give time for pedestrian to start crossing safely, and the flashing green indication should give time to complete the crossing. An average pedestrian crossing speed of 1.1(m/s) was estimated by analyzing the field data which was slower than the 1.2(m/s) currently used. Furthermore, the study proposed that design speed for the flashing green time should be slow speed for considerations pedestrian safety, not the average speed. The 0.78-1.01(m/s) of pedestrian speed was estimated at the elementary school areas that indicated 0.2(m/s) slower than the other areas. The pedestrian starting time (perception/reaction time) and time headway from front to back of herd was estimated to determine minimum pedestrian green time. the pedestrian starting time was estimated to determine minimum pedestrian green time. The pedestrian starting time was ranged 2.52-4.29 seconds. The time interval between the pedestrian rows was found to be 1.25-1.86 seconds, which declines as the pedestrian rows increases, The equation to calculate the pedestrian signal, which declines as the pedestrian rows increases. The equation to calculate the pedestrian signal time is proposed using the pedestrian starting time, the time interval between the pedestrian rows, and pedestrian crossing speed given area types (commercial, business, mixed, and elementary school areas), number of both-directional pedestrians for a cycle, crosswalk length and width.

• Quality Improvement in Health Care
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• v.12 no.1
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• pp.6-16
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• 2006

Objectives : The purpose of this study was to identify the characteristics influencing consultation and waiting time in ambulatory patients. Methods : This study was conducted in a tertiary teaching hospital. Subjects were a total of 10,383 ambulatory patients. Consultation time was measured by time spent for meeting with his/her physician per patient. Waiting time was defined as the time difference between each patient's reserved time and time to meet with his/her physician for ambulatory care. Multiple regression analyses were performed to determine the factors influencing consultation and waiting time. Results : Consultation time was different according to patient' age, previous experience of clinic visit, recent admission history, medical department, specialist care, type of reservation, and day of the week. Significant factors influencing waiting time were patient' age, residential area, previous experience of clinic visit, recent admission history, medical department, specialist care, time spent after ambulatory care begins, and day of the week. Conclusions : The medical department was the strongest factor affecting both consultation time and waiting time. The ambulatory reservation management systems should take into account patient characteristics as well as care-related features.

• Korean Journal of Health Education and Promotion
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• v.33 no.5
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• pp.1-12
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• 2016

Objectives: This study aimed to examine the association between sitting time and BMI-defined low weight and overweight/obesity in Korean adolescents. Methods: Data were from Adolescent Health Behavior Online Survey (KYRBS) in 2015 including 63,345 adolescents aged 12-18 years. The analysis investigated low-weight and overweight/obesity odds ratio(OR) according to study sitting time and leisure sitting time adjusted for sex, school grade, social-economic status(SES), physical activity and sleeping time. Results: After adjusting for sex, school grade, SES, physical activity and sleeping time, study sitting time and leisure sitting time were not significantly associated with low-weight. However, leisure sitting time was positively associated with overweight/obesity. Conclusions: Health program to less sitting time should be established with consideration for differences in risk according to sex, age, SES and active leisure time through the school physical class should be provided to adolescents. Additionally, strategies to promote healthy weight are required to integrate sitting time, physical activity and sleeping time in Korean adolescents.

• Journal of Family Resource Management and Policy Review
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• v.19 no.4
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• pp.55-70
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• 2015

This study aims to clarify the difference between scores for time management practice and the self-evaluation of time use according to time rules in families. This study used data obtained from the first survey on after-school activities in 2008, conducted by the Benesse Educational Research and Development Institute in Japan. The study sample consists of 3,372 middle school students. First, scores for independence and planning were highest in third grade, yet the score for regularity was also lowest in third grade. There will be different lifestyles even among middle school students of the same grade, so it is necessary to consider their characteristics and family rules. Second, the scores for independence, regularity and planning were lowest in groups whose families had rules about time (time rules for curfew, time rules for watching television, time rules for playing games), but in which those rules were not kept. These results were similar for both boys and girls and show that it is more important keep rules rather than to make rules.

• The Korean Journal of Community Living Science
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• v.16 no.1
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• pp.3-14
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• 2005

The importance of time grows greater these days. For that reason, much research has been conducted to investigate time use. In particular, time spent in housework has been a focus in the human ecology. This study aimed to look into the field of research about time spent in housework from 1991 to 2004. To conduct the inquiry, 35 research projects were analyzed by subject. It turned out that most of the research studied the actual state of time use and related variables. Secondly, the research was classified by the measurement method, such as who wrote the time log or questionnaire, what type of response the researcher wanted and what kind of recording method was used. In 30 research projects, respondents wrote in their time logs and questionnaires by themselves. A few research projects presented certain types of behavior as examples of the actions in everyday life. For the recording method, 22 of the projects employed the time log method and 11 used questionnaires. Thirdly, all the research was categorized by the respondent of each project. 14 projects were targeted .at housewives and 14 were for married couples. Lastly, the definition of time spent in housework was used to consider these 35 studies. Most of the research studies defined the 'time spent in housework' as the total amount of the time spent in eating, clothing, housing, family care and household management.

• Journal of the Korean Home Economics Association
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• v.47 no.8
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• pp.13-24
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• 2009

This study investigated college students' time management behavior and time satisfaction according to the use of the time-matrix. Data were collected from 400 college students in Seoul by a self-administered questionnaire. Collected data were subjected to descriptive and comparative statistical analyses using the software SPSS(version 12.0). The conclusions of this study were as follows; 1. The use of time-matrix was categorized into 4 task groups: (1) not urgent but important, (2) urgent but notimportant, (3) neither urgent nor important, (4) urgent and important. 2. Time-management-behavior of planning was categorized into 3 components: standard setting, reality overlapping and implementing into 3 components(i.e., checking, adjusting, facilitating condition). 3. In all domains except overlapping, 'not urgent but importance' was the most popular managerial behavior. 4. However, 'neither urgent nor important' was voted the most popular in terms of managerial satisfaction. This study provides useful knowledge on managerial time-use categorization. Furthermore also contributes towards the knowledge base of time-managerial behaviors and dispels stereotypical-thinking that only bing busy all the time using is an indication of good time management behavior. Finally, this study advocates use of the time-matrix to achieve efficient time management.