Bifurcation and Stability Problems in Fluid Dynamics

Thesis (PhD) - Indiana University, Mathematics, 2007My dissertation is to study the bifurcation, stability and phase transitions of incompressible fluid flows. Bifurcation is a versatile methodology to trace solutions of physical problems along with the system parameter and to investigate their structure. The study is oriented toward a nonlinear dynamic theory for the underlying physical problems consisting of 1)complete bifurcation when the system parameter crosses some critical values, 2)asymptotic stability of bifurcated solutions and 3)the structure/pattern of the bifurcated solutions and phase transitions in the physical spaces. The study in the first two directions is related to application of a new bifurcation theory, called attractor bifurcation, which was developed by T. Ma and S. Wang. The third direction of the study is related to geometric study of fluid flows and includes structural stability theory

Exploratory Study on the Applicability of the Public Service Motivation Concept to South Korea

Recently, a group of scholars has explored the possible variations in public service motivation (PSM) according to sociocultural context. Despite the theoretical consensus on the interplay between social conditions and PSM, we still lack empirical research on how PSM can be applied to distinctive sociocultural contexts across the world. Bearing these points in mind, this research examines whether the concept of PSM can be applied to South Korea. Specifically, this study examines various motivational grounds for public service manifested in occupational meanings, whether the identified dimensions can be integrated into the concept of PSM, and how such motivational characteristics can be considered as particular dimensions of PSM in South Korea. In addition, various antecedents of PSM suggested in previous literature are reexamined. Due to the nature of these research questions, this study used a mixed-methods approach to explore whether, and in what ways, PSM could be applied to South Korean society. The two methods used were personal interviews using the grounded-theory approach, and survey data analysis, by means of structural equation modeling (i.e., measurement models) and hierarchical regression analysis. The overall findings of this study about Korean society supported the core of the conceptual definition of PSM. However, they also provided evidence that PSM can have distinctive dimensions and different combinations of dimensions as a manifestation of social contexts (i.e., Confucian legacy, administrative tradition, shared perception of the desirable role of public servants and government). In particular, a critical aspect of Korean respondents’ motivation for public service was based on their personal interests and on their need to have a certain level of “influence” on other people and on the society, in an attempt to “contribute to the development” of social progress. These empirical results revealed variability of rational and normative aspects of PSM in the Korean contexts; however, the affective aspects – self-sacrifice and compassion— could be applied across the board. With regard to the antecedents of PSM, the role of institutionalization in organizational settings (e.g., formation of social identity, value socialization) provided evidence in support of the previously suggested theoretical arguments

Delineation of high resolution climate regions over the Korean Peninsula using machine learning approaches

In this research, climate classification maps over the Korean Peninsula at 1 km resolution were generated using the satellite-based climatic variables of monthly temperature and precipitation based on machine learning approaches. Random forest (RF), artificial neural networks (ANN), k-nearest neighbor (KNN), logistic regression (LR), and support vector machines (SVM) were used to develop models. Training and validation of these models were conducted using in-situ observations from the Korea Meteorological Administration (KMA) from 2001 to 2016. The rule of the traditional Koppen-Geiger (K-G) climate classification was used to classify climate regions. The input variables were land surface temperature (LST) of the Moderate Resolution Imaging Spectroradiometer (MODIS), monthly precipitation data from the Tropical Rainfall Measuring Mission (TRMM) 3B43 product, and the Digital Elevation Map (DEM) from the Shuttle Radar Topography Mission (SRTM). The overall accuracy (OA) based on validation data from 2001 to 2016 for all models was high over 95%. DEM and minimum winter temperature were two distinct variables over the study area with particularly high relative importance. ANN produced more realistic spatial distribution of the classified climates despite having a slightly lower OA than the others. The accuracy of the models using high altitudinal in-situ data of the Mountain Meteorology Observation System (MMOS) was also assessed. Although the data length of the MMOS data was relatively short (2013 to 2017), it proved that the snowy, dry and cold winter and cool summer class (Dwc) is widely located in the eastern coastal region of South Korea. Temporal shifting of climate was examined through a comparison of climate maps produced by period: from 1950 to 2000, from 1983 to 2000, and from 2001 to 2013. A shrinking trend of snow classes (D) over the Korean Peninsula was clearly observed from the ANN-based climate classification results. Shifting trends of climate with the decrease/increase of snow (D)/temperate (C) classes were clearly shown in the maps produced using the proposed approaches, consistent with the results from the reanalysis data of the Climatic Research Unit (CRU) and Global Precipitation Climatology Centre (GPCC)

The influence of authoritarian organizational culture in the South Korean civil service: organization of land management, organization management, human resource management, healthcare and social welfare

In earlier work by the author, human resource management in the South Korean public sector was analysed in terms of professionalism, sustainability, transparency, motivation and support systems (Park, 2015). One finding was that when the central government establishes and introduces a new system in the public sector, even though the new system has limitations and the majority of staff know the limitations they rarely report them to their seniors or the central government for solution. The earlier study suggested that the finding may originate from an organizational culture based on military style. Many civil servants have also pointed out the necessity of escape from an administrative culture based on authoritarianism for advanced administration, but the administrative culture has not been improved, according to surveys conducted between 2007 and 2016 (Kim, 2016). As for authoritarian organizational culture, this study also has referred to experience of military service, the past military regime, Confucianism, the East Asian model and Asian values. From this point of view, this study has reviewed authoritarian organizational culture conceptually and analysed the nature and effects of organizational culture in the South Korean civil service in terms of authoritarianism. For this study, there are five research questions: (1) What is the nature of authoritarian organizational culture?; (2) To what extent is authoritarian organizational culture present in the South Korean civil service?; (3) What are the effects of authoritarian organizational culture in the South Korean civil service?; (4) Has authoritarian organizational culture changed in the South Korean civil service?; and (5) How does authoritarian organizational culture operate in the South Korean civil service? Authoritarian organizational culture has been conceptualized in terms of collectivism, Confucianism, paternalism and bureaucracy in this study. Based on the conceptual approach, the key element of authoritarian organizational culture is hierarchy and conformity. In particular, the top-down approach is strong, while the bottom-up approach is weak in the hierarchical structure. Aside from the two key elements, other elements are also involved in authoritarian organizational culture such as loyalty, respect, group orientation, expertise, and power and resource inequality. When beginning this study, finding a strong authoritarian organizational culture in the South Korean civil service was expected. According to the findings, however, the organizational culture in the South Korean civil service is not as authoritarian as civil servants think, although the civil service does have some residual authoritarian characteristics. Around 70% of the respondents said that the South Korean civil service shows authoritarian tendencies, when asked directly. However, the response in most general scenarios showed flexible and reasonable tendencies. On the other hand, the response in more serious scenarios, such as the audit scenario, did show authoritarian tendencies. Over 80% of the survey respondents perceived authoritarian organizational culture negatively. Inefficiency, low morale, lack of creativity and communication, and risk of corruption and improper decision-making were also referred to as negative effects. On the other hand, positive effects were also pointed out, such as rapidity, efficiency, convenience, high morale, organization management and cohesion of professional or small groups. Efficiency and morale were referred to from both negative and positive perspectives. Over 60% of the survey respondents in this study said that the organizational culture in the South Korean civil service has changed towards a flexible culture. On the other hand, one finding suggested that recently the younger generation has shown authoritarian tendencies, while the organizational culture has changed from an authoritarian to a flexible style. Given the two perspectives, it could be argued that organizational culture has changed from an authoritarian to a flexible organizational culture but the change does not mean that younger staff are less authoritarian than older staff. Political elements and promotion are deeply related with the operation of authoritarian organizational culture. For instance, elections are of paramount importance to politicians and certain interest groups are highly influential in elections. In the relationship between politicians and interest groups, politicians ask for the support of interest groups during an election period. After the elections, the group demands protection and expansion of their interests from the (elected) politicians, and the elected politicians, with the support of the interest group, instruct civil servants to meet these demands directly and indirectly. In the civil service, compliance with instructions from the top level is highly important because it affects not only current but also future human resource affairs directly or indirectly, such as promotion, disciplinary measures and transfer. In order to be promoted or not to suffer disadvantages, civil servants follow even political or controversial instructions, which eventually strengthens and maintains the authoritarian organizational culture in the civil service. In particular, there are more possibilities for authoritarian organizational culture to work through promotion and political elements at the senior level than the junior level. There are few possibilities for politics and promotion to be used to maintain and reinforce authoritarianism at the junior level because there are many positions at junior levels and junior civil servants can be promoted without political elements. On the other hand, there are comparatively more possibilities for politics and promotion to be used to maintain and reinforce authoritarianism at the senior level. The senior has more authority and power than the junior, while senior positions are few. Therefore, political elements could be deeply involved in promotion to senior positions, although not all promotions at the senior levels are closely related with political elements. In addition, some civil servants could prepare for or consider political activities, such as running for election for a certain political party

Koreas Experiences with Development: Revisiting MDGs from a Time Perspective

As interest in Millennium Development Goals surges, criticism targeting their applicability to developing and underdeveloped countries has also sharply increased. While Millennium Development Goals highlight important development goals, targets, and indices, they lack a time perspective. Koreas experience suggests that it is impractical to pursue all developmental goals simultaneously. Instead, prioritizing goals based on country-specific contexts and approaching them sequentially is an approach better suited to underdeveloped and developing countries, because of their limited resources and underdeveloped social conditions, and can be more effective in achieving multiple goals in the long term

Measurement-based Close-in Path Loss Modeling with Diffraction for Rural Long-distance Communications

In this letter, we investigate rural large-scale path loss models based on the measurements in a central area of South Korea (rural area) in spring. In particular, we develop new close-in (CI) path loss models incorporating a diffraction component. The transmitter used in the measurement system is located on a hill and utilizes omnidirectional antennas operating at 1400 and 2250 MHz frequencies. The receiver is also equipped with omnidirectional antennas and measures at positions totaling 3,858 (1,262 positions for LOS and 2,596 positions for NLOS) and 4,957 (1,427 positions for LOS and 3,530 positions for NLOS) for 1400 and 2250 MHz, respectively. This research demonstrates that the newly developed CI path loss models incorporating a diffraction component significantly reduce standard deviations (STD) and are independent of frequency, especially for LOS beyond the first meter of propagation, making them suitable for use with frequencies up to a millimeter-wave.Comment: 5 pages, 5 figure