• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.1
• /
• pp.355-365
• /
• 1991

New definition for the interaction of flames is introduced and interacting turbulent diffusion flames issuing from two rectangular nozzles are investigated on the basis of the definition. Theoretical study through numerical model is carried out and experiment for validation is conducted. The characteristics of interaction due to the variation of major parameters such as nozzle spacing, Reynolds number and nozzle aspect ratio are studied. Results show that strong interaction occurs for small nozzle spacing, small Reynolds number and large aspect ratio. In order of their magnitude, the intensity of interactions on the individual transport mechanism is momentum, heat and mass. It is also found that interaction makes flames longer, tilted and finally merged. Increase of velocities and temperature, decrease of oxygen concentration and depression of turbulence are occurred in the region between flames.

• Journal of the Korean Chemical Society
• /
• v.21 no.5
• /
• pp.339-352
• /
• 1977

The authors' theory developed in the preceding Paper 1 was applied to plastic deformation of ceramics, metals, alloys and single crystals. For polycrystalline substances, the flow mechanisms due to dislocation movement and grain boundary movement appear together or separately according to the experimental conditions whereas for single crystals, only the mechanism of dislocation movement appears. The parameters appearing in the flow equations $({\alpha}_{d1},\;1/{\beta}_{d1})and\;({\alpha}_{gj}/X_{gj},\;1/{\beta}_{gj})$ (j = 1 or 2), and the activation enthalpies ${\Delta}H_{k1}^{\neq}$ (k = d or g) were determined and tabulated. Here, the subscript d1 indicates the first kind of dislocation flow units and gj expresses the jth kind of grain boundary flow units. The predictions of the theory were compared with experiment with good agreement. Concerning the activation enthalpies, it was found that ${\Delta}H_{d1}^{\neq}$ 〉{\Delta}H_{g1}^{\neq}$ and that the former agrees with the activation enthalpy for bulk self-diffusion whereas the latter agrees with the activation enthalpy for grain boundary self-diffusion. These facts support the adequacy of the authors' theory which is considered as a generalized theory of plastic deformation.

• Nuclear Engineering and Technology
• /
• v.20 no.1
• /
• pp.9-18
• /
• 1988

Previously determining the fuel loading pattern is based on the trial and error method. For a candidate pattern, the core analysis is performed and the pattern is examined whether it satisfies the imposed constraints such as the power peaking or not. The pattern, then, is revised by the shuffling of assemblies and the revision is repeated until all of the conditions are met. This method unavoidably requires many iterative diffusion calculations, computing times and accumulated experiences. To overcome these disadvantages, a new method which is called backward diffusion calculation is introduced. If the most desirable power distribution is already known, the optimal loading pattern can be obtained by solving the backward diffusion equation with simple calculation. In this study, the basic equation for the backward diffusion calculation is derived and the optimal power and fuel distributions are searched in one-dimensional cylindrical geometry by using the proposed method. In addition, the basis to determine the optimal power and fuel distributions is suggested for the real core geometry.

• Journal of Technology Innovation
• /
• v.27 no.3
• /
• pp.113-142
• /
• 2019

Based on the Knowledge Spillover Theory of Entrepreneurship, this study analyzes the relationship between technological entrepreneurship and national competitiveness. It also analyzes how innovation-driven economy moderates this relationship. Using data on technological entrepreneurship, national competitiveness indexes and economy development stages from 83 countries over 2011 to 2014, this study finds that a ratio of technology-based start-ups in a country has a U-shaped relationship with national competitiveness. this study also finds that countries that are in the innovation-driven economy strengthen this relationship. This finding shows that a higher ratio of technology-based start-ups of a country does not have unconditional positive effects on national competitiveness, thus, related environments and conditions should be elaborately matched. In particular, this finding also implies that policies related to technology-based start-ups should have a proper fit with the level of economic development of the country so that the positive effects of technological entrepreneurship on national competitiveness can be strengthened.

• Water for future
• /
• v.27 no.1
• /
• pp.123-131
• /
• 1994

A plunge pool is often employed as an energy-dissipating device at the end of a spillway or a pipe culvert. A jet from spillways or pipes frequently generates a scour hole which threatens the stability of the hydraulic structure. Existing scour prediction formulas of plunge pool of spillways or pipe culverts give a wide range of scour depths, and it is, therefore, difficult to accurately predict those scour depths. In this study, a new experimental method and new scour prediction formulas under submerged circular jet for large bed materials with shallow tailwater depths were developed. A major variale, which was not used in previous scour prediction equations, was the ratio of jet size to bed material size. In this study, jet momentum acting on a bed particle and jet diffustion theory were employed to derive scour prediction formulas. Four theoretical formulas were suggested for the two regions of jet diffusion, i.e., the region of flow establishment and the region of established flow. The semi-theoretically developed scour prediction formulas showed close agreement with laboratory experiments performed on a movable bed made of large spherical particles.

• Journal of Internet Computing and Services
• /
• v.18 no.6
• /
• pp.101-112
• /
• 2017

The purpose of this study was to examine the factors affecting innovation resistance and intention of use of social TV non-users focused on innovation diffusion theory and innovation resistance model. The results were as follows: First, compatibility among perceived innovation characteristics by social TV non-users influenced negatively on innovation resistance, and complexity among perceived innovation characteristics by social TV non-users influenced positively on innovation resistance. Second, perceived risk by social TV non-users influenced positively on innovation resistance. Third, compatibility among perceived innovation characteristics by social TV non-users influenced positively on social TV intention to use. And complexity among perceived innovation characteristics by social TV non-users influenced negatively on social TV intention to use. Fourth, perceived risk by social TV non-users influenced not significantly on social TV intention to use. Fifth, innovation resistance by social TV non-users influenced negatively on social TV intention to use.

• Management & Information Systems Review
• /
• v.36 no.2
• /
• pp.239-260
• /
• 2017

This study is to explore the factors that may affect the social adoption diffusion of innovative technology, focusing on smart mobility. It reviewed the literature on theory of social acceptance-diffusion and technology adoption model of innovative products, set up structural equation model that includes the causes and effects of perceived usefulness(the nexus among influences, perceived usefulness and purchase intention) and empirically tested the relationship. The survey, covering 534 non-users, was conducted from August 1, 2016 through August 12, 2016. The results show that compatibility and relative advantage significantly positively affect adoption intention through perceived usefulness, and that communication significantly negatively affect. However, complexity and service quality do not have significant positive effects on perceived intention and purchase intention. Some implications to promote social acceptance of smart mobility based on the results of the study are offered.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.3C
• /
• pp.314-319
• /
• 2010

The chirp spread spectrum (CSS) technique that spreads the data signal over a wider frequency band via chirp signal for transmission has attracted much attention in the field of wireless communications due to capability to resist multipath fading signals. However, there has been little mathematical analysis for the performance of CSS-based communication systems in the multipath fading environments. In this paper, we study the influence of the multipath channel on the direct modulation (DM) scheme with M-ary phase shift keying (MPSK). When a chirp signal is transmitted on the Rayleigh fading channel and affected by additive white Gaussian noise (AWGN), we derive the theoretical performance. From numerical results, it is confirmed that the analytic symbol error rate (SER) agrees closely with the empirical SER.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2017.10a
• /
• pp.140-141
• /
• 2017

Big data analysis, in the large amount of data stored as the data warehouse which it refers the process of discovering meaningful new correlations, patterns, trends and creating new values. Thus, Big data analysis is an effective analysis of various big data that exist all over the world such as social big data, machine to machine (M2M) sensor data, and corporate customer relationship management data. In the big data era, it has become more important to effectively analyze not only structured data that is well organized in the database, but also unstructured big data such as the internet, social network services, and explosively generated web documents, e-mails, and social data in mobile environments. By the way, a meta analysis refers to a statistical literature synthesis method from the quantitative results of many known empirical studies. We reviewed a total of 750 samples among 50 studies published on the topic related as IDT between 2000 and 2017 in Korea.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2022.05a
• /
• pp.4-4
• /
• 2022

낙동강 하구 환경/생태 복원을 위하여 "해수유입"으로 하구환경을 조성하는 사업이 추진되고 있으며, 해수 유입 규모와 빈도에 따른 생태환경변화를 예측하는 연구수요가 증가하고 있는 상황이다. 보다 구체적으로는 단기간의 해수유입에 의한 흐름 및 염분 확산범위 예측과 더불어 보다 장기간의 지형변화, 수질환경 변화, 생태환경 변화 등에 대한 예측이 필요한 상황이다. 그리고 그 예측의 대부분을 수치모델에 크게 의존하고 있는 상황이다. 그러나, 수치모형을 이용한 단기 예측은 가까운 미래에 대한 입력조건을 사용하여야 하기 때문에 입력조건에 대한 불확실성이 포함되고, 환경생태모형의 불확실성에 따른 예측 한계 등으로 인하여 오차가 누적되기 때문에 직접적인 활용에 크게 제한이 따를 수 있다. 또한 운영과정에서 어떤 분산, 편향 오차 등이 지속적으로 발생하는 경우, 모델 예측 결과에 대한 신뢰수준이 크게 감소하기 때문에 모델의 적절한 운영기법이 요구된다. 모델은 관심을 가지는 자연현상에 대한 근사(approximation)이고, 예상하지 못한 오차가 발생할 수 있기 때문에 관측 자료를 이용한 자료동화(data assimilation) 과정이 운영모델에서는 필수적인 부분이다. 이론적인 기반이 탄탄한 유체역학 기반 기상예측의 경우에도, 가용한 모든 지점의 관측 자료를 이용한 자료 동화과정을 통하여 모델 예측 결과를 개선하여 나가는 과정을 포함하여 운영하고 있다. 이 과정이 포함하는 중요한 개념은 수치모델이 가지고 있는 (예측 수준의) 한계를 인정하고, 수치모델에 전적으로 의존하는 것이 아니라 관측 자료를 이용하여 그 한계를 저감하여 나가는 과정이다. 모니터링은 모델의 한계를 알려주는 지표이다. 모델링과 모니터링의 불가피한 상호의존 관계를 의미하는 이 개념은 단기간의 흐름, 염분 확산 예측으로 한정되지 않고, 장기적인 변화가 예상되는 생태환경변화 모델에도 적용이 된다. 즉각적인 변화보다는 장기적인 관점에서 파악하여야 하는 생태학적인 변화는 보다 다양한 인자가 관여하기 때문에 어떤 측면에서는 모델보다는 적절한 빈도와 항목에 대한 관측계획 수립(monitoring design)이 더 중요하다고 할 수 있다. 이론적인 질량보존(mass conservation) 방정식을 기반으로 하는 모델은 다양한 현실적인 인자의 영향을 받기 때문에 모델의 한계를 인정하고, 모니터링 자료를 적극적으로 활용하여 불확실성을 저감하는 접근방식이 요구된다.