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Ilsang Woo,Areum Lee,Seung Chai Jung,Hyunna Lee,Namkug Kim,조세진,Donghyun Kim,Jungbin Lee,선우준,Dong-Wha Kang 대한영상의학회 2019 Korean Journal of Radiology Vol.20 No.8
Objective: To develop algorithms using convolutional neural networks (CNNs) for automatic segmentation of acute ischemic lesions on diffusion-weighted imaging (DWI) and compare them with conventional algorithms, including a thresholding-based segmentation. Materials and Methods: Between September 2005 and August 2015, 429 patients presenting with acute cerebral ischemia (training:validation:test set = 246:89:94) were retrospectively enrolled in this study, which was performed under Institutional Review Board approval. Ground truth segmentations for acute ischemic lesions on DWI were manually drawn under the consensus of two expert radiologists. CNN algorithms were developed using two-dimensional U-Net with squeeze-and-excitation blocks (U-Net) and a DenseNet with squeeze-and-excitation blocks (DenseNet) with squeeze-and-excitation operations for automatic segmentation of acute ischemic lesions on DWI. The CNN algorithms were compared with conventional algorithms based on DWI and the apparent diffusion coefficient (ADC) signal intensity. The performances of the algorithms were assessed using the Dice index with 5-fold cross-validation. The Dice indices were analyzed according to infarct volumes (< 10 mL, ≥ 10 mL), number of infarcts (≤ 5, 6–10, ≥ 11), and b-value of 1000 (b1000) signal intensities (< 50, 50–100, > 100), time intervals to DWI, and DWI protocols. Results: The CNN algorithms were significantly superior to conventional algorithms (p < 0.001). Dice indices for the CNN algorithms were 0.85 for U-Net and DenseNet and 0.86 for an ensemble of U-Net and DenseNet, while the indices were 0.58 for ADC-b1000 and b1000-ADC and 0.52 for the commercial ADC algorithm. The Dice indices for small and large lesions, respectively, were 0.81 and 0.88 with U-Net, 0.80 and 0.88 with DenseNet, and 0.82 and 0.89 with the ensemble of U-Net and DenseNet. The CNN algorithms showed significant differences in Dice indices according to infarct volumes (p < 0.001). Conclusion: The CNN algorithm for automatic segmentation of acute ischemic lesions on DWI achieved Dice indices greater than or equal to 0.85 and showed superior performance to conventional algorithms.
Mind-Wandering in task-oriented group : An application of The Theory of Interpersonal Behavior
Ilsang Ko 한국경영정보학회 2023 한국경영정보학회 학술대회논문집 Vol.2023 No.06
Mind-wandering consists of the process of thinking task-unrelated thoughts (TUT) during task performance. In a task-oriented group, the subject and the subject matter of team members’ mindwandering episodes are of critical interest to the team's performance. However, many writers suggested that mind-wandering may be more common in some circumstances than others. Understanding the social-psychological factors that precipitate mind-wandering in a technological setting is necessary because mind-wandering influences numerous outcomes connected with taskoriented groups. Therefore, this paper aims to explore whether certain social-psychological factors predict self-reported engagement behavior in a number of TUT in the assessment of attitudes. Specifically, our objectives are to put in place behavioral experience sampling methodologies and probe-caught methodologies for measuring online mind-wandering. We intend to design a set of virtual teams using laboratory experiments followed by survey. Our study aims to add to the body of research on virtual teams and mind-wandering by determining the relation between attitude, social factors, and emotions of team members and self-reported engagement in TUT.
Equilibrium and dynamical evolution of a self‐gravitating system embedded in a potential well
Yoon, Ilsang,Lee, Hyung Mok,Hong, Jongsuk Blackwell Publishing Ltd 2011 Monthly notices of the Royal Astronomical Society Vol.414 No.3
<P><B>ABSTRACT</B></P><P>Isothermal and self‐gravitating systems bound by non‐conducting and conducting walls are known to be unstable if the density contrast between the centre and the boundary exceeds critical values. We investigate the equilibrium and dynamical evolution of isothermal and self‐gravitating systems embedded in a potential well, which can be the situation of many astrophysical objects such as the central parts of the galaxies, or clusters of galaxies with potential dominated by dark matter, but is still limited to the case where the potential well is fixed during the evolution. As the ratio between the depth of the surrounding potential well and the potential of the embedded system becomes large, the potential well becomes effectively the same boundary condition as the conducting wall, which behaves like a thermal heat bath. We also use the direct <I>N</I>‐body simulation code, <SMALL>nbody6</SMALL> to simulate the dynamical evolution of the stellar system embedded in potential wells and propose the equilibrium models for this system. In a deep potential well, which is analogous to the heat bath with high temperature, the embedded self‐gravitating system is dynamically hot, and loosely bound or can be unbound since the kinetic energy increases due to the heating by the potential well. On the other hand, the system undergoes core collapse by self‐gravity when a potential well is shallow. Binary heating can stop the collapse and leads to the expansion, but the evolution is very slow because the potential as a heat bath can absorb the energy generated by the binaries. The system can be regarded as quasi‐static. Density and velocity dispersion profiles from the <I>N</I>‐body simulations in the final quasi‐equilibrium state are similar to our equilibrium models assumed to be in thermal equilibrium with the potential well.</P>
Ko, Ilsang 한국경영과학회 1997 한국경영과학회지 Vol.22 No.3
An AI approach with tabu search is designed to solve multi-level knapsack problems. The approach performs intelligent actions with memories of historic data and learning effect. These actions are developed not only by observing the attributes of the optimal solution, the solution space, and its corresponding path to the optimal, but also by applying human intelligence, experience, and intuition with respect to the search strategies. The approach intensifies, or diversifies the search process appropriately in time and space. In order to create a good neighborhood structure, this approach uses two powerful choice rules that emphasize the impact of candidate variables on the current solution with respect to their profit contribution. "Pseudo moves." similar to "aspirations" support these choice rules during the evaluation process. For the purpose of visiting as many relevant points as possible, strategic oscillation between feasible and infeasible solutions around the boundary is applied. To avoid redundant moves, short-term (tabu-lists), intermediate-term (cycle-detection), and long-term (recording frequency and significant solutions for diversification) memories are used. Test results show that among the 45 generated problems (these problems pose significant or insurmountable challenges to exact methods) the approach produces the optimal solutions in 39 cases.
Ko, Ilsang 조선대학교 경영경제연구소 1996 經營經濟硏究 = Management and economics research Vol.19 No.2
In building a system within an object-oriented environment, several factors of problem characteristics should be considered carefully to determine what kind of objects be created, what kind of relationships between objects be developed to reach a parent-child structure, and what attributes and behaviors be defined within each object. These factors include the decomposability of problem domain, its stability, its structuredness, the role of entities, their changeability, their number, their complexity, their possible groups, and the decomposability of processes. The same factors not only impact important OOAD design decisions, but also be used as a tool to assess whether the application system is well-designed or not. Two prototypical models, the City Network System and the Oochnori Gameboard, are developed and programmed in Smalltalk, a well-known object-oriented programming language. These models are compared together in order to explain the impact of problem characteristics on design constructs. The suggested factors contribute to making important design decisions on class requirements, especially on class groupings and hierarchies. This study also suggests dozens of questions to be tested to evaluate the design of the application system.