1,721,039 research outputs found
Structural dynamics of keyword networks: Liquid crystal display and plasma display panel cases
No full textThis study focuses on understanding scientific evolution by using keyword co-occurrence networks, where keywords appearing in a scientific article are linked with a weight equal to the number of co-occurrences. To characterize structural changes of the network, we examine distributions of sums of weights by node over time. In particular, a change of power-law behavior is utilized to explore scientific evolution, such as emerging scientific paradigms and advancing normal science. As an illustration of the method used, the development of Liquid Crystal Displays (LCDs) and Plasma Display Panels (PDPs) is tracked. We detect two-tiered power-law distributions in the initial stage of scientific growth in both technologies due to differences in research intensity between two groups. The groups of keywords more likely to attract researchers' interest than others are incrementally developed until the mid-2000s to overtake those prior. Finally, we can capture a merging point of the dichotomous structure of PDPs but LCDs maintain the structural separation throughout the adjustment area. We expect that this structural investigation of keyword co-occurrence networks provides an indicator to diagnose the research evolution in that field. (C) 2016 Published by Elsevier B.V.1120sciessciscopu
Application of gravity model on the Korean urban bus network
No full textMobility models have been studied to describe the underlying mechanism of human mobility. The mobility patterns in various transportation systems were understood with the gravity model by estimating the traffic as a simple function of population and distance. Compared to most studies on large-scale systems, we focused on the validity and characteristics of gravity model for intraurban mobility. Several variations of gravity model are applied on the urban bus systems of five medium-sized cities in Korea. The gravity model successfully estimates the intraurban traffic without universal exponents for cities. From the change of exponents by predictor types, we figure out the effect by a non-trivial relation between traffic and population in the urban areas. (C) 2016 Elsevier B.V. All rights reserved.1131Nsciescopu
A strategic management approach for Korean public research institutes based on bibliometric investigation
No full textAs a process of knowledge manufacture, research activities are interpretable from the well-known economic perspectives of production and consumption. We therefore aim to investigate the contents of institutes' research portfolio from a knowledge production and consumption perspective. A Hirsch-type-index and mean reference age serve as indicators of knowledge activity. Based on both indicators, we divide research institutes into four categories. This approach is applied to Government-funded Research Institutes (GRIs) in Korea that are dedicated to major disciplines within science and technology. We recognize GRIs' contribution to the development in the characteristic areas. A tailored enhancement strategy is discussed for promising GRIs to improve their knowledge activity. Our results have implications for GRIs' research portfolio management. In terms of R&D portfolio constitution, we reveal that Korean GRIs' research themes concentrate on the strategic research such as chemistry, information and communications technology, and semiconductors. We also point out the possible fragility of the national R&D system, as national leading technologies are reliant on a few giant institutes.X1110Nsciessciscopu
The double power law in human collaboration behavior: The case of Wikipedia
No full textWe study human behavior in terms of the inter-event time distribution of revision behavior on Wikipedia, an online collaborative encyclopedia. We observe a double power law distribution for the inter-editing behavior at the population level and a single power law distribution at the individual level. Although interactions between users are indirect or moderate on Wikipedia, we determine that the synchronized editing behavior among users plays a key role in determining the slope of the tail of the double power law distribution. (C) 2016 Elsevier B.V. All rights reserved.1141sciescopu
DETERMINATION OF DESIGN ALTERNATIVES AND PERFORMANCE CRITERIA FOR SAFETY SYSTEMS IN A NUCLEAR-POWER-PLANT VIA SIMULATED ANNEALING
No full textThis study presents an efficient methodology that derives design alternatives and performance criteria for safety functions/systems in commercial nuclear power plants. Determination of the design alternatives and intermediate-level performance criteria is posed as a reliability allocation problem. The reliability allocation is performed in a single step by means of the concept of two-tier noninferior solutions in the objective and risk spaces within the top-level probabilistic safety criteria (PSC). Two kinds of two-tier noninferior solutions are obtained: desirable design alternatives and intolerable intermediate-level PSC of safety functions/systems. The weighted Chebyshev norm (WCN) approach with an improved Metropolis algorithm in simulated annealing is used to find the two-tier noninferior solutions. This is very efficient in searching for the global minimum of the difficult multiobjective optimization problem (MOP) which results from strong nonlinearity of a probabilistic safety assessment (PSA) model and nonconvexity of the problem. The methodology developed in this study can be used as an efficient design tool for desirable safety function/system alternatives and for the determination of intermediate-level performance criteria. The methodology is applied to a realistic streamlined PSA model that is developed based on the PSA results of the Surry Unit 1 nuclear power plant. The methodology developed in this study is very efficient in providing the intolerable intermediate-level PSC and desirable design alternatives of safety functions/systems
Intercity express bus flow in Korea and its network analysis
No full textWe investigated the express bus flow in Korea and its network topology. By using a gravity type model, we found that the bus flow between cities depends on the square root of the product of the population size of city A and the population size of city B. On the other hand, the total bus flow of a city depends on only its population size. These different dependences on population originate from the network property of the express bus network. (c) 2012 Elsevier B.V. All rights reserved.X115sciescopu
EFFECT OF STRETCHING TREATMENT ON THE PRECIPITATION KINETICS OF AN AL-2.33WT-PERCENT-LI-2.48WT-PERCENT-CU ALLOY
No full textAccuracy test for link prediction in terms of similarity index: The case of WS and BA models
No full textLink prediction is a technique that uses the topological information in a given network to infer the missing links in it. Since past research on link prediction has primarily focused on enhancing performance for given empirical systems, negligible attention has been devoted to link prediction with regard to network models. In this paper, we thus apply link prediction to two network models: The Watts-Strogatz (WS) model and Barabasi-Albert (BA) model. We attempt to gain a better understanding of the relation between accuracy and each network parameter (mean degree, the number of nodes and the rewiring probability in the WS model) through network models. Six similarity indices are used, with precision and area under the ROC curve (AUC) value as the accuracy metrics. We observe a positive correlation between mean degree and accuracy, and size independence of the AUC value. (C) 2015 Elsevier B.V. All rights reserved.X11119Nsciescopu
Relationship between efficiency and predictability in stock price change
No full textIn this study, we evaluate the relationship between efficiency and predictability in the stock market. The efficiency, which is the issue addressed by the weak-form efficient market hypothesis, is calculated using the Hurst exponent and the approximate entropy (ApEn). The predictability corresponds to the hit-rate; this is the rate of consistency between the direction of the actual price change and that of the predicted price change, as calculated via the nearest neighbor prediction method. We determine that the Hurst exponent and the ApEn value are negatively correlated. However, predictability is positively correlated with the Hurst exponent. (C) 2008 Elsevier B.V. All rights reserved.X112019sciescopu
Usefulness of Self-Expandable Stent for Recanalization of Intracranial Atherosclerotic Disease: Preliminary Experience with Enterprise Stent
Full text linkPURPOSE: The purpose of this preliminary study is to evaluate the efficacy and safety of the Enterprise stent for intracranial atherosclerotic disease (ICAD) in patients who presented with acute stroke due to vessel steno-occlusion and in patients with symptomatic disease despite optimum medical management. MATERIALS AND METHODS: A retrospective data analysis was performed on 15 consecutive patients who were treated with Enterprise stenting for recanalization of symptomatic intracranial steno-occlusive arteries due to underlying ICAD. Their clinical and radiological data were reviewed to evaluate procedural results, periprocedural and postprocedural complications, and clinical outcome. RESULTS: Enterprise stents were deployed as a rescue method in 15 patients for recanalization of steno-occlusion. All patients achieved final modified thrombolysis in cerebral infarction (mTICI) score improvement (53.3% with a mTICI score from 0 to 2b or 3, 46.7% with a mTICI score from 1 to 3). Two postprocedural complications (1 symptomatic intracranial hemorrhage and 1 severe brain edema, 13.3%) occurred among 15 patients. Among 12 patients with acute ischemic stroke (AIS), 6 patients (50%) had improvement in their National Institute of Health Stroke Scale of more than 4 at discharge. Seven patients (58.3%) had a good functional outcome with 3-month modified Rankin Score (mRS
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