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Examining user perceptions of smartwatch through dynamic topic modeling
Ha, T.,Beijnon, B.,Kim, S.,Lee, S.,Kim, J.H. Pergamon Press 2017 TELEMATICS AND INFORMATICS Vol.34 No.7
Since the 2010s, various companies have begun to manufacture wearable smartwatch devices, but the current sales of these products are not impressive. This study investigates how the limitations of the smartwatch are related to perceptual discomforts. Theoretically, this study evaluates the claim that the discomfort that users appear to have with the smartwatch stem from failed remediation. Users perceive the smartwatch more as a set of functional sensors rather than a watch or smartphone. Specifically, from the remediation perspective, the authors asked how users perceive the functions of the smartwatch. This study used dynamic topic modeling for topics on the smartwatch on Reddit. This study reports that the smartwatch has failed to provide a proper way to use the remediated content that it provides. Suggestions for future studies are addressed.
Ha, T.,Lee, S. Pergamon Press 2017 Information processing & management Vol.53 No.5
Recommendation systems are becoming important with the increased availability of online services. A typical approach used in recommendations is collaborative filtering. However, because it largely relies on external relations, such as items-to-items or users-to-users, problems occur when the relations are biased or insufficient. Focusing on that limitation, we here suggest a new method, item-network-based collaborative filtering, which recommends items through four steps. First, the system constructs item networks based on users' item usage history and calculates three types of centrality: betweenness, closeness, and degree. Next, the system secures significant items based on the betweenness centrality of the items in each user's item network. Then, by using the closeness and degree centrality of the secured items, the algorithm predicts preference scores for items and their rank orders from each user's perspective. In the last step, the system organizes a recommendation list based on the predicted scores. To evaluate the performance of our system, we applied it to a sample dataset of 196 Last.fm users' listening history and compared the results with those from existing collaborative filtering methods. The results showed that the suggested method performed better than the basic item-based and user-based collaborative filtering methods in terms of Accuracy, Recall, and F1 scores for top-k recommendations. This indicates that an individual user's item relations can be utilized to remedy the problems occurring when the external relations are biased or insufficient.
Finite element model updating of multi-span greenhouses based on ambient vibration measurements
Ha, T.,Kim, J.,Cho, B.H.,Kim, D.J.,Jung, J.E.,Shin, S.H.,Kim, H. Elsevier Science B.V., Amsterdam 2017 BIOSYSTEMS ENGINEERING Vol.161 No.-
<P>Plastic greenhouses are often designed with low levels of safety. As a result there has been an increasing number of structural failures due to abnormal climatic conditions such as heavy snow and strong winds. Standardised prototypes are often used to facilitate the design process, but these prototypes cannot withstand every extreme loading condition. To aid the accurate evaluation of the disaster resilience of plastic greenhouse structures, finite element (FE) analysis for specific load cases is essential in their design process. In plastic greenhouses, clamp connectors and swivel couplers are generally used to connect beams to columns and arched rafters to purlins, and columns are usually driven directly into the ground to support the entire structure. In the FE analysis, however, connections and supports are idealised as fully rigid or frictionless-pinned, which does not accurately reflect realistic conditions. In this study, ambient vibration tests were performed on two full-scale models to identify the dynamic properties of multi-span greenhouses. FE model updating was then carried out to determine the rigidity factors of connections and supports that yield the same dynamic properties as built structures. The results showed that the modelling of connections and supports causes significant changes in modal frequencies. They also showed that the connection modelling condition contributed more to the dynamic parameters of the multi-span greenhouses than the support modelling condition. (C) 2017 IAgrE. Published by Elsevier Ltd. All rights reserved.</P>
Ha, T.,Jung, Y.,Kim, J.Y.,Park, S.Y.,Kang, D.K.,Kim, T.H. Royal College of Radiologists, etc 2019 Clinical radiology Vol.74 No.10
<P><B>AIM</B></P> <P>To compare the diagnostic performance of abbreviated magnetic resonance imaging (MRI) and full diagnostic MRI with computer-aided diagnosis (CAD) system in patients with a personal history of breast cancer and to evaluate how the kinetic features affect the performance of two radiologists.</P> <P><B>MATERIALS AND METHODS</B></P> <P>Between 1 January 2014 and 31 December 2017, 3,834 breast MRI examinations in 2,310 patients with a history of breast cancer comprised the study population. MRI images were reviewed retrospectively by two radiologists. First, two radiologists independently reviewed T1-weighted images scanned at 90 seconds after the contrast medium injection and T2-weighted images. After 6 months, the two readers reviewed contrast-enhanced T1-weighted images with five consecutive delayed images using CAD. The diagnostic performance of the abbreviated-sequence and full-sequence MRI were compared.</P> <P><B>RESULTS</B></P> <P>Fifty-one intramammary recurrences were detected with breast MRI in 47 patients. Of the 51 tumour recurrences, 36 (70.6%) lesions occurred >3 years after initial cancer surgery and seven (13.7%) lesions at <2 years after initial surgery. The sensitivity and specificity were 92.2–94.1% and 97.6–98.6% on the abbreviated sequence and 94.1–96.1% and 97.9–98.3% on the full diagnostic MRI. Of 51 malignant lesions, six showed delayed persistent pattern, of which three lesions were non-mass enhancement and three lesions were small enhancing masses <1 cm.</P> <P><B>CONCLUSION</B></P> <P>Overall diagnostic performances of abbreviated MRI and full diagnostic MRI were similar in both readers. The CAD-generated kinetic features could affect reader performance and the sensitivity could be improved or the specificity improved according to the reader.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Using a CAD system could cause false negative or false positive according to the readers and lesion types. </LI> <LI> The delayed persistent kinetic curve pattern could decrease the sensitivity especially in small cancers or cancers presented as non-mass enhancement. </LI> <LI> The diagnostic performance of full-dynamic sequence with CAD system was not significantly different with that of abbreviated sequence. </LI> </UL> </P>
Ha, T.,Cho, J.,Park, J.,Min, K.,Kim, H.S.,Lee, E.,Jyoung, J.Y. Pergamon Press ; Elsevier Science Ltd 2011 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.36 No.19
Generally, the GDL of a PEM fuel cell experiences three external attacks: dissolution of water, erosion of gas flow, and corrosion of electric potential. Of these degradation factors, this study focuses on the carbon corrosion of electric potential and investigates its impact through the accelerated carbon corrosion test. This study confirms that carbon corrosion occurs at the GDL, which decreases the operating fuel cell's performance. To discover the effects of carbon corrosion, the GDL property changes are measured through various devices, including a scanning electron microscopy, a thermo gravimetric analyzer, and a tensile stress test. Carbon corrosion causes not only loss of weight and thickness but also degradation of mechanical strength in the GDL. In addition, the GDL shows serious damage in its center.
An interactive 3D movement path manipulation method in an augmented reality environment
Ha, T.,Billinghurst, M.,Woo, W. Butterworths ; Elsevier Science Ltd 2012 INTERACTING WITH COMPUTERS Vol.24 No.1
In this paper, we evaluate a path editing method using a tangible user interface to generate and manipulate the movement path of a 3D object in an Augmented Reality (AR) scene. To generate the movement path, each translation point of a real 3D manipulation prop is examined to determine which point should be used as a control point for the path. Interpolation using splines is then used to reconstruct the path with a smooth line. A dynamic score-based selection method is also used to effectively select small and dense control points of the path. In an experimental evaluation, our method took the same time and generated a similar amount of errors as a more traditional approach, however the number of control points needed was significantly reduced. For control manipulation, the task completion time was quicker and there was less hand movement needed. Our method can be applied to drawing or curve editing methods in AR educational, gaming, and simulation applications.