• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.506-512
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• 2019

Although graphene has been successfully grown in large scale via chemical vapor deposition (CVD), it is still questionable whether the mechanical properties of CVD graphene are equivalent to those of exfoliated graphene. In addition, there has been an issue regarding how the tilt angle of the grain boundary (GB) affects the strength of graphene. We investigate the mechanical properties of CVD graphene with nanoindentation from atomic force microscopy and transmission electron microscopy. Surprisingly, the samples with GB angles of 10° and 26° yielded similar fracture stresses of ~ 80 and ~ 79 GPa, respectively. Even for samples with GB exhibiting a wider range, from 0° to 30°, only a slightly wider fracture stress range (~ 50 to ~ 90 GPa) was measured, regardless of tilt angle. The results are contrary to previous studies that have reported that GBs with a larger tilt angle yield stronger graphene film. Such a lack of angle dependence of GB can be attributed to irregular and well-stitched GB structures.

• Journal of Communications and Networks
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• v.15 no.4
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• pp.370-382
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• 2013

Distributed massive MIMO systems, which have high bandwidth efficiency and can accommodate a tremendous amount of traffic using algorithms such as zero-forcing beam forming (ZFBF), may be deployed in large public venues with the antennas mounted under-floor. In this case the channel gain matrix H can be modeled as a multi-banded matrix, in which off-diagonal entries decay both exponentially due to heavy human penetration loss and polynomially due to free space propagation loss. To enable practical implementation of such systems, we present a multi-banded matrix inversion algorithm that substantially reduces the complexity of ZFBF by keeping the most significant entries in H and the precoding matrix W. We introduce a parameter p to control the sparsity of H and W and thus achieve the tradeoff between the computational complexity and the system throughput. The proposed algorithm includes dense and sparse precoding versions, providing quadratic and linear complexity, respectively, relative to the number of antennas. We present analysis and numerical evaluations to show that the signal-to-interference ratio (SIR) increases linearly with p in dense precoding. In sparse precoding, we demonstrate the necessity of using directional antennas by both analysis and simulations. When the directional antenna gain increases, the resulting SIR increment in sparse precoding increases linearly with p, while the SIR of dense precoding is much less sensitive to changes in p.

• ETRI Journal
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• v.27 no.4
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• pp.341-354
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• 2005

The adaptation of video according to the heterogeneous and dynamic resource constraints on networks and devices, as well as on user preferences, is a promising approach for universal access and consumption of video content. For optimal adaptation that satisfies the constraints while maximizing the utility that results from the adapted video, it is necessary to devise a systematic way of selecting an appropriate adaptation operation among multiple feasible choices. This paper presents a general conceptual framework that allows the formulation of various adaptations as constrained optimization problems by modeling the relations among feasible adaptation operations, constraints, and utilities. In particular, we present the feasibility of the framework by applying it to a use case of rate adaptation of MPEG-4 video with an explicit modeling of adaptation employing a combination of frame dropping and discrete cosine transform coefficient dropping, constraint, utility, and their mapping relations. Furthermore, we provide a description tool that describes the adaptation-constraint-utility relations as a functional form referred to as a utility function, which has been accepted as a part of the terminal and network quality of service tool in MPEG-21 Digital Item Adaptation (DIA).

• Smart Structures and Systems
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• v.1 no.2
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• pp.185-215
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• 2005

Advanced signal processing techniques have been long introduced and widely used in structural health monitoring (SHM) and nondestructive evaluation (NDE). In our research, we applied several signal processing approaches for our embedded ultrasonic structural radar (EUSR) system to obtain improved damage detection results. The EUSR algorithm was developed to detect defects within a large area of a thin-plate specimen using a piezoelectric wafer active sensor (PWAS) array. In the EUSR, the discrete wavelet transform (DWT) was first applied for signal de-noising. Secondly, after constructing the EUSR data, the short-time Fourier transform (STFT) and continuous wavelet transform (CWT) were used for the time-frequency analysis. Then the results were compared thereafter. We eventually chose continuous wavelet transform to filter out from the original signal the component with the excitation signal's frequency. Third, cross correlation method and Hilbert transform were applied to A-scan signals to extract the time of flight (TOF) of the wave packets from the crack. Finally, the Hilbert transform was again applied to the EUSR data to extract the envelopes for final inspection result visualization. The EUSR system was implemented in LabVIEW. Several laboratory experiments have been conducted and have verified that, with the advanced signal processing approaches, the EUSR has enhanced damage detection ability.

• Earthquakes and Structures
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• v.7 no.1
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• pp.101-117
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• 2014

This paper presents a reliability-based analysis on seismic performance of timber-steel hybrid shear wall systems. Such system is composed of steel moment resisting frame and infill wood frame shear wall. The performance criteria of the hybrid system with respect to different seismic hazard levels were determined through a damage assessment process, and the effectiveness of the infill wood shear walls on improving the seismic performance of the hybrid systems was evaluated. Performance curves were obtained by considering different target non-exceedance probabilities, and design charts were further established as a function of seismic weight. Wall drift responses and shear forces in wood-steel bolted connections were used as performance criteria in establishing the performance curves to illustrate the proposed design procedure. It was found that the presence of the infill wood shear walls significantly reduced the non-performance probabilities of the hybrid wall systems. This study provides performance-based seismic evaluations on the timber-steel hybrid shear walls in support of future applications of such hybrid systems in multi-story buildings.

• Perspectives in Nursing Science
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• v.5 no.1
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• pp.17-31
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• 2008

Purpose: The purpose of this study was to evaluate the usability of a prototype personal digital assistant (PDA)-based decision support system for the management of obesity through usability testing with end-users (Advanced Practice Nurses [APNs]) prior to its implementation in clinical settings. Methods: This descriptive study used observational and think aloud techniques to address the research question: what usability problems are perceived by end-users? Five APNs were provided with the scenarios and the list of tasks to evaluate the application. Their verbalizations were recorded through Morae usabil ity software. Data analysis was based on the data captured through Morae, transcriptions, notes, and the end-user survey. Results: End-users completed all the required tasks without encountering a severe usability problem, and agreed that the system was easy to use. clear, concise, and useful. Usability issues that were unrecognized by the developer or usability experts were identified by APNs. The usability problems were categorized according to positive characteristics, negative characteristics, and recommendations. The usability issues were discussed with the project team members, and solutions were suggested to improve the user interface of the PDA-based decision support system before the final implementation. Conclusions: This approach had an important impact on making the system easier to use and more useful from the perspective of design and content. The results of this evaluation provided iterative feedback regarding the design and implementation of the PDA-based decision support system for the management of obesity.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.267-267
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• 2012

전 지구적으로 발생하고 있는 기후변화로 인한 기상이변으로 자연재해 발생빈도 및 피해규모는 증가하고 있는 추세로 나타나고 있다. 이에 따라 많은 연구는 자연재해에 직간접적으로 영향을 미치고 있는 홍수와 가뭄의 변화에 초점이 맞추어져 있는 것이 사실이다. 하지만, 최근에 우리나라의 경우 지난 2011년 2월에는 동해안의 폭설로 인하여 동해안지방 최심신적설량 극값 1위를 경신하였고, 2010년 1월 서울에는 40년만에 최대 적설량을 기록하는 등 최근 한반도에서 발생한 적설로 인하여 사회적 경제적 피해가 증가하고 있다. 따라서, 지구온난화에 기인한 기후변화 연구에서 상대적으로 소홀했던 적설량과 관련한 연구의 중요성도 대두되고 있다. 본 연구에서는 적설량에 온도 및 강수가 미치는 영향을 평가하기 위하여 관측기상자료를 이용하였다. 적설량은 기상인자들의 복잡한 비선형 조합으로 발생하기 때문에 적설량에 영향을 미치는 온도, 강수, 적설량의 비선형 과정들을 고려할 수 있는 신경망 모형을 이용하여 적설량 예측 모형을 구성하였다. 30년 이상의 관측자료를 보유하고 있는 기상청 산하 58개 관측지점의 자료를 이용하여 2002년 이전에 관측된 온도, 강수, 적설량을 지점별로 훈련시켰으며 이를 적설량 예측에 활용하고자 하였다. 이를 위해 구성된 신경망 모형에 2002년 이후 지점별 온도, 강우자료를 이용하여 적설량을 산정하고 통계분석을 실시한 결과 적설량 예측에 적용이 가능함을 확인하였다.

• Journal of Korea Water Resources Association
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• v.38 no.6 s.155
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• pp.439-448
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• 2005

This paper introduces the wavelet transform that was improved by the fourier transform to assess periodicities and trends, we assessed propriety with examples of two monthly precipitation data, annual precipitation, SOI index and SST index. The wavelet transform can effectively assess the power spectrum corresponding to frequency as maintaining chronological characteristics. The results of the analysis using the wavelet transform showed that the monthly precipitation have the strongest power spectrum near that of 1 year, and the annual precipitation represent the dominated spectrum in the band of 2-8 years. Also, the SOI index and SST index indicate the strongest power spectrum in the band of 2-8 years.

• Smart Structures and Systems
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• v.24 no.6
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• pp.745-757
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• 2019

Road surface deteriorations such as potholes have caused motorists heavy monetary damages every year. However, effective road condition monitoring has been a continuing challenge to road owners. Depth cameras have a small field of view and can be easily affected by vehicle bouncing. Traditional image processing methods based on algorithms such as segmentation cannot adapt to varying environmental and camera scenarios. In recent years, novel object detection methods based on deep learning algorithms have produced good results in detecting typical objects, such as faces, vehicles, structures and more, even in scenarios with changing object distances, camera angles, lighting conditions, etc. Therefore, in this study, a Deep Learning Pothole Detector (DLPD) based on the deep region-based convolutional neural network is proposed for autonomous detection of potholes from images. About 900 images with potholes and road surface conditions are collected and divided into training and testing data. Parameters of the network in the DLPD are calibrated based on sensitivity tests. Then, the calibrated DLPD is trained by the training data and applied to the 215 testing images to evaluate its performance. It is demonstrated that potholes can be automatically detected with high average precision over 93%. Potholes can be differentiated from manholes by training and applying a manhole-pothole classifier which is constructed using the convolutional neural network layers in DLPD. Repeated detection of the same potholes can be prevented through feature matching of the newly detected pothole with previously detected potholes within a small region.

• Proceedings of the Ginseng society Conference
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• 2002.10a
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• pp.545-555
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• 2002

Ginsenosides of 20(S)-protopanaxadiol and 20(S)-protopanaxatriol classification including the aglycones, PD, PI and ginsenosides Rh2, Rhl were shown to posses characteristic effects on proliferation of THP-l human leukaemia cells. A similar result was not apparent for ginsenoside Rg3 or dexamathasone. The concentration to inhibit $50\%$ of cells $(LC_{50})$ for PD, Rh2, PI and Rhl were 13 ${\mu}g/mL,\;15{\mu}g/mL,\;19{\mu}g/mL\;and\;210\;{\mu}g/mL$ respectively. Cell cycle analysis showed apoptosis with PD and PI treatment of THP-1 cells resulting in a build up of sub-G1 cells after 24, 48 and 72 hours of treatment. Rh2, and dexamathasone treatments also increased apoptotic cells after 24 hours, where as Rhl did not. After 48 and 72 hours Rh2, Rhl and dexamathasone similarly increased apoptosis, but these effects were significantly (P<0.05) lower than observed for both PD and PI treatments. Furthermore, treatments that produced the largest build up of apoptotic cells were also found to have the largest release of lactate dehydrogenase (LDH). It can be concluded from these studies that the presence of sugars to PD and PI aglycone structure reduces the potency to induce apoptosis, and alternately alter membrane integrity. These cytotoxic effects to THP-l cells were different from dexamethasone.