• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.4
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• pp.1227-1240
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• 2014

Abandoned mines often cause environmental problems, such as alteration of landscape, metal contamination, and landslides due to a heavy rainfall. Geotechnical and rheological tests were performed on waste materials corrected from Imgi waste rock dump, located in Busan Metropolitan City. Debris flow mobility was examined with the help of 1-D BING model which was often simulated in both subaerial and subaqueous environments. To determine flow curve, we used a vane-penetrated rheometer. The shear stress (${\tau}$)-shear rate (${\dot{\gamma}}$) and viscosity(${\eta}$)-shear rate (${\dot{\gamma}}$) relationships were plotted using a shear stress control mode. Well-known rheological models, such as Bingham, bilinear, Herschel-Bulkley, Power-law, and Papanastasiou concepts, were compared to the rheological data. From the test results, we found that the tested waste materials exhibited a typical shear shinning behavior in ${\tau}$-${\dot{\gamma}}$ and and ${\eta}$-${\dot{\gamma}}$ plots, but the Bingham behavior is often observed when the water contents increased. The test results show that experimental data are in good agreement with rheological models in the post-failure stage during shearing. Based on the rheological properties (i.e., Bingham yield stress and viscosity as a function of the volumetric concentration of sediment) of waste materials, initial flowing shape (5 m, 10 m, and 15 m) and yield stress (100 Pa, 200 Pa, 300 Pa, and 500 Pa) were input to simulate the debris flow motion. As a result, the runout distance and front velocity of debris flow are in inverse propositional to yield stress. In particular, when the yield stress is less than 500 Pa, most of failed masses can flow into the stream, resulting in a water contamination.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.5B
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• pp.253-263
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• 2005

This paper proposed a mobile multicast technique to satisfy end-to-end QoS for various user requirements in mobile network environment. In order to provide seamless mobility, fast handoff technique was applied. By using L2 mobile trigger, it was possible to minimize remarkable amount of packet loss by delay occurred during handoff. To provide efficient multicast, concept of hierarchy was introduced to Xcast++, which results in a creation of HXcast++. HXcast++ optimized transfer path of multicast and reduced expensive multicast maintenance costs caused by frequent handoff. Suggestion of GMA (Group Management Agent) mechanism allows joining to group immediately without waiting IGMP Membership query during handoff. GMA mechanism will minimize the delay for group registration process and the resource usage due to delay of withdrawal process. And also use of buffering & forwarding technique minimized packet loss during generation of multicast tree. IntServ/RSVP was used to provide End-to-End QoS in local domain and DiffServ was used in global domain. To minimize reestablishment of RSVP session delay, extended HXcast++ control messages ware designed to require PATH message. HXcast++ proposed in this thesis is defined as multicast technique to provide end-to-end QoS and also to satisfy various user requirements in mobile network environment.

• Journal of Adhesion and Interface
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• v.21 no.3
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• pp.86-92
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• 2020

We confirmed the effects on the device performances and the charge injection characteristics of organic field-effect transistor (OFET) by selectively differently controlling the surface energies on the contact region of the substrate where the source/drain electrodes are located and the channel region between the two electrodes. When the surface energies of the channel and contact regions were kept low and increased, respectively, the field-effect mobility of the OFET devices was 0.063 ㎠/V·s, the contact resistance was 132.2 kΩ·cm, and the subthreshold swing was 0.6 V/dec. They are the results of twice and 30 times improvements compared to the pristine FET device, respectively. As the results of analyzing the interfacial trap density according to the channel length, a major reason of the improved device performances could be anticipated that the pi-pi overlapping direction of polymer semiconductor molecules and the charge injection pathway from electrode is coincided by selective surface treatment in the contact region, which finally induces the decreases of the charge trap density in the polymer semiconducting film. The selective surface treatment method for the contact region between the electrode and the polymer semiconductor used in this study has the potential to maximize the electrical performances of organic electronics by being utilized with various existing processes to lower the interface resistance.

• Journal of the Korean Applied Science and Technology
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• v.27 no.2
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• pp.137-143
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• 2010

Oxide semiconductors Thin-film transistors are an exemplified one owing to its excellent ambient stability and optical transparency. In particular zinc oxide (ZnO) has been reported because It has stability in air, a high electron mobility, transparency and low light sensitivity, compared to any other materials. For this reasons, ZnO TFTs have been studied actively. Furthermore, we expected that would be satisfy the demands of flexible display in new generation. In order to do that, ZnO TFTs must be fabricated that flexible substrate can sustain operating temperature. So, In this paper we have studied low-temperature process of zinc oxide(ZnO) thin-film transistors (TFTs) based on silicon nitride ($SiN_x$)/cross-linked poly-vinylphenol (C-PVP) as gate dielectric. TFTs based on oxide fabricated by Low-temperature process were similar to electrical characteristics in comparison to conventional TFTs. These results were in comparison to device with $SiN_x$/low-temperature C-PVP or $SiN_x$/conventional C-PVP. The ZnO TFTs fabricated by low-temperature process exhibited a field-effect mobility of $0.205\;cm^2/Vs$, a thresholdvoltage of 13.56 V and an on/off ratio of $5.73{\times}10^6$. As a result, We applied experimental for flexible PET substrate and showed that can be used to ZnO TFTs for flexible application.

• Journal of the Korean Society of Clothing and Textiles
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• v.40 no.4
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• pp.669-684
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• 2016

This study investigates Korean fighter pilot's usage and satisfaction of a flight duty uniform (FDU). The survey was conducted from October 2014 to March 2015 using Focus Group Interview (FGI) and questionnaires. FGI collected qualitative data about duty and requirements; subsequently, surveys were performed to collect quantitative data about wearing conditions and satisfaction with FDU. The results of the FGI and the questionnaire were as follows. Type of pilot duty was divided into two parts, flight duty and ground duty. It is important to consider duties as well as factors related to survival when developing FDU. According to anthropometric data and wearing size, the basic size for apparel grading should be changed from actual size, 'M95XL' to 'M100L'. It is also necessary to improve the whole sizing system. Further studies about body form changes in pilot's movement are needed to improve mobility because the respondents perceived some restrictions at several body parts in movement with the coverall uniform. Summer FDU had a low satisfaction level in vent hole function and appearance. Furthermore, protection problems in the vent hole were also an issue. Making a seasonal classification of FDU fabric will be more effective than a vent hole to increase a pilot's thermal satisfaction. Respondents had a passive stance towards FDU reform (including pocket change); therefore, a new FDU design strategy should concentrate on improving current FDU functions like mobility (or comfort) rather than dramatic changes. Pilots complained about the quality stability of FDU; therefore, quality control by military administration as well as concrete and clear design instructions by the developer should be attained together. The results obtained in this study are expected to be used as an important basis for the further development of FDU.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.12
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• pp.34-43
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• 2007

Recently, in addition to the sharp increase of mobile nodes, various kinds of wireless technologies are available for mobile nodes. If IPv6 technology is applied to the network, multi-homing terminals which have several public IP addresses on one interface will be common. Accordingly, there are many research activities on mobility management for multi-interface, multi-homming nodes. In this paper we propose an extended fast handover mechanism for multi-interface MIPv6 environments that uses multi-interface FBU (MFBU) message instead of the existing FBU message. The MFBU message has the "tunnel destination" mobility option that points a specific tunnel destination other than NAR, and "T" flag that indicates the existence of tunnel destination option. The proposed mechanism can improve the TCP performance by mitigating packet reordering during FMIPv6 handover that can cause unnecessary congestion control due to 3 duplicate ACKs. In this paper, we implemented a multi-Interface MIPv6 simulator by extending a single-interface MIPv6 simulator in NS-2, and showed that the performance of TCP traffic is improved by using the proposed multi-interface fast MIPv6.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.2
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• pp.89-103
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• 2020

As we face an aging society, the demand for personal mobility for disabled and aged people is increasing. In fact, as of 2017, the number of electric wheelchair in the country continues to increase to 90,000. However, people with disabilities and seniors are more likely to have accidents while driving, because their judgment and coordination are inferior to normal people. One of the causes of the accident is the interference of personal vehicle steering control due to unbalanced road surface conditions. In this paper, we introduce a encoder type semantic segmentation algorithm that can recognize road conditions at high speed to prevent such accidents. To this end, more than 1,500 training data and 150 test data including road surface damage were newly secured. With the data, we proposed a deep neural network composed of encoder stages, unlike the Auto-encoding type consisting of encoder and decoder stages. Compared to the conventional method, this deep neural network has a 4.45% increase in mean accuracy, a 59.2% decrease in parameters, and an 11.9% increase in computation speed. It is expected that safe personal transportation will be come soon by utilizing such high speed algorithm.

• Journal of the Korean Association of Geographic Information Studies
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• v.24 no.2
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• pp.102-116
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• 2021

For the safe operation of autonomous vehicles, the representative technology of the 4^th industrial revolution era, a combination of various technologies such as sensor technology, software technology and car technology is required. An autonomous vehicle is a vehicle that recognizes current location and situation by using the various sensors, and makes its own decisions without depending on the driver. Perfect recognition technology is required for fully autonomous driving. Since the precise road maps provide various road information including lanes, stop lines, traffic lights and crosswalks, it is possible to minimize the cognitive errors that occur in autonomous vehicles by using the precise road maps with location information of the road facilities. In this study, the definition, necessity and technical trends of the precise road map have been analyzed, and the HD(High Definition) map prototype based on the web GIS has been built in the autonomous driving-specialized areas of Daegu Metropolitan City(Suseong Medical District, about 24km), the Happy City of Sejong Special Self-Governing City(about 33km), and the FMTC(Future Mobility Technical Center) PG(Proving Ground) of Seoul National University Siheung Campus using the MMS(Mobile Mapping System) surveying results given by the National Geographic Information Institute. In future research, the built-in precise road map service will be installed in the autonomous vehicles and control systems to verify the real-time locations and its location correction algorithm.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.1
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• pp.59-66
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• 2022

In order to solve the problem of urban traffic congestion, Urban Air Mobility (UAM) concept using Electric Vertical Take-off and Landing (eVTOL) aircraft has been gaining popularity, and many domestic and international studies are underway. However, since these aircraft inevitably fly over densely populated areas, it is essential to ensure safety, which starts with accurately analyzing the crash risk. In this paper, the locations and impact speeds of crash are computed using six degree-of-freedom simulations of an eVTOL aircraft in a fixed-wing mode. System malfunction was modeled by a sudden loss of thrust with control surfaces being stuck during cruise. Because most of these eVTOL aircraft are still under development, a methodology of constructing a six degree-of-freedom dynamics model from generic specification is also developed. The results show that the crash locations are highly concentrated right under the aircraft within a square that has an edge length similar to the cruise altitude. Speed distribution is more complicated because almost identical crash locations can be achieved by two very different paths resulting in a large variation in the speeds.

• Korea Trade Review
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• v.42 no.1
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• pp.141-163
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• 2017

The purpose of this study to analyze the relationship among three characteristics of O2O commerce and extended goal-directed behavior(EGB) model(trust, desire and intention to use). From June to July in 2015, the questionnaires were sent to Chinese customers using O2O commerce. Among 494 questionnaires gathered, 433 valid ones are analyzed using SPSS and AMOS. Among ten research hypotheses derived from prior research and the research model, eight hypotheses are tenable, while the rest hypotheses are untenable. Online features of mobility and Offline features of service quality. The Online features of mobility bring consumers convenience but also has some latent customer privacy issue. On other hand, because of the untenable hypothesis, there is inconformity between online service and offline service, and customer have distrust on the O2O commerce. To achieve continuous online consumption, offline businesses need to improve their service. The perceived quality of selling company exerts a significant effect on the customers' reliability for the brand equity of open market company and selling company, such as the brand awareness of the open market, open market image, brand awareness of selling company, and the perceived quality of selling company. Thus, selling company should improve self-brand service and quality in order to improve customers' reliability. In addition, the consumer characteristics of attitude, subjective norm, and perceived behavioral control are all tenable. These results mean that O2O commerce is a favorite way of consumption by Chinese consumers.