• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.3
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• pp.110-119
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• 2017

This study develops a passive traffic signal priority control algorithm for emergency vehicles. The passive priority control estimates and applies signal times for each signalized intersection on the emergency vehicle's route when an emergency call is received. As signals are controlled before the emergency vehicle leaves for its destination, it is possible to clear the queues at each intersection more effectively. Most of the previous studies applied preemption, which ends green time of cross streets when the emergency vehicle arrives at each intersection. This study applies green extension and early green in order not to shift the order of phases, and guarantees minimum green time for each phase. Simulation results show that the delay of emergency vehicles decreases when the signals are controlled. It is expected that delays can be decreased further by integrating the active priority control with the passive priority control algorithm presented in this study.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.7
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• pp.39-47
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• 2012

The combination of the broadband property and the wide area coverage of satellite communications enables high speed transmission. Every user in the region under the satellite beam coverage can tranceiver and one can simultaneously communicate with multiple users. For these reasons, it is one of commendable telecommunication networks for information transfer. Since the satellite communications use open channels, it is likely to cause jamming with unwanted interference signals. In the thesis, APSK (Amplitude Phase Shift Keying) is employed, which is recommended for DVB-S2 due to high-speed transmission and excellent bandwidth efficiency. For obtaining reliable communication under the jamming environments, the communication satellite transponder rests on the polyphase filter bank structure, which enables switching among the subchannels and gain control on each subchannel, resulting in effectively eliminating jamming. Furthermore, the nulling scheme, one of the various anti-jamming approaches, is investigated, in which unwanted jamming signals are eliminated in the frequency domain after passing through the analysis part of the polyphase filter bank. The performance of the nulling scheme is evaluated for tone jamming and partial band jamming in terms of BER and EVM. The simulation results indicate that the nulling scheme improve the BER and EVM performance over the case without any anti-jamming approach.

• Journal of the Korean Magnetics Society
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• v.19 no.3
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• pp.106-112
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• 2009

$Ni_{1-x}Mg_xFe_2O_4$ ferrite system was studied by using X-ray diffraction and $M{\ddot{o}}ssbauer$ spectroscopy. The samples were prepared by ceramic sintering method with Mg content x. The X-ray diffraction patterns of samples show phase of cubic spinel structure. There are no remarkable changes of lattice constants in $Ni_{1-x}Mg_xFe_2O_4$ ferrite system. The $M{\ddot{o}}ssbauer$ spectra were consisted of two sets of six lines, respectively, corresponding to $Fe^{3+}$ at tetrahedral and octahedral sites. The magnetic hyperfine field of samples was decreased as increasing Mg contents x in both sites and it was shown Yafet-Kittel magnetic structure. $NiFe_2O_4$ was shown complete inverse spinel, but $NiFe_2O_4$ was shown partial inverse spinel which absorption area ratio (oct/tet) was 1.449 in $M{\ddot{o}}ssbauer$ spectrum.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.23-27
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• 2017

This paper proposes an approach to predict the reliability of high temperature heaters by identifying their primary failure modes and mechanisms in the field. Test specimens were designed to have the equivalent stress conditions with the high temperature heaters in the field in order to examine the effect of stress conditions on the solder joint failures. There failures often result from cracking due to intermetallic compound (IMC) or void formation within a solder joint. Aging tests have been performed by exposing the test specimens to a temperature of $170^{\circ}C$ in order to reproduce solder joint failures in the field. During the test, changes in IMC formation were investigated by scanning electron microscopy (SEM) on the cross-sections of the test specimens, while changes in void formation were monitored both by resistance spectroscopy and by micro-computed tomography (microCT), alternately. The test results demonstrated the void volume within the solder increased as the time at the high temperature increased. Also, the phase shift of high frequency resistance was found to have high correlation with the void volume. These results implied the failure of high temperature heaters can be non-destructively predicted based on the correlation.

• Journal of the Korean Institute of Landscape Architecture
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• v.43 no.1
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• pp.139-156
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• 2015

The knowledge-based society of the 21st century requires a new kind of professional. Studio education has been the core pedagogical method to bridge the practical world and higher education in the field of landscape architecture. However, it is questioned whether studio classes have truly been performed from the learners' perspectives to solidify the competencies to meet the demands of the changing society. This study tries to draw key issues related to studio pedagogy in order to make a foundation for the improvement of studio classes in landscape architectural education. Five issues regarding landscape architectural studio education have been suggested through the literature review of three categories: the core competencies required for the future professionals, the pedagogical paradigm shift, and the changes along the evolution of landscape professions and curricula. The first issue is suggested as to approach the competencies from the holistic and systematic approach to define landscape architectural professionals for the 21st century. Second, studio classes should be redefined in the context of an entire curriculum, and, as a consequence, the linkage among the individual courses is found to be important. Third, design studio classes need to be restructured to have differentiated pedagogical objectives for the development of the learning phase. Fourth, it becomes crucial to research the pedagogical methodology and the reflective actions of instructors. Finally, it is required to think about what it means to be practical in the context of studio classes and the enhancement of educational infrastructure for the studio classes is to be important.

• Journal of the Korean Institute of Landscape Architecture
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• v.42 no.2
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• pp.91-102
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• 2014

Recent trends in urban policies show the increasing importance of urban parks. Moreover the park policy and planning are increasingly important for the good urban park system. Comparative studies in the operational system and planning contents of the parks and green space plans of the major cities would be timely and meaningful. This study aims to provide a comparative study in operational system and planning contents of the Parks and Green Space Master Plan at urban scale. Sites include London, New York, Berlin, Sydney and Seoul. Analyses are focused on the master plans and strategy reports of each city. Frameworks for analysis are divided into operational system and planning contents. The results are as follows. First, the Parks and Green Space Plans as an open space planning linked to related resources would contribute to both integrated resources management and practice of the fairness. Second, evolution from quantity to quality of the parks and green space plan enhances revitalization and regeneration. Third, shift from the 'supply oriented plan' to 'need based plan' model provides flexible planning model to meet the demographic change, trend change, preference and use. Fourth, planning agents, enlarged opportunities for participation within each phase, diversified of the participants lead the changes from the passive participation to active one. In order to improve the practicability of the parks and green space master plan, a flexible planning strategy including social awareness changes and park governance is required.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.9
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• pp.4185-4190
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• 2013

We executed the property changes of the sintered MgO (99.9% purity, 300nm size) specimens with addition to CaO content of 0.00wt%, 0.25wt%, and 0.50wt%, processed at 7GPa, for 5min, 600~$800^{\circ}C$. To investigate the micro-structure and physical property changes of the sintered MgO(-CaO), we employed a scanning electron microscopy(SEM), X-ray diffractomerty(XRD), Vickers hardness, and density. The SEM result showed that MgO powder of 300nm size was changed into sintered structure of 520nm by high pressure and low temperature sintering, regardless of the CaO contents. According to the XRD analysis, no CaO phase observed, while MgO peaks shift indicated the existence of CaO in the MgO matrix. The Vickers hardness result showed that hardness of sintered MgO-CaO increased by 12% compared pure MgO under the same temperature conditions. It implied that we can obtain the same hardness with $100^{\circ}C$ lowered sintering temperatures by addition of CaO. The density results showed that it was possible to obtain density of 98%, which is 5% greater than that of pure MgO at low temperature of $600^{\circ}C$.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.2
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• pp.103-110
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• 2010

In this paper, a new mode changeable asymmetric full bridge dc/dc converter is proposed to solve the freewheeling current problem of the conventional zero voltage switching(ZVS) phase shift full bridge(PSFB) dc/dc converter of low output voltage and high output current applications. The proposed converter is operated as an asymmetric full bridge converter when the duty cycle is less than 50% and active clamp full bridge converter when the duty cycle is greater than 50%. As a result, since its freewheeling current is eliminated, the conduction loss is lower than that of the conventional ZVS PSFB dc/dc converter. Moreover, ZVS of all power switches can be ensured along a wide load ranges and output current ripple is very small. Therefore, high efficiency of the proposed converter can be achieved. Especially since its operation mode is changed to the active clamp full bridge converter during hold up time and can be operated with 50~100% duty ratio, it can produce the stable output voltage along wide input voltage range. The operational principles, theoretical analysis and design considerations are presented. To confirm the operation, validity and features of the proposed converter, experimental results from a 1.2kW($400V_{dc}/12V_{dc}$) prototype are presented.

• Polymer(Korea)
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• v.24 no.3
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• pp.314-325
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• 2000

Thermal degradation of thermoplasitc polyurethane modified polycarbonate has been investigated by means of DSC, GPC and FT-IR techniques. The polyurethanes used in this study are TPU-35 and TPU-53 containing 35.5 and 53.4 wt% of hard segments, respectively. The more content of hard segment, the higher the glass transition temperature (T$_{g}$) of TPU was observed. On the other hand, the T$_{g}$ of the TPU modified PC decreased with the content of TPU and the annealing temperature regardless of the hard segment contents. The latter behavior nay arise from the thermal degradation of TPU upon annealing process: the observed thermal degradation temperatures were at 240 and 25$0^{\circ}C$ for the PC/TPU-35 and PC/TPU-53, respectively. The molecular weight, molecular weight distribution and viscosity agree well with the DSC measurement, which implicates a thermal degradation of TPU. In addition, thermal stability of the TPU modified PC linearly decreased with an incorporation of TPU. Transesterification or any interaction was not observed using FT-IR: the evidence was no frequency shift or any variance betwere the carbonyl stretching and NH group. For the specimens prepared below the degradation temperature, the enhancement of the thickness dependent impact strength of the PC/TPU blend was observed, and the morphology of the two blends was compared.d.

• Journal of the Korean Vacuum Society
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• v.20 no.6
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• pp.442-448
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• 2011

Self-assembled InAs/InAlGaAs quantum dots (QDs) grown on an InP (001) substrate have been investigated by using photoluminescence (PL) and time-resolved PL measurements. The single layer (QD1) and seven stacks (QD2) of InAs/InAlGaAs QDs grown by the conventional S-K growth mode were used. The PL peak at 10 K was 1,320 nm for both QD1 and QD2. As the temperature increases from 10 to 300 K, the PL peaks for QD1 and QD2 were red-shifted in the amount of 178 and 264 nm, respectively. For QD1, the PL decay increased with increasing emission wavelength from 1,216 to 1,320 nm, reaching a maximum decay time of 1.49 ns at 1,320 nm, and then decreased as the emission wavelength was increased further. However, the PL decay time for QD2 decreased continuously from 1.83 to 1.22 ns as the emission wavelength was increased from 1,130 to 1,600 nm, respectively. These PL and TRPL results for QD2 can be explained by the large variation in the QD size with stacking number caused by the phase separation of InAlGaAs.