• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권8호
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• pp.3366-3383
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• 2020

The Poisson point process (PPP) is widely used in wireless network modeling and performance analysis because it can provide tractable results for heterogeneous cellular networks (HetNets) analysis. However, it cannot accurately reflect the spatial distribution characteristics of the actual base stations (BSs). Considering the fact that the distribution of macro base stations (MBSs) is exclusive, the deployment of MBSs is modeled by the Matérn hard-core point process (MHCPP), and the deployment of pico base stations (PBSs) is modeled by PPP. This paper studies the performance of multiantenna HetNets and improves the energy efficiency (EE) of HetNets by optimizing the transmit power of PBSs. We use a simple approximate method to study the signal-to-interference ratio (SIR) distribution in two-tier MHCPP-PPP HetNets and derive the coverage probability, average data rate and EE of HetNets. Then, an optimization algorithm is proposed to improve the EE of HetNets. Finally, three transmission technologies are simulated and analyzed. The results show that multiantenna transmission has better system performance than single antenna transmission and that selecting the appropriate transmit power for a PBS can effectively improve the EE of the system. In addition, two-tier MHCPP-PPP HetNets have higher EE than two-tier PPP-PPP HetNets.

• Structural Engineering and Mechanics
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• 제73권4호
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• pp.427-436
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• 2020

The use of final IGS precise orbit and clock products for high-rate GNSS-PPP proved its effectiveness in capturing dynamic displacement of engineering structures caused by earthquakes. However, the main drawback of using the final products is that they are available after approximately two weeks of data collection, which is not suitable for timely measures after an event. In this study, the use of ultra-rapid products (observed part), which are available after a few hours of data collection, and rapid products, which are available in less than 24 hrs, are investigated and their results are compared to the more precise final products. The tests are designed such that harmonic oscillations with different frequencies and amplitudes and ground motion of a simulated real earthquake are generated using a single axis shake table and the PPP was used to capture these movements by monitoring time-change of the table positions. To evaluate the accuracy of PPP using ultra-rapid, rapid and final products, their results were compared with relative GNSS positioning and LVDT (Linear Variable Differential Transformer) data, treated as reference. The results show that the high-rate GNSS-PPP solutions based on the three products can capture frequencies of harmonic oscillations and dynamic displacement with good accuracy. There were slight differences between ultra-rapid, rapid and final products, where some of the tested events indicated that the latter two produced are more accurate and provide better results compared to the ultra-rapid product for monitoring short-term dynamic displacements.

• 대한토목학회논문집
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• 제42권6호
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• pp.887-892
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• 2022

국제적인 철도 사업은 개도국의 재정 부족 등 다양한 대외적 환경변화로 인해 재정사업에서 민간 투자사업(PPP)으로의 변경이 보편화되고 있다. 하지만, 철도 시설물은 도로 등 다른 인프라 시설물 보다는 철도 생애주기 특성상 사업개발, 건설 및 운영단계까지 막대한 건설자금 및 O&M 비용이 소요된다. 따라서 투자 대비 일정 수준의 수익률이 보장되지 않는다면 해외 특히 예측불허한 상황들이 발생하는 개발도상국에서의 해외철도 민간투자사업의 수행은 매우 어려운 실정이다. 본 연구에서는 글로벌 철도시장 동향 정보 및 기존 문헌 고찰을 통해 국내기업의 해외철도 민간투자사업 진출시 취약점 및 위험요인들을 살펴보고 그 의미와 대응 방안들에 대한 논의를 통하여 해외철도사업 진출시 국내기업의 경쟁력을 강화하는 방향을 제시하고자 한다.

• 대한토목학회논문집
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• 제35권2호
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• pp.471-480
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• 2015

민간투자사업에 대한 부정적인 시각으로 인해 민간투자사업 시장은 축소되었으나, 최근 국내 재정사업의 축소로 인해 민간투자사업에 대한 필요성이 다시금 제기되고 있다. 민간투자사업은 건설사, special purpose company (SPC), 재무투자자 등 다양한 참여자들 간의 이해관계가 복잡하여 사업의 성과를 판단하기 위해서는 참여자 간 관점 차이에 대한 고려가 필요하나, 기존의 연구는 재무적 관점의 수익성 예측, 또는 리스크 식별을 통한 수익성 예측을 중심으로 수행되었다. 이러한 점을 고려하여 본 연구에서는 민간투자사업 주요 참여자별 특성에 따른 민간투자사업 성과예측 모델을 개발하였다. 이를 위해 첫째, 다양한 분야의 문헌고찰을 통해 민간투자사업의 조직구조를 분석하였으며, 건설사, SPC, 재무투자자의 관점에서 민간투자사업 수익성 영향요인을 도출하였다. 둘째, 도출된 수익성 영향인자들을 바탕으로 민간투자사업 관련 전문가 설문조사 및 인터뷰를 실시하였다. 셋째, 구조방정식 모델(structural equation model)을 통해 민간투자사업의 구성개념들 간에 직접효과와 간접효과를 분석하여 민간투자사업의 수익성 및 수익안정성 측면에서의 성과를 거시적으로 이해할 수 있는 모델을 개발하였다. 넷째, 모델을 통해 도출된 결과를 바탕으로 민간투자사업의 재도약을 위한 발전방안을 제시하였다. 향후 본 모델을 통해 수익성과 수익안정성 측면에서 건설사, 재무투자자, SPC 운영사의 사업성과 예측이 가능하며, 이에 따른 대응전략을 모색하는데 활용 가능할 것으로 기대된다.

• Biomolecules & Therapeutics
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• 제24권6호
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• pp.595-603
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• 2016

(E)-3-Phenyl-1-(2-pyrrolyl)-2-propenone (PPP) is a pyrrole derivative of chalcone, in which the B-ring of chalcone linked to ${\beta}$-carbon is replaced by pyrrole group. While pyrrole has been studied for possible Src inhibition activity, chalcone, especially the substituents on the B-ring, has shown pharmaceutical, anti-inflammatory, and anti-oxidant properties via inhibition of NF-${\kappa}B$ activity. Our study is aimed to investigate whether this novel synthetic compound retains or enhances the pharmaceutically beneficial activities from the both structures. For this purpose, inflammatory responses of lipopolysaccharide (LPS)-treated RAW264.7 cells were analyzed. Nitric oxide (NO) production, inducible NO synthase (iNOS) and tumor necrosis factor-${\alpha}$ (TNF-${\alpha}$) mRNA expression, and the intracellular inflammatory signaling cascade were measured. Interestingly, PPP strongly inhibited NO release in a dose-dependent manner. To further investigate this anti-inflammatory activity, we identified molecular pathways by immunoblot analyses of nuclear fractions and whole cell lysates prepared from LPS-stimulated RAW264.7 cells with or without PPP pretreatment. The nuclear levels of p50, c-Jun, and c-Fos were significantly inhibited when cells were exposed to PPP. Moreover, according to the luciferase reporter gene assay after cotransfection with either TRIF or MyD88 in HEK293 cells, NF-${\kappa}B$-mediated luciferase activity dose-dependently diminished. Additionally, it was confirmed that PPP dampens the upstream signaling cascade of NF-${\kappa}B$ and AP-1 activation. Thus, PPP inhibited Syk, Src, and TAK1 activities induced by LPS or induced by overexpression of these genes. Therefore, our results suggest that PPP displays anti-inflammatory activity via inhibition of Syk, Src, and TAK1 activity, which may be developed as a novel anti-inflammatory drug.

• 한국재료학회지
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• 제13권5호
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• pp.338-342
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• 2003

Adhesion between Cu and low-k films has been investigated. Low-k films deposited using a mixture of hexamethyldisilane(HMDS) and Para-xylene had a dielectric constant as low as 2.7, showing the thermally stable properties up to $400^{\circ}C$. In this study, Ti glue layer, boron dopant, and $N_2$plasma treatment were used to improve adhesion property of between Cu and low-k films. Ti glue layer slightly improved adhesion property. After $N_2$plasma treatment, the adhesion property was significantly improved due to the increased roughness and the formation of new binding states between Ti and plasma-treated PPpX : HMDS. However, $300^{\circ}C$ annealing of $N_2$plasma treated sample caused the diffusion of Cu into the PPpX : HMDS, degrading the low-k properties. In the case of Cu(B)/Ti/PPpX : HMDS, the adhesion was remarkably increased. This enhanced adhesion was attributed to formation of Ti-boride at the Cu-Ti interface. It is because the formed Ti-boride prevented the diffusion of Cu into the PPpX : HMDS and the Cu-Ti reaction at the Ti interface.

• Journal of Positioning, Navigation, and Timing
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• 제8권4호
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• pp.209-214
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• 2019

Precise point positioning (PPP) requires precise orbit and clock products. International GNSS service (IGS) real-time service (RTS) data can be used in real-time for PPP, but it may not be possible to receive these corrections for a short time due to internet or hardware failure. In addition, the time required for IGS to combine RTS data from each analysis center results in a delay of about 30 seconds for the RTS data. Short-term orbit prediction can be possible because it includes the rate of correction, but the clock correction only provides bias. Thus, a short-term prediction model is needed to preidict RTS clock corrections. In this paper, we used a long short-term memory (LSTM) network to predict RTS clock correction for three minutes. The prediction accuracy of the LSTM was compared with that of the polynomial model. After applying the predicted clock corrections to the broadcast ephemeris, we performed PPP and analyzed the positioning accuracy. The LSTM network predicted the clock correction within 2 cm error, and the PPP accuracy is almost the same as received RTS data.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.893-896
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• 2003

Plasma polymerized para-xylene (PPpX) thin films deposited by plasma enhanced chemical vapor deposition (PECVD) were used to passivate the organic light emitting diodes (OLEDs). For OLEDs, indium tin oxide (ITO), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-diphenyl-4,4'-diamine (TPD), tris(8-hydroxyquinoline) aluminum $(Alq_{3})$ and aluminum (Al) were used as the anode, the hole transport layer (HTL), the emitting layer (EML) and the cathode, respectively. The OLED device with the PPpX passivation film (passivated device) showed similar electrical and optical characteristics to those of the OLED device without the PPpX passivation film (control device), indicating that the PECVD process did not degrade the performance of the OLEDs notably. The lifetime of the passivated device was two times longer than that of the control device. Passivation of OLEDs with PPpX films also suppressed the growth of dark spots. The density and size of dark spots of the passivated device were much smaller than those of the control device.

• Journal of Positioning, Navigation, and Timing
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• 제3권4호
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• pp.155-161
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• 2014

The purpose of this study is to develop precise point positioning (PPP) algorithms based on GLONASS code-pseudorange, verify their performance and present their utility. As the basic correction models of PPP, we applied Inter Frequency Bias (IFB), relativistic effect, satellite antenna phase center offset, and satellite orbit and satellite clock errors, ionospheric errors, and tropospheric errors that must be provided on a real-time basis. The satellite orbit and satellite clock errors provided by Information-Analytical Centre (IAC) are interpolated at each observation epoch by applying the Lagrange polynomial method and linear interpolation method. We applied Global Ionosphere Maps (GIM) provided by International GNSS Service (IGS) for ionospheric errors, and increased the positioning accuracy by applying the true value calculated with GIPSY for tropospheric errors. As a result of testing the developed GLONASS PPP algorithms for four days, the horizontal error was approximately 1.4 ~ 1.5 m and the vertical error was approximately 2.5 ~ 2.8 m, showing that the accuracy is similar to that of GPS PPP.

• Journal of Positioning, Navigation, and Timing
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• 제10권2호
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• pp.75-82
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• 2021

Fields of high-precision positioning applications are growing fast across the mass market worldwide. Accordingly, the industry is focusing on developing methods of applying State-Space Representation (SSR) corrections on low-cost GNSS receivers. Among SSR correction types, this paper analyzes Safe Position Augmentation for Real Time Navigation (SPARTN) messages being offered by the SAfe and Precise CORrection DAta (SAPCORDA) company and validates positioning algorithms based on them. The first part of this paper introduces the SPARTN format in detail. Then, procedures on how to apply Basic-Precision Atmosphere Correction (BPAC) and High-Precision Atmosphere Correction (HPAC) messages are described. BPAC and HPAC messages are used for correcting satellite clock errors, satellite orbit errors, satellite signal biases and also ionospheric and tropospheric delays. Accuracies of positioning algorithms utilizing SPARTN messages were validated with two types of positioning strategies: Code-PPP using GPS pseudorange measurements and PPP-RTK including carrier phase measurements. In these performance checkups, only single-frequency measurements have been used and integer ambiguities were estimated as float numbers instead of fixed integers. The result shows that, with BPAC and HPAC corrections, the horizontal accuracy is 46% and 63% higher, respectively, compared to that obtained without application of SPARTN corrections. Also, the average horizontal and vertical RMSE values with HPAC are 17 cm and 27 cm, respectively.