• Title/Summary/Keyword: Free Space Loss

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A Study on Link Analysis of Telemetry Rocket-borne Antenna (텔레메트리 로켓 탑재 안테나의 회선 분석에 관한 연구)

  • 김성완;황수설;이재득
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.15 no.3
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    • pp.311-318
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    • 2004
  • It is required to design the RF link with sufficiently stable signal margin to minimize bit errors and improve the quality of received data in the telemetry system modulated digitally like PCM/FM. In case of the vehicle flying at a high speed, the variation of the gain pattern between transmitting and receiving antenna and the fee space loss due to flight distance cause the fluctuation of link. In this paper, KSR(Korea Sounding Rocket)- III, the first domestic liquid rocket which was successfully launched in Nov. 2002 is introduced. The SNR(signal-to-noise ratio) variation of the telemetry signal which was measured at S-band ground station, the one which was simulated considering the flight trajectory, and the attitude variation such as roll, pitch and yaw are compared, analyzed, and agree very well. In addition, two virtual flying situations are simulated and evaluated-only one antenna is equipped in one case, and rocket is roll-free in the other.

Wall charge effects on structural properties of a coarse-grained FENE polyelectrolyte confined in slit nanochannels by Brownian dynamics simulation

  • Jeon, Jong-Gu;Chun, Myung-Suk
    • Korea-Australia Rheology Journal
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    • v.19 no.2
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    • pp.51-59
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    • 2007
  • A polyelectrolyte chain confined in a slit nanochannel exhibits a structural transition from the one in free space. In this paper, the effect of the long-range electrostatic interactions between the xanthan polyelectrolyte and the slit wall on the confined xanthan conformation is investigated via the Brownian dynamics simulation. A neutral and two negatively charged surfaces of polydimethylsiloxane (PDMS) and glass are combined to make four kinds of slit channels with different charge characteristics: i) neutral-neutral, ii) glass-glass, iii) neutral-PDMS and iv) neutral-glass walls. Their walls are characterized by uniform surface charge densities determined from experimental data of zeta potential. Both the nonmonotonic chain size variation and the loss of long-range bond vector correlation, previously observed under confinement in the PDMS-PDMS slit, are also found in the neutral slit, demonstrating the nonelectrostatic origin of such crossover behaviors. As expected, the effect of wall charges is negligible at sufficiently high medium ionic strength of 100mM but it becomes significant in the opposite limit of 0.01mM. In the latter case, the high charge density of glass walls strengthens the effective confinement of a negatively charged polyelectrolyte and produces a xanthan structure comparable to that confined in a much narrower neutral slit. The obtained structural data suggest the possibility of controlling the structure of confined polyelectrolytes by the modification of surface charge characteristics of micro/nanofluidic devices in combination with the adjustment of the medium ionic strength.

Two Cases of Auricular Salvage after Wide Excision of Malignant Tumor at Periauricular Area (이개 주변 악성종양의 광범위절제술 후 이개의 보존 2례)

  • Kim, Kyul-Hee;Chung, Chul-Hoon;Chang, Yong-Joon;Lee, Jong-Wook;Rho, Young-Soo;Kim, Chang-Woo
    • Korean Journal of Head & Neck Oncology
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    • v.25 no.1
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    • pp.39-42
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    • 2009
  • Wide excision for curative treatment of malignant tumor on periauricular area often leads to loss of the external ear. But the auricle has rich vascular supply, Conservation of auricular contour is possible through salvage and engineering of remained auricular tissue. We experienced two cases of auricular salvage after wide excision of malignant tumor. In the first case, we performed two-staged technique. In first step, we covered soft tissue defect on periauricualr area with the anterolateral thigh free flap and remained auricle was floating over the flap after split-thickness skin graft was applied on it's posterior raw surface because it's survival was not confirmed. Second step was reposition of remained auricule on the anterolateral thigh flap. In the second case, we packed in periauricular dead space and external auditory canal with temoporalis muscle and temporoparietal fascial flap and then covered the flap with split thickness skin graft. In these two cases, there were no recurrence of tumors and we obtained cosmetically & functionally satisfactory results.

Characteristics of Antenna Factor for a Calculable Dipole Antenna above Ground Plane in 1~3 GHz Frequency Band (1~3 GHz 대역용 계산가능 다이폴안테나의 접지판 위 안테나 인자 특성)

  • Lim, Sung-Min;Kim, Sang-Myung;Jung, Sung-Woo;Kim, Ki-Chai
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.19 no.9
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    • pp.1991-1998
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    • 2015
  • This paper presents the antenna factor characteristics of a calculable dipole antenna with a hybrid balun, installed above ground plane vertically and horizontally, using Method of Moments (MoM). An expression for the antenna factor is formulated using the concept of power mismatch loss. The input impedance and effective length of the antenna, which are in the formula of the antenna factor, are calculated using the MoM. The results show that the antenna factors above a ground plane are agreed with the free space antenna factors within ± 0.14 dB. The horizontal antenna factors are varied more by 0.2 dB than the vertical antenna factors.

A Study on the Propagation Characteristics of Wireless Communication System for Firefighters in Kimhae Site (김해지역 소방무선통신시스템의 전파특성 연구)

  • Lee, Su-Bin;Ko, Bong-Jin
    • Journal of Advanced Navigation Technology
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    • v.19 no.2
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    • pp.168-174
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    • 2015
  • Wireless communication system for firefighters has an important role as the last communication method between the commander and the firefighters in disaster sites like fire. But the operation of Gyeongnam wireless communication system is installed, and maintained and controlled without criteria for the selection of a transmitting station and the analysis of propagation environment because of the lack of budget and the absence of professional personnel. To improve the performance of the radio station, this paper theoretically calculated free space loss of UHF 400 MHz band used by all firefighters in Gyeongnam and diffractions caused by single and multiple obstacles and computed the error after comparing the results of the actual measurement to those of simulation with FRAS operated by KFL. In the results, Deygout model was the most consistent with the actual measurement for 400MHz band in Kimhae site.

Learning Curve and Complications Experience of Oblique Lateral Interbody Fusion : A Single-Center 143 Consecutive Cases

  • Oh, Bu Kwang;Son, Dong Wuk;Lee, Su Hun;Lee, Jun Seok;Sung, Soon Ki;Lee, Sang Weon;Song, Geun Sung
    • Journal of Korean Neurosurgical Society
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    • v.64 no.3
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    • pp.447-459
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    • 2021
  • Objective : Oblique lateral interbody fusion (OLIF) is becoming the preferred treatment for degenerative lumbar diseases. As beginners, we performed 143 surgeries over 19 months. In these consecutive cases, we analyzed the learning curve and reviewed the complications in our experience. Methods : This was a retrospective study; however, complications that were well known in the previous literature were strictly recorded prospectively. We followed up the changes in estimated blood loss (EBL), operation time, and transient psoas paresis according to case accumulation to analyze the learning curve. Results : Complication-free patients accounted for 43.6% (12.9%, early stage 70 patients and 74.3%, late stage 70 patients). The most common complication was transient psoas paresis (n=52). Most of these complications occurred in the early stages of learning. C-reactive protein normalization was delayed in seven patients (4.89%). The operation time showed a decreasing trend with the cases; however, EBL did not show any significant change. Notable operation-induced complications were cage malposition, vertebral body fracture, injury to the ureter, and injury to the lumbar vein. Conclusion : According to the learning curve, the operation time and psoas paresis decreased. It is important to select an appropriately sized cage along with clear dissection of the anterior border of the psoas muscle to prevent OLIF-specific complications.

Preparation and Microwave Absorption Properties of the Fe/TiO2/Al2O3 Composites

  • Li, Yun;Cheng, Haifeng;Wang, Nannan;Zhou, Shen;Xie, Dongjin;Li, Tingting
    • Nano
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    • v.13 no.11
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    • pp.1850125.1-1850125.12
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    • 2018
  • To reduce the imbalance of impedance matching between the magnetic metal nanowires and free space, $Fe/TiO_2$ core/shell nanowire arrays with different diameters were fabricated in the templates of anodic aluminum oxide membranes by electrodeposition. The influences of the microstructure on the microwave absorption properties of the $Fe/TiO_2/Al_2O_3$ composites were studied by the transmission/reflection waveguide method. It was demonstrated experimentally that both the interfacial polarization and the diameter of the $Fe/TiO_2$ core/shell nanowires have critical effects on the microwave absorption properties. We also investigated the angle dependence of the microwave absorption properties. Due to the interfacial polarization and associated relaxation, the $Fe/TiO_2/Al_2O_3$ composites exhibited optimal microwave absorption properties when microwave propagation direction was accordant with the axis of the nanowires. Finally, we managed to obtain an optimal reflection loss of below -10 dB (90% absorption) over 10.2-14.8 GHz, with a thickness of 3.0 mm and the minimum value of -39.4 dB at 11.7 GHz.

A Study of Critical Items and Related Standards on Designing for Passive Apartments (패시브 공동주택 계획을 위한 설계 중점항목 및 관련 기준 연구)

  • Lee, Myoung-Ju
    • Journal of the Architectural Institute of Korea Planning & Design
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    • v.34 no.7
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    • pp.21-29
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    • 2018
  • This study aimed to find and suggest the purpose of future plans, critical items on designing and Related standards to amend construction standards for domestic energy saving and environmentally friendly housings. It would also activate and increase the supplies of passive house minimizing the problems on current apartment housings in winter and reducing heating energy which brings fine dust pollution. After defining the standard model of Korean apartment housings(reference model), this study calculated the amount of heating energy demand per unit area annually as applying the yearly changed standards from 2008 to 2017 to existing standard model. It turned out that applying 2017 construction standards of energy saving and eco-friendly housings to reference model has saved up to 75% of heating energy demand comparing to the one applied 2008's. However, it still could not solve the fundamental problems such as winter fungus, condensation, freezing, freeze and burst, and insulation weakness space, and could not be free from fine dust particles. To solve them, this study suggested improved standards adding critical items on design related to outside insulation, cut off the heat-bridge, enforce air-tightness and heat change efficiency on heat recovery ventilator. As a result, it has reduced more than 10% of heat demand from 2017. It would be more than 90% of savings from 2008 if we make the amount of heat loss be zero on heat bridge on designing stage in the future.

Evaluation of the Absorbing Performance of Radar-absorbing Structure with Periodic Pattern after the Low-velocity Impact (주기패턴 레이더 흡수 구조의 저속충격 후 흡수 성능 평가)

  • Joon-Hyung, Shin;Byeong-Su, Kwak
    • Composites Research
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    • v.35 no.6
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    • pp.469-476
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    • 2022
  • In this paper, the microwave absorbing characteristics after the impact of the radar-absorbing structure (RAS) consisting of periodic pattern sheet (PPS) and glass fiber-reinforced plastic (GFRP) were experimentally investigated. The fabricated RAS effectively absorbed the microwave in the X-band (8.2-12.4 GHz). In order to induce the damage to the RAS, a low-velocity impact test with various impact energy of 15, 40, and 60 J was conducted. Afterward, the impact damage was observed by using visual inspection, non-destructive test, and image processing method. Moreover, the absorbing performance of intact and damaged RAS was measured by the free-space measurement system. The experiment results revealed that the delamination damage from the impact energy of 15 J did not considerably affect the microwave absorbing performance of the RAS. However, fiber breakage and penetration damage with a relatively large damaged area were occuured when the impact energy was increased up to 40 J and 60 J, and these failures significantly degraded the microwave absorbing characteristics of the RAS.

Evaluation of Applicability of Circuit-analog Radar Absorbing Structures for High Temperature in 350℃ and Hot-wet Environment (고온용 Circuit-analog 전파흡수구조의 350℃ 및 열 수분 환경에서의 적용성 평가)

  • Min-Su Jang;Ho-Beom Kim;Heon-Suk Hong
    • Composites Research
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    • v.36 no.5
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    • pp.335-341
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    • 2023
  • We proposed a high-temperature circuit-analog radar absorbing structures (CA-RAS), and evaluated radar absorption performance and tensile properties in 350℃ and a hot-wet environment. The CA-RAS was implemented with a glass/cyanate ester composites and a square resistive pattern layer, and reflection loss was measured by 350℃ and after exposure of hot-wet condition using free space measurement. And the tensile strength at 350℃ and after exposure of hot-wet condition was measured according to the ASTM D638. The proposed CA-RAS showed a 4 GHz of -dB bandwidth and -20 dB of a peak value at 350℃. In addition, there was no deterioration in absorption performance after exposure to a hot-wet condition. The tensile strength value of more than 95% compared to the strength of the glass/cyanate ester composite was confirmed at 350℃ and after exposure of hot-wet condition. Through this, the applicability of CA-RAS proposed in this study was confirmed as a load bearing structure for stealth weapon exposed to high temperature and hot-wet environment.