• 한국초전도ㆍ저온공학회논문지
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• 제8권2호
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• pp.20-24
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• 2006

Recently, utility network is becoming more and more complicated and huge due to IT and OA devices. In addition to, demands of power conversion devices which have non-linear switching devices are getting more and more increased. Consequently, because of the non-linear power semiconductor devices, current harmonics are unavoidable. Sometimes those current harmonics flow back to utility network and become one of the main reasons which can make the voltage distortion. Also, it makes noise and heat loss. On the other hands, voltage sag from sudden increasing loads is also one of the terrible problems inside of utility network. In order to compensate the current harmonics and voltage sag problem, AF(active filter) systems could be a good solution method. SMES is a very good promising source due to it's high response time of charge and discharge. Therefore, the combined AF and SMES system can be a wonderful device to compensate both harmonics current and voltage sag. However, SMES needs a superconducting magnetic coil. Because of using this superconducting magnetic coil, quench problem caused by unexpected reasons have always been unavoidable. Therefore, to solve out mentioned above, this paper presents a decisive method using shunt and series active filter system combined with SMES. Especially, authors analyzed the change of original energy capacity of SMES regarding to the size of resistance caused by quench of superconducting magnetic coil.

• Nanomaterials
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• 제12권22호
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• pp.4096-4107
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• 2022

In this work, a hybrid-phase transition field-effects-transistor (hyper-FET) integrated with phase-transition materials (PTM) and a multi-nanosheet FET (mNS-FET) at the 3 nm technology node were analyzed at the device and circuit level. Through this, a benchmark was performed for presenting device design guidelines and for using ultra-low-power applications. We present an optimization flow considering hyper-FET characteristics at the device and circuit level, and analyze hyper-FET performance according to the phase transition time (TT) and baseline-FET off-leakage current (I_OFF) variations of the PTM. As a result of inverter ring oscillator (INV RO) circuit analysis, the optimized hyper-FET increases speed by +8.74% and reduces power consumption by -16.55%, with IOFF = 5 nA of baseline-FET and PTM TT = 50 ps compared to the conventional mNS-FET in the ultra-low-power region. As a result of SRAM circuit analysis, the read static noise margin is improved by 43.9%, and static power is reduced by 58.6% in the near-threshold voltage region when the PTM is connected to the pull-down transistor source terminal of 6T SRAM for high density. This is achieved at 41% read current penalty.

• 대한조선학회논문집
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• 제50권3호
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• pp.190-198
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• 2013

In order to predict acoustic pressure distributions by exterior incident wave at Cylindrical Hydrophone Array (CHA) sensor's positions, acoustic pressure analysis is performed by using beam tracing method. Beam tracing method is well-known of reliable pressure analysis methods at high-frequency range. When an acoustic noise source is located at the center of rectangular room, acoustic pressure analysis is performed by using both beam tracing method and Power Flow Boundary Element Method (PFBEM). By comparing with results of beam tracing method and those of PFBEM, the accuracy of beam tracing method is verified. We develop the CHA pressure analysis program by verified beam tracing method. The developed software is composed of model input, sensor array creator, analysis option, solver and post-processor. We can choose a model option of 2D or 3D. The sensor array generator is connected to a sonar which is composed of center position, bottom, top and angle between sensors. We also can choose an analysis option such as analysis frequency, beam number, reflect number, etc. The solver module calculates the ray paths, acoustic pressure and result of generating beams. We apply the program to 2D and 3D CHA models, and their results are reliable.

• Journal of Communications and Networks
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• 제16권5호
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• pp.548-558
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• 2014

Load distribution is vital to the performance of multipath transport. The task becomes more challenging in real-time multimedia applications (RTMA), which impose stringent delay requirements. Two key issues to be addressed are: 1) How to minimize end-to-end delay and 2) how to alleviate packet reordering that incurs additional recovery time at the receiver. In this paper, we propose sub-packet based multipath load distribution (SPMLD), a new model that splits traffic at the granularity of sub-packet. Our SPMLD model aims to minimize total packet delay by effectively aggregating multiple parallel paths as a single virtual path. First, we formulate the packet splitting over multiple paths as a constrained optimization problem and derive its solution based on progressive approximation method. Second, in the solution, we analyze queuing delay by introducing D/M/1 model and obtain the expression of dynamic packet splitting ratio for each path. Third, in order to describe SPMLD's scheduling policy, we propose two distributed algorithms respectively implemented in the source and destination nodes. We evaluate the performance of SPMLD through extensive simulations in QualNet using real-time H.264 video streaming. Experimental results demonstrate that: SPMLD outperforms previous flow and packet based load distribution models in terms of video peak signal-to-noise ratio, total packet delay, end-to-end delay, and risk of packet reordering. Besides, SPMLD's extra overhead is tiny compared to the input video streaming.

• 한국산업보건학회지
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• 제27권4호
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• pp.333-351
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• 2017

Objectives: This study examines the relationships between indoor radon concentrations and distribution from soil geological mapping in the Hwacheon and Jangsu areas. Methods: GIS and a pivot table were used for inquiries about indoor radon contents, soil characteristics, and geological differences. Results: The Hwacheon area was characterized by the presence of normal and reverse faults as a passage of runoff for radon, sufficient occurrences of minerals containing uranium within granite as a radon source, a high concentration of radon within the granite area and clear differences of radon concentrations between granitic and metamorphic areas. The Jangsu area was characterized by the presence of normal faults, wide distributions of alluvium, and ambiguities on radon concentrations indoors among areas of geological differences. Considering the granite area and alluvium surrounded with granite areas, the characteristics of radon concentrations within soils and indoors in the Jangsu area are similar to those of the Hwacheon area. High concentrations are found with entisol and inceptisol in the Hawcheon area, but with entisol, inceptisol, and ultisol in the Jangsu area. High radon concentrations are found in sandy loam and/or loam. High concentrations are found in recently constructed or brick buildings, but low concentrations in traditional or prefabricated houses showing a high possibility of outward flow. Conclusions: The overall results suggest that radon concentrations in the Hwacheon and Jangsu area are dominantly influenced by geological characteristics with additional artificial influences.

• 한국물환경학회지
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• 제39권4호
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• pp.316-328
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• 2023

In this study, the characteristics of nonpoint pollutant outflow and contribution rate of pollution in Songya-stream mainstream and tributaries were analyzed. Further, water pollution management and improvement measures for pollution-oriented rivers were proposed. An on-site investigation was conducted to determine the inflow of major pollutants into the basin, and it was found that pollutants generated from agricultural land and livestock facilities flowed into the river, resulting in a high concentration of turbid water. Based on the analysis results of the pollution load data calculated through actual measurement monitoring (flow and water quality) and the occurrence and emission load data calculated using the national pollution source survey data, the S3 and S6 were selected as the concerned pollution tributaries in the Songya-stream basin. Results of cluster analysis using Pearson correlation coefficient evaluation and Density based spatial clustering of applications with noise (DBSCAN) technique showed that the S3 and S6 were most consistent with the C2 cluster (a cluster of Songya-stream mainstream owned area) corresponding to the mainstream of Songya-stream. The analysis results of the major pollutants in the concerned pollution tributaries showed that livestock and land pollutants were the major pollutants. Consequently, optimal management techniques such as fertilizer management, water gate management in paddy, vegetated filter strip and livestock manure public treatment were proposed to reduce livestock and land pollutants.

• 지구물리와물리탐사
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• 제21권3호
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• pp.171-182
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• 2018

탄성파 처리 기술개발 분야의 오픈-소스 소프트웨어인 Madagascar를 이용하여 신호 대 잡음비가 낮고 속도정보가 불확실한 현장 탄성파 자료에 대해 자료처리를 수행하고, 오픈-소스 소프트웨어의 현장 적용성을 시험하였다. 파이썬(python) 기반의 Madagascar는 방법론적으로는 다차원 자료 분석이 가능하고, 처리 공정의 재현성이 뛰어나 효율적인 자료처리가 가능하다는 장점이 있지만, 다소 복잡한 사용법과 자료 구조 시스템으로 인해 현장 자료에 대한 자료처리 사례는 많지 않다. 본 연구에서는 현장 자료에 대한 Madagascar의 효용성을 확인하기 위해 기본적인 탄성파 자료처리(자료입력, 지형 정보 일치, 진동수-파수 필터, 예측 곱풀기, 속도 분석, 수직 시간차 보정, 겹쌓기, 참반사 보정)를 수행하였다. 테스트를 위해 사용한 현장 자료는 서해 군산분지에서 에어건 음원과 480채널의 스트리머로 취득한 해양 탄성파 탐사자료이며, 각 자료처리 단계마다의 결과를 Landmark사의 상용 소프트웨어인 ProMAX (SeisSpace R5000)을 사용하여 처리한 결과와 비교하였다. 그 결과 데이터 입출력 및 관리, 처리 과정의 재현성 및 자동 속도 분석 측면에서는 Madagascar가 상대적으로 높은 효율성을 보였고, 신호 품질 향상을 위한 전처리 결과는 상용 소프트웨어와 유사함을 확인하였다. 반면에, 심부 지층에 대한 영상화 결과는 상용 소프트웨어로 처리한 결과가 보다 뛰어남을 확인하였다. 이러한 결과는 상용 소프트웨어의 경우 다양한 겹반사 제거 모듈이 적용되었고, 상호 대화식 인터페이스로 인해 보다 정교한 자료처리가 가능하였기 때문이다. 그러나, Madagascar의 경우에도 현재 전 세계에서 많은 연구자들이 다양한 자료처리 알고리듬을 개발하여 지속적으로 공개하고 있기 때문에, 향후 이러한 최신 알고리듬을 적용한다면 상업용 수준의 자료처리가 가능해져 보다 향상된 결과를 도출할 수 있을 것이다.

• Korean Journal of Radiology
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• 제21권1호
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• pp.58-67
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• 2020

Objective: Third-generation dual-source computed tomography (3rd-DSCT) allows dynamic myocardial CT perfusion imaging (dynamic CTP) with a 10.5-cm z-axis coverage. Although the increased radiation exposure associated with the 50% wider scan range compared to second-generation DSCT (2nd-DSCT) may be suppressed by using a tube voltage of 70 kV, it remains unclear whether image quality and the ability to quantify myocardial blood flow (MBF) can be maintained under these conditions. This study aimed to compare the image quality, estimated MBF, and radiation dose of dynamic CTP between 2ndDSCT and 3rd-DSCT and to evaluate whether a 10.5-cm coverage is suitable for dynamic CTP. Materials and Methods: We retrospectively analyzed 107 patients who underwent dynamic CTP using 2nd-DSCT at 80 kV (n = 54) or 3rd-DSCT at 70 kV (n = 53). Image quality, estimated MBF, radiation dose, and coverage of left ventricular (LV) myocardium were compared. Results: No significant differences were observed between 3rd-DSCT and 2nd-DSCT in contrast-to-noise ratio (37.4 ± 11.4 vs. 35.5 ± 11.2, p = 0.396). Effective radiation dose was lower with 3rd-DSCT (3.97 ± 0.92 mSv with a conversion factor of 0.017 mSv/mGy∙cm) compared to 2nd-DSCT (5.49 ± 1.36 mSv, p < 0.001). Incomplete coverage was more frequent with 2nd-DSCT than with 3rd-DSCT (1.9% [1/53] vs. 56% [30/54], p < 0.001). In propensity score-matched cohorts, MBF was comparable between 3rd-DSCT and 2nd-DSCT in non-ischemic (146.2 ± 26.5 vs. 157.5 ± 34.9 mL/min/100 g, p = 0.137) as well as ischemic myocardium (92.7 ± 21.1 vs. 90.9 ± 29.7 mL/min/100 g, p = 0.876). Conclusion: The radiation increase inherent to the widened z-axis coverage in 3rd-DSCT can be balanced by using a tube voltage of 70 kV without compromising image quality or MBF quantification. In dynamic CTP, a z-axis coverage of 10.5 cm is sufficient to achieve complete coverage of the LV myocardium in most patients.

• 수산해양기술연구
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• 제37권4호
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• pp.302-307
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• 2001

본 연구는 잠수기 어업용 수중무선전화기를 설계하는데 있어 최적의 반송 주파수와 송신 신호의 음원 준위를 결정할 목적으로 우리 나라 잠수기 주 조업장의 하나인 거제와 통영 해역의 해양 배경소음과 조업중인 잠수기 어장의 수중 소음에 대하여 검토, 고찰한 결과를 요약하면 다음과 같다. 1. 거제와 통영의 잠수기 어장의 해양 배경 소음을 분석한 결과, 음압 준위는 25∼301kHz 부근에서 가장 낮아 52∼57dB이었고, 주변 통항 선박량과 산업시설이 많은 거제 해역이 통영 해역보다 약 5dB 더 높았다. 2. 거제와 통영의 잠수기 어선의 조업중의 수중소음을 비교하면, 최저 음압준위는 30kHz 부근에서 거제 어장에서는 67dB로서 통영의 62d묘보다 5dB 높은 음압 준위를 나타냈다. 이것은 거제 해역은 잠수기 어선의 규모도 통영 해역의 잠수기 어선보다 약간 크고, 분사기를 사용하여 작업하는데 비해 통영 해역은 잠수기 어선의 크기도 상대적으로 작고, 주 어획 대상물이 달라 분사기를 사용하지 않는 것이 그 원인으로 판단된다. 3. 거제 해역의 패류 채취용 분사기를 사용할 때의 수중 소음의 음압 준위는 102dB었다. 4. 거제 해역의 조업중에 대한 수중 배경 소음을 67dB라 가정할 때, 최대 500m까지 통화하기 위한 송신 신호의 음원 준위는 131dB 정도이다. 그러나, 통영 해역의 잠수기 조업은 분사기를 사용하지 않는 조업으로 이 경우 배경 소음은 약 62dB로서 송신 신호의 음원 준위는 126dB정도이다. 잠수기 조업중이 아닌 경우 즉, 스쿠버 다이버용 수중무선 전화기인 경우에는 배경 소음이 52∼57dB이므로 송신 신호의 음원 준위는 l16∼121dB이면 될 것으로 판단된다. 협동학습 모형이 수학 수업에 보다 발전적으로 널리 적용되기를 기대한다.cal results well visualized the streamlines, pressure fields, and speed vectors of a simple cambered and slot cambered otter board with slot size 0.02C. The slot cambered one with slot size 0.02C was shown that pressure field was distributed moderately on front and back side of otter board. And, the delay and decrease of separation were favorably achieved by flow through slot. 4. Computed result on the pattern of hydrodynamic field and the values of C/sub L/ and C/sub D/ by the commercial CFD code, FLUENT, show almost the same as those of the experimental result.erence was found in its fragrance. And, no difference was found in brightness and viscosity between samples. As a result of conducting the palatability test, no difference was showed in the appearance, but as for the overall palatability

• 설비공학논문집
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• 제12권12호
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• pp.1098-1125
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• 2000

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering in 1998 and 1999 has been done. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environment. The conclusions are as follows. 1) A review of the recent studies on fluid flow, turbomachinery and pipe-network shows that many experimental investigations are conducted in applications of impingement jets. Researches on turbulent flows, pipe flows, pipe-networks are focused on analyses of practical systems and prediction of system performance. The results of noise reduction in the turbomachinery are also reported. 2) A review of the recent studies on heat transfer analysis and heat exchanger shows that there were many papers on the channel flow with the application to the design of heat exchanger in the heat transfer analysis. Various experimental and numerical papers on heat exchanger were also published, however, there were few papers available for the analysis of whole system including heat exchanger. 3) A review of the recent studies on heat pump system have focused on the multi-type system and the heat pump cycle to utilize treated sewage as the heat source. The defrosting and the frosting behaviors in the fin-tube heat exchanger is experimentally examined by several authors. Several papers on the ice storage cooling system are presented to show the dynamic simulation program and optimal operation conditions. The study on the micro heat pipes for the cooling of high power electronic components is carried out to examine the characteristics of heat and mass transfer processed. In addition to these, new type of separate thermosyphon is studied experimentally. 4) The recent studies on refrigeration/air conditioning system have focused on the system performance and efficiency for new alternative refrigerants. New systems operating with natural refrigerants are drawing lots of attention. In addition to these, evaporation and condensation heat transfer characteristics of traditional and new refrigerants are investigated for plain tubes and also for microfin tubes. Capillary tubes and orifice are main topics of research as expansion devices and studies on thermophysical properties of new refrigerants and refrigerant/oil mixtures are widely carried out. 5) A review of the recent studies on absorption cooling system shows that numerous experimental and analytical studies on the improvement of absorber performance have been presented. Dynamic analysis of compressor have been performed to understand its vibration characteristics. However research works on tow-phase flow and heat transfer, which could be encountered in the refrigeration system and various phase-change heat exchanger, were seemed to be insufficient. 6) A review of recent studies on duct system shows that the methods for circuit analysis, and flow balancing have been presented. Researches on ventilation are focused on the measurement of ventilation efficiency, and variation of ventilation efficiency with ventilation methods by numerous experimental and numerical studies. Furthermore, many studies have been conducted in real building in order to estimate indoor thermal environments. Many research works to get some information for cooling tower design have been performed but are insufficient. 7) A review on the recent studies on architectural thermal environment and building mechanical systems design shows that thermal comfort analysis is sitting environment, thermal performance analysis of Korean traditional building structures., and evaluation of building environmental load have been performed. However research works to improve the performance of mechanical system design and construction technology were seemed to be insufficient.