• 천문학논총
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• 제30권2호
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• pp.591-592
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• 2015

X1822-371 is a low mass X-ray binary with an accretion disk corona exhibiting partial eclipses and pulsations in the X-ray band. We update its orbital ephemeris by combining new RXTE observations and historical records, with a total time span of 34 years. There were 11 RXTE observations in 2011 but the eclipsing profile can be seen in only 4 of them. The eclipsing center times were obtained by fitting the profile with the same model as previous studies. Combined with the eclipsing center times reported by Iaria et al. (2011), the O-C analysis was processed. A quadratic model was applied to fit the O-C results and produced a mean orbital period derivative of $\dot{P}_{orb}=1.339(25){\times}10^{-10}s/s$, which is slightly smaller than previous records. In addition to the orbital modulation from the orbital profile, we also present our preliminary results for measuring the orbital parameters using the orbital Doppler effect from the pulsation of the neutron star in X1822-371. The updated orbital parameters from eclipsing profiles will be further compared with the ones from pulsar timing.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.2
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• pp.347-352
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• 2006

Narrowband interference can severely degrade the performance of GPS receivers. Detecting the presence of interference and then characterizing it can lead to its removal. Receivers can be reconfigured to focus on other signals or satellites that are less vulnerable to that interference at that moment. Using hardware reconfigurability of FPGA receivers and characterizing the effect of narrowband interference on the GNSS signal quality lead us to a new RFI mitigation technique in which the highest quality and less vulnerable signal can be chosen at each moment. In the previous work [1], the post processing capability of a software GPS receiver, has been used to detect and characterize the CW interference. This is achieved by passing the GPS signal and the interference through the correlator. Then, using the conventional definition of C/No as the squared mean of the correlator output divided by its variance, the actual C/No for each satellite is calculated. In this work, first the 'Exclusion zone' for each satellite signal has been defined and then by using some experiments the effects of different parameters like signal power, jamming power and the environmental noise power on the Exclusion zone have been analyzed. By monitoring the Doppler frequency of each satellite and using the actual C/No of each satellite using the traditional definition of C/No and actual data from a software GPS receiver, the decision to reconfigure the receiver to other signal can be made.

• 대한원격탐사학회지
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• 제26권3호
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• pp.297-304
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• 2010

Since the change in Doppler centroid according to moving targets brings alteration to the phase in azimuth differential signals of synthetic aperture radar (SAR) data, one can measure the velocity of the moving targets using this effect. In this study, we will investigate theoretically measuring the velocity of an object from azimuth differential signals by using range compressed data which is the interim outcome of treatment from the simulated SAR raw data of moving targets on the background of sea clutter. Also, it will provide evaluation for the elements that affect the estimation error of velocity from a single SAR sensor. By making RADARSAT-1 simulated image as a specific case, the research includes comparisons for the means of velocity measurement classified by the directions of movement in the four following cases. 1. A case of a single target without currents, 2. A case of a single target with tidal currents of 0.5 m/s, 1 m/s, and 3 m/s, 3. A case of two targets on a same azimuth line moving in a same direction and velocity, 4. A case of a single target contiguous to land where radar backscatter is strong. As a result, when two moving targets exist in SAR image outside the range of approximately 256 pixels, the velocity of the object can be measured with high accuracy. However, when other moving targets exist in the range of approximately 128 pixels or when the target was contiguous to the land of strong backscatter coefficient (NRCS: normalized radar cross section), the estimated velocity was in error by 10% at the maximum. This is because in the process of assuming the target's location, an error occurs due to the differential signals affected by other scatterers.

• 한국산학기술학회논문지
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• 제22권2호
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• pp.311-318
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• 2021

수중에서는 공기 중에서의 신호 전달과는 달리 음파에 의해 신호가 전달된다. 또한 음파는 해수면, 해저면, 수온, 염분 등 다양하고, 복잡한 수중 환경 특성으로 인해 직접 혹은 반사 등의 간접 경로로 전달된다. 이런 복잡한 수중 환경에서 잠수함의 생존성과 적 함정으로부터 피탐 위험성의 정도를 파악하기 위해 반드시 수행하는 시험이 수중방사 소음 측정 시험이다. 수중방사 소음 측정을 위한 여러 조건들 중 가장 중요한 것이 측정 센서와 잠수함과의 거리이다. 보통 수중방사 소음의 음원 준위 측정은 측정 센서와 잠수함과의 최근접 점(CPA : Closet Point of Approach) ±수 미터내에서 이루어져야 측정한 음원 준위 값을 유효한 것으로 간주한다. 이에 본 연구에서는 다중 경로 신호들의 도플러 천이 주파수 및 다른 도달 시간 차 신호를 추정하는 방법으로 수중음원에 대한 거리 추정 방법을 제시하였다. 제안한 방법의 타당성을 고찰하기 위해 수중 채널 전달 모델 기반의 모의실험을 수행하였다.

• 한국정보통신학회논문지
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• 제23권11호
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• pp.1434-1442
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• 2019

본 논문에서는 인천 덕적도 부근 해안에서 2017년 7월 5일부터 24시간 동안 채널 변화를 지속적으로 측정하였다. 수중 채널은 실시간으로 시간 축에서 변화와 주파수 축에서 변화가 발생함에 따라서 다양한 채널 환경 특성을 가지고 있으며, 다중 경로 페이딩 및 도플러 효과 등으로 인하여 수중 통신 성능저하가 발생한다. 따라서, 본 연구에서는 실해역 수중 통신 환경에서의 통신 성능 향상을 위하여 시간 및 주파수 영역에서의 반복 전송 다이버시티 기법을 적용하여 수중 채널 환경에서의 OFDM 시스템 성능 분석에 관한 연구를 수행하였다. 수집한 데이터를 이용하여 시간과 주파수 영역에서의 채널 환경 비교를 수행하였으며, 파일럿 배치 간격과 시간 및 주파수 축에서의 반복 전송 회수에 따른 BER 성능 분석을 수행하였다.

• 한국가시화정보학회지
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• 제19권3호
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• pp.84-91
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• 2021

Effervescent tablets generate gas bubbles when chemical reaction occurs between water and tablets. Most of previous studies have been focused on pharmaceutical characteristics of tablets. However, for their applications in disinfectants, cleaners, and pesticides, physical characteristics of bubbles released from the effervescent tablets when they are in water are important. In this study, we experimentally investigated the characteristics of microbubbles generated by an effervescent tablet made of sodium bicarbonate and tartaric acid using PDPA and high-speed camera. Microbubbles were generated using different weights of effervescent tablet as well as in different water temperature. The experimental study shows increase in reaction time, bubble concentration and rise velocity as the weight of effervescent tablet increases from 1 to 20 g. The decrease in average bubble diameter was observed when the temperature of water increased from 25 to 45 ℃. Further, reaction time varies inversely with increase in water temperature, while bubble rise velocity is directly proportional to increase in water temperature. Effervescent table continuously generates the bubble with approximately constant diameter (235 ㎛) in the water. However, bubble concentration and bubble rise velocity decreased over time.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• 제25권2호
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• pp.147-162
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• 2022

Purpose: To design a prospective study on endovascular closure of congenital portosystemic shunts. The primary endpoint was to assess the safety of endovascular closure. The secondary endpoint was to evaluate the clinical, analytical and imaging outcomes of treatment. Methods: Fifteen patients (age range: 2 days to 21 years; 10 male) were referred to our center due to congenital portosystemic shunts. The following data were collected prior to treatment: age, sex, medical history, clinical and analytical data, urine trimethylaminuria, abdominal-US, and body-CT. The following data were collected at the time of intervention: anatomical and hemodynamic characteristics of the shunts, device used, and closure success. The following data were collected at various post-intervention time points: during hospital stay (to confirm shunt closure and detect complications) and at one year after (for clinical, analytical, and imaging purposes). Results: The treatment was successful in 12 participants, migration of the device was observed in two, while acute splanchnic thrombosis was observed in one. Off-label devices were used in attempting to close the side-to-side shunts, and success was achieved using Amplatzer™ Ductus-Occluder and Amplatzer™ Muscular-Vascular-Septal-Defect-Occluder. The main changes were: increased prothrombin activity (p=0.043); decreased AST, ALT, GGT, and bilirubin (p=0.007, p=0.056, p=0.036, p=0.013); thrombocytopenia resolution (p=0.131); expansion of portal veins (p=0.005); normalization of Doppler portal flow (100%); regression of liver nodules (p=0.001); ammonia normalization (p=0.003); and disappearance of trimethylaminuria (p=0.285). Conclusion: Endovascular closure is effective. Our results support the indication of endovascular closure for side-to-side shunts and for cases of congenital absence of portal vein.

• Archives of Plastic Surgery
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• 제37권5호
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• pp.519-525
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• 2010

Purpose: Of various effects of relaxin, we assumed that anti-fibrotic effects, neovascularization effects and vasodilatation effects of relaxin might enhance the survival rate of skin flap. In the current study, we used adenovirus expressing relaxin genes to examine whether these genes could enhance the survival rate of a skin flap. Methods: A total of 30 Sprangue-Dawley rats were divided into three groups: RLX group (10; relaxin virus injected group), CTR group (10; no gene coded virus injection group), and PBS group (10; PBS injected group). Each group was intradermally injected with the virus ($10^7$ PFU) and PBS 48 hours before and immediately before the flap elevation. A distally based flap $3{\times}9\;cm$ in size was elevated on the dorsal aspect of each rat. Following this, a flap was placed in the original location and then sutured using a #4-0 Nylon. A surviving area of the flap was measured and then compared on postoperative days 3, 7 and 10. Using a laser Doppler, the amount of blood flow was measured. On postoperative day 10, tissues were harvested for histologic examination and the number of blood vessels was counted. Results: There was a significant increase in the area of the flap survival in the RLX group on postoperative days 3 and 7. The Doppler measurement also showed significantly increased blood flow immediately after the operation and on postoperative days 7 and 10. The number of blood vessels was significantly greater in the RLX group in the tissue harvested on postoperative day 10. The VEGF concentration was significantly higher in the RLX group than others in the tissues harvested on postoperative day 10. Conclusion: Following an analysis of the effects of relaxin-secreting adenovirus on the survival of a flap, the surviving area of the flap and the blood flow also increased. A histopathology also showed an increase in the number of blood vessels and the concentration of VEGF.

• 한국항행학회논문지
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• 제21권2호
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• pp.171-178
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• 2017

본 논문에서는 위성항법장치 (GPS; global positioning system)를 보조센서로 사용하는 위치추정알고리즘의 성능을 검증하기 위해 호버링타입 무인잠수정에 알고리즘을 적용하여 실제 해역에서 실험을 수행하였다. 적용된 알고리즘은 무인잠수정에 탑재된 도플러 속도계 (DVL; doppler velocity logger), TCM (tilt-compensated compass module)을 이용한 추측항법의 시간에 따라 누적되는 위치오차를 개선하기 위한 알고리즘이다. 수면에서 GPS 위치정보를 수신하여 무인잠수정의 위치와 진북에 대한 TCM의 방향각 바이어스 오차를 추정하고, 이를 통해 진북 (geodetic north) 기준의 좌표계에 대한 추측항법을 수행한다. 실제 해역에서 방향각 제어 실험을 수행한 결과, 위치추정알고리즘을 통해 기존 추측항법의 위치오차가 개선되고 TCM의 방향각 바이어스 오차를 추정함을 확인하였다.

• Journal of Radiation Protection and Research
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• 제29권4호
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• pp.263-268
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• 2004

한국원자력연구소에서 감마선과 전자를 동시측정하기 위한 목적으로 제작된 Prototype phowich를 이용하여 감마선에 대한 섬광체의 비선형성에 대한 연구를 수행하였다. 제작된 Prototype phoswich는 $2'{\times}2'$ CsI(Tl)와 Plastic scintillator 그리고 하나의 PMT로 구성되어 있다. 몬테칼로 방법을 이용하여 $^{137}Cs$과 $^{60}Co$ 선원의 Prototype phoswich 계측기의 반응함수(Detector Response Function, 이하 DRF)를 구하였으며 이를 점증하기 위하여 제작된 Prototype phoswich를 이용, 실험을 통하여 DRF를 구한 뒤 비교하였다. 계측기의 DRF를 정확하게 모사하기 위하여 CsI(Tl) 섬광체의 Electron response와 섬광체 내에서의 광전효과를 고려하는 Simplified elec윤on cascade sequence 정보를 이용하여 CsI(Tl) 섬광체의 감마선에 대한 비선형성을 계산하였다. $^{137}Cs$ 선원의 경우 전산모사를 통하여 구한 DRF 결과는 실험값과 비교적 잘 일치함을 알 수 있었으나 $^{60}Co$의 경우에는 선원의 결과와는 달리 전산모사 결과와 실험값에 약간의 차이가 남을 알 수 있었다. 이는 $^{137}Cs$ 선원과는 달리 $^{90}Co$은 1.17 MeV와 1.13 MeV 두 개의 광자를 동시에 방출하기 때문에 동시효과에 의한 불착실성 등이 그 외 다른 불확실성 등과 함께 증폭되어 나타나기 때문이다. 본 연구를 통해 Phoswich내 CsI(Tl)의 감마선 비선형성에 대한 분석을 수행하였으며 이를 통하여 비선형성이 고려된 개선된 Phoswich DRF를 생산하고 이를 실험값과 비교 검증할 수 있었다. 섬광체의 Electron channel운g effect, Doppler broadening effect 및 Transfer resolution 등과 같은 후속연구가 추가된다면 좀더 정확한 Phoswich의 DRF를 전산 모사하는 것이 가능해질 것이다.