30 research outputs found
Area-based velocimetry using TDLAS for low-speed flow
No full textThis study presents an absorption-area-based method for the measurement of gas flow velocity using diode laser absorption spectroscopy. In the proposed method, the gas flow velocity is determined using the area difference between the absorption lines. To verify the proposed method, flow velocity measurements are conducted for test conditions with a velocity range of 5–30 m/s in a low-speed wind tunnel, and the results are compared with those of the conventional method using the Doppler-shifted peak. Oxygen in the air is selected as the target gas. By comparing the flow velocity measurement results of the conventional method and the proposed area-based method, it is confirmed that the measurement precision is improved when the proposed area-based method is used. Moreover, the measurement accuracy of the proposed area-based method is significantly improved at a relatively low-speed range of 5–10 m/s compared to the conventional method.
Pressure, temperature, and velocity measurement of supersonic flows using TDLAS with triangular laser beam path
No full textThis study presents tunable diode laser absorption spectroscopy techniques for simultaneous measurement of pressure, temperature, and velocity of supersonic flows. A triangular laser beam path is proposed to facilitate single-side installation of the tunable diode laser absorption spectroscopy system, velocity measurement in the passage with parallel side walls, and signal amplification by enhancing laser path length in the flow. Flow properties such as pressure, temperature, and velocity are determined from a single absorption line through a proposed spectroscopic analysis procedure. To demonstrate the proposed techniques, a tunable diode laser absorption spectroscopy system that detects an absorption line of molecular oxygen is utilized, and supersonic air flows are generated using a shock tunnel and a blow-down type wind tunnel. Through shock tunnel and wind tunnel testing, it is confirmed that the proposed tunable diode laser absorption spectroscopy techniques can be used for supersonic flow diagnosis.
Experimental performance evaluation of a single-body typed TDLAS sensor using a scramjet ground test facility
No full textThe performance evaluation of a single-body typed TDLAS sensor was experimentally conducted using a scramjet ground test facility. The scramjet ground test facility includes model scramjet isolator and combustor. The model scramjet isolator of the test facility can simulate the air flow condition of total temperature of 1,220 K, total pressure of 862 kPa, and Mach number of 2.43 which are representative of the internal flow condition of the scramjet isolator. To evaluate the performance of the single-body typed TDLAS sensor, the TDLAS sensor was flush-mounted on the model scramjet isolator wall of the test facility during the ground test, and the structural integrity and operability of the TDLAS sensor were analyzed based on the robustness of the TDLAS's components, the stability of signal acquisition, and an accuracy of the measured data. The experimental ground test results demonstrated that the single-body typed TDLAS sensor in this study can withstand and operate well under the harsh mechanical and thermal environments of the model scramjet isolator.
TouchPhoto: Enabling Independent Picture Taking and Understanding for Visually-Impaired Users
No full textThis paper presents TouchPhoto, which provides visualaudio- tactile assistive features to enable visually-impaired users to take and understand photographs independently. A user can take photographs under auditory guidance and record audio tags to aid later recall of the photographs' contents. For comprehension, the user can listen to audio tags embedded in a photograph while touching salient features, e.g., human faces, using an electrovibration display. We conducted two user studies with visually-impaired users, one for picture taking and the other for understanding and recall, in a two-month interval. They considered auditory assistance as very useful for taking and understanding photographs and tactile features as helpful but to a limited extent. © 2019 Copyright held by the owner/author(s).1
고속 유동 진단을 위한 레이저 흡수 분광법 기반 소형 기체분석 센서의 설계
No full text학위논문(박사) - 한국과학기술원 : 항공우주공학과, 2022.8,[viii, 142 p. :]To diagnose the operation state of a high-speed aerospace engine, a non-intrusive sensor that can measure the flow properties could be required. The tunable diode laser absorption spectroscopy (TDLAS), which can characterize the flow through spectroscopic measurement and analysis by using a tunable laser source, is a suitable technique for such high-speed flow diagnosis. In this study, a laser absorption spectroscopy-based compact gas analysing sensor for high-speed flow diagnosis is designed and applied to stationary gas conditions and supersonic flow conditions which have various pressures and temperatures.
A gas analysing sensor for an air-breathing engine intake is designed based on laser absorption spectroscopy. The number of optical and electrical components is reduced and the characteristics are optimized to detect the weak absorption lines of oxygen molecules while making the gas analysing sensor smaller. A triangular spiral-shaped laser beam path, which could be applied to a rectangular flow passage, is proposed for the doppler shift detection and absorption strength amplification. The design concepts of adjustable hardware components are proposed to miniaturize the gas analysing sensor. The procedure of converting the temporal raw signal measured by the gas analysing sensor into a spectral absorbance is introduced.
A spectroscopy method for the designed gas analysing sensor is proposed to measure multiple gas properties from a single absorption line. Although the usage of multiple absorption lines can improve the measurement accuracy and the number of measurable gas properties, measurement of multiple absorption lines could be difficult in the designed gas analysing sensor because it utilizes a single laser source. Therefore, a spectroscopy method that can measure the multiple gas properties is required. In the singleline absorption spectroscopy method proposed in this study, absorbance loss that may occur in the direct absorption spectroscopy is predicted and the measured absorption line is recovered by using the predicted absorbance. Multiple gas properties such as pressure and temperature are then determined by matching the recovered absorption line with the calculated line. To verify that the proposed single-line absorption spectroscopy method could be used for gas property measurement, air conditions with various pressures and temperatures are made in a gas chamber. The gas properties of the test conditions measured using the gas analysing sensor are compared with the gas properties measured using the traditional sensors.
To verify that the designed compact gas analysing sensor is applicable for the high-speed flow diagnosis, supersonic wind tunnel tests are performed. A shock tunnel and a supersonic wind tunnel with an electric heater are used as the ground facilities. The pressure, temperature, and speed of the generated supersonic flow are measured using the designed compact gas analysing sensor with the proposed single-line absorption spectroscopy method. The measured flow properties are compared with the values measured and calculated using traditional techniques such as pressure sensors, shock angle measurement via flow visualization, and isentropic relation calculation. It is confirmed that the compact gas analysing sensor designed in this study could be applicable for the high-speed flow diagnosis.한국과학기술원 :항공우주공학과
Single-cell RNA sequencing of human nail unit defines RSPO4 onychofibroblasts and SPINK6 nail epithelium
No full textKim et al. conducted single-cell RNA sequencing to determine the transcriptome profiles of human nail units using polydactyly specimens to demonstrate mesenchymal and epithelial cell populations, characterized by RSPO4 and SPINK6 respectively. RSPO4 + onychofibroblasts localized with LGR6 + nail matrix, leading to WNT/ β-catenin activation and suggesting a role for onychofibroblasts in onychomatricoma pathogenesis
Study of hypersonic stagnation flow in a shock tube
No full text학위논문(석사) - 한국과학기술원 : 항공우주공학과, 2018.8,[vi, 74 p. :]우주 발사체의 재진입 상황에서 발생하는 마하 20 이상의 극초음속 환경에 대한 연구는 1960년대 이후로 활발히 진행되어 왔다. 반면 마하 10 이하의 속도로 지구 대기권 내에서 순항하는 비행체는 다양한 초음속 추진 기관의 발전 따라 2010년도 이후로 현재까지도 활발히 개발이 진행되고 있다. 대기권 내에서 마하 10 이하의 속도를 가지는 극초음속 비행체의 정체점 환경에 대한 정확한 모사나 열화학적 및 물리적 현상에 대한 이해는 아직 공개된 바 없으나 비행체 개발에 있어 중요한 문제이다.
본 연구에서는 지상 시험 장비인 충격파관을 사용하여 마하 10 이하의 극초음속 비행체 선두부의 정체점 유동 환경을 모사함과 동시에, 비행체의 표면 상태를 모사할 수 있는 세가지 기법이 도입되었다. 충격파관에서 끝단벽과 반사충격파 사이에서 형성되는 조건 5를 비행체 선두부의 유동 환경으로 모사하였다. 끝단벽의 표면 물질 모사를 위해 열차폐 재료에서 사용되는 탄소, 규소 및 산소로 구성된 코팅재를 사용하였으며, 비교 실험을 위해 스테인레스 스틸로 제작된 끝단벽을 사용하였다. 실제 비행체에서 공력 가열을 통해 온도가 상승한 표면을 모사하기 위해 전열선을 이용한 끝단벽 가열 기법을 개발하였으며, 이를 통해 표면 온도를 1000 K으로 상승시켰다. 그리고 삭마 현상에 의한 표면 거칠기 변화를 모사하기 위해 사포를 사용하여 거칠기를 변화시켰다. 이러한 표면의 재질, 온도, 거칠기의 변화가 기체-표면 간의 화학 반응과 복사에 미치는 영향을 관찰하였다. 유동 가시화 기법을 통해 표면에서 발생하는 물리·화학적 양상을 관찰하고 이를 UV에서 가시광 파장 대역에서의 방출 분광 분석 기법을 통하여 열·화학적 특성을 파악하였다. 유동 가시화 기법을 통해 거친 탄소 표면 실험에서 표면 물질이 유동 속으로 빠르게 침투하는 것을 확인하였다. 유동 속으로 침투한 입자들은 입자 구름을 형성하였으며, 극히 짧은 시간 내에도 주변 유동의 온도에 의해 가열되어 강한 흑체 복사을 내는 것이 확인되었다. 이러한 입자 구름에서 발생한 발광은 가시광 파장 대역에서의 총 복사 세기에서 큰 비중을 차지하는 것이 관찰되었다. 나트륨, 칼륨, 그리고 칼슘은 탄소 코팅 물질에 극소량 함유되어 있으며, 거친 탄소 표면 끝단벽 실험에서 더 강한 방출선을 내는 것이 확인되어 표면 물질의 유동 침투 현상이 원자 수준에서 도 일어남을 확인하였다. 가열된 탄소 표면에서 OH 분자의 A-X 천이에 의한 분자 방출선의 세기가 약화되는 것이 관찰되어 뜨거운 표면에서는 차가운 표면과는 다른 화학 반응이 있을 것으로 예측되었다. 마하 20 이상의 유동 환경에 비해 활발한 표면 화학 반응은 관찰되지 않았고, CN 등의 강한 가시광 복사원도 관찰되지 않았으나, 표면에서 떨어져 나온 입자들에 의한 흑체 복사가 전체 복사량에서 큰 영향을 차지하는 것이 관찰되었다.한국과학기술원 :항공우주공학과
