1,720,967 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.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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