120 research outputs found
Design and Assessment of Short-in-length Shape Transition Hypersonic Inlet with Circular Throat
No full textThis paper presents the design of an efficient, short-length shape transition inlet for hypersonic propulsion systems, operating at Mach 4 to 6. The inlet was shortened by approximately 24 % using a Busemann flow based on the median operating Mach number for streamline-tracing instead of the maximum operating Mach number. Additional upper circular arc of capture shape resulted in a compact compression surface that well preserves internal compression of the Busemann flow, and increased pressure rise by up to 31 % with higher total pressure recovery. The inlet was notched for maximum operating Mach number to minimize air spillage, and the range of operating Mach number and angle of attack was extended. Viscous effects were compensated by a proper truncation angle in order to maintain the exact circular throat shape for efficient manufacturing. The length-reduced inlet showed a wide operating range and high compression performance.
Promoter Single-nucleotide Polymorphisms Affecting Gene Regulation and being Associated with Drug Response or Cancer Susceptibility
No full textMechanical modelling of vestibular hair cell’s amplifying mechanism.
No full textINTRODUCTION: Vestibular hair cell is the basic sensory unit of nature’s inertia sensor. It has high sensitivity over broad dynamic range by combination of negative stiffness and adaptation mechanism.[1][2] To examine these biophysical mechanisms with a mechanical point of view[3], we developed a mechanical model of vestibular hair cell. We measure the system response and stiffness and observe similar characteristics with hair cell. This results help to better understanding of vestibular hair cell function.
METHODS: A mechanical model of stereocilia on hair cell consists of two inverted pendulums that demonstrate a pair of adjacent stereocilia. To make negative stiffness which induced by a transduction channels’ sudden opening, use pair of magnet which make repulsive force. Adaptation mechanism is mimicked by using stepping motor similar with molecular motor on stereocilia. Stiffness and temporal response was measured using force sensor and motion capture system.
RESULTS: Similar results from physiological stereocilia were observed. Negative stiffness region was observed near the origin and this region was shifted as motor made magnet moving side-to-side. And the spontaneous oscillation which known to induced by the interplay of the negative stiffness and the adaptation of the stereocilia also observed. Parameter study of the model well demonstrated the role of each system component.
CONCLUSIONS: Integration of adaptation and negative stiffness mechanism of hair cell was mechanically mimicked by two inverted pendulums and interacting moving magnet pair controlled by stepping motor and results is similar to the physiological measurement.
ACKNOWLEDGEMENTS: The work was supported by the Pioneer Research Program fund of the
Ministry of Education, Science and Technology.
Fig.1 Mechanical model of hair cell and force-displacement relation & time response of vestibular hair cell model.
REFERENCES
1. P.Martin. et al. PNAS. Vol.97, No.22, pp.12026-12031. 2000.
2. Peter G. Gillespie & Richard G. Walker. NATURE, Vol.413, 13. 2001.
3. Koeun Lim, Sukyung Park. Journal of Biomechanics. 42, 2158-2164. 2009
DNA-Sequencing RNA Ladders for High-Throughput Genomic Analysis by Mass Spectrometry Symposium Lecture
No full textTranscriptional Sequencing RNA Ladders for Large-Scale Mass Spectrometric Analysis of Genomic Polymorphism and Diversity Symposium Lecture
No full textRobust ridge regression estimators for nonlinear models with applications to high throughput screening assay data
No full textStatistical theory and robust methodology for nonlinear models with application to toxicology
No full textNonlinear regression models are commonly used in dose-response studies, especially when researchers are interested in determining various toxicity characteristics of a chemical or a drug. There are several issues one needs to pay attention to when fitting nonlinear models for toxicology data, such as structure for the error variance in the model and the presence of potential influential and outlying observations. In this dissertation I developed robust statistical methods for analyzing nonlinear regression models, which are based on robust M-estimation and preliminary test estimation (PTE) procedures. In the first part of this research the M-estimation methods in heteroscedastic nonlinear models are considered for two cases. In one case, the error variance is proportional to some known function of mean response, while in the other case the error variance is modeled as a polynomial function of dose. The asymptotic properties of the proposed M-procedures and the asymptotic efficiency of the proposed M-estimators are provided. In the second part I consider PTE-based methodology using M-methods for estimating the regression parameters. Based on the outcome of the preliminary test, the proposed methodology determines the appropriate error variance structure for the data and accordingly chooses the suitable estimation procedure. Since the resulting methodology uses M-estimators, it is expected to be robust to outliers and influential observations, although such issues have not been explored in this dissertation. Consequently, one does not have to pre-specify the error structure for the variances not does the user have to perform model diagnostics to choose a method of estimation. Some asymptotic results will be given to obtain the asymptotic covariance matrix of the PTE. Finally numerical studies are presented to illustrate the methodology. The results of the numerical studies suggest that the PTE using M-methods performs well and is robust to the error variance structure
유선추적형 극초음속 흡입구의 길이 단축을 위한 설계방법 연구
No full text학위논문(박사) - 한국과학기술원 : 항공우주공학과, 2024.2,[vii, 66 p. :]A scramjet propulsion system is the only promising design candidate for sustained hypersonic flight. A scramjet engine offers advantages over other air-breathing engines due to its lack of moving components and simple structure. These are achieved through the dual function of a scramjet inlet, which not only ingests but also compresses freestream air. A scramjet inlet is located at the front end of the propulsion system and is responsible for one of the key processes in the thermodynamic cycle by providing the necessary flow to the combustion chamber through an appropriate compression process. Therefore, the primary objective of an inlet design is to develop an aerodynamic surface that efficiently compresses the incoming air to enhance combustion, while also considering geometric constraints. A streamline-tracing technique is one of the methods used in aerodynamic design, generating the surface of the inlet by tracing streamlines of a known flow field with isentropic compression characteristics such as a Busemann flow field. A REST (Rectangular-to-Elliptical Shape Transition) type inlet is a representative example of streamline-traced inlets. A REST-type inlet, generated by integrating the streamline-tracing method with the shape transition, features a rectangular capture shape and an elliptical throat shape, exhibiting the isentropic compression characteristics of the Busemann flow field. By employing a notch process, unnecessary portions for compression are eliminated, resulting in reduced internal drag and improved starting characteristics. Streamline-traced inlets deliver the air with higher total pressure to the combustion chamber compared to wedge-type inlets, which rely on multiple oblique shock waves. However, a drawback of streamline-traced inlets is that the flow requires a longer compression length to undergo the isentropic compression process. Considering the short residence time of supersonic flow in the combustion chamber and the characteristics of the propulsion system that require an additional boosting device, the length of the inlet becomes a critical factor in both propulsion and aircraft design. This study presents a design method aimed at reducing the length of a scramjet inlet operating at Mach 4 to 6. The REST-type inlet was employed as a baseline, and the effect of each design feature was analyzed through computational fluid dynamics. Typically, hypersonic inlet designs have adopted the maximum operating Mach number as the design point in order to minimize flow spillage, resulting in an increase in the inlet length with higher opearating Mach number. However, in this study, the streamline-tracing method was employed with the Busemann flow field of the median operating Mach number, rather than the maximum operating Mach number. This approach reduced the length of the inlet by approximately 24%. To maximize the utilization of the reduced compression length, an additional circular arc was introduced along the outermost streamline of the Busemann flow field in the upper part of the capture shape. This modification resulted in a spatially efficient inlet shape while preserving the isentropic compression characteristics of the Busemann flow. As a result, the compression ratio was increased by 31% with a similar total pressure recovery. The inlet was notched for maximum operating Mach number to minimize air spillage, and the range of operating Mach number and angle of attack was extended. Viscous effects were compensated by an appropriate truncation angle in order to preserve the exact circular throat shape for efficient manufacturing. The length-reduced inlet showed a wide operating range and high compression performance.한국과학기술원 :항공우주공학과
A minimum combination t-test method for testing differences in population means based on a group of samples of size one
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