1,720,962 research outputs found
Sum-of-Squares-Based Region of Attraction Analysis for Gain-Scheduled Three-Loop Autopilot
No full textA conventional method of designing a missile autopilot is to linearize the original nonlinear dynamics at several trim points, then to determine linear controllers for each linearized model, and finally implement gain-scheduling technique. The validation of such a controller is often based on linear system analysis for the linear closed-loop system at the trim conditions. Although this type of gain-scheduled linear autopilot works well in practice, validation based solely on linear analysis may not be sufficient to fully characterize the closed-loop system especially when the aerodynamic coefficients exhibit substantial nonlinearity with respect to the flight condition. The purpose of this paper is to present a methodology for analyzing the stability of a gain-scheduled controller in a setting close to the original nonlinear setting. The method is based on sum-of-squares (SOS) optimization that can be used to characterize the region of attraction of a polynomial system by solving convex optimization problems. The applicability of the proposed SOS-based methodology is verified on a short-period autopilot of a skid-to-turn missile. © 2018, The Korean Society for Aeronautical & Space Sciences and Springer Nature Singapore Pte Ltd.
Extended Kalman filter design using bearing and time-to-go measurement for a homing missile guidance
No full text오환성 트리터핀계 화학물 루페올의 여드름 치료 효과
Get PDF학위논문 (박사)-- 서울대학교 대학원 : 의학과, 2015. 2. 서대헌.Acne vulgaris is a nearly universal cutaneous disease characterized by multifactorial pathogenic processes. Because current acne medications have various side effects, investigating new pharmacologically active molecules is important for treating acne. As natural products generally provide various classes of relatively safe compounds with medicinal potentials, we screened various medicinal plants to explore the novel acne medication. Among them, lupeol, a pentacyclic triterpene, from the hexane extract of Solanum melongena L was identifed. Lupeol targeted most of the major pathogenic factors of acne with desired physicochemical traits. It strongly suppressed lipogenesis by modulating IGF-1R/PI3K/Akt/SREBP-1 signaling pathway in SEB-1 sebocytes, and reduced inflammation by suppressing the NF-κB pathway in SEB-1 sebocytes and HaCaT keratinocytes. Lupeol exhibited only a minimal effect on cell viability and possibly modulated dyskeratosis of epidermal keratinocyte. It also decreased the viability of P. acnes. Finally, lupeol improved facial acne and was well tolerated in a 4-week double-blind, randomized, split-face, small-scale clinical trial. These results provide a therapeutic rationale for the use of lupeol in acne treatment.Abstract ----ⅰ
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Abstract in Korean -----42Docto
컨벡스 프로그래밍을 이용한 공대지 유도무기의 중기궤적 최적화 연구
No full text학위논문(박사) - 한국과학기술원 : 항공우주공학과, 2020.2,[v, 74 p. :]For the last decade, research using convex optimization has been attempted for various problems in the aerospace engineering field. Since the convex optimization is robust to initial conditions and ensures convergence within the polynomial time, there are several papers on trajectory optimization problems for powered descent guidance in Mars exploration field where the initial condition is uncertain. In the case of air-to-ground missiles, the approach using convex optimization is effective to generate the optimal trajectory quickly and robustly because of various initial conditions and complex constraints in engagement scenarios within the operating range of a platform. This paper deals with the method of optimizing the mid-course trajectory of air-to-ground missiles using convex programming approaches. The problem of minimizing total energy and maximizing final velocity of mid-course trajectory, which are frequently used in the mid-course guidance phase, is addressed with the maximum altitude constraint. However, since the missile trajectory optimization problem is generally described as a nonlinear optimization problem due to dynamic equations and non-convex constraints, an appropriate transformation is required to apply the convex optimization technique. First, in order to enhance the covergence capability, we applied the method of control dynamics augmentation or control variable augmentation, and then applied the partial linearization method to the nonlinear equation and discretized it based on the trapezoidal rule. In addition, to cope with the non-convex control constraint that occurs in the control variable augmentation problem, the lossless convexification is proved using the maximum principle of the optimal control theory. Finally, simulation results of the proposed convex programming approaches are compared with the results of nonlinear programming to confirm the effectiveness and robustness.한국과학기술원 :항공우주공학과
출력재정의를 통한 고기동 미사일의 자동 조종 장치 설계
No full text학위논문(석사) - 한국과학기술원 : 항공우주공학전공, 2005.2, [ viii, 60 p. ]An autopilot design is proposed to control an agile tail-controlled missile system. Traditional autopilot design for the guided missile employs acceleration and rate feedback together with proportional and integral control to stabilize the missile and to track the guidance command signals. However, the gain scheduling method is time-consuming job and it doesn``t assure the performance between two linearization points.
Feedback linearization using nonlinear transformation techniques dynamically linearizes nonlinear systems into linear ones. A plant inversion method, one of the feedback linearization techniques, cannot directly adapt to the non-minimum phase system because of the plant inversion characteristics. To avoid the difficulties associated with the non-minimum phase dynamics of missile acceleration, the plant inversion is applied via output redefinition. Output redefinition method is used to transform the non-minimum phase system to the minimum phase system. Output redefinition method gives us an indirect or direct way to obtain the adequate results.
Nonlinear control require an accurate system and aerodynamic model. And at high angle-of-attack region, the large moment and force are generated because of the asymmetric vortex around the nose of missile system. PID error feedback control, on-line neural network and sliding mode control are used to eliminate the approximation error of the models and to stabilize the attitude of missile. The performances of the proposed autopilots are compared and analyzed through numerical simulations.한국과학기술원 : 항공우주공학전공
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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