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Lee, Chae Heun,Hyun, Chul,Lee, Jang Gyu,Choi, Jin Yung,Sung, Sangkyung The Korean Institute of Electrical Engineers 2013 Journal of Electrical Engineering & Technology Vol.8 No.1
This paper proposes a new guidance law, which considers the Field of View (FOV) of the seeker when a missile has a strapdown seeker mounted instead of a gimbal seeker. When a strapdown seeker, which has a narrow FOV, is used for tracking a target, the FOV of the seeker is an important consideration for guidance performance metrics such as miss distance. We propose a new guidance law called hybrid guidance (HG) to address the shortcomings of conventional guidance laws such as proportional navigation guidance (PNG), which cannot maintain lock-on conditions against high speed targets due to the narrow FOV of the strapdown seeker. The aim of the HG law is to null miss distance and to maintain the look angle within the FOV of the strapdown seeker. In order to achieve this goal, we combine two guidance laws in the HG law. One is a PNG law to null the LOS rate, and the other is a sliding mode guidance (SMG) law derived to keep the look angle within the FOV by employing a Lyapunov-like function with a sliding mode control methodology. We also propose a method to switch these two guidance laws at certain look angles for better guidance performance.
Lee, Byungjin,Lee, Young Jae,Sung, Sangkyung The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2
A novel attitude determination method is investigated that is computationally efficient and implementable in low cost sensor and embedded platform. Recent result on attitude reference system design is adapted to further develop a three-dimensional attitude determination algorithm through the relative velocity incremental measurements. For this, velocity incremental vectors, computed respectively from INS and GPS with different update rate, are compared to generate filter measurement for attitude estimation. In the quaternion-based Kalman filter configuration, an Euler-like attitude perturbation angle is uniquely introduced for reducing filter states and simplifying propagation processes. Furthermore, assuming a small angle approximation between attitude update periods, it is shown that the reduced order filter greatly simplifies the propagation processes. For performance verification, both simulation and experimental studies are completed. A low cost MEMS IMU and GPS receiver are employed for system integration, and comparison with the true trajectory or a high-grade navigation system demonstrates the performance of the proposed algorithm.
Lee, Jongmin,Song, Hyungmin,Sung, Sangkyung,Kim, Chang Joo,Lee, Sangwoo The Korean Society for Aeronautical and Space Scie 2014 International Journal of Aeronautical and Space Sc Vol.15 No.3
We present a study of vertical dynamics control of an electrostatically levitated gyro-accelerometer considering the wobbling effect and propose a tilt stabilization method with newly introduced control electrodes. Typically, a rotor in a vacuum rotates at high velocity, which may create a drift rate and lead to displacement instability due to the tilt angle of the rotor. To analyze this, first we set up a vertical dynamic equation and determined simulation results regarding displacement control. After deriving an equation for drift dynamics, we analyzed the drift rate of the rotor and the wobbling effect for displacement control quantitatively. Then, we designed new sub-electrodes for moment control that will decrease the drift amplitude of wobbling dynamics. Finally, a simulation study demonstrated that the vertical displacement control with the wobbling compensation electrodes mitigated the rotor's drift rate, showing the effectiveness of the newly proposed control electrodes.
Strong-field quantum control of 2 + 1 photon absorption of atomic sodium.
Lee, Sangkyung,Lim, Jongseok,Park, Chang Yong,Ahn, Jaewook Optical Society of America 2011 Optics express Vol.19 No.3
<P>We demonstrate ultrafast coherent control of multiphoton absorption in a dynamically shifted energy level structure. In a three-level system that models optical interactions with sodium atoms, we control the quantum interference of sequential 2 + 1 photons and direct threephoton transitions. Dynamic change in energy levels predicts an enormous enhancement of |7<i>p</i>??state excitation in the strong-field regime by a negatively chirped pulse. In addition, the |4<i>s</i>??state excitation is enhanced symmetrically by nonzero linear chirp rates given as a function of laser peak intensity and laser detuning. Experiments performed by ultrafast shaped-pulse excitation of ground-state atomic sodium verifies the various strong-field contributions to |3<i>s</i>??|7<i>p</i>??and |3<i>s</i>??|4<i>s</i>??transitions. The result suggests that for systems of molecular level understanding adiabatic control approach with analytically shaped pulses becomes a more direct control than feedback-loop black-box approaches.</P>
Strong-field two-photon absorption in atomic cesium: an analytical control approach
Lee, Sangkyung,Lim, Jongseok,Ahn, Jaewook The Optical Society 2009 Optics express Vol.17 No.9
<P>We have considered an analytical control of two-photon absorption process of atoms in the strong-field interaction regime. The experiment was performed on gaseous cesium atoms strongly interacting with a shaped laser-pulse from a femtosecond laser amplifier and a programmable pulse-shaper. When this shaped laser-pulse transfers the atomic population from the 6s ground state to the 8s excited state, we have found that both positively- and negatively-chirped laser pulses, compared with a Gaussian pulse, enhance this excitation in the strong-field regime of laser-atom interaction. This unusual phenomena is explained because the temporal shape of the laser intensity compensates the effect of dynamic Stark shift for the two-photon resonant condition to be optimally maintained. We provide analytic calculations using the strong-field phase matching, which show good agreement with the experiment.</P>
Performance comparison between 87Rb‑natural Xe–N2 and 87 Rb–129Xe–131Xe–N2 atom spin gyroscopes
Lee Sangkyung,Lee Deok Young,Shim Kyu Min,Yim Sin Hyuk 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.3
We have developed an atom spin gyroscope that uses a Rb–Xe vapor cell. The signal-to-noise ratio (SNR) and the angular random walk (ARW) of a Rb-natural Xe–N 2 vapor cell and a Rb–129Xe–131Xe–N 2 vapor cell were compared in terms of the Allan deviation. The low SNR of the 131 Xe signal was the main limitation of the ARW in the 87Rb-natural Xe–N 2 atom spin gyroscope. The 87Rb–129Xe–131Xe–N 2 atom spin gyroscope with a partial pressure ratio of 129 Xe to 131 Xe of 1:5 provided a SNR of 879 and a transverse relaxation time of 19.6 s, respectively, for an 131 Xe signal. Compared to the 87Rb-natural Xe–N 2 atom spin gyroscope, the 87Rb–129Xe–131Xe–N 2 atom spin gyroscope with an improved SNR showed that the magnetic-fieldinduced noise limited the ARW of our system. To stabilize the bias magnetic field, we applied a magnetic field feedback of 300-fT resolution with a 4-Hz bandwidth. As a result, the correlation between the magnetic field and the rotation rate from the atom spin gyroscope output was removed. The 87Rb–129Xe–131Xe–N 2 atom spin gyroscope achieved an ARW of 0.11◦∕ h1∕2 and a bias instability of 0.5◦∕h.
Expression and Fuctional Analysis of Yeast ARS Binding Factor I Gene and Its Mutant Genes in Yeast
Lee, Sangkyung,So, In Seop,Cho, Gi-Nam,Jung, Gu-Hung,Rho, Hyune Mo,Kim, Jiyoung 경희대학교 유전공학연구소 1993 遺傳工學論文集 Vol.5 No.-
ABF I is a DNA binding protein which plays roles in DNA replication and in DNA transcription. The nucleotide sequence of cloned ABF I gene revealed several motifs characteristic of DNA binding proteins. In order to locate the protein domains which are important for function of ABF I, several ABF I mutants were generated by site-directed mutagenesis and expressed in S. cerevisiae with a temperature-sensitive lethal mutation in the ABF I gene. The abf1-ts strain showed rapid growth arrest at the non-permissive temperature but showed normal growth at the non-permissive temperature when a plasmid containing ABF I gene was introduced into the yeast cells. Among several mutant ABF I genes tested, mutant ABF I gene with a base substitution corresponding to the position of 61th His to Ala or of 360th Leu to Arg did not support growth of the is mutant at the non-permissive temperature. Our results indicate that the histidine residue in the putative zinc-finger region and the leucine residue in the leucine zipper region were important for the function of the ABF I in yeast.
Lee, Byungjin,Yun, Sukchang,Lee, Hyung-Keun,Lee, Young Jae,Sung, Sangkyung The Korean Society for Aeronautical and Space Scie 2016 International Journal of Aeronautical and Space Sc Vol.17 No.2
This paper proposes a new method achieving computationally efficient attitude reference system for low cost strapdown sensors and microprocessor platform. The main idea in this method is to define and compare velocity differential vectors, geometrically computed from INS and GPS data with different update rate, for generating attitude error measurements which is further used for filter construction. A quaternion based Kalman filter configuration is applied for the attitude estimation with the adapted measurement model of differential vector comparison. Linearized model for Extended Kalman Filter and low pass filtered characteristics of measurement greatly extend the affordability of the proposed algorithm to the field of simple low cost embedded systems. For performance verification, experiment are done employing a practical low cost MEMS IMU and GPS receiver specification. Performance comparison with a high grade navigation system demonstrated good estimation result.