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Heejung Yu,Youngchul Sung,Haksoo Kim,Lee, Y. H. IEEE 2012 IEEE transactions on signal processing Vol.60 No.4
<P>In this paper, the beam design for signal-space interference alignment in slowly fading multiuser multiple-input multiple-output (MIMO) interference channels is considered. Based on a linear formulation for interference alignment, a predictive beam tracking algorithm is proposed using matrix perturbation theory. The proposed algorithm, based on a mixture of iteration and update, computes interference-aligning beamforming vectors at the current time by updating the previous beam vectors based on the channel difference between the two time steps during the predictively updating phase, and yields significant reduction in computational complexity compared with existing methods recalculating beams at each time step. The tracking performance of the algorithm is analyzed in terms of mean square error and sum rate loss between the predictively updating approach and the recalculating approach, and the impact of imperfect channel knowledge is also investigated under the state-space channel model. Numerical results show that the proposed algorithm has almost the same performance as non-predictive methods in sum rate. Thus, the proposed algorithm provides a very efficient way to realize interference alignment in a realistic slowly fading MIMO channel environment.</P>
Heejung Yu,Youngchul Sung IEEE 2010 IEEE transactions on signal processing Vol.58 No.9
<P>In this correspondence, the problem of interference alignment for <I>K</I>-user time-invariant multi-input multi-output interference channels is considered. The necessary and sufficient conditions for interference alignment are converted to a system of linear equations that have dummy variables. Based on this linear system, a new algorithm for beam design for interference alignment is proposed by minimizing the overall <I>interference misalignment</I>. The proposed algorithm consists of solving a least squares problem iteratively. The convergence of the proposed algorithm is established, and its complexity is analyzed. The performance of the proposed algorithm is also evaluated numerically. It is shown that the proposed algorithm has faster convergence and lower complexity than the previous method with a comparable sum rate performance in the most practical case of two receive antennas.</P>
Heejung Yang,Jeom Yong Kim,Sun Ok Kim,Young Hyo Yoo,Sang Hyun Sung 고려인삼학회 2014 Journal of Ginseng Research Vol.38 No.3
Background: Ginsenosides, the major ingredients of Panax ginseng, have been studied for many decades in Asian countries as a result of their wide range of pharmacological properties. The less polar ginsenosides, with one or two sugar residues, are not present in nature and are produced during manufacturing processes by methods such as heating, steaming, acid hydrolysis, and enzyme reactions. ¹H-NMR and <SUP>13</SUP>C-NMR spectroscopic data for the identification of the less polar ginsenosides are often unavailable or incomplete. Methods: We isolated 21 compounds, including 10 pairs of 20(S) and 20(R) less polar ginsenosides (1-20), and an oleanane-type triterpene (21) from a processed ginseng preparation and obtained complete ¹H-NMR and <SUP>13</SUP>C-NMR spectroscopic data for the following compounds, referred to as compounds 1-21 for rapid identification: 20(S)-ginsenosides Rh2 (1), 20(R)-Rh2 (2), 20(S)-Rg3 (3), 20(R)-Rg3 (4), 6´-O-acetyl-20(S)-Rh2 [20(S)-AcetylRh2] (5), 20(R)-AcetylRh2 (6), 25-hydroxy-20(S)-Rh2 (7), 25-hydroxy-20(S)-Rh2 (8), 20(S)-Rh1 (9), 20(R)-Rh1 (10), 20(S)-Rg2 (11), 20(R)-Rg2 (12), 25-hydroxy-20(S)-Rh1 (13), 25-hydroxy-20(R)-Rh1 (14), 20(S)-AcetylRg2 (15), 20(R)-AcetylRg2 (16), Rh4 (17), Rg5 (18), Rk1 (19), 25-hydroxy-Rh4 (20), and oleanolic acid 28-O-β-D-glucopyranoside (21).
Anti-Differentiation Effect of B, D- <i>Seco</i> limonoids of <i>Swietenia mahogani</i>
Yang, Heejung,Choi, Mina,Lee, Dong Young,Sung, Sang Hyun Medknow PublicationsMedia Pvt Ltd 2017 Pharmacognosy magazine Vol.13 No.50
<P><B>Background:</B></P><P>Obesity is a pathological state caused by abnormal or excessive accumulation of fat. <I>Swietenia mahogani</I> JACQ., known as West Indian mahogany, is a medium-sized semi-evergreen tree belonging to Meliaceae. Their seeds are used in Indonesian folk medicine as a treatment for hypertension, diabetes, malaria, and it also has anti-feedant activities. The major components of <I>S. mahogani</I> are B, D-seco limonoids, a type of irregular triterpenes are well known.</P><P><B>Objective:</B></P><P>We tried to find the bioactive components, which have the inhibitory activity on adipocyte differentiation from the seeds of <I>S. mahogani</I>.</P><P><B>Material and Methods:</B></P><P>3T3-L1 cells, derived from mouse preadipocyte, are widely used in studying adipogenesis process. In this study, we used 3T3-L1 cells to find natural products with the inhibitory activity on adipocyte differentiation. <I>S. mahogani</I> seeds were dried and extracted with 100% MeOH.</P><P><B>Results:</B></P><P>The methanolic extract was fractionated by bioassay-guided method to give nine B, D-seco limonoids (1-9) with slight structural modifications. Among nine compounds, compounds 4, 6 and 8 exhibited significant inhibitory effects of cell differentiation on 3T3-L1 cells. Those compounds have tigloyl residue at C-3 in common. Besides, compounds with no tigloyl residue at C-3 showed insignificant effect. Nevertheless, not all compounds with tigloyl residue at C-3 exerted significant inhibitory effect.</P><P><B>Conclusion:</B></P><P>These results suggested that tigloyl residue at C-3 may play a role in the anti-proliferative activity on a dipogenesis and the refined extract of <I>S. mahogani</I> may have a potential to be developed as a therapeutic agent to treat obesity.</P><P><B>SUMMARY</B></P><P><P>Nine irregular seco-limonoids were isolated from <I>Swietenia mahogani</I>.</P><P>Total extract and CHCl3 fraction of <I>S. mahogani</I> showed the significant inhibitory activities on 3T3-L1 cell differentiation.</P><P>A tigloyl residue at C-3 in an aglycone may play a role in the anti-proliferative activity on adipogenesis.</P></P> >[FIG OMISSION]</BR>