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Molecular Propulsion: Chemical Sensing and Chemotaxis of DNA Driven by RNA Polymerase
Yu, Hua,Jo, Kyubong,Kounovsky, Kristy L.,Pablo, Juan J. de,Schwartz, David C. American Chemical Society 2009 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.131 No.16
<P>Living cells sense extracellular signals and direct their movements in response to stimuli in environment. Such autonomous movement allows these machines to sample chemical change over a distance, leading to chemotaxis. Synthetic catalytic rods have been reported to chemotax toward hydrogen peroxide fuel. Nevertheless individualized autonomous control of movement of a population of biomolecules under physiological conditions has not been demonstrated. Here we show the first experimental evidence that a molecular complex consisting of a DNA template and associating RNA polymerases (RNAPs) displays chemokinetic motion driven by transcription substrates nucleoside triphosphates (NTPs). Furthermore this molecular complex exhibits a biased migration into a concentration gradient of NTPs, resembling chemotaxis. We describe this behavior as 'Molecular Propulsion', in which RNAP transcriptional actions deform DNA template conformation engendering measurable enhancement of motility. Our results provide new opportunities for designing and directing nanomachines by imposing external triggers within an experimental system.</P>
CANDELS Sheds Light on the Environmental Quenching of Low-mass Galaxies
Guo, Yicheng,Bell, Eric F.,Lu, Yu,Koo, David C.,Faber, S. M.,Koekemoer, Anton M.,Kurczynski, Peter,Lee, Seong-Kook,Papovich, Casey,Chen, Zhu,Dekel, Avishai,Ferguson, Henry C.,Fontana, Adriano,Giavalis American Astronomical Society 2017 ASTROPHYSICAL JOURNAL LETTERS - Vol.841 No.2
<P>We investigate the environmental quenching of galaxies, especially those with stellar masses (M-*) < 10(9.5) Me-circle dot, beyond the local universe. Essentially all local low-mass quenched galaxies (QGs) are believed to live close to massive central galaxies, which is a demonstration of environmental quenching. We use CANDELS data to test whether or not such a dwarf QG-massive central galaxy connection exists beyond the local universe. For this purpose, we only need a statistically representative, rather than complete, sample of low-mass galaxies, which enables our study to z greater than or similar to 1.5. For each low-mass galaxy, we measure the projected distance (d(proj)) to its nearest massive neighbor (M-* > 10(10.5) M-circle dot) within a redshift range. At a given z and M-*, the environmental quenching effect is considered to be observed if the d(proj) distribution of QGs (d(proj)(Q)) is significantly skewed toward lower values than that of star-forming galaxies (d(proj)(SF)). For galaxies with 10(8) M-circle dot < M-* < 10(10) M-circle dot, such a difference between d(proj)(Q) and d(proj)(SF) is detected up to z similar to 1. Also, about 10% of the quenched galaxies in our sample are located between two and four virial radii (R-Vir) of the massive halos. The median projected distance from low-mass QGs to their massive neighbors, d(proj)(Q)/R-Vir, decreases with satellite M-* at M-* less than or similar to 10(9.5) M-circle dot, but increases with satellite M-* at M-* greater than or similar to 10(9.5) M-circle dot. This trend suggests a smooth, if any, transition of the quenching timescale around M-* similar to 10(9.5) M-circle dot at 0.5 < z < 1.0.</P>
Trust-Tech based Parameter Estimation and its Application to Power System Load Modeling
Choi, Byoung-Kon,Chiang, Hsiao-Dong,Yu, David C. The Korean Institute of Electrical Engineers 2008 Journal of Electrical Engineering & Technology Vol.3 No.4
Accurate load modeling is essential for power system static and dynamic analysis. By the nature of the problem of parameter estimation for power system load modeling using actual measurements, multiple local optimal solutions may exist and local methods can be trapped in a local optimal solution giving possibly poor performance. In this paper, Trust-Tech, a novel methodology for global optimization, is applied to tackle the multiple local optimal solutions issue in measurement-based power system load modeling. Multiple sets of parameter values of a composite load model are obtained using Trust-Tech in a deterministic manner. Numerical studies indicate that Trust-Tech along with conventional local methods can be successfully applied to power system load model parameter estimation in measurement-based approaches.
Trust-Tech based Parameter Estimation and its Application to Power System Load Modeling
Byoung-Kon Choi,Hsiao-Dong Chiang,David C. Yu 대한전기학회 2008 Journal of Electrical Engineering & Technology Vol.3 No.4
Accurate load modeling is essential for power system static and dynamic analysis. By the nature of the problem of parameter estimation for power system load modeling using actual measurements, multiple local optimal solutions may exist and local methods can be trapped in a local optimal solution giving possibly poor performance. In this paper, Trust-Tech, a novel methodology for global optimization, is applied to tackle the multiple local optimal solutions issue in measurement-based power system load modeling. Multiple sets of parameter values of a composite load model are obtained using Trust-Tech in a deterministic manner. Numerical studies indicate that Trust-Tech along with conventional local methods can be successfully applied to power system load model parameter estimation in measurement-based approaches.
Jing-Han Chen,Chi-Te Liang,Chun-Feng Huang,Da-Ren Hang,David A. Ritchie,J. C. Hsiao,Jyun-Ying Lin,Michelle Y. Simmons,Ming-Gu Lin,S. H. Lo,Tsai-Yu Huang 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3
By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional electron systems (2DESs), we study the low-field Landau quantization when the thermal damping is reduced with decreasing temperature. Magneto-oscillations following the Shubnikov-de Haas (SdH) formula are observed even when their amplitudes are so large that the deviation to such a formula is expected. Our experimental results show the importance of the positive magneto-resistance to the extension of the SdH formula under the damping induced by the disorder.
Discovery and Characterization of the Tuberculosis Drug Lead Ecumicin
Gao, Wei,Kim, Jin-Yong,Chen, Shao-Nong,Cho, Sang-Hyun,Choi, Jongkeun,Jaki, Birgit U.,Jin, Ying-Yu,Lankin, David C.,Lee, Ji-Ean,Lee, Sun-Young,McAlpine, James B.,Napolitano, José,G.,Franzblau, Sc American Chemical Society 2014 ORGANIC LETTERS Vol.16 No.23
<P>The new tuberculosis (TB) lead ecumicin (<B>1</B>), a cyclic tridecapeptide, was isolated from <I>Nonomuraea sp.</I> MJM5123, following a high-throughput campaign for anti-TB activity. The large molecular weight of 1599 amu detected by LC-HR-MS precluded the initial inference of its molecular formula. The individual building blocks were identified by extensive NMR experiments. The resulting two possible planar structures were distinguished by LC-MS<SUP>2</SUP>. Determination of absolute configuration and unambiguous structural confirmation were carried out by X-ray crystallography and Marfey’s analysis.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/orlef7/2014/orlef7.2014.16.issue-23/ol5026603/production/images/medium/ol-2014-026603_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ol5026603'>ACS Electronic Supporting Info</A></P>