Showing papers by "Yuan-Chih Chang published in 2009"
TL;DR: This examination quantitatively verifies the dominant role of atomic-scale corrugations in the Kapitza anomaly observed at 1-10 K and further opens a new path to nondestructively estimate subnanoscale roughness of buried interfaces.
Abstract: We report a direct determination of the specular scattering probability of acoustic phonons at a crystal boundary by observing the escape of incident coherent phonons from the coherent state during reflection. In the sub-THz frequency range where the phonon wavelength is much longer than the lattice constant, the acoustic phonon-interface interaction is found to agree well with the macroscopic theory on wave scattering from rough surfaces. This examination thus quantitatively verifies the dominant role of atomic-scale corrugations in the Kapitza anomaly observed at 1-10 K and further opens a new path to nondestructively estimate subnanoscale roughness of buried interfaces.
58 citations
TL;DR: Results support the previous hypothesis that ATP-dependent axial rotation of RadA nucleoprotein helical filament promotes homologous recombination and identify a hinge region between NTD and polymerization motif as responsible for rigid body movement of NTD.
Abstract: RecA family proteins, including bacterial RecA, archaeal RadA, and eukaryotic Dmc1 and Rad51, mediate homologous recombination, a reaction essential for maintaining genome integrity. In the presence of ATP, these proteins bind a single-strand DNA to form a right-handed nucleoprotein filament, which catalyzes pairing and strand exchange with a homologous double-stranded DNA (dsDNA), by as-yet unknown mechanisms. We recently reported a structure of RadA left-handed helical filament, and here present three new structures of RadA left-handed helical filaments. Comparative structural analysis between different RadA/Rad51 helical filaments reveals that the N-terminal domain (NTD) of RadA/Rad51, implicated in dsDNA binding, is highly flexible. We identify a hinge region between NTD and polymerization motif as responsible for rigid body movement of NTD. Mutant analysis further confirms that structural flexibility of NTD is essential for RadA's recombinase activity. These results support our previous hypothesis that ATP-dependent axial rotation of RadA nucleoprotein helical filament promotes homologous recombination.
15 citations
TL;DR: In this study, all the fabrication processes -- such as CNT attachment, CNT orientation manipulation, and apex trimming -- are integrated into a single UHV TEM system and will be shown in detail as the procedures of CNT probe fabrication by a series of high-resolution TEM images.
Abstract: An application of ultra-high vacuum transmission electron microscopy (UHV TEM) is demonstrated for the fabrication of carbon nanotube (CNT) probes. In this study, all the fabrication processes—such as CNT attachment, CNT orientation manipulation, and apex trimming—are integrated into a single UHV TEM system. The in situ work under UHV conditions (<5 × 10−10 mbar) allows us to clean the tip surface at the start of the fabrication process to ensure a good contact between the tip and CNT. Furthermore, the CNT size can be user-selected to meet the various needs for scanning probe microscopy (SPM). Most importantly, the in situ trimming enables a multi-walled CNT to have the sharpness of a single-walled CNT. The three advantages mentioned above are designed to improve conventional methods and will be shown in detail as the procedures of CNT probe fabrication by a series of high-resolution TEM images. Finally, we compare the scanned image via our CNT probes and conventional probes, where the typical artefacts coming from the conventional ones are addressed. We believe the technique we have developed here will further enhance the resolution of SPM measurements.
12 citations