Myung Chul Choi

In this article we present experimental results demonstrating an approach to controlling the size and spatial patterning of defect domains in a smectic liquid crystal (LC) by geometric confinement in surface-modified microchannels. By confining the LC 4'-octyl-4-cyanobiphenyl in mum-sized rectangular channels with controlled surface polarity, we were able to generate defect domains that are not only nearly uniform in size but also arranged in quasi-2D ordered patterns. Atomic force microscopy me

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTDirect Observation of Biaxial Confinement of a Semiflexible Filament in a ChannelM. C. Choi, C. D. Santangelo, O. Pelletier, J. H. Kim, S. Y. Kwon, Z. Wen, Y. Li, P. A. Pincus, C. R. Safinya, and M. W. KimView Author Information Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea, Materials Research Laboratory and Department of Materials, Physics, Molecular, Cellular, and Developmental Biology, University of C

The effect of secondary blocking on the output for 7-16 MeV electron beams is investigated for the two most widely used methods of field shaping, i.e.,(a) shield on surface, and (b) shield at end of cone with subsequent air gap. For those two methods differences in output on the order of 10% are observed. These effects are explained in terms of the blocking geometry and its influence on scattered radiation.

Tubulin-based nanotubes (TNTs) to deliver microtubule-targeting agents (MTAs) for clinical oncology are reported. Three MTAs, docetaxel (DTX), laulimalide (LMD), and monomethyl auristatin E (MMAE), which attach to different binding sites in a tubulin, are loaded onto TNTs and cause structural changes in them, including shape anisotropy and tubulin layering. This drug-driven carrier transformation leads to changes in the drug-loading efficiency and stability characteristics of the carrier. TNTs c

We present a novel technique to measure diffusion coefficients of insoluble surfactant monolayers. We merge a surfactant-coated droplet with a fluorescently labeled planar monolayer. During the merging process, a monolayer on a droplet displaces the existing planar monolayer, leaving a dark area when viewed under a fluorescence microscope. We measure fractional intensities as the dyes recover, which allows diffusion coefficients to be computed. We validate this technique with the two most common

Optical trapping of nanometer-sized lipid vesicles has been challenging due to the low refractive index contrast of the thin lipid bilayer to the aqueous medium. Using an "optical bottle", a recently developed technique to measure interactions of nanoparticles trapped by an infrared laser, we report, for the first time, quantitative measurements of the trapping energy of charged lipid vesicles. We found that the trapping energy increases with the relative amount of anionic lipids (DOPG) to neutr

By virtue of their native structures, tubulin dimers are protein building blocks that are naturally preprogrammed to assemble into microtubules (MTs), which are cytoskeletal polymers. Here, polycation-directed (i.e., electrostatically tunable) assembly of tubulins is demonstrated by conformational changes to the tubulin protofilament in longitudinal and lateral directions, creating tubulin double helices and various tubular architectures. Synchrotron small-angle X-ray scattering and transmission

The fundamental question regarding the fractionation phenomenon is whether diffusion alone is responsible for it or whether an additional advection dynamic is involved. We studied the fractionation by diffusion of particles in spatially heterogeneous environments. By experimentally observing the time-sequential fractionation patterns of dye particles diffusing across a solid-solid interface of varying polyacrylamide gel densities, we found that the two-component diffusion model accurately captur

With the emerging proteomics era the scientific community is beginning the daunting task of understanding the structures and functions of a large number of self-assembling proteins. Here, our study was concerned with the effect of the microtubule-associated-protein (MAP) tau on the assembled structure of taxol-stabilized microtubules. Significantly, the synchrotron small angle x-ray scattering (SAXS) technique is able to quantitatively detect angstrom level changes in the average diameter of the

Nanoparticles exhibiting geometrical and chemical anisotropies hold promise for environmentally responsive materials with tunable mechanical properties. However, a comprehensive understanding of their interfacial behaviors remains elusive. In this paper, we control the interfacial anchoring orientation of polystyrene nanodumbbells by adjusting interparticle forces. The film nanostructure is characterized by the orientation angle analysis of individual dumbbells from cross-sectional EM data: dumb

When the electron beam is generated from the cathode, the electrode sheath plasma is also generated, and hence the perveance of diode is being varied to change the diode output characteristics. In our pulsed power system "Chundoong", the perveance characteristics have been experimentally investigated, from which the sheath plasma expansion speed has been found to be an about 3 cm//spl mu/s inside the diode. It is shown inside the diode that the sheath plasma expansion gives the influence on the