2,390 research outputs found
Phase behavior of polymer/liquid crystal blends
No full textThe thermodynamic phase behavior of blends of a low molecular-weight liquid crystal (LC), 4-cyano-4'-n-heptylbiphenyl (7CB), and each of two amorphous polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), was studied as a function of temperature or LC concentration. Phase diagrams for both the binary PMMA/7CB and PS/7CB blends were constructed from DSC and optical microscopic observations showing that 7CB was partially miscible in both PMMA and PS. The study revealed an important observation that there existed a polymer/isotropic LC two-phase state at a given composition besides the polymer/nematic LC two-phase state and the polymer/solid crystalline LC two-phase state. The polymer/isotropic LC two-phase morphology was clearly observed by the phase-contrast optical microscope in the temperature range between the homogeneous single-phase state and the polymer/nematic LC two-phase state, while DSC or cross-polarized light microscopy failed to detect the existence of the polymer/isotropic LC two-phase state. This was also confirmed by a light-scattering experiment. At a low ratio of LC in both the PMMA/7CB and PS/7CB blends, direct transformation between the homogeneous single-phase state and the polymer/nematic LC two-phase state was observed without going through the polymer/isotropic LC two-phase state
Temperature dependence of the nucleation effect of sorbitol derivatives on polypropylene crystallization
No full textThe temperature dependence of the nucleation effect of three sorbitol derivatives on the crystallization of isotactic polypropylene (iPP) was studied by means of isothermal crystallization kinetic analysis. Isothermal crystallization thermograms obtained by differential scanning calorimetry (DSC) were analyzed based on the Avrami equation. The Avrami analysis for the nucleated iPP was carried out with DSC data collected to 35% relative crystallinity, and the rate constants were corrected assuming the heterogeneous nucleation and three dimensional growth of iPP spherulites. A semi-empirical equation for the radial growth rate of iPP spherulites was given as a function of temperature and was used to determine the number of effective nuclei at different temperatures. The number of effective nuclei in the nucleated samples was estimated to be 3 x 10(2) approximately 10(5) times larger than that in the neat iPP. The logarithmic numbers of the effective nuclei decreased linearly with decreasing degree of supercooling in the range of crystallization temperatures tested. The temperature dependence of the effect of the nucleating agents on iPP crystallization was given quantitatively in terms of the deactivation factor defined as a fraction of the particles that are active at a particular temperature but inert at the temperature one degree higher. The nucleation activity and its temperature dependence are considered to be cooperative effects of many factors, including the dispersion and the physical or chemical nature of the agent as well as the interaction between the agent and the polymer. It is suggested that the temperature dependence of the effect of a nucleating agent should be treated as a characteristic of a given polymer/ nucleating agent mixture
OsBWMK1 mediates SA-dependent defense responses by activating the transcription factor OsWRKY33
No full textMitogen-activated protein kinases (MAPKs) play important roles in responses to various environmental stresses. In a previous study, we demonstrated that OsBWMK1, which localizes in the nucleus, mediates PR gene expression by activating the OsEREBP1 transcription factor, and that the constitutive expression of OsBWMK1 also enhances resistance against pathogen infections [Y.H. Cheong, B.C. Moon, J.K. Kim, C.Y. Kim, M.C. Kim, I.H. Kim, C.Y. Park, J.C. Kim, B.O. Park, S.C. Koo, H.W. Yoon, W.S. Chung, C.O. Lim, S.Y. Lee, M.J. Cho, BWMK1, rice mitogen-activated protein kinase, locates in the nucleus and mediates pathogenesis-related gene expression by activation of a transcription factor, Plant Physiol. 132 (2003) 1961.1972]. Here, we report that OsBWMK1 phosphorylates OsWRKY33, which binds to the W-box element (TTGACCA) in several PR gene promoters, thereby enhancing DNA-binding activity of the factor to its in vitro cognate binding site. Transient coexpression of OsBWMK1 and OsWRKY33 in Arabidopsis protoplasts elevates SA-dependent expression of the GUS-reporter gene driven by the W-box element and the PR1 promoter. Furthermore, the levels of SA and H2O2 are elevated in 35S-OsBWMK1 transgenic plants that show HR-like cell death. Altogether, OsBWMK1 may mediate SA-dependent defense responses by activating the WRKY transcription factor in plants.open
A secure and privacy enhanced protocol for location-based services in ubiquitous society
No full textThe Design of the Enclosure Box of Powertrain Using CFD to Satisfy Pass-by Noise Reduction and Engine Cooling Performance
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Synthesis and characterization of polyethylenimine-graft-poly(L-lactide-co- glycolide) block copolymers for gene delivery
No full textPolyethylenimine-graft-poly(L-lactide-co-glycolide) (PEI-g-PLGA) block copolymers were prepared by a ring-opening polymerization of L-lactide and glycolide using PEI as a macroinitiator and stannous octoate as a catalyst in dimethylformamide at 100°C. The molecular structure of the block copolymers was evaluated with 1H-NMR, and the molecular weight of the block copolymers was determined with gel permeation chromatography. The thermal properties were investigated using differential scanning calorimetery and thermogravimetric analysis. The zeta-potential of the pDNA/copolymer complexes was evaluated with dynamic laser light scattering. Cytotoxicity and gene transfection efficiency of PEl-g-PLGA were tested in vitro using human embryonic kidney 293 cell culture. The pDNA/copolymer complexes (N/P = 10) showed a lower zeta-potential than pDNA/PEI25kDa complex, suggesting the lower toxicity of the pDNA/copolymer complexes. The copolymer composition was found to significantly affect the gene transfection efficiency of the pDNA/copolymer complexes. The copolymers with lower contents of PLGA showed higher gene transfection efficiency. These results indicate that these block copolymers are promising candidates for gene delivery vehicles, featuring good biocompatibility, potential biodegradability, and relatively high gene transfection efficiency.N
A novel DS/SS code acquisition technique based on seed accumulation of sequence generator
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