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61.
The purpose of this paper is to classify real hypersurfaces of quaternionic projective spaces whose Ricci tensor satisfy a pair of conditions on the maximal quaternionic distribution
. 相似文献
62.
We present a general criterion for determining the dynamic instability of a thin polymer film that is strongly confined to a substrate. When such a polymer film is heated above its glass transition temperature, it dewets from the substrate by a spinodal dewetting scenario, in which the onset of the instability is governed by dispersion force and residual thermal stress. It turns out that the thermal stress plays an important role when there is a special interaction between a polymer and a substrate. 相似文献
63.
Kim KS Park JM Kim J Suh SB Tarakeshwar P Lee KH Park SS 《Physical review letters》2000,84(11):2425-2428
Ab initio calculations have been employed to investigate the peculiar change in magnetic property (from diamagnetic to paramagnetic) of the dianionic C60-dimer phase in a rapidly cooled AC60 samples ( A: alkali metal). We first note that the triplet state of (C60)-22 which was never considered previously is nearly degenerate with the singlet state, and the transition barrier between the two states is reasonably small. This explains the susceptibility increase with an increase in temperature and the magnetic phase transition in the process of the dimer to monomer phase transition. 相似文献
64.
S.J. Chung B. Karunagaran S. Velumani C.-H. Hong H.J. Lee E.-K. Suh 《Applied Physics A: Materials Science & Processing》2007,86(4):521-524
We have investigated the optical properties of AlxGa1-xN/GaN heterostructures (x=0.08, 0.15, 0.33) grown by metal organic chemical vapor deposition on sapphire using photoluminescence
(PL) and persistent photoconductivity (PPC) measurements. For the AlxGa1-xN/GaN heterostructures (HS) containing high Al composition, we observed an anomalous temperature-dependent photoluminescence
and persistent photoconductivity effects. These results show a strong dependence of the physical properties of AlxGa1-xN/GaN HS on the Al content and layer thickness. The anomalous temperature-dependent PL is usually attributed to the presence
of carrier localization states. These phenomena are explained based on the alloy compositional fluctuations in the AlxGa1-xN/GaN HS. From the PPC measurements, the photocurrent (PC) quenching was observed for AlxGa1-xN/GaN HS and it is explained by the metastable states formed in the underlying GaN layer. Also, the mechanisms behind the
PC quenching and PPC phenomena are explained in detail.
PACS 72.20.Jv; 72.40.+w; 78.55.Cr 相似文献
65.
Jaehong Kim Sung Heum Park Jinwoo Kim Shinuk Cho Youngeup Jin Joo Young Shim Hyunmin Shin Sooncheol Kwon Il Kim Kwanghee Lee Alan J. Heeger Hongsuk Suh 《Journal of polymer science. Part A, Polymer chemistry》2011,49(2):369-380
Newly designed 2H‐benzimidazole derivatives which have solubility groups at 2‐position have been synthesized and incorporated into two highly soluble carbazole based alternating copolymers, poly[2,7‐(9‐(1′‐octylnonyl)‐9H‐carbazole)‐alt‐5,5‐(4′,7′‐di(thien‐2‐yl)‐2H‐benzimidazole‐2′‐spirocyclohexane)] (PCDTCHBI) and poly[2,7‐(9‐(1′‐octylnonyl)‐9H‐carbazole)‐alt‐5,5‐(4′,7′‐di(thien‐2‐yl)‐2H‐benzimidazole‐2′‐spiro‐4′′‐((2′′′‐ethylhexyl)oxy)‐cyclohexane)] (PCDTEHOCHBI) for photovoltaic application. These alternating copolymers show low‐band gap properties caused by internal charge transfer from an electron‐rich unit to an electron‐deficient moiety. HOMO and LUMO levels are –5.53 and –3.86 eV for PCDTCHBI, and –5.49 and –3.84 eV for PCDTEHOCHBI, respectively. Optical band gaps of PCDTCHBI and PCDTEHOCHBI are 1.67 and 1.65 eV, respectively. The new carbazole based the 2H‐benzimidazole polymers show 0.11–0.13 eV lower values of band gaps as compared to that of carbazole based benzothiadiazole polymer, poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT), while keeping nearly the same deep HOMO levels. The power conversion efficiencies of PCDTCHBI and PCDTEHOCHBI blended with [6,6]phenyl‐C71‐butyric acid methyl ester (PC71BM) are 1.03 and 1.15%, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
66.
In this paper, we report a fluorescent sensing system based on the palladium-catalyzed Heck reaction between N-methyl vinylpyridinium and 4-bromo-N,N′-dimethylaniline. Generation of a new fluorophore as a product enhances fluorescence and permits selective detection of palladium(II) among other metal species. 相似文献
67.
68.
Highly monodisperse polymethylmethacrylate (PMMA) microparticles crosslinked with carboxylic group-containing urethane acrylates
(CUA) were produced by simple dispersion polymerization in methanol solution. In contrast to conventional crosslinkers, the
CUA employed as a crosslinker was excellent for maintaining the monodispersity of PMMA microparticles even at moderate crosslinker
concentrations (to about 5 wt%). It was believed that the CUA helped form the monomer-swellable surface of primary particles,
because of the structurally long tetramethylene oxide groups in the molecule. Carboxylic groups in the molecular backbone
resulted in larger primary particles by increasing the solubility of the monomer mixture in the medium. Owing to these larger
primary particles, the crosslinked PMMA particles showed lower polymerization rates than the linear ones during particle growth.
However, at high CUA concentrations (about 10 wt%), bimodal distributions were observed. This was attributed to the high crosslinking
density of the primary particle surfaces. Therefore, monomer diffusion toward the polymer phase was restricted, resulting
in more favorable secondary nucleation in the medium.
Received: 12 May 1998 Accepted: 19 August 1998 相似文献
69.
Byung‐Soo Kim Bumsu Kim Kyung‐Do Suh 《Journal of polymer science. Part A, Polymer chemistry》2008,46(3):1058-1065
Sulfonated polystyrene (PS) particles were prepared by the sulfonation of PS microspheres with H2SO4. Then, composite particles were synthesized by layer‐by‐layer (LbL) self‐assembly with funtionalized multiwall carbon nanotubes (fMCNTs) and polyelectrolytes on sulfonated PS particles. The amount of fMCNTs on PS particles was adjusted by controlling the number of fMCNT layers by LbL self‐assembly. Composite particles were characterized by ζ‐potential analysis, scanning electron microscopy, and thermal analysis. The electrorheological (ER) properties of composite particles in insulating oil was investigated with varying the number of fMCNT layers under controlled electric fields. It was observed that the number of fMCNT layers was a critical factor to determine the ER properties of composite particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1058–1065, 2008 相似文献
70.
Youngeup Jin Minjung Lee Sun Hee Kim Suhee Song Youngran Goo Han Young Woo Kwanghee Lee Hongsuk Suh 《Journal of polymer science. Part A, Polymer chemistry》2008,46(13):4407-4419
New electroluminescent polyfluorenevinylenes (PFV) copolymers with carbazole group, CzPFVs, have been synthesized by the GILCH polymerization. The carbazole groups were introduced as pendant to increase the electron rich ability of the copolymers. All CzPFVs exhibited absorption spectra with maximum peaks at around 417 nm. In the PL emission spectra of CzPFVs, maximum peaks around 463 nm and shoulder peaks around 490–500 nm were exhibited. By adjusting the feed ratios of carbazole groups in the CzPFVs, it is possible to have the higher current density and brightness, and the lower turn‐on voltage due to increasing hole injection ability. The maximum luminescence of CzPFV9 was 2003 cd/m2 at 7 V. The introduction of carbazole contents in PFVs can enhance the device performance to result in stable PL and EL spectra with high current density and brightness due to the increased hole injection ability and reduced interchain interaction between polymer backbones. Especially, the 1:1 mixture of CzPFV10 and PVK didn't show aggregation effect in PL spectra even after annealing the thin film at 80 °C up to 60 min, since the interchain interaction among polymer backbones with fluorenevinylene units was reduced. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4407–4419, 2008 相似文献