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991.
Bekyarova E Thostenson ET Yu A Kim H Gao J Tang J Hahn HT Chou TW Itkis ME Haddon RC 《Langmuir : the ACS journal of surfaces and colloids》2007,23(7):3970-3974
We report an approach to the development of advanced structural composites based on engineered multiscale carbon nanotube-carbon fiber reinforcement. Electrophoresis was utilized for the selective deposition of multi- and single-walled carbon nanotubes (CNTs) on woven carbon fabric. The CNT-coated carbon fabric panels were subsequently infiltrated with epoxy resin using vacuum-assisted resin transfer molding (VARTM) to fabricate multiscale hybrid composites in which the nanotubes were completely integrated into the fiber bundles and reinforced the matrix-rich regions. The carbon nanotube/carbon fabric/epoxy composites showed approximately 30% enhancement of the interlaminar shear strength as compared to that of carbon fiber/epoxy composites without carbon nanotubes and demonstrate significantly improved out-of-plane electrical conductivity. 相似文献
992.
Keith C Amaranatha Reddy R Prehm M Baumeister U Kresse H Chao JL Hahn H Lang H Tschierske C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(9):2556-2577
A novel class of bent-core molecules with oligo(siloxane) or carbosilane units at both ends was synthesized and the self-organization of these molecules was investigated by polarizing microscopy, DSC, X-ray scattering, dielectric and electrooptical methods. Depending on the size of the silicon-containing segments, smectic and columnar liquid crystalline phases are formed. Most smectic phases are low birefringent and composed of macroscopic domains of opposite handedness (dark conglomerate phases). The switching process in these smectic phases is surface stabilized ferroelectric and, depending on the conditions, two distinct slow relaxation processes to nonpolar structures were observed. It is proposed that the smectic phases are built up by chiral and polar SmCsPF layer stacks which are separated by anticlinic interfaces. If the size of these layer stacks is sufficiently large a coupling to the substrate surfaces takes place and ferroelectric switching is observed. It is also suggested that the sponge-like layer distortion, occurring in the low birefringent mesophases, is due to an escape from the local polar order within these SmCsPF layer stacks. For compounds with larger silylated units a steric frustration arises, which leads to layer modulation (columnar ribbon phases) and this is associated with a transition from ferroelectric to antiferroelectric switching. All compounds show a switching of the molecules around the long axis which reverses the layer chirality. 相似文献
993.
A test fixture, developed for evaluating the preand postbuckling response of simply supported, nearly flat, rectangular corrugated
board panels subjected to edge compression is evaluated. The test fixture enables loading of panels into the postbuckling
regime until collapse. The shadowmoiré method verified that buckling in the first mode occurred, and that there was symmetry
of the adge-boundary conditions. Through an iterative regression model, experimental curves of load versus out-of-plane displacement
for isotropic panels were fitted to an equation governing the nonlinear postbuckling response. This method provides the critical
buckling load, a postbuckling parameter and the amplitude of initial imperfection of the panel. Comparison with analytical
results revealed that simply supported boundary conditions were closely achieved. Examination of compressively loaded corrugated
board panels showed that collapse occurred due to compressive failures of the facings in the highly stressed edge regions
without severe influence from stress concentrations at load introduction and edge supports. 相似文献
994.
The fracture behavior of center-notched unidirectional borsic/titanium composites under uniaxial tensile loading has been investigated. Load-crack-opening displacement (COD) curves were obtained for crack length-to-width ratios ranging from 0.05 to 0.5. The COD was measured across the crack surfaces by means of laser interferometric displacement gage (gage length of 500 μm). As expected, the interferometric displacement gage (IDG) was very sensitive to the appearance of damage at the crack tip, yielding nonlinear load-COD curves. The crack-tip damage in borsic/titanium was found to grow coplanarly with the original crack and consist of fiber breaks and matrix plastic deformation, the former preceding the latter. The failure mode and the crack-tip-damage growth were found to be different from those observed in unidirectional boron/aluminum and these differences are discussed. The examination techniques include radiography, SEM, photomicrographs, interference microscope and optical-interferometry technique. It was found that the fracture strengths and crack-tip-damage growth can be analyzed by the analytical models proposed in the literature. The resistance-curve method was also tried and found to be applicable. A correlation has been established among the fracture strength, crack-opening displacement and failure mode. 相似文献
995.
996.
Dongyup Hahn Jungwook Chin Hiyoung Kim Inho Yang Dong Hwan Won Merrick Ekins Hyukjae Choi Sang-Jip Nam Heonjoong Kang 《Tetrahedron letters》2014
One monocyclofarnesol-derived sesquiterpenoid (1), four new meroterpenoids (2–5) as well as two isolation artifacts (6–7) and a known sesquiterpenoid (8) were isolated from the marine sponge Ircinia sp. Their chemical structures were elucidated via analyses of spectroscopic data, which included NMR and HRMS data. Two terpenoids, 1 and 4, showed PPARδ agonistic activities, with EC50 values of 18 and 30 μg/mL, respectively. 相似文献
997.
Hanpeng Jin Tristan Tsai Yuan Tan Prof. F. Ekkehardt Hahn 《Angewandte Chemie (International ed. in English)》2015,54(46):13811-13815
Neutral 4‐iodo‐N‐ethylimidazole 3 oxidatively adds to [Pt(PPh3)4] to give, in the presence of different tetraalkylammonium salts, complexes trans‐[ 4 ], trans‐[ 5 ], and trans‐[ 6 ] containing an anionic C4‐bound heterocycle with an unsubstituted ring‐nitrogen atom. Complex trans‐[ 4 ] reacts with the proton source NH4I under protonation of the ring‐nitrogen atom to produce complex trans‐[ 7 ]I which bears an NH,NR‐substituted aNHC ligand. The reaction of trans‐[ 4 ] with CH3I yields the complex trans‐[ 8 ]I which has a classical aNHC ligand with two alkylated ring‐nitrogen atoms. 相似文献
998.
999.
Hans Hahn 《Mathematische Zeitschrift》1919,4(3-4):306-313
Ohne Zusammenfassung 相似文献
1000.
Lilly Hahn 《Monatshefte für Mathematik》1914,25(1):303-320
Ohne Zusammenfassung 相似文献