Carbon nanotips with a high-aspect ratio were directly grown on Pt films. Carbon nanotips grew up to 5.4 m length and 64 nm diameter under a Ϫ120 V bias. Compared to the hollow structure of carbon nanotubes, transmission electron microscopy images indicate its solid body, which is made of graphite. Carbon nanotips possess good field emission characteristics, that is, a turn-on field of 1.5 V/m and 761 A/cm 2 under 2.2 V/m. The Pt films provide a good conduction path for electron transport from the cathode to the emission site and do not act as catalysts.
The question of whether the vegetative source or kernel sink represents the major constraint for grain yield of maize (Zea mays L.) has not been satisfactorily answered. In a field experiment, the sink of two hybrids, Pioneer brand 3732 (P3732) and B73 ✕ Mol7 was modified through cross‐pollination to study effects of sink alteration on dry matter and N accumulation. The two hybrids were grown with 268 kg N ha−1 spring‐applied in a randomized split‐plot design with four replications. Sib‐pollination and reciprocal crosses were made by controlling the pollen source. Dry weight and N content in plant parts as well as black layer development in kernels were analyzed at various stages during kernel maturation. Modification of the P3732 endosperm genotype by cross‐pollination with B73 X Mol7 pollen significantly increased kernel weight, kernel protein content and protein concentration, and grain yield. These increases were the result of increased assimilate production in vegetative tissues rather than improved partitioning efficiency. The P3732 crossed kernels delayed black layer development for about 10 d. Increases in protein concentration were primarily in the form of zein. In contrast, modification of the B73 ✕ Mo 17 endosperm by crosspollination with P3732 pollen had no effect on these traits. The effects of sink alteration on total plant dry matter and N accumulation were also different between P3732 and B73 ✕ Mol7 in that sink alteration of P3732 increased the accumulation of these two traits in vegetative tissues during the period of grain‐fill. These observations confirm that sink determination of grain yield is hybridspecific.
We study the formation of porous polymer nanostructures fabricated by the surface-induced phase separation of polymer solutions in anodic aluminum oxide (AAO) templates. Poly(methyl methacrylate) (PMMA) and tetrahydrofuran (THF) are used to investigate the evolution process of the surface-induced phase separation. With the longer immersion time of the AAO template in the polymer solution, the size of the solvent-rich droplet is increased by the coarsening process, resulting in the formation of porous polymer nanostructures. The coarsening mechanism is further evaluated by changing the experimental parameters including the immersion time, the polymer concentration, the polymer molecular weight, and the solvent quality. Under conditions in which polymer solutions have higher viscosities, the coarsening process is slowed down and the formation of the porous nanostructures is prohibited. The prevention of the porous nanostructures can also be realized by adding water to the PMMA/THF solution before the immersion process.
Front Cover: The fabrication of polymer fibers with anisotropic cross‐sections is achieved by pressing electrospun polymer fibers with flat or patterned substrates while the samples are thermally annealed. The shapes and morphologies of the pressed polymer fibers are controlled by the experimental conditions. Hierarchical polymer fibers with nanorods can also be fabricated by pressing the fibers with porous anodic aluminum oxide templates. Further details can be found in the article by J.‐T. Chen*, Y.‐H. Kao, T.‐Y. Kuo, J.‐T. Liou, Y.‐J. Chiu, C.‐W. Chu, M.‐H. Chi, and C.‐C. Tsai on page 239.
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