The spin‐coated thin‐film morphology of poly(4‐vinylpyridine) has been studied by AFM; the dark lines or disks (circular holes) in the AFM height images correspond to the depressed regions. An epitaxy‐like “nano‐trench” pattern was observed in the noncrystalline polymer film deposited on the crystalline graphite substrate. The transition from surface‐templated to isotropic dewetting occurs during 3 nm of the film thickness increase. This study presents an example of ordered nanopatterns emerging from the chaotic spin‐coating process. The well‐defined “nano‐trench” morphology offers an opportunity for the study of the nanoconfinement effect and provides a unique means for surface patterning and nanolithography.
The template reaction of salicylaldehyde and its substituted derivatives and 2-hydroxy-5-bromobenzylamine or 2-hydroxy-5-chlorobenzylamine with copper(II) acetate in dimethyl sulphoxide (dmso) afforded eight dinuclear Cu(II) complexes, [Cu2(L)2(dmso)2] (H2 L = N-salicylidene-2-hydroxy-5-bromobenzylamine, N-salicylidene-2-hydroxy-5-chlorobenzylamine and their 5-bromo, 5-nitro and 5-methyl-substituted salicylidene derivatives). These Cu(II) complexes were characterised by IR and UV-VIS-NIR spectroscopy, electric conductivity, cyclic voltammetry, and temperature dependence of magnetic susceptibilities (4.5–300 K). In the THF solution, the complexes are nonelectrolytes and exhibit a characteristic CT band due to phenoxido-bridging at 360–384 nm. In the cyclic voltammograms, an irreversible reduction process was observed at ?1.18–1.54 V vs Fc/Fc+. Single-crystal X-ray crystallography revealed that two Cu(II) ions were bridged by the two phenoxido-oxygen atoms of the two Schiff-base ligands with axial coordination of dmso molecules forming a square pyramid with a Cu-Cu distance of 3.0628(8)–3.0931(6) °A. In accordance with the crystal structures, the magnetic interaction between the two Cu(II) ions is relatively anti-ferromagnetic with ?2J value of 386–575 cm?1. The axial coordination effect of the dmso molecule was discussed in relation to the correlation between the Cu-O-Cu angle and the ?2J value. 相似文献
Multiple shocklets are frequently generated in transonic diffuser flows. The present paper investigates the formation of
these shocklets with a high-speed CCD camera combined with the schlieren method. It is observed that compression waves steepen
while propagating upstream, and eventually become new shock waves. The ordinary shock wave is found to move upstream beyond
the nozzle throat or to disappear while moving downstream depending on the pressure ratio across the nozzle. This phenomenon
is also analyzed with the one-dimensional Euler equations by assuming a pressure disturbance given by the sine function at
the channel exit. The calculated results are found to reproduce quite well the experimental behavior of the shocklets. The
effect of the frequency of disturbance is also studied numerically, and it is shown that the multiple shocklet pattern appears
when the amplitude of disturbance is not large and the diverging part of the channel downstream of the ordinary shock wave
is long.
Received 26 June 1998 / Accepted 15 March 1999 相似文献
Heme dioxygenases catalyze the oxidation of L-tryptophan to N-formylkynurenine (NFK), the first and rate-limiting step in tryptophan catabolism. Although recent progress has been made on early stages in the mechanism, there is currently no experimental data on the mechanism of product (NFK) formation. In this work, we have used mass spectrometry to examine product formation in a number of dioxygenases. In addition to NFK formation (m/z = 237), the data identify a species (m/z = 221) that is consistent with insertion of a single atom of oxygen into the substrate during O(2)-driven turnover. The fragmentation pattern for this m/z = 221 species is consistent with a cyclic amino acetal structure; independent chemical synthesis of the 3a-hydroxypyrroloindole-2-carboxylic acid compound is in agreement with this assignment. Labeling experiments with (18)O(2) confirm the origin of the oxygen atom as arising from O(2)-dependent turnover. These data suggest that the dioxygenases use a ring-opening mechanism during NFK formation, rather than Criegee or dioxetane mechanisms as previously proposed. 相似文献
A 1.5-ns address access time, 256-kb BiCMOS SRAM has been developed. To attain this ultra-high-speed access time, an emitter-coupled logic (ECL) word driver is used to access 6-T CMOS memory cells, eliminating the ECL-MOS level-shifter time delay. The RAM uses a low-power active pull down ECL decoder. The chip contains 11-K, 60-ps ECL circuit gates. It provides variable RAM configurations and general logic functions. RAM power consumption is 18 W; chip power consumption is 35 W. The chip is fabricated by using a 0.5-μm BiCMOS process. The memory cell size is 58 μm2 and the chip size is 11×11 mm 相似文献