In situ Raman spectroelectrochemistry has been used to distinguish between thin single-wall carbon nanotubes (SWCNT) and the inner tubes of double-wall carbon nanotubes (DWCNT). The spectroelectrochemical method is based on the different change of the electronic structure of the inner tube in DWCNT and that of SWCNT during electrochemical charging, which is reflected in the Raman spectra. During electrochemical charging the inner tubes of DWCNT exhibit a delayed attenuation of the intensities of their Raman modes as referred to the behavior of SWCNT of similar diameter. The changes are pronounced for the radial breathing mode (RBM), and thus, these modes are diagnostic for the distinction of inner tubes of DWCNT from the thin SWCNT. The different sensitivities of inner and outer tubes to the applied electrochemical charging is a simple analytical tool for differentiation of SWCNT and DWCNT in a mixture. The significance of the proposed method is demonstrated on a commercial DWCNT sample. 相似文献
A new bifunctional coupling agent with an oxazinone and a lactamate group is synthesized. It is shown by means of model reactions that in the presence of aliphatic hydroxy compounds the reaction of the coupling agent is highly selective. At 220 °C, a conversion of the lactamate group of about 90% is observed under elimination of lactam. In a second reaction the oxazinone group is converted with an aliphatic amino compound. This high selectivity is utilized in the synthesis of segmented polyester/polyamide block copolymers by sequential conversion of the coupling agent with hydroxy‐terminated polyesters [poly(butylene terephthalate) (PBT) and polycaprolactone (PCL)] and amino‐terminated polyamide 12 (PA12) under the conditions of reactive extrusion. In the case of the PA12/PBT block copolymer, ductile behavior is observed, whereas the PA12/PCL block copolymer shows elastic properties. Both polymers are phase separated on the nanometer‐scale, as evidenced by AFM and SEM. The thermal behavior of the polymers is affected by the influence of the individual blocks.
The world of endohedral fullerenes was significantly enlarged over the past seven years by the cluster fullerenes, which contain structures such as the M(2)C(2) carbides and the M(3)N nitrides. While the carbide clusters are generated under the standard arc-burning conditions according to stabilization conditions, the nitride cluster fullerenes (NCFs) are formed by varying the composition of the cooling gas atmosphere in the arc-burning process. The special conditions for NCF synthesis is described in detail and the optimum conditions for the production of NCFs as the main product in fullerene syntheses are given. A general review of all NCFs reported to date consists of the structures, properties, and stability of the NCFs as well as the abundance of the NCFs in the fullerene soot. It is shown that all cages with even carbon atoms from C(68) to C(98) are available as endohedral nitride cluster structures (with the exception of C(72), C(74), and C(76)). Specifically, the NCFs form the largest number of structures that violate the isolated pentagon rule (IPR). Finally some practical applications of these cluster fullerenes are illustrated and an outlook is given, taking the superior stability of these endohedral fullerenes into account. 相似文献
Photolyses of the α‐, β‐ and γ‐cyclodextrin complexes of 2‐aziadamantane ( 1 ) in the solid state afforded markedly different product distributions, as determined by quantitative GC and HPLC analyses. The results are discussed with respect to the structures of the inclusion complexes. 相似文献
Skin friction – a dominant performance parameter for casing rotary drilling piles in cohesive soils. The paper deals with basic treatment of the problem of the skin friction at casing tube while setting up casing rotary drilling piles. A practical forecast algorithm will be presented to determine the necessary torsional moment from the calculated mean skin friction and so to realize a good performance and economic selection of drilling rigs. 相似文献
It has been shown that ternary surfactant synergism can be predicted on the basis of nonideality parameters of binary subsystems
derived from advancing contact angles. Studies with appropriate surfactant mixtures of glucamides, ether sulfates, secondary
alkane sulfonates, and alkylamidopropyl betaines were performed on substrates of different polarity. 相似文献
Indroduction The signal-to-noise ratio of in vivo diffusion tensor imaging (DTI) is usually very limited, especially if high resolution
data is acquired. In a variety of settings, the signal of diffusion weighted images can drop below the background noise level
yielding an underestimated diffusion constant. In this work, we report two new artefacts in DTI that are important in this
regime.
Methods Both artifacts are described analytically and numerically and are demonstrated in DTI phantoms and in subjects in vivo.
Results First, eigenvectors are systematically shifted towards distinct ‘attractive’ orientations of the gradient scheme. Second,
certain eigenvalues can be overestimated due to the underestimation of the measured diffusion, which can result in the misordering
of eigenvalues
Discussion We show that these effects are relevant for current clinical settings of DTI. 相似文献