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91.
Preparation and Crystal Structures of Niobium-Tantalum-Nitride Phases (Nb, Ta)N~1 Ta? Nb alloys with graduated composition are nitrided with NH3 at 1100–1450°C. The mononitrides formed are investigated by X-ray diffraction. Their nitrogen content is evaluated by chemical analysis. Seven Ta? Nb nitride phases are observed. Depending on the temperature, the phases appear in a strictly defined sequence along the variation of the Ta:Nb relation. Corresponding to this sequence, the density (formula volume) of this nitride phases varies. 相似文献
92.
93.
Winfried Eckart 《Continuum Mechanics and Thermodynamics》2000,12(5):341-362
In this paper we propose a phenomenological theory for electrorheological fluids. In general these are suspensions which undergo dramatic changes in their material properties if they are exposed to an electric
field. In the context of continuum mechanics these fluids can be modeled as non-Newtonian fluids. Recalling the governing equations of rational thermodynamics and electrodynamics of moving media (Maxwell-Minkowski-equations), we derive suitable governing equations of electrorheology using essentially two assumptions concerning magnetic
quantities. Furthermore we introduce a 3-dimensional nonlinear constitutive equation for the Cauchy stress tensor which is an extension of the model proposed by Ružička (see [14]). Assuming a viscometric flow, we compare the shear stress of our model with other well known models and fit the parameters by using measurements that
were obtained in a rotational viscometer. Excellent agreement between model and measurements is achieved. On the basis of
these results we propose a 3-dimensional model, the so-called extended
Casson
-model. This model is investigated further for a channel flow configuration with a homogeneous electric field. We determine analytical solutions for the electric field, the velocity and the volumetric flow rate and illustrate the velocity
profiles and the predicted pressure drop. The velocity profiles are flattened compared to parabolic profiles and become more
flat if the electric field increases.
Received March 21, 2000 相似文献
94.
95.
Benjamin S. Nehls Frank Galbrecht David J. Brauer Christian W. Lehmann Ullrich Scherf Tony Farrell 《Journal of polymer science. Part A, Polymer chemistry》2006,44(19):5533-5545
A helical step‐ladder polyarylene incorporating chiral (R)‐2,2′‐dioctoxy‐1,1′‐binaphthyl units was synthesized for the first time. The first step involved the preparation of a precursor poly(arylene ketone) via a palladium‐mediated Suzuki‐type cross‐coupling reaction with the aid of microwave heating. Two polymer‐analog reaction steps, the reduction of the keto groups to tertiary alcohol functionalities and subsequent intramolecular Friedel–Crafts cyclization, gave a step‐ladder polymer ( 6 ) in good yields with reasonable mean average molecular weights greater than 13,000. The regioselective cyclization pattern in the α position of the naphthalene core was confirmed by a comparison of the NMR data of the polymer with those of the corresponding model ladder oligomers, 12 and 13 , and also a single‐crystal structure of 13 . The optical spectra of the oligomers and polymers indicated that there was little electronic interaction across the binaphthyl units. The circular dichroism spectrum of 6 exhibited a strong bisignate Cotton effect in the π–π* absorption region of the planar chromophores, which reflected the strong exciton coupling within the helical polymer chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5533–5545, 2006 相似文献
96.
97.
G. Brauer W. Anwand W. Skorupa C. Teichert J. Cizek P.G. Coleman A. Kohyama 《Applied Surface Science》2006,252(9):3342-3351
A SiC/SiC composite is characterized by X-ray diffraction, atomic force microscopy and various positron spectroscopies (slow positron implantation, positron lifetime and re-emission). It is found that besides its main constituent 3C-SiC the composite still must contain some graphite. In order to better interpret the experimental findings of the composite, a pyrolytic graphite sample was also investigated by slow positron implantation and positron lifetime spectroscopies. In addition, theoretical calculations of positron properties of graphite are presented. 相似文献
98.
99.
Background
Performing music requires fast auditory and motor processing. Regarding professional musicians, recent brain imaging studies have demonstrated that auditory stimulation produces a co-activation of motor areas, whereas silent tapping of musical phrases evokes a co-activation in auditory regions. Whether this is obtained via a specific cerebral relay station is unclear. Furthermore, the time course of plasticity has not yet been addressed. 相似文献100.
Kuriplach J Brauer G Anwand W Skorupa W 《Physical review letters》2003,91(19):199601; discussion 199602