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201.
202.
 The non-monotonic shear flow of a viscoelastic equimolar aqueous surfactant solution (cetylpyridinium chloride-sodium salicylate) is investigated rheologically and optically in a transparent strain-controlled Taylor Couette flow cell. As reported before, this particular wormlike micellar solution exhibits first a shear thinning and then a pronounced shear-thickening behavior. Once this shear-thickening regime is reached, a transient phase separation/shear banding of the solution into turbid and clear ring-like patterns orientated perpendicular to the vorticity axis, i.e., stacked like pancakes, is observed (Wheeler et al. 1998; Fischer 2000). The solution exhibit several unique features as no induction period of the shear induced phase, no structural build-up at the inner rotating cylinder, jumping pancake structure of clear and turbid ringlike phases, and oscillating shear stresses appear once the pancake structure is present. According to our analysis this flow phenomenon is not purely a mechanical or rheological driven hydrodynamic instability but one has to take into account structural changes of the oriented micellar aggregates (flow induced non-equilibrium phase transition) as proposed by several authors. Although this particular flow behavior and the underlying mixture of shear induced phases and mechanical instabilities is not fully understood yet, some classification characteristics based on a recent theoretical approach by Schmitt et al. (1995) and Porte et al. (1997) where a strong coupling between the flow instability (non-homogeneous flow profile due to the bands) and the structural changes causes the observed transient phenomena can be derived. In reference to the presented model the observed orientation of the rings is typical for complex fluids that undergo a spinodal phase separation coupled with a thermodynamic flow instability. In contrast to other shear banding phenomena, this one is observed in parallel plate, cone-plate, and Couette flow cell as well as under controlled stress and controlled rate conditions. Therefore, it adds an additional aspect to the present discussion on shear banding phenomena, i.e., the coupling of hydrodynamics and phase transition of rheological complex fluids. Received: 8 January 2001 Accepted: 15 May 2001  相似文献   
203.
The force input mobility of an infinite elastic circular cylindrical shell filled with fluid is derived by using the spectral equations of motion. Mobilities are evaluated and their physical interpretations are discussed for a steel shell of thickness ha = 0·05 filled with water and vibrating in the n = 0, 1 and 2 circumferential modes. The results are subsequently used to analyze the related situations of wave transmission through a radial ring constraint and the far field vibrational energy distributions between the contained fluid and the shell wall for line and point driving forces.  相似文献   
204.
A decentralized model-based control strategy is designed to reduce low-frequency sound radiation from periodically stiffened panels. While decentralized control systems tend to be scalable, performance can be limited due to modeling error introduced by the unmodeled interaction between neighboring control units. Since bounds on modeling error are not known in advance, it is difficult to ensure the decentralized control system will be robust without making the controller overly conservative. Therefore an iterative approach is suggested, which utilizes frequency-shaped loop recovery. The approach accounts for modeling error introduced by neighboring control loops, requires no communication between subsystems, and is relatively simple. The control strategy is evaluated numerically using a model of a stiffened aluminum panel that is representative of the sidewall of an aircraft. Simulations demonstrate that the iterative approach can achieve significant reductions in radiated sound power from the stiffened panel without destabilizing neighboring control units.  相似文献   
205.
Re-Active Passive devices have been developed to control low-frequency (<1000 Hz) noise transmission through a panel. These devices use a combination of active, re-active, and passive technologies packaged into a single unit to control a broad frequency range utilizing the strength of each technology over its best suited frequency range. The Re-Active Passive device uses passive constrained layer damping to cover relatively high-frequency range (>150 Hz), reactive distributed vibration absorber to cover the medium-frequency range (50–200  Hz), and active control for controlling low frequencies (<150 Hz). The actuator was applied to control noise transmission through a panel mounted in the Transmission Loss Test Facility at Virginia Tech. Experimental results are presented for the bare panel, and combinations of passive treatment, reactive treatment, and active control. Results indicate that three Re-Active Passive devices were able to increase the overall broadband (15–1000 Hz) transmission loss by 9.4 dB. These three devices added a total of 285 g to the panel mass of 6.0 kg, or approximately 5%, not including control electronics.  相似文献   
206.
The microwave spectrum of n-propyl isocyanide has revealed the existence of two rotational isomers, trans (methyl trans to the isocyanide substituent), and gauche. Plausible structures have been fitted to the data, giving the gauche dihedral angle as 119° ± 2° from the trans position. Stark effect measurements have yielded dipole moments for the two rotamers: μtrans = 4.16 ± 0.02 D and μgauche = 4.10 ± 0.09 D. The rotational constants of the trans form are A = 23 700 ± 100, B = 2407.632 ± 0.020, and C = 2278.853 ± 0.030 MHz, and those of the gauche form are A = 10 208.983 ± 0.030, B = 3479.219 ± 0.015, and C = 2859.981 ± 0.015 MHz. It has been found from relative intensity measurements that the gauche ground state is slightly more stable than the trans ground state, with an energy difference of 99 ± 45 cm?1. Several vibrationally excited states have been assigned to the torsional motion around the central carbon-carbon bond, the CNC bending motion, and the methyl internal rotation. The torsional vibration frequency is 114 ± 20 cm?1 in the trans form and 123 ± 20 cm?1 in the gauche form. A four-term potential function for internal rotation about the central CC bond has been determined.  相似文献   
207.
208.
Expressions are obtained for the limiting behavior of ensemble expectations, as functions of coverage, of the number of simultaneous occurrences of various structures when indistinguishable single particles are arranged on a two-dimensional lattice. For the general expressions obtained no restrictions are placed on the geometrical nature of the lattice. Averages for specific geometrical arrays, such as rectangular and hexagonal arrays, may be calculated directly from the general results.  相似文献   
209.
Anodic oxidation of diphenyldiselenide in acetonitrile in the presence of an alkene gives acetamidoselenides.  相似文献   
210.
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