Frequency influence experimental results

Becanse there are many factors involved in the dynamic mechanical compression of polyolefin foams, the Taguchi method was employed in a Perkin Elmer DM A7 dynamic mechanical analyser to establish a method to improve the measurement process. The signal-to-noise ratio was measured to determine how the variability could be improved. Control and noise factors were evaluated and levels chosen, with details being tabulated. Appendix A describes some of the factors. Tests were conducted on two closed cell foams. NA2006 foam is 48 kg/cu m LDPE and NEE3306 foam is 32 kg/cu m EVA. Different factors were shown to influence results for E and tan delta but an optimum combination is proposed for the simultaneous measurement of both properties. The results were less variable as frequency was increased. Small differences in the dynamic response of different materials should be measurable because of the low variability in the experimental results. 18 refs. 

Of importance for any experimental technique which is to be used to fit some complex reaction model is the way in which experimental errors influence the result [93]. The error structure for the EHD method utilising the RDE has been analysed in detail by Orazem et al. [94]. These authors showed that information could reliably and accurately be extracted even at high modulation frequencies (up to 20 Hz). In principle the determination of Sc should only require data at low modulation frequency. They demonstrated that extraction of accurate values for Sc required data which had been recorded over a relatively wide frequency range and had been weighted according to a reliable model for the errors. They also showed that the EHD (7 - Cl) response could be fitted empirically to the form ... 

A summary is made of the general classes of phenomena which can influence the reactivity of functional groups at heterogeneous interfaces, and potential pitfalls are pointed out in the reliance upon molecular analogy. Experimental results are reviewed pertaining to the thermodynamic and kinetic encounter frequencies of reagents on crosslinked polystyrenes and the chemisorption of olefins on oxide-free surfaces of elemental carbon. 

The second major section (Section III), comprising the bulk of the chapter, pertains to the studies of IVR from this laboratory, studies utilizing either time- and frequency-resolved fluorescence or picosecond pump-probe methods. Specifically, the interest is to review (1) the theoretical picture of IVR as a quantum coherence effect that can be manifest in time-resolved fluorescence as quantum beat modulated decays, (2) the principal picosecond-beam experimental results on IVR and how they fit (or do not fit) the theoretical picture, (3) conclusions that emerge from the experimental results pertaining to the characteristics of IVR (e.g., time scales, coupling matrix elements, coupling selectivity), in a number of systems, and (4) experimental and theoretical work on the influence of molecular rotations in time-resolved studies of IVR. Finally, in Section IV we provide some concluding remarks. 

The influence of strain amplitude in an oscillating shear flow (at fixed frequency) on the structural and viscoelastic properties of an ER fluid has been investigated in a MD simulation by Wang et al. [319] and compared with experimental results by Lemaire et aL [331]. With increasing strain amphtude the structure changes from isolated columns to sheet-like structures perpendicular, slanted and paraUel to the oscillating direction. 

For the film thickness, as a first approximation, one can take that Lf = K. Another simplifying assumption is that the viscosity changes abruptly at the boundary between the film and the solution. Estimation of the viscosity of the film as a function of potential is very difficult, since electro-neutrality is not maintained in the diffuse double layer, and it is difficult to take into account the influence of the electric field in the double layer on the viscosity of the film. Instead, the viscosity of the film, tjf, can be taken as a parameter, to fit the theoretical curve to the experimental results. To do this one substracts from the observed frequency shift the contribution of the mass effect caused by electrostatic adsorption of ions [Eq. (56)]. 

A single selected experiment with glass and a single experiment with alumina, both conducted at mild thermal conditions, were used to adjust the collision frequency pre-factor Tcoii- In this way, the value of Fcoii = 10m (/coll = 1.6 s ) was obtained for glass, and Fcoii = 45 m (/cou = 4.1 s ) for alumina. Once this parameter was fitted, it was used without further change for comparison with all other data gained with the respective material. A deeper discussion on the effect of the number of collisions on model response, more details about equipment and material properties, and a full documentation of the experimental results can be found in Terrazas-Velarde (2010). Here, just a few comparisons with measured data are presented to show that the model can reliably describe the influence of process parameters. 

In Fig. 4.12 we compare the experimental results of the internal fiiction with the numerical calculations for frequencies at 535 Hz and at 15 MHz using Efjke = 10 K, tq = 10 s, and a rather small distribution width relative value in comparison with the plateau [24]. It is worth pointing out, that for PMMA, since the changes produced by the free parameters Eq, tq and oq compete with each other, it is not possible to find another set of values which can explain the results as well as we can. It is important to note that the internal friction data for both polymers indicate a much smaller thermally activated contribution to the phonon attenuation for PMMA than for PS, in spite of the fact that in the quantum tunneling regime both samples show similar results. This difference may influence the low-temperature heat release because the number of excited states that are available after the cooling process will be different. 

Walters reached a similar conclusion from his experimental results. He obtained the friction-temperature relations at constant sliding speed. The temperature of maximum friction at a constant speed, increases linearly with the glass transition temperature. It appeared however, that in a graphical plot of the linear relation the point corresponding to the results obtained with butyl rubber falls distinctly outside the line. In our work with butyl rubber such an anomalous behaviour has been confirmed. Instead of relating the speed of maximum friction to Tg, Grosch related it to the frequency at which the loss modulus is a maximum. That correlation has been found to be valid to several rubbers includ ing butyl rubber. On the other hand, it is not surprising to expect that besides Tg, there are other parameters which have an important influence upon friction properties. 

Further, it should be emphasized that the nature of the active N itself, that is, ammonia or N plasma, drastically influences growth kinetics. Actually, the above considerations on the growth diagram as well as all experimental results reported in this chapter refer to plasma-assisted molecular-beam epitaxy (MBE), active N being obtained by radio frequency cracking of N2 in a plasma cell. 

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