Ultrasonic measurement

Benguigui and co workers [16,17] are the only group which has measured the ultrasonic modulus and absorption of side chain PLC. The PLC studied is a polymethylsiloxane with the following chemical structure  

This PLC has an isotropic-nematic transition temperature (T ) of 374 K, a nematic—smectic-A transition temperature of 345 K and a 

Benguigui et ah [16] have also measured the longitudinal velocity as a function of angle relative to the 3 axis, from which the stiffness constants C, C, and C, have been deduced. The axial shear 

For side chain PLCs there are two orienting molecular elements which can influence the elastic properties the mesogenic groups and the monomer units of the polymer backbone. The fact that is 

The value for P3 was obtained from AH (from Eyring plots) because E = AH + RT. AG° was taken as equal to AH°, and from literature values of AH° estimates of PA were obtained. The constants Pj-P4 were then derived from the experimental data and the foregoing equation. 

For the 1,2,4,6-tetramethylpiperidine equilibrium 123 124, AH° = 1.0 kcal mol-1, and for the N-methylpiperidine equilibrium, AH° = 0.88 kcal mol 1 and refer to measurements made on pure liquids. These values are much lower than those obtained by most other techniques (Table XI) and it is agreed2 that values of AH0 obtained by spectroscopic methods are more reliable than those from ultrasonic techniques. AH (axial - transition state) values, however, are in agreement with those from other methods, and for Af-methylpiperidine a value of 5.02 kcal mol-1 has been obtained from Eyring plots and a value of 5.76kcal mol l, using the foregoing equation.171 

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For the repetitive inspections the required hydrotest can only be performed for a limited number of the small cylinders, and even then the drums have to be removed from the line and the cylinders will be supported in defined distances for the weight of the water and the pressurisation. For the new and long cylinders even this is impossible, because they loose due to the additional weight of the water and the over-pressurisation their roundness and balances. Therefore the law in the most countries within and outside of the EU accept as a replacement of the hydrotest an additional application of different NDT methods, which were often done by an ultrasonic measurement of the wall thickness of the cylindrical part and a MT of the flat covers. 

Acknowledgments. This study was funded by the Swedish National Flight Research Programme (NFFP) in project NFFP-274. The author would acknowledge the assistance of Bertil Grelsson from CSM Materialteknik AB for performing the ultrasonic measurements. 

Table 1. Three different ultrasonic measuring techniques for thickness measurement.

T. Leon-Salamanca and D. E. Bray, "Ultrasonic Measurement Of Residual Stress In Steels Using Critically Refracted Longitudinal Waves (L j )," R j". NDE 6(4) 1995 (in press). 

Winter T. G., Hill G. L. High-temperature ultrasonic measurements of rotational relaxation in hydrogen, deuterium, nitrogen and oxygen, J. Acoust. Soc. Am. 42, 848-58 (1967). 

L.C. Lynworth, Ultrasonic Measurements for Process Control Theory, Techniques, Applications, Academic Press, New York, NY (1989). 

The viscosity coefficients at dislocation cores can be measured either from direct observations of dislocation motion, or from ultrasonic measurements of internal friction. Some directly measured viscosities for pure metals are given in Table 4.1. Viscosities can also be measured indirectly from internal friction studies. There is consistency between the two types of measurement, and they are all quite small, being 1-10% of the viscosities of liquid metals at their melting points. It may be concluded that hardnesses (flow stresses) of pure... 

L. S. Wilson and D. E. Robinson, Ultrasonic measurement of small displacements and deformations of tissue, Ultrason. Imaging, 1982, 4, 71-82. 

Ultrasonic measurements of methyl formate, ethyl formate, methyl acetate, ethyl acetate, and n-propyl formate show that the cis conformation is more stable than the /ra/ist68-,71 ... 

Hinrichs and Thuen [28] used ultrasonic attenuation to determine the proper time for pressure application during an otherwise traditional pre-established cure cycle. Because dielectric is an electrical property, it is influenced by moisture content and temperature as well as viscosity, so it may vary quantitatively. Ultrasonic measurements are also affected by other parameters (i.e., void content), but they are a mechanical measurement rather than an electric one. The ultrasonic sensors used by Hinrichs unfortunately were less reliable than the dielectric sensors. 

NMR measurements9 give the barrier to ring inversion in N-methylpiperi-dine as AGL28" 11.8-12.0 kcal mol-1. If a AG value of 6.0 kcal mol-1 for the 7V-Meax - transition state process, as suggested by ultrasonic measurements,171 is accepted (AG ultrasonic measurements are more reliable than AG°, see Section II,I) and if AG° for the N-methylpiperidine equilibrium is taken as 2.7 kcal mol-1,125 then the other half barrier (iV-Meeq - transition state) is obtained2 as 8.7 kcal mol-1, which is consistent with the overall pattern of N-Me inversion half barriers. 

In each case, the volumetric rate of flow can be determined by measuring the liquid levels in the appropriate place. This is often achieved using an ultrasonic measuring system (Fig. 6.7d) in which the time taken for an ultrasonic wave to be reflected from the liquid surface is measured (see also Section 6.5.5). Accuracies of 2.5 mm/m distance between sensor and liquid surface are not uncommon. Standard designs of open channel restrictions can be found in BS 3680(l4). 

The objectives of this chapter are to introduce the basic concepts of ultrasonic propagation in materials, to describe some of the most important methods for measuring and interpreting ultrasonic measurements, and to outline existing and possible applications of the technique in the food industry. 

Continuous wave methods are the most accurate means of making ultrasonic measurements. Even so, they are used less frequently than pulse methods because measurements are more time consuming and laborious to carry out, are more difficult to automate, and the measurement cell requires a high degree of precision engineering. These techniques therefore tend to be used in specialized research laboratories where accurate measurements are important. Continuous wave ultrasound is utilized in a variety of different techniques, but the most commonly used is the interferometer [10,11]. 

Measurement cell. The measurement cell should be made of a material which does not react with the sample. The cell walls should be of an appropriate thickness and acoustic impedance so that any reverberations in the cell walls do not interfere with the signal from the sample. The internal walls of the cell should be smooth and parallel so that scattering or oblique reflection of the ultrasonic wave do not cause errors in the velocity and attenuation measurements. Ultrasonic measurements are particularly sensitive to temperature and so it is important to either use a thermostated measurement cell, or to measure the temperature and make a suitable correction. 

L.C. Lynworth, Ultrasonic measurements for process control theory, techniques, applications, Academic Press, San Diego, 1989. 

Ultrasonic measurements (5 MHz) made at ambient temperature on amine-crosslinked epoxies (Morel et al., 1989), or styrene-crosslinked vinyl esters (Bellenger et al., 1994), show that K is effectively proportional to the cohesive energy density ... 

The key elements of an ultrasonic measurement system are a transducer, which converts an electrical impulse into mechanical vibration, a signal generator to produce the original electrical excitation signal, and a display... 

Some of the simplest ultrasonic measurements involve the detection of the presence/absence of an object or its size from ultrasonic spectrum (Coupland and McClements, 2001). An ultrasonic wave incident on an ensemble of particles is scattered in an amount depending on size and concentration of the particles. As the ultrasonic parameters depend on the degree of the scattering, it can therefore be used to provide information about particle size. 

For Agar gel, experimental study of these coefficients were performed [7], The coefficient E was determined by compressive tests. Ultrasonic measurements of the Poisson s ratio v showed that it is almost equal to 0.5. Compressibility K (fig. 3) is deduced from K = Ej(3(1 — 2//)). 

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