Loss index

The dielectric constant (permittivity) and loss index are determined by ASTM-D150. Permittivity is the ratio of the capacitance of the polymer to that of air. 

Somewhat greater improvements were found in the thermooxidative stability of the fluorinated materials, though the effect for most part was still only moderate with the greatest difference found to be about 40°C. These stability improvements were most notable when comparisons were made at the 2% index, and (in contrast to the anaerobic results) often became less pronounced at the 5 and 10% weight loss indexes. 

Secondary endpoints Binary restenosis at 4 months follow-up (defined as > 50% diameter stenosis by QCA) Quantitative coronary angiography endpoints including late loss, loss index, late absolute MLD at 4 months Incidence of (sub)acute stent thrombosis (SAT) to 30 day follow-up, MACE at 4 and 9 months... 

For a given f and e, the heating efficiency is directly proportional to E and tan 6. The product of these two parameters is called the loss index, e". Loss index of 0.2 or more results in good heatability 0.08-0.2, fairly good heatability 0.01-0.08, poor heatability and under 0.01 there is little or no response (2). 

The loss index of silicone elastomers made from polydimethyl siloxane, generally speaking, is low due to their low values of dielectric constant and loss tangent. The dielectric constant of polydimethylsiloxane is almost independent of the frequency, where as the tan 6 is highly dependent on the frequency in the micro-wave region (3, 4 ) At 3 x 109 Hz, a 1000 cs polydimethylsiloxane fluid has a tan 6 of about 0.0096 and a dielectric constant of 2.76. This gives a loss index of 0.0264, which puts polydimethyl siloxane in the poor heatability category. 

One can, however, increase the loss index of silicone polymers by increasing either E or tan 6 of the material. This can be done in two ways, i.e.,... 

B. Introduce an additive, which has a high loss index. 

In the former approach, the loss index can be increased by changing the substituents on silicone. Vincent et al (5 ) reported that as the R group in Me3SiO(MeRSiO)xSiMe3 was changed from methyl to a bulky polar group, the dielectric constant and loss factor increased drastically. This is shown in Table I. 

In the additive approach, the loss index is increased by placing a high-loss material in contact with a low-loss material. The high-loss material heats and transfers its heat to the low-loss load. Some examples of such additives are carbon black in rubber, NaCl in urea-formaldehyde glue for wood and polyvinylchloride in polyurethane foam (2). 

Additive Approach. As mentioned previously, dimethylsilicone compounds respond poorly to microwave heating because of the low "loss index". To make the dimethylsilicone compounds respond to microwave, one can change the structure of polydiorganosiloxane as shown above, or introduce additives which have a high "loss index" such as carbon black. The latter was demonstrated by applying microwave (2450 M Hz) to a mixture of 10 g of base... 

The ratio of the loss index to its relative permittivity, the tangent of its loss angle, 5 or the cotangent of its phase angle, 0. 

ASTM D150 Standard Test Methods for AC Loss Characteristics and Permittivity (Dielectric Constant) of Solid Electrical Insulation includes the determination of relative permittivity, dissipation factor, loss index, power factor, phase angle, and loss angle through specimens of solid electrical insulating materials when the standards used are lumped impedances. The frequency range that can be covered extends from less than 1 Hz to several hundred megahertz. 

Rolla et ah, used microwave dielectric measurements to monitor the polymerization process of mono functional n-butyl acrylate as well as 50/50 w/w blends with a difunctional hexane-diol diacrylate that gave highly cross-linked networks. In these real time cure experiments the decreasing acrylate monomer concentration was studied via a linear correlation with the dielectric loss index at microwave frequencies. This correlation is a result of the largely different time scales for dipolar polarization in the monomer on one hand and in the polymerized reaction product on the other hand. 

Fig. 16-15. Frequency-temperature contours of dielectric constants, e, and loss index, e", for nylon.

Dielectric Loss Index. A measure of a dielectric loss defined by the product of the power factor and the permittivity (dielectric constant). 

As with the dynamic mechanical relaxations, it is also possible to check the dielectric behavior of the sample. In this case the thermal analysis is carried out measuring the dielectric constant, dissipation factor, loss index, and phase angle as a function of temperature and frequency. In order to see a dielectric effect, a dipole must be connected with the molecular motion. In this way dielectric relaxation may be more specific than DMA. A combination of DMA, dielectric measurements, and DSC is often needed for a detailed interpretation of the properties of the materials. ... 

For each criterion related to a pipeline section and for each accident scenario, the risk is defined as the expected value of losses, as per the definitions found in Berger (1985) and Keeney and Raiffa (1976). In this statement, the risk is considered to be the result of summing the losses associated with each specific scenario 6 and each section x for the three consequence dimensions considered, multiplied by the probabilities of accident scenarios added to the losses indexed... 

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