Temperature effects loss factor

Fig. 4. Effect of nanocomposites on mechanical loss factor tan 8 vs temperature...

The dimensionless x-loss factors are parameters that effect temperature, and occur in modified forms in many correlations in the literature for compartment fire temperature. 

Henry s Law constant (i.e., H, see Sect. 2.1.3) expresses the equilibrium relationship between solution concentration of a PCB isomer and air concentration. This H constant is a major factor used in estimating the loss of PCBs from solid and water phases. Several workers measured H constants for various PCB isomers [411,412]. Burkhard et al. [52] estimated H by calculating the ratio of the vapor pressure of the pure compound to its aqueous solubility (Eq. 13, Sect. 2.1.3). Henry s Law constant is temperature dependent and must be corrected for environmental conditions. The data and estimates presented in Table 7 are for 25 °C. Nicholson et al. [413] outlined procedures for adjusting the constants for temperature effects. 

Peripheral nerve functions are not affected equally by local anesthetics. Loss of sympathetic function usually is followed by loss of temperature sensation sensation to pinprick, touch, and deep pressure and last, motor function. This phenomenon is called differential blockade. Differential blockade is the result of a number of factors, including the size of the nerve, the presence and amount of myelin, and the location of particular fibers within a nerve bundle. For conduction to be effectively blocked, the local anesthetic must exert its effects over the distance between several nodes of Ranvier. Since the smallest nerves (C fibers) have no myelin, they can be most easily blocked thus, sympathetic functions often are blocked soon after a local anesthetic is applied to a particular nerve bundle. Small myelinated nerves have correspondingly short distances between nodes of Ranvier and therefore are often blocked next. These nerves subserve temperature and sharp pain sensation. Larger nerves then become blocked, accounting for the loss of function up to and including motor innervation. 

It is seen from equation (28) that the constant (9) merely effects the magnitude of (0) but the constant (0) and f(v) condition the shape of the temperature profile and produces the curious shaped peaks recorded by the detector. The constant (9) can be considered as the heat loss factor of the cell, it should be noted that the magnitude of f(v) will depend on the value of (Ca) the ratio of the effective volume of the cell to the plate volume of the column. 

For many applications low-temperature flexibility of the plasticized composition is also important. Plasticizers of low viscosity and low viscosity-temperature gradient are usually effective at low temperature. There is also a close relationship betv/een rate of oil extraction and low-temperature flexibility plasticizers effective at low temperature are usually rather readily extracted from the resin. Plasticizers containing linear alkyl chains are generally more effective at low temperature than those containing rings. Low-temperature performance is evaluated by measuremen t of stiffness in flexure or torsion or by measurement of second-order transition point, brittle point or peak dielectric loss factor. 

Figures 2.37 and 2.38, show the isochronal curves of the permittivity and loss factor for P2NBM and P3M2NBM as a function of temperature at fixed frequencies. A prominent relaxation associated with the dynamic glass transition is observed in both polymers. Clearly the effect of the methyl substitution in position 3 of the norbornyl group is to decrease the temperature of this relaxational process.

In a typical ramped cure, the specimen begins with a relatively small loss factor, which initially increases as the temperature is increased due to a decrease in viscosity, but which later decreases due to the effects of cure. This has been illustrated schematically in Fig. 18 38), where the topmost curve represents the initial increase and subsequent decrease of the actual bulk tan 8 for a specimen during cure. The remaining curves are the values of tan 8 that would be observed experimentally in the presence of either an electrode polarization layer or an added blocking/release layer for various values of the ratio L/2tb. Note that even a thin release layer, for example a 25 pm (.001") layer placed between 5 mm spaced plates, results in an L/2tb ratio of 100. Examination of Fig. 18 shows that for this value of L/2tb, the maximum value of tan 8 actually produces a minimum in the experimental tan 8X, and that two subsidiary maxima appear in tan 8X. 

Figure 21 shows the permittivity and loss factor for an isothermal cure (137 °C) of DGEBA (EPON 825 n = 0) with diaminodiphenyl sulfone (DDS)47. To a first approximation, the data are the mirror image of Fig. 20, supporting the idea that the effect on electrical properties of the increase in Tg during isothermal cure might be similar to the effect of a decrease in temperature at fixed Tg. Examination of Fig. 21 shows one important difference between the temperature and cure dependences, namely that the relaxed permittivity decreases with cure time under isothermal conditions. This is a direct result of the changing chemistry, as discussed further in Section 4.3. The detailed behavior of the dipolar mobility is examined in Section 4.4, and of the ionic mobility in Section 4.5. 

This Section addresses the effects of temperature and cure on the dominant dipolar relaxation, i.e., the a-transition between the unrelaxed and relaxed permittivity, with its associated loss-factor peak. As illustrated in Figs. 20 and 21, this dipolar relaxation is observed as the temperature increases through Tg, or during a cure, as Tg increases toward and even through the cure temperature. 

It was of general interest to investigate the effectiveness of the damping materials in terms of any synergisms that may arise because of special mixing modes. The bandwidth "constant K indeed is not a constant and depends on the chemistry and other factors of the system, see above. However K is only useful for loss moduli-temperature behavior. No similar theory for tan 6 temperature exists, and... 

The power-loss meter is the most common type of dielectric moisture meter. It senses the product of the dielectric constant and loss factor. Generally, the loss factor increases with wood moisture content but may exhibit variations from this behavior depending on the frequency of measurement (JO, 11, 14). An increase in temperature produces effects similar to increasing moisture content, with interaction between these two parameters. Therefore, temperature adjustments of meter readings are complex, sometimes increasing and sometimes decreasing the scale reading as temperature increases... 

Major results. Figure 14.7 shows that the resistivity of aluminum-filled PMMA changes abruptly. Smaller volumes of filler contribute a little to resistivity but, after certain threshold value of filler concentration, further additions have little contribution. A similar relationship was obtained for nickel powder the only difference is in the final value of resistivity, which was lower for nickel due to its higher conductivity. The same conclusions can be obtained from conductivity deteiminations of epoxy resins filled with copper and nickel. Figure 14.8 shows the effect of temperature on the electric conductivity of butyl rubber filled with different grades of carbon black. In both cases, conductivity decreases with temperature, but lamp black is substantially more sensitive to temperature changes. Even more pronounced changes with temperature were detected for the dielectric loss factor and dissipation factor for mineral filled epoxy." ... 

Both the dipole-relaxation time and the ionic conductivity are related to the glass-transition temperature Fg. As a material is heated through its glass-transition temperature, static dipoles gain mobility and start to oscillate in an electric field. This causes an increase in permittivity and a loss-factor peak is noted. Obviously this motion is affected by frequency (lower frequencies have greater effects). This effect is shown in Figure 3.62 (Prime, 1997a), which shows the peaks in permittivity and loss factor at Tg. 

The addition of electrolytes to a solution decreases the viscosity of a fresh polymer solution as will be discussed in the next section. High temperatures less than the thermodegrading conditions (less than 70-100°C depending on the polymer) cause a drop in the viscosity. This is also a reversible change associated with the change in the conformation of the chains in solution. The temperature effect on solution viscosity will be discussed. The effects of salt, temperature, severe shear, and aging will be discussed from the standpoint of viscosities and chain conformations in solution. First of all, the factors causing temporary viscosity losses will be presented. 

The loss factor (s") for higher- and medium-moisture content cheese increases gradually with temperature (5°C-85°C). The trend is opposite for low-moisture cheese. The increase in s" for high- and medium-moisture cheese could be attributed to ionic conduction. It was reported that the effect of temperature was more pronounced at lower frequencies than at higher frequencies (above 1 GHz) (Nelson and Bartley, 2000). Models were also developed to predict the effects of moisture and salt content. These models can provide the effects of frequency, temperature, and compositions on microwave processing of cheese. 

Beef is one of the important meats in many different cuisines and is consumed all over the world. It is a rich source of selenium, zinc, iron, vitamin B, and carnitine. The dielectric constant (s ) and the loss factor (s") of beef both increase at higher temperatures. For example, s values of lean beef at 27.12MHz were 36.0 and 68.8 at -5°C and -1°C, respectively. Temperatures in the range of -1°C and 10°C did not have a significant effect on s and s" at any microwave frequency. Higher temperature had more effect on s" for all meats at 27.12 MHz and s" increased with temperature (Ryynanen, 1995 Shukla and Anantheswaran, 2001). 

Mirin is a condiment with almost 40%-50% sugar and is widely used in Japanese cuisine. Dielectric loss factor of mirin is affected by both the dipolar loss component and the ionic conductivity. Ionic conductivity is lower at higher microwave frequencies. The combined effect of temperature, microwave frequency, and sugar content is complex and hard to describe. Nevertheless, the e" increases with frequency and temperature. The penetration depth decreases as the processing temperature increases. The effect of temperature on the is significant at lower processing frequencies at higher frequencies, temperature has only moderate effect on the d. Tanaka et al. (2005) reported similar results for soy sauce. It was noted by Liao et al. (2003) that this trend is distinctive for thick or complex solutions. 

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