Specific resistance compounds

The effects of specific fillers in molded goods appHcations are known (52), and are of special importance for water- and acid-resistant compounds. It is good pohcy to contact the suppHers for specific recommendations to meet the balance of properties required. 

Figure 24 Plot of the specific resistance from a series of Ln2 xMx Cu04 compounds as plotted against the "c/a" axial ratio. The broken trapezoid (dotted lines) outlines the hypothetical region for materials having a semiconductor to metal transition. From Reference 121.

Analogous to sampling TIN with the filter pack method, sampling with a quartz- or glass-fiber filter followed by a sorbent can provide a relatively accurate measure of the total (i.e., vapor plus particle phase) concentration of specific PAH compounds. Such methodologies were reviewed by Lee et al. (73). Selection of a sorption medium for collection of vapor-phase PAHs is influenced by air-flow resistance, collection efficiency, breakthrough volume, the effort required to purify the medium for use, and the efficiency with which the PAH can be recovered from the sorbent. 

Because antiozonants and waxes, which to be effective must form a surface bloom, are used to enhance ozone resistance it is usual to condition test pieces in the strained state before exposure. The usual conditioning period is between 48 and 96h and the test pieces should be kept in the dark and in an ozone-free atmosphere. For this treatment to be effective, the test piece surface must not of course be touched in the course of subsequent handling. Where specifications wish to specifically exclude compounds which rely on an adequate wax film for protection, the conditioning period is dispensed with. Hill and Jowett47 in a criticism of ozone test methods strongly make the point that the conditioning process should be relevant to service conditions if a discriminating evaluation of waxes is to be made. 

Unlike carbon monofluoride, the compound retains an electrical conductivity which, however, is about two powers of ten lower than that of the original graphite. W. and G. Riidorff found a specific resistance of 2-4 ohm cm at a pressure of 750 kg/cm . Measurements by McDonnell et al. (45) also showed a similar strong decrease in conductivity on going from graphite to C4F. 

A number of phases have been measured 18) using a probeless technique 48). The results are plotted and compared with the pure elements Rb and Cs in Fig. 20. The earlier data of Brauer 49) differ by less than 10% of the absolute values. The metallic nature of all samples (at least qualitatively) verifies the bond model. The specific resistivity p of an alkali metal suboxide is in the same order of magnitude as with the pure elements Rb and Cs (JO). The compound CS7O exhibits a residual resistivity ratio (rrr) defined as p (260 K)/p (T -> 0 K) in the order of 200, near to the value found for Cs (JO). The value for the compound CsnOa is approximately 50. The temperature dependence of the ideal resistivity (corrected for the residual resistivity) of e.g. CS7O is very similar to that of Rb and Cs. 

It is envisioned that the defensive systems of plants include preformed physical and chemical barriers as well as inducible defenses that also can be either physical or chemical. An example of an inducible defense is the synthesis of specific antimicrobial compounds such as phytoalexins or phytoanticipins. However, in other instances plants react to pests by developing long-lasting, broad-spectrum systemic resistance to later attacks by pathogens. This type of resistance is referred to as systemic acquired resistance, and was discovered in tobacco by Ross (1961). This form of resistance is almost universally... 

YbPtAl, YbNiGa, and YbPtIn are metallic conductors. The three compounds show Kondo-like minima in the specific resistivity and steep decreases at low temperature resulting from the onset of magnetic ordering (Trovarelli et al. 2000, Diehl et al. 1995). Such a steep decrease also occurs for YbNLA.1, however, crystal-field effects dominate the resistivity behavior in the high-temperature region (Diehl et al. 1995). 

The value of C T for YbNiSb extrapolated to OK is 150mJ/molK. Together with the high value of the specific resistivity, YbNiSb may be classified as a low-carrier heavy-fermion compound (Dhar et al. 1993). 

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