Resistivity pressure dependence

From the pressure dependence of the resistivity p p) a value of the energy gap hE between the 4f -5d states can be obtained. The experimental data suggest the following resistivity-pressure dependence ... 

The development of active ceramic-polymer composites was undertaken for underwater hydrophones having hydrostatic piezoelectric coefficients larger than those of the commonly used lead zirconate titanate (PZT) ceramics (60—70). It has been demonstrated that certain composite hydrophone materials are two to three orders of magnitude more sensitive than PZT ceramics while satisfying such other requirements as pressure dependency of sensitivity. The idea of composite ferroelectrics has been extended to other appHcations such as ultrasonic transducers for acoustic imaging, thermistors having both negative and positive temperature coefficients of resistance, and active sound absorbers. 

S-layer ultrafiltration membranes (SUMs) are isoporous structures with very sharp molecular exclusion limits (see Section III.B). SUMs were manufactured by depositing S-layer-carrying cell wall fragments of B. sphaericus CCM 2120 on commercial microfiltration membranes with a pore size up to 1 pm in a pressure-dependent process [73]. Mechanical and chemical resistance of these composite structures could be improved by introducing inter- and intramolecular covalent linkages between the individual S-layer subunits. The uni-... 

Measurements of filtration rates should be repeated at different pressures or different vacuum levels. This gives information on the influence of pressure on the specific cake resistance. The specific resistance of cakes that are difficult to filter is often pressure-dependent. Thus, use of excessive pressure can result in blocking of the cake, causing filtration to stop. In the case of compressible cakes, information is needed over the whole range of pressures being considered for industrial filters since extrapolation of compressibility beyond the experimentally covered region is always risky. The larger the scale of an experimental filter, the less risky predictions based on the experimental data. 

The speed with which adaptations appear, such as, for example, resistance to pesticides, depends on the pressure of selection. When using pesticides, the pressure is practically 100% and, therefore, new characteristics appear very rapidly, in just 2-3 generations. The speed with which resistance appears depends also on the population size of the target species the larger the population, the more probable that resistance will appear in some members of the first generation. The populations of target species are always large otherwise there would be no reason to try to suppress them. Therefore, in each suppressed population, there will inevitably be more resistant individuals. 

Depending on the technical requirements such as corrosion resistance, pressure and temperature stability, industrial scale azo pigment synthesis is carried out in appropriate equipment. Suitable materials include cast iron, stainless steel, steel lined with rubber, acid-proof brick, enamel, synthetic resins supported by glass fiber, and wood. 

One other type of oxygen sensor has received considerable attention as an alternative to the galvanic type of sensor. This is the resistive type of sensor which uses a metal oxide whose resistance is dependent on the oxygen partial pressure (6). While a number of different oxides have been used, titanium oxide appears to have the best combination of properties for automotive applications (y. 

Resistivity of filter cakes depends on the conditions of formation of which the pressure is the major one that has been investigated at length. The background of this topic is discussed in Section 11.3, but here the pressure dependence will be incorporated in the filtration equations. Either of two forms of pressure usually is taken,... 

Strain Gages. Essentially, they are based on electrical measurements of strains produced by the action of stress. There are several ways for measuring strains, but the most convenient is the resistance method. The apparatus used for these measurements, known as "resistance manometer , depends upon the change in resistance of a metal (such as platinum, manganin or mercury) when subjected to pressure. The change in resistance is usually measured by means of a very sensitive Wheatstone bridge, but it may also be measured by a potentiometer or by an... 

Fig. 9. (a) Scaled resistivity p(T)/p (300 K) vs. T/Tq for YbFe4Sbi2> where Tq is the scaling temperature. Inset shows the pressure dependence of Tq. (b) Scaled resistivity of CeFe4Sbi2 vs. T/Tq. Inset shows pressure dependence of Tq. The room temperature resistivity of both compounds was about 0.8 m cm at ambient pressure (E.D. Bauer et al., 2000). 

The pressure-dependent electrical resistivity of the heavy-fermion compound YbNi2B2C (see also Section 4.12) could be explained by competing contributions from crystal-electric-field splitting and Kondo effect (Oomi et al., 2006). The pressure-dependent room-temperature thermoelectric power of YNi2B2C exhibits a peak around 2 GPa, which was explained by changes in the Fermi-surface topology (Meenakshi et al., 1998). A possible correlation with a small peak in the temperature-dependent thermopower around 200 K (Fisher et al., 1995 Section 3.4.3) needs further investigation. 

Equation 1.43 shows that the magnitude of the intersegmental pressure depends on the applied voltage and the lengths, free cross-sectional areas and resistivities of the two column segments. 

Figure 5. The complex a -(EDT-TTF)[Pd(dmit)2]. Pressure-dependence of the resistivity a, ambient pressure b, 2 c, 5 d, 10 kbar) and (insert) non-ohmic behavior at ambient pressure for an injected current of 150 pA ( ) and 1.5 mA (—). [Adapted From (97).]...

The output rate of the extruder is a function of screw speed, screw geometry, and melt viscosity. The pressure developed in the extruder system is largely a function of die resistance and dependent on die geometry and melt viscosity. Extrusion pressures are lower than those encountered in injection molding. They are typically 500 to 5000 psi (3.5 to 35 MPa). In extreme cases, extrusion pressures may rise as high as 10,000 psi (69 MPa). Variants on the single screw include the barrier or melt extraction screw and the vented screw (Chapter 3). 

The following examples of phase transition investigations demonstrate the potentialities of the discussed equipment. In fig. 4 there is resistance vs pressure dependence for HgSe... 

K and room temperature [74]. Several interpretations of this anomalous pressure dependence have been proposed along with the calculations of the ambient pressure resistivity mentioned previously. The fact that (TSeT)2Cl is an exception and the disappearance of the anomalous pressure dependence of vh at high pressure seems to indicate that it is a specific property of quasi-one- and quasi-two-dimensional materials. 

The very large pressure coefficient of the susceptibility (Fig. 14a) and conductivity in the metallic regime (d In room temperature [6]) raises a serious problem for the comparison with theory, which usually computes constant-volume temperature dependences. Hence the temperature dependence at constant pressure that is observed in actual experiments must be transformed into constant-volume data since the change of volume (due to the thermal expansion) cannot be ignored between 300 and 50 K. No detailed determinations of the constant-volume resistivity have been performed so far. However, a crude estimate of the intrinsic temperature dependence can be performed using the thermal expansion and the pressure dependence of the a axis at various temperatures [59] (Fig. 14b). 

Figure 14 (a) Pressure dependence of the spin susceptibility x (T,T)-l/2 from NMR data. (From Ref. 41b.) (b) Constant-pressure and constant-volume temperature dependences of the resistivity of (TMTSF)2AsF6 derived point by point from the constant-pressure data of Fig. 12. The lattice parameters are from Ref. 33 and the pressure coefficient of the conductivity from Ref. 57.

An unusual pressure-dependent resistivity has been reported for (TMTSF)2P02F2 (47). This compound has a metal-insulator transition at 135 K at ambient pressure, which is quite high considering that the anion volume of P02F2 is very close to that of C104. Furthermore, pressure has a relatively small effect, and even at pressures of 14.5 kbar... 

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