Pressure dependence hydrostatic

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. 

Equivalent hydrostatic pressure Pressure dependence of Curie temperature Change in compressibility Change in specific heat Change in thermal expansion... 

The fluid pressure in the rock at the bottom of a well is commonly defined as pore pressure (also called formation pressure, or reservoir pressure). Depending on the maturity of the sedimentary basin, the pore pressure will reflect geologic column overburden that may include a portion of the rock particle weight (i.e., immature basins), or a simple hydrostatic column of fluid (i.e., mature basins). The pore pressure and therefore its gradient can be obtained from well log data as wells are drilled. These pore pressure data are fundamental for the solution of engineering problems in drilling, well completions, production, and reservoir engineering. 

This form assumes that the effect of pressure on the molar volume of the solvent, which accelerates reactions of order > 1 by increasing the concentrations when they are expressed on the molar scale, has been allowed for. This effect is usually small, ignored but in the most precise work. Equation (7-41) shows that In k will vary linearly with pressure. We shall refer to this graph as the pressure profile. The value of A V is easily calculated from its slope. The values of A V may be nearly zero, positive, or negative. In the first case, the reaction rate shows little if any pressure dependence in the second and third, the applied hydrostatic pressure will cause k to decrease or increase, respectively. A positive value of the volume of activation means that the molar volume of the transition state is larger than the combined molar volume of the reactant(s), and vice versa. 

The pressure dependence of the thermal variation of has proved to be a useful diagnostic probe to show that the formation of [HS-LS] spin pairs is not fortuitous but that they are the preferentially formed species in the dinuclear-type complexes [9]. It is shown next that application of external hydrostatic pressure can help to unravel features of this whole class of compounds, which usually can be revealed by variation of chemical composition. 

The influence of pressure has also been used to tune the ST properties of these ID chain compounds. Application of hydrostatic pressure ( 6 kbar) on [Fe(hyptrz)3] (4-chlorophenylsulfonate)2 H20 (hyptrz=4-(3 -hydroxypro-pyl)-l,2,4-triazole) provokes a parallel shift of the ST curves upwards to room temperature (Fig. 5) [41]. The steepness of the ST curves along with the hysteresis width remain practically constant. This lends support to the assertion that cooperative interactions are confined within the Fe(II) triazole chain. Thus a change in external pressure has an effect on the SCO behaviour comparable to a change in internal electrostatic pressure due to anion-cation interactions (e.g. changing the counter-anion). Both lead to considerable shifts in transition temperatures without significant influence on the hysteresis width. Several theoretical models have been developed to predict such SCO behaviour of ID chain compounds under pressure [50-52]. Figure 5 (bottom) also shows the pressure dependence of the LS fraction, yLS, of... 

Fig. 19 Pressure dependence of on-set of k-(ET)2Cu2(CN)3 by the uni-axial strain and hydrostatic pressure methods...

Fig. 52 Temperature dependence of H T2 at 21.3 MHz at different external hydrostatic pressures. The arrow indicates the approximate centre of the pressure-dependent line narrowing process a BPA-PC and b BPA-dio-PC (from [44])...

The behaviour of the phonons can be related to pressure induced structural modifications. Unfortunately, for the Y123 compounds, the variation of the bond lengths as a function of pressure has been studied only for low pressures, up to 0.56 GPa [23] and there are no data available for an independent verification of the predictions of local structural modifications. The structural hydrostatic pressure measurements have found a similar pressure dependence of the a- and c-axes for the underdoped and overdoped Y123, while, for the b axis, the underdoped exhibits a larger compression ( 20%) than the overdoped sample [23], The Raman data for low pressures... 

Figure 111 2 6. The hydrostatic pressure dependence of the energy for the Ag Raman modes of the Y123x compounds. The lines are 3rd order polynomial best fits to the data...

When lava is emplaced, bubbles containing equal amounts of gas at the base and top of a flow are subject to different total pressures due to difference in overburden. At the top of the flow, there is atmospheric pressure only, while at the base there is an additional hydrostatic overburden of lava. The atmospheric pressure-dependence of vesicle size can be expressed by the ratio of vesicle size modes at the top and bottom of a flow ... 

Calibration of the pressure is best accomplished using the Ruby scale. Generally this is done using a metal gasket between the two diamond windows surrounding the sample in which a liquid (such as Nujol or Teflon oil) is added to produce hydrostatic pressure. The technique measures the pressure dependence of the sharp Ruby Ri fluorescence transition at 692.8 nm, although the R2 band at 694.2 nm can also be used. The Ruby fluorescence is induced by the blue excitation of the Ar+ (488.0 nm) or the He- C d (441.6nm) lasers. 

The hydrostatic pressure dependence of the zone centre phonon modes has been determined in n-type bulk GaN [6,32] and GaN/sapphire (n = 9 x 10 16 cm 3) (TABLE 7) [33], Phonon modes and their hydrostatic pressure behaviour have been calculated in first-principles calculations [34],... 

It is necessary to bear in mind that although Eqs. (4.9) and (4.10) are rigorously fulfilled at any hydrostatically equilibrium state of the foam, the capillary pressure exerts a strong influence on the drainage and foam stability. At a certain value of the capillary pressure, depending of foam dispersity and the foam film type, the foam lifetime becomes very short and the foam breaks down instantaneously. 

To determine the activation parameters AH, A and Ay for the binding and release of NO, the kinetics was stndied at different temperatures (6-30 °C) and hydrostatic pressnres (0.1-170 MPa). The kon and kotr values determined from hnear dependences of kobs versus [NO] at each temperature and pressure allowed the construction of Eyring plots for the on and off reaction. Activation parameters can be calculated from the plots. Because of the small intercepts in the plots of kobs versus [NO] in the pressure-dependent study, the activation volume for the off reaction could not be determined accurately in this way. This value, however, could be measured in a stopped-flow experiment using the NO-trapping method. 

Fig. 35. Hydrostatic pressure dependence of the bending moment-displacement curves of a notched PP sample...

In the same way, the dilatation for a system under a time-dependent hydrostatic pressure can be written... 

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