Stress and electric fields

Certainly the most prominent feature of the breakdown process is its dependence on the polarity of the electric field relative to the shock-velocity vector. This effect is manifest in current pulse anomalies from minus-x orientation samples or positively oriented samples subjected to short-pulse loading (see Fig. 4.8). The individual effects of stress and electric field may be delineated with short-pulse loadings in which fields can be varied by utilizing stress pulses of various durations [72G03]. 

Tieleman, D.P., Leontiadou, H., Mark, A.E., Marrink, S.J. Simulation of pore formation in lipid bilayers by mechanical stress and electric fields. J. Am. Chem. Soc. 2003,125, 6382-3. 

Generally the linear approximation suffices, but, because the refractive index can be measured with considerable precision, the change in the impermeability tensor due to stress and electric field should be written as... 

There are two important points to remember regarding the applicability of Neumann s principle. First, forces imposed on a crystal, including mechanical stresses and electric fields, can have any arbitrary direction or orientation. These types... 

For such theory, a,p,y,d,2., and are expansion coefficients that are extracted from the experimentally measured quasistatic hysteretic response of a single-crystal. Physically, the first three terms of the right hand side of the first row of the Helmholtz free energy expressoin defines the equilibrium, stress and electric field free variants of the system. The fourth term couples an externally specified electric field to the local state of polarization of the solid. Such contribution biases the stability of those variants that are closer (or parallel) to the applied field. The fifth term... 

Electric displacement A in both Eqs. (5.16) and (5.21) is expressed as a function of the temperatnre change at the same conditions (i.e. at constant mechanical stress and electric field). It results in the following relationship between pyroelectric coefficients... 

The pyroelectric coefficient (p) of a material under constant stress and electric field is defined hy the following expression ... 

The thermodynamical derivation of piezoelectricity includes two steps (1) The relevant mechanical or electrical quantities are calculated as partial derivatives of the Gibbs free energy with respect either to one of the two mechanical or to one of the two electrical observables, respectively. (2) The second partial derivative of the Gibbs free energy with respect to the other domain (electrical or mechanical, respectively) yields one of the piezoelectric coefficients. Because there is one intensive (force-like or voltage-like) observable, namely, mechanical stress and electrical field, and one extensive (displacement-like) observable, namely, mechanical strain and electrical displacement, in each of the two domains, we have four possible combinations of one mechanical and one electrical observable in total. Thus, we obtain four different piezoelectric coefficients that are usually abbreviated as d, e, g, and h. As the sequence of the two partial derivations can be reversed, we arrive at two different expressions for each coefficient one for direct piezoelectricity (mechanical stimulus leads to an electrical response) and one for inverse or converse piezoelectricity (electrical stimulus leads to a mechanical response). For example, the piezoelectric d coefficient is given by the two alternative terms ... 

An application of hydrostatic pressure to VDF-IVPE oopolymers causes regularization of the crystal structure as in the cases of tensile stress and electric field [12,163,164]. In the regkw of relatively low pressure p, the transition temperature increases at a rale... 

Kumada et al. (1970) observed that the sideways velocity of domain walls driven by electric field increased linearily with fields applied along [001]. Walls may also be driven with shear stress in the (001) plane. Reversing either stress or field direction reverses the direction of wall movement. Flippen (1975) has found that stress and electric field effects on wall velocity are additive following the expression... 

Dynamic experiments involving the study of changes in materials in real time, as a function for example of temperature, stress or magnetic and electric fields. 

The term piezoelectric nonlinearity is used here to describe relationship between mechanical and electrical fields (charge density D vs. stress a, strain x vs. electric field E) in which the proportionality constant d, is dependent on the driving field, Figure 13.1. Thus, for the direct piezoelectric effect one may write D = d(a)a and for the converse effect x = d(E)E. Similar relationships may be defined for other piezoelectric coefficients (g, h, and e) and combination of electro-mechanical variables. The piezoelectric nonlinearity is usually accompanied by the electro-mechanical (D vs. a or x vs. E) hysteresis, as shown in Figure 13.2. By hysteresis we shall simply mean, in the first approximation, that there is a phase lag between the driving field and the response. This phase lag may be accompanied by complex nonlinear processes leading to a more general definition of the hysteresis [2],... 

Polymorphic transitions are known to be induced by an external field such as tensile stress, hydrostatic pressure or shearing stress, high electric field and others. Crystalline phase transitions under tensile stress are discussed in Chapter 6 in relation with the observed changes in microhardness. 

The forces acting on the control volume include surface forces, such as pressure forces, and shear stresses caused by velocity gradients and body forces, such as gravity. We consider only the pressure forces in the analysis that follows the effects of other forces, such as gravity and electric fields, will be discussed in more detail in a later chapter (and from a rather different viewpoint too). Actually, the system as a whole is assumed to be at constant pressure and there is, therefore, no net force acting on the mixture as a whole. 

Many researches have been conducted to clarify the mechanism of the volume change of polyelectrolyte gels. The H NMR imaging experiments have been made and provided spatial information on the change in the distribution and motion of water in the PMAA gel induced by stress [24] and electric fields [25-27]. The solvent, water, plays an important role in the deformation of the hydro-swollen PMAA gel and Yasunaga and Ando [28-... 

Optical and electrical DC properties of AlGaN/GaN HEMTs fabricated from heterostructures grown on Si (111) substrates by MOCVD were studied. The correlation between the optical properties and electrical performances of the structures was established. An increased concentration of nonradiative centers, strains and electric field in the GaN layer correspond to worse 2DEG properties. The main origin of the increased defect density is assumed to be insufficient compensation of the stress caused by the Si substrate. 

---