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Modern studies which dealt with the frequency domain analysis showed that a frequency-domain approach has an essential advantage and mentioned an inner qualitative relationship between the subsurface structure and its frequency spectra. This paper deals with the acoustic spectral response of sand and sandstone sediments at the sea bottom. An acoustic data collection campaign was conducted over two sand sites and two sandstone sites. The analysis of the results shows that reflections of acoustic signals from sand and sandstone sea bottom are characterized by various spectral features in the 2.75–6.75 kHz range. The differences in acoustic response of sand and sandstone can be quantified by examining the maximal normalized reflected power, the mean frequency, and the number of crossings at different power levels. The statistical value distribution of these potential classifiers was calculated and analyzed. These classifiers, and especially the roughness of the spectrum quantified by the number of crossings parameter can give information to assess the probability for sand or sandstone based on the reflected spectra and be used for actual distinction between sand and sandstone in sub bottom profiler data collection campaigns.

Tel Aviv was established in 1909 by a Jewish group from Jaffa who gathered to form the ‘Ahuzat Bayit’ (literally ‘Homestead’) society. The society’s goal was to form a ‘Hebrew urban centre’, inspired by Western cities, outside Jaffa’s walls. ‘Tel Aviv’ is the Hebrew title of Theodor Herzl’s Altneuland (‘Old New Land’) translated from the German. The name was chosen in 1910 from several suggestions: it was thought fitting as it embraced the idea of a renaissance in the ancient Jewish homeland. ‘Tel’ is a man-made mountain accumulating layers of civilization built one over the other and symbolizing the ancient; and ‘Aviv’ is Hebrew for ‘spring’, symbolizing renewal. Thus in its name Tel Aviv evokes the renaissance of the Jewish people in their historical homeland. It is the first Hebrew city in the new age.

The influence of the electrical body forces and electrical tractions on the nonlinear response of ferroelectric stack actuators is analytically investigated. While the role of the electrical body forces and tractions in the response of piezoelectric actuators is well documented (and in many cases is not significant), the questions of their effect on ferroelectric active materials is still of interest. To examine this influence, the analytical model for the electro-mechanical behavior of a ferroelectric stack actuator is augmented to account for the electrical body forces along the actuator and the electrical tractions at the material–electrode interfaces. Focusing on the effect of the electrical forces and tractions on the ferroelectric domain switching phenomenon, the model is used for the numerical analysis of a ferroelectric layer and for the comparison with the case that neglects the electrical body forces and traction. The comparison theoretically designates cases in which the effect of the electrical body forces and tractions may be prominent and other cases where the classical approach that neglects these effects can be adopted.

Motivated by the uniqueness and potential of the nonlinear range of piezoelectric and ferroelectric smart materials and structures, a static physically nonlinear ferro-electro-elastic beam theory which takes the effect of domain switching into account is developed. The kinematic assumptions adopt the geometrically linear Bernoulli–Euler form for the mechanical components and a first-order theory for the electrical potential, and lay the basis for further augmentation to higher order theories. The beam theory includes the field equations that correspond to the static case, the boundary conditions and the constitutive equations of ferro-electro-elasticity. The general 3-D constitutive equations are reduced to comply with the beam theory and formulated as ordinary differential equations by means of a set of generalized electro-mechanical stiffnesses. A micromechanical constitutive model that accounts for the loading history and for the domain switching phenomenon is adopted and an iterative solution procedure that incorporates the micromechanical approach is suggested. A numerical example that demonstrates the impact of the domain switching on the nonlinear electromechanical static response of a ferro-electro-elastic beam is presented and discussed. The quantitative assessment of this behavior takes a step towards new structural applications that cope with or even take advantage of the nonlinear ferro-electro-elastic range.

A conceptual design and an operational algorithm for an advanced piezoelectric–ferroelectric stack actuator are developed. The actuator takes advantage of the large strains due to the domain-switching phenomenon and utilizes the nonlinear range of response of the ferroelectric material. As a result, the proposed conceptual design allows for deformations that are considerably larger than the ones obtained using conventional piezoelectric actuators and contributes to overcoming the travel range and performance limitations of standard actuators. The shape control algorithm is based on a discrete optimization of the domain state of the active layers and it allows the operation and the shape control of the advanced actuator in spite of the nonlinear and hysteretic material response. The conceptual design of the advanced actuator and the capabilities of the shape control algorithm are demonstrated through numerical examples. The results demonstrate the contribution of the approach to extending the operational range of the actuator through a continuous and controllable response. A summary, conclusions, and directions of future research towards realization of the concept close the paper.

The ability to enhance and to improve the efficiency of piezoelectric actuators through extending their operational range into the non-linear regime is analytically investigated. Motivated by the limited strain actuation capabilities of the existing piezoelectric actuators, it is proposed to take advantage of the non-linear ferroelectric regime, which involves large remanent strains. In order to examine this hypothesis, an analytical model for the one-dimensional electro mechanical behavior of a ferroelectric structure operated in the non-linear range is developed. The model is applicable to rod actuators, to an active layer in a stack actuator, or to an active fiber in a Micro-Fiber-Composite actuator. The governing equations and the boundary conditions, the non-linear, hysteretic, and history-dependent constitutive relations, and the solution procedure are developed and discussed. Illustrative examples that examine an active layer operating against a dead load, against a linear spring, and against a uniformly distributed load are presented and discussed. The non-linear response is also compared with the response to electrical loads in the linear range and with the prediction of the linear piezoelectric theory. Emphasis is placed on the potential advantages that can be achieved through the operation in the non-linear range.

The variational principle of virtual work, the governing equations, and the boundary conditions for nonlinear ferroelectric structures are developed. The variational principle takes into account the presence of electrical body forces and body moment as well as the physical nonlinearity that results from the dissipative domain switching effect. The switching phenomenon also involves large strains. Hence, the geometrical nonlinearity is also taken into account and the electro-mechanical principle of virtual work is formulated in an Eulerian and Lagrangian type of description. The variational principle is used for the derivation of the generalized equilibrium equations (field equations) and the generalized boundary conditions. The governing equations for the ferroelectric structure are derived taking into account the nonlinear constitutive equations, the large deformations, and the spatial variation of the material tensors associated with the domain switching phenomenon.

Mycorrhizal colonization and growth dependency were studied at a single rate of phosphorous application in wild and cultivated primitive and modern wheats, inoculated with Glomus intraradices Schenck & Smith. Mycorrhizal colonization found in Triticum timopheevii var. araraticum (AAGG) was higher than that found in the other tetraploid wheats (AABB). Mycorrhizal dependency was higher in representatives of the D genome donor — Aegilops squarrosa, compared with representatives of the A and possible B genome donors T. monococcum and Ae. sharonensis, Ae. longissima and Ae. speltoides, respectively. The nature of response to VAM in hexaploid wheat was controlled by factors of the A and B genomes which are epistatic over those located in the D genome. The high mycorrhizal colonization and dependency which was found in T. timopheevii var. araraticum may indicate special genomic affinity possessed by the G genome of wheat in VAM interaction. Based on the 27 wheat lines and species tested in this study only low correlation between G. intraradices colonization and its contribution to plant growth can be suggested.

Macro Fiber Composite (MFC) actuators, which are commonly integrated in modern smart structures, may be subjected to high levels of mechanical loads. Opposed to the electrical actuation, these loads are not always controlled or anticipated by the user. Thus, they may yield a response that is beyond the linear range due to a stress induced ferro-elastic domain switching. In this paper, the phenomenon of domain switching and mechanical depolarization in the MFC actuator and the resulting degradation of the actuation capabilities are investigated. As an illustrative numerical example, the response of MFC layers in an active beam element is analyzed. Emphasis is placed on the location of the fiber segment along the active beam with a distinction between the compressed and the tensed layers. The results highlight the range of effects associated with the potential nonlinear response of the active structure under high levels of mechanical load.Copyright © 2008 by ASME