Path-dependent Vortex Switching in Ferroelectric Nanoplate Junctions Toward a Memory Device Concept

Ferroelectric vortex has attracted much attention as a promising candidate for memories with high density and high stability. It is a crucial problem to precisely manipulate the vortex chirality in order to utilize it to store information. Nevertheless, so far, a practical and direct strategy for vortex switching is still lacking. Moreover, the strong coupling of chirality between neighboring vortices in continuous systems like superlattices limits the application of ferroelectric-vortex-based memories. Here, we design a ferroelectric nanoplate junction to break the strong coupling between neighboring vortices. Phase-field simulation results demonstrate that the vortex chirality of the nanoplates could be efficiently tuned by sweeping local electric and thermal fields in the nanoplate junction. More importantly, the weak coupling between two neighboring nanoplates through the intermediate junction brings a deterministic vortex switching behavior. Based on this, we propose a concept of vortex memory devices. Our study provides an effective way to control the vortex chirality and suggests an opportunity for designing new memory devices based on ferroelectric vortex.

A Novel Geopolymer Foam Based On ZSM-5 Zeolite Fabricated Using Templating Emulsion/Chemical Foaming Method and Its Application in Batch and Continuous Dye Removal Systems

Geopolymers as sustainable and environmentally friendly “green materials”, can be synthesized by utilizing waste material and by-products. A porous geopolymer foam adsorbent based on ZSM-5 zeolite was prepared using templating emulsion/chemical foaming method in different conditions and used for dye removal in batch and continuous systems. The parameters affecting the dye adsorption including temperature, concentration, and pH, kinetics, isotherm, and thermodynamics of the process were investigated. The results of the geopolymer foam synthesis showed that thermal pretreatment of the zeolite has a positive effect on the strength and adsorption capacity. Moreover, the increase in sodium silicate more than the stoichiometric reduces the strength and adsorption capacity. The findings obtained from the batch adsorption process showed that the adsorption kinetics of the pseudo-second-order model and the adsorption isotherm of the Temkin model is adjusted with the experimental data. Thermodynamic results indicated that the process of dye adsorption with geopolymer foam is exothermic. The results from continuous experiments indicated more compatibility of the adsorption process with the models of Thomas and Bohart-Adams. The maximum adsorption capacity of methylene blue in batch and continuous processes was 9.82 and 8.17 mg/g. The adsorbent reduction was performed successfully by chemical and thermal processes.

IMPROVED ANALYSIS OF A PROPPED CANTILEVER UNDER LATERAL VIBRATION

Continuous systems are sometimes analysed as lumped masses connected by massless elements. This reduces the structure’s degree of freedom and therefore simplifies the analysis. However this over simplification introduces an error in the analysis and the results are therefore approximate. In this work sections of the vibrating beam were isolated and the equations of the forces causing vibration obtained using the Hamilton’s principle. These forces were applied to the nodes of an equivalent lumped mass beam and the stiffness modification needed for it to behave as a continuous beam obtained. The beam’s stiffness was modified using a set of stiffness modification factors to . It was observed that by applying these factors in the dynamic analysis of the beam using the Lagrange’s equation, we obtain the exact values of the fundamental frequency irrespective of the way the mass of the beam was lumped. From this work we observed that in order to obtain an accurate dynamic response from a lumped mass beam there is need to modify the stiffness composition of the system and no linear modification of the stiffness distribution of lumped mass beams can cause them to be dynamically equivalent to the continuous beams. This is so because the values of the modification factors obtained for each beam segment were not equal. The stiffness modification factors were obtained for elements at different sections of the beam

Continuous Stability TS Fuzzy Systems Novel Frame Controlled by a Discrete Approach and Based on SOS Methodology

Generally, the continuous and discrete TS fuzzy systems’ control is studied independently. Unlike the discrete systems, stability results for the continuous systems suffer from conservatism because it is still quite difficult to apply non-quadratic Lyapunov functions, something which is much easier for the discrete systems. In this paper and in order to obtain new results for the continuous case, we proposed to connect the continuous with the discrete cases and then check the stability of the continuous TS fuzzy systems by means of the discrete design approach. To this end, a novel frame was proposed using the sum of square approach (SOS) to check the stability of the continuous Takagi Sugeno (TS) fuzzy models based on the discrete controller. Indeed, the control of the continuous TS fuzzy models is ensured by the discrete gains obtained from the Euler discrete form and based on the non-quadratic Lyapunov function. The simulation examples applied for various models, by modifying the order of the Euler discrete fuzzy system, are presented to show the effectiveness of the proposed methodology.

Alternative Methods of the Largest Lyapunov Exponent Estimation with Applications to the Stability Analyses Based on the Dynamical Maps—Introduction to the Method

Controlling stability of dynamical systems is one of the most important challenges in science and engineering. Hence, there appears to be continuous need to study and develop numerical algorithms of control methods. One of the most frequently applied invariants characterizing systems’ stability are Lyapunov exponents (LE). When information about the stability of a system is demanded, it can be determined based on the value of the largest Lyapunov exponent (LLE). Recently, we have shown that LLE can be estimated from the vector field properties by means of the most basic mathematical operations. The present article introduces new methods of LLE estimation for continuous systems and maps. We have shown that application of our approaches will introduce significant improvement of the efficiency. We have also proved that our approach is simpler and more efficient than commonly applied algorithms. Moreover, as our approach works in the case of dynamical maps, it also enables an easy application of this method in noncontinuous systems. We show comparisons of efficiencies of algorithms based our approach. In the last paragraph, we discuss a possibility of the estimation of LLE from maps and for noncontinuous systems and present results of our initial investigations.