Nanomechanics of flexoelectric switching

We examine the phenomenon of flexoelectric switching of polarization in ultrathin films of barium titanate induced by a tip of an atomic force microscope (AFM). The spatial distribution of the tip-induced flexoelectricity is computationally modeled both for perpendicular mechanical load (point measurements) and for sliding load (scanning measurements), and compared with experiments. We find that (i) perpendicular load does not lead to stable ferroelectric switching in contrast to the load applied in the sliding contact load regime, due to nontrivial differences between the strain distributions in both regimes: ferroelectric switching for the perpendicular load mode is impaired by a strain gradient inversion layer immediately underneath the AFM tip; while for the sliding load regime, domain inversion is unimpaired within a greater material volume subjected to larger values of the mechanically induced electric field that includes the region behind the sliding tip; (ii) beyond a relatively small value of an applied force, increasing mechanical pressure does not increase the flexoelectric field inside the film, but results instead in a growing volume of the region subjected to such field that aids domain nucleation processes; and (iii) the flexoelectric coefficients of the films are of the order of few nC/m, which is much smaller than for bulk BaTiO3 ceramics, indicating that there is a “flexoelectric size effect” that mirrors the ferroelectric one

Nanomechanics of flexoelectric switching

We examine the phenomenon of flexoelectric switching of polarization in ultrathin films of barium titanate induced by a tip of an atomic force microscope (AFM). The spatial distribution of the tip-induced flexoelectricity is computationally modeled both for perpendicular mechanical load (point measurements) and for sliding load (scanning measurements), and compared with experiments. We find that (i) perpendicular load does not lead to stable ferroelectric switching in contrast to the load applied in the sliding contact load regime, due to nontrivial differences between the strain distributions in both regimes: ferroelectric switching for the perpendicular load mode is impaired by a strain gradient inversion layer immediately underneath the AFM tip; while for the sliding load regime, domain inversion is unimpaired within a greater material volume subjected to larger values of the mechanically induced electric field that includes the region behind the sliding tip; (ii) beyond a relatively small value of an applied force, increasing mechanical pressure does not increase the flexoelectric field inside the film, but results instead in a growing volume of the region subjected to such field that aids domain nucleation processes; and (iii) the flexoelectric coefficients of the films are of the order of few nC/m, which is much smaller than for bulk BaTiO3 ceramics, indicating that there is a “flexoelectric size effect” that mirrors the ferroelectric one

High-energy photoemission final states beyond the free-electron approximation

Three-dimensional (3D) electronic band structure is fundamental for understanding a vast diversity of physical phenomena in solid-state systems, including topological phases, interlayer interactions in van der Waals materials, dimensionality-driven phase transitions, etc. Interpretation of ARPES data in terms of 3D electron dispersions is commonly based on the free-electron approximation for the photoemission final states. Our soft-X-ray ARPES data on Ag metal reveals, however, that even at high excitation energies the final states can be a way more complex, incorporating several Bloch waves with different out-of-plane momenta. Such multiband final states manifest themselves as a complex structure and added broadening of the spectral peaks from 3D electron states. We analyse the origins of this phenomenon, and trace it to other materials such as Si and GaN. Our findings are essential for accurate determination of the 3D band structure over a wide range of materials and excitation energies in the ARPES experiment

A review on probabilistic graphical models in evolutionary computation

Thanks to their inherent properties, probabilistic graphical models are one of the prime candidates for machine learning and decision making tasks especially in uncertain domains. Their capabilities, like representation, inference and learning, if used effectively, can greatly help to build intelligent systems that are able to act accordingly in different problem domains. Evolutionary algorithms is one such discipline that has employed probabilistic graphical models to improve the search for optimal solutions in complex problems. This paper shows how probabilistic graphical models have been used in evolutionary algorithms to improve their performance in solving complex problems. Specifically, we give a survey of probabilistic model building-based evolutionary algorithms, called estimation of distribution algorithms, and compare different methods for probabilistic modeling in these algorithms

Study of anharmonic vibrational properties in 3D crystals using molecular dynamics simulations

The Ministry of Education, Youth and Sports under grant CEDAMNF CZ.02.1.01/0.0/0.0/15_003/0000358 (Czech Republic)

Mathematical modeling of a biogenous filter cake and identification of oilseed material parameters

Mathematical modeling of the filtration and extrusion process inside a linear compression chamber has gained a lot of attention during several past decades. This subject was originally related to mechanical and hydraulic properties of soils (in particular work of Terzaghi) and later was this approach adopted for the modeling of various technological processes in the chemical industry (work of Shirato). Developed mathematical models of continuum mechanics of porous materials with interstitial fluid were then applied also to the problem of an oilseed expression. In this case, various simplifications and partial linearizations are introduced in models for the reason of an analytical or numerical solubility; or it is not possible to generalize the model formulation into the fully 3D problem of an oil expression extrusion with a complex geometry such as it has a screw press extruder.We proposed a modified model for the oil seeds expression process in a linear compression chamber. The model accounts for the rheological properties of the deformable solid matrix of compressed seed, where the permeability of the porous solid is described by the Darcy's law. A methodology of the experimental work necessary for a material parameters identification is presented together with numerical simulation examples

Effect of multiple pantographs on their dynamic interaction with a catenary system

The work was supported from European Regional Development Fund-Project ”Research and Development of Intelligent Components of Advanced Technologies for the Pilsen Metropolitan Area (InteCom)” (No. CZ. 02.1.01/0.0/0.0/17 048/0007267)

Strategic Importance of the Quality of Information Technology for Improved Competitiveness of Agricultural Companies And Its Evaluation

The article discusses the issue of the use of information technology in the search for potential competitive advantages in agricultural companies. Information technology in agriculture should provide a clearly defined benefit for the management’s decision-making. If information technology is not being used to its full potential and if the results are interpreted incorrectly, the overall impact may be damaging to the position of companies in the competitive environment. Investment in information technology requires considerable sums that should return in the form of faster and better decision-making in which digitalized corporate processes play a complex role. Strategic decision-making concerning investments in information technology in various types of agricultural businesses varies depending on their size, focus, economic situation etc. In the context of the current state of agriculture in the Czech Republic and after a detailed analysis of available literature, the authors conclude that the issues of quality of information technology have not yet been systematically examined and resolved in Czech agricultural companies. For this reason, they consider it fruitful to focus their attention on this subject. The main objective of the paper is to develop and apply a methodological model for evaluating the quality of information technology in an agricultural business. In addition, we want to examine the broader impact of the criterion of IT quality from the perspective of its strategic importance for competitiveness and the extent to which it supports strategic management in practice

Kinetics of the laser-induced solid phase crystallization of amorphoussilicon: time-resolved Raman spectroscopy and computersimulations

Tato práce ukazuje, že laserem indukovaná krystalizace instrumentovaná Ramanovo spektroskopií je, z obecného pohledu, efektivním nástrojem pro studium kinematiky tepelne aktivované crystalizace. Je ukázáno, pro krystalizaci pevné fáze amorfního křemíku ve formě tenké vrstvy, že integrální intenzita Ramanovo spektra odpovídající krystalické fázi roste lineárné v časově logaritmickém měřítku. Byl vytvořen matematický model pro simulaci krystalizace v nehomogenním teplotním poli. Model je založen na řešení Ekonalovo rovnice a Arheniovo zákoně. Počítačové simulace úspěšně aproximují kinetiku krystalizace.This study demonstrates that a laser-induced crystallization instrumented with Raman spectroscopy is, in general, an effective tool to study the thermally activated crystallization kinetics. It is shown, for the solid phase crystallization of an amorphous silicon thin film, that the integral intensity of Raman spectra corresponding to the crystalline phase grows linearly in the time-logarithmic scale. A mathematical model, which assumes random nucleation and crystal growth, was designed to simulate the crystallization process in the non-uniform temperature field induced by laser. The model is based on solving the Eikonal equation and the Arhenius temperature dependence of the crystal nucleation and the growth rate. These computer simulations successfully approximate the crystallization process kinetics and suggest that laser-induced crystallization is primarily thermally activated