Intermolecular hydrogen bonds impede long-range (anti-)ferroelectric order of water. We confine H
O molecules in nanosized cages formed by ions of a dielectric crystal. Arranging them in channels at ...a distance of ~5 Å with an interchannel separation of ~10 Å prevents the formation of hydrogen networks while electric dipole-dipole interactions remain effective. Here, we present measurements of the temperature-dependent dielectric permittivity, pyrocurrent, electric polarization and specific heat that indicate an order-disorder ferroelectric phase transition at T
≈ 3 K in the water dipolar lattice. Ab initio molecular dynamics and classical Monte Carlo simulations reveal that at low temperatures the water molecules form ferroelectric domains in the ab-plane that order antiferroelectrically along the channel direction. This way we achieve the long-standing goal of arranging water molecules in polar order. This is not only of high relevance in various natural systems but might open an avenue towards future applications in biocompatible nanoelectronics.
Collaborative learning is a promising avenue in education research. Learning from others and with others can foster deeper learning at a multiple-choice assignment, but it is hard to control the ...level of students' pure guessing. This paper addresses the problem of promoting collaborative learning through regulation of guessing when students use clickers to answer multiple-choice questions of various levels of difficulty. The study is aimed at identifying how the difficulty of the task and students' levels of knowledge influence on the degree of partial guessing. To answer this research question, we developed two research models and validated them by testing 84 students with regard to the students' level of knowledge and the penalty announcement. The findings of this research reveal that: a) the announcement of penalty has a negative effect on promoting collaborative learning even if it leads to reducing pure guesses in test results; b) questions that require higher-order thinking skills promote collaborative learning to a greater extent; c) creating mixed level groups of students seems advisable to enhance learning from collaboration and, thus, to decrease the degree of pure guessing.
•The announcement of penalty for guessing has a negative effect on promoting collaborative learning.•Questions that require higher-order thinking skills promote collaborative learning to a greater extent.•Creating mixed level groups of students seems advisable to enhance collaborative learning and to decrease pure guessing.
Water is characterized by large molecular electric dipole moments and strong interactions between molecules; however, hydrogen bonds screen the dipole-dipole coupling and suppress the ferroelectric ...order. The situation changes drastically when water is confined: in this case ordering of the molecular dipoles has been predicted, but never unambiguously detected experimentally. In the present study we place separate H
O molecules in the structural channels of a beryl single crystal so that they are located far enough to prevent hydrogen bonding, but close enough to keep the dipole-dipole interaction, resulting in incipient ferroelectricity in the water molecular subsystem. We observe a ferroelectric soft mode that causes Curie-Weiss behaviour of the static permittivity, which saturates below 10 K due to quantum fluctuations. The ferroelectricity of water molecules may play a key role in the functioning of biological systems and find applications in fuel and memory cells, light emitters and other nanoscale electronic devices.
Previous research indicates that solution to pole optimization problem for the generalized Laguerre functions can be found by vanishing at least one of two clearly stated Laguerre coefficients. The ...aim of this paper is to prove uniqueness of a certain coefficient leading to the optimal solution. To achieve this purpose, we employed connection coefficients method to work out specific recurrence relations suitable for the continuous generalized Laguerre functions in the case of the optimal pole position. The proposed results were extended to the discrete Laguerre functions using modified bilinear transform and introducing the rational z-transform of the Meixner-like functions. The findings of this research present a postulated and proved theorem and conducted computational experiments to support the theoretical results.
•We proved uniqueness of a certain Laguerre coefficient leading to the optimal pole position.•We provided the solid evidence based on connection coefficients method for the continuous Laguerre functions.•We extended the proposed results to the discrete Laguerre functions using modified bilinear transform.
•Programmed trajectory motion control (PTMC) performs secondary generation control.•PTMC achieves the target state faster, compared to conventional methods.•PTMC is well suited for synchronization of ...islands with the mains udder disturbances.
The paper presents the concept of adaptive control in electrical power systems, based on programmed trajectory motion of synchronous generators. The feasibility of the method is tested in a range of simulation experiments. The key feature of the technique is the use of a simple reference model which defines the dynamics of the controlled parameters.
As a result, the voltage vector angle, velocity and acceleration are delivered to the exact, rather than approximate, target values in a predictable, coordinated, robust and efficient manner.
Compared to other adaptive methods, such as model predictive control, the technique makes a more efficient use of computational resources, which makes it particularly beneficial if implemented at lower levels of control system hierarchy. It also shows a promising level of robustness against disturbances during the control process.
We envisage that the most relevant practical applications are the stabilization and synchronization of small to medium size synchronous machines connected to distribution grid, and management (corrective control and resynchronization) of islanded sub-systems, such as microgrids.
Simulations also indicate relatively short control time and improved stability against perturbations. With a proper choice of reference model, the need for bi-polar control action does not arise and the target values are achieved by uni-polar action only.
Both the stabilization and the synchronization tasks are accomplished by means of one control algorithm, which improves the quality of control, especially in post-emergency operating conditions. The time-domain modeling results reported in the paper were obtained from software-based simulators.
The origin of complex irregular dynamics in a cardiovascular system is still being actively debated. Some hypotheses suggest the crucial role of stochastic modulation of cardiovascular parameters, ...while others argue for the importance of cardiac pacemakers' chaotic deterministic dynamics. In the present study, we estimate the largest Lyapunov exponent and the correlation dimension for the 4-h experimental interbeat intervals and the chaotic signals generated by the mathematical model of the cardiovascular system. We study the complexity of the mathematical model for such cases as the autonomic blockade, the exclusion of all the stochastic components, and the absence of variability of respiration. The obtained results suggest that the complexity of the heart rate variability is largely due to the chaotic dynamics in the loops of autonomic control of circulation.
This paper is motivated by previous research that demonstrates the importance of the explicit solution to the pole position problem. The main purpose of this paper is to solve the two-parameter pole ...position problem for the Meixner filters with an extra parameter. To attain the objective, we extended the theoretical results provided for the discrete Laguerre filters and proposed the approach to optimizing the extra parameter using the connection coefficients method. The present research yields a series of computational experiments to test this approach, to verify the theoretical results, and to point up the positive outcomes of using the Meixner filters.
•We solved the two-parameter pole position problem for the Meixner filters with an extra parameter.•We extended the theorem provided for the discrete Laguerre filters to the Meixner filters.•We proposed an approach to optimizing the extra parameter using connection coefficients method.
Quantum-chemical modeling of structure and cation migration barriers in Nafion-like ammonium substituted ionomers plasticized with dimethyl sulfoxide (DMSO) was investigated by ab initio ...calculations. We use B3LYP/6-31G* hybrid density functional methods and the PBE/PAW method taking into account the gradient corrections and periodic boundary conditions. It is shown that at a low content of DMSO (n ≤ 4), NH4+ cation removal from the SO3−-group occurs with a significant energy cost (>0.4 eV). As the amount of DMSO increases, both the separation energy and the barriers to ammonium ion migration decrease to 0.1–0.2 eV. Ab initio molecular dynamics modeling demonstrated that at a moderate temperature (~350 K), there is a rapid (~15 ps) redistribution of the DMSO molecules between the Nafion chains located at distances ≤2 nm.
•Ab initio calculations of Nafion-NH4/nDMSO like electrolytes were performed.•Ammonium ion migration on the n has been investigated.•Strong ion-ion interactions determine a poor transport properties at n < 6.•Formation of the ion-conducting channels was observed.•DMSO redistribution between the Nafion chains lain at a distance ≤2 nm was shown.
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