Inversion,chemical complexity,and interstitial transport in spinels

Spinels with the generic chemical formula AB₂O₄ have potential applications in nuclear energy and batteries. In both cases, their functionality is related to mass transport through the crystal. Here, using long-time atomistic simulations, we examine the impact of the cation structure on interstitial transport in two spinel chemistries, inverse MgGa₂O₄ and double MgAlGaO₄. We emphasize two aspects of the transport properties: the unit mechanisms that are described by individual barriers, for which we introduce pole-figure-like plots, and the aggregate behavior of those unit mechanisms. Compared to previous work on normal spinels, we find that inversion significantly reduces the rate of interstitial transport in these structures and has an impact on the stability of defects as they move through the lattice. In particular, B cation interstitials are found to be kinetically stable only in the inverse MgGa₂O₄. These results provide new insight into relationship between structure, chemistry, and transport in spinels.     

Images of a First‐Order Spin‐Reorientation Phase Transition in a Metallic Kagome Ferromagnet

First‐order phase transitions, where one phase replaces another by virtue of a simple crossing of free energies, are best known between solids, liquids, and vapors, but they also occur in a wide range of other contexts, including even elemental magnets. The key challenges are to establish whether a phase transition is indeed first order, and then to determine how the new phase emerges because this will determine thermodynamic and electronic properties. Here it is shown that both challenges are met for the spin reorientation transition in the topological metallic ferromagnet Fe₃Sn₂. The magnetometry and variable temperature magnetic force microscopy experiments reveal that, analogous to the liquid–gas transition in the temperature–pressure plane, this transition is centered on a first‐order line terminating in a critical end point in the field‐temperature plane. The nucleation and growth associated with the transition is directly imaged, indicating that the new phase emerges at the most convoluted magnetic domain walls for the high temperature phase and then moves to self‐organize at the domain centers of the high temperature phase. The dense domain patterns and phase coexistence imply a complex inhomogenous electronic structure, which can yield anomalous contributions to the electrical conductivity.     

多尺度高阶FDTD逆时偏移在煤田地震勘探中的应用

目前煤田地震勘探的主要难点是深部复杂构造的成像。随着逆时偏移技术的发展，针对煤田地震勘探，如何在保证偏移成像精度的前提下，提高成像计算效率是急需解决的问题之一。从成像区域网格离散化的角度出发，针对高速层过采样和低速夹层采样不足问题，提出赋予研究对象多尺度网格的概念，具有较好的灵活性，能够对同一个地质模型采用疏密结合的方式成像。首先，根据速度模型设计多尺度网格模型，低速区域采用小尺度网格覆盖，高速区域采用大尺度网格覆盖;其次，采用高阶FDTD方法计算多尺度模型内各点的波场值，尤其过渡带内的点;最后，根据成像条件完成地下介质的逆时偏移成像。实验结果表明在保证模拟相同阶数精度条件下，多尺度逆时偏移方法比传统方法计算效率平均提升25.05%。     

Reduced basis method for managed pressure drilling based on a model with local nonlinearities

To circumvent restrictions of conventional drilling methods, such as slow control actions and inability to drill depleted reservoirs, a drilling method called managed pressure drilling (MPD) has been developed. In MPD, single-phase flow processes can be modeled as a feedback interconnection of a high-order linear system and a low-order nonlinear system. These nonlinearities appear locally both inside and at the boundaries of the computational domain. To obtain a fast simulation platform for real-time purposes (eg, online model-based controller implementation), model order reduction is required for MPD. However, the local nonlinearities render applying model order reduction techniques challenging. In this study, a new approach is proposed to deal with such nonlinearities within the reduced basis (RB) context and it is successfully tested on a model for MPD. Contrary to the classical RB technique, the proposed approach not only does not generate nonphysical spikes at the locations of these local nonlinearities but also yields high speedup factors. The obtained reduced-order model can be used for efficient online simulation and controller design for drilling systems with MPD.     

Hybrid make-to-stock and make-to-order systems: a taxonomic review

Production planning and control (PPC) systems that employ aspects from both make-to-order (MTO) and make-to-stock (MTS) production control are known as hybrid MTS/MTO systems. While both MTO and MTS separately have been studied extensively, their combined use has received less attention. However, the literature on this topic is growing and this paper shows that the review performed in this paper is an important addition to the field. We categorise relevant literature according to a novel taxonomy and show that hybrid MTS/MTO production control can be used in different contexts. In addition, an overview of the modelling techniques and methods used in these papers is provided. Based on the reviewed literature, relevant research questions and directions for future research are identified. Finally, it is shown that hybrid MTS/MTO production control is prevalent in practice by discussing research with industrial applications. The paper contains an overview of research on hybrid MTS/MTO production control to be used as reference for researchers active in the field, and provides managerial insights and directions for future research on this topic.     

The application of convergent beam electron diffraction (CBED) analysis on transformation‐induced plasticity (TRIP) steels

Convergent beam electron diffraction (CBED) in transmission electron microscopy (TEM) was applied to determine local carbon concentrations in low‐carbon transformation‐induced plasticity (TRIP) steels. High‐order Laue‐zone (HOLZ) lines were experimentally obtained for comparison with simulation results. A new procedure for calculating carbon content is thus proposed. Retained austenite (RA) is classified into three types by morphology; the relationship between the carbon content and the corresponding RA morphology is discussed based on CBED results. Furthermore, results of X‐Ray diffractometry measurements are also used for comparison.     

Ferroelectric and electromechanical performance of diverse engineered states of Mn-doped 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 ceramics

The materials processing history has a great influence on their properties and finally determines their application effect. In this paper, the ferroelectric, polarization-switching current, and strain properties of Mn-doped 0.75Pb(Mg_1/3Nb_2/3)O₃-0.25PbTiO₃ ceramics were studied in fresh state, aged state, and poled state, respectively. Compared with the symmetric polarization-electric-field (P-E) hysteresis loops, current-density-electric-field (J-E) curves, and bipolar electric-field-induced strain (S-E) curves in fresh state samples, asymmetric P-E loops, J-E curves, and bipolar S-E curves were obtained in poled state samples. Well-aged-state samples exhibit double hysteresis P-E loop, four peaks J-E curves, and symmetric S-E curves without negative strain. The symmetry-conforming short-range order (SC-SRO) principle of point defects and internal electric field E_i is employed to clarify the different phenomenon of three states. Results indicated that randomly oriented defect polarization P_D in aged samples can reverse the spontaneous polarization P_S back and result in the double hysteresis P-E loop and four peaks J-E curves. The oriented P_D and resulting E_i in poled-state samples will lead to the asymmetric loops and strain memory effect.     

基于秩序与非秩序理论的文创产品卡通形象设计研究

目的 从秩序与非秩序理论出发,研究文创产品卡通形象的设计方法.方法 对秩序与非秩序理论的视觉机制和创制理论进行梳理,结合实例,阐述了其与文创产品卡通形象设计之间的联系,分析文创产品卡通形象中的秩序与非秩序的表现形式,提出基于秩序与非秩序理论文创产品卡通形象设计的主要原则,归纳出一套基于秩序与非秩序理论的文创产品卡通形象设计流程与方法,指导设计实践,并验证这些理论方法在设计实践中有效性与可行性.结论 通过对秩序与非秩序理论的研究,文创产品卡通形象设计时应注意提高辨识度、亲和力和便于衍生设计的原则.探索基于秩序与非秩序理论的设计流程与方法,按照界定主题、主体形象设计、主体形象拓展、衍生品应用四个环节开展整体方案设计,为文创产品卡通形象设计提供新的思路与方法.     

Coexistence of antiferro- and ferrimagnetism in the spinel ZnFe2O4 with an inversion degree δ lower than 0.3

Samples with inversion parameter values (δ) ranging from 0.27 to 0.14 while maintaining the crystallite size value have been successfully fabricated from commercially available powders by mechanical grinding and thermal annealing treatments at temperatures ranging between 400 and 600 °C. Detailed characterization studies of these samples using X-ray, neutron diffraction and magnetic measurements have confirmed for the first time the simultaneous coexistence at 2 K of short range antiferromagnetic and ferrimagnetic ordering for a wide range of the inversion parameter. The magnetic phase diagram obtained is different from the one previously reported, which shows at 2 K the coexistence of long range antiferromagnetic order and short range order for values of inversion parameters less than 0.1 and the presence of a ferrimagnetic order only for values of δ > 0.2. At room temperature, the Rietveld analysis of NPD patterns and the magnetization curves showed a paramagnetic behavior in the samples with δ ≤ 0.1. For the samples with higher cationic inversion, typical hysteresis curves of ferrimagnetic materials were observed and the saturation magnetization values obtained agree quite well with the net magnetic moment obtained from the Rietveld refinement of the neutron diffraction patterns.