What determines if a grain boundary acts as a crack initiation site during fatigue? The grain boundary defines a mismatch of slip systems, which strongly depends on the three-dimensional positions of ...the boundary plane. In the case of a coherent Σ3 twin boundary, the boundary plane, and thus the mismatch between the slip systems, is known for all possible combinations of active slip systems. Thus, the tendency for crack initiation can be reduced to a purely geometric calculation.
Mixed organolead halide perovskites (MOHPs), CH3NH3Pb(BrxI1−x)3, have been shown to undergo phase segregation into iodide‐rich domains under illumination, which presents a major challenge to their ...development for photovoltaic and light‐emitting devices. Recent work suggested that phase‐segregated domains are localized at crystal boundaries, driving investigations into the role of edge structure and the growth of larger crystals with reduced surface area. Herein, a method for growing large (30×30×1 μm3) monocrystalline MAPb(BrxI1−x)3 single crystals is presented. The direct visualization of the growth of nanocluster‐like I‐rich domains throughout the entire crystal revealed that grain boundaries are not required for this transformation. Narrowband fluorescence imaging and time‐resolved spectroscopy provided new insight into the nature of the phase‐segregated domains and the collective impact on the optoelectronic properties.
Iodide‐rich clusters form and grow in the MAPb(BrxI1−x)3 single crystal under continuous light illumination. A combination of widefield microscopy and confocal microscopy provides detailed insight into phase segregation in individual MAPb(BrxI1−x)3 microplatelets.
Turning Ocean Mixing Upside Down Ferrari, Raffaele; Mashayek, Ali; McDougall, Trevor J. ...
Journal of physical oceanography,
07/2016, Letnik:
46, Številka:
7
Journal Article
Recenzirano
Odprti dostop
It is generally understood that small-scale mixing, such as is caused by breaking internal waves, drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes. ...However, the observational evidence that the strong turbulent fluxes generated by small-scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom boundary than above implies that small-scale mixing converts light waters into denser ones, thus driving a net sinking of abyssal waters. Using a combination of theoretical ideas and numerical models, it is argued that abyssal waters upwell along weakly stratified boundary layers, where small-scale mixing of density decreases to zero to satisfy the no density flux condition at the ocean bottom. The abyssal ocean meridional overturning circulation is the small residual of a large net sinking of waters, driven by small-scale mixing in the stratified interior above the bottom boundary layers, and a slightly larger net upwelling, driven by the decay of small-scale mixing in the boundary layers. The crucial importance of upwelling along boundary layers in closing the abyssal overturning circulation is the main finding of this work.
Regional public affairs will become more complex when contradictions emerge between administrative boundaries and policy issues that require cross‐boundary collaboration. Breaking administrative ...boundaries has become a prerequisite for facilitating inter‐local government collaboration. This study categorizes governance boundaries into the administrative boundary and the ecology‐based policy boundary and then examines how these two governance boundaries and their interactive relationship contribute to the intergovernmental collaboration network in China's regional atmospheric governance (RAG). Using data on the atmospheric governance collaboration from 30 cities in the Yangtze River Delta region from 2013 to 2018, we employ the MR‐QAP model to find that cities within the same administrative boundary are more likely to collaborate and cities within the ecology‐based policy boundary, compared with those beyond, are more likely to collaborate but with a lagging effect. Ecology‐based policy boundary has a positive but lagging moderating effect on the contribution of the administrative boundary to the formation of intergovernmental collaboration networks.
Resumen
Los asuntos públicos regionales se volverán más complejos cuando surjan contradicciones entre los límites administrativos y las cuestiones de política que requieren una colaboración transfronteriza. Romper los límites administrativos se ha convertido en un requisito previo para facilitar la colaboración entre gobiernos locales. Este estudio clasifica los límites de gobernanza en el límite administrativo y el límite de política basado en la ecología y luego examina cómo estos dos límites de gobernanza y su relación interactiva contribuyen a la red de colaboración intergubernamental en la gobernanza atmosférica regional (RAG) de China. Usando datos sobre la colaboración de gobernanza atmosférica de 30 ciudades en la región del delta del río Yangtze de 2013 a 2018, empleamos el modelo MR‐QAP para encontrar que las ciudades dentro del mismo límite administrativo tienen más probabilidades de colaborar y las ciudades dentro de la política basada en la ecología. frontera, en comparación con los que están más allá, es más probable que colaboren, pero con un efecto retardado. La frontera política basada en la ecología tiene un efecto moderador positivo pero rezagado en la contribución de la frontera administrativa a la formación de redes de colaboración intergubernamental.
摘要
当行政边界与需要跨边界协作的政策问题之间出现矛盾时，区域公共事务将变得更加复杂。打破行政边界已成为促进地方政府间合作的前提。本研究将治理边界分为行政边界和基于生态的政策边界，随后分析了这两种治理边界及其相互作用关系如何对中国区域大气治理(RAG)中的政府间协作网络作贡献。通过使用2013年至2018年长三角地区30个城市的大气治理协作数据，我们采用多元回归二次分配程序(MR‐QAP)模型发现，同一行政边界内的城市更有可能进行协作，并且在基于生态的政策边界内的城市与边界之外的城市相比，前者更有可能合作，但存在滞后效应。基于生态的政策边界对“行政边界对政府间协作网络形成所作的贡献”具有正向但滞后的调节作用。
Developing a facile method to prepare high‐quality perovskite films without using the antisolvent technique is critical for upscaling production of perovskite solar cells (PVSCs). However, the ...as‐prepared formamidinium (FA)‐based perovskite films often exhibit poor film quality with high density of defects if antisolvent is not used, limiting the photovoltaic performance and long‐term stability of derived PVSCs. Herein, this work adopts pre‐synthesized 3D methylammonium lead chloride (MAPbCl3) and 1D 2‐aminobenzothiazole lead iodide (ABTPbI3) microcrystals into self‐drying perovskite precursors, which serve as seed crystals to promote nucleation and growth of FAPbI3‐based perovskites without requiring antisolvent extraction. The combined binary microcrystals facilitate the formation of a dense and pinhole‐free perovskite film with a stable perovskite lattice and defect‐healed grain boundaries, enabling efficient charge carrier transfer and reduced non‐radiative recombination loss. As a result, the best‐performing inverted architecture device exhibits a champion power conversion efficiency of 23.27% for small‐area devices (0.09 cm2) and 21.52% for large‐area devices (1.0 cm2). These values are among the highest efficiencies reported for antisolvent‐free PVSCs. Additionally, the unencapsulated device shows enhanced moisture, thermal, and operational stabilities, and maintains 92% of its initial efficiency after being held at the maximum power point for 1000 h.
By employing pre‐synthesized 3D methylammonium lead chloride (MAPbCl3) and 1D 2‐aminobenzothiazole lead iodide (ABTPbI3) microcrystals into a self‐drying perovskite precursor, this work successfully modifies the crystallization process without antisolvents and reduces defects at grain boundaries. Furthermore, the best‐performing inverted device exhibits a champion power conversion efficiency of 23.27% for small‐area devices (0.09 cm2) and 21.52% for large‐area devices (1.0 cm2).
Abstract
Solidification processing is essential to the manufacture of various metal products, including additive manufacturing. Solidification grain boundaries (SGBs) result from the solidification ...of the last liquid film between two abutting grains of different orientations. They can migrate, but unlike normal GB migration, SGB migration (SGBM) decouples SGBs from solidification microsegregation, further affecting material properties. Here, we first show the salient features of SGBM in magnesium-tin alloys solidified with cooling rates of 8−1690 °C/s. A theoretical model is then developed for SGBM in dilute binary alloys, focusing on the effect of solute type and content, and applied to 10 alloy systems with remarkable agreement. SGMB does not depend on cooling rate or time but relates to grain size. It tends to occur athermally. The findings of this study extend perspectives on solidification grain structure formation and control for improved performance (e.g. hot or liquation cracking during reheating, intergranular corrosion or fracture).
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•Special WC/WC grain boundaries are modeled using DFT.•The Σ=2 twist grain boundary is modeled with a Peierls–Nabarro model.•The Σ=2 twist grain boundary energy is predicted to be ...small, 0.7J/m2.•No Co segregation to the Σ=2 twist grain boundary is predicted.
In this work, we model Σ=2 and Σ=1{101¯0}‖{101¯0} WC/WC boundaries in WC–Co using density functional theory (DFT). In particular, the misfit structure of the Σ=2 twist boundary is modeled explicitly with a previously developed Peierls–Nabarro model for misfit dislocations. The grain boundary energy of the twist boundary is found to be 0.7J/m2, which is small in comparison with energies of general WC/WC boundaries. The misfit structure can be described as a square network of screw dislocations with Burgers vectors 16〈12¯13〉. Our calculations show that Co will not segregate to the Σ=2 twist boundary, which contrasts with predictions for other WC/WC boundaries that typically give half a monolayer of segregated Co.
This article is concerned with boundary stabilization of one-dimensional linear hyperbolic systems with characteristic boundaries. We assume that the systems satisfy a physically relevant structural ...stability condition for hyperbolic relaxation problems, which describe various non-equilibrium phenomena. By introducing new and simple Lyapunov functions, the structural stability condition is used to derive stabilization results for problems with characteristic boundaries. The result is illustrated with an application to the transport of neurofilaments in axons—a phenomenon studied in neuroscience.
The recently discovered Cusub.46Zrsub.33.5Hfsub.13.5Alsub.7 (at.%) bulk metallic glass (BMG) presents the highest glass-forming ability (GFA) among all known copper-based alloys, with a ...record-breaking critical casting thickness (or diameter) of 28.5 mm. At present, much remains to be explored about this new BMG that holds exceptional promise for engineering applications. Here, we report our study on the crystallization behavior of this new BMG, using isochronal and isothermal differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). With the calorimetric data, we determine the apparent activation energy of crystallization, the Avrami exponent, and the lower branch of the isothermal time–temperature–transformation (TTT) diagram. With XRD and TEM, we identify primary and secondary crystal phases utilizing samples crystallized to different degrees within the calorimeter. We also estimate the number density, nucleation rate, and growth rate of the primary crystals through TEM image analysis. Our results reveal that the crystallization in this BMG has a high activation energy of ≈360 kJ/mole and that the primary crystallization of this BMG produces a high number density (≈10sup.21 msup.−3 at 475 °C) of slowly growing (growth rate < 0.5 nm/s at 475 °C) Cusub.10(Zr,Hf)sub.7 nanocrystals dispersed in the glassy matrix, while the second crystallization event further produces a new phase, Cu(Zr,Hf)sub.2. The results help us to understand the GFA and thermal stability of this new BMG and provide important guidance for its future engineering applications, including its usage as a precursor to glass–crystal composite or bulk nanocrystalline structures.
Abstract
Crystal-inspired approach is found to be highly successful in designing extraordinarily damage-tolerant architected materials. i.e. meta-crystals, necessitating in-depth fundamental studies ...to reveal the underlying mechanisms responsible for the strengthening in meta-crystals. Such understanding will enable greater confidence to control not only strength, but also spatial local deformation. In this study, the mechanisms underlying shear band activities were investigated and discussed to provide a solid basis for predicting and controlling the local deformation behaviour in meta-crystals. The boundary strengthening in polycrystal-like meta-crystals was found to relate to the interaction between shear bands and polygrain-like boundaries. More importantly, the boundary type and coherency were found to be influential as they govern the transmission of shear bands across meta-grains boundaries. The obtained insights in this study provide crucial knowledge in developing high strength architected materials with great capacity in controlling and programming the mechanical strength and damage path.
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