Local Redistribution Research Articles

Room-Temperature Ferroelectricity of Paraelectric Oxides Tailored by Nano-Engineering

Inducing clear ferroelectricity in the quantum paraelectric SrTiO3 is important for triggering methods to discover hidden phases in condensed matter physics. Several methods such as isotope substitution and freestanding membranes could introduce ferroelectricity in SrTiO3 toward nonvolatile memory applications. However, the stable transformation from quantum paraelectric SrTiO3 to ferroelectricity SrTiO3 at room temperature still remains challenging. Here, we used multiple nano-engineering in (SrTiO3)0.65/(CeO2)0.35 films to achieve an emergent room-temperature ferroelectricity. It is shown that the CeO2 nanocolumns impose large out-of-plane strains and induce Sr/O deficiency in the SrTiO3 matrix to form a clear tetragonal structure, which leads to an apparent room-temperature ferroelectric polarization up to 2.5 μC/cm2. In collaboration with density functional theory calculations, it is proposed that the compressive strains combined with elemental deficiency give rise to local redistribution of charge density and orbital order, which induce emergent tetragonality of the strained SrTiO3. Our work thus paves a pathway for architecting functional systems in perovskite oxides using a multiple nano-design.

Effect of Blade Geometry on γ' Lattice Parameter and Primary Orientation of SX Cored Turbine Blades (I).

The γ' lattice parameter aγ' and the α angle defining the primary crystal orientation of the single-crystalline cored turbine blades made of CMSX-4 superalloy were measured in the areas located near the selector situated asymmetrically, considering the top view of the blade. The distributions of the aγ' and the α angle were determined along the lines parallel to the vertical blade axis Z using X-ray diffraction methods. The relations between changes in the aγ'(Z) and α(Z) were analyzed on the Z levels where the shape of the blade's cross-section changes. For the first time, the local increase in aγ'(Z) was found near the root-airfoil connection level and near certain other root levels, which is related to the change in blade section shapes on such levels. The local extremes in α(Z), representing the dendrite bend, were observed at these levels. The increase in the aγ'(Z) with the local bending of dendrites was discussed concerning the local redistribution of alloying elements and local residual stresses of the γ-dendrites. For the first time, a method of analyzing the local bending of the dendrites was proposed by studying the behavior of the α(Z). The presented results concern the first stage of the research covering areas relatively close to the selector, considering the top view of the blades. The second stage will include the analysis of the areas of the blade localized at a longer distance from the selector.

Catfish Effect Induced by Anion Sequential Doping for Microwave Absorption

AbstractHeteroatom doping engineering is desirable in tuning crystal structures and electrical properties, which is considered an opportunity to further develop microwave absorption materials. However, the competition mechanism and priority among doped atoms have not been revealed, which are insufficient to guide the most reasonable dielectric coupling model and design high‐performance absorbers. In this work, based on in situ N and O, ex situ S is introduced through external thermal driving, leading to fierce competition among anions. Specifically, S atoms replace pyrrole N, drive out lattice O, and create O vacancies, bringing more extensive local charge redistribution and stronger electron interaction, thus activating the defect‐induced polarization (3–6 times higher than conduction loss) in the middle/high‐frequency region. Therefore, the effective absorption bandwidth (EAB) of 9.03 GHz and the minimum reflection loss (RLmin) of −64.05 dB at a filling rate of 10 wt.% are obtained, which improves the record of carbon absorbers as reported. Through macro‐designs, i.e., multi‐layer gradient metamaterial, or utilizing other advantages, e.g., cost‐effective, stable chemical properties and wide‐angle absorption, porous carbon may possess a great application prospect in the naval field.

Majority choice of taxation and redistribution in a federation

To study redistribution and taxation in a federation, we provide a model with a central government and multiple local governments, the former with power to levy an income tax for redistribution, and the latter choosing a local income tax, property tax, lump-sum tax or subsidy, and a local public good. Policy is set by majority choice at each tier of government by households that differ by income and by ability to move among local jurisdictions. We provide sufficient conditions for existence of equilibrium and examine its properties. Central findings are federal income distribution, little local redistribution, and local preference for property taxation over income taxation to fund local public goods.

Lattice distortion optimized hybridization and superlubricity of MoS2/MoSe2 heterointerfaces via Moiré patterns

The moiré superlattices (MSL) of twist two-dimensional van der Waals heterointerfaces accompanying with interfacial lattice distortion present abundant attractive physical properties, including fast interlayer charge-transfer, superconductor-insulator transition, emerging topological phase. Attributing to the optimized atomic lateral forces and elimination of interlayer lock-in by moiré superlattice, the superlubricity can be achieved and its theoretical foundations are still under extensive investigations. Here, the contributions of moiré-induced lattice distortions on the superlubricity of twist MoS2/MoSe2 heterointerfaces are comprehensively investigated by first-principles calculations. The localized electronic redistribution and the orbital hybridization by lattice distortions result in the band evolutions, reflecting the features of high symmetry points under different interfacial orientations. Moreover, the characteristic moiré potential periodically modulating the sliding energy barrier is observed in terms of a sinusoid function, which is stressed to correlate the fluctuation of interlayer charge density with variation of displacement by the fitted dominated parameter α relating to the moiré potential. Therefore, the present procedure explores the variation tendency of energy barrier with band gap and twist angle and can be treated as an essential strategy to reveal the essence of moiré and superlubricity and pave a path to accelerate the development of advanced materials with excellent tribology performance.

Synthesis of bifunctional NiFe layered double hydroxides (LDH)/Mo-doped g-C3N4 electrocatalyst for efficient methanol oxidation and seawater splitting

To boost the oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) of pristine NiFe-layered double hydroxides (LDH), the NiFe-LDH/Mo-doped graphitic carbon nitride (NiFe-LDH/MoCN) heterojunction was synthesized herein through hydrothermal method. The establishment of built-in electric field in NiFe-LDH/MoCN heterojunction enhanced the electrochemical oxidation activities towards both seawater splitting and methanol oxidation, via the improving electrocatalyst surface wettability and conductivity. Almost 10-fold enhancement of turnover frequency (TOF) and electrochemical active surface area (ECSA) than pure NiFe-LDH implied more active sites to participate in catalytic reactions via Mo doping and the formation of heterostructure. Moreover, the local charge redistribution demonstrated in the NiFe-LDH/MoCN interface region may favor the adsorption of methanol and OH− in the seawater. The present work may expound the strong coupling interaction and the establishment of built-in electric field in the interface between NiFe-LDH and semiconductor to enhance both methanol oxidation and seawater oxidation for NiFe-LDH.

Investigating the influence of freezing rate and frozen storage conditions on a model sponge cake using synchrotron X-rays micro-computed tomography

Synchrotron X-rays micro-computed tomography was applied to visualize and quantify 3D ice crystal changes into a model sponge cake after freezing and subsequent frozen storage. Model sponge cake samples were submitted to two different freezing rates (fast: 17.2 °C min−1 and slow: 0.3 °C min−1), then stored at constant and fluctuating temperatures over a two weeks period. 3D images were acquired at frozen state thanks to a thermostated cell (CellStat) and processed using a grey level based segmentation method. Image analysis revealed that the ice volume fraction is conserved during storage but ice crystal size and location change whatever the freezing rate and the storage conditions. Maximum local thicknesses increase both inside (from 20 µm to 50 µm) and outside (from 47 µm to 70 µm) the matrix during the fourteen days storage period. Both specific surface areas between starch and ice (SSAice/starch) and between air and ice (SSAair/ice) also evolve with storage duration: SSAice/starch decreases up to − 30 % while SSAair/ice increases up to + 13 % depending on the freezing rates and the storage conditions. These results highlighted that, during storage, ice crystals evolve according to two different mechanisms depending on the freezing rate: fast freezing leads to a local redistribution of water both within the starch matrix and within the pores, while slow freezing results in both local redistribution within the starch matrix and water migration towards the pores. In addition, stable storage temperatures favor local water redistribution whereas water migration from the starch matrix towards the pores was greater in the case of fluctuating storage temperatures. This study shows that freezing and frozen storage conditions have a synergistic effect on the microstructure evolution of sponge cake due to recrystallization phenomena.

Microstructural characterization of atomized U3Si2 powders with different silicon contents (7.4–7.8 wt%)

Atomization processes are used to produce uranium-based powders for the manufacturing of dispersion fuel for nuclear research reactors. Whereas this process is considered worldwide as a reference for U-Mo powder production, its use for U3Si2 is still limited.In this paper, the microstructure of as-atomized nearly stoichiometric (7.4 wt% Si) and hyper-stoichiometric (7.6 and 7.8 wt% Si) U3Si2 powders is studied in detail. A wide range of analytical techniques were applied: X-ray diffraction (XRD), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM), electron backscattered diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS) at both micrometer (SEM) and nanometer (STEM) scales. These analyzes lead to an original description of the microstructure of these as-atomized U3Si2 particles.It is shown that most of atomized particles contain only a few U3Si2 grains, some being even monocrystalline. The main secondary phase present in hyper-stoichiometric batches is an U20Si16C3-like phase. Other minor phases are also encountered, some of them containing metallic impurity elements. These features are attributed to the uranium raw material composition and to a slight contamination by carbon during the powder synthesis.The nature and morphology of secondary phases present in U3Si2 atomized particles appear thus to be linked not only to the silicon excess but also to the presence of impurities which probably strongly segregate during the very fast solidification of the alloy droplets. A slight superficial oxidation of particles also occurs and induces a local redistribution of silicon.

Linear and Nonlinear Kelvin–Helmholtz Instability and Magnetohydrodynamic Wave Emission in Sheared Astrophysical Plasma Flows

The evolution of the Kelvin–Helmholtz instability (KHI) and magnetohydrodynamic (MHD) wave emission is investigated at shear-flow boundaries of magnetized plasmas. While MHD wave emission has been suggested to be only possible during the nonlinear stages, we find that there is also significant wave emission during the KHI’s linear stages. These emitted MHD waves may have stronger impacts than KHI surface waves since they can act to transport energy away from the local region of the shear flow. The removal of energy from the shear-flow region, instead of just the local redistribution considered in previous studies, and its propagation away from the interface could have major implications for the evolution of astrophysical objects characterized by fast plasma flow shears.

Electric vehicle charging guidance based on weighted complex network

The charging station malfunction may deny the charging service for the electric vehicles at the station. As a result, the vehicles need to select other stations. How to make an optimal selection is difficult for the owners. An optimal charging guidance strategy based on a weighted complex network is proposed for the owners to select the optimal station. All the charging stations are modelled as a complex network in which the stations and the roads among them are defined as nodes and edges, respectively. Furthermore, each edge is weighted by the state of charge (SOC) of the vehicle, the charging price, and the distance and traffic conditions between these two stations. The bigger edge weight indicates the smaller probability that the owner at one node of the edge select the other node of the edge for charging, and vice versa. Based on the weighted complex network model, the local load redistribution method is presented to guide the charging of vehicles at the malfunctioning station. Consequently, the optimal scheduling of the vehicles is realized under the guidance strategy proposed in this paper. Finally, some contrast experiments are carried out to illustrate the effectiveness and the superiority of the proposed method.

An Unsaturated Bond Strategy to Regulate Active Centers of Metal-Free Covalent Organic Frameworks for Efficient Oxygen Reduction.

Unsaturated environment is the key to affect catalytic activity of the oxygen reduction reaction (ORR). Unveiling the effect of unsaturated sites toward ORR activity is of importance due to the vague unsaturated states. Reported here is a proof-of-concept strategy on the evaluation of unsaturated bonds (UBs) on adjacent carbon environment by precisely developing two metal-free vinyl-/azo-decorated covalent organic frameworks (Vinyl-COF and Azo-COF) as catalysts. The as-prepared UB-COFs exhibit good performance than the control Py-COF and comparable to the most reported carbon catalysts. Supported by theory calculations and in situ Raman spectra-electrochemistry, it is revealed that the UBs in organic catalysts can produce para-activation, identifying the para C=N groups as active centers. Importantly, the intrinsic UBs can induce local charge redistribution, and make the molecular skeleton possess high isosurface map distribution, with an efficient affinity for oxygen intermediates.

An Unsaturated Bond Strategy to Regulate Active Centers of Metal‐Free Covalent Organic Frameworks for Efficient Oxygen Reduction

AbstractUnsaturated environment is the key to affect catalytic activity of the oxygen reduction reaction (ORR). Unveiling the effect of unsaturated sites toward ORR activity is of importance due to the vague unsaturated states. Reported here is a proof‐of‐concept strategy on the evaluation of unsaturated bonds (UBs) on adjacent carbon environment by precisely developing two metal‐free vinyl‐/azo‐decorated covalent organic frameworks (Vinyl‐COFandAzo‐COF) as catalysts. The as‐prepared UB‐COFs exhibit good performance than the controlPy‐COFand comparable to the most reported carbon catalysts. Supported by theory calculations and in situ Raman spectra‐electrochemistry, it is revealed that the UBs in organic catalysts can producepara‐activation, identifying theparaC=N groups as active centers. Importantly, the intrinsic UBs can induce local charge redistribution, and make the molecular skeleton possess high isosurface map distribution, with an efficient affinity for oxygen intermediates.

(Invited) Micromechanical Aspects of GaN Hemt Performance and Reliability

Performance and reliability of microelectronic devices are governed by the mechanical strain. Typically, strain engineering implies uniformly distributed strain. However, we offer a different perspective by hypothesizing that very small but localized strain (or stress) may have significant impact on the overall behavior of AlGaN/GaN high electron mobility transistors (HEMTs). Micro to nanoscale confined mechanical stress fields may develop unavoidably and are ignored because their spatial average is insignificant. We exploit high resolution techniques such as transmission electron microscopy (TEM) and micro-Raman spectroscopy to spatially resolve the stress field in GaN HEMTs to demonstrate the stress localization and then radiation effects.To study stress localization effects on the global electrical characteristics, we introduced a highly localized strain relief by milling a 20×30 μm2 micro trench about 70 μm deep on the backside of an 800×840 μm2 size HEMT die. The resulting local relaxation of in-plane residual strain was mapped using micro-Raman technique. Our results show that a decrease of only 0.02% strain can decrease the overall output saturation current up to ~20 %. The drop of output current is attributed to reduced two-dimensional electron gas (2DEG) sheet carrier density and electron mobility due to the strain relief in the device layers. However, the mechanistic process of strain relief also causes defect generation at the interfaces, which increases leakage current. Our technique for localized strain re-distribution could be an effective tool to surrogate the influence of inherent localized strain build-up across the channel of electronic devices.To study radiation effects, we exposed the HEMTs to gamma rays (up to 10 megaRads dose at 180 kiloRads per hour). We report the thermal and mechanical responses in terms of the changes in lattice strain and temperature, which were simultaneously characterized by changes in phonon frequency of E2 (high) and A1 (LO) from on- state and unpowered/pinched off reference states. Lower doses of radiation improved the electrical properties, however degradation initiated at about 1 megaRads. We observed about 16% decrease in saturation current and 6% decrease in transconductance at the highest dose. However, leakage current increase by 3 orders of magnitude was the most notable radiation effect. We observed temperature increase by 40% and mechanical stress increase by a factor of three at dose of 10 megaRads compared to the pristine devices. Spatial mapping of mechanical stress along the channel identifies the gate region as mechanically affected area, whereas the thermal degradation was mostly uniform. Transmission electron microscopy showed contrast changes reflecting high vacancy concentration in the gate region. These findings suggest that localized stress (mechanical hotspots) may increases vulnerability to radiation damage by accommodating higher concentration of defects that promote leakage current.Finally, we present experimental results on a novel concept of electron wind force driven room temperature annealing of GaN and SiC devices. This technique was applied on Gamma irradiated HEMT and SiC diodes. We demonstrate full recovery of the HEMTs irradiated to 10 mega-Rads gamma radiation. About 200% performance improvement was recorded for the SiC diodes. Our hypothesis is that mechanical stress waves are instrumental in eliminating interfacial defects.

Well-defined metal-N4 sites coordinated defective carbon as efficient electrocatalysts for high performance lithium–sulfur batteries

The practical application of lithium–sulfur batteries has been limited by the detrimental shuttling behavior and sluggish conversion kinetics of lithium polysulfides (LiPSs), especially under high sulfur loading and lean electrolyte dosage. Although experimental and theoretical studies show that introducing defect and Fe–N4 site in carbon materials is the desirable strategy to expedite LiPSs conversion, the synergetic effect between them for sulfur redox chemistry is hardly explored. Herein, derived from a well-define Fe–N4 macrocyclic pristine iron phthalocyanine molecules (FePc) coordinated on the defective carbon nanosheets (FePc-DC), the marriage and synergetic effect between defective carbon and FePc molecules can induce remarkable Fe center electron delocalization and regulate the local electron redistribution between FePc-DC interfaces, thus brings improved LiPSs adsorption ability and conversion reaction rate. Meanwhile, the robust two-dimensional flake texture with large surface area and abundant porosity ensures robust physical confinement and fast electron/ion transfer. Attributed to such unique features, the lithium–sulfur batteries with FePc-DC cathode delivers good electrochemical performance with high areal capacity of 5.53 mAh/cm2 under high sulfur mass loading of 4.9 mg/cm2 and low electrolyte/sulfur ratio of 6.5 μL/mg, demonstrating great potential in advanced Li–S batteries.

Redistribution of carrier localization in InGaN-based light-emitting diodes for alleviating efficiency droop

We propose an efficient method for reducing efficiency droop in InGaN QWs by redistributing carrier localization via thermal annealing, which results in increased internal quantum efficiency (IQE) in this study. Entire structures of InGaN-based light-emitting diode (LED) were grown using metal-organic chemical vapor deposition. After thermal annealing, the photoluminescence (PL) intensity of the InGaN LED was gradually increased up to 900 °C, as confirmed by room-temperature macro-PL spectroscopy. The temperature-dependent PL spectra indicated that the In-rich InGaN cluster's local energy band was flattened by the thermal annealing treatment. Moreover, excitation power-dependent PL spectroscopy confirmed that redistribution of carrier localization in InGaN QWs alleviated the efficiency droop phenomenon. Furthermore, the flattened local energy band of the In-rich InGaN cluster and the increased carrier localization site implied improved IQE.

Do tidal sand waves always regenerate after dredging?

Tidal sand waves are rhythmic bedforms found on sandy continental shelves that pose a threat to offshore activities. While emphasis is placed on studying their natural morphodynamic evolution, little is known about if and how fast sand waves recover after dredging. This work presents an analysis of multibeam echosounder data collected at three former sand extraction sites on the Belgian continental shelf. At one of the sites, sand waves seemed to reappear approximately 5 years after dredging had stopped, which did not happen at the other two sites during the measurement period (5 and 9 years). The lack of recovery in those sites is likely the result of larger depths and smaller local sediment availability compared with the site where recovery occurred. Furthermore, these data reveal that in the latter site sand wave recovery was established mainly through local sediment redistribution.•Tidal sand waves are isolated from bathymetric data of the Belgian continental shelf.•At only one of the three sites, sand waves seemed to regenerate after dredging.•Possible explanations are differences in water depth and local sediment availability.•The regenerating tidal sand waves do so as a result of local redistribution of sand.

Placing U.S. Federal Housing Policy on a Secure Foundation: The SHELTER Plan

Problem, research strategy, and findings U.S. housing advocates have called for a fundamental rethinking of the nation’s federal housing policies. In this study, I examined the geographic and household-level consequences of a plan that redistributes federal income tax expenditures from homeowners to very-low-income households. I propose, defend, and illustrate the effects of the SHELTER plan, a redistributive policy that a) is revenue neutral, b) is tenure neutral, c) is progressive, d) prioritizes local redistribution, and e) targets excess revenues to affordable housing production subsidies in communities where an increase in cash-based housing assistance is most likely to inflate housing rents. I demonstrate that the savings from the elimination of four homeownership tax expenditures would provide more than enough revenue to fund a universal housing allowance for all very-low-income households. Ignoring housing market adjustments, the plan would reduce housing cost burdens for the nation’s very-low-income renters by 36% and reduce very-low-income homeowners’ cost burdens by 28%. Takeaway for practice The SHELTER plan would provide a new foundation for local affordable housing and community development practice. Very-low-income households would receive a guaranteed housing allowance with no strings attached and local planners would have new roles in the design and implementation of localized solutions to the affordable housing crisis.

Room temperature deposition of freestanding BaTiO3 films: temperature-induced irreversible structural and chemical relaxation

The room temperature aerosol deposition method is especially promising for the rapid deposition of ceramic thick films, making it interesting for functional components in energy, mobility, and telecommunications applications. Despite this, a number of challenges remain, such as an enhanced electrical conductivity and internal residual stresses in as-deposited films. In this work, a novel technique that integrates a sacrificial water-soluble buffer layer was used to fabricate freestanding ceramic thick films, which allows for direct observation of the film without influence of the substrate or prior thermal treatment. Here, the temperature-dependent chemical and structural relaxation phenomena in freestanding BaTiO3 films were directly investigated by characterizing the thermal expansion properties and temperature-dependent crystal structure as a function of oxygen partial pressure, where a clear nonlinear, hysteretic contraction was observed during heating, which is understood to be influenced by lattice defects. As such, aliovalent doping and atmosphere-dependent annealing experiments were used to demonstrate the influence of local chemical redistribution and oxygen vacancies on the thermal expansion, leading to insight into the origin of the high room temperature conductivity of as-deposited films as well as greater insight into the influence of the induced chemical, structural, and microstructural changes in room temperature deposited functional ceramic thick films.Graphical abstract

Effects of Roach Rutilus rutilus Collapse on Abundance, Distribution and Diet of Great Cormorants Phalacrocorax carbo in a Large River in North-West Europe

Aquatic habitats are subject to multifactorial changes including global warming, invasive species colonisation, modification of organic and micro-pollutant discharge and, for large rivers in Europe, drastic physical modification (e.g. channelisation, impoundments). The Meuse River in Belgium is one of these multi-stressed environments, in which recent decreases of fish populations were observed, with the loss of 90% of Roach Rutilus rutilus biomass in only a few years. In the light of this fish stock collapse, diet modification and local population evolution of a key avian predator, the Great Cormorant Phalacrocorax carbo, were examined. The diet composition and daily consumption rates of the Great Cormorants feeding in the river were largely similar to that seen before the fish population collapsed. Numbers of wintering Great Cormorants decreased by 90%, as did Roach numbers, and thus the predation pressure was adjusted to the decreased fish availability. The number of night-roosts and locations remained unchanged and no redistribution to adjacent habitats was observed at the regional scale. We suggest a bottom-up chain of responses where a fish collapse forced a reduction in Cormorant numbers, being the main piscivorous avian predator, rather than a modification of Cormorant prey composition and/or a local redistribution to adjacent wetlands (top-down). The factors that govern the establishment of a small and productive breeding population remain to be explained, but we hypothesise that the start of breeding could well have been alleviated by the large decrease in number of wintering birds.

BREAK OF A CABLE OF A CABLE ROPE

Establishing the influence of changes in time properties of rubber on the stress state of the rubber-traction body with a damaged cable. The method of research consists in the analytical solution of the model of the humorous traction body taking into account the rupture of the continuity of the cable and the change in the properties of the rubber. The dependences of the change of the stress state of the traction body of the humotross with the broken structure due to the rheology of the rubber shell are established. An algorithm for determining the stress state of a rubber traction body in case of a broken one is formulated. Structure and manifestations of rubber shell rheology. It is shown that the loads on the cables caused by the discontinuity of one of them lead to a local redistribution of forces almost only between two cables - damaged and adjacent; in case of damage non-extreme cable forces change almost only in three cables - damaged and two related to it. At the same time there are no extreme values ​​of internal efforts of loading of cables depend on the change in the shear modulus of the rubber material over time. Significant rubber shifts were detected occur between the damaged rope and adjacent to the length of the rope; shear angles the rubber between other cables is much smaller relative to the displacements in the local redistribution zone forces and stresses and change slightly due to the aging of the rubber over time. The mechanism of influence of changes of properties of rubber on pressure is established the condition of the traction body, taking into account the rupture of the continuity of the cable and changes in the properties of the rubber. Taking into account the dependence of the stress-strain state of the rope with local violations of the cable base from changes in the mechanical properties of rubber provides the ability to predict the stress state of the rope to improve safety and reliability the use of rubber traction bodies that have a significant service life. Further research should focus on the development of a method of continuous automatic control of rope damage in the rope.