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A discrete element method (DEM) based approach is used to study the relationships between material attributes (MAs), processing parameters (PPs), and quality attributes (QAs) for the knife milling of maize stalks. An approximate DEM shape model was conceptualized based on real maize stalks and calibrated based on experimental bending test data for flexural properties (elastic bending stiffness, elastic bending angle limit, elastoplastic ratio, etc.). DEM simulations of maize stalk comminution in a Jordan Reduction Solutions ("JRS") knife mill were performed to investigate the relationships between the MAs (maize stalk size and breakage stress limit), PPs (impeller rotational speed), and QAs (mass throughput and output particle size distribution (PSD)). The DEM results suggest that stalk length has little influence on mass throughput and PSD, whilst stalks with larger cross sections tend to generate larger sizes of milled particles given the same breakage stress limit. Both the DEM and experimental results show that faster impeller rotation (or higher power) does not necessarily generate higher throughput or smaller output PSD, especially for maize stalks of higher breakage stress limit. The correlations between these MAs, PPs and QAs are found highly stochastic, though breakage stress limit dictates mass throughput, regardless of stalk size. The DEM-predicted output particle size tended to match the experimental data with coarse PSDs based on sieve size but showed weakened fidelity with finer material, indicating the potential for further model improvement. [Display omitted] • Novel DEM model is introduced for simulation of knife milling of maize stalks. • Stalk shell breakage stress limit dictates mass throughput, regardless of stalk size. • Milled particle size is influenced by stalk cross-section area but not stalk length. • Faster impeller rotation may not produce higher throughput or smaller particle size. • DEM predictions match experiments on higher end of milled particle size distribution. [ABSTRACT FROM AUTHOR]

An extended population balance model (PBM) and a deep learning-based enhanced deep neural operator (DNO+) model are introduced for predicting particle size distribution (PSD) of comminuted biomass through a large knife mill. Experimental tests using corn stalks with varied moisture contents, mill blade speeds, and discharge screen sizes are conducted to support model development. A novel mechanism in the extended PBM allows for including additional input parameters such as moisture content, which is not possible in the original PBM. The DNO+ model can include influencing factors of different data types such as moisture content and discharge screen size, which significantly extends the engineering applicability of the standard DNO model that only admits feed PSD and outcome PSD. Test results show that both models are remarkably accurate in the calibration or training parameter space and can be used as surrogate models to provide effective guidance for biomass preprocessing design. [Display omitted] • An extended population balance model (PBM) is developed for biomass comminution. • Biomass feed moisture is added in the PBM as a new input parameter. • An enhanced deep neutral operator (DNO+) model is developed for biomass comminution. • DNO+ allows for influencing factors such as moisture and screen size as extra inputs. • Both models are remarkably accurate in the calibration or training parameter space. [ABSTRACT FROM AUTHOR]

An experiment-informed discrete particle simulation study was performed to investigate the role of flexural particles in the shear flow of milled pine residues. Physical pine anatomical fraction samples were tested in an FT4 powder rheometer. A chip model for bark/stem chips and a fiber model for needles were proposed for DEM. The FT4 simulations show mixed fibers/chips require higher force and torque to drive shear flow than pure chips or fibers. The mass fraction and flexibility of fibers reveal nonlinear inter-dependency on impacting the shear flow of mixed fibers/chips. Polydisperse fibers well match the needle-rich samples on the flow attributes, while polydisperse mixed fibers/chips agree reasonably with the bark/stem-rich samples. The DEM study indicates that the flowability of pine residue biomass is determined collectively by various material attributes of the anatomical fractions, which must be considered when developing preprocessing methods for conversion-ready biomass with adequate material handling performance. [Display omitted] • Conducted dynamic shear flow test for pine anatomical fractions in an FT4 rheometer. • Developed DEM particle shape model strategy for mixed pine needles and woody chips. • Mixture of needles and chips are less flowable than pure needles and chips. • A specific set of needle mass fraction and flexibility exists for worst flowability. • Biomass flowability is governed by coupled effects of various material attributes. [ABSTRACT FROM AUTHOR]

With the purpose of quantifying and understanding the elastoplastic flexural behaviour of corn stalks, this work presents a novel three-point cyclic bending test for characterizing the biomechanical properties of controlled corn stalks. The tests have resulted the first-of-its-kind biomechanical database of corn stalks subjected in repeated bending. Moreover, an experiment-informed bending stiffness model is introduced to calculate the elastic bending angle limits, elastoplastic bending angle limits, elastic bending stiffnesses (or effective bending stiffness), and plastic ratios as well as their variabilities in the tested samples, revealing unique insights into the corn stalk flexural properties. The overall elastic bending limit decreased (from 3.4 to 1.7°) with increasing stalk size, whilst the effective bending stiffness increased (from 7.0 to 43 N m rad−1 in median value). The elastoplastic behaviour of the stalks is more consistent and independent of stalk size where in median value the elastoplastic bending limit ranged from 6.9 to 8.8° and the ratio of elastoplastic stiffness to elastic stiffness ranged from 0.40 to 0.42. Furthermore, statistical analysis of the samples and empirical results have presented insightful expressions to relate the stalk scales to responses, or distributions in properties for a population of corn stalks. The database and statistical analysis and regression expression from this work also allow for parameterizing existing numerical models for simulations of corn stalks and development of more sophisticated deformation models. • First-of-its-kind biomechanical database of corn stalks in repeated bending. • Corn stalk bending strength is dominated by the properties of the shell. • The corn stalk bending stiffness increases with increasing stalk diameter. • Experiment-informed bending properties ready for supplying discrete element modeling. [ABSTRACT FROM AUTHOR]

The properties of lignocellulosic biomass, such as bulk physical, thermal, and mechanical properties, as well as the mobility of enzymes or catalysts, are largely affected by porosity, pore structures, and pore size distribution. While X-ray computed tomography (CT) has been introduced to effectively produce 3D volumetric images of material microstructure, a quantitative porosity analysis from the 3D images has never been done. This work introduces a first-of-its-kind X-ray CT-based quantitative porosity analysis method and applies the developed toolkit to characterize the internal porosity distribution of loblolly pine. A sample loblolly pine chip was scanned by a nano-resolution X-ray CT system and digitally reconstructed after a sequence of image processing operations. A comprehensive porosity analysis was then performed to quantify the envelope porosity, the spatial distribution of local porosity, and the directional porosity. Solutions to the various challenges in image processing, porosity calculation, and large data handling are provided. [Display omitted] • X-ray computed tomography-based quantitative porosity analysis method is developed. • 3D X-ray CT images of loblolly pine obtained and used for digital reconstruction. • Envelop porosity, local porosity, and directional porosity are defined and quantified. • Local and direction porosity reveals the spatial distribution and heterogeneity. • The method can quantify the heterogeneous porosity distributions at the microscale. [ABSTRACT FROM AUTHOR]

The design of handling equipment for granular biomass primarily requires experiments. Discrete element models (DEM) can provide designers with detailed insight into the behaviour of granular materials. However, granular biomass comprising complex-shaped particles is difficult to model with DEM. A tomography-informed DEM approach and an exhaustive assessment of the ability of the approach to predict the bulk behaviour of milled pines using experimental data is presented. Nano-CT scan was conducted to obtain 3D particle surface geometries as the basis for particle shape approximation by a polyhedral model and a sphero-polyhedral model. These models were applied in the simulation of a compressibility test. Our parametric study showed that particle Young's modulus and restitution coefficient are the two main properties influencing the simulated bulk behaviour of the DEM particles and that the level of approximating DEM particle shape for real particles is critical for accurately replicating the bulk behaviour of milled pines. The polyhedral model demonstrated better suitability than its sphero-polyhedral counterpart for modelling pine particles. The polyhedral model calibrated in a compressibility test was then applied in the simulations of a friction test without additional parameter tuning. Interlocking was dominant in the shear of bulk pine particles. Remarkably, the polyhedral model predicted the frictional behaviour of the pine particles when compared to the experimental results. The limitations of the model, as well as possible ways for enhancement, are discussed. This work provided novel insights into the suitability of complex-shaped DEM models for granular woody biomass. [ABSTRACT FROM AUTHOR]

The many-body dissipative particle dynamics (mDPD) is a prominent mesoscopic multiphase model for fluid transport in mesoconfinement. However, it has been a long-standing challenge for mDPD (and other multiphase-enabled DPD models) to accurately predict real-fluid static and dynamic properties simultaneously. We have developed a modified mDPD model to overcome the issue and a rigorous calibration approach that uses reference data, including experimental and/or molecular dynamics (MD) simulations to parameterise the modified mDPD for real fluids. We choose heptane as a representative example of hydrocarbon in source rocks to demonstrate the model's capability to accurately predict the equation of state (EOS), free surface tension, diffusivity, and viscosity. Our timing test shows that the modified mDPD is 400–500 times faster than its MD counterpart for simulating bulk heptane in equivalent volumes. To further demonstrate the robustness of the model, we revisited the benchmark problem of mesoscopic modelling of water, in which all the previous works on DPD reported only a limited portion of the water properties. We show that the modified mDPD can provide accurate modelling of water static and dynamic properties and an EOS that matches the experimental data to a large range of confinement pressure. [ABSTRACT FROM AUTHOR]

Physical experiments and discrete element model (DEM) simulations are conducted to evaluate particle characteristics and operation parameter effects on screw feeding performance for rotary shear-milled Douglas fir. Three performance metrics are used: mass flow rate, shaft driving torque, and specific energy consumption. The impact of particle size, particle size distribution (PSD), shaft rotational speed (rpm), and hopper dimensions on the performance are investigated. All employed performance metrics reveal the superior flowability of the 2-mm particles in contrast to the larger 6-mm counterpart. Remarkably, wider PSD results in poorer flowability than the two mono-sized particles, proving the flowability enhancement achieved by narrower PSD of the woody feedstock. More importantly, DEM simulations unveil PSD-induced degradation in flowability is attributed to mechanical interlocking and particle segregation effects. Furthermore, higher shaft rpm causes higher mass flow rate at the cost of higher specific energy consumption due to viscous dissipation and changes in flow pattern. [Display omitted] • Impact of woody biomass attributes on screw feeding performance is evaluated. • Experiment and simulation reveal superior flowability of the smaller particle size. • Narrower particle size distribution enhances granular flowability of dry particles. • Higher shaft speed leads to higher mass flow rate and specific energy consumption. • Key mechanisms: mechanical interlocking, particle segregation, and viscous losses. [ABSTRACT FROM AUTHOR]

[Display omitted] • A bonded-sphere DEM model developed for irregular-shaped deformable particle flow. • Comprehensive analysis of hopper flows performed for rigid and deformable particles. • Increase in particle stiffness increases packing porosity and decreases flow rate. • Simulation results matched Walker's solution and extended Beverloo formula. Many natural and engineered granular materials have relatively deformable particles. Besides particle size and shape, particle deformability is another salient factor that significantly impacts the material's flow behavior. In this work, the flow of irregular-shaped deformable particles in a wedge-shaped hopper is investigated using discrete element simulations. A bonded-sphere model is developed to simultaneously capture irregular particle shapes and particle-wise deformations (e.g., compression, deflection, and distortion). Quantitative analysis of the effects of irregular shapes and particle deformations shows that the increase in particle stiffness tends to increase initial packing porosity and decrease the flow rate in the hopper. Rigid particles tend to have clogging issues, whereas deformable particles have less chance to, indicating particle deformation reduces the critical bridging width in the hopper flow. Detailed analysis of stress fields is also conducted to provide insights into the mechanism of particle flow and clogging. Stresses and discharge rates calculated from numerical simulations are compared and show good agreement with Walker's theory and the extended Beverloo formula. Simulations with various particle shape combinations are also performed and show that the initial packing porosity decreases with an increasing percentage of fibers while the discharge rate has a complex dependency on particle shapes. [ABSTRACT FROM AUTHOR]

Abstract The design of efficient lignocellulosic biomass feedstock systems is challenging, as current laboratory characterization and design methods were developed primarily for fine powders with relatively low compressibility. The discrete element method (DEM) is gaining prominence as an alternative method for modeling the bulk flow and transport of particulate materials in hoppers and feeders. However, prior DEM simulations investigating the flow of wood chips modeled the particles as simple rigid geometries such as spheres, rods or blocks, and neglected the effects of particle deformability and irregular shapes. As a consequence, those simplified DEM models may not provide enough key diagnosis to help improve the design of biomass feeding and handling equipment. This work presents a bonded-sphere DEM approach for characterizing the mechanical behavior of bulk flexible, deformable pinewood chips in a cyclic stress loading test. Clustered spheres that can bend and twist via elastic bonds are used to model irregular-shape particles in real pinewood chip samples. An axial compression tester, which contains 0.06 million bonded-sphere particles (1.35 million spheres) in a quarter cylinder, is simulated with a domain size similar to the experiments. With careful calibration, the simulations have delivered the bulk densities and the bulk moduli of elasticity that are in good agreement with those measured in the corresponding experiments. However, it is also been found challenging for the present DEM model to accurately predict the overall stress-strain behavior of bulk pinewood chips, especially the large sustained plastic deformation during unloading. Additional numerical tests have shown that the adjustment in certain contact parameters (e.g. bond stiffness) can lead to profound solution improvement, but meanwhile will induce extra challenges such as increased computing time. Future work will include an elasto-plastic particle bond model to enhance the simulation fidelity. Graphical abstract Unlabelled Image Highlights • A bonded-sphere DEM model is used to for deformable, irregular-shape wood chips. • Particle deformability and shape irregularity of wood chips are both considered. • A particle conceptualization is devised to approximate real pinewood chip shapes. • Simulation results agree reasonably well with physical experiments in cyclic loading tests. [ABSTRACT FROM AUTHOR]

Band alignments of La2Hf2O7 (LHO) films grown on fully depleted SiGe on insulator (FD SGOI) substrates have been investigated by x-ray photoelectron technique. The valence and conduction band offsets for LHO/FD SGOI systems are determined to be 3.25 and 1.49 eV, respectively. Such asymmetric band alignment can be modulated to be quite symmetric by the surface nitridation of FD SGOI using NH3 treatment. The impact of NH3-treatment temperature on band offsets is also investigated. [ABSTRACT FROM AUTHOR]

Milled pine exhibits variabilities in flow properties due to complex particle characteristics, making it challenging to ensure continuous feeding and transport in biorefineries. This work presents discrete element method (DEM) simulations of wedge-shaped hopper discharge of milled pine based on an experiment-informed DEM contact model capable of capturing the non-linearly hysteretic strain-hardening behavior of milled pine. Parametric studies of hopper discharge over varying hopper processing parameters and pine material attributes are conducted. The mass flow rate and critical arching distance predicted by DEM agree reasonably with the experiment and finite element results in the literature. Two processing parameters (opening width and semi-inclination angle) and two material attributes (rolling friction and moisture-induced cohesion) are shown to critically influence the hopper discharge dynamics. Moreover, DEM results show that the hopper with a larger inclination angle or milled pine with higher moisture content or rolling friction exhibit a higher critical arching distance. [Display omitted] • A coarse-grained DEM model is applied for milled pine hopper discharge flow. • Criticality of various processing parameters and material attributes is studied. • Two hopper-clogging mechanisms related to the material attributes are unveiled. • Correlation between critical arching distance and wedge hopper geometry is obtained. [ABSTRACT FROM AUTHOR]

A conceptual Enhanced Geothermal System (EGS) model, where water is circulated through a pair of parallel injection and production wells connected by a set of single large wing fractures, is designed, modeled, and evaluated in this work. The water circulation and heat extraction in the fractured reservoirs is modeled as a fully coupled process of fluid flow and heat transport. Using a newly developed, open-source, finite element based geothermal simulation code, FALCON, simulation results were obtained for a 30-year operation at a depth of 3 km and geothermal gradient of 65 ° C per km of depth. With a sensitivity study of the heat production to the design parameters, preferable fracture horizontal spacing, downward deviation angle of the parallel wells, and injection flow rate are recommended. Upscaling calculations of the developed EGS model have shown that, an industrial production-level system may be achievable if it consists of 40 equidistant fractures that connect two 1.2 km long parallel well sections with a well separation of 500 m; and if a system of these dimensions operates for 30 years at a flow rate of 0.1 m 3 /s, with an electric power output at least 5 MW and pumping power of less than 1 MW. In particular, the performance metrics demonstrated in this work match well with those suggested by others, thus indicating the general applicability of our conceptual models. [ABSTRACT FROM AUTHOR]

FALCON (Fracturing And Liquid CONvection) is a hybrid continuous/discontinuous Galerkin finite element geothermal reservoir simulation code based on the MOOSE (Multiphysics Object-Oriented Simulation Environment) framework being developed and used for multiphysics applications. In the present work, a suite of verification and validation (V&V) test problems for FALCON was defined to meet the design requirements, and solved to the interests of enhanced geothermal system modeling and simulation. The intent for this test problem suite is to provide baseline comparison data that demonstrates the performance of FALCON solution methods. The test problems vary in complexity from a single mechanical or thermal process, to coupled thermo-hydro-mechanical processes in geological porous medium. Numerical results obtained by FALCON agreed well with either the available analytical solutions or experimental data, indicating the verified and validated implementation of these capabilities in FALCON. Whenever possible, some form of solution verification has been attempted to identify sensitivities in the solution methods, and suggest best practices when using the FALCON code. [ABSTRACT FROM AUTHOR]

Hydra-TH is a hybrid finite-element/finite-volume incompressible/low-Mach flow simulation code based on the Hydra multiphysics toolkit being developed and used for thermal-hydraulics applications. In the present work, a suite of verification and validation (V&V) test problems for Hydra-TH was defined to meet the design requirements of the Consortium for Advanced Simulation of Light Water Reactors (CASL). The intent for this test problem suite is to provide baseline comparison data that demonstrates the performance of the Hydra-TH solution methods. The simulation problems vary in complexity from laminar to turbulent flows. A set of RANS and LES turbulence models were used in the simulation of four classical test problems. Numerical results obtained by Hydra-TH agreed well with either the available analytical solution or experimental data, indicating the verified and validated implementation of these turbulence models in Hydra-TH. Where possible, some form of solution verification has been attempted to identify sensitivities in the solution methods, and suggest best practices when using the Hydra-TH code. [ABSTRACT FROM AUTHOR]

[Display omitted] • An original set of hysteretic nonlinear contact models for DEM. • An original set of unconditionally stabilized viscous damping models. • Detailed documentation of model formulations benefits DEM research community. • DEM simulations capture bulk cyclic stress–strain behavior of milled pine chips. A monosphere discrete element method (DEM) model is introduced for elucidating the bulk mechanical behavior of granular biomass. This model considers each sphere as a representative elementary volume in bulk particles and is highly scalable in computation. To compensate for the simplification of particle shapes, we propose a set of hysteretic nonlinear contact models for approximating the bulk strain-hardening phenomena of granular biomass in handling and storage conditions. These contact models comprise of simple polynomial and/or exponential functions to allow for easy calibration. To ensure numerical stability, we have derived unconditionally stabilized viscous damping force models. The resultant DEM model is implemented in LIGGGHTS-INL and applied to simulate an axial compressibility test for milled pine chips. Results show that the DEM model can reproduce the bulk stress–strain profiles of the physical samples and that the predicted bulk compressibility and constrained modulus under repeated compression agree reasonably with the experimental data. [ABSTRACT FROM AUTHOR]

• The first study of liquid hydrocarbon nanochannel flow with channel size over 20 nm. • A strong threshold of pressure gradient in single-nanochannel flow is observed. • The heptane viscosity is non-homogeneous and exhibits a shear-thinning phenomenon. • The hydrocarbon flow reduction in silica nanochannels is first reported. A modified many-body dissipative particle dynamics (mDPD) model recently developed for realistic mesoscale multiphase flow simulations is rigorously parameterized, calibrated, and applied for elucidating the flow mechanisms of hydrocarbon liquids (i.e., heptane in this work) in amorphous silica cylindrical nanochannels with inner diameters ranging from 4.5 to 22.5 nm. The simulation results suggest the presence of a strong threshold of pressure gradient under which heptane cannot be driven to flow. The threshold for the 4.5 nm diameter pore is 10 to 100 times as high as for the 9–22.5 nm diameter pore, highlighting a remarkable nanoconfinement effect. Fluid viscosity is found to exhibit a shear-thinning phenomenon with intensity to weaken with increasing channel diameter — a phenomenon not observed in nanochannel flow of liquid water and gas in literature. Most remarkably, the radial profiles of average longitudinal flow velocity fitted by the modified Hagen-Poiseuille equation showed a negative slip length (−2.5% to −0.5% relative to the diameter) and a reduction of apparent permeability by 16% to 23%. This finding suggests silica nanochannels tend to deter hydrocarbon flow, a phenomenon that is opposed to the flow enhancement reported in most of the prior nanochannel flow studies in literature. [ABSTRACT FROM AUTHOR]

Abstract: A reconstructed discontinuous Galerkin (RDG) method based on a hierarchical WENO reconstruction, termed HWENO (P1P2) in this paper, designed not only to enhance the accuracy of discontinuous Galerkin methods but also to ensure the nonlinear stability of the RDG method, is presented for solving the compressible Euler equations on tetrahedral grids. In this HWENO (P1P2) method, a quadratic polynomial solution (P2) is first reconstructed using a Hermite WENO reconstruction from the underlying linear polynomial (P1) discontinuous Galerkin solution to ensure the linear stability of the RDG method and to improve the efficiency of the underlying DG method. By taking advantage of handily available and yet invaluable information, namely the derivatives in the DG formulation, the stencils used in the reconstruction involve only von Neumann neighborhood (adjacent face-neighboring cells) and thus are compact. The first derivatives of the quadratic polynomial solution are then reconstructed using a WENO reconstruction in order to eliminate spurious oscillations in the vicinity of strong discontinuities, thus ensuring the nonlinear stability of the RDG method. The developed HWENO (P1P2) method is used to compute a variety of flow problems on tetrahedral meshes to demonstrate its accuracy, robustness, and non-oscillatory property. The numerical experiments indicate that the HWENO (P1P2) method is able to capture shock waves within one cell without any spurious oscillations, and achieve the designed third-order of accuracy: one order accuracy higher than the underlying DG method. [Copyright &y& Elsevier]

Abstract: A Hermite WENO reconstruction-based discontinuous Galerkin method RDG(P1P2), designed not only to enhance the accuracy of discontinuous Galerkin method but also to ensure linear stability of the RDG method, is presented for solving the compressible Euler equations on tetrahedral grids. In this RDG(P1P2) method, a quadratic polynomial solution (P2) is first reconstructed using a least-squares method from the underlying linear polynomial (P1) discontinuous Galerkin solution. By taking advantage of handily available and yet invaluable information, namely the derivatives in the DG formulation, the stencils used in the reconstruction involve only von Neumann neighborhood (adjacent face-neighboring cells) and thus are compact and consistent with the underlying DG method. The final quadratic polynomial solution is then obtained using a WENO reconstruction, which is necessary to ensure linear stability of the RDG method. The developed RDG method is used to compute a variety of flow problems on tetrahedral meshes to demonstrate its accuracy, efficiency, robustness, and versatility. The numerical experiments demonstrate that the developed RDG(P1P2) method is able to maintain the linear stability, achieve the designed third-order of accuracy: one order accuracy higher than the underlying DG method without significant increase in computing costs and storage requirements. [Copyright &y& Elsevier]

Abstract: B-site modification lead strontium zirconate titanate Pb0.4Sr0.6Zr x Ti1− x O3 (PSZT, x =0–0.7) thin films were prepared on Pt/TiO2/SiO2/Si substrates by a sol–gel method. The XRD results indicate that paraelectric PSZT thin films at room temperature are obtained as x approaches 0.2. The temperature-dependent dielectric and hysteresis loop measurements reveal that the thin films have diffuse phase transition characteristics and relaxor-like behavior with nano-polar regions in the paraelectric films at room temperature. The Curie temperature of the PSZT thin films varies with the Zr contents, exhibiting a complex trend. This can be attributed to two competitive factors: higher mobility of Ti4+ than Zr4+ and smaller open space left for the displacement of Ti ions with the increase of Zr content. The further increase of the Zr contents leads to the simultaneous decrease of dielectric constant, dielectric loss and tunability. PSZT (x =0.4) thin film shows the largest figure of merit of 24.3 with a moderate tunability of 55.8% and a dielectric loss of 0.023. This suggests that B-site ions have different roles in modifying the electrically tunable performance of PSZT thin films for tunable microwave device applications. [Copyright &y& Elsevier]

Well-developed bipolar resistive switching behaviors have been revealed in Pt/GaOx/ITO stacks without an electroforming process. By substituting platinum with titanium as the top electrode, switching polarity changed from 'counter-Figure-8' to 'Figure-8.' The modulation of Schottky barrier at the Pt/GaOx interface induced by migration of oxygen vacancies was proposed to explain the switching in Pt/GaOx/ITO stacks, while the switching in Ti/GaOx/ITO stacks was ascribed to the redox reaction at the Ti/GaOx interface. Our experimental result further confirms the migration of oxygen vacancies in the vicinity of the electrode area plays an important role in the resistive switching process. [ABSTRACT FROM AUTHOR]

Complex impedance spectroscopy has been employed to investigate the conduction behavior of (Ba,Sr)(Zr,Ti)O3 thin films in the low- and high-resistance states for resistive switching applications. The domination of the grain bulk effect on the resistive switching is demonstrated. The analyses of activation energies for the conduction in the low- and high-resistance states have been executed comparatively. It is proposed that the first and the second ionization of oxygen vacancies are responsible for the conduction in the low- and high-resistance states, respectively. The transition of conduction mechanism is also discussed. [ABSTRACT FROM AUTHOR]

An organic bistable device with a structure Cu/Cu2S/copperphthalocyanine (Cu-Pc)/Pt was fabricated. Compared to the single layer organic device composed of Cu/Cu-Pc/Pt, the bilayer devices were observed to show distinct bistability with the resistance ratio of the off/on states up to 107 and low switch voltage (0.75–0.85 V). At least 105 switching cycles were achieved in the “write-read-erase-read” cycle voltage. The filament mechanism for the device is supported by the “metallic” behavior in their temperature dependence of the resistance in the on state. Such a memory device provides a promising structure for the nonvolatile memory. [ABSTRACT FROM AUTHOR]

Polycrystalline (Ba,Sr)(Zr,Ti)O3 thin films sandwiched between two Pt electrodes have been revealed to exhibit hysteretic current-voltage (I-V) characteristics and resistive switching at room temperature. High- and low-resistance states, as well as a less abrupt state transition, occur during the voltage cycle. The maximum ratio between these two resistance states is about 230. Analyses of I-V behaviors have been executed, and it is proposed that space-charge-limited-current conduction in higher voltage region caused by asymmetric electron trapping centers is responsible for such transition of resistance states. [ABSTRACT FROM AUTHOR]

The tunable property and thermal stability of (Ba0.25Pb0.25)Sr0.5TiO3 films derived by pulsed laser deposition have been investigated. The substitution of Pb for Ba in (Ba,Sr)TiO3 (BST) system has been revealed to raise the transition temperature close to room temperature (RT) and enhance the tuning property. It is proposed that nanopolar regions would occur in the films in the paraelectric state at RT, arising from the addition of Pb2+ into the A site of pervoskite structure of BST. This induces the relaxor behavior and diffuse phase transition. Hence, low temperature-dependent tunability is obtained due to the broadening of dielectric constant peak. These results demonstrated that Pb substitution could be a simple and effective method to obtain high tunability and good temperature stability simultaneously. [ABSTRACT FROM AUTHOR]

Perovskite‐oxide‐based ferroelectric tunnel junctions (FTJs) hold great potential for applications in non‐volatile memory and neuromorphic computing due to their unique properties. However, the challenges in synthesizing high crystalline quality perovskite oxides directly on silicon wafer limit the applications of these FTJs in conventional Si‐based integrated circuits, let alone the neural networks. Herein, perovskite oxide FTJs with an ON/OFF ratio up to 1.2×106, writing/erasing speed down to 1 nanosecond, and cycling endurance (>106) are achieved by integrating ultrathin freestanding ferroelectric perovskite oxide membranes directly on silicon wafers using a wet‐transfer method. Moreover, synapses based on these FTJs exhibit long‐term plasticity. For handwritten digits recognition task, the convolutional neural network (CNN) simulation is implemented achieving a recognition accuracy up to 98.9% based on the experimental performance, close to the result of 99.2% by software‐floating‐point‐based CNN. This work sheds light on the integration of ferroelectric perovskite oxides directly on silicon for high‐performance FTJ‐based non‐volatile memory and synaptic devices. [ABSTRACT FROM AUTHOR]

This work presents an experiment-informed, semi-empirical, elasto-plastic bond model for the discrete element modeling of woody biomass particles. The model renders nonlinear plastic deformation of materials when subjected to compression/tension, bending, and twisting, essential for accurately simulating the behavior of biomass in comminution. The model is implemented in an open-source DEM package LIGGGHTS and is assessed in a number of verification tests. The model is applied to simulate the fracturing test of notched loblolly pine blocks. Reduced bond strength is prescribed to the weak planes along the growth rings. It is found that the square-root formulation for describing the elasto-plastic normal bond contact delivers the best agreement with the experimental data over its linear and quadratic counterparts. Furthermore, the model predicts a strong anisotropic behavior of wood blocks with regard to the grain orientations, indicating that the cutting angle should be an important attribute for the optimization of biomass comminution. [Display omitted] • An experiment-informed, semi-empirical, nonlinear elasto-plastic bond model proposed • Model is capable of simulating irregular particle shapes via the bonded-sphere approach. • Model is applied to fracturing test simulation of loblolly pine wood blocks. • Material nonlinearity and anisotropy due to growth ring are captured. • The square-root form of proposed bond model delivers the best performance. [ABSTRACT FROM AUTHOR]

Transition metal-free half-metallicity recently has been the subject of intense research activity due to its potential in spintronics application. By employing density functional theory calculations, we revealed that F-intercalated GaN bilayers exhibit robust p orbital-based half-metallicity against the intercalant concentration and biaxial strain of −10% to 10%. The stable half-metallicity results from a spontaneous phase transition through Stoner instability and can be attributed to unusually high density of states near the Fermi level due to the quasi-flat bands. These findings provide a strategy to design transition-metal free half-metallic materials for futuristic spintronic applications. [ABSTRACT FROM AUTHOR]

Organic field-effect transistors (OFETs) with polymer charge-trapping dielectric, which exhibit many advantages over Si-based memory devices such as low cost, light weight, and flexibility, still suffer challenges in practical application due to the unsatisfied endurance characteristics and even the lack of fundamental of behind mechanism. Here, we revealed that the degradation of endurance characteristics of pentacene OFET with poly(2-vinyl naphthalene) (PVN) as charge-storage layer is dominated by the deep hole-traps in PVN by using the photo-stimulated charge de-trapping technique with the fiber-coupled monochromatic-light probes. The depth distribution of hole-traps in PVN film of pentacene OFET is also provided. [ABSTRACT FROM AUTHOR]

We explore scaling laws for adapting a bonded-sphere discrete element method (BS-DEM) model developed for woody structural mechanics at the millimeter scale to model the mechanics of realistic lignocellulosic biomass microstructures. Two scaling approaches, i.e., the reverse coarse graining (RCG) and equivalent bulk behavior (EBB), are proposed based on the classical mechanics principles and assessed in the single-particle compression and rectangular cuboid block tension tests. The EBB approach is recommended for BS-DEM models with general 3D geometries and is applied to simulate the microindentation test on a realistic microscale pinewood specimen. Simulations are performed to elucidate the impact of specimen thickness and loading position on the specimen's force–deformation behavior. The range of Young's modulus obtained from the calibrated BS-DEM simulations can match the experimental measurements. This is the first-of-its-kind study that has explored scale-bridging modeling approaches in biomass micromechanics and has proposed solutions based on BS-DEM models in the microscale. [Display omitted] • First-of-its-kind reverse scaling laws for bonded-sphere discrete element model. • Reverse coarse graining applicable for maintaining equivalent single-bond behavior. • Equivalent bulk behavior recommended for BS-DEM model with general 3D geometries. • Impact of specimen thickness and loading position on material response analyzed. • Young's moduli from simulations using EBB can match the experimental measurements. [ABSTRACT FROM AUTHOR]

Mn-doped La(Fe,Si) 13 compounds have been demonstrated as excellent candidates for magnetic refrigeration applications. However, the origins of Mn-dependent magnetic properties are still unclear. Here, by employing density functional theory calculations and Monte Carlo simulations, the changes in magnetic moment, total magnetic exchange coupling constant J total , atomic local environment, and Curie temperature T C of Mn-doped La(Fe,Si) 13 compounds were investigated. Mn atoms were found to prefer 96i sites and anti-parallelly couple with Fe atoms. The reduction of total magnetic moments during Mn substitution originates from the decreasing magnetic moments of Fe and anti-ferromagnetic coupling between Mn and Fe. Moreover, Mn dopants lead to the decrease in J total and T C , and the analysis of atomic local environment indicates that the weakening of J total can be mainly attributed to the shrinkage of the intra-icosahedral bond between Fe-I and Fe-II. This work offers a theoretical comprehension of the fundamental magnetic properties of Mn-doped La(Fe,Si) 13 compounds. [Display omitted] [ABSTRACT FROM AUTHOR]

The commercialization of bioenergy has been significantly limited by various material handling issues due to the poor flowability of granular biomass materials. Addressing these issues demands a fundamental understanding of flow physics and robust models to predict the multi-regime flow behavior of biomass particles. In this study, we investigated the multi-regime flow behavior of loblolly pine chips, a widely used bioenergy feedstock, through combined experiments and simulations. A quasi-static hypoplastic model and a cross-regime Drucker–Prager (DP)- μ (I) model were utilized and validated against inclined plane flow experiments to understand the quasi-static and dense flow behavior of milled pine chips. The results show that along the inclined plane, loblolly pine chips mainly present in heap flow (varying thickness along the plane), and in plane flow (iso-thickness along the plane) only when the inclination closes to the material's critical state internal friction angle. The results also show that the multi-regime DP- μ (I) model predicts a completely different velocity profile from the hypoplastic model. DP- μ (I) model can capture the flow behavior of pine chips in both flow regimes well but at the cost of extra parameter determination, and the shear-rate dependent rheology model can successfully capture the flow of elongated high-frictional particles. These findings advance the scientific understanding of the multi-regime flow behavior of granular biomass materials and shed light on formulating novel constitutive models to assist granular biomass handling in the bioenergy industry. [Display omitted] • A multi-regime constitutive model is formulated to model granular biomass flow. • Quasi-static and dense flow behaviors are studied with an inclined plane tester. • Shear rate dependency of elongated high-frictional particles are studied. • Flow patterns and stopping profiles are governed by flow regimes. [ABSTRACT FROM AUTHOR]

This study examines the role of nano B 4 C addition in improving the mechanical properties of Ti–6Al–4V (Ti64) alloys fabricated by laser melting deposition under as-built and heat-treated conditions. However, the enrichment of reinforcing phases generated by in situ production at grain boundaries causes a serious reduction in ductility, limiting the development of high-performance titanium matrix composites. To avoid this deficiency, the fabricated titanium matrix composites (TMCs) were subjected to three different heat treatment programmers, namely, subtransus heat treatment, supertransus heat treatment and triple heat treatment. The effects of B 4 C addition and heat treatment on microstructure, texture and mechanical properties were systematically investigated. The results show that TiB and TiC, synthesized in situ, promote the precipitation of α-Ti with a non-Burgess orientation relationship, and weakening the texture intensity of α-Ti. The ultimate tensile strength of the in situ synthesized (TiB + TiC) reinforced Ti64 composites is 1168 MPa, which is 35.5 % higher than the ultimate tensile strength of the Ti64 alloys. However, this effect resulted in a decrease in elongation at break to 2.5 %. An excellent combination of strength and fracture strain of 1060 MPa and 9.3 %, respectively, was simultaneously achieved for the heat-treated TMCs. The excellent ductility is mainly attributed to the microstructure consisting of primary equiaxed-α, ultrafine α s lamellar and retained β phase has been obtained after triple heat treatment. This finding offers significant guidance for the additive manufacturing of TMCs microstructures in order to attain the desired mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: We report non-saturating linear magnetoresistance (LMR) in silver-poor composite thin films of Ag10Ge15Te75 (AGT). The LMR increases with decreasing temperature and reaches a value of 110% at 200K under a magnetic field of 70kOe. The observed magnetoresistance is proportional to carrier mobility due to identical temperature dependencies. The microstructures of AGT films annealed at different temperature are investigated by TEM observations. The observed LMR effect is resulting from the inhomogeneous distribution of conductivity caused by highly conductive Ag2Te and GeTe4 precipitates, which generate a current distortion in the surrounding amorphous silver-poor Ag–Ge–Te matrix. [Copyright &y& Elsevier]

With the advancement of renewable energy, the processing and handling of biomass feedstocks has drawn enormous research interest. The key to economically viable and operationally reliable biomass handling processes involves a complete understanding of the flow behavior of different feedstocks as functions of the inherent critical material properties environmental conditions, and critical processing parameters. This review introduces the basic principles and methods in bulk solids flow and highlights recent efforts to understand the flow behavior of biomass feedstocks. The effects of inherent properties, environmental parameters, and handling equipment on the flow behavior of biomass feedstocks are presented. Particle size, shape, moisture, consolidation stress, temperature, storage time at rest, chemical treatment, and the material and geometry of the handling equipment all substantially influence biomass flowability. The limitations of current studies and the potential methods to overcome them are presented. Finally, an outlook for future research effort is provided, with proposed opportunities for improving the characterization of biomass flow. [Display omitted] [ABSTRACT FROM AUTHOR]

Unipolar resistance switching characteristics are observed in fully transparent indium-doped SnO2/MgO/F-doped SnO2 device. In addition to the transmittance above 90% for visible light, the devices show good endurance and retention characteristics. The resistance-temperature relation curves and the corresponding Arrhenius plot confirm the semiconducting conduction behavior of both the high resistance state and the low resistance state. Experimental results indicate that Ohmic and trap controlled space-charge-limited conduction mechanism controlled the charge carriers transport at the low voltage and high voltage regions, respectively. This work presents a candidate material MgO for the application on the future see-through electronic devices. [ABSTRACT FROM AUTHOR]

The growth of Ag-nanofilaments in the solid electrolyte films of memristors based on Ag30S2P14O42 is investigated. After the formation of the Ag-nanofilaments in the solid electrolyte, the memory cells are switched to the high conductive state. With a positive voltage applied on the Ag electrode of the cells, the Ag-nanofilaments gradually become thicker due to the reduction and diffusion of Ag+ cations in the solid electrolyte. The relationship between the thickening rate of the Ag-nanofilaments and the concentration of the Ag+ cations surrounding them is analyzed, and the results show that the thickening of the Ag-nanofilaments is determined by the reduction and diffusion of Ag+ cations in the solid electrolyte. [ABSTRACT FROM AUTHOR]

Switchgrass is a perennial herbaceous plant regarded as a biomass energy crop in the United States for its high adaptability and yield potential. Processing and handling of switchgrass particles are challenging due to the erratic mechanical and flow behavior originating from their intrinsic particulate properties. In this work, we present a bonded-sphere discrete element model designed specifically for switchgrass particles. The model simultaneously captures three key particulate features, i.e., fibrous particle shapes, a wide range of particle sizes, and particle deformability. Realistic yet computationally efficient particle shape templates are created based on the image analysis data of switchgrass specimens. A fitting procedure is proposed to ensure both the particle width and length distributions are captured, a unique requirement for fibrous particles. Two full-scale numerical models, i.e., a uniaxial compression model and a Schulze ring shear model, are developed using information from physical experiments. The model is calibrated using experimental data of chopped-small switchgrass specimens, and then, is validated using data of chopped-large specimens in both compression and ring-shear tests. Numerical results show that the numerical models capture bulk densities accurately (with an error of 3%) while slightly underestimate the bulk friction angle. Furthermore, an extensive sensitivity analysis reveals that (1) switchgrass particles with rougher edges (due to different processing techniques) exhibit a higher shear strength and a lower flowability; (2) stiffer particles yield a lower bulk density (up to 21% lower) compared to more deformable particles, indicating particle deformability should be incorporated when modeling biomass flow in a preprocessing system. • A bonded-sphere discrete element model designed specifically for switchgrass particles. • Fibrous particle shapes, particle sizes, and particle deformability are explicitly captured. • Realistic yet computationally efficient shape templates are developed based on image data. • Model is validated in both compression and Schulze ring shear tests. • Particle deformability significantly impacts bulk density. [ABSTRACT FROM AUTHOR]

Abstract: Unipolar resistive switching behavior has been investigated in Pt/Co3O4/Pt stacks. The resistance ratio of the high- and low- resistance states is over 5×103. The “ON/OFF” operation of the memory cells can be repeated more than 200 times at room temperature. The resistance of the two states can be kept for more than 16h without showing degradation. The temperature dependence of the resistance shows a metallic behavior at the low-resistance state, but a semiconductor-behavior at the high-resistance state. The mechanism responsible for the observed unipolar resistive switching behavior has been discussed. [ABSTRACT FROM AUTHOR]

The microstructural evolution and resistive switching of glassy Ag30Ge17Se53 electrolyte films clipped by Ag active electrode, at which a positive bias was applied, and Pt inert electrode, were investigated by transmission electron microscopy observations and I-V measurements as functions of the period of electrical field treatment. It is revealed that an electrical field induced precipitation reaction forming conductive particles with orthorhombic Ag2Se structure and followed growth and networking of these particles, leading to an electrical percolation, are responsible for the transition from high resistive to high conductive state of the system. The kinetics of the precipitation reaction was also analyzed. [ABSTRACT FROM AUTHOR]

• Ferromagnetic metallic NiFe is used as top electrode. • URS persists with a thin Al 2 O 3 layer insert between NiFe and NiO. • Ni conductive filament is confirmed by the observation of AMR. • Insert of Al 2 O 3 layer narrows the distribution of reset voltages. Noble metals are generally used as electrodes in resistive switching devices. In this work, ferromagnetic metallic NiFe is used as top electrode on NiO films, and stable unipolar resistive switching (URS) behavior has been observed after a forming process. By inserting a thin Al 2 O 3 layer between NiFe and NiO, URS persists with increasing the thickness of Al 2 O 3 layer up to 20 nm. The URS behavior can be attributed to the formation and rupture of metallic Ni filaments in NiO layer, which penetrate through the thin Al 2 O 3 layer, and have been confirmed by the observation of anisotropic magnetoresistance. With further increasing the thickness of Al 2 O 3 layer up to 30 nm, forming free bipolar resistive switching (BRS) behavior is observed, which is due to the oxygen vacancy accumulation and dissipation at the interface because the thick Al 2 O 3 layer blocks the penetration of Ni filaments. By inserting a thin Al 2 O 3 layer with thickness below 20 nm, the distribution of the reset voltages in URS is significantly narrowed. [ABSTRACT FROM AUTHOR]

[Display omitted] Nucleotide-binding oligomerization domain (NOD)-like receptor type 2 protein (NLRP2) was reported to inhibit NF-κB in response to inflammatory stimuli, but its role in tumors remains elusive. We screened out NLRP2 from mouse models of breast cancer metastasis. Bioinformatics analysis showed NLRP2 expression was positively correlated with survival rate and negatively correlated with the potential of cancer metastasis. Its significance in Triple-Negative Breast Cancer (TNBC) was investigated by gain- and loss-of-function studies in vivo and vitro. Re-expression of NLRP2 dramatically inhibited the growth and metastasis of the xenograft model of MDA-MB-231 cells. Mechanically, NLRP2 confined hnRNPK within cytoplasm, which in turn blocked vimentin mRNA production. Not only that, NLRP2 further enhanced the H 2 O 2 -induced high level of p53&Bax and hence dramatically increased the apoptosis rate (fivefold). Likewise, carboplatin-treated cells showed decreased cell viability, suggesting that patients of TNBC with high level of NLRP2 respond well to chemotherapeutics. Under the stimulus of H 2 O 2 , NLRP2–hnRNPK no longer stayed in the cytoplasm, but entered the nucleus to increase the expression of p53 and hence enhanced corresponding apoptosis effect, increasing Bax expression. It suggested that NLRP2 helps p53 enter the nucleus to induce apoptosis. This study revealed a novel function of NLRP2 that modulated oncogenic and anti-oncogenic characteristics of hnRNPK, and provided a new biomarker for TNBC chemotherapy. [ABSTRACT FROM AUTHOR]

Graphical abstract A high-intensity compact ultrasonic irradiation assisted technique results in novel hierarchically porous N-doped graphene microsheets (PNGTMSs) with a highly interconnected three-dimensional network nanostructure allowing well-dispersion of near-spherical Ni 2 P nanoflowers. High porosity and optimal thickness allow the whole volume of an isolated microsheet in PNGTMSs to be ion-accessible. Combined with good dispersion of Ni 2 P and rich exposed interfaces, the Ni 2 P-PNGTMSs composite shows higher specific capacitances and superior rate capability than most reported similar graphene-based composites. Asymmetric solid-state cell displays a high output voltage of 1.8 V and delivers high energy densities over those reported for similar devices as well as remarkable cycling stability. Highlights • Novel hierarchical PNGTMSs feature the advantages of both 2D and 3D graphene. • Achieved by a high-intensity compact ultrasound assisted technique. • New insights into ultrasonic activation are proposed. • Ni 2 P-PNGTMSs composite shows high capacity, superior rate capability and stability. • Asymmetric supercapacitor achieves high energy density and power densities. Abstract Severe restacking of single-atom-thick two-dimensional graphene and too long ion diffusion path in a thick three-dimensional porous graphene film are both main current problems limiting performance maximization of graphene as an energy storage material. Herein, we report an advance toward the design and fabrication of novel hierarchically porous N-doped graphene thin microsheets (PNGTMSs) with a honeycomb-like network structure allowing good dispersion of near-spherical Ni 2 P nanoflowers (NFs) by high-intensity compact ultrasound assisted technique. New insights into ultrasonic activation inducing a preferential self-assembly in a planar direction are proposed. High porosity and thin thickness of <500 nm allow the whole interior of isolated microsheets to be ion-accessible, which endows PNGTMSs with advantages of both two-dimensional and three-dimensional graphene as well as enhanced electrical conductivity. Combined with Ni 2 P nanosheet-built NFs and their good dispersion as well as rich exposed interfaces, Ni 2 P-PNGTMSs exhibits specific capacitance of 1100 F g−1 at 1.0 A g−1. Asymmetric solid-state device delivers an energy density of 39.8 Wh kg−1 (at 450.6 W kg−1) and remarkable cycling stability with 97% capacitance retention after 5000 charge-discharge cycles. This work provides a convenient and scalable strategy for control over graphene nanostructures and their composites for highly enhanced energy storage. [ABSTRACT FROM AUTHOR]