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Understanding the behavior of intrinsic defects and helium (He) in tungsten oxides is useful for the application of tungsten (W) in a fusion environment because of the oxidation of W surfaces. The formation and diffusion energies of intrinsic defects and He in monoclinic γ-WO3 have been investigated using first-principles density functional theory calculations. The formation energy and diffusion activation energy of O defects are lower than W defects. O vacancy prefers to diffuse along the ⟨ 001 ⟩ direction, then followed by ⟨ 010 ⟩ and ⟨ 100 ⟩ directions; however, the W vacancy is immobile at temperatures lower than 2000 K. The stability of Schottky defects (SDs) is sensitive to their geometry and orientation. W interstitials prefer to move along the [100] direction, while O interstitials jump around W atoms rather than through the W quasi-cubic centers. He interstitial atoms are predicted to have a high solubility and an anisotropic diffusion mechanism in γ-WO3. In addition, the effect of biaxial strain on the solubility and diffusivity of He interstitials was investigated. He interstitials prefer to reside at individual sites rather than clusters. He atoms are weakly trapped by single vacancies or SDs. Vacancies assist the local migration of nearby He. Correspondingly, He self-clustering and bubble formation are less likely to form in γ-WO3 relative to bcc W. The energetics obtained in this work can be used to predict the microstructure evolution of the WO3 layer on a W substrate exposed to He plasmas at different temperatures. [ABSTRACT FROM AUTHOR]

In this paper, a variant of the improved discrete velocity method (VIDVM) is proposed for flows in the whole Knudsen number regimes. This method retains the advantage of the improved discrete velocity method (IDVM), which calculates numerical fluxes through a self-adaptive strategy by combining the microscopic reconstruction and the macroscopic reconstruction. Like the IDVM, the microscopic reconstruction for VIDVM is also based on the collisionless Boltzmann solver. However, different from IDVM, the macroscopic reconstruction for VIDVM is established on the Euler solver instead of the Navier–Stokes solver. Considering that the Euler solver merely computes the inviscid fluxes while the Navier–Stokes solver additionally calculates the viscous fluxes, the present method could be more efficient than IDVM. To validate the accuracy and efficiency of the present scheme, some benchmark cases from the continuum regime to the free molecular regime are conducted. Results reveal that the present scheme can predict the flow as well as IDVM, but the present solver is more efficient than IDVM. [ABSTRACT FROM AUTHOR]

The Grad's 13 distribution function was derived through a third-order Hermite polynomial expansion in terms of peculiar velocity. Recently, it has been adopted to construct a gas kinetic flux solver called G13-GKFS for simulation of flows from the continuum regime to the rarefied regime. However, this Grad's distribution function only considers the contracted polynomials that strictly satisfy orthogonality. In other words, the third-order terms of C i C 1 2 , C i C 2 2 , and C i C 3 2 share the same coefficients ( γ i ). However, the results from the discrete velocity method reveal that those coefficients could be different, especially in the rarefied regime. This may affect the accuracy of numerical results in the rarefied region. In order to consider different coefficients of the third-order terms, we propose a complete third-order polynomial expansion to approximate the distribution function in this work. To show the capability of current distribution function, a new GKFS is developed for flows from the continuum regime to the rarefied regime. Some benchmark cases are solved to demonstrate that the new GKFS outperforms the G13-GKFS in the rarefied regime. [ABSTRACT FROM AUTHOR]

A compact online proton spectrometer based on a CMOS plate detector was proposed for the diagnosis of picosecond intense-laser accelerated protons. Inside the CMOS plate detector, a composite structure that composed of a scintillator screen, a fiber optic plate (FOP), and a CMOS sensor was designed to detect the protons safely and efficiently. The scintillator screen converted the incident protons to visible light, which, in turn, was collected by using the FOP and detected by using the CMOS sensor. An additional aluminum housing was designed to decrease the strong electromagnetic pulse (EMP) impact on the electronic readout system from picosecond laser–plasma interaction. This online spectrometer is compact and cost-effective than the system based on the micro-channel plate or scintillator screen in combination with an electron multiplying CCD camera and has better resistance to radiation damage than the system based on a single CMOS sensor. [ABSTRACT FROM AUTHOR]

Integrators are critical instruments used for magnetic measurement systems (MMSs) in tokamaks, and, currently, the Experimental Advanced Superconducting Tokamak (EAST) has over 600 deployed. However, these integrators, designed with real-time drift compensation, will not be able to support longer pulse operations in the near future due to saturation and drift. To address these issues, this paper proposes a new alternating integration system combining analog integration with drift digital rectification. This system utilizes a microcontroller unit (MCU) to control two parallel analog integrators to work alternatively, compensate their drifts based on their respective error characteristics, and assemble the two integration segments together. The designed architecture provides highly flexible capabilities in operation modes and error correction, which make the system operation and maintenance highly automated. Performance tests on the EAST experiment site show that the prototype integrator can meet the requirements of real-time plasma control for a duration of hour-level. [ABSTRACT FROM AUTHOR]

This work investigates the detailed difference between dielectric function models, the Mermin model and the full Penn algorithm (FPA) model, for the determination of an electron inelastic mean free path (IMFP) with optical energy loss function (ELF), as an extension of our previous study [Da et al., Surf. Interface Anal. 51, 627 (2019)] by using the simple Drude-type ELF. In the conventional normal Mermin (NM) model, the approximations of ELF by the Drude equation will introduce inevitable fitting error. In order to enhance the accuracy of the NM model, our previous proposed extended Mermin model [Da et al., Phys. Rev. Lett. 113, 063201 (2014)], which is renamed as a super-extended Mermin algorithm (SE-MA) now, is employed to eliminate the error by expanding the definition of Drude oscillators used in the NM. In the SE-MA, the Drude-like oscillators allow the existence of negative strengths to express the fine structures of phonon–electron scattering and the plasmon lifetime broadening effect. Because in our previous study, the simple Drude-type ELF cannot include these complex structures, in this work, the electron IMFPs are calculated for five realistic materials, Al, Si, Cu, Au, and MgO. The difference between IMFPs calculated by the SE-MA model and the FPA model is material dependent and is significant in the low energy region, which is analyzed by using the Fano plot. This is due to the more important role played by the plasmon lifetime broadening effect. [ABSTRACT FROM AUTHOR]

Ferroelectricity and magnetism seldom coexist due to mutual exclusiveness. Recent attempts have been made to achieve the coexistence of ferroelectricity and magnetism in polar magnets. In this paper, we investigated the magnetic properties, dielectric relaxation, and magnetodielectric (MD) effect of polar Dy2Cu2O5 ceramic. At the antiferromagnetic ordering temperature, the dielectric constant (ɛ) curves exhibit a spontaneous change in slope, indicating strongly coupled charge and spin degrees of freedom. With increase in the magnetic field intensity, the simultaneous suppression of the dielectric anomaly and the antiferromagnetic transformation demonstrates the existence of the MD effect. It is important to note that ɛ varies nonmonotonically with the magnetic field. Below the magnetic ordering temperature, ɛ increases continuously before the metamagnetic transition and then decreases after that. The results are discussed in terms of the magnetic field-induced change of spin configuration and spin–phonon coupling. Moreover, two dielectric relaxation-related steps are observed, which are correlated with the electrons hopping within and among the zigzag chains of Cu2+, respectively. This work helps understand the dielectric behavior and the MD effect in materials with complicated spin structures. [ABSTRACT FROM AUTHOR]

In this paper, mesoporous nitrocellulose (NC)/graphene oxide (GO) composite aerogel is manufactured by a sol-gel method followed by supercritical carbon dioxide drying. The effects of GO on the microstructure, decomposition, and thermal conductivity are studied. The laser absorption, laser ignition property, and combustion performance of NC aerogel and NC/aerogel are also investigated. The results indicate that NC/GO aerogel is established by the combination of NC nano-fibers and GO sheets, and the aerogels are mesoporous with average pore size at 40 nm. Moreover, the thermal stability of aerogels is decreased by the nano-structure of NC, and the laser absorption is significantly increased by the nano-porous structure and the adoption of GO. In addition, the laser ignition and combustion efficiency are also greatly improved by the nano-porous aerogel structure and the incorporation of evenly uniformly dispersed GO sheets with high photothermal conversion efficiency and thermal conductivity. Laser ignition times reduced by 73.7% and 99.6% are obtained, and flame propagation rates up to 4.7 and 12.3 times are observed for NC aerogel and NC/5 wt. % GO aerogel, respectively. [ABSTRACT FROM AUTHOR]

Interest exists in utilizing boron (B) wall conditioning of fusion tokamaks containing tungsten (W) plasma facing components, in order to improve plasma confinement. To understand the interactions of B with W surfaces, first-principles density functional theory calculations have been performed to model the adsorption, diffusion, and solution of B near the W(100), W(110), and W(111) surfaces. The results show that B within a distance of 0.6 nm above the surfaces is adsorbed to the surfaces without activation barriers. B atoms are strongly adsorbed on the W(100) surface with an adsorption energy of 7.80 eV, which is 1.22 and 1.35 eV larger than on the W(110) and W(111) surfaces. B diffusion on the W(100), W(110), and W(111) surfaces has an activation energies of 2.08, 1.12, and 1.47 eV, respectively; while, diffusion from the adsorption sites into the bulk requires 2.2–2.3 eV. The B solution energy below a clean W(100) surface is the lowest, followed by the W(111) and W(110) surfaces. B clustering and B-induced surface deformation as a function of B coverage has been investigated. B on the W(100) surface occupy epitaxial sites at coverages of 0–1.25 ML, but form clusters at higher coverages. B clustering on the W(110) and W(111) surfaces is expected throughout the adsorption process. Compared to a clean surface, B atoms on the W(100) reduce the surface effect on the B solution energy below the surface, while the presence of B on the W(110) and W(111) surfaces generally decreases or increases the B solution energy below surfaces, respectively. [ABSTRACT FROM AUTHOR]

Dirac semimetals are classified into different phases based on the types of Dirac fermions. Tuning the transition among different types of Dirac fermions in one system remains a challenge. Recently, KMgBi was predicted to be located at a critical state in which various types of Dirac fermions can be induced owing to the existence of a flatband. Here, we carried out systematic studies on the electronic structure of KMgBi single crystals by combining angle-resolve photoemission spectroscopy and scanning tunneling microscopy/spectroscopy. The flatband was clearly observed near the Fermi level. We also revealed a small bandgap of ∼20 meV between the flatband and the conduction band. These results demonstrate the critical states of KMgBi that transition among various types of Dirac fermions can be tuned in one system. [ABSTRACT FROM AUTHOR]

In this work, a radial basis function differential quadrature-based physics-informed neural network (RBFDQ-PINN) is proposed to simulate steady incompressible flows. The conventional physics-informed neural network (PINN) makes use of the physical equation as a constraint to ensure that the solution satisfies the physical law and the automatic differentiation (AD) method to calculate derivatives at collocation points. Although the AD-PINN is expedient in evaluating derivatives at arbitrary points, it is time-consuming with higher-order derivatives and may lead to nonphysical solutions with sparse samples. Alternatively, the finite difference (FD) method can facilitate the calculation of derivatives, but the FD-PINN will increase the computational cost when handling random point distributions, especially with higher-order discretization schemes. To address these issues, the radial basis function differential quadrature (RBFDQ) method is incorporated into the PINN to replace the AD method for the calculation of derivatives. The RBFDQ method equips with high efficiency in the calculation of high-order derivatives as compared with the AD method and great flexibility in the distribution of mesh points as compared with the FD method. As a result, the proposed RBFDQ-PINN is not only more efficient and accurate but also applicable to irregular geometries. To demonstrate its effectiveness, the RBFDQ-PINN is tested in sample problems such as the lid-driven cavity flow, the channel flow over a backward-facing step, and the flow around a circular cylinder. Numerical results reveal that the RBFDQ-PINN achieves satisfactory accuracy without any labeled collocation points, whereas the AD-PINN struggles to solve some cases, especially for high Reynolds number flows. [ABSTRACT FROM AUTHOR]

The interaction of xenon (Xe) bubbles with small self-defects in uranium dioxide (UO2) has been studied using molecular statics simulations. The results show that the pressure and size of bubbles have a minimal impact on the heterogeneity of the interaction between a charge neutral Xe bubble and charged point defects, while the local charge distribution around the bubble overwhelmingly determines the interaction strength and critical interaction distance. The charge effect on the interactions between Xe bubbles and defects was further confirmed by assessing the point defect interaction energies with negatively or positively charged Xe bubbles. The Xe density, or pressure, has a much smaller effect on the interaction energy between charged bubbles and small defects at least for low and medium pressure bubbles. The interactions between charged Xe bubbles and point defects basically follow the Coulomb electrostatic interaction law, which is independent of the empirical potentials employed for the Xe–UO2 system in this work. [ABSTRACT FROM AUTHOR]

A systematic study has been performed based on a Monte Carlo simulation for the investigation of secondary electron yields, backscattering coefficients, and total electron yields for eight compound semiconductor materials, i.e., AlN, TiN, VN, VC, GaAs, InAs, InSb, and PbS, at different incident electron energies in the range 0.1–10 keV. Our Monte Carlo simulation model is based on the Mott cross section for electron elastic scattering as calculated by a partial wave method and a dielectric functional approach to electron inelastic scattering with the full Penn algorithm. We used Palik's optical data for lower photon energies below 100 eVs and Henke's data for higher photon energies. The cascade production of secondary electrons in electron inelastic scattering and low energy is included in the simulation. The simulated results of electron backscattering coefficients are compared with the experimental data available in the literature. Considering the fact that the experimental data for these compound materials are not available, we have compared them with experimental data for elements having the nearest mean atomic numbers. The simulation predicted much larger backscattering coefficient values than the empirical Staub formula. [ABSTRACT FROM AUTHOR]

We have performed a systematic Monte Carlo simulation of primary and secondary electron trajectories to predicate the mean escape depth of secondary electron emission for six compound semiconductors, i.e., TiN, VN, GaAs, InAs, InSb, and PbS. Mott's cross section is used for the description of electron elastic scattering in the simulation model, and the full-Penn's dielectric function approach is adopted for the modeling of electron inelastic scattering, where the energy loss function obtained with the optical data is contributed from phonon excitation, interband transition of the loosely bound valance electrons, and inner-shell electron excitations. We have calculated the excitation depth distribution function, emission depth distribution function, and their combining effect in probability depth distribution function at different primary energies for the excited and emitted secondary electrons in these materials. The calculation leads to the primary energy dependence of mean escape depth whose values are found in the range of 0.4–1.4 nm for these materials. [ABSTRACT FROM AUTHOR]

Hydrogen (H) solution, migration, and binding to vacancies near the tungsten/tungsten carbide (W/WC) interfaces based on hcp WC or bcc W (W/WCb and Wb/WC) have been studied by first-principles simulations to provide insights into the effect of C on H behavior in W exposed to C deposition in fusion reactors. The H behavior near the W/WC interfaces is related to the tensile or compressive strain due to the lattice match and interfacial effects. Near the W/WCb interface, the H solution energy in hcp WC increases approaching the interface, while it decreases from the W side to the interface. The configuration change of the W slab significantly decreases the H solution energy but has only a modest effect on the H migration energy barrier in comparison with the values in bcc W. The interface enhances the H binding to vacancies in WC layers. Both the interface and configuration adjustment of the W slab reduce the H binding to vacancies on the W side of the interface. Near the Wb/WC interface, H solution energies in both WC and W slabs weakly decrease approaching the interface. The configuration change of the WC slab significantly increases the H solution energy and binding energy to vacancies but decreases the H migration energy barrier in comparison with the values in hcp WC. The H energetics near the W/WC interfaces indicate the likelihood of H localization and diffusion in the W side of the interface, rather than diffusing through the interface into WC layers. [ABSTRACT FROM AUTHOR]

Angle-resolved photoemission spectroscopy with sub-micrometer spatial resolution (μ-ARPES), has become a powerful tool for studying quantum materials. To achieve sub-micrometer or even nanometer-scale spatial resolution, it is important to focus the incident light beam (usually from synchrotron radiation) using x-ray optics, such as the zone plate or ellipsoidal capillary mirrors. Recently, we developed a laser-based μ-ARPES with spin-resolution (LMS-ARPES). The 177 nm laser beam is achieved by frequency-doubling a 355 nm beam using a KBBF crystal and subsequently focused using an optical lens with a focal length of about 16 mm. By characterizing the focused spot size using different methods and performing spatial-scanning photoemission measurement, we confirm the sub-micron spatial resolution of the system. Compared with the μ-ARPES facilities based on the synchrotron radiation, our LMS-ARPES system is not only more economical and convenient, but also with higher photon flux (>5 × 1013 photons/s), thus enabling the high-resolution and high-statistics measurements. Moreover, the system is equipped with a two-dimensional spin detector based on exchange scattering at a surface-passivated iron film grown on a W(100) substrate. We investigate the spin structure of the prototype topological insulator Bi2Se3 and reveal a high spin-polarization rate, confirming its spin-momentum locking property. This lab-based LMS-ARPES will be a powerful research tool for studying the local fine electronic structures of different condensed matter systems, including topological quantum materials, mesoscopic materials and structures, and phase-separated materials. [ABSTRACT FROM AUTHOR]

The diffusion and self-clustering nucleation behavior of hydrogen (H) without vacancies below tungsten (W) surfaces are important for understanding the retention of deuterium (D) in W crystals exposed to high-flux and low-energy D plasma. The H migration energy and binding energy of H to self-clusters near the W(100), W(110), and W(111) surfaces have been investigated by first-principles computer simulations using density functional theory. H diffusion from adsorption sites on the W(100), W(110), and W(111) surfaces into solute sites in the bulk requires energies of at least 1.21, 1.78, and 1.80 eV, respectively, while 0.27, 0.31, and 0.24 eV for the reverse process. In addition, the lateral diffusion of H between two subsurface layers below the W surfaces has been investigated. Two H atoms at a depth of 0.08 nm below the W(110) surface have the highest binding energy, followed by H atom pairs below the W(111) and W(110) surfaces. The nucleation and stability of H clusters depend on the surface orientation. A planar configuration between the first nearest neighbor {100} planes is energetically favorable for H self-clustering below the W(100), W(110), and W(111) surfaces. The thermal stability of a platelet containing 16 H atoms below the W surfaces at 300 and 600 K was also studied by ab initio molecular dynamics simulations, which indicate that the H platelet below a W(111) surface is more stable than that below either the W(100) or the W(110) surface. [ABSTRACT FROM AUTHOR]

The effect of post-growth annealing (PGA) on dot-in-well (DWELL) structures grown on Si substrates has been studied. The photoluminescence (PL) measurements showed that, compared to the DWELL structures directly grown on GaAs, the PGA process induces a distinct difference in the tuning of the emission properties. Then, transmission electron microscopy imaging of the samples revealed that PGA improved the uniformity of quantum dots (QDs) while the size of the QDs increased, in agreement with a corresponding red shift and a decrease of the full width at half maximum in the PL emission spectrum. Finally, energy-dispersive x-ray linescan provided a quantitative analysis of the composition change of DWELL grown on Si in the as-grown, 700 °C annealed, and 800 °C annealed samples. The change in the InL/GaK concentration ratio became gradual between the QDs and surrounding materials after 800 °C annealing. The analysis of the optical properties, morphology evolution, and compositional change of the QDs as a function of the annealing temperature showed good agreement. [ABSTRACT FROM AUTHOR]

Understanding the interaction between hydrogen (H) and helium-vacancy (He-V) complexes in tungsten (W) is important for the development of plasma-facing materials in fusion reactors. H trapping by HexVy complexes in bulk W, as well as the H solution behavior and H trapping by HexV complexes near W(100), W(111), and W(110) surfaces, has been investigated by first-principles computer simulations using density function theory. The results show that the sequential H binding energies to HexV complexes in bulk W decrease with the increasing number of H and He. For the HexV2 complexes in bulk W, H prefers to trap at interstitial sites near the junction of the di-vacancy, where the H can minimize the isosurface of optimal charge density. The most stable interstitial sites for H below W surfaces are dependent on the surface orientation. Our calculations indicate that H atoms tend to prefer a depth of 0.3 nm below the W(100) and W(111) surfaces due to the surface reconstruction. The binding energy of H to a HeV complex near W surfaces has the most significant orientation dependence below the W(111) surface, followed by the W(100) and W(110) surfaces. Compared with the bulk value, the largest difference in the average binding energy of H to the stable HexV complexes at the three W surfaces is about 0.2 eV. Furthermore, the effect of surfaces on the H binding energy to HexV complexes can be ignored for depths greater than 0.65 nm. [ABSTRACT FROM AUTHOR]

Density function theory calculations have been performed to study the stability of small helium-vacancy (He-V) complexes near tungsten (W) surfaces of different orientations. The results show that the stability of vacancies and He-V complexes near W surfaces depends on surface orientation. However, as the depth below the surface increased beyond about 0.65–0.8 nm, the stability of He-V complexes is similar to the bulk. The formation energies of single vacancies and di-vacancies at depths less than 0.2 nm below the W(110) surface are higher than for W(100) or W(111) surfaces, but have lower energies at depths between 0.2 and 0.65 nm. The formation energies of He-V complexes below W surfaces are sensitive to the geometric orientation of the He and vacancy, especially below the W(111) surface. Within about 0.2 nm of the top layer of the three W surfaces, neither a vacancy nor a di-vacancy can trap He. Because of the lower formation energy of He-V complexes and higher He binding energy to vacancies below the W(110) surface, the He desorption from the W(110) surface is less likely to occur than from the W(100) and W(111) surfaces. Our results provide fundamental insight into the differences in surface morphology changes observed in single W crystals with different surface orientations under He plasma exposure. [ABSTRACT FROM AUTHOR]

In this article, we studied the effect of magnetic interaction on β-relaxations of FexNi72−xSi4.8B19.2Nb4 (x = 0, 10, 30, 50, 72) metallic glasses (MGs). It is found that, with the substitution of Fe by Ni, the β-relaxation changes from a shoulder to an excess wing, suggesting an entropic effect on the suppression of β-relaxation. A peak caused by ferromagnetic transformation appears in the loss modulus curve of Fe30Ni42Si4.8B19.2Nb4 MG with suppressed β-relaxation, which is sensitive to stress and strain. In addition, the β-relaxation can be further varied by annealing under a transverse or longitudinal magnetic field. The results suggest that the entropy-suppressed β-relaxation in MGs can be affected by magnetic interaction that could help to improve their mechanical properties. [ABSTRACT FROM AUTHOR]

An efficient improved discrete velocity method (IDVM) with inner iteration is presented to simulate the steady flows in all flow regimes in this work. It is an extension of our previous implicit IDVM to achieve a faster convergence rate. In the previous method, both the discrete velocity Boltzmann equation (DVBE) and the corresponding macroscopic governing equations are solved synchronously, where the computational discrete cost is dominated by the calculation of the DVBE since the number of distribution functions is far larger than that of macroscopic conservative variables. Furthermore, the convergence rate of the calculation of the DVBE is affected by the predicted equilibrium state obtained from the solution of macroscopic governing equations. To provide a more accurate predicted equilibrium state for the fully implicit discretization of the DVBE, an inner iteration is introduced into the solution of macroscopic governing equations, and the flux Jacobian of these equations is evaluated by the difference of numerical fluxes of Navier–Stokes equations rather than the Euler equation-based flux splitting method used in the previous implicit IDVM. This more accurate prediction procedure endows the developed method to accelerate the computation greatly, especially in the continuum flow regime. Numerical results indicate that, in the continuum flow regime, the present method is about one order of magnitude faster than the previous implicit IDVM and one to two orders of magnitude faster than the conventional semi-implicit DVM. [ABSTRACT FROM AUTHOR]

To search for half-metallic materials for spintronic applications, instead of using an expensive trial-and-error experimental scheme, it is more efficient to use first-principles calculations to design materials first, and then grow them. In particular, using a priori information of the structural stability and the effect of the spin--orbit interaction (SOI) enables experimentalists to focus on favorable properties that make growing half-metals easier. We suggest that using acoustic phonon spectra is the best way to address the stability of promising half-metallic materials. Additionally, by carrying out accurate first-principles calculations, we propose two criteria for neglecting the SOI so the half-metallicity persists. Based on the mechanical stability and the negligible SOI, we identified two half-metals, β-LiCrAs and β-LiMnSi, as promising half-Heusler alloys worth growing. [ABSTRACT FROM AUTHOR]

From the aspect of the multiscale nature of the rarefied flow, a simple hybrid strategy is proposed in this paper in the process of flux reconstruction to couple the improved discrete velocity method (IDVM) and the G13-based gas kinetic flux solver (G13-GKFS). The flow field is divided into the IDVM area and G13 area according to the kinetic nature of the Knudsen layer and the criteria of the local Knudsen number. By eliminating the storage of the distribution functions and evolution of the microscopic equation, the reduction of the computational effort and memory storage can be achieved without sacrificing the accuracy in the whole flow field. Four different non-equilibrium cases from the micro-flow to the supersonic flow are tested by the present hybrid method. The results show good performance and better efficiency. Furthermore, under the framework of the present hybrid method, different non-equilibrium distribution functions with higher-order moments could be employed and coupled easily. [ABSTRACT FROM AUTHOR]

A series of polycrystalline YMn1-xRuxO3 (0≤x≤0.2) samples were prepared by traditional solidstate reaction method. Effects of doping on the microstructures and magnetic properties were investigated. Microstructural results reveal that samples crystallize in a single hexagonal structure with P63cm group for x≤0.1. Lattice parameters a, c, and unit-cell volume of YMn1-xRuxO3 are found to increase with doping content, which are ascribed to the larger radius of Ru3+ than that of Mn3+. Weak ferromagnetism is found and is enhanced with increasing doping concentration x. The bond angles of Mn-O3-Mn and Mn-O4-Mn are changed in the opposite trends, which break the Mn-Mn exchange interaction, thus the antiferromagnetic ordering. The MnO5 bipyramid is found to be relieved and the trimerization of Mn ions is weakened. These structural modifications result in the increase of weak ferromagnetism ordering in samples. [ABSTRACT FROM AUTHOR]

NiAs-type manganese telluride (MnTe) films with preferred crystallographic plane of (110) were prepared on Si/SiO2 substrates by pulsed laser deposition. X-ray diffraction(XRD) of the films was studied at different temperatures. The XRD peak of MnTe (110) films shifts to higher angle with decreasing temperature, showing the decrease of the lattice parameter. Resistivity of the films was studied in the temperature range of 2-350 K. The bump between 150 and 250 K was observed in the films, which may be related to the special s-d and p-d overlaps induced by the compressed lattice. The magnon drag effect near its Néel temperature TN and enlarged magnetic-elastic coupling below 100 K were observed and analyzed in details. [ABSTRACT FROM AUTHOR]

In this study, a high-order implicit least squares-based finite difference-finite volume (ILSFD-FV) method with a lattice Boltzmann flux solver is presented for the simulation of two-dimensional incompressible flows on unstructured grids. In this method, a high-order polynomial based on Taylor series expansion is applied within each control cell, where the unknown spatial derivatives at each cell center are approximated by the least squares-based finite difference scheme. The volume integral of the high-order polynomial over the control cell results in a pre-multiplied coefficient matrix in the time-dependent term. This makes the high-order method be implicit in nature. With this feature, a high-order implicit Runge–Kutta time integration scheme, namely, the explicit first-stage singly diagonally implicit Runge–Kutta (ESDIRK) scheme, is applied to obtain the time-accurate solutions for flow problems. The non-linear system of equations arising from each ESDIRK stage except for the first explicit stage is solved by a dual time stepping approach. A matrix-free lower-upper symmetric Gauss–Seidel solver is then used to efficiently march the solution in the pseudo time. The present high-order ILSFD-FV method is verified and validated by both steady and unsteady 2D incompressible flow problems. Numerical results indicate that the developed implicit method outperforms its explicit counterpart in terms of the convergence property and computational efficiency. The speedup ratio of the computational effort is about 3–22. [ABSTRACT FROM AUTHOR]

NaZn13-type La(Fe0.94Co0.06)11.8Si1.2 alloys were manufactured to investigate the influence of their microstructural change on magnetic refrigeration performance during magnetic field cycling. The magnetic refrigeration performance measurements indicate that both the large magnetic entropy change value (ΔS=14.1 J kg-1 K-1) and maximum adiabatic temperature change (Δ=2.2K) are favorable for the alloys to be superior candidate of magnetic refrigerants. However, the alloys exhibit nearly 10% decrease of ΔS and ΔT when they performed cycling ten-thousand times. More than thousand times of cycles induce local stress and grain cleavages presented by the accumulation of irreversible microstructure changes such as micro-cracks and sub-boundaries. According to the domain observation for the alloys with different field cycles, these microstructure characteristics accompany with the reconfiguration of the local magnetic domains and increase of domain wall energy, which are considered to be the reason of the decrease of ΔS. [ABSTRACT FROM AUTHOR]

A sort of composite solder was produced by adding Y2O3 nanoparticles in Sn3.0Ag0.5Cu solder. The microstructure and tensile strength of solder joint were investigated. It was found that the size of intermetallic compounds and tensile strength of solder joint were notably influenced by the nanoparticles. The growth behaviors of intermetallic compounds Ag3Sn and Cu6Sn5 were suppressed due to the addition of Y2O3 nanoparticles. The tensile test results revealed that the strength of composite solder joint was higher than that of solder joint without nanoparticles addition. It is indicated that Y2O3 nanoparticles should play important roles in strengthening of joint by hampering dislocation movement. [ABSTRACT FROM AUTHOR]

In this work, the explicit formulations of the Grad's distribution function for 13 moments (G13)-based gas kinetic flux solver (GKFS) for simulation of flows from the continuum regime to the rarefied regime are presented. The present solver retains the framework of GKFS, and it combines some good features of the discrete velocity method (DVM) and moment method. In the G13-GKFS, the macroscopic governing equations are first discretized by the finite volume method, and the numerical fluxes are evaluated by the local solution of the Boltzmann equation. To reconstruct the local solution of the Boltzmann equation, the initial distribution function is reconstructed by the Grad's distribution function for 13 moments, which enables the G13-GKFS to simulate flows in the rarefied regime. Thanks to this reconstruction, the evolution of distribution function is avoided, and the numerical fluxes can be expressed by explicit formulations. Therefore, the computational efficiency of G13-GKFS is much higher than that of DVM. The accuracy and computational efficiency of the present solver in explicit form are examined by several numerical examples. Numerical results show that the present solver can predict accurate results for flows in the continuum regime and reasonable results for flows in the rarefied regime. More importantly, the central processing unit time of the present solver is about 1% of that of DVM for two-dimensional (2D) microflow problems, and it is about twice of the conventional Navier–Stokes solver for 2D continuum flows. [ABSTRACT FROM AUTHOR]

Based on a recent experimental data of elastic transmissivity and the elastic reflectivity measured on graphene, we have performed a theoretical study on electron inelastic mean free path (IMFP) and elastic mean free path (EMFP) by an improved approximation in a classical electron trajectory framework. A hump feature, which is considered to be owing to the out-of-plane mode of the π + σ plasmon, is clearly shown in our IMFP results of multilayer graphene while it is not seen in that of monolayer graphene. The obtained EMFPs are one order of magnitude greater than previously reported results. This work shows that the classical electron trajectory framework still works for revealing the physics picture of low-energy electron interaction with graphene, even for the transverse direction of monolayer graphene, which is the thinnest material. [ABSTRACT FROM AUTHOR]

Within the framework of the high-order finite volume (FV) method, a high-order gas kinetic flux solver (GKFS) is developed in this work for simulation of two-dimensional incompressible flows. Generally, in the conventional high-order FV method, the inviscid and viscous fluxes are treated separately. However, different from the conventional high-order FV method, the high-order GKFS evaluates the inviscid and viscous fluxes simultaneously from the local asymptotic solution to the Boltzmann equation, which consists of the equilibrium distribution function and its substantial derivative at the cell interface. By introducing a difference scheme with the high-order accuracy in space to discretize the substantial derivative, a high-order accurate local asymptotic solution to the Boltzmann equation can be obtained. The numerical flux of the Navier–Stokes equations can then be calculated by the moments of the local asymptotic solution. Since this local asymptotic solution is relatively simple, the numerical fluxes of the Navier–Stokes equations can be given explicitly for the high-order GKFS, which is the function of the left and the right states and their first-order derivatives. Numerical results showed that the developed solver can achieve the desired accuracy on both the quadrilateral mesh and the triangular mesh and its efficiency is higher than the second-order counterpart when achieving comparable accuracy of solution. [ABSTRACT FROM AUTHOR]

This paper presents numerical investigations of the mix convection between a rotating inner sphere and a concentric cubical enclosure, using the recently developed immersed boundary-simplified lattice Boltzmann method. The validity of the method has been established through benchmark tests, and a grid independence study is also carried out to ensure the accuracy of the conveyed results. Various factors that may influence the mixed convection system, such as the rotational direction, Rayleigh number, and rotational Reynolds number, are considered in the present study. Three representative rotational axes, namely, the vertical, the horizontal, and the diagonal axes, are selected. The Rayleigh number spans from 104 to 106, which covers the transition range from a conduction-dominated system to a convection-dominated one. Moreover, the rotational Reynolds number varies from 0 to 300. Distinct flow patterns, global heat transfer behavior, and the heat transfer rates on cubic walls are studied to reveal the characteristics of this problem. It is found that the rotationality of the inner sphere would increase the global heat transfer rate of the system and the rotating motion would stimulate heat transfer in the radial direction of the rotational axis while suppressing the thermal expansion in the axial direction. [ABSTRACT FROM AUTHOR]

The least square-based finite difference-finite volume (LSFD-FV) method has been developed and successfully applied to solve various two-dimensional flow problems with a high-order of accuracy. In this paper, the extension of the LSFD-FV method to the three-dimensional (3D) case on unstructured grids is presented. Different from other existing high-order methods, the LSFD-FV method combines the good features of the least square-based finite difference (LSFD) scheme for derivative approximation and the finite volume (FV) discretization for conservation of physical laws. Within each control cell, a high-order polynomial resultant from a Taylor series expansion is used to approximate the solution in the FV discretization of governing equations, where the derivatives are approximated by the LSFD scheme. As a result, the mesh-free nature of the LSFD scheme endows the LSFD-FV method with the flexibility on unstructured grids. Additionally, the straightforward algorithm of the LSFD scheme and the direct utilization of the Taylor series polynomial make the LSFD-FV method user-friendly and easy to implement. Furthermore, the inviscid and viscous fluxes are simultaneously evaluated by lattice Boltzmann and gas kinetic flux solvers in this work, which avoids additional and complicated treatment for the viscous discretization. Accuracy studies on unstructured hexahedral and tetrahedral grids validate the third-order of accuracy of the 3D LSFD-FV method. Various 3D incompressible and compressible numerical experiments are also presented. The results show that the proposed method enjoys the higher accuracy than the conventional second-order method on the same mesh. When the same accuracy is achieved, the present high-order method has superior computational efficiency to the second-order counterpart. [ABSTRACT FROM AUTHOR]

Al-doped ZnO thin films (AZO) have been deposited on amorphous glass substrates by DC sputtering at different substrate temperatures Ts. X-Ray diffraction results reveal that AZO thin films have a hexagonal wurtzite structure with (002) preferred orientation. (002) peaks indicate that the crystalline structure of the films is oriented with c-axis perpendicular to the substrate. Three-dimensional (3D) atomic force microscopy images of AZO thin films deposited on glass substrate at 200 °C, 300 °C, and 400 °C, respectively, shows the improvement of the crystallinity and the homogeneity of AZO thin films with Ts which is in agreement with the noise measurements. The noise was characterized between 1 Hz and 100 kHz and we have obtained 1/f spectra. The noise is very sensitive to the crystal structure especially to the orientation of the crystallites which is perpendicular to the substrate and to the grain boundaries which generate a high current flow and a sharp increase in noise. Through time, Rsh and [αμ]eff increase with the modification of the crystallinity of AZO thin films. Study of noise aging shows that the noise is more sensitive than resistivity for all AZO thin films. [ABSTRACT FROM AUTHOR]

Except for a few anomalous solids and liquids, materials expand upon heating. For liquids, this should be reflected as a shift in the peak positions in the pair correlation function, g(r), to higher r. Here, we present the results of a detailed study of the volume thermal expansion coefficients and the temperature dependences of g(r) for a large number of binary, ternary, and quaternary liquids in the equilibrium and supercooled (metastable liquid below the liquidus temperature) states. The data were obtained from x-ray scattering and volume measurements on levitated liquids using the electrostatic levitation technique. Although the volumes of all liquids expand with increasing temperature, the peak positions in g(r) for the first coordination shells contract for the majority of alloy liquids studied. The second and third peaks in g(r) expand, but at rates different from those expected from the volume expansion. This behavior is explained qualitatively in terms of changes in the coordination numbers and bond-lengths as clusters in liquids break up with increasing temperature. [ABSTRACT FROM AUTHOR]

In this work, we used a template-free method to synthesize zinc sulfide (ZnS) materials. The photocatalytic performances of the samples were evaluated, and the physical natures of the ZnS nanocrystals were determined by photoluminescence (PL). Interestingly, the temperature-dependent PL variations of the samples were very different in connection with the synthesis condition. Combined with a series of catalytic experiments, it suggested that the intrinsic self-absorption of PL and photon recycling play key roles in photocatalysis. This work gives a new idea for understanding the photocatalysis and presents a new strategy to design ZnS related photocatalysts for further applications. [ABSTRACT FROM AUTHOR]

Strain-engineered phase boundaries in epitaxial bismuth ferrite films has been investigated via thermodynamics analysis in good agreement with both experimental and first principle studies, and a novel orthorhombic-rhombohedral (OR) phase boundary is found to exist under tensile misfit strain. In contrast to more widely studied tetragonal-rhombohedral phase boundary in bismuth ferrite where enhanced piezoelectric response is largely attributed to extrinsic mechanism, the OR phase boundary is found to show enhanced intrinsic piezoelectric response, and the change of the polarization slope at phase boundary is found to be the key to the enhancement. Difference between strain-engineered phase boundaries and classical morphotropic phase boundary in lead zirconate titanate is also noticed. [ABSTRACT FROM AUTHOR]

Metal-semiconductor-metal ultraviolet photodetectors were fabricated by using the sputtered Ga-doped ZnO (GZO) thin films on sapphire substrate as an active layer. Current-voltage (I-V) and opto-electrical characteristics of the devices were investigated. It is found that the peak optical responsivity of the devices can be significantly improved by selecting appropriate thermal annealing temperature, i.e., from 12.0 A/W (annealed at 500 °C) and 54.0 A/W (700 °C). Furthermore, dark current of the devices drops by two orders of magnitude after annealing process. The significant improvement in performance of the device is ascribed to the removal of massive defect centers of the GZO thin films and increase of Schottky barrier height between the GZO and metal electrodes after thermal annealing at appropriate temperatures. [ABSTRACT FROM AUTHOR]

The oblique drop impact on the thin film is numerically investigated in this paper with special attention paid to its splashing dynamics at moderate impingement angles (45° ≤ α ≤ 75°). A three-dimensional multiphase lattice Boltzmann flux solver associated with the diffuse interface method is adopted after being validated against reference data. Efforts are made to recover the complex flow features in the oblique drop impact on the thin film at various impingement angles, film thicknesses (δ), Ohnesorge numbers (Oh), and Weber numbers (We). We found that the later stage of radial propagation of the jet base and the free rim is dominated by inertia and can be well correlated with dimensionless time τ through the square-root law. The elevation of the free rim exhibits a linear relationship with time and varies with Oh and We, indicating its connection to the splashing of minor droplets, which is also an outcome of inertia, viscosity, and surface tension. Moreover, the onset of droplet splashing is generally insensitive to δ. Based on that, a correlation between the splashing limit and the impingement angle is established and shows good agreement with numerical results at moderate impingement angles. [ABSTRACT FROM AUTHOR]

An immersed boundary–simplified lattice Boltzmann method (IB-STLBM) is proposed in this paper for the simulation of incompressible thermal flows with immersed objects. The fractional step technique is adopted to resolve the problem in two successive steps. In the predictor step, the simplified thermal lattice Boltzmann method (STLBM) is utilized to resolve the intermediate flow variables without considering the immersed objects. The STLBM is advantageous over the conventional thermal lattice Boltzmann method (TLBM) in memory cost, boundary treatment, and numerical stability. In the corrector step, the boundary condition-enforced immersed boundary method (IBM) is used to give correction values of velocity and temperature for accurate interpretation of the Dirichlet boundary conditions on the surface of the immersed objects. Based on the present IBM, some novel strategies can be applied in the evaluation of hydrodynamic forces or thermal parameters of the immersed objects. Five numerical examples are presented for comprehensive validation of the accuracy and robustness of IB-STLBM in various two- and three-dimensional thermal flow problems. [ABSTRACT FROM AUTHOR]

Cu-doped ZnSe/ZnS/L-Cys core–shell QDs are prepared by both nucleation doping and growth doping in an aqueous synthesis method. Transport of photogenerated free charge carriers (FCCs) in these Cu-doped QDs is probed via a combination of surface photovoltaic (SPV), photoacoustic (PA), and electric-field-induced SPV techniques, supplemented by the UV–VIS absorption spectrum and Raman spectrum. The results confirm that the two doping mechanisms result in different doping locations and microelectronic structures of the Cu-doped QDs. The distinctive microelectronic structure of the QDs prepared by nucleation doping, as compared with those prepared by growth doping, results in a number of favorable SPV characteristics. For example, the QDs prepared by nucleation doping exhibit a higher SPV response intensity at 600 nm because of a higher concentration of photogenerated FCCs. The ratio of the strongest SPV response and the strongest PA signal of the QDs prepared by nucleation doping is up to 2.41 times greater than those of the QDs prepared by growth doping. This is because the greater numbers of photogenerated FCCs in the QDs prepared by nucleation doping generate the PV effect rather than the PA effect that is caused by a nonradiative de-excitation process. The position of the shoulder peak of the SPV response at a long wavelength of the QDs prepared by nucleation doping is significantly red-shifted compared with that of the QDs prepared by growth doping, leading to a broader SPV response range in the visible region. The QDs prepared by nucleation doping have a more obvious donor feature than those prepared by growth doping. [ABSTRACT FROM AUTHOR]

The recently discovered three-dimensional topological insulator Bi2Te3 is studied as function of pressure in terms of crystal structures, resistance, and Hall coefficient. The superconductivity is found in phase I (ambient phase) Bi2Te3 with Tc ∼ 3 K, which is related to the topological features. The evolution of crystal structure with pressure is investigated by high pressure synchrotron radiation experiments that reveal structural transitions occurring at about 8 GPa, 13 GPa, and 16 GPa, respectively. Furthermore, the high pressure phases of Bi2Te3 are also superconducting but with much higher Tc ∼ 8 K. The superconducting transitions are compared with those for Bi, Te elements. A global phase diagram of Bi2Te3 as function of pressure up to 30 GPa is obtained. [ABSTRACT FROM AUTHOR]

A monolithic, epitaxially-integrated, vertically-aligned, multi-band photodetector architecture has been demonstrated via the successful growth and fabrication of metamorphic back-to-back n-i-p/p-i-n In0.61Ga0.39P/In0.14Ga0.86As visible/near-IR dual-detector devices. The back-to-back diode design enables simultaneous and independent operation of detectors in both bands with low optical cross talk (<-10 dB outside the 690-720 nm range) and complete electrical isolation between the sub-detectors. The high electronic quality of the resultant metamorphic materials was confirmed via deep level transient spectroscopy, which revealed total trap concentrations of 5 × 1012 cm-3 for the In0.14Ga0.86As and 2 × 1014 cm-3 for the In0.61Ga0.39P sub-detectors, enabling low, room temperature reverse bias (-2 V) dark current densities of 4 × 10-8 A cm-2 and 7 × 10-12 A cm-2, respectively. High responsivity and specific detectivity values, at a working bias of -2 V, were measured: 0.41 A/W and 8.6 × 1011 cm Hz1/2/W for the In0.14Ga0.86As sub-detectors (at 980 nm), and 0.30 A/W and 2.0 × 1014 cm Hz1/2/W for the In0.61Ga0.39P sub-detectors (at 680 nm). The successful integration of high-quality lattice-mismatched materials, combined with the excellent sub-detector performances, demonstrate the potential for extending such a multi-band photodetector technology to achieve simultaneous detection of a wide range of wavelength bands with tunable cut-off wavelengths. [ABSTRACT FROM AUTHOR]

Correlation between the elastic modulus (B) and the Raman shift (Δω) of TiO2 and their responses to the variation of crystal size, applied pressure, and measuring temperature have been established as a function depending on the order, length, and energy of a representative bond for the entire specimen. In addition to the derived fundamental information of the atomic cohesive energy, binding energy density, Debye temperature and nonlinear compressibility, theoretical reproduction of the observations clarified that (i) the size effect arises from the under-coordination induced cohesive energy loss and the energy density gain in the surface up to skin depth; (ii) the thermally softened B and Δω results from bond expansion and bond weakening due to vibration; and, (iii) the mechanically stiffened B and Δω results from bond compression and bond strengthening due to mechanical work hardening. With the developed premise, one can predict the changing trends of the concerned properties with derivatives of quantitative information as such from any single measurement alone. [ABSTRACT FROM AUTHOR]

A complete study is given in this paper on the structural properties of Ba(Sr,Ti)O3 (BST) thin films which present various preferred orientations: (111) and (001) fiber and epitaxial textures. The films are deposited in situ at 800 °C by sputtering on Si/SiO2/TiOx/Pt substrates and the orientation is controlled by monitoring the concentration of O2 in the reactive plasma or by prior deposition of a very thin TiOx buffer layer between BST films and substrates. The epitaxial films are obtained on (001)-alpha-Al2O3 substrates covered with TiOx buffer layers. In order to analyze finely the preferred orientations, the texture, the microstructural features, and the anisotropy-related quantities such as residual stresses in the films, the conventional Bragg-Brentano θ - 2θ x-ray diffraction diagrams is shown not to be sufficient. So, we systematically used x-ray combined analysis, a recently developed methodology which gives access to precise determination of the structure (cell parameters and space group) of the films, their orientation distributions (texture strengths and types) and mean crystallite sizes, their residual stresses. This fine structural analysis shows important modifications between the film qualities which induce differences in BST films electrical behavior, permittivity, loss tangent, and tunability. [ABSTRACT FROM AUTHOR]

The microstructure and magnetic viscosity of bulk amorphous Nd60Fe20Al5Co10B5,prepared by suction casting the molten alloy into a copper mold under an argon atmosphere, have been investigated. The results show that clusters with size 3-5 nm are found to be embedded in the amorphous matrix of as-cast bulk amorphous Nd60Fe20Al5Co10B5 alloy. The Nd60Fe20Al5Co10B5 alloy shows hard magnetic behavior at room temperature, with an intrinsic coercivity of 360 kA/m and a remanence of 69.39 mT. The magnetic viscosity of bulk amorphous Nd60Fe20Al5Co10B5 has been investigated on the major hysteresis loop, and simple logarithmic time dependence is observed. A value for the fluctuation field of 8.24 kA/m is obtained. Analysis based on a Henkel plot is used to confirm the existence of magnetic interaction among clusters. The coercivity mechanism responsible for the hard magnetic behavior of bulk amorphous Nd60Fe20Al5Co10B5 alloy is also discussed. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy (XPS) and contact angle measurements have been made to characterize patterned organic light-emitting-diode (OLED) substrates comprising indium-tin-oxide and a photoresist, both of which are modified by treatment with oxygen and tetrafluoromethane in a radiofrequency (13.56 MHz) low-power (∼1 W) capacitively coupled plasma as a function of time. Correlations between the surface chemical compositions from XPS and the contact angle, θ, are evaluated in order that the wettability of very small areas may be predicted. Very clear correlations for both the indium-tin-oxide and the photoresist surfaces are obtained enabling the prediction of the contact angles for these plasma-treated OLED materials from XPS data to a standard uncertainty of 9% in cos θ. These correlations need to be extended to a wider range of compositions in order to establish the physicochemical properties of particular surface functional groups that control water contact angles by this method. [ABSTRACT FROM AUTHOR]

ZnO nanotubes (ZNTs) have been successfully evolved from ZnO nanorods (ZNRs) by a simple chemical etching process. Two peaks located at 382 and 384 nm in the UV emission region has been observed in the room temperature photoluminescence (PL) spectrum of ZNTs since the surface band bending in ZNTs induces the coexistence of indirect and direct transitions in their emission process. In addition, a strong enhancement of total luminescence intensity at room temperature in ZNTs has also be observed in comparison with that of ZNRs. Both temperature-dependent PL and time-resolved PL results not only further testify the coexistence of indirect and direct transitions due to the surface band bending but also reveal that less nonradiative contribution to the emission process in ZNTs finally causes their stronger luminescence intensity. [ABSTRACT FROM AUTHOR]