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Antiferroelectric materials are proposed as a potential solution to achieve multi-state memories, but the fundamental physical mechanism underlying the memory effect still needs to be clarified. Here, we study the memory effect in a typical antiferroelectric ceramic of Pb0.99Nb0.02[(Zr0.6Sn0.4)0.95Ti0.05]0.98O3 by systematically analyzing various hysteresis loops of polarization intensity and current density vs. electric field, where the kinetic behaviors are concerned about for the first time. The parallel pre-poling electric field reduces the critical electric field of antiferroelectric-ferroelectric phase transition, while the antiparallel field increases it. The memory behavior is significantly enhanced with the increasing of pre-poling time, but exhibits a remarkable weakening with the relaxation time increasing. It is a combined effect of electric-field-induced preferentially oriented antiferroelectric domains and internal bias electric field. This work not only improves comprehending in memory effect in antiferroelectric materials, but also enlightens the deeper understanding of other physical properties related to field-induced phase transitions.

This study investigates the search capability, stability, and computational efficiency of four improved penalty-free constraint-handling techniques (CHTs), including the death penalty, the Deb rule, the filter method, and the mapping strategy, in structural optimization using harmony search (HS). The first three general-purpose CHTs have been improved by hybridizing with a structural analysis filter strategy to enhance their computational efficiency based on the characteristics of structural optimization and the solution updating rule of the HS. This study also has modified the mapping operator of the mapping strategy to handle size and shape optimization with Euler buckling constraints. Four numerical examples examine the performances of these CHTs. The comparative results show that the mapping strategy exhibits apparent superiority both in search capability and stability among the four. However, it also demands the most computational cost, and the improved Deb rule becomes the most competitive method while considering computational efficiency. The difference between the death penalty and the Deb rule method is that the feasible solution initialization process required by the death penalty method will deteriorate its computational efficiency in problems with small feasible space. The filter method always reserves some infeasible solutions to guide the search in the iteration process. However, its performances are inferior to the other three approaches in four benchmark problems.

Modeling error and measurement noise are inevitable and lead to a significant discrepancy between Finite element model (FEM) and a real structure. Finite element model updating (FEMU) is, therefore, necessary to match the measured data with a predicted response from FEM for advancing structural health monitoring (SHM). Bayesian approach has been proposed to identify the most probable values (MPVs) of physical parameters and provide parameters’ uncertainties. However, the current Bayesian approach has challenges in high-dimensional problems and requires high computational costs in the complex structure. In this study, a new Bayesian updating framework is proposed using Differential Evolution Adaptive Metropolis (DREAM) sampling method with a variance-based global sensitivity analysis (GSA) and Kriging model to enhance the Bayesian approach’s performance and computational efficiency. Firstly, variance-based GSA is used to eliminate insignificant parameters to measured responses and reduce model dimensionality. Secondly, a Kriging model is employed as a surrogate of the time-consuming FE model for reducing the computational burden. DREAM is essentially a multi-chain sampling method, which parallelly runs different paths for all possible solutions and accurately approximates the posterior distribution density function (PDF) for the Bayesian approach. The demonstration of the proposed updating framework of a real-world cable-stayed pedestrian bridge is presented.

To overcome the inaccurate frequency band division in empirical wavelet transform (EWT) induced by high noise and modulation edge band, this study proposes an improved EWT (IEWT) and applies it to operational modal analysis (OMA) in civil structures. The IEWT segments the frequency band using spectral trend determined with removing the high-frequency components of the Fourier spectrum. The synchroextracting transform is employed to denoise the frequency components obtained from IEWT combined with the random decrement technique and Hilbert transform to identify modal parameters. The effectiveness of IEWT and the proposed modal analysis method is comprehensively verified by a full-scale cable-stayed footbridge. The results demonstrate that the proposed IEWT, random decrement technique, and Hilbert transform can accurately identify the modal parameters from multi-setup ambient vibration measurements.

Background: To investigate the expression of microRNA-29c (miR-29c) in glioma and its effects on cell proliferation and apoptosis. Methods: A retrospective analysis was performed on 76 glioma patients in People's Hospital of Weifang, Weifang, Shandong, China from May 2013 to June 2017 (experimental group) and 63 healthy subjects in the same period (control group). qRT-PCR was used to detect the miR-29c expression. Changes of serum miR-29c expression level and the correlation of miR-29c of glioma patients with the degree of tumor differentiation and pathological type were observed. Cells were grouped before transfection into blank group (no transfection), negative control group (transfected with miRNA NC) and experimental group (transfected with miR-29c mimics). CCK-8 assay was used to detect cell proliferation, flow cytometry to detect apoptosis. Results: Expression of miR-29c in serum was significantly lower in experimental group than that in control group (P

The phase composition and their evolution in ferroelectrics are very complex near the morphotropic phase boundary (MPB), especially under multiple fields of electric field and temperature, which results in versatile behaviors of electrocaloric effect (ECE). This paper systematically studied the phase transitions and associated ECEs in the 〈001〉, 〈011〉 and 〈111〉 oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-30PT) single crystals with the chemical composition in the MPB area. Based on the dielectric and polarization responses under multi-fields, the refined electric field-temperature phase diagrams are established, wherein the ECE properties are closely related to the electric-field-induced phase transitions and exhibit a complex evolution across positive and negative values. The negative ECE originates from the transition from a monoclinic phase to a tetragonal or orthogonal phase under the noncollinear electric field, so it only appears in the 〈001〉 or 〈011〉 oriented crystals. Conversely, the transition from the tetragonal phase to the rhombohedral or orthogonal phase in the 〈111〉 or 〈011〉 oriented crystals induces a positive ECE peak with ∆Tmax = 0.40 K (@10 kV/cm). Just above Tm, the positive ECE reaches ∆Tmax = 0.61 K, 0.63 K and 0.68 K in the 〈001〉, 〈011〉 and 〈111〉 oriented crystals, respectively. In addition, there is an abnormal net endothermic phenomenon around the monoclinic-tetragonal or monoclinic-orthogonal phase boundaries due to the electric-field-induced irreversible transition.

Relaxor ferroelectrics, with polar nanoregions (PNRs), are good candidates for electrocaloric (EC) refrigeration. This study investigates the EC performance of the Pb1−1.5x La x Zr0.8Ti0.2O3 relaxor ferroelectric ceramics by the direct measurement using a modified differential scanning calorimeter. All the ceramics exhibit pure perovskite phase with a dense microstructure. The results indicate that the increasing La substitution strengthens the relaxor behaviour, promotes the transition from non-ergodic to ergodic state, and enhances the thermal stability of EC property (instability η

Electron beam melting was utilized to investigate the behavior of carbon flow by melting 100 g of multi-crystalline silicon in an electron beam furnace for five minutes. Carbon and nitrogen are the constituent impurities in contaminated Si samples with an average weight of 13 % and 9, respectively. The electron beam melting experiment caused redistribution of the impurities along the periphery and bottom of the Si sample with a pie-shaped structure. Investigations through scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed that the impurities were silicon nitride and silicon carbide. It was determined that Si3N4 has a rod-shaped microstructure, whereas SiC has a granular morphology. By segregating the impurities redistributed through this technique, pure Si was obtained in the remaining sample.

Removal of boron from silicon is a tough task by traditional directional solidification and vacuum refining techniques, due to its large and inappropriate segregation coefficient and low saturated vapor pressure. At high temperature boron react with oxygen to form volatile boron oxides which can be evaporated. So, the removal procedure of boron from silicon melt is investigated by incorporating a small amount of water vapor above the melted surface. The results show that boron is oxidized to mainly form BO and evaporated with 28% removal efficiency by average. It is considered that oxygen atoms experience a series of physical and chemical processes, such as a chemical reaction in the bulk of the melt, evaporation from the melt surface, transportation across the gas phase and ionization due the electron beam, which is conducive to the continuous removal of boron.

Electrocaloric effect (ECE) in ferroelectric (FE)/antiferroelectric (AFE) materials offers a promising high-efficient and zero-emission solid-state cooling technology, whose materials design is usually focused on the morphotropic phase boundary (MPB) between two FE phases. This work constructs an MPB between an orthorhombic AFE and a rhombohedral FE phase in Pb

This study introduces the dynamic impact factor (IF) assessment of a concrete filled steel tube (CFST) butterfly arch bridge with both experimental and numerical results. The modal parameters are identified from the measured accelerations and the IFs are computed from the dynamic strain responses. Four well-known bridge design codes are applied to assess the experimental IFs. A vehicle-bridge coupled vibration system is established to numerically investigate certain effects of vehicle speed, road roughness and structural damping on the IF. Both experimental and numerical results indicate that the IFs of distinct structural components vary significantly, suggesting that a uniform formula is insufficient to describe the impact effect of the whole bridge, which has been generally adopted in many bridge design codes. For the irregular shaped CFST arch bridge, the experimental method is currently the most accurate way to determine dynamic IF. New methodologies must be developed to support the engineers to design safer complex bridges and new formulations must be developed to be part of the bridge codes.

Footbridges usually suffer from vibrations induced by the actions of pedestrians, which calls for various control measures to improve the serviceability. This study described the dynamic analysis and Tuned Mass Damper (TMD) implementation for a single-pylon cable-stayed footbridge scaled model, aimed at providing an experimental case study regarding of vibration control design of slender structures. A scaled model for the real footbridge was designed based on similarity principles. Then, the dynamic behavior of the footbridge was assessed by ambient vibration tests. The natural frequencies and mode shapes were identified from operational vibration measurements by covariance-driven stochastic subspace identification algorithm. The frequency of first vertical bending modes is 2.10 Hz, falling into the human walking frequency range [1.6, 2.4] Hz. Therefore, the footbridge needs vibration control to improve its serviceability. Finally, a self-made TMD using lead, spring and oil buffer was implemented on the scaled model of the footbridge. The laboratory forced vibration test was employed to illustrate the effectiveness of the TMD. By installing TMD, the acceleration response at mid-span of the footbridge was remarkably reduced. The study could provide meaningful reference for vibration control design of the full-scale footbridge.

Carbon and their compounds were removed successfully through electron beam melting (EBM), so that those areas (contaminated with carbon) of ingot were recycled and reused. During EBM process, the numerical simulation results show that there is great temperature gradient existing in the melt. During EBM, the melt near copper crucible shows low temperature and bad fluidity. Carbon in silicon melt flows, precipitated and gathered in this area so that it is separated. The flow mechanism of SiC in silicon melt was investigated. After EBM, carbon enriches in the form of SiC at the bottom of the ingot but not in the center. This technology is applied on industrial scale EBM equipment. The results show that a majority of SiC was deposited in the bottom of the refining crucible and the carbon contaminations are not found in the most of the area of the solidified ingot in crucible.

The electrocaloric effect (ECE) in the ferroelectric ceramics is determined by both the composition and the microstructure. This paper demonstrated the influences of the microstructure features on the ECE in BaTiO 3 ceramics. When the sintering temperature rises, the particles are fused together, the grain size is enlarged and the pore amount decreases, so the ECE ΔT max increases significantly. If the sintering temperature further rises to 1300 °C, the intergranular pores transform to intragranular, so the ΔT peak is enhanced but the value other than the peak is reduced. The ΔT max lowers slightly since the amount of intragranular pores gradually reduces after a second sintering for long time. The clarification of the influences of the microstructure features is instructive for the ECE material design for practical applications.

This paper demonstrated the thickness dependence of electrocaloric effect (ECE) in Ba0.8Sr0.2TiO3 ferroelectric ceramics. The high-temperature sintered sample has inhomogeneous properties along the thickness direction although the microstructure has uniform features throughout. The core zone exhibits a much lower resistivity than that of the whole sample because of more ions' valence variation. Under a same electric field of 30 kV/cm, the ECE ΔT drops from 1.35 K to 1.12 K by reducing the thickness step by step. But the thinnest core sample can sustain much higher electric fields (>50 kV/cm) and exhibits a larger ΔT of 1.67 K, i.e. it has a high ECE value despite a low ECE strength.

A new method for SiC elimination from multicrystalline silicon with Al addition by using the chemical reaction between Al and SiC is conducted in this study. Inclusion-free region is obtained when Al addition content increases to 5.4% and 7.9%. SiC particles tend to pile up around Al during the process and precipitate at ingot bottom. Furthermore, Al-Si alloying occurs at the inclusion-free region. The electron probe micro analysis mapping illustrates the existence of carbon in the precipitated Al which indicates the occurrence of chemical reaction between SiC particles and Al during the process. The results can be an effective way to eliminate SiC for silicon scraps recycling.

Computational cost reduction and the best solution seeking are frequently encountered during model updating for complex structures. In this study, a hybrid algorithm using kriging model and genetic algorithms (GAs) is proposed for updating the Finite Element (FE) model of complex bridge structures employing both static and dynamic experimental measurements. The kriging model is first established to approximate the implicit relationship between structural parameters and responses, serving as a surrogate model for complex FE model when deriving analytical responses. An objective function is later defined based on the residual between analytical response values and experimental measured ones. GAs are finally employed to find the best solution by searching on the whole design space of updating parameters selected based on a sensitivity analysis. To verify the proposed algorithm, Caiyuanba Yangtze River Bridge, a double decked of roadway and light railway bridge with a main span of 420 m is used. Both frequencies and displacements predicted by the updated model are more close to experimental measured ones. The results show that the kriging surrogate model has good accuracy in predicting response and can be used as a surrogate model to reduce computational cost, and GAs provide a higher chance to obtain global best solution.

This paper demonstrated the electrocaloric effect (ECE) in BaTiO 3 ceramics with Ce doping in either A or B sites, which were prepared by the solid-state reaction method. All sintered samples have pure perovsikte phase, whether Ce doping in A or B sites, but the properties are different from each other. For A-site doping of Ba 1-x Ce x TiO 3 , the Curie temperature gradually shifts to lower temperature because the doped Ce ion have smaller radius than Ba ion, while the phase transition is diffused and the latent heat drops. Then the ECE ΔT peak shifts accordingly and ΔT max reduces gradually except small Ce doping. For B-site doping of BaCe x Ti 1 -x O 3 , the phase transition is diffused more significantly but the Curie temperature hardly moves, so that the ECE peak is depressed but does not shift.

A large amount of silicon in the form of silicon scraps is wasted annually in photovoltaic industry because of the presence of silicon carbide inclusions. Silicon carbide inclusions must be eliminated so that silicon scraps can be recycled. This study investigated the electromagnetic separation of silicon carbide inclusions in multicrystalline silicon by imposition of supersonic-frequency magnetic field. Silicon carbide particles tend to migrate to the ingot side and to the top and bottom of the central region of the ingot under increasing holding time. During separation process, the penetrating aluminum can react with silicon carbide and then dissolve some of the inclusions. In this work, the separation efficiency reaches up to 89.3% at a holding time of 45 min. This method is a potentially effective means of recycling silicon scraps.

The behavior of boron redistribution in silicon with and without oxide layer after electron beam injection (EBI) was investigated. Special defect shapes were generated on the surface of bare and oxidized silicon wafers. Secondary ion mass spectrometer was used to measure the boron profile. The results showed that after long EBI time, boron tended to be induced from both sides of the transition region between the oxide layer and silicon. For the sample without oxide layer after EBI, boron tended to diffuse towards the surface and its concentration obviously reduced inside the silicon. The results of the study show the potential use of the process in removing boron impurity in silicon.

Relaxor ferroelectrics continue to attract great attention for applications, including electrocaloric refrigeration, but the commonly used, indirect method of electrocaloric characterization based on the Maxwell relation often leads to artifacts. This analysis of long- and short-range ferroelectric order and the electrocaloric effect in Pb${}_{0.91}$La${}_{0.06}$Zr${}_{0.8}$Ti${}_{0.2}$O${}_{3}$ uses both direct and indirect characterizations, to clarify the applicability of the Maxwell relation to the physics of the relaxor, and the origin of discrepancies. It also suggests how to design relaxors with large electrocaloric effect by exploiting the transitions between polar nanoregions.

As an emerging solid-state refrigeration technology with zero-emission and high energy conversion efficiency, there is a compelling need for ferroelectric materials with giant electrocaloric effects (ECEs) at room temperature suitable for refrigeration applications. The complex perovskite antiferroelectric (AFE), PbMg0.5W0.5O3, containing non-equivalent B-site ions with a symmetric giant positive and negative ECE near room temperature is presented. At the Curie temperature of 36 °C, the first-order AFE–paraelectric phase transition gives rise to a large enthalpy change of 3.92 J g−1, more than four times that of BaTiO3. This leads to a significant ECE under the influence of an electric field. The direct electrocaloric characterization shows that the adiabatic temperature change, ΔT, exhibits symmetric peaks with a giant positive maximum of 1.79 K (ΔS = 1.68 J kg−1 K−1) at 36 °C and a negative maximum of −2.02 K (ΔS = −1.93 J kg−1 K−1) at 34 °C. The ultrahigh magnitude of ΔT near room temperature makes PbMg0.5W0.5O3 a superior electrocaloric material far beyond traditional PbZrO3-based AFEs. The coexistence of symmetric giant positive and negative ΔT to further improve cooling efficiency is expected. In addition, the good reversibility and negligible leakage current should pave the way for practical applications.

To improve the calculation efficiency and to avoid the updating results being affected by optimization algorithms, a direct calculation of updating parameters method based on Kriging model for model updating is proposed in this paper. The proposed method first generates the data samples of updating parameters by using Latin hypercube Design (LHD). The corresponding structural response is calculated by initial finite element model. Then, the explicit function between updating parameters and structural responses is obtained based on kriging theory. Finally, the best design parameters are directly solved using the experimentally obtained structural response as the objective value based on the established Kriging model. Model updating of Caiyuanba Yangtze River Bridge is employed to test the proposed method. The results show that the model updating based on direct calculation method avoids the iterative calculation and improves the computational efficiency. The proposed method can provide the approximate accuracy level compared with the traditional Kriging model method.

The development of photovoltaic industry demands great amount of multicrystalline silicon. Carbon and SiC in silicon need to be contained in a limited amount since they can cause great adverse affect to solar cells. The behavior of carbon and its precipitation SiC in silicon by electron beam melting (EBM) with a slow cooling pattern was investigated in this study. SiC is found to sedimentate to ingot bottom after EBM. The presence of Si 3 N 4 can be heterogeneous nucleation agent for SiC to nucleate continually and both of them precipitate to the ingot bottom. The comprehensive effect of slow solidification condition, temperature gradient and melt convection causes the sedimentation of SiC. It is also found that oxygen plays an important role on the migration of the dissolved carbon. The formation of carbon-oxygen complexes tend to migrate to ingot top since oxygen can transfer from silicon melt to vacuum environment during EBM.

Ferroelectrics are promising candidate materials for electrocaloric refrigeration. Materials with a large electrocaloric effect (ECE) near room temperature and a broad working temperature range are getting closer to practical applications. However, the enhanced ECE is always achieved under high electric field, which limits their wide cooling applications. In this paper, the phase diagram of lead-free BaHf x Ti 1−x O 3 (BHT) ferroelectric ceramics was established. A large ECE under relatively low electric field ( ΔE = 10 kV/cm) is firstly reported in BHT ferroelectric ceramics. The direct temperature change ( ΔT = 0.35 °C under 10 kV/cm) in BHT ceramics is comparable with those reported in the literature under high electric fields. Meanwhile, the electrocaloric efficiency ( ΔT/ΔE = 0.35 K mm kV −1 under 10 kV/cm) is thirteen percent higher than the best value reported previously under high electric field ( ΔE = 145 kV/cm). We demonstrate that the ECE can be greatly enhanced by tuning the composition of the lead-free BHT ceramics to its first-order phase transition (FPT), invariant critical point (ICP) or diffuse phase transition (DPT). It is shown that the enhancement in ECE is strongly dependent on the nature of structural phase transition and electric field coupling effect, which has been confirmed by both the indirect and direct ECE measurements. A phenomenological explanation based on Landau model was also proposed to understand this phenomenon. Our findings in this work may provide a better understanding and design methodology for developing more practically useful electrocaloric materials.

The recycling of Si scraps has become a serious concern in the industry because of the increasing amount of Si waste generated during ingot production. In this work, an operative method is proposed to process Si scraps and separate SiC from Si by coupling electromagnetic field melting with Al/SiC wetting and interaction. This method yields an inclusion-free SiC particle-enriched region that tends to migrate to the top of ingots with increasing melting time. A micron-grade SiC-rich layer is formed at the ingot edge. A petal-shaped SiC particle group is formed by Al addition and precipitates at the bottom of the ingot. A separation efficiency of 88.1% is obtained after melting for 45 min. The results show that the proposed process is an effective way to eliminate SiC from recycled Si scrap.

Due to insufficient test data, insufficient constraint equations and uncertain objective function, the local optimal solution and the global optimal solution of the objective function in finite element model updating may represent the actual parameters of the structure. Based on this, this paper proposes an improved artificial fish school algorithm. By combining the niche technology with the artificial fish school algorithm, the improved algorithm can systematically find multiple global optimal solutions and local optimal solutions of the objective function. Aiming at the difficulty of determining the niche radius, an adaptive niche radius mechanism is proposed. The improved algorithm is used to study the multi-alternatives problem of finite element model updating after verifying its feasibility through numerical simulation analysis. In the case of benchmark framework model updating, it is confirmed that multi-alternative problems exist and the global optimal solution of the objective function does not necessarily represent the true parameters of the structure. In case 2, the improved algorithm combined with the Kriging model is applied to the model updating of a cable-stayed footbridge, and 15 sets of solutions are obtained, in which the error objective function values of the measured and theoretical values of the bridge modes are close but the solutions are completely different. Combining with the actual bridge condition and reanalysis technology, the author takes the suboptimal solution 2 as the most representative solution of the bridge parameters, which reduces the possibility of misjudgment of structural parameters.

In this paper, alternating electromagnetic field and directional solidification are used to separate SiC and Si3N4 in polycrystalline silicon tailings. It is found the inclusion particles move downward at the center of the ingot and moving upward at the edge of the ingot by a variety of forces during the directional solidification process. The electromagnetic force accelerates the melt flow and enhances the lift force, so that larger particles can be pushed to the top of the ingot. Rod-shaped Si3N4 and block-shaped SiC particles show symbiotic relationship between each other. The aggregation of inclusion particles adsorbs metallic impurities, especially volatile metals, due to the effects of mushy region and short-circuit diffusion. The average conversion efficiency of the solar cells (Al-BSF method) prepared using the recycled silicon reached 18.56%, which meets the demand of the solar cells.

The exploration of new color-tunable materials for solid-state lighting based on InGaN semiconductors has attracted great attention. Herein a series of Ce3+, Tb3+ and Ce3+/Tb3+ co-doped Y2Si3O3N4 phosphors have been developed. The intense green emission peaking at 543 nm was observed in the Y2Si3O3N4:Ce3+,Tb3+ phosphors. Energy transfer (ET) process from Ce3+ to Tb3+ was verified via the variations of the lifetime values of Ce3+, and the ET mechanism is ascribed to the dipole–dipole interaction. The ET critical distance has been calculated by the concentration quenching method. It is believed that the Ce3+/Tb3+-activated Y2Si3O3N4 phosphors can serve as potential materials for near ultraviolet (n-UV) light emitting diode (LED).

The behavior of carbon in multicrystalline silicon scraps by electron beam melting was investigated in this study. It was found that the process favors nucleation of SiC on Si 3 N 4. Furthermore, carbon tends to gather to top surface of the ingots with increasing melting time, and the reaction between oxygen and carbon favors carbon migration. The melt convection and temperature gradient caused by electron beam are employed to be the dominate reason the phenomenon occurs. The results can provide guidance in silicon recycling.