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3 at.% Er3+, x at.% Ho3+: SrF2 (x = 0, 0.05, 0.1, 0.5, 1, 2) transparent ceramics, as the potential material for the 2.7 μm solid-state laser, were fabricated by hot-pressed sintering. XRD, TEM, SEM, and EDS measurements were used to investigate the phase composition, morphology, microstructure, and distribution of the elements of the nanoparticles and transparent ceramics. Results showed that the Er3+ ions and Ho3+ ions do not alter the SrF2 crystal structure, and they are distributed uniformly in the sample. With the increase of the Ho3+ doping concentration, the lattice parameter decreased from 5.799 A to 5.784 A, and the average grain size decreased gradually. The maximum transmittance of as-obtained ceramics is approximately 93 % which is close to the theoretical transmittance of SrF2. Moreover, the absorption spectra, emission spectra, and the lifetime of Er3+ and Ho3+ were investigated. The energy transfer processes between Er3+ and Ho3+ were discussed. After co-doping Ho3+, the lifetime difference between Er3+:4I11/2 and Er3+:4I13/2 levels was shortened from 8.50 ms to 1.12 ms. All the results show that the incorporation of Ho3+ with proper doping concentration is beneficial for achieving 2.7 μm laser output in Er3+: SrF2 transparent ceramics.

x at. % Er3+, 3 at. % Dy3+: CaF2 transparent ceramics (x=1-5) with good transparency were fabricated by hot-pressed sintering. The phase composition of nanoparticles and transparent ceramics, microstructure, in-line transmittance, upconversion spectra and lifetime of transparent ceramics, as well as energy transfer mechanism between Er3+ and Dy3+ were investigated. The mean grain sizes of nanoparticles decreased from 33.0 nm to 26.2 nm with the Er3+ doping concentration increasing from 1 to 5 at.%. The microstructure of ceramic samples presented nearly dense microstructure and EDS analysis indicated Er3+ and Dy3+ were uniformly incorporated into CaF2 lattice. Under 900 nm excitation, the emission intensity for 4F9/2→6H15/2 transition of Dy3+ decreased and for 4S3/2→4I15/2 transition of Er3+ increased, the lifetime for the 4F9/2 level of Dy3+ decreased while the 4F7/2 level of Er3+ increased with the raise of Er3+ doping concentration. The energy transfer mechanism was proved to be the dipole-dipole interaction. The upconversion luminescence color was tuned from orange through yellow to green by changing the Er3+/Dy3+ ratio. In addition, the Vickers hardness, fracture toughness, and the thermal conductivity of Er3+, Dy3+: CaF2 transparent ceramics were discussed. All the results showed the Dy3+ could be used as a sensitizer for Er3+: CaF2 transparent ceramic in the upconversion field.

Sodium-ion batteries (SIBs) with huge cost advantages will show extraordinary talents in low-speed electric vehicles, energy storage, and base station communications. Manganese oxides are promising candidates for cathode materials, rapid capacity decay, and poor electrochemical performance that limit its commercial applications. Here, the nanosheets with exposed active crystal planes are prepared through a simple NH3∙H2O-assisted sol-gel process and subsequent high-temperature calcination. The unique structure considerably reduces the Na+ diffusion path for the excellent Na+ diffusion kinetics. The final results confirm that the NMO-pH6 sample, exposed to the active planes, has high energy density (557.9 Wh kg−1 at 0.1 C) and outstanding electrochemical performance, especially the rate performance (93.8 mAh g−1 at 5 C and 79.95 %, 100 cycles at 1 C). More importantly, it will facilitate the further construction of advanced cathode materials for high-performance SIBs.

Li-rich oxides are considered as the most commercial potential cathode materials due to the high theoretical specific discharge capacity. Here, ZrO2 in different crystalline states are applied as the coating layers to enhance the electrochemical performance of hollow Li[Li0.2Mn0.54Ni0.13Co0.13]O2 materials. Meanwhile, a series of characterizations (XRD, SEM, TEM, EDX etc.) are conducted to compare the effects of ZrO2 coating layer with different crystalline states on the host material. The results elucidate that the Li-rich Mn-based material with the polycrystal ZrO2 coating layer has a slight advantage in rate performance, while the host material with the single crystal ZrO2-coating layer has a better cycling performance and effectively suppresses voltage decay with the effect of excellently inhibiting layered to spinel-like phase transition and metal dissolution during charging and discharging process.

The artificial ground freezing (AGF) method has been widely used in underground engineering construction. As the main load-bearing elements of the AGF method, the strength of frozen walls is expected to play a crucial role in engineering stability. To improve the accuracy of quantitative evaluations of engineering stability, it is necessary to grasp the strength characteristics of frozen rock during service. To achieve this, the red sandstone taken from a frozen shaft project was tested via triaxial compression at different temperatures (−5°C,−10°C,−15°C,−20°C,−25°C, and −30°C). After that, a damage constitutive model with a Weibull distribution was derived to characterize the damage development of the frozen sandstone. Based on the validated model, the variation of damage degree was analyzed. The results show that the crack initiation stress, crack dilation stress, and peak strength all increase with decreasing temperature. The crack damage threshold increases as the frozen sandstone strength increases. The presented damage constitutive model can reflect the damage evolution of frozen sandstone. When the stress exceeds the crack initiation stress, the damage degree begins to increase, and it increases quickly when the stress approaches the peak strength. The model parameters can reflect the influence of negative temperatures on the strength of frozen sandstone. The crack damage threshold could be treated as an essential intrinsic property for predicting the failure process of frozen sandstones. The results can provide an important reference for the design and construction of frozen ground engineering.

An important source of time-dependent pile deformation is creep behavior at pile-frozen soil interface in permafrost regions. A creep model for pile-frozen soil/ice interfaces was proposed based on a series of multistage creep tests. The test results show that the creep behavior of the pile-frozen soil/ice interfaces is easily observed at a steady rate larger than 0 even at a small load level, which increases as the increase of load level. The elastic shear modulus increases at a slowing down rate with the increase of load level. The interfaces are mainly strengthened during the creep process until the occurrence of the accelerating creep, which is more obvious for frozen soil. A large amount of ice in frozen soil can enhance the creep rate and reduce the carrying capacity of pile foundation. The viscosity [Formula: see text] reflecting steady creep rate, the instantaneous shear modulus [Formula: see text], and the critical stress [Formula: see text] required for describing damage behaviors distribute in the form of Bigaussian asymmetric peak function with ice content. The Burger model considering ice effect and damage effect is feasible to describe the entire creep behavior of the interfaces. Sensitivity analysis reveals that ice content in frozen soil has a marked influence on pile deformation, a cooling method can probably adjust the creep deformation of pile in frozen soil with high ice content.

In cold regions, the long-term stability of engineering facilities is unavoidably influenced by the negative temperature, freeze-thaw process, dry-wet process, and dynamic loading conditions induced by earthquakes and traffic loads. In order to investigate the effects of different cyclic stress paths on the evolution of dynamic mechanical properties of frozen silt clay, a series of cyclic triaxial tests with variation confining pressure (VCP) or constant confining pressure (CCP) were performed. Triaxial low-temperature apparatus (MTS-810) was taken advantage of to simulating various cyclic stress paths by changing cyclic loading conditions of axial stress and confining pressure. In this paper, the evolution features of the axial resilient modulus, damping ratios, and the shape of hysteresis loops with an increase in the number of load cycles under different dynamic stress paths are comprehensively studied. The results show that the loading angle of cyclic stress path and the phase difference between cyclic axial stress and confining pressure are the main factors that remarkably affect the development characteristics of the resilient modulus and damping ratio. With increasing of the loading angle and phase difference, the resilient modulus increases, but damping ratio increases with increasing of loading angle and with decreasing of phase difference. With the continuous increase in the number of loading cycles, the samples of frozen soil show compacting and hardening characteristics. With an increase in the number of load cycles, the shape of hysteresis loop becoming narrows, the resilient modulus decreases at the initial stage and then gradually increases, and the damping ratio stably decreases. According to contrastively analyzing the evolution of dynamic parameters and the shape features of hysteresis loops under various cyclic stress paths, it can be clearly discovered that the evolution of sample microstructure and the development of dynamic characteristics of frozen samples have obvious dependence on the cyclic stress path. Therefore, the effects of variable confining pressure (VCP) on dynamic behaviors of frozen soils are nonnegligible in practical cold region engineering.

SrF2 transparent ceramic is a promising upconversion material due to the low phonon energy. The effect of different sintering temperatures on Er:SrF2 transparent ceramics was investigated. The suitable sintering temperature for Er:SrF2 transparent ceramics was 900 °C by hot-pressed sintering in this study. High quality of Er:SrF2 transparent ceramics with different doping concentrations were obtained. The upconversion luminescence spectra and decay behavior were compared between Er:SrF2 and Er:CaF2 transparent ceramics with different Er3+ doping concentration. The green emission of 5 at.% Er:SrF2 ceramic was much stronger than that of 5 at.% Er:CaF2 ceramic, while the red emission of Er:SrF2 ceramic was almost the same as that of Er:CaF2 ceramic. The upconversion luminescence lifetime of Er:SrF2 transparent ceramics was longer than that of Er:CaF2.All the results indicated Er:SrF2 transparent ceramics was a candidate for green fluorescent upconversion materials.

New Sn-Ti microspheres were first successfully synthesized by a PVP-assisted sol-gel method in this paper, and their performance in the B–V oxidation of cyclohexanone was investigated. The XRD, N2 sorption, SEM, Py-IR, UV–Vis, XPS, EDX, Elemental mapping and TEM characterization techniques were utilized to investigate their physical and chemical properties. Based on the proposal possible formation mechanism, in the MTS-x sample synthesis procedure, the introduction of PVP as a stabilizer and dispersant can coordinate the hydrolysis rate of two different precursors resulting in the hindrance of their agglomerations. And the HDA as a precipitation accelerator and morphology control agent can be beneficial to the formation of spheres by increasing the hydrogen-bonding interactions. The MTS-12 as well as the weight percent of tin to titanium species of 12 with specific regular microspheres has the highest cyclohexanone conversion of 97.8% and the highest e-caprolactone selectivity of 98.2%, which is better than the bulk Sn-TiO2 catalyst even though that the weight percent of tin to titanium species was 18. The catalysts with higher accessible active sites and shorter diffusion channels would provide a valuable theoretic reference for the industrial process of the B–V oxidation of cyclohexanone for the preparation of caprolactone.

Li-rich cathode materials have higher discharge capacity and lower cost than conventional electrode materials such as LiCoO2. However, they suffer from rapid capacity fading caused by irreversible phase transition and interfacial instability during the electrochemical cycling. La–Co–O (denoted as LC) compound possess good electronic conductivity and superior thermal stability, which could be used as a promising coating layer to suppress Mn dissolution as well as to facilitate electrical transfer. Furthermore, La–Co–O (LC) coating layer could decrease the Mn3+ ions on the surface of Li1.2Mn0.54Ni0.13Co0.13O2 (denoted as LMNC), thus stabilize the surface structure. Herein, we present La–Co–O (LC) coating layer on the surface of LMNC via an artful sol-gel-based method with a thickness below 50 nm. XPS, EDS and TEM tests were applied to confirm the existence of LC coating layer. 2 mol% LC coated LMNC sample shows much improved cycle stability at 1C (206.3 mAh g−1, 86.2% capacity retention after 100 cycles) and good rate capability especially at high rates. In addition, LC coating could effectively suppress voltage fading of LMNC. EIS results reveal that the LC modified LMNC materials exhibit better electrochemical kinetics than the pristine one.

In order to obtain the heat transfer characteristics of the helium gap in conditions of different material thicknesses and linear power in high-temperature ranges, on the basis of previous research...

With the development of cold region engineering, it is crucial to study the mechanical properties of frozen soil. In practice, frozen soil is inevitably subject to impact loading, making the study of frozen soil under impact loading necessary for engineering in cold regions. The split–Hopkinson pressure bar (SHPB) is an important experimental means for obtaining the dynamic performance of materials. In this study, an SHPB experiment was conducted on frozen soil under confining pressure. The frozen soil exhibited an evident strain rate effect and temperature effect under confining pressure. The SHPB experiment on frozen soil under confining pressure was simulated numerically using LS-DYNA software and the Holmquist–Johnson–Cook (HJC) material model. A loading simulation with passive confining pressure and active confining pressure was completed by adding an aluminum sleeve and applying a constant load. The simulation results obtained using the above methods were in good agreement with the experimental results. The strength of the frozen soil under confining pressure was greater than that of the uniaxial impact, and there was an evident confining pressure effect. Furthermore, the confining pressure provided by passive confinement was larger than that provided by active confinement. The passive confining pressure energy absorption efficiency was higher than for the active confining pressure due to the need to absorb more energy under the same damage conditions. The frozen soil exhibited viscoplastic failure characteristics under confining pressure.

This paper describes the use principle and application fields of vortex diodes. Unfortunately, all the published studies have not taken into account the restrictions on the coolant flow rate in the...

Photo-responsive adsorption-photocatalysis nanocomposites are generally used in water and wastewater decontamination; however, the prolonged adsorption capacity of composites and the role of adsorption in concomitant photocatalysis are typically neglected. These composites can be regenerated under light irradiation as their adsorption capacity decreases. Herein, a novel adsorption-photocatalysis bifunctional nanocomposite, Bi-doped TiO2 supported on powdered activated carbon (Bi2O3/TiO2/PAC), was prepared using the sol-impregnation-hydrothermal procedure. Bi2O3/TiO2/PAC with a secondary calcination temperature of 700°C under a nitrogen atmosphere was selected for maximum adsorption capacity on Methyl Orange (MO). The composite displayed an excellent adsorption capacity and was easily separated and recycled. The results demonstrate that 71.2% photocatalytic regeneration efficiency could be attained under visible light irradiation for 1 hr at an intensity of 750 W/m2 and pH 7. Characterization of the as-prepared Bi2O3/TiO2/PAC nanocomposite (700°C) indicates that it possesses a highly specific surface area and great optical properties, showing bifunctional adsorption-photocatalysis characteristics. The p-n heterojunction of the composite played a dominant role in the photocatalytic regeneration process, and effective degradation of MO could be achieved along with composite regeneration.

2 at.% Yb:Sr5(PO4)3F nanoparticles were synthesized by co-precipitation method. By using XRD, FT-IR and FE-SEM measurements, the influence of reactive conditions, including pH value, reactive temperature and mixing mode on the phase composition and microstructure of these nanoparticles were investigated. The results showed that pure Yb:Sr5(PO4)3F nanopowders were produced by adding sodium hydroxide solution into S-FAP emulsion under alkaline environment or neutral environment. Agglomeration degree of the nanoparticles decreases and then increases with the increase of pH value and the aggregation was lowest when the pH value was 12. Spherical or nearly spherical nanoparticles with mean size of 24.0 nm were obtained in the environment of 20 °C and pH = 12. TEM results showed that the powders produced by fast mixing model (fast stirring and fast mixing) have more homogenous microstructure. The Yb:Sr5(PO4)3F ceramic with a transmittance of 45% at 1500 nm was fabricated by hot-pressing the synthesized nanopowders. SEM results showed that residual pores and unsintered second phase are the main scattering sources of the as-prepared Yb:S-FAP ceramics.

Li-rich Mn-based-layered oxides are considered to be the most felicitous cathode material candidates for commercial application of lithium-ion batteries on account of high energy density. Nevertheless, defects containing an unsatisfactory initial Coulombic efficiency and rapid voltage decay seriously impede their practical utilization. Herein, a coating layer with three distinct crystalline states are employed as a coating layer to modify Li[Li0.2Mn0.54Ni0.13Co0.13]O2, respectively, and the effects of coating layers with distinct crystalline states on the crystal structure, diffusion kinetics, and cell performance of host materials are further explored. A coating layer with high crystallinity enables mitigatory voltage decay and better cyclic stability of materials, while a coating layer with planar defects facilitates Li+ transfer and enhances the rate performance of materials. Consequently, optimizing the crystalline state of coating substances is critical for preferable surface modification.

With compact structure and enhanced heat transfer capacity, helical-coiled once through steam generators (HTSGs) are widely used in the small modular reactors (SMRs). Nevertheless, the inside centrifugal forces make the flow more complicated, and increase the frictional pressure drop, which is closely related to the dual test of alternating thermal stress and flow instability. Therefore, the analysis of the friction factor in helically coiled tubes is significant to the efficient and safe operation of HTSGs. While the friction factor of single-phase flow in helically coiled tubes was fully studied and extensive correlations have been validated by a large amount of experimental data, the friction factor of two-phase flow still lacks feasible prediction due to its much more complexity. The existed correlations of two-phase flow in helically coiled tubes are mostly based on specified experimental parameters, so the applicable range is limited. Few scholars have tried to extend these correlations to broader applicability, but the trivial applicable range is unsuitable for program development or engineering design, which needs an accurate prediction of friction factor in a wider range. In this paper, existing frictional pressure drop correlations are investigated. The accuracy of single-phase frictional pressure drop correlations is verified through the comparison of calculation results. Since the known experimental data cannot cover a wide range of parameters, two assumptions are proposed, and the rationality is verified through the existing experimental data and calculation analysis. Based on the two assumptions and calculation, a set of calculation correlations for frictional pressure drop of two-phase flow in helically coiled tubes are proposed. The accuracy of this calculation model is validated by experimental data. The scope of application of this model is: D / d = 15–100, P = 0.12–6.3MPa, G = 200–1500kg / m2s, which is sufficient to support the design and operation of steam generators and the development of the simulation programs.

China Fusion Engineering Test Reactor (CFETR) is aimed to meet the technical gaps between International Thermonuclear Experimental Reactor (ITER) and future fusion DEMO reactors, tritium self-sufficiency must be guaranteed for the operation of fusion reactors. Helium Cooled Ceramic Breeder (HCCB) blanket is one of the promising candidate blanket schemes for CFETR. Tritium generated in Li4SiO4 pebble bed is carried out by purge gas, it is crucial to study the tritium behavior in the blanket from the tritium fuel cycle point of view. In this paper, the effective diffusivity of tritium in purge gas is conducted based on Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) coupled simulation considering the influence of the pebble bed structure. The flow characters analysis of purge gas is carried out by CFD simulation as well, which includes velocity field distribution, pressure field distribution and pressure drop. Based on the macro parameters conducted above, the tritium transport process in blanket including tritium permeation into coolant, tritium inventory in blanket and tritium carried out by purge gas is simulated based on a 2D model set up in COMSOL Multiphysics, the results can be the reference for the design of Tritium Extraction System (TES) and Coolant Purification System (CPS).

The system analysis computer code RELAP5 MOD3.2 was developed for thermal hydraulic study of light water reactor as well as non-nuclear loop-type system using water as coolant. The purpose of this work is to modify the code for system analysis of Lead Bismuth Eutectic (LBE) cooled fast reactor (LFR) and non-nuclear systems. The thermo-physical properties of LBE together with the heat transfer correlations for liquid metal were incorporated into the RELAP5 MOD3.2 code. The methods of code modifications are universal for other working fluids and will not affect the code original performance．The validation of the modified RELAP5 code was done in comparison with test results from two different test facilities. The first one is Natural Circulation Experimental (NACIE) facility performed by ENEA and the results of test number 21 at power of 22.5 kW was taken for comparison. The simulated profiles of temperatures, mass flow rate of LBE agree well with the test data. The other test is from Natural Circulation Capability Loop (NCCL) facility conducted by Xi'an Jiaotong University. Five different power levels (4.5kW, 5.8kW, 7.5kW, 9.8kW and 15kW) under natural circulation conditions are considered. Results obtained for LBE mass flow rate and temperature difference were compared with code predictions. The results show that the calculation results are in consistent with the experimental data. The capability and reliability of the modified RELAP5 code has been demonstrated for further analysis of LFRs.

High optical quality of Er3+:CaF2 transparent ceramics were successfully fabricated by hot pressing method. The maximum transmittance reached to 93% which was close to theoretical transmittance in 2 mol% Er3+:CaF2 transparent ceramics. The upconversion luminescence of ceramics samples were investigated in detail upon 980 ​nm, 808 ​nm excitation and 980 ​nm ​+ ​808 ​nm two-wavelength excitation, respectively. UC transition mechanism about red emission at 808 ​nm excitation was different from that at 980 ​nm excitation. Owing to the synergistic effect at simultaneous 980 ​nm and 808 ​nm excitation, energy losses caused by multi-phonon relaxation and the energy mismatch between 4f levels and excited photons could be suppressed. The strategy of multi-wavelength excitation might broaden the applications of upcoversion ceramics materials.

The long-term serviceability of infrastructures in cold regions is inevitably affected by such dynamic loads in practical works as earthquake loading and vehicle loading. In order to study the deformation characteristics of frozen soil under the seismic loading, namely P-waves and S-waves coupled action, different cyclic stress paths were simulated by using triaxial testing equipment with bidirectional cyclic loading function. The results indicate that the cyclic shear stress was main factor in the development of permanent axial strain of frozen sample, while the cyclic normal stress had limited impact. In the case of same stress path, the clockwise rotational-direction of the cyclic stress path is more conducive to the accumulation of the axial permanent strain. In addition, the residual strain generated is greater in the loading process than in the unloading one under the similar conditions. The synchronous vibration of normal stress and shear stress makes the elastic strain maintain larger value than the reverse synchronous vibration, but the asynchronous vibration makes the residual strain keep larger than the synchronous vibration under the condition of the same number of loading cycle.

Nd3+ doped SrF2 and CaF2 transparent ceramics were fabricated by vacuum hot-press sintering and the absorption spectra, emission spectra as well as luminescence decays of the samples were measured. Judd-Ofelt (J–O) theory was used to analyze the optical performance of Nd3+ in these two isostructural hosts. The Nd: SrF2 transparent ceramic was found to have smaller line strength, larger radiative lifetime and smaller Ω2 value (corresponding to more ionic Nd3+-ligand bonding and more symmetry of Nd3+ environment). These features made it easier for Nd: SrF2 to realize population inversion and strong emission, thus doing good to laser performance. The strong emission of 4F3/2 → 4I9/2 transition in Nd: SrF2, which was predicted by J–O theory and demonstrated by luminescence spectrum, made it possible to achieve effective laser output around 900 nm. The intensity parameters and radiative lifetimes of ceramics were found comparable with their corresponding single crystals.

In the present study, we theoretically and experimentally investigated a typical and practical heterogeneous ice nucleation process on auto windshield under nocturnal radiative cooling and subfreezing conditions. During the experiment, a general class A passenger car was placed outdoors in a subfreezing environment (i.e., 44.14° N, 126.45° E) during nights in January, with a purpose to produce a nocturnal radiative cooling condition for supercooling the windshield to trigger the ice nucleation. The results revealed a distinctive three-stage frosting process: (I) inhomogeneous occurrence of incipient ice nucleation; (II) small-sized ice crystals grew into large-sized ones primarily based on the incipient nucleation sites, together with a continual formation of new nucleation sites and a merging between large-sized and small-sized crystals; (III) large-sized ice crystals coalesced into large-scale groups, tending to make a full ice coverage. Unlike the classical three-period frosting process, the present study exhibited an absence of the drop-wise condensation but with a presence of dendritic crystals nearly parallel to the supercooled surface. Besides, the incipient ice nucleation was first initiated on the upper part of the windshield, which then propagated downward with a further heat loss of the windshield due to the continual nocturnal radiation. Meanwhile, the probable presence of surface roughness or contamination was much more likely to trigger an earlier initiation of incipient heterogeneous ice nucleation. Additionally, the arrival of saturation point, rather than the nominal supersaturation state (i.e., the condensation nucleation point), could be expected to approximately mark the initiation of icing under a practical engineering condition. Higher relative humidity tended to induce an earlier occurrence of ice nucleation and produce a larger surface coverage.

A series of uniaxial and triaxial experiments are performed to analyze the mechanical behavior of foamed concrete (FC). The experimental results indicate that for uniaxial loading, foamed concrete demonstrates brittle failure under a uniaxial tension and small compression deformation. A 1D damage constitutive model is then established and expected to predict the nonlinear responses of foamed concrete under a large compression deformation. For triaxial loading, the level of confining pressure significantly influences the multiaxial mechanical behavior of foamed concrete due to its hydrostatically compressible characteristic. An elliptic phenomenological yield criterion based on three loading paths is further proposed and extended to consider the density-dependent effect by modifying the corresponding material constants as a function of material density. The comparisons between the theoretical predictions and experimental results reveal that the present yield criterion can give a good description of the tension/compression asymmetry, pressure dependence, and density sensitivity of the yield loci under the effective stress-mean stress space.

The antibiotic sulfamethazine (SMT) has emerged as a water pollutant that is recalcitrant to conventional water treatment process. A number of technologies based on hydroxyl radical or sulfate radical induced SMT degradation have been described, but photo-induced degradation is not widely examined. Herein, photocatalysts of Bi-doped TiO2 nano-composites supported by powdered activated carbon (PAC) were prepared, with variable molar ratios of Bi/Ti (0.06:1(6%), 0.08:1(8%), 0.1:1(10%) and 0.12:1(12%)) by a sol-hydrothermal method. The ratio of 10% (Bi-Ti/PAC (10%)) was most efficient to degrade SMT. Experimental variables during photocatalytic degradation were optimized for solution pH, catalyst dosage, initial SMT concentration, and coexisted anions. Under optimal conditions of 1.0 g/L catalyst, 20 mg/L initial SMT concentration, pH 6.0 and visible light irradiation at 400–780 nm, the degradation rate reached 81.18% in 300 min. Compared to Bi-Ti(10%) nano-composite without PAC, pure TiO2 or commercially available P25, Bi-Ti/PAC(10%) was superior for SMT degradation with a degradation kinetic rate of 0.00531 min−1. The properties of the prepared photocatalysts were characterized by X-ray powder diffraction, scanning electron microscope, X-ray photo-electron spectroscopy, Brunauer-Emmett-Teller and ultraviolet-visible diffuse reflection spectroscopy. This revealed that Bi-Ti/PAC (10%) had a smaller crystal size, larger specific surface area, larger pore size, stronger visible light absorption ability and lower band gap energy than pure TiO2. Ten intermediates of SMT were identified and a possible degradation pathway was proposed.

In this work, earth abundant CaI2 compound has been applied to regulate the thermoelectric performance of SnTe by codoping in both the anion and cation sites for the first time. The carrier concentration has been effectively tuned to a reasonable range due to the electron donor nature of ITe+ point defects; on the other hand, the Seebeck coefficient has been significantly enhanced because of the resulted valence band convergence and band gap enlargement. More importantly, the phonon and carrier scattering have been tailored tactically, and a relatively high power factor with a significantly lowered thermal conductivity have been achieved simultaneously. In consequence, an enhanced figure of merit ZT ∼1.2 at 873 K was attained in the SnTe-3% CaI2 sample.

The present paper reports the results of a laboratory experiment that aimed to investigate the residual deformation and stiffness changes of frozen silty clays under cyclic triaxial loading. Two sets of cyclic stress magnitude — namely, low and high level — were applied to the reconstituted artificial frozen soil specimens with identical properties, and the effect of six levels of confining pressure was examined. The results indicate that two distinct development categories of residual axial strain with number of loading cycles are induced by the low- and high-level cyclic stress. The dynamic Young’s modulus derived from each test experiences a significant increase with the number of loading cycles, which is partly attributed to the cyclic densification. A special observation from the tests under high-level cyclic stress along with a confining pressure of 0.3 MPa also indicates that the dynamic Young’s modulus keeps as a relatively constant value when the change of residual volumetric deformation transfers from compression to dilation. The empirical relationships were proposed to properly reflect the development of the residual axial strain and dynamic Young’s modulus with the number of loading cycles.

0.2–5.0 at% Pr3+-doped CaF2 transparent ceramics were fabricated by hot-pressed processing for the first time. The phase compositions, microstructure and optical characteristics of the presented transparent ceramics were examined systematically. The average in-line transmittance of Pr:CaF2 transparent ceramics (2.0 mm thick) with high Pr3+ doping concentrations (1.0–5.0 at%) exceeds 86% at the wavelength of 1200 nm. The absorption spectrum manifests that the prepared Pr:CaF2 transparent ceramics contain some absorption peaks overlapped with emission bands of the commercial InGaN laser diodes. Further, a detailed investigation on the visible emission properties as a function of Pr3+ concentrations in CaF2 transparent ceramics was reported. The emission spectra presented two main characteristic peaks at 496 nm (bluish green) and 656 nm (red) corresponded to the transitions of 3P0→3H4 and 3P0→3F2 for Pr3+ activator ions. With the increase of the Pr3+ doping concentrations, the emission intensity and decay lifetimes decreased generally attributed to the concentration quenching effect. Details on energy transfer mechanism of Pr3+ in CaF2 transparent ceramics were demonstrated and discussed.

Higher efficient degradation of methyl orange (MO) was demonstrated with nanometer-sized high-silica SAPO-5. By a hydrothermal process, synthesized high-silica SAPO-5 and low-silica SAPO-5 showed Si-to-Al ratios of 4.20 and 0.11, respectively. High-silica SAPO-5 showed much better MO degradation efficiency with a dosage of 70 mg in MO solution with a concentration of 10 mg/L under ultraviolet illumination. High-silica SAPO-5 also exhibited good producibility for preparation and stable photocatalytic activity even after the fifth recycling test. Optical characterizations of DRS, XPS, photocurrent density and time-resolved fluorescence were carried out for SAPO-5 samples. Finally, free radical and hole scavenging experiments were investigated for high-silica SAPO-5, and a MO photodegradation mechanism based on the charge transfer excited state of [Al2+–O−]* was proposed. This work highlights great prospects of high-silica SAPO-5 for organic pollutant removal with virtues of ideal efficiency and environmental friendliness.

The deformation and failure of materials and structures under high speed impact is a major problem in aerospace, automotive engineering and protection engineering. In this paper, based on peridynamics (PD) model, the deformation and damage mechanism of the bio-inspired nacre nanocomposite against the impact was discussed. According to the existing experiments, the crack evolution and propagation process of “brick-mortar” split-layer microstructure under the impact were approached systematically. According to the result that impact damage only occurs on the top of bio-inspired nacre nanocomposite, it is concluded that peridynamics can be well applied to the analysis of nacre nanocomposites under impact.

As one of the quickest inorganic scintillators, BaF2 crystal is projected to be used in medical treatment, high energy physics, geological research, and other sectors. A series of Pr:BaF2 polycrystalline transparent ceramics with nominal Pr3+ concentrations (0.1–5 at%) were synthesized via HP sintering in this research. XRD, FE-SEM, and TEM measurements were used to analyze the phase composition and microstructure of BaF2 precursor powders with varying Pr-doping levels, and the results demonstrated that as concentration increases, the size of the nanopowders decreases. Furthermore, the morphology shifted from uniform square to uneven sheet. Cross-sectional SEM pictures of all samples revealed a clean grain boundary with no remaining pores or contaminants. The absorption spectra, emission spectra, and fluorescence lifetime of a group of Pr:BaF2 transparent ceramics with excellent optical transmittance were measured and discussed after hot-pressing the precursor powders synthesized via co-precipitation method at 900 °C under an axial pressure of 50 MPa for 4 h.

Due to the low nuclear safety risk, low initial investment cost and short construction period, integrated small nuclear reactors have received wide attention from all over the world. As advanced new type of nuclear reactors, the technologies of integrated small nuclear reactors are in the process of exploration and development. Steam generators are used as the heat transfer system for energy exchange between the primary and secondary circuit in reactors, and their heat transfer analysis is very important for reactor design and development. Due to the simple structure, strong heat exchange capacity and timely load following, Once-Through Steam Generators (OTSGs) are the mainly used steam generators in the design of integrated small nuclear reactors. RELAP5/MOD4.0 is a commercial software developed by Innovative System Software, LLC for transient analysis of light water reactors (LWR). After years of development and improvement, RELAP5 has been a basic tool for analysis and calculation of various simulators of nuclear power plants. However, when RELAP5 models steam generators, only structural models related to straight pipes can be established, which is very inconvenient for the heat transfer research of Once-Through Steam Generators. In this paper, Once-Through Steam Generators with specified structural parameters are taken as the research object. The heat transfer calculation is performed on the simplified inclined tube models by RELAP5 code and the theoretical calculation of the spiral tube heat transfer models is also carried out. Comparing the steam outlet temperature on the primary and secondary sides, the heat exchange power, the average heat transfer coefficient and the tube length of different heat exchange zones under given primary and secondary side inlet fluid conditions, it is confirmed that the RELAP5 heat transfer calculation is verified for simplifying Once-Through Steam Generators with inclined tube models.

As key heat transfer system in small and medium size pressurized water reactors, once-through steam generators are important parts of energy exchange between primary and secondary circuits, and are very important for the design and operation of reactors. However, two-phase flow and heat transfer in once-through steam generators are very complicated. When a reactor experience power rising and descending transient, the heat removal of once-through steam generator, the flow rate, the inlet fluid temperature and outlet steam temperature will all change accordingly. Especially when a reactor is running at a low power, the flow rate of the secondary side of OTSG is extremely small and the single-phase region of the secondary side of OTSGs is also too small. The two-phase flow instability may occur, which has a serious impact on reactor operation and safety. So, a reasonable power-up and power-down transient scheme is required to ensure operational stability when starting up and shutting down a reactor. RELAP5/MOD4.0 is a commercial software developed by Innovative System Software, LCC for transient analysis of light water reactors (LWR). After years of development and improvement, RELAP5 has been a basic tool for analysis and calculation of various simulators of nuclear power plants. Scholars all over the world have carried out a large number of analysis of two-phase flow stability using RELAP5, and the results are reliable. This paper takes once through steam generators with given structural parameters as the research object, and uses RELAP5 as the calculation tool. The influencing factors of flow instability are discussed in this paper, and the operating parameters of the fluid on the primary and secondary sides are designed to satisfy the flow stability under different powers. And a set of power-up and power-down schemes for stable operation is proposed.

An electrothermal phase transition actuator based on a superaligned carbon nanotube film and elastomers has been designed and fabricated. Compared with a conventional electrothermal bimorph actuator using cantilever structures, this new-type actuator introduces a novel concept of phase transition large-deformation actuation. The actuator consists of an enclosed cavity made up of highly elastic elastomers and an embedded carbon nanotube based electrical heater. A low-boiling liquid was injected into the cavity and it can vaporize rapidly to make the elastic cavity expand significantly when electrically heated. The size and speed of the expansion can be easily controlled by the applied voltage (electrical power). The expanded elastomer membrane can lift more than 1000 times of its own weight. The cyclic actuation test shows the excellent durability of the actuator. A heart-shaped closed liquid circulation system based on the phase transition pump-type actuators has been made, which can work like a real heart. Owing to the advantages of low driving voltage, large deformation, simple fabrication, easy operation, lightweight and durability, we think that the phase transition actuator will have great potential usage in various areas, such as artificial muscles, soft robots, sensors, and especially in the biomedical field.

In a coagulation-flocculation process, optimal separation of the resultant aggregates plays a decisive role on coagulation performance and provides a lower burden for subsequent treatment units. This separation highly depends on the stability of the micro-flocs formed during the initial, rapid stage of coagulation. In this work, a two-stage addition of aluminium sulphate (alum, Al2(SO4)3) was employed by adding 0.04 and 0.08 mM Al2(SO4)3 at the beginning and the end of rapid mixing, respectively. The coagulation performance and floc characteristics were compared to conventional single addition with the same total coagulant dosage, and the effects of variable rapid-mixing speeds (160–850 rpm) and duration time (10–120 s) were investigated. The results showed that the residual turbidity of two-stage coagulant addition was 85.1% lower than single addition when applied at a mixing speed of 580 rpm and a duration time of 120 s. The underlying coagulation mechanism revealed that the two-step addition more effectively neutralized colloids and formed larger aggregates that settled better and could more easily be removed. Moreover, the aggregates were less firm, which was attributed to different interactions among the micro-flocs, the second addition of Al2(SO4)3 and destabilized colloids. The present work provides data to broaden the window of rapid-mixing environments for more effective coagulation.

A series of laboratory experiments, including oedometer tests, direct shear tests, and mercury intrusion porosity (MIP) tests, were conducted to investigate the effects of repeated wetting-drying-freezing-thawing (WDFT) cycles on the mechanic behaviors and pore characteristics of compacted loess. The results of mechanical tests indicate that the WDFT weathering can cause significant deterioration of mechanical properties for compacted loess. As the number of treatment cycles increases, vertical compression strain and coefficient of collapsibility of the loess specimens increase while the cohesion decreases. The compacted and noncollapsible loess specimen exhibits collapse again after the 7 WDFT cycles. The results of MIP tests show that WDFT cycles have a main influence on the pores with a pore diameter of 1∼35 μm between the soil aggregates, and medium pore contents (10∼35 μm) increase significantly with the increasing number of WDFT cycles. By comparing compression and collapse characteristics of the loess specimens subjected to wetting-drying, freeze-thaw, and WDFT cycles, we found that the dry-wet action plays the dominant role in the deterioration of engineering properties of compacted loess during WDFT cycles.

The current paper reports an experimental investigation that aims to determine the effects of freeze-thaw cycles (cycle number and freezing low temperature) on the dynamic responses of frozen subgrade soil. The test results indicate that the curve level for the dynamic shear modulus (damping ratio) first decreases (increases) and then remains approximately stable at a small strain range with increasing freeze-thaw cycles. These critical cycle numbers for the dynamic shear modulus (damping ratio) are different at the three freezing low temperatures. A theoretical model is developed to describe the evolutionary features of the dynamic shear modulus (damping ratio) under different conditions. The development of accumulative plastic deformation is strongly sensitive to freeze-thaw cycles and freezing low temperatures. Two-stage evolutionary features for the resilient modulus with a loading cycle number were experimentally verified under different conditions. The freeze-thaw attenuation coefficient was adopted to evaluate the property deterioration with increasing freeze-thaw cycles. The comparison results display good agreement between the experimental data and the predicted curve determined from this proposed theoretical model. This investigation provides a useful and important reference for assessing the degeneration of engineering properties for frozen subgrade soil exposed to freeze-thaw cycles.

This study aims to provide an understanding of the damage evolution and dynamic mechanical behavior of frozen soil under freezethaw (F-T) loading and impact loading.We used the split Hopkinson pressure bar (SHPB) device to evaluate the dynamic mechanical properties of frozen soil at different numbers and temperatures of F-T cycles. Our results indicate that the F-T process has a strong influence on the dynamic mechanical behavior of frozen soil. The peak stress of the frozen soil gradually weakens with an increase in the number of F-T cycles until the cycle number reaches the critical value for the steady state of the soil specimen (approximately 37 cycles). We observed a decrease in the peak stress of the frozen soil with a decrease in freezing temperature. We defined the F-T damage using wave impedance, which characterizes the microstructural properties of frozen soil, coupled it with the impact damage that satisfies the twoparameter Weibull distribution, and obtained the total damage of the frozen soil under F-T loading and impact loading. By combining the discretized ZhuWangTang (ZWT) model with the plastic theory that satisfies the DruckerPrager (D-P) yield criterion, which is based on the improved hardening criterion with strain rate terms, we constructed a viscoelasticplastic constitutive model with damage in frozen soil under F-T loading and impact loading. The results predicted by this model agree with the experimental data, validating its feasibility.

In-TBM breeder box coolant leak is one of four reference accidents identified for China Dual-functional Lithium Lead Test Blanket Module (DFLL-TBM), which will result in the pressurization of the TBM LiPb breeding zones and cooling system. In order to analyze In-TBM breeder box coolant leak accident, there is a need to simulate the mixing of liquid metal and non-condensable gas. While the current system safety code RELAP/SCDAPSIM/MOD4.0 which was initially designed to predict the behavior of light water reactor systems is incapable of modeling the mixture of liquid metal fluids and non-condensable gas. This paper first briefly introduce the reason for RELAP/SCDAPS/MOD4.0’s incapability of modeling liquid metal in contact with a non-condensable gas. Then, a solution to solve the problem and the modification of the RELAP/SCDAPSIM/MOD4.0 code is proposed. Several typical problems involving liquid metal in contact with helium were simulated and the results demonstrate the feasibility and validity of the modified RELAP/SCDAPS/MOD4.0 in modeling the mixing of liquid metal and non-condensable gas. Last but not least, the modified RELAP/SCDAPS/MOD4.0 is used for transient analysis of In-TBM breeder box coolant leaks. Since both lead-lithium eutectic alloy and helium serve as TBM coolants, the Lithium Lead Cooling System (LLCS) and the Helium Cooling System (HCS) were modeled to investigate the thermal-hydraulic characteristic of the TBM system and its influence on ITER safety under the accident conditions. Results show that LLCS pressurization during In-TBM breeder box coolant leak is adequately handled by the safety accessories provided in LLCS and the highest temperature of the first wall is far below its melting point during the accident process.

A novel heterogeneous Fenton-like photocatalyst, Fe-doped graphitic carbon nitride (Fe-g-C3N4), was produced by facile two-step calcination method. This Fe–g–C3N4 catalyzed rhodamine B degradation in the presence of H2O2 accompanied with visible light irradiation. transmission electron microscopy(TEM), x-ray diffraction (XRD), FT-IR, x-ray photoelectron spectroscopy (XPS), and photoluminescence fluorescent spectrometer (PL) characterization analysis methods were adopted to evaluate the physicochemical property of samples. It can be observed that the Fe-g-C3N4 exhibited excellent photocatalytic Fenton-like activity at a wide pH range of 3–9, with rhodamine B(RhB) degradation efficiency up to 95.5% after irradiation for 45 min in the presence of 1.0 mM H2O2. Its high activity was ascribed to the formation of Fe–N ligands in the triazine rings that accelerated electron movement driving the Fe(III)/Fe(II) redox cycle, and inhibited photo-generated electron hole re-combinations for continuous generation of reactive oxygen species by reactions between Fe(II) and H2O2. The main active oxygen species were hydroxyl radicals, followed by superoxide radicals and hole electrons. This produced catalyst of Fe–g–C3N4 shows excellent reusability and stability, and can be a promising candidate for decontamination of wastewater.

Graphitic carbon nitride is a promising photocatalyst for environmental purification, but the photocatalytic performance is limited significantly due to its narrow visible-light adsorption and high photo-reduced electron-hole recombination rate. This work developed a novel way to overcome the two defects and obtained obvious effect. CoAPO-5 was used to broaden visible-light adsorption range by conducting g-C3N4/CoAPO-5 binary composite. In further, rGO was integrated into the binary system to form novel ternary composite. rGO performs as a electron mediator, which can inhibit photo-reduced electron-hole recombination efficiently. The samples were characterized by XRD, SEM, PL, IR and DRS. The photocatalytic performances for degrading RhB (10mg/L) indicated that g-C3N4/CoAPO-5/rGO have much higher activity than g-C3N4/CoAPO-5 because of synergistic effect. When the doping content of rGO in g-C3N4/CoAPO-5 was 0.5%, the degradation efficiency was improved by 14%.

The compression, tension, shear and combined shear-compression tests with different loading rates were conducted to investigate the mechanical behaviour of PA66 specimens. The initial yield and post-yield behaviour were analysed to determine the parameters in theoretical models. Results showed that the yield criterion based on three stress invariants gives the best description of the initial yield behaviour of PA66. The post-compression/tensile behaviour of PA66 was described by a hyperbolic function. The subsequent yield function was proposed based on the combination of initial yield surface and mixed work hardening model. The ratio of compression and tensile strength was utilized to appropriately characterize the kinematic hardening. Additionally, the effects of loading rate on PA66 yield stress and post-yield behaviour can be described by Eyring theory. On the basis of the general observations and classical elastoplastic theory, a macroscopic phenomenological constitutive was constructed to describe the mechanical behaviour of PA66.

In this study, a database of triaxial compressive tests on unsaturated frozen soils is compiled to investigate the mechanical behavior that has not been considered in previous studies. The results for the stress-strain volume changes are presented first. Then, the physical mechanisms that might control the deformation of unsaturated frozen soils, namely, volumetric compression and frictional sliding, are used to interpret the changes in volume and deviator stress during the tests. The relationship between the compression rate due to the mean stress and the dilation rate due to shearing determines the changes in sample volume and shear stress with an increasing axial strain. The test results indicate that confining pressure and temperature significantly affect the phase transformation state, the post-peak strength, and the maximum dilation ratio. A higher post-peak strength ratio is observed in tests performed at higher confining pressure or under a higher temperature. As the confining pressure is increased, the shear stress at the phase transformation state initially increases and then decreases or stabilizes. However, the maximum dilation ratio decreases considerably and tends to reach zero after a certain confining pressure is reached. Both the deviator stress at the phase transformation state and the maximum dilation ratio are higher under a lower temperature given constant confining pressure. Ice cementation and pressure melting are attributed to the specific features of frozen soils compared to those of unfrozen soils. This paper provides new insights into the mechanical behavior of frozen soils.

0.5–5.0 at.% Nd3+ doped (Ca0.94Gd0.06)F2.06 transparent ceramics were fabricated by vacuum hot-pressing sintering. The structural, spectroscopic and thermal properties of Nd:(Ca0.94Gd0.06)F2.06 transparent ceramics, as well as the influence of Nd3+ content on these properties were investigated. The as-fabricated ceramic samples exhibited high transparency and nearly pore-free microstructure. The absorption peaks located at 538 nm, 576 nm, 736 nm, 792 nm and 865 nm were attributed to the transitions from ground state to the excited states of Nd3+ ions, and the absorption coefficients increased linearly with Nd3+ content increasing. The emission band of the sample doped with 1 at.% Nd3+ concentration exhibited the highest emission intensity, while the lifetime decreased sharply with the increase of Nd3+ concentration. In addition, with Nd3+ content increasing from 0.5 to 5.0 at.%, the thermal expansivity coefficients increased slightly, while the thermal conductivity decreased from 4.21 to 2.36 W/m K at room temperature.

In order to enhance hole/electron separation and charge transfer in photocatalysts, the heterostructured g-C3N4/CoAPO-5 hybrids materials were synthesized via a simple grinding method and were investigated using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The optical properties of g-C3N4/CoAPO-5 hybrids materials were measured by ultraviolet-visible diffuse-reflectance spectroscopy (DRS), photoluminescence (PL) spectra and ultraviolet-visible absorption (UV-Vis) spectra. Under visible-light illumination, this work shows the heterogeneous g-C3N4/CoAPO-5 hybrids present a superior photocatalytic activity.