二维g-C3N4与Ag-TiO2复合光催化剂降解气态乙醛抗失活研究

光催化剂失活是影响其在去除低浓度VOCs的实际应用中的主要因素之一。本研究将TiO₂与2D石墨碳氮化碳(g-C₃N₄)复合, 显著提高了光催化剂的稳定性。当Ag改性的Ag-TiO₂(AT)用于降解乙醛气体时, 反应60 min后开始发生失活现象, 反应延长至400 min则完全失活。而AT与g-C₃N₄复合改性后的样品g-C₃N₄/ Ag-TiO₂(CAT)具有优异的光催化性能和稳定性, 反应至600 min未发生失活。原位FT-IR、PL和光电流的研究表明, 当AT催化降解乙醛时, 反应中间体会在表面积累导致催化剂失活。而引入的g-C₃N₄可以为中间体提供更多的吸附位点, 从而提高稳定性。此外, 引入g-C₃N₄还有利于电荷分离和产生活性氧物种, 促进乙醛和中间体降解。本研究揭示了2D材料在开发稳定可持续降解VOCs的光催化剂方面的实用性。     

Design and Simulation of Flow Field for Bone Tissue Engineering Sca old Based on Triply Periodic Minimal Surface

A novel method was proposed to design the structure of a bone tissue engineering scafold based on triply periodic minimal surface.In this method,reverse engineering software was used to reconstruct the surface from point cloud data.This method overcomes the limitations of commercially available software packages that prevent them from generating models with complex surfaces used for bone tissue engineering scafolds.Additionally,the fluid feld of the scafolds was simulated through a numerical method based on fnite volume and the cell proliferation performance was evaluated via an in vitro experiment.The cell proliferation and the mass flow evaluated in a bioreactor further verifed the flow feld simulated using computational fluid dynamics.The result of this study illustrates that the pressure value drops rapidly from 0.103 Pa to 0.011 Pa in the y-axis direction and the mass flow is unevenly distributed in the outlets.The mass flow in the side outlets is observed to be approximately 24.3 times higher thanthe bottom.Importantly,although the mean value of wall shear stress is signifcantly more than 0.05 Pa,there is stil a large area with a suitable shear stress below 0.05 Pa where most cells can proliferate well.The result shows that th inlet velocity 0.0075 m/s is suitable for cell proliferation in the scafold.This study provides an insight into the design analysis,and in vitro experiment of a bone tissue engineering scafold.     

Influences of processing parameters and heat treatment on microstructure and mechanical behavior of Ti-6Al-4V fabricated using selective laser melting

Selective laser melting (SLM) has provided an alternative to the conventional fabrication techniques for Ti-6Al-4V alloy parts because of its flexibility and ease in creating complex features. Therefore, this study investigated the effects of the process parameters and heat treatment on the microstructure and mechanical properties of Ti-6Al-4V fabricated using SLM. The influences of various process parameters on the relative density, tensile properties, impact toughness, and hardness of Ti-6Al-4V alloy parts were studied. By employing parameter optimization, a high-density high-strength Ti-6Al-4V alloy was fabricated by SLM. A relative density of 99.45%, a tensile strength of 1 188 MPa, and an elongation to failure of 9.5% were achieved for the SLM-fabricated Ti-6Al-4V alloy with optimized parameters. The effects of annealing and solution aging heat treatment on the mechanical properties, phase composition, and microstructure of the SLM-fabricated Ti-6Al-4V alloy were also studied. The ductility of the heat-treated Ti-6Al-4V alloy was improved. By applying a heat treatment at 850 ℃ for 2 h, followed by furnace cooling, the elongation to failure and impact toughness were found to be increased from 9.5% to 12.5%, and from 24.13 J/cm² to 47.51 J/cm², respectively.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00389-y     

An iterative Q‐learning scheme for the global stabilization of discrete‐time linear systems subject to actuator saturation

In this paper, we propose a model‐free algorithm for global stabilization of linear systems subject to actuator saturation. The idea of gain‐scheduled low gain feedback is applied to develop control laws that avoid saturation and achieve global stabilization. To design these control laws, we employ the framework of parameterized algebraic Riccati equations (AREs). Reinforcement learning techniques are developed to find the solution of the parameterized ARE without requiring any knowledge of the system dynamics. In particular, we present an iterative Q‐learning scheme that searches for a low gain parameter and iteratively solves the parameterized ARE using the Bellman equation. Both state feedback and output feedback algorithms are developed. It is shown that the proposed scheme achieves model‐free global stabilization under bounded controls and convergence to the optimal solution of the ARE is achieved. Simulation results are presented that confirm the effectiveness of the proposed method.     

Properties of Chemically Synthesized Nano-geopolymer Cement based Self-Compacting Geopolymer Concrete(SCGC)

The physical and mechanical properties of self-compacting geopolymer concrete(SCGC) using chemically synthesized nano-geopolymer cement was investigated. Nano-geopolymer cement was synthesized using nano-silica, alkali activator, and sodium aluminate in the laboratory. Subsequently, nine nanogeopolymer cement sbased SCGC mixes with varying nano-geopolymer cement content, alkali activator content, coarse aggregate(CA) content, and curing temperature were produced. The workability-related fresh properties were assessed through slump flow diameter and slump flow rate measurements. Mechanical performances were evaluated through compressive strength, splitting tensile strength, and modulus of elasticity measurements. In addition, rapid chloride penetration test, water absorption, and porosity tests were also performed. It was assessed that all mix design parameters influenced the fresh and hardened properties of SCGC mixes. Based on test results, it was deduced that nano-geopolymer cement SCGC performed fairly well. All the SCGC mixes achieved the 28-day compressive strength in the range of 60-80 MPa. Additionally, all mixes attained 60% of their 28-day strength during the first three days of elevated temperature curing. FTIR and SEM analyses were performed to evaluate the degree of polymerization and the microstructure respectively for SCGC mixes.     

Design and development of ceramic-based composites with tailored properties for cutting tool inserts

A successful approach to the development of tailored cutting tool materials requires the development of innovative concepts at each step of manufacturing, from the material design, synthesis of composite powders, to their processing and sintering. In this paper, a computational design approach is applied in the development of reinforced ceramic-based cutting tool inserts with tailored structural and thermal properties. Several potential filler materials are considered at the material design stage for the improvement of structural and thermal properties of a selected matrix material. Properties, such as an improved thermal conductivity and reduced coefficient of thermal expansion are essential for an effective cutting tool insert to absorb thermal shock at varying temperatures. In addition, structural properties such as elastic modulus have to be maintained within a moderate range. A mean-field homogenization theory and effective medium approximation using an in-house code are applied for predicting potential optimum structural and thermal properties for the required application. This is done by considering the effect of inclusions as a function of volume fraction and particle size in the ceramic base matrix. Single inclusion composites such as alumina-silicon (Al₂O₃-SiC) and alumina-cubic boron nitride (Al₂O₃-cBN) as well as hybrid composite such as alumina-silicon-cubic boron nitride (Al₂O₃-SiC-cBN) are developed using the Spark Plasma Sintering (SPS) process in line with the designed range of filler size and volume fraction to validate the computational results. It is found that the computational material design approach is precise enough in predicting the target properties of a designed hybrid composite material for cutting tool inserts.     

Dynamic Response in Ba1−xSrxTiO3 and Anomalous Behavior at the Phase Boundary Composition

The dynamic response of Barium Strontium Titanate (Ba_1?xSr_xTiO₃, x = 0.6–0.9) is presented over a temperature range spanning various structural phase transitions and for compositions that extend from the ferroelectric (FE) phase to the FE‐Antiferrodistortive (AFD) phase boundary. We find that while the in‐phase part of the dielectric response is insensitive to applied frequencies over the range 400–500 kHz for all compositions, strong dispersive effects are observed in general for the out of phase part, for almost all compositions. The dielectric peaks corresponding to the lower temperature structural transitions (e.g. tetragonal to orthorhombic T–O etc.) exhibit frequency dependence, while the higher temperature cubic to tetragonal (C–T) transition does not show dispersive effects. The only exception to this is for the Ba_0.1Sr_0.9TiO₃ composition, lying at the boundary of the FE and AFD phases. Detailed frequency dependence studies of this composition (x = 0.9) show that the (C–T) transition exhibits an abrupt change in the dispersive features for high frequencies f > 10 kHz. These features include the constancy of peak temperature, large drop in the magnitude of the losses and a noticeable broadening of the associated loss peak. The anomalous features in the behavior of x = 0.9 composition are attributed to slow relaxation processes in the AFD phase at the boundary separating the FE and AFD phases.     

Buckling behavior improvement of steel plate shear wall systems

To improve buckling stability and to prevent early elastic buckling of infill plates, vertical and horizontal plate stiffeners are designed for steel plate shear wall (SPSW) systems. Furthermore, effective design of stiffeners for SPSW systems results in improved structural behavior, such as increase of stiffness, capacity and energy absorption. In this paper, the effect of stiffeners is studied on SPSW structural behavior and consequently a rational method is proposed to determine the minimum required moment of inertia for stiffeners resulting in local buckling mode of the infill plate. The proposed requirement is then compared to results obtained from tests previously conducted, as well as those gained from finite element (FE) analyses performed for this study. Copyright © 2007 John Wiley & Sons, Ltd.