Effect of heat treatment on the roughness and mechanical properties of dental lithium disilicate glass-ceramics

In dental clinics, it is common to perform small fitting adjustments in dentures using a micro-grinding tool after testing them in the patient's mouth. This procedure increases local roughness and can lead to formation of microcracks on the prosthesis surface. This study aimed to investigate the benefits of a post-finishing heat treatment to surface roughness and crack healing and its effect on the flexural strength of lithium disilicate (LD) dental glass-ceramics. Commercially available lithium metasilicate, Li₂SiO₃, samples were heat treated at 840 °C for 7 min to induce the phase transformation into LD, Li₂Si₂O₅. The LD samples were characterized by X-ray Diffraction, Scanning Electron Microscopy, Vickers hardness, Young’s modulus, and fracture toughness. One of the surfaces of the LD samples was sanded aiming to simulate the denture fitting adjustments performed in the dentist’s laboratory, generating a rough surface, Group 1. Half of the LD samples had their biaxial flexural strength evaluated by the piston-on-three-ball test (P–3B) and the other half were submitted to a second short-term heat treatment (840 °C - 5 min), Group 2, and later assessed by the P–3B. Roughness parameters in both groups were measured by 3D optical profilometry. After the crystallization heat treatment, formation of elongated LD crystals, Li₂Si₂O₅, 35% amorphous phase, and residual Li₃PO₄ was observed. In addition, the following mechanical property values were obtained: Vickers hardness = 5.8 ± 0.1 GPa, fracture toughness = 2.2 ± 0.1 MPa m^1/2, and Young’s modulus = 100.3 ± 0.3 GPa. The samples in Group 1 showed bending strength of 206 ± 30 MPa and the following roughness parameters: Ra = 0.45 ± 0.16 μm, Rz = 22.7 ± 6.7 μm, and PV = 27.7 ± 7.1 μm. In the samples in Group 2, the Ra, Rz and PV roughness parameters were 0.31 ± 0.12 μm, 5.2 ± 2.5 μm, and 9.2 ± 4.7 μm, respectively. With this decrease in roughness, the bending strength increased by 62%, with a mean value of 331 ± 59 MPa. In the need for machine finishing of LD-based glass-ceramic dental prostheses, the use of a second short-term heat treatment at 840 °C for 5 min generates considerable gains in bending strength, increasing the lifecycle of the prosthesis as a result of reduced surface roughness caused by softening of the remaining amorphous phase in the glass-ceramic. These conditions can be adapted to each chemical and crystallographic composition of the glass-ceramic under study.     

Deterministic and probabilistic ship pitch prediction using a multi-predictor integration model based on hybrid data preprocessing,reinforcement learning and improved QRNN

The deterministic and probabilistic prediction of ship motion is important for safe navigation and stable real-time operational control of ships at sea. However, the volatility and randomness of ship motion, the non-adaptive nature of single predictors and the poor coverage of quantile regression pose serious challenges to uncertainty prediction, making research in this field limited. In this paper, a multi-predictor integration model based on hybrid data preprocessing, reinforcement learning and improved quantile regression neural network (QRNN) is proposed to explore the deterministic and probabilistic prediction of ship pitch motion. To validate the performance of the proposed multi-predictor integrated prediction model, an experimental study is conducted with three sets of actual ship longitudinal motions during sea trials in the South China Sea. The experimental results indicate that the root mean square errors (RMSEs) of the proposed model of deterministic prediction are 0.0254°, 0.0359°, and 0.0188°, respectively. Taking series #2 as an example, the prediction interval coverage probabilities (PICPs) of the proposed model of probability predictions at 90%, 95%, and 99% confidence levels (CLs) are 0.9400, 0.9800, and 1.0000, respectively. This study signifies that the proposed model can provide trusted deterministic predictions and can effectively quantify the uncertainty of ship pitch motion, which has the potential to provide practical support for ship early warning systems.     

Influence of accelerated curing on the compressive strength of polymer-modified concrete

In recent building practice, rapid construction is one of the principal requisites. Furthermore, in designing concrete structures, compressive strength is the most significant of all parameters. While 3-d and 7-d compressive strength reflects the strengths at early phases, the ultimate strength is paramount. An effort has been made in this study to develop mathematical models for predicting compressive strength of concrete incorporating ethylene vinyl acetate (EVA) at the later phases. Kolmogorov-Smirnov (KS) goodness-of-fit test was used to examine distribution of the data. The compressive strength of EVA-modified concrete was studied by incorporating various concentrations of EVA as an admixture and by testing at ages of 28, 56, 90, 120, 210, and 365 d. An accelerated compressive strength at 3.5 hours was considered as a reference strength on the basis of which all the specified strengths were predicted by means of linear regression fit. Based on the results of KS goodness-of-fit test, it was concluded that KS test statistics value (D) in each case was lower than the critical value 0.521 for a significance level of 0.05, which demonstrated that the data was normally distributed. Based on the results of compressive strength test, it was concluded that the strength of EVA-modified specimens increased at all ages and the optimum dosage of EVA was achieved at 16% concentration. Furthermore, it was concluded that predicted compressive strength values lies within a 6% difference from the actual strength values for all the mixes, which indicates the practicability of the regression equations. This research work may help in understanding the role of EVA as a viable material in polymer-based cement composites.     

Data requirements for improving the Quantitative Risk Assessment of liquid hydrogen storage systems

Quantitative Risk Assessment (QRA) supports the development of risk-informed safety codes and standards which are employed to enable the safe deployment of hydrogen technologies essential to decarbonize the transportation sector. System reliability data is a necessary input for rigorous QRA. The lack of reliability data for bulk liquid hydrogen (LH₂) storage systems located on site at fueling stations limits the use of QRAs. In turn, this hinders the ability to develop the necessary safety codes and standards that enable worldwide deployment of these stations. Through a QRA-based analysis of a LH₂ storage system, this work focuses on identifying relevant scenario and probability data currently available and ascertaining future data collection requirements regarding risks specific to liquid hydrogen releases. The work developed consists of the analysis of a general bulk LH₂ storage system design located at a hydrogen fueling station. Failure Mode and Effect Analysis (FMEA) and traditional QRA modeling tools such as Event Sequence Diagrams (ESD) and Fault Tree Analysis (FTA) are employed to identify, rank, and model risk scenarios related to the release of LH₂. Based on this analysis, scenario and reliability data needs to add LH₂-related components to QRA are identified with the purpose of improving the future safety and risk assessment of these systems.     

空间曲线的特征识别与高质量非均匀采样

为避免传统均匀采样方法因忽视曲线重要特征而生成不理想的采样结果,获得给定数量且由特征点和辅助点组成的采样点序列,提出基于特征识别的高质量空间曲线非均匀采样方法.首先使用抛物线插值法得到曲线上所有曲率极大值点和挠率极大值点的近似位置,经筛选后产生特征点,以更好地抓住空间曲线的轮廓特征.然后定义基于弧长、曲率和挠率加权组合的特征函数,并以此自适应地选取曲线上的辅助点.与3种主流采样方法比较的实验结果表明,该方法能够获得更高质量的采样结果且具有更好的实用性,从而进一步改善空间曲线的B样条拟合效果.     

电子雷管技术的推广应用助力爆破器材安全管理工作

电子雷管技术提高了爆破器材的本质安全。通过对电子雷管技术发展历程的介绍,对其推广应用的可行性进行了深入分析,论述了电子雷管技术的推广应用对爆破器材安全管理工作的促进作用,并提出了今后推广应用中还需加强的工作。     

Ammonia mitigation and induction effects on hydrogen environment embrittlement of SCM440 low-alloy steel

The effect of ammonia (NH₃) contained in hydrogen (H₂) gas on hydrogen environment embrittlement (HEE) of SCM440 low-alloy steel was studied in association with the NH₃ concentration, loading rate, and gas pressure. NH₃ worked as both mitigator of the HEE and inducer of hydrogen embrittlement (HE) depending on the testing conditions. The mitigation of the HEE was achieved by the deactivation of the iron (Fe) surface for H₂ dissociation caused by the preferential adsorption of NH₃ on the Fe surface, which is enhanced by the increase in the NH₃ concentration and decrease in the H₂ gas pressure. NH₃ induced HE was caused due to creating hydrogen by the NH₃ decomposition. Since the NH₃ decomposition rate is low, the induction effect was observed when the loading rate was low. The effect of NH₃ was determined by the competition of the mitigation and induction effects.     

Effects of multiple freeze–thaw cycles on meat quality,nutrients, water distribution and microstructure in bovine rumen smooth muscle

This study investigated the effect of 5 freeze–thaw cycles (freezing at −18°C for 12 h and then thawing at 4°C for approximately 12 h) on the meat quality, proximate composition, water distribution and microstructure of bovine rumen smooth muscle (BSM). As the number of freeze–thaw cycles increased, BSM pH, shear force, water content and protein content decreased by 3.06%, 35.50%, 14.49% and 21.11%, respectively, whereas BSM thawing loss, cooking loss, pressing loss, total aerobic count (TAC), ash content and fat content increased by 108.12%, 47.75%, 78.33%, 90.99%, 105% and 35.20%, respectively. The freeze–thaw cycles resulted in greater protein and lipid oxidation, as evidenced by a 36.46% reduction in the sulfhydryl content and a 209.06% and 338.46% increase in the carbonyl and malondialdehyde contents, respectively. Ice crystal formation disrupted the structural integrity of the muscle tissue. Low-field nuclear magnetic resonance results showed that the freeze–thaw cycles prolonged the relaxation times (T_2b, T₂₁ and T₂₂), indicating that immobile water shifted to free water, and consequently, free water mobility increased. After 3 freeze–thaw cycles, the decline in shear force slowed, the increase in thawing loss became accelerated, and the TAC approached the domain value (6 log colony-forming units/g). Therefore, the number of freeze–thaw cycles of smooth muscle during transport, storage and distribution should be controlled to 3 or fewer. The current results provide a theoretical basis and data support for the further utilisation and culinary processing of smooth muscle.     

Improved room-temperature hydrogen storage performance of lithium-doped MIL-100(Fe)/graphene oxide (GO) composite

Li⁺ doping is regarded as an effective strategy to enhance the room-temperature hydrogen storage of metal-organic frameworks (MOFs). In this work, Li⁺ is doped into both MIL-100(Fe) and MIL-100(Fe)/graphene oxide (GO) composite, and it is demonstrated that the hydrogen uptake of Li⁺ doped MIL-100(Fe)/GO (2.02 wt%) is improved by 135% compared with Li⁺ doped MIL-100(Fe) (0.86 wt%) at 298 K and 50 bar, which is ascribed to its higher isosteric heat of adsorption (7.33 kJ/mol) resulting from its more accessible adsorption sites provided by doped Li⁺ ions and ultramicropores. Grand canonical Monte Carlo (GCMC) simulation reveals that Li⁺ ions distributing in the interface between MIL-100(Fe) and GO within MIL-100(Fe)/GO composite is favorable for hydrogen adsorption owing to the increased number of adsorption sites, thus contributing to the enhanced hydrogen storage capacity. These findings demonstrate that MIL-100(Fe)/GO is a more promising Li⁺ doping substrate than MIL-100(Fe).