Numerical simulation and optimization of Al alloy cylinder body by low pressure die casting

Shrinkage defects can be formed easily at Critical location during low pressure die casting (LPDC) of aluminum alloy cylinder body. It has harmful effect on the products. Mold fi lling and solidifi cation process of a cylinder body was simulated by using of Z-CAST software. The casting method was improved based on the simulation results. In order to create effective feeding passage, the structure of casting was modifi ed by changing the location of strengthening ribs at the bottom, without causing any adverse effect on the part’s performance. Inserting copper billet at suitable location of the die is a valid way to create suitable solidifi cation sequence that is benefi cial to the feeding. Using these methods, the shrinkage defect was completely eliminated at the critical location

A Stop-Probability Approach for O-D Service Frequency on High-Speed Railway Lines

Train stop planning provides appropriate service for travel demand and stations and plays a significant role in railway operation. This paper formulates stop planning from the point of view of direct travel between origin-destination (O-D) stations and proposes an analytical method to theoretically derive optimal service frequencies for O-D demand on different levels. Considering different O-D demand characteristics and train service types, we introduce the concept of stop probability to present the mathematical formulation for stop planning with the objective of minimizing per capita travel time, which is solved by an iterative algorithm combined with local search. The resulting optimal stop probabilities can be used to calculate the required service frequency for each train type serving different demand categories. Numerical examples, based on three real-life high-speed railway lines, demonstrate the validity of the proposed method. The proposed approach provides a more flexible and practical way for stop planning that explicitly takes into account the importance of different stations and passenger travel characteristics. Document type: Articl

Oxidation behavior and mechanical properties of Ti-enriched MoSiBTiC alloy

Mo-Si-B alloys are one of leading candidates for ultra-high-temperature applications. Macroalloying of Ti to the Mo-Si-B systems improves both strength/density ratio and high-temperature oxidation resistance. However, the study for Ti-added Mo-Si-B alloys have been still limited very much. In this study, Ti-enriched MoSiBTiC alloy with the composition of 38Mo-17Si-5B-20Ti-10TiC (at.%) was addressed from the viewpoint of oxidation and high temperature deformation. Alloy ingots of the 38Mo-17Si-5B-20Ti-10TiC alloy were prepared by conventional Ar arc-melting. Heat treatment was carried out in vacuum at 1600 or 1700 °C for 24 h. It was found that both the as-cast and heat-treated samples are composed of five phases, i.e., Mo solid solution, Mo3Si, Mo5SiB2, Ti5Si3 and TiC. Micro-cracks were often observed across Ti5Si3 phase, which were generated by thermal stress caused by the strong thermal expansion anisotropy of Ti5Si3. Oxidation behavior was investigated through the specific weight change against time at 1100 and 1300 °C in the atmosphere of pO2/pAr=0.25. The alloy displayed relatively good oxidation resistance. The oxidation rate coefficient obtained from the oxidation curves was below 10-2 g2m-4s-1 even at 1300 °C. This value is comparable to that of the TMS173 nickel-based SX superalloy. Mechanical property was examined by high-temperature compression tests. At 1400 °C, the peak stress reached over 700 MPa, which is at the same level as that of 1st-generation MoSiBTiC alloys [1]. Mechanical properties would be improved by microstructure controlling because the micro-cracking in Ti5Si3 degrades the strength and toughness of the alloy. Hot-working should be effective to destroy the inhomogeneous cast microstructure and facilitate microstructure refinement for the Ti-enriched MoSiBTiC alloy. [1] S. Miyamoto et al., Metall. Mater. Trans. A, 45 (2014) 1112

Triple-Phase Shift Modulation for Dual Active Bridge based on Simplified Switching Loss Model

In this paper the dual active bridge (DAB) is analyzed and three modulation approaches are proposed and tested to improve the converter's efficiency. Zero-voltage switching maps are reported to show the most favorable operating conditions to reduce switching and conduction losses contributions. The results are validated considering an experimental DAB converter prototype. It is shown that accounting ZVS with the characterization of switching behavior of the devices allows significant improvements with respect to simply give a constraint on the instantaneous current switching values, at the reported operating conditions

Characterization of the residual stresses in spray-formed steels using neutron diffraction

Neutron diffraction was used to characterize the residual stresses in an as-sprayed tube-shaped steel preform. The measured residual stress distributions were compared with those simulated using finite element method by taking into account the effects of the thermal history, porosity and different phases of the sprayed preform. The porosity was measured using X-ray microcomputed tomography. The study revealed for the first time the correlation between the distribution of porosity and residual stress developed in the as-sprayed preform

Expression Profiles Analysis Identification and Interaction of Key Genes and Micrornas in Hepatocellular Carcinoma

Background. Hepatocellular carcinoma is one of the most common malignant tumors, with rapid development and high malignancy. MicroRNAs have been reported to play important roles in hepatocellular carcinoma progression. Aim. To identify the key genes and miRNAs in HCC, and to explore their potential molecular mechanisms. Methods. Gene expression profiles of GSE15471 (mRNA profile) and GSE57555 (miRNA profile) were downloaded from gene expression omnibus, which were analysed using R software and bioconductor packages. The gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichments of DEGs were performed using the DAVID database, and the protein–protein interaction networks of the DEGs were constructed from the STRING database. In addition, targets of differentially expressed miRNAs were predicted by the online resource miRDB. Result. In total, 191 differentially expressed genes were identified, including 142 upregulated and 49 downregulated genes. Functional analysis revealed that these DEGs were associates with wound healing, endodermal cell-cell adhesion, activation of MAPK activity and negative regulation of cell proliferation. In addition, we identified five DEMs, which were upregulated and downregulated. hsa-miR-122-5p may target the PDK4, and hsa-miR-21-5p probably targets SPOCK1 and PAIP2B. Conclusions. We applied integrated bioinformatics to identify key pathogenic genes involved in hepatocellular carcinoma and provide new clues for further studies of hepatocellular carcinoma

Optimizing microbial- and enzyme-induced carbonate precipitation treatment regimes to improve the performance of recycled aggregate concrete

Recycled aggregate concrete (RAC) typically suffers from inferior properties due to old mortar on the surface of recycled aggregate (RA), and the practical application of two proposed treatment methods, microbial-induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP), has encountered challenges in determining optimal culture medium and precipitation regimes. This study initially aimed to address these challenges by establishing the feasibility of using chloride-free cultivation medium to avoid introducing chloride ions that could damage the steel reinforcement. The optimal Ca concentration in the precipitation culture medium was determined as 0.3 mol/L for MICP and 0.5 mol/L for EICP. Furthermore, the optimal precipitation regimes for MICP and EICP treatments were identified as I-S (5 cycles) and M-S (3 cycles), respectively. The quantitative evaluation of the above factors enabled the direct practical application of these optimal treatment regimes. The performance of RAC was significantly improved after both MICP and EICP treatments compared to untreated RAC, with EICP treatment demonstrating superior performance. The precipitated CaCO3 formed during MICP treatment consisted mainly of spherical vaterite crystals, while the precipitation formed during EICP treatment comprised vaterite, calcite, and aragonite. These differences in phase and mechanism between MICP and EICP treatments could explain the variations in the performance of RAC.</p