Fracture toughness of ceramic moulds for investment casting with ice patterns

Abstract

Ice patterns can be used to make ceramic investment moulds for metal castings. Owing to the characteristics of ice, the ceramic mould must be made at subzero temperatures and consequently, requires a different formulation than shells built at room temperature. Success of this process depends greatly on the fracture toughness of mould materials. The present paper describes the experimental results of fracture toughness of mould materials processed from different compositions. The Taguchi method was used to reduce the trial runs. The parameters considered included the ratio of fibre containing fused silica and aluminosilicate powders, the volume of binder and the volume of catalyst. The microstructure and green fracture surface of test bars were also examined to understand the underlying mechanism. While conducting the four point bend test on ceramic mould samples, some samples had exceedingly low strengths appearing as outliers in the Weibull analysis. Examination of these low strength ceramic samples improved understanding of failure of mould materials. Sound moulds have been made for the investment casting process with ice patterns based on the analysis of experimental results. The casting of an M8 bolt is used to demonstrate that metal castings of complex geometry can be fabricated using ice patterns. The measured tolerances are within the required tolerance range.     

抗菌肽PR-39重组腺病毒表达质粒的构建及鉴定

目的构建抗菌肽PR-39(Proline-arginine rich 39-amino acid peptide,PR-39)重组腺病毒表达质粒。方法从含抗菌肽PR-39核心编码区的质粒中扩增PR-39基因,亚克隆至穿梭质粒pAdTrace-TO4中,构建重组穿梭质粒,经PmeⅠ酶切线性化后,转化感受态AdEasier细胞,构建重组腺病毒质粒,转染HEK293细胞,包装出重组腺病毒,扩增后进行病毒滴度检测。将重组腺病毒感染鼠胚胎间充质干细胞C3H10T1/2,通过荧光显微镜观察红色荧光蛋白(Red fluorescent protein,RFP)的表达,RT-PCR法检测PR-39基因的转录水平。结果重组腺病毒穿梭质粒pAd-Trace-TO4-PR-39经KpnⅠ和HindⅢ双酶切及测序鉴定证明构建正确;重组腺病毒质粒pAdPR-39经PacⅠ酶切鉴定,证明目的基因已整合到腺病毒基因组中;第4代重组腺病毒AdPR-39的病毒滴度为1010IU/ml;感染重组腺病毒AdPR-39的C3H10T1/2细胞可表达RFP;PR-39基因在C3H10T1/2细胞内成功转录。结论已成功构建携带RFP的PR-39重组腺病毒表达质粒,在鼠胚胎间充质干细胞C3H10T1/2中可高效表达。     

Requirements for computational rule checking of requests for proposals (RFPs) for building designs in South Korea

This study reports on the requirements for developing computer-interpretable rules for checking the compliance of a building design in a request for proposal (RFP), especially in the building information modeling (BIM) environment. It focuses on RFPs for large public buildings (over 5 million dollars) in South Korea, which generally entail complex designs. A total of 27 RFPs for housing, office, exhibition, hospital, sports center, and courthouse projects were analyzed to develop computer-interpreted RFP rules. Each RFP was composed of over 1800 sentences. Of these, only three to 366 sentences could be translated into a computer-interpretable sentence. For further analysis, this study deployed context-free grammar (CFG) in natural language processing, and classified morphemes into four categories: i.e., object (noun), method (verb), strictness (modal), and others. The subcategorized morphemes included three types of objects, twenty-nine types of methods, and five levels of strictness. The coverage applicability of the derived objects and methods was checked and validated against three additional RFP cases and then through a test case using a newly developed model checker system. The findings are expected to be useful as a guideline and basic data for system developers in the development of a generalized automated design checking system for South Korea.     

KTX反场箍缩装置纵场线圈结构设计与电磁分析

KTX反场箍缩装置的主要参数介于RFX装置与MST装置之间。反场箍缩的外加纵场需跟随等离子体电流的演化而变化,同时由于RFP中的磁面对于外部特别是等离子体边界处的径向磁场较敏感,所以需外部线圈的磁场更加精细,这对于线圈的磁场分布、误差场以及波纹度等的设计提出了更高的要求。根据KTX物理目标参数要求,提出矩形和楔形截面纵场磁体线圈设计方案,借助有限元软件和程序分析了其电磁场空间分布和结构受力大小。结果表明,6.4°楔形截面方案相比矩形截面方案在控制误差场方面更具有可行性。