Effects of the porcelain-fused-to-metal firing process on the surface and corrosion of two Co–Cr dental alloys

The aim of this study was to evaluate the effects of a simulated porcelain-fused-to-metal (PFM) firing process on the surface, corrosion behavior, and cell culture response of two cobalt–chromium (Co–Cr) dental alloys. Two Co–Cr dental alloys were tested—a high and a low molybdenum (Mo)-containing alloys. Before PFM firing, as-cast alloy specimens were examined for their microstructure, surface composition, and hardness. Corrosion behavior was evaluated using electrochemical impedance spectroscopy tests. Mouse 3T3 fibroblasts were exposed indirectly to specimens and MTT cell proliferation assays were performed after 3 and 6 days. The cell culture medium exposed to specimens was analyzed for metal ion release. After firing, similar alloy specimens were examined for the same properties. The tests showed that the PFM firing changed both alloys’ microstructures and hardness values. After PFM firing, the corrosion resistance of the low Mo-containing Co–Cr alloy decreased statistically, which corresponded with a reduction of Cr and oxygen levels in the surface oxides via X-ray photoelectron spectroscopy. Also, the MTT assay of this alloy decreased significantly corresponding with an obvious increase of Co release after the firing. For the high Mo-containing Co–Cr alloy, the surface composition, corrosion resistance, and cell culture response were not significantly changed after PFM firing. The results suggested that the corrosion resistance and biocompatibility of the low Mo-containing Co–Cr alloy decreased after PFM firing, whereas the firing process had little effect on the same properties of the high Mo-containing Co–Cr alloy.     

Risk-based grouping for checked baggage screening systems

With millions of bags checked at over 7000 baggage screening locations in US daily, the checked baggage screening system may be exploited by the terrorists to do harm to the homeland security. Due to such a huge amount of luggage, how to improve the effectiveness and efficiency of the screening system becomes a challenging task. In this paper, we propose a risk-based cost-effectiveness model where checked bags are classified into several risk classes according to their risk characteristics. According to their risk levels, bags from different classes may go through different device combinations sequentially. For a multiple-device screening system, we determine the optimal sequence of the screening devices and the separate grouping strategies for bags from different risk classes with the objective of minimizing the expected cost per bag. Based on a detailed numerical study, we compare our model with three other cost-effectiveness models (the first model assumes that there is only one risk class, the second model assumes that there is only one group for each risk class, and the third model assumes that all devices in a device combination need to be gone through). Our major conclusions are that our proposed model is beneficial compared with other three models and moreover, the relative benefit becomes larger when the authority commands a stricter upper bound for the probability of false clear.     

The effect of roll-processing orientation on stress corrosion cracking of warm-rolled 304L stainless steel in oxygenated and deoxygenated high temperature pure water

Stress corrosion crack growth rates of 304L stainless steel after one-directionally warm-rolled along the longitudinal (L) direction were measured in oxygenated and deoxygenated pure water at 288 °C. The fracture mode is mainly intergranular in the Transverse-longitudinal (T-L) orientation specimen, while it is occasionally intergranular in the Longitudinal-transverse (L-T) orientation specimen. The crack growth rates in the T-L orientation are higher than those in the L-T orientation in both oxygenated and deoxygenated environments, which is related to the effective cracking growth path as the result of microstructural anisotropy and applied loading direction.     

冰箱聚氨酯环戊烷高压发泡模塑生产成套设备的安全要点

介绍了以环戊烷为发泡剂的冰箱高压发泡模塑生产成套设备的安全设计原则和具体实施内容,重点介绍了环戊烷/多元醇预混系统、聚氨酯环戊烷高压发泡机和聚氨酯冰箱发泡模塑生产线的安全要点。     

浅析北京郊区公路绿化的现状与发展

以城、郊为界将北京公路绿化状况分为两部分,并进行了分析比较,从而找出两者现状差异,并根据效区公路绿化中的不足,从提高认识、加大投入、合理设计、科学养护4个方面找到解决问题的方法。     

建筑施工中常见问题及预防措施

对建筑工程施工中易被忽视的几种问题进行探讨,并提出了相应的预防措施.     

热压成型机PLC控制系统设计

对热压成型机的结构、原理及生产工艺进行了全面的分析,以OMRON公司CPM2APLC为系统主机,采用一体化三相调压模块SCR、一体化温度变送器SBW等集成模块,设计了具有手动和自动两种工作方式的热压成型机PLC控制系统。系统工作可靠,操作简单,能有效的对热压成型机设备进行控制。     

执行依赖启发式动态规划在同步发电机励磁系统中的应用

介绍了一种控制同步发电机励磁系统的新方法,即执行依赖启发式动态规划(ADHDP)对同步发电机励磁电压的自适应控制.执行依赖启发式动态规划是近似动态规划(ADP)的一种算法,ADP利用非线性函数拟合方法逼近动态规划的性能指标函数,以获得最优解或次优解.仿真结果表明,基于执行依赖启发式动态规划算法的励磁控制效果优于传统励磁...     

基于柔性多层绕组的集成EMI滤波器

本文提出一种基于柔性多层集成L—C绕组的新型EMI滤波器集成结构。通过采用此种结构,可以将共模电感,差模电感与共模电容集成为1个单元。与平面PCB绕组的集成EMI滤波器比较,具有铜损显著减小的特点。本文还介绍了实验样机和实验结果。     

基于PLC控制的锅炉燃烧系统设计

通过PLC工业燃油锅炉燃烧控制系统的设计,讨论PLC控制系统中数据的采集、处理及相关的接口电路的软硬件结构应用设计。设计充分考虑了系统的抗干扰对策,实现锅炉燃烧系统控制工作稳定可靠,满足控制精度的要求。