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991.
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993.
针对筒体带大接管的内压容器在相贯区附近会产生较高的应力集中这一问题,考虑材料的塑性变形特性,对不同开孔率的内压容器结构进行了一系列的弹塑性有限元分析。计算结果表明,纵向对称面筒体与接管的内相贯处是应力集中最严重的部位,外相贯处由于有焊接接头而使应力集中大大缓解。在逐步加载过程中,加载前期相贯区周边应力呈线性增长,一定程度后主要表现为高应力范围的扩大。对于均处于塑性阶段的结构而言,开孔率的大小对高应力区的分布范围影响较大。与未带接管的大开孔结构相比,接管的添加大大降低了孔周边的应力集中。 相似文献
994.
Qingyu Liu Guang Zhu Kan Wang Jianhua Zhang Chunjie Dong 《Materials and Manufacturing Processes》2016,31(4):391-396
Understanding the effect of processing parameters on the tool electrode wear during micro-electrical discharge machining (micro-EDM) is helpful to predict and compensate the electrode wear, so as to improve the machining precision. In this paper, experiments are carried out and the influences of tool electrode diameter on the micro-EDM process are discussed based on the skin effect and area effect. It is demonstrated that the machining speed, tool wear, and taper rate are different with the increase of tool electrode diameter. Due to the skin effect and area effect, larger electrode diameter results in higher material removal rate along with higher tool wear rate. The electrode material removal increment is more than the workpiece material removal increment with the increase of tool electrode diameter, which leads to the increase of relative tool wear ratio. Discharge energy is concentrated on the tool surface which enhances the possibility of discharge on the side face and the corner of the tool electrode during the micro-EDM, especially when drilling with a larger tool electrode. As a result, a tool electrode with larger diameter results in a higher taper rate. 相似文献
995.
TiO2 Nanorod Array Constructed Nanotopography for Regulation of Mesenchymal Stem Cells Fate and the Realization of Location‐Committed Stem Cell Differentiation 下载免费PDF全文
Jichuan Qiu Jianhua Li Shu Wang Baojin Ma Shan Zhang Weibo Guo Xiaodi Zhang Wei Tang Yuanhua Sang Hong Liu 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(13):1770-1778
As a physical cue for controlling the fate of stem cells, surface nanotopography has attracted much attention to improve the integration between implants and local host tissues and cells. A biocompatible surface TiO2 nanorod array is proposed to regulate the fate of bone marrow derived mesenchymal stem cells (MSCs). TiO2 substrates with different surface nanotopographies: a TiO2 nanorod array and a polished TiO2 ceramic are built by hydrothermal and sintering processes, respectively. The assessment of morphology, viability, gene expression, and protein characterization of the MSCs cultured on the different TiO2 substrates proves that a TiO2 nanorod array promotes the osteogenic differentiation of MSCs, while a TiO2 ceramic with a smooth surface suppresses it. Periodically assembled TiO2 nanorod array stripes on the smooth TiO2 ceramic are constructed by a combination of microfabrication and a chemical synthesis process, which realizes the location‐committed osteogenic differentiation of MSCs. A route to control the differentiation of MSCs by a nanostructured surface, which can also control the location and direction of MSCs on the surface of biomaterials with micro‐nano scale surface engineering, is demonstrated. 相似文献
996.
Grigorios Loukides Aris Gkoulalas-Divanis Jianhua Shao 《Knowledge and Information Systems》2013,36(1):153-210
Transaction data are increasingly used in applications, such as marketing research and biomedical studies. Publishing these data, however, may risk privacy breaches, as they often contain personal information about individuals. Approaches to anonymizing transaction data have been proposed recently, but they may produce excessively distorted and inadequately protected solutions. This is because these approaches do not consider privacy requirements that are common in real-world applications in a realistic and flexible manner, and attempt to safeguard the data only against either identity disclosure or sensitive information inference. In this paper, we propose a new approach that overcomes these limitations. We introduce a rule-based privacy model that allows data publishers to express fine-grained protection requirements for both identity and sensitive information disclosure. Based on this model, we also develop two anonymization algorithms. Our first algorithm works in a top-down fashion, employing an efficient strategy to recursively generalize data with low information loss. Our second algorithm uses sampling and a combination of top-down and bottom-up generalization heuristics, which greatly improves scalability while maintaining low information loss. Extensive experiments show that our algorithms significantly outperform the state-of-the-art in terms of retaining data utility, while achieving good protection and scalability. 相似文献
997.
998.
A typical thermal-contact sensor (TCS) used in hard-disk drives was investigated by the simulation. Analytical solution to solve temperature variation of sensor due to frictional heat was built to estimate the sensor temperature rise under variable heating power and interference height between the head and disk. To accurately and systematically qualify sensor-temperature distribution and resistance variation under certain variable conditions and sensor time constant, head housing a TCS was modeled by ANSYS commercial software, and thermal-mechanics of TCS coupled with air bearing dynamics was simulated. Simulated results indicated that a TCS with a proper size of 1 μm or less had a maximum resistance variation on friction induced heating to generate a maximum TCS signal output. The sensor-heating maximum protrusion was less that 0.1 nm, and time constant of TCS is about 0.125 μs and its response frequency is about 8 MHz. With a highly accurate measurement system, TCS can detect out asperities of tens of nanometers or less. These results will be helpful in developing and designing thermal-contact sensors for use in hard-disk drives. 相似文献
999.
1000.
稳步推进长江流域综合管理的思考 总被引:1,自引:0,他引:1
在分析国外流域管理发展历程与现状的基础上,介绍了流域综合管理的概念、内涵、目标和任务。针对长江流域涉水事务管理现状和存在问题,从健全管理法规、创新管理体制、建立管理机制、完善管理制度、加强执法监督、提升管理能力等六个方面提出了推进长江流域综合管理的对策和措施。 相似文献