2维全自动亥姆霍兹线圈磁块测量方法

在波荡器和扭摆器的研制过程中,为提高磁块的测量效率和精度,提出了2维全自动亥姆霍兹线圈磁块测量方法。通过理论推导得到仅采用2维全自动旋转而不需要3维旋转就可以实现磁块的全自动测量,降低了磁块全自动测量的实现难度。根据该方法的理论,已成功研制出一台2维全自动亥姆霍兹线圈测量装备,并在上海光源的磁块测量中使用。系统地给出2维全自动亥姆霍兹线圈磁块的测量理论和方法,并对测量误差进行了分析,该系统实现了磁块剩磁测量的高效率、高精度和高重复性,可以在30 s内完成单磁块的测量,重复性和精度均好于510-4。     

Adaptive synchronization of chaos in permanent magnet synchronous motors based on passivity theory

An adaptive synchronization control method is proposed for chaotic permanent magnet synchronous motors based on the property of a passive system. We prove that the controller makes the synchronization error system between the driving and the response systems not only passive but also asymptotically stable. The simulation results show that the proposed method is effective and robust against uncertainties in the systemic parameters.     

Adaptive synchronization of chaos in permanent magnet synchronous motors based on passivity theory

An adaptive synchronization control method is proposed for chaotic permanent magnet synchronous motors based on the property of a passive system.We prove that the controller makes the synchronization error system between the driving and the response systems not only passive but also asymptotically stable.The simulation results show that the proposed method is effective and robust against uncertainties in the systemic parameters.     

人牙釉质的酸蚀行为研究

通过体外原位酸蚀试验,采用显微硬度仪、台阶仪、SEM和EDX等考察了在pH=3.20的柠檬酸溶液作用下,人牙釉质表面硬度、组织结构、化学组成等性能随酸蚀时间的变化关系,初步分析了牙釉质在柠檬酸溶液中的酸蚀过程和机制.结果表明,在柠檬酸溶液中腐蚀1 min后,牙釉质无明显酸蚀损伤;腐蚀3 min后,牙釉质表面硬度及Ca、P含量均明显降低,釉质表面旱现酸蚀损伤,腐蚀深度为0.236 μm;随酸蚀时间继续延长,牙釉质表面损伤进一步加剧.形貌分析显示:在腐蚀初期,人牙釉质内的釉柱先于相邻釉间质发生酸蚀剥落,而釉柱丧失会进一步加剧釉间质的酸蚀,两者互相促进,最终导致牙釉质表面发生实质性的硬组织丧失.     

纳米晶复合永磁材料的交换耦合相互作用和磁性能

本介绍了纳米磁性材料晶粒交换耦合相互作用的有关理论。采用不同模型讨论了晶粒交换耦合相互作用对纳米单相软磁材料、永磁材料及双相复合永磁材料磁性能的影响。简述了用δM（H）曲线和不可逆磁导率的变化研究晶粒交换耦合相互作用及反磁化过程的方法。讨论了合金分配比、添加元素、制备及热处理工艺对磁体硬磁性能的影响。从理论和实验两方面分析、研究了纳米复合永磁材料的反磁化过程和矫顽力机制。     

Application of Tungsten-Rhodium Permanent Chemical Modifier in Slurry Analysis: Determination of Cadmium

 A tungsten-rhodium coating on the integrated platform of a transversely heated graphite atomiser (THGA) was used as a permanent chemical modifier for the determination of Cd in sediment slurries by electrothermal atomic absorption spectrometry. Slurries were ultrasonicated during 20 s before being delivered to the previously W-Rh treated platform. The permanent W-Rh modifier remains stable by approximately 250 measurements when 20 μl of slurries containing up to 1.0% m/v are delivered into the atomiser. In addition, the permanent modifier increases the tube lifetime up to 720 analytical firings. Also, when the W-Rh permanent modifier was employed, there was less variation of the slope of the analytical curves during the total atomiser lifetime, resulting in a decreased need of re-calibration during routine analysis, increasing the sample throughput. The atomiser lifetime was limited to the THGA wall durability, because the W-Rh treated platform was intact after more than 720 analytical firings. Detection limits based on integrated absorbance for 1.0% m/v slurries were 1.5 ng g⁻¹ Cd for 250 μg W +200 μg Rh permanent modifier and 11.5 ng⁻¹ Cd for 5 μg Pd +3 μg Mg(NO₃)₂. Results for the determination of cadmium in sediment slurries using the W-Rh permanent modifier were in agreement with those obtained with dissolved sample solutions by using Pd + Mg(NO₃)₂, since no statistical differences were found by the paired t-test at the 99% level. Received September 6, 1999. Revision December 1, 1999.     

矩形永磁体磁场分布的解析表达式

从分子环流模型出发,利用毕奥-萨伐尔定理,对于仅在一个方向均匀完全充磁的矩形永磁块体,导出了其外部空间磁场分布的解析表达式．该解析式能精确描述一块至多块按极性相反并列放置时矩形永磁体外部空间的磁场分布．针对单块永磁体,还分析了磁场分布与永磁体几何尺寸之间的依赖关系,以及磁场大小随外部空间点离开永磁体表面距离之间的关系;定量分析了横向磁场的强度均匀度和分布均匀度随永磁体几何尺寸和离开永磁体表面距离的变化规律．     

Bone Grafts and Substitutes in Dentistry: A Review of Current Trends and Developments

After tooth loss, bone resorption is irreversible, leaving the area without adequate bone volume for successful implant treatment. Bone grafting is the only solution to reverse dental bone loss and is a well-accepted procedure required in one in every four dental implants. Research and development in materials, design and fabrication technologies have expanded over the years to achieve successful and long-lasting dental implants for tooth substitution. This review will critically present the various dental bone graft and substitute materials that have been used to achieve a successful dental implant. The article also reviews the properties of dental bone grafts and various dental bone substitutes that have been studied or are currently available commercially. The various classifications of bone grafts and substitutes, including natural and synthetic materials, are critically presented, and available commercial products in each category are discussed. Different bone substitute materials, including metals, ceramics, polymers, or their combinations, and their chemical, physical, and biocompatibility properties are explored. Limitations of the available materials are presented, and areas which require further research and development are highlighted. Tissue engineering hybrid constructions with enhanced bone regeneration ability, such as cell-based or growth factor-based bone substitutes, are discussed as an emerging area of development.     

单片机在牙齿光学检测中的应用

本文论述了8031单片机在牙齿光学检测系统中所起的作用。并描述了牙齿活力和脱钙的检测方法。这种方法,是通过对牙齿表面磷光或反射光的客观测量来实现的。从而,解决了以前人们曾不能解决的问题。     

粘结NdFeB永磁体化学镀Ni-Cu-P防护层工艺过程研究

研究了粘结NdFeB永磁体化学镀Ni Cu P合金防护层的工艺过程。研究表明:粘结磁体经碱性去油、缓蚀酸洗、镀前隔离与活化处理后再进行化学镀Ni Cu P,可获得镀层光亮平整,结合力好,孔隙率为每平方厘米0.5个,腐蚀速率为0.07mg·cm-2·h-1的耐蚀性镀层,该镀层对磁体磁性能无不良影响。