Optimization of Added Permanent Magnet Amount in Synchronous Reluctance Machines for High Performance

ＩｎｔｒｏｄｕｃｔｉｏｎＳｙｎｃｈｒｏｎｏｕｓｒｅｌｕｃｔａｎｃｅ（ＳＲ）ａｎｄｐｅｒｍａｎｅｎｔｍａｇｎｅｔ（ＰＭ）ｍａｃｈｉｎｅｓ,ｗｈｉｃｈａｒｅｓｅｐａｒａｔｅｌｙｄｅｖｅｌｏｐｅｄａｎｄｕｓｅｄｉｎｉｎｄｕｓｔｒｉａｌａｐｐｌｉｃａｔｉｏｎ...     

Metallurgical factors determining the coercivity of ND-FE-B magnets

In Nd-Fe-B based permanent magnets a high magnetocrystalline anisotropy of the hardmagnetic phase is necessary for a high intrinsic coercivity. In fact, metallurgical parameters (distribution of phases, chemical composition and crystal structures of phases) and processing parameters (alloy preparation, size and shape of particles, sintering and annealing treatments) determine the value of the coercive force of each sintered Nd-Fe-B magnet. Our analytical electron microscope study shows that melt-spun and sintered Nd-Fe-B based magnets contain more or less a distribution of nucleation centres for reversed domains, such as iron-rich phases and-iron precipitates within the hardrnagnetic 2141-grains. A continuous non-magnetic layer phase between the hardrnagnetic 2141-grains increases the expansion field of reversed domains and increase the coercivity. In melt-spun magnets the contribution of the pinning of magnetic domain walls becomes effective during the magnetization reversal process.     

Computing the Kekulé structure count for alternant hydrocarbons

A fast computer algorithm brings computation of the permanents of sparse matrices, specifically, molecular adjacency matrices. Examples and results are presented, along with a discussion of the relationship of the permanent to the Kekulé structure count. A simple method is presented for determining the Kekulé structure count of alternant hydrocarbons. For these hydrocarbons, the square of the Kekulé structure count is equal to the permanent of the adjacency matrix. In addition, for alternant structures the adjacency matrix for N atoms can be written in such a way that only an N/2 × N/2 matrix need be evaluated. The Kekulé structure count correlates with topological indices. The inclusion of the number of cycles improves the fit. When comparing with previous results, the variance decreases 74%. The calculated standard heat of formation correlates with the logarithm of the Kekulé structure count. This heat increments 349 kJ/mol each time the Kekulé structure count increases by one order of magnitude. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Synthesis and characterization of MCM-48 tubular membranes

MCM-48 membranes have been prepared on alumina supports of different pore sizes. A battery of characterization techniques has been used to study the physical properties and the quality of the membranes prepared. The highest quality membranes were prepared on supports with pore size of up to 60 nm. The MCM-48 membranes were tested in the separation of gas phase mixtures and a cyclohexane/O₂ selectivity higher than 270 was obtained. The selective separation of organic compounds from inert components is a result of the cooperative effects of capillary condensation in MCM-48 pores and of the specific interactions of the permeating compounds and the membrane material.     

Direct determination of selenium in urine samples by electrothermal atomic absorption spectrometry using a Zr plus Rh-treated graphite tube and co-injection of Rh as chemical modifier

Different chemical modifiers for use with electrothermal atomic absorption spectrometry (ET AAS) were investigated in relation to determining the selenium in human urine samples. The samples were diluted in a solution containing 1% v/v HNO₃ and 0.02% m/v cetyltrimethylammonium chloride (CTAC). Studying the modifiers showed that the use of either Ru or Ir as the permanent modifier gave low sensitivity to Se and the peak shape was very noisy, while Zr or Rh gave no peak at all. The same occurred when Zr was used in solution. For mixtures of permanent modifiers, Ir plus Rh or Zr plus Rh gave very low sensitivity, Zr plus Rh with co-injection of Ir in solution was also not efficient, Zr plus Rh in solution gave good sensitivity, but the best results were obtained with a mixture of Zr and Rh as the permanent modifier and co-injection of Rh in solution. Using this last modifier, the following dilutions with the HNO₃ and CTAC were studied: 1:1, 1:2, 1:3 and 1:4. The best dilution was 1:1, which promoted good sensitivity and a more defined peak shape and made it possible to correct for the background using a deuterium arc lamp. Under these conditions, a characteristic mass of 26±0.2 pg was obtained for Se in aqueous solution. Six certified urine samples were analyzed using matrix matching calibration and the measured concentrations were in agreement with the certified values, according to a t-test at the 95% confidence level. Recovery tests were carried out and the recoveries were in the range 100–103%, with relative standard deviation better than 9%. The limit of detection (LOD, 3 sd, n=10) was 3.0 μg L⁻¹ in the sample. The treated graphite tube could be used for at least 600 atomization cycles without significant alteration of the analytical signal.     

城市建筑复合绿化方法研究

探讨了当代城市中绿化建设的理想化模式,对城市复合绿化模式进行了比较、分析,并结合建筑师爱米利奥的覆盖理论,提出了与建筑空间紧密结合的,多层次、多维度的复合绿化模式.针对当前城市绿化中仅注重局部利益,忽视整体效益的弊病,提倡将城市绿化及建筑两大系统加以整合,突出其综合效益的最大化.     

园林绿化种植设计初探

阐述了选择树种在种植设计中的重要性，提出了树种选择的原则，讨论了近年来在设计中出现的问题。     

一类非自治传染病SIS模型概周期解存在惟一性

对系数是概周期函数的传染病SIS模型进行了研究,得到了概周期解存在惟一的一个充分条件.     

永磁发电机用永磁材料的选择

介绍了永磁材料的性能特点，分析了两种常用永磁材料的性能对小型农用车发电机性能、工作稳定性和经济性的影响，确定小型农用车发电机应选用铁氧体永磁材料．     

利用驻极体提供均匀外场和屏蔽外场的设计

利用驻极体具有的可任意切割、拼装、黏接的特性，从静电学的基本规律及由泊松方程构成的静电边值问题出发，对驻极体既可对外提供电场又可设计为屏蔽电场的2个相异思维的研究结果展开了讨论，从而，从理论上指出驻极体既可以制成提供均匀外场的材料又可以制成一种透气性静电屏蔽材料．这为驻极体的工程实际应用提供了基础．