Optimization of Selective Assembly for Shafts and Holes Based on Relative Entropy and Dynamic Programming

Selective assembly is the method of obtaining high precision assemblies from relatively low precision components. For precision instruments, the geometric error on mating surface is an important factor affecting assembly accuracy. Different from the traditional selective assembly method, this paper proposes an optimization method of selective assembly for shafts and holes based on relative entropy and dynamic programming. In this method, relative entropy is applied to evaluate the clearance uniformity between shafts and holes, and dynamic programming is used to optimize selective assembly of batches of shafts and holes. In this paper, the case studied has 8 shafts and 20 holes, which need to be assembled into 8 products. The results show that optimal combinations are selected, which provide new insights into selective assembly optimization and lay the foundation for selective assembly of multi-batch precision parts.     

Controllable synthesis and enhanced visible photocatalytic degradation performances of Bi2WO6–carbon nanofibers heteroarchitectures

Bi₂WO₆–carbon nanofibers (Bi₂WO₆–CNFs) heteroarchitectures were fabricated by two steps consisting of the preparation of CNFs by electrospinning and growth of Bi₂WO₆ on the CNFs through ethylene glycol solvothermal processing. The results showed that the loading amounts of Bi₂WO₆ on the surface of CNFs could be controlled by adjusting the precursor concentration for the fabrication of Bi₂WO₆–CNFs heteroarchitectures during the solvothermal process. The photocatalytic tests revealed that the obtained Bi₂WO₆–CNFs heteroarchitectures showed higher photocatalytic property under visible light to degrade Rhodamine B than pure Bi₂WO₆ synthesized by solvothermal process in the absence of CNFs owing to improved separation efficiency of photogenerated electrons and holes. Moreover, the Bi₂WO₆–CNFs heteroarchitectures could be separated easily by sedimentation due to their one-dimensional nanostructural property. Meanwhile, the photocatalytic activity of Bi₂WO₆–CNFs heteroarchitectures was stable during the recycling due to the strong interactions between Bi₂WO₆ nanosheets and CNFs. Trapping experiment suggested that ${\text{O}}_{ 2}^{ \cdot - }$ , instead of OH·, was the main active species during the photocatalytic process of the Bi₂WO–CNFs heteroarchitectures.     

Optimized design of two-pump fiber optical parametric amplifier and its noise characteristics

In the paper, based on the pump depleted model of two-pump fiber optical parametric amplifier (FOPA), the simulations are done to indicate the effect of amplifier parameters on gain characteristics, such as the input signal power, the wavelength separation between the two pumps, the fiber length, the nonlinear coefficient and the fourth-order dispersion of fiber. By optimizing the amplifier parameters, when FOPA attains low gain-saturation, the FOPA has a higher gain, a broader flat gain bandwidth and a lower noise figure. However, with the enhancement of gain-saturation the parametric gain decreases, the flat gain bandwidth becomes narrow and the noise figure also increases.     

Design and parametric amplification analysis of dispersion-flat photonic crystal fibers

We present a modified method to design photonic crystal fibers (PCFs) with flattened dispersion characteristic. Using this modified PCF we design a broadband fiber optical parametric amplifier (FOPA),which provides a gain of 8 dB with 1.5-dB uniformity over a 260-nm bandwidth. Both the simulation results of total dispersion of PCF and the gain spectrum of FOPA are demonstrated.     

A hybrid Bayesian network learning method for constructing gene networks

A Bayesian network (BN) is a knowledge representation formalism that has proven to be a promising tool for analyzing gene expression data. Several problems still restrict its successful applications. Typical gene expression databases contain measurements for thousands of genes and no more than several hundred samples, but most existing BNs learning algorithms do not scale more than a few hundred variables. Current methods result in poor quality BNs when applied in such high-dimensional datasets. We propose a hybrid constraint-based scored-searching method that is effective for learning gene networks from DNA microarray data. In the first phase of this method, a novel algorithm is used to generate a skeleton BN based on dependency analysis. Then the resulting BN structure is searched by a scoring metric combined with the knowledge learned from the first phase. Computational tests have shown that the proposed method achieves more accurate results than state-of-the-art methods. This method can also be scaled beyond datasets with several hundreds of variables.     

Morphology and thermal properties of polyhedral oligomeric silsesquioxane/polybutadiene nanocomposites prepared by anionic polymerization

The morphology and thermal properties of Allylisobutyl Polyhedral Oligomeric Silsesquioxane (POSS)/Polybutadiene (PB) nanocomposites prepared through anionic polymerization technique were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results of XRD, SEM and TEM showed that the aggregation of POSS in PB matrix occurred obviously, forming crystalline domains and the size of POSS particles increased with increasing POSS content. The DSC and TGA results indicated that the glass transition temperature (T _g) of the nanocomposites was significantly increased and the maximum degradation temperature (T _dmax) of nanocomposites was slightly increased compared with pure PB, implying an increase in thermal stability.     

Study on microwave induced plasma atomic absorption spectrometry (MIP-AAS) for the determination of calcium in axial viewing mode

A low-power surface-wave plasma device (surfatron) is employed as an atomizer for microwave induced plasma atomic absorption spectrometry (MIP-AAS) and a desolvation-condensation apparatus has been used to remove the solvent in the aerosol. An axial viewing absorption technique is adopted for the determination of calcium. The matrix effect on its determination has been investigated in detail. Some enhancing effects are observed on the calcium absorbance in the presence of organic additives. A possible mechanism for this enhancement is discussed.     

朗缪探针移动数控装置

一、前言 利用朗缪探针来探测等离子体参数及其分布规律,既简便又有效,其要求是探针及其传动机构的引入不要影响或尽量小影响装置的真空度以及等离子体行为。 等离子体参数的空间分布靠移动探针的几何位置测出。探针移动的最简易的方法是手动。它的缺点不仅在抽插探针的过程中影响到装置的真空度,而且对于由扰动引起的某些随时     

原位插层聚合制备聚丁二烯/蒙脱土纳米复合材料及其结构与性能研究

采用负离子引发原位插层聚合法制备了聚丁二烯(PB)/有机蒙脱土(OMMT)纳米复合材料(NC).对OMMT纯化方法、OMMT种类和溶剂等因素对聚合反应的影响进行了研究.不同方法纯化的OMMT消耗的BuLi量相差一倍;采用OMMT-DK1制备的NC具有较宽的分子量分布,而采用OMMT-DK1B和OMMT-DK4制备的NC则具有较窄的分子量分布;OMMT在环己烷中不溶解,在甲苯和二甲苯等溶剂中可形成均匀溶液.采用XRD、TEM和H-NMR等仪器对PB/OMMT NC的插层结构、化学结构和形态进行了分析;采用DSC、TGA和DMA等仪器对PB/OMMT NC的Tg、热学性能和动态力学性能进行了研究,结果表明,采用负离子原位插层聚合可得到剥离型PB/OMMT纳米复合材料;与OMMT插层复合明显改变了PB的微观结构组成,在OMMT含量为6.2wt%时,1,2-结构含量增加了近一倍,Tg和Tdc分别增加了10 K和16 K;E′、E″均明显提高,而tanδ下降.     

Facile syntheses of 2,2-dimethyl-6-(2-oxoalkyl)-1,3-dioxin-4-ones and the corresponding 6-substituted 4-hydroxy-2-pyrones

A variety of 2,2-dimethyl-6-(2-oxoalkyl)-1,3-dioxin-4-ones 5a-l and the corresponding 6-substituted 4-hydroxy-2-pyrones 3a-l were prepared in high yields under mild reaction conditions by the reaction of 2,2,6-trimethyl-1,3-dioxin-4-one 4 with 1-acylbenzotriazoles 9 in the presence of LDA followed by thermal cyclization of 5a-l to 3a-l. Synthesis of novel 6-(1-benzoylalkyl)-2,2-dimethyl-1,3-dioxin-4-ones 12a-c was achieved by alkylation of dioxinone 5a and their subsequent cyclization gave 5-alkyl-4-hydroxy-2-pyrones 13a-c.