Rounding and stability in centreless grinding

The paper presents a method for selecting grinding conditions and assists researchers to understand the complex dynamics of centreless grinding. It overcomes the problem of deriving dynamic stability charts for particular geometries and difficulty of interpreting such charts to adjust work speed to overcome lobing problems. Classic dynamic stability charts cannot assess stability levels in proximity to integer lobes, a particular problem for centreless grinding. The paper overcomes these problems employing a simply calculated new dynamic stability parameter A_dyn. The new parameter A_dyn simplifies the optimisation of grinding variables including set-up geometry and work speed in relation to resonant frequency. It is difficult to interpret relative dynamic stability of centreless grinding by classical methods for different set-ups, work speeds and numbers of lobes. A new method is employed in this paper based on the well-established Nyquist stability criterion. The dynamic stability parameter A_dyn is based on the real part of the characteristic equation. It is easily computed and presented on a single chart for particular work speed, resonant frequency and for a wide range of numbers of lobes. The method clearly shows the effect on rounding strength both for stable and unstable conditions. Most authors computing dynamic stability charts have ignored positive down boundaries and negative up boundaries showing a lack of a comprehensive treatment for a situation that conflicts with recommendations for conventional positive up boundaries. The new method simplifies this problem.Small differences in set-up geometry and work speed selection can be easily assessed. The new method can be used as a diagnostic tool for adjusting grinding conditions to overcome roundness problems. The user is not constrained by a historic set-up range since there are practical situations where other set-ups are preferred such as small tangent angles for large and heavy work-pieces, and even negative tangent angle for some types of centreless machine.Previous research is reviewed to provide an understanding of the need for a new approach to stability. Practical implications are explained for selection of grinding conditions. The method is supported by reference to experimental results.     

Combustion characteristics of cotton stalk in FBC

The present work reports studies on the mixing and combustion characteristics of cotton stalk with 10–100 mm in length in FBC. Experiments on a cold model show that cotton stalk cannot fluidize, and adding bed material can improve the fluidization condition. Cotton stalk can mix well with 0.6–1 mm alumina at fluidization number N = 3–7. However, when the fluidization number is higher more than 7, the mixing bed will exist a little segregation comparing with N = 3–7. Thermogravimetric experiments show that cotton stalk can be ignited easily at a lower temperature, and its devolatilization and combustion are quick. Fluidized-bed combustion of cotton stalk was tested in a 0.2 MW_th test facility. According to the temperature distribution along the bed height, when the primary and secondary air is adapted cotton stalk can be burned stably in the fluidized bed. During pure cotton stalk combustion tests, silica sand and alumina are used as bed material to compare their agglomeration characteristics. SEM/EDX analysis on agglomerate samples after combustion about 38 h suggests that the high alkali metals content causes the formation of the coating around silica sand particles. The coating consists of compounds with low-melting temperature results in agglomeration of silica sand particles. By contrast, alumina is difficult to react with alkali metals from biomass ash, and the agglomeration of alumina was not found at 910 °C. It is found that alumina is more favorable than silica sand particle for use in a fluidized bed in cotton stalk combustion.     

An unusual 3-D asymmetric mixed valence copper-azido complex with pyrazinecarboxylate as co-ligand showing rare net topology: Hydrothermal synthesis,structure and magnetic properties

A new 3-D mixed valence copper-azido coordination polymer, [Cu^I · Cu^II(N₃)(pzc)₂ (H₂O)]_n1, has been synthesized and characterized, and its magnetic properties studied. In this compound, the azide acts as rare asymmetric μ_1,1,3 bridging mode. The azide ligands and the Cu(2) ions act as 3-connecting nodes, and the Cu(1) ions act as 4-connecting nodes. The overall net takes rare topology with the Schläfli symbol of (6.8²)(6.8²)(6.8⁵).     

Extrusion of AlSBA-15 molecular sieves: An industrial point of view

AlSBA-15 in the powder form with different n_Si/n_Al ratios (45, 136 and 215) were synthesized by hydrothermal technique. The powdered materials were made into cylindrical extrudates with the addition of bentonite as a binder. The AlSBA-15 materials were characterized by XRD, N₂ adsorption, AAS and thermogravimetric analysis. The orderly growth of AlSBA-15 is evidenced by its XRD. The surface area of the powder catalyst is around 950 m²/g and that of extrudate is close to 600 m²/g. Vapor phase alkylation of phenol with tert-butanol was carried out over the extrudates of AlSBA-15 as a model reaction. The activity of AlSBA-15 extrudates follows the order: AlSBA-15 Si/Al = 45 > AlSBA-15 Si/Al = 136 > AlSBA-15 Si/Al = 215. The reaction products were found to be 2-TBP, 4-TBP and 2,4-DTBP. The selectivity to para tertiary butylation is higher than other reactions.     

基于ESL设计方法的数字滤波器的设计与验证

通过对ESL设计方法的研究,提出了一种采用ESL设计方法实现数字滤波器的设计与验证的方案。首先介绍了Synplicity公司提供的ESL设计工具Synplify DSP,重点研究使用Synplify DSP进行数字滤波器的设计,然后从Synplify DSP模块转换成VHDL语言,并进行协同验证,达到了理想的效果。     

Effect of experimental methodology on the JND of the black level for natural images

Abstract— The effect of experimental methodology on the Just Noticeable Difference (JND) of the black level (BL) is assessed using a set of representative natural images. Two methodologies, known in psychophysics to determine JNDs, are mutually compared: an adapted method of adjustment with a same‐difference task and a one‐up‐two‐down staircase method with a two‐alternative forced‐choice task. Thus far, the literature has shown contradictory results for which of the two methods yields the lower difference thresholds. Experimental results show that the second method yields lower JNDs, but is slightly less efficient. Based on this second method, it was found that the JND of the BL for natural images ranges from 0.2 to 1.0 cd/m², varying with image content significantly.     

Evolution of road-surface skid-resistance and texture due to polishing

In this paper, works are conducted to have a better understanding of the evolution of the road-surface texture due to traffic polishing. Examples are shown for two aggregates having respectively low and high - polishing-resistances. Surface profiles measured at different polishing stages are analyzed. Roughness parameters characterizing asperity height and sharpness are calculated and their evolution is compared with the friction evolution.     

高层框架-简体结构弹塑性分析方法的改进

采用杆系-层间模型,提出多阶变刚度框架-简体结构的连续-离散化方法,推导出框架-筒体结构的单元刚度矩阵和整体刚度矩阵.编制了考虑框架与筒体协同工作,并且能够分析每根杆件的结构动力时程分析程序,程序中考虑了简体空间作用、P-△效应等,该程序已应用于一些高层建筑的结构分析.     

ADAPTIVE ALGORITHM FOR CONSISTENTMA PARAMETER ESTIMATION VIATHIRD ORDER CUMULANT

This paper addresses the problem of adaptive,consistent parameter estimation for a MA model from the 3rd order cumulant of the system output. The proposed adaptive algorithm is derived by using the new linear equation system (J. K. Tugnait, 1990), which is proved to have unique solution,and hence guarantees the consistence of the MA parameters. Simulation results are provided to show the performance of the new algorithm.     

数控车床实习方法探讨

介绍了三种数控实习方法,训练学生对数控车床的操作.