Cubic Bézier approximation of a digitized curve

In this paper we present an efficient technique for piecewise cubic Bézier approximation of digitized curve. An adaptive breakpoint detection method divides a digital curve into a number of segments and each segment is approximated by a cubic Bézier curve so that the approximation error is minimized. Initial approximated Bézier control points for each of the segments are obtained by interpolation technique i.e. by the reverse recursion of De Castaljau's algorithm. Two methods, two-dimensional logarithmic search algorithm (TDLSA) and an evolutionary search algorithm (ESA), are introduced to find the best-fit Bézier control points from the approximate interpolated control points. ESA based refinement is proved to be better experimentally. Experimental results show that Bézier approximation of a digitized curve is much more accurate and uses less number of points compared to other approximation techniques.     

耐候钢连铸工艺的改进

分析耐候钢连铸出现的问题,认为凝固时应力过大和磷铜元素偏析造成晶界脆化是出现铸坯纵裂的主要原因;结晶器中喂稀土丝恶化保护渣性能,影响结晶器与坯壳间的润滑与传热,并使热流不均匀是连铸漏钢的主因。采用钙处理代喂稀土丝工艺,以及减缓连铸一、二次冷却强度,改进保护渣后,连铸缺陷获得极大改善。     

DTM350-600磨煤机大轴断裂分析

针对陕西渭河发电有限责任公司5号炉磨煤机乙磨大轴断裂失效进行了金属分析。结果表明应加强制造质量监控和实施设备全过程金属监督。     

FIC-330汽轮机组前箱齿轮断裂原因分析

蒲城1、2号机组自2001年10月19日以来，主油泵齿轮断齿5次，主齿轮断齿3次，严重危害机组的安全稳定运行。断齿原因涉及备品加工、检修安装、运行问题。经分析频繁断齿的主要原因为西航加工的备品齿轮齿表面渗碳强化层不均匀，硬度梯度大，断裂处渗碳层仅为0．3mm，齿根底存在严重的加工刀痕，使齿轮的接触和弯曲疲劳强度大幅下降。在刀痕底部形成压痕点，萌生裂纹，在渗碳层产生沿晶断裂，断裂过程为剪切断裂。     

变频调速地面驱动螺杆泵稠油开采技术

针对地面驱动螺杆泵抽油杆断、脱频繁，单井提液调参难以控制等问题，开发了螺杆泵井的变频调速装置及自动控制系统。该技术准确、实时地监控螺杆泵井的扭矩，转速等工况参数，并对螺杆泵井实施变频调速，自动控制从科学合理的调参。该技术的应用进一步提高了螺杆泵井的管理水平，有效的减缓了抽油杆的频繁断，脱问题，延长了检泵周期。     

数控加工中断的手动恢复技术

详细介绍了数控加工中断的手动恢复再加工技术,能使机床由中断加工的地方开始继续原来的加工,节省了加工时间,提高了生产效率。并列举了一个玩具模加工中断的应用实例。     

The relationship between crystallization and break temperature of mould flux

ABSTRACT

Many researchers believe that crystallization is responsible for drastic viscosity changes near the break temperature of mould flux; however, there are no reasonable experimental data to support this view. In this study, the complete crystallization process is recorded in situ by inhibiting the volatilization of fluoride, and the relationship between viscosity change and crystallization near the break temperature is studied. Mould flux with a basicity of 0.65 had no break temperature, and no crystallization occurs within the temperature range of the viscosity test. The other three mould fluxes begin to crystallize before the break temperature, but the crystal volume fractions at the break temperature are different. The break temperature of mould flux is the crystallization temperature with a critical crystal volume fraction, which is related to the viscosity before the break temperature. The higher the viscosity, the smaller the critical crystal volume fraction. Therefore, break temperature?≤?initial crystallization temperature.     

Testing for a break in persistence under long-range dependencies

Abstract.  We show that tests for a break in the persistence of a time series in the classical I (0)/ I (1) framework have serious size distortions when the actual data-generating process (DGP) exhibits long-range dependencies. We prove that the limiting distribution of a CUSUM of squares-based test depends on the true memory parameter if the DGP exhibits long memory. We propose adjusted critical values for the test and give finite sample response curves that allow easy implementation of the test by the practitioner and also ease in computing the relevant critical values. We furthermore prove the consistency of the test for a simple breakpoint estimator also under long memory. We show that the test has satisfying power properties when the correct critical values are used.     

Effect of organic and mineral matters on kinetic and performance of flocculation

Flocculation is a complicated and delicate stage since several parameters intervene and react with each other. The study of these flocculation parameters was the subject matter of various works. A view of literature shows that floc strength depends on its dimensions, structure, and age. However, flocculation constants K_A and K_B depend on the settling time, coagulant dosing and initial particle concentration. The aim of this present work is to visualize the effect of the dispersed particle's nature on floc strength and the evolution of kinetic constants K_A and K_B. In order to show the effect of a particle's nature, we studied six various synthetic suspended particles, namely: kaolin, often used by the authors; dam's mud; vegetal peat; mineralised secondary sludge, and two mixtures of mud and peat.The study comes out with:

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The breakup of floc is more significant when the organic matter rate is important.

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As the content of organic matter increases, the optimal disturbance power decreases.

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The interaction between mineral and organic matters is shown: it appears that an addition of mineral matter decreases the breakup constant K_B.

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The suspensions which contain less than 25% of organic matter behave like mineral suspensions with high effectiveness of turbidity elimination, low coagulant consumption, low residual coagulant, and the formed floc is strong.

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The flocculation of suspensions which contain 50% or more of organic matter exhibits excessive coagulant with poor elimination of turbidity, and the formed floc is fragile.

     

常一中换热器失效原因分析

通过对失效的常一中换热器进析了全面的检验及分析后，认为常一中换热器的壳体、管束和紧固螺栓的开裂是在含有碳酸盐的高温循环水的介质中，由于应力腐蚀而产生的沿晶脆性断裂，并提出了改进措施。