Tomographic reconstruction from experimentally obtained cone-beam projections

Direct reconstruction in three dimensions for two-dimensional projection data has been achieved by cone-beam reconstruction techniques. In this paper explicit formulas for a cone-beam convolution and back-projection reconstruction algorithm are given in a form which can be easily coded for a computer. The algorithm is justified by analyzing tomographic reconstructions of a uniformly attenuating sphere from simulated noisy projection data. A particular feature of this algorithm is the use of a one-dimensional rather than two-dimensional convolution function, greatly speeding up the reconstruction. The technique is applicable however large the cone angle of data capture and correctly reduces to the pure fan-beam reconstruction technique in the central section of the cone. The method has been applied to data captured on a cone-beam CT scanner designed for bone mineral densitometry.     

Digital restoration of scintigraphic images by a two-step procedure

A two-step procedure for restoring scintigraphic images is described. The first step uses a local-statistics algorithm for improvement in signal-to-noise ratio by smoothing the Poisson noise. The second step aims at improvement in spatial resolution by removing the linear blur using the iterative restoration algorithm. We present some results of computer simulations and restoration of scintigraphic images that demonstrate the effectiveness of the proposed procedure.     

Recursive algorithms for implementing digital image filters

The B-spline functions are used to develop recursive algorithms for the efficient implementation of two-dimensional linear digital image filters. These filters may be spatially varying. The B-splines are used in a representation of the desired point spread function. We show that this leads to recursive algorithms and hardware implementations which are more efficient than either direct spatial domain filter realizations or FFT implementations. The Z-transform is used to develop a discrete version of Duhamel's theorem. A computer architecture for B-spline image filters is proposed and a complexity analysis and comparison to other approaches is provided.     

Back pain in Grand Prix drivers: a 'found' experiment

The 'found' experiment uses a natural change in conditions to investigate the possible effects of those conditions. In this case, the natural change was reduction in stiffness of Grand Prix suspensions between 1982 and 1983. The effects of this change on back pain in drivers were investigated and it was found that both the incidence and severity of back pain decreased significantly. Of the various possible sources of back pain, only the ride changed over the same period. This suggests that mechanical shock and vibration are a significant cause of driving related back pain.     

Use of electron microscopy on microstructure characterization of high chromium cast irons

The physical metallurgy underlying the development of cast microstructures in abrasion resistant high chromium cast irons, and their structural modification by thermal treatments is relatively complex. Structural characterisation via electron microscopy therefore has a key role to play in furthering our understanding of the phase transformations that control the microstructures and hence the service performances of these irons as wear parts. This paper shows how both scanning and especially transmission electron microscopy can provide valuable information on the nature of eutectic and secondary carbides and on the matrix structures in these irons. Particular attention is given to current characterisation research on conventionally cast 30%Cr irons that are used for applications involving corrosive wear e.g. slurry pumps and on a semi-solid cast 27%Cr iron that has a potential for applications in industry.     

带冲孔接管的蒸汽发生器封头的制造

克鲁索-罗华公司发展了一种制造蒸汽发生器封头的新方法。这种方法的特点主要是在于使用一个轧出或锻出的单件厚板圆盘,先行模锻成球面形状,然后用专用工具冲出接管。这样得出的产品就可以兼而具有先前两种工艺方法即整铸法(例如铸造封头)和锻造法(例如组合封头)的优点。它可以不用任何焊接。克鲁索公司的锻造厂为了发展这种工艺方法,曾制定和执行了一个重大的试验研究计划,其中包括了:-按照缩小的比例制造几个零件-和富兰马汤公司共同定出封头的最佳设计-按比例1:1进行冲孔试验-在试件上作非破坏性和破坏性检查。在取得十分令人满意的结果之后,克鲁索-罗华公司就用这种方法着手制造八个封头。其中有两个已经向富兰马汤公司交货。我们认为也可以利用这种方法来生产类似形状的零件。     

用有限单元法分析轴承稳定性

术语c—轴承底部间隙,D—轴预直径,‘—轴承偏心距,h:—台阶或油腔深度,K—油膜厚度比,L—轴承轴向长度,L,—油腔轴向长度,L,—油腔轴向长度比,N—轴颈转速,牙—轴承外载荷,S—桑氏数(Somtnorfield数) 户m; em多 Cm; Cm;(c h:)/e, Cm多 Cm; L,/L多 r·P‘m; N;(瓮笋)白:—轴承偏心率,e/c;0—圆周座标,“(度);内—进油槽位置,。(度);“—平均动力粘度,N一em一s一汁x—减去进油槽后的圆弧长度“(度);xp—减去进油槽后的油腔角度,。(度);。—轴颈转速,s一、。.—刚性转子稳定性参数。 典型的压力阻断式或台阶式油腔轴承就是在衬垫上切出…     

淬火介质冷却能力的测定及评价

首先,要区别冷却能力(cooling power)和淬硬能力(hardening Dower)两个概念。冷却能力的各种试验方法,与现有的及推荐的淬火介质试验标准是同时存在的。针对被淬火材料(钢),提出了许多淬硬能力的试验方法。其中的一些方法已经提到过。在过去的年代,人们用许多方法描述淬火介质与淬火钢之间的相互关系。目前根据标准试验所记录的淬火介质冷却曲线,提出了一些新的确定淬硬能力的方法。根据对现有淬火介质淬硬能力的了解,针对每一种用途,选择最适宜的一种,是最简便的。文中给出了适合碳钢和低合金钢淬硬能力的几种商品淬火介质的明细表。     

反向洗涤装置的计算

文中公式与图表有助于溶质回收率、洗液速率和洗涤段数的计算,从而使反向洗涤装置的设计最为经济合理。用适宜的溶剂以洗     

包中精炼装置的设计、实现及其在锻造钢锭上的应用

CREUSOT-LOREI公司的布勒伊钢厂曾于一九七九年底安装了一套100t电弧加热的钢水包精炼装置。本文简要介绍一下该装置的情况及其操作方法。使用结果表明:电炉的生产常大大得到改善,同时又降低了铁合金的费用,用单独一台电炉即可生产出其重量需用两炉钢水的钢锭。改善了成分的分散情况,能获得很低的硫、磷含量,可按常规进行操作,又具有很大的可靠性。浇注温度的调节有明显改善。包中精炼看来是一种极好的手段,可以用来生产高级钢锭,经济效果也很好。