Graphical comparison of sets of repair data

Many products accumulate repairs and repair costs. Analysis of such recurrence data requires special statistical models and methods, which do not appear in basic reliability books. This expository paper presents models and methods for plotting and comparing two such data sets using confidence limits. The methods are applied here to repair data on automatic and manual transmissions of cars. Computer programs that perform the calculations and make the plots are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

How to simulate normal data sets with the desired correlation structure

The Cholesky decomposition is a widely used method to draw samples from multivariate normal distribution with non-singular covariance matrices. In this work we introduce a simple method by using singular value decomposition (SVD) to simulate multivariate normal data even if the covariance matrix is singular, which is often the case in chemometric problems. The covariance matrix can be specified by the user or can be generated by specifying a subset of the eigenvalues. The latter can be an advantage for simulating data sets with a particular latent structure. This can be useful for testing the performance of chemometric methods with data sets matching the theoretical conditions for their applicability; checking their robustness when the hypothesized properties fail; or generating data from multi-stage or multi-phase processes.     

Determination of the effective mode-I toughness of a sinusoidal interface between two elastic solids

A finite element model of crack propagation along a sinusoidal interface with amplitude A and wavelength λ between identical elastic materials is presented. Interface decohesion is modeled with the Xu and Needleman (J Mech Phys Solid 42(9):1397, 1994) cohesive traction–separation law. Ancillary calculations using linear elastic fracture mechanics theory were used to explain some aspects of stable and unstable crack growth that could not be directly attained from the cohesive model. For small aspect ratios of the sinusoidal interface (A/λ ≤ 0.25), we have used the analytical Cotterell–Rice (Intl J Fract 16:155–169, 1980) approximation leading to a closed-form expression of the effective toughness, K _Ic , given by where is the work of separation, E is Young’s modulus, and ν is Poisson’s ratio. For A/λ > 0.25, both the cohesive zone model and numerical J-integral estimates of crack tip stress intensity factors suggest the following linear relationship: Parametric studies show that the length of the cohesive zone does not significantly influence K _Ic , although it strongly influences the behavior of the crack between the initiation of stable crack growth and the onset of unstable fracture. An erratum to this article can be found at     

Determination of residual stresses in welded components by finite element analysis

The continued safe and reliable operation of plant invariably has to consider the assessment of defects in welded structural components. This requires some estimate of the residual stresses that have developed during the welding fabrication process. There is an increasing use of computational weld mechanics to evaluate residual stresses and this paper describes the development of guidelines for using finite element analysis, which are now incorporated into the EDF Energy R6 defect assessment procedure, to determine stresses for use in the procedure. Prior to use in assessment the predicted results should be validated by comparison with measurements and the guidelines provide advice on the differing standards of validation which may be applied including the manufacture and testing of validation mock-ups.

This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.     

A comparison of two methods of analysing staircase fatigue test data

When the fatigue strength of components or material is tested by the staircase or up‐and‐down method, the data can be analysed in either the fatigue strength domain, which is the most popular approach, or the life domain, based on life regression models. In this paper we exploit a simple relationship between families of models in the two domains to obtain an estimate of the distribution of fatigue strength directly from a fitted life regression model. We use simulation to compare the two approaches, concluding that for estimating important features of the fatigue strength distribution the method of maximum likelihood is more effective if it is applied in the life domain. In particular, it is more robust to the choice of x_h, the step height of the staircase, provided x_h is in the range σ_X–2σ_X, where σ_X is the standard deviation of the log‐strengths. Most of our results are insensitive to the value of the initial stress amplitude. Copyright © 2007 John Wiley & Sons, Ltd.     

Communications and cohesion: a comparison between two command and control paradigms

This article negotiates a path between the ecological validity of field trials, the precision of mathematical modelling and the formality of lab-based experimentation. It does this by taking a longitudinal approach to comparing two types of command and control organisations. The object of the study was to use social network and simple time series analysis to test the assumption that organisational design factors can lead to systematic changes in the quantity, structure and type of communication. Further that these changes lead to corresponding improvements in team cohesion over time. The longitudinal design enables novice teams to become expert in their task, for critical task variables to be preserved and controlled, and for effects to emerge over time. It is apparent that contemporary advances in command and control architectures may not be merely technically effective (in terms of enhanced communications) but also jointly optimised (in terms of greater team cohesion).     

Thermoviscoelastic model of a layer between two bodies and conditions of their conjugation

On the basis of the Kelvin-Voigt-type thermomechanical theory of viscoelasticity, by the method of averaging over the thickness, we develop a thermoviscoelastic model of thin intermediate layer and establish generalized Winkler-type thermomechanical conjugation conditions for solid bodies in the dynamical mode for the case of imperfect thermal contact. It is shown that these conditions can be regarded as a generalization of the classical model. Relations convenient for practical applications are deduced. Various classical conditions of thermomechanical contact and their generalizations are obtained as a result of the limiting transition performed under additional assumptions concerning the moduli of elasticity of the intermediate layer. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 3, pp. 35–43, May–June, 2007.     

两种超声清洗槽的声场分布比较

本文作者设计了一种斜底式超声清洗槽，并通过实验研究了它的声场分布，与平底式超声清洗槽相比，这种新型清洗槽深度方向的声场均匀性得么了改善，但水平方向的声场均匀性变化不大。     

Development and Validation of a Rapid HPLC Method for the Determination of Ketotifen in Pharmaceuticals

ABSTRACT

In the present study, a simple, sensitive, rapid, and stability-indicating high performance liquid chromatographic (HPLC) method with ultraviolet detection for the analysis of ketotifen was developed and validated. The method was applied to the determination of ketotifen in pharmaceutical formulations (tablets and syrups). The HPLC method utilized isocratic elution technique with a reversed phase C8 column, detection at 297 nm and a mixture of methanol, triethylamine phosphate buffer (pH 2.8; 0.04 M), and tetrahydrofuran (43: 55: 2, v/v/v) as mobile phase at a flow rate of 1.2 mL/min. Total analysis time was about 7 min with typical retention time of ketotifen of about 5 min. The method was validated for selectivity, linearity, accuracy, and precision following International Conference of Harmonization, 1996 (ICH) recommendations. Due to its simplicity and accuracy, the method can be used for routine quality control analysis.     

Determination of ranged sets of design specifications by incorporating design-space heterogeneity

Setting design specifications (targets) is a critical task in the early stages of the design process. Flexible targets can accommodate uncertainty and changes in design by postponing design commitments and preserving design freedom. In this article, a new method is developed for obtaining a ranged set of design specifications that meets design criteria whilst incorporating design-space heterogeneity; meaning some areas in the design attribute space are more achievable than the others. The proposed method has two notable features. First, a quantization algorithm based on rough-set theory is used to decompose a design attribute space into sub-regions on the basis of how well they meet design criteria. Second, a new design-flexibility measure is used as a metric to select the most desired ‘target region’ on the bases of both the size of the region and the influence of potential design alternatives on overall achievability. The proposed approach enhances the capacity of a design system to adapt to evolving design knowledge, as well as to unexpected changes. The proposed method is demonstrated by a numerical example and the design of a domestic blender.     

A comparison of disciplinary structure in science between the G7 and the BRIC countries by bibliometric methods

Using a collection of papers gathered from the Web of Science, and defining disciplines by the JCR classification, this paper compares the disciplinary structure of the G7 countries (representing high S&T level countries) and the BRIC countries (representing fast breaking countries in S&T) by using bibliometric methods. It discusses the similarity and the balance of their disciplinary structure. We found that: (1) High S&T level countries have a similar national disciplinary structure; (2) In recent years the disciplinary structure of the BRIC countries has become more and more similar to that of the G7 countries; (3) The disciplinary structure of the G7 countries is more balanced than that of the BRIC countries (4) In the G7 countries more emphasis goes to the life sciences, while BRIC countries focus on physics, chemistry, mathematics and engineering.     

Incineration of a small particle of wet sewage sludge: a numerical comparison between two states of the surrounding atmosphere

The main goal of this paper is to elaborate a mathematical model that represents the physics and chemistry involved when a small particle of wet sewage sludge is incinerated. Compared to existing models, our study includes both drying and heterogenous combustion of the pyrloysis residue of the processed sludge. This model relies on the assumption of homogeneous composition and temperature for the particle under study. It includes drying, pyrolysis (controlled by a four successives steps reaction pathway) and combustion of the resulting char. The ability of the model is illustrated using it in two different process conditions (representing thermogravemetric analysis and fluidized bed conditions) in order to investigate the influence of the surrounding atmosphere. It is found, that fluidized bed conditions reduce the burnout time of a small particle by enhancing the rate at which heat is transferred to that particle. It is also shown that high heating rates enhance the tar yield.     

On the flow between two rotating disks enclosed by a cylinder

Summary The flow field inside a cylindrical container caused by the impulsively started constant co-rotation or counter rotation of the top-bottom endwalls with fixed sidewall is described. After a transient phase from an initial state at rest a steady flow situation is reached. The unsteady axisymmetric Navier-Stokes equations describing the transient flow are expressed in vorticity-stream function form. For large values of Reynolds number (based on angular velocity on the lower endwall) an upwind differencing in the spatial derivatives for the convective terms is used. A fourth-order accurate compact difference scheme is applied to solve the Poisson equation. The results show that the slight co-rotation of the topbottom endwalls induces a breakdown bubble at a critical value of the Reynolds number which is much smaller than the value of the Reynolds number for the onset of vortex breakdown in a flow due to rotation either of the top or bottom end wall. On the other hand, a weak counter-rotation of top-bottom endwalls suppresses the vortex breakdown. The question of whether the similarity solutions are locally useful in describing the flow between finite disks is also addressed.     

Sign constraints improve the detection of differences between complex spectral data sets: LC-IR as an example

Spectroscopy is a fast and rich analytical tool. On many occasions, spectra are acquired of two or more sets of samples that differ only slightly. These data sets then need to be compared and analyzed, but sometimes it is difficult to find the differences. We present a simple and effective method that detects and extracts new spectral features in a spectrum coming from one set with respect to spectra of another set on the basis of the fact that these new spectral features are essentially positive quantities. The proposed procedure (i) characterizes the spectra of the reference set by a component model and (ii) uses asymmetric least squares (ASLS) to find differences with respect to this component model. It should be stressed that the method only focuses on new features and does not trace relative changes of spectral features that occur in both sets of spectra. A comparison is made with the conventional ordinary least squares (OLS) approach. Both methods (OLS and ASLS) are illustrated with simulations and are tested for size-exclusion chromatography with infrared detection (SEC-IR) of mixtures of polymer standards. Both methods are able to provide information about new spectral features. It is shown that the ASLS-based procedure yields the best recovery of new features in the simulations and in the SEC-IR experiments. Band positions and band shapes of new spectral features are better retrieved with the ASLS than with the OLS method, even those which could hardly be detected visually. Depending on the spectroscopic technique used, the ASLS-based method facilitates identification of the new chemical compounds.     

General method to derive the relationship between two sets of Zernike coefficients corresponding to different aperture sizes

Zernike polynomials have been widely used to describe the aberrations in wavefront sensing of the eye. The Zernike coefficients are often computed under different aperture sizes. For the sake of comparison, the same aperture diameter is required. Since no standard aperture size is available for reporting the results, it is important to develop a technique for converting the Zernike coefficients obtained from one aperture size to another size. By investigating the properties of Zernike polynomials, we propose a general method for establishing the relationship between two sets of Zernike coefficients computed with different aperture sizes.     

Qualifying the use of RIS data for patient dose by comparison with DICOM header data

A system was developed in 2008 to calculate patient doses using Radiology Information System (RIS) data and presents these data as a patient dose audit. One of the issues with this system was the quality of user-entered data. It has been shown that Digital Imaging and Communication in Medicine (DICOM) header data can be used to perform dose audits with a high level of data accuracy. This study aims to show that using RIS data for dose audits is not only a viable alternative to using DICOM header data, but that it has advantages. A new system was developed to pull header data from DICOM images easily and was installed on a workstation within a hospital department. Data were recovered for a common set of examinations using both RIS and DICOM header data. The data were compared on a result-by-result basis to check for consistency of common fields between RIS and DICOM, as well as assessing the value of data fields uncommon to both systems. The study shows that whilst RIS is not as accurate as DICOM, it does provide enough accurate data and that it has other advantages over using a DICOM approach. These results suggest that a 'best of both worlds' may be achievable using Modality Performed Procedure Step (MPPS).     

等距映射和局部线性嵌入算法集成的转子故障数据集降维方法

经数据分析途径实现机器智能的故障决策引发出了关于故障数据集的降维问题。通过将等距映射算法(Isometric Mapping,ISOMAP)、局部线性嵌入(Locally Linear Embedding,LLE)算法的优缺点进行互补,提出一种适用于非线性数据集降维的核框架下等距映射与局部线性嵌入相结合的KISOMAPLLE算法。该算法能够同时满足全局距离保持性和局部结构保持能力的数据降维基本要求。用典型的人工数据集和转子故障数据集进行的降维验证结果表明,该算法能够继承ISOMAP、LLE两种算法的各自优良性能,具有能够显著提高典型非线性数据集分类精度的性能。