Task analysis for error identification: Theory,method and validation

This paper presents the underlying theory of Task Analysis for Error Identification. The aim is to illustrate the development of a method that has been proposed for the evaluation of prototypical designs from the perspective of predicting human error. The paper presents the method applied to representative examples. The methodology is considered in terms of the various validation studies that have been conducted, and is discussed in the light of a specific case study.     

A finite volume method for the approximation of convection–diffusion equations on general meshes

A new finite volume method is presented for approximating convection–diffusion equations. This method allows general (unstructured, non‐matching, distorted) meshes to be used without the numerical results being too much altered. The method has been tested for some well‐known benchmarks involving convection and convection–diffusion operators in two space dimensions. These numerical experiments show that it is between first and second‐order accurate, according to the type of the underlying mesh. Further numerical experiments regarding the striation equations have been carried out successfully. Copyright © 2012 John Wiley & Sons, Ltd.     

FEM-simulation of the hardening behavior of FCC single crystals

Summary Although the deformation behaviour of single crystals has been investigated experimentally and theoretically for several decades, a generally accepted theory for the underlying hardening processes has not been found yet. In the last years, computer simulations offered additional investigation possibilities, whereby especially the use of constitutive equations in combination with the finite element method has delivered important results. The publication reports on an FEM crystal plasticity model-which was previously used for multicrystals-and its application to single crystals. The model is designed for the low temperature behaviour of pure fcc metal crystals. The rate dependent equations include kinematic and isotropic hardening, with formulations founded on the responsible slip system processes. The obtained simulation results coincide very well with typical single crystal experiments like tensile or latent hardening tests, which confirms the chosen mathematical approaches. It is shown that both kinematic and isotropic processes determine hardening, whereby the underlying slip system interactions play an important role. Moreover, experimentally not visible processes can be studied in detail and are discussed concerning the metal physics theories, which finally contributes to a better understanding of metal deformation behaviour.     

Lamb wave excitation with piezoelectric wafers – an analytical approach

Summary The excitation of Lamb waves with piezoelectric wafers is analytically modeled with help of the Fourier transform method combined with the Residue theorem for the inverse transform. The calculation utilizes a decomposition of the load in a symmetric and an antisymmetric part and leads to the well known Rayleigh-Lamb-frequency equation. A solution for the whole waveguide continuum including the excitation zone is given. It is shown that the solution satisfies not only the underlying partial differential equations but also the given boundary conditions which has not been verified before.     

Organometallic route to nanocomposite synthesis

The nature and scope of different varieties of nanocomposite materials are described. The practical and basic aspects of the physical properties of nanocomposites are discussed. The principles underlying the preparation of diphasic materials involving either ceramic-metal or glass-metal combinations are delineated. The sol-gel technique involving suitable organometallic compounds has been shown to be a versatile method for making these materials. A brief survey is given about the different materials made to date following the organometallic route.     

Effects of viscoelastic properties of engine cover sealing system on noise and vibration attenuation

Automobile engine cam cover seals are made of elastomeric materials and used to seal the interfaces between cover and underlying structures. The design of engine cam cover seals has been traditionally focused on the sealability aspects. Recently, there has been additional demand that these seals be designed as vibration isolators to attenuate the radiated noise from the engine. To accomplish this goal, the frequency-dependent viscoelastic properties of the sealing components will have to be considered during the design process. This article examines the frequency-dependent viscoelastic properties of some commonly used elastomeric seals at various mounting configurations. An analytical spatial transmissibility method is used for evaluating the design of elastomeric sealing system for reducing vibration and radiated noise.     

Partial analytical solution of a model used for measuring oxygen diffusion coefficients of polymer films by luminescence quenching

Many aspects of optical chemical sensor design would benefit from a better knowledge of the diffusion properties of the analyte in the polymer host. The response times of such sensors to a step change of analyte concentration are of vital interest for many applications of fast-responding sensors. Further, the diffusion properties govern their quenching behavior and their sensitivity. A method for determination of the diffusion constant of oxygen in polymers has been developed and used by several groups in the past. The underlying mathematical model for luminescence quenching by molecules of a gas in a single sensing layer on an impermeable support has not yet been completely derived in an analytical form and still uses tedious numerical methods. We present a partial analytical solution to the problem of modeling the time dependence of luminescence generated by in- or out-diffusion of a gaseous quencher in a polymer film in which a luminophor is immobilized and offer a suitable method to predict sensor response times.     

Aspects of signal-dependent noise characterization

An automated method is presented for analyzing signal-dependent noise. Signal-dependent noise is present in many types of data-acquisition processes and has been investigated by other researchers with various methods. Regardless of the noise analysis methods, often the starting point is based on a particular signal-dependent noise model, which also forms the basis for our study. The approach determines whether the estimated noise variance is dependent on the signal by approximating the functional relation within the constraints of the assumed signal-noise model. The method relies on the Fourier attributes of the signal and noise and uses the wavelet expansion for separating these components. The technique does not rely on the underlying noise and signal probability distributions. Two-dimensional simulations as well as mammography data are used to illustrate the merits of the approach.     

Finite element analysis of non-local effects in ductile fracture

The paper introduces a weight function for the nonlocal analysis of ductile damage that has the potential to provide approximately uniform averaged field variables over a limited region. When this region is identified with the underlying microstructural length scale of the material, the method is consistent with the view that, once damage is significant, a damaging cell behaves as a uniform entity. The analyses through which these effects have been studied concerned a unit cell idealizing a periodic array of large voids, connected by material that is capable of nucleating smaller-scale porosity.     

THE BOUNDARY NODE METHOD FOR POTENTIAL PROBLEMS

The Element-Free Galerkin (EFG) method allows one to use a nodal data structure (usually with an underlying cell structure) within the domain of a body of arbitrary shape. The usual EFG combines Moving Least-Squares (MLS) interpolants with a variational principle (weak form) and has been used to solve two-dimensional (2-D) boundary value problems in mechanics such as in potential theory, elasticity and fracture. This paper proposes a combination of MLS interpolants with Boundary Integral Equations (BIE) in order to retain both the meshless attribute of the former and the dimensionality advantage of the latter! This new method, called the Boundary Node Method (BNM), only requires a nodal data structure on the bounding surface of a body whose dimension is one less than that of the domain itself. An underlying cell structure is again used for numerical integration. In principle, the BNM, for 3-D problems, should be extremely powerful since one would only need to put nodes (points) on the surface of a solid model for an object. Numerical results are presented in this paper for the solution of Laplace's equation in 2-D. Dirichlet, Neumann and mixed problems have been solved, some on bodies with piecewise straight and others with curved boundaries. Results from these numerical examples are extremely encouraging. © 1997 by John Wiley & Sons, Ltd.     

Dynamic crack propagation in elastoplastic thin‐walled structures: Modelling and validation

In this paper, a method to analyse and predict crack propagation in thin‐walled structures subjected to large plastic deformations when loaded at high strain rates—such as impact and/or blast—has been proposed. To represent the crack propagation independently of the finite element discretisation, an extended finite element method based shell formulation has been employed. More precisely, an underlying 7‐parameter shell model formulation with extensible directors has been extended by locally introducing an additional displacement field, representing the displacement discontinuity independently of the mesh. Of special concern in the paper has been to find a proper balance between, level of detail and accuracy when representing the physics of the problem and, on the other hand, computational efficiency and robustness. To promote computational efficiency, an explicit time step scheme has been employed, which however has been discovered to generate unphysical oscillations in the response upon crack propagation. Therefore, special focus has been placed to investigate these oscillations as well as to find proper remedies. The paper is concluded with three numerical examples to verify and validate the proposed model.Copyright © 2013 John Wiley & Sons, Ltd.     

The weighted priors approach for combining expert opinions in logistic regression experiments

ABSTRACT

When modeling the reliability of a system or component, it is not uncommon for more than one expert to provide very different prior estimates of the expected reliability as a function of an explanatory variable such as age or temperature. Our goal is to incorporate all information from the experts when choosing a design about which units to test. Bayesian design of experiments has been shown to be very successful for generalized linear models, including logistic regression models. We use this approach to develop methodology for the case where there are several potentially non-overlapping priors under consideration. While multiple priors have been used for analysis in the past, they have never been used in a design context. The Weighted Priors method performs well for a broad range of true underlying model parameter choices and is more robust when compared to other reasonable design choices. We illustrate the method through multiple scenarios and a motivating example. Additional figures for this article are available in the online supplementary information.     

An Extended Equation of State Modeling Method I. Pure Fluids

A new technique is proposed here to represent the thermodynamic surface of a pure fluid in the fundamental Helmholtz energy form. The peculiarity of the present method is the extension of a generic equation of state for the target fluid, which is assumed as the basic equation, through the distortion of its independent variables by individual shape functions, which are represented by a neural network used as function approximator. The basic equation of state for the target fluid can have the simple functional form of a cubic equation, as, for instance, the Soave–Redlich–Kwong equation assumed in the present study. A set of nine fluids including hydrocarbons, haloalkane refrigerants, and strongly polar substances has been considered. For each of them the model has been regressed and then validated against volumetric and caloric properties generated in the vapor, liquid, and supercritical regions from highly accurate dedicated equations of state. In comparison with the underlying cubic equation of state, the prediction accuracy is improved by a factor between 10 and 100, depending on the property and on the region. It has been verified that about 100 density experimental points, together with from 10 to 20 coexistence data, are sufficient to guarantee high prediction accuracy for different thermodynamic properties. The method is a promising modeling technique for the heuristic development of multiparameter dedicated equations of state from experimental data.     

Copper disk pyrheliometer of high accuracy

A copper disk pyrheliometer has been designed and constructed that utilizes a new methodology to measure solar radiation. By operating the shutter of the instrument and measuring the heating and cooling rates of the sensor at the very moment when the sensor is at the same temperature, the solar radiation can be accurately determined with these rates. The method is highly accurate and is shown to be totally independent of the loss coefficient in the measurement. The pyrheliometer has been tested using a standard irradiance lamp in the laboratory. The uncertainty of the instrument is identified to be +/-0.61%. Field testing was also conducted by comparing data with that of a calibrated (Eppley) Normal Incidence Pyrheliometer. This paper spells out details of the construction and testing of the instrument; the analysis underlying the methodology was also covered in detail. Because of the high accuracy, the instrument is considered to be well suited for a bench standard for measurement of solar radiation.     

Improved Newton-Raphson digital image correlation method for full-field displacement and strain calculation

The two-dimensional in-plane displacement and strain calculation problem through digital image processing methods has been studied extensively in the past three decades. Out of the various algorithms developed, the Newton-Raphson partial differential correction method performs the best quality wise and is the most widely used in practical applications despite its higher computational cost. The work presented in this paper improves the original algorithm by including adaptive spatial regularization in the minimization process used to obtain the motion data. Results indicate improvements in the strain accuracy for both small and large strains. The improvements become even more significant when employing small displacement and strain window sizes, making the new method highly suitable for situations where the underlying strain data presents both slow and fast spatial variations or contains highly localized discontinuities.     

Noncompact groups and the excitation spectrum in superfluid helium-4

It has been shown that the underlying symmetry algebra in the superfluid ⁴He can be extended to the spectrum-generating noncompact groups. This method furnishes the excitation energy of this system, exact in the framework of the symmetry algebra.     

Ellipsometrische Charakterisierung von C‐Schutzschichten für die Speichertechnologie

Spectroscopic Ellipsometry is a fast, non‐destructive and reliable method for characterizing thin films, based on interaction between incident light and a multilayer system. For our investigations, light in the visible spectral range has been used to characterize protective carbon coatings with thicknesses of 2‐7nm on magnetic hard disks. The specific disk layer stack has been described with an adequate one‐layer model. With regard to an accurate analysis of the covering carbon coating a reproducible procedure for determining the underlying metallic material has been developed. The measured ellipsometric parameters (ψ, Δ) display a linear dependence on carbon film thickness which shows an appropriate application of the used model down to a thickness of 2 nm. By means of simulation calculations, criteria for the selection of optimized wavelengths with respect to film characterization has been established. Furthermore, an increasing extinction coefficient κ with rising nitrogen content in the carbon coating could be stated. Apparent time instabilities in the determination of layer thickness d and extinction coefficient κ of the carbon film could be explained as due to adsorption processes on the surface.     

Silicon nanotubes from sacrificial silicon nanowires: fabrication and manipulation via embedding in flexible polymers

In the present work we report a simple method to fabricate Si nanotubes (NTs) starting from the growth of self-assembled sacrificial Si nanowires that, at the same time, embeds them into a polyimide matrix, allowing a very easy manipulation of these nano-objects, including removal, transfer and positioning. Our all-silicon fabrication method is completely compatible with the Si technology platform and is therefore implementable using the existing technology. Transferred NTs show good electrical contact with underlying electrodes, and relatively low resistance values have been measured. All these features demonstrate the effectiveness of the transfer method and the potentiality of the NTs in electronics. Finally, optical reflectivity of the NTs has been measured in the near UV-near IR spectral range.