A review of models for single particle compression and their application to silica microspheres

We report on the deformation behavior of single silica microspheres. For the first time a detailed discussion on the quantitative evaluation of force–deformation data in the elastic and plastic regime is given. The microspheres are compressed between two flat plates of a custom built manipulation device supported by a scanning electron microscope. The device allows a high sample throughput enabling full statistical evaluation of force–deformation data of single microspheres. Existing theories describing the deformation behavior of single spheres are discussed and applied to the elastic and plastic deformation regime of silica microspheres. The results obtained from the theories are compared between each other and values reported in literature. The silica microspheres exhibit a significantly different deformation behavior than expected from bulk fused silica, i.e. a distinct plastic deformation behavior. Furthermore, a significant decrease in Young’s modulus and hardness was observed caused by high porosity and reduced crosslinking of silicon atoms, respectively, that is inherent to silica produced by Stöber synthesis. However, the calculated contact pressures exceed the compressive strength of bulk fused silica by at least a factor of two as an effect of a reduced amount of material flaws in microstructures.     

A study of diffusion models and their application to porous catalysts

A new model of diffusion in porous catalysts is proposed, namely a macropore model. A comparison between test results and calculations indicates a close agreement.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 4, pp. 708–719, October, 1973.     

Methodology for fitting and updating predictive accident models with trend

Reliable predictive accident models (PAMs) (also referred to as Safety Performance Functions (SPFs)) have a variety of important uses in traffic safety research and practice. They are used to help identify sites in need of remedial treatment, in the design of transport schemes to assess safety implications, and to estimate the effectiveness of remedial treatments. The PAMs currently in use in the UK are now quite old; the data used in their development was gathered up to 30 years ago. Many changes have occurred over that period in road and vehicle design, in road safety campaigns and legislation, and the national accident rate has fallen substantially. It seems unlikely that these ageing models can be relied upon to provide accurate and reliable predictions of accident frequencies on the roads today. This paper addresses a number of methodological issues that arise in seeking practical and efficient ways to update PAMs, whether by re-calibration or by re-fitting. Models for accidents on rural single carriageway roads have been chosen to illustrate these issues, including the choice of distributional assumption for overdispersion, the choice of goodness of fit measures, questions of independence between observations in different years, and between links on the same scheme, the estimation of trends in the models, the uncertainty of predictions, as well as considerations about the most efficient and convenient ways to fit the required models.     

Batch sequential design to achieve predictive maturity with calibrated computer models

Sequential experiment design strategies have been proposed for efficiently augmenting initial designs to solve many problems of interest to computer experimenters, including optimization, contour and threshold estimation, and global prediction. We focus on batch sequential design strategies for achieving maturity in global prediction of discrepancy inferred from computer model calibration. Predictive maturity focuses on adding field experiments to efficiently improve discrepancy inference. Several design criteria are extended to allow batch augmentation, including integrated and maximum mean square error, maximum entropy, and two expected improvement criteria. In addition, batch versions of maximin distance and weighted distance criteria are developed. Two batch optimization algorithms are considered: modified Fedorov exchange and a binning methodology motivated by optimizing augmented fractional factorial skeleton designs.     

A framework to practical predictive maintenance modeling for multi-state systems

A simple practical framework for predictive maintenance (PdM)-based scheduling of multi-state systems (MSS) is developed. The maintenance schedules are derived from a system-perspective using the failure times of the overall system as estimated from its performance degradation trends.

The system analyzed in this work is a flow transmission water pipe system. The various factors influencing PdM-based scheduling are identified and their impact on the system reliability and performance are quantitatively studied. The estimated times to replacement of the MSS may also be derived from the developed model.

The results of the model simulation demonstrate the significant impact of maintenance quality and the criteria for the call for maintenance (user demand) on the system reliability and mean performance characteristics. A slight improvement in maintenance quality is found to postpone the system replacement time by manifold. The consistency in the quality of maintenance work with minimal variance is also identified as a very important factor that enhances the system's future operational and downtime event predictability.

The studies also reveal that in order to reduce the frequency of maintenance actions, it is necessary to lower the minimum user demand from the system if possible, ensuring at the same time that the system still performs its intended function effectively.

The model proposed can be utilized to implement a PdM program in the industry with a few modifications to suit the individual industrial systems’ needs.     

On two predictive models for the vertical swell percentage of expansive clays

The general swelling model (termed the W-Model) based on local Israeli research has recently been updated by applying the Excel-solver command (ESC) analysis to new local test results obtained from 897 undisturbed specimens. In this analysis, the goodness-of-fit statistics classify the category of their associated regression only as fair. Thus, it seems necessary to explore the possibility of enhancing the outputs of this regression analysis by following the formulation of another existing model, in the present case that of the U.S. Corps of Engineers (termed the CE-Model), by again applying the ESC analysis to these new local test results. The statistical fit of the new CE-Models is shown to be slightly superior to the W-Models. However, in terms of practical implementation, no preference can be assigned to one of these two models although a preference model is suggested. This study concludes with the analysis of issues concerning equilibrium suction variations with depth, and their dependence on pavement-sealing capacities.     

On the predictive ability of mechanistic models for the Haitian cholera epidemic

Predictive models of epidemic cholera need to resolve at suitable aggregation levels spatial data pertaining to local communities, epidemiological records, hydrologic drivers, waterways, patterns of human mobility and proxies of exposure rates. We address the above issue in a formal model comparison framework and provide a quantitative assessment of the explanatory and predictive abilities of various model settings with different spatial aggregation levels and coupling mechanisms. Reference is made to records of the recent Haiti cholera epidemics. Our intensive computations and objective model comparisons show that spatially explicit models accounting for spatial connections have better explanatory power than spatially disconnected ones for short-to-intermediate calibration windows, while parsimonious, spatially disconnected models perform better with long training sets. On average, spatially connected models show better predictive ability than disconnected ones. We suggest limits and validity of the various approaches and discuss the pathway towards the development of case-specific predictive tools in the context of emergency management.     

Spallation models and their relevance to steam-grown oxides

Abstract

An overview is given of existing models of oxide spallation with particular emphasis on their relevance to the mechanical integrity of steam-grown oxide layers on alloys used in power generating systems. Although the bulk of the experimental and modelling work over the last decade has been undertaken on alumina-forming high-temperature alloys, the understanding obtained can be used advantageously to identify likely key factors affecting the mechanical response of alloys at lower temperatures. Various aspects are addressed, such as the mechanisms of cracking and spallation, but a central issue is whether creep rates in the multi-layered scale formed on ferritic alloys can ever be high enough to relax possible growth stresses and to permit the Critical Strain Energy Criterion to be used as a method for predicting oxide spallation.     

Magnetic properties of thin ferromagnetic films in relation to their structure

The influence of film structure on magnetic properties is primarily due to the creation of spatially fluctuating local anisotropies which make the magnetization direction inhomogeneous. The deviation from homogeneous magnetization of domains, the so-called ripple, influences a great number of static, quasistatic and dynamic effects via the intrinsic demagnetizing field. The ripple theory is expressed in terms of only one phenomenological constant, the structure constant S, which covers completely the influence of the film structure on the deviations of real thin film behaviour from that of ideal single domains.     

Structural identification for electromagnetic system linear dynamic models and the relation to total power resolution

A structural identification method is proposed for linear dynamic models for single-phase alternating-current electromagnetic systems of source-load type. Matrix equations are derived that relate the Gram matrices of the Krylov bases to the power matrix, from which one can obtain the resolution of the total power. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 26–29, June, 2006.     

Traffic safety assessment and development of predictive models for accidents on rural roads in Egypt

This paper starts by presenting a conceptualization of indicators, criteria and accidents' causes that can be used to describe traffic safety. The paper provides an assessment of traffic safety conditions for rural roads in Egypt. This is done through a three-step procedure. First, deaths per million vehicle kilometers are obtained and compared for Egypt, three other Arab countries and six of the G-7 countries. Egypt stands as having a significantly high rate of deaths per 100 million vehicle kilometers. This is followed by compiling available traffic and accident data for five main rural roads in Egypt over a 10-year period (1990-1999). These are used to compute and compare 13 traffic safety indicators for these roads. The third step for assessing traffic safety for rural roads in Egypt is concerned with presenting a detailed analysis of accident causes. The paper moves on to develop a number of statistical models that can be used in the prediction of the expected number of accidents, injuries, fatalities and casualties on the rural roads in Egypt. Time series data of traffic and accidents, over a 10 years period for the considered roads, is utilized in the calibration of these predictive models. Several functional forms are explored and tested in the calibration process. Before proceeding to the development of these models three ANOVA statistical tests are conducted to establish whether there are any significant differences in the data used for models' calibration as a result of differences among the considered five roads.     

空间材料的原子氧侵蚀理论和预测模型

低地轨道环境中的原子氧对航天器材料的侵蚀导致材料的性能变坏甚至失效,原子氧的侵蚀机理和防护技术是当前空间环境效应研究的热点．在对原子氧效应机理已有理解的基础上,准确预测空间材料在低地轨道环境中由原子氧引起的侵蚀效应,可对设计者在工程选材和飞行器设计提供帮助。本文综述了近年来发展的原子氧与空间材料相互作用的理论模型和侵蚀速率预测模型,并对各种模型进行了分析,也指出了关于原子氧效应的研究重点．     

A predictive model for particulate-filled composite materials

A predictive model for particulate-filled composite materials has been developed. The model uses a combination of finite element analysis and spatial statistical techniques; this combination allows the results from finite element analysis to be applied to real materials. The model is applied to epoxy resin filled with glass spheres. Predicted values of stiffness are compared with experimental measurements, and excellent agreement is found. The model is used to investigate stress distributions and the results are compared with experimental observations of fracture under varying conditions; the fracture behaviour of these materials is significantly elucidated.     

A taxonomy for simulation modeling based on programming language principles

Although many diverse areas employ simulation models, no agreed-upon taxonomy has been developed to categorize and structure simulation models for all science and engineering disciplines. The discipline of simulation is often splintered due to this lack of structure, with ad hoc model classes such as 'discrete event,' 'continuous' and 'combined.' These classes most often reflect the method of execution used on a model rather than the design structure of the model. We present a uniform model design taxonomy whose categories are inspired from categories in programming language principles within the field of computer science. The taxonomy includes a set of primitive model types (conceptual, declarative, functional, constraint, spatial) and a way of integrating primitive model types together (multimodeling). These model types are discussed using a single application: a robot server for an assembly line. We have found this taxonomy enables simulators to more easily define and categorize their models as well as to understand how model types from seemingly disparate application areas are interrelated.     

A response-modeling alternative to surrogate models for support in computational analyses

Often, the objectives in a computational analysis involve characterization of system performance based on some function of the computed response. In general, this characterization includes (at least) an estimate or prediction for some performance measure and an estimate of the associated uncertainty. Surrogate models can be used to approximate the response in regions where simulations were not performed. For most surrogate modeling approaches, however, (1) estimates are based on smoothing of available data and (2) uncertainty in the response is specified in a point-wise (in the input space) fashion. These aspects of the surrogate model construction might limit their capabilities.One alternative is to construct a probability measure, G(r), for the computer response, r, based on available data. This “response-modeling” approach will permit probability estimation for an arbitrary event, E(r), based on the computer response. In this general setting, event probabilities can be computed: prob(E)=∫_rI(E(r))dG(r) where I is the indicator function. Furthermore, one can use G(r) to calculate an induced distribution on a performance measure, pm. For prediction problems where the performance measure is a scalar, its distribution F_pm is determined by: F_pm(z)=∫_rI(pm(r)z)dG(r). We introduce response models for scalar computer output and then generalize the approach to more complicated responses that utilize multiple response models.     

Recent void shrinkage models and their applicability to diffusion bonding

Abstract

Recent void shrinkage models are reviewed and refined. The role of surface selfdiffusion is discussed for modelling void shrinkage by selfdiffusion along the void surface and bond interface. The refinement of the existing models makes it possible to discuss the effect of void crushing by power law creep, the validity of combining models of diffusion and creep, and the applicability of the existing models. The discrepancies between the various models are demonstrated by reference to the stress dependence of void shrinkage rate (log–log plots). The void crushing rate due to power law creep of the surrounding matrix is highly dependent on the degree of bulk deformation, i.e. the severity of bulk constraint. The applicability of the combined models of creep and diffusion are therefore limited by this condition.

MST/1502     

A predictive analysis for optimum contour-after-wear for magnetic heads

Reliable reproduction of recorded signals is dependent upon a good head-tape interface, and particularly, upon adequate contact pressure at the gap. In the case of grooved magnetic heads the pressure profiles are complex 3-dimensional surfaces. The head contours, as machined, may cause pressure profiles which are unfavorable to good signal reproduction. A mathematical analysis is outlined, which forecasts the progressively changing head contours and pressure profiles in terms of the average depth of head wear due to passage of tape (magnetic or lapping tape). The analysis indicates the amount of wear needed to substantially improve the pressure profile. Good correlation is shown between the theoretical predictions and actual test values.