bluuebunny/crossref_metadata_2025_split huggingface dataset:
A distributed computing approach to system dynamics
Authors: Duggan Jim 
Published: August 2002

AbstractThis article describes ongoing research into the application of distributed computing technologies to system dynamics. To date, a distributed modelling environment has been constructed. This is designed to support geographically dispersed decision makers—for example, participants in a virtual organisation who may wish to examine scenarios for their interconnected value chain. The implementation is based on distributed object technology and is tested using a negative feedback model of a business supply chain. Copyright © 2002 John Wiley & Sons, Ltd.
Oxidation studies of Au‐Al alloys using x‐ray photoelectron spectroscopy (XPS) and x‐ray absorption near‐edge structure (XANES)
Authors: Piao H. , McIntyre N. S. 
Published: August 2002

AbstractThe oxidation of thin‐film Au‐ Al alloy, as well as pure Al, has been studied using XPS across a wide range of water vapour and air exposures (0.1 L to 1 × 1014 L). The alloys and the pure Al all undergo a similar set of oxide growth kinetics. In addition to the three stages of early growth kinetics identified for Al in previous studies, a fourth stage is identified at air exposure doses of >109 L. During this stage, the average composition of the film changes from Al2O3 to Al2O3·H2O. The Al 2p lineshapes for the oxides grown on pure Al and Au‐Al alloy are different; the origins of this appear to result, in part, from a change in the Fermi level as the oxide thickens. The Al L2,3 X‐ray absorption near‐edge structure (XANES) furthermore provides a complementary probe of the different oxide structures on alloy and Al metal. Thus, their chemical characteristics are affected also by the presence of the gold. This difference in oxide structure is detected at the interface and not through the oxide generally. Copyright © 2001 John Wiley & Sons, Ltd.
Effects of temperature and Ar+ ion bombardment on the initial oxidation stages of polycrystalline aluminium with water vapour
Authors: Do T. , McIntyre N. S. 
Published: August 2002

AbstractThe initial stages of oxide formation following the interaction of water vapour with polycrystalline aluminium surfaces have been studied using x‐ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Attenuation of the electron signal from the metallic substrate has been used to follow the oxidation kinetics of aluminium as a function of energy and dose of Ar+ ion bombardment and temperature. The effects of energy and doses of Ar+ ion bombardment on oxidation kinetics have been examined in the energy range 1–5 keV and ion dose ranging from 1.3 × 1016 to 3.8 × 1017 ions cm−2. Although the increase in energy of Ar+ ion bombardment slightly modified the oxidation kinetics, the effects of ion dose on oxidation kinetics are shown to be more complex. There is a threshold dose of Ar+ ions above which the surface activity becomes significantly reduced; this is ascribed to cluster formation blocking the surface diffusion pathway in the near‐surface region. The oxidation kinetics of aluminium also have been studied in a range of temperature from room temperature up to 573 K. As the temperature increases, the oxidation rate of aluminium decreases due to a decrease in the sticking probability of water molecules on the aluminium surfaces. The observed temperature dependence of the oxidation kinetics is likely to be due to a precursor mechanism of water desorption. Copyright © 2001 John Wiley & Sons, Ltd.
Auger depth profiling of heat‐treated Au/Ni thin films
Authors: Abdul‐Lettif Ahmed M. 
Published: August 2002

AbstractGold/nickel thin films heat treated in the temperature range 200–500°C, have been analysed for composition–depth profiles using Auger electron spectroscopy in combination with simultaneous Ar+ ion sputtering. The present investigation indicates that pronounced nickel diffusion through the gold layer takes place due to annealing at 500°C for 5 min, whereas a noticeable nickel diffusion through the gold layer needs 3 h of annealing at 200°C. The measured concentration profiles suggest diffusion mechanisms involving infinitely fast grain boundary diffusion coupled with defect‐enhanced diffusion into the grains. Copyright © 2002 John Wiley & Sons, Ltd.
ToF‐SIMS studies of carbon‐fibre composite fracture surfaces and the development of controlled Mode in situ fracture
Authors: Prickett A. C. , Smith P. A. , Watts J. F. 
Published: August 2002

AbstractThe application of mechanical test methods and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) to characterize the intralaminar failure of unidirectional carbon‐fibre‐reinforced polymer (CFRP) composites under different modes of loading is discussed. The development of a fracture stage that is able to generate fracture surfaces in situ within the spectrometer under a pure mode I tensile loading and a predominantly mode II shear loading is documented. The preparation of microtomed sections is shown to be a convenient and reliable method for the production of samples of heavily cross‐linked materials, such as matrix materials for CFRP composites, particularly for analysis in older ToF‐SIMS systems because of the reduced sample charging effects. Spectra from the bulk matrix material are compared with those from composite fracture surfaces. It is shown that the mechanism of failure in both of the composite loading situations is matrix dominated. Copyright © 2001 John Wiley & Sons, Ltd.
Synthesis of 6‐(1′‐pyrrolyl)‐n‐hexyltrichlorosilane and 6‐(1′‐pyrrolyl)‐n‐hexyltrimethoxysilane: XPS characterization of their monolayers self‐assembled on polycrystalline titanium surfaces
Authors: Cossement D. , Pierard C. , Delhalle J. , Pireaux J.‐J. , Hevesi L. , Mekhalif Z. 
Published: August 2002

AbstractIn this work are reported the synthesis of 6‐(1′‐pyrrolyl)‐n‐hexyltrichlorosilane (PyHTCS) and 6‐(1′‐pyrrolyl)‐n‐hexyltrimethoxysilane (PyHTMS) and the XPS characterization of polycrystalline titanium surfaces modified with these two molecules (10−3 M in toluene). PyHTCS forms densely packed monolayers after 15 min of reaction, whereas PyHTMS chemisorbs poorly, even after 2 h of reaction. Copyright © 2001 John Wiley & Sons, Ltd.
Tapping mode and phase imaging of biaxially oriented polyester films
Authors: Beake Ben D. , Leggett Graham J. , Shipway Philip H. 
Published: August 2002

AbstractThe surface morphology and mechanical properties of biaxially drawn poly(ethylene terephthalate) film surfaces have been investigated with tapping mode scanning force microscopy. Imaging with high tapping forces caused tip‐induced wear of the polymer surface. The damage was avoided by tapping at lower force. It is then possible to utilize phase detection imaging to provide ready access to surface properties such as stiffness and adhesion. Phase imaging has revealed a wealth of detailed surface structure information not seen in previous studies of heterogeneous polyester film materials. Not only are the different components of heterogeneous materials resolved with remarkable clarity, but detailed information is also provided on the phase morphology of individual components and on homogeneous polyester film materials. Copyright © 2001 John Wiley & Sons, Ltd.
Selection effects in randomized trials with count data
Authors: Cook Richard J. , Wei Wei 
Published: August 2002

AbstractSelection criteria are specified in clinical trials to define the study population from which the sample will be obtained. It is common for one of these criteria to be based on historical or baseline measurements of the clinical sign or symptom that will serve as the response variable in the trial. The effect of such selection criteria has been studied extensively for normally distributed responses, but less is known about the situation in which the response is a count or a possibly recurrent event. In this paper we examine the bias and relative efficiency of some common methods of analysis for count data in the presence of selection criteria. The investigation is carried out using asymptotic theory pertaining to misspecified models and by simulation. Applications involving data from an epilepsy trial and a study of transient myocardial ischaemia illustrate the effect of ignoring the selection mechanism. Copyright © 2002 John Wiley & Sons, Ltd.
Non‐parametric confidence interval estimation for competing risks analysis: application to contraceptive data
Authors: Choudhury Jahar B. 
Published: August 2002

AbstractNon‐parametric maximum likelihood estimation of the cause specific failure probability, and of its standard error, in the presence of competing risks is discussed with reference to some contraceptive use dynamics data from Bangladesh. The cause specific incidence function provides an intuitively appealing summary curve for failure rates and probabilities, such as probabilities of discontinuation of different kinds of contraception, based on right‐censored data of the particular event. Dinse and Larson's formula can be utilized to calculate the standard error of the cause specific probability for the failure type of interest, and to construct pointwise confidence intervals. The accuracy of these intervals, as well as those based on the log(‐log) transformation and the arcsine transformation, are compared by simulations. We find that Dinse and Larson's formula, used in conjuction with a log(‐log) transform, yields reliable standard error estimates and accurate coverage in samples of small and large size, and can be recommended for use in this situation. Copyright © 2002 John Wiley & Sons, Ltd.
Baseline information in structural failure time estimators for the effect of observed treatment compliance
Authors: Loeys T. , Goetghebeur E. 
Published: August 2002

AbstractStructural accelerated failure time models allow expression of the effect of treatment actually received in placebo‐controlled randomized trials with non‐compliance. Without further assumptions, the structural parameter is typically estimated via a series of auxiliary logrank tests, searching for the structural parameter that back‐transforms treated survival times to latent treatment‐free survival times which are equally distributed between randomized arms. In this paper we investigate to what extent score tests involving baseline covariates provide more powerful auxiliary tests and lead to more precise estimates of the structural parameter without compromising the α‐level. We propose a set of estimating equations which combines score components for covariate effects based on the control arm only, with a log‐likelihood score for treatment effect based on both arms. Analytic results for exponential models as well as simulation studies for the semi‐parametric approach indicate that in many practical situations this incorporation of baseline covariates leads to more precise estimators of the structural effect. Relative efficiency is shown to depend on the selective nature of compliance. In a leukaemia trial we find the length of the 95 per cent confidence interval for the structural parameter is reduced to two‐thirds of the original length by incorporating baseline covariates in this way. Copyright © 2002 John Wiley & Sons, Ltd.
Enhancing the value delivered by the statistician throughout drug discovery and development: putting statistical science into regulated pharmaceutical innovation
Authors: Enas Gregory G. , Andersen John S. 
Published: August 2002

AbstractWith the dawn of the 21st century, the pharmaceutical industry faces a dramatically different constellation of business and scientific predictors of success than those of just a few years ago. Significant advances in science at the genetic, molecular and cellular levels, combined with progress demonstrated around the globe with drug regulations, have increased business and competitive opportunities. This has occurred in search of better and cheaper medicines that reach patients with unmet medical needs as quickly as possible. Herein lie new opportunities for those who can help business and regulatory leaders make good decisions about drug development and market authorization as quickly and efficiently as possible in the presence of uncertainty. The statistician is uniquely trained and qualified to render such value. We show how the statistician can contribute to the process of drug innovation from the very early stages of drug discovery until patients, payers and regulators are satisfied. Indeed, the very nature of regulated innovation demands that efficient and effective processes are implemented which yield the right information for good decision making. The statistician can take the lead in setting a strategy that directs such processes in the direction of greatest value. This demands skills that enable one to identify important sources of variability and uncertainty and then leverage those skills to make decisions. If such decisions call for more information, then the statistician can render experimental designs which generate the right information needed to make the decision in an efficient, timely manner. To add value to the enterprise, statisticians will have to become more intimately associated with business and regulatory decisions by building on their traditional roles (for example, numerical analyst, tactician) and unique skill sets (for example, analysis, computation, logical thought and work process, precision, accuracy). Business and regulatory savvy, coupled with excellent communication and interpersonal skills, will allow statisticians to help create the knowledge needed to drive success in the future. Copyright © 2001 John Wiley & Sons, Ltd.
Estimation of gender bias in clinical trials
Authors: Meinert Curtis L. , Gilpin Adele Kaplan 
Published: August 2002

AbstractThe perception is that the clinical trials enterprise has been biased in favour of males by devoting a disproportionate effort to males and to the diseases and conditions afflicting them – a perception reinforced by a few high profile male‐only heart trials undertaken in the 1970s and 1980s. The perception was sufficient to cause the U.S.A. Congress to enact legislation to require that a clinical trial ‘is designed and carried out in a manner sufficient to provide for a valid analysis of whether the variables being studied in the trial affect women … differently than other subjects in the trial’. Observed effort differentials are based on counts of single‐gender trials indexed in MEDLINE and published in U.S. journals. Differentials are compared to those expected using male–female differentials in mortality and years of potential life loss due to mortality before age 65 to estimate effort bias. The ratios of female‐only to male‐only published trials were 0.53, 0.89 and 0.95 for the decades of 1966–1975, 1976–1985 and 1986–1995, respectively. The expected ratios, if single‐gender trials were done in proportion to female–male mortality differentials, would be 0.57, 0.56 and 0.57, respectively. The differences in observed versus expected female to male ratios correspond to a slight excess of male‐only trials in the decade of 1966–1975 and to sizeable excesses in female‐only trials in the decades of 1976–1985 and 1986–1995. The results do not support the perception that women have been understudied relative to males in clinical trials. Most differentials favour females, whether based on mortality or years of potential life loss due to mortality before age 65 years. Copyright © 2001 John Wiley & Sons, Ltd.
Predicting analysis times in randomized clinical trials
Authors: Bagiella Emilia , Heitjan Daniel F. 
Published: August 2002

AbstractRandomized clinical trial designs commonly include one or more planned interim analyses. At these times an external monitoring committee reviews the accumulated data and determines whether it is scientifically and ethically appropriate for the study to continue. With failure‐time endpoints, it is common to schedule analyses at the times of occurrence of specified landmark events, such as the 50th event, the 100th event, and so on. Because interim analyses can impose considerable logistical burdens, it is worthwhile predicting their timing as accurately as possible. We describe two model‐based methods for making such predictions during the course of a trial. First, we obtain a point prediction by extra‐polating the cumulative mortality into the future and selecting the date when the expected number of deaths is equal to the landmark number. Second, we use a Bayesian simulation scheme to generate a predictive distribution of milestone times; prediction intervals are quantiles of this distribution. We illustrate our method with an analysis of data from a trial of immunotherapy in the treatment of chronic granulomatous disease. Copyright © 2001 John Wiley & Sons, Ltd.
Evaluating inter‐hospital variability in mortality rates over time, allowing for time‐varying effects
Authors: Galai Noya , Simchen Elisheva , Braun Dalit , Mandel Micha , Zitser‐Gurevich Yana 
Published: August 2002

AbstractIn outcome studies, quality of care in various institutions is typically assessed by comparing observed to expected outcome rates, after adjusting for patients' case‐mix factors in logistic regression models. However, differences in patterns of outcome rates over time, especially when there is a distinction between the determinants affecting early and later events, are rarely studied. We use six‐month mortality after coronary artery bypass graft operation (CABG) as an example. We present a statistically valid approach to estimate expected survival curves for different subgroups, based on a Cox survival model with time‐varying effects. Bootstrap confidence intervals around the expected survival curves are constructed. This approach is applied for examining the pattern of deviation of high‐mortality hospitals after CABG. Implications for quality assessment in comparative outcome studies are discussed. Copyright © 2002 John Wiley & Sons, Ltd.
A model for foetal growth and diagnosis of intrauterine growth restriction
Authors: Hooper Peter M. , Mayes Damon C. , Demianczuk Nestor N. 
Published: August 2002

AbstractA model for foetal growth is developed and used to construct tools for diagnosis of intrauterine growth restriction. Foetal weight estimates are first transformed to normally distributed z‐scores. The covariance structure over gestational ages is then estimated using a novel regression model. The diagnostic tools include individual growth curves with error bounds, probabilities to assess whether a foetus is small for its gestational age, and residual scores to determine whether current growth rates are unusual. The methods were developed sing data from 13593 ultrasound examinations involving 7888 oetal subjects. The model shows that median foetal growth elocity increases up to a gestational age of 35 weeks and then ecreases during the final weeks of pregnancy. When growth is xpressed as change in log weight, or equivalently as change oportional to current weight, the model reveals a constant celeration as gestational age increases from 14 to 42 weeks. Copyright © 2002 John Wiley & Sons, Ltd.
Bias adjustment in analysing longitudinal data with informative missingness
Authors: Park Soomin , Palta Mari , Shao Jun , Shen Lei 
Published: August 2002

AbstractThe recent biostatistical literature contains a number of methods for handling the bias caused by ‘informative censoring’, which refers to drop‐out from a longitudinal study after a number of visits scheduled at predetermined intervals. The same or related methods can be extended to situations where the missing pattern is intermittent. The pattern of missingness is often assumed to be related to the outcome through random effects which represent unmeasured individual characteristics such as health awareness. To date there is only limited experience with applying the methods for informative censoring in practice, mostly because of complicated modelling and difficult computations. In this paper, we propose an estimation method based on grouping the data. The proposed estimator is asymptotically unbiased in various situations under informative missingness. Several existing methods are reviewed and compared in simulation studies. We apply the methods to data from the Wisconsin Diabetes Registry Project, a longitudinal study tracking glycaemic control and acute and chronic complications from the diagnosis of type I diabetes. Copyright © 2002 John Wiley & Sons, Ltd.
Ecological investigation of firm effects in horizontal mergers
Authors: Lubatkin Michael , Schulze William S. , Mainkar Avinash , Cotterill Ronald W. 
Published: August 2002

AbstractUsing an ecological lens, we extend strategic management and industrial organization theory to investigate the performance effects of horizontal mergers. We theorize that firms differ in their ability to benefit from horizontal mergers; that the products involved in the merger differ in their ability to attain and sustain any increase in performance above their premerger level; and that resource niches in which each product competes differ in terms of competitive constraints. We then test these predictions using longitudinal data specified at the product–market level, a unit of analysis that is less influenced by aggregation bias than are industry, firm, and even line‐of‐business level data. Our findings demonstrate how organizational ecology, when coupled with strategic management and industrial organization economic theories, can enrich our understanding of horizontal mergers. Copyright © 2001 John Wiley & Sons, Ltd.
Corporate boards and outside stakeholders as determinants of environmental litigation
Authors: Kassinis George , Vafeas Nikos 
Published: August 2002

AbstractEach year, hundreds of firms are prosecuted for violating environmental laws and hundreds of millions of dollars in penalties are assessed. At the same time, a much larger number of firms escape the various costs associated with litigation by adhering to the provisions of the same laws and regulations. It is not a priori apparent why this dichotomy exists. In this paper we draw on corporate governance and stakeholder theories to empirically investigate environmental lawsuits. Specifically, we compare the pre‐lawsuit profile of 209 violators to a sample of matched control firms between 1994 and 1998. We find that the likelihood of becoming a lawsuit defendant increases with board size, with the fraction of directors in industrial firms, and with the fraction of inside ownership, and decreases with the number of directorships held by outside directors. These findings are robust to alternative dependent variable specifications. Together, our results suggest that managers, researchers, and policy‐makers need to direct their attention to the corporate board as the core decision‐making unit forming corporate environmental policies. Copyright © 2002 John Wiley & Sons, Ltd.
A case study in repeated maintenance
Authors: Wang Shuanglin , Schach Stephen R. , Heller Gillian Z. 
Published: August 2002

AbstractRTP is a widely used commercial real‐time product that has been maintained over a period of 13 years. We have analyzed multiple versions of RTP, which is written in C and Assembler. We measured increases in dependencies within the code between successive versions and performed statistical analyses on the data. There was no significant difference between the maintenance of Assembler files and C files. Also, there was no significant difference between the versions written by the original developers and those written by maintenance programmers not involved in the original development. The differences between individual programmers were very highly significant. Our interpretation of these results is that the skill of the individual programmer is an important factor in ensuring that a software product remains maintainable over its lifetime and that software engineering education and training are therefore of major importance. Copyright © 2001 John Wiley & Sons, Ltd.