bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tribosurface and lubricant characterization by ToF‐SIMS
Authors: Gunst U. , Zabel W.‐R. , Poll G. , Arlinghaus H. F. 
Published: August 2004

AbstractThe interaction of moving counterparts with lubricants generates tribosurfaces and tribointerfaces. These tribological boundary layers and their characteristics are important for the lifetime of sliding and rolling bearings. The properties of these structurally and chemically untailored surfaces are of interest for the design of long‐life lubricants and high‐hardness, wear‐resistant surfaces. ToF‐SIMS is a means for characterizing lubricants and the elemental and molecular surface compositions of tribological boundary layers. Especially the capability for the retrospective analysis of depth and lateral chemical distributions on the basis of parallel mass detection and high mass resolution enables tribological research of formerly unknown chemical surface and interface distributions. We have used ToF‐SIMS to investigate lubricants for high‐speed applications, as well as for the tribosurface characterization of high‐speed rolling element bearings. The results show that ToF‐SIMS is a very useful surface‐diagnostic tool for obtaining information about surface compositions of tribological systems. The measured surface spectra as well as lateral and depth distributions correlate with tribological models and give insights into tribological interaction mechanisms at micro‐ and nanoscopic levels. Copyright © 2004 John Wiley & Sons, Ltd.
The very beginning of plastic deformation during sliding contact on amorphous carbon coatings
Authors: Wienss A. , Jacoby B. 
Published: August 2004

AbstractVarious thin amorphous carbon coatings (5–12 nm) as well as silicon oxide surfaces were scratched by means of a diamond tipped cantilever, simulating a hard scratching particle with a radius of 80–100 nm. Using advanced image processing, ultra‐shallow scratches with depths of only 1–2 Å can be visualized and analysed, even on surfaces with RMS roughness values up to 10 Å. This enables us to evaluate the conditions in terms of local pressure and speed under which plastic deformation initially takes place. Different deformation mechanisms could be deduced for different types of surfaces. Repeated measurements suggest a local compression of the amorphous low‐density structures underneath the tip. Using a simple force balance model, it can be estimated that in the initial phase of plastic deformation, the lateral force acting on the tip is dominated by the friction force and not yet by a ploughing term.This sub‐nanometre scratching technique has been developed for the mechanical characterization and optimization of ultra‐thin amorphous carbon coatings used as protective layers in hard disk drives. Copyright © 2004 John Wiley & Sons, Ltd.
Surface analysis of metals using tribostimulated electron emission
Authors: Momose Yoshihiro , Iwashita Masahisa 
Published: August 2004

AbstractA new surface analysis method using tribostimulated electron emission (called TriboEE) has been developed to estimate the ability for metals in practical use to emit electrons. This method uses an exoelectron emission phenomenon observed only while metal surfaces are mechanically rubbed with a polytetrafluoroethylene (PTFE) rotator. The number of electrons emitted from copper and iron metals during rubbing was measured using a newly hand‐made electron counting device, and its relationship to the XPS results of the metal surfaces was investigated. The metal surfaces were prepared as follows: ultrasonic cleaning in acetone (sample I), abrasion with an emery paper (II), and oxidation by heating in air (III). The number of emitted electrons depended strongly on the preparations, resulting in the order I ≈ II < III for copper and II ≪ I ≈ III for iron. The number of emitted electrons for each surface preparation tended to increase with an increase in the surface composition of fluorine of PTFE debris attached to the surface. The adsorption amount of the fluorine for sample III was much greater than that for samples I and II. Copyright © 2004 John Wiley & Sons, Ltd.
A lateral force microscopy study of friction between glassy carbon and different surfaces
Authors: Stiess S. , Richter A. , King B. V. , Reitsma M. , Smith R. 
Published: August 2004

AbstractA Nanoscope III atomic force microscope (AFM) was used to measure the friction between glassy carbon microspheres, glued to the AFM cantilever, and flat surfaces of silicon, carbon, steel and silver. The measured friction data was fitted using the Derjaguin–Müller–Toporov (DMT) model. The work of adhesion between the spheres and the surfaces ranged from 0.45 mNm−1 for the carbon surface to 19 mNm−1 for the silicon surface. The work of adhesion was found to be proportional to the interfacial shear strength for silver, steel and carbon. Copyright © 2004 John Wiley & Sons, Ltd.
Tribological interactions at the wheel–workpiece interface in surface grinding of construction stone
Authors: Xu Xipeng 
Published: August 2004

AbstractThis study was conducted to elucidate the interactions at the tool–workpiece interface during surface grinding of three typical granites—black, gray and red—by using a diamond wheel. The consumed power, the forces and temperatures generated at the grinding zone were in‐process monitored and the morphological features of ground granite surfaces were examined. The average load per diamond grit, energy partitions at the wheel–granite interface, and diamond tip temperatures were subsequently estimated based on the measurements of force, power and temperature. The normal force was found to be comparable for the three workpieces, but the tangential force was greater in either wet grinding red granite or dry grinding black granite due to their different removal mechanisms and friction conditions. Approximately linear relationships between the power and ploughed surface area generated per unit time per unit width were established for the three granites and the surface energy for the red granite was found to be higher than for the other two granites. The energy partitions into the granite were found to be about one‐third. Copyright © 2004 John Wiley & Sons, Ltd.
A study of the surface chemistry, morphology and wear of silicon based MEMS
Authors: Li J. , Cui Z. , Baker M. A. 
Published: August 2004

AbstractPolysilicon microelectromechanical systems (MEMS) are the subject of intense research activity. This paper reports on the surface chemistry, topography and nanowear properties of a MEMS test structure fabricated at Sandia National Laboratories, studied using XPS and atomic force microscopy (AFM). XPS C 1s and Si 2p spectra from the polysilicon components, silicon nitride substrate and a reference Si wafer are compared. The results confirm the presence of a self‐assembled monolayer (SAM) on the MEMS surface. An island‐like morphology is found on both polysilicon and silicon nitride surfaces of the MEMS. The islands take the form of caps, being up to 0.5 µm in diameter and 20 nm in height. It is concluded that a dual columnar and equiaxed microstructure develops during growth of these low pressure chemical vapour deposition (LPCVD) layers and the islands are caps to the columnar structures. A 35 µN load applied to the AFM diamond tip leads to a wear depth of 1.4 ± 0.13 nm and 2.1 ± 0.06 nm on the polysilicon and silicon nitride MEMS equiaxed surfaces, respectively. Under the same load, greater wear of the columnar caps on both surfaces is observed. The results suggest that the morphology present on the polysilicon surface will be worn flat during operation and will not adversely affect the wear properties of the polysilicon components. Copyright © 2004 John Wiley & Sons, Ltd.
Low frictional copper oxide film prepared with sodium hydroxide solution
Authors: Oishi T. , Goto M. , Kasahara A. , Tosa M. 
Published: August 2004

AbstractIn order to prepare a copper oxide film with low friction, we studied the chemical treatment of copper in aqueous sodium hydroxide solution. Copper plate with roughness about 100 nm as substrate was immersed in 0.1–10 M NaOH (M ≡ mol/dm3) for a fixed reaction time. The XRD result showed that copper oxide film of CuO or Cu2O grew on the surface of the substrate. SEM observation showed that the substrate surface became rough with the reaction time. A friction coefficient (µ) as low as 0.08 was achieved in the air when the substrate was immersed in 10 M of NaOH for 1000 sec. The coefficient changed from 0.08 to 0.4 according to the reaction time and the NaOH concentration. The change in friction coefficient as a function of surface roughness of the oxide film indicated that the surface morphology on the sub‐micrometre scale could strongly affect the friction of the oxide film. The coefficient of the oxide film measured in a vacuum was nearly as low as the coefficient in the air. The prepared copper oxide film can be therefore a good candidate for solid lubricant both in the air and in a vacuum. Copyright © 2004 John Wiley & Sons, Ltd.
Interface study for liquid–solid state surface by means of the S K‐edge NEXAFS method
Authors: Yagi S. , Matsumura Y. , Soda K. , Hashimoto E. , Taniguchi M. 
Published: August 2004

AbstractThe adsorption behavior of a sulfur‐containing amino acid molecule on a transition metal surface has been investigated in the bio‐catalytic and surface reaction fields. For a liquid sample there are many difficulties in x‐ray absorption fine structure (XAFS) measurement in the soft x‐ray energy region. In this study we have constructed a new XAFS measurement system with He‐path and Be window at soft x‐ray beamline (BL‐3) at the Hiroshima Synchrotron Radiation Center (HSRC). Copyright © 2004 John Wiley & Sons, Ltd.
Sensitivity of score tests for zero‐inflation in count data
Authors: Lee Andy H. , Xiang Liming , Fung Wing K. 
Published: August 2004

AbstractIn many biomedical applications, count data have a large proportion of zeros and the zero‐inflated Poisson regression (ZIP) model may be appropriate. A popular score test for zero‐inflation, comparing the ZIP model to a standard Poisson regression model, was given by van den Broek. Similarly, for count data that exhibit extra zeros and are simultaneously overdispersed, a score test for testing the ZIP model against a zero‐inflated negative binomial alternative was proposed by Ridout, Hinde and Demétrio. However, these test statistics are sensitive to anomalous cases in the data, and incorrect inferences concerning the choice of model may be drawn. In this paper, diagnostic measures are derived to assess the influence of observations on the score statistics. Two examples that motivated the application of zero‐inflated regression models are considered to illustrate the importance of sensitivity analysis of the zero‐inflation tests. Copyright © 2004 John Wiley & Sons, Ltd.
Modelling the distribution of ischaemic stroke‐specific survival time using an EM‐based mixture approach with random effects adjustment
Authors: Ng S. K. , McLachlan G. J. , Yau Kelvin K. W. , Lee Andy H. 
Published: August 2004

AbstractA two‐component survival mixture model is proposed to analyse a set of ischaemic stroke‐specific mortality data. The survival experience of stroke patients after index stroke may be described by a subpopulation of patients in the acute condition and another subpopulation of patients in the chronic phase. To adjust for the inherent correlation of observations due to random hospital effects, a mixture model of two survival functions with random effects is formulated. Assuming a Weibull hazard in both components, an EM algorithm is developed for the estimation of fixed effect parameters and variance components. A simulation study is conducted to assess the performance of the two‐component survival mixture model estimators. Simulation results confirm the applicability of the proposed model in a small sample setting. Copyright © 2004 John Wiley & Sons, Ltd.
Statistical assessment of mediational effects for logistic mediational models
Authors: Huang Bin , Sivaganesan Siva , Succop Paul , Goodman Elizabeth 
Published: August 2004

AbstractThe concept of mediation has broad applications in medical health studies. Although the statistical assessment of a mediational effect under the normal assumption has been well established in linear structural equation models (SEM), it has not been extended to the general case where normality is not a usual assumption. In this paper, we propose to extend the definition of mediational effects through causal inference. The new definition is consistent with that in linear SEM and does not rely on the assumption of normality. Here, we focus our attention on the logistic mediation model, where all variables involved are binary. Three approaches to the estimation of mediational effects—Delta method, bootstrap, and Bayesian modelling via Monte Carlo simulation are investigated. Simulation studies are used to examine the behaviour of the three approaches. Measured by 95 per cent confidence interval (CI) coverage rate and root mean square error (RMSE) criteria, it was found that the Bayesian method using a non‐informative prior outperformed both bootstrap and the Delta methods, particularly for small sample sizes. Case studies are presented to demonstrate the application of the proposed method to public health research using a nationally representative database. Extending the proposed method to other types of mediational model and to multiple mediators are also discussed. Copyright © 2004 John Wiley & Sons, Ltd.
Estimating vaccine efficacy using auxiliary outcome data and a small validation sample
Authors: Chu Haitao , Halloran M. Elizabeth 
Published: August 2004

AbstractIn vaccine studies, a specific diagnosis of a suspected case by culture or serology of the infectious agent is expensive and difficult. Implementing validation sets in the study is less expensive and is easier to carry out. In studies using validation sets, the non‐specific or auxiliary outcome is measured on each participant while the specific outcome is measured only for a small proportion of the participants. Vaccine efficacy, defined as one minus some measure of relative risk, could be severely attenuated if based only on the auxiliary outcome. Applying missing data analysis techniques could thus correct the bias while maintaining statistical efficiency. However, when the sample size in the validation sets is small and the vaccine is highly efficacious, all specific outcomes are likely to be negative in the validation set in the vaccinated group. Two commonly used missing data analysis methods, the mean score method and multiple imputation, depend on the ad hoc continuity correction when none of the specific outcomes are positive and the normality or log‐normality assumption of relative risk, which may not hold when the relative risk is highly skewed, to estimate the confidence interval. In this paper, we propose a Bayesian method to estimate vaccine efficacy and its highest probability density (HPD) credible set using Monte Carlo (MC) methods when using auxiliary outcome data and a small validation sample. Comparing the performance of these approaches using data from a field study of influenza vaccine and simulations, we recommend to use the Bayesian method in this situation. Copyright © 2004 John Wiley & Sons, Ltd.
Marginalized transition models for longitudinal binary data with ignorable and non‐ignorable drop‐out
Authors: Kurland Brenda F. , Heagerty Patrick J. 
Published: August 2004

AbstractWe extend the marginalized transition model of Heagerty to accommodate non‐ignorable monotone drop‐out. Using a selection model, weakly identified drop‐out parameters are held constant and their effects evaluated through sensitivity analysis. For data missing at random (MAR), efficiency of inverse probability of censoring weighted generalized estimating equations (IPCW‐GEE) is as low as 40 per cent compared to a likelihood‐based marginalized transition model (MTM) with comparable modelling burden. MTM and IPCW‐GEE regression parameters both display misspecification bias for MAR and non‐ignorable missing data, and both reduce bias noticeably by improving model fit. Copyright © 2004 John Wiley & Sons, Ltd.
Separating within and between effects in family studies: an application to the study of blood pressure in children
Authors: Mann Vera , De Stavola Bianca L. , Leon David A. 
Published: August 2004

AbstractIn epidemiology the analyses of family or twin studies do not always fully exploit the data, as information on differences between siblings is often used while between‐families effect are not considered. We show how cross‐sectional time‐series linear regression analysis can be easily implemented to estimate within‐ and between‐families effects simultaneously and how these effects can then be compared using the Hausman test. We illustrate this approach with data from the Uppsala family study on blood pressure in children with age ranging from 5.5 to 12.3 years for the younger and from 7.5 to 13.8 years for the older siblings. Comparing the effect of differences in birth weight on blood pressure within‐family (in full siblings) and between‐families (in unrelated children) allows us to study the contributions of fixed and pregnancy‐specific maternal effects on birth weight and consequently on blood pressure. Our data showed a 0.88 mmHg decrease (95 per cent confidence interval: −1.7 to −0.03 mmHg) in systolic blood pressure for one standard deviation increase in birth weight between siblings within a family and 0.88 mmHg (95 per cent confidence interval: −1.6 to −0.2 mmHg) decrease in systolic blood pressure for one standard deviation increase in birth weight between unrelated children. These estimates were controlled for sex, age, pubertal stage, body size and pulse rate of the children at examination and for maternal body size and systolic blood pressure. The within‐ and between‐families effects were not significantly different, p=0.19, suggesting that fixed and pregnancy‐specific factors have similar effects on childhood systolic blood pressure. Copyright © 2004 John Wiley & Sons, Ltd.
Strength of accumulating evidence and data monitoring committee decision making
Authors: George Stephen L. , Freidlin Boris , Korn Edward L. 
Published: August 2004

AbstractThe data monitoring committee (DMC) is a vital component of a randomized clinical trial. Its responsibilities include stopping the trial early for extreme results. The decision to stop the trial must be based on a careful synthesis of statistical methodology and clinical judgment. It is critical to ensure the validity of this complex process. In this paper we present results of a survey of 21 DMC members conducted to investigate how they evaluate accumulating evidence. The results indicate that some DMC members may be over‐interpreting developing trends in the data. Copyright © 2004 John Wiley & Sons, Ltd.
CrossOver: an algorithm for the construction of efficient cross‐over designs
Authors: John J. A. , Russell K. G. , Whitaker D. 
Published: August 2004

AbstractA cross‐over experiment involves the application of sequences of treatments to several subjects over a number of time periods. It is thought that the observation made on each subject at the end of a time period may depend on the direct effect of the treatment applied in the current period, and the carry‐over effects of the treatments applied in one or more previous periods. Various models have been proposed to explain the nature of the carry‐over effects. An experimental design that is optimal under one model may not be optimal if a different model is the appropriate one. In this paper an algorithm is described to construct efficient cross‐over designs for a range of models that involve the direct effects of the treatments and various functions of their carry‐over effects. The effectiveness and flexibility of the algorithm are demonstrated by assessing its performance against numerous designs and models given in the literature. Copyright © 2004 John Wiley & Sons, Ltd.
QT analysis: a complex answer to a ‘simple’ problem
Authors: Li Lang , Desai Mehul , Desta Zeruesenay , Flockhart David 
Published: August 2004

AbstractProlongation of the QT interval on a surface electrocardiogram is a biomarker for a potentially life‐threatening arrhythmia. It is used by drug developers and regulatory agencies as a measure of drug safety. Heart rate or RR interval (the inverse of heart rate) correction of the QT interval is necessary because of the QT interval shortening that accompanies physiologic decreases in the RR interval. When a drug alters the RR interval, it is important to distinguish a QT change that is due to a drug effect versus an artefact of a heart rate change. A two‐step off‐drug subject‐specific QT correction analysis is discussed. At the first step, a linear mixed model based only on the placebo (off‐drug) RR/QT data produces a correction coefficient that can be applied to a generic formula, and QT intervals are corrected for heart rate on both placebo and treatment period data using that formula. At step two, the heart rate corrected QT interval (QTc) is then compared between placebo and treatment groups at a pre‐specified heart rate (usually 60 bpm) based on another linear mixed model. This two‐step QT analysis implicitly assumes the slope of log(QT) versus log(RR) is unchanged by drug. Practically, it is important to understand how much this assumption can bias the QT prolongation estimates if it is not valid. We propose a one‐step off–on‐drug subject‐specific QT correction analysis that would pool placebo and treatment period RR/QT data and derive different subject specific coefficients for the treatment and placebo data based on a linear mixed model, which can avoid the unchanged slope assumption. It is also a known unbiased and the most efficient method. The applications of both methods are demonstrated through the QT analysis of haloperidol, a neuroleptic known to prolong QTc. Both theoretical and empirical results show that, although the two‐step off‐drug QT correction analysis is biased, the bias is small in the case of haloperidol (0.1–0.2ms). The two‐step off‐drug QT correction analysis is shown to be almost as efficient as our one‐step off‐ and on‐drug QT analysis. Copyright © 2004 John Wiley & Sons, Ltd.
Practical recommendations to minimize software capability evaluation risks
Authors: Saiedian Hossein 
Published: August 2004

AbstractMany organizations, and, in particular, the US Department of Defense, find the Capability Maturity Model's (CMM) software capability evaluation (SCE) to be a useful tool for evaluating the maturity and capability of a number of competing software contractors and thus selecting a prospective contractor. The evaluation commonly takes place during the acquisition phase of a software project in order to focus on identifying and reducing risks associated with quality, scheduling, and budget. When an unbiased evaluation is performed, the information revealed can help determine potential risks in selecting a particular candidate contractor. However, there are many ways to manipulate the outcome of the SCE by the evaluation team or the candidate contractor. It is important that the potential flaws and shortcomings in the SCE be identified and eliminated to ensure a viable evaluation. This article briefly discusses the concerns associated with and flaws in conducting SCEs and proposes a number of practical recommendations to eliminate or substantially reduce them. Copyright © 2004 John Wiley & Sons, Ltd.