bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transgenic mouse models of hepatitis B virus‐associated hepatocellular carcinoma
Authors: Singh Mahavir , Kumar Vijay 
Published: June 2003

AbstractThe multi‐factorial and multi‐step nature of cancer development makes analysis difficult in cell culture and non‐genetic animal models. Recent progress in technology has allowed the development of several transgenic animal models addressing various aspects of liver diseases caused by hepatitis B virus in human patients. The experimental data from these studies in vivo highlight the importance of HBV gene products that alone or in conjunction with other host cellular protein(s) can deregulate the cell cycle control checkpoints in the hepatocytes of transgenic mice leading to the development of hepatocellular carcinoma. Moreover, these models are extremely useful in analysing and ascertaining the stages of malignant transformation linked to multiple genetic and non‐genetic events of cancer development and in developing novel strategies of intervention. Copyright © 2003 John Wiley & Sons, Ltd.
Polynomial time approximation schemes for dense instances of minimum constraint satisfaction
Authors: Bazgan Cristina , Fernandez de la Vega W. , Karpinski Marek 
Published: June 2003

AbstractIt is known that large fragments of the class of dense Minimum Constraint Satisfaction (MIN‐CSP) problems do not have polynomial time approximation schemes (PTASs) contrary to their Maximum Constraint Satisfaction analogs. In this paper we prove, somewhat surprisingly, that the minimum satisfaction of dense instances ofkSAT‐formulas, and linear equations mod 2, Ek‐LIN2, do have PTASs for anyk.The MIN‐Ek‐LIN2 problems are equivalent to thek‐ary versions of the Nearest Codeword problem, the problem which is known to be exceedingly hard to approximate on general instances. The method of solution of the above problems depends on the development of a new density sampling technique fork‐uniform hypergraphs which could be of independent interest. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 73–91, 2003
Three theorems regarding testing graph properties
Authors: Goldreich Oded , Trevisan Luca 
Published: June 2003

AbstractProperty testing is a relaxation of decision problems in which it is required to distinguish YES‐instances (i.e., objects having a predetermined property) from instances that are far from any YES‐instance. We presents three theorems regarding testing graph properties in the adjacency matrix representation. More specifically, these theorems relate to the project of characterizing graph properties according to the complexity of testing them (in the adjacency matrix representation). The first theorem is that there exist monotone graph properties in 𝒩𝒫 for which testing is very hard (i.e., requires to examine a constant fraction of the entries in the matrix). The second theorem is that every graph property that can be tested making a number of queries that is independent of the size of the graph can be so tested by uniformly selecting a set of vertices and accepting iff the induced subgraph has some fixed graph property (which is not necessarily the same as the one being tested). The third theorem refers to the framework of graph partition problems, and is a characterization of the subclass of properties that can be tested using a one‐sided error tester making a number of queries that is independent of the size of the graph. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 23–57, 2003
Deterministic approximation of the cover time
Authors: Feige Uriel , Rabinovich Yuri 
Published: June 2003

AbstractThe cover time is the expected time it takes a random walk to cover all vertices of a graph. Despite the fact that it can be approximated with arbitrary precision by a simple polynomial time Monte‐Carlo algorithm which simulates the random walk, it is not known whether the cover time of a graph can be computed in deterministic polynomial time. In the present paper we establish a deterministic polynomial time algorithm that, for any graph and any starting vertex, approximates the cover time within polylogarithmic factors. More generally, our algorithm approximates the cover time for arbitrary reversible Markov chains. The new aspect of our algorithm is that the starting vertex of the random walk may be arbitrary and is given as part of the input, whereas previous deterministic approximation algorithms for the cover time assume that the walk starts at the worst possible vertex. In passing, we show that the starting vertex can make a difference of up to a multiplicative factor of$\Theta(n^{3/2}/\sqrt{\log\, n})$in the cover time of ann‐vertex graph. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 1–22, 2003
Rate of convergence of crossover operators
Authors: Ollivier Yann 
Published: June 2003

AbstractWe study the convergence of mating operators on {0, 1}n. In particular, we answer questions of Rabani, Rabinovich, and Sinclair (1998) by giving tight estimates on the divergence between the finite‐ and infinite‐population processes, thus solving positively the problem of the simulability of such quadratic dynamical systems. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 58–72, 2003
Space complexity of random formulae in resolution
Authors: Ben‐Sasson Eli , Galesi Nicola 
Published: June 2003

AbstractWe study the space complexity of refuting unsatisfiable randomk‐CNFs in the Resolution proof system. We prove that for Δ ≥ 1 and any ϵ > 0, with high probability a randomk‐CNF overnvariables and Δnclauses requires resolution clause space of Ω(n/Δ1+ϵ). For constant Δ, this gives us linear, optimal, lower bounds on the clause space. One consequence of this lower bound is the first lower bound for size of treelike resolution refutations of random 3‐CNFs with clause density Δ ≫n. This bound is nearly tight. Specifically, we show that with high probability, a random 3‐CNF with Δnclauses requires treelike refutation size of exp(Ω(n/Δ1+ϵ)), for any ϵ > 0. Our space lower bound is the consequence of three main contributions: (1) We introduce a 2‐player Matching Game on bipartite graphsGto prove that there are no perfect matchings inG. (2) We reduce lower bounds for the clause space of a formulaFin Resolution to lower bounds for the complexity of the game played on the bipartite graphG(F) associated withF. (3) We prove that the complexity of the game is large wheneverGis an expander graph. Finally, a simple probabilistic analysis shows that for a random formulaF, with high probabilityG(F) is an expander. We also extend our result to the case ofG‐PHP, a generalization of the Pigeonhole principle based on bipartite graphsG. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 92–109, 2003
Calculated bulk vacancy formation energy (Ev) for a Schottky defect in Al single crystals
Authors: Terblans J. J. 
Published: June 2003

AbstractIn this paper the bulk vacancy formation energies (Ev) of Al single crystals (with different surface orientations (111), (100) and (110)) were calculated with the embedded atom method using the empirical many‐body potential of Sutton and Chen. These calculations indicate that there is a significant difference in the bulk vacancy formation energy underneath different surface orientations. The crystal with the (111) surface had the highest bulk vacancy formation energy and the crystal with the (110) surface had the lowest bulk vacancy formation energy. Copyright © 2003 John Wiley & Sons, Ltd.
Quantitative SIMS analysis of SiC
Authors: Kudriavtsev Yu. , Villegas A. , Godines A. , Asomoza R. , Usov I. 
Published: June 2003

AbstractWe performed a systematic study of ion‐implanted 6H‐SiC standards to find the optimal regimes for SIMS analysis. Relative sensitivity factors (RSFs) were acquired for operating conditions typical of practical SIMS applications. The experimental SiC RSFs were compared with those found for silicon:1 the matrix effect was insignificant in most cases. It was found that the SiO− cluster ion cannot represent correctly the real oxygen distribution in SiC. The physics of the effect is discussed. Copyright © 2003 John Wiley & Sons, Ltd.
Mechanism of electroless deposition of Ni–W–P alloys by adding surfactants
Authors: Hamid Z. Abdel 
Published: June 2003

AbstractThis paper describes an electroless deposition method for the formation of a thin metallic film containing mainly nickel with significant amounts of tungsten (up to 25%) and phosphorus (5–10%). The film was deposited from an aqueous electrolyte that contained sodium tungstate as a source of tungsten, nickel sulphate as a source of nickel and hypophosphite as the reducing agent and a source of phosphorus. The surfactants were p‐hexyloxy‐p‐sodium sulphonate azobenzene (HSA) with the formula H13C6OC6H4N2 C6H4SO3Na and p‐hexylbenzyltriethanol ammonium chloride (HBC) with the formula H13C6H4CH2N+ (C2H4OH)3Cl−, added as stabilizers.In this study the process parameters of typical solutions, such as temperature, pH and concentration of tungstate salt and the concentration of different surfactants, were presented and discussed. Adsorption of the surfactants on a metal surface was dependent, among other things, on the structure of their hydrophobic and hydrophilic portions. The effect of adsorption of these surfactants on a metal surface was examined above and below the critical micelle concentration (CMC). The deposition process involves several reactions that occur simultaneously and are described in detail in this work. The mechanism for interaction of the surfactants with the steel surface was proposed through the isotherm for adsorption from aqueous solution. Furthermore, the surface properties of the surfactants were measured, particularly the CMC, the surface tension reduction and the maximum surface excess Γmax.The tungsten percentage in the deposit layer was strongly influenced by the plating conditions and the critical concentration of each surfactant. The results were discussed according to the surface properties of the additive. The thin film of Ni–W–P achieved high crystal refinement and high hardness, it was smooth and uniform and it exhibited superior corrosion resistance. Copyright © 2003 John Wiley & Sons, Ltd.
Study of the degradation of plasma‐oxidized polystyrene by time‐ and angle‐resolved x‐ray photoelectron spectroscopy
Authors: Tremblay M.‐C. , Paynter R. W. 
Published: June 2003

AbstractAngle‐resolved x‐ray photoelectron spectroscopy (ARXPS) measurements were made, in repeated sequences employing Al and Mg x‐ray sources alternately, on a polystyrene sample that had been exposed to an oxygen plasma. It was observed that oxygen was lost from the sample over a period of 5 h and 40 min. The ARXPS data sets were corrected for the time displacement between consecutive measurements at different photoemission angles and fitted with three simple models in order to extract oxygen concentration–depth profiles, consistent with the data, as a function of time. The oxygen depth profiles were found to evolve in a consistent manner, indicating both a loss of average oxygen content and thickness in the ‘oxidized polymer layer’. Copyright © 2003 John Wiley & Sons, Ltd.
Ultrathin SiO2 on Si IV. Intensity measurement in XPS and deduced thickness linearity
Authors: Seah M. P. , Spencer S. J. 
Published: June 2003

AbstractThe procedures for measuring the intensities and for subsequent calculation of the thickness of thermal SiO2 layers on Si in the range 0.3–8 nm have been evaluated to determine the best measurement protocols. This work is based on earlier work where the measurements for (100) and (111) Si surfaces indicate the need to work at a reference geometry. In the spectra, the Si 2p peaks may be separated clearly into the substrate Si and the overlayer SiO2 but it is recommended here that, for accuracies better than 1%, the interface oxides are also analysed. The analysis here is for thermal oxides. Oxides grown by other routes may require a modification of this analysis. It is shown that, in evaluating the data to determine the layer thickness, the failure to remove x‐ray satellites or the use of a straight‐line background will both lead to unacceptable errors that may exceed 5%. On the other hand, if a Shirley background is used consistently for both the peak area analysis and for evaluation of the ratio of intensities for bulk SiO2 and Si, Ro, the results should be linear over the above range to within ±0.025 nm. This excellent result includes the non‐linearities arising from elastic scattering effects and the data reduction method. Equations are provided, together with a value of Ro for Mg and Al x‐rays, to calculate the oxide thicknesses with the above linearity. In order to determine the oxide thickness accurately, the relevant inelastic mean free paths also must be known. Theoretical evaluations are only accurate to 17.4% and so better values need to be obtained by calibration. This paper provides the infrastructure to do this. Crown Copyright © 2003 Published by John Wiley & Sons, Ltd.
Uranium association with corroding carbon steel surfaces
Authors: Eng C. W. , Halada G. P. , Francis A. J. , Dodge C. J. , Gillow J. B. 
Published: June 2003

AbstractWe investigated the association of uranium with clean and corroded surfaces of 1010 carbon steel. Studying steel contaminated by uranium species will have an important effect on the development of methods used to clean radioactively contaminated metal waste. X‐ray photoelectron spectroscopy, synchrotron infrared microspectroscopy and laboratory‐based Fourier transform infrared analysis of steel surfaces exposed to uranyl nitrate showed the presence of crystallized hydrated uranyl oxides, uranyl hydroxides, iron oxyhydroxides and iron oxides. In general, heavily corroded areas physically shield the uranium species, which tended to associate spatially with hydroxyl groups and lepidocrocite. Lightly corroded areas contained uranium species with stronger axial U–O bonding. Infrared spectroscopy, Rutherford backscattering spectroscopy and energy‐dispersive spectroscopy mapping analysis revealed that the uranium species are well distributed within the upper micron of the thick corrosion layer and associated more with areas of high hydroxide content. Parameters such as the concentration of uranyl nitrate solution used to expose the carbon steel coupons, the method of contamination (dipped or sprayed with dilute uranyl nitrate solution) and the degree of corrosion (accelerated corrosion before and/or after contamination) played significant roles in the distribution and nature of the uranyl hydroxide/iron oxyhydroxide corrosion products found on the surface of all coupons. These factors must be considered in the development and optimization of decontamination processes for metal waste. Copyright © 2003 John Wiley & Sons, Ltd.
In situ SERS study of the adsorption of inhibitors of carbon dioxide corrosion
Authors: Durnie William H. , De Marco Roland , Jefferson Alan , Kinsella Brian J. 
Published: June 2003

AbstractA specially designed electrochemical cell incorporating a rotating disc electrode has been used for in situ surface‐enhanced Raman spectroscopy (SERS) studies of the adsorption of inhibitors of carbon dioxide corrosion onto silver‐coated mild steel electrodes. It is shown that SERS‐active inhibitors comprising aromatic moieties may be detected using the SERS technique. Furthermore, the efficacy of adsorption of corrosion inhibitors employed in the present study is optimal near the open cell or corrosion potential, demonstrating that electrode polarization induces electrostatic forces of repulsion that retard the adsorption of the inhibitor to the corroding steel surface. Copyright © 2003 John Wiley & Sons, Ltd.
Evaluation of the sputtering rate variation in SIMS ultra‐shallow depth profiling using multiple short‐period delta layers
Authors: Homma Y. , Takenaka H. , Toujou F. , Takano A. , Hayashi S. , Shimizu R. 
Published: June 2003

AbstractWe have developed multiple short‐period delta layers as a reference material for SIMS ultra‐shallow depth profiling. Boron nitride delta layers and silicon spacer layers were sputter‐deposited alternately, with a silicon spacer thickness of 1–5 nm. These delta‐doped layers were used to measure the sputtering rate change in the initial stage of oxygen ion bombardment. A significant variation of sputtering rate was observed in the initial 3 nm or less. The sputtering rate in the initial 3 nm was estimated to be about four times larger than the steady‐state value for 1000 eV oxygen ions. Copyright © 2003 John Wiley & Sons, Ltd.
Some statistical methods for investigating the date of birth as a disease indicator
Authors: Le Chap T. , Liu Ping , Lindgren Bruce R. , Daly Kathleen A. , Scott Giebink G. 
Published: June 2003

AbstractSome methods of temporal statistics are presented and proposed for investigating the date of birth as a disease predictor. A subject's birthday is proposed to be used as a continuous variable with a circular distribution, a special type of interval scale without a true zero point. Three types of endpoints are then considered: a dichotomous endpoint; a continuous endpoint; and time‐to‐event. A study of otitis media is used for illustration. We found, for example, that children born in late winter to early spring tend to have higher cord blood pneumococcal antibody concentration and lower risk of disease as compared to those born in summer to early fall perhaps due largely to exposure to indoor pollution by pregnant mothers. Copyright © 2003 John Wiley & Sons, Ltd.
Age‐specific back‐projection of HIV diagnosis data
Authors: Becker Niels G. , Lewis James J. C. , Li Zhengfeng , McDonald Ann 
Published: June 2003

AbstractA method for reconstructing the HIV infection curve from data on both HIV and AIDS diagnoses is enhanced by using age as a covariate and by using the diagnosis data to estimate parameters that were previously assumed known. Maximum likelihood estimation is used for parameters of the induction distribution. Each of the set of parameters that specify the baseline rate of infection over time and the set of parameters giving the relative susceptibility over age are estimated by maximizing the likelihood subject to a smoothness requirement. We find that estimating the extra parameters is feasible, producing estimates with good precision. Including age as a covariate gives 90 per cent confidence intervals for the HIV incidence curve that are about 20 per cent narrower than those obtained when age data are not used. Copyright © 2003 John Wiley & Sons, Ltd.
Analysis of pregnancy and other factors on detection of human papilloma virus (HPV) infection using weighted estimating equations for follow‐up data
Authors: Ziegler Andreas , Kastner Christian , Chang‐Claude Jenny 
Published: June 2003

AbstractGeneralized estimating equations have been well established to draw inference for the marginal mean from follow‐up data. Many studies suffer from missing data that may result in biased parameter estimates if the data are not missing completely at random. Robins and co‐workers proposed using weighted estimating equations (WEE) in estimating the mean structure if drop‐out occurs missing at random. We illustrate the differences between the WEE and the commonly applied available case analysis in a simulation study. We apply the WEE and reanalyse data of a longitudinal study of pregnancy and human papilloma virus (HPV) infection. We estimate the response probabilities and demonstrate that the data are not missing completely at random. Upon use of the WEE, we are able to show that pregnant women have an increased odds for an HPV infection compared with non‐pregnant women after delivery (p=0.027). We conclude that the WEE are useful for dealing with monotone missing data due to drop‐outs in follow‐up data. Copyright © 2003 John Wiley & Sons, Ltd.
An overview of the variables selection methods for the minimum sum of absolute errors regression
Authors: André Carmen D. S. , Narula Subhash C. , Elian Silvia N. , Tavares Rodrigo A. 
Published: June 2003

AbstractThe minimum sum of absolute errors regression is a robust alternative to the least squares regression whenever the errors follow a distribution for which the sample median is a more efficient estimator of location parameter than the sample mean, the errors follow a long tailed distribution, there are outliers in the values of the response variable in the data or the absolute error loss function is more appropriate than the quadratic loss function. Often an initial model may contain a large number of variables. However, in many situations, it is neither necessary nor important to include all the variables in the model. The methods for variable selection for the minimum sum of absolute errors regression are not as well documented and known as for the least squares regression. Our objective is to present an overview of the procedures to fit models with fewer variables and some criteria for selecting a model. Copyright © 2003 John Wiley & Sons, Ltd.
Joint models for efficient estimation in proportional hazards regression models
Authors: Slasor Peter , Laird Nan 
Published: June 2003

AbstractIn survival studies, information lost through censoring can be partially recaptured through repeated measures data which are predictive of survival. In addition, such data may be useful in removing bias in survival estimates, due to censoring which depends upon the repeated measures. Here we investigate joint models for survival T and repeated measurements , given a vector of covariates . Mixture models indexed as f(T∣) f(∣T,) are well suited for assessing covariate effects on survival time. Our objective is efficiency gains, using non‐parametric models for in order to avoid introducing bias by misspecification of the distribution for . We model (T∣) as a piecewise exponential distribution with proportional hazards covariate effect. The component (∣T,) has a multinomial model. The joint likelihood for survival and longitudinal data is maximized, using the EM algorithm. The estimate of covariate effect is compared to the estimate based on the standard proportional hazards model and an alternative joint model based estimate. We demonstrate modest gains in efficiency when using the joint piecewise exponential joint model. In a simulation, the estimated efficiency gain over the standard proportional hazards model is 6.4 per cent. In clinical trial data, the estimated efficiency gain over the standard proportional hazards model is 10.2 per cent. Copyright © 2003 John Wiley & Sons, Ltd.
Adjusting for publication bias in the presence of heterogeneity
Authors: Terrin Norma , Schmid Christopher H. , Lau Joseph , Olkin Ingram 
Published: June 2003

AbstractIt is known that the existence of publication bias can influence the conclusions of a meta‐analysis. Some methods have been developed to deal with publication bias, but issues remain. One particular method called ‘trim and fill’ is designed to adjust for publication bias. The method, which is intuitively appealing and comprehensible by non‐statisticians, is based on a simple and popular graphical tool called the funnel plot. We present a simulation study designed to evaluate the behaviour of this method. Our results indicate that when the studies are heterogeneous (that is, when they estimate different effects), trim and fill may inappropriately adjust for publication bias where none exists. We found that trim and fill may spuriously adjust for non‐existent bias if (i) the variability among studies causes some precisely estimated studies to have effects far from the global mean or (ii) an inverse relationship between treatment efficacy and sample size is introduced by the studies' a priori power calculations. The results suggest that the funnel plot itself is inappropriate for heterogeneous meta‐analyses. Selection modelling is an alternative method warranting further study. It performed better than trim and fill in our simulations, although its frequency of convergence varied, depending on the simulation parameters. Copyright © 2003 John Wiley & Sons, Ltd.