bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal effects on stereolithography tools during injection moulding
Authors: Sá Ribeiro Armando , Hopkinson Neil , Henrique Ahrens Carlos
Published: May 2004

In this work, the changes to stereolithography (SL) resin mechanical properties during the injection moulding process were evaluated. A multi‐impression SL mould was built and used to inject a series of small flat mouldings. The fixed half SL tool insert included recesses to accommodate tensile test specimens. Tensile test specimens made from SL resin were positioned in these recesses and plastic parts were injected. After injecting a predetermined number of mouldings, tensile tests were performed using the tensile test specimens. The results from the tensile tests show that the thermal cycling encountered during the injection moulding process did not significantly affect the mechanical properties of the resin. Observations indicate that decrease in the temperatures encountered in the tool may lead to longer tool life.
New reporting models for business: who needs them?
Authors: Illingworth David
Published: May 2004

The Institute of Chartered Accountants in England and Wales (ICAEW) has recently launched a major new project to address the growing international concern that existing business reporting models are inadequate, and that recent attempts to develop new solutions and reach a global consensus have failed. David Illingworth, President of the ICAEW, explores how key players in the market including investors, managers, regulators and commentators can begin to assess the underlying issues which need to be addressed and shape a reform program that meets their collective aspirations and needs.
Measuring and improving the capital planning process
Authors: Adams Chris , Bourne Mike , Neely Andy
Published: May 2004

Much research has been done into capital planning approaches on both sides of the Atlantic over several decades, but it has tended to be one‐dimensional – focusing almost exclusively on the application of financial appraisal techniques. Meanwhile little has been done to examine either the efficacy of other elements of the process or executives’ satisfaction with the way the process works. Members of Cranfield School of Management’s Centre for Business Performance, sponsored by Accenture, set the record straight with both literature and practitioner research into the capital planning process that also presents a new framework and develops best practice principles.
From segmentation to fragmentation
Authors: Fuat Firat A. , Shultz Clifford J.
Published: May 2004

Attempts to contribute to the growing literature on postmodernism and marketing by addressing the changes in the market and the corresponding changes that have to take place in marketing strategies. Assesses the implications of postmodernism for marketing managers and other marketing practitioners, and proposes the marketing strategies that are needed to respond to the changes in the market with the growing influence of postmodernity. Discusses directions for future research.
A Marginal Mixed Baseline Hazards Model for Multivariate Failure Time Data
Authors: Clegg Limin X. , Cai Jianwen , Sen Pranab K.
Published: May 2004

Summary.In multivariate failure time data analysis, a marginal regression modeling approach is often preferred to avoid assumptions on the dependence structure among correlated failure times. In this paper, a marginal mixed baseline hazards model is introduced. Estimating equations are proposed for the estimation of the marginal hazard ratio parameters. The proposed estimators are shown t o be consistent and asymptotically Gaussian with a robust covariance matrix that can be consistently estimated. Simulation studies indicate the adequacy of the proposed methodology for practical sample sizes. The methodology is illustrated with a data set from the Framingham Heart Study.
Modeling Clustered, Discrete, or Grouped Time Survival Data with Covariates
Authors: Ross Eric A. , Moore Dirk
Published: May 2004

Summary.We have developed methods for modeling discrete or grouped time, right‐censored survival data collected from correlated groups or clusters. We assume that the marginal hazard of failure for individual items within a cluster is specified by a linear log odds survival model and the dependence structure is based on a gamma frailty model. The dependence can be modeled as a function of cluster‐level covariates. Likelihood equations for estimating the model parameters are provided. Generalized estimating equations for the marginal hazard regression parameters and pseudolikelihood methods for estimating the dependence parameters are also described. Data from two clinical trials are used for illustration purposes.
Statistical Quality Control of Variety Trial Data
Authors: Öfversten Jukka
Published: May 2004

Summary.I propose detection criteria for identifying an abnormal or erroneous data vector provided by a single variety trial in a longer series of variety trials. The test criteria are based on the linear effects estimated separately for each studied trial using global variance components estimated from the whole series of variety trials. The criteria comprise three mutually independent test statistics. The first one is a quadratic form in the estimated fixed effects, the second one is a quadratic form in the estimated realized linear random effects not including the residual effects, and the third one is a quadratic form in the estimated realized residual effects. Under the null hypothesis defining a valid data vector, the three quadratics have independentx2distributions. Under natural alternative hypotheses, they have noncentralx2distributions. Decomposing the total variation of the data vector studied into quadratic forms due to different types of the realized linear effects intuitively justifies the resulting test criteria. The decomposition may also be used to show that the resulting tests are likelihood ratio tests. I further present computational procedures that allow us to dispense with the need for prior estimation of the linear effects.
Modification of Sample Size in Group Sequential Clinical Trials
Authors: Cui Lu , Hung H. M. James , Wang Sue‐Jane
Published: May 2004

Summary. In group sequential clinical trials, sample size reestimation can be a complicated issue when it allows for change of sample size to be influenced by an observed sample path. Our simulation studies show that increasing sample size based on an interim estimate of the treatment difference can substantially inflate the probability of type I error in most practical situations. A new group sequential test procedure is developed by modifying the weights used in the traditional repeated significance two‐sample mean test. The new test has the type I error probability preserved at the target level and can provide a substantial gain in power with the increase of sample size. Generalization of the new procedure is discussed.
A Bayesian Hierarchical Approach for Combining Case‐Control and Prospective Studies
Authors: Muller Peter , Parmigiani Giovanni , Schildkraut Joellen , Tardella Luca
Published: May 2004

Summary.Motivated by the absolute risk predictions required in medical decision making and patient counseling, we propose an approach for the combined analysis of case‐control and prospective studies of disease risk factors. The approach is hierarchical to account for parameter heterogeneity among studies and among sampling units of the same study. It is based on modeling the retrospective distribution of the covariates given the disease outcome, a strategy that greatly simplifies both the combination of prospective and retrospective studies and the computation of Bayesian predictions in the hierarchical casecontrol context. Retrospective modeling differentiates our approach from most current strategies for inference on risk factors, which are based on the assumption of a specific prospective model. To ensure modeling flexibility, we propose using a mixture model for the retrospective distributions of the covariates. This leads to a general nonlinear regression family for the implied prospective likelihood. After introducing and motivating our proposal, we present simple results that highlight its relationship with existing approaches, develop Markov chain Monte Carlo methods for inference and prediction, and present an illustration using ovarian cancer data.
Efficiency Robust Tests for Survival or Ordered Categorical Data
Authors: RYAN LOUISE M. , Freidlin Boris , Podgor Marvin J. , Gastwirth Joseph L.
Published: May 2004

Summary. The selection of a single method of analysis is problematic when the data could have been generated by one of several possible models. We examine the properties of two tests designed to have high power over a range of models. The first one, the maximum efficiency robust test (MERT), uses the linear combination of the optimal statistics for each model that maximizes the minimum efficiency. The second procedure, called the MX, uses the maximum of the optimal statistics. Both approaches yield efficiency robust procedures for survival analysis and ordinal categorical data. Guidelines for choosing between them are provided.
Modeling a Categorical Variable Allowing Arbitrarily Many Category Choices
Authors: Agresti Alan , Liu I‐Ming
Published: May 2004

Summary. This article discusses the modeling of a categorical variable for which subjects can select any number of categories. For c categories, the response variable consists of a cross‐classification of c binary components, one pertaining to each category. Using data from a survey (Loughin, T. M. and Scherer, P. N., 1998, Biometrics, 54, 630–637) in which Kansas farmers indicated their primary sources of veterinary information, we discuss simultaneous logit modeling of the binary components of the multivariate response. The use of maximum likelihood or quasi‐likelihood fitting provides chi‐squared tests with degrees of freedom df = C(r ‐ 1) for testing the independence between each of the c response components and an explanatory variable with r categories. These tests are alternatives to the weighted chi‐squared test and the bootstrap test proposed by Loughin and Scherer for this hypothesis.
Modeling Tumor Onset and Multiplicity Using Transition Models with Latent Variables
Authors: Dunson D. B. , Haseman J. K.
Published: May 2004

Summary.We describe a method for modeling carcinogenicity from animal studies where the data consist of counts of the number of tumors present over time. The research is motivated by applications to transgenic rodent studies, which have emerged as an alternative to chronic bioassays for screening possible carcinogens. In transgenic mouse studies, the endpoint of interest is frequently skin papilloma, with weekly examinations determining how many papillomas each animal has at a particular point in time. It is assumed that each animal has two unobservable latent variables at each time point. The first indicates whether or not the tumors are in a multiplying state and the second is the potential number of additional tumors if the tumors are in a multiplying state. The product of these variables follows a zero‐inflated Poisson distribution, and the EM algorithm can be used to maximize the observed‐data pseudo‐likelihood, based on the latent variables. A generalized estimating equations robust variance estimator adjusts for dependency among outcomes within individual animals. The method is applied to testing for a dose‐related trend in both tumor incidence and multiplicity in carcinogenicity studies.
Genomic Control for Association Studies
Authors: Devlin B. , Roeder Kathryn
Published: May 2004

Summary. A dense set of single nucleotide polymorphisms (SNP) covering the genome and an efficient method to assess SNP genotypes are expected to be available in the near future. An outstanding question is how to use these technologies efficiently to identify genes affecting liability to complex disorders. To achieve this goal, we propose a statistical method that has several optimal properties: It can be used with case‐control data and yet, like family‐based designs, controls for population heterogeneity; it is insensitive to the usual violations of model assumptions, such as cases failing to be strictly independent; and, by using Bayesian outlier methods, it circumvents the need for Bonferroni correction for multiple tests, leading to better performance in many settings while still constraining risk for false positives. The performance of our genomic control method is quite good for plausible effects of liability genes, which bodes well for future genetic analyses of complex disorders.
Empirical Bayes Estimation of Random Effects Parameters in Mixed Effects Logistic Regression Models
Authors: Ten Have Thomas R. , Localio A. Russell
Published: May 2004

Summary. We extend an approach for estimating random effects parameters under a random intercept and slope logistic regression model to include standard errors, thereby including confidence intervals. The procedure entails numerical integration to yield posterior empirical Bayes (EB) estimates of random effects parameters and their corresponding posterior standard errors. We incorporate an adjustment of the standard error due to Kass and Steffey (KS; 1989, Journal of the American Statistical Association84, 717–726) to account for the variability in estimating the variance component of the random effects distribution. In assessing health care providers with respect to adult pneumonia mortality, comparisons are made with the penalized quasi‐likelihood (PQL) approximation approach of Breslow and Clayton (1993, Journal of the American Statistical Association88, 9–25) and a Bayesian approach. To make comparisons with an EB method previously reported in the literature, we apply these approaches to crossover trials data previously analyzed with the estimating equations EB approach of Waclawiw and Liang (1994, Statistics in Medicine13, 541–551). We also perform simulations to compare the proposed KS and PQL approaches. These two approaches lead to EB estimates of random effects parameters with similar asymptotic bias. However, for many clusters with small cluster size, the proposed KS approach does better than the PQL procedures in terms of coverage of nominal 95% confidence intervals for random effects estimates. For large cluster sizes and a few clusters, the PQL approach performs better than the KS adjustment. These simulation results agree somewhat with those of the data analyses.
Closed Testing Procedures for Group Sequential Clinical Trials with Multiple Endpoints
Authors: Tang Dei‐In , Geller Nancy L.
Published: May 2004

Summary. A simple approach is given for conducting closed testing in clinical trials with multiple end‐points in which group sequential monitoring is planned. The approach allows a flexible stopping time; the earliest and latest stopping times are described. The paradigm is applicable both to clinical trials with multiple endpoints and to the one‐sided multiple comparison problem of several treatments versus a control. The approach leads to enhancements of previous methods and suggestions for new methods. An example of a respiratory disease trial with four endpoints is given.
Test‐Based Exact Confidence Intervals for the Difference of Two Binomial Proportions
Authors: Chan Ivan S. F. , Zhang Zhongxin
Published: May 2004

Summary. Confidence intervals are often provided to estimate a treatment difference. When the sample size is small, as is typical in early phases of clinical trials, confidence intervals based on large sample approximations may not be reliable. In this report, we propose test‐based methods of constructing exact confidence intervals for the difference in two binomial proportions. These exact confidence intervals are obtained from the unconditional distribution of two binomial responses, and they guarantee the level of coverage. We compare the performance of these confidence intervals to ones based on the observed difference alone. We show that a large improvement can be achieved by using the standardized Z test with a constrained maximum likelihood estimate of the variance.
Nonparametric Identification of the Minimum Effective Dose
Authors: Chen Yuh‐Ing
Published: May 2004

Summary. We consider identifying the minimum effective dose (MED) in a dose‐response study, where the MED is denned to be the lowest dose level producing an effect over that of the zero‐dose control. Proposed herein is a nonparametric procedure based on the Mann–Whitney statistic incorporated with the step‐down closed testing scheme. A numerical example demonstrates the feasibility of the proposed nonparametric procedure. Finally, the comparative results of a Monte Carlo level and power study for small sample sizes are presented and discussed.
A Mover–Stayer Model for Longitudinal Marker Data
Authors: Albert Paul S.
Published: May 2004

Summary.Studies of chronic disease often focus on estimating prevalence and incidence in which the presence of active disease is based on dichotomizing a continuous marker variable measured with error. Examples include hypertension, asthma, and depression, where active disease is defined by setting a threshold on a continuous measure of blood pressure, respiratory function, and mood, respectively. This paper proposes a model for inference about prevalence and incidence when active disease is determined by dichotomizing a continuous marker variable in a population‐based study. In this formulation, it is postulated that there are three groups of people, those that are not susceptible to the disease, those who are always in the disease state, and those who have the potential to transition between the disease and the disease‐free states over time. The model is used to estimate the prevalence and incidence of the disease in the population while accounting for measurement error in the marker. An EM algorithm is used for parameter estimation and the methodology is illustrated on Pramingham heart study hypertension data. A simulation study is conducted in order to demonstrate the importance of accounting for measurement error in estimating prevalence and incidence for this example.
Semiparametric Regression for Periodic Longitudinal Hormone Data from Multiple Menstrual Cycles
Authors: Zhang Daowen , Lin Xihong , Sowers MaryFran
Published: May 2004

Summary.We consider Semiparametric regression for periodic longitudinal data. Parametric fixed effects are used to model the covariate effects and a periodic nonparametric smooth function is used to model the time effect. The within–subject correlation is modeled using subject‐specific random effects and a random stochastic process with a periodic variance function. We use maximum penalized likelihood to estimate the regression coefficients and the periodic nonparametric time function, whose estimator is shown to be a periodic cubic smoothing spline. We use restricted maximum likelihood to simultaneously estimate the smoothing parameter and the variance components. We show that all model parameters can be easily obtained by fitting a linear mixed model. A common problem in the analysis of longitudinal data is to compare the time profiles of two groups, e.g., between treatment and placebo. We develop a scaled chi‐squared test for the equality of two nonparametric time functions. The proposed model and the test are illustrated by analyzing hormone data collected during two consecutive menstrual cycles and their performance is evaluated through simulations.
Estimation and Testing with Overdispersed Proportions Using the Beta‐Logistic Regression Model of Heckman and Willis
Authors: Slaton Terra L. , Piegorsch Walter W. , Durham Stephen D.
Published: May 2004

Summary.Methods are presented for modeling dose‐related effects in proportion data when extra‐binomial variability is a concern. Motivation is taken from experiments in developmental toxicology, where similarity among conceptuses within a litter leads to intralitter correlations and to overdispersion in the observed proportions. Appeal is made to the well‐known beta‐binomial distribution to represent the overdispersion. From this, an exponential function of the linear predictor is used to model the dose‐response relationship. The specification was introduced previously for econometric applications by Heckman and Willis; it induces a form of logistic regression for the mean response, together with a reciprocal biexponential model for the intralitter correlation. Large‐sample, likelihood‐based methods for estimating and testing the joint proportion‐correlation response are studied. A developmental toxicity data set illustrates the methods.
Predictive Accuracy and Explained Variation in Cox Regression
Authors: Schemper Michael , Henderson Robin
Published: May 2004

Summary.We suggest a new measure of the proportion of the variation of possibly censored survival times explained by a given proportional hazards model. The proposed measure, termedV, shares several favorable properties with an earlierV1but also improves the handling of censoring. The statistic contrasts distance measures between individual 1/0 survival processes and fitted survival curves with and without covariate information. These distance measures,DxandD, respectively, are themselves informative as summaries of absolute rather than relative predictive accuracy. We recommend graphical comparisons of survival curves for prognostic index groups to improve the understanding of obtained values forV, Dx, andD.Their use and interpretation is exemplified for a Yorkshire lung cancer study on survival. From this and an overview for several well‐known clinical data sets, we show that the likely amount of relative or absolute predictive accuracy is often low even if there are highly significant and relatively strong prognostic factors.
The Combination of Population Pharmacokinetic Studies
Authors: Wakefield Jonathan , Rahman Nargis
Published: May 2004

Summary.Pharmacokinetic data consist of drug concentrations with associated known sampling times and are collected following the administration of known dosage regimens. Population pharmacokinetic data consist of such data on a number of individuals, possibly along with individual‐specific characteristics. During drug development, a number of population pharmacokinetic studies are typically carried out and the combination of such studies is of great importance for characterizing the drug and, in particular, for the design of future studies. In this paper, we describe a model that may be used to combine population pharmacokinetic data. The model is illustrated using six phase I studies of the antiasthmatic drug fluticasone propionate. Our approach is Bayesian and computation is carried out using Markov chain Monte Carlo. We provide a number of simplifications to the model that may be made in order to ease simulation from the posterior distribution.
The Impact of Restrictive Entry Criterion During the Placebo Lead‐in Period
Authors: Landin R. , DeBrota D. J. , DeVries T. A. , Potter W. Z. , Demitrack M. A.
Published: May 2004

Summary. In the study of depression, most randomized clinical trials have design features that attempt to sample from a stable patient population. One commonly used design feature is to require patients to maintain some minimum baseline symptom severity score during a placebo lead‐in period. One intent of this design feature is to evaluate the behavior of patients prior to administration of active medication. If, during the lead‐in period, patients do not maintain minimum symptom severity, the patients are excluded from the remainder of the study, the theory being that the excluded patients are not part of a stable patient population and hence are not likely to demonstrate efficacy of a truly effective treatment. This presentation investigates the effectiveness of a restrictive entry criterion and proposes an alternative explanation for what is usually defined as placebo response.
Mixed Effects Logistic Regression Models for Longitudinal Ordinal Functional Response Data with Multiple‐Cause Drop‐Out from the Longitudinal Study of Aging
Authors: Ten Have Thomas R. , Miller Michael E. , Reboussin Beth A. , James Margaret K.
Published: May 2004

Summary. In the context of analyzing ordinal functional limitation responses from the Longitudinal Study of Aging, we investigate the association between current functional limitation and previous year's limitation and its modification by physical activity and multiple causes of drop‐out. We accommodate the longitudinal nature of the multiple causes of informative drop‐out (death and unknown loss‐to‐follow‐up) with a mixed effects logistic model. Under the proposed model with a random intercept and slope, the ordinal functional outcome and multiple discrete time survival profiles share a common random effect structure. This shared parameter selection model assumes that the multiple causes of drop‐out are conditionally independent of the functional limitation outcome given the underlying random effect representing an individual's trajectory of general health status across time. Although it is not possible to fully assess the adequacy of this assumption, we assess the robustness of the approach by varying the assumptions underlying the proposed model, such as the random effects distribution and the drop‐out component. It appears that between‐subject differences in initial functional limitation are strongly associated with future functional limitation and that this association is stronger for those who do not have physical activity regardless of the random effects and informative dropout specifications. In contrast, the association between current functional limitation and previous trajectory of functional status within an individual is weaker and more sensitive to changes in the random effects and drop‐out assumptions.
Estimating Risk Difference in Multicenter Studies Under Baseline‐Risk Heterogeneity
Authors: Böhning Dankmar , Sarol Jesus
Published: May 2004

Summary. In this paper, we consider the case of efficient estimation of the risk difference in a multicenter study allowing for baseline heterogeneity. We consider the optimally weighted estimator for the common risk difference and show that this estimator has considerable bias when the true weights (which are inversely proportional to the variances of the center‐specific risk difference estimates) are replaced by their sample estimates. In addition, we propose a new estimator for this situation of the Mantel‐Haeiiszel type that is unbiased and, in addition, has a smaller variance for small sample sizes within the study centers. Simulations illustrate these findings.
The ultrastructure of the spermatozoon of the lizardIguana iguana(Reptilia, Squamata, Iguanidae) and the variability of sperm morphology among iguanian lizards
Authors: Vieira Gustavo H. C. , Colli Guarino R. , Báo Sônia N.
Published: May 2004

The spermatozoon ofIguana iguanais filiform and resembles that of other iguanian lizards, being most similar toTropidurus. All sperm synapomorphies of Tetrapoda, Amniota and Squamata are present in the sperm ofIguana iguana. By reconstructing the evolution of 30 sperm characters we identified a novel synapomorphy of Iguania: the presence of a well‐developed acrosomal ridge at the level of the epinuclear lucent zone. Because of the poor topological resolution among iguanian clades we could not discount the possibility of convergence or neutral selection as determinant of the variability in characteristics of the sperm cell. In agreement with previous studies, we identified heterogeneous rates of evolution among the three main regions of the sperm cell, namely the head, midpiece and tail.
Constructive and Classical Models for Results in Economics and Game Theory
Authors: Prasad Kislaya
Published: May 2004

A standard approach in economic theory is to use a formal language to prove results about an economy or a game. In this paper, model theory is used to examine interpretations of such results. The particular focus is on constructive theorems, since results established by constructive methods are valid for many different interpretations, whereas classical theorems are valid more narrowly. I discuss why non‐classical models may be of interest and also describe applications of model theory to economics in classical contexts, e.g. non‐standard analysis. The paper advocates a viewpoint suggesting that constructive models are tools for studying worlds in which agents’ knowledge of the world is incomplete.
Production of Ideas by Means of Ideas: A Turing Machine Metaphor
Authors: Zambelli Stefano
Published: May 2004

In this paper production of knowledge is modelled in terms of Turing machines or compositions of Turing machines. The input tape and the output tape of the machines are seen as the encoding of ideas generated by Turing machines. This allows us, among other things, to define and measure the complexity of ideas and knowledge in the simple terms of algorithmic and computational complexity. Moreover the very existence of the halting problem allows for the introduction of a non‐stochastic notion of uncertainty. Consequently uncertainty may be modelled not as the outcome of a predefined probability distribution, but in terms of the randomness associated with the halting problem. In this way the ‘frequency distribution of innovations’ is endogenously generated by the choices of the Turing machines. It is shown that a vast variety of alternative dynamic behaviours in knowledge evolution and hence in productivity can be generated. One can observe clusters of emerging innovations, persistent and increasing emergence of new discoveries as well as periods of explosive evolutions followed by stasis periods.
Induction: From Kolmogorov and Solomonoff to De Finetti and Back to Kolmogorov
Authors: McCall John J.
Published: May 2004

This paper compares the solutions to “the induction problem” by Kolmogorov, de Finetti, and Solomonoff. Brief sketches of the intellectual history of de Finetti and Kolmogorov are also composed. Kolmogorov's contributions to information theory culminated in his notion of algorithmic complexity. The development of algorithmic complexity was inspired by information theory and randomness. Kolmogorov's best‐known contribution was the axiomatization of probability in 1933. Its influence on probability and statistics was swift, dramatic, and fundamental. However, Kolmogorov was not satisfied by his treatment of the frequency aspect of his creation. This in time gave rise to Kolmogorov complexity. De Finetti, on the other hand, had a profound vision early in his life which was encapsulated in his exchangeability theorem. This insight simultaneously resolved a fundamental philosophical conundrum—Hume's problem, and provided the bricks and mortar for de Finetti's constructive probabilistic theory. Most of his subsequent research involved extensions of his representation theorem. De Finetti was against determinism and celebrated quantum theory, while Kolmogorov was convinced that in every seemingly indeterministic manifestation there lurked a hidden deterministic mechanism. Solomonoff introduced algorithmic complexity independently of Kolmogorov and Chaitin. Solomonoff's motivation was firmly focused on induction. His interest in induction was to a marked extent sparked by Keynes’ 1921 seminal book. This interest in induction has never faltered, remaining prominent in his most recent research. The decisive connection between de Finetti and Kolmogorov was their lifelong interest in the frequency aspect of induction. Kolmogorov's solution to the problem was algorithmic complexity. De Finetti's solution to his frequency problem occurred early in his career with the discovery of the representation theorem. In this paper, we try to explain these solutions and mention related topics which captured the interest of these giants.
Economic Dynamics and Computation—Resurrecting the Icarus Tradition
Authors: Velupillai K. Vela
Published: May 2004

Computation over the reals, without abandoning the paradigm of the digital computer, raises difficult issues at the interface between recursion theory, numerical analysis and dynamical systems. In this paper an attempt is made to provide economic and mathematical justifications for returning to the analogue computing traditions that were once felicitously practised in economics.
An Essay in λ‐Calculus
Authors: Pasquali Corrado
Published: May 2004

This paper aims at presenting λ‐calculus and at suggesting how and why its abstractions set can be fruitfully used as a tool for representing entities populating the economic realm and how it can be conceived of as a language which is well suited to capturing some basic facts and features pertaining to complex organizational dynamics. I will present and discuss some of Walter Fontana's ideas on which this paper is largely grounded. The backbone and main idea of this essay is that λ‐calculus offers us the chance of adopting a precisely defined syntactical—as opposed to quantitative—mind‐set in representing the entities which populate a scientific theory. In particular, I shall try to illustrate the idea that syntax can be conceived of as an abstract theory of objects’ behavior when objects themselves are not represented solely in terms of their quantitative properties but as carriers of specific structure–action relationships and of construction possibilities.
Intelligent Versus Random Beavers—an Agent‐Based Approach in Facing the Busy Beaver Problem
Authors: Perrone Alessandro , Ferraris Gianluigi
Published: May 2004

Since Tibor Rado in 1962 defined the busy beaver game, several approaches have used computer technology to search for ‘best’ candidates to solve it. In this paper we follow an ‘evolutionary approach’ to solving it using agent‐based techniques. This approach includes techniques to reduce the number of inspected Turing machines and to accelerate simulation of Turing machines using agent‐based techniques; in particular we use the ‘Swarm simulation toolkit’. Our approach uses a variety of learning techniques such as genetic algorithms, classifier systems multiple genetic algorithms and random search to explore the universe of the ‘best solution’ to the game.
Tritrophic interactions and trade‐offs in herbivore fecundity on hybridising host plants
Authors: Cattell Maria V. , Stiling Peter
Published: May 2004

Abstract. 1. Interspecific plant hybridisation can have important evolutionary consequences for hybridising plants and for the organisms that they interact with on multiple trophic levels. In this study the effects of plant hybridisation on the abundance of herbivores and on the levels of herbivore parasitism were investigated.

2.Borrichia frutescens,B. arborescens, and their hybrid (B. × cubana) were censused forAsphondylia borrichiaegalls andPissonotus quadripustulatusplant hoppers in the Florida Keys. Levels of egg parasitism were determined by dissecting parental and hybrid stems and galls for herbivore and parasite eggs and larvae. Stem toughness and gall size are plant‐mediated modes of protection from parasitism and these were also measured. For gall midges, fly size was measured as an estimate of fecundity.

3. Field censuses indicated that herbivore abundances varied on hybrid hosts relative to parent plant species and that the different herbivore species exhibited different patterns of abundance.Asphondylia borrichiaegall numbers followed the additive pattern of abundance whileP. quadripustulatusnumbers most closely resembled the dominance pattern.

4. Parasitism ofP. quadripustulatuseggs was high onB. frutescensand the hybrids, and low onB. arborescens, which also had significantly tougher stems.Asphondylia borrichiaesuffered the highest levels of parasitism onB. frutescens, the host plant which produced the smallest galls. OnB. arborescens, which produced the largest galls, levels ofA. borrichiaeparasitism were lowest. Both parasitism and gall size were intermediate on the hybrid plants. Galls onB. arborescensand hybrid plants produced significantly smaller flies then those fromB. frutescenssuggesting that, when selecting hosts from among parent species and hybrids, gall flies may face a trade‐off between escape from natural enemies and maximising fecundity.
How Did It Happen?
Authors: Brennan Michael J.
Published: May 2004

This paper discusses the factors that led up to the stock price bubble of the 1990s. Foremost among these, it is argued, was the conventional view that stocks are the investment of choice for the long‐run investor regardless of their price. This conventional view was based on a misunderstanding of academic theories developed over the past half century. Additional factors were the changing nature of US pensions which placed much more responsibility on the shoulders of the individual investor, and agency problems in investment management and the production of information about firm profitability. Finally there is some evidence that required rates of return were declining during this period.

(J.E.L.: G10 and G23).
Patents and R&D as Real Options
Authors: Schwartz Eduardo S.
Published: May 2004

This article develops and implements a simulation approach to value patents and patent‐protected R&D projects based on the Real Options approach. It takes into account uncertainty in the cost‐to‐completion of the project, uncertainty in the cash flows to be generated from the project, and the possibility of catastrophic events that could put an end to the effort before it is completed. It also allows for the possibility of abandoning the project when costs turn out to be larger than expected or when estimated cash flows turn out to be smaller than anticipated. This abandonment option represents a very substantial part of the project's value when the project is marginal or/and when uncertainty is large. The model presented can be used to evaluate the effects of regulation on the cost of innovation and the amount on innovative output. The main focus of the article is the pharmaceutical industry. The framework, however, applies just as well to other research‐intensive industries such as software or hardware development.

(J.E.L.:G31, O22, O32).
Corporate Decisions, Information and Prices: Do Managers Move Prices or Do Prices Move Managers?
Authors: Giammarino Ronald , Heinkel Robert , Hollifield Burton , Li Kai
Published: May 2004

Seasoned equity offerings involve two significant events: registration followed by the decision to complete the issue or withdraw the registration. We present an empirical analysis of the interaction between seasoned equity issues, insider trading and the incorporation of information in prices around these two events. We find that the manager moves prices through corporate decisions but not personal ones. Specifically, the market reacts to the registration and the registration triggers information acquisition by the market, which is shown to influence the manager's final decision. Trading by managers during this interval does not, however, move prices.

(J.E.L.: G14, G23, G32).
Interview: Robert A G Monks
Authors: Crainer Stuart
Published: May 2004

Born into a moneyed New England family, Robert A G Monks graduated from Harvard Law School, founded corporate governance consulting firm Institutional Shareholder Services and the investment fund Lens and served in the Reagan administration. But over recent years Monks has become an unlikely activist, leading the growing clamour for greater rights for shareholders. Along the way he has managed to write best‐selling books including The New Global Investors: How Shareholders Can Unlock Sustainable Prosperity Worldwide and has just had his first novel published. Interview by Stuart Crainer.
Interview: Jeff Skoll
Authors: Dearlove Des
Published: May 2004

Jeff Skoll, co‐founder of eBay, philanthropist and the man behind the Skoll Centre for Social Entrepreneurship at Oxford University's Saïd Business School, talks about why he is so passionate about social entrepreneurship. Interview by Des Dearlove.
Investment, uncertainty and irreversibility
Authors: Khuong Ninh Le , Hermes Niels , Lanjouw Ger
Published: May 2004

This paper investigates the irreversibility of investments and the impact this has on the nature of the relationship between investment and uncertainty. The empirical analysis uses firm‐level data and is based on a survey of 210 rice‐milling firms in the Mekong River Delta in Vietnam, which was carried out during the year 2000. We show that uncertainty reduces investment of rice millers in the presence of irreversibility, as is predicted by the real options approach to investment. We do not find evidence that the negative association between uncertainty and investment is influenced by the degree of irreversibility.
How labile are the egg‐laying preferences of seed beetles?
Authors: Messina Frank J.
Published: May 2004

Abstract. 1. Previous studies have produced conflicting results with respect to the genetic lability of host preference in the seed beetleCallosobruchus maculatus.

2. In this study, replicate lines of an Asian population were kept on an ancestral host (mung bean) or switched to a novel host (cowpea). After 40+ generations, lines were assayed for host preference (in choice tests) and host acceptance (under no‐choice conditions), and were compared to African lines chronically associated with cowpea.

3. Host preference diverged in the expected direction. When presented a mixture of cowpeas and mung beans, females from the cowpea lines laid a greater fraction of their eggs on cowpea than did females from the mung bean lines. Preference for cowpea was nearly as strong in the cowpea lines as it was in the cowpea‐adapted African lines.

4. In contrast, the experimental host shift did not affect long‐term host acceptance. African females laid more eggs if given cowpeas than if given mung beans, but realised fecundities in the cowpea and mung bean lines were similar on the two hosts. Females from all lines laid more eggs if they were reared on cowpea than on mung bean, but rearing host had no effect on either relative host acceptance or host preference.

5. Comparisons with earlier studies suggest that the lability of host preference varies among beetle populations, which precludes generalisation at the species level. Because lines were maintained under no‐choice conditions, modification of host preference probably occurred via a lower acceptance threshold for the novel host, without a concomitant change in the long‐term acceptance of the ancestral host.
Percentage of canals filled in apical cross sections – an in vitro study of seven obturation techniques
Authors: Jarrett I. S. , Marx D. , Covey D. , Karmazin M. , Lavin M. , Gound T.
Published: May 2004

Aim  To compare the apical density of several obturation techniques when used in palatal roots of extracted maxillary molars.

Methodology  Seventy extracted molars were randomly divided into seven groups with 10 teeth each. The palatal root canals were instrumented to size 60 MAF, coated with Kerr's Pulp Canal Sealer, and obturated using one of seven techniques. The palatal roots were separated from the crowns, decalcified, and sectioned horizontally at 2 and 4 mm from the apex. The cross‐sections were photographed through a microscope, the photos were analysed, and the amount of area in the canal that was obturated with gutta‐percha was measured. The means for the 20 sections per group were calculated and the means were compared using mixed analysis of variance test.

Results  Simplifill used in accordance with the manufacturer's directions and Thermafil had the greatest mean obturated area, but neither were statistically better than mechanical lateral or warm vertical compaction (WVC; Schilder Technique). Simplifill as recommended and Thermafil were statistically better than cold lateral (P = 0.0210 and 0.0433, respectively), WVC (continuous wave) (P = 0.0006 and 0.0015), and the modified Simplifill group (P = 0.0010 and 0.0012). In addition, mechanical lateral and WVC (Schilder) had statistically more obturated area than WVC (continuous wave) (P = 0.0054 and 0.0073) and modified Simplifill (P = 0.0015 and 0.0016). Cold lateral and WVC (continuous wave) had significantly more obturated area than modified Simplifill (P = 0.0040 and 0.0087).

Conclusions  Simplifill as recommended, Thermafil, mechanical lateral and WVC (Schilder) obturation techniques created more complete obturation using gutta‐percha at the 2 and 4 mm levels than cold lateral, WVC (continuous wave), and Simplifill not used as directed.
VirA of Agrobacterium tumefaciens is an intradimer transphosphorylase and can actively block vir gene expression in the absence of phenolic signals
Authors: Brencic Anja , Xia Qi , Winans Stephen C.
Published: May 2004

The VirA–VirG two‐component system regulates the 30‐gene vir regulon in response to host‐released chemical signals. VirA is a homodimeric membrane‐spanning histidine protein kinase. Here, we show that mutations in two essential VirA residues, His‐474 and Gly‐657, can be complemented by the formation of mixed heterodimers, indicating that each subunit of a VirA dimer transphosphorylates the opposite subunit. VirA contains a receiver domain that inhibits kinase activity. We use the forced heterodimer system to show that the two receiver domains of a VirA dimer act independently and that each inhibits the phosphoacceptor subdomain of the opposite subunit. We also demonstrate that merodiploid strains co‐expressing constitutive VirA mutants and wild‐type VirA show levels of vir gene expression far lower than haploid strains expressing just the constitutive alleles. The fact that wild‐type VirA can actively block vir gene expression in the absence of phenolic signals suggests that it might have a phospho‐VirG phosphatase activity. The receiver domain of VirA is essential for this activity, whereas residues H474 and G657 of the kinase domain are not required. Merodiploid strains co‐expressing a constitutive VirA allele and an allele that is kinase inactive but proficient in the inhibitory activity show strongly inducible vir gene expression, indicating that the inhibitory activity is modulated by environmental signals.
The quormone degradation system of Agrobacterium tumefaciens is regulated by starvation signal and stress alarmone (p)ppGpp
Authors: Zhang Hai‐Bao , Wang Chao , Zhang Lian‐Hui
Published: May 2004

A unique signal degradation system has recently been discovered in Agrobacterium tumefaciens. Upon entering stationary phase, A. tumefaciens terminates quorum sensing‐dependent Ti‐plasmid conjugation by degradation of acyl homoserine lactone (AHL) quormone via the enzyme AttM (AHL‐lactonase). attM, together with attK and attL, constitute one transcriptional unit subjected to the control of a common promoter. AttJ, the other member of the signal degradation system, is an IclR‐like negative transcriptional factor, which tightly represses the expression of AttM at the early stage of bacterial growth. In this study, we found that this quormone degradation system is activated by either carbon or nitrogen starvation. Quormone degradation was significantly delayed when bacterial culture was supplemented with extra carbon or nitrogen source in the nutrient‐limited minimal medium before the onset of stationary phase. To identify the signalling pathway and regulatory mechanisms that mediate quormone degradation, we constructed a reporter strain A6(attKLM::lacZ) in which the promoterless lacZ was transcriptionally fused to the attKLM promoter. Transposon mutagenesis of strain A6(attKLM::lacZ) led to identification of the relA gene, which encodes the stress alarmone (p)ppGpp synthetase. Tn5 knock‐out of relA abolished the stationary phase‐dependent expression of attM. We concluded that the A. tumefaciens quormone degradation system is coupled to and regulated by the generic (p)ppGpp stress response machinery.