bluuebunny/crossref_metadata_2025 huggingface dataset:
Rigorous lower bounds for the critical infection rate in the diffusive contact process
Authors: Sudbury Aidan
Published: October 2002

The contact process is an interacting particle system which models a spatially restricted infection. In the basic contact process the infection can only spread to an uninfected neighbour, but the diffusive contact process allows an infected individual to move to an uninfected site. If the infection rate is too low, the process will die out. If the individual can move (or diffuse), the disease can spread with a lower infection rate. An idea of the relationship between these rates is obtained by obtaining rigorous lower bounds for the critical infection rate for various values of the diffusion rate. In this paper we also improve the lower bound for the critical infection rate for the basic contact process from 1.539 to 1.5517.
Estimation of critical values in interacting particle systems
Authors: Gouet Raúl , López F. Javier , Sanz Gerardo
Published: October 2002

The estimation of critical values is one of the most interesting problems in the study of interacting particle systems. The bounds obtained analytically are not usually very tight and, therefore, computer simulation has been proved to be very useful in the estimation of these values. In this paper we present a new method for the estimation of critical values in any interacting particle system with an absorbing state. The method, based on the asymptotic behaviour of the absorption time of the process, is very easy to implement and provides good estimates. It can also be applied to processes different from particle systems.
Explicit formulae for stationary distributions of stress release processes
Authors: Borovkov K. , Vere-Jones D.
Published: October 2002

Stress release processes are special Markov models attempting to describe the behaviour of stress and occurrence of earthquakes in seismic zones. The stress is built up linearly by tectonic forces and released spontaneously when earthquakes occur. Assuming that the risk is an exponential function of the stress, we derive closed form expressions for the stationary distribution of such processes, the moments of the risk, and the autocovariance function of the reciprocal risk process.
A note on uniformization for dynamic non-negative systems
Authors: van Dijk Nico M. , Sladký Karel
Published: October 2002

The classical technique of uniformization (or randomization) for bounded continuous-time Markov chains and Markov reward structures is extended to dynamic systems generated by arbitrary non-negative generators. Most notably, these include so-called input-output models in economic analysis. The results are of practical interest for both computational and theoretical purposes. Particularly, the recursive computation and the limiting behaviour of cumulative reward structures for non-negative dynamic systems is concluded as a special application. Two numerical examples are included to illustrate the conditions and the results.
Stochastic models for dependent life lengths induced by common pure jump shock environments
Authors: Li Haijun
Published: October 2002

The lifelengths of components of a system are usually dependent due to the common random production and operating environments. In this paper, we introduce a multi-variate pure jump Markov process to describe a large class of damage processes on various system components driven by common environmental shocks, and establish some dependence properties (association) for such a process and its multivariate increment process. These strong association properties describe both spatial dependence and temporal dependence of a multivariate pure jump process, and also provide a vehicle to derive some structural properties of component lifelengths of the systems operating in such an environment. Some bounds for the joint survival functions of component lifelengths are also obtained.
Multicomponent lifetime distributions in the presence of ageing
Authors: Fan Juanjuan , Ghurye S. G. , Levine Richard A.
Published: October 2002

Lifetime distributions for multicomponent systems are developed through the interplay of ageing and stress shocks to the system. The ageing process is explicitly modeled by an exponential function with rate affected by the magnitude of stresses from a compound Poisson process shock model. Applications of these life distributions and associated failure rates towards the study of multicomponent system survival are discussed. In particular, we illustrate the behavior of these survival functions in relevant subsets of the parameter space.
Oriented graphs generated by random points on a circle
Authors: Itoh Yoshiaki , Maehara Hiroshi , Tokushige Norihide
Published: October 2002

Extending the cascade model for food webs, we introduce a cyclic cascade model which is a random generation model of cyclic dominance relations. Put n species as n points Q1,Q2,…, Qn on a circle. If the counterclockwise way from Qi to Qj on the circle is shorter than the clockwise way, we say Qi dominates Qj. Consider a tournament whose dominance relations are generated from the points on a circle by this rule. We show that when we take n mutually independently distributed points on the circle, the probability of getting a regular tournament of order 2r+1 as the largest regular tournament is equal to (n/(2r+1))/2n-1. This probability distribution is for the number of existing species after a sufficiently long period, assuming a Lotka-Volterra cyclic cascade model.
Evaluating policies for generalized bandits via a notion of duality
Authors: Crosbie J. H. , Glazebrook K. D.
Published: October 2002

Nash's generalization of Gittins’ classic index result to so-called generalized bandit problems (GBPs) in which returns are dependent on the states of all arms (not only the one which is pulled) has proved important for applications. The index theory for special cases of this model in which all indices are positive is straightforward. However, this is not a natural restriction in practice. An earlier proposal for the general case did not yield satisfactory index-based suboptimality bounds for policies — a central feature of classical Gittins index theory. We develop such bounds via a notion of duality for GBPs which is of independent interest. The index which emerges naturally from this analysis is the reciprocal of the one proposed by Nash.
Weak convergence of high-speed network traffic models
Authors: Resnick Sidney , van den Berg Eric
Published: October 2002

We consider a network traffic model consisting of an infinite number of sources linked to a server. Sources initiate transmissions to the server at Poisson time points. The duration of each transmission has a heavy-tailed distribution. We show that suitable scalings of the traffic process converge to a totally skewed stable Lévy motion in Skorohod space, equipped with the Skorohod M1 topology. This allows us to prove a heavy-traffic theorem for a single-server fluid model.
A spatial model of range-dependent succession
Authors: Krone Stephen M. , Neuhauser Claudia
Published: October 2002

We consider an interacting particle system in which each site of the d-dimensional integer lattice can be in state 0, 1, or 2. Our aim is to model the spread of disease in plant populations, so think of 0 = vacant, 1 = healthy plant, 2 = infected plant. A vacant site becomes occupied by a plant at a rate which increases linearly with the number of plants within range R, up to some saturation level, F1, above which the rate is constant. Similarly, a plant becomes infected at a rate which increases linearly with the number of infected plants within range M, up to some saturation level, F2. An infected plant dies (and the site becomes vacant) at constant rate δ. We discuss coexistence results in one and two dimensions. These results depend on the relative dispersal ranges for plants and disease.
A new representation for the characteristic function of strictly geo-stable vectors
Authors: Klebanov Lev B. , Mittnik Stefan , Rachev Svetlozar T. , Volkovich Vladimir E.
Published: October 2002

A new representation for the characteristic function of the multivariate strictly geo-stable distribution is presented. The representation is appealing from a parametric viewpoint: its parameters have an intuitive probabilistic interpretation; and it is particularly useful for estimating the parameters of the geo-stable distribution.
Evaluating first-passage probabilities for spectrally one-sided Lévy processes
Authors: Rogers L. C. G.
Published: October 2002

Fast stable methods for inverting multidimensional Laplace transforms have been developed in recent years by Abate, Whitt and others. We use these methods here to compute numerically the first-passage-time distribution for a spectrally one-sided Lévy process; the basic algorithm is not easy to apply, and we have to develop a variant of it. The numerical performance is as good as the original algorithm.
Existence of phase transition of percolation on Sierpiński carpet lattices
Authors: Shinoda Masato
Published: October 2002

We study Bernoulli bond percolation on Sierpiński carpet lattices, which is a class of graphs corresponding to generalized Sierpiński carpets. In this paper we give a sufficient condition for the existence of a phase transition on the lattices. The proof is suitable for graphs which have self-similarity. We also discuss the relation between the existence of a phase transition and the isoperimetric dimension.
Bayesian inference for Markov chains
Authors: Eichelsbacher Peter , Ganesh Ayalvadi
Published: October 2002

We consider the estimation of Markov transition matrices by Bayes’ methods. We obtain large and moderate deviation principles for the sequence of Bayesian posterior distributions.
Large deviation theorems for weighted sums applied to a geographical problem
Authors: Bonin Olivier
Published: October 2002

A large deviation expansion is used to evaluate the impact of errors in a geographical database on the computation of travel times. We work in the framework of discrete random variables and improve a theorem by Book to solve this problem. Simulations are provided to illustrate the methodology.
Correlation models with long-range dependence
Authors: Ma Chunsheng
Published: October 2002

This paper is concerned with the correlation structure of a stationary discrete time-series with long memory or long-range dependence. Given a sequence of bounded variation, we obtain necessary and sufficient conditions for a function generated from the sequence to be a proper correlation function. These conditions are applied to derive various slowly decaying correlation models. To obtain correlation models with short-range dependence from an absolutely summable sequence, a simple method is introduced.
Bounds for the American perpetual put on a stock index
Authors: Paulsen V.
Published: October 2002

Let us consider n stocks with dependent price processes each following a geometric Brownian motion. We want to investigate the American perpetual put on an index of those stocks. We will provide inner and outer boundaries for its early exercise region by using a decomposition technique for optimal stopping.
Boundary crossing probability for Brownian motion
Authors: Pötzelberger Klaus , Wang Liqun
Published: October 2002

Wang and Pötzelberger (1997) derived an explicit formula for the probability that a Brownian motion crosses a one-sided piecewise linear boundary and used this formula to approximate the boundary crossing probability for general nonlinear boundaries. The present paper gives a sharper asymptotic upper bound of the approximation error for the formula, and generalizes the results to two-sided boundaries. Numerical computations are easily carried out using the Monte Carlo simulation method. A rule is proposed for choosing optimal nodes for the approximating piecewise linear boundaries, so that the corresponding approximation errors of boundary crossing probabilities converge to zero at a rate ofO(1/n2).
Regenerative processes in the infinite mean cycle case
Authors: Mitov K. V. , Yanev N. M.
Published: October 2002

A class of non-negative alternating regenerative processes is considered, where the process stays at zero random time (waiting period), then it jumps to a random positive level and hits zero after some random period (life period), depending on the evolution of the process. It is assumed that the waiting time and the lifetime belong to the domain of attraction of stable laws with parameters in the interval (½,1]. An integral representation for the distribution functions of the regenerative process is obtained, using the spent time distributions of the corresponding alternating renewal process. Given the asymptotic behaviour of the process in the regenerative cycle, different types of limiting distributions are proved, applying some new results for the corresponding renewal process and two limit theorems for the convergence in distribution.
On the convergence of evolution processes with time-varying mutations and local interaction
Authors: Chen Hsiao-Chi , Chow Yunshyoung
Published: October 2002

This paper analyzes players’ long-run behavior in an evolutionary model with time-varying mutations under both uniform and local interaction rules. It is shown that a risk-dominant Nash equilibrium in a 2 × 2 coordination game would emerge as the long-run equilibrium if and only if mutation rates do not decrease to zero too fast under both interaction methods. The convergence rates of the dynamic system under both interaction rules are also derived. We find that the dynamic system with local matching may not converge faster than that with uniform matching.
Burn-in procedures for a generalized model
Authors: Cha Ji Hwan
Published: October 2002

In this paper two burn-in procedures for a general failure model are considered. There are two types of failure in the general failure model. One is Type I failure (minor failure) which can be removed by a minimal repair or a complete repair and the other is Type II failure (catastrophic failure) which can be removed only by a complete repair. During a burn-in process, with burn-in Procedure I, the failed component is repaired completely regardless of the type of failure, whereas, with burn-in Procedure II, only minimal repair is done for the Type I failure and a complete repair is performed for the Type II failure. In field use, the component is replaced by a new burned-in component at the ‘field use age’Tor at the time of the first Type II failure, whichever occurs first. Under the model, the problems of determining optimal burn-in time and optimal replacement policy are considered. The two burn-in procedures are compared in cases when both the procedures are applicable.
Expression of viral and human dUTPase in Epstein‐Barr virus‐associated diseases
Authors: Fleischmann Johann , Kremmer Elisabeth , Greenspan John S. , Grässer Friedrich A. , Niedobitek Gerald
Published: October 2002

Deoxyuridine triphosphatase (dUTPase) catalyses the hydrolysis of dUTP to dUMP and pyrophosphate thus preventing the incorporation of uracil into replicating DNA. Previous studies of several virus models have suggested that viral dUTPases may be required for virus replication in resting cells whereas in proliferating cells cellular dUTPase may substitute for a mutant viral protein. Using monoclonal antibodies and immunohistochemistry, Epstein‐Barr virus‐associated non‐neoplastic and neoplastic diseases were studied for the expression of viral and human dUTPases. Oral hairy leukoplakia, an AIDS‐associated lesion of the tongue, is known to support EBV replication in the upper epithelial cell layers. In agreement with this, strong focal expression of EBV dUTPase was detected in the upper epithelial cell layers of oral hairy leukoplakia whereas expression of human dUTPase was confined to the basal proliferative cell compartment. Furthermore, in infectious mononucleosis tonsils, rare scattered small lymphoid cells expressed EBV dUTPase, consistent with the expression pattern of other EBV lytic cycle antigens. These findings are in agreement with the notion that EBV replicates in resting cells. Three EBV‐associated tumours, Hodgkin lymphoma, Burkitt lymphoma and nasopharyngeal carcinoma, lacked detectable expression of EBV dUTPase, in agreement with the notion that EBV infection is largely latent in these tumours. By contrast, expression of human dUTPase was observed regularly in these tumours. These results suggest that EBV dUTPase may be a suitable target for anti‐viral therapy and that inhibitors of human dUTPase should prove useful for the treatment of human tumours, including EBV‐associated cancers. J. Med. Virol. 68:568–573, 2002. © 2002 Wiley‐Liss, Inc.
Long‐term immunogenicity of an inactivated virosome hepatitis A vaccine
Authors: Bovier P.A. , Bock J. , Loutan L. , Farinelli T. , Glueck R. , Herzog C.
Published: October 2002

The aim of this study was to predict the long‐term protection induced after immunisation with inactivated, aluminium‐free virosome hepatitis A vaccine. The study population consisted of adult volunteers enrolled in four different clinical trials. Lower 95% confidence interval limits and seroconversion rate were calculated by using a linear mixed model to estimate the persistence of serum antibodies over time. To assess the robustness of the mathematical model, several sensitivity analyses were performed with more conservative protective threshold (20 mIU/ml vs. 10 mIU/ml), higher yearly decline rate, and exclusion of volunteers who had increasing titres over time. Based on 190 volunteers with at least two valid assessments of titres from year 3 onward, the median duration of protection was 55.5 years, with a lower limit of the 95% CI of 48.7 years. Duration below 25.3 years was predicted for only 5% of the subjects. Women tended to have higher titres to start with, but their rate of decline was higher, resulting in similar duration of protection overall. The use of a more conservative threshold, higher yearly decline rate, and exclusion of volunteers with increasing titres over time did notaffect these results. According to this model, 95% of the volunteers should have anti‐HAV titres above the minimum protective threshold for 20 years or more following immunisation with two doses of this aluminium‐free vaccine. J. Med. Virol. 68:489–493, 2002. © 2002 Wiley‐Liss, Inc.
Teacher beliefs and cultural models: A challenge for science teacher preparation programs
Authors: Bryan Lynn A. , Atwater Mary M.
Published: October 2002

The purpose of this paper is to present an argument for developing science teacher education programs that examine teachers' beliefs about multicultural issues and their impact on science teaching and learning. In the paper, we (a) delineate a rationale for the study of teacher beliefs about issues of culture and its impact on science teaching and learning; (b) assert three major categories of teacher beliefs to examine for designing teacher education programs that aim to meet the challenges of increasingly culturally diverse classrooms; and (c) discuss implications for science teacher education programs and research. Research has shown that knowing teachers' beliefs and designing instruction and experiences to explicitly confront those beliefs facilitate refinement of and/or transformation of beliefs and practices (Bryan & Abell, J Res Sci Teaching, 36, 121–140, 1999; Harrington & Hathaway, J Teacher Education, 46, 275–284, 1995; Hollingsworth, Am Educational Res J, 26(2), 160–189, 1989; Olmedo, J Teaching Teacher Education, 13, 245–258, 1997; Tobin & LaMaster, J Res Sci Teaching, 32, 225–242, 1995). Furthermore, prior to student teaching, preservice teachers need to be at least culturally sensitive teachers (Gillette, In Teacher Thinking in Cultural Contexts, F. A. Rios (Ed.); Albany, NY: State University of New York Press; 1996, pp. 104–128). Science educators need to continue to identify those beliefs and practices that undergird desirable and equitable science instruction. © 2002 Wiley Periodicals, Inc. Sci Ed 86:821–839, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/sce.10043
Full fixed cost recovery lot sizing with quantity discounts
Authors: Britney R.R. , Kuzdrall P.J. , Fartuch N.
Published: October 2002

Purchasers must often make lot sizing decisions when facing price schedules of price‐quantity discounts. It is important to determine the supplier's pricing philosophy when establishing a solution procedure.

One approach is to evaluate total costs at all of the appropriate break points. This offers limited information: a lot size and a set of total costs. This is especially true in the case of full fixed cost recovery pricing. In actual practice price schedules can be extremely lengthy: indeed, it may be in the supplier's best interests to offer comprehensive discount schedules. This situation complicates the purchaser's decision making process.

An efficient alternative, which solves the price‐quantity discount problem when the supplier insists on a full fixed cost recovery schedule, is presented. Computations are reduced to a few simple steps; the result is a least total cost lot size for a simple linear package price model given parameters obtained by an appropriate analysis of the supplier's price‐quantity discount schedule. A starting point is determined and the choice of the lot size is made using a simple criterion. Rapid convergence is assured, given a reasonably well‐behaved schedule.
Scheduling operating room surgical procedures with early and late completion penalty costs
Authors: Charnetski J.R.
Published: October 2002

This work explores the impact of a statistical scheduling technique on two classes of idle times in hospital operating suites. Initially, a mathematical model designed to minimize a weighted sum of the two types of idle time was constructed and optimized. However the minimum solution obtained presented large inequities in the distribution of idle time costs. An example demonstrates the disproportionately high waiting time costs found for one type of waiting cost relative to the other idle time cost. Because the two types of costs were to be absorbed by two different groups, this type of optimal solution was deemed to be unacceptable. For this reason, an “equalizing” solution approach was developed.

To provide a realistic basis for the model, over 2,000 actual surgical procedure times were used to model the operation of an operating room suite. The operation was then simulated using a two‐stage Monte Carlo method to approximate the distribution of times and procedure types. Idle time functions for early and late completion were then statistically fitted to obtain estimates of the expected idle times as a function of the amount of time scheduled by procedure type. Both types of solution, the optimizing and the equalizing, were examined.

By using the ratio of the two types of idle time costs, we were able to avoid the problem of having to attach specific numerical values to the individual waiting time costs. Both solutions provided capacity/utilization ranges for effective scheduling to either minimize or equalize the two types of costs. Suggestions for implementation using computer‐assisted scheduling methods are discussed.
A polynomial goal programming approach to a class of quality control problems
Authors: Kumar Tayi Giri
Published: October 2002

The traditional quality control approach based on statistical tools has been very useful and effective when output and input qualities can be denned in terms of a single characteristic. However, in process industries such as paper, the output quality is denned in terms of two or more distinct characteristics; hence, reducing the deviation of one output characteristic from its permissible limits could result in forcing other output and/or input characteristics to deviate from their respective limits. Compounding this phenomenon is the fact that most of these industries produce substantial amounts of pollutants whose characteristics are a function of the input and output characteristics. Thus, with increasing costs of waste treatment and stringent pollution standards, there arises a notion of a trade‐off between attaining market specified output characteristics and meeting federally regulated pollution standards.

In this article a general process quality control problem has been formulated that reflects the above trade‐off both in terms of a linear and a polynomial goal programming problem. Major advantages and differences between the two formulations are highlighted and illustrated with a practical example drawn from the paper industry.

Three separate cases each with different priorities assigned to the output, pollutant and input characteristics are developed and solved under both formulations. Based on the analysis it is observed that the different solutions that result are contingent on the assumptions concerning the priorities associated with each goal and the manner by which one chooses to incorporate tradeoffs between goals in the objective function. Additionally, it is found that the solutions obtained under polynomial goal programming formulation are more conducive for implementation in practical quality control contexts.
An evaluation of overtime policies for a repair shop
Authors: Scudder Gary D.
Published: October 2002

This article presents the first attempt to develop and examine overtime policies for a repair shop environment. Overtime is used to augment repair capacity as needed to offset short‐term demand fluctuations. If overtime provides sufficient additional repair capacity, it may be possible to reduce investment in spare parts inventory.

The use of overtime in a repair shop requires managerial attention to several issues. In this article, the following five issues are examined: The relationship between overtime policies and spares stocking levels The timing of overtime—reactive or proactive The amount of overtime to use The level in the product structure at which overtime is most beneficial The priority scheduling and labor assignment policies used

Six overtime policies are developed that explore the above issues. These are examined using a simulation model of a hypothetical repair shop. Since the focus of the article is on overtime policies, a single labor assignment policy is used in conjunction with two priority scheduling rules.

The results indicate that reactive overtime policies work well in this environment and overtime is most effective at the lowest level of the product structure, where repair times are relatively shorter. In addition, lowest level parts provide more usage flexibility to handle anticipated future failures.
Methods of cell formation in group technology: A framework for evaluation
Authors: Vakharia Asoo J.
Published: October 2002

Group technology is a manufacturing philosophy that attempts to provide some of the operational advantages of a line layout while maintaining some of the strategic advantages of the job shop layout. In designing a productive process that will adopt this manufacturing strategy, one of the primary problems encountered is the formation of component families and production cells. The production cell is a group of machines or processes of functionally dissimilar types that are placed together and dedicated to the manufacture of a specific range of component families.

Several researchers in operations management have proposed methods of forming production cells and component families. These methods differ in terms of information requirements and also in terms of the final cell design. Furthermore, the objectives for each method are quite different and it thus seems that the focus has been on the method rather than its appropriateness in a particular situation. This article reviews some of the most publicized methods of group formation and analyzes the type of cells that could be formed using these methods. Subsequently, an evaluative framework is presented where the relative advantages of each type of production cell are discussed in terms of several strategic and operational factors. This framework is of particular use as it highlights the fact that in implementing a cellular manufacturing system, most organizations will face a trade‐off of strategic and operational “costs.” Finally, the appropriateness of the cell types with respect to the degree of customer interaction is also discussed.
Reducing vendor delivery uncertainties in a JIT environment
Authors: Hill Arthur V. , Vollmann Thomas E.
Published: October 2002

Just‐in‐time (JIT) manufacturing systems have found wide acceptance in the automotive industry as well as in other industries such as electronic assembly. One of the key features of JIT systems is frequent reliable deliveries from local vendors.

This article considers two major points related to managing inbound transportation from these local vendors. The first point is that vendor delivery uncertainties can be reduced if the JIT manufacturer takes over the responsibility for inbound logistics from all JIT vendors. In other words, we are suggesting that the manufacturing firm (vendee) pick up raw materials and purchased parts from its vendors rather than having the vendors deliver. The second major point is that a simple economic analysis and a computer‐based decision support system (like that we propose in this article) could be used to help schedule the JIT pickups.

The article begins with a description of why deliveries are critical in the JIT environment and why vendee pickup from local vendors can be a better alternative than vendor delivery. When a manufacturer manages its own inbound local deliveries it benefits from more timely information on upsets, reduced transportation costs, reduced transaction costs, and most importantly, reduced uncertainty in deliveries.

We then turn to a model for how to schedule JIT pickups. This model addresses the following “JIT Vendor Pickup Problem”: For a given number of vehicles with limited capacity, find a one‐week JIT vendor pickup schedule that will minimize the total incremental carrying, travel, and pickup costs subject to the constraint that the vendee does not run out of any item from any vendor.

In the above problem definition, the demand rates for all items are assumed to be constant over the short term. This model can be imbedded in a computer‐based decision support system to facilitate the daily scheduling of the pickups from the vendors.

In the conclusion, we deal with the expected benefits to the vendee for managing its own incoming JIT pickups and then propose a model that could be used to implement this concept.
Maximizing the net present value of a project subject to materials and capital constraints
Authors: Smith‐Daniels Dwight E. , Smith‐Daniels Vicki L.
Published: October 2002

Large projects in a variety of industries must be scheduled subject to constraints on capital availability with the objective of maximizing their net present value. The effects of capital and materials costs and constraints have been discussed separately in the project management literature, but they have yet to be treated in an integrated fashion. A framework summarizing the previous research on resource constrained project scheduling is presented in this article and the limited role of monetary objectives in the previous research is illustrated. A new approach to the project scheduling problem is presented where the net present value of a project is maximized subject to capital and material constraints. The major benefit of this approach is that it allows managers to optimize the monetary objectives for a project.

A series of examples illustrates the necessity of considering materials costs and constraints in project management. The inclusion of materials management factors in developing a project schedule is shown to lead to lower total project costs. It is demonstrated that the failure to consider materials in the initial planning of a project may lead to either unprojected delays in a project, higher costs, or both.

Continued research on this problem is needed in a number of areas. Due to the computational complexity and importance of this problem in practice, it is necessary to develop heuristic approaches to derive project schedules. Future research should compare the results for the existing approaches that minimize project duration to those with monetary objective functions to determine the magnitude of the monetary difference between the former and the latter. Finally, the approach considered in this article should be extended to the multiproject environments where it is necessary to make capital allocation decisions among competing projects.
Operations strategy: A literature review
Authors: Anderson John C. , Cleveland Gary , Schroeder Roger G.
Published: October 2002

Competitive pressures on American business have created the need for improved understanding and practice of operations strategy. Over the past 20 years some 80 articles and several books have been written on the subject. These writings, while diverse in nature and placement, serve to shape what we know about operations strategy and the opportunities for improved practice and meaningful research.

This paper examines an underlying argument that exists within the literature that proper strategic positioning or aligning of operations capabilities can significantly impact competitive strength and business performance of an organization. The discussion is organized around four related premises: (1) that there exists a strategic, as opposed to a tactical, view of operations, (2) that there must be some synergistic process of integrating business and operations strategic issues, (3) that there are operations decision or policy areas which demonstrate strategic opportunities, and (4) that conceptual structures exist by which to target and focus operations strategy.

The paper concludes that the literature and emerging research support each of these premises to varying degrees. The authors believe that further understanding of these premises could be benefited by more careful and consistent definition of operations strategy concepts and terminology, by more attention being placed on the content and process of operations strategy, by more empirical study, and finally by more emphasis being placed on service operations strategy.
A note on workload‐dependent due date assignment rules
Authors: Ragatz Gary L.
Published: October 2002

For many production systems, delivery performance relative to promised job due dates is a critical evaluation criterion. Delivery performance is affected by the way in which work is dispatched on the shop floor, and also by the way the job due dates are assigned to begin with. This pape shows how information regarding congestion levels on the shop floor can be used to assign due dates to arriving jobs in such a way that the mean tardiness of jobs is decreased without increasing the average length of the promised delivery lead times.

Baker and Bertrand suggested a modification of the Total Work (TWK) rule for assigning job due dates which adjusts the job flow allowance according to the level of congestion in the shop. Their method gives longer flow allowances to jobs which arrive when the system is congested. Although their modified TWK rule results in lower mean tardiness in many settings, it also generally results in a higher proportion of jobs tardy.

This paper presents an alternative modification of the TWK rule which, in most cases, provides mean tardiness as low as or lower than Baker and Bertrand's rule and also results in a lower proportion of jobs tardy. The alternative rule suggested here still results in higher proportion of tardy jobs than the non‐workload adjusted rule in most settings, but suggestions are made for how this problem might be addressed.
Lasting improvements in manufacturing performance: In search of a new theory
Authors: Ferdows Kasra , De Meyer Arnoud
Published: October 2002

Is there a way to avoid trading off one capability for another in manufacturing? The prevailing wisdom says no. But some manufacturers seem to have been able to defy that: compared to their competitors, they have better quality, are more dependable, respond faster to changing market conditions and in spite of all that, achieve lower costs. How can this be explained?

Our aim here is to provide an explanation. We contend that the nature of the trade‐offs among manufacturing capabilities is more complex than has been assumed. Depending on the approach taken for developing each capability, the nature of the trade‐offs change. In certain cases not only can trade‐offs be avoided altogether, but in fact one capability would enhance another. They become cumulative. Moreover, when a capability is developed in this way, it is likely to be more lasting and less fragile than if it were developed at the expense of other capabilities.

We go on to suggest a model which shows how this can be done: To build cumulative and lasting manufacturing capability, management attention and resources should go first toward enhancing quality, then—while the efforts to enhance quality are further expanded—attention should be paid to improve also the dependability of the production system, then—and again while efforts on the previous two are further enhanced—production flexibility (or reaction speed) should also be improved, and finally, while all these efforts are further enlarged, direct attention can be paid to cost efficiency. We use data from 1988 European Manufacturing Futures Survey (167 respondents) to test and illustrate our model.

While we cannot “prove” our model, nevertheless, we believe there is enough evidence for a critical reexamination of traditional managerial approaches for improving manufacturing performance. For example, except for the cases when there are obvious slacks in the production system, the belief that costs can come down quickly and lastingly needs to be questioned. Lasting cost efficiency in production can be achieved only through improvements in other capabilities.
An analysis of customer satisfaction with waiting times in a two‐stage service process
Authors: Davis Mark M. , Maggard Michael J.
Published: October 2002

A purely operational approach to providing customer service measures the speed of the service in terms of how long the customer actually waits prior to being served. A more appropriate method. perhaps, is to deal directly with the issue of customer service by measuring customer satisfaction with the wait. In this paper a model is developed which integrates the marketing perspective of customer satisfaction and the operations management perspective of customer waiting time. With this model, the goal of the service manager is to provide an acceptable level of customer satisfaction in lieu of a maximum acceptable average waiting time, which is the current practice. This new approach to defining customer service raises several interesting managerial issues in the design and staffing of a two‐stage (or, for that matter, a multi‐stage) process. For example, is a customer equally satisfied waiting the same amount of time before each stage in the process? If not, what type of strategy does the service manager employ in assigning workers to each of the stages? In order to address these issues, a major portion of this paper focuses on the definition and measurement of customer satisfaction. The application of the model to a real world situation is illustrated using empirical data collected in a two‐stage fast food operation. The results indicate that the speedy acknowledgement of customer arrivals into the system, that is, the prompt taking of customer orders, is more important to the customers than is the time waiting for their orders to be processed. In other words, a customer's wait prior to entering the first stage of the system impacts on customer satisfaction much more than the wait prior to entering stage two. The conclusion from this analysis is that in a sequential, multi‐stage process, management should design and staff the system so that the shortest wait for the customer occurs prior to the first stage.
Enhancing the customer contact model
Authors: Mersha Tigineh
Published: October 2002

Most services are provided in the presence of the customer. In most service operations, the customer is not only present but also directly participates in the service delivery process. Such encounters with the service system and the customer's involvement in the service production process have important implications for operations efficiency and effectiveness. Thus, the nature and extent of contact between the customer and the service system should be carefully evaluated in designing service facilities.

One approach that has been considered a useful conceptual tool for aiding operations managers in their service design decisions is the customer contact model (CCM). This model classifies service systems into “high contact,” “low contact” and “mixed” services based on the extent of contact between the customer and the service facility. Recently, however, this model's effectiveness as a service management tool has been challenged. CCM has been criticized for failing to sufficiently distinguish between service systems that involve high interaction and customization and those that primarily provide accommodation. The model's capability to assess a service facility's potential efficiency has also been questioned.

This paper reevaluates CCM in view of the recent concerns raised about it and offers some extensions which improve the model's performance. It proposes a broadened definition of “customer contact” and differentiates between “active” and “passive” contact. Based on these distinctions, it presents a revised approach for classifying services and for assessing the potential efficiency of service facilities. The extensions provided in this paper would help overcome many of CCM's shortcomings and thus enhance its potential as a viable tool for managing service operations. Therefore, this study, while recognizing the valid criticisms leveled at CCM, asserts that the customer contact concept still provides a useful framework for understanding, designing and controlling service systems.
Active Timing Decisions of Equity Mutual Funds
Authors: Radcliffe Robert , Brook Robert , Levy Hah
Published: October 2002

In this paper we examine an aspect ofprofessional investment management which has not been adequately documented and studied; the extent to which equity mutualfund managers actively adjust their portfolio’s equity risk evosure over time. Estimates of a portfolio’s quarter-end beta are developed using the actual stock ho~~gs oft~~~ol~ at the quarter-end. Changes in these beta estimates fivm one quarter to the next are shown to arise frtm both passive and active asset allocation. Wefind that active risk adjust~nt domi~~s~ssive rebalancing and that equity risk exposunz is quite variable over time. Thus, individual investors who estimate the equity risk inherent in a portfolio bused on a single time series return beta might seriously misestimate the portfolio’s current equity risk. We also test whether active risk management is better characterized LISanticipatory offuture market events or reactive to past market events.
Differential role of PPARγ in the regulation of UCP‐1 and adipogenesis by TNF‐α in brown adipocytes
Authors: Porras Almudena , Valladares Amparo , Álvarez Alberto M. , Roncero Cesar , Benito Manuel
Published: October 2002

Extracellular regulated kinases (ERKs) mediate the inhibitory effect of tumor necrosis factor α (TNF‐α) on uncoupling protein‐1 (UCP‐1), but not on lipid accumulation. TNF‐α‐induced ERK‐dependent peroxisome proliferator activator receptor γ (PPARγ) phosphorylation could be responsible for UCP‐1 downregulation. Thus, the negative effect of TNF‐α on UCP‐1 mRNA expression at 4–5 h, under basal conditions or in cells treated with the PPARγ agonist, rosiglitazone, was reversed by the MEK1 inhibitor PD98059. In contrast, fatty acid synthase and malic enzyme mRNA downregulation was not prevented. Moreover, rosiglitazone has no positive effect on adipogenic gene expression or lipid accumulation. Therefore, there is a differential regulation of thermogenic and adipogenic differentiation by PPARγ, which might account for the differences in the TNF‐α regulation through ERKs.
A survey of Cdk5 activator p35 and p25 levels in Alzheimer's disease brains
Authors: Tseng Huang-Chun , Zhou Ying , Shen Yong , Tsai Li-Huei
Published: October 2002

P25, a calpain cleavage product of the cyclin‐dependent kinase 5 (Cdk5) activator p35, causes prolonged activation of Cdk5. Although p25 has been shown to accumulate in brains of patients with Alzheimer's disease (AD), it is not known whether p25 accumulation in AD is brain region‐specific. We analyzed the amounts of p25 and p35 in human autopsy samples from multiple brain regions including frontal cortex, inferior parietal cortex and hippocampus using immunoblotting assays. Our results show that the p25–p35 indices are higher in AD than in the control groups in all three brain regions. The most significant difference in p25–p35 indices between AD and control groups is in the frontal cortex. No significant difference in calpain activity between AD and control groups is observed, indicating that postmortem calpain activation cannot account for the elevation of p25/p35 ratios in AD brains. Our results support the notion that p25 accumulation deregulates Cdk5 activity in AD brains, and the deregulated Cdk5 activity may contribute to the pathogenesis of AD.
Murine peripherin gene sequences direct Cre recombinase expression to peripheral neurons in transgenic mice
Authors: Zhou Li , Népote Virginie , Rowley Daniel L , Levacher Béatrice , Zvara Agnes , Santha Miklos , Mi Qing-Sheng , Simonneau Michel , Donovan David M
Published: October 2002

Spatially and temporally regulated somatic mutations can be achieved by using the Cre/loxP recombination system of bacteriophage P1. To develop a cell type‐specific system of gene targeting in the peripheral nervous system, we generated the transgenic mouse lines expressing Cre recombinase under the control of the mouse peripherin gene promoter. The activity of the Cre recombinase during embryonic development was examined by mating the peripherin‐Cre transgenic mice to the knock‐in Cre‐mediated recombination reporter strain, R26R. Analysis of F1 embryos from this cross showed specific excision of loxP‐flanked sequences in the dorsal root ganglia, trigeminal ganglia, and olfactory epithelium, in a pattern very similar to the expression of the endogenous mouse peripherin gene, and the previously reported peripherin‐lacZ transgenic mice. Thus, the peripherin‐Cre mouse described here will provide a valuable tool for Cre‐loxP‐mediated conditional expression in the peripheral nervous system.
Generation of formate by the formyltransferase/hydrolase complex (Fhc) from Methylobacterium extorquens AM1
Authors: Pomper Barbara K , Saurel Olivier , Milon Alain , Vorholt Julia A
Published: October 2002

Methylobacterium extorquens AM1 possesses a formyltransferase (Ftr) complex that is essential for growth in the presence of methanol and involved in formaldehyde oxidation to CO2. One of the subunits of the complex carries the catalytic site for transfer of the formyl group from tetrahydromethanopterin to methanofuran (MFR). We now found via nuclear magnetic resonance‐based studies that the Ftr complex also catalyzes the hydrolysis of formyl‐MFR and generates formate. The enzyme was therefore renamed Ftr/hydrolase complex (Fhc). FhcA shares a sequence pattern with amidohydrolases and is assumed to be the catalytic site where the hydrolysis takes place.