bluuebunny/crossref_metadata_2025 huggingface dataset:
Short-Term Variations and Long-Term Dynamics in Commodity Prices
Authors: Schwartz Eduardo , Smith James E.
Published: April 2003

In this article, we develop a two-factor model of commodity prices that allows meanreversion in short-term prices and uncertainty in the equilibrium level to which prices revert. Although these two factors are not directly observable, they may be estimated from spot and futures prices. Intuitively, movements in prices for long-maturity futures contracts provide information about the equilibrium price level, and differences between the prices for the short- and long-term contracts provide information about short-term variations in prices. We show that, although this model does not explicitly consider changes in convenience yields over time, this short-term/long-term model is equivalent to the stochastic convenience yield model developed in Gibson and Schwartz (1990). We estimate the parameters of the model using prices for oil futures contracts and apply the model to some hypothetical oil-linked assets to demonstrate its use and some of its advantages over the Gibson-Schwartz model.
The Inverse Newsvendor Problem: Choosing an Optimal Demand Portfolio for Capacitated Resources
Authors: Carr Scott , Lovejoy William
Published: April 2003

The classical newsvendor problem is one of optimally choosing a level of capacity to respond to a known demand distribution. The inverse newsvendor problem is one of optimally choosing a demand distribution with fixed capacity. The applications of the inverse problem include industrial settings where demand management is relatively less costly than capacity adjustments. Demand distributions are chosen from an opportunity set, which reflects the set of market opportunities for the firm. We analyze the firm's profit as a function of these demand alternatives, provide solution methods and insights, and identify inefficient and dominated distributions. We provide results when the opportunity set is known or only partially known. We extend the results to cases in which there are multiple prioritized customer classes that share the firm's productive capacity. This paper was motivated by an industrial application in a firm selling a semicommodity product into three prioritized industrial sectors. We review the application of our methods to this setting.
Market Information and Firm Performance
Authors: Raju Jagmohan S. , Roy Abhik
Published: April 2003

The value of new information depends on how accurate the information is, but it may also depend on the characteristics of the firm and the nature of the industry it operates in. We develop a game-theoretic model to understand how firm and industry characteristics moderate the effect of market information on firm profits. Our results suggest that information is more valuable when product substitutability is higher, suggesting that information is of greater value in more competitive industries. Our results also suggest that although industry size does not affect the value of information, information is more valuable for larger firms. We find that, except under some conditions, more precise market information has a greater impact on profits in a Stackelberg mode of conduct than in a Bertrand-Nash mode.
Dynamic Economic Lot Size Model with Perishable Inventory
Authors: Hsu Vernon Ning
Published: April 2003

This paper considers an economic lot size (ELS) model for perishable products where an inventory stock's deterioration rate and its carrying cost in each period depend on the age of the stock. We discuss situations where the traditional ELS models are not applicable, and propose a new model with general concave production and inventory cost functions. We explore the structural properties of the optimal solutions and use them to develop a dynamic programming algorithm which solves the problem in polynomial time. We also consider special cases of the general model which are solvable with reduced computational complexities.
A Primal-Dual Variant of the IRI-IMAI Algorithm for Linear Programming
Authors: Tütüncü Reha H.
Published: April 2003

A local acceleration method for primal-dual potential-reduction algorithms is introduced. The method developed here uses modified Newton search directions to minimize the Tanabe-Todd-Ye (TTY) potential function, and can be regarded as a primal-dual variant of the Iri-Imai algorithm based on the multiplicative analogue of Karmarkar's potential function. When iterates are close to an optimal solution, the TTY potential function has negative curvature along the generated search directions. Therefore, large reductions in the potential function can be obtained, guaranteeing polynomial and quadratic convergence to nondegenerate solutions.
Separation of Partition Inequalities
Authors: Baïou Mourad , Barahona Francisco , Mahjoub Ali Ridha
Published: April 2003

Given a graph G = (V, E) with nonnegative weights x(e) for each edge e, a partition inequality is of the form x(δ(S1,…,Sp)) ≥ ap + b. Here δ(S1,…,Sp) denotes the multicut defined by a partition S1,…,Sp of V. Partition inequalities arise as valid inequalities for optimization problems related to k-connectivity. We give a polynomial algorithm for the associated separation problem. This is based on an algorithm for finding the minimum of x(δ(S1,…,Sp)) − p that reduces to minimizing a symmetric submodular function. This is handled with the recent algorithm of Queyranne. We also survey some applications of partition inequalities.
Approximation Algorithms for Disjoint Paths and Related Routing and Packing Problems
Authors: Baveja Alok , Srinivasan Aravind
Published: April 2003

Given a network and a set of connection requests on it, we consider the maximum edge-disjoint paths and related generalizations and routing problems that arise in assigning paths for these requests. We present improved approximation algorithms and/or integrality gaps for all problems considered; the central theme of this work is the underlying multicommodity flow relaxation. Applications of these techniques to approximating families of packing integer programs are also presented.
General Interior-Point Maps and Existence of Weighted Paths for Nonlinear Semidefinite Complementarity Problems
Authors: Monteiro Renato D. C. , Zanjácomo Paulo R.
Published: April 2003

Extending the previous work of Monteiro and Pang (1998), this paper studies properties of fundamental maps that can be used to describe the central path of the monotone nonlinear com-plementarity problems over the cone of symmetric positive semidefinite matrices. Instead of focusing our attention on a specific map as was done in the approach of Monteiro and Pang (1998), this paper considers a general form of a fundamental map and introduces conditions on the map that allow us to extend the main results of Monteiro and Pang (1998) to this general map. Each fundamental map leads to a family of “weighted” continuous trajectories which include the central trajectory as a special case. Hence, for complementarity problems over the cone of symmetric positive semidefinite matrices, the notion of weighted central path depends on the fundamental map used to represent the central path.
Asymptotic Analysis of Congested Communication Networks
Authors: Bonnans J. Frédéric , Haddou Mounir
Published: April 2003

This paper is devoted to the mathematical study of a routing problem in telecommunication networks, when the cost function is the average delay of communications. We establish asymptotic expansions for the value function and solutions in the vicinity of a congested nominal problem. The study is strongly related to the one of a partial inverse barrier method for linear programming.
A Supply Network Model with Base-Stock Control and Service Requirements
Authors: Ettl Markus , Feigin Gerald E. , Lin Grace Y. , Yao David D.
Published: April 2003

We develop a supply network model that takes as input the bill of materials, the (nominal) lead times, the demand and cost data, and the required customer service levels. In return, the model generates the base-stock level at each store—the stocking location for a part or an end-product, so as to minimize the overall inventory capital throughout the network and to guarantee the customer service requirements. The key ingredient of the model is a detailed, albeit approximate, analysis of the actual lead times at each store and the associated demand over such lead times, along with a characterization of the operation at each store via an inventory-queue model. The gradients are derived in explicit forms, and a conjugate gradient routine is used to search for the optimal solution. Several numerical examples are presented to validate the model and to illustrate its various features.
Probabilistic Analysis of Renewal Cycles: An Application to a Non-Markovian Inventory Problem with Multiple Objectives
Authors: Parlar Mahmut
Published: April 2003

Many stochastic optimization problems are solved using the renewal reward theorem (RRT). Once a regenerative cycle is identified, the objective function is formed as the ratio of the expected cycle cost to the expected cycle time and optimized using the standard techniques. Application of the RRT requires only the first moments of the cycle-related random variables. However, if the start of a cycle corresponds to an important event, e.g., end of a period of shortages in an inventory problem, knowing only the expected time—and the cost—of the cycle may not give enough information on the functioning of the stochastic system. For example, it may be useful to know the probability that the cycle cost, or more importantly, the average cost per unit time will exceed predetermined levels. In this paper we provide a complete description of the cycle-related random variables for a stochastic inventory problem with supply interruptions. We assume a general phase-type distribution for the supplier's availability (ON) periods and an exponential distribution for the OFF periods. The first passage time of an embedded Markov chain of the ON/OFF process is used to develop the expressions for the exact distribution and the moments of the cycle time and cycle cost random variables. We then describe a method for computing the probability that the average cost per unit time will exceed a predetermined level. This method is used to construct an “efficient frontier” for the two criteria of (i) average cost and (ii) the probability of exceeding it. The efficient frontier is used to find a solution to the multiple-criteria optimization problem.
A Staggered Ordering Policy for One-Warehouse, Multiretailer Systems
Authors: Chen Fangruo , Samroengraja Rungson
Published: April 2003

We consider a one-warehouse, N-identical-retailer model. Random demands occur at the retailers with complete backlogging. The retailers replenish their inventories from the warehouse, which in turn orders from an outside supplier with unlimited stock. Each retailer places an order every N periods according to a base-stock policy, and the reorder intervals of the retailers are staggered so that only one retailer places an order in each period. The warehouse orders according to an (s, S) policy based on its own inventory position. We consider two allocation policies, past priority allocation (PPA) and current priority allocation (CPA), which specify how the retailer orders are filled at the warehouse. For the PPA model, we provide an exact procedure for computing the long-run average total cost. Based on the exact procedure, we develop an approximate model that can be used to determine near-optimal control parameters for both the PPA and the CPA model. We conduct a computational study to test the effectiveness of the approximate model and to compare the performance of the two allocation policies.
Dynamic Allocation of Kidneys to Candidates on the Transplant Waiting List
Authors: Zenios Stefanos A. , Chertow Glenn M. , Wein Lawrence M.
Published: April 2003

The crux of the kidney allocation problem is the trade-off between clinical efficiency and equity. We consider a dynamic resource allocation problem with the tri-criteria objective of maximizing the quality-adjusted life expectancy of transplant candidates (clinical efficiency) and minimizing two measures of inequity: a linear function of the likelihood of transplantation of the various types of patients, and a quadratic function that quantifies the differences in mean waiting times across patient types. The dynamic status of patients is modeled by a set of linear differential equations, and an approximate analysis of the optimal control problem yields a dynamic index policy. We construct a large-scale simulation model using data from over 30,000 transplants, and the simulation results demonstrate that, relative to the organ allocation policy currently employed in the United States, the dynamic index policy increases the quality-adjusted life expectancy and reduces the mean waiting time until transplantation for all six demographic groups (two sexes, races, and age groups) under consideration.
Coordination of Production/Distribution Networks with Unbalanced Leadtimes
Authors: Bramel Julien , Goyal Shobhna , Zipkin Paul
Published: April 2003

We investigate multiproduct, multilocation production/distribution networks with deterministic, stationary demands. Most research on such systems assumes zero leadtimes. Methods using fixed reorder intervals that are power-of-two multiples of a base planning period have proved to be very successful for such systems. The same methods apply to networks with positive leadtimes, provided the leadtimes are balanced in a specific sense. We explore networks with general, unbalanced leadtimes. A key result is a lower bound on the cost of any feasible policy. Other results concern policy heuristics and their performance. For a large class of networks, we construct a policy whose cost is within 45% of the lower bound. For general networks, the performance guarantee is 1:02√(1+η), where η is a number dependent on the network topology only. In general, the best performance bound is obtained by systematically reducing the order intervals derived from the corresponding zero-leadtime system.
Periodic Scheduling with Service Constraints
Authors: Anily Shoshana , Bramel Julien
Published: April 2003

We consider the problem of servicing a number of objects in a discrete time environment. In each period, we may select an object that will receive a service in the period. Each time an object is serviced, we incur a servicing cost dependent on the time since the object's last service. Problems of this type appear in many contexts, e.g., multiproduct lot-sizing, machine maintenance, and several problems in telecommunications. We assume that at most one object can be serviced in a given period. For the general problem with m objects, which is known to be 𝒩𝒫-Hard, we describe properties of an optimal policy, and for the specific case of m = 2 objects, we determine an optimal policy.
Exact Analysis of Continuous Review (R,Q) Policies in Two-Echelon Inventory Systems with Compound Poisson Demand
Authors: Axsäter Sven
Published: April 2003

We consider a two-level inventory system with one central warehouse and N retailers. All installations apply different continuous review installation stock (R,Q) policies. The retailers face independent compound Poisson demand processes. Transportation times are constant. We present a method for exact evaluation of control policies that provides the complete probability distributions of the retailer inventory levels.
Optimal Admission Control and Sequencing in a Make-to-Stock/Make-to-Order Production System
Authors: Carr Scott , Duenyas Izak
Published: April 2003

In this paper, we address the problem of admission control and sequencing in a production system that produces two classes of products. The first class of products is made-to-stock, and the firm is contractually obliged to meet demand for this class of products. The second class of products is made-to-order, and the firm has the option to accept (admit) or reject a particular order. The problem is motivated by suppliers in many industries who sign contracts with large manufacturers to supply them with a given product and also can take on additional orders from other sources on a make-to-order basis.

We model the joint admission control/sequencing decision in the context of a simple two-class M/M/1 queue to gain insight into the following problems: 1. How should a firm decide (a) when to accept or reject an additional order, and (b) which type of product to produce next? 2. How should a firm decide what annual quantity of orders to commit to when signing a contract to produce the make-to-stock products?
The Stability of Two-Station Multitype Fluid Networks
Authors: Dai J. G. , Vande Vate J. H.
Published: April 2003

This paper studies the fluid models of two-station multiclass queueing networks with deterministic routing. A fluid model is globally stable if the fluid network eventually empties under each nonidling dispatch policy. We explicitly characterize the global stability region in terms of the arrival and service rates. We show that the global stability region is defined by the nominal workload conditions and the “virtual workload conditions,” and we introduce two intuitively appealing phenomena—virtual stations and push starts—that explain the virtual workload conditions. When any of the workload conditions is violated, we construct a fluid solution that cycles to infinity, showing that the fluid network is unstable. When all the workload conditions are satisfied, we solve a network flow problem to find the coefficients of a piecewise linear Lyapunov function. The Lyapunov function decreases to zero, proving that the fluid level eventually reaches zero under any nonidling dispatch policy. Under certain assumptions on the inter arrival and service time distributions, a queueing network is stable or positive Harris recurrent if the corresponding fluid network is stable. Thus, the workload conditions are sufficient to ensure the global stability of two-station multiclass queueing networks with deterministic routing.
Free-Flight and en Route Air Safety: A First-Order Analysis
Authors: Barnett Arnold
Published: April 2003

Under present arrangements, U.S. commercial planes do not travel “as the crow flies” from origin to destination; rather, they are generally restricted to paths within a grid. New technologies, however, raise the possibility of moving to a “free-flight” regime under which planes could fly directly from point to point. Striving for general insight rather than definitive conclusions, we use geometrical probability to assess how free-flight could affect the safety and efficiency of en route air traffic operations. We work with two air traffic control sectors: one hypothetical and the other based on actual traffic patterns over Albany, New York. Though tentative, the results suggest that—so long as certain operational constraints are retained—the changed geometry of flight paths after a transition to free-flight might tend in itself to diminish mid-air collision risk. Much depends, however, on whether the human/technological capabilities of future air traffic control can match the extraordinary effectiveness of the existing system.
Solving the Two-Connected Network with Bounded Meshes Problem
Authors: Fortz Bernard , Labbé Martine , Maffioli Francesco
Published: April 2003

We study the problem of designing at minimum cost a two-connected network such that the shortest cycle to which each edge belongs (a “mesh”) does not exceed a given length K. This problem arises in the design of fiber-optic-based backbone telecommunication networks. A Branch-and-Cut approach to this problem is presented for which we introduce several families of valid inequalities and discuss the corresponding separation algorithms. Because the size of the problems solvable to optimality by this approach is too small, we also develop some heuristics. The computational performances of these exact and approximate methods are then thoroughly assessed both on randomly generated instances as well as instances suggested by real applications.
A Production/Inventory System Subject to Failure with Limited Repair Capacity
Authors: Iravani Seyed M.R. , Duenyas Izak , Olsen Tava Lennon
Published: April 2003

We consider a production/inventory system consisting of M machines and K (K≤M) repair crews in which machines are subject to time dependent failures. The repair operations on each machine require one repair crew during the whole operation. In this production/inventory system, each machine is assigned to produce a different item according to a make-to-stock routine. Inventories of each item service a Poisson demand process, and the unsatisfied demands are lost. The objective is to minimize the sum of the average holding and lost-sales penalty costs.

We formulate the joint problem of (1) allocating the limited number of repairmen to failed machines and (2) deciding how much finished goods inventory to keep as a Markov decision process. We show that the optimal policy has a very complicated structure. We introduce two models to compute optimal base-stock policies in systems with identical machines, where first break first repair (FBFR) or preemptive priority (PPRI) repair policies are used. Then we present two heuristics to perform the same optimization analysis in systems with different machines. Finally, we compare the combination of the optimal base-stock policy (as the production policy) and the FBFR and PPRI policies (as the repair policies) to the optimal dynamic policy, and through numerical examples we show that this integration creates a solution that is close to the optimal dynamic policy. The results indicate that simple policies for determining finished goods inventory levels and repair crew assignment to failed machines can work well as long as the two problems are addressed in a coordinated manner.
Top Management-Team Diversity and Firm Performance: Examining the Role of Cognitions
Authors: Kilduff Martin , Angelmar Reinhard , Mehra Ajay
Published: April 2003

Demography research rarely examines the black box within which the cognitive diversity of the top management team is assumed to affect firm performance. Using data from 35 simulated firms run by a total of 159 managers attending executive education programs, the current research tested several hypotheses concerned with (a) the relationship between demographic and cognitive team diversity and (b) the reciprocal effects of diversity and firm performance. Results showed that members of high-performing teams tended to preserve multiple interpretations early in the team's life cycle, but that they moved toward greater clarity near the end of the life cycle. These high-performing teams, therefore, exhibited both early interpretative ambiguity and late heedful interrelating. Cognitive diversity in teams affected and was affected by changes in firm performance. Surprisingly, there was no evidence of any effect of demographic diversity on measures of cognitive diversity.
Internal Capital Markets: Benefits, Costs, and Organizational Arrangements
Authors: Liebeskind Julia Porter
Published: April 2003

Diversification not only internalizes transactions of goods and services, but it also internalizes transactions of capital. Hence, the value of diversification will depend, inter alia, on whether internal capital markets are relatively efficient or inefficient. This essay reviews and discusses the possible benefits and costs of internal capital markets by conducting a careful comparative institutional analysis. The essay concludes that internal capital markets can add value to lines of business only under a limited number of circumstances. Some recent developments in the organization of internal capital markets in diversified firms can be understood as attempts to increase their efficiency.
Making Connections: Complementary Influences on Communication Media Choices, Attitudes, and Use
Authors: Treviño Linda Klebe , Webster Jane , Stein Eric W.
Published: April 2003

Theorizing about communication media attitudes and behaviors has drawn upon multiple theories (e.g., media richness, social influence). But these theories have often been pitted against each other rather than considered as complementary in more comprehensive studies. Furthermore, previous research has tended to focus more on newer communication media such as electronic mail rather than more traditional media. Finally, communication media research has studied attitudes toward media, use of media, and only occasionally media choice. Yet, all three dependent variables are important.

This comprehensive survey hypothesized and tested multiple influences (based on multiple theories) in a study of media attitudes and behaviors. The media included electronic mail, fax, letters, and face-to-face meetings. The outcomes included media choice (an individual's decision to use a medium in a particular communication incident), media use (an individual's general pattern of use over time), and media attitudes (an individual's general subjective evaluation of media).

Results suggested that a number of factors differentiated among media choices, including medium symbolism, message equivocality, distance between message partners, perceived media richness, number of message recipients, and perceived message recipients' attitudes. General attitudes toward the different media were influenced most consistently by perceived medium richness. New media attitudes were also influenced by person/technology interaction factors. General medium use was influenced by different factors for the different media.

The results generally supported a comprehensive theoretical approach to understanding media attitudes and behaviors. All of the theories have some merit in explaining media attitudes and behaviors. But different factors, derived from different theories, were more important in accounting for each of the dependent variables'media choices, attitudes, and use. We hope that this investigation will help research in this area move toward the development of more integrative theoretical models.
A Grounded Model of Organizational Schema Change During Empowerment
Authors: Labianca Giuseppe , Gray Barbara , Brass Daniel J.
Published: April 2003

We analyzed employee resistance to an organizational change project in which employees were empowered to participate in the design of a new organizational structure. What emerged from our analysis was the importance of cognitive barriers to empowerment. Employees' resistance appeared to be motivated less by intentional self-interest than by the constraints of well-established, ingrained schemas. Resistance was also fueled by skepticism among the employees about management's commitment to the new decision-making schema, especially because employees judged managerial actions to be inconsistent with their new espoused framework. A grounded model of schema change is developed for changes in organizational decision-making schemas during empowerment efforts. Theoretical implications and suggestions for improving organizational change efforts are proposed.
Resource Partitioning, the Founding of Specialist Firms, and Innovation: The American Feature Film Industry, 1912–1929
Authors: Mezias John M. , Mezias Stephen J.
Published: April 2003

Past research has established that large bureaucratic firms are less innovative than other firms. This reduced innovativeness is likely to be exacerbated when large firms engage in market control. In cultural industries, the effects can be especially pernicious, resulting in the failure to provide audiences with artistic quality or product diversity. We investigate the population dynamics of one cultural industry: the early American feature film industry. Specifically, we examine the hypothesis that concentration among large generalist firms will be associated with higher rates of foundings of specialist producers and specialist distributors. We also investigate the question of whether these specialists are more innovative. Specifically, we examine the hypothesis that specialists were more active than were generalists in the creation of new film genres in the early years of the American film industry. We find that increased concentration among generalists had a positive effect on foundings of specialist producers and specialist distributors, and that the specialists were more active in the creation of new film genres. Implications of these findings for future research, both on cultural industries and on the population dynamics of the founding of specialist firms, are discussed.
Cultural Industries Revisited
Authors: Hirsch Paul M.
Published: April 2003

In my early “Processing Fads and Fashions: An Organization-Set Analysis of Cultural Industry Systems” (1972), the middle “throughput” phase, or most organizational aspect of cultural industries, was emphasized. In this depoliticized exploration of what Adorno (1991) had earlier characterized as the industrialization of high culture, and Powdermaker (1950) as Hollywood's “dream factory,” I emphasized the key roles of gatekeeper and distributor organizations as critical in connecting the artist/creators to audience/consumers of mass, or “popular” culture (as it had more acceptingly come to be called). Altogether, this network of organizations—from creators (artists, musicians, actors, writers) and brokers (agents), through the cultural product's producers (publishers, studios), distributors (wholesalers, theaters), and media outlets—collectively constitute cultural industries. This article on industries producing “cultural products”—defined as “ ‘nonmaterial’ goods directed at a public of consumers, for whom they generally serve an esthetic or expressive, rather than a clearly utilitarian function” (Hirsch 1972 p. 641)—appeared at the same time that organizational sociology's focus on what became known as the “production of culture” took off, and continued to flourish into the 1990s (Peterson 1994, Crane 1992).

How has the study of cultural industries changed over the last generation? A simple answer is that the subject—the key role of distribution and the importance of organizational middlemen in the making and sale of popular culture—remains analytically the same. From actors, musicians, and writers; through studios, labels and publishers, to videocassettes, movie theaters, record stores, and booksellers (in stores or via the Internet)—cultural products flow. How this sequence is organized and traversed remains a fascinating forest of power plays and techniques, employed by role-occupants in the same positions as have existed since the advent of mass media. While this substantive field has changed little analytically, what we also see is a wondrous expansion in the disciplinary approaches being taken to examine the multitude of topics available for examination under the broad rubric and framing of the term, “cultural industries.” Because I was a graduate student at the time (my roommate dared me to submit the “Processing…” paper to the American Journal of Sociology), it is a great pleasure to find the concept has retained its value for other researchers since that time.

In this article, I will (1) reexamine and discuss the original framing of the term cultural industries; (2) briefly review some of the more recent complementary perspectives which expand the possible arenas for studying this topic; and (3) append a short note on how the more recent inclusion of nonprofit cultural products(e.g., symphonies, museums) in this framework poses interesting analytical questions and opportunities.
Occupational exposure of non‐smoking restaurant personnel to environmental tobacco smoke in Finland
Authors: Johnsson Tom , Tuomi Tapani , Hyvärinen Markku , Svinhufvud Juha , Rothberg Mari , Reijula Kari
Published: April 2003

Background

Environmental tobacco smoke (ETS) exposure levels in different restaurant types in Finland were assessed before the National Tobacco Act restricting smoking in restaurants was activated.

Methods

Exposure to ETS was determined by measuring nicotine in the breathing zone of non‐smoking restaurant workers and by quantification of the nicotine metabolites cotinine and 3‐hydroxycotinine in the urine of these workers during one whole work week. Altogether 23 workers from 15 restaurants were included in the study.

Results

The geometric mean (GM) breathing‐zone nicotine level was 3.9 μg/m3 (3.7 μg/m3 in pubs, 1.4 μg/m3 in dining restaurants, and 10.2 μg/m3 in nightclubs). The GM cotinine and trans‐3′‐hydroxycotinine level in urine were 3.3 ng/mg(creatinine) and 15.3 ng/mg(creatinine), respectively. The exposure to ETS of restaurant workers in dining restaurants was clearly lower than that of workers in pubs and nightclubs as indicated by all ETS‐markers used in the present study. During the work week, the cotinine and 3′‐hydroxycotinine levels in urine of the study subjects increased. The correlation between breathing zone nicotine and urine cotinine and hydroxycotinine was 0.66 for both compounds. Post‐shift cotinine and hydroxycotinine levels were not significantly higher than the pre‐shift levels.

Conclusions

If 9 ng cotinine/mg(creatinine) is considered as the level above which heavy exposure has occurred, then this level was exceeded by 14 (∼60%) subjects at least once during the work week. Nicotine metabolite concentrations in the urine increased during the work week in 80% of the subjects, and the increase was especially noticeable for subjects working in both pubs and nightclubs. The study indicates that measures to restrict ETS exposure in restaurants are needed. Am. J. Ind. Med. 43:523–531, 2003. © 2003 Wiley‐Liss, Inc.
Fine structure of acetal resins and its effect on mechanical properties
Authors: Hammer C. F. , Koch T. A. , Whitney J. F.
Published: April 2003

Stable, high molecular‐weight polyoxymethylene resins show the room temperature x‐ray crystalline patterns expected from early work on unstable or low molecular weight polyoxymethylene resins. High‐temperature studies show the specific features of this resin to be: (1) disappearance of crystalline peaks at 180°C., and (2) a super‐cooling of 15°C. (i.e., nucleation periods much greater than 15 minutes for temperatures above 165°C.). Studies utilizing optical birefringence show similar melting and freezing behavior. Birefringence studies show effect of quench temperature and melt time and temperature on the average spherulite size and appearance. Under suitable conditions, very large (1 mm. diameter) spherulites can be grown. The effect of variations in the fine structure (spherulite size, crystallite size, and degree of crystallinity) on mechanical properties of thin sections shows that: (1) an increase in crystallinity (by specific volume) gives higher moduli, higher yield strengths, and lower values of elongation to break; (2) smaller spherulites increase the ductility, or ability to retain ductility as the rate of strain of the test is increased; (3) changes in crystallite size over a twofold range have lesser effects on these properties.
γ‐irradiation of styrene copolymers
Authors: Burlant W. , Green D. , Taylor C.
Published: April 2003

Copolymers of styrene‐methyl methacrylate were irradiated in vacuo with γ‐rays; viscosity changes and gas yields (moles gas per mole methyl methacrylate in copolymer) for H2, CO, CO2, CH4, HCOOCH3, and CH3OH were examined at doses of 1.0 Mrep to 10.0 Mrep. It was found that styrene molecules protect the copolymer from degrading while decreasing the gas yields up to a styrene concentration of about 0.5 mole fraction; above this concentration, these radiation effects are independent of composition. When styrene–methyl acrylate copolymers were irradiated, styrene offered protection aganist gelation but simultaneously increased the gas yields (gases liberated were identical with those from the first system).
Molecular weight distribution and polymerization kinetics in some new catalytic processes
Authors: Mussa C. I. V.
Published: April 2003

Some features of the molecular weight distributions found by experiment for low pressure polyethylenes are examined; an analytical interpretation of them is suggested which is in agreement with the polymerization mechanism resulting from kinetic investigations of Natta and co‐workers. Such interpretation is based on the consideration of the distribution of the individual times of growth (or of the “lifetimes”) of the single macromolecules. It is assumed that (a) these lifetimes tend to be distributed according to the Gauss formula, such as a series of events tending to be distributed at random about a mean; and (b) the growth of any single macromolecule proceeds at a rate which can be considered as the rate of a chain reaction. Possible deviations from such simplified scheme are taken into account. A distribution formula of a generalized Lansing‐Kraemer type is deduced, giving an explanation of all the observed features of the molecular weight distribution.
The emulsion polymerization of methyl methacrylate
Authors: Zimmt W. S.
Published: April 2003

The kinetics of the emulsion polymerization of methyl methacrylate have been examined in the light of recent advances in theory. It has been found that, if allowance is made for the decrease in the termination rate, the kinetics of the reaction can be predicted up to the point where all monomer is absorbed by growing monomer‐polymer particles. In order to do this it must be assumed that the efficiency of initiation is low and is a function of the size and number of growing particles in the latex. A possible explanation for these observations is discussed.
Measurement of x‐ray diffraction of biaxially oriented specimens of isotactic polypropylene
Authors: Sobue Hiroshi , Tabata Yoneho
Published: April 2003

A highly biaxially oriented isotactic polypropylene was obtained by stretching and rolling repeatedly. In such treatment, it was confirmed by x‐ray examination that the 010 spacing was oriented parallel to the plane of rolling.
Diffusion‐controlled mechanical properties of polyvinyl alcohol and polyvinyl formals
Authors: Yamamura Hitoshi , Kuramoto Naoya
Published: April 2003

The elongation of polyvinyl alcohol and of formalized polyvinyl alcohol films under constant load for a wide range of conditions of temperature and humidity seems to be affected predominantly by the diffusion of water molecules into these polymeric films, as these films have many water‐sensitive bonds. In order to obtain a perspective of the diffusion mechanism of water molecules into these polymer films, the theoretical analysis of creep curves is here worked out. Since the diffusion is a time‐dependent, non‐Fickian process, the time dependence of the diffusion coefficient is considered into our theoretical treatment. It is also assumed that the elongation is caused only by the breaking of hydrogen bonds due to the absorption of water molecules in amorphous regions of the polymer film.

To evaluate theoretical equations for the creep curves in accordance with a simple Voigt model, the parameter α for the rate of diffusion is conveniently substituted for by K, the parameter for the rate of elongation. Experiments were performed at temperatures from 20 to 50°C. at 60% R. H., and also at different relative humidities ranging from 40 to 80% at a constant temperature of 30°C. A series of creep curves for PVA and PVF, the latter having a degree of formal substitution ranging from 6% to 42.5% were obtained.

In analyzing the observed creep curves by the present theoretical treatment, we can easily compute the values of K through application of the condition for the characteristic inflection point of each curve, i.e., d2γ/dt2 = 0. By use of the values of K thus obtained and by application of the theory of absolute reaction rates, the activation energy and entropy for the diffusion process of water molecules are duly determined. The values thus obtained are also compared with those calculated by Hauser and McLaren. The activation energy and entropy are highest and lowest, respectively for PVF (6%); this is made adequately explicable by the fact that the proportion of amorphous polymer in these films is found to be maximum when the degree of formalization is between 10 and 20%.
Thermal‐oxidative degradation of poly(ethyl acrylate)
Authors: Steele Richard , Jacobs Harvey
Published: April 2003

The thermal‐oxidative degradation of films of poly(ethyl acrylate) about 35 μ thick were studied in the temperature range of 80 to 120°C. The degradation was followed by determining intrinsic viscosity changes, absorption of oxygen, and production of titratable acidity in the polymer. From viscosity results an apparent activation energy of 28.6 kcal. was calculated. Only very slight degradation occurred when the polymer was heated in a vacuum. In air, the reaction is inhibited by the presence of hydroquinone, while the addition of benzoyl peroxide caused a rapid degradation even in a vacuum. The rate of oxygen absorption was found to be similar to that typical of autocatalytic oxidations. Oxygen diffusion did not appear to be the rate‐determining factor in the degradation of films 10 to 70 μ thick. The weight loss during degradation was very small, but infrared and mass spectra indicated the presence of carbon dioxide, ethanol, formic acid, and water among the volatile products. A degradation mechanism based on hydroperoxide formation and decomposition is suggested.
Physical characteristics of osmotic membranes of organic polymers
Authors: Reid Charles E. , Kuppers James R.
Published: April 2003

The mechanism of water transport across cellulosic membranes under high pressure differentials was studied in an attempt to explain the semipermeability of these films when used as osmotic membranes for ionic solutions. Diffusion coefficients and activation entropy values for the diffusion of water and other fluids through various polymer films were determined, and compressive deformation of cellulose acetate and cellophane films was measured. Activation entropy values for the diffusion of water across both cellulose acetate and cellophane films illustrated that water molecules are constrained to states of high order as they are transported across the membrane under high pressure differentials. Activation entropy values for the diffusion of methanol through cellulose acetate film failed to support the proposition that chains of this polymer may actually be crosslinked by hydrogen‐bonded water. It appeared, rather, that but one hydrogen of the water molecule was involved in hydrogen bonding to the polymer. A significant reorientation of the polymer in the pressure interval in which cellulose acetate film is induced into a semipermeable condition was indicated by pressure‐dependent fluctuations of diffusion coefficients and activation entropy values in this interval. The greater elastic modulus of wet cellulose acetate film under a compressive force applied normal to the film surface demonstrated a strong interaction between water and polymer chains in the cellulose acetate‐water structure. The capacity of the film for bound water was also increased by repeated compression while wet. Wet cellophane films deformed plastically under compression. Crosslinking polymer chains of cellophane film with cupric ions prevented plastic flow and, at the same time, increased the semipermeability of the film for sodium chloride solutions.
Molecular weight distributions from gel‐sol ratios
Authors: Bueche F. , Harding S. W.
Published: April 2003

A method for determining molecular weight distributions is presented, based upon the partition of polymer molecules between gel and sol in a partly crosslinked system. It is assumed that the polymer sample consists of a series of molecular weight species, and analysis of previously developed theories covering this situation yields an expression which equates the weight fraction of gel to a summation involving the weight fraction of the material in each species and the number of crosslinked units in the sample. The data are presented in the form of a graph showing how the weight fraction of gel varies as a function of the number of crosslinked units in the sample. Data for the graph are obtained from swelling measurements made in the usual manner. The procedure is outlined for using the information from the graph to make a step‐by‐step evaluation of the fractional weight of each molecular weight species in the sample for as many fractions as may be arbitrarily chosen. Both a first approximation method and a more refined second approximation method are outlined. The procedure has been applied to samples of natural rubber, synthetic rubbers, and to two known molecular weight distributions.
A gel point method for the estimation of overall apparent activation energies of polymerization
Authors: Gough L. J. , Smith I. T.
Published: April 2003

The gel time, measured under isothermal conditions, may be taken as a measure of the overall rate of polymerization of a given system under certain circumstances. This enables us to estimate the Arrhenius activation energy from such measurements. A simple piece of apparatus is described which has been used to measure the overall activation energy of some epoxy resin polymerizations. The agreement with previously published data is reasonable.
Single‐point determination of intrinsic viscosity
Authors: Valles R. J. , Otzinger M. C. , Levi D. W.
Published: April 2003

The Schulz and Blaschke equation in the rearranged form of Hart was used for reasonably precise calculation of the intrinsic viscosity from a single measured specific viscosity for stereoregular polybutene‐1 in Decalin and for a series of alkyl methacrylate polymers in good and poor solvents. A single value of N can be used for each system provided careful measurements are made at specific viscosities somewhat below 1.
Studies on the γ‐irradiation of natural rubber latex
Authors: Minoura Yuji , Asao Mamoru
Published: April 2003

Vulcanized latex was obtained by the γ‐irradiation of natural rubber latex. The optimum cure was attained with ca. 2 × 107 r, in the case of 40% latex. Owing to the acceleration action of the water present, rubber in latex crosslinked more easily than it did in previously dried latex film, but no appreciable difference was found between the crosslinking in latices of various water contents. The protein in the latex deteriorated under γ‐irradiation, but the properties of the latex were not damaged. The maximum tensile strength of the film obtained by drying this irradiated latex was larger than that of solid rubber irradiated in air; this may correspond to the fact that the irradiation, even when carried out in air, brought about no side reactions such as oxidation, etc., of rubber in latex. The aging behavior of the irradiated film was quite superior, the tensile strength being greater after aging than before.
Radiation crosslinking of vinyl chloride–vinyl stearate copolymer
Authors: Miller A. A.
Published: April 2003

The crosslinking of internally plasticized polyvinyl chloride–stearate copolymer by irradiation with high‐energy electrons was studied. Based on gel yields and swelling as a measure of relative crosslinking, the effect of added tetra‐functional monomers, and of carbon black and silica fillers are discussed. Crosslinking by dicumyl peroxide a t 170°C. even in the presence of a stabilizer, causes concurrent decomposition (dehydrochlorination) which is avoided in the radiation‐crosslinking process. The heat stability of the copolymer is not impaired by radiation crosslinking under the proper conditions. Results of tensile measurements a t 25 and 150°C. are given for the radiation‐crosslinked copolymer with and without filler reinforcement.