bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of social rank in the angelfish, Pterophyllum scalare, on locomotor and feeding activities in a novel environment
Authors: Gómez-Laplaza L. M. , Morgan E.
Published: April 2003

To investigate differences in behaviour associated with social rank and environmental conditions, a comparison was made between swimming and feeding activities of dominant and subordinate angelfish, housed in groups of six, with those of angelfish housed singly in identical laboratory aquaria. Subordinate individuals were less active, less ready to feed and consumed less food items than dominants, but their feeding and activity levels were still greater than those displayed by isolated fish used as controls. When fish from each of the above categories were transferred to a novel, identical tank to be tested individually for a 6-day period, little change was observed in previously isolated fish. In contrast, the previous social experience had a marked influence on the behaviour of the other individuals, the effects being related to the social status. The strongest initial response to the new environment was shown by subordinate individuals, with a significant increase in swimming and a significant decrease in feeding compared to the group situation. Subordinates were significantly more active than dominants, who in turn moved more than previously isolated fish. Dominants and subordinates were now similarly reluctant to feed, and their food consumption was less than that of previously isolated fish. With time in the novel environment a significant reduction of swimming activity and a recovery of feeding measures were detected, but levels were still depressed in relation to the group condition, and lower in subordinates than in dominants, indicating the long-lasting effects of the previous social interactions. The results have clear implications for laboratory studies using groups of fish in which social hierarchies may be established prior to individuals being tested singly in a novel environment.
Drive out Fear (Unless You Can Drive It in): The Role of Agency and Job Security in Process Improvement
Authors: Repenning Nelson P.
Published: April 2003

Understanding the wide range of outcomes achieved by firms trying to implement Total Quality Management (TQM) and similar process improvement initiatives presents a challenge to management theory: A few firms reap sustained benefits from their programs, but most efforts fail and are abandoned. In this paper I study one dimension of this phenomenon: the role of impending layoffs in determining employee commitment to process improvement. Currently, the literature provides two opposing theories concerning the effect of job security on the ability of firms to implement change initiatives. The “Drive Out Fear” school argues that firms must commit to job security, while the “Drive In Fear” school emphasizes the positive role that insecurity plays in motivating change. In this study a contract theoretic model is developed to analyze the role of agency in process improvement. The main insight of the study is that there are two types of job security, internal and external, that have opposing impacts on the firm's ability to implement improvement initiatives. The distinction is useful in explaining the results of different case studies and can reconcile the two change theories.
A Supplier's Optimal Quantity Discount Policy Under Asymmetric Information
Authors: Corbett Charles J. , de Groote Xavier
Published: April 2003

In the supply-chain literature, an increasing body of work studies how suppliers can use incentive schemes such as quantity discounts to influence buyers' ordering behaviour, thus reducing the supplier's (and the total supply chain's) costs. Various functional forms for such incentive schemes have been proposed, but a critical assumption always made is that the supplier has full information about the buyer's cost structure. We derive the optimal quantity discount policy under asymmetric information and compare it to the situation where the supplier has full information.
Effects of Process Maturity on Quality, Cycle Time, and Effort in Software Product Development
Authors: Harter Donald E. , Krishnan Mayuram S. , Slaughter Sandra A.
Published: April 2003

The information technology (IT) industry is characterized by rapid innovation and intense competition. To survive, IT firms must develop high quality software products on time and at low cost. A key issue is whether high levels of quality can be achieved without adversely impacting cycle time and effort. Conventional beliefs hold that processes to improve software quality can be implemented only at the expense of longer cycle times and greater development effort. However, an alternate view is that quality improvement, faster cycle time, and effort reduction can be simultaneously attained by reducing defects and rework. In this study, we empirically investigate the relationship between process maturity, quality, cycle time, and effort for the development of 30 software products by a major IT firm. We find that higher levels of process maturity as assessed by the Software Engineering Institute's Capability Maturity Model™ are associated with higher product quality, but also with increases in development effort. However, our findings indicate that the reductions in cycle time and effort due to improved quality outweigh the increases from achieving higher levels of process maturity. Thus, the net effect of process maturity is reduced cycle time and development effort.
A Combinatorial Auction with Multiple Winners for Universal Service
Authors: Kelly Frank , Steinberg Richard
Published: April 2003

We describe a discrete-time auction procedure called PAUSE (Progressive Adaptive User Selection Environment) for use in assigning COLR (Carrier of Last Resort) responsibility for universal service. The auction incorporates synergies by permitting all combinatorial bids, is transparent to the bidders, allows for multiple winners, and minimizes the possibility of bidder collusion. The procedure is computationally tractable for the auctioneer and thus very efficient to run. The inherent computational complexity of combinatorial bidding cannot be eliminated. However, in this auction the computational burden of evaluating synergies rests with the bidders claiming those synergies, while the auctioneer simply checks that a bid is valid.
Behind the Learning Curve: Linking Learning Activities to Waste Reduction
Authors: Lapré Michael A. , Mukherjee Amit Shankar , Van Wassenhove Luk N.
Published: April 2003

This exploratory research on a decade of Total Quality Management in one factory opens up the black box of the learning curve. Based on the organizational learning literature, we derive a quality learning curve that links different types of learning in quality improvement projects to the evolution of the factory's waste rate. Only 25% of the quality improvement projects—which acquired both know-why and know-how—accelerated waste reduction. The other 75% of the projects either impeded or did not affect waste reduction. In complex and dynamic production environments, locally acquired knowledge is difficult to disseminate. The combination of know-why and know-how facilitates its dissemination.
Nonparametric Estimation of the Cumulative Intensity Function for a Nonhomogeneous Poisson Process from Overlapping Realizations
Authors: Arkin Bradford L. , Leemis Lawrence M.
Published: April 2003

A nonparametric technique for estimating the cumulative intensity function of a nonhomogeneous Poisson process from one or more realizations on an interval is extended here to include realizations that overlap. This technique does not require any arbitrary parameters from the modeler, and the estimated cumulative intensity function can be used to generate a point process for simulation by inversion.
Supply Chain Inventory Management and the Value of Shared Information
Authors: Cachon Gérard P. , Fisher Marshall
Published: April 2003

In traditional supply chain inventory management, orders are the only information firms exchange, but information technology now allows firms to share demand and inventory data quickly and inexpensively. We study the value of sharing these data in a model with one supplier, N identical retailers, and stationary stochastic consumer demand. There are inventory holding costs and back-order penalty costs. We compare a traditional information policy that does not use shared information with a full information policy that does exploit shared information. In a numerical study we find that supply chain costs are 2.2% lower on average with the full information policy than with the traditional information policy, and the maximum difference is 12.1%. We also develop a simulation-based lower bound over all feasible policies. The cost difference between the traditional information policy and the lower bound is an upper bound on the value of information sharing: In the same study, that difference is 3.4% on average, and no more than 13.8%. We contrast the value of information sharing with two other benefits of information technology, faster and cheaper order processing, which lead to shorter lead times and smaller batch sizes, respectively. In our sample, cutting lead times nearly in half reduces costs by 21% on average, and cutting batches in half reduces costs by 22% on average. For the settings we study, we conclude that implementing information technology to accelerate and smooth the physical flow of goods through a supply chain is significantly more valuable than using information technology to expand the flow of information.
A Structure-Exploiting Tool in Algebraic Modeling Languages
Authors: Fragnière Emmanuel , Gondzio Jacek , Sarkissian Robert , Vial Jean-Philippe
Published: April 2003

A new concept is proposed for linking algebraic modeling languages with structure-exploiting solvers. SPI (Structure-Passing Interface) is a program that retrieves structure from an anonymous mathematical program built by an algebraic modeling language. SPI passes the special structure of the problem to an SES (Structure-Exploiting Solver). An integration of SPI and SES leads to SET (Structure-Exploiting Tool) and can be used with any algebraic modeling language. This approach relies on the idea that most exploitable block structures can be easily detected from the algebraic formulation of models. It should enable algebraic modeling languages to access the large body of algorithmic techniques which require problem structure.
Equivalent Representations of Set Functions
Authors: Grabisch Michel , Marichal Jean-Luc , Roubens Marc
Published: April 2003

This paper introduces four alternative representations of a set function: the Möbius transformation, the co-Möbius transformation, and the interactions between elements of any subset of a given set as extensions of Shapley and Banzhaf values. The links between the five equivalent representations of a set function are emphasized in this presentation.
On Dual Convergence of the Generalized Proximal Point Method with Bregman Distances
Authors: Iusem Alfredo , Monteiro Renato D.C.
Published: April 2003

The use of generalized distances (e.g., Bregman distances), instead of the Euclidean one, in the proximal point method for convex optimization, allows for elimination of the inequality constraints from the subproblems. In this paper we consider the proximal point method with Bregman distances applied to linearly constrained convex optimization problems, and study the behavior of the dual sequence obtained from the optimal multipliers of the linear constraints of each subproblem. Under rather general assumptions, which cover most Bregman distances of interest, we obtain an ergodic convergence result, namely that a sequence of weighted averages of the dual sequence converges to a specific point of the dual optimal set. As an intermediate result, we prove under the same assumptions that the dual central path generated by a large class of barriers, including the generalized Bregman distances, converges to the same point.
On a Queueing Network Model for Cellular Mobile Telecommunications Networks
Authors: Boucherie Richard J. , van Dijk Nico M.
Published: April 2003

This paper presents a queueing network description of a cellular mobile communications network. These cellular networks are characterised by the call lengths, the fresh call arrival rate, and the handover rates, as well as the capacity restrictions on the number of calls because of limited bandwidth. In the resulting queueing network the routing probabilities depend on the age of the customers. This queueing network is amenable to analysis via known methods. In particular, insensitivity results are generalised to also include capacity restrictions under age-dependent routing and to include call holding time distributions of customers moving from one queue to another.
Operations Research at Bell Laboratories Through the 1970s: Part I
Authors: Dawson Cree S. , McCallum Charles J. , Murphy R. Bradford , Wolman Eric
Published: April 2003

This historical account of operations research at Bell Laboratories was drafted in the late 1970s when the authors were part of the Operations Research Center within Bell Laboratories at AT&T; it has not previously appeared in the open literature. We have added a few references to later publications that describe particular aspects of the period covered. Discussions of technological practices and organizational arrangements expressed in the present tense represent a viewpoint of about 1980, before “divestiture” split up the Bell System. The principal topics in this issue of Operations Research are the organizational history, and teletraffic theory and engineering. Upcoming issues of Operations Research will include parts II and III of this account, comprising capacity expansion in telephone networks, operations analysis, applied statistics, and related OR activities. A comprehensive table of contents for parts I, II, and III can be found in the Online Collection of the Operations Research Home Page, at www.informs.org/pubs .
Incorporating Fuel Constraints and Electricity Spot Prices into the Stochastic Unit Commitment Problem
Authors: Takriti Samer , Krasenbrink Benedikt , Wu Lilian S.-Y.
Published: April 2003

The electric power industry is going through deregulation. As a result, the load on the generating units of a utility is becoming increasingly unpredictable. Furthermore, electric utilities may need to buy power or sell their production to a power pool that serves as a spot market for electricity. These trading activities expose utilities to volatile electricity prices. In this paper, we present a stochastic model for the unit commitment that incorporates power trading into the picture. Our model also accounts for fuel constraints and prices that may vary with electricity prices and demand. The resulting model is a mixed-integer program that is solved using Lagrangian relaxation and Bender's decomposition. Using this solution approach, we solve problems with 729 demand scenarios on a single processor to within 0.1% of the optimal solution in less than 10 minutes. Our numerical results indicate that significant savings can be achieved when the spot market is entered into the problem and when stochastic policy is adopted instead of a deterministic one.
Using Branch-and-Price-and-Cut to Solve Origin-Destination Integer Multicommodity Flow Problems
Authors: Barnhart Cynthia , Hane Christopher A. , Vance Pamela H.
Published: April 2003

We present a column-generation model and branch-and-price-and-cut algorithm for origin-destination integer multicommodity flow problems. The origin-destination integer multicommodity flow problem is a constrained version of the linear multicommodity flow problem in which flow of a commodity (defined in this case by an origin-destination pair) may use only one path from origin to destination. Branch-and-price-and-cut is a variant of branch-and-bound, with bounds provided by solving linear programs using column-and-cut generation at nodes of the branch-and-bound tree. Because our model contains one variable for each origin-destination path, for every commodity, the linear programming relaxations at nodes of the branch-and-bound tree are solved using column generation, i.e., implicit pricing of nonbasic variables to generate new columns or to prove LP optimality. We devise a new branching rule that allows columns to be generated efficiently at each node of the branch-and-bound tree. Then, we describe cuts (cover inequalities) that can be generated at each node of the branch-and-bound tree. These cuts help to strengthen the linear programming relaxation and to mitigate the effects of problem symmetry. We detail the implementation of our combined column-and-cut generation method and present computational results for a set of test problems arising from telecommunications applications. We illustrate the value of our branching rule when used to find a heuristic solution and compare branch-and-price and branch-and-price-and-cut methods to find optimal solutions for highly capacitated problems.
An Integer Optimization Approach to a Probabilistic Reserve Site Selection Problem
Authors: Haight Robert G. , Revelle Charles S. , Snyder Stephanie A.
Published: April 2003

Interest in protecting natural areas is increasing as development pressures and conflicting land uses threaten and fragment ecosystems. A variety of quantitative approaches have been developed to help managers select sites for biodiversity protection. The problem is often formulated to select the set of reserve sites that maximizes the number of species or ecological communities that are represented, subject to an upper bound on the number or area of selected sites. Most formulations assume that information about the presence or absence of species in the candidate sites is known with certainty. Because complete information typically is lacking, we developed a reserve selection formulation that incorporates probabilistic presence-absence data. The formulation was a discrete 0/1 optimization model that maximized the number of represented vegetation communities subject to a budget constraint, where a community was considered represented if its probability of occurrence in the set of selected sites exceeded a specified minimum reliability threshold. Although the formulation was nonlinear, a log transformation allowed us to represent the problem in a linear format that could be solved using exact optimization methods. The formulation was tested using a moderately sized reserve selection problem based on data from the Superior National Forest in Minnesota.
Manufacturing to Order with Random Yield and Costly Inspection
Authors: Grosfeld-Nir Abraham , Gerchak Yigal , He Qi-Ming
Published: April 2003

This study considers a situation where a contractor receives an order that it commits to satisfy in full. The fulfillment of the contract requires manufacturing and inspection. Because the number of defective units within a produced lot is not known in advance, it is possible that after examining the lot, it is learned that the number of conforming units is short of the demand. If so, further manufacturing and inspection are required. Once enough conforming units are found, the inspection terminates, and the remaining uninspected units, as well as all defectives, are scrapped.

Whereas previous “multiple production runs” studies implicitly assumed that inspection costs are negligible, we include these costs as a key part of the problem. It turns out that the optimal production lot size depends on the inspection cost. Our model is very general: We provide a framework to calculate the optimal batch and the expected number of inspections for any yield pattern, as well as for any inspection procedure. We also provide results and numerical examples concerning specific yield patterns that are common in practice.
A Relational Modeling System for Linear and Integer Programming
Authors: Atamtürk A. , Johnson E. L. , Linderoth J. T. , Savelsbergh M. W. P.
Published: April 2003

We discuss an integer linear programming modeling system based on relational algebra. In this system, all modeling related activities, such as model formulation, model instantiation, and model and instance management, are done using simple operations such as selection, projection, and predicated join.
From Security to Mobility: Generalized Investments in Human Capital and Agent Commitment
Authors: Galunic D. Charles , Anderson Erin
Published: April 2003

This paper considers the impacts of different investments in human capital (firm-specific versus generalized investments) on employee commitment to the firm. The resource-based literature has stressed that only firm-specific human capital is likely to generate organizational rents, since those assets are more likely to be inimitable, rare, and therefore a better basis for sustained competitive advantage. Generalized investments in human capital (i.e., investments in capabilities that people can transfer and deploy to other firms or settings) are to be avoided. However, observing lessons from the literature on psychological contracts and organizational commitment, we argue that generalized investments may have value for the firm through their effects on worker commitment to the firm. The gain in worker commitment is valuable to firms given the fragile state of the contemporary employment relation, in which the lack of job security is likely to breed diminished employee commitment. This is particularly a concern for employment relations consisting of externalized labor (i.e., contract work or selfemployed professionals operating as agents of the firm), in which agent commitment is vital but likely to be more scarce. In this paper we focus on the externalized workers (independent agents) of two insurance firms in addressing these issues. A sample of 237 agents shows support for the benefits of generalized investments on agent commitment, questioning conventional wisdom that such investments should be avoided. We also examine the impact of relation-specific investments and other key antecedents on agent commitment, concluding that a mixture of strategic investments in human capital should be considered, taking into account their impacts on the firm-worker psychological contract. We also examine the impact of agent commitment on agent performance in this context, finding committed agents do provide greater value to the insurer.
The Effective Design of Work Under Total Quality Management
Authors: Victor Bart , Boynton Andrew , Stephens-Jahng Theresa
Published: April 2003

In this research, we address the question: Why do many total quality management implementations fail? We develop a theoretical model in which the total quality management role for line employees results in a dual work design that requires both standardized production and continuous improvement. We propose that workers effectively integrate both types of work by switching, defined as shifting between standardized production and continuous work while on the job in response to situational cues. Alternatively, workers can respond to the challenges of a job involving both types of work by avoiding the continuous improvement work. Switching and avoidance are associated with different performance and attitudinal outcomes. We present evidence drawn from an exploratory field study which suggests that line employees who effectively integrate standardized production and continuous improvement work by switching experienced less job stress and greater job satisfaction. Moreover, plants which were more effective in total quality management performance had a greater proportion of line employees using switching.
Instabilities of Strategic Alliances: An Internal Tensions Perspective
Authors: Das T. K. , Teng Bing-Sheng
Published: April 2003

The instabilities of strategic alliances have been examined in the literature through a number of theoretical approaches. Alliance instabilities refer to major changes or dissolutions of alliances that are unplanned from the perspective of one or more partners. Although the literature identifies certain characteristics of strategic alliances that may lead to their unplanned dissolution, the extent of our understanding of this subject appears to be fragmented and incomplete. In this article we propose a comprehensive framework for adequately understanding alliance instabilities based on the notion of internal tensions. We suggest that strategic alliances are sites in which conflicting forces develop and which can be viewed as being constituted by three key pairs of competing forces—namely, cooperation versus competition, rigidity versus flexibility, and short-term versus long-term orientation. This tensions framework helps us in explaining the intrinsic vulnerability of alliances in terms of a wide range of internal contradictions and enables us to examine, in an integrated manner, the incidence, dynamics, and eventual dissipation of the inherent instabilities. We discuss the interrelationships among the different internal tensions and their impacts on different types of strategic alliances. We also examine the termination of alliances through mergers/acquisitions and dissolution. Finally, we suggest ways to empirically test the various ideas and propositions developed here and indicate directions for further research.
The Social Capital of French and American Managers
Authors: Burt Ronald S. , Hogarth Robin M. , Michaud Claude
Published: April 2003

Accumulating empirical evidence on American managers shows that social-capital effects on performance are a function of the information and control benefits of bridging structural holes—the disconnections between nonredundant contacts in a network. Is that network form of social capital unique to Americans? France seemed to us a productive site for comparative research because the image from past research is that French managers are more regulated than Americans; more regulated by bureaucratic authority and more regulated by peer pressure, with both amplified by the greater reliance in France on internal labor markets. People comfortable with knowing their place in a chain of bureaucratic control could be uncomfortable with the negotiated control exercised by network entrepreneurs, so the positive association between structural holes and performance in the United States could be negligible or even reversed for French managers.

We use network and performance data on two study populations of senior managers, one in France and one in the United States, to describe social capital similarities and differences between the populations. The network form of social capital is similar in the two populations: More successful French managers, like Americans, tend to have networks rich in structural holes. The French and American managers make similar distinctions between kinds of relationships. Relations that bridge structural holes are similarly detached from routine work activities for the French and the Americans. The interesting difference is that social capital develops differently in the two populations. The French managers operate with a less porous social boundary around their firm and associate negative emotions with bridge relations. Reinforcing Aix-en-Provence observations on the significance of adult education for Franco-German differences in organization, we find that exposure to peers in other firms via executive education is for our French managers the only factor positively associated with the social capital of bridge relationships.
Towards A Culturally Sensitive Approach To Organization Structuring: Where Organization Design Meets Organization Development
Authors: Bate Paul , Khan Raza , Pye Annie
Published: April 2003

This article describes an holistic model of intervention geared to achieving transformational change by interweaving culture and structure through the warp and weft of leadership processes. That is, it brings together organization design and organization development by advocating a culturally sensitive approach to organization structuring. Our emphasis is on process throughout and our thesis is based on empirical evidence. We undertook a lengthy action research project (which we prefer to call “action ethnography”) at a large hospital trust in England. In the process of elaborating this field study, we move from an organization which was seen to be “gridlocked” and to have “lost its steering capacity”, through one which was bringing development and design together by way of pilot projects and transitional structures, to one where collective dialogue and debate finally led to some collective and sensible sensemaking.

Exploring this relationship between culture and structure enables us to put people back into design and with them, their meanings, aspirations and assumptions. It also means that we are careful to avoid detailing specific design choices or offering organizational archetypes: this article is primarily about the process issues that surround redesign rather than organization design per se, as indeed any redesign is ultimately highly specific and context-driven. Instead, however, we articulate a four-phase change model, focusing on the delicate processes by which to reframe the culture-structure relationship, enabling an organization to move towards fundamental change.
Adding Value to Innovation: Impressionism and the Transformation of the Selection System in Visual Arts
Authors: Wijnberg Nachoem M. , Gemser Gerda
Published: April 2003

Valuation of cultural products tends to be problematic. In this paper, we provide insight into how valuation of cultural products takes place by describing the changing role and significance of different types of selection systems. Three basic types of selection systems are distinguished: market selection, peer selection, and expert selection. We show that the rise of a group of painters known as the Impressionists was facilitated by a change in the selection system of the visual arts industry from one dominated by peers into one dominated by experts. In the new selection system, innovativeness has become the most highly prized product characteristic, while a range of experts have begun to play an essential role, certifying the innovativeness of either individual artists or groups of artists.
Crossroads—Conventions: An Interpretation of Deep Structure in Organizations
Authors: Gomez Pierre-Yves , Jones Brittany C.
Published: April 2003

To describe human action as purely the product of rational calculation leaves unanswered the question of how human beings can act in the absence of any structure for calculating the likely outcome of their actions. If the answer is that they cannot, how can any such structure be stable and comprehensive enough to enable action without becoming either inert or deterministic?

In this paper, we seek to understand how free will and social context can interact to produce both structure and action. This is accomplished through the development of a framework based on the notion of convention. Organizations, in this view, are grounded in “effort conventions” of what constitutes “normal” effort at work, that structure the action of those who work within the organization, and in turn reinforce these structures. We show how humans can calculate within a context of socially constructed beliefs, and how these beliefs can evolve, provided that they remain essentially nonjustified and beyond the reach of rational calculation. It is this mix of rational calculation and nonrational beliefs that form the core of our model.

We begin by defining the nature of a convention and its properties. We then describe the evolutionary dynamics of conventions, and show that conventions exist in competition with other conventions and evolve over time. Our model of convention is then linked to other notions, advanced in the managerial literature, which point to a kind of ‘deep structure’ that lies at the heart of organizations. We conclude by outlining how this notion can shed new light on the analysis of organizations.
Hand injuries due to high‐pressure injection devices for painting in shipyards: Circumstances, management, and outcome in twelve patients
Authors: Valentino Matteo , Rapisarda Venerando , Fenga Concettina
Published: April 2003

Background

Injuries due to high‐pressure injections are frequently underestimated occupational accidents, which may have disabling outcomes.

Methods

The occupational injuries logbooks of two shipyards were examined. Twelve accidents due to the utilization of high‐pressure equipment were reported. Data were obtained by reviewing the employers' logbooks and hospital records.

Results

Contaminants were epoxy paint and stucco, paint solvent, hydraulic and industrial oil. In three cases, the palm was injured and the fingers in nine. In 91% of cases, the accident occurred in the last 2 hr of the work shift. Mishandling (n = 9) and rupture of the high‐pressure equipment (n = 3) were the causes. Mean time to medical treatment was 42.5 hr (SD 56.0). Ten workers were permanently disabled.

Conclusions

Prompt surgical intervention with debridement and decompression was done in two workers, who healed completely. The ten patients who were not treated immediately eventually experienced a high rate of disability and five of them also suffered amputation. Am. J. Ind. Med. 43:539–542, 2003. © 2003 Wiley‐Liss, Inc.
A study of diffusion in solids of arbitrary shape, with application to the drying of the wheat kernel
Authors: Becker H. A.
Published: April 2003

A general mathematical approach to the rigorous treatment of experimental data on nonstationary‐state diffusion in solids of complex shape is developed. The general solution for a uniform initial concentration, c0, and a constant surface concentration, cs, at times greater than zero is shown to be of the form

in the neighborhood of time zero, and

in the neighborhood of time infinity, where c is the average concentration at time t; S and V are the surface area and volume of the solid, respectively; D is the diffusion coefficient; and f″ (0), α, and β are constants dependent on solid shape. The vacuum drying of wheat has been studied, and it is shown that, for the wheat kernel, f″ (0) = 0.588, α = 0.862; and β2 = 1.301. The diffusion coefficient is an Arrhenius‐type function of temperature given by D = D0 exp {‐E/RT} where D0 = 76.8 cm.2/sec. and E = 12.20 kcal./mole.
Dynamic mechanical properties of nylon 66 and the plasticizing effect of water vapor on nylon. II
Authors: Quistwater J. M. R. , Dunell B. A.
Published: April 2003

The dynamic tensile modulus and energy loss have been measured for nylon 66 monofilaments at 9 and 60°C. over a wide humidity range in forced longitudinal vibration experiments. The frequency range covered was about 3 to 30 cycles/sec. (radian frequency 20 to 200 sec.−1). The results show dispersion of mechanical properties with change in humidity at both temperatures. At 60°C. a well‐defined maximum in the energy loss was observed, similar to that obtained previously at 35°C., but occurring at a somewhat lower water content. If a maximum in the energy loss exists at 9°C. (it is not well‐defined), it occurs very near 100% R.H. A time‐humidity superposition procedure is discussed by means of which the individual curves of modulus against frequency for the various humidities can be combined into a single “master curve” of modulus against reduced frequency. The order of magnitude of the activation energy for the dissipation mechanism has been estimated at 60–80 keal./mole.
Diisocyanate‐linked polymers. I. Dilute‐solution properties of toluene diisocyanate‐extended polypropylene glycol
Authors: Moacanin J.
Published: April 2003

A study was made of the dilute solution properties and the molecular weight distribution of a polyurethane polymer prepared from polypropylene glycol 2025 and toluene‐2,4‐diisocyanate by a bulk polymerization under anhydrous conditions at 60°C. Such conditions were chosen to minimize possible side reactions which could produce branching. The polymer, which had a weight‐average molecular weight of 36,500, was separated into fourteen fractions by fractional precipitation from a benzene solution with isooctane as precipitant. The fractions were characterized by light scattering measurements on methanol solutions and by dilute solution viscosities in methanol, benzene, and a theta‐solvent. The molecular weight distribution of the unfractionated polymer and the relations between molecular weight and intrinsic viscosity in the various solvents were determined. Polymer configurations and interaction parameters are discussed.
Determination of degree of crosslinking in natural rubber vulcanizates. Part III
Authors: Mullins L.
Published: April 2003

Improvement in methods of characterizing the stress‐strain properties of vulcanized rubber and of determining its molecular weight prior to vulcanization are described. Experimental results obtained previously by Mullins, Moore, and Watson, in an attempt to relate the physical properties of natural rubber to their network structure, are critically re‐examined to take account of these developments. It is shown that if empirical corrections are made for the effect of network flaws due to chain ends and for a second type of network defect equivalent to chain entanglements, then estimates of the degree of crosslinking derived from physical measurements and from chemical determinations are in remarkably close accord.
Chemorheological study of cured polysulfide liquid polymers
Authors: Colodny P. C. , Tobolsky A. V.
Published: April 2003

The effect of curing agents and their reaction products upon the disulfide interchange reaction of cured liquid polysulfide polymers was studied. The curing process involved the oxidation of the mereaptan terminals of the liquid polymer to disulfide linkages or the reaction of these end groups with some polyfunctional reagent. Several different types of cure were attempted on the same batch of the liquid polymer including oxidation by metallic oxides, organic peroxides, and hydroperoxides, p‐quinonedioxime, and catalyzed air oxidation. Cures were also obtained by the use of diisocyanates. The disulfide interchange was studied by means of stress relaxation. It was found that the rate of exchange was greatly accelerated by the presence of ionic or alkaline materials. In their absence the exchange reaction proceeded quite slowly. The incorporation of excess sulfur also increased the reaction rate. The mechanism of the reaction is believed to be predominantly ionic.
Investigations of the phenomena of coacervation
Authors: Turska E. , Utracki L.
Published: April 2003

The object of the work was to ascertain the characteristic features which could provide a basis for distinguishing between the formation of the coacervate and that of a new liquid phase resulting from the limited miscibility of components. Various multicomponent systems containing the polymer were examined, and as a model we examined a system unable to form coacervates in which the polymer was replaced by a small‐molecule substance of a similar solubility. Measurements of the changes in the volumes of the liquid phases were carried out and the polymer content in the particular phases was determined. It was ascertained that the characteristic feature for the coacervate is a maximum on the curve which indicates the dependence of the volume of the phase richer in polymer on the quantity of the nonsolvent used. The polyethylene terephthalate coacervate was obtained and certain new systems containing polyamides were proved to be able to form coacervates.
Condensation polymers from diisocyanates and dioximes
Authors: Campbell Tod W. , Foldi Veronika S. , Parrish Robert G.
Published: April 2003

Diisocyanates condense readily with the two active hydrogen atoms in dioximes to give high molecular weight linear condensation polymers. In several cases these polymers, such as the one from cyclohexanedione dioxime and 4,4′‐biphenylene diisocyanate,
magnified image
may be converted to tough films or fibers. Thermal, hydrolytic, and light stability of these polymers were in general poor.
Large‐scale polymer fractionation by gradient elution. Some operating principles
Authors: Pepper D. C. , Rutherford P. P.
Published: April 2003

A detailed analysis of the factors operating in polymer fractionation by gradient elution column methods is offered. A comparison between experimental fractionations of a range of polystyrenes indicates that the most important single factor is the concentration of polymer permitted in the eluant. For the logarithmic composition gradient considered here, the average concentration in the eluant may be controlled through control of the volume of the eluant in the mixing vessel. This volume should be not less than 200 times the volume of the polymer sample, and considerably larger if the polymer is of high molecular weight.
Effect of oxygen pressure on the thermal degradation of a methylphenylsilicone
Authors: Scala L. C. , Hickam W. M. , Loeffler M. H.
Published: April 2003

The manner in which changes in air pressure affect the thermal and oxidative degradation of a methylphenylsilicone was investigated as a function of time. A closed, gas‐circulating system of 1500‐cc. volume, incorporating a magnetic balance for following loss of weight in the sample, was employed. Finely ground samples were heated at 400°C. for 7 hours with initial pressures of air ranging from 700 to 50 mg. Hg. Mass spectrometric and infrared analyses identified the gaseous and the volatile products. At all pressures, low molecular weight silicones represented a major portion of the weight loss. Final weight losses in air approximated 10%, and approached, at the lowest pressure (50 mm.), the 7% observed in argon. Water and benzene were evolved, the latter at a rate that decreased with decrease in pressure. Traces of phenol, formaldehyde, propane, and higher molecular weight hydrocarbons were also given off. The evolution of carbon dioxide, carbon monoxide, methane, and hydrogen and the consumption of oxygen were followed in detail. Changes in air pressure from 700 to 300 mm. did not alter appreciably the rates of product evolution, oxygen consumption, and of weight loss. At lower presures (300 to 50 mm.), however, the molar ratio of the total noncondensed gases generated to total oxygen consumed increased, indicating a possible change in reaction mechanism.
Measurement of the flow of thermosetting molding compound
Authors: Ito Katsuhiko
Published: April 2003

The extrusion rheometer, suggested by the author, is used for the relative measurement of the flow of thermosetting molding compounds in a curing process which is more complicated and difficult to measure than that of thermoplastics. Allyl polyester molding compound, which contains asbestos as a filler in the amount of 50% and Luperco ATC as a catalyzer in the amount of 4%, is used as a test sample of the thermosetting compound. Because the unsaturated polyester which is used as a resin in the test sample of the thermosetting compound contains diallyl phthalate monomer, which acts as a crosslinking component in the radical polymerization reaction, there is no volatile by‐product in the curing reaction. Therefore, breathing during the molding of this test sample is not needed, and this allyl polyester molding compound is considered to be most suitable to use as the test sample of the thermosetting molding compound. Several factors which exert an influence on the flow of the thermosetting compound in the curing process are investigated, and recommended testing conditions are determined. Although the flow curve of the thermosetting molding compound in the extrusion rheometer is not as simple as that of thermoplastics, the flow characteristics of the thermosetting molding compound can be evaluated and compared by the factors Rf, vf, fts, and fte, which are obtained from the flow curve. As an example, the influences of time‐aging effect and various fillers on the flow of the thermosetting molding compound are examined by the above method.
A loss in curing test for tire cords
Authors: Reegen S. L. , Sabo J.
Published: April 2003

A laboratory method for determining the effect of curing conditions on the tensile strength of tire cords has been developed which makes use of rubber‐cord pads cured in a mold. The tensile strengths of the cured cords embedded in rubber are measured after removal from the mold. The method is suitable for nylon cords, either bare or dipped. It has been determined that tensile strength losses during curing of nylon are caused by shrinkage of the cords in the presence of moisture.
Mechanism of antioxidant action in the stabilization of hydrocarbon systems
Authors: Shelton J. Reid
Published: April 2003

Four antioxidant classifications, based on differences in the method by which they exert their effect, are noted. The mechanism of the chain‐stopping action is discussed in terms of four different reactions which have been proposed. The participation of the antioxidant in the mechanism of inhibited thermal oxidation is reviewed. The hydrogen donation mechanism as the first step in the chain‐stopping mechanism has been investigated by observing the effect of replacing the active hydrogen of the antioxidant by deuterium. Contrary to the findings of some prior workers, a kinetic isotope effect has been demonstrated with a secondary aryl amine antioxidant as well as with phenols. These results, together with other supporting evidences reported in the literature, indicate that abstraction of a hydrogen from the antioxidant is the initial step in the usual mechanism by which antioxidants serve as chain stoppers in the oxidation of hydrocarbon systems.
A study of time dependence of polyethylene flow in capillary viscometry
Authors: Schreiber H. P.
Published: April 2003

It is known that polyethylene extruding from a capillary viscometer does not attain a steady‐state output rate immediately following a pressure imposition. The time dependence of output rate was studied quantitatively, and under some extrusion conditions was found to be of surprisingly large magnitude. The most notable effect is an overall rise in the output rate; its magnitude and duration depends on the extrusion pressure and temperature and on the entry geometry of the die employed. The magnitude of the effect is also characteristic of particular polyethylene samples and seems associated with smooth filament extrusion of the polymer. The steady‐state output rate can exceed the initial rate by as much as 40%. The rising output rate characteristic has been associated with a decreasing melt viscosity. This is taken to be the result of configurational changes occurring in the extruding melt. The data are shown to be qualitatively consistent with this postulate.