bluuebunny/crossref_metadata_2025 huggingface dataset:
Operations Research at Bell Laboratories through the 1970s: Part III
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. 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 http://or.pubs.informs.org .
Topological Design of Two-Level Telecommunication Networks with Modular Switches
Authors: Chamberland Steven , Sansò Brunilde , Marcotte Odile
Published: April 2003

In this article we propose a mixed 0-1 linear programming model for the topological network design problem with modular switches such as the ones that will be used in asynchronous transfer mode (ATM) frame relay and other broadband networks. The model includes the location of switches, their configuration with respect to ports and multiplexers, the design of an access network with a star topology, and a backbone network with a fixed topology (ring or tree). To obtain a solution, we propose a greedy heuristic that provides a good starting solution, and a tabu search heuristic to improve the solution. Finally, we present an example of the application of the heuristics and results for a set of randomly generated problems with up to 500 users and 30 potential switch sites. For the hundreds of problems generated, the tabu algorithm produced solutions that were, on average, within 1.5% of the optimal solution, and in the worst case within 4.95% of the optimal solution.
Optimal Guaranteed Return Portfolios and the Casino Effect
Authors: Dert Cees , Oldenkamp Bart
Published: April 2003

In this paper we address the problem of determining optimal portfolios that may include options in a framework of return maximization with risk constraints relative to a benchmark, as well as in terms of absolute returns. The model we propose allows for deterministic constraints as well as probabilistic constraints. We derive properties of optimal and feasible portfolios and present a linear programming model to solve the problem. The optimal portfolios have payoff functions that reflect a gambling policy. We show that optimal solutions to a large class of portfolio models that maximize expected return subject to downside risk constraints are driven by this casino effect and present tractable conditions under which it occurs in our model. We propose to control the casino effect by using chance constraints. Using results from financial theory, we formulate an LP model that maximizes expected return subject to worst-case return constraints and chance constraints on achieving prespecified levels of return. The results are illustrated with real-life data on the S&P 500 index.
Analysis of the Effects of Uncertainty, Risk-Pooling, and Subcontracting Mechanisms on Project Performance
Authors: Gutierrez Genaro , Paul Anand
Published: April 2003

The problem of designing a contract mechanism to allocate the component subprojects of a large project to a pool of contractors has important implications for project success. Our research analytically addresses issues involved in diversifying risk for the project owner by partitioning the project and assigning the subprojects to multiple contractors whose performance characteristics are imperfectly known. We begin by giving a precise analytical treatment of the effect of activity variance on expected project duration, characterizing the cases when an increase in activity variance pushes up the expected project duration. In the case of a homogeneous project consisting of serial subprojects, we show that disaggregating the project and assigning the subprojects to the contractors on a piecemeal basis reduces variance of project duration while leaving the mean unchanged. On the other hand, in the case of a homogeneous project consisting of parallel subprojects, aggregating the subprojects and assigning the aggregated project to one of the contractors reduces mean project duration.
The Optimal Performance of the Global Firm: Formalizing and Extending the Integration- Responsiveness Framework
Authors: Devinney Timothy M. , Midgley David F. , Venaik Sunil
Published: April 2003

With the increasing globalization of business, there has been growing interest in how to create and manage a successful international enterprise. Although researchers and practitioners have grappled with the issue of globalization for some time, there is no one model that encompasses the range of phenomena we observe in the global economy, nor have those models that do exist been precisely formalized.

This paper provides an expanded approach to thinking about the organizational forms and linkages that exist in international business operations. Building on the popular integration-responsiveness framework of international strategic orientation, we develop a more expansive approach that is better able to account for the diversity of organizational forms and strategic choices open to managers. By adding a third set of environmental pressures, incorporating the beliefs of managers, and by employing the idea of efficient frontiers, we reformulate the integration-responsiveness framework, making it more consistent with modern economic models of the firm. Our integration-responsiveness-completeness (IRC) model argues that global firms can respond to these fundamental and competing pressures by configuring themselves in a variety of ways—rather than normatively prescribing that the transnational form is optimal. In addition, our model has methodological ramifications. Its formal structure suggests that empirical techniques that focus on the best rather than average performance are necessary to adequately investigate the performance differences among alternative organizational forms. This may explain the paradoxical lack of empirical support for a link between organizational form and performance.
Disseminating Innovations in Health Care
Authors: Berwick Donald M.
Published: April 2003

Health care is rich in evidence-based innovations, yet even when such innovations are implemented successfully in one location, they often disseminate slowly—if at all. Diffusion of innovations is a major challenge in all industries including health care. This article examines the theory and research on the dissemination of innovations and suggests applications of that theory to health care. It explores in detail 3 clusters of influence on the rate of diffusion of innovations within an organization: the perceptions of the innovation, the characteristics of the individuals who may adopt the change, and contextual and managerial factors within the organization. This theory makes plausible at least 7 recommendations for health care executives who want to accelerate the rate of diffusion of innovations within their organizations: find sound innovations, find and support "innovators," invest in "early adopters," make early adopter activity observable, trust and enable reinvention, create slack for change, and lead by example.
Screening and Management of Adult Hearing Loss in Primary Care
Authors: Bogardus Sidney T. , Yueh Bevan , Shekelle Paul G.
Published: April 2003

Hearing loss is one of the most common chronic health conditions and has important implications for patient quality of life. However, hearing loss is substantially underdetected and undertreated. We present clinical cases to illustrate common situations in which primary care physicians may be called on to identify or to manage hearing loss. With the data reported in the companion scientific review as a guide, we present potential answers to important questions pertaining to hearing loss and suggest ways in which primary care physicians can improve the detection, evaluation, and treatment of hearing loss. The cases focus on screening for chronic hearing loss, evaluation of hearing loss, and treatment of patients with presbycusis.
Prader‐Willi syndrome and the evolution of human childhood
Authors: Haig David , Wharton Robert
Published: April 2003

The kinship theory of genomic imprinting predicts that imprinted genes have effects on asymmetric kin (relatives with different degrees of matrilineal and patrilineal relatedness). The most important interaction with such a relative is a child's interaction with its mother. Therefore, the study of imprinted genes and their phenotypic effects promises to provide insights into the evolution of mother–child relations. Prader‐Willi syndrome (PWS) is caused by the absence of expression of genes at 15q11–q13 that are normally expressed only when paternally derived. The kinship theory predicts that children with PWS will fail to express behaviors that have increased mothers' costs of child‐rearing. Our analysis focuses on aspects of the PWS phenotype that affect appetite and feeding. Immediately after birth, children with PWS have little appetite and are usually unable to suckle, but at some stage (usually within the first 2 years) they develop a voracious appetite and an obsession with food. We conjecture that this change in appetite reflects evolutionary forces associated with weaning. Immediately after birth, when a child is completely dependent on the breast, poor appetite reduced maternal costs. However, once a child was able to consume supplemental foods, maternal costs would have been reduced by children with increased, nonfastidious appetites. Am. J. Hum. Biol. 15:320–329, 2003. © 2003 Wiley‐Liss, Inc.
Early Developmental conditions and reproductive success in humans: Downstream effects of prenatal famine, birthweight, and timing of birth
Authors: Lummaa Virpi
Published: April 2003

Growth, survival, and breeding success of individuals in populations of wild mammals are influenced by the climatic and nutritional conditions that individuals experience during their early development. Recent findings have shown that early conditions also have consequences for subsequent survival and reproductive performance in humans. Environmental conditions which affect early development of individuals, such as the quality and quantity of nutrition received in utero and infancy, predict the onset of many chronic diseases in adulthood, affect longevity and may also influence a range of measures of reproductive performance in both food‐limited and contemporary Western human populations. These associations are proposed to result from foetal programming, where a stimulus or insult during a critical period early in life may permanently affect body structure, physiology, and metabolism. Here I review studies showing how birthweight, season of birth, or exposure to prenatal starvation affect different aspects of an individual's subsequent reproductive success in humans and the growth, survival, and reproductive performance of the offspring produced. I show that early maternal and environmental conditions can have a large impact on human reproductive strategies and fitness that can span across generations. Am. J. Hum. Biol. 15:370–379, 2003. © 2003 Wiley‐Liss, Inc.
Validation of expert assessment of occupational exposures
Authors: Fritschi Lin , Nadon Louise , Benke Geza , Lakhani Ramzan , Latreille Benoit , Parent Marie‐Elise , Siemiatycki Jack
Published: April 2003

Background

Assessment by experts may be the best method available for retrospective occupational exposure measurement in community‐based studies. This study was undertaken to examine the validity of occupational exposure assessment by comparing the ratings of experienced raters with previously recorded industrial hygiene measurements.

Methods

We obtained 50 measurements from industrial hygiene records, covering a variety of jobs and substances and created 47 job descriptions around these measurements. Three raters were asked to assess exposure to a checklist of 19 substances (including those substances which had been measured). We estimated the sensitivity of the raters in correctly detecting those substances known to have been present.

Results

Using a liberal criterion for the ratings, the average sensitivity among the raters was 90%. Using a more stringent criterion, the average sensitivity was 73%. Among substances coded as present, the raters were quite accurate in rating the relative concentration and frequency of exposure.

Conclusions

This trial demonstrated that a team of experienced raters could successfully characterize jobs in which important exposures occurred. Am. J. Ind. Med. 43:519–522, 2003. © 2003 Wiley‐Liss, Inc.
Individual and combined impacts of biomechanical and work organization factors in work‐related musculoskeletal symptoms
Authors: Huang Grant D. , Feuerstein Michael , Kop Willem J. , Schor Kenneth , Arroyo Freya
Published: April 2003

Background

Investigations of work‐related low back (LB) and upper extremity (UE) disorders have increasingly utilized multivariable models that include biomechanical/physical and work organization factors. However, the nature of any interactive effects is not well understood.

Methods

Using questionnaires, high and low exposure groups for biomechanical/physical factors, cognitive demands, cognitive processing, interpersonal demands, participatory management, skill discretion, and time pressure for 289 individuals (U.S. Marines) were identified. Musculoskeletal symptom status was also determined by questionnaire. Individual and biomechanical–psychosocial combinations were examined in adjusted multivariable logistic regression analyses.

Results

Time pressure was associated with both LB and UE symptoms (odds ratio(s) (OR) range = 2.13–3.09), while higher biomechanical exposures were risk factors for LB symptoms (OR = 2.07; 95% confidence intervals (CI): 1.00–4.35) and concurrent LB and UE symptoms (OR = 2.80; CI: 1.35–5.83). Greater risks for concurrent LB and UE symptoms were indicated for combinations involving higher biomechanical exposure and: time pressure (OR = 2.21; CI: 1.19–4.10); cognitive demands (OR = 2.25; CI: 1.23–4.09); cognitive processing (OR = 2.08; CI: 1.16–3.75); interpersonal demands (OR = 2.44; CI: 1.35–4.41); participatory management (OR = 2.50; CI: 1.30–4.81). Results did not suggest any interaction between biomechanical and work organization factors.

Conclusions

While no synergism was indicated, the present findings emphasize the need to consider both biomechanical factors and specific work organization factors, particularly time pressure, in reducing musculoskeletal‐related morbidity. Am. J. Ind. Med. 43:495–506, 2003. Published 2003 Wiley‐Liss, Inc.
Physical properties of high molecular weight acetal resins
Authors: Linton W. H. , Goodman H. H.
Published: April 2003

Information is presented on those physical properties where measurement is greatly facilitated by thermal stability greater than previously known in polyoxymethylenes, and properties of a mechanical nature characteristic of high molecular weight polymeric materials. The high molecular weight polyoxymethylenes studied possess the characteristic properties of a semicrystalline material in the high molecular weight range. The melting point, stiffness, and tensile strength of these materials substantially exceed those for linear polyethylene, which suggests that the effective chain interactions are enhanced by ease of close packing of the chains. High density and high crystallinity are in accord with this picture.
Condensation polymers containing fluorine. II. Physical characterization of linear polyesters from hexafluoropentanediol
Authors: Gouinlock E. V. , Verbanic C. J. , Schweiker G. C.
Published: April 2003

A number of fluorinated polyesters have been prepared by condensing hexafluoropentanediol with one or more dibasic acid chlorides, and melting and glass transition temperatures and rates of crystallization have been determined, largely by means of volume dilatometry. The relation between [η] in chloroform at 30° and M̄n for hexafluoropentylene adipate (HFPA) was found to be [η] = 3.20 × 10−5 M̄n. The melting point Tm was found to increase from 34.5° to 104° as the isophthalate content in a series of adipate copolyesters increased from 0 to 100 mole‐%. The glass transition Tg increases from −57° to −31° as isophthalate content increases from 0 to 50 mole‐%. Tg is raised about 6° by the crosslinking of the polyesters. Rates of crystallization were determined for two HFPA samples with M̄n's of 13,000 and 19,500. Maxima in these rates occurred at about ‐13° and ‐15°, respectively. Respective t½ values for (linear) HFPA, vulcanized HFPA, and a copolyester containing 20 mole‐% isophthalate are 48, 1140, and 27,200 min., respectively, at ‐10°. All the crystallization isotherms conform to Avrami's equation, (Vt − V∞)/(Vt − V∞) = exp {−αt″} for n = 6 over the initial stages of the process. At 1° both HFPA isotherms agree with the above equation over a large part of the process; however, as the isotherm temperature decreases, the equilibrium degree of crystallinity, as judged by the overall specific volume change, decreases and the isotherms diverge from Avrami's equation over progressively larger portions of the process. The product of the maximum rate of crystallization for each isotherm with either t½ or τi, the “induction time,” decreases with decreasing temperature, as would be expected in view of Avrami's equation. The value of 6 observed for n, a constant determined by the nucleation and growth mechanisms, is anomalous since only values of 1 to 4 are theoretically predictable. Values over the range of 1 to 4 have been observed experimentally by other workers for a variety of polymers.
Glass transition in polymers
Authors: Saito Shogo , Nakajima Tatsuji
Published: April 2003

Glass transition phenomena in several polymers were studied by dielectric and dilatometric measurements. The dielectric measurements were made over the frequency range of 10−4 or 10−1 to 106 cycles/sec. and the temperature range of the glass transition. In the dilatometric study, volume relaxation curves and volume vs. temperature curve were obtained. The transition in three amorphous polymers, (polyvinyl acetate, polystyrene, and polymethyl methacrylate), depends upon frequency or rate of cooling and seems to be an apparent transition. In three crystallizable polymers, (vinylidene chloride‐vinyl chloride copolymer, polyethylene terephthalate, and polyacrylonitrile), the magnitude of the dielectric absorption decreases steeply with decreasing temperature in the transition range, and the transition by the volume expansion remains when equilibrium is attained. The transition in the three crystallizable polymers seems to be a real one. Temperature dependences of the activation energies of the dielectric relaxation processes have been described.
Determination of degree of crosslinking in natural rubber vulcanizates. Part IV. Stress‐strain behavior at large extensions
Authors: Mullins L.
Published: April 2003

Departures from behavior predicted by the statistical theory of rubberlike elasticity, which occur at high extensions, are ascribed to the finite extensibility of network chains. By use of a non‐Gaussian statistical theory, a relation is obtained between the extension ratio λ*, the extension at which departures are small but significant and the degree of crosslinking. Experimental results on the dependence of λ* on the degree of crosslinking and on the degree of swelling are in good agreement with theoretical predictions. It is shown that the additional determination of λ* permits the calculation of both the degree of crosslinking and the extent of network flaws due to chain ends, from a single simple extension stress‐strain curve. The calculation of these two basic parameters has hitherto been unattainable from measurements on vulcanized rubbers alone. This development provides a new technique of particular value in studies of the degradation of vulcanized networks.
Anisotropy in thermoplastic moldings and their impact strength
Authors: Keskkula Henno , Norton J. W.
Published: April 2003

The machanical anisotropy of several thermoplastic polymers has been investigated, and the relationship with a practical dart drop impact measurement has been explored. It has been shown that the unnotched Izod impact strength of a specimen taken perpendicular to flow orientation can be correlated with the dart drop impact strength. Further, the effect of several dart drop test variables, such as drop height, dart tip radius, and specimen size, have been investigated and reported. It has been concluded that the conventional strength measurement of injection‐molded specimens may lead to erroneous appraisal of the practical strength of a material. Testing at an orientation normal to flow or by multiaxial stressing as in a dart drop test is suggested.
The effect of radiation on the melt index of polyethylene
Authors: Harper B. G.
Published: April 2003

Five different types of polyethylene were irradiated in air and their melt indices determined as a function of the radiation dose. A resonant transformer electron beam generator was the source of radiation, and cellophane dye dosimetry was used to determine the radiation dose. The melt index was found to change uniformly with dose, and a single empirical equation was derived which describes the curves for all five types of polyethylene. By using the melt index as a measure of crosslinking, it was shown that the effect of radiation intensity on crosslinking is negligible.
Relation of structure to properties in polyurethanes
Authors: Cluff E. F. , Gladding E. K.
Published: April 2003

A polyurethane bearing pendant hydroxyl groups and carbon‐carbon double bonds was prepared. Curing was carried out by diisocyanates of different lengths and by an accelerated sulfur recipe. The vulcanizate properties of modulus, hardness, and resilience were found to be independent of both the length and chemical nature of the crosslink. Compression set, however, was always higher for the sulfur cures, an effect which can be attributed to the disulfide structure of this particular crosslink. Both physical and chemical evidence support this structure. Diisocyanate curing of the dolyurethane via the hydroxyl groups is a clean‐cut, essentially quantitative reaction which provided an absolute method for determining the degree of crosslinking. Excellent agreement was obtained between the physical degree of crosslinking as determined by equilibrium modulus and the chemical degree of crosslinking. This agreement provides further verification of the network‐statistical theory of rubber elasticity in highly swollen systems. No chain entanglement was observed.
The superstructure of melt‐crystallized polyethylene. I. Screwlike orientation of unit cell in polyethylene spherulites with periodic extinction rings
Authors: Fujiwara Yasuna
Published: April 2003

The ringed structure in polyethylene spherulites was investigated by an x‐ray microdiffraction method. A spherulite with extinction rings whose interval is about 50 μ was observed when viewed under the polarization microscope. An asymmetric x‐ray diffraction fibrous pattern about the b axis was obtained for this specimen. This indicates that in the area of spherulite (several microns in diameter) the unit cells are never randomly oriented around a common b axis but have nearly similar orientations. A series of micro‐diffraction patterns was obtained at intervals of 13 μ (about 1/4 the extinction fringe interval), and it was shown that the unit cells have screwlike orientations with their common b axis along the spherulite radius. The distance corresponding to one‐half the pitch of the screw is just in accordance with the extinction ring interval.
Polymers from vinyl fluoride
Authors: Kalb G. H. , Coffman D. D. , Ford T. A. , Johnston F. L.
Published: April 2003

The free‐radical polymerization of vinyl fluoride has been studied with the use of organic peroxide and azo initiators over the temperature range of 60–150°C. and at pressures of 75–1000 atm. Molecular weights of the polymers by osmotic pressure or radiotracer techniques were found to vary over the range of 45,000 to 180,000 depending on polymerization conditions employed. Stabilized high molecular weight polyvinyl fluoride may be compression‐molded into tough, high‐impact strength bars, or the unstabilized material may be cast into films from solvents such as dimethylformamide. The films, which may be cold drawn, are tough, brilliantly clear, and have tensile strengths near 8000 lb./in.2 They are also extremely resistant to weathering, maintaining clarity and cold drawability even after ten years' exposure in Florida.
The structure of chlorosulfonated polyethylene
Authors: Nersasian Arthur , Andersen Donald E.
Published: April 2003

The chlorines in chlorosulfonated polyethylene have been characterized by kinetic analysis according to the method of Salomon. It is found that 2.7% of the total chlorine is primary, 89.8% secondary, 3.5% tertiary, and 4% is sulfonyl chloride. These results are in accord with statistical calculations based on a polyethylene model containing the same methylene‐to‐methyl group ratio as the polyethylene precursor. The types and approximate quantities of dichlorides in the chlorosulfonated polyethylene have been determined by reactions with potassium iodide and zinc dust
The tensile properties of highly filled polymers. Effect of filler concentrations
Authors: Bills Kenneth W. , Sweeny Keith H. , Salcedo Frank S.
Published: April 2003

The systematic study of the variation in tensile properties with the extent of loading in highly filled systems has received little attention even though it is important to a variety of industries. An investigation was therefore made of the mechanical properties of a polyurethan rubber loaded with uniform glass spheres. Systems containing up to 62.5 vol.% fillers were investigated in tension on a strain rate range of 0.074 to 1850 min.−1 and temperatures of −50 to +80°C. The mechanical behavior at low extensions was found to be represented by the generalized Maxwell model. The Williams‐Landel‐Ferry relationship was satisfactorily applied to the reduction of the data. Good agreement was obtained between the glassy‐state transition temperature calculated from the reduced tensile data and from experimental differential thermal analysis results. The increase in the modulus with increasing filler content was satisfactorily described by an empirical modification of the Eilers relationship. The application of the reduced tensile data to the calculation of the stress relaxation modulus is also shown. Reasonable agreement was obtained between the calculated and experimental data.
Response of elastomers to any forcing function
Authors: Berger M.
Published: April 2003

The dynamic behavior of elastomers is usually studied in terms of a sinusoidal system. The theoretical and practical limitations of such analysis are discussed. A method which permits calculation of dynamic properties over a wide range of frequencies and forcing functions is described. The theoretical justification and limitations as well as the experimental setup are presented. Using SBR, natural rubber, and butyl, examples of the dynamic responses for various forcing functions are shown. The analogue computer is used to show properties of the above described rubbers which are useful from both the theoretical and application‐oriented viewpoints.
The development of crystallinity and transparency in irradiated polyethylene
Authors: Levy Boris
Published: April 2003

A procedure has been developed for producing highly transparent polyethylene by use of high‐energy electron irradiation above the melting point. The polyethylene retains about 60% of its original tensile strength after receiving the optimum irradiation dose of 50 Mrad at room temperature followed by 50 Mrad at 150°C. The transparency of a 0.02 in. sample increases from about 20% to 75% under this treatment. Changes in transparency with time and temperature, during cooling of the polyethylene from 150°C. to various quench temperatures were investigated as a function of irradiation dose. The increase in transparency is a result of reduction in crystallinity, in size of crystallites and spherulites, and in rate of crystallization caused by the restraints imposed by the radiation‐induced crosslinking.
Peel testing of adhesive bonded metal
Authors: Yurenka S.
Published: April 2003

In this paper the subject of peel is divided into two parts: (1) A mathematical determination of peeling stresses in an adhesive bond due to the applied peeling loads which leads to a mathematical definition of “peel strength.” (2) A review of suitable peel test methods examined in the light of this definition. Employing the assumption that the adhesive bond behaves as an ideal homogeneous elastic material under load, the classical derivation of the deflection of a loaded beam on an elastic foundation is applied to the calculation of peel strength of a metal adhesive. This theory results in a mathematical definition of peel strength and offers a reasonable explanation of the effects of the important variables such as metal and adhesive thickness and strength properties and provides a basis for the comparison and evaluation of the few testing methods presently in use.
Relaxation processes in vulcanized rubber. II. Secondary relaxation due to network breakdown
Authors: Gent A. N.
Published: April 2003

An experimental study is described of a “secondary” relaxation process in stretched vulcanizates, which becomes dominant after long periods at normal temperatures. It is shown to be affected markedly by the temperature, the atmosphere in which the test is conducted, and the presence of oxidation inhibitors. It is therefore attributed to oxidative deterioration of the molecular structure. In some vulcanizates, however, a similar or even greater relaxation is found to occur in vacuo, and this is attributed to the failure of specific crosslink structures. The extent of recovery on releasing the extended test pieces has also been investigated for a number of natural rubber vulcanizates.
Stress crazing of some amorphous thermoplastics
Authors: Spurr O. K. , Niegisch W. D.
Published: April 2003

Tensile stress‐induced crazing in polystyrene, poly(methyl methacrylate), and polycarbonate has been carefully examined by optical and electron microscopy. Examination of the surface of crazed specimens and the cross sections of individual crazes leads to the conclusion that the crazes are not void cracks, but are filled with a craze matter. The craze matter is readily distinguishable from the surrounding resin and is seen to exist in continuity with it. Further experiments confirm the existence of the craze matter and tend to indicate its structural and mechanical properties. These experiments include: microscopic examination of the walls of fractured crazes, micro x‐ray diffraction of craze matter, studies of the strength of crazed specimens under static loads and under increasing tensions, studies of the effect of heat and solvent on crazed specimens, and observations on the ability of crazes to form special networks. The results indicate that the craze matter may be formed by localized resin deformation leading to a load bearing oriented structure. A hypothesis of the mechanism of craze formation is proposed in light of the new and varied information reported in the paper. Study of the kinetics of craze growth suggests the division of the mechanism into three parts: initiation, propagation, and termination. The initiation step describes the concentration of strain energy and the precursory molecular arrangements in the immediate vicinity of inhomogeneities. These are the changes which occur during the time lapse between stress application and first appearance of crazes. The propagation step comprises the sudden and relatively rapid localized resin deformation which creates the craze matter. The shapes of the growing crazes and their diminishing growth rates are attributable to known resin properties. The termination step represents the apparent cessation of craze growth with continued long times of stress application. At this stage in the existence of crazes the proposed hypothesis must blend into the theories of time delayed rupture. It is concluded that stress crazing is basically a molecular slippage rather than a molecular cleavage phenomenon. Considerations, therefore, are to be directed more towards intermolecular forces than intramolecular forces.
The early stages of isotactic polypropylene oxidation
Authors: Russell C. A. , Pascale J. V.
Published: April 2003

The initial stages of isotactic polypropylene oxidation were investigated by oxidizing at 130°C. to various extents up to 10 ml. of oxygen consumed per gram of polymer. The development of infrared absorption bands in the carbonyl regions was followed, as increasing amounts of oxidation occurred. The oxidation uptake curves showed that both autocatalytic rate and induction time depended primarily on the thickness of the sample, contrary to the case of polyethylene. This indicated the initiation process was primarily diffusion controlled for samples of the thickness range studied. The presence of copper shortened the induction times and increased the autocatalytic rate. In this case, the dependency of the induction time on thickness was less. Dielectric data showed that polypropylene became unsuitable electrically at about the point where the autocatalytic oxidation set in. It was also found that the effects of prior exposure to oxidative conditions were cumulative to a considerable extent, and thus resulted in shorter induction times.
Study of epoxy compounds. Part I. Curing reactions of epoxy resin and acid anhydride with amine and alcohol as catalyst
Authors: Tanaka Yoshio , Kakiuchi Hiroshi
Published: April 2003

The curing reaction of an epoxy resin and acid anhydride with an amine and/or alcohol was studied kinetically. No etherification reaction occurred at 70–140°C. and the initial reaction rate was proportional to the concentration of epoxide, acid anhydride, and catalyst (tertiary amine or alcohol). The apparent activation energies of the reaction in two systems of epoxy resin–hexahydrophthalic anhydride/triethanolamine (0.5 wt. %) were obtained as 14.1 and 14.4 kcal./mole. The effects of the substitution R of the tertiary amine NR3 or alcohol R3COH as catalyst on the curing reaction of the epoxy resin and acid anhydride were studied. The polar reaction constant ρp for amines, obtained negatively, indicates that electron‐repelling substituents of NR3 increase the curing rate; ρp for alcohols, obtained positively, indicates that electron‐withdrawing substituents of R3COH increase the rate of curing reaction. These results supported the proposed curing mechanism better.
Mathematical description of the stress‐strain behavior of filled binders
Authors: Brock Fred H.
Published: April 2003

The result of a phenomenological study in the analysis of uniaxial and biaxial tensile behavior of a variety of filled systems is described. A correlation is given that appears to serve as a tensile failure criterion for most of the systems investigated. The storedenergy function W, assumed to be equal to the area under the stress‐strain curve, has been found to obey the relation W = A(1 – exp {–B(Q – 3)}), where A and B are constants and Q is related to the first or second strain invariant. In general, the total stored energy up to break, divided by A, has a value between 0.7 and 0.8, which appears to be independent of strain rate and temperature. This constancy has also been verified by an independent set of data.
Gas permeation through lexan polycarbonate resin
Authors: Norton Francis J.
Published: April 2003

Values have been determined over a considerable temperature range for the permeation rate, diffusion constant, and solubility of the following gases in Lexan: H2, H2O, He, Ne, O2, argon, CO2, and SF5. There is some discussion of the interrelationships and the variation of activation energies with molecular weight.
Melt elasticity and viscosity of neoprene WB at high shear rates
Authors: Eckert Roger E.
Published: April 2003

An elastomer developed for superior processing characteristics, Neoprene WB, has been studied in a capillary rheometer from 80–125°C. and shear rates of 0.4–11,000 sec.−1 Both the viscous and elastic properties of the bulk polymer are evaluated from pressure drop measurements. Per cent increase in diameter of the elastomer when extruded (“die swell”) and its surface characteristics provide direct evidence of extrusion processibility. A principle of corresponding shear rates at different temperatures simplifies the understanding and application of rheometer data. Data on all responses obtained at a low temperature can be laterally superposed to higher shear rate to agree with data obtained at higher temperature. Equilibrium shear stress vs. shear rate curves show Neoprene WB undergoes shear thinning with, for example, viscosity at 100°C. dropping from over 106 poise at low shear rate to 5 × 102 poise at high. The entrance or elastic effect drops very slowly to a minimum with increasing shear and then rises rapidly. This shear rate‐temperature condition at which the entrance effect is a minimum is a critical condition for the polymer; it is the transition from smooth to rough extrudate. Die swell of smooth extrudates increases as the shear rate is increased but decreases with greater orifice length to diameter ratio. Above the transition the die swell of rough extrudates drops to a minimum and then rises again at still higher shear rates.
Protective effect of nitrous oxide on radiation‐induced degradation of polyisobutylene
Authors: Okada Yoichi
Published: April 2003

Polyisobutylene was irradiated by γ‐rays from a Co60 source in vacuum and in nitrous oxide atmosphere. The irradiated specimens in N2O were damaged to a lesser extent than those in vacuum. Irradiated specimens were dissolved in CCl4 and their viscosity was measured at 30°C. A plot of reciprocal of viscosity‐average molecular weight against dose gives a straight line in each case for specimens irradiated in vacuum and in N2O. Moreover, the presence of nitrous oxide reduces the extent of main‐chain fracture to 63%. The degree of branching is nearly the same for all of the specimens, since Huggins' constant k' is constant (k' = 0.40) throughout our experiments. It can be concluded that the N2O has a protective effect for main‐chain fracture of polyisobutylene.
Characteristics of experimental cis‐1,4‐polyisoprene latices
Authors: Preiss D. M. , Sawyer W. M. , Simpson W. C.
Published: April 2003

Experimental latices of synthetic cis‐1,4‐polyisoprene and films and cellular objects produced from them are described. The latices of the synthetic polymers with molecular weights of about 2,000,000 are stabilized by anionic surfactants and have weight median particle diameters of about 0.9 μ and log normal particle size distribution. Tensile properties and flow characteristics of unvulcanized latex films could be regulated by introduction of controlled, small, amounts of crosslinking into the latex. Procedures used for crosslink density determination on cis‐polyisoprene latex at various stages of use are described. Vulcanized latex films having maximum tensile strengths (5500–6000 p.s.i. and 800–950% elongation) were obtained when the final crosslink density was in the range 1.0–1.6 × 10−4 moles of effective chains/cc. Use of the synthetic cis‐polyisoprene latex in production of foam is described. Gelation with sodium silicofluoride at room temperature occurs within 2–10 minutes. Production of a controlled level of crosslinking in the latex prior to frothing and gelling was found to improve the uniformity of cell structure of foams and to increase their resistance to compression. Excessive crosslinking in the latex during maturation was shown to cause a loss of tensile strength in cured products presumably because the coalescence of latex particles during gelation is adversely affected. The properties of synthetic cis‐1,4‐polyisoprene latices and the physical properties of films and foams derived from them are shown in general to be very similar to those of natural rubber latex and its products.
Thermosetting vinyl and acrylic copolymers
Authors: Kelly D. P. , Melrose G. J. H. , Solomon D. H.
Published: April 2003

Infrared spectra indicate that carboxyl‐substituted acrylic copolymers react appreci8bly with a butylated melamine–formaldehyde resin when heated at 120°C. for 30 min., but under these conditions acid catalysis is needed before epoxy‐ or amido‐substituted copolymers will crosslink with the melamine–formaldehyde resin. Two methods have been used to synthesize hydroxyl‐substituted acrylic copolymers. First, a glycidyl methacrylate copolymer was reacted with diethplamine. Second, an acrylic acid copolymer was heated under reflux with butylene oxide in the presence of a basic catalyst. This second method was used to esterify a vinyl toluene–acrylic acid–acrylamide copolymer which was subsequently treated with paraformaldehyde. The resulting hydroxy‐methylolamido copolymer intercondensed when heated at 120°C. for 30 min., somewhat as did the hydroxy copolymer with melamine–formaldehyde resin blends.
Polyhydroxyethers. II. Effect of structure on properties of high molecular weight copolymers from dihydric phenol mixtures and epichlorohydrin
Authors: Reinking N. H. , Barnabeo A. E. , Hale W. F.
Published: April 2003

The glass transition temperature and gas barrier properties of a number of high molecular weight thermoplastic hydroxyether copolymers have been determined. These copolymers were derived from mixtures of two dihydric phenols and epichlorohydrin. The property data are analyzed in terms of copolymer composition and the random or alternating distribution of monomer units in the polymer chains. In general, the glass transition temperatures of the copolymers were found to be intermediate between the values for the two homopolymers. In one system, good agreement between the experimental data and a simplified equation for the prediction of glass transition temperatures of amorphous, random copolymers was obtained. No differences in the glass transition behavior of random and alternating hydroxyether copolymers could be detected. Gas barrier properties, in general, were found to be intermediate in value between those of corresponding homopolymers. The exceptions are discussed in terms of polymer structure variations.
Dilatation of granular filled elastomers under high rates of strain
Authors: Farris R. J.
Published: April 2003

An apparatus has been developed for measuring the dilatation of specimens tested in uniaxial tension in a constant volume chamber by determining the change in the volume of air around the specimen through precise measurement of air pressure. The dilatometer can be used on standard testing machines and has shown reproducible values at testing speeds from 0.66 to 666%/min., and temperatures from −75 to 210°F. Typical stress strain curves are shown with the simultaneously recorded dilatation versus strain.
High speed testing as a measure of the resistance to penetration of needle‐punched felts
Authors: Laible Roy C. , Supnik Ross H.
Published: April 2003

Needle‐punched felt samples differing widely in ballistic performance have been subjected to four different types of high speed mechanical tests. These tests included penetration, tensile, compression, and instrumented dart‐drop methods. The results from one of these high speed tests, the penetration test, can be consistently related to the ballistic resistance of the felts. This penetration test utilizes a compression cage equipped with a penetrant and is operated at test speeds about two decades lower than those realized ballistically. The other three tests are of only limited use in evaluating felts.
Exploratory studies in photomechanics
Authors: Becker Herbert , Zachar Andrew W.
Published: April 2003

Exploratory tests were conducted on a specially designed and fabricated photoviscoelastic plastic in order to develop a form for the relationship between fringe order and the mechanical behavior of the plastic. Because of the possible dependence of fringe order upon both stress and strain, the relationship has been termed the photomechanical law. The results which have been obtained so far were inconclusive. In addition, numerous problem areas were discovered which indicate the type of program which may lead to the photomechanical law.
Modification of the brice light‐scattering photometer for photoelectric polarimetry by the rouy method
Authors: Kahn Leo D. , Calhoun Robert R. , Witnauer Lee P.
Published: April 2003

Construction details for modifying the Brice light‐scattering photometer for use in photoelectric polarimetry have been given. The measuring technique is based on the Rouy method, which is perhaps the most sensitive of all photoelectric methods of measuring the optical rotation of liquids, especially at small angles. A standard deviation of 0.01° has been observed with the use of an instrument modified in this way.
Effect of atmosphere on radiation‐induced crosslinking of polyethylene. Part IV. Sensitizing effect of nitrous oxide and xenon
Authors: Okada Yoichi
Published: April 2003

Low density polyethylene film was irradiated with gamma‐rays from Co60 in atmospheres of nitrous oxide and xenon. A plot of solubility (S + S1/2) against reciprocal of irradiation dose gives a nearly straight line in each case. The probability of crosslinking increases by 44% in N2O as compared with vacuum irradiation, and increases by 10% in Xe. On the other hand, the probability of main‐chain scission is scarcely affected by these gases. Therefore the increase in gel fraction due to these gases is not due to the protection against main‐chain scission, but is caused mainly by the sensitization against crosslinking. Furthermore, the formation of trans vinylene unsaturation is also sensitized by these gases.
Curing relations of hexakis(methoxymethyl)melamine and its combinations with acrylic polymers
Authors: Saxon Robert , Lestienne Firmin C.
Published: April 2003

The curing of hexakis(methoxymethyl)melamine (HMM) alone and in blends with functionally substituted acrylic polymers was monitored by means of torsional braid analysis, infrared spectroscopy, weight change, and analysis of the volatile by‐products. HMM alone, when heated with a strong acid catalyst, forms thermoset condensation polymers which evidently have the same methylene‐bridged structure as conventional melamine‐formaldehyde resins; the major elimination product is methylal. When HMM is blended with an acrylic polymer containing methacrylic acid units, the acrylic chains are crosslinked by elimination of methanol and formation of methylene ester linkages between the acid groups and the melamine. The crosslinking reaction proceeds with or without strong acid catalysis and is many times faster than the self‐condensation of HMM. Acrylic polymers containing primary hydroxyl groups (derived from 2‐hydroxyethyl methacrylate) also undergo acid‐catalyzed reaction with HMM, and at a rate so much faster than analogous carboxylated polymers, that storage stability of the catalyzed resin becomes a serious problem. If a weaker catalyst, such as phthalic anhydride, is used, the curing reaction is very much slower. In order to develop the maximum number of new linkages, according to any of the experimental criteria, all of these systems must be heated for longer times, or at higher temperatures, than are customarily used in thermosetting resin technology. Thus the known utility and durability of such acrylic/melamine resins are achieved with only a fraction of the total number of crosslinks which are potentially capable of formation.