bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of rarefaction on the computation of aerodynamic parameters in hypersonic flow
Authors: Zuppardi G , Paterna D
Published: April 2003

The results from two well-known and widely accepted codes, the Navier—Stokes solver FLUENT and the direct simulation Monte Carlo (DSMC) solver DS2G, have been analysed in order to fix the levels of the flow field rarefaction where the codes can work properly for the computation of aerodynamic forces and heat flux on a spacecraft during the re-entry. This subject has already been widely investigated; thus the purpose of the present work is to provide a further contribution. In order to make realistic computations, a probable path of a typical capsule, returning from an interplanetary mission to Earth, has been considered in the altitude range 50—120 km. Proper use of FLUENT was fixed at the free-stream Knudsen number Kn∞ < 7×10−5. Attempts have been made to increase this limit, but with no success. More specifically, a finer mesh as well as a slip velocity and temperature jump were considered. Physical conditions like the lack of isotropy of the pressure tensor and the failure of the classical phenomenological equations, both increasing with the rarefaction, are very probably the causes of the failure of FLU EN T. The basic principle of the DSMC solver is valid at each rarefaction level; a sensitivity analysis on the characteristic dimension of the cell, on the time step and on the number of simulated molecules verified that the restrictions on DS2G are imposed only by the capability of the computer. As neither experimental data nor numerical results are available at the present test conditions, the evaluation of the results relies just on qualitative considerations about the trends of experimental data, reported in the literature, of a sphere in a hypersonic transitional regime.
A dynamic model of ceramic/fibre-reinforced plastic hybrid composites under projectile striking
Authors: Zhang Z , Shen J , Zhong W , Sun Z
Published: April 2003

A dynamic model of ballistic impact against ceramic/FRP (fibre-reinforced plastic) hybrid composites is presented in this paper. This model describes each status of the projectile and armour at different instants in the process of impact. Based on the Florence and low-velocity models, a three-phase impact theory is developed which forms a dynamic model. Equations are given for different impact phases to depict erosion, momentum and displacement of the projectile and target, which are then used by the computer to make calculations and simulations. Furthermore, the dynamic model has been checked to find agreement with ballistic tests. The dynamic model will be very helpful in the estimation of ballistic impact properties and optimum design of the ceramic/FRP hybrid composites.
Intra- and Intermolecular Photochemical Properties of Poly(amidoamine) Dendrons with an Anthracene at Focal Point
Authors: Fujitsuka Mamoru , Ito Osamu , Takaguchi Yutaka , Tajima Tomoyuki , Ohta Kazuchika , Motoyoshiya Jiro , Aoyama Hiromu
Published: April 2003

Photophysical and photochemical properties of poly(amidoamine) dendrons containing an anthracene at the focal point have been studied by the steady-state and transient spectroscopic methods in solution. The fluorescence lifetime of the anthracene moiety in the higher generation dendron (G3.5) is slightly shorter than that of the lower generation homologue (G0.5). On the other hand, the triplet lifetime of G3.5 is longer than that of G0.5. The bimolecular rate constants for energy transfer from the triplet states of the anthracene moiety to O2 (kO2) and for T–T annihilation (kTT) were almost the same for the anthryl dendrons, G3.5 and G0.5, suggesting that the dendron groups do not hinder the approach of O2 or the anthracene moiety. Photodimerization of G3.5 took place at a similar rate to G0.5, while the photodissociation rates of these anthracene dimers increase in the order of anthracene > G0.5 > G3.5, suggesting the presence of some attractive forces between dendron wedges.
Exploration of Thermophilic Esterases/Lipases for Asymmetric Desymmetrization of Norbornane Derivatives
Authors: Kashima Yasuhiro , Liu Jianxiu , Takenami Shigeharu , Niwayama Satomi
Published: April 2003

Asymmetric monohydrolysis of a series of norbornane derivatives by a thermophilic esterase/lipase library was examined. Three esterases/lipases showed high enantioselectivities toward dialkyl bicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylates with high chemical yields.
The puzzle-feeder as feeding enrichment for common marmosets (Callithrix jacchus): a pilot study
Authors: de Rosa C. , Vitale A. , Puopolo M.
Published: April 2003

The use of a puzzle-feeder, as feeding enrichment, was investigated in three families of captive common marmosets ( Callithrix jacchus). The study was carried out as a simultaneous choice test between two cages: one contained the puzzle-feeder, the other contained the usual food dishes, but otherwise both were arranged similarly. The monkeys were allowed to choose whether to feed from the usual dishes, or from the puzzle-feeder which required more effort. They were observed for two sessions in which they were differently motivated to feed. The enriched cage was always visited first, the marmosets managed to extract food from the puzzle-feeder, and spent more time eating from the puzzle-feeder when less hungry. These data contribute to a wider understanding on the use, and the effects, of feeding enrichments with different captive non-human primates.
Case report of a possible familial predisposition to metabolic bone disease in juvenile rhesus macaques
Authors: Wolfensohn S. E.
Published: April 2003

Deficiencies of dietary calcium and/or vitamin D will cause hypocalcaemia, leading to metabolic bone disease. The disease commonly affects young rapidly growing animals and this is a report of the condition in a colony of rhesus macaques ( Macaca mulatta). A clinical problem of metabolic bone disease was seen in 1993, when it was treated and resolved satisfactorily. However it recurred in 1999 following changes in management and husbandry of the colony, at which time the clinical manifestations were more serious. The animals had bowed tibia, fibula, radius and ulna and enlarged epiphyses, were reluctant to climb and jump, had a 'hopping' gait and poor growth. The syndrome had a multifactorial aetiology involving a combination of staff and management changes, a borderline nutritional deficit, a lack of daylight for production of vitamin D, and a possible familial predisposition.
The Importance of Organizational Structure for the Adoption of Innovations
Authors: DeCanio Stephen J. , Dibble Catherine , Amir-Atefi Keyvan
Published: April 2003

Organizational structure affects both the overall behavior of firms and the situations of individuals and subunits within firms. The effect of exogenous changes in the environment (market prices, costs, or regulations) on organizations can be partitioned into the immediate direct effect of the change and the full effect after organizational structure has had time to adjust. This paper develops a computational model of the diffusion of a profitable innovation through a firm, and uses numerical simulations to calculate the relative importance of the direct and structural adjustment components of changes in profitability. One finding is that a failure to recognize the importance of organizational structure on the performance of firms will lead to serious bias in estimation of the costs or benefits of a change in external circumstances. The type of network model developed also has implications for the individuals and divisions that make up the firm. We examine some of the structural characteristics of well-adapted organizations, and show that asymmetries and economic inequalities emerge even when the individual agents' personal characteristics are identical.
Managing the Delivery of Dialysis Therapy: A Multiclass Fluid Model Analysis
Authors: Zenios Stefanos A. , Fuloria Prashant C.
Published: April 2003

Motivatedby the exceptionally high mortality statistics of dialysis patients and the ongoing debate about the adequacy of the current reimbursement for dialysis in the United States, we pursue a detailed analysis of the dialysis delivery system. The analysis is based on a multiclass fluid model for the dialysis facility, which combines a pharmacokinetics model of dialysis and an empirically validated model of dialysis-specific mortality. Assuming that the facility operates under budget and capacity constraints, our analysis determines the main factors that affect the delivery of dialysis. Numerical results, which are representative of the dialysis environment in the US, demonstrate the accuracy of the model and provide concrete insights about the operations of the dialysis facility. A major finding is that an improvement in the technology of dialysis is likely to have a more substantial impact on the overall life expectancy of the dialysis population as compared to an increase in the dialysis reimbursement rate.
The Gas Transmission Problem Solved by an Extension of the Simplex Algorithm
Authors: De Wolf Daniel , Smeers Yves
Published: April 2003

The problem of distributing gas through a network of pipelines is formulated as a cost minimization subject to nonlinear flow-pressure relations, material balances, and pressure bounds. The solution method is based on piecewise linear approximations of the nonlinear flow-pressure relations. The approximated problem is solved by an extension of the Simplex method. The solution method is tested on real-world data and compared with alternative solution methods.
Parameter-Free Elicitation of Utility and Probability Weighting Functions
Authors: Abdellaoui Mohammed
Published: April 2003

This paper proposes a two-step method to successively elicit utility functions and decision weights under rank-dependent expected utility theory and its “more descriptive” version: cumulative prospect theory. The novelty of the method is that it is parameter-free, and thus elicits the whole individual preference functional without imposing any prior restriction. This method is used in an experimental study to elicit individual utility and probability weighting functions for monetary outcomes in the gain and loss domains. Concave utility functions are obtained for gains and convex utility functions for losses. The elicited weighting functions satisfy upper and lower subadditivity and are consistent with previous parametric estimations. The data also show that the probability weighting function for losses is more “elevated” than for gains.
Determinants of User Innovation and Innovation Sharing in a Local Market
Authors: Morrison Pamela D. , Roberts John H. , von Hippel Eric
Published: April 2003

It is known that end users of products and services sometimes innovate, and that innovations developed by users sometimes become the basis for important newcommercial products and services. It has also been argued and to some extent shown that such innovations will be found concentrated in a “lead user” segment of the user community. However, neither the characteristics of innovating users nor the scope of the community that they “lead” has been explored in depth.

In this paper, we explore the characteristics of innovation, innovators, and innovation sharing by library users of OPAC information search systems in Australia. This market has capable users, but it is nonetheless clearly a “follower” with respect to worldwide technological advance. Wefind that 26% of users in this local market nonetheless do modify their OPACs in both major and minor ways, and that OPAC manufacturers judge many of these user modifications to be of commercial interest. We find that we can distinguish modifying from nonmodifying users on the basis of a number of factors, including their “leading-edge status” and their in-house technical capabilities. We find that many innovating users freely share their innovations with others, and find that we can distinguish users that share information about their modifications from users that do not. We conclude by considering some implications of our findings for idea generation practices in marketing.
On the Determination of Subjective Probability by Choices
Authors: Karni Edi , Mongin Philippe
Published: April 2003

The paper explores the uniqueness properties of the subjective probabilities in two axiomatizations of state-dependent preferences. Karni, Schmeidler, and Vind's (KSV 1983) system depends on selecting an arbitrary auxiliary probability, and as such, does not guarantee the uniqueness of the derived subjective probability. However, an axiom system initially designed by Karni and Schmeidler (KS 1981) and further elaborated upon here does guarantee the desired uniqueness as well as a useful property of “stability” of the derived solution. When the preference relation displays state-independence, even the KS probabilities may not agree with those derived from the classic Anscombe-Aumann (AA 1963) theorem. However, we claim that, in this case, the KS rather than the AA probabilities are the appropriate representation of the agent's beliefs.
Turning Datamining into a Management Science Tool: New Algorithms and Empirical Results
Authors: Cooper Lee G. , Giuffrida Giovanni
Published: April 2003

This article develops and illustrates a new knowledge discovery algorithm tailored to the action requirements of management science applications. The challenge is to develop tactical planning forecasts at the SKU level. We use a traditional market-response model to extract information from continuous variables and use datamining techniques on the residuals to extract information from the many-valued nominal variables, such as the manufacturer or merchandise category. This combination means that a more complete array of information can be used to develop tactical planning forecasts. The method is illustrated using records of the aggregate sales during promotion events conducted by a 95-store retail chain in a single trading area. In a longitudinal cross validation, the statistical forecast (PromoCast™) predicted the exact number of cases of merchandise needed in 49% of the promotion events and was within ± one case in 82% of the events. The dataminer developed rules from an independent sample of 1.6 million observations and applied these rules to almost 460,000 promotion events in the validation process. The dataminer had sufficient confidence to make recommendations on 46% of these forecasts. In 66% of those recommendations, the dataminer indicated that the forecast should not be changed. In 96% of those promotion events where “no change” was recommended, this was the correct “action” to take. Even including these “no change” recommendations, the dataminer decreased the case error by 9% across all promotion events in which rules applied.
Executive Compensation in the Information Technology Industry
Authors: Anderson Mark C. , Banker Rajiv D. , Ravindran Sury
Published: April 2003

An innovative business practice attributed to the information technology (IT) industry is the aggressive use of employee stock options to compensate executives and other employees. In this study, we investigate whether the greater use of stock options in the IT industry can be explained on the basis of general economic relationships that apply to firms in all industries. To examine differences in compensating top executives, we estimate a system of simultaneous equations that is designed to accommodate interconnections between performance, the level of compensation, and the mix of compensation components. We document that the shares of both bonus and option pay increase with performance and that the pay level and the extent of incentive pay positively affect firm performance. We identify economic factors that may influence the use of options and show that there are significant differences in these factors between IT and other industries. We find that, while much of the greater use of options by IT firms is explained by the economic factors, significant residual differences remain. We also find that, when performance and other factors are considered, the level of executive pay in the IT industry is not higher than in other industries.
Distribution of Knowledge, Group Network Structure, and Group Performance
Authors: Rulke Diane L. , Galaskiewicz Joseph
Published: April 2003

This study investigates the effect of knowledge distribution and group structure on performance in MBA game teams. We found that group performance was contingent on the distribution of knowledge within the group and networks of social relationships among group members. Studying 39 teams of MBA students in two management simulation games, we found that, in general, groups that had broadly distributed knowledge, i.e., groups made up of members who had general knowledge, outperformed groups that had knowledge concentrated in different members, i.e., groups made up of members who had specialized or both specialized and general knowledge. However, the advantage that the former enjoyed over the latter disappeared when groups of specialists or mixed groups had decentralized network structures.
Exact and Heuristic Solutions for a Shipment Problem with Given Frequencies
Authors: Bertazzi Luca , Speranza Maria Grazia , Ukovich Walter
Published: April 2003

We consider the problem of shipping several products from an origin to a destination when a discrete set of shipping frequencies is available, in such a way that the sum of the transportation and inventory costs is minimized. This problem, which is known to be NP-hard, has applications in transportation planning and in location analysis. In this paper we derive dominance rules for the problem solutions that allow a tightening of the bounds on the problem variables and improve the efficiency of a known branch-and-bound algorithm. Moreover, we present some heuristics and compare them with two different modifications of an EOQ-type algorithm for the solution of the problem with continuous frequencies.
On Characterizations of P- and P 0-Properties in Nonsmooth Functions
Authors: Song Yoon , Gowda M. Seetharama , Ravindran G.
Published: April 2003

For a Fréchet differentiable function f from a closed rectangle Q in Rn into Rn, a result of Gale and Nikaido essentially asserts that f is a P-function on Q if the Jacobian matrix Jf(x) is a P-matrix for all x ∈ Q, and a result of Moré and Rheinboldt asserts that f is a P0-function on Q if and only if Jf(x) is a P0-matrix for all x ∈ Q. In this article, we generalize these results to nonsmooth functions that admit H-differentials. Specialized to a locally Lipschitzian function f from Rn into itself, our results say that f is a P-function if the (Clarke) generalized Jacobian ∂f(x) consists of P-matrices at all x, and when f is semismooth, f is a P0-function if and only if the Bouligand differential ∂Bf(x) consists of P0-matrices at all x.
Variational Analysis of Functionals of Poisson Processes
Authors: Molchanov Ilya , Zuyev Sergei
Published: April 2003

Let F(Π) be a functional of a (generally nonhomogeneous) Poisson process Π with intensity measure μ. Considering the expectation EμF(Π) as a functional of μ from the cone 𝕄 of positive finite measures, we derive closed form expressions for its Fréchet derivatives of all orders that generalize the perturbation analysis formulae for Poisson processes. Variational methods developed for the space 𝕄 allow us to obtain first and second order sufficient conditions for various types of constrained optimization problems for EμF. We study in detail optimization over the class of measures with a fixed total mass a and develop a technique that often allows us to obtain the asymptotic behavior of the optimal intensity measure in the high intensity setting when a grows to infinity. As a particular application we consider the problem of optimal placement of stations in the Poisson model of a two-layer telecommunication network.
Optimal Commonality in Component Design
Authors: Thonemann Ulrich W. , Brandeau Margaret L.
Published: April 2003

Increased competition and more demanding customers have forced companies to offer a wide variety of products. Component commonality can help companies reduce the cost of providing product variety to their customers. However, determining the extent to which component commonality should be used is difficult. In this paper we present an approach to determine the optimal level of component commonality for end-product components that do not differentiate models from the customer's perspective. The work was inspired by and applied to a wire-harness design problem faced by a major automobile manufacturer. We model the component design problem as a mathematical program that considers production, inventory holding, setup, and complexity costs (the cost in indirect functions caused by component variety). We develop two approaches to solve the problem: a branch-and-bound algorithm that can solve small- and medium-size problems optimally, and a simulated annealing algorithm that can solve large-size problems heuristically. We apply both algorithms to the wireharness design problem faced by the automobile manufacturer and to a number of randomly generated test problems. We show that an optimal design achieves high cost savings by using significantly fewer variants than a no-commonality design but significantly more variants than a full-commonality design. We apply sensitivity analysis to identify extreme conditions under which the no-commonality and full-commonality designs perform well, and we identify the key cost drivers for our application. Finally, we describe the impact of our analysis on the company's subsequent component design decisions.
A Tabu Search Heuristic for the Capacitated arc Routing Problem
Authors: Hertz Alain , Laporte Gilbert , Mittaz Michel
Published: April 2003

The Capacitated Arc Routing Problem arises in several contexts where streets or roads must be traversed for maintenance purposes or for the delivery of services. A tabu search is proposed for this difficult problem. On benchmark instances, it outperforms all known heuristics and often produces a proven optimum.
Optimality of Myopic Ordering Policies for Inventory Model with Stochastic Supply
Authors: Khang Do Ba , Fujiwara Okitsugu
Published: April 2003

This paper addresses a discrete time inventory model where the maximum amount of supply from which instantaneous replenishment orders can be made is a random variable. Optimal ordering policies are characterized as critical number policies with monotone increasing optimal critical values. A sufficient condition is then presented for myopic ordering policies to be optimal.
Measurement-Based Usage Charges in Communications Networks
Authors: Courcoubetis Costas , Kelly Frank , Weber Richard
Published: April 2003

We study usage-sensitive charging schemes for broadband communications networks. We argue that a connection's “effective bandwidth” is a good proxy for the quantity of network resource that the connection consumes and can be the basis for a usage charge. The determination of effective bandwidth can be problematic, however, since it involves the moment-generating function of the cell arrival process, which may be difficult to model or measure. This article describes methods of computing usage charges from simple measurements and relating these to bounds on the effective bandwidth. Thus we show that charging for usage on the basis of effective bandwidths can be approximated well by charges based on simple measurements.
Heuristics for Balancing Turbine Fans
Authors: Amiouny Samir V. , Bartholdi John J. , Vande Vate John H.
Published: April 2003

We develop heuristics for a problem that models the static balancing of turbine fans: load point masses at regularly spaced positions on the periphery of a circle so that the residual unbalance about the center—which corresponds to the axis of rotation of the fan—is as small as possible. We give worst-case guarantees for our heuristics in terms of residual unbalance. For the case of an even number of blades, we show that one of our heuristics provides the same worst-case guarantee (with respect to the ideal of perfect balance) as does total enumeration. Furthermore, computational tests show that our heuristics are orders of magnitude faster and not far from optimum on average.
Operations Research Trajectories: The Anglo-American Experience from the 1940s to the 1990s
Authors: Kirby Maurice W.
Published: April 2003

This paper is derived from the author's sponsored history of Operations Research in Britain from its formal inception in the later 1930s. It is inspired by the knowledge that any history of OR in Britain that ignores the interrelationship with OR in the United States would be grossly incomplete. This relates not only to the period of military collaboration in World War II but also to the profound influence on British operations researchers of American-derived techniques and methods. The Anglo-American perspective serves also to highlight major contrasts, as well as striking similarities in the development of OR in both countries. The paper advocates the need for ongoing research into the history of OR as an essential complement to the advancing frontier of knowledge, both in theory and in practice. Virtually all disciplines worthy of university-level study have their chroniclers, and this should apply with no less force to OR in the light of its impressive trajectory of development and early acknowledgment of its utilitarian value in a wide variety of settings in the public and private sectors.
Global Stochastic Optimization with Low-Dispersion Point Sets
Authors: Yakowitz Sidney , L'Ecuyer Pierre , Vázquez-Abad Felisa
Published: April 2003

This study concerns a generic model-free stochastic optimization problem requiring the minimization of a risk function defined on a given bounded domain in a Euclidean space. Smoothness assumptions regarding the risk function are hypothesized, and members of the underlying space of probabilities are presumed subject to a large deviation principle; however, the risk function may well be nonconvex and multimodal. A general approach to finding the risk minimizer on the basis of decision/observation pairs is proposed. It consists of repeatedly observing pairs over a collection of design points. Principles are derived for choosing the number of these design points on the basis of an observation budget, and for allocating the observations between these points in both prescheduled and adaptive settings. On the basis of these principles, large-deviation type bounds of the minimizer in terms of sample size are established.
Making Sense in Hypercompetitive Environments: A Cognitive Explanation for the Persistence of High Velocity Competition
Authors: Bogner William C. , Barr Pamela S.
Published: April 2003

This paper explores the cognitive aspects underlying industries in hypercompetitive environments. Hypercompetition represents a state of competition with rapidly escalating levels of competition and reduced periods of competitive advantage for firms. In hypercompetitive industries member firms act boldly and aggressively to create a state of competitive disequilibrium. In this paper we explore the particular conditions that managers encounter in making sense of hypercompetitive industries and argue that the nature of these conditions is such that conventional sensemaking frameworks will not work. We then describe the “adaptive sensemaking” practices established in the literature for dealing with temporary turbulence and suggest that in hypercompetition those processes continue indefinitely. We argue that these processes can become institutionalized as standard operating procedures within firms, and as shared recipes within industries, which in turn perpetuates hyperturbulent conditions.
Biocultural aspects of obesity in young Mexican schoolchildren
Authors: Brewis Alexandra
Published: April 2003

Obesity related to over‐nutrition is investigated in a sample of 219 Mexican children from affluent families, ages 6–12 years. Defined as weight‐for‐age at or above the 95thpercentile, obesity rates in middle childhood are very high in this population, being 24.2% of children (29.4% of boys and 19.1% of girls). Binary logistic regression shows that children are more likely to be obese if they are boys, from small households with few or no other children, and have more permissive, less authoritarian parents. Diet at school and activity patterns, including television viewing, are not different for boys and girls and so do not explain this gender variation. The value placed on children, especially sons, in smaller middle‐class families, can result in indulgent feeding because food treats are a cultural index of parental caring. Parents also value child fatness as a sign of health. These obese Mexican children have no greater social problems (peer rejection or stigma) or psychological problems (anxiety, depression, or low self esteem) than their non‐obese peers. More study specifically focused on feeding practices in the home environment is required to explain very high rates of child obesity. The differences in obesity risk related to specific aspects of children's developmental microniche emphasize the importance of including a focus on gender as a socio‐ecological construct in human biological studies of child growth, development, and nutrition. Am. J. Hum. Biol. 15:446–460, 2003. © 2003 Wiley‐Liss, Inc.
Biological effects of asbestos: New York Academy of Sciences 1964
Authors: Greenberg Morris
Published: April 2003

Background

In 1964, the New York Academy of Sciences held a conference on asbestos that was to promote the slow decline in the fortunes of asbestos. It brought together a Who's Who of international scientists who had conducted and reported on experimental and human studies of the effects of asbestos. Very little new data were presented at the conference, but by bringing together a compendium of knowledge of the adverse effects of asbestos, it served further notice to asbestos‐using industry of the major public health problem that they had created. With the assistance of its employees and certain scientists, industry mounted public relations exercises to counter the adverse publicity of lung cancer and malignant mesothelioma. Attempts were made to minimize the impact of these diseases by suggesting that their alleged associations with asbestos were spurious, and by diversionary ad hominem attacks on Professor Irving J. Selikoff who had played an important role in the organization of the conference.

Methods

Consideration of the contents of the meeting program, other previously published information and documents revealed through legal discovery by Chase Manhattan Bank provide the sources on which this paper is based.

Conclusions

Today, asbestos is no longer seen as a material indispensable on technical grounds and a mainstay of industry and the economy. Its progressive banning in developed countries may be seen as the consequence of the momentum initiated in New York in 1964. Am. J. Ind. Med. 43:543–552, 2003. © 2003 Wiley‐Liss, Inc.
Thermally stable high molecular weight polyoxymethylenes
Authors: Schweitzer C. E. , Macdonald R. N. , Punderson J. O.
Published: April 2003

In this, the first of a series of five papers, the historical development of formaldehyde polymers, beginning with the work of Butlerov and continuing through the investigations of Staudinger and his collaborators, is reviewed. Recent studies in these laboratories have led to thermally stable high polymers of formaldehyde. Initiators and the role of impurities in the polymerization are described. An explanation is offered to account for differences in thermal stabilities between old and new polymers. Esterification, by which further increases in thermal stability are achieved, is described. It is proposed that the generic term “acetal resin” be used to described high polymers that are composed of repeating oxymethylene units.
The ball‐milling of cellulose fibers and recrystallization effects
Authors: Howsmon J. A. , Marchessault R. H.
Published: April 2003

A study has been made of the effect of fine structure on the decrystallization process which results from the ball‐milling of cellulose. The rate of decrystallization is sensitive to the type of fine structure and is accelerated by the presence of moisture. The extent of chain degradation was greater in air atmosphere than in carbon dioxide, suggesting that mechanically induced free radical degradation occurs along with other chain‐breaking processes. A study of the density and moisture regain of the samples after various times of milling showed that a linear relation between regain and density held over the entire range studied. The relation was the same for native and regenerated cellulose. The process of recrystallization of the ball‐milled samples was studied under various conditions and compared to the hydrolytically induced recrystallization of rayons. The type of lattice which develops on recrystallization was found to depend on the original lattice, the extent of ball‐milling and the conditions of recrystallization. A highly ball‐milled sample could be made to recrystallize as cellulose I, II, or IV depending on the conditions.
Infrared study of polypropylene
Authors: Luongo J. P.
Published: April 2003

The structural configurations that distinguish the atactic phase from the isotactic phase give rise to infrared spectra characteristic of each phase. Since these differences are quite significant, a method is proposed with which the isotacticity can be determined. The relation between the isotactic phase and crystallinity is considered, and its application to this study is discussed. The formation of oxygen‐containing degradation products was followed during accelerated oxidation and the products identified. There is also evidence that more numerous oxygen containing degradation products form in polypropylene than in polyethylene. The type of unsaturation was also determined, and its presence confirmed by chlorination.
Condensation of poly(4‐vinylacetophenone) with various araldehydes
Authors: Unruh C. C. , Smith A. C.
Published: April 2003

The preparation of condensation products of poly(4‐vinyl‐acetophenone) with various substituted benzaldehydes is described. As in the case of the products obtained by condensing the poly(4‐vinylacetophenone) with benzaldehyde, these, too, show to varying degrees the property of becoming insoluble when exposed to light. This sensitivity to light is generally higher where the aldehyde used contains electrondonating substituent groups in the para‐position. This, in turn, is also related to the ability of such products to absorb a larger proportion of the longer wavelength portion of the emitted light.
Compounding rubber for radiation resistance
Authors: Anderson Herbert R.
Published: April 2003

Compounding techniques to improve the radiation resistance of butadiene‐styrene tread vulcanizates in a radiation field are described. These include extension of rubber with an aromatic oil, incomplete curing of stocks containing sulfur vulcanization agents, and incorporation of additives. Incomplete curing produces vulcanization intermediates, which are affected by the ratio of sulfur to accelerator and by cure temperature and which are resistant to radiation. A combination of all these factors improved the lifetime of cold‐rubber tread vulcanizates by a factor of 5 to 6. Swelling and stress‐relaxation techniques are applied to follow quantitatively changes in the polymeric network, which are used to explain changes in stress‐strain properties. These techniques indicate that much of the scission that occurs is more than compensated for by crosslinking. Dilution of the polymer network with an aromatic oil decreases the ratio of crosslinking to scission to produce a more radiation‐resistant material. In the absence of oil, the decrease in radiation damage obtained by incomplete curing and with antirads is primarily the retardation of the crosslinking reaction. However, in the presence of oil, incomplete curing promotes and antirads retard radiation‐induced crosslinking and scission about equally. Substitution of air for helium as an irradiation atmosphere serves to accentuate the scission reaction and to lessen radiation‐induced changes in physical properties. A number of previously unreported retarders of radiation damage (antirads) are described.
X‐ray diffraction by hairs and feathers. Part II
Authors: Venkateswarlu K. , Pillai S. Padmanabha
Published: April 2003

The tail hairs of various mammals were subjected to different chemical treatments for different times and their x‐ray diffraction photographs obtained. The powder rings recorded in the case of buffalo hair disappeared after the fiber was treated in acetic or formic acid for 48 hr. On the other hand, inorganic salt solutions were practically inert.
Creep studies on gelatin at 100% relative humidity
Authors: Eliassaf J. , Eirich F. R.
Published: April 2003

The creep behavior of gelatin films was studied at 100% R. H. Under a given load the films either extend to an equilibrium length or break. Equilibrium stress–strain curves were obtained at 26.5, 31.5, 36.5, and 46.5°C. At 26.5°C., gelatin films exhibit essentially rubberlike behavior; at the higher temperatures they become stiffer. The films are brittle at 46.5°C. This course of behavior is explained by a decrease in uptake of moisture from the surrounding atmosphere with increasing temperature. At 26.5°C., enough water is absorbed (27%) to plasticize the gelatin, whereas the reduced amount absorbed at 46.5°C. (15%) is insufficient to modify the glass‐like behavior of dry gelatin. These results indicate that poor performance of gelatin used as glue under hot and humid conditions is not due to a deliquescent behavior; the latter occurs only on direct contact of gelatin with liquid water.
The strain dependence of rubber viscoelasticity. Part II. The influence of carbon black
Authors: Mason P.
Published: April 2003

Elastic and viscous components of the dynamic Young's modulus were measured at strains up to 80% and over a temperature range of −30°C. to +30°C. for natural rubber containing 18% by volume of carbon black. These components were derived from the velocity and attenuation of 1 kcycle/sec. longitudinal waves in stretched filaments. Two types of carbon black were examined, with mean particle diameters of about 0.4 microns (MT black) and 0.04 microns (HAF black). It was possible to represent the strain dependence of the modulus components of the MT‐filled material by the linear relations previously developed for the gum rubber; division by a volume loading factor derived from the Guth‐Simha‐Gold equation gave close agreement with the corresponding values for the gum at the same strain and temperature. The strain dependence of the HAF‐filled rubber was analyzed with reference to the equilibrium modulus‐extension curve. This material showed increases in modulus components much greater than indicated by the volume loading factor and the temperature coefficients of these components were much less than for the gum rubber. The glass‐transition temperature of −65.7°C. for the gum rubber was not significantly affected by the presence of either carbon black.
Instrumentation and machines for dynamic tests
Authors: Scheetz Howard A. , Koh Severino L. , Brennan J. Norton
Published: April 2003

It has been shown that use of wide‐band instrumentation in dynamic mechanical measurements can reveal the presence of high‐frequency ringing and other mechanical defects in the wave form. The use of low‐pass filters to suppress electrical noise can hide such defects. It is therefore better to eliminate the electrical noise at the source. If the mechanical irregularities in the waveform are not tolerable, they must be removed by improving the design of the testing device. The drop tester described in this report illustrates one possible way in which this may be done.
Defects present within adhesive layers
Authors: Tarkow Harold
Published: April 2003

A technique is described for liberating the adhesive layer from adhesive‐bonded aluminum panels. Procedures are described for demonstrating directly the presence of defects within adhesive layers. The presence of a variety of types of defects is undoubtedly responsible for the inability to develop a general nondestructive test for evaluating adhesivebonded panels.
Some mechanical and optical properties of CFN polymers
Authors: Kawai H. , Stein R. S.
Published: April 2003

Mechanical and optical studies have been carried out on high temperature fluorinated triazine‐derived elastomers. These behave as crosslinked rubbers, having low ultimate elongations and tensile strengths and showing a tendency toward development of a crystallike order.
Unsaturation in irradiated marlex 50 polyethylene: Dose rate and post‐irradiation effects
Authors: Fydelor P. J. , Pearson R. W.
Published: April 2003

Infrared absorption spectroscopy has been used to demonstrate dose rate dependence of trans‐vinylene unsaturation in irradiated Marlex 50 polyethylene. When the irradiated polymer is stored in vacuum a decrease is observed in trans‐vinylene absorbance over a period of several weeks. After high dose rate irradiation the decay is preceded by an initial increase. These phenomena are ascribed to the reaction of “trapped” radicals.
Poly(4‐methyl‐1‐pentene) and some soluble crystalline copolymers
Authors: Campbell Tod W.
Published: April 2003

Poly(4‐methyl‐1‐pentene) has been prepared by polymerizing the monomer over a catalyst made from titanium tetrachloride and lithium aluminum tetradecyl. The molecular weight of the crystalline polymer was invariably too high for fiber preparation, even when polymerization variables were varied drastically, so a technique for thermal cracking was developed. By heating grease‐free, crystalline poly(4‐methyl‐1‐pentene) in a vacuum at about 280°, it was possible to lower smoothly the molecular weight of the polymer to any desired value, without undesirable crosslinking or by‐product formation. The polymer was melt‐spun by conventional techniques to highly oriented, tough fibers. Copolymerization of 10–25% 1‐hexene and other linear 1‐olefins with 4‐methyl‐1‐pentene gives products which are still high‐melting, but which are readily soluble in such solvents as cyclohexane or chloroform, in contrast to the homopolymer which is only slightly soluble. Polymerization in solvents for the copolymer gave solutions which were converted to fibers and film without intermediate isolation of polymer or removal of the catalyst. An interesting terpolymer in which divinylbenzene was the third component was found to be initially soluble, but was readily crosslinked at elevated temperature.
Isobutylene copolymers of vinylbenzyl chloride and isopropenylbenzyl chloride
Authors: Jones Giffin D. , Runyon James R. , Ong Josephine
Published: April 2003

The styrene derivatives vinylbenzyl chloride and isopropenylbenzyl chloride were prepared and copolymerized with isobutylene and propylene in order to produce polymers with reactive halogens. Vinylbenzyl chloride and isobutylene have relative reactivities such that the copolymer is much richer in isobutylene than the starting mixture, while with isopropenylbenzyl chloride and isobutylene the difference in reactivities is less and is in the opposite direction. Copolymers containing small amounts of the reactive benzylic chlorine were vulcanized, either with amines or with a conventional butyl rubber cure. Permselective membranes were prepared from copolymers rich in benzylic chlorine.
Nonaqueous fluid xanthation of alkali cellulose
Authors: McDermott D. E.
Published: April 2003

Xanthation can be accomplished by slurrying the alkali cellulose in an organic liquid chosen to be miscible with carbon disulfide, immiscible with water, and a nonsolvent for sodium hydroxide, alkali cellulose, cellulose xanthate, and other components of viscose. Straight‐chain hydrocarbons, such as n‐hexane and n‐heptane, satisfy these requirements and function very well. A viscose preparation system using this method of xanthation would consist of a slurry step wherein the alkali cellulose and carbon disulfide are reacted in the selected organic liquid, a filtering step to remove the xanthate from the liquid, and a mixing operation to dissolve the xanthate in weak alkali to produce viscose. Because of the near‐perfect distribution of carbon disulfide throughout the reaction, this method of xanthation produces filterable viscoses a t very low degree of substitution. It is also possible to produce viscose of identical composition at widely different process conditions by various combinations of temperature, reaction time, and carbon disulfide concentration.
The resilience of chemically modified cottons. II. Reactions of cellulose with formaldehyde under acid conditions
Authors: Dusenbury J. H. , Pacsu E. , Teulings E. P. , Lobunez W.
Published: April 2003

A study has been made of the reactions of cellulose with formaldehyde under acid conditions, where the fabrics are baked at elevated temperature. These treatments have involved cotton cellulose in a “dry” or relatively unswollen state and have resulted in the treated fabrics exhibiting improved crease rccovery both dry and wet. It has been found that boiling 1% acetic acid solution reduces the acetal contents of the treated fabrics and causes corresponding decreases in both dry and wet crease‐recovery improvement. The reproducibility of these treatments, with respect both to extents of formaldehyde incorporation and to dry and wet crease recovery, is found to be very good within a single treatment and, more importantly, tietween different treatments carried out under the same conditions. The rates of acetal removal by the boiling 1% acetic acid and the relationships between acetal content and crease‐recovery improvement have been found to be fairly complex. A study has also been made of the rates of acetal removal by boiling 1% acetic acid for samples of cotton card sliver treated with acid and subsequently heated in sealed tubes with paraformaldehyde. The rates of acetal removal in this case have been observed to be qualitatively similar to those observed for treated fabrics. The implications of these findings are discussed.
Treatment of teflon to promote bondability
Authors: Benderly Asaf A.
Published: April 2003

Various methods are reviewed whereby Teflon and other polyfluorocarbon resins can be surface treated in order to enhance their bondability with ordinary adhesives. The features of these methods are compared and some conclusions are drawn as to their relative usefulness. Particular emphasis is placed on the sodium‐naphthalene‐tetrahydrofuran treatment system and reference is made to a few military applications wherein sodium‐treated Teflon has been employed.