bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphological studies of liquid‐crystalline cellulose derivatives. I. Liquid‐crystalline characteristics of hydroxypropyl cellulose in 2‐hydroxyethyl methacrylate solutions and in polymer composites prepared by bulk polymerization
Authors: Nishio Y. , Yamane T. , Takahashi T.
Published: April 2003

The formation of liquid‐crystalline structure in hydroxypropyl cellulose (HPC) in the solvent 2‐hydroxyethyl methacrylate (HEMA) is described. In addition, an attempt is made to preserve the ordered structure of HPC in a composite by polymerizing the solvent. Optical evidence, including refractive index, absorption spectra, polarized‐light microscopy, and x‐ray diffraction, indicates that HPC‐HEMA solutions exhibit the cholesteric nature of the mesophase over limited concentration and temperature ranges. The polymer composite (HPC‐PHEMA) prepared from the liquid‐crystalline solution by polymerization of HEMA is endowed with anisotropic organization reflecting liquid‐crystalline character. Detailed morphological observations of the composite by electron microscopy show many round particles composed of parallel‐stacked, disklike lamellae, and aggregate bodies developed by coalescence of neighboring particles.
Simultaneous differential scanning calorimetry and small‐angle x‐ray scattering
Authors: Russell T. P. , Koberstein J. T.
Published: April 2003

A method is described for performing simultaneous measurements of small‐angle x‐ray scattering and differential scanning calorimetry. The experiment is made possible through a combination of the high flux afforded by the storage ring at the Stanford Synchrotron Radiation Laboratory, a linear position‐sensitive detector with rapid response time, and a differential scanning calorimeter developed for optical microscopy. The feasibility of the technique is illustrated by examining the melting and crystallization of a polyethylene specimen. This example demonstrates the power of the technique and the accuracy and reliability of the scattering and thermal data.
Dilute‐solution properties of ring polystyrenes
Authors: Roovers J.
Published: April 2003

The temperature ΘA2 at which the second virial coefficient A2 is zero for ring polystyrenes is 28.5°C in cyclohexane, independent of molecular weight in the range 2 × 104 to 4.5 × 105. This cannot be explained solely by the Candau–Rempp–Benoit theory, which takes into account the effect of segment density on ΘA2 The radius of gyration of a ring is found to be approximately one‐half that of a linear polymer with the same molecular weight. The intrinsic viscosities [η] and intrinsic translational friction coefficients [f] of ring polystyrenes with molecular weights ranging from 7 × 103 to 4.5 × 105 have been measured in cyclohexane at 34.5°C (Θ, the Flory theta temperature for linear polystyrenes) and in toluene (a good solvent). The results are compared with those for linear polystyrene. It is found that the Mark–Houwink exponent is less than one‐half in cyclohexane at Θ. In toluene it is 0.67 compared to 0.73 for linear polystyrene. The hydrodynamic measurements suggest that large rings are less expanded than the linear polymers with the same molecular weight, contrary to many predictions.
The influence of tetraalkylammonium counterions on the conformational transition of an alternating copolymer of maleic acid and n‐butyl vinyl ether in aqueous solutions
Authors: Shimizu Toshio , Kwak Jan C. T. , Minakata Akira
Published: April 2003

pH titration curves for the neutralization of an alternating co‐polymer of maleic acid and n‐butylvinylether (MAnBVE) with tetrabutylammoniumhydroxide (TBAOH) are reported, and compared to the case of neutralization with NaOH or tetraethylammoniumhydroxide (TEAOH). With TBA+ counterions the compact form of the polymer is stabilized, remaining the preferred form up to higher net charge densities. This tendency is enhanced at higher temperature. Free energy changes of the conformational transition are higher for TBA+ than for TEA+ or Na+ as counterions.
The effect of heating rate on the melting of polytetrafluoroethylene
Authors: Starkweather Howard W.
Published: April 2003

When virgin polytetrafluoroethylene is heated at intermediate rates, two melting peaks are observed. As the heating rate is increased, the higher‐temperature peak grows at the expense of the lower‐temperature one without any significant change in the total heat of fusion. It is suggested that the higher‐temperature peak represents a transition to a strained melt which subsequently changes to the more stable equilibrium melt. After recrystallization from the melt, there is only a single melting peak which occurs at a lower temperature than peaks for the virgin polymer. All of these transitions are subject to superheating.
The determination of longitudinal crystal moduli in polymers by spectroscopic methods
Authors: Fanconi Bruno , Rabolt John F.
Published: April 2003

Experimental methods for determining longitudinal crystal moduli of polymers were evaluated in light of recent proceesing methods that produced macroscopic Young's moduli which exceeded ultimate values as found by the x‐ray diffraction method. The spectroscopic techniques of Raman and coherent inelastic neutron scattering yielded higher longitudinal crystal moduli than x‐ray diffraction, and from calculations described herein it is concluded that these spectroscopic values are better estimates of the maximum Young's moduli in fully aligned and crystalline polymeric materials.
Corrections to calculations of the radius of gyration of polydisperse gaussian coils when scattering measurements at low angle are missing
Authors: Ullman Robert
Published: April 2003

The initial slopes and intercepts of Zimm plots of scattering experiments yield the centroidal radius of gyration of the scattering particle. In many cases, it is not possible to measure at sufficiently low angle to obtain accurate initial slopes and intercepts. Errors for missing data can be corrected by using calculated scattering functions as models. Such corrections are given here for polydisperse Gaussian coils.
Concentration distribution of elements in heterogeneous polymer systems determined by electron microprobe analysis
Authors: Popova E. D. , Avdeev N. N. , Chalych A. E.
Published: April 2003

A technique for analysis of composition variations in heterogeneous polymer systems permits investigation of materials with both uniform and nonuniform distribution of heterostructural components. To illustrate the method, determinations have been made of concentration profiles of dibromo‐diallyl‐phthalate formed in porous PVC in two different ways.
Model calculation of the thermal conductivity of polymer crystals
Authors: Choy C. L. , Wong S. P. , Young K.
Published: April 2003

A linear lattice model without adjustable parameters provides an accurate description of the magnitude and temperature dependence of the thermal conductivity of Kc of polyethylene crystals parallel (∥) and perpendicular (⟂) to the chain direction. The model shows that heat is transported principally by phonons polarized transverse (T) to the chain direction. Phonons polarized longitudinal (L) to the chain direction contribute about 20% to the heat transport along the chain direction, and negligibly to heat transport perpendicular to the chain direction. Thermal resistance is caused by LTT three‐phonon umklapp scattering in the parallel direction, and by TTT scattering in the perpendicular direction. The calculated values for large crystals are K = 465 W m−1 K−1, K = 0.16 W m−1 K−1 at 300 K, in agreement with experimental estimates and implying an anisotropy ratio of K/K ≈ 3000. The axial thermal conductivity of polyethylene crystals is extremely high and comparable to that of copper. Comparison with experimental data on semicrystalline samples at lower temperature yields a crude value of mean free path for boundary scattering of about 50 nm, agreeing in order of magnitude with the size of crystalline blocks.
Analysis of the effect of electrical conductance of ferroelectric polymers on D‐E hysteresis curves measured by the sawyer–tower method
Authors: Ikeda Susumu , Kobayashi Shin'ichi , Wada Yasaku
Published: April 2003

The D‐E (electric displacement vs. field) hysteresis curve of a ferroelectric polymer is conventionally measured by the Sawyer–Tower method. The effect of the electrical conductance of the polymer on the measured hysteresis curve is theoretically analyzed and a new method is proposed for elimination of the error arising from the conductance. Examples of original and corrected hysteresis curves of vinylidene fluoride–trifluoroethylene copolymer are presented.
Rough‐surface crystallization: Some applications to poly(ethylene oxide)
Authors: Sadler D. M.
Published: April 2003

A model incorporating a rough (disordered) crystal growth surface is capable of treating many of the observations and measurements on the crystal growth of short chains of poly(ethylene oxide) from the melt. A simple preliminary treatment if presented which aims primarily to analyze the growth rate data within one growth “branch,” i.e., for a regime in which crystal thickness is approximately constant. Under these conditions the growth rate is approximately linear with crystallization temperature, as expected for rough growth surfaces, but not for smooth (faceted) ones. Simulation results are included which are in agreement with a simple equation and with experiment. The analysis enables the growth rates for different branches to be compared in a systematic way. A very steep decrease in growth rate with increasing crystal thickness is clearly illustrated, together with some influence of molecular weight. The general trend for chain folding can be seen as a consequence of this steep decrease. Parallel work on systems in which crystal thicknesses vary continuously with crystallization temperature led to the realization that “rounding off” will occur at the crystal perimeter and that this will give rise to an entropic barrier for the crystal advance. This argument is presented in the context of extended‐chain and once‐folded crystallization, from which it is clear that growth rates should be much lower as crystal thicknesses increase, and for folded‐chain as compared with extended‐chain crystals. Different morphologies are interpreted in terms of changes in surface structure which are probably due to kinetic as well as equilibrium effects.
Wetting properties of polyacetylene films
Authors: Schonhorn H. , Baker G. L. , Bates F. S.
Published: April 2003

The wetting characteristics of free‐standing polyacetylene films were determined by using a standard series of wetting liquids. As‐prepared films of cis‐polyacetylene were found to contain a significant polar contribution to the surface free energy, which became nearly entirely dispersive upon thermal isomerization to the trans form. Both isomeric forms are characterized by a critical surface tension of wetting γc ≈ 51 mN/m, which is considerably higher than that normally obtained from organic polymers. These results have been interpreted with respect to surface oxidation and tested by examining an oxidized film.
Crystallization behavior of poly(3,3‐bisethoxymethyl oxetane) and poly(3,3‐bisazidomethyl oxetane)
Authors: Hardenstine K. E. , Henderson G. V. S. , Sperling L. H. , Murphy C. J. , Manser G. E.
Published: April 2003

Two crystal modifications have been found for poly(3,3‐bisethoxymethyl oxetane) [poly‐ (BEMO)] by wide‐angle x‐ray powder diffraction and differential scanning calorimetry, while only one modification has been found for poly(3,3‐bisazidomethyl oxetane) [poly(BAMO)]. Melting temperatures for the two polymers were nearly the same, varying from about 70 to about 90°C depending on the thermal treatment; higher crystallization temperatures resulted in higher melting temperatures. The equilibrium melting temperature T was found to be 125 and 128°C for poly(BEMO) and poly(BAMO), respectively, by using the Hoffman‐Weeks extrapolation procedure. Measurement of the melting‐point depression of Poly(BEMO) and poly(BAMO) in dibutyl phthalate yielded enthalpy of fusion values of 2.25 and 12.8 kcal/mol, respectively. The percent crystallinity for poly(BEMO) and poly(BAMO), respectively, was calculated to be 55‐60 and 13‐30% based on DSC and x‐ray analysis.
The superposition of small deformations on large deformations: Measurements of the incremental relaxation modulus for a polyisobutylene solution
Authors: McKenna G. B. , Zapas L. J.
Published: April 2003

The incremental relaxation modulus ΔG(t) for a concentrated solution of polyisobutylene has been determined from step‐shear experiments in which a small deformation Δγ was superimposed on a large deformation γ1; ΔG(t) was found to decrease with increasing γ1 and to increase with the time te after the imposition of the large deformation. It was also observed that the “apparent relaxation specturm” associated with δG(t) narrows and shifts to shorter times when compared to the spectrum associated with the linear viscoelastic relaxation modulus G(t). The results are well described by the nonlinear constitutive equation of the BKZ elastic fluid theory.
Study of spin–lattice relaxation and local motion in dissolved poly[2,2‐propanediylbis(3,5‐dimethyl‐4, hydroxyphenyl)carbonate]
Authors: Roy Ajoy K. , Jones Alan Anthony
Published: April 2003

Proton and carbon‐13 spin–lattice relaxation times are reported for 10‐wt % solutions of tetramethyl bisphenol‐A polycarbonate. The relaxation times for both nuclei were measured at two Larmor frequencies and as a function of temperature. These relaxation times are interpreted in terms of three motions: segmental motion, restricted rotational diffusion, and backbone methyl‐group rotation. The Hall–Helfand correlation function is used to describe the segmental motion. Internal rotation is described by the usual Woessner approach and restricted anisotropic rotational diffusion by the Gronski approach. As demonstrated by its higher activation energy, correlated segmental motion appears to be slower than the unsubstituted polycarbonate of BPA. In addition, the single‐transition processes seem to be still less important than correlated backbone transitions. Phenylene‐group rotation is described in terms of restricted rotational diffusion instead of complete anisotropic rotation. The time scale for backbone methyl‐group rotation is comparable to that in BPA, a fact indicative of weaker cooperativity between this motion and the other motions. Rotation of the methyl group attached to the phenylene ring is too fast to significantly contribute to relaxation except by partially averaging the dipole–dipole interactions. The higher activation energies for segmental motion observed in solution for this methyl‐substituted polycarbonate relative to the unsubstituted polycarbonate parallel a significant increase in the glass transition temperature observed for the substituted material. The restricted pheylene‐group rotation in solution is also parallelled by a large upward shift of the low‐temperature loss peak in the glassy polymer.
The role of molecular diffusion in the adhesion of EPDM and EPR elastomers
Authors: Ellul M. D. , Gent A. N.
Published: April 2003

Adhesion of lightly crosslinked sheets of EPDM (ethylene–propylene–diene terpolymer) to themselves and to a Mylar substrate has been investigated over wide ranges of peel rate and test temperature. The effect of incorporating ethylene–propylene copolymer (EPR) before crosslinking, to yield a loose macromolecular network containing dissolved linear EPR macromolecules, was also studied. The self‐adhesion of these materials was found to be much greater than their adhesion to Mylar, over a wide range of effective peel rates. This is attributed to interdiffusion of EPR and EPDM molecular strands. At extremely low peel rates the enhancement of adhesion was smaller, probably because of back‐diffusion, and at high rates, the strength of adhesion became high in all cases. These results are compared to those obtained previously for polyisobutylene‐co‐ isoprene networks containing linear polyisobutylene molecules. The enhancement of self‐adhesion at intermediate rates of peel was considerably greater for the EPDM‐based materials, probably because of a lower degree of crosslinking and a greater tendency to form molecular entanglements.
A SAXS study of a single crack and craze in plasticized polystyrene
Authors: Brown H. R. , Mills P. J. , Kramer E. J.
Published: April 2003

Small‐angle x‐ray scattering (SAXS) was used to study the structure along a single craze that had broken down to form a crack along part of its length. This study was made possible by use of radiation from the synchrotron source CHESS which is sufficiently intense to permit examination of just a single craze. The total scattering from the craze was in excellent agreement with that expected from a knowledge of its dimensions and fibril volume fraction and width. This fact adds confidence to the interpretation of the scattering pattern of the craze as part diffraction, part reflection, and demonstrates that SAXS is a technique that may be used to measure craze volume within a sample. The craze was shown to grow in width by surface drawing with a constant structure, and then the fibrils broke to form a crack. The broken fibrils contracted and their diameters increased but they appeared to stay parallel with a constant fibril‐axis radial distribution function.
The structure of MDI/BDO‐based polyurethanes: Diffraction studies on model compounds and oriented thin films
Authors: Briber Robert M. , Thomas Edwin L.
Published: April 2003

Polyurethanes based on MDI/BDO are known to crystallize in three distinct forms. Two of these crystal structures, type II and type III, have been characterized by electron and x‐ray diffraction experiments on model compounds and oriented thin films of a 77% hard‐segment polyurethane elastomer. The model compounds were of the form BDO(MDI/BDO)n with n = 1, 2, 3. Results from the model compounds indicate that the MDI/BDO repeat crystallizes in the type‐II structure, which has a contracted conformation with a monomer repeat length of 1.70 nm. MDI/BDO‐based polyurethanes also exhibit the type‐II structure under quiescent crystallization conditions. Studies of oriented thin films of an MDI/BDO‐based polyurethane indicate that a change in crystal form occurs on stretching to the fully extended monomer conformation. This crystal form is termed type III and has a monomer repeat length of 1.92 nm.
Thermal and mechanical properties of short‐segment block copolyesters and copolyether–esters
Authors: Castles Janis L. , Vallance Michael A. , McKenna J. Michael , Cooper Stuart L.
Published: April 2003

The effects of chain structure and processing variables on the microstructure and linear viscoelastic behavior of a series of copolyether–ester block polymers are described. In addition, the random copolyester analogs of the hard block are examined. The ester segments are composed of two isomers, poly(tetramethylene terephthalate) (PTMT) and poly(tetramethylene isophthalate) (PTMI), which possess significantly different crystallization kinetics. The ratio of PTMT to PTMI in the series has been systematically varied to alter the crystallizability without changing the chemical composition. The results of differential scanning calorimetry, wide‐angle x‐ray diffraction, and dynamic mechanical characterization are presented. Copolymerization of a second ester shortens the average sequence length of the first ester, resulting in melting‐point depression for crystals of the first polyester and substantial lowering of the dynamic mechanical storage modulus above the glass transition of the intercrystalline phase. The melting‐point depression may be predicted by using Flory's model for random copolymers, but the calculated heats of fusion are significantly lower than those obtained from diluent melting‐point depression.
Relation of internal rotational isomerism barriers to the flow activation energy of entangled polymer melts in the high‐temperature Arrhenius region
Authors: Ngai K. L. , Plazek D. J.
Published: April 2003

A strong correlation between internal rotational isomerism barriers and the flow activation energy of entangled polymer melts in the high‐temperature Arrhenius region is observed. This correlation is predicted by a coupling model but is not expected by any other model that we are aware of.
Polymerization of furil in the solid state by reaction with AsF5 at the solid–gas interface
Authors: Burzynski Ryszard , Prasad Paras N.
Published: April 2003

Solid‐state polymerization of furil, induced by reaction with AsF5 at the solid–gas interface, has been investigated by means of vibrational analysis of the reactant and the product. Infrared spectra are consistent with the mode of Polymerization which involves an α,α′ linkage and subsequent loss of hydrogen atoms. The C/H elemental analysis suggests that the polymer consists of around six or seven monomeric units. The reaction product is found to be unstable at high temperatures; a prolonged annealing at this temperature leads to a different structure, possibly, by the opening of the furan rings. The x‐ray powder diffraction study shows that the polymeric furil is crystalline, with a lattice similar to that of the monomer, but contains a considerable amount of disorder.
Spectroscopic studies of polymerized surfactants: 1,2‐bis(10,12‐tricosadiynoyl)‐sn‐glycero‐3‐phosphocholine
Authors: Schoen Paul E. , Yager Paul
Published: April 2003

Spectroscopic studies have been performed on aqueous dispersions of the surfactant 1,2‐bis(10,12‐tricosadiynoyl)‐sn‐glycero‐3‐phosphocholine before and after polymerization with ul‐traviolet light. Monomers of this lipid can, under certain conditions, convert from the expected spherical liposomal form to a unique phase consisting of hollow tubules. To determine the molecular conformation of these structures we have used Raman and infrared spectroscopies to probe the structure of the hydrocarbon chains and head groups of the lipids, and used absorption spectroscopy and resonance enhanced Raman scattering of the colored polymer to monitor the length and structure of the diacetylenic polymer backbone. Unusual CH stretch‐ing Raman bands imply that the hydrocarbon chain packing in the monomeric bilayers is different from that observed in other phosphatidylcholines, and that a distrubance in alkyl chain packing occurs on polymerization. Depending on irradiation conditions and the dispersal state of the lipid the polymer chains may be of at least three different colors, from which distinct resonance Raman spectra are obtained. The effective bond conjugation lengths range from quite short in the yellow polymer produced in sonicated vesicles to extremely long in a blue component seen in polymerized tubules.
Cyclization of methacrylate–functional silane on particulate clay
Authors: Ishida Hatsuo , Miller James D.
Published: April 2003

Physically absorbed γ‐methacryloxypropyltrimethoxysilane (γ‐MPS) deposited from aqueous alcohol on particulate clay exists as low‐molecular‐weight cyclic, caged polysilsesquioxanes. These structures are incapable of forming high‐molecular‐weight chains or networks because of this internal cyclization tendency. The behavior is extremely different from that found in bulk solutions or when organofunctional silanes are adsorbed on low‐surface‐area glass or metal substrates. Fourier‐transform infrared spectroscopy and gel permeation chromatography were used to characterize the silane species deposited in bulk and on the surface of particulate clay. The cyclization tendency is postulated from analysis of the behavior of hydrolyzed γ‐methacryloxypropyltrimethoxysilane upon cocondensation with other organofunctional silanes and under variable cure conditions.
Application of a new structural theory to polymers. I. Uniaxial stress in crosslinked rubbers
Authors: Lee Michael C. H. , Williams Michael C.
Published: April 2003

A continuum rheological theory, endowed with generalized structural significance, has recently been developed. Based on nonequilibrium thermodynamics, it relates stress σ, strain rate \documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon$\end{document} and temperature in terms of material evolution through a series of structural states. The theory has previously had success in dealing with crystalline metals and surface physics, and here it is applied to crosslinked rubbery polymers in the nominally amorphous condition. Structure is believed to be related to interchain associations, chain entanglements, chain ends, and other defects in the hypothetical ideal network which by itself would lead to neo‐Hookean predictions in uniaxial deformation, σnH ∝ λ2 — λ−1, where λ is the stretch ratio. Predictions are made for σ(λ) in both tension and compression and shown to be more compatible with data than either σnH(λ) or the Mooney—Rivlin expression σMR(λ). Only two parameters are required, moduli Go (reflecting initial structure) and Gs (the steady‐state condition), and rate effects are incorporated through Go(\documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon$\end{document}) and Gs(\documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon$\end{document}). The phenomena of yielding and stress softening in cyclic tensile loading are also predicted, suggesting advantages to this approach relative to conventional viscoelastic continuum models.
Structure of iodide ion arrays in iodinated nylon 6 and the chain orientation induced by iodine in nylon 6 films
Authors: Murthy N. S. , Szollosi A. B. , Sibilia J. P. , Krimm S.
Published: April 2003

Two species of iodide ions (I3− and I5−) are found in iodine—nylon 6 complexes. Orientation of I5− arrays (most likely I2/I3− complex) along the polymer chain and I3− ions perpendicular to the chain axis in uniaxially drawn films and in films with planar orientation suggests that there is and intrinsic relation between the direction of iodide ion arrays and nylon 6 chains. When an unoriented film of nylon 6 in the amorphous or the α crystalline form is treated with an aqueous solution of iodine—potassium iodide, the I3− species in the resulting iodine—nylon complex lie in planes parallel to the surface of the film, and I2/I3− units are oriented normal to the surface of the film. The γ form obtained by desorbing the iodine from this complex shows considerable uniaxial rientation with the nylon chains oriented perpendicular to the plane of the film; this orientation is maintained during the γ to α transition. It is proposed that the iodine‐induced orientation of the nylon 6 chains is due to the nucleating effects of the iodide ion species as the iodine diffuses unidirectionally into the film.
Tube relaxation: A quantitative molecular model for the viscoelastic plateau of entangled polymeric media
Authors: Viovy Jean Louis
Published: April 2003

The relaxation of an entangled polymeric medium in the viscoelastic plateau is investigated theoretically by using the slip‐link representation of topological constraints. In addition to the chain retraction process introduced by Daoudi and investigated theoretically by Doi, we show that two processes contribute significantly to the relaxation: The first, “equilibration across slip‐links,” is a longitudinal reequilibration between parts of the chain which have been differently extended or compressed, depending on their initial orientation relatively to the strain tensor. The second, “tube relaxation,” is a mean‐field representation of the loss of topological constraints on one chain due to the retraction of the others. Closed analytical expressions for the stress accounting for these three processes are derived and compared with previous theories: the relaxation should be much more progressive than previously predicted, and the terminal time for retraction is reduced significantly by tube relaxation.
An x‐ray diffraction study of nonlinear polyethylene. I. Room‐temperature observations
Authors: Vonk C. G. , Pijpers A. P.
Published: April 2003

In this investigation on samples of high‐ and low‐density polyethylene and ethylene‐vinyl acetate copolymers, crystallinities ϕW and crystalline densities ρcW were obtained with the aid of wide‐angle x‐ray scattering (WAXS) methods. From small‐angle x‐ray scattering (SAXS) the following characteristics were obtained either directly or by combination with the WAXS data: values, or limiting values, of the crystallinity ϕS; crystal densities ρcS; thicknesses of the diffuse boundary layer; number‐average thicknesses of the crystalline and amorphous layers; and both number and weight averages of the long periods. It was shown that a discrepancy between ϕS and ϕW cannot be attributed to the occurrence of large amorphous regions outside the regular stacks of lamellae; the data were reconciled by assuming that the WAXS crystallinities pertain to the cores of the crystalline lamellae, whereas part of the diffuse boundary layers is comprised in the values of ϕS. The ρcW and ρcS data of the nonlinear samples show systematic differences, which were attributed to partial incorporation of side groups in the crystalline regions at a concentration estimated to be of the order of 20–40% of the overall concentration. With increasing side‐group concentration, the thickness of the core of the crystalline lamellae was found to approach the average length of the linear chain segments between side groups. On the basis of these observations a scheme for the crystallization of nonlinear polyethylene is proposed according to which a number of side groups is encapsulated by the growing crystal. The data can be explained by assuming that all chains, offered at a crystal face where growth takes place, crystallize directly, irrespective of whether the crystallizing stem carries a side group. Further crystallization would then proceed by chain folding at both ends of the first stem, until a noncrystallizable unit is met. In this scheme, allowance is made for about half the stems in the crystals to be connected by folds; this is required in view of the “overcrowding” effect. Finally, the effect of cooling rate and molecular weight on the thicknesses of the crystalline and amorphous layers is discussed, and differences between the amorphous densities of high‐and low‐density polyethylene are noted.
Stability of the γ form and the development of the α form in nylon 6
Authors: Murthy N. S. , Aharoni S. M. , Szollosi A. B.
Published: April 2003

The structure of nylon 6 fibers is analyzed by x‐ray diffraction. Our results suggest that only two forms of nylon 6, α and γ, along with lattice distortion and crystallite size, are sufficient to explain the whole range of crystalline structures observed in nylon 6. The γ phase is the preferred initial form in a number of nylon 6 samples. The lattice distortion of the γ form along the chain axis varies from 0.8 to 2.4%, depending on the processing conditions. Upon annealing nylon 6 fibers, the α form is produced primarily by γ‐to‐α conversion in high‐orientation fibers, while additional α form can also crystallize from the amorphous phase in low‐orientation fibers. Finally, we show that α crystallites are favored during conditioning of poorly crystallized fibers in a humid atmosphere, and therefore fibers with α as the major crystalline form are produced upon drawing these conditioned fibers. Fibers drawn without lag time contain primarily the γ phase.
Visual data mining
Authors: Wegman Edward J.
Published: April 2003

Data mining strategies are usually applied to opportunistically collected data and frequently focus on the discovery of structure such as clusters, bumps, trends, periodicities, associations and correlations, quantization and granularity, and other structures for which a visual data analysis is very appropriate and quite likely to yield insight. However, data mining strategies are often applied to massive data sets where visualization may not be very successful because of the limits of both screen resolution, human visual system resolution as well as the limits of available computational resources. In this paper I suggest some strategies for overcoming such limitations and illustrate visual data mining with some examples of successful attacks on high‐dimensional and large data sets. Copyright © 2003 John Wiley & Sons, Ltd.
Dimension reduction and graphical exploration in regression including survival analysis
Authors: Cook R. Dennis
Published: April 2003

Recent advances in dimension reduction and visualization can greatly facilitate the exploratory and diagnostic stages of a regression analysis. This paper contains an expository discussion of selected methodology that came from these advances. Various applications are described, including new results on survival regressions with censoring. All of the methodology described in this paper is available in Arc, a recently released computer program that integrates many standard regression methods with recent developments in regression graphics. Arc implementations are indicated throughout the discussion. Copyright © 2003 John Wiley & Sons, Ltd.
An investigation of error sources and their impact in estimating the time to the most recent ancestor of spatially and temporally distributed HIV sequences
Authors: Burr Tom L. , Gattiker James R. , Gerrish Philip J.
Published: April 2003

This is an investigation of significant error sources and their impact in estimating the time to the most recent common ancestor (MRCA) of spatially and temporally distributed human immunodeficiency virus (HIV) sequences. We simulate an HIV epidemic under a range of assumptions with known time to the MRCA (tMRCA). We then apply a range of baseline (known) evolutionary models to generate sequence data. We next estimate or assume one of several misspecified models and use the chosen model to estimate the time to the MRCA. Random effects and the extent of model misspecification determine the magnitude of error sources that could include: neglected heterogeneity in substitution rates across lineages and DNA sites; uncertainty in HIV isolation times; uncertain magnitude and type of population subdivision; uncertain impacts of host/viral transmission dynamics, and unavoidable model estimation errors. Our results suggest that confidence intervals will rarely have the nominal coverage probability for tMRCA. Neglected effects lead to errors that are unaccounted for in most analyses, resulting in optimistically narrow confidence intervals (CI). Using real HIV sequences having approximately known isolation times and locations, we present possible confidence intervals for several sets of assumptions. In general, we cannot be certain how much to broaden a stated confidence interval for tMRCA. However, we describe the impact of candidate error sources on CI width. We also determine which error sources have the most impact on CI width and demonstrate that the standard bootstrap method will underestimate the CI width. Copyright © 2003 John Wiley & Sons, Ltd.
Bayesian analysis of quantitative antimicrobial assays
Authors: Varbanov Alex R. , Taylor Charles H.
Published: April 2003

Quantitative antimicrobial assays are used to assess the efficacy of chemical germicides. Standard methods for statistical analysis use log reduction (LR), the difference on the log scale between average surviving microbes for control and test carriers, as an efficacy measure. These methods have several deficiencies. The LR parameter is not on the original response scale, which complicates its interpretation. The presence of two different definitions of LR makes the statistical inference even more difficult. Current statistical methods for antimicrobial assay analysis rely on asymptotic normal theory, which might not work well for small samples. In addition, they do not appropriately incorporate censored (‘too numerous to be counted’) observations in the analysis. To overcome those problems, a new Bayesian approach is introduced here. It has also the advantages of more flexible statistical inference, and incorporated prior information in the model. Copyright © 2003 John Wiley & Sons, Ltd.
Sampling minority groups in health surveys
Authors: Kalsbeek William D.
Published: April 2003

Sampling racial and ethnic minority groups in population‐based health studies presents the statistical designer with a variety of notable challenges, many of which can be traced to the manner in which the sampling frame maps into the set of group members. A brief review of sampling approaches aimed at race/ethnic groups is followed by findings on two particularly important statistical issues one may face when sampling minorities: the implications of the geographic diffusion of minorities within sampled area clusters, and the relative utility of different forms of space and time sampling to deal with sometimes dramatic change over time in the linkage between entries on a sampling frame and members of relatively mobile minority groups. Simulated findings from practical illustrations involving the sampling of Hispanics are presented to address each issue. Copyright © 2003 John Wiley & Sons, Ltd.
Spatial prediction of counts and rates
Authors: Gotway Carol A. , Wolfinger Russell D.
Published: April 2003

In this paper we provide both theoretical and empirical comparisons of marginal and conditional methods for analysing spatial count data. We focus on methods for spatial prediction developed from a generalized linear mixed model framework and compare them with the traditional linear (kriging) predictor. Prediction methods are illustrated and compared through a case study based on real data and through a detailed simulation study. The paper emphasizes a better understanding of the strengths and weaknesses of each approach. Published in 2003 by John Wiley & Sons, Ltd.
Vorstellung und Validierung des Gestaltwahrnehmungstests zur Messung der Feldabhängigkeit
Authors: Hergovich Andreas
Published: April 2003

Zusammenfassung. Der Gestaltwahrnehmungstest als computergestütztes Verfahren zur Messung der Feldabhängigkeit wird vorgestellt. Die Aufgabe der Testpersonen besteht darin, eine in einem Muster (geometrische wie auch “sinnvolle” Figuren) versteckte (“eingebettete”) Suchfigur zu identifizieren. Das 30 Items umfassende Verfahren wurde nach dem dichotomen logistischen Modell von Rasch konstruiert. An einer Stichprobe von 460 Personen konnte Modellgültigkeit nachgewiesen werden. Die angegebenen Item- und Personenparameter sprechen für eine gute Differenzierung im mittleren Leistungsbereich. Die Reliabilität des Tests im Rahmen der probabilistischen Testtheorie beträgt .87, zusätzlich werden Ergebnisse mehrerer Untersuchungen zur internen Konsistenz (α = .85 bis α = .95) und zur Split-Half-Reliabilität (r = .83 bis .94) präsentiert. Die Retest-Reliabilität wurde in einer Studie (n = 89) berechnet und lag bei .65. Einige Studien konnten die Konstruktvalidität des Verfahrens belegen. In einer Untersuchung an 177 Personen wurde eine Korrelation von .51 zwischen Gestaltwahrnehmungstest und Embedded-Figures-Test (EFT) gefunden, der Zusammenhang mit einem Intelligenzdiagnostikum (dem Wiener-Matrizen-Test) lag bei .30. Schließlich werden die Ergebnisse zweier Untersuchungen zu interindividuellen Differenzen zwischen Feldabhängigen und Feldunabhängigen (die Stichproben wurden jeweils nach dem Median im Gestaltwahrnehmungstest halbiert) referiert. Ein Experiment zeigte, daß Feldabhängige im Rahmen einer Urteilsaufgabe die kognitive Komponente schlechter von der affektiven Komponente trennen können als Feldunabhängige. Die Ergebnisse einer weiteren Studie deuten darauf hin, daß sich Feldabhängige in einem sozialen Dilemma kooperativer als Feldunabhängige verhalten.
Trierer Inventar zur Erfassung von chronischem Streß (TICS): Skalenkonstruktion, teststatistische Überprüfung und Validierung der Skala Arbeitsüberlastung
Authors: Schulz Peter , Schlotz Wolff
Published: April 2003

Zusammenfassung. Angeregt durch Befunde der Streßforschung, wonach chronischer Streß und nicht akute Belastungen mit klinisch relevanten Beeinträchtigungen der Gesundheit in Zusammenhang steht, wurde das Trierer Inventar zur Erfassung von chronischem Streß (TICS) entwickelt. Der Fragebogen erfaßt sechs Aspekte von chronischem Streß: Arbeitsüberlastung, Arbeitsunzufriedenheit, soziale Belastung, Fehlen sozialer Anerkennung, Sorgen/Besorgnis und belastende Erinnerungen. Die Chronizität der Belastung wird durch die Häufigkeit retrospektiv erfragter Streßerfahrungen erhoben. Zur Beantwortung der Items stehen fünfstufige Ratingskalen zur Verfügung. In der hier vorgestellten Untersuchung mit N = 157 Probanden konnten die in Vorstudien ermittelten Skalen des TICS faktorenanalytisch bestätigt werden. Die sechs Skalen zeigen zufriedenstellende Reliabilitätskoeffizienten. Es können erste Ergebnisse zur Validierung des Fragebogens berichtet werden. In zwei Studien ergaben sich signifikante Korrelationen zwischen der Skala Arbeitsüberlastung und (a) verschiedenen Skalen des Gießener Beschwerdebogens (GBB) sowie (b) der Konzentration des Streßhormons Cortisol. Die Skala differenziert zwischen 19 Tinnituspatienten und 16 gesunden Kontrollpersonen.
Sind Raumvorstellung und Reasoning separierbare Fähigkeitsdimensionen? Dimensionalitätsanalysen zweier Rasch-skalierter Tests: 3DW und WMT
Authors: Gittler Georg
Published: April 2003

Zusammenfassung. Es wurde das dichotome logistische Modell von Rasch eingesetzt, um ein bei Kubinger veröffentlichtes Ergebnis zu überprüfen, welches besagt, daß ein Raumvorstellungstest (Dreidimensionaler Würfeltest von Gittler ) und ein Reasoning-Test (Wiener Matrizen-Test von Formann & Piswanger ) gemeinsam Rasch-homogen seien. Anhand zweier Datensätze - darunter auch der bei Kubinger zitierte - konnte nachgewiesen werden, daß die beiden Tests nicht dieselbe Fähigkeitsdimension erfassen, sondern jeweils etwas Spezifisches. Daraus können positive Aussagen hinsichtlich Validität und Nützlichkeit der Tests abgeleitet werden. Abgesehen von der diagnostisch-inhaltlichen Tragweite dieses Ergebnisses ist auch das methodische Vorgehen interessant, weil es bei der simultanen Modellprüfung zweier Rasch-homogener Subskalen ein seit Stelzl bekanntes Methodenproblem - Insensitivität des Likelihood-Ratio-Tests von Andersen - gibt. Durch den Einsatz trennschärferer Teilungskriterien und die Anwendung eines Modelltests von Martin-Löf konnte dieses Problem bewältigt werden. Sofern Rasch-homogene Tests zur Verfügung stehen, ist das exemplarisch aufgezeigte Vorgehen auch universell geeignet, um die Eigenständigkeit von Intelligenzdimensionen zu überprŭfen.
KIT: Kontrolliertes Interaktions-Tagebuch zur Erfassung sozialer Interaktionen, Beziehungen und Persönlichkeitseigenschaften
Authors: Asendorpf Jens B. , Wilpers Susanne
Published: April 2003

Zusammenfassung. Das Tagebuchverfahren KIT wird vorgestellt. Erfaßt werden alle psychologisch bedeutsamen sozialen Interaktionen eines Beobachtungszeitraums. Durch Aggregation über Interaktionen desselben Interaktionspartners werden soziale Beziehungen, und durch Aggregation über Beziehungen derselben Person werden Persönlichkeitseigenschaften diagnostiziert. Um die Nachteile retrospektiver Erinnerungen zu minimieren, wird die Durchführung strenger als üblich kontrolliert. Dennoch erwies sich KIT als praktikabel. In einer Längsschnittstudie führten 144 Studierende das Tagebuch jeweils 3 Wochen lang im ersten und 113 auch im zweiten Semester. Die Qualität einzelner enger Beziehungen und wichtiger Beziehungstypen (z.B. heterosexuelle Peer-Beziehungen) wurde mit hoher Reliabilität erfaßt. Vergleiche mit Beziehungs- und Persönlichkeitsfragebögen ergaben eine befriedigende Validität. Das Instrument, Beispieldaten und Auswertungsprogramme sind über das Internet allgemein zugänglich.
Die deutsche Fassung des social phobia and anxiety inventory for children (SPAI-C-D): Psychometrische Eigenschaften und Normierung
Authors: Melfsen Siebke , Florin Irmela , Walter Hans-Jörg
Published: April 2003

Zusammenfassung. Das “Social Phobia and Anxiety Inventory for Children (SPAI-C)” wurde ins Deutsche übersetzt (SPAI-C-D). Zusammen mit allgemein gebräuchlichen Selbstbeschreibungs-Maßen zur Erfassung der Angst und einer vom Lehrer auszufüllenden Ratingskala wurde es zwei Normalstichproben von insgesamt 481 Schülerinnen und Schülern im Alter von 8 bis 16 Jahren vorgelegt. An der Gesamtstichprobe wurden auch Normen für das Testverfahren gewonnen. Der Vergleich einer Gruppe von 71 sozial ängstlichen mit 39 nicht sozial ängstlichen Kindern zeigte einen signifikanten Unterschied im SPAI-C-D-Gesamtwert. An zwei weiteren Stichproben wurde die Retestreliabilität nach zwei und nach vier Wochen überprüft. Die Studien beschreiben den SPAI-C-D als reliables und valides Meßinstrument, das zwischen sozialphobischen, sozial ängstlichen und nicht sozial ängstlichen Kindern differenzieren kann.
Validierungsstudie zum Gießener Beschwerdebogen für Kinder und Jugendliche (GBB-KJ) bei gesunden und chronisch kranken Jugendlichen
Authors: Roth Marcus
Published: April 2003

Zusammenfassung. In der vorliegenden Untersuchung wurde die Reliabilität (interne Konsistenz), die faktorielle Validität sowie die kriteriumsbezogene Validität (Kriterium: Vorhandensein einer chronischen Erkrankung) des Gießener Beschwerdebogens für Kinder und Jugendliche (GBB-KJ), einem Fragebogen zur Erfassung subjektiver körperlicher Beschwerden, überprüft. Die Analysen wurden in einer Schülerstichprobe 12- bis 15-jähriger Jugendlicher (N = 258) sowie in Stichproben mit chronisch kranken Jugendlichen gleichen Alters (Asthmatiker: N = 54; Diabetiker: N = 47) durchgeführt. Bei sämtlichen Skalen zeigten sich gute bis zufriedenstellende interne Konsistenzen (α = .74-.85). Die Korrelationen zwischen den Subskalen lagen überwiegend im mittleren Bereich (r < .60). Weiterhin ließ sich die Skalenbildung des Verfahrens durch Faktorenanalysen weitgehend bestätigen. Jedoch zeigte sich, daß weder auf Skalen-, noch auf Itemebene eine Differenzierung zwischen Jugendlichen mit Asthma bzw. Diabetes und körperlich gesunden Altersgenossen möglich ist. Letzterer Befund wirft Fragen bezüglich der Gültigkeit des GBB-KJ auf.
Skalen zur Selbstwirksamkeit und Entscheidungsbalance im Prozeß der Verhaltensänderung von Rauchern
Authors: Jäkle Christian , Keller Stefan , Baum Erika , Basler Heinz-Dieter
Published: April 2003

Zusammenfassung. Im Kontext des transtheoretischen Modells von Prochaska werden in Anlehnung an amerikanische Originalversionen Skalen zur Erfassung der Konstrukte Selbstwirksamkeit und Entscheidungsbalance entwickelt sowie deren Testgüte überprüft. Die Stichprobe besteht aus 279 Jemals-Rauchern aus einer Gesamtheit von 592 Personen, die am “Check ab 35”, einer Gesundheitsuntersuchung nach § 25 SGB V, in 60 allgemeinärztlichen Praxen teilnahmen. Ihnen wurden u.a. folgende Skalen vorgelegt: Selbstwirksamkeits-Skala zur Raucherentwöhnung (SER), Entscheidungsbalance-Skala zur Raucherentwöhnung (EBR) und Skala zur Messung der Stufen der Verhaltensänderung nach Prochaska ( Velicer, DiClemente, Prochaska & Brandenburg, 1985 ). Die SER ist eine eindimensionale Skala und besteht aus 9 Items mit einer inneren Konsistenz von α = 0.95 und Retest-Reliabilität (6 Wochen) von r = 0.85. Die EBR ist zweidimensional, wobei mit jeweils 5 Items auf der einen Dimension die wahrgenommenen Vorteile und auf der anderen Dimension die wahrgenommenen Nachteile des Nichtrauchens abgebildet werden. Die internen Konsistenzen beider Skalen betragen α = 0.85 bzw. 0.83, die Retest-Reliabilitäten r = 0.73 bzw. 0.66. Mit fortgeschrittener Stufe der Verhaltensänderung nehmen sowohl Selbstwirksamkeitserwartung als auch die wahrgenommenen Vorteile des Nichtrauchens in ihrer Ausprägung zu und die wahrgenommenen Nachteile ab. Der Einsatz der Skalen im Prozeß der Verhaltensänderung läßt eine Verbesserung der Spezifität der Interventionen erwarten.