bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of fatigue failure of polystyrene
Authors: Baltenneck F. , Trotignon J‐P , Verdu J. 
Published: April 2004

AbstractTo study the mechanism of crack initiation in the fatigue of amorphous polymers, flexural fatigue tests have been performed on injection molded samples (ISO 1 standard 4 mm thick 10 mm large) of polystyrene homopolymer (PS), at a frequency of 10 Hz. Two types of fatigue tests were performed: (i) Monosequential Fatigue Test (MFT) in which cycling loading is not interrupted: (ii) Polysequential Fatigue Test (PFT) during which fatigue periods alternate with rest periods. The number of cycles to rupture has been determined for various values of the strain amplitude, temperature and duration of rest periods. Two kinetics regimes were observed: (i) at temperature higher than 75°C, the thermal regime is quasi adiabatic and failure results from polymer softening. In this regime, rest periods have a strong stabilizing effect, since they limit self heating; (ii) At temperatures lower than 75°C, the thermal regime is quasi isothermal and fracture results from crazing followed by brittle rupture. Rest periods (on the order of half fatigue lifetime) have no effect on the number of cycles to rupture. The influence of temperature here is considerably lower than in the “adiabatic” regime. The endurance limit values ϵ∞ are close to the critical strains for crazing ϵC in static conditions. A kinetic model based on the above observations is proposed for strain amplitudes close to the endurance limit (2ϵ∞ ≥ ϵ ≥ ϵ∞). This model reasonably fits the experimental data.
Microindentation testing of inhomogeneous microstructures in welded polyethylene
Authors: Lu Y. , Shinozaki D. M. 
Published: April 2004

AbstractA microcomputer controlled microindenter with a flat cylindrical microindenter face has been used to measure the variation of storage modulus and loss factor that results from differences in microstructure in high density polyethylene (HDPE). The microstructural variations have been produced by butt welding the polyethylene and varying the thermal histories of the weld. The dynamic mechanical thermal analysis data from the microindenter have been compared to similar tests on uniform bulk material run in bending using a commercial analyzer. The normalization procedure used on the microindenter data was justified by examining the calculated stress fields under the indenter tip. The quantities measured using the microindenter are consistent with the measured changes in crystallinity.
Biaxial orientation of poly(vinyl chloride) compounds: Interaction between drawing, structure, and properties
Authors: Gilbert M. , Liu Z. , Hitt D. J. 
Published: April 2004

AbstractRigid poly(vinyl chloride) (PVC) sheets were stretched uniaxially (at constant width), equally biaxially, and unequally biaxially to various draw ratios. Tensile properties, density, and birefringence of the stretched sheets were measured, and their wide angle X‐ray diffraction traces recorded. Comparison of results showed the highest crystallite and overall orientation and density in the uniaxial samples, and lowest values for the equal biaxial samples. Drawing resulted in the alignment of some existing crystallites in the plane of the film, together with the formation of new mesomorphous structures. Changes in tensile strength were attributed to overall orientation.
A sensitive mechanical test for slow crack growth in polyethylene
Authors: Lu Xici , Zhou Zhiqiang , Brown Norman 
Published: April 2004

AbstractSlow crack growth (SCG) in a wide variety of polyethylenes has been investigated by a constant tensile load test (the PENT test) for a single edge notched specimen. The PENT test is very sensitive to the changes in molecular structure and morphology of polyethylene. The resistance to SCG depends on the density of the tie molecules and the strength of the crystals.
Analysis of nonlinearly elastic cantilever snap beams for assembly of plastic parts
Authors: Gupta Mahesh 
Published: April 2004

AbstractAccounting for the nonlinear stress‐strain behavior of plastics is important for good design of a snap joint. A constitutive equation for approximating the nonlinear stress‐strain behavior of plastics is introduced in this paper. The equations for the stress, strain, and deflection of a cantilever beam, based upon the newly introduced constitutive equation are presented. In comparison with the experimental results, the cantilever deflection predicted from the nonlinear analysis is found to be about 50% more accurate than the corresponding predictions from the linear analysis.
Conductive polymer blends with low carbon black loading: High impact polystyrene/thermoplastic elastomer (styrene‐isoprene‐styrene)
Authors: Tchoudakov R. , Breuer O. , Narkis M. , Siegmann A. 
Published: April 2004

AbstractElectrical resistivity and morphology of high impact polystyrene (HIPS)/styrene‐isoprene‐styrene copolymer (SIS)/carbon black (CB) blends were studied. Conductive CB particles locale preferentially within the HIPS phase of the HIPS/SIS blends. The blends studied remain conductive as long as HIPS maintains a continuous phase and the effective CB concentration within HIPS surmounts its percolation threshold. Thus, blends containing 2 phr CB depict significant changes in resistivity with the HIPS/SIS composition, transforming from insulative to conductive. SIS/CB mixtures exhibit an unusual behavior, explained by a physical model suggested in this paper and extended to the HIPS/SIS/CB systems.
The viscosity reducing effects of very low concentrations of a thermotropic copolyester in a matrix of HDPE
Authors: Whitehouse C. , Lu X. H. , Gao P. , Chai C. K. 
Published: April 2004

AbstractA thermotropic liquid crystalline polymer (TLCP), denoted as TLCP(1), was used as a processing aid for high density polyethylene (HDPE). The TLCP was a copolyester of hydroxybenzoic acid, hydroquinone and sebacic acid and was blended with HDPE to give 0.2, 0.5 and 2 wt% TLCP(1) blends. At a temperature of 185°C, when TLCP(1) is in the nematic regime, the processing window for HDPE was increased tenfold from a maximum shear rate of 100 s−1 for pure HDPE to 1170 s−1 for a 2 wt% TLCP(1) blend. There were large viscosity reductions of between 85% and 90% compared with the pure HDPE when the blended material was used at a wall shear stress value of approximately 2.4 × 105 Pa. This viscosity reduction was attributed to the TLCP(1) droplets changing shape from spheres to slender fibrils under shear flows.
Modeling the secondary cavity of two‐cavity dies
Authors: Ruschak Kenneth J. , Weinstein Steven J. 
Published: April 2004

AbstractDies having two distribution cavities and slots are sometimes used in film‐forming applications demanding high uniformity. The flow distribution accomplished by the primary cavity and slot is improved by the secondary cavity and slot. In the primary cavity, the main flow direction is lengthwise, and the flow resembles that in a duct. On the other hand, the main flow direction in the secondary cavity is in the plane of the cross section. Nonetheless, in previous literature, the same flow equation is vised for both cavities. The principal result of this work is a flow equation for the secondary cavity that takes account of the underlying cross flow. Applying this equation shows that both inertia and pseudoplasticity adversely affect the performance of a secondary cavity and slot.
Novel synthesis of polyethylene–poly(dimethylsiloxane) copolymers with a metallocene catalyst
Authors: Ciolino Andrés E. , Barrera Galland Griselda , Luján Ferreira María , Villar Marcelo A. 
Published: April 2004

AbstractPolyethylene–poly(dimethylsiloxane) copolymers were synthesized in solution from an ethylene monomer and an ω‐vinyl poly(dimethylsiloxane) (PDMS) macromonomer at 363 and 383 K with EtInd2ZrCl2/methylaluminoxane as a catalyst. The copolymers obtained were characterized with Fourier transform infrared spectroscopy, 1H and 13C NMR, size exclusion chromatography, and differential scanning calorimetry. The rheological properties of the molten polymers were determined under dynamic shear flow tests at small‐amplitude oscillations, whereas the physical arrangement of the phase domains was analyzed with scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX). The analysis of the catalyst activity and the resulting polymers supported the idea of PDMS blocks or chains grafted to polyethylene. The changes in the rheological behavior and the changes in the Fourier transform infrared and NMR spectra were in agreement with this proposal. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2462–2473, 2004
Effects of slip on the viscosity of polymer melts
Authors: Adhikari N. P. , Goveas J. L. 
Published: April 2004

AbstractWe use existing scaling theories by de Gennes, Brochard, and Ajdari to calculate the apparent viscosity of multilayer blends with weakly entangled interfaces. The lowering of the apparent viscosity with respect to the bulk is a manifestation of interfacial slip. The theoretical predictions are compared with the recent experimental data of Zhao and Macosko. The theory is able to describe a continuous transition from a low‐slip regime to a high‐slip regime when the bulk rheology is still Newtonian, in agreement with experiments. However, the dependence of the apparent viscosity on the shear rate and layer thicknesses is much stronger than what is observed experimentally. The apparent viscosity is also calculated for dilute polymer emulsions. We modify a theory of Palierne, which is valid in the linear viscoelastic regime for the bulk, to include the effects of interfacial slip. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1888–1904, 2004
Molecular mobility and structure of ultrasonically treated unfilled butadiene rubber
Authors: Oh Jeong Seok , Isayev Avraam I. , Wagler Todd , Rinaldi Peter L. , Meerwall Ernst Von 
Published: April 2004

AbstractWe have used 1H NMR relaxation and pulsed‐gradient spin–echo diffusion, 13C NMR relaxation, and quantitative bulk measurements to characterize molecular mobility in unfilled butadiene rubber before and after an intense ultrasound treatment. In an effort to improve our understanding of the treatment process, we have performed the characterization at the molecular level. The 1H NMR T2 relaxation decay has been successfully described with a three‐component model, which shows the evolution of the proportions and intermolecular mobilities of the changing spectrum of the motional species. The intramolecular mobility of the carbon backbone and structure has been examined with 13C NMR, which shows significant isomerization resulting from the ultrasound treatment. The diffusion rates of the ultrasonically treated samples reflect the measured changes in the molecular weights of the sol fractions. This investigation is the first to characterize the details of the delicate balance of the crosslinking, backbone modification, chain scission, and network degradation as an ultrasound treatment progresses. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1875–1887, 2004
Availability of pesticide‐treated seed on arable fields
Authors: de Snoo Geert R , Luttik Robert 
Published: April 2004

AbstractA study of the availability of pesticide‐treated seed on arable fields was performed. The research was carried out in three different areas of The Netherlands (soil types ranging between sand and heavy clay) and included the following topics: drilling techniques, soil conditions, location on the field and spillage. The results show that there is a large variation among the various crops in the percentage of seed remaining on the soil surface. This is mainly caused by differences in drilling techniques and soil conditions. The percentage of surface seeds after standard drilling is approximately four times higher than after precision drilling. The best correlation for the impact of soil conditions was found for the overall measure of clod weight. Large differences in seed densities (factor of 3.5) were found between the headland and the field centre. Spillage occured in most crops investigated, with an average of two spills per field. Based on the field data it is recommended to use in the current risk assessment for birds and mammals the following percentages of seed remaining on the soil surface: 0.5% for precision drilling, 3.3% for standard drilling in spring and 9.2% for standard drilling in autumn. Copyright © 2004 Society of Chemical Industry
Prediction of field atrazine persistence in an allophanic soil with Opus2
Authors: Müller Karin , Smith Roger E , James Trevor K , Holland Patrick T , Rahman Anis 
Published: April 2004

AbstractA modified version of the model Opus was applied to measurements of soil water dynamics and atrazine (6‐chloro‐N2‐ethyl‐N4‐isopropyl‐1,3,5‐triazine‐2,4‐diamine) persistence in a Bruntwood silt loam soil (Haplic Andosol, FAO system) in Hamilton, New Zealand. The modified model, Opus2, is briefly described and parameter estimation for the simulations is discussed. Soil water dynamics were more accurately described by applying measured soil hydraulic properties than by estimating them using pedotransfer functions. A parameter sensitivity analysis revealed that degradation was the most relevant process in simulating pesticide behaviour by Opus2. The Arrhenius equation incorporated in Opus2 did not correctly describe the effect of temperature on degradation rates obtained at 10, 20 and 30 °C. However, as the Arrhenius coefficient is a very sensitive parameter and soil temperature variation was relatively narrow in the field, the Arrhenius coefficient was approximated from the laboratory study. The simulation results obtained were superior to modelling at constant temperature. Field measured persistence of atrazine in the topsoil was underpredicted using the half‐life determined in the laboratory at 10 °C. Modelling with a lag phase followed by accelerated degradation by use of a sigmoidal degradation equation in Opus2 significantly improved the modelling results. Nevertheless, degradation processes in the laboratory under controlled conditions did not accurately represent field dissipation, however well the laboratory degradation data could be described by simple kinetic equations. The study indicates the importance of improving field techniques for measuring degradation, and developing laboratory protocols that yield degradation data that are more representative of pesticide dynamics in field soils. Copyright © 2003 Society of Chemical Industry
Comparison of anti‐feedant and insecticidal activity of nimbin and salannin photo‐oxidation products with neem (Azadirachta indica) limonoids
Authors: Simmonds Monique SJ , Jarvis Andrew P , Johnson Shaun , Jones Graeme R , Morgan E David 
Published: April 2004

AbstractPhoto‐oxidation of the neem limonoids nimbin and salannin with UV light in the presence of oxygen gives two isomeric lactone products per limonoid, nimbinolide and isonimbinolide, and salanninolide and isosalanninolide, respectively. When compared in insect tests with the important limonoids of neem seeds, azadirachtin, nimbin and salannin, isonimbinolide and isosalanninolide show activity greater than that of nimbin or salannin and in some respects show activity approaching that of azadirachtin. The photo‐oxidation products were tested for anti‐feedant activity and toxicity against larvae of three species of Lepidoptera, Spodoptera littoralis (Boisd), Spodoptera frugiperda (FE Smith) and Helicoverpa armigera (Hübner) and nymphs of the locusts Schistocerca gregaria (Forskål) and Locusta migratoria (L). Copyright © 2003 Society of Chemical Industry
Organization of designed nanofibrils assembled from α‐helical peptides as determined by electron microscopy
Authors: Kajava Andrey V. , Potekhin Sergey A. , Corradin Giampietro , Leapman Richard D. 
Published: April 2004

AbstractSelf‐assembling peptides present attractive platforms for engineering materials with controlled nanostructures. Recently, an α‐helical fibril forming peptide (αFFP) was designed that self‐assembles into nanofibrils at acid pH. Circular dichroism spectroscopy, electron‐microscopy and x‐ray fibre diffraction data showed that the most likely structure of αFFP fibrils is a five‐stranded coiled coil rope. In the present study, scanning transmission electron microscopy (STEM) was used to improve our understanding of the αFFP fibril structure. The measurements of fibril mass per length suggest that there are ten α‐helices in transverse sections of the fibrils. Based on the known data, it is proposed that a predominant fibrillar structure of αFFP is a dimer of α‐helical five‐stranded protofilaments wrapped around a common axis. It is shown that these structures have an axial dimension of 58 ± 16 nm and a width of 4 ± 1 nm. A small number of thin fibrils is also observed in the negative stained preparation and STEM images. The thin fibrils may correspond to the single protofilament. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Computational study of the conformational preferences of the (R)‐8‐amino‐pentacyclo[5.4.0.02,6.03,10.05,9] undecane‐8‐carboxylic acid monopeptide
Authors: Bisetty Krishna , Gomez‐Catalan Jesus , Aleman Carlos , Giralt Ernest , Kruger Hendrik G. , Perez Juan J. 
Published: April 2004

Abstractα‐Amino acids are important building blocks for the synthesis of a large number of bioactive compounds and pharmaceutical drugs. However, a literature survey revealed that no theoretical conformational study of α‐amino acids with cage carbon frameworks has been performed to date. This paper reports the results of a conformational study on the (R)‐8‐amino‐pentacyclo[5.4.0.02, 6.03,10.05,9] undecane‐8‐carboxylic acid monopeptide (cage monopeptide), using molecular mechanics and ab initio methods. The in vacuo Ramachandran maps computed using the different parameterizations of the AMBER force field show the C7eq structure as the most favourable conformation, in contrast to the C7ax structure, that is the lowest energy conformation at the ab initio level. Analysis of these maps reveals the helical preference for the monopeptide and provides the potential for the cage residue to be incorporated into constrained peptide analogues. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Synthesis and characterization of a sulfated and a non‐sulfated cyclic CCK8 analogue functionalized with a chelating group for metal labelling
Authors: De Luca Stefania , Morelli Giancarlo 
Published: April 2004

AbstractTwo cyclic peptides, cyclo29, 34[Dpr29, Lys34(DTPA‐Glu)]‐CCK8 (1) and cyclo29, 34[Tyr27(SO3H), Dpr29, Lys34(DTPA‐Glu)]‐CCK8 (2), bearing the chelating moiety DTPA‐Glu covalently bound to the Lys side chain have been synthesized by solid‐phase methodology. The presence in compound 2 of many acidic functions characteristic of the chelating agent increases the lability of the sulfate group on the Tyr side chain. This finding suggests that prolonged acid treatments should be avoided during the preparation of such peptides. Sulfation of cyclo29, 34[Dpr29, Lys34(DTPA‐Glu)]‐CCK8 was performed using a pyridine–SO3 complex as reagent. This reaction has been found to be the most suitable synthetic strategy for obtaining compound 2 in good yield. Cyclo29, 34[Tyr27(SO3H), Dpr29, Lys34(DTPA‐Glu)]‐CCK8 is a new promising CCK8 analogue, able to coordinate radioactive isotopes of metal ions such as 111In(III), and to bind, in a selective way, the CCKA‐R receptor. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Cosolvent‐assisted oxidative folding of a bicyclic α‐conotoxin ImI
Authors: Nielsen Jacob S. , Buczek Pawel , Bulaj Grzegorz 
Published: April 2004

Abstractα‐Conotoxin ImI is a 12‐amino acid peptide, found in the venom of the marine snail Conus imperialis. This conotoxin is a selective antagonist of α7 nicotinic acetylcholine receptors. To produce biologically active α‐ImI, disulfide bonds must be formed between Cys2–Cys8 and Cys3–Cys12. Oxidative folding of bicyclic conotoxins, such as α‐ImI, has been traditionally achieved using two‐step oxidation protocols with orthogonal protection on two native pairs of cysteines. In this work, two alternative oxidation protocols were explored: (1) the recently described one‐pot oxidation of t‐butyl/4‐methylbenzyl protected Cys pairs and (2) direct oxidative folding. In contrast to the first method, the latter one resulted in high yields of correctly folded α‐ImI. The addition of organic cosolvents, such as methanol, ethanol or isopropanol into the folding mixture significantly increased the accumulation of the native peptide. This effect was also observed for another conotoxin, α‐PnIA. It is suggested that cosolvent‐assisted direct oxidation might be of general use for other bicyclic α‐conotoxins, but efficiency should be assessed on a case‐by‐case basis. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.
Quasi‐one dimensional organic conductors: interplay between a magnetic field and the dimensionality
Authors: Haddad S. , Charfi‐Kaddour S. , Nickel C. , Héritier M. , Bennaceur R. 
Published: April 2004

AbstractWe briefly review some key properties of the quasi‐one dimensional organic conductors. We focus on some puzzling issues of the normal state in particular the problem of dimensional crossover. We show that several features of the normal state are consistent with the Luttinger liquid description. We stress on the competition between the magnetic field and the dimensionality. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
First‐principles study on the creation of holes in high Tc cuprates
Authors: Ambrosch‐Draxl C. , Sherman E. Ya. , Auer H. , Thonhauser T. 
Published: April 2004

AbstractWe investigate the charge redistribution in high Tc cuprates as a function of pressure, composition, and doping. To this extent we have performed first‐principles calculations based on density functional theory for several representatives of the Hg based cuprates. In particular, we focus on the creation of holes in the copper‐oxygen planes. Conclusions are drawn about the similarities and differences between the three parameters influencing the superconducting transition temperature. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The formation of RCCCO and CCC(O)R (R = Me, Ph) neutral radicals from ionic precursors in the gas phase: the rearrangement of CCC(O)Ph
Authors: Peppe Salvatore , McAnoy Andrew M. , Dua Suresh , Bowie John H. 
Published: April 2004

AbstractNeutrals MeCCCO, CCC(O)Me, PhCCCO and CCC(O)Ph have been made by neutralisation of [MeCCCO]+, [CCC(O)Me]−, [PhCCCO]+ and [CC(CO)Ph]−. Neutrals MeCCCO, CCC(O)Me and PhCCCO are stable for the microsecond duration of the neutralisation experiment. A joint experimental and theoretical study (energies calculated at the B3LYP/aug‐cc‐pVDZ//B3LYP/6‐31G(d) level of theory) suggests that the neutral radical CCC(O)Ph rearranges via a four‐centred ipso radical cyclisation/ring opening to form the isomer PhCCCO in an exothermic reaction. 13C labelling confirms that the rearrangement does not involve O migration. Some of the PhCCCO radicals formed in this reaction are sufficiently energised to effect decomposition to give PhCC and CO. Copyright © 2004 John Wiley & Sons, Ltd.
The analysis of thyroxine in human serum by an ‘exact matching’ isotope dilution method with liquid chromatography/tandem mass spectrometry
Authors: Hopley Chris J. , Stokes Peter , Webb Kenneth S. , Baynham Michael 
Published: April 2004

AbstractA method for the analysis of thyroxine in human serum, utilising ‘exact matching’ isotope dilution mass spectrometry (IDMS) in combination with liquid chromatography/tandem mass spectrometry (LC/MS/MS), has been developed with a limit of quantification of 0.5 ng g−1 of thyroxine in human serum. The extraction and clean‐up of thyroxine from serum involves an efficient protein‐precipitation stage followed by a solid‐phase extraction procedure to produce an extract essentially free from interfering compounds. The method is reproducible, with expanded uncertainties of less than 2%, and is relatively fast to perform. Copyright © 2004 John Wiley & Sons, Ltd.