bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular mobility in polycyanurate networks investigated by viscoelastic measurements and molecular simulations
Authors: Georjon Olivier , Schwach Gregoire , Gerard Jean‐François , Galy Jocelyne , Albrand Michel , Dolmazon Rene
Published: April 2004

The dynamic mechanical behavior of a series of polycyanurate networks has been studied in the glassy state as a function of cyanate conversion. Two relaxations, β and γ, were defined and the Arrhenius dependence and Starkweather treatments were applied. To understand the origin of these sub‐Tg relaxations, molecular modeling (both mechanics and dynamics) was used on model molecules representative of the network structure. Two types of molecular motion were examined: rotation of the phenylene ring and crankshaft of the chain segment between crosslinks (i.e., triazine rings).
Viscoelastic relaxations in polyepoxide joints related to the strength of bonded structures at impact rate shear loading
Authors: Lataillade J. L. , Cayssials F.
Published: April 2004

The aim of this paper is to show the excellent impact behavior of a modified epoxy joint on consideration of the viscoelastic relaxation processes of an adhesive. The investigation of the epoxy joint properties, over a range of strain rates (\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ \cdot $\end{document}= 10−2to 104S−1) and temperatures (−30, 24, 60, 80°C), shows that there is a good correlation between high impact resistance and the presence of a secondary transition. We successfully applied the Bauwens approach to explain the strain rate sensitivity of the yield stress in terms of a difference in relaxation times at low and high strain rates (α and β). Our purpose is to confirm these results by applying the Escaig model, which reviews thermoset behavior in terms of a thermally activated dislocation propagation mechanism. The Bauwens approach and the Escaig model lead to the same conclusion: They indicate that there is a critical strain rate\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ \cdot $\end{document}β(T), correlated to a critical temperatureTβ(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^ \cdot $\end{document}), that corresponds to the limits between the two modes of deformation required to free the different kind of molecular motions implied in the deformation process, the α mode to the α + β mode. But at low temperature (−30°C), these models are no longer valid, which means that there is a heterogeneous deformation process, characterized by local molecular motions, which involve a decrease of the polymer entropy and a permanent evolution of molecular structure.
The three successive stages of creep of PMMA between 55°c and 90°c
Authors: Chérière J. M. , Bélec L. , Gacougnolle J. L.
Published: April 2004

After cooling from 140°C, the physical aging of poly(methyl methacrylate), PMMA, has been studied at 55, 70, 84, and 90°C by means of temporary microcreep tests. The systematic analysis of recoveries reveals that at 90°C, creep follows successively three different stages. After stress application, creep starts by a logarithmic function of time, while recovery follows exactly the same kinetics. An Andrade creep begins after the logarithmic creep: It is in fact the beginning of the Kohlrausch‐Williams‐Watts creep with an exponent of 0.36. This creep is fully recoverable, but the duration of this recovery is ∼3 times the creep duration. The third stage of creep is superimposed on the Andrade creep and follows a power law in t0.8, but it is not recoverable in the usual duration of experiments. By comparison with the recoverable creep of PMMA studied by Plazek above Tg, which can be fitted by a KWW law with an exponent 0.8, this third creep is interpreted as the beginning of the rubbery deformation.
Polymers under mechanical stress: Deformation of the nanostructure of isotactic polypropylene revealed by scanning force microscopy
Authors: Castelein G. , Coulon G. , G'sell C.
Published: April 2004

Scanning force microscopy (SFM) was used to study the lamellar morphology of α and β spherulites in bulk intruded isotactic polypropylene (iPP) samples deformed under shear stress. The iPP specimens were sheared at a constant shear rate at room temperature. Just beyond yielding, at a shear strain level of 0.5, the lamellar structure of the α‐spherulites resembles that for unsheared iPP; few cracks are observed along the interfaces between neighboring α‐spherulites: this behavior is attributed to a “cross‐hatched” lamellar texture of the α‐spherulites. In β‐spherulites, at the same shear strain, SFM observations reveal the presence of nanocracks perpendicular to the principal tensile strain axis, going through stacks of crystalline lamellae. Profuse local lamellar kinkings occur along the principal compressive strain axis and few nanocracks parallel to the molecular axis are seen in individual lamellae that lie along the shear direction. Neither particular preferred lamellar orientation nor localization of deformation within shear bands has been detected.
Interface and mechanical coupling effects in model particulate composites
Authors: Alberola N. D. , Mele P.
Published: April 2004

Dynamic mechanical spectra of polystyrene (PS) or styrene‐co‐methacrylic acid copolymer (SAMA) filled by various amounts of raw or coated glass beads have been recorded in the glass transition (Tg) region of the polymers used as the matrix. The relative contribution of the two key features governing the magnitude of the main mechanical relaxation, i.e., (i) the mechanical coupling between phases, and (ii) the physico‐chemical interactions at the polymer/filler interface, is separated by an original mechanical modeling, which gives evidence only for the reinforcement effect of the polymer matrix. Thus, by comparing experiment and theory, it was shown that the decrease in the tanδ maximum displayed by PS reinforced by high volume fractions of raw glass beads mainly results from an improvement of the reinforcement effect, because of the presence of clusters of particles. In contrast, for SAMA copolymer used as the matrix, it was found, in addition, a decrease in the molecular mobility of chains due to interactions at the polymer/coated glass bead interface. Differential scanning calorimetry and scanning electron microscopy analysis agree with this conclusion.
Durability of sheet molding compounds: Influence of hydrothermal aging on morphology and molecular mobility at microscopic scale
Authors: Blancon R. , Martinez‐vega J. J. , Merle G. , Camino G. , Polishchuk A. Ya. , Luda M. P. , Revellino M.
Published: April 2004

The physicochemical aging for parts of Sheet Molding Compound should be considered for their lifetime management and reusability. This material has a complex morphology and contains porosity due to the process and to shrinkage compensation. This SMC study has two complementary approaches. One describes the morphological consequences of water uptake, showing the decrease in the total amount and the fractal dimension of micro‐voids by scanning electron microscopy and image processing. The other shows, by mechanical spectrometry, the effect of water on physical or chemical bonds. In both cases, the “low profile agent” in SMC plays an important role. The molecular mobility was taken as a sensor parameter for the structural changes at the molecular scale, highlighting and quantifying the first steps of the aging. The loss factor level increases, and the activation energies are modified, even for the first aging days. The analysis shows recovery for the material near the relaxation peak of the low profile agent, since the curve recovers its initial shape.
Kinetics of fatigue failure of polystyrene
Authors: Baltenneck F. , Trotignon J‐P , Verdu J.
Published: April 2004

To 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

A 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

Rigid 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

Slow 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

Accounting 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

Electrical 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

A 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

Dies 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

Polyethylene–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

We 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

We 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

A 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

A 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

Photo‐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

Self‐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

α‐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

Two 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

α‐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

We 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

We 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

Neutrals 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

A 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.
Nanospray analysis of the venom of the tarantula Theraphosa leblondi: a powerful method for direct venom mass fingerprinting and toxin sequencing
Authors: Legros Christian , Célérier Marie‐Louise , Henry Maud , Guette Catherine
Published: April 2004

Mass spectrometric methods, including matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐TOFMS), on‐line liquid chromatography/electrospray ionisation mass spectrometry (LC/ESI‐MS), and nanospray ionisation/hybrid quadrupole time‐of‐flight mass spectrometry (nanoESI‐QqTOFMS), were applied to characterize by mass fingerprinting the venom of the French Guyanese tarantula Theraphosa leblondi. Of these techniques direct nanoESI‐QqTOFMS, which allowed the detection of 65 protonated molecules with high mass accuracy, appeared to give the best results. Three major peptides, TlTx1, TlTx2 and TlTx3, were sequenced using a combination of nanoESI‐MS/MS and enzyme digestion/MS and MS/MS experiments. Each sequence was confirmed by automated Edman sequencing. In patch‐clamp experiments these peptides were found to have a specific inhibitory effect on the voltage‐dependent potassium channel, Kv4.2. Copyright © 2004 John Wiley & Sons, Ltd.
On Closure UnderStuttering
Authors: Păun Dimitrie O. , Chechik Marsha
Published: April 2004

Abstract.

For over a decade, researchers in formal methods have
tried to create formalisms that permit natural specification of
systems and allow mathematical reasoning about their
correctness. The availability of fully automated reasoning tools
enables non-experts to use formal methods effectively—their
responsibility reduces to specifying the model and expressing
the desired properties. Thus, it is essential that these
properties be represented in a language that is easy to use,
sufficiently expressive and succinct. Linear-time temporal logic
(LTL) is a formalism that has been used extensively by
researchers for program specification and verification. One of
the desired properties of LTL formulas is
closure under stuttering
.
That is, we do not want the interpretation of formulas to change
over traces where some states are repeated. This property is
important from both practical and theoretical prospectives; all
properties which are closed under stuttering can be expressed in
LTL

−X

—a fragment of LTL
without the ‘next’ operator. However, it is often difficult to
express properties in this fragment of LTL. Further, determining
whether a given LTL property is closed under stuttering is
PSPACE-complete. In this paper, we introduce a notion of
edges
of LTL formulas and
present a formal theory of closure under stuttering. Edges allow
natural modelling of systems with events. Our theory enables
syntactic reasoning about whether the resulting properties are
closed under stuttering. Finally, we apply the theory to the
pattern-based approach of specifying temporal formulas.
Adolescent lottery and scratchcard players: do their attitudes influence their gambling behaviour?
Authors: Wood Richard T.A , Griffiths Mark D
Published: April 2004

This paper examines the link between attitudes and behaviour in relation to adolescent participation on the National Lottery and scratchcards by applying the theory of planned behaviour. A questionnaire constructed by the authors was administered to a sample of 1195 adolescents between the ages of 11 and 15 years (550 male, 641 female, 4 unspecified). In this paper, all data relating to factors associated with adolescent attitudes toward the National Lottery and scratchcards, and the links with any subsequent gambling behaviour, were analysed. Results revealed that young people's attitudes are an accurate predictor of their gambling behaviour on these activities, and that social cognitive theory provides an explanation of how these attitudes may develop. In light of these findings, a number of suggestions are given on how to discourage young people from gambling.
Weapon‐carrying at Swiss schools? A gender‐specific typology in context of victim and offender related violence
Authors: Kuntsche Emmanuel N , Klingemann Harald K.‐H
Published: April 2004

After reviewing prevalence rates, this work tries to identify gender specific groups in which weapon‐carrying occurs in the context of victim and offender related violent behaviours. k‐Means cluster and logistic regression analyses were calculated, based on a cross‐sectional survey of a national representative sample of 1549 15‐year‐olds as part of the Health Behaviour in School‐Aged Children (HBSC) international collaborative study. The victims and offenders of violence concern mainly female bullies and physically violent boys. In the male victim–offender group, 17% had already taken a weapon to school. Another male group emerged in which 95% had already taken a weapon to school. Members of this group revealed an elevated level of acting violently but a low level of being the victim. Among the minority girls who were offenders and victims of physical violence, everyone has already taken a weapon to school. Based on these results, homogenous risk groups can be targeted for violence prevention.
On the origin of floral morphological novelties
Authors: He Chaoying , Münster Thomas , Saedler Heinz
Published: April 2004

Floral morphological novelties, like homeotic changes of whorl 1 organs, can easily arise by modifying existing regulatory networks. Ectopic expression of B‐function MADS‐box genes in whorl 1 leads to a replacement of sepals by petals, as is found in the Liliaceae. In cases where leaf‐like sepals or even inflated calyces develop, which ultimately envelop the mature fruit as in Physalis, ectopic expression of a vegetative MADS‐box gene seems to be responsible. Current knowledge concerning the origin of such morphological novelties is reviewed.
Structure of human PRL‐3, the phosphatase associated with cancer metastasis
Authors: Kim Kyoung-Ah , Song Jin-Sue , Jee JunGoo , Sheen Mee Rie , Lee Chulhyun , Lee Tae Gyu , Ro Seonggu , Cho Joong Myung , Lee Weontae , Yamazaki Toshio , Jeon Young Ho , Cheong Chaejoon
Published: April 2004

PRL‐3, a novel class protein of prenylated tyrosine phosphatase, is important in cancer metastasis. Due to its high levels of expression in metastatic tumors, PRL‐3 may constitute a useful marker for metastasis and might be a new therapeutic target. Here, we present the solution structure of the phosphatase domain of a human PRL‐3 (residues 1–162) in phosphate‐free state. The nuclear magnetic resonance (NMR) structure of PRL‐3 is similar to that of other known phosphatases with minor differences in the secondary structure. But the conformation and flexibility of the loops comprising the active site differ significantly. When phosphate ions or sodium orthovanadate, which is a known inhibitor, are added to the apo PRL‐3, the NMR signals from the residues in the active site appeared and could be assigned, indicating that the conformation of the residues has been stabilized.
Reconstitution and functional characterization of the unusual bi‐subunit type I DNA topoisomerase from Leishmania donovani
Authors: Brata Das Benu , Sen Nilkantha , Ganguly Agneyo , Majumder Hemanta K.
Published: April 2004

Leishmania donovani topoisomerase I is an unusual bi‐subunit enzyme. The activity of the enzyme has been detected when the genes of the individual subunits were co‐expressed in yeast [J. Biol. Chem. 278 (2003) 3521]. Here, we report for the first time, the in vitro reconstitution of the two recombinant proteins, LdTOP1L and LdTOP1S, corresponding to the large and small subunits and localization of the active enzyme in both the nucleus and kinetoplast. The proteins were purified from bacterial extract and the activity was measured by plasmid DNA relaxation assay. LdTOP1L and LdTOP1S form a direct 1:1 heterodimer complex through protein–protein interaction. Under standard relaxation assay condition (50 mM KCl and 10 mM Mg2+), reconstituted enzyme (LdTOP1LS) showed reduced processivity as well as 2‐fold reduced affinity for DNA compared to eukaryotic monomeric rat liver topoisomerase I (RLTOP1). Cleavage assay at various salt concentrations reveals that Camptothecin (CPT) enhanced the formation of “cleavable complex” at low salt. Interaction between the two subunits leading to the formation of an active complex could be explored as an insight for development of new therapeutic agents with specific selectivity.
Integrative analysis of multiple gene expression profiles applied to liver cancer study
Authors: Kyoon Choi Jung , Young Choi Jong , Ghon Kim Dae , Wook Choi Dong , Yeo Kim Bu , Ho Lee Kee , Il Yeom Young , Sook Yoo Hyang , Joon Yoo Ook , Kim Sangsoo
Published: April 2004

A statistical method for combining multiple microarray studies has been previously developed by the authors. Here, we present the application of the method to our hepatocellular carcinoma (HCC) data and report new findings on gene expression changes accompanying HCC. From the cross‐verification result of our studies and that of published studies, we found that single microarray analysis might lead to false findings. To avoid those pitfalls of single‐set analyses, we employed our effect size method to integrate multiple datasets. Of 9982 genes analyzed, 477 significant genes were identified with a false discovery rate of 10%. Gene ontology (GO) terms associated with these genes were explored to validate our method in the biological context with respect to HCC. Furthermore, it was demonstrated that the data integration process increases the sensitivity of analysis and allows small but consistent expression changes to be detected. These integration‐driven discoveries contained meaningful and interesting genes not reported in previous expression profiling studies, such as growth hormone receptor, erythropoietin receptor, tissue factor pathway inhibitor‐2, etc. Our findings support the use of meta‐analysis for a variety of microarray data beyond the scope of this specific application.
Deep-ocean predation by a high Arctic cetacean
Authors: Laidre K.L. , Heide-Jørgensen M.P. , Jørgensen O.A. , Treble M.A.
Published: April 2004

A bioenergetic model for two narwhal (Monodon monoceros) sub-populations was developed to quantify daily gross energy requirements and estimate the biomass of Greenland halibut (Reinhardtius hippoglossoides) needed to sustain the sub-populations for their 5-month stay on wintering grounds in Baffin Bay. Whales in two separate wintering grounds were estimated to require 700 tonnes (s.e. 300) and 90 tonnes (s.e. 40) of Greenland halibut per day, assuming a diet of 50% Greenland halibut. Mean densities and length distributions of Greenland halibut inside and outside of the narwhal wintering grounds were correlated with predicted whale predation levels based on diving behavior. The difference in Greenland halibut biomass between an area with high predation and a comparable area without whales, approximately 19 000 tonnes, corresponded well with the predicted biomass removed by the narwhal sub-population on a diet of 50–75% Greenland halibut.
Small-scale distribution of juvenile gadoids in shallow inshore waters; what role does maerl play?
Authors: Kamenos Nicholas A. , Moore P.Geoffrey , Hall-Spencer Jason M.
Published: April 2004

The indirect effects of demersal fisheries, such as habitat degradation, are currently thought to be impacting gadoid stocks. Maerl fulfils nursery area prerequisites for several invertebrate species, so its role in similar ecosystem service provision for gadoids has been addressed. Juvenile cod (Gadus morhua), saithe (Pollachius virens), and pollack (Pollachius pollachius) in shallow (<7 m) inshore waters were surveyed with fykenets and scuba off western Scotland over a period of 12 months. Juvenile densities were highest from September to November, and at that time, significantly more were present during the day and associated with maerl (that lacked macroalgal cover) than with heavily vegetated rocky and gravel substrata. Juvenile cod were present throughout the year, whereas saithe appeared in July, and pollack from September to January. With its abundance of food, maerl probably has a high holding capacity for juvenile gadoids, and thus is an important part of the inshore nursery system.
Matrix metalloproteinase‐9 expression, tartrate‐resistant acid phosphatase activity, and DNA fragmentation in vascular and cellular invasion into cartilage preceding primary endochondral ossification in long bones
Authors: Takahara Masatoshi , Naruse Takuji , Takagi Michiaki , Orui Hiroshi , Ogino Toshihiko
Published: April 2004

Vascular and cellular invasion into cartilage are essential for endochondral ossification. Recently it has been shown that matrix metalloproteinase‐9 (MMP‐9)/gelatinase B is a key regulator of growth plate angiogenesis and apoptosis of hypertrophic chondrocytes. To study vascular and cellular invasion into cartilage preceding primary endochondral ossification in long bones, precursor femurs from 13‐ to 16‐day‐old murine embryos were sectioned. Tartrate‐resistant acid phosphatase (TRAP) activity, in situ hybridization for matrix metalloproteinase‐9 (MMP‐9), immunostaining for CD31, and in situ detection of apoptosis (TUNEL) were studied. TRAP activity, MMP‐9 mRNA, and CD31 expression were initially detected in the intertrabecular spaces of the perichondral collar, and then in cells migrating into the cartilage. The first cells involved in the primary invasion into cartilage were CD31‐positive vascular endothelial cells and MMP‐9‐positive cells, followed by TRAP‐positive cells. At the cartilage‐marrow interface, CD31‐positive vascular endothelial cells and MMP‐9‐positive cells were predominant. These results suggest that MMP‐9‐positive cells cooperate with vascular endothelial cells in cartilage angiogenesis. TUNEL‐positive staining was detected on chondrocytes attached to the inner surface of the perichondral collar, and also detected in the area where cartilage was removed. These results suggest that chondrocytes separated from the cartilage matrix may undergo apoptosis. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Coating of titanium implants with type‐I collagen
Authors: Rammelt Stefan , Schulze Eva , Bernhardt Ricardo , Hanisch Uwe , Scharnweber Dieter , Worch Hartmut , Zwipp Hans , Biewener Achim
Published: April 2004

Purpose: Type‐I collagen, the major structural protein in bone, has beneficial properties regarding bone regeneration. Little is known about the potential effects of collagen coating on orthopedic implants.

Methods: 3 to 6 μg/cm2 of lyophilized type‐I collagen was absorbed on titanium rods. Six coated and uncoated pins of 0.9 mm diameter were inserted into the tibia of adult male Wistar rats for 1, 2, 4, 7, 14, and 28 days. Specimens were embedded in methacrylate‐based Technovit 9100N resin. From one portion cutting and grinding sections were obtained. The implant was removed from the other half that was depolymerized, sectioned, and mounted for immunohistochemistry.

Results: At day 4, the interface around the collagen‐coated implants displayed a granulation tissue with higher numbers of cathepsin D‐positive mononucleated cells compared to the uncoated implants (p <0.05). Active osteoblasts, reactive for osteopontin, were increased around the collagen‐coated pins at day 4 and 7 (p < 0.01). After 28 days of implantation, direct bone contact averaged 74.9% around the collagen‐coated implants and 62.1% around uncoated implants (NS). The amount of newly formed bone averaged 76.3% around the collagen‐coated pins and 67.8% around the uncoated pins (NS). The histomorphometric findings were confirmed by SRμCT in two specimens.

Conclusions: The earlier observation of mononuclear phagocytozing cells and the earlier and higher expression of bone‐specific matrix proteins suggest an increased early bone remodeling around titanium pins through collagen coating. A tendency towards increased bone formation was observed around the coated implants. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.