bluuebunny/crossref_metadata_2025_split huggingface dataset:
Long‐chain branching in low‐density polyethylene
Authors: Moore W. R. A. D. , Millns W. 
Published: March 2007

AbstractA sample of a commercial low‐density polyethylene was fractionated and values of number − Mn and weight‐average Mw, molecular weights obtained together with intrinsic viscosities [η], measured in decalin at 135° and in a theta‐solvent, diphenyl at 118°. Results are compared with those obtained using samples of high‐density polyethylene, of narrow molecular weight distribution, in decalin at 135° and in diphenyl at 125°.Values of the z‐average mean square radius of gyration (S−2)z, are converted to the weight‐average unperturbed state. The branching parameters g and g1 thus obtained, indicate that long‐chain branching increases with increasing molecular weight. Intrinsic ivscosities under theta‐conditions for the low‐density polyethylene fractions lead to a relationship [η]θ = Kw0·20, agreeing with the treatment of Zimm and Kilb.Some of the approximations involved in the estimation of long‐chain branching are discussed.
Flammability of plastics II. Effect of additives on the flame
Authors: Learmonth G. S. , Thwaite D. G. 
Published: March 2007

AbstractSetchkin ignition tests and candle‐burning tests have been shown to provide a numerical index of the effect of flame retardant agent on polyesters. Experimental details for a number of commercial halogenated retardants, which were tested, are given and some conclusions are made about the nature of their action.
Calorimetric method for the determination of rates of emulsion polymerisation applied to methyl methacrylate
Authors: Barrett K. E. J. , Thomas H. R. 
Published: March 2007

AbstractA small‐scale calorimetric method developed for following the rate of polymerisation of monomers in solution and in bulk has now been adapted by construction of a stirred reaction vessel for the study of rates of emulsion polymerisation recipes. Results obtained for the emulsion polymerisation of methyl methacrylate are compared with those for polymerisation under bulk conditions.
Factors affecting the setting speeds of emulsion‐based adhesives
Authors: Pritchard P. D. , Jennings C. , Sellars K. 
Published: March 2007

AbstractIn the packaging industry increase of machine speeds requires adhesives with faster setting speeds. A range of polyvinyl acetate homopolymers and copolymers has been examined on a standard paper under a standard breaking load. For the polymers examined, setting speed was increased by the use of polyvinyl alcohol as stabiliser in preference to other colloids or surfactants, by addition of polyvinyl alcohol, by copolymerisation with ‘soft’ monomers and by addition of solvent. Setting speeds were decreased by reducing the solids content, particularly below 45%, and by incorporation of inorganic fillers.Theories to explain these results are proposed.
Positively charged polyvinyl acetate emulsions—their preparation and properties
Authors: Dargan D. S. W. , Dexter R. W. 
Published: March 2007

AbstractThe preparation of positively charged polyvinyl acetate emulsions and measurement of their adsorption characteristics are described. The properties of two representative preparations, a homopolymer and a vinyl acetate‐alkyl acrylate copolymer, are given. The high adsorption of cationic emulsions makes them suitable for papers or boards which require a high polymer content to modify the properties of the sheet. Their use in the preparation of thermoplastic board is discussed.
New thermosetting resins for high performance composites
Authors: Harris G. I. 
Published: March 2007

AbstractInvestigations leading to the development of a new family of heat‐stable thermosets, the XylokRegistered trademark.
resins, are outlined. These polymers are the condensation products of aralkyl ethers or halides with phenols, and in some instances other classes of aromatic, heterocyclic and organometallic compounds, in the presence of a Friedel‐Crafts catalyst. They are fast curing and Xylok composites have been prepared with glass, asbestos and carbon fibre reinforcement, which give excellent high‐temperature mechanical strength and strength retention on prolonged exposure up to 250°. A comparative evaluation of the mechanical and electrical properties of a series of glasscloth laminates prepared with various classes of thermosetting resins has shown the Xylok resins to give outstanding overall performance. In addition, the chemical and radiation resistance, and ablative, wear and frictional properties of the Xylok composites suggest that they will find use in chemical plant, aircraft aerospace and bearing applications. Asbestos flour‐filled Xylok moulding compounds have been shown to give similar flow and curing characteristics to phenolic based products, but the mouldings are significantly more heat stable.
The synthesis of new regular copolymers and small molecules by an anionic condensation process
Authors: Richards D. H. , Scilly N. F. 
Published: March 2007

AbstractA technique based on the ‘living’ polymerisation system is described for preparing regular copolymers and small molecules. It consists of preparing a solution of monomer and a linking agent in tetrahydrofuran under an inert atmosphere; on addition of alkali metal, reaction takes place to yield polymers. A variety of dihalides, and also diepoxides and halo‐epoxides, can be used to prepare a wide range of new polymers. The method can be adapted to yield small molecules.
Selection of glass‐reinforced plastics materials for large marine structures
Authors: Beale R. F. 
Published: March 2007

AbstractSome of the material investigations which are necessary before a glass‐reinforced plastic (GRP) can be selected for use in large marine structures are described. The requirements of large‐scale manufacture are as important as mechanical performance when the basic constituents of the laminate, the polyester resin and the glass reinforcements, are being selected. Various production problems which can arise, and the need for detailed quality control, are discussed. Other areas of investigation which are appropriate are the performance of joints and fasteners, and the influence of the glass reinforcement on the impact resistance of the laminate.
Review of gel permeation chromatography
Authors: Lambert A. 
Published: March 2007

AbstractGel permeation chromatography (g.p.c.) with organic solvents is of immense value in the characterisation of plastics and resins. Topics reviewed here are column packings and packing techniques, instrumental features, theories of the separating process and of instrumental dispersion, the use of g.p.c. to measure molecular size and hydrogen bonding, the applications of g.p.c. to low molecular weight polymers, applications to high molecular weight polymers, work on glass beads (as opposed to organic beads) and high resolution g.p.c.
Polyalkylene sulphides
Authors: Cooper W. 
Published: March 2007

AbstractThe polymerisation of alkylene sulphides, particularly ethylene sulphide and propylene sulphide, initiated by salts of cadmium and zinc, or ammonia and tertiary amine catalysts, is discussed. Kinetic features of the reactions are considered and practical recipes for high and low molecular weight polymers are given. Side reactions leading to rearranged polymers or to desulphuration are discussed.Polyethylene sulphide is a high melting point, plastics material whilst polypropylene sulphide is a soft rubber or, in the isotactic form, a low melting point plastics material.Homopolymers of propylene sulphide or its unsaturated copolymers give useful oil‐resistant rubbers.The molecular weight of polypropylene sulphide is readily controlled by the addition of thiol chaintransfer agents, and low molecular weight polymers of variable functionality with thiol, amine or other reactive end‐groups are readily made. These polymers are co‐reactive with phenolic, amino or epoxy resins in laminates, adhesives and coatings.
Influence of radiation wavelength on photo‐oxidation of unstabilised PVC
Authors: Martin K. G. , Tilley R. I. 
Published: March 2007

AbstractUnstabilised PVC has been photo‐oxidised by exposure to xenon‐arc radiation from which shorter wavelengths had been removed by a series of filters. The wavelength sensitivity was found to correspond approximately to the complete ultraviolet region of the solar spectrum, maximum photo‐oxidation rates occurring at about 370 nm. Solar radiation data for Melbourne have been presented to show that variation in the ultra‐violet component with time of day and season is unimportant, to the extent that global radiation data may be utilised to characterise an exposure site with respect to the rate of photooxidation of PVC at that site.
Comparison of phonic analysis and whole word‐reading on first graders' cumulative words read and cumulative reading rate: An extension in examining instructional effectiveness and efficiency
Authors: Schmidgall Melissa , Joseph Laurice M. 
Published: March 2007

AbstractThis study compared the instructional effectiveness and efficiency of three word‐reading interventions on cumulative number of words read accurately and cumulative learning rate. Participants were six first graders who needed intensive intervention services. Alternating treatment designs were used to compare the effects of interspersal drill, a phonic analysis method consisting of word boxes (WB), and traditional drill and practice procedure on word‐reading performance. The current study extended this line of inquiry by including a phonic analysis condition and a measure of generalization. Results revealed that four students' cumulative word‐reading performances were greater under the phonic analysis condition. However, all students' cumulative rate of reading words was greater under the traditional drill and practice condition. As a group, there were no significant differences across conditions on maintaining and generalizing words. © 2007 Wiley Periodicals, Inc. Psychol Schs 44: 319–332, 2007.
Tryptic digestion of ubiquitin standards reveals an improved strategy for identifying ubiquitinated proteins by mass spectrometry
Authors: Denis Nicholas J. , Vasilescu Julian , Lambert Jean‐Philippe , Smith Jeffrey C. , Figeys Daniel 
Published: March 2007

AbstractUbiquitination plays an essential role in maintaining cellular homeostasis by regulating a multitude of essential processes. The ability to identify ubiquitinated proteins by MS currently relies on a strategy in which ubiquitinated peptides are identified by a 114.1 Da diglycine (GG) tag on lysine residues, which is derived from the C‐terminus of ubiquitin, following trypsin digestion. In the following study, we report a more comprehensive approach for mapping ubiquitination sites by trypsin digestion and MS/MS analysis. We demonstrate that ubiquitination sites can be identified by signature peptides containing a GG‐tag (114.1 Da) and an LRGG‐tag (383.2 Da) on internal lysine residues as well as a GG‐tag found on the C‐terminus of ubiquitinated peptides. Application of this MS‐based approach enabled the identification of 96 ubiquitination sites from proteins purified from human MCF‐7 breast cancer cells, representing a 2.4‐fold increase in the number of ubiquitination sites that could be identified over standard methods. Our improved MS‐based strategy will aid future studies which aim to identify and/or characterize ubiquitinated proteins in human cells.
Cellular processes underlying maturation of P19 neurons: Changes in protein folding regimen and cytoskeleton organization
Authors: Inberg Alex , Bogoch Yoel , Bledi Yaniv , Linial Michal 
Published: March 2007

AbstractEmbryonal carcinoma P19 cells provide an ideal model to study molecular programs along differentiation. Upon induction by retinoic acid (RA), the cells undergo a program of differentiation that generates functioning neurons within 60 h. RA induced cells that were plated as sparse (1000 cells/mm2) or dense (4000 cells/mm2) cultures showed a marked difference in the culture morphology with the dense cultures exhibiting rapid maturation and accelerated neurite outgrowth. The protein expression levels of the sparse and dense cultures were compared 48 h following RA. Cell extracts were separated by 1‐DE and 2‐DE and differential expression (>four‐fold) proteins were identified by MS. Here, we focus on 20 proteins associated with cytoskeletal regulation and stress‐dependent protein refolding. The first group includes drebrin, cofilin, α‐internexin, vimentin, and nestin. Among the proteins in the second group are subunits of the TCP‐1, and several chaperones of the Hsp70 and Hsp90 families. We show that coordinated remodeling of the cytoskeleton and modulations in chaperone activity underlie the change in neurite extension rate. Furthermore, a proteomics‐based analysis applied on P19 neurons demonstrated pathways underlying neuronal outgrowth, suggesting that a malfunction of such pathways leads to neuropathological conditions.
Mathematical modeling of crystallization analysis fractionation of ethylene/1‐hexene copolymers
Authors: Anantawaraskul Siripon , Jirachaithorn Preechathorn , Soares João B. P. , Limtrakul Jumras 
Published: March 2007

AbstractCrystallization analysis fractionation (Crystaf) is a polymer characterization technique for estimating the chemical composition distributions of semicrystalline copolymers. Although Crystaf has been widely used during the recent years, it is still a relatively new polymer characterization technique. More quantitative understanding of its fractionation mechanism is essential for further developments. In this work, three ethylene/1‐hexene copolymers with different 1‐hexene fractions, but similar number‐average molecular weights, were analyzed by Crystaf at several cooling rates. A mathematical model was proposed to describe the effect of comonomer fraction and cooling rate on Crystaf fractionation from a fundamental point of view. The model describes the experimental Crystaf profiles of ethylene/1‐hexene copolymers with different 1‐hexene fractions measured at distinct cooling rates very well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1010–1017, 2007
The water mediated ring closing in the formose reaction
Authors: Jalbout Abraham F. , Pavanello Michele , Adamowicz Ludwik 
Published: March 2007

AbstractIn this work, we investigate the ring closing mechanisms leading to the formation of formose by high‐level ab initio theoretical calculations. We suggest that a water‐mediated ring closing mechanism (through the use of H3O+) is energetically the most favorable pathway for this process. Solvent effects have also been computed and the results further confirm our assertion of the catalytic effect of water in the ring‐closing mechanism of the formose reaction. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Electron propagator studies of vertical electron detachment energies and isomerism in purinic deoxyribonucleotides
Authors: Zakjevskii V. V. , Dolgounitcheva O. , Zakrzewski V. G. , Ortiz J. V. 
Published: March 2007

AbstractElectron propagator calculations in the Partial Third Order Approximation were performed on major and minor conformational isomers of 2′‐deoxyriboadenosine 5′‐monophosphate (dAMP−) and 2′‐deoxyriboguanosine 5′‐monophosphate (dGMP−). Resulting vertical electron detachment energies (VEDEs) correspond extremely well with the experimental values available from the literature. The first VEDE in dGMP− is caused by electron detachment from the guanine moiety and is well separated from the rest of the spectrum. The offset of the ionization band in the case of dAMP− is caused by two, almost degenerate detachments, one from the phosphate group and another from the adenine π1 molecular orbital. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
ONIOM quantum chemistry study of cyclic nucleotide recognition in phosphodiesterase 5
Authors: O'Brien Kerrie A. , Salter E. A. , Wierzbicki A. 
Published: March 2007

AbstractCyclic nucleotide phosphodiesterases (PDEs) are enzymes that contribute to the regulation of cyclic nucleotides in the cell by catalyzing the hydrolysis reaction of the O3′‐phosphorous bond, yielding the noncyclic nucleotide as the product. The principal substrates are cyclic 3′,5′‐adenosine and ‐guanosine monophosphate (cAMP and cGMP). PDE5, an important target of drug inhibition, is known to be highly selective for hydrolysis of cGMP. We use all‐quantum hybrid calculations to accurately describe the binding interactions between PDE5 and cAMP/cGMP for the first time. The main reasons for cGMP preference in PDE5 are found to be to the fixed orientation of a conserved glutamine residue (Gln 817) together with the fixed orientation of a nonconserved glutamine residue (Gln 775). We report ONIOM(B3LYP/6‐31g(d):PM3MM) binding energies, which reflect favorable guanine alignment with Gln 817 and steric crowding of adenine by Gln 775. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Morse potential eigen‐energies through the asymptotic iteration method
Authors: Al‐Dossary O. M. 
Published: March 2007

AbstractThe eigen‐energies of the rotating Morse potential based on the original Pekeris approximation are obtained by means of the asymptotic iteration method. This approach is applied to several diatomic molecules, and it is shown that the numerical results for the eigen‐energies are all in excellent agreement with the ones obtained before. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Multistage electrospray ionization mass spectrometric analyses of sulfur‐containing iridoid glucosides in Paederia scandens
Authors: Zhou Yan , Zou Xu , Liu Xin , Peng Shu‐lin , Ding Li‐sheng 
Published: March 2007

AbstractPaederia scandens is a traditional Chinese herbal medicine that possesses important bioactive sulfur‐containing iridoid glucosides. This study reports the investigation of the fragmentation behavior of four sulfur‐containing iridoid glucosides isolated from P. scandens by ion trap electrospray ionization tandem mass spectrometry (ESI‐MSn). Both multistage electrospray ionization (ESI‐MSn) experiments in an ion trap instrument and high‐resolution and accurate mass measurement in an ESI‐Q‐TOF mass spectrometer in positive mode were used to elucidate the main fragmentation pathways of these compounds. These experiments yielded essentially the same product ions in both ion trap and Q‐TOF instruments, and their fragmentation patterns were found useful for their characterization, which were applied to elucidate a trace compound in the extracts of P. scandens by on‐line LC/ESI‐MSn. Major and diagnostic product ions have been identified and their origins are proposed. Copyright © 2007 John Wiley & Sons, Ltd.
An online method combining a thermal conversion elemental analyzer with isotope ratio mass spectrometry for the determination of hydrogen isotope composition and water concentration in geological samples
Authors: Gong Bing , Zheng Yong‐Fei , Chen Ren‐Xu 
Published: March 2007

AbstractAn online continuous‐flow method, combining a thermal conversion elemental analyzer (TC/EA) with isotope ratio mass spectrometry (MS), is evaluated for the determination of both the hydrogen isotope composition and the water concentration of hydrous and nominally anhydrous minerals. The technique involves reduction of hydrous minerals or nominally anhydrous minerals by reaction with glassy carbon at 1450°C in a helium stream. The product gases, H2 and CO, are separated on a gas chromatographic column prior to analysis in the mass spectrometer. Calibration curves for the H concentration analysis were generated from a standard of benzoic acid (C7H6O2) that has an H concentration of 5.0 wt%; the analytical uncertainties were better than ±0.05% in our runs. Two standards of material with given δD values, polyethylene IAEA‐CH‐7 and biotite NBS‐30, were tested for the purpose of calibrating a natural garnet 04BXL02 representing nominally anhydrous minerals. Preheating at 90°C for 12 h was found to be suitable for removing adsorption water on the sample surface. This results in constant δD values and total H2O contents for the garnet, with weighted means of −94 ± 1‰ and 522 ± 11 ppm (wt), respectively. The TC/EA‐MS technique allows routine analysis of sample sizes as small as 0.01 µL H2O. For natural minerals, absolute reproducibilities for δD values are ±0.5‰ to ±2‰ (1σ) and relative uncertainties for total H2O concentrations are at levels of ±1% to ±3% (1σ). Therefore, this online method can be used for the quantitative determination of H isotope composition and H2O concentration of either hydrous or anhydrous minerals. Copyright © 2007 John Wiley & Sons, Ltd.
2‐Substituted benzofuran fragment ion formation in the electron ionization mass spectra of 6‐alkyl‐ and 6‐aryldibenzo(d,f)(1,3)dioxepine derivatives. 1. Spirocyclization of the molecular ions in the gas phase
Authors: Begala Michela , Tocco Graziella , Meli Gabriele , Podda Gianni , Urru Silvana A. M. 
Published: March 2007

AbstractThe formation of 2‐substituted benzo[b]furan ions in the electron ionization (EI) mass spectra of a series of 6‐alkyl‐ and 6‐aryldibenzo(d,f)(1,3)dioxepines has been studied by means of exact mass measurements and multiple‐stage mass spectrometry conditions using an ion trap mass spectrometer. The proposed mechanism of formation of benzo[b]furan ions requires the formation of a spirocyclic cyclohexadienone system, which undergoes elimination of a cyclopentadienone molecule. A parallel with the chemical conversion of arylmethyl‐substituted dibenzo(d,f)(1,3)dioxepines into an analogous spirocyclic system was also underlined. Copyright © 2007 John Wiley & Sons, Ltd.
Iterative interference cancellation and channel estimation in multibeam satellite systems
Authors: Millerioux J. P. , Boucheret M. L. , Bazile C. , Ducasse A. 
Published: March 2007

AbstractThis paper deals with the use of non‐linear multiuser detection techniques to mitigate co‐channel interference on the reverse link of multibeam satellite systems. These techniques allow more capacity efficient frequency reuse strategies than classical ones, as they make possible to cope with lower C/I. The considered system takes as a starting point the DVB‐RCS standard, with the use of convolutional coding, and the use of the Ka‐band.We propose different iterative interference cancellation schemes, which operate at the beamformer outputs, and which use information from decoders. The proposed receivers assume an initial single‐user synchronization step: frame synchronization and timing recovery, and then perform channel estimation: beamformer coefficients; signal carrier phases and signal amplitudes.In a first step, these receivers are evaluated by simulation in terms of bit error rate and of channel estimation error on two interference configurations. For one of these receivers, sensitivity to imperfect timing recovery and to low‐frequency offsets from user terminals is evaluated.In a second step, since the receiver performances highly depend on the interference configuration, we propose an approach to evaluate performances on a multibeam coverage (by taking into account the variability of interference configurations on the coverage). This method is used to compare different receivers on an example based on a coverage designed on a digital focal array feed reflector antenna. Copyright © 2007 John Wiley & Sons, Ltd.
CEO tenure and organizational performance: an intervening model
Authors: Simsek Zeki 
Published: March 2007

AbstractWhile CEO job tenure is seen as influencing firm performance, the intervening mechanisms that govern this influence have remained largely unexplored. Given that individuals in the firm most closely influenced by the CEO are members of the top management team (TMT), we focus on the CEO‐TMT interface as one important intervening mechanism. Specifically, our tested model suggests that CEO tenure indirectly influences performance through its direct influences on TMT risk‐taking propensity and the firm's pursuit of entrepreneurial initiatives. Results from structural equation modeling are consistent with this model and support its associated hypotheses. In the discussion, we trace the implications of our study for research and practice. Copyright © 2007 John Wiley & Sons, Ltd.