bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of filler size distribution on the mechanical and physical properties of alumina‐filled silicone rubber
Authors: Zhou Wenying , Yu Demei , Wang Caifeng , An Qunli , Qi Shuhua 
Published: May 2008

AbstractThe properties of silicone rubber filled with three kinds of binary mixtures of alumina particles with different size distribution (i.e., 30 μm + 0.5 μm, 10 μm + 0.5 μm, and 5 μm + 0.5 μm) were investigated as a function of relative volume fraction of the 0.5 μm particles in the hybrid alumina (Vs) at a fixed total filler content of 55 vol%. The results indicate that each binary mixture of alumina‐filled silicone rubber exhibited improved thermal conductivity and tensile strength, and decreased dielectric constant, compared to a single particle size filler‐reinforced one, and the maximum improvements were obtained at the Vs ranging from 0.2 to 0.35; the coefficient of thermal expansion (CTE) of filled silicone rubber obviously reduced with increase in the Vs, whereas the elongation at break slightly decreased. At Vs = 0, the larger particles‐filled silicone rubber showed higher thermal conductivity, CTE, dielectric constant, and elongation at break, and lower tensile strength compared with the those of the smaller particles‐filled one. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Influence of compatibilizer precursor structure on the phase distribution of low density poly(ethylene) in a poly(ethylene terephthalate) matrix
Authors: Coltelli Maria‐Beatrice , Harrats Charef , Aglietto Mauro , Groeninckx Gabriel 
Published: May 2008

AbstractIn attempt to enhance the compatibility of PET/LDPE blends by using a proper functionalized polymer as third component, diethyl maleate (DEM)‐functionalized ultralow density poly(ethylene) (ULDPE‐g‐DEM) and styrene‐b‐(ethylene‐co‐1‐butene)‐b‐styrene triblock copolymer (SEBS‐g‐DEM) were prepared by radical functionalization in the melt. Immiscible PET/LDPE blends having compositions of 70/30 and 80/20 by weight were then extruded in the presence of 1–10% by weight of ULDPE‐g‐DEM and SEBS‐g‐DEM as compatibilizer precursors and ZnO (0.3% by weight) as transesterification catalyst. In both cases, evidences about the occurring of compatibilization between the two immiscible phases, thanks to the studied reactive processes, were obtained. Moreover, the phase distribution and particle size of blends were deeply investigated. Completely different kinds of phase morphology were achieved, as ULDPE‐g‐DEM stabilized a dispersed phase morphology, whereas SEBS‐g‐DEM favored the development of a cocontinuous phase morphology. The observed differences are tentatively explained onthe basis of reactivity and physical features of polymers. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.
A study on a primitive artificial esterase model: reactivity of a calix[4]resorcinarene bearing carboxyl groups
Authors: Cevasco Giorgio , Galatini Andrea , Pirinççioğlu Necmettin , Thea Sergio , Williams Andrew 
Published: May 2008

AbstractThe host molecule octacarboxymethyl calix[4]resorcinarene 1 catalyses the hydrolysis of substituted phenyl N‐methylpyridinium‐4‐carboxylate esters 3a–f by complexation followed by intracomplex reaction via an anhydride intermediate. The reactivity in the presence of 1 is higher than that of the background at low pH; at high pH an inversion of reactivity occurs, the background becomes predominant since the host inhibits hydrolysis of the esters. The reactivity of esters 3a–f complexed with the host suffers little change in effective charge on the phenolic oxygen (−0.15 units) in contrast with the changes observed in alkaline hydrolysis (−0.28 units) and in the hydrolysis of the model monoaryl glutarate esters (‐1.02 units). The less negative effective charge in the transition state for host 1 catalysis compared with that in the glutarate case is ascribed to stronger solvation by water molecules in the complex compared with that due to water molecules in the bulk solvent.
The role of stereoelectronic interactions in the conformational isomerism of some phosphorus‐containing model compounds
Authors: Freitas Matheus P. , Rittner Roberto , Tormena Cláudio F. , Abraham Raymond J. 
Published: May 2008

AbstractThe rotational isomerism of model phosphorus‐containing compounds was evaluated by using theoretical methodologies. The trans rotamer of chloromethylphosphonic acid dichloride (1) was found to be the prevailing form in the gas phase and in non‐polar solvents, with an inverse behaviour from chloroform solution. Although the use of direct spin–spin coupling constants (SSCCs) do not apply for the quantitative determination of conformers in 1, due to the small dependence of J with conformation, the observed measurements and calculated individual couplings suggest that the gauche conformer is progressively stabilized with increasing the solvent polarity. In addition, theoretical calculations at the CBS‐Q level for the corresponding phosphine of 1 (compound 2) showed the gauche rotamer as the prevailing one in the isolated state. Natural Bond Orbital (NBO) analysis indicated that steric and electrostatic effects rule the rotational isomerism of 1, while the anomeric effect nP → σ*CCl also plays an important role on the conformational equilibrium of 2. Copyright © 2008 John Wiley & Sons, Ltd.
Photochemistry of thiophene‐S‐oxide derivatives
Authors: Heying Melanie J. , Nag Mrinmoy , Jenks William S. 
Published: June 2008

AbstractPhotolysis of substituted thiophene‐S‐oxides in solution results in the formation of either the corresponding thiophene or furan, in addition to uncharacterized materials. No good rationalization is available for the choice of which pathway may predominate, but it is demonstrated that the photolysis of 2,5‐bistrimethylsilylthiopene‐ S‐oxide produces O(3P) in the same manner as the well‐established photolysis of dibenzothiophene‐S‐oxide. Copyright © 2008 John Wiley & Sons, Ltd.
Impact of intermolecular hydrogen bond on structural properties of phenylboronic acid: quantum chemical and X‐ray study
Authors: Cyrański Michał K. , Jezierska Aneta , Klimentowska Paulina , Panek Jarosław J. , Sporzyński Andrzej 
Published: May 2008

AbstractThe molecular structure and properties of phenylboronic acid were investigated experimentally using X‐ray structural analysis and spectroscopic methods. Infrared (IR) spectroscopy measurements were performed to assess the hydrogen bonding strength. The experimental part is enhanced by computational results concerning the geometrical and electronic structure. The molecular dimer (basic structural motif) was investigated on the basis of density functional theory (DFT) and Møller–Plesset second order (MP2) perturbation theory. The basis‐set superposition error (BSSE) was calculated to correct the binding energy. Atoms in molecules (AIM) and topological analysis of electron localization function (ELF) were applied to study the intermolecular hydrogen bond properties and localization pattern for the neighborhood of the boron atom. The anharmonicity of the hydrogen bond potential function was studied by solving the time‐independent Schrödinger equation. Potential energy distribution (PED) analysis of the normal modes was performed to identify the characteristic frequencies of the studied system. Subsequently, the interaction energy for the dimeric form was decomposed using the symmetry‐adapted perturbation theory (SAPT) scheme. Car–Parrinello molecular dynamics (CPMD) gave an insight into dynamical processes occurring in the phenylboronic acid dimerin vacuo. The hydrogen bridge protons in the phenylboronic acid are not shifted significantly toward the acceptor. Lower dimerization energy with respect to the carboxylic acid dimers is explained on the basis of the interaction energy decomposition as the effect of diminished induction term. The employment of SAPT and CPMD approaches is a step forward in the understanding of the physico‐chemical nature of the large family represented by the investigated compound. Copyright © 2008 John Wiley & Sons, Ltd.
H‐shaped (ABCDE type) quintopolymer via click reaction [3 + 2] strategy
Authors: Gungor Eda , Durmaz Hakan , Hizal Gurkan , Tunca Umit 
Published: May 2008

AbstractH‐shaped quintopolymer containing different five blocks: poly(ε‐caprolactone) (PCL), polystyrene (PS), poly(ethylene glycol) (PEG), and poly(methyl methacrylate) (PMMA) as side chains and poly(tert‐butyl acrylate) (PtBA) as a main chain was simply prepared from a click reaction between azide end‐functionalized PCL‐PS‐PtBA 3‐miktoarm star terpolymer and PEG–PMMA‐block copolymer with alkyne at the junction point, using Cu(I)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as a catalyst in DMF at room temperature for 20 h. The H‐shaped quintopolymer was obtained with a number–average molecular weight (Mn) around 32,000 and low polydispersity index (Mw/Mn) 1.20 as determined by GPC analysis in THF using PS standards. The click reaction efficiency was calculated to have 60% from 1H NMR spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4459–4468, 2008
Stilbene‐containing polyactylenes: Molecular design, synthesis, and relationship between molecular structure and NLO properties
Authors: Su Xinyan , Xu Hongyao , Guo Quanzhen , Shi Guang , Yang Junyi , Song Yinglin , Liu Xiangyang 
Published: May 2008

AbstractPolyacetylenes (P1–P4) containing different stilbene groups, [(CHC) PhCHCHPhR]n(ROCmH2m+1 (m = 4 (P1), 10 (P2), 16 (P3)), or NO2 (P4)) were designed and synthesized, respectively, using [Rh(nbd)Cl]2 as a catalyst. Their structures and properties were characterized and evaluated by FTIR, 1H‐NMR, 13C‐NMR, GPC, and UV, PL, respectively. The optical limiting and nonlinear optical properties were investigated by using a frequency doubled, Q‐switched, mode‐locked Continuum ns/ps Nd:YAG laser system and their optical limiting mechanism was discussed. It is surprising to see that the stilbene pendants endow the polyacetylenes with a high thermal stability (Td ≥ 270 °C), novel optical limiting properties and large third‐order nonlinear optical susceptibilities (up to 4.61 × 10−10 esu). The optical limiting mechanism is mainly originated from reverse saturable absorption of molecules. In addition, it is found that the polymer with electron accepted NO2 moiety exhibits better optical properties than that with electron donated alkoxy group because of larger π electron delocalization and dipolar effect. The strong interaction between stilbene pendants and the polyene main chain significantly results in red‐shift of fluorescence emitting peak. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4529–4541, 2008
Structural comparison of products from peroxide‐initiated grafting of vinylsilane and silane‐functionalized nitroxyl to hydrocarbon and polyolefin substrates
Authors: Weaver J. D. , Chowdhury A. K. , Mowery D. M. , Esseghir M. , Cogen J. M. , Chaudhary B. I. 
Published: May 2008

AbstractIt has been demonstrated that peroxide‐initiated grafting of vinylsilanes to polyethylene results in a nonuniform distribution of silane groups on the polymer chain due to a chain‐transfer mechanism, leading to inefficient utilization of silane with respect to gel fraction in a crosslinked material. In this article, we demonstrate that grafting a nitroxyl free radical that contains a silane functional group gives a more uniform distribution of silane functionality. Model compounds were synthesized by grafting a silane‐functionalized TEMPO derivative and a vinylsilane to cyclooctane, and their structures were compared. The product grafted with vinyltriethoxysilane consisted of essentially all multigrafted product with an average of 2.26 silane grafts per cyclooctane molecule, which is in close agreement with published data, while the product of grafting the silane‐functional nitroxyl consisted of only the monografted species; no multigrafted product was detected. This confirms that grafting a silane‐functionalized nitroxyl occurs via bimolecular combination of free radicals that is not affected by chain‐transfer and suggests that the process may lead to more efficient utilization of silane as indicated by higher gel fraction for a given level of grafted silane. Synthetic work to prepare silane‐functionalized TEMPO derivatives and preliminary studies to graft them to polyolefins are discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4542–4555, 2008
Hydrogen‐bond‐assisted syndiotactic‐specific radical polymerizations of N‐alkylacrylamides: The effect of the N‐substituents on the stereospecificities and unusual large hysteresis in the phase‐transition behavior of aqueous solution of syndiotactic poly(N‐n‐propylacrylamide)
Authors: Hirano Tomohiro , Nakamura Kimihiko , Kamikubo Takahiro , Ishii Satoshi , Tani Kanami , Mori Takeshi , Sato Tsuneyuki 
Published: May 2008

AbstractThe radical polymerizations of N‐alkylacrylamides, such as N‐methyl‐(NMAAm), N‐n‐propyl‐(NNPAAm), N‐benzyl‐(NBnAAm), and N‐(1‐phenylethyl)acrylamides (NPhEAAm), at low temperatures were investigated in the absence or presence of hexamethylphosphoramide (HMPA) and 3‐methyl‐3‐pentanol (3Me3PenOH), which induced the syndiotactic specificities in the radical polymerization of N‐isopropylacrylamide (NIPAAm). In the absence of the syndiotactic‐specificity inducers, the syndiotacticities of the obtained polymers gradually increased as the bulkiness of the N‐substituents increased. Both HMPA and 3Me3PenOH induced the syndiotactic specificities in the NNPAAm polymerizations as well as in the NIPAAm polymerizations. The addition of 3Me3PenOH into the polymerizations of NMAAm significantly induced the syndiotactic specificities, whereas the tacticities of the obtained polymers were hardly affected by adding HMPA. In the polymerizations of bulkier monomers, such as NBnAAm and NPhEAAm, HMPA worked as the syndiotactic specificity inducer at higher temperatures, whereas 3Me3PenOH hardly influenced the stereospecificity, regardless of the temperatures. The phase‐transition behaviors of the aqueous solutions of poly(NNPAAm)s were also investigated. It appeared that the poly (NNPAAm) with racemo dyad content of 70% exhibited unusual large hysteresis between the heating and cooling processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4575–4583, 2008
New Method for Prediction of the Gurney Energy of High Explosives
Authors: Keshavarz Mohammad Hossein 
Published: June 2008

AbstractAn empirical new correlation is used to calculate the Gurney velocity as an important parameter for the estimation of explosive energy output without considering the heat contents of explosives and detonation products. The number of nitrogen molecules as well as the ratios of oxygen to carbon and hydrogen to oxygen are the fundamental factors in the new method. The new correlation may be applied to any CaHbNcOd explosive, in which b is nonzero, at any loading density. The calculated Gurney velocity for both pure and explosive formulations shows good agreement with respect to measured values. Moreover, there is no need to use any assumed decomposition reaction.
Computational study of colipase interaction with lipid droplets and bile salt micelles
Authors: Kerfelec Brigitte , Allouche Maya , Colin Damien , Van Eyck Marie Hélène , Brasseur Robert , Thomas Annick 
Published: May 2008

AbstractColipase is a key element in the lipase‐catalyzed hydrolysis of dietary lipids. Although devoid of enzymatic activity, colipase promotes the pancreatic lipase activity in physiological intestinal conditions by anchoring the enzyme at the surface of lipid droplets. Analysis of structures of NMR colipase models and simulations of their interactions with various lipid aggregates, lipid droplet, and bile salt micelle, were carried out to determine and to map the lipid binding sites on colipase. We show that the micelle and the oil droplet bind to the same side of colipase 3D structure, mainly the hydrophobic fingers. Moreover, it appears that, although colipase has a single direction of interaction with a lipid interface, it does not bind in a specific way but rather oscillates between different positions. Indeed, different NMR models of colipase insert different fragments of sequence in the interface, either simultaneously or independently. This supports the idea that colipase finger plasticity may be crucial to adapt the lipase activity to different lipid aggregates. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Effect of mixed macromolecular crowding agents on protein folding
Authors: Zhou Huan‐Xiang 
Published: May 2008

AbstractIn cells, proteins fold and unfold in the presence of macromolecules with various sizes and shapes. Recent experiments by Liang and coworkers (J Biol Chem 2004;279:55109–55116; J Mol Biol 2006;364:469–482) show that protein refolding is enhanced by a mixture of two different crowding agents relative to the individual crowding agents and an optimal mixing ratio exists. Here, we present a theory that predicts the existence of an optimal mixing ratio. The theory is based on models for calculating the changes in the chemical potentials of the folded and unfolded states by a mixture of crowders. The existence of an optimal mixing ratio results from the dependences of these chemical‐potential changes on crowder sizes and concentrations, which can be argued to be quite general. We further predict that, for any crowding agent, the stabilizing effect can be optimized both by varying the molecular weight and the mixing ratio of two species with different molecular weights. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Molecular strategies for protein stabilization: The case of a trehalose/maltose‐binding protein from Thermus thermophilus
Authors: Scirè Andrea , Marabotti Anna , Aurilia Vincenzo , Staiano Maria , Ringhieri Paola , Iozzino Luisa , Crescenzo Roberta , Tanfani Fabio , D'Auria Sabato 
Published: May 2008

AbstractThe trehalose/maltose‐binding protein (MalE1) is one component of trehalose and maltose uptake system in the thermophilic organism Thermus thermophilus. MalE1 is a monomeric 48 kDa protein predominantly organized in α‐helix conformation with a minor content of β‐structure. In this work, we used Fourier‐infrared spectroscopy and in silico methodologies for investigating the structural stability properties of MalE1. The protein was studied in the absence and in the presence of maltose as well as in the absence and in the presence of SDS at different p2H values (neutral p2H and at p2H 9.8). In the absence of SDS, the results pointed out a high thermostability of the MalE1 α‐helices, maintained also at basic p2H values. However, the obtained data also showed that at high temperatures the MalE1 β‐sheets underwent to structural rearrangements that were totally reversible when the temperature was lowered. At room temperature, the addition of SDS to the protein solution slightly modified the MalE1 secondary structure content by decreasing the protein thermostability. The infrared data, corroborated by molecular dynamics simulation experiments performed on the structure of MalE1, indicated that the protein hydrophobic interactions have an important role in the MalE1 high thermostability. Finally, the results obtained on MalE1 are also discussed in comparison with the data on similar thermostable proteins already studied in our laboratories. Proteins 2008. © 2008 Wiley‐Liss, Inc.
Effects of uniaxial stress on the magnetic properties of thin films and GMR sensors prepared on polyimide substrates
Authors: Özkaya Berkem , Saranu Srinivasa Rao , Mohanan Senthilnathan , Herr Ulrich 
Published: June 2008

AbstractThe effects of externally applied uniaxial stress on the magnetic properties of Co thin films and pseudo‐spin‐valve (PSV) structures on flexible polyimide substrates were investigated. The advantage of the polyimide substrate is its flexibility and high elasticity (∼1%), which cannot be achieved using conventional crystalline substrates. The Co layers exhibit a macroscopic easy axis induced by the preparation process. When the stress is applied perpendicular to the induced in‐plane easy axis, the magnetic domains in the film rotate towards the applied stress direction, which was confirmed using Kerr microscopy and magneto‐optical Kerr effect (MOKE) magnetometer measurements. A Co/Cu/Ni PSV system was prepared on polyimide substrate with dc magnetron sputtering. Applying uniaxial stress leads to opposite rotation of the magnetisation directions in both layers to each other due to different signs of the magnetostriction coefficients of Co and Ni. The magnetisation and giant magnetoresistance (GMR) curves under applied stress were recorded using in situ MOKE and current in‐plane four‐point probe techniques, respectively. When the stress is applied perpendicular to the external magnetic field (Hext), the operating range of the GMR sensor increases, whereas the sensitivity decreases. Anisotropy energies and saturation magnetostriction values of the Co and Ni layer were determined by fitting the GMR and magnetisation curves using a micromagnetic model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Complex oxide scintillators: Material defects and scintillation performance
Authors: Nikl M. , Laguta V. V. , Vedda A. 
Published: June 2008

AbstractAn overview of recognized structural defects, impurities and related trapping levels and their role in the scintillation mechanism is provided and discussed in single crystal materials belonging to tungstate, Ce‐ or Pr‐doped aluminum perovskite, garnet and finally to Ce‐doped silicate scintillators. New achievements and open problems in deeper understanding of electron and hole self‐trapping phenomena and of the nature of defects in the crystal structure and their ability to localize migrating charge carriers are indicated. Fast optical ceramics and nanocomposite materials are pointed out as possible future advanced scintillators. Such novel technologies can in principle explore materials which are not available in the bulk single crystal form, but their figure‐of‐merit is dramatically dependent on the surface‐interface defect states and related trapping and nonradiative recombination phenomena. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Band‐structure calculations and electron momentum densities of AgCl and AgBr
Authors: Rathor A. , Arora G. , Ahuja B. L. 
Published: June 2008

AbstractWe report the band‐structure calculations and the first ever electron momentum densities of AgCl and AgBr. Isotropic Compton profiles of these compounds are measured at an intermediate resolution using a 20 Ci 137Cs Compton spectrometer. We have computed Compton profiles, energy bands, density of states and charge density using Hartree–Fock and density‐functional theories. It is seen that the Hartree–Fock theory‐based Compton line shapes are in a better agreement with the measurements. In addition, we have also derived the energy bands and density of states using the full‐potential linearized augmented plane‐wave method. The Compton data is also analyzed at the equal‐valence‐electron‐density scale. The present data shows that AgBr is more covalent than AgCl, which is in agreement with the present Mulliken's population analysis, valence charge densities and other available ionicity trends. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
DC characteristics of AlGaN/GaN high electron mobility transistors
Authors: Inada Masaki , Nakajima Akira , Piao Guanxi , Shimizu Mitsuaki , Yano Yoshiki , Ubukata Akinori 
Published: June 2008

AbstractThe dependence of DC operating characteristics on the device dimensions in AlGaN/GaN HEMTs is systematically obtained varying the device parameters in relatively wide range. The maximum transconductance gm,max and the maximum drain current ID,max depend on both the source‐gate distance LSG and the gate length LG rather than LG only, and proportional to (LSG+LG)–0.5, which is different from the case of the GaAs or Si FET model. Influence of the source‐gate distance LSG on the DC characteristics of AlGaN/GaN high electron mobility transistors is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)