bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytical study of the buoyancy–drag equation
Authors: Bouquet Serge , Gandeboeuf Pierre , Pailhoriès Pierre 
Published: August 2007

AbstractThe buoyancy–drag equation (BDE) is used for describing the time evolution of the mixing zone, between two fluids, due to Rayleigh–Taylor instabilities in a highly non‐linear regime. The BDE is similar to an equation of motion for each fluid and, in addition to the inertial term, it contains a buoyancy term (proportional to the external acceleration experienced by the system) and a friction proportional to the square of the velocity. In this paper, the integrability of the BDE is studied using Lie point symmetries. Two relevant situations are studied analytically. First, for a constant acceleration, the general solution with two arbitrary constants is derived. On the other hand, for accelerations varying like a power of time, we obtain a one‐parameter family of solutions. These theoretical results can be compared with the various experimental results published in the current literature. Copyright © 2007 John Wiley & Sons, Ltd.
Theory and finite element computation of cyclic martensitic phase transformation at finite strain
Authors: Stein Erwin , Sagar Gautam 
Published: August 2007

AbstractA generalized variational formulation, including quasi‐convexification of energy wells for arbitrarily many martensitic variants in case of mono‐crystals for linearized strains, was developed by Govindjee and Miehe (Comp. Meth. Appl. Mech. Eng. 2001; 191(3–5):215–238) and computationally extended by Stein and Zwickert (Comput. Mech. 2006; in press). This work is generalized here for finite strain kinematics with monotonous hyperelastic stress–strain functions in order to account for large transformation strains that can reach up to 15%.A major theoretical and numerical difficulty herein is the convexification of the finite deformation phase transformation (PT) problems for multiple phase variants, n⩾2. A lower bound of the mixing energy is provided by the Reuss bound in case of linear kinematics and an arbitrary number of variants, shown by Govindjee et al. (J. Mech. Phys. Solids 2003; 51(4):I–XXVI). In case of finite strains, a generalized representation of free energy of mixing is introduced for a quasi‐Reuss bound, which in general holds for n⩽2.Numerical validation of the used micro–macro material model is presented by comparing verified numerical results with the experimental data for Cu82Al14Ni4 monocrystals for quasiplastic PT, provided by Xiangyang et al. (J. Mech. Phys. Solids 2000; 48:2163–2182). The zigzag‐type experimental stress–strain curve within PT at loading, called ‘yield tooth’, is approximated within the finite element analysis by a smoothly decreasing and then increasing axial stress which could not be achieved with linearized kinematics yielding a constant axial stress during PT. Copyright © 2007 John Wiley & Sons, Ltd.
Coupling electrical and mechanical effects in discrete element simulations
Authors: Renouf M. , Fillot N. 
Published: August 2007

AbstractWhen investigating the electrical characteristics of granular assemblies under dynamical solicitations (powder, steel bead assemblies, etc.), it is difficult to distinguish between effects that are purely electrical and those that are strongly dependent on mechanical effects. Although numerous experimental works have permitted better understanding of the static electrical behaviour of such media, it is difficult to determine the effects control the multi‐physical behaviour of the medium, especially under dynamical solicitations.In the present paper, numerical investigations of the electrical characteristics of granular material are proposed. Moreover, it presents the formulation of a new model, embedded in the general scheme of discrete element methods, that couples electrical and mechanical effects and takes into account the oxidation phenomenon. Numerical simulations on the basis of experimental works are performed to
validate the model, and the results of dynamical simulations are discussed. Copyright © 2007 John Wiley & Sons, Ltd.
From patronage politics to community deliberation: the recent experience of democratic school management in Brazil
Authors: Borges André 
Published: August 2007

AbstractThe article discusses the limits and possibilities of school empowerment within education systems plagued by pervasive patronage politics. The analysis focuses on reform initiatives implemented by Brazilian sub‐national governments throughout the 1980s and 1990s to allow for the election of school principals by parents, teachers and students. Until the implementation of this reform, state and local authorities had relied on the school system as a source of patronage resources, and principals were nominated according to political criteria. The new system of democratic school management was expected to undermine this patronage‐based system and foster community participation in school decisions. The article relies on secondary evidence to assess the impact of school elections in what concerns the participation of parents, students and teachers in school affairs and the relationship between schools, party politicians and education administrators. It concludes that high levels of social inequality and the lack of a universalistic and effective system of welfare provision constitute serious obstacles to the empowerment of disadvantaged groups in developing societies such as Brazil. On the other hand, the article argues that school empowerment has the potential to undermine resilient patronage structures, by introducing universalistic mechanisms of decision‐making and making school administrators more accountable to their constituencies. Copyright © 2007 John Wiley & Sons, Ltd.
A comparison of pioglitazone and rosiglitazone for hospitalization for acute myocardial infarction in type 2 diabetes
Authors: Gerrits Charles M. , Bhattacharya Mondira , Manthena Shivaji , Baran Robert , Perez Alfonso , Kupfer Stuart 
Published: August 2007

AbstractBackgroundRecent studies have raised concerns about potential increased cardiovascular (CV) risk in type 2 diabetes patients treated with some peroxisome proliferator‐activated receptor gamma (PPAR‐gamma) agonists.ObjectiveTo ascertain the risk of hospitalization for acute myocardial infarction (AMI) in type 2 diabetes patients treated with pioglitazone relative to rosiglitazone.MethodologyUsing data covering 2003–2006 from a large health care insurer in the US, a retrospective cohort study was conducted in patients who initiated treatment with pioglitazone or rosiglitazone. The hazard ratio (HR) of incident hospitalization for AMI after initiation of treatment with these drugs was estimated from multivariate Cox's proportional hazards survival analysis; similarly, the HR was ascertained for hospitalization for the composite endpoint of AMI or coronary revascularization (CR).ResultsA total of 29 911 eligible patients were identified in the database; 14 807 in the pioglitazone and 15 104 in the rosiglitazone group. Baseline demographics, medical history, and dispensed medications were generally well balanced between groups. The unadjusted HR for hospitalization for AMI was 0.82, 95%CI: 0.67–1.01. After adjustment for baseline covariates the HR was 0.78, 95%CI: 0.63–0.96. The adjusted HR for the composite of AMI or CR was 0.85, 95%CI: 0.75–0.98.ConclusionThis retrospective cohort study showed that pioglitazone, in comparison with rosiglitazone, is associated with a 22% relative risk reduction of hospitalization for AMI in patients with type 2 diabetes. Copyright © 2007 John Wiley & Sons, Ltd.
Synthesis and proton conductivity of poly(styrene sulfonic acid)/heterocycle‐based membranes
Authors: Göktepe Fadime , Bozkurt Ayhan , Günday Şeyda T 
Published: August 2007

AbstractBACKGROUND: High proton conduction through anhydrous polymer electrolyte membranes is crucial for the application to chemical energy conversion devices such as fuel cells. In this context, novel proton conductors were produced by doping poly(styrene sulfonic acid) (PSSA) with 1H‐1,2,4‐triazole (Tri) and 1.12‐diimidazol‐2‐yl‐2,5,8,11‐tetraoxadodecane (imi3), and their physicochemical properties were investigated.RESULTS: Different polymer electrolyte membranes were produced by doping of PSSA with Tri and imi3. PSSATrix and PSSAimi3x electrolytes were obtained where x is the doping ratio describing moles of Tri or imi3 per mole of SO3H unit. The membranes demonstrated adequate thermal stability at least up to 200 °C and the dopants acted as plasticizers shifting the Tg values to lower temperatures. PSSATri1 has a maximum proton conductivity of 0.016 S cm−1 at 150 °C and the proton conductivity of PSSAimi30.5 is approximately 10−4 S cm−1 at room temperature.CONCLUSIONS: Transparent, homogeneous and freestanding films of PSSATrix and PSSAimi3x were produced. It was demonstrated that both Tri and imi3 are efficient proton solvents in PSSA host matrix, and they yielded promising defect‐type conductivities compared to benzimidazole. Tri‐doped membranes clearly showed better conductivity performance at higher temperatures (T > 100 °C). Both PSSATrix and PSSAimi3x polymer electrolytes can be suggested for fuel cell applications. Copyright © 2007 Society of Chemical Industry
Polyamide–silica nanocomposites: mechanical, morphological and thermomechanical investigations
Authors: Sarwar Muhammad Ilyas , Zulfiqar Sonia , Ahmad Zahoor 
Published: August 2007

AbstractBACKGROUND: The physical properties of polyamides can be enhanced through incorporation of inorganic micro‐ and nanofillers such as silica nanoparticles. Transparent sol‐gel‐derived organic‐inorganic nanocomposites were successfully prepared by in situ incorporation of a silica network into poly(trimethylhexamethylene terephthalamide) using diethylamine as catalyst. Thin films containing various proportions of inorganic network obtained by evaporating the solvent were characterized using mechanical, dynamic mechanical thermal and morphological analyses.RESULTS: Tensile measurements indicate that modulus as well as stress at yield and at break point improved while elongation at break and toughness decreased for the hybrid materials. The maximum value of stress at yield point (72 MPa) was observed with 10 wt% silica while the maximum stress at break point increased up to 66 MPa with 20 wt% silica relative to that of pure polyamide (44 MPa). Tensile modulus was found to increase up to 2.59 GPa with 10 wt% silica in the matrix. The glass transition temperature and the storage moduli increased with increasing silica content. The maximum increase in the Tg value (144 °C) was observed with 20 wt% silica. Scanning electron microscopy investigation gave the distribution of silica, with an average particle size ranging from 3 to 24 nm.CONCLUSION: These results demonstrate that nanocomposites with high mechanical strength can be prepared through a sol‐gel process. The increase in the Tg values suggests better cohesion between the two phases, and the morphological results describe a uniform dispersion of silica particles in the polymer matrix at the nanoscale. Copyright © 2007 Society of Chemical Industry
Facile synthesis and characterization of hyperbranched poly(ether amide)s generated from Michael addition polymerization of in situ created AB2 monomers
Authors: Lin Ying , Dong Zhong‐Ming , Liu Xiao‐Hui , Li Yue‐Sheng 
Published: August 2007

AbstractA new straightforward strategy for synthesis of novel hyperbranched poly (ether amide)s from readily available monomers has been developed. By optimizing the reaction conditions, the AB2‐type monomers were formed dominantly during the initial reaction stage. Without any purification, the AB2 intermediate was subjected to further polymerization in the presence (or absence) of an initiator, to prepare the hyperbranched polymer‐bearing multihydroxyl end‐groups. The influence of monomer, initiator, and solvent on polymerization and the molecular weight (MW) of the resultant polymers was studied thoroughly. The MALDI–TOF MS of the polymers indicated that the polymerization proceeded in the proposed way. Analyses of 1H NMR and 13C NMR spectra revealed the branched structures of the polymers obtained. These polymers exhibit high‐moderate MWs and broad MW distributions determined by gel permeation chromatography (GPC) in combination with triple detectors, including refractive index, light scattering, and viscosity detectors. In addition, the examination of the solution behavior of these polymers showed that the values of intrinsic viscosity [η] and the Mark–Houwink exponent α were remarkably lower compared with their linear analogs, because of their branched nature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4309–4321, 2007
Layer‐by‐layer assembly of weak‐strong copolymer polyelectrolytes: A route to morphological control of thin films
Authors: Tjipto Elvira , Quinn John F. , Caruso Frank 
Published: August 2007

AbstractMultilayer films were assembled from a strong polyelectrolyte (poly(diallyldimethylammonium chloride), PDADMAC) and a copolymer containing both strongly charged styrene sulfonate moieties and weakly charged maleic acid moieties (poly(4‐styrenesulfonic acid‐co‐maleic acid), PSSMA). Growth of PSSMA/PDADMAC multilayers was linear, as characterized by UV‐vis spectroscopy and quartz crystal microgravimetry. The influence of both the pH of the PSSMA adsorption solutions and the ratio of SS:MA in the PSSMA on multilayer properties was investigated. Fourier transform infrared spectroscopy results showed that the ionization of carboxylic acid groups in PSSMA/PDADMAC multilayers did not vary significantly with changes in the PSSMA assembly pH. However, the multilayers showed different thicknesses, surface morphologies, and stability to post‐assembly pH treatment. We also demonstrate that PSSMA/PDADMAC multilayers are significantly more stable than PSSMA/PAH multilayers after post‐assembly pH treatment (i.e. the films remain intact when exposed to pH extremes). In addition, the surface morphology of two films (PSSMA 1:1 assembled at pH 5.8, post‐treated at pH 2 and PSSMA 3:1 assembled at pH 5.8, post‐treated at pH 11) changed significantly when the films were exposed to solutions of different pH and, in the former case, this change in film morphology was reversible. The porous morphology after treatment at pH 2 could be reversed to give a significantly smoother film after subsequent exposure to water for 24 h. Our results demonstrate that by the rational choice of the assembly pH of PSSMA, stable and pH‐responsive films can be obtained via the sequential assembly of PSSMA and PDADMAC. These films have potential in controlled release applications where film stability and pH‐responsive behavior are essential. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4341‐4351, 2007
Synthesis and properties of wholly aromatic polymers bearing cardo fluorene moieties
Authors: Liou Guey‐Sheng , Yen Hung‐Ju , Su Yi‐Ting , Lin Hung‐Yi 
Published: August 2007

AbstractThree series of aromatic polyamides, polyesters, and poly(1,3,4‐oxadiazole)s containing bulky fluorene structures were prepared from 9,9‐bis(4‐carboxyphenyl) fluorene. All of the polymers were readily soluble in many organic solvents and showed useful thermal stability associated with high glass‐transition temperatures in the range of 220–366 °C. These wholly aromatic polymer films were colorless, with high optical transparency, and exhibited UV‐vis absorption bands at 266–348 nm and photoluminescence maximum bands at 368–457 nm within the purple to green region in N,N‐dimethylacetamide (DMAc) solutions. The poly(amine‐amide) Ic exhibited excellent electrochromic contrast and coloration efficiency, changing color from the colorless neutral form to green and then to the dark blue oxidized forms with good stability of electrochromic characteristics. Almost all of these wholly aromatic polymer films were colorless and showed high optical transparency. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4352–4363, 2007
Dual mode model for mixed gas permeation of CO2, H2, and N2 through a dry chitosan membrane
Authors: El‐Azzami Louei A. , Grulke Eric A. 
Published: August 2007

AbstractDry chitosan is an excellent candidate for facilitated transport membranes that can be utilized in industrial applications, such as fuel cell operations and other purification processes. This article is the first to report temperature effects on transport properties of CO2, H2, and N2 in a gas mixture typical of such applications. At a feed pressure of 1.5 atm, CO2 permeabilities increased (0.381–26.1 barrers) at temperatures of 20–150 °C with decreasing CO2/N2 (19.7–4.55) and CO2/H2 (3.14–1.71) separation factors. The pressure effect on solubilities and permeabilities were fitted to the extended dual mode model and its corresponding mixed gas permeation model. The dual mode and transport parameters, the sorption heats and the activation energies of Henry's and Langmuir's regimes and their pre‐exponential parameters were determined. The Langmuir's capacity constants were utilized to estimate chitosan's glass transition temperature (CO2: 172 °C, N2: 175 °C, and H2: 171 °C). The activation energies of diffusion in the Henry's law and Langmuir regimes were dependent on the collision diameter of the gases. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2620–2631, 2007
Fractionation and characterization of a protein–polysaccharide complex from Pleurotus tuberregium sclerotia
Authors: Tao Yongzhen , Yan Fan , Zhang Lina 
Published: August 2007

AbstractA water‐soluble sample (TM4b), extracted from sclerotia of Pleurotus tuberregium, was analyzed using elemental analysis, one‐ and two‐dimensional 1H and 13C NMR. The results indicated that TM4b was protein–polysaccharide complex, and the polysaccharide moiety was hyperbranched β‐D‐glucan with residuals branched at C3, C2, C4, and C6 positions. A preparative size‐exclusion chromatography (SEC) column combined with nonsolvent addition method was used to fractionate TM4b, and nine fractions were obtained. Solution properties of TM4b in 0.15 M aqueous NaCl were studied using static laser light scattering and viscometry at 25 °C. The dependences of intrinsic viscosity ([η]) and radius of gyration (〈S2〉) on weight–average molecular weight (Mw) for TM4b in the Mw range from 1.89 × 104 to 2.58 × 106 were found to be [η] = 0.21M and 〈S2〉 = 3.63M. It indicated that TM4b existed as compact sphere conformation in the aqueous solution. Atomic force microscopy image further confirmed that the TM4b molecules exhibited globular shape in the solution. This work gave valuable information on fractionation and chain conformation characterization of the globular protein–polysaccharide complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2546–2554, 2007
Microrheological studies of regenerated silk fibroin solution by video microscopy
Authors: A. Raghu , R. Somashekar , Ananthamurthy Sharath 
Published: August 2007

AbstractWe have carried out studies on the rheological properties of regenerated silk fibroin (RSF) solution using video microscopy. The degummed silk from the Bombyx mori silkworm was used to prepare RSF solution by dissolving it in calcium nitrate tetrahydrate‐methanol solvent. Measurements were carried out by tracking the position of an embedded micron‐sized polystyrene bead within the RSF solution through video imaging. The time dependent mean squared displacement (MSD) of the bead in solution and hence the complex shear modulus of this solution was calculated from the bead's position information. We present here the results of rheological measurements of the silk polymer network in solution over a frequency range, whose upper limit is the frame capture rate of our camera at full resolution. By examining the distribution of MSD of beads at different locations within the sample volume, we demonstrate that this probe technique enables us to detect local inhomogeneities at nanometre length scales, not detectable either by a rheometer or from diffusing wave spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2555–2562, 2007
Influence of the draw ratio on the tensile and fracture behavior of NMMO regenerated silk fibers
Authors: Corsini Paola , Perez‐Rigueiro José , Guinea Gustavo V. , Plaza Gustavo R. , Elices Manuel , Marsano Enrico , Carnasciali Maria M. , Freddi Giuliano 
Published: August 2007

AbstractThe tensile properties and fracture surfaces of N‐methylmorpholine‐N‐oxide (NMMO) regenerated silk fibroin fibers produced with a range of draw ratios has been characterized and related to their microstructure with data obtained from Raman spectroscopy and birefringence measurements. The spinning process allows control of two different draw ratios, coagulation, and postspinning, and it has been found that the microstructure and the properties of the fibers can be modified by the proper combination of both draw ratios. NMMO regenerated silk fibroin fibers subjected to postspinning drawing yield tensile properties comparable to other regenerated fibers and strain at breaking comparable to natural Bombyx mori silk fibers. Tensile strength; however, is still significantly lower than that of natural fibers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2568–2579, 2007
Nonlinear rheological behavior of silica filled solution‐polymerized styrene butadiene rubber
Authors: Sun Jin , Song Yihu , Zheng Qiang , Tan Hong , Yu Jie , Li Hong 
Published: August 2007

AbstractThe reinforcement and nonlinear viscoelastic behavior have been investigated for silica (SiO2) filled solution‐polymerized styrene butadiene rubber (SSBR). Experimental results reveal that the nonlinear viscoelastic behavior of the filled rubber is similar to that of unfilled SSBR, which is inconsistent with the general concept that this characteristic comes from the breakdown and reformation of the filler network. It is interesting that the curves of either dynamic storage modulus (G′) or loss tangent (tan δ) versus strain amplitude (γ) for the filled rubber can be superposed, respectively, on those for the unfilled one, suggesting that the primary mechanism for the Payne effect is mainly involved in the nature of the entanglement network in rubbery matrix. It is believed there exists a cooperation between the breakdown and reformation of the filler network and the molecular disentanglement, resulting in enhancing the Payne effect and improving the mechanical hysteresis at high strain amplitudes. Moreover, the vertical and the horizontal shift factors for constructing the master curves could be well understood on the basis of the reinforcement factor f(φ) and the strain amplification factor A(φ), respectively. The surface modification of SiO2 causes a decrease in f(φ), which is ascribed to weakeness of the filler–filler interaction and improvement of the filler dispersion. However, the surface nature of SiO2 hardly affects A(φ). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2594‐2602, 2007