bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Zr Phosphate/PVDF Nanocomposites by Vibrational Spectroscopy
Authors: Casciola Mario , Donnadio Anna , Pica Monica , Valentini Valeria , Piaggio Paolo 
Published: December 2005

AbstractA study of the vibrational spectra obtained by various spectroscopic techniques (FTIR: T, ATR, PAS; FT‐Raman) was performed on nanocomposites of α‐zirconium phosphate [α‐ZrP] in poly(vinylidenefluoride) [PVDF] matrices of different morphology and composition. As the morphology of both dense and porous nanocomposite materials was carefully observed by electron microscopy (SEM, TEM and EDS), the vibrational spectra could be discussed in order to highlight the effectiveness of each spectroscopic technique for the characterization of this type of samples. Some results are presented showing that, by using the proper technique for each type of material, vibrational spectroscopy is very useful not only to determine composition and homogeneity of the nanocomposite but also to understand more specific points like the chain conformation of the polymer matrix and its interaction with the inorganic particles.
Experimental Testing of Lateral and Depth Resolution in Imaging Methods
Authors: Wilhelm Peter , Chernev Boril , Pölt Peter 
Published: December 2005

AbstractA polymer laminate and a PA‐PTFE blend were studied by various imaging methods (FT‐IR, Raman, ESEM). Different lateral and depth resolution of the methods were used to gain complementary information on the structure of the materials. Radiation damage caused by the electron beam during ESEM investigation was studied by Raman global imaging.
Optical Absorption and Photo‐Luminescence Spectra of Molecular van der Waals Systems: Frenkel Exciton Resonance Effects
Authors: Fleming Alexander J. , Coleman Jonathan N. , Blau Werner J. 
Published: December 2005

AbstractApplying the principle of conservation of energy, the photo‐absorption‐luminescence (p‐a‐l) cycle of resonant Frenkel excitons in aggregates is explained in terms of the p‐a‐l cycles of isolated molecules. The method employed to measure the Stokes shift of Frenkel Exciton Resonance (FER) systems, derived from our model, is found to differ significantly from that employed currently. Our postulate, that the aggregate v‐e transition energy, in the frame of reference of a resonant exciton, decreases as function of the localisation length of the exciton, is demonstrated by the excellent agreement of the model with existing data. This has allowed the determination of the localisation length of resonant excitons from readily available spectra. As the localisation length is a good indicator of the order of a system, this result will be useful in molecular self‐assembly (MSA) research. Results from the model suggest that Frenkel exciton resonance is vibrationally modulated, and the collective exciton eigenstate of a resonant Frenkel exciton can couple the v‐e manifolds of 2Nmolecules together via the electronic resonance interaction, even in the absence of direct intermolecular vibrational coupling. In essence, we demonstrate that the photo‐physics of an exciton that is resonant over many molecules is fundamentally determined by the photo‐physics of the isolated molecule just as one would expect.
Novel Biodegradable Poly(pentadecalactone‐co‐oxo‐crown ether) Studied with Solid‐State 1H and 13C NMR
Authors: Magusin Pieter C.M.M. , Mezari Brahim , van der Mee Lars , Palmans Anja R.A. , Meijer E.W. 
Published: December 2005

AbstractTwo grades of a novel biodegradable copolymer of ω‐pentadecalactone (PDL) and 2‐oxo‐12‐crown‐4 (OC), with respective molar compositions of 77/23 and 52/48, were characterized with 1D and 2D MAS 1H and 13C NMR spectroscopy. The results indicate that both copolymers are semi‐crystalline with PDL divided over the crystalline and amorphous phase, and OC exclusively located in the amorphous phase. Proton T2 and T1ρ relaxation confirm the existence of small crystalline domains.
Characterization of Thin Polymer Films on the Nanometer Scale with Confocal Raman AFM
Authors: Schmidt U. , Hild S. , Ibach W. , Hollricher O. 
Published: December 2005

AbstractThe combination of an atomic force microscope (AFM) with a Confocal Raman Microscope (CRM) has been used to study the composition of various thin films of polymer blends. The high spatial resolution of the AFM enables the morphological characterization of the polymer blends on the nanometer scale. Furthermore, when operating the AFM in Digital Pulsed Force Mode (DPFM), topographic information and local stiffness can be simultaneously recorded. This allows the material‐sensitive characterization of heterogeneous materials. Thin films where PMMA (at room temperature a glassy polymer) is blended with two different styrene‐butadiene rubbers are investigated. The presence of PMMA in both phase‐separated thin films allows the comparison of the mechanical properties of the two different rubber phases using DPFM‐AFM. When PMMA is blended with PET due to their similar mechanical properties (both are in the glassy state at room temperature) the assignment of the two phases to the corresponding polymers by AFM is rather difficult. Here, Raman spectroscopy provides additional information on the chemical composition of materials. In combination with a confocal microscope, the spatial distribution of the various phases can be determined with a resolution down to 200 nm. Therefore, the topographically different structures observed in AFM images can be associated to the chemical composition by using the Confocal Raman Microscope (CRM).
Network Density and Diene Conversion in Peroxide‐Cured Gumstock EPDM Rubbers. A Solid‐State NMR Study
Authors: Orza Ramona A. , Magusin Pieter C.M.M. , Litvinov Victor M. , van Duin Martin , Michels M.A.J. 
Published: December 2005

AbstractPeroxide‐cross‐linked EPM and EPDM rubbers have been investigated with magic‐angle spinning 1H NMR spectroscopy and static 1H NMR relaxometry. The results yield a consistent nanoscale picture of the chemical and physical network properties in terms of chemical cross‐links formed via macro‐radical combination, chemical cross‐links formed via addition to the double bonds, and physical cross‐links resulting from chain entanglements.
Compositional Mapping of Polymer Surfaces by Chemical Force Microscopy Down to the Nanometer Scale: Reactions in Block Copolymer Microdomains
Authors: Schönherr Holger , Feng Chuan Liang , Tomczak Nikodem , Vancso G. Julius 
Published: December 2005

AbstractThe laterally resolved analysis of the chemical surface composition of surface‐treated block copolymers by atomic force microscopy (AFM) pull‐off force mapping in the force volume (FV) mode and the automated analysis of the FV data is discussed. Poly(tert‐butyl acrylate) (PtBA) microdomains residing in a polystyrene (PS) matrix at the surface of cyclohexane‐treated polystyrene‐block‐poly(tert‐butyl acrylate) (PtBA‐b‐PS) block copolymer thin films were domain‐selectively deprotected, activated and chemically modified, as also shown by fluorescence microscopy. AFM pull‐off force mapping in conjunction with an automated analysis of the data provided real space evidence for the successful conversion of reactive esters located in the PtBA domains and showed that AFM and related approaches, such as chemical force microscopy (CFM), can indeed contribute to assess changes in heterogeneous surface chemical composition of polymers down to sub‐50 nm length scales.
Infrared Spectroscopy and X‐Ray Diffraction Studies of CH…O Hydrogen Bonding and Thermal Behavior of Biodegradable Poly(hydroxyalkanoate)
Authors: Sato Harumi , Murakami Rumi , Zhang Jianming , Mori Katsuhito , Takahashi Isao , Terauchi Hikaru , Noda Isao , Ozaki Yukihiro 
Published: December 2005

AbstractInfrared (IR) spectra and wide‐angle X‐ray diffraction (WAXD) patterns of poly(3‐hydroxybutyrate) (PHB) and its copolyester, poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), P(HB‐co‐HHx) (HHx = 12 mol%) were measured over a temperature range of 20 °C to higher temperatures (PHB, 185 °C, HHx = 12 mol%, 140 °C) to explore their structure change and thermal behavior and molecular interaction. The WAXD measurements revealed that the a lattice parameter increases significantly with temperature, while the b lattice parameter varies a little in the crystalline PHB and P(HB‐co‐HHx). It seems that the intermolecular interaction between the CO group of one helical structure and the CH3 group of the other helical structure decreases along the a axis of crystalline PHB and P(HB‐co‐HHx) with temperature. The temperature‐dependent IR spectral variations were analyzed for the CH stretching, CO stretching, CH3 deformation, and COC stretching variation regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It was found from the anomalous frequencies of the CH3 asymmetric stretching and CO stretching bands of PHB and P(HB‐co‐HHx) and the X‐ray crystallographic structure of PHB that there is an intermolecular interaction (CH…OC hydrogen bond) between the CO group and the CH3 group combining two helical structures in PHB and P(HB‐co‐HHx). In this review paper we discuss the role of the CH…OC hydrogen bonding and the crystal and lamella structure of PHB and P(HB‐co‐HHx) (HHx = 12 mol %) in comparison with the structure of Nylon.
High‐resolution FMRI at 1.5T using balanced SSFP
Authors: Miller Karla L. , Smith Stephen M. , Jezzard Peter , Pauly John M. 
Published: December 2005

AbstractThe resolution in conventional BOLD FMRI is considerably lower than can be achieved with other MRI methods, and is insufficient for many important applications. One major difficulty in robustly improving spatial resolution is the poor image quality in BOLD FMRI, which suffers from distortions, blurring, and signal dropout. This work considers the potential for increased resolution with a new FMRI method based on balanced SSFP. This method establishes a blood oxygenation sensitive steady‐state (BOSS) signal, in which the frequency sensitivity of balanced SSFP is used to detect the frequency shift of deoxyhemoglobin. BOSS FMRI is highly SNR efficient and does not suffer from image distortions or signal dropout, making this method an excellent candidate for high‐resolution FMRI. This study presents the first demonstration of high‐resolution BOSS FMRI, using an efficient 3D stack‐of‐segmented EPI readout and combined acquisition at multiple center frequencies. BOSS FMRI is shown to enable high‐resolution FMRI data (1 × 1 × 2 mm3) in both visual and motor systems using standard hardware at 1.5 T. Currently, the major limitation of BOSS FMRI is its sensitivity to temporal and spatial field drift. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Investigating brain metabolism at high fields using localized 13C NMR spectroscopy without 1H decoupling
Authors: Deelchand Dinesh Kumar , Uğurbil Kâmil , Henry Pierre‐Gilles 
Published: December 2005

AbstractMost in vivo 13C NMR spectroscopy studies in the brain have been performed using 1H decoupling during acquisition. Decoupling imposes significant constraints on the experimental setup (particularly for human studies at high magnetic field) in order to stay within safety limits for power deposition. We show here that incorporation of the 13C label from 13C‐labeled glucose into brain amino acids can be monitored accurately using localized 13C NMR spectroscopy without the application of 1H decoupling. Using LCModel quantification with prior knowledge of one‐bond and multiple‐bond JCH coupling constants, the uncertainty on metabolites concentrations was only 35% to 91% higher (depending on the carbon resonance of interest) in undecoupled spectra compared to decoupled spectra in the rat brain at 9.4 Tesla. Although less sensitive, 13C NMR without decoupling dramatically reduces experimental constraints on coil setup and pulse sequence design required to keep power deposition within safety guidelines. This opens the prospect of safely measuring 13C NMR spectra in humans at varied brain locations (not only the occipital lobe) and at very high magnetic fields above 4 Tesla. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Influence of vascular filling and perfusion on BOLD contrast during reactive hyperemia in human skeletal muscle
Authors: Duteil S. , Wary C. , Raynaud J. S. , Lebon V. , Lesage D. , Leroy‐Willig A. , Carlier P. G. 
Published: December 2005

AbstractMechanisms generating BOLD contrast are complex and depend on parameters that are prone to large variations, in particular in skeletal muscle. Here, we simultaneously measured perfusion by ASL, and BOLD response in the calf muscle of 6 healthy volunteers during post‐ischemic reactive hyperemia. We tested whether the relation between the two was altered for varying degrees of leg vascular replenishment induced by prior positioning of the leg at different heights relative to the heart. We found that the BOLD response depended on perfusion, but also on the degree of repletion of leg blood vessels. We conclude that simultaneous determination of perfusion by ASL is important to identify the mechanisms underlying BOLD contrast in the skeletal muscle. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.
Generalized pointwise bias error bounds for response surface approximations
Authors: Goel Tushar , Haftka Raphael T. , Papila Melih , Shyy Wei 
Published: December 2005

AbstractThis paper proposes a generalized pointwise bias error bounds estimation method for polynomial‐based response surface approximations when bias errors are substantial. A relaxation parameter is introduced to account for inconsistencies between the data and the assumed true model. The method is demonstrated with a polynomial example where the model is a quadratic polynomial while the true function is assumed to be cubic polynomial. The effect of relaxation parameter is studied. It is demonstrated that when bias errors dominate, the bias error bounds characterize the actual error field better than the standard error. The bias error bound estimates also help to identify regions in the design space where the accuracy of the response surface approximations is inadequate. It is demonstrated that this information can be utilized for adaptive sampling in order to improve accuracy in such regions. Copyright © 2005 John Wiley & Sons, Ltd.
Local maximum‐entropy approximation schemes: a seamless bridge between finite elements and meshfree methods
Authors: Arroyo M. , Ortiz M. 
Published: December 2005

AbstractWe present a one‐parameter family of approximation schemes, which we refer to as local maximum‐entropy approximation schemes, that bridges continuously two important limits: Delaunay triangulation and maximum‐entropy (max‐ent) statistical inference. Local max‐ent approximation schemes represent a compromise—in the sense of Pareto optimality—between the competing objectives of unbiased statistical inference from the nodal data and the definition of local shape functions of least width. Local max‐ent approximation schemes are entirely defined by the node set and the domain of analysis, and the shape functions are positive, interpolate affine functions exactly, and have a weak Kronecker‐delta property at the boundary. Local max‐ent approximation may be regarded as a regularization, or thermalization, of Delaunay triangulation which effectively resolves the degenerate cases resulting from the lack or uniqueness of the triangulation. Local max‐ent approximation schemes can be taken as a convenient basis for the numerical solution of PDEs in the style of meshfree Galerkin methods. In test cases characterized by smooth solutions we find that the accuracy of local max‐ent approximation schemes is vastly superior to that of finite elements. Copyright © 2005 John Wiley & Sons, Ltd.
Theory and numerics for finite deformation fracture modelling using strong discontinuities
Authors: Fagerström Martin , Larsson Ragnar 
Published: December 2005

AbstractA general finite element approach for the modelling of fracture is presented for the geometrically non‐linear case. The kinematical representation is based on a strong discontinuity formulation in line with the concept of partition of unity for finite elements. Thus, the deformation map is defined in terms of one continuous and one discontinuous portion, considered as mutually independent, giving rise to a weak formulation of the equilibrium consisting of two coupled equations. In addition, two different fracture criteria are considered. Firstly, a principle stress criterion in terms of the material Mandel stress in conjunction with a material cohesive zone law, relating the cohesive Mandel traction to a material displacement ‘jump’ associated with the direct discontinuity. Secondly, a criterion of Griffith type is formulated in terms of the material‐crack‐driving force (MCDF) with the crack propagation direction determined by the direction of the force, corresponding to the direction of maximum energy release. Apart from the material modelling, the numerical treatment and aspects of computational implementation of the proposed approach is also thoroughly discussed and the paper is concluded with a few numerical examples illustrating the capabilities of the proposed approach and the connection between the two fracture criteria. Copyright © 2005 John Wiley & Sons, Ltd.
Continued fraction absorbing boundary conditions for convex polygonal domains
Authors: Guddati Murthy N. , Lim Keng‐Wit 
Published: December 2005

AbstractContinued fraction absorbing boundary conditions (CFABCs) are highly effective boundary conditions for modelling wave absorption into unbounded domains. They are based on rational approximation of the exact dispersion relationship and were originally developed for straight computational boundaries. In this paper, CFABCs are extended to the more general case of polygonal computational domains. The key to the current development is the surprising link found between the CFABCs and the complex co‐ordinate stretching of perfectly matched layers (PMLs). This link facilitates the extension of CFABCs to oblique corners and, thus, to polygonal domains. It is shown that the proposed CFABCs are easy to implement, expected to perform better than PMLs, and are effective for general polygonal computational domains. In addition to the derivation of CFABCs, a novel explicit time‐stepping scheme is developed for efficient numerical implementation. Numerical examples presented in the paper illustrate that effective absorption is attained with a negligible increase in the computational cost for the interior domain. Although this paper focuses on wave propagation, its theoretical development can be easily extended to the more general class of problems where the governing differential equation is second order in space with constant coefficients. Copyright © 2005 John Wiley & Sons, Ltd.
Maximum likelihood estimation of stochastic chaos representations from experimental data
Authors: Desceliers Christophe , Ghanem Roger , Soize Christian 
Published: December 2005

AbstractThis paper deals with the identification of probabilistic models of the random coefficients in stochastic boundary value problems (SBVP). The data used in the identification correspond to measurements of the displacement field along the boundary of domains subjected to specified external forcing. Starting with a particular mathematical model for the mechanical behaviour of the specimen, the unknown field to be identified is projected on an adapted functional basis such as that provided by a finite element discretization. For each set of measurements of the displacement field along the boundary, an inverse problem is formulated to calculate the corresponding optimal realization of the coefficients of the unknown random field on the adapted basis. Realizations of these coefficients are then used, in conjunction with the maximum likelihood principle, to set‐up and solve an optimization problem for the estimation of the coefficients in a polynomial chaos representation of the parameters of the SBVP. Copyright © 2005 John Wiley & Sons, Ltd.
An explicit material point finite element method for hyper‐velocity impact
Authors: Zhang X. , Sze K. Y. , Ma S. 
Published: December 2005

AbstractIn this paper, an explicit material point finite element (FE) method is proposed and a computer code EMPFE‐3D is developed for simulating hyper‐velocity impact. The material domain is discretized by a mesh of finite elements. The momentum equations are solved on a predefined computational grid (like the material point method) in the large deformation zone, and on the FE mesh (like the traditional FE method) elsewhere. The grid may be fixed in space or moved in a predefined way. The nodes covered by the grid are treated as material particles, and the remaining nodes are treated as FE nodes. The proposed method yields the same results as the traditional FE method if the grid vanishes. On the other hand, it yields the same results as the material point method if the grid covers the entire material domain at all time steps. The method combines the advantages of Eulerian and Lagrangian descriptions of motion while eliminates their drawbacks due to element entanglement and numerical dissipation. The method is computationally efficient and can be easily implemented in an existing explicit FE code like DYNA3D. Copyright © 2005 John Wiley & Sons, Ltd.
Coupled mechanics and finite element for non‐linear laminated piezoelectric shallow shells undergoing large displacements and rotations
Authors: Varelis Dimitris , Saravanos Dimitris A. 
Published: December 2005

AbstractA theoretical framework is presented for analysing the coupled non‐linear response of shallow doubly curved adaptive laminated piezoelectric shells undergoing large displacements and rotations. The formulated mechanics incorporate coupling between in‐plane and flexural stiffness terms due to geometric curvature, coupling between mechanical and electric fields, and encompass geometric non‐linearity effects due to large displacements and rotations. The governing equations are formulated explicitly in orthogonal curvilinear co‐ordinates and are combined with the kinematic assumptions of a mixed‐field shear‐layerwise shell laminate theory. Based on the above formulation, a finite element methodology together with an incremental‐iterative technique, based on Newton–Raphson method is formulated. An eight‐node coupled non‐linear shell element is also developed. Various evaluation cases on laminated curved beams and cylindrical panels illustrate the capability of the shell finite element to predict the complex non‐linear behaviour of active shell structures including buckling, which is not captured by linear shell models. The numerical results also show the inherent capability of piezoelectric shell structures to actively induce large displacements through piezoelectric actuators, by jumping between multiple equilibrium states. Copyright © 2005 John Wiley & Sons, Ltd.
Design sensitivity analysis in large deformation elasto‐plastic and elasto‐viscoplastic problems
Authors: Kowalczyk Piotr 
Published: December 2005

AbstractImplicit time integration algorithm derived by Simo for his large‐deformation elasto‐plastic constitutive model is generalized, for the case of isotropy and associative flow rule, towards viscoplastic material behaviour and consistently differentiated with respect to its input parameters. Combining it with the general formulation of design sensitivity analysis (DSA) for non‐linear finite element transient equilibrium problem, we come at a numerically efficient, closed‐form finite element formulation of DSA for large deformation elasto‐plastic and elasto‐viscoplastic problems, with various types of design variables (material constants, shape parameters). The paper handles several specific issues, like the use of a non‐algorithmic coefficient matrix or sensitivity discontinuities at points of instantaneous structural stiffness change. Computational examples demonstrate abilities of the formulation and quality of results. Copyright © 2005 John Wiley & Sons, Ltd.