bluuebunny/crossref_metadata_2025_split huggingface dataset:
Signal‐to‐noise ratio and parallel imaging performance of a 16‐channel receive‐only brain coil array at 3.0 Tesla
Authors: de Zwart Jacco A. , Ledden Patrick J. , van Gelderen Peter , Bodurka Jerzy , Chu Renxin , Duyn Jeff H. 
Published: December 2003

AbstractThe performance of a 16‐channel receive‐only RF coil for brain imaging at 3.0 Tesla was investigated using a custom‐built 16‐channel receiver. Both the image signal‐to‐noise ratio (SNR) and the noise amplification (g‐factor) in sensitivity‐encoding (SENSE) parallel imaging applications were quantitatively evaluated. Furthermore, the performance was compared with that of hypothetical coils with one, two, four, and eight elements (n) by combining channels in software during image reconstruction. As expected, both the g‐factor and SNR improved substantially with n. Compared to an equivalent (simulated) single‐element coil, the 16‐channel coil showed a 1.87‐fold average increase in brain SNR. This was mainly due to an increase in SNR in the peripheral brain (an up to threefold SNR increase), whereas the SNR increase in the center of the brain was 4%. The incremental SNR gains became relatively small at large n, with a 9% gain observed when n was increased from 8 to 16. Compared to the (larger) product birdcage head coil, SNR increased by close to a factor of 2 in the center, and by up to a factor of 6 in the periphery of the brain. For low SENSE acceleration (rate‐2), g‐factors leveled off for n > 4, and improved only slightly (1.4% averaged over brain) going from n = 8 to n = 16. Improvements in g for n > 8 were larger for higher acceleration rates, with the improvement for rate‐3 averaging 12.0%. Magn Reson Med 51:22–26, 2004. Published 2003 Wiley‐Liss, Inc.
Optimizing the sequence parameters for double‐quantum CRAZED imaging
Authors: Marques J.P. , Bowtell R. 
Published: December 2003

AbstractThe evolution of magnetization during repeated application of the double‐quantum‐(DQ)‐CRAZED sequence is analyzed, with the aim of identifying sequence parameters that maximize sensitivity to signal produced by the distant dipole field (DDF). Phase cycling schemes that allow cancellation of signals following undesired coherence pathways are also described. Simulations and imaging experiments carried out at 3 T on phantoms and the human head were used to verify the analysis. The results indicate that in the absence of phase cycling, the DDF‐related signal‐to‐noise ratio (SNR) per unit time is maximized using TR = 2.05 T1, along with values of the RF flip angles (α ≈ 90° and β ≈ 60°), and echo time (TE = T2) that have previously been shown to maximize the DDF‐related signal at long TR. However, with TR = 2.05 T1 there can also be a significant signal contribution due to stimulated echo effects (up to 40% of the signal for water at 3 T and TE = 70 ms). Using a two‐step phase cycle, the stimulated echo signal is eliminated and the maximum SNR per unit time occurs for TR = 2.76 T1. It is also demonstrated that sensitivity to signal changes caused by small variations in T2 is maximized by setting TE = 2T2. Magn Reson Med 51:148–157, 2004. © 2003 Wiley‐Liss, Inc.
Grafting sulfobetaine monomer onto silicone surface to improve haemocompatibility
Authors: Yuan Youling , Zang Xiaopeng , Ai Fei , Zhou Jun , Shen Jian , Lin Sicong 
Published: December 2003

AbstractSilicone rubber has been used as a biomaterial for more than two decades and displays good mechanical and optical properties, but its chemical nature, poor antithrombogenicity, as well as its hydrophobicity, prevents its use in many demanding biomedical applications. In order to provide modified silicone with enhanced haemocompatibility, surface modification techniques were used. Ozonization was used to introduce active peroxide groups onto the silicone film surface and, subsequently, graft polymerization of N,N′‐dimethyl‐N‐methacryloyloxyethyl‐N‐(3‐sulfopropyl) ammonium (DMMSA), a zwitterionic sulfobetaine structure, onto the ozone activated silicone surface was conducted. Surface analysis was accomplished by means of attenuated total reflectance‐Fourier‐transform infrared (ATR‐FTIR), and X‐ray photoelectron spectra (XPS), and scanning electron microscopy (SEM) and contact angle measurement. ATR‐FTIR and XPS investigation confirmed the graft polymerization. The grafted film possessed a relatively hydrophilic surface as indicated by contact angle measurement. The blood compatibility of the grafted films was evaluated by platelet adhesion in platelet‐rich plasma (PRP) and protein adsorption in bovine fibrinogen using silicone film as the reference. No platelet adhesion was observed for the grafted films incubated in PRP for 120 min. The protein adsorption was reduced on the grafted films after incubated in bovine fibrinogen for 120 min. These results confirmed that the improved blood compatibility was obtained by grafting this new zwitterronic sulfobetaine structure onto silicone film. Copyright © 2003 Society of Chemical Industry
Determination of radial structural properties and spectral dispersion curves of poly(aryl ether ether ketone) fibre
Authors: El‐Bakary MA 
Published: December 2003

AbstractPoly(aryl ether ether ketone) (PEEK) fibre was studied using a variable wavelength interferometric technique (VAWI). This technique was used in conjunction with a Pluta polarizing interference microscope to determine the spectral dispersion curves of fibre refractive indices and birefringence fibre. The results were used to calculate the dispersion properties of the fibre, ie dispersion and oscillation energies, Cauchy's constants of dispersion relation and the natural wavelength of the fibre. The radial refractive index and birefringence profiles were also determined, taking into consideration the refraction of light beam by the fibre, and some radial structural profiles were then calculated using a ring‐zonal model. The measurements of these radial profiles are required for optimizing the spinning and processing of manufactured textile fibres. The Fraunhofer diffraction pattern of a He–Ne laser beam was used to determine the average thickness of the fibre. Microinterferograms are presented for illustration. Copyright © 2003 Society of Chemical Industry
Poly(4‐methyl‐1‐pentene)/clay nanocomposites: effect of organically modified layered silicates
Authors: Wanjale Santosh D , Jog Jyoti P 
Published: December 2003

AbstractThe preparation and properties of poly(4‐methyl‐1‐pentene) (PMP)/clay nanocomposites are reported. Melt intercalation of PMP is carried out with organoclays of different cation/charge exchange capacities and modifiers to facilitate intercalation of the polymer into the silicate layers. The effect of modifiers on the structure and properties of PMP/clay nanocomposites is explored. XRD patterns confirm the intercalation of polymer in the layered silicates as evidenced by the increase in the inter‐layer spacing which is dependent on the type of modifier used. Dynamic mechanical analysis shows increments in the storage modulus over the temperature range studied for all of the three clays, but the extent depends on the type of clay modifier used. The coefficient of thermal expansion is lower for all of the nanocomposites, as compared to the pristine polymer, indicating improved dimensional stability Copyright © 2003 Society of Chemical Industry
Toughening of epoxy resin systems using low‐viscosity additives
Authors: Varley Russell J 
Published: December 2003

AbstractThis study has evaluated three low‐viscosity epoxy additives as potential tougheners for two epoxy resin systems. The systems used were a lower‐reactive resin based upon the diglycidyl ether of bisphenol A (DGEBA) and the amine hardener diethyltoluene diamine, while the second epoxy resin was based upon tetraglycidyl methylene dianiline (TGDDM) and a cycloaliphatic diamine hardener. The additives evaluated as potential tougheners were an epoxy‐terminated aliphatic polyester hyperbranched polymer, a carboxy‐terminated butadiene rubber and an aminopropyl‐terminated siloxane. This work has shown that epoxy‐terminated hyperbranched polyesters can be used effectively to toughen the lower cross‐linked epoxy resins, i.e. the DGEBA‐based systems, with the main advantage being that they have minimal effect upon processing parameters such as viscosity and the gel time, while improving the fracture properties by about 54 % at a level of 15 wt% of additive and little effect upon the Tg. This result was attributed to the phase‐separation process producing a multi‐phase particulate morphology able to initiate particle cavitation with little residual epoxy resin dissolved in the continuous epoxy matrix remaining after cure. The rubber additive was found to impart similar levels of toughness improvement but was achieved with a 10–20 °C decrease in the Tg and a 30 % increase in initial viscosity. The siloxane additive was found not to improve toughness at all for the DGEBA‐based resin system due to the poor dispersion within the epoxy matrix. The TGDDM‐based resin systems were found not to be toughened by any of the additives due to the lack of plastic deformation of the highly cross‐linked epoxy network Copyright © 2003 Society of Chemical Industry
On the fractal character of polymer spherulites: an ultra‐small‐angle X‐ray scattering study of poly[(R)‐3‐hydroxybutyrate]
Authors: Owen Anthony , Bergmann Antje 
Published: December 2003

AbstractUltra‐small‐angle X‐ray scattering (USAXS) and small‐angle X‐ray scattering (SAXS) measurements are presented for poly[(R)‐3‐hydroxybutyrate] (PHB) crystallized at room temperature. The USAXS patterns indicated that the spherulites had a radially orientated fibrillar nanostructure with fractal geometry over a length scale ranging from 12 nm up to at least 300 nm, with a mass fractal dimension of approximately 2.7 in aged samples. The SAXS patterns indicated that the fibrils themselves were built up of bundles of crystalline lamellae separated by layers of disordered material, with a period length of approximately 6 nm. The SAXS measurements during primary crystallization gave an initial fractal dimension of 4 during spherulite growth, due to the sharp phase boundary between the spherulites and the melt. Copyright © 2004 Society of Chemical Industry
Finite element simulation of mechanical property evolvement of silicone rubber in the hot vulcanizing process
Authors: Jia Yuxi , Sun Sheng , Liu Lili , Ji Zhong 
Published: December 2003

AbstractThe technical outline of integrated research on the mechanical properties, the crosslinked structure and the hot vulcanizing technology of silicone rubber materials is formulated. From the statistics of rubber elasticity, the relationship of stored energy function and crosslinked structure parameters is constructed. Following the stress–strain theory of elastomers, related expressions for the mechanical properties and the crosslinked structure are deduced. On the basis of previous research findings, numerical expressions of the mechanical properties of silicone rubber in hot vulcanizing process are obtained. Consequently, the properties of silicone rubber can be predicted and the crosslinked structure can be controlled based on a forward simulation method, or the processing parameters and the initial polymeric material can be optimized on the basis of a backward simulation method Copyright © 2003 Society of Chemical Industry
Design of lactide copolymers as biomaterials
Authors: Ouchi Tatsuro , Ohya Yuichi 
Published: December 2003

AbstractA very important goal of researchers today is providing poly(L‐lactide) (PLA)‐based polymers with controllable degradation profiles, various (soft or elastic) mechanical properties, reactivity for chemical modification, and other functionalities while keeping the favorable characteristics of PLA. This article concerns the synthetic methods and properties of the following novel lactide copolymers: (1) random and block copolymers of depsipeptide and L‐lactide with reactive (ionic) side‐chain groups, (2) comb‐type PLA and branched PLA, and (3) PLA‐grafted polysaccharide and PLA with terminal saccharide residues. Poly(depsipeptide‐random‐L‐lactide)s and polydepsipeptide‐block‐poly(L‐lactide)s with reactive (ionic) side‐chain groups should be useful for the preparation of matrices and microspheres with reactive surfaces because of their amphiphilic structures. Comb‐type PLA and branched PLA show lower crystallinities than linear PLA. PLA‐grafted polysaccharide should be useful for the preparation of matrices with various microstructures and mechanical and degradation properties through the introduction of hydrophilic segments. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 453–462, 2004
Synthesis and characterization of linear tetrablock quarterpolymers of styrene, isoprene, dimethylsiloxane, and 2‐vinylpyridine
Authors: Fragouli Panagiota G. , Iatrou Hermis , Hadjichristidis Nikos 
Published: December 2003

AbstractA series of five tetrablock quarterpolymers of styrene, isoprene, dimethylsiloxane, and 2‐vinylpyridine with molecular weights varying from 117 × 103 to 177 × 103 and having different compositions were synthesized. The synthesis was based on recent advances in the controlled high‐vacuum anionic polymerization of hexamethylcyclotrisiloxane and on the selective linking of poly(dimethylsiloxane)lithium with the chlorosilane group of the heterofunctional linking agent chloromethylphenylethylene dimethylchlorosilane. Combined characterization results by size exclusion chromatography, membrane osmometry, and NMR spectroscopy suggested that the synthesized multiblock multicomponent polymers had a high degree of structural and compositional homogeneity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 514–519, 2004
New photocleavable structures. II. α‐Cleavable photoinitiators based on pyridines
Authors: Liska R. , Herzog D. 
Published: December 2003

AbstractA series of novel pyridine‐based type I photoinitiators were synthesized. UV spectroscopy revealed absorption characteristics very similar to those of a commercially available hydroxyalkylphenone [2‐hydroxy‐2‐methyl‐1‐phenyl propan‐1‐one (1b)]. Photo‐differential scanning calorimetry was used to study the polymerization kinetics of lauryl acrylate photoinitiated by the new pyridines. Under a nitrogen atmosphere, a 3‐substituted derivative [2‐hydroxy‐2‐methyl‐1‐pyridin‐3‐yl‐propan‐1‐one (3b)] gave results comparable to those obtained with 1b. Measurements under air indicated decreased sensitivity toward oxygen quenching reactions. Additionally, pyridine derivatives showed good water solubility (4.9 g/100 mL). Preliminary steady‐state photolysis experiments with 2,2,6,6‐tetramethyl‐1‐piperidinyloxy as a radical scavenger were carried out, and the α‐cleavage mechanism was found to be the main reaction pathway. The quantum yields of α‐cleavage were approximately 0.30 ± 0.04 for 3b and 0.18 ± 0.03 for 1b. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 752–764, 2004
Controlling the water content of never dried and reswollen bacterial cellulose by the addition of water‐soluble polymers to the culture medium
Authors: Seifert Marit , Hesse Stephanie , Kabrelian Vasken , Klemm Dieter 
Published: December 2003

AbstractFor the modification of medically useful biomaterials from bacterially synthesized cellulose, fleeces of Acetobacter xylinum have been produced in the presence of 0.5, 1.0, and 2.0% (m/v) carboxymethylcellulose (CMC), methylcellulose (MC), and poly(vinyl alcohol) (PVA), respectively, in the Hestrin‐Schramm culture medium. The incorporation of the water‐soluble polymers into cellulose and their influence on the structure, crystal modifications, and material properties are described. With IR and solid‐state 13C NMR spectroscopy of the fleeces, the presence of the cellulose ethers and an increase in the amorphous parts of the cellulose modifications (NMR results) have been detected. The incorporation is represented by a higher product yield, too. As demonstrated by scanning electron microscopy, a porelike cellulose network structure forms in the presence of CMC and MC. This modified structure increases the water retention ability (expressed as the water content), the ion absorption capacity, and the remaining nitrogen‐containing residues from the culture medium or bacteria cells. The water content of bacterial cellulose (BC) in the never dried state and the freeze‐dried, reswollen state can be controlled by the CMC concentration in the culture solution. The freeze‐dried, reswollen BC‐CMC (2.0%) contains 96% water after centrifugation, whereas standard BC has only 73%. About 98% water is included in a BC‐MC composite in the wet state, and about 93% is included in the reswollen state synthesized in the presence of 0.5, 1.0, or 2.0% MC. These biomaterial composites can be stored in the dried state and reswollen before use, reaching a higher water absorption than pure, never dried BC. The copper ion capacity of BC‐CMC composites increases proportionally with the added amount of CMC. BC‐CMC (0.5%) can absorb 3 times more copper ions than original BC. In the case of 0.5 and 1.0% PVA additions to the culture solution, this polymer cannot be detected in the cellulose fleeces after they are washed. Nevertheless the presence of PVA in the culture medium effects a decreased product yield, a retention of nitrogen‐containing residues in the material during purification, a reduced water absorption ability, and a slightly higher copper ion capacity in comparison with original BC. The water content of freeze‐dried, reswollen BC‐PVA (0.5%) is only 62%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 463–470, 2004
Analysis of surface mobility in polystyrene films with monodisperse and bimodal molecular weights by lateral force microscopy
Authors: Kajiyama Tisato , Tanaka Keiji , Takahara Atsushi 
Published: December 2003

AbstractThe surface glass‐transition temperature (T) in monodisperse polystyrene (PS) films was examined on the basis of the temperature dependence of the lateral force at a given scanning rate. T of the PS films was found to be markedly lower than the corresponding bulk glass‐transition temperature over the entire molecular weight range (4900–1,460,000). Also, the apparent activation energy of the surface segmental motion in the PS films was 230 ± 10 kJ mol−1, significantly smaller than that for bulk PS. Finally, T measurement by lateral force microscopy was applied to binary PS mixtures with different molecular weights. On the basis of the Gordon–Taylor equation, the surface composition of the shorter component in the blend films was successfully obtained. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 639–647, 2004
Synthesis of block copolymers by combined ultrasonic irradiation and reverse atom transfer radical polymerization processes
Authors: Degirmenci Mustafa , Catalgil‐Giz Huceste , Yagci Yusuf 
Published: December 2003

AbstractA two‐step procedure based on ultrasonic irradiation and reverse atom transfer radical polymerization (RATRP) for the synthesis of block copolymers is described. In the first step of the procedure, a stable chlorine‐end‐capped polymer is formed upon the ultrasonic irradiation of poly(methyl methacrylate) (PMMA) in dry benzene in the presence of a copper chloride/2,2′‐bipyridine catalyst. Heating the system to 110 °C initiates the polymerization of the second monomer, styrene, and this results in the formation of the block copolymers. The degradation behavior of PMMA under ultrasonic irradiation has also been studied. The agreement of the experimentally obtained molecular weights and theoretical molecular weights and the unimodal shapes of the gel permeation chromatography curves of the block copolymers indicate the controlled nature of the RATRP process initiated by polymeric radicals formed by sonication. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 534–540, 2004
Sequence and structural analysis of cellular retinoic acid‐binding proteins reveals a network of conserved hydrophobic interactions
Authors: Gunasekaran Kannan , Hagler Arnold T. , Gierasch Lila M. 
Published: December 2003

AbstractAbstract Proteins in the intracellular lipid‐binding protein (iLBP) family show remarkably high structural conservation despite their low‐sequence identity. A multiple‐sequence alignment using 52 sequences of iLBP family members revealed 15 fully conserved positions, with a disproportionately high number of these (n=7) located in the relatively small helical region. The conserved positions displayed high structural conservation based on comparisons of known iLBP crystal structures. It is striking that the β‐sheet domain had few conserved positions, despite its high structural conservation. This observation prompted us to analyze pair‐wise interactions within the β‐sheet region to ask whether structural information was encoded in interacting amino acid pairs. We conducted this analysis on the iLBP family member, cellular retinoic acid‐binding protein I (CRABP I), whose folding mechanism is under study in our laboratory. Indeed, an analysis based on a simple classification of hydrophobic and polar amino acids revealed a network of conserved interactions in CRABP I that cluster spatially, suggesting a possible nucleation site for folding. Significantly, a small number of residues participated in multiple conserved interactions, suggesting a key role for these sites in the structure and folding of CRABP I. The results presented here correlate well with available experimental evidence on folding of CRABPs and their family members and suggest future experiments. The analysis also shows the usefulness of considering pair‐wise conservation based on a simple classification of amino acids, in analyzing sequences and structures to find common core regions among homologues. Proteins 2003. © 2003 Wiley‐Liss, Inc.
Free energies of binding of polychlorinated biphenyls to the estrogen receptor from a single simulation
Authors: Oostenbrink Chris , van Gunsteren Wilfred F. 
Published: December 2003

AbstractRelative free energies of binding to the ligand‐binding domain of the estrogen receptor have been calculated for a series of 17 hydroxylated polychlorinated biphenyls. Because traditional thermodynamic integration or perturbation approaches are hardly feasible for these numbers of compounds, the one‐step perturbation approach is applied and is shown to yield accurate results based on only two 2‐ns molecular dynamics simulations of an unphysical, judiciously chosen, reference state. The mean absolute difference between the calculated and experimental binding free energies for the 17 compounds is 3.4 kJ/mol, which illustrates the accuracy of the GROMOS biomolecular force field used. Excluding the three largest ligands from the comparison reduces the deviation to 2.0 kJ/mol (i.e., < kBT). Apart from the relative free energy, structural information about the binding mode and binding orientation for every compound can also be extracted from the simulation, showing that a ligand bound to its receptor cannot be represented by a single conformation, but it samples an ensemble of different orientations. Proteins 2004;54:000–000. © 2003 Wiley‐Liss, Inc.