bluuebunny/crossref_metadata_2025 huggingface dataset:
Zirconocene‐catalysed propene polymerisation: kinetics, mechanism, and the role of the anion
Authors: Song Fuquan , Hannant Mark D. , Cannon Roderick D. , Bochmann Manfred
Published: June 2004

The olefin polymerisation activity of metallocene catalysts strongly depends on the counteranion provided by the activator system. The relative activities of a number of new diborate anions [Z(BAr3)2]− have been quantified (Z = CN, NH2, N(CN)2; Ar = C6F5 or o‐C6F4C6F5). The kinetic parameters for the initiation, propagation and termination steps of propene polymerisations catalysed by (SBI)ZrCl2 have been determined using quenched‐flow kinetic and batch techniques [SBI = rac‐Me2Si(1‐Ind)2]. Comparison of two activator systems, (i) CPh3[B(C6F5)4] / triisobutylaluminium (TIBA) and (ii) methylaluminoxane (MAO) shows, surprisingly, that the concentration of species actively involved in chain growth at any one time is comparable for both systems, although the MAO‐activated catalyst is about 20 times less active than the borate system. It is concluded that the counteranion remains sufficiently strongly bound to the metal centre throughout the chain growth sequence to modulate the energetics of monomer insertion. A model suggesting that the monomer binding follows an associative interchange (Ia) mechanism is proposed.
Highly active and stereoselective olefin polymerization catalysts generated by the transfer‐epimetallation of olefins or acetylenes with dialkyltitanium(IV) complexes: three‐membered metallocycles as active catalyst sites‡
Authors: Eisch John J. , Gitua John N. , Otieno Peter O. , Adeosun Adetenu A.
Published: June 2004

Efficient transfer‐epimetallations of simple olefins and acetylenes by R2TiL2 reagents (R = Bun, But; L = X) are readily achieved in THF at −78°C to generate titanacyclopropa(e)ne intermediates, readily capable of inserting various unsaturated addends (olefin, acetylene, nitrile). Analogous epimetallations conducted in hydrocarbons lead to the isotactic stereoselective polymerization of 1‐alkenes and the cyclotrimerization of acetylenes. In place of the widely accepted Arlman‐Cossee model for the active catalytic site, namely a Ti‐C bond on the TiCl3 crystal lattice, the 2‐substituted‐1‐halotitanacyclopropyl cation formed in hydrocarbon media is proposed as the active site for stereoselective olefin polymerization.
Polymerization of acrylate monomers by iron(II) complexes bearing bis(imido)pyridyl or phosphine ligands
Authors: Castro Pascal M. , Lankinen Mikko P. , Uusitalo Anne‐Marja , Leskelä Markku , Repo Timo
Published: June 2004

Iron(II) complexes bearing bis(imido)pyridyl or phosphine ligand were used for the polymerization of tert‐butylacrylate and other (meth)acrylates after activation with methylaluminoxane. Phosphine based catalysts turned to be more active than the bis(imido)pyridyl ones. tert‐Butylacrylate was the best polymerized monomer, while methylmethacrylate was slowly converted to poly(methylmethacrylate) and no activity was observed in the polymerization of styrene. Influence of the MAO to complex ratio was investigated and kinetics studies were conducted. Based on these results, a schematic representation of the polymerization mechanism was proposed.
Styrene polymerization by ziegler‐natta catalysts based on bis(salicylaldiminate)nickel(II) complexes and methyl aluminoxane
Authors: Carlini Carlo , Macinai Alessandro , Raspolli Galletti Anna Maria , Sbrana Glauco
Published: June 2004

The homopolymerization of styrene by using different catalytic systems based on bis(salicylaldiminate)nickel(II) and methylaluminoxane was investigated. In particular, the effect on catalyst activity and polymer characteristics by electron withdrawing groups located on the phenolic moiety was studied. The influence of the bulkiness of the substituents on the N‐aldimine ligand was also ascertained. Finally the catalytic performances were investigated as a function of the main reaction parameters, such as temperature, Al/Ni molar ratio and duration.
Polymerization of propene by post‐metallocene catalysts
Authors: Lamberti Marina , Mazzeo Mina , Pappalardo Daniela , Zambelli Adolfo , Pellecchia Claudio
Published: June 2004

In the last few years several non‐metallocene catalysts have been disclosed as efficient catalysts for the stereospecific polymerization of propene.

In this paper we summarize some recent literature data and some new results concerning the stereochemical mechanism of propene polymerization promoted by late transition metal systems and group 4 metal bis(phenoxyimine) systems. NMR analysis of the fine structure of the polymers obtained, in some cases using isotopically enriched reagents, provides valuable information on the regiochemistry and stereochemistry of the polymerization.
Macromonomers and coordination polymerization
Authors: Lahitte Jean‐François , Peruch Frédéric , Isel François , Lutz Pierre Joseph
Published: June 2004

The present work discusses the synthesis of well‐defined comb‐shaped polymers or graft copolymer structures based on coordination (co)polymerization of macromonomers. Polystyrene macromonomers with various polymerizable entities were synthesized first by induced deactivation reactions. The homopolymerization of these macromonomers in the presence of selected early or late transition metal catalysts was examined. Comb‐shaped polymers could be obtained over a large range of DP values. The results were compared to those obtained by anionic homopolymerization. Some results on the copolymerization of these PS macromonomers with ethylene in the presence of VERSIPOLTM type catalysts were presented.
A combined density functional theory and molecular mechanics (QM/MM) study of single site ethylene polymerization catalyzed by [Cp{NC(tBu)2}TiR+] in the presence of the counterion, CH3B(C6F5)3−
Authors: Vanka Kumar , Xu Zhitao , Ziegler Tom
Published: June 2004

A density functional study was conducted on the approach and insertion of ethylene monomer into the Ti‐Cα bond of the catalyst system, CpNC(tBu)2RTi‐μ‐Me‐B(C6F5)3 (R= methyl, propyl). A validated QM/MM model was used to represent the counterion. Solvent effects were incorporated with single point solvent calculations done with cyclohexane (ϵ = 2.023) as the solvent. For R=Me (the initiation step), approach and insertion of the ethylene was found to be endothermic, with the barrier for insertion being 12.7 kcal/mol for the most favourable case. For R=Pr (the propagation step), the insertion barrier was found to decrease slightly (11.5 kcal/mol for the most favorable case), corroborating experimental evidence of decrease in insertion barrier with increase in chain length. Termination by chain transfer to monomer was also considered, and found to be unfavourable, in comparison to insertion, by 8.6 kcal/mol for the propagation step. Solvent effects were found to be significant for the propagation step, changing the rate determining step from insertion to uptake for the most favorable case of insertion.
On‐line monitoring and fingerprint technology: new tools for the development of new catalysts and polyolefin materials
Authors: Tuchbreiter Arno , Marquardt Jürgen , Kappler Bernd , Honerkamp Josef , Mülhaupt Rolf
Published: June 2004

The High‐Output Polymer Screening (HOPS) combines process‐relevant automated reactor systems and rapid polymer characterization with on‐line polymerization monitoring and automated data acquisition (“electronic notebook”) in order to make effective use of advanced data mining tools. This has led to the development of fingerprint technology based upon correlations between spectroscopic data and polymerization process conditions, catalyst compositions, as well as polymer end‐use properties. Infrared spectroscopic fingerprints proved to be very useful for accelerating polymer analyses including characterization of polymer molecular architectures as well as non‐destructive testing of the mechanical, thermal and other end‐use polymer properties. Such spectroscopic fingerprints represent important components of effective on‐line quality control systems. With ATR‐FT‐IR probes on‐line monitoring of catalytic olefin copolymerization was performed in solution to measure in real time copolymerization kinetics, catalyst productivities, catalyst deactivation as well as copolymerization parameters and copolymer sequence distributions. Monomer consumption and comonomer incorporation were monitored simultaneously. Advanced fingerprint technology can reduce significantly the need for time‐ and money consuming polymer testing and can also stimulate the search for new catalyst systems and polymeric materials.
Synthesis of polyolefin based materials with improved thermo‐oxidative stability
Authors: Dolatkhani Marc , Cramail Henri , Deffieux Alain , Ribeiro Maria Rosário , Santos Jorge M. , Bordado João M.
Published: June 2004

Polyolefin based materials with chemically bonded phenol compounds have been synthesized. Two unsaturated polyolefins: an ethylene/propylene/5,7‐dimethyl‐1,6‐octadiene terpolymer and an ethylene/5,7‐dimethyl‐1,6‐octadiene copolymer, were used as starting materials. The functionalisation method involves a two‐step procedure that consists in the hydrochlorination of the substituted pending double bonds, followed by grafting of the phenol compound. This procedure was found to be more effective for the terpolymer than for the corresponding copolymer. The reasons for this are discussed. A thermogravimetric study, in air atmosphere shows that, poly(ethylene‐co‐5,7‐dimethyl‐1,6‐octadiene) grafted with 2‐tert‐butyl‐4‐methylphenol present improved thermo‐oxidative stability when compared to a polyethylene reference.
Equilibrium Swelling of an Epoxy‐Resin in Contact with Water – A Molecular Dynamics Simulation Study
Authors: Dömötör Gyula , Hentschke Reinhard
Published: June 2004

Full Paper: We have studied the equilibrium swelling of an idealized model network based on a realistic epoxy‐resin in contact with water using the molecular dynamics simulation method. We use a novel method to measure the water chemical potential inside the network as function of water concentration. The equality of the water chemical potential computed in this fashion with the bulk water chemical potential under the same thermodynamic conditions determines the equilibrium water content and the swelling ratio. We study the dependence of the water content as function of temperature and as function of the size of the atomic partial charges.

Schematic representation of the simulation volume. Spheres represent epoxy units with n = 0. The dashed lines represent curing agent units with m = 5.

image

Schematic representation of the simulation volume. Spheres represent epoxy units with n = 0. The dashed lines represent curing agent units with m = 5.
Herstellung verbundverstärkter Aluminiumprofile für ultraleichte Tragwerke durch Strangpressen
Authors: Kleiner M. , Schomäcker M. , Schikorra M. , Klaus A.
Published: June 2004

Auf Grund ähnlicher spezifischer Steifigkeits‐ und Festigkeitseigenschaften von Aluminium und Stahl lassen sich in der Anwendung bei leichten Rahmenstrukturen durch gegenseitige Werkstoffsubstitution nur geringe Leichtbaugewinne erzielen. Lediglich die Verwendung von z. B. Kohlefaserwerkstoffen oder Höchstleistungsstählen lässt eine Gewichtsreduktion für den Einsatz von Rohren oder Profilen in ultraleichten Strukturen erwarten. Am Lehrstuhl für Umformtechnik (LFU) der Universität Dortmund ist ein Verfahren entwickelt worden, das durch ein modifiziertes Strangpressen zur Herstellung von Verbundprofilen geeignet ist. Ausgehend von konventionellen Aluminium‐Pressblöcken werden hierbei verschiedenartige endlose Verstärkungselemente innerhalb der Wandstärke der Profilmatrix eingebettet. Für das Verfahren, das im Rahmen des Sonderforschungsbereiches SFB/TR10 erforscht wird, ist die Entwicklung neuartiger Strangpresswerkzeuge erforderlich. Durch experimentelle Untersuchungen auf einer 2,5 MN Laborstrangpresse wurden erfolgreich erste Verbundprofile hergestellt. Zur Vertiefung des Prozessverständnisses und der Prognose der Wirksamkeit neuer Werkzeugkonzepte wurden parallel FEM‐Simulationen durchgeführt. Die mit Hilfe des Verfahrens hergestellten geraden Verbundprofile lassen sich auf Grund möglicher Gefügeschädigungen nicht biegen. In Kombination mit dem ebenfalls am LFU entwickelten Verfahren Runden beim Strangpressen werden diese Verbundprofile jedoch auch mit gekrümmter Kontur herstellbar sein.
Hydromechanisches Tiefziehen und Hochdruckblechumformung als Verfahren zur Herstellung komplexer Bauteile aus Magnesiumfeinblechen des Typs AZ31B‐0
Authors: Viehweger B. , Richter G. , Düring M. , Karabet A. , Sviridov A. , Hartmann H. , Richter U.
Published: June 2004

Eine gute Umformbarkeit von Blechhalbzeugen aus Magnesiumknetlegierungen stellt sich bekanntlich bei Anwendung von Umformtemperaturen im Bereich von 175 °C – 240 °C ein. Anhand der wirkmedienbasierten Umformverfahren hydromechanisches Tiefziehen und Hochdruckblechumformung ist an handelsüblichen AZ31B‐0 Feinblechen die Einstellung unterschiedlicher Umformparameter erprobt worden. Unter Verwendung von Umformtemperaturen von 175 °C, 200 °C, 225 °C und 240 °C und entsprechend angepassten Niederhalterdrücken ist eine praxisnahe Versuchsgeometrie „Minihood”︁ ausgeformt worden. Im Hinblick auf angewendete Umformverfahren und Versuchsparameter wurde an den Versuchsbauteilen die Blechdickenabnahme und die Radienausprägung bewertet und verglichen. Für ausgewählte Versuchsbauteile, umgeformt mittels der Hochdruckblechumformung bei Temperaturen von 175 °C und 225 °C, ist eine ergänzende Untersuchung hinsichtlich der durch den Umformvorgang verursachten Veränderungen von Oberflächenkennwerten durchgeführt worden. Anhand dieser Ergebnisse werden Hinweise auf die Grenzen des Einsatzes der o.g. Umformverfahren für Magnesiumblech des Legierungstyps AZ31B‐0 gegeben.
Untersuchungen zur Herstellung flächig gekrümmter Bauteile durch den Einsatz der Robotertechnik beim Freiformschmieden
Authors: Ziegelmayer O. , Schneider V. , Kopp R. , Dürr O.
Published: June 2004

Der Prozess des Freiformschmiedens zeichnet sich durch seine hohe Flexibilität der einsetzbaren Werkstoffe und der mittels einfacher Werkzeuge erzielbaren Halbzeuggeometrien aus. Um eine höhere Komplexität bei gleichzeitig höherer Reproduzierbarkeit gegenüber den in heutigen industriellen Anlagen produzierbaren Bauteilformen schaffen zu können, wurde vor einigen Jahren am Institut für Bildsame Formgebung (IBF) der RWTH Aachen ein Sechs‐Achsen Schwerlast‐Industrieroboter als Schmiedemanipulator (Tragfähigkeit ∼300 kg) als Ergänzung zu einer hydraulischen Freiformschmiedepresse (Maximalkraft: 6,3 MN) installiert.

Diese Anlage bietet die Voraussetzung, Bauteile mit einer flächigen Krümmung im industrienahen Maßstab mittels Warmumformung herzustellen, wobei die Teile sich mittels gezielter Massenvorverteilung für nachfolgende Gesenkschmiede‐Operationen nutzen lassen. Eine industrielle Anwendung hierfür stellt bspw. ein Rumpfspant für die Luftfahrtindustrie dar, der aus Aluminium hergestellt wird und u. a. auch strengen werkstofflichen Anforderungen unterliegt.
Temperatureinfluss auf den Adhäsionsverschleiß beim Umformen von Aluminiumblechen
Authors: Groche P. , Nitzsche G.
Published: June 2004

Die Adhäsionsneigung von Aluminiumblechen führt beim Tiefziehen zu verstärktem Werkzeugverschleiß in Form von Aufschweißungen. Um wirksame Maßnahmen zur Reduzierung des Adhäsionsverschleißes treffen zu können, müssen die Mechanismen bekannt sein, die zur Adhäsionsbildung führen. Die Temperatur in der Umformzone wird dabei in den existierenden Theorien nicht berücksichtigt. Zur Untersuchung dieses Parameters werden die in der Umformzone vorliegenden thermischen und mechanischen Beanspruchungen grundlegend numerisch analysiert sowie experimentell im Modellversuch überprüft. Mit Hilfe temperierter Werkzeuge wird anschließend eine definierte Temperatur in der Umformzone eingestellt, die den Werkzeugtemperaturen im realen Presswerk entspricht. Während bei einem konventionellen System ohne Erwärmung kein Adhäsionsverschleiß festzustellen ist, kommt es mit erwärmten Werkzeugen zur Bildung von Aufschweißungen. Um den Adhäsionsverschleiß zu reduzieren, müssen daher Maßnahmen getroffen werden, die den vorhandenen Temperatureinfluss berücksichtigen.
Delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC) and T2 characteristics of human knee articular cartilage: Topographical variation and relationships to mechanical properties
Authors: Kurkijärvi J.E. , Nissi M.J. , Kiviranta I. , Jurvelin J.S. , Nieminen M.T.
Published: June 2004

The macromolecular structure and mechanical properties of articular cartilage are interrelated and known to vary topographically in the human knee joint. To investigate the potential of delayed gadolinium‐enhanced MRI of cartilage (dGEMRIC), T1, and T2 mapping to elucidate these differences, full‐thickness cartilage disks were prepared from six anatomical locations in nonarthritic human knee joints (N = 13). Young's modulus and the dynamic modulus at 1 Hz were determined with the use of unconfined compression tests, followed by quantitative MRI measurements at 9.4 Tesla. Mechanical tests revealed reproducible, statistically significant differences in moduli between the patella and the medial/lateral femoral condyles. Typically, femoral cartilage showed higher Young's (>1.0 MPa) and dynamic (>8 MPa) moduli than tibial or patellar cartilage (Young's modulus <0.9 MPa, dynamic modulus <8 MPa). dGEMRIC moderately reproduced the topographical variation in moduli. Additionally, T1, T2, and dGEMRIC revealed topographical differences that were not registered mechanically. The different MRI and mechanical parameters showed poor to excellent linear correlations, up to r = 0.87, at individual test sites. After all specimens were pooled, dGEMRIC was the best predictor of compressive stiffness (r = 0.57, N = 77). The results suggest that quantitative MRI can indirectly provide information on the mechanical properties of human knee articular cartilage, as well as the site‐dependent variations of these properties. Investigators should consider the topographical variation in MRI parameters when conducting quantitative MRI of cartilage in vivo. Magn Reson Med 52:41–46, 2004. © 2004 Wiley‐Liss, Inc.
Deconvolution of dynamic contrast‐enhanced MRI data by linear inversion: Choice of the regularization parameter
Authors: Sourbron Steven , Luypaert Rob , Van Schuerbeek Peter , Dujardin Martine , Stadnik Tadeusz , Osteaux Michel
Published: June 2004

Truncated singular value decomposition (TSVD) is an effective method for the deconvolution of dynamic contrast‐enhanced MRI. Two robust methods for the selection of the truncation threshold on a pixel‐by‐pixel basis—generalized cross validation (GCV) and the L‐curve criterion (LCC)—were optimized and compared to paradigms in the literature. The methods lead to improvements in the estimate of the residue function and of its maximum and converge properly with SNR. The oscillations typically observed in the solution vanish entirely and perfusion is more accurately estimated at small mean transit times. This results in improved image contrast and increased sensitivity to perfusion abnormalities, at the cost of 1–2 min in calculation time and isolated instabilities in the image. It is argued that the latter problem may be resolved by optimization. Simulated results for GCV and LCC are equivalent in terms of performance, but GCV is faster. Magn Reson Med 52:209–213, 2004. © 2004 Wiley‐Liss, Inc.
Design of symmetric‐sweep spectral‐spatial RF pulses for spectral editing
Authors: Cunningham Charles H. , Vigneron Daniel B. , Chen Albert P. , Xu Duan , Hurd Ralph E. , Sailasuta Napapon , Pauly John M.
Published: June 2004

Spectral‐spatial RF (SSRF) pulses allow simultaneous selection in both frequency and spatial domains. These pulses are particularly important for clinical and research MR spectroscopy (MRS) applications for suppression of large water and lipid resonances. Also, the high bandwidth of the subpulses (5–10 kHz) greatly reduces the spatial‐shift errors associated with different chemical shifts. However, the use of high‐bandwidth subpulses along with enough spectral bandwidth to measure a typical range of metabolite frequencies (e.g., 300 Hz at 3 T) can require RF amplitudes beyond the limits of the RF amplifier of a typical scanner. In this article, a new method is described for designing nonlinear‐phase 180° SSRF pulses that can be used for spectral editing. The novel feature of the pulses is that the spectral profile develops as a symmetric sweep, from the outside edges of the spectral window towards the middle, so that coupled components are tipped simultaneously and over a short interval. Pulses were designed for lactate editing at 1.5 T and 3 T. The spectral and spatial spin‐echo profiles of the new pulses were measured experimentally. Spectra acquired in phantom experiments showed a well‐resolved, edited lactate doublet, with 91% to 93% editing efficiency. Magn Reson Med 52:147–153, 2004. © 2004 Wiley‐Liss, Inc.
Correction for gradient nonlinearity in continuously moving table MR imaging
Authors: Polzin Jason A. , Kruger David G. , Gurr David H. , Brittain Jean H. , Riederer Stephen J.
Published: June 2004

Recently, a number of methods have been demonstrated for large field of view MR imaging using continuous table motion. As with conventional, fixed‐table MRI, the spatial encoding is performed using magnetic field gradients. However, it is demonstrated in this work that as a consequence of every measurement being made at a slightly different displacement between the object and the gradient field, gradient nonlinearities are manifest as blurring in addition to spatial distortion. Moreover, the blurring is spatially dependent. It is also shown that correcting all phase‐encoding steps individually or in groups can reduce these effects. Phantom and in vivo results are shown which demonstrate the effectiveness of the correction. Magn Reson Med 52:181–187, 2004. © 2004 Wiley‐Liss, Inc.
Opiate tolerance by heroin self‐administration: An fMRI study in rat
Authors: Xi Zheng‐Xiong , Wu Gaohong , Stein Elliot A. , Li Shi‐Jiang
Published: June 2004

Functional MRI (fMRI) was employed to determine whether repeated heroin self‐administration (SA) produces tolerance or sensitization in the brain of heroin‐SA rats. Twelve rats were evenly divided into saline and heroin (0.06 mg/kg, 4 hr/day) SA groups. There was a progressive increase in drug‐SA behavior and daily heroin intake during the 8–9 days of heroin‐SA training. Within 24 hr after the last session of daily SA, acute heroin (0.1 mg/kg) administration induced regional blood oxygen level‐dependent (BOLD) signals in both groups of rats. The positive BOLD signals appeared mainly in the cortical regions, including the prefrontal cortex, cingulate, and olfactory cortex, while the negative BOLD signals were predominantly located in subcortical regions such as caudate and putamen, nucleus accumbens, thalamus, and hypothalamus. However, the number of activated voxels or BOLD‐signal intensity was significantly less in heroin‐SA rat in regions of prefrontal cortex, nucleus accumbens, and thalamus, etc., compared to the changes in the saline control rats. Application of γ‐vinyl GABA (100 mg/kg), an irreversible GABA‐transaminase inhibitor, failed to block opiate actions in the heroin‐SA rats. Together, these data suggest that repeated heroin‐SA produces tolerance or desensitization of opiate actions in the rat brain, which may in turn potentiate drug SA behavior and drug intake. Magn Reson Med 52:108–114, 2004. © 2004 Wiley‐Liss, Inc.
Use of spherical harmonic deconvolution methods to compensate for nonlinear gradient effects on MRI images
Authors: Janke Andrew , Zhao Huawei , Cowin Gary J. , Galloway Graham J. , Doddrell David M.
Published: June 2004

Spatial encoding in MR techniques is achieved by sampling the signal as a function of time in the presence of a magnetic field gradient. The gradients are assumed to generate a linear magnetic field gradient, and typical image reconstruction relies upon this approximation. However, high‐speed gradients in the current generation of MRI scanners often sacrifice linearity for improvements in speed. Such nonlinearity results in distorted images. The problem is presented in terms of first principles, and a correction method based on a gradient field spherical harmonic expansion is proposed. In our case, the amount of distortion measured within a typical field of view (FOV) required for head imaging is sufficiently large that without the use of some distortion correction technique, the images would be of limited use for stereotaxy or longitudinal studies, where precise volumetric information is required. Magn Reson Med 52:115–122, 2004. © 2004 Wiley‐Liss, Inc.
Signal‐to‐noise ratio behavior of steady‐state free precession
Authors: Reeder Scott B. , Herzka Daniel A. , McVeigh Elliot R.
Published: June 2004

Steady‐state free precession (SSFP) is a rapid gradient‐echo imaging technique that has recently gained popularity and is used in a variety of applications, including cardiac and real‐time imaging, because of its high signal and favorable contrast between blood and myocardium. The purpose of this work was to examine the signal‐to‐noise ratio (SNR) behavior of images acquired with SSFP, and the dependence of SNR on imaging parameters such as TR, bandwidth, and image resolution, and the use of multi‐echo sequences. In this work it is shown that the SNR of SSFP sequences is dependent only on pulse sequence efficiency, voxel dimensions, and relaxation parameters (T1 and T2). Notably, SNR is insensitive to bandwidth unless increases in bandwidth significantly decrease efficiency. Finally, we examined the relationship between pulse sequence performance (TR and efficiency) and gradient performance (maximum gradient strength and slew rate) for several imaging scenarios, including multi‐echo sequences, to determine the optimum matching of maximum gradient strength and slew rate for gradient hardware designs. For standard modern gradient hardware (40 mT/m and 150 mT/m/ms), we found that the maximum gradient strength is more than adequate for the imaging resolution that is commonly encountered with rapid scouting (3 mm × 4 mm × 10 mm voxel). It is well matched for typical CINE and real‐time cardiac imaging applications (1.5 mm × 2 mm × 6 mm voxel), and is inadequate for optimal matching with slew rate for high‐resolution applications such as musculoskeletal imaging (0.5 × 0.8 × 3 mm voxel). For the lower‐resolution methods, efficiency could be improved with higher slew rates; this provokes interest in designing methods for limiting dB/dt peripherally while achieving high switching rates in the imaging field of view. The use of multi‐echo SSFP acquisitions leads to substantial improvements in sequence performance (i.e., increased efficiency and shorter TR). Magn Reson Med 52:123–130, 2004. Published 2004 Wiley‐Liss, Inc.
NMR measurement of brain oxidative metabolism in monkeys using 13C‐labeled glucose without a 13C radiofrequency channel
Authors: Boumezbeur Fawzi , Besret Laurent , Valette Julien , Vaufrey Françoise , Henry Pierre‐Gilles , Slavov Velislav , Giacomini Eric , Hantraye Philippe , Bloch Gilles , Lebon Vincent
Published: June 2004

We detected glutamate C4 and C3 labeling in the monkey brain during an infusion of [U‐13C6]glucose, using a simple 1H PRESS sequence without 13C editing or decoupling. Point‐resolved spectroscopy (PRESS) spectra revealed decreases in 12C‐bonded protons, and increases in 13C‐bonded protons of glutamate. To take full advantage of the simultaneous detection of 12C‐ and 13C‐bonded protons, we implemented a quantitation procedure to properly measure both glutamate C4 and C3 enrichments. This procedure relies on LCModel analysis with a basis set to account for simultaneous signal changes of protons bound to 12C and 13C. Signal changes were mainly attributed to 12C‐ and 13C‐bonded protons of glutamate. As a result, we were able to measure the tricarboxylic acid (TCA) cycle flux in a 3.9 cm3 voxel centered in the monkey brain on a whole‐body 3 Tesla system (VTCA = 0.55 ± 0.04 μmol.g−1.min−1, N = 4). This work demonstrates that oxidative metabolism can be quantified in deep structures of the brain on clinical MRI systems, without the need for a 13C radiofrequency (RF) channel. Magn Reson Med 52:33–40, 2004. © 2004 Wiley‐Liss, Inc.
Diffusion measurements free of motion artifacts using intermolecular dipole‐dipole interactions
Authors: Kennedy Scott D. , Zhong Jianhui
Published: June 2004

Diffusion encoding, or diffusion weighting, is commonly achieved by applying a pair of balanced pulsed‐field gradients during spin evolution. An alternative way to obtain diffusion measurements is to select dipolar correlation distances using the distant dipolar field (DDF) in systems with abundant spin density, such as water in tissues. Diffusion weighting using this effect is unique in that the refocusing “gradient” is carried within the sample, and thus the macroscopic motion of the sample is not expected to interfere with signal formation. The experiments presented here demonstrate that in moving phantoms, the phase shift of the signal due to linear motion is minimal in diffusion‐weighted (DW) DDF measurements, and that motion artifacts in images of moving phantoms and the abdomen of live mice are small compared to standard pulsed‐field‐gradient methods. The technique may facilitate the use of DWI in typically motion‐prone regions such as the abdomen, lungs, and heart. Magn Reson Med 52:1–6, 2004. © 2004 Wiley‐Liss, Inc.
Ultrasound‐guided MRI: Preliminary results using a motion phantom
Authors: Günther Matthias , Feinberg David A.
Published: June 2004

In principal, both ultrasound (US) imaging and MRI can be performed simultaneously within the magnetic field of the scanner due to their different physical natures (i.e., sound waves vs. electromagnetic radiation). One potential application is to use US information for dynamic spatial organ localization to improve MR imaging, similar to MR navigator echoes. In this work, preliminary results are presented for US‐guided MRI using position and orientation information extracted from US data to update the image slice position of an SSFP sequence in real time. Effective prospective motion compensation is shown for a phantom whose sinusoidal displacement can be fully corrected. Possible applications of simultaneous US‐MRI acquisitions include real‐time US‐guided cardiac MRI or interventional procedures. Magn Reson Med 52:27–32, 2004. © 2004 Wiley‐Liss, Inc.
Development programs for one‐shot systems using multiple‐state design reliability models
Authors: Shevasuthisilp Suntichai , Vardeman Stephen B.
Published: June 2004

Design reliability at the beginning of a product development program is typically low, and development costs can account for a large proportion of total product cost. We consider how to conduct development programs (series of tests and redesigns) for one‐shot systems (which are destroyed at first use or during testing). In rough terms, our aim is to both achieve high final design reliability and spend as little of a fixed budget as possible on development. We employ multiple‐state reliability models. Dynamic programming is used to identify a best test‐and‐redesign strategy and is shown to be presently computationally feasible for at least 5‐state models. Our analysis is flexible enough to allow for the accelerated stress testing needed in the case of ultra‐high reliability requirements, where testing otherwise provides little information on design reliability change. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004
Central nervous system inflammatory response after cerebral infarction as detected by magnetic resonance imaging
Authors: Saleh Andreas , Wiedermann Dirk , Schroeter Michael , Jonkmanns Cornelia , Jander Sebastian , Hoehn Mathias
Published: June 2004

Brain inflammation contributes to the tissue injury caused by ischemic stroke. Macrophages as the most abundant inflammatory cell population in stroke lesions can be visualized using ultrasmall superparamagnetic iron oxide (USPIO) as a cell‐specific contrast agent for magnetic resonance imaging (MRI). The aim of our present study was to delineate the inflammatory response during experimental cerebral infarction by means of USPIO‐enhanced MRI and to correlate the spatial distribution of USPIO‐induced MR signal alterations with cellular infiltration and iron deposition. To this end USPIOs were administered to Wistar rats 5 days after photothrombotic cerebral infarction. MR imaging at 7 T performed 24 h later displayed a rim‐like signal loss around the infarction in the USPIO treated animals. On histological brain sections obtained from the same animals after MRI the distribution of iron and ED1+ phagocytes was in full spatial agreement with the signal loss seen on T2*‐weighted images. Our study validates USPIO‐enhanced MRI as an important tool for the noninvasive visualization of brain inflammation in stroke and other CNS pathologies. Copyright © 2004 John Wiley & Sons, Ltd.
Water diffusion in the different microenvironments of breast cancer
Authors: Paran Yael , Bendel Peter , Margalit Raanan , Degani Hadassa
Published: June 2004

The parameters that characterize the intricate water diffusion in tumors may serve to reveal their distinct pathology. Specifically, the application of diffusion magnetic resonance imaging (MRI) can aid in characterizing breast cancer, as well as monitoring response to therapy. We present here a non‐invasive, quantitative MRI investigation, at high spatial resolution, of water diffusion in hormonal dependent MCF7 breast tumors implanted orthotopically in immunodeficient mice. Distinctive MRI protocols were designed in this study, utilizing a broad range of diffusion times and diffusion gradient strengths. Application of these protocols allowed water diffusion in the tissue extracellular and intracellular compartments to be distinguished, and the effect of restricted diffusion and water exchange on the water diffusion in these compartments to be evaluated. Pixel‐by‐pixel analysis yielded parametric maps of the estimated volume fraction and apparent diffusion coefficient of each compartment. The diffusion of the water in the extracellular microenvironment was approximately two fold slower than that of free water, and in the intracellular compartment was about one order of magnitude slower than that of free water and demonstrated restriction of water diffusion at long diffusion times. Mapping of the water fraction in each compartment was further employed to monitor changes during tumor progression and to assess tumor response to hormonal manipulation with a new antiestrogenic drug, tamoxifen methiodide (TMI). It was found that, in parallel to the growth arrest by this drug, the volume fraction of the slowly diffusing water increased, suggesting a TMI‐induced cell swelling. This study can serve as a basis for extending diffusion breast MRI in the clinical setting. Copyright © 2004 John Wiley & Sons, Ltd.
In vivo elasticity measurements of extremity skeletal muscle with MR elastography
Authors: Uffmann Kai , Maderwald Stefan , Ajaj Waleed , Galban Craig G. , Mateiescu Serban , Quick Harald H. , Ladd Mark E.
Published: June 2004

MR elastography (MRE) has been shown to be capable of non‐invasively measuring tissue elasticity even in deep‐lying regions. Although limited studies have already been published examining in vivo muscle elasticity, it is still not clear over what range the in vivo elasticity values vary. The present study intends to produce further information by examining four different skeletal muscles in a group of 12 healthy volunteers in the age range of 27–38 years. The examinations were performed in the biceps brachii, the flexor digitorum profundus, the soleus and the gastrocnemius. The average shear modulus was determined to be 17.9 ( ± 5.5), 8.7 ( ± 2.8), 12.5 ( ± 7.3) and 9.9 ( ± 6.8) kPa for each muscle, respectively. To ascertain the reproducibility of the examination, the stiffness measurements in two volunteers were repeated seven times for the biceps brachii. These examinations yielded a mean shear modulus of 11.3 ± .7 and 13.3 ± 4.7 kPa for the two subjects. For elasticity reconstruction, an automated reconstruction algorithm is introduced which eliminates variation due to subjective manual image analysis. This study yields new information regarding the expected variation in muscle elasticity in a healthy population, and also reveals the expected variability of the MRE technique in skeletal muscle. Copyright © 2004 John Wiley & Sons, Ltd.
1H and13C HR‐MAS spectroscopy of intact biopsy samplesex vivoandin vivo1H MRS study of human high grade gliomas
Authors: Martínez‐Bisbal M. Carmen , Martí‐Bonmatí Luis , Piquer José , Revert Antonio , Ferrer Pilar , Llácer José L. , Piotto Martial , Assemat Olivier , Celda Bernardo
Published: June 2004

High‐resolution magic angle spinning (HR‐MAS) one‐ and two‐dimensional1H and13C nuclear magnetic resonance (NMR) spectroscopy has been used to study intact glioblastoma (GBM) brain tumour tissue. The results were compared within vitrochemical extract andin vivospectra. The resolution of1H one‐dimensional,1H TOCSY and13C HSQC HR‐MAS spectra is comparable to that obtained on perchloric extracts.13C HSQC HR‐MAS spectra have been particularly useful for the identification of 37 different metabolites in intact biopsy tumours, excluding water and DSS components. To our knowledge, this is the most detailed assignment of biochemical compounds obtained in intact human tissue, in particular in brain tumour tissue. Tissue degradation during the recording of the NMR experiment was avoided by keeping the sample at a temperature of 4°C. Detailed metabolical compositions of 10 GBM (six primary, two secondary and two unclassified) were obtained. A good correlation betweenex vivoandin vivoMRS has been found. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis of third‐order non‐linear optical polymers based on conjugated poly(heteroarylene methines)
Authors: Yi Wenhui , Feng Wei , Cao Meng , Wu Hongcai
Published: June 2004

A series of 10 new poly(heteroarylene methylenes) containing one pyrrole or thiophene ring alternating with a carbon atom in the main chain were synthesized and characterized. The polymers which were synthesized in the air were found to be partially dehydrogenated by the oxygen, that is, the bridge carbon atoms between pyrrole or thiophene rings were partially sp3 atoms and partially sp2 atoms. However the polymers which were synthesized in the flowing nitrogen atmosphere were found to be deoxidized, that is the bridge atoms were sp3 atoms. The deoxidized polymers could be oxidatively dehydrogenated with tetrchlorobenzoquinone. These polymers are useful model systems to investigate the effect of conjugation length on the electronic and optical properties of conjugated polymers. Third‐order optical non‐linearities of the reulting polymers were studied by z‐scan techniques. The results show that the reulting polymers exhibited large third‐order optical non‐linear susceptibilities as large as 10−8 esu. Copyright © 2004 John Wiley & Sons, Ltd.
Electroinduced oxidative copolymerization of N‐vinyl carbazole with methyl ethyl ketone formaldehyde resin
Authors: Ustamehmetoğlu Belkıs , Saraç A. Sezai , Kızılcan Nilgün , Akar Ahmet
Published: June 2004

In this study, a novel procedure to obtain the non‐crosslinked, photoconductive, white form of the linear copolymer of N‐vinyl carbazole (NVCz) and methyl ethyl ketone formaldehyde resin (MEKF‐R) is reported. A possible mechanism of copolymerization is suggested. The yield of the copolymer is increased almost 10 times by the addition of catalytic amounts of ceric ammonium nitrate as an oxidant during the electrochemical polymerization of NVCz in the presence of MEKF‐R in a divided electrochemical cell. Since cerium(III) is readily oxidized to cerium(IV) at the anode, the concentration of cerium(IV) remained constant and the deposition of green poly(NVCz) can be prevented. Copyright © 2004 John Wiley & Sons, Ltd.
Preparation and characterization of a polyimide nanofoam through grafting of labile poly(propylene glycol) oligomer
Authors: Han Sang Hyub , Do Jin‐Sek , Kader M. Abdul , Lee Joong‐Hee , Lee Myong‐Hoon , Nah Changwoon
Published: June 2004

Preparation of a polyimide nanofoam (PI‐F) for microelectronic applications was carried out using a polyimide precursor synthesized from poly[(amic acid)‐co‐(amic ester)] and grafted with a labile poly(propylene glycol) (PPG) oligomer. Polyimide precursor was synthesized by partial esterification of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA). The precursor was then grafted with bromide‐terminated poly(propylene glycol) in the presence of K2CO3 in hexamethylphosphoramide and N‐methylpyrrolidone, imidized at 200°C in nitrogen and the product was subsequently decomposed in air at 300°C to eliminate the labile PPG oligomer to produce PMDA/ODA polyimide nanofoam. Nuclear magnetic resonance spectroscopy (1H‐NMR) and Fourier transform infrared spectroscopy (FT‐IR) techniques were used to characterize the formation of polyimide precursor and extent of grafting of PPG with polyimide. The results of thermogravimetric analysis (TGA) showed three step decomposition of nanofoam with the removal of PPG at 350°C and decomposition of polyimide at around 600°C. The polyimide nanofoams were also characterized by small angle X‐ray scattering (SAXS), field‐emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM). The morphology showed nanophase‐separated structures with uniformly distributed and non‐interconnected pores of 20–40 nm in size. Dynamic mechanical analysis (DMA) indicated higher storage modulus for the foamed structure compared to the pure PI with reduction in loss tangent for the former system. Copyright © 2004 John Wiley & Sons, Ltd.
Improvement of properties of silica‐filled styrene‐butadiene rubber composites through plasma surface modification of silica
Authors: Mathew G. , Huh M.‐Y. , Rhee J. M. , Lee M.‐H. , Nah C.
Published: June 2004

The performance of plasma surface modified silica filler in styrene‐butadiene rubber (SBR) matrix has been analyzed. The conditions of plasma modification have been optimized by taking secant modulus as a standard parameter and the occurrence of the modification has been confirmed by surface area determination and Fourier transform infrared spectroscopy. The plasma‐modified surface of silica has been found to be composed of carbon–carbon double bonds and carbon–hydrogen bonds. Silane treatment also has been carried out on silica filler surface for a comparative assessment of its influence in the curing behavior and filler–rubber interaction. The cure reactions of all the rubber compounds have been found to be proceeded according to first‐order kinetics. A reduction in the cure reaction rate constant has been observed with the loading of unmodified and surface modified silica, emphasizing the cure deactivation of the matrix rubber by the silica filler. The filler dispersion, as revealed by scanning electron microscopy, has been found to be greatly improved by the plasma as well as silane treatment. The filler–rubber interaction has been found to be greatly improved by both surface treatments, but the best balance of mechanical properties has been observed with plasma surface modification only. Copyright © 2004 John Wiley & Sons, Ltd.
Low‐density polyethylene films doped with europium(III) complex: their properties and applications
Authors: Pogreb Roman , Finkelshtein Binyamin , Shmukler Yuri , Musina Albina , Popov Oleg , Stanevsky Oleg , Yitzchaik Shlomo , Gladkikh Alexander , Shulzinger Alexander , Streltsov Vladimir , Davidov Dan , Bormashenko Edward
Published: June 2004

Light‐converting polyethylene film containing europium(III) complex with phenanthroline was manufactured under an extrusion process. The film was characterized first by means of time‐of‐flight secondary‐ion‐mass spectrometry (TOF‐SIMS), ultraviolet‐visible‐infrared (UV‐vis‐IR) spectroscopy, then a study of excitation and luminescence spectra, quantum yield and lifetime of luminescence. The quantum yield of luminescence was measured as 5±2%, and the lifetime of luminescence was determined about 470 μsec. TOF‐SIMS surface mapping showed the uniform distribution of europium(III) over the film. Visualization of strong picosecond UV laser beams through the use of the developed film has been demonstrated. Copyright © 2004 John Wiley & Sons, Ltd.
Development of anti‐asparaginase antibodies in childhood acute lymphoblastic leukemia
Authors: Zalewska‐Szewczyk Beata , Andrzejewski Witalij , Bodalski Jerzy
Published: June 2004

L‐asparaginase is a basic agent of antileukemic therapy, but allergic reactions against the drug and the development of anti‐asparaginase antibodies are significant side‐effects. The aim of our study was to estimate the presence of anti‐asparaginase antibodies and to correlate the results with clinically apparent allergic reactions and with L‐asparaginase activity during the treatment. We examined 13 children with newly diagnosed acute lymphoblastic leukemia (ALL), treated according to the Polish Pediatric Leukemia/Lymphoma Group protocol, based on ALL‐BFM 95. Enzyme activity was estimated in serum samples, collected before each L‐asparaginase administration, using the photometrical method. Anti‐asparaginase antibody concentration was measured by enzyme‐linked immunosorbent assay (ELISA) at the two time points: at the last day of L‐asparaginase treatment in the induction and the reinduction phase. The mean L‐asparaginase activity was 273 IU/L in the induction phase; no anti‐asparaginase antibodies in this phase of treatment were found. The mean L‐asparaginase activity was 425 IU/L in the reinduction phase of treatment; in five children anti‐asparaginase antibodies were detected. In four of these five children low L‐asparaginase activity and/or allergic reactions against L‐asparaginase were noted. Our observations suggest a correlation between the presence of anti‐asparaginase antibodies and L‐asparaginase activity in childhood ALL. © 2004 Wiley‐Liss, Inc.
Adenocarcinoma of the cervix and vagina in pediatric patients
Authors: McNall René Y. , Nowicki Philip D. , Miller Brigitte , Billups Catherine A. , Liu Tiebin , Daw Najat C.
Published: June 2004

Here we report our combined analysis of vaginal mesonephric adenocarcinoma (MA) in a 13 years old treated at our institution and of reported vaginal or cervical MA and clear‐cell adenocarcinoma in 37 patients 18 years old or younger. Tumors in 27 patients arose in the vagina; 8 (21%) had metastases at diagnosis. The predominant symptom was vaginal bleeding; 62% of patients were exposed to diethylstilbestrol in utero. The 3‐year survival estimate was 71% ± 11%. Surgical treatment and metastasis at diagnosis were significant predictors of survival. The association between tumor excision and excellent outcome suggests that radical hysterectomy or pelvic exenteration is unnecessary. Radiotherapy as an adjunct may have contributed to this outcome. © 2004 Wiley‐Liss, Inc.
An NMR method towards the routine chiral determination of natural products
Authors: Jaki Birgit , Franzblau Scott , Pauli Guido F.
Published: June 2004

State‐of‐the‐art structure elucidation and dereplication of natural products is incomplete without the determination of enantiomeric purity, especially when compounds are to be biologically evaluated. An NMR procedure is presented in order to distinguish and determine enantiomers in natural product samples. The method is also of value in the structure elucidation process by providing information, which is otherwise of a non‐routine nature. Using enantiomeric 1‐acetoxychavicol acetates and carvones as model compounds, this study presents a chiral NMR procedure that allows distinction and determination of chiral antipodes of natural products in a routine set‐up. Copyright © 2004 John Wiley & Sons, Ltd.