bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism and Kinetics of the Induction Period in Nitroxide Mediated Thermal Autopolymerizations. Application to the Spontaneous Copolymerization of Styrene and Maleic Anhydride
Authors: Bonilla‐Cruz José , Caballero Laura , Albores‐Velasco Martha , Saldívar‐Guerra Enrique , Percino Judith , Chapela Víctor 
Published: March 2007

AbstractRecently we reported an experimental and theoretical (simulation) investigation on the mechanism of the induction period and the initial polymerization stages in the nitroxide mediated autopolymerization of styrene. In this paper we extend some of the results presented there and perform preliminary induction period experiments for the study of the mechanism and kinetics of the spontaneous copolymerization of styrene (S) and maleic anhydride (MA) in the presence of TEMPO and 4‐OH‐TEMPO. With even small amounts of MA (2% wt) the induction period is dramatically reduced by a factor of about 20 in comparison with the nitroxide‐mediated styrene autopolymerization at 120 °C. Our results suggest that the initiation mechanism involves a first step of reaction between S and MA. We speculate that this reaction is a Diels‐Alder cycloaddition followed by hydrogen abstraction through a monomer or TEMPO assisted homolysis to form a radical pair (monomer case) or a single radical (TEMPO case), which either initiates polymerization or is trapped by TEMPO depending on the conditions. Hall and Padias have studied similar electron donor‐acceptor co‐monomer pairs and favor the formation of a tetramethylene diradical as the initiating species for spontaneous copolymerization. In any case, the rate‐limiting step would be the initial reaction of S and MA. These induction experiments allow us to obtain an initial estimate of the order of magnitude for the kinetic constant of the rate‐limiting step, as 10−6 Lmol−1s−1.
NMR Spectroscopy in the Optimization and Evaluation of RAFT Agents
Authors: Klumperman Bert , McLeary James B. , van den Dungen Eric T.A. , Pound Gwenaelle 
Published: March 2007

AbstractThe selection of a suitable mediating agent in Reversible Addition‐Fragmentation Chain Transfer (RAFT) mediated polymerization is crucial to the degree of control that can be achieved. An overview of work from the Stellenbosch group is presented in which the use of NMR spectroscopy as a tool for evaluating RAFT‐agents is highlighted. The occurrence of selective initialization, i.e. the selective conversion of a RAFT‐agent into its single monomer adduct is discussed for various classes of monomers, as well as for copolymerization. One of the general rules for living polymerization is that chains should start growing early in the polymerization reaction. Selective initialization is claimed to be the extreme case where all chains have begun growing after the conversion of only one monomer equivalent per RAFT‐agent.
A Missing Reaction Step in Dithiobenzoate‐Mediated RAFT Polymerization
Authors: Buback Michael , Janssen Olaf , Oswald Rainer , Schmatz Stefan , Vana Philipp 
Published: March 2007

AbstractThe debate on the mechanism of dithiobenzoate‐mediated RAFT polymerization may be overcome by taking the so‐called “missing step” reaction between a highly reactive propagating radical and the three‐arm star‐shaped product of the combination reaction of an intermediate RAFT radical and a propagating radical into account. The “missing step” reaction transforms a propagating radical and a not overly stable three‐arm star species into a resonance‐stabilized RAFT intermediate radical and a stable polymer molecule. The enormous driving force behind the “missing step” reaction is estimated via DFT calculations of reaction enthalpies and reaction free enthalpies.
Reaction Calorimetry for the Development of Ultrasound‐Induced Polymerization Processes in CO2‐Expanded Fluids
Authors: Kemmere Maartje F. , Kuijpers Martijn W.A. , Keurentjes Jos T.F. 
Published: March 2007

AbstractA strong viscosity increase upon polymerization hinders radical formation during an ultrasound‐induced bulk polymerization. Since CO2 acts as a strong anti‐solvent for most polymers, it can be used to reduce the viscosity of the reaction mixture. In this work, a process for the ultrasound‐induced polymerization in CO2‐expanded fluids has been developed. Temperature oscillation calorimetry has been applied to study the influence of CO2 on the viscosity during the ultrasound‐induced polymerization. In contrast to polymerizations in bulk, the results show that a low viscosity is maintained during polymerization reactions in CO2‐expanded methyl methacrylate (MMA). As a consequence, a constant or even increasing polymerization rate is observed when pressurized CO2 is applied. Moreover, the ultrasound‐induced polymer scission in CO2‐expanded MMA is demonstrated, which appears to be a highly controlled process. Finally, a preliminary sustainable process design is presented for the production of 10 kg/hour pure PMMA (specialty product) in CO2‐expanded MMA by ultrasound‐induced initiation.
Production of Polyacrylic Acid Homo‐ and Copolymer Films by Electrochemically Induced Free‐Radical Polymerization: Preparation and Swelling Behavior
Authors: Bünsow Johanna , Johannsmann Diethelm 
Published: March 2007

AbstractFilms of polyacrylic acid hydrogels were produced on a conducting substrate by means of electrochemically initiated polymerization (EIP). An electro‐chemical quartz crystal microbalance was used to monitor film growth in situ. Homopolymer and copolymer films of polyacrylic acid and poly‐N‐isopropylacrylamide were characterized by FTIR spectroscopy. The degree of swelling of these films could be tuned via the pH.
Reversible Addition Fragmentation Chain Transfer Mediated Dispersion Polymerization of Styrene
Authors: Saikia Prakash J. , Lee Jung Min , Lee Byung H. , Choe Soonja 
Published: March 2007

AbstractPolystyrene microspheres have been synthesized by the reversible addition‐fragmentation chain transfer (RAFT) mediated dispersion polymerization in an alcoholic media in the presence of poly(N‐vinylpyrrolidone) as stabilizer and 2,2′‐azobisisobutyronitrile as a conventional radical initiator. In order to obtain monodisperse polystyrene particles with controlled architecture, the post–addition of RAFT agent was employed to replace the weak point from the pre‐addition of RAFT. The feature of preaddition and postaddition of RAFT agent was studied on the polymerization kinetics, particle size and its distribution and on the particle stability. The living polymerization behavior as well as the particle stability was observed only in the postaddition of RAFT. The effects of different concentration on the postaddition of RAFT agent were investigated in terms of molecular weight, molecular weight distribution, particle size and its distribution. The final polydispersity index (PDI) value, particle size and the stability of the dispersion system were found to be greatly influenced by the RAFT agent. This result showed that the postaddition of RAFT agent in the dispersion polymerization not only controls the molecular weight and PDI but also produces stable monodisperse polymer particles.
Acid Cleaning of Steel Using Arghel Echo Friendly Corrosion Inhibitor
Authors: Khamis E. , Hefnawy A. , El‐Demerdash A.M. 
Published: March 2007

AbstractAcid cleaning of mild steel dissolution by 1M sulfuric acid/10 % methanol (test solution) in presence of Arghel herb extract as green inhibitor were monitored by potentiodynamic and electrochemical impedance techniques in the temperature range 30–60oC. At all temperature, the corrosion rate decreased with increasing inhibitor concentration. Potentiodynamic polarization measurements indicated that the inhibitor has strong effect on the corrosion behavior of the steel and behave as mixed type inhibitor. Impedance results indicate that the charge transfer controls the dissolution mechanism of steel across the phase boundary in the absence and the presence of the inhibitor. The inhibition efficiency obtained from various employed methods is in good agreement.Thermodynamic and activation parameters obtained from this study indicated that the presence of the Arghel increases the activation energy, and the adsorption process of the inhibitor on the metal surface is spontaneous.
Oxidationsverhalten von HVOF–gespritzten MCrAlY–Schichten
Authors: Mărginean G. , Frunzăverde D. , Brandl W. 
Published: March 2007

AbstractDer Einfluss zweier Spritzparameter (Kerosindurchfluss und Brennkammerdruck) auf das Hochtemperaturoxidationsverhalten von HVOF ‐ gespritzten MCrAlY ‐ Schichten wurde anhand von CoNiCrAlY ‐ Schichten mit 15 Gew.‐% Aluminium untersucht. Verschiedene Testproben wurden nach dem thermischen Spritzen zur Verbesserung des Aufbaus (Homogenisierung, Verminderung der Porosität und der inneren Spannungen, Ausscheidung neuer Phasen) wärmebehandelt und anschließend bei 950 °C für 3000 Minuten in synthetischer Luft oxidiert. Um den Einfluss der unterschiedlichen Spritzparameter auf das Oxidationsverhalten der Schichten zu erfassen wurde die thermogravimetrische Analyse (TG) eingesetzt. Zusätzlich wurde vor und nach der Oxidation der Aufbau der Schichten mit Hilfe der Rasterelektronenmikroskopie (REM) und Röntgendiffraktometrie (XRD) untersucht. Die Ergebnisse zeigten eindeutig, dass das Oxidationsverhalten der HVOF‐gespritzten Schichten abhängig von den Spritzparametern ist. Eine Erhöhung des Kerosindurchflusses bzw. des Brennkammerdruckes führen zu einer Verbesserung des Oxidationsverhaltens dieser Beschichtungen.
Self‐reported adherence versus pill count in Parkinson's disease: The NET‐PD experience
Authors: Elm Jordan J. , Kamp Cornelia , Tilley Barbara C. , Guimaraes Paulo , Fraser Debbie , Deppen Patricia , Brocht Alicia , Weaver Chris , Bennett Susan ,   NINDS NET‐PD Investigators and Coordinators
Published: March 2007

AbstractPurposeTo compare the Morisky medication adherence questionnaire to pill counts as measures of adherence in the NET‐PD futility clinical trials. Background: Like in other chronic diseases, non‐adherence with medications occurs in Parkinson's disease (PD), although nonadherence has not been of significant concern in most PD clinical trials. The most common approach to assessment is to do a pill count at each visit. The simple, 4‐question Morisky medication adherence questionnaire may provide an alternative approach to monitoring treatment adherence in PD.MethodsAdherence data from two NET‐PD Phase II clinical trials enrolling a total of 413 participants were analyzed. The association between demographic and clinical characteristics and adherence was explored.ResultsNinety‐percent of participants took 80% or more of the study drug. However, the Morisky medication adherence questionnaires showed 56% report high and 44% report medium adherence. Agreement between the two measures is fair (ICC = 0.40).ConclusionsOverall adherence as assessed by pill count appears high. The Morisky medication adherence questionnaire may be useful in PD clinical trials, since it is moderately correlated to pill count and may be more sensitive to nonadherence. © 2007 Movement Disorder Society
Clinical and genetic characterizations of 16q‐linked autosomal dominant spinocerebellar ataxia (AD‐SCA) and frequency analysis of AD‐SCA in the Japanese population
Authors: Nozaki Hiroaki , Ikeuchi Takeshi , Kawakami Akio , Kimura Akio , Koide Reiji , Tsuchiya Miyuki , Nakmura Yuusaku , Mutoh Tatsuro , Yamamoto Hiroko , Nakao Naoki , Sahashi Ko , Nishizawa Masatoyo , Onodera Osamu 
Published: March 2007

AbstractAutosomal dominant spinocerebellar ataxias (AD‐SCAs) form a clinically and genetically heterogeneous group of neurodegenerative disorders. Recently, a single nucleotide substitution in the 5′‐untranslated region of the puratrophin‐1 gene was found to be associated with one type of AD‐SCA linked to chromosome 16q (16q‐SCA). To obtain further insight into the contribution of the C‐to‐T substitution in the puratrophin‐1 gene to the clinical and genetic characteristics of patients with 16q‐SCA, we analyzed 686 families with 719 individuals diagnosed with progressive ataxia. We found C‐to‐T substitution in the puratrophin‐1 gene in 57 unrelated families with 65 affected individuals. The mean age at onset in the patients with 16q‐SCA was 59.1 (range, 46–77). Ataxia is the most common initial symptom. The elderly patients over 65 occasionally showed other accompanying clinical features including abnormalities in tendon reflexes, involuntary movements, and reduced vibration sense. We also examined the frequency of the AD‐SCA subtype, considering the effects of age at onset. In the 686 AD‐SCA families, SCA6 and Machado‐Joseph disease/SCA3 are frequent subtypes, followed by dentatorubral‐pallidoluysian atrophy and 16q‐SCA. 16q‐SCA is not a rare subtype of Japanese AD‐SCA, particularly in patients with ages at onset over 60. © 2007 Movement Disorder Society
Video documented follow‐up of liver transplantation in Wilson's disease with predominant neurological manifestation
Authors: Suess Thorsten , Bokemeyer Martin , Schomerus Georg , Donnerstag Frank , Manns Michael Peter , Klempnauer Juergen , Kolbe Hans , Weissenborn Karin 
Published: March 2007

AbstractWilson's disease (WD) is a rare autosomal‐recessive disorder of copper metabolism with predominantly hepatic and extrapyramidal motor symptoms. Copper chelating therapy has proven to be an effective treatment for WD. Yet, if conservative treatment fails, liver transplantation (LT) often is the only remaining therapeutic option. The indication for LT especially in patients with stable liver function but severe neurological manifestation is debated controversially. In this case report, we document the follow up of neurological symptoms in WD after LT for the first time on video. © 2007 Movement Disorder Society
Imaging of shifted stimulated echoes and multiple spin echoes
Authors: Mori Susumu , Hurd Ralph E. , Van Zijl Peter C. M. 
Published: March 2007

AbstractIt is shown that a repetitive pulse sequence consisting of two 90° pulses and gradients in a 1:2 ratio around the second 90° pulse generates interscan shifted stimulated echoes (SSTEs) and intrascan multiple spin echoes (MSEs). Separation of these two types of signals is accomplished using specific gradient crusher schemes. The intensity of the SSTEs is an order of magnitude larger than that of the MSEs and determines the signal contrast if both effects are selected simultaneously. The SSTE sequence generates improved contrast between gray and white matter, even at high field, which is explained in terms of increased inverse T1‐weighting for the interscan echo. The MSE image has low signal to noise and no detectable contrast. The effect of interscan diffusion weighting is also discussed.
Three‐dimensional spectral‐spatial excitation
Authors: Morrell Glen , Macovski Albert 
Published: March 2007

AbstractA method of three‐dimensional spectral‐spatial excitation is presented which is selective simultaneously in two spatial dimensions and in the spectral or chemical shift dimension. This method can be used to create spectral passbands whose center frequency varies as a function of spatial location within an imaging plane. This variation of passband center frequency may be specified by an acquired main field (B0) map; the resulting excitations compensate for inhomogeneity of the B0 field. In vivo images are presented in which three‐dimensional spectral‐spatial excitation allows selective water‐only imaging in the presence of large B0 inhomogeneity where conventional spectrally selective imaging fails. Phantom studies give a detailed profile of the performance of three‐dimensional spectral‐spatial pulses suitable for water‐only or fat‐saturation imaging. These pulses may also be useful for fat and water suppression in spectroscopic imaging. Performance constraints imposed by limited gradient slew rates are analyzed and quantified.
Numerical model for calculation of apparent diffusion coefficients (ADC) in permeable cylinders—comparison with measured ADC in spinal cord white matter
Authors: Ford J. Chetley , Hackney David B. 
Published: March 2007

AbstractWe have implemented a numerical method for calculation of the apparent diffusion coefficient (ADC) in spinal cord injury, which takes into account the distribution of axon diameters and permeability found in spinal cord white matter, as well as relative axonal volume. We propose a procedure for determining the status of axonal integrity from measured ADC values. These methods have been applied to a well characterized rat spinal cord injury model, affording a prediction of the increase in axonal permeability which is presumed to be closely related to functional deficit. ADC values are compared to those calculated from analytical formulas in the literature, and possible factors underlying the ADC behavior are explored. Calculated results indicate both axonal swelling and cell membrane permeability to be important factors contributing to ADC in traumatic spinal cord injury.
Rapid cardiac imaging with turbo BRISK
Authors: Doyle Mark , Walsh Edward G. , Foster Robert E. , Pohost Gerald M. 
Published: March 2007

AbstractA variety of variable and constant rate, sparse sampling strategies have previously been proposed to rapidly image dynamically changing objects. The majority of these strategies compile a k‐space data set for any given time point by substituting k‐space data from the most recently sampled time positions (extracted from the sparsely sampled set). The BRISK technique, is a variable rate, sparse sampling technique which additionally incorporates an interpolation scheme to more accurately represent k‐space data at positions which were not directly sampled. Here, strategies are introduced that allow turbo concepts to be incorporated with BRISK. Simulations are conducted to compare the efficacy of the turbo BRISK acquisition and processing strategy against a constant rate, sparse sampling strategy with direct substitution of the most recently acquired k‐space lines. It is shown that turbo BRISK generates images of similar quality in approximately half the time as the uniform sampling rate, sparse sampling strategy. Data from turbo BRISK acquisitions of multicardiac phase image sets, obtained on a normal volunteer and cardiac patients are presented.
Three‐dimensional projection imaging with half the number of projections
Authors: Boada Fernando E. , Christensen James D. , Gillen Joseph S. , Thulborn Keith R. 
Published: March 2007

AbstractThis study demonstrates a sampling scheme for three‐dimensional projection imaging with half the number of projections. The angular distribution of projections is designed so that the oversampling of the low spatial frequencies, in tandem with a partial Fourier algorithm, can be used to recreate purposely missing projections. The performance of the sampling scheme and its associated reconstruction algorithm are illustrated with computer‐simulated as well as experimental data sets. We find that this technique produces images of comparable quality to the conventional projection imaging scheme. Although a 30% loss of signal‐to‐noise ratio (SNR) results from its use, the algorithm should prove useful for applications where robustness against motion artifacts and reduced T2* signal loss are desired.
High resolution electron paramagnetic resonance imaging of biological samples with a single line paramagnetic label
Authors: Kuppusamy Periannan , Wang Penghai , Chzhan Michael , Zweier Jay L. 
Published: March 2007

AbstractThe application of electron paramagnetic resonance imaging (EPRI) to obtain information from biological samples has been limited by the lack of ideal single line radical labels. The commonly used nitroxides exhibit multiple lines causing either hyperfine‐based limitations in the maximum obtainable image resolution or hyperfine‐based artifacts in the reconstructed image. The use of a novel single‐line triarylmethyl paramagnetic label that enables marked enhancement in image quality and resolution is reported. This label exhibits a single line EPR spectrum that is sharp (linewidth ∼60 mG in the absence of oxygen) and relatively stable in tissues. The potential of this label in enabling high resolution EPR imaging of biological samples was demonstrated in a series of phantoms and isolated biological organs such as the rat kidney. The images demonstrate that resolutions better than 100 μm could be obtained at L‐band on samples of up to 20 mm in size.
In vivo determination of intra‐myocellular lipids in human muscle by means of localized 1H‐MR‐spectroscopy
Authors: Boesch Chris , Slotboom Johannes , Hoppeler Hans , Kreis Roland 
Published: March 2007

AbstractIntra‐myocellular lipids (IMCL) are stored in droplets in the cytoplasm of muscle cells and are an energy storage form readily accessed during long‐term exercise. 1H‐MR spectroscopy methods are presented for noninvasive determination of IMCL in human muscle. This is based on (a) the separation of two resonances in the lipid‐CH2‐region, with the one assigned to IMCL being independent of muscle orientation relative to the magnetic field and (b) the fact that IMCL resonances scale along with signal amplitudes of metabolites in the muscle cell (e.g., creatine) when voxel size is increased, while lipid signals of bulk fat show a disproportionate growth. Inter‐individual and intra‐individual reproducibility studies indicate that the error of the method is about 6% and that IMCL levels differ significantly between identical muscles in different subjects, as well as intra‐individually when measured at 1 week intervals. IMCL determinations in a single subject before and after strenuous exercise indicate that lipid stores recover with a t1/2 of about 1 day.
Magnetic susceptibility measurement of insoluble solids by NMR: Magnetic susceptibility of bone.
Authors: Hopkins Jeffrey A. , Wehrli Felix W. 
Published: March 2007

AbstractMeasurements of the volume magnetic susceptibility of solids using the classical Gouy balance approach are hampered by variations in apparent density of the packed powder. In this paper a quantitative NMR measurement of the volume magnetic susceptibility of powdered solids is described and the volume susceptibility of bone is reported. The technique is based on the measurement of changes in incremental linewidth (1/πT2′) induced in a marker fluid whose susceptibility can be predictably modified by changing the composition, such as by addition of a soluble diamagnetic compound. The spectroscopic linewidth of the marker fluid is determined by the susceptibility difference between the fluid and the suspended solid. Changes in the linewidth are accompanied by bulk magnetic susceptibility induced frequency shifts in the fluid resonance. Correlating the two dependencies allows measurement of the absolute volume susceptibility of the solid. The susceptibility of bovine rib bone was found to be −0.90 ± 0.02 × − 10−6 (CGS) confirming previous estimates which suggested bone to be more diamagnetic than the marrow constituents. Knowledge of the susceptibility of bone is relevant in view of the growing interest in MRI osteodensitometric techniques.